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Impact of activated charcoal on the mineralisation of 14C-phenanthrene in soils
Abstract
The development of phenanthrene catabolism in four soils amended with varying concentrations of activated charcoal (AC) (0%, 0.1%, 1% and 5%), a type of black carbon, was investigated. Mineralisation of (14)C-phenanthrene was monitored after 1, 25, 50 and 100 d soil-PAH contact time; lag phases, rates and extents of mineralisation of the (14)C-phenanthrene to (14)CO(2) were determined. At concentrations >0.1% AC rates and extents of mineralisation were reduced by more than 99%. This revealed that the presence of >0.1% AC in soils may substantially diminish the rate at which the catabolic activity of indigenous soil microflora develops in contaminated soil. Soil C, which had the highest organic carbon (OC) content, consistently exhibited the highest extents of degradation. It is suggested that, in accordance with other researchers, OC may have blocked available phenanthrene sorption sites. This enhanced phenanthrene availability ultimately facilitated a greater level of catabolic activity within this soil. Such results reflect the complex nature of interactions between soil, biota and contaminants and their influence on the degradation of contaminants in the environment.
... Microbial degradation of PAHs through mineralization is a wellknown approach to remediating soils polluted with PAHs (Peng et al., 2008;Ghosal et al., 2016). This is because of the degrading effect of some microbial enzymes on PAHs (Rhodes et al., 2010;Obuekwe and Semple, 2013;Ogbonnaya et al., 2016;Umeh et al., 2018). However, soil nutrients are essential for microbial activities and degradation of PAHs (Chiu et al., 2009). ...
... Therefore biodegradation potential of PAH in soil may be influenced by the amount of nutrient and organic carbon in contaminated soil (Zhang et al., 2012). The lag phase is an indication of the microflora adaptation or acclimatization to the presence of 14 C -phenanthrene, resulting in increased mineralization (Couling et al., 2010;Rhodes et al., 2010). Addition of digestate to soil had an effect on the adaptation of the soil microbial community as revealed from the data obtained in this study. ...
... Both spiked and non-spiked soils with WD amendment had the highest phenanthrene degraders in this study. Microbial adaptation to the contaminant is very important in any degradation process (Couling et al., 2010;Rhodes et al., 2010). Correlation studies showed a positive relationship between the rate and extent of 14 C-phenanthrene mineralization and the bacterial number (total heterotrophic and phenanthrene-degrading bacteria) after 1 and 30 d only. ...
The impact of whole digestate (WD) and its fractions (solid [SD] and liquid [LD]) on ¹⁴C-phenanthrene mineralization in soil over 90 d contact time was investigated. The ¹⁴C-phenanthrene spiked soil was aged for 1, 30, 60 and 90 d. Analysis of water-soluble nitrogen, phosphorus, total (organic and inorganic) carbon, and quantitative bacterial count were conducted at each time point to assess their impact on mineralization of ¹⁴C-phenanthrene in soils. Indigenous catabolic activity (total extents, maximum rates and lag phases) of ¹⁴C-phenanthrene mineralization were measured using respirometric soil slurry assay. The soil amended with WD outperformed the SD and LD fractions as well as showed a shorter lag phase, higher rate and extent of mineralization throughout the study. The digestates improved (P < 0.05) the microbial population and nutritive content of the soil. However, findings showed that spiking soil with phenanthrene generally reduced the growth of microbial populations from 1 to 90 d and gave a lower nutritive content in comparison with the non-spiked soil. Also, soil fertility and bacteria count were major factors driving ¹⁴C-phenanthrene mineralization. Particularly, the non-phenanthrene degraders positively influenced the cumulative mineralization of ¹⁴C-phenanthrene after 60 d incubation. Therefore, the digestates (residue from anaerobic digestion) especially WD, which enhanced ¹⁴C-phenanthrene mineralization of the soil without minimal basal salts medium nor additional degraders should be further exploited for sustainable bioremediation of PAHs contaminated soil.
... In the presence of BC, fastest rates and extents of biodegradation of polycyclic aromatic hydrocarbons (PAHs) can be dramatically reduced (Rhodes et al., 2008(Rhodes et al., , 2010Xia et al., 2010). Furthermore, extractability of PAHs from contaminated soils by hydroxypropyl-β-cyclodextrin (HPCD) has been shown to be influenced by the presence of BC (Rhodes et al., 2008;Towell et al., 2011). ...
... At 25 d contact time, soil amended with CP 2 yielded significantly less (p < 0.05) 14 CO 2 than the other two BC-amended soils, while significantly more 14 C-phenanthrene (p < 0.05) was mineralised in soil with P3-1 at 50 d than the other two BC-treated soils. Overall, these results were in agreement with previous studies by Rhodes et al. (2008Rhodes et al. ( , 2010. These trends have been attributed to the strong sorptive capacity of BC (Cornelissen et al., 2005;Rhodes et al., 2012). ...
... Moreover, a fraction of 14 C-phenanthrene may have become inaccessible to microorganisms due to entrapment in collapsed pores on BC particles (Sander and Pignatello, 2007;Semple et al., 2013). However, the extent to which 14 C-phenanthrene mineralisation was inhibited in BC-amended soils was much greater than those observed by Rhodes et al. (2008Rhodes et al. ( , 2010. At least 6% of spiked 14 C-phenanthrene was mineralised in each soil treatment in research by Rhodes et al. (2008) all treatments (0%-5% AC dry weight) in the study by Rhodes et al. (2008), while Rhodes et al. (2010) only obtained biodegradation extents lower than 1% in soils treated with 5% AC. ...
The presence of black carbon (BC) in soil drastically reduced the mineralization of C-phenanthrene and its extractability by hydroxylpropyl- -cyclodextrin (HPCD) extractions. This study also tested the effects of pH on the HPCD extraction of C-phenanthrene in soils with BC. Extractions using 60 mM HPCD solutions prepared in deionized water (pH 5.89) and phosphate buffers (pH 7 and 8) were conducted on C-phenanthrene-spiked soils amended with three different types of BC (1% dry weight) after 1, 25, and 50 d of ageing. Biodegradation assays using a Pseudomonassp. strain were also carried out. Results showed that after 1 and 25 d, HPCD at pH 7 extracted significantly more C-phenanthrene (p 0.05) from BC-amended soils than the other two solutions (un-buffered and pH 8), while HPCD at pH 8 extracted statistically similar (p 0.05) amounts of phenanthrene compared to the un-buffered solution. At 50 d, HPCD at pH 8 generally extracted more C-phenanthrene from all treatments. It was proposed that higher pH promoted the dissolution of soil organic matter (SOM), leading to a greater solubility of phenanthrene in the solvent phase and enhancing the extractive capability of HPCD solutions. Although correlations between extractability and biodegradability of C-phenanthrene in BC-amended soils were poor, increasing pH was demonstrated a viable approach to enhancing HPCD extractive capability from the C-PAH from soil.
... On the other hand, their close affinity to hydrophobic substances and their strong sorption reduce the leaching and bioavailability of contaminants (Cornelissen et al., 2005;Koelmans et al., 2006;Pignatello et al., 2006). Though the weaker leaching reduces the contamination of groundwater, but also as a result of the slower biodegradation those compounds may tend to accumulate in the soil (Rhodes et al., 2010). Studies on the fate of PAHs in biochar amended soils are important due to the hazard to human health caused by those compounds, and it permits better understanding of the actual risk related to soil amendment or remediation during biochars application. ...
... However, it should be emphasized that the bioavailability of PAHs (because of high affinity to biochar) in biochar-amended soil can be considerably lower than in soils with similar levels of PAHs but free of any biochar content. Research shows (Cornelissen et al., 2005;Koelmans et al., 2006;Rhodes et al., 2010) that hydrophobic contaminants (such as PAHs) are strongly bound with biochar, which reduces their bioavailability. It also needs to be noted that in spite of the absolute increase in the content of PAHs in the biochar amended soil the concentration of those compounds was still at levels meeting the permissible norms in most European countries (Maliszewska-Kordybach, 1996). ...
... The persistence of organic contaminants introduced into soil depends on its kind and physicochemical properties, environmental conditions such as temperature, rainfall, intensity of light, and also on bioavailability and on the activity of soil microorganisms (Cerniglia, 1992;Doick et al., 2005;Oleszczuk, 2006;Park et al., 1990;Quilliam et al., 2013;Rhodes et al., 2010). After the application of biochar, PAHs introduced with it into soil may undergo volatilisation, photodegradation, desorption, leaching, biotransformation and secondary adsorption and incorporation into the structure of humic substances (Cabrerizo et al., 2011;Park et al., 1990;Pignatello et al., 2006). ...
In the present study the persistence of polycyclic aromatic hydrocarbons (PAHs) applied with biochar to acidic soil (loamy sand) was studied in two and half year field experiment. An experiment was carried out in three experimental plots (15 m(2) each). The biochar was introduced in the following doses: soil without fertilization - control (C-BC00), soil with 30 t ha(-1) (B-BC30) and soil with 45 t ha(-1) (A-BC45) of biochar. Biochar addition to soils resulted in an increase in the PAHs content from 0.239 μg g(-1) in control soil to 0.526 μg g(-1) and 1.310 μg g(-1) in 30 and 45 t ha(-1) biochar-amended soil respectively. However during the experimental period the PAHs content decreased to a level characteristic for the control soil. The highest losses of PAHs were observed during the first 105 days of the experiment. Three and four rings PAHs were the most susceptible for degradation and leaching. Migration of PAHs from 0-10 cm to 10-20 cm soil horizon was also observed.
... Soils contain a wide variety of indigenous microflora that possess catabolic potential to degrade contaminants, such as polycyclic aromatic hydrocarbons (PAHs) [1]. Indeed, microbial degradation is a major loss pathway for PAHs from soil [1,2]. ...
... Soils contain a wide variety of indigenous microflora that possess catabolic potential to degrade contaminants, such as polycyclic aromatic hydrocarbons (PAHs) [1]. Indeed, microbial degradation is a major loss pathway for PAHs from soil [1,2]. The ability of microbes to adapt to PAHs and the time required for adaptation to occur, in part, determines the persistence of organic contaminants [3]. ...
... This suggests that SOM may compete for adsorption sites and block pore sites on black carbon. Furthermore, Rhodes et al. [1] showed that higher concentrations (>0.1%) of activated charcoal (AChar) reduced the extent and rate of 14 C-phenanthrene mineralisation in soils by reducing indigenous microbial catabolic activity. More recently, Bushnaf et al. [21] showed rapid biodegradation of alkanes in biochar amended soils. ...
The impact of increasing amendments of two particle sizes of biochar (≤2 mm
and 3–7 mm), applied at 0%, 0.01%, 0.1% and 1% concentrations, on the development of
indigenous phenanthrene catabolism was investigated in two soils with different soil
organic matter contents. Mineralisation of 14C-phenanthrene was measured after 1, 20,
60 and 100 d soil-phenanthrene-biochar aging period. The presence of biochar in the
pasture soil (low OM) resulted in a decrease in the lag phase of 14C-phenanthrene
mineralisation, with higher maximum rates of mineralisation following 20 d aging. Higher
extents of 14C-phenanthrene mineralisation were observed in the Kettering loam soil (high
OM), which was more prominent with 0.01% biochar amendments (p < 0.05) at 61.2% and
64.9% in ≤2 mm and 3–7 mm biochar amended soils, respectively. This study illustrates
the potential role for biochar to enhance microbial catabolic activity to degrade common
petroleum contaminants. It however depends on contaminant concentration, aging period,
and soil properties.
... Similar reports are available on application of active carbon in biodegradation of hydrocarbons including degradation of 3,4-di chlropropionanilide, 3,4-di chloroaniline, 2,4,6-trinitrotoluene (Vasilyeva et al. 2006(Vasilyeva et al. , 2010, Anthracene (Owabor and Aluyor 2008), 2,6-dichlorophenol (Agarry et al. 2013b), and diesel fuel (Semenyuk et al. 2014). Thus, application of active carbon contributes to remediation of soil and improves biological degradation (Rhodes et al. 2008(Rhodes et al. , 2010. ...
... These observations may be due to the fact that biochar leads to increase in uptake of organic pollutants as well as improvement of soil structure, oxygen concentration, and water retention capacity as essential parameters for enhancing microbial activity, transfer and degradation of pollutants, and eventually, reduction in TPH. The weight of organic pollutants absorbed by biochar may be 10 to 1000 times higher than other organic matters in soil (Chen and Yuan 2011;Ippolito et al. 2012;Oleszczuk et al. 2012;Quilliam et al. 2013;Tang et al. 2013;Accardi-Dey and Gschwend 2003;Rhodes et al. 2010;Meynet et al. 2014;Lehmann et al. 2011;Guerin 2015;Chan and Xu 2012;Park et al. 2011). Figure 3 shows the activity of microorganisms responsible for hydrocarbon degradation in gasoil-polluted soils as affected by various biochar and active carbon size and weights. ...
... Similar reports are available on application of active carbon in biodegradation of hydrocarbons including degradation of 3,4-di chlropropionanilide, 3,4-di chloroaniline, 2,4,6-trinitrotoluene (Vasilyeva et al. 2006(Vasilyeva et al. , 2010, Anthracene (Owabor and Aluyor 2008), 2,6-dichlorophenol (Agarry et al. 2013b), and diesel fuel (Semenyuk et al. 2014). Thus, application of active carbon contributes to remediation of soil and improves biological degradation (Rhodes et al. 2008(Rhodes et al. , 2010. ...
... These observations may be due to the fact that biochar leads to increase in uptake of organic pollutants as well as improvement of soil structure, oxygen concentration, and water retention capacity as essential parameters for enhancing microbial activity, transfer and degradation of pollutants, and eventually, reduction in TPH. The weight of organic pollutants absorbed by biochar may be 10 to 1000 times higher than other organic matters in soil (Chen and Yuan 2011;Ippolito et al. 2012;Oleszczuk et al. 2012;Quilliam et al. 2013;Tang et al. 2013;Accardi-Dey and Gschwend 2003;Rhodes et al. 2010;Meynet et al. 2014;Lehmann et al. 2011;Guerin 2015;Chan and Xu 2012;Park et al. 2011). Figure 3 shows the activity of microorganisms responsible for hydrocarbon degradation in gasoil-polluted soils as affected by various biochar and active carbon size and weights. ...
In the present study, total petroleum hydrocarbon biodegradation by wheat straw biochar and active carbon (TPH) was investigated in gasoil-polluted soil around oil refinery of Shiraz, Iran. The experiment was conducted as split-split-plot in time based on completely randomized design with three replications. Various weights of biochar and active carbon (0, 20, 40, 60, 80, and 100 g kg−1) were assigned to main plots, whereas particle sizes (1–2 mm for biochar and 0.05–2.05 mm for active carbon) were assigned to subplots, and the effects were monitored weekly. Biodegradation constant (K) for active carbon ranged from 0.0139 to 0.0328 day−1, whereas it varied from 0.0145 to 0.0369 day−1 for biochar. Also, this value was 0.0088 for control soil. Half-life for control soil was 78.7 days, which decreased as result of applying various size and weights of active carbon (21.13–49.8 days) and biochar (18.7–47.8 days). Thus, the technology used in this study provides a cheap, efficient, and environment friendly method which may be successfully applied in gasoil-polluted soils to enhance the environment for plants and soil microorganisms.
... However, soils and sediments are very complex and heterogeneous matrices with a wide range of sorbent phases. Sorbent phases, such as black carbon, other carbonaceous materials and clay minerals, can also contribute to entrapping HOCs [3,4,11,[21][22][23][24][25]. Hence, the sole use of K oc to predict or explain the nature of sorption, HOC sorption, is rather too simplistic [26,27]. ...
... Two and three compartments, first-order equations are often used to describe the desorption behaviour of HOCs in contaminated soils (Eqs. 1 and 2), and associated mechanisms have been described in detail elsewhere [17,23,52,53]. ...
Many publications on contaminant bioavailability in soils often state that the use of total contaminant concentrations in risk assessment is an overly conservative approach. Such conservatism makes traditional risk assessment approaches and contaminated land decision-making expensive. The risk-based approach to contaminated land management strives to identify and manage the potential risks of significant harm being caused to humans and ecological receptors, following exposure to contaminated land. Risk-based approaches are more cost-effective than the traditional approaches from the perspective of contaminated land management. Contaminant bioavailability or bioaccessibility is one of the critical concepts that underpins risk-based approaches to contaminated land management. Bioavailability describes the fraction of the total contaminant concentration that desorbs from soil and is immediately available to cause harm to a living organism, after passing through the organism’s membrane. Bioaccessibility describes what is available and potentially available under natural environmental conditions and during realistic timeframes. The reliable measurements of either contaminant bioavailability or bioaccessibility is therefore critical; in this regard, a thorough understanding of contaminant sequestration and desorption behaviour is required. This chapter discusses the fate of HOCs in soils, bioavailability and bioaccessibility of organic contaminants and their associated desorption-based measurements.
... We assume that increasing the PAH-tot content at the end of the experiment may result from the release of these contaminants from biochar structures. Similar finding was also observed by , and Rhodes et al. (2010) and Dutta et al. (2017) who found that even a small degradation of a biochar causes the discharge of PAHs to the soil. Interesting results of research on the desorption kinetic of freshly bound Phe in soil were presented by Marchal et al. (2013) who observed that after 14 days, as much as 41% of Phe adsorbed on biochar added to soil may undergo desorption. ...
... The literature data prove that the strength of this impact may depend on biochar properties. Many studies indicate that the addition of biochar to the soil caused the immobilization of PAHs Rhodes et al. 2010) affecting the decrease of its freely dissolved forms over time (Oleszczuk et al. 2012;Koltowski et al. 2016). According to Dutta et al. (2017), Tag et al. (2016), Beesley et al. (2011), andChen et al. (2008), increasing the biochar pyrolysis temperature increases the degree of carbonization, which extends the surface sorption area but reduces the abundance of amorphous organic matter. ...
Purpose
The aim of the research was to assess the effect of biochar addition on aging, degradation, and sorption processes of polycyclic aromatic hydrocarbons (PAHs) to soil organic matter. The study was carried out as a sorption experiment in strictly controlled water and air conditions, which allowed for the accurate observation and prediction of PAH behavior in soils.
Materials and methods
Four soils were fortified with a PAH mixture (Fluorene-Flu, Anthracene-Ant, Phenanthrene-Phe, Pyrene-Pyr, Chrysene-Chry) at 20 mg kg⁻¹ of single-compound concentration level. The experiment was carried out in two trials: soils + 5PAHs amended with biochar and soil + 5PAHs without biochar addition with incubation times of 0, 1, 3, 6, and 9 months. After each interval time, the extractable (E-SOM) and stable organic matter (S-SOM) were measured as well as PAHs determined in two forms: total concentration (PAH-tot) and residual concentration (PAH-rest) after E-SOM extraction. The PAH loss and half-life times were estimated according to pseudo first-order kinetics equation.
Results and discussion
The amounts of PAH-tot in the soils without biochar decreased by an average of 92%, while in soil with biochar, this was 41% after 9 months of aging. The amount of PAHs-rest bounded with S-SOM after 9 months of incubation varied from 0.9 to 3.5% and 0.2 to 1.3% of the initial PAH concentration, respectively, for soils non-induced and induced by biochar. In soils without biochar, Flu, Ant, Phe, and Pyr exhibited similar T1/2 (43–59 days), but Chry was characterized by a much higher and broader T1/2 than other hydrocarbons (67–280 days). Biochar addition to the soils significantly influenced the half-life changes for all PAHs. The highest changes were noted for Phe (14-fold increase), and the lowest was for Flu (7-fold increase).
Conclusions
The addition of exogenous-rich carbon material such as biochar to the soil significantly changes the behavior and sorption potential of PAHs in the soil. Soils enriched with biochar are characterized by a higher persistence of PAHs, longer aging time, and lower affinity for sorption by native organic matter structures. Soils freshly polluted by PAH are mainly sorbed by E-SOM, which significantly increases their accessibility and reduces formation of bound-residues in the soil.
... In addition, biochar can also reduce bioavailability, volatization and leaching of organic pollutants due to sorption on biochar. In general, a lower microbial degradation of organic pollutants was found in biochar-amended soils due to lowering the bioavailability (Yang et al., 2006;Yang et al., 2010;Rhodes et al., 2010;Beesley et al., 2011). At the same time, the toxicity, leaching and volatilization can be reduced due to sorption. ...
... However, organic nutrient additions might counteract the negative effect of biochar additions on degradation by concurrence for sorption sites on biochar (Rhodes et al., 2010;Wang et al., 2017). ...
Lindane is a persistent organo-chlorine insecticide which has been extensively used
worldwide for the control of agricultural, wood and medical pests, despite known its
tendency to bioaccumulate and its toxicity to non-target organisms. As a result of the high
persistence and long-time extensive usage, environmental contaminations of global
dimensions exist. To bioremediate these soils, different bioremediation strategies were
tested, based on biochar application, and degradation by the white rot fungi Pleurotus
ostreatus, and a combined approach using biochar and P. ostreatus. In order to simulate
realistic in situ remediation treatments, economically and feasible application rates and
typical lindane pollution levels were used. The efficiency and effectiveness of each
remediation treatment in non-sterile and sterile soils during 50 days of incubation was
evaluated according to lindane dissipation processes (extractable, non-extractable,
volatilized and mineralized radioactivity) and growth (ergosterol content) and activity
(respiration) of P. ostreatus and indigenous soil microbes. Fungal treatment and biochar
application showed best remediation success in terms of lindane dissipation either due to
mineralization or immobilization. Sterile soils were strongly colonized by P. ostreatus and
particularly high lindane mineralization (8.73-11.7 %) and immobilization (16.9-24.5 %)
were observed. Non-sterile inoculated soil showed a similar magnitude of immobilization
(10.54-24 %) but lower mineralization (2.4-2.7 %). However, the mechanisms of lindane
immobilization by P. ostreatus, i.e. whether lindane was only sorbed or also incorporated
into fungal tissue, still remains to be clarified. Biochar amendments resulted in lower
volatilization of lindane from soil and had a positive effect on fungal growth in terms of
respiration rate and visually observable mycelium. Moreover, it enabled a better
colonization of the non-sterile soil and therefore, biochar amendments might provide a
useful tool to introduce fungal inoculum for future in situ remediation measures. However,
the fungal growth (ergosterol content) and lindane mineralization were lower in biocharamended soils. This may be due to the strong sorption of mineralized lindane (14CO2) and ergosterol to biochar, which might have resulted in lower recoveries by the methods used. A lower extraction efficiency for ergosterol-spiked soils has already been demonstrated in this study. It therefore remains to be clarified whether the biochar had a negative effect on fungal growth and mineralization or whether this can be attributed to inadequate extraction methods. Moreover, it should be examined to what extent common methods for measuring the mineralization of a pollutant can be applied to biochar-amended soils, or whether the methodologies must be changed for this purpose. In addition, it remains to be clarified in the future to what extent these results can be transferred to a field trial.
... When IMONPsAP was used, not all of the materials showed an increase in porosity and/or surface area [31,75,76]. Improvements were observed using PTBIIs [100][101][102] and mixed results were obtained using CCP, PCBFNPs, and IFNPsAP. Using metal salts or oxides led to differing results. ...
... Using biochar for soil restoration and/or amendment has been widely reported to be highly efficient [82][83][84] because inorganic [85][86][87] and organic [88][89][90][91] contaminants are highly adsorbed and the biochar also restores nutrients [92][93][94], regulates bacterial activity [95][96][97], and maintains the soil biota [98][99][100][101]. However, little is known about using biochar-based nanocomposites for the same purpose. ...
Immobilizing nanomaterials in highly porous, surface active, structurally stable biochar creates novel nanocomposites that combines the well-known advantages of both materials. The exceptional contaminant adsorption and/or catalytic degradation capabilities of these nanocomposites have attracted the attention of the scientific community for possible use in environmental applications. This paper reviews the different methodologies for synthesizing biochar-supported nanomaterials, the key physical and chemical characteristics of these nanomaterials, and their performance in environmental applications, as well as identifies current knowledge gaps and potential directions for further research and development.
... However, while the use of sorbents such as AC limits the pollutant mobility and eco-toxicity, it also reduces microbial bio-accessibility, and consequently may hinder the natural microbial biodegradation processes in soils. This may ultimately result in an increased persistence of HOCs in the environment (Rhodes et al., 2008(Rhodes et al., , 2010. A reduced HOC bioavailability could potentially lead to unfavourable shifts in the soil microbial community composition, brought about by the reduced opportunity for growth of HOCs degraders and/or a metabolic switch to other forms of carbon substrates over HOCs. ...
... This result confirms that AC amendment from the start limits crude oil availability for biodegradation and results in slower mineralisation of crude oil components. Previous studies have already shown how the addition of AC reduces or hinders the rate of hydrocarbon mineralisation to CO 2 by limiting the substrate bioaccessibility (Oyelami et al., 2014;Rhodes et al., 2008Rhodes et al., , 2010. In this study, we furthermore demonstrated that AC amendment had a much lesser impact on crude oil polluted soil respiration if added after 5 months ('Soil & oil & AC at time 5 months' compared to 'Soil & oil' batches). ...
The use of activated carbon (AC) amendments to reduce exposure risks for hydrophobic contaminants like polycyclic aromatic hydrocarbons (PAHs) by adsorption is an innovative soil remediation approach. However, AC amendment side-effects on the pollution biodegradation are poorly understood. This study assessed for optimized nutrient ratio conditions, effects of 5% soil wet weight AC amendments, if added from the beginning or after five months, on the outcomes of one year of crude oil polluted soil bioremediation. CO2, residual hydrocarbon concentrations and microbial community structure analysis revealed how AC amendment hindered crude oil biodegradation much more, if added from the start, as compared to after 5 months, i.e. after the initial phase of biodegradation. Putative crude oil degrading microorganisms from the genera Marinobacter, Parvibaculum, Salinibacterium, Muricauda, and Alcanivorax were more sensitive to the AC amendment than those from the genus Rhodococcus. Rhodococci possess hydrophobic cell walls which may enable them to accumulate hydrocarbons in the AC amended soil, despite of their reduced availability. AC amendment from the start had the highest alkane and total US EPA PAH residues, but was more effective than one year of bioremediation, with or without AC amendment after 5 months, in reducing PAH availability in the soil.
... One significant disadvantage of sorbent amendments is that they generally lead to reduced biodegradation of PAHs because the sorbed PAHs have a reduced microbial bioaccessibility and cannot, therefore, be degraded (Rhodes et al., 2008;Rhodes et al., 2010;Cho et al., 2012;Arp et al., 2014). For example, the mineralization extent of phenanthrene (PHE) decreased by up to 50% with amendment of 5% BC (Rhodes et al., 2008); whereas for AC amendment, it declined from 87.2% (in absence of AC) to 0.4% (5% AC) (Rhodes et al., 2010). ...
... One significant disadvantage of sorbent amendments is that they generally lead to reduced biodegradation of PAHs because the sorbed PAHs have a reduced microbial bioaccessibility and cannot, therefore, be degraded (Rhodes et al., 2008;Rhodes et al., 2010;Cho et al., 2012;Arp et al., 2014). For example, the mineralization extent of phenanthrene (PHE) decreased by up to 50% with amendment of 5% BC (Rhodes et al., 2008); whereas for AC amendment, it declined from 87.2% (in absence of AC) to 0.4% (5% AC) (Rhodes et al., 2010). This is potentially problematic as many regulatory standards, and site-specific remediation targets, are based on total concentrations, and not bioavailable concentrations (Latawiec et al., 2010;Ortega-Calvo et al., 2015). ...
... Soil type can have a significant effect on PAH degradation, for example soils with enhanced sorptive capacity (due to high levels of SOM) may show a reduced mass transfer rate of PAHs in soil solution (Macloed & Semple, 2002). However, in contaminated soils with high pollutant levels, sorbent saturation would result in more freely available PAHs, which could lead to increased levels of degradation (Cornelissen et al., 2005;Rhodes et al., 2010). Additionally, as biochar is capable of stimulating soil microbial activity, its addition to soil could strongly influence the degradation of naturally occurring PAH in soil. ...
... Alternatively, as biochar can effectively absorb organic contaminants, it could decrease microbial mineralization by limiting the bioavailability of the contaminants (Rhodes et al., 2008(Rhodes et al., , 2010Xia et al., 2010;Quilliam et al., 2012). The sorbing abilities of biochar might prove to be beneficial from the perspective of groundwater quality, as sorption of PAHs onto biochar surfaces would presumably limit the rate of PAH leaching from soils (Hale et al., 2012). ...
Residual pollutants including polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), and carbon(aceous) nanoparticles are inevitably generated during the pyrolysis of waste biomass, and remain on the solid co-product called biochar. Such pollutants could have adverse effects on the plant growth as well as microbial community in soil. Although biochar has been proposed as a “carbon negative strategy” to mitigate the greenhouse gas emissions, the impacts of its application with respect to long-term persistence and bioavailability of hazardous components are not clear. Moreover, the co-occurrence of low molecular weight VOCs with PAHs in biochar may exert further phytotoxic effects. This review describes the basic need to unravel key mechanisms driving the storage versus emission of these organics and the dynamics between the sorbent (biochar) and soil microbes. Moreover, there is an urgent requirement for standardized methods for quantitative analysis of PAHs and VOCs in biochar under environmentally relevant conditions. Current research gap includes the influence of biochar application technology on the short- and long-term fate of PAHs and VOCs, long-term studies on PAHs/VOCs release, and for proper control of biochar quality and associated risk assessment. This article is protected by copyright. All rights reserved.
... Marchal (2013) demonstrated for phenanthrene sorbed to soils that the stronger the adsorbent (AC, biochar, compost), the lower desorbed concentration, and the lower the microbial degradation (Marchal 2013). These results are not unique (Rhodes 2010), but they may be specific to adsorbates having high heats of adsorption like phenanthrene. Three-ring PAH, as is phenanthrene, degradation has been reported to be inhibited by AC, but 4 and 5-ring PAHs degradation is supported by AC (García-Delgado 2019). ...
In-situ remediation of petroleum hydrocarbons (PHCs) using activated carbon (AC) is an emerging technology intended to enhance sorption and biodegradation mechanisms in soil and groundwater systems. The combination of pore types, source material, activation process, and grind of a particular AC influences its efficacy in subsurface remediation. When high-energy injection techniques are employed, installation of carbon-based injectate (CBI) slurries can be conducted in practically any geological setting, from sandy aquifers to low-permeability zones and weathered or fractured rock. Following an adequate CBI installation throughout the target treatment zone or as a permeable reactive barrier, dissolved PHC concentrations are typically observed to rapidly decrease. After a new equilibrium is formed, PHC concentrations typically decrease over time due to the biodegradation. PHC biodegradation, in association with the CBIs, is indicated by the presence of appropriate microbial communities found to grow on AC and is supported by multiple lines of evidence. Further research is encouraged to optimize the biodegradation and regeneration processes of CBI products for in-situ remediation of PHCs.
... This seems to contradict the fact that reduced extractability and bioavailability would lead to reduced biodegradation efficiency, and consequently, more pollutant would remain in the soil (Arp et al., 2014;Xiong et al., 2017). For example, the addition of black carbon significantly reduced the extractability and microbial mineralization of hydroxypropyl- cyclodextrin and phenanthrene in soil (Rhodes et al., 2008;Rhodes et al., 2010). Some studies argue that biochar, with a high porosity, a large specific surface area, and rich nutrients, provides a suitable shelter for microorganisms and increases the abundances of pollutant-degrading bacteria (Anyika et al., 2014;Kong et al., 2018;Ye et al., 2019). ...
Polycyclic aromatic hydrocarbons (PAHs) in soil pose a threat to the health of humans and other organisms due to their persistence. The remediation method of combined application of biochar and earthworms has received growing attention owing to its effectiveness in PAHs removal. However, the earthworm–biochar interaction and its influence on PAHs in soil has not been systematically reviewed. This review focuses on the effectiveness of combined application of earthworms and biochar in the remediation of PAHs-contaminated soils and the underlying mechanisms, including adsorption, bioaccumulation, and biodegradation. Earthworm–biochar interaction activates the functional microorganisms in soil and the PAHs-degradaing icroorganisms in earthworm guts, promoting PAHs biodegradation. This review provides a theoretical support for the combined application of biochar and earthworms in the remediation of PAHs-contaminated soils,points out the limitations of this remediation method, and finally shows the prospects for future research.
... However, the soil amendment with these sorbents usually reduce the accumulation of BaP and other PAHs in plant phytomass . The main reason of the phenomenon is the strong binding of highly condensed PAHs in the nanoporous space of those sorbents through π-π-bonds between aromatic rings of PAHs and graphite-like surface inside split-like pores of GAC or biochar (Chen and Chen, 2009;Rhodes et al., 2010;Hale et al., 2011). Similar or/and other mechanisms of PAHs binding by peat, vermiculite or kaolinite can influence on lower availability of the adsorbed compounds, which should be studied in future. ...
Due to the extensive oil extraction and transportation that occurs in oil-producing countries, many lands remain contaminated because of accidental leakages. Despite its low cost and environmentally safe nature, bioremediation technology is not always successful, mainly because of the soil toxicity to the degrading microbial populations and plants. Here we report a three-year microfield experiment on the influence of natural sorbents of mineral (zeolite, kaolinite, vermiculite, diatomite), organic (peat), carbonaceous (biochar) origin, and a mixed sorbent ACD (composed of granular activated carbon and diatomite) on the bioremediation of grey forest soil contaminated with weathered crude oil (40.1 g total petroleum hydrocarbons (TPH) kg⁻¹). Optimal doses of the sorbents significantly accelerated bioremediation of petroleum-contaminated soil through bioaugmentation followed by phytoremediation. The main reason for the influence of the sorbent amendments relied upon the creation of optimal conditions for the activation of hydrocarbon-utilizing bacteria and plant growth due to the reduction of soil toxicity, as well as maintaining an optimal pH and water-air regime in the soil. That happened because of reducing the soil hydrophobicity, increasing porosity and water holding capacity. The content of the TPH in the best samples (2 % biochar or ACD) reduced to their local permissible concentration accepted for remediated soils in the Russian Federation (≤5 g kg⁻¹) after two warm seasons compared to that after three warm seasons in the other samples. Although some sorbents decelerated biodegradation of highly condensed polycyclic aromatic hydrocarbons (PAHs, including benzo(a)pyrene) in the soil, the overall risk from the residual contaminants present in the remediated soil and plants was minimized. The final total content of the main PAHs in the sorbent-amended soils did not exceed the maximal permissible levels that are accepted in most EU countries (1000–40,000 μg kg⁻¹), and they did not accumulate in the aboveground phytomass of grasses in dangerous concentrations.
... Urease can promote the hydrolysis of nitrogen-containing organic matter (Cordero, Snell, and Bardgett 2019), alkaline phosphatase is the main enzyme that participated in the P cycle (Dick and Burns 2011), and catalase can decompose the peroxide produced during metabolism (Liu et al. 2017). Rhodes et al. (2010) found the activated charcoal impacted the mineralization interactions between soil, biota, and contaminants and their influence on pollutant environmental degradation. Rojas-Tapias et al. (2012) Found the high OM content enhanced the microbial activities in saline-sodic soil due to producing SOC during the OM mineralization to decrease salinity impact in crops. ...
Soil carbon and microbial biomass were substantially depleted following long-term incubation for saline-sodic and calcareous soils. The objectives of the present study were to investigate changes in (i) soil CO2-emissions and (ii) soil fertility and SOM decomposition (iii) soil enzymes activities during the incubation period under various organic and biological soil treatments. Both soils were incubated for 150 days with 9 treatments included 2 levels of spent grain, which referred to as 10 g kg−1 soil (S1), and 20 g kg−1 soil (S2); two levels of compost were referred to as 10 g kg−1 soil (M1), and 20 gkg−1(M2); Azospirillum brasilense (A1) was inoculated 5% of weight of the soil; the mix of both sources M1 and S1 (M1S1); the combination of both sources A1 with M1 and S1 (A1M1) and (A1S1); all treatments were used and compared to the control. All treatments were mixed with 400 g soil samples and incubated at 28°C. Results showed that the average cumulative CO2 emission for both soils regarding to S2 and A1 treatments had the highest values, 548.3 and 364 (mg C100g−1 soil), respectively. While the lowest value was observed for the control treatment 89.12 and 40.13 (mg C100g−1 soil) for calcareous and saline soils, respectively. The dehydrogenase and urease enzymes were often decreased slightly and did not respond to adding labile substrate, and did not restrict soil breathing. The S2 treatment possessed the dehydrogenase and urease enzymes highest values in calcareous soil, 720 (μgTPFml−1) and 309 (mgNH3−Hg−1h−1), respectively, after incubation periods. In conclusion, the findings support the idea that the soil organic matter amendments increased soil respiration over long-term incubation and compensate the absence of microbial biomass and enzymes in calcareous more than saline soils and enhance soil-plant nitration.
... Comparison of means for the interaction of time × active carbon size and weight on microbial respiration (Fig 4) 230 showed that in overall, microbial respiration in all active carbon treatments increased over time compared with 231 the beginning of the experiment. In all 10-day periods, among active carbon treatments, the highest and lowest Rhodes et al. 2010). Also, according to Ramsay et al. (2000) and Schaefer and Juliane (2007) ...
In this study, the effect of different sizes and weights of active carbon as a remediator was evaluated on reduction or removal of petroleum hydrocarbons of a soil polluted by petroleum sludge. The present pilot study was conducted as a split plot in time experiment based on a completely randomized design with three replicates under laboratory conditions for period of 60 days. The experimental treatments included active carbon weights and sizes of 100g and 0.3mm (W100S0.3), 100g and 1.5mm (W100S1.5), 100g and 4mm (W100S4), 150g and 0.3mm (W150S0.3), 150g and 1.5mm (W150S1.5), 150g and 4mm (W150S4) and control (C). Total petroleum hydrocarbon (TPH) and microbial respiration were measured each ten days. The results showed that concentration of TPH decreased with increasing active carbon weight and size. The highest and lowest TPH concentration at all 10-day intervals was associated with control and W150S0.3 treatments. Decreased TPH was accompanied by increased microbial respiration. In general, TPH biodegradation constant (K) increased and half-life times (T 1/2 ) decreased by increasing active carbon application with smaller sizes. The lowest value for TPH biodegradation percentage was associated with W100S4 and W100S1.5 treatments. Active carbon treatments of W150S0.3 and W150S1.5 led the best TPH biodegradation in petroleum sludge-polluted soil. Therefore, active carbon remediator may be applied as a low-cost, efficient and environment-friendly strategy for remediation of petroleum pollution in soil.
... Substrates are generally more bioavailable when dissolved, but direct and dual-phase transformation of adsorbed POP are also possible (Lian & Xing, 2017;Pagnozzi et al., 2021;Tong et al., 2014;Wang et al., 2020). CM amendments do not always increase contaminant biotransformation (Marchal et al., 2013;Meynet et al., 2012;Vasilyeva et al., 2010), and some studies suggest inhibition (Quilliam et al., 2013;Rhodes et al., 2008;Rhodes et al., 2010). Additionally, adsorption of NOM and nutrients to CM directly affects POP availability via competitive adsorption reactions (Ding et al., 2008;Pan & Xing, 2010), leading to retention and/or release of adsorbed POP (Hilber & Bucheli, 2010;Jonker & Koelmans, 2002). ...
Carbonaceous materials (CM) enhance the abundance and activity of bacteria capable of persistent organic (micro)pollutant (POP) degradation. This review synthesizes anaerobic bacterial responses to minimally modified CM in non-fuel cell bioremediation applications at three stages: attachment, metabolism, and biofilm genetic composition. Established relationships between biological behavior and CM surface properties are identified, but temporal relationships are not well understood, making it difficult to connect substratum properties and “pioneer” bacteria with mature microorganism-CM systems. Stark differences in laboratory methodology at each temporal stage results in observational, but not causative, linkages as system complexity increases. This review is the first to critically examine relationships between material and cellular properties with respect to time. The work highlights critical knowledge gaps that must be addressed to accurately predict microorganism-CM behavior and to tailor CM properties for optimized microbial activity, critical frontiers in establishing this approach as an effective bioremediation strategy.
... Soil amendment by carbonaceous sorbents reduces the bioavailability of various organic pollutants (Chai et al. 2012;Denyes et al. 2013), their toxicity and accumulation in living organisms (Brennan et al. 2014). The effective immobilization of hydrophobic organic pollutants in soils amended with activated carbon was shown by Kołtowski et al. (2017), Oen et al. (2012), Rhodes et al. (2010) and Vasilyeva et al. (2001Vasilyeva et al. ( , 2010. Recently, different types of biochar have been produced with sorption properties similar to those from activated carbon, but they are considered more perspective adsorbents due to lower cost compared to activated carbon (Qin et al. 2013;Ahmad et al. 2014;Huggins et al. 2016;Liu et al. 2017a). ...
Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon, highly persistent and toxic and a widespread environmental pollutant. Although various technologies have been developed to remove BaP from the environment, its sorption through solid matrixes has received increasing attention due to cost-effectiveness. The present research compares the adsorption capacity of Haplic Chernozem, granular activated carbon and biochar in relation to BaP from water solution. Laboratory experiments with different initial BaP concentrations in the liquid phase and different ratios of the solid and liquid phases show that Freundlich model describes well the adsorption isotherms of BaP by the soil and both sorbents. Moreover, the BaP isotherm sorption by the Haplic Chernozem is better illustrated by the Freundlich model than the Langmuir equation. The results reveal that the sorption capacity of the carbonaceous adsorbents at a ratio 1:20 (solid to liquid phases) is orders of magnitude higher (13 368 ng mL−1 of activated carbon and 3 578 ng mL−1 of biochar) compared to the soil (57.8 ng mL−1). At the ratio of 0.5:20, the adsorption capacity of the carbonaceous sorbents was 17–45 times higher than that of the soil. This is due to the higher pore volume and specific surface area of the carbonaceous sorbents than soil particles, assessed through scanning electron microscopy. The sorption kinetic of BaP by Chernozem was compared with the adsorption kinetics by the carbonaceous sorbents. Results indicate that the adsorption dynamic involves two steps. The first one is associated with a fast BaP adsorption on the large available surface and inside macro- and meso-pores of the sorbent particles of the granular activated carbon and biochar. Then, the adsorption is followed by a slower process of BaP penetration into the microporous space and/or redistribution into a hydrophobic fraction. The effectiveness of the sorption process depends on both the sorbent properties and the solvent competition. Overall, the granular activated carbon and biochar are highly effective adsorbents for BaP, whereas the Haplic Chernozem has a rather limited capacity to remove BaP from contaminated solutions.
... Results also showed that the loss of 14 C-phenanthrene and 14 Coctacosane residues followed a biphasic curve for both soils with a short period of rapid loss. These findings are also comparable with several studies which have demonstrated that hydrocarbon biphasic loss phases Table 6 Ratios of extraction: 14 C-phenanthrene mineralisation extents using methanol: water and HPCD for soil A and B treatments at each timepoint over 341 d. are resultant from rapid degradation controlled by the microbial activity, followed by slow degradation limited by the mass transfer of hydrocarbons to the aqueous phase (Swindell and Reid, 2006;Rhodes et al., 2010a;Masy et al., 2016). Other causes of this behaviour can be related to a shift within the microbial population (Zhen et al., 2021), which has been previously reported to result on the modification of the biodegradation patterns. ...
This study investigated the extractability, bioaccessibility and biodegradation of ¹⁴C-phenanthrene and ¹⁴C-octacosane in two soils from former oil refinery facilities over 341 days. The impact of biostimulation and bioaugmentation treatments was also evaluated. At 0, 31, 62, 124 and 341 days, the loss and extractability (using dichloromethane, methanol:water and hydroxypropyl-β-cyclodextrin (HPCD)) of the ¹⁴C-hydrocarbons were measured. Further at each time point, the mineralisation of the ¹⁴C-hydrocarbons was measured respirometrically under the different conditions. In general, extractions with methanol: water and HPCD were similar for both hydrocarbons in the different treatments; however, these values were less that those measured with DCM. Overall, significantly higher (p ≤ 0.05) amounts of ¹⁴C-phenanthrene were lost, readily extracted and mineralised in the soils, with treatments having little impact upon the degradation of this hydrocarbon over 341 days. Conversely, bioaugmentation significantly increased the loss of ¹⁴C-octacosane residues from soils and sustained degradation after 31 days. Surprisingly, HPCD and methanol:water both under-predicted the extent to which the contaminants were degraded at each time point. Determining the likelihood of effective biodegradation by the stimulation of indigenous microorganisms or through bioaugmentation needs to be assessed by both chemical and biological measurements of bioaccessibility, rather than just by that which is totally extractable from soil. However, soils which have high loadings of organic matter and/or organic contaminants may prevent accurate assessment of contaminant bioaccessibility, as measured by HPCD.
... These results are consistent with the findings from Fabbri et al. (2013), Keiluweit et al. (2012), Wang et al. (2017a, b), and Zhou et al. (2014). In addition, on contaminated sites, hardwood biochars have been found to reduce soil PAH accumulation by 45% (Gomez-Eyles et al. 2011), while Pinus radiataderived biochar reduced phenanthrene by > 99% (Rhodes et al. 2010). Eucalyptus-derived biochar reduced diuron sorption (Yu et al. 2006), chlorpyrifos, and carbofuran (Yu et al. 2009). ...
There are thousands of abandoned mine land (AML) sites in the U.S. that need to be restored to reduce wind and water erosion, provide wildlife forage, shade streams, and improve productivity. Biochar created from woody biomass that would normally be burned in slash piles can be applied to soil to improve soil properties and is one method to restore AML soil productive capacity. Using this ‘waste’ biomass for biochar and reclamation activities will reduce wildfire risk, air pollution from burning, and particulates released from burning wood. Biochar has the potential to improve water quality, bind heavy metals, or decrease toxic chemical concentrations, while improving soil health to establish sustainable plant cover, thereby preventing soil erosion, leaching, or other unintended, negative environmental consequences. Using forest residues to create biochar also helps reduce woody biomass and improves forest health and resilience. We address concerns surrounding organic and inorganic contaminants on the biochar and how this might affect its’ efficacy and provide valuable information to increase restoration activities on AMLs using biochar alone or in combination with other organic amendments. Several examples of AML biochar restoration sites initiated to evaluate short- and long-term above- and belowground ecosystem responses are presented.
... Microbial adaptation or acclimation to the presence of phenanthrene resulted in increased PAH catabolic activity with time. This was demonstrated by reduction in lag phases, with increases in the rates and extents of phenanthrene mineralisation with time (Macleod and Semple 2002;Lee et al. 2003;Macleod and Semple 2006;Rhodes et al. 2010;Couling et al. 2010). However, significant decreases in rates and extents of phenanthrene catabolism were observed in most of the metal-amended treatments after 63 days. ...
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... A lower PAH biodegradation in biochareamended experiments has been associated with a strong PAH sorption by biochar and a consequently reduced PAH bioavailability (Rhodes et al., 2010;Wang et al., 2012), (Fig. 3). Biochar addition has been reported to negatively affect bioaugmentation and phytoremediation likely due to an increase of pH , a decrease of PAH concentration in the sediment and the nutrient retention in biochar (Janssen et al., 2012;Oleszczuk et al., 2014) (Fig. 3). ...
The contamination of sediments by polycyclic aromatic hydrocarbons (PAHs) has been widely spread for years due to human activities, imposing the research and development of effective remediation technologies for achieving efficient treatment and reuse of sediments. In this context, the amendment of biochar in PAH–contaminated sediments has been lately proposed as an innovative and sustainable technology. This review provides detailed information about the mechanisms and impacts associated with the supplementation of biochar to sediments polluted by PAHs. The properties of biochar employed in these applications have been thoroughly examined. Sorption onto biochar is the main mechanism involved in PAH removal from sediments. Sorption efficiency can be significantly improved even in the presence of a low remediation time (i.e. 30 d) when a multi–PAH system is used and biochar is provided with a high dosage (i.e. by 5% in a mass ratio with the sediment) and a specific surface area of approximately 360 m2 g−1. The use of biochar results in a decrease (i.e. up to 20%) of the PAH degradation during bioaugmentation and phytoremediation of sediments, as a consequence of the reduction of PAH bioavailability and an increase of water and nutrient retention. In contrast, PAH degradation has been reported to increase up to 54% when nitrate is used as electron acceptor in low–temperature biochar–amended sediments. Finally, biochar is effective in co–application with Fe2+ for the persulfate degradation of PAHs (i.e. up to 80%), mainly when a high catalyst dose and an acidic pH are used.
... There has been significant progress in developing in situ bioremediation for pesticides [25, [86][87][88]92,111,112,134,151,154,159,162,180,181,182,185,188,202,204,206,244,277,283,284,286]. These methods fall into three general categories; phytoremediation, bioremediation by indigenous organisms and bioaugmentation. ...
Management and destruction of obsolete pesticides and the remediation of pesticide-contaminated soil are significant global issues with importance in agriculture, environmental health and quality of life. Pesticide use and management have a history of problems because of insufficient knowledge of proper planning, storage, and use. This manuscript reviews recent literature with an emphasis on the management of obsolete pesticides and remediation of pesticide-contaminated soil. The rhizosphere of plants is a zone of active remediation. Plants also take up contaminated water and remove pesticides from soil. The beneficial effects of growing plants in pesticide-contaminated soil include pesticide transformation by both plant and microbial enzymes. This review addresses recent advances in the remediation of pesticide-contaminated soil with an emphasis on processes that are simple and can be applied widely in any country.
... Biochar can also be used to remediate these organic contaminated soils, resulting in their reduced toxicity, mobility, and bioavailability, which was attributed to microbial activity primed/regulated by biochar application (Beesley et al. 2010(Beesley et al. , 2011. Rhodes et al. (2010) observed a > 99% reduction of phenanthrene in a contaminated soil with 0.1% activated biochar amendment as biochar addition accelerated microbial mineralization of phenanthrene and, thus, its detoxification in the soil. In addition, microbial-assisted degradation of chlorpyrifos and carbofuran was observed in spring onion-cultivated soil amended with Eucalyptus spp.-derived biochar (Yu et al. 2009). ...
Application of biochar to soils changes soil physicochemical properties and stimulates the activities of soil microorganisms that influence soil quality and plant performance. Studying the response of soil microbial communities to biochar amendments is important for better understanding interactions of biochar with soil, as well as plants. However, the effect of biochar on soil microorganisms has received less attention than its influences on soil physicochemical properties. In this review, the following key questions are discussed: (i) how does biochar affect soil microbial activities, in particular soil carbon (C) mineralization, nutrient cycling, and enzyme activities? (ii) how do microorganisms respond to biochar amendment in contaminated soils? and (iii) what is the role of biochar as a growth promoter for soil microorganisms? Many studies have demonstrated that biochar-soil application enhances the soil microbial biomass with substantial changes in microbial community composition. Biochar amendment changes microbial habitats, directly or indirectly affects microbial metabolic activities, and modifies the soil microbial community in terms of their diversity and abundance. However, chemical properties of biochar, (especially pH and nutrient content), and physical properties such as pore size, pore volume, and specific surface area play significant roles in determining the efficacy of biochar on microbial performance as biochar provides suitable habitats for microorganisms. The mode of action of biochar leading to stimulation of microbial activities is complex and is influenced by the nature of biochar as well as soil conditions.
... Biochar physical and chemical properties may influence the soil immediately surrounding biochar particles (also known as the "charosphere") to a greater extent than bulk soil not in direct contact (Quilliam et al., 2013a). For example, mineralization of labeled substrates has been used as a measure of degradative potential in many studies with biochar-amended soils (Rhodes et al., 2010;Ogbonnaya et al., 2014;Shan et al., 2015), and 14 C-labeled glucose mineralization varied among niches (Quilliam et al., 2013a). Moreover, biochar stimulation of subzero remediation may increase subzero liquid water content and nutrient fluxes in frozen soil (Karppinen et al., 2017b). ...
When soil is frozen, biochar promotes petroleum hydrocarbon (PHC) degradation, yet we still do not understand why. To investigate microbial biodegradation activity under frozen conditions, we placed 60‐μm mesh bags containing 6% (v/v) biochar created from fishmeal, bonemeal, bone chip, or wood into PHC‐contaminated soil, which was then frozen to −5°C. This created three soil niches: biochar particles, the charosphere (biochar‐contiguous soil), and bulk soil outside of the bags. After 90 d, ¹³C‐phenanthrene mineralization reached 55% in bonemeal biochar and 84% in bone chip biochar charosphere soil, compared with only 43% in bulk soil and 13% in bone chip biochar particles. Soil pH remained near neutral in bone chip and bonemeal biochar treatments, unlike wood biochar, which increased alkalinity and likely made phosphate unavailable for microorganisms. Generally, charosphere soil had higher aromatic degradative gene abundances than bulk soil, but gene abundance was not directly linked to ¹³C‐phenanthrene mineralization. In bone chip biochar‐amended soils, phosphate successfully predicted microbial community composition, and abundances of Bosea and Caulobacter increased in charosphere soil. Biochar effects on charosphere soil were dependent on feedstock material and suggest that optimizing the charosphere in bone‐derived biochars may increase remediation success in northern regions.
Core Ideas
¹³C‐phenanthrene was mineralized in the charosphere of bone chip biochar particles.
pH and nutrient availability were dependent on biochar type and sampling location.
Biochar effects are localized in specific spatial niches of the soil.
... Since the leaching was not allowed from soil samples, this decline in biochar amended soils has been ascribed to sorption of the tested OCPs onto biochars. Furthermore, biochar provides enough opportunity for enhance physical entrapment in its highly porous structure (Rhodes et al., 2010). Previous studies have shown that the biochar (wood pellets) amended soils completely sorbed aminocyclopyrachlor and bentazone herbicide (Cabrera et al., 2014). ...
... It is known that the concentration and quality of the organic compounds formed in biochar also depend on the initial raw material and temperature of pyrolysis. However, it has been demonstrated that PAH availability in biocharamended soils is lower than that of non-amended soils polluted by PAHs (Rhodes et al. 2010), due to the high affinity of PAHs and other hydrophobic organic compounds with biochar. Furthermore, the PAH content decreased in the biochar-amended soils in 2014, particularly in the B treatment, although their concentrations were still significantly higher than those of the control soils. ...
Incorporation of biochar into agricultural soils has been repeatedly proposed as an effective strategy to mitigate climate change with beneficial effects on soil properties and crop production. Results from previous field experiments showed that, when applied to vineyards, biochar amendment increased yield without a negative impact on grape quality, decreasing water stress during droughts and improving soil physical and chemical properties. Despite those positive impacts, the long-term effects of biochar treatment on soil fertility and ecological toxicity have seldom been studied at a real farm scale. We investigated the effects of biochar amendment on vineyard soil subjected to a single and a repeated biochar application focusing on total heavy metal concentration and availability, concentration and persistence of polycyclic aromatic hydrocarbons (PAHs), soil toxicity, and soil microbial community structure over a 5-year period. Our results showed that a longer term biochar application in a vineyard has no impact on soil microorganisms and does not retain toxic compounds (PAH and heavy metals). For the first time in biochar research, we investigate the biochar effect on a perennial crop and correlate the PAH retention with soil microbiota. Our research demonstrates that biochar application in a Mediterranean vineyard does not have a negative impact on soil ecology, reinforcing the perception that biochar is a sustainable option at farm scale, meeting the needs of agronomy and climate change mitigation.
... Nevertheless, currently there is a lack of information on the effect of biochar on the persistence of PAHs in sewage sludge-amended soil under natural conditions. Based on research on soil amendment with biochar alone, it is known that binding PAHs by biochar can also have an effect on increasing the persistence of these compounds in soils, for example by reducing their biodegradation (Cornelissen et al., 2005;Rhodes et al., 2010). On the other hand, however, research shows that the presence of biochar in soil increases soil microorganisms activity (Oleszczuk et al., 2014a), which contributes to accelerated biodegradation of PAHs occurring naturally in soil (Quilliam et al., 2012). ...
The application of sewage sludge with biochar as fertilizer may be a new method improves soil properties. Biochar increases of the crops productivity and reduction of bioavailability of contaminants. In the present study the persistence of sum of 16 (Σ16) PAHs (US EPA 16 PAHs) in a sewage sludge-amended soil (11t/h) and in a sewage sludge-amended soil with the addition of biochar (at a rate of 2.5, 5 or 10% of sewage sludge (dry weight basis)) was determined. This study was carried out as a plot experiment over a period of 18months. Samples for analysis were taken at the beginning of the study and after 6, 12 and 18months from the beginning of the experiment. Application of sewage sludge as a soil amendment did not cause a significant change (P≥0.05) in the soil content of Σ16 PAHs. In turn, the addition of biochar with sewage sludge to the soil, regardless of the contribution of biochar in the sewage sludge, resulted in a significant decrease in PAH content already at the beginning of the experiment. Throughout the experiment, in all treatments the PAH content varied, predominantly showing a decreasing trend. Ultimately, after 18months the content of Σ16 PAHs decreased by 19% in the experiment with sewage sludge alone and by 45, 35 and 28% in the experiment with sewage sludge and the 2.5%, 5.0% and 10% biochar rates, respectively. After 18months of the study, the largest losses in the sewage sludge-amended soil were observed for 2- and 3-ring PAHs. In the sewage sludge- and biochar-amended soil, compared to the beginning of the study and the sewage sludge-amended soil, the highest losses were found for 5- and 6-ring PAHs (2.5 and 5.0% rates) as well as for 5- and 2-ring PAHs (10% rate).
... Soils contain a wide variety of indigenous microflora that possesses catabolic potential to degrade organic contaminants, such as PAHs (Rhodes et al. 2010). However, the catabolic potential of microbes is influenced by contaminant concentration, its bioavailability, chemical stability (Tian et al. 2002;Semple et al. 2007), the presence of co-contaminants (Couling et al. 2010), nonaqueous phase liquids (NAPLs) (Lee et al. 2003) and soil organic matter (Gourlay et al. 2005). ...
Any substance foreign to a biological system is known as xenobiotic compound. The manufacturing and processing of xenobiotic chemicals on the large scale have led to serious surface and subsurface soil contamination. Biotransformation
of the hazardous pollutants to less toxic substances or their complete mineralization represents an economical substitute to clean up soil and water. In principle, fungi by virtue of their enzymes can biodegrade any naturally existing biopolymers and some of the synthetic polymers as well. Degradation of polymers largely depends on the fungal extracellular enzymes, namely, oxidoreductases and hydrolases. White-rot ligninolytic fungal strains such as T. versicolor and P. ostreatus have been recognized to be the major decomposers of biopolymers via laccase-mediated transformation. Moreover, the ligninolytic fungal strains carrying enzyme Mn-peroxidase activity demonstrated the maximum degradation of naphthalene (69 %). Many non-ligninolytic species degrade polycyclic aromatic hydrocarbons (PAHs) via cytochrome P450 monooxygenase and epoxide hydrolase-catalyzed reactions to form transdihydrodiols. Remediation of nitro-aromatics along with their recalcitrant carcinogenic intermediates, possessing the worst degree of toxicity hazardous rating 3, has been described by utilizing fungal species such as Phanerochaete chrysosporium or Pseudomonas sp. ST53. Additionally, white-rot fungi possessing oxidative enzymes have the ability of TNT degradation and mineralization to CO2. On the other hand, fungal laccases have been reported to catalyze the transformation of the model endocrine disruptors, alkylphenols and biphenyls. For instance, T. versicolor catalyzed the partial transformation of nonylphenol into carbon dioxide. Discovering the new beneficial fungal strains in addition to isolation, engineering, and sequencing of new useful enzymes is highly desirable to further strengthen the biodegradation of contaminated soil.
... Soils contain a wide variety of indigenous microflora that possesses catabolic potential to degrade organic contaminants, such as PAHs (Rhodes et al. 2010). However, the catabolic potential of microbes is influenced by contaminant concentration, its bioavailability, chemical stability (Tian et al. 2002;Semple et al. 2007), the presence of co-contaminants (Couling et al. 2010), nonaqueous phase liquids (NAPLs) (Lee et al. 2003) and soil organic matter (Gourlay et al. 2005). ...
The different xenobiotic compounds, such as insecticides, fungicides, herbicides, chlorinated derivatives and polycyclic aromatic hydrocarbons (PAHs), which are widely used in agricultural activities for increased crop production and other human benefits, can enter the soil and water environments and cause significant toxic impacts on the soil health, microorganisms, ecosystem, human health and environmental quality. The application of biochar to soil can improve soil health and fertility, soil organic matter, nutrient content, pH and soil water retention and aggregation, but reduce soil greenhouse gas emissions, soil bulk density, erosion potential and leaching of pesticides and nutrients to surface and groundwater and mitigate climate change impacts. The biochar has high potential to remediate the soils contaminated by xenobiotic compounds reducing their mobility and bioavailability in soil. This book chapter has reviewed (1) biochar production properties and their effects on soil fertility, physical, chemical and biological properties; (2) the fate and behaviour of xenobiotics in soil, illustrating their interaction with soil constituents and uptake by plants; and (3) the remediation techniques to reduce mobility and bioavailability of the xenobiotic compounds through biochar application to soil. Depending on the type, amount of biochar applied and the physicochemical properties of the biochar itself, it may change the soil properties as well as impact the use, rates, efficacious properties and fates of xenobiotic compounds used in agronomic management. The effects of biochar on the fate and mobility of xenobiotic compounds in soil ecosystems depend on the soil types and properties. Since biochars contain colloidal-sized particles that move through soil pore water flows, colloid-facilitated transport could actually enhance mobility and leaching of xenobiotic compounds in the presence of biochar. Increased sorption to soils and recalcitrance of pesticides leading to longer residence times in the environment is desirable if bioactivity is still acceptable, and it controls the target pest. However, longer residence time may also create some environmental problems, such as greater leaching potential or carry-over problems into the following season.
... In this method, a 14 C-hydrocarbon at a known amount of 14 C-activity (Bq g À1 ) and a known concentration of its 12 C-homologue (mg kg À1 ) is amended into soil and the extent to which it is catabolised to 14 CO 2 is measured. This can be as a result of indigenous soil microflora [9][10][11] or following the addition of a microbial inoculum [12,13], with the amount of 14 CO 2 used as a measure of bioavailability for a wide range of aromatic [14] and aliphatic [15] hydrocarbons in soil. ...
Bioavailability is recognised as being important in the study of biodegradation and ecotoxicity of organic contaminants in soils and sediments. The bioavailability of organic contaminants is controlled by biological, chemical and physical interactions and, as a result, will differ between soil types and biota. Over the last 30 years, numerous investigations have been carried out to quantify chemical bioavailability in soil. Much of this research has focussed on using microbial degradation as a measure of bioavailability as well as chemical assessments, with numerous methods published. Chemical methods described in this chapter rely on the extraction of hydrocarbons using aqueous solutions of cyclodextrin, which have been shown to provide a robust and reproducible measurement of the amount of hydrocarbon that is biodegradable when compared with biological approaches also described in this chapter. Clearly, a simple aqueous extraction that predicts the microbial degradable fraction of hydrocarbons will prove to be useful in the assessment of contaminated land by offering a predictive measure of amount of a contaminant(s) that may be removed before embarking on full-scale bioremediation.
... Biochar can increase the sorption of organic pollutants (Chen and Yuan 2011;Ippolito et al. 2012;Oleszczuk et al. 2012;Quilliam et al. 2013b;Tang et al. 2013). In particular, PAHs adsorbed by biochar per unit mass can be 10-1000 times more than other types of organic C in soils (Accardi-Dey and Gschwend 2003; Rhodes et al. 2010). A large number of studies have shown that biochar can also reduce bioavailability of organic pollutants (Ippolito et al. 2012;Quilliam et al. 2013b) through adsorbing nutrients (Joseph et al. 2010) and producing toxicity to microorganisms (Oleszczuk et al. 2013;Quilliam et al. 2013b). ...
Remediation of soils contaminated with petroleum is a challenging task. Four different bioremediation strategies, including natural attenuation, biochar amendment, phytoremediation with ryegrass, and a combination of biochar and ryegrass, were investigated with greenhouse pot experiments over a 90-day period. The results showed that planting ryegrass in soil can significantly improve the removal rate of total petroleum hydrocarbons (TPHs) and the number of microorganisms. Within TPHs, the removal rate of total n-alkanes (45.83 %) was higher than that of polycyclic aromatic hydrocarbons (30.34 %). The amendment of biochar did not result in significant improvement of TPH removal. In contrast, it showed a clear negative impact on the growth of ryegrass and the removal of TPHs by ryegrass. The removal rate of TPHs was significantly lower after the amendment of biochar. The results indicated that planting ryegrass is an effective remediation strategy, while the amendment of biochar may not be suitable for the phytoremediation of soil contaminated with petroleum hydrocarbons.
... As discussed previously, biochar is particularly effective at adsorbing and sequestering organic contaminants (Beesley et al., 2010;Denyes et al., 2012;Gomez-Eyles et al., 2013b). As a result, enhanced sorption of hydrophobic organic compounds such as PAHs could decrease microbial mineralization by decreasing bioavailability to degrading organisms (Quilliam et al., 2013b;Rhodes et al., 2008Rhodes et al., , 2010Song et al., 2012;Xia et al., 2010;Xin et al., 2014). This sorption is generally viewed as positive as it will result in reduced toxic effects by the contaminant and minimize HOC transfer up the food chain. ...
Research into the use of biochar for the remediation of contaminated soils has expanded rapidly over the past 5 yr. We review recent developments in the field and present the findings emanating from small-scale batch sorption experiments, through soil incubations and bioassays, to large-scale field experiments. We discuss the evidence that these experiments have contributed toward a mechanistic understanding of how biochar is capable of remediating soils contaminated with both organic and inorganic contaminants. The effects of biochar pyrolysis temperature, biochar source material, soil type, and contaminant type on the performance of biochars for remediation are identified. The risks associated with applying biochar to uncontaminated agricultural soils are discussed. Knowledge gaps and questions are identified which, if addressed, will considerably advance the application of biochar as a soil remediation tool in the future.
... The sorption ability of biochar in some cases exceeds that of the natural soil organic matter by a factor of 10-100 (Cornelissen et al., 2005). A large number of studies have reported a significant reduction in organic pollutants in biochar-amended soils (Brändli et al., 2008;Beesley et al., 2010;Rhodes et al., 2010;Gomez-Eyles et al., 2011;Yao et al., 2012a, b). The mechanisms proposed are mainly the surface adsorption and partition. ...
Biochar as a soil amendment is confronted with the challenge that it must benefit soil health as it can be by no means separated from soils once it is added. The available literature even though sparse and mostly based on short-term studies has been encouraging and the trend obtained so far has raised many hopes. Biochar has been reported to positively impact an array of soil processes ranging from benefiting soil biology, controlling soil-borne pathogens, enhancing nitrogen fixation, improving soil physical and chemical properties, decreasing nitrate (NO-3) leaching and nitrous oxide (N2O) emission to remediation of contaminated soils. However, very little biochar is still utilized as soil amendment mainly because these benefits are yet to be quantified, and also the mechanisms by which the soil health is improved are poorly understood. Due to the infancy of research regarding this subject, there are still more questions than answers. The future research efforts must focus on carrying out long-term experiments and uncover the mechanisms underlying these processes so that key concerns surrounding the use of biochar are addressed before its large scale application is recommended.
... The good log-log correlations between bioaccessible PAHs and bioaccumulated PAHs may be influenced by partitioning between the turnip epidermis and the pore water fraction of the PAHs. It is not clear why the correlation in the control treatment was worse than the biochar amendment; these correlations are to some extent influenced by mineralization of PAHs in the soil and turnip roots, which in turn are dependant on soil characteristics such as C content, soil aeration, inorganic nutrients, microbial activities and the complex interactions between them [45]. ...
The influence of amending a contaminated soil with different dry-pyrolyzed biochars on the bioaccessibility and biouptake of polycyclic aromatic hydrocarbons (PAH) and potentially toxic elements (PTE) in turnip (Brassica rapa L.,) was investigated. This is the first study to examine the influence of biochar amendments on turnips grown in a contaminated soil. The biochars came from different local feedstocks, including sewage sludge biochar (SSBC), soybean straw biochar (SBBC), rice straw biochar (RSBC) and peanut shell biochar (PNBC). The biochars were applied to soil at 2% and 5% amendments, and the resulting influence on various soil and porewater properties were quantified. The bioaccessible concentrations of PAHs in soil and their bioaccumulation in B. rapa L. significantly (P<0.05) decreased in the biochar amended soils. Biochar additions significantly (P≤0.05) reduced the bioaccumulation of PTEs (As, Cd, Cu, Pb and Zn) in B. rapa L, though not as much as for PAHs. The most effective biochar at reducing both PAHs and PTEs was PNBC (P≤0.05). Amendments of 5% biochar were more effective at reducing contaminant bioaccessibility than amendments at 2% (P<0.05). Crop yield, however, increased the most for the 2% biochar amendments, in particular for SSBC (with a 49% increase in crop yield compared to the non-amended soil). Therefore, which biochar would be the most advantageous in this system would require a cost-benefit analysis between increasing crop yield (best achieved with 2% SSBC amendments) and decreasing the PAH and PTE uptake (best achieved with 5% PNBC amendments).
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... Excavation of contaminated soil to landfill, considered environmentally disruptive and economically unfeasible (Salt et al., 1995;Mench et al.,2010).Modern remediation approaches increasingly assisted natural attenuation and phytostabilization often primed by the addition of soil amendments (Kumpiene et al. 2008;Clemente et al.,2005;Clemente et al.,2006;Hartley and Lepp,2008).The sorption of the chemical also is affected by soil properties including water, organic matter, clay, sand, and oxide contents, and soil pH (Koskinen and Clay, 1997;Laird and Koskinen, 2008).The soil organic matter (SOM) comprises of rubbery and glassy phases, where the latter comprises of black carbon geosorbents (Cornelissen et al., 2005;Rhodes et al.,2010a).Black carbon (BC) is the collective term thermally altered partly charred to highly condensed forms of organic carbon, which includes chars, charcoals, biochars, soots and graphite (Schmidt and Noack, 2000). BC acts as recalcitrant to influence mobility, extractability ,bioavailability of HOCs in soil (Rhodes et al.,2008a;Sundelin et al., 2004;Amonette et al.,2003) and also aids in stabilizing and restoring SOM in soils (Amonette et al., 2003). ...
Agricultural activities and soils emit greenhouse gases, and emissions occur in the conversion of land. Agricultural soils have lost a large portion of their antecedent soil organic carbon storage, becoming a source of atmospheric carbon-dioxide. Biochar is charcoal, optimized with characteristics deemed useful in agriculture, interest in biochar stems from its potential agronomic benefits and carbon sequestration ability. As a soil amendment, biochar can stabilize carbon belowground and potentially increase agricultural and forest productivity, which appear to be sensitive to the conditions prevailing during its formation. Proposed mechanisms evidence point to added environmental function in the mitigation of diffuse pollution and emissions of trace gases from soil; precluding the possibility of contaminants accumulating in soil from the incorporation of biochar. Biochar alters soil properties, encourages microbial activity and enhances sorption of inorganic and organic compounds. Research studies point to their ability to increase the plant available water in the soil which enables the plants to survive longer with water shortage, increase soil fertility and agricultural yields, improve soil structure, aeration and water penetration, and land reclamation. Biochar stability depends on the molar ratio of oxygen to carbon (O: C) in the resulting black carbon and appears to provide, at minimum, a 1000-year biochar half-life. The aim of this review is to provide a sound knowledge, and to recommend future research to systematically understand biochar-Ninteractions over the long term relating to biochar application to soils and the perspective areas yet to be explored.
Background and objectives: In the oil-rich country of Iran, pollution of soil with petroleum compounds is a very important factor for pollution. Gasoil is one of the major products of crude oil and is a major source of environmental pollution. Currently, there is an urgent need to prevent the expansion and distribution of oil pollutions as well as their derivatives.Organic carbon has gained attention as an effective compound in applied management programs of environment conservation. The present study aimed to evaluate the refining of total petroleum hydrocarbon content, determining its kinetic model during the application of refiner and quantitative investigation of the effect of active carbon weight and grain size on the attenuation rate of total petroleum hydrocarbon.
Materials and methods: The soil polluted with gasoil was collected from the vicinity of the gasoil tanker located in Shiraz refinery. Then, after measurement of the amount initial total petroleum hydrocarbon content and physical and chemical properties of the polluted soil, 700 gram soil samples containing active carbon at 0.05 and 2.05 mm sizes and 20, 40, 60, 80 and 100 g kg-1 weight doses were prepared as pilot. The samples were then rested in a 50% constant humidity for four weeks at 28 ± 2 °C, and were aerated and incubated two times a week. Finally, the results of the changes in the total petroleum hydrocarbon and microbial activity over time were reported after statistical analysis.
Results: The results showed that the application of active carbon had a significant effect on the reduction of gasoil pollution of the soil. The results related to determination of the kinetic model for the reduction of pollution during the biochar application process showed that the kinetic of reduction in total petroleum hydrocarbon was of first order equation; so that in 100 g kg-1 active carbon treatment, the lowest half- life was 21.13 days, and the half- life of control soil was 78.76. The results of total petroleum hydrocarbon showed that there was a significant reduction of total petroleum hydrocarbon content in all active carbon treatments. Investigation of bio- respiration (activity index of degrading microorganisms) showed that the application of active carbon in smaller sizes and amount higher weights led to improved hydrocarbon degradation. The biological efficiency of active carbon was calculated 38 percent at the end of the 60 day period.
Conclusion: Application of active carbon refiner in the gasoil- polluted soil is a cheap, effective and environment- compatible method which provides a suitable environment for the plants and soil microorganisms if utilized properly in the polluted soil. This method may be utilized in remediation of the polluted soils as a pre-refining method alone or along with other biological methods (depending on the extent of the pollution and the required remediation).
Biochar has been of considerable importance for various environmental applications in recent years. It has exhibited substantial advantages like favourable structural and surface properties, easy process of preparation and widely available feedstocks. These set of exceptional properties make it an efficient, cost-effective and environment friendly source for diversified elimination of pollutants. The heterogeneity of physico-chemical properties offers a possibility for biochar to optimize its efficacy for targeted applications. This review aims to highlight the critical role that biochar plays in various environmental applications, be it in soil, water or air. In particular the article offers a comprehensive review of the recent research findings and updates related to the diversified role of biochar. Also, the interaction of pollutants with biochar functional groups and the impact of variation of parameters on biochar attribute relevant to specific pollutant removal, modifications, mechanisms involved and competence for such removal has been discussed. Different technologies for production of biochar have also been summarized with an emphasis on post treatment of biochar, such as modification and doping. In addition to this, the underlying gaps in the studies carried out so far and recommendations for future research areas in biochar have also been deliberated.
Biochars can strongly sorb hydrophobic organic contaminants in soils. However, contribution of contaminants in different binding sites to their biodegradation in biochar-amended soils is not clear. In this work, wheat straw biochars were prepared at pyrolysis temperatures of 400 °C (BC400) and 700 °C (BC700). During a 42-day experiment, degradation rate constant of phenanthrene in soils was in the order of treatment without biochar (1.64 × 10⁻² d⁻¹) > treatment with BC700 (0.96 × 10⁻² d⁻¹) > treatment with BC400 (0.30 × 10⁻² d⁻¹). At the beginning, amendment of BC400 and BC700 reduced the rapidly desorbing fraction of phenanthrene in soils by 44.8% and 92.5%, respectively. At the end, both phenanthrene and microbial biomass highly concentrated on the biochar separated from soils. The results of a coupled model of desorption and biodegradation revealed that only phenanthrene in rapidly desorbing sites was degraded in BC400-amended soils, whereas degradation of phenanthrene in both rapidly and slowly desorbing sites occurred in BC700-amended soils, contributing 24.4% and 75.6% of the degradation, respectively. High fraction (>95%) of biodegradable phenanthrene in slowly desorbing sites was the key reason for higher biodegradation rate of phenanthrene in soils with BC700 than in soils with BC400.
This study investigated the impact of wheat straw biochars pyrolyzed at temperatures of 100–700 ℃ (BC100-BC700) on biodegradation of phenanthrene in soils. During a 42-day experiment, biochar amendment reduced the biodegradation ratio of phenanthrene in soils by no change-77.0%. The biodegradation ratio decreased with the increase of pyrolysis temperature from 100 to 400 ℃ and then increased with the increase of pyrolysis temperature from 400 to 700 ℃, exhibiting a U-shape. Meanwhile, desorbing fraction of phenanthrene extracted by n-butanol declined with increasing pyrolysis temperature. Biochar-derived dissolved organic carbon (DOC) obviously influenced the soil DOC contents which were negatively correlated with the total relative abundances of dominant polycyclic aromatic hydrocarbon (PAH)-degraders. These results indicated that in soils amended with biochars pyrolyzed at low temperatures (i.e. 100–400 ℃), both the reduced bioavailability of phenanthrene and the reduced PAH-degrader abundance resulted in decreasing phenanthrene degradation with pyrolysis temperature. In soils amended with biochars pyrolyzed at high temperatures (i.e. 500–700 ℃; HT-biochars), two possible reasons contribute to increasing phenanthrene degradation with pyrolysis temperature: (1) high sorbed-phenanthrene concentration due to large specific surface area and high aromaticity of the biochars, and (2) the increased dominant PAH-degrader abundance for the removal of sorbed-phenanthrene due to the impact of HT-biochars on soil properties (mainly on DOC content).
Biochar, used as a soil amendment, arose from the influx of new understanding of the origin of the “Terra Preta” soils rediscovered in the Amazon. Current theory assumes that active measures were taken centuries ago (CE 450–950) to enrich soils with burnt biomass (char), bone, and manure. These active measures over time resulted in extremely fertile soils rich in plant nutrients, microbial activity, and reactive functional groups that influence cation exchange capacity and a host of other physicochemical soil properties. A wealth of research resulting from this rediscovery has demonstrated that laboratory and commercial grade biochar may enhance soil health and plant growth and can be used as a soil amendment in forestry, agriculture, degraded landscapes, and contaminated soils. However, not all biochars are alike or have the same uses, as variable feedstocks and thermoconversion conditions influence biochar properties. Similarly, the landscape to which they are applied will express variable reactions due to differences in soil type, climate, vegetation, and management. In this chapter the occurrence, production and properties of biochar, and how these properties influence specific soil conditions and reactions is described. We then discuss the proposed, prescribed, and applied uses for biochar on the landscape. We finish with mention of potential hazards from biochar use and gaps in our knowledge.
Pesticides are extensively used in the modern agricultural system. The inefficient and extensive use of pesticides during the last 5 to 6 decades inadvertently led to serious deterioration of environmental quality with health risk to living organisms including humans. It is important to use some environmentally-friendly and sustainable approaches to remediate and restore and maintain soil quality. Biochar has gained considerable attention globally as a promising soil amendment because it has the ability to adsorb and as such minimize the bioavailability of pesticides in soils. This review emphasizes the recent trends and implications of biochar in pesticide-contaminated soils, as well as highlights need of the pesticides use and associated environmental issues in context of the biochar application. The overarching aim of this review is to signify the role of biochar on primary processes such as effect of biochar on the persistence, mineralization, leaching and efficacy of pesticides in soil. Notably, the effects of biochar on pesticide adsorption-desorption, degradation and bioavailability under various operating/production conditions are critically discussed. This review delineates the indirect imoact of biochar on pesticides persistence in soils and proposes key recommendations for future research which are essential for the remediation and restoration of pesticides-impacted soils.
Biochar is seeing increased usage as an amendment in agricultural soils but the significance of nanoscale interactions between this additive and engineered nanoparticles (ENP) remains unknown. Corn, lettuce, soybean and zucchini were grown for 28 d in two different soils (agricultural, residential) amended with 0–2000 mg engineered nanoparticle (ENP) CeO2 kg−1 and biochar (350 °C or 600 °C) at application rates of 0–5% (w/w). At harvest, plants were analyzed for biomass, Ce content, chlorophyll and lipid peroxidation. Biomass from the four species grown in residential soil varied with species and biochar type. However, biomass in the agricultural soil amended with biochar 600 °C was largely unaffected. Biochar co-exposure had minimal impact on Ce accumulation, with reduced or increased Ce content occurring at the highest (5%) biochar level. Soil-specific and biochar-specific effects on Ce accumulation were observed in the four species. For example, zucchini grown in agricultural soil with 2000 mg CeO2 kg−1 and 350 °C biochar (0.5–5%) accumulated greater Ce than the control. However, for the 600 °C biochar, the opposite effect was evident, with decreased Ce content as biochar increased. A principal component analysis showed that biochar type accounted for 56–99% of the variance in chlorophyll and lipid peroxidation across the plants. SEM and μ-XRF showed Ce association with specific biochar and soil components, while μ-XANES analysis confirmed that after 28 d in soil, the Ce remained largely as CeO2. The current study demonstrates that biochar synthesis conditions significantly impact interactions with ENP, with subsequent effects on particle fate and effects.
s
Wheat straw biochars produced at 400 and 700 °C (BC400 and BC700) were used to investigate their effects on the growth of Vallisneria spiralis and the dissipation of phenanthrene and pyrene in sediments. Biochar amendment inhibited the growth of V. spiralis to some extent at the end of 54-day experiment, and the inhibition was stronger by BC700 than by BC400. In unplanted sediments, PAH dissipation was significantly retarded by BC400 but slightly increased by BC700 although bioavailable fraction of the contaminants extracted by butanol was more significantly reduced by the addition of BC700. It is possible that the contaminants sorbed to BC700 are still bioavailable to bacteria. Planting V. spiralis significantly enhanced the dissipation of phenanthrene and pyrene in biochar-unamended sediments, but showed only small effect on the dissipation in biochar-amended sediments. Moreover, redox potential was much higher in planted sediments than in unplanted sediments no matter whether the biochars were amended or not, suggesting that oxygen is not the limiting factor for the degradation in biochar-amended sediments.
At many sites contaminated with hydrophobic organic chemicals such as polycyclic aromatic hydrocarbons (PAH), it has been observed that a fraction of pollutants are sequestered with time, thus remaining unavailable for biodegradation. In order to find suitable solutions for improving the biodegradation potential at a given site, predictions can be done for evaluating the consequence of changing the conditions for microbial growth and degradation. For optimisation of the remediation strategy and for interpreting observed effects, a combined model was developed for simultaneously considering dissolution from an organic chemical phase (non-aqueous phase liquids or solids), ad/desorption, sequestration (aging), microbial metabolism and growth, and the formation of non-extractable residues. The model has been verified from experimental observations in various aspects (Marchal et al. 2013, Kästner et al. 2014, Adam et al. 2014; see also contribution of Rein et al., on dissolution and microbial degradation of different PAH).
In the present study, this model was used for the simulation of bioremediation options for the clean-up of PAH-contaminated soils. The objectives were to understand the behaviour of PAH compounds in contaminated environments and to give recommendations for bioremediation measures based on this knowledge. We analysed the turnover of PAH by combining ad/desorption models for organic compounds with models for the growth and degradation kinetics of microbes. We modelled several scenarios and interpreted the observed effects, such as increasing distribution coefficient (Kd) and persistence of the PAH with time, decreasing degradation rates with concentration, and effects of amendments on sorption and degradation. Based on the kinetics of the processes and the fluxes in the system, we can provide a robust mathematical definition of the terms “bioavailability” and “bioaccessibility”. Finally, the model was applied to evaluate the most effective remediation strategy for PAH contaminated soils and sediments.
The modelling results indicate that the addition of degrader bacteria is only effective for a short time-period. The addition of sorbents may decrease the bioavailable fraction. And thus decrease plant uptake and toxicological risk, but may increase the persistent residual fraction. The persistence of a compound in aged soils can be overcome by increasing the desorption flux (e.g., by detergents or solvents e.g. acetone) and by stimulating bacterial growth by amendment with complex co-substrates (compost, root exudates). In addition, substrate affinity is an important factor for the competitiveness of bacteria in microbial communities under varying environmental conditions and in particular for varying available substrate abundances. It will thus finally determine the community structure at contaminated sites in general and particularly how the microbial community structure is affected by remediation measures.
This study investigated the impact of different types of carbon nanomaterials (CNMs) namely C60, multi-walled carbon nanotubes (MWCNT) and fullerene soot on the catabolism of 14C- phenanthrene in soil by indigenous microorganisms. Different concentrations (0%, 0.01%, 0.1% and 1%) of the different CNMs were blended with soil spiked with 50 mg kg-1 of 12C-phenanthrene, and aged for 1, 25, 50 and 100 d. An increase in concentration of MWCNT- and FS amended to soils showed a significant difference (P = 0.014) in the lag phase, maximum rates and overall extents of 14C- phenanthrene mineralisation. Microbial cell numbers did not show an obvious trend, but it was observed that control soils had the highest population of heterotrophic and phenanthrene degrading bacteria at all time points.
Activated carbon amendment to contaminated soil has been proposed as an alternative remediation strategy to the management of persistent organic pollutant in soils and sediments. The impact of varying concentrations (0%, 0.01%, 0.1% and 1.0%) of different types of AC on the development of phenanthrene catabolism in soil was investigated. Mineralisation of 14C-phenanthrene was measured using respirometric assays. The increase in concentration of CB4, AQ5000 or CP1 in soil led to an increase in the length of the lag phases. Statistical analyses showed that the addition of increasing concentrations of AC to the soil significantly reduced (P < 0.05) the extent of 14C-phenanthrene. For example, for CB4-, AQ5000- and CP1-amended soils, the overall extent of 14C-phenanthrene mineralisation reduced from 43.1% to 3.28%, 36.9% to 0.81% and 39.6% to 0.96%, respectively, after 120 d incubation. This study shows that the properties of AC, such as surface area, pore volume and particle size, are important factors in controlling the kinetics of 14C-phenanthrene mineralisation in soil.
Organic pollutants (e.g. polyaromatic hydrocarbons (PAH)) strongly sorb to carbonaceous sorbents such as black carbon and activated carbon (BC and AC, respectively). For a creosote-contaminated soil (Σ15PAH ) and an urban soil with moderate PAH content (Σ15PAH ), total organic carbon–water distribution coefficients (KTOC) were up to a factor of 100 above values for amorphous (humic) organic carbon obtained by a frequently used Linear-Free-Energy Relationship. This increase could be explained by inclusion of BC (urban soil) or oil (creosote-contaminated soil) into the sorption model.AC is a manufactured sorbent for organic pollutants with similar strong sorption properties as the combustion by-product BC. AC has the potential to be used for in situ remediation of contaminated soils and sediments. The addition of small amounts of powdered AC (2%) to the moderately contaminated urban soil reduced the freely dissolved aqueous concentration of native PAH in soil/water suspensions up to 99%. For granulated AC amended to the urban soil, the reduction in freely dissolved concentrations was not as strong (median 64%), especially for the heavier PAH. This is probably due to blockage of the pore system of granulated AC resulting in AC deactivation by soil components. For powdered and granulated AC amended to the heavily contaminated creosote soil, median reductions were 63% and 4%, respectively, probably due to saturation of AC sorption sites by the high PAH concentrations and/or blockage of sorption sites and pores by oil.
Biotransformation is controlled by the biochemical activity of microorganisms and the mass transfer of a chemical to the microorganisms. A generic mathematical concept for bioavailability is presented taking both factors into account. The combined effect of mass transfer of a substance to the cell and the intrinsic activity of the cell using the substance as primary substrate, is quantified in a bioavailability number (Bn). The concept can easily be extended to secondary substrates. The approach has been applied to explain the observed kinetics of the biotransformation of organic compounds in soil slurries and in percolation columns. The model allowed us to predict threshold concentrations below which no biotransformation is possible. Depending on the environmental system and the chemical involved, predicted threshold concentrations span a range of 11 orders of magnitude from nanograms to grams per liter and match with published experimental data. Mass transferand not the intrinsic microbial activityis in most cases the critical factor in bioremediation.
A study was conducted to determine factors affecting the sequestration and changes in bioavailability as phenanthrene persists in soils. Phenanthrene became sequestered in seven soils differing appreciably in organic matter and clay content as measured by earthworm uptake, bacterial mineralization, or extractability. Phenanthrene also became sequestered as it aged in soil aggregates of various sizes as measured by decline in availability to a bacterium, a mild extractant, or both. Wetting and drying a soil during aging reduced the amount of phenanthrene recovered by a mild extractant and the rate and extent of bacterial mineralization of the hydrocarbon. After biodegradation of phenanthrene added to the soil, more of the compound remained if it had been aged than if it had not been aged. Wetting and drying the soil during aging further increased the amount of phenanthrene remaining after biodegradation. The rate and extent of bacterial mineralization of phenanthrene were less in leached than in unleached soil. Aging/sequestration is thus markedly affected by soil properties and environmental factors.
Naturally occurring, macromolecular dissolved organic matter (NOM) is known to foul activated carbon adsorbents, reducing the ability of fixed-bed adsorbers to efficiently remove targeted synthetic organic contaminants (SOCs). An accurate description of the effects of NOM competition on SOC adsorption equilibria is required to develop dynamic models, which have application to process design and analysis. A model was developed, using an approach based on the Ideal Adsorbed Solution Theory (IAST), to predict trichloroethylene (TCE) adsorption by activated carbon preloaded with humic acid. The IAST model was formulated for a bisolute system in which TCE and humic acid single-solute uptakes were described by the Langmuir-Freundlich and Freundlich isotherms, respectively. The humic mixture was modeled as a single component based on previous studies that identified the low-molecular-weight hydrophobic fraction as the most reactive with regard to preloading effects. Isotherms for this fraction, isolated from whole humic acid using ultrafiltration, were measured, and molar concentrations were computed based on an average molecular weight determined using size-exclusion chromatography. The IAST model was modified to reflect the hypothesis that TCE molecules can access adsorption sites which humic molecules cannot and that no competition can occur on these sites. The model was calibrated with data for TCE uptake by carbon preloaded with the low-molecular-weight humic acid fraction and was verified by predicting TCE uptake by carbon preloaded with whole humic acid. Further improvement to the model was possible by accounting for pore blockage as a mechanism which can reduce the effective surface area available in TCE.
This review highlights the ubiquity of black carbon (BC) produced by
incomplete combustion of plant material and fossil fuels in peats,
soils, and lacustrine and marine sediments. We examine various
definitions and analytical approaches and seek to provide a common
language. BC represents a continuum from partly charred material to
graphite and soot particles, with no general agreement on clear-cut
boundaries. Formation of BC can occur in two fundamentally different
ways. Volatiles recondense to highly graphitized soot-BC, whereas the
solid residues form char-BC. Both forms of BC are relatively inert and
are distributed globally by water and wind via fluvial and atmospheric
transport. We summarize, chronologically, the ubiquity of BC in soils
and sediments since Devonian times, differentiating between BC from
vegetation fires and from fossil fuel combustion. BC has important
implications for various biological, geochemical and environmental
processes. As examples, BC may represent a significant sink in the
global carbon cycle, affect the Earth's radiative heat balance, be a
useful tracer for Earth's fire history, build up a significant fraction
of carbon buried in soils and sediments, and carry organic pollutants.
On land, BC seems to be abundant in dark-colored soils, affected by
frequent vegetation burning and fossil fuel combustion, thus probably
contributing to the highly stable aromatic components of soil organic
matter. We discuss challenges for future research. Despite the great
importance of BC, only limited progress has been made in calibrating
analytical techniques. Progress in the quantification of BC is likely to
come from systematic intercomparison using BCs from different sources
and in different natural matrices. BC identification could benefit from
isotopic and spectroscopic techniques applied at the bulk and molecular
levels. The key to estimating BC stocks in soils and sediments is an
understanding of the processes involved in BC degradation on a molecular
level. A promising approach would be the combination of short-term
laboratory experiments and long-term field trials.
Existing field data indicate that soot may significantly affect the environmental speciation of polycyclic aromatic hydrocarbons (PAHs). To expand hydrophobic partition models to include soot partitioning, we need to quantify fsc, the soot fraction of the solid matrix, and Ksc, the soot-carbon-normalized partition coefficient. To this end, we have developed a method that allows quantification of soot carbon in dilute and complex sedimentary matrices. Non-soot organic carbon is removed by thermal oxidation, and inorganic carbonates are removed by acidification, fol lowed by CHN elemental analysis of the residual soot carbon. The selectivity of the soot carbon method was confirmed in tests with matrices of known compostion. The soot quantification technique was applied to two sets of natural sediments, both previously analyzed for PAHs. The input histories of PAHs and soot recorded in a lacustrine sediment core followed the same general trends, and we thus infer a coupling between the two. Our measures of fsc and calculations of Ksc, approximated from studies of PAH sorption onto activated carbon, were applied to rationalize previously generated in situ Kocvalues. Intriguingly, we find that the elevated PAH Kd values of two marine sediment−porewater systems are now quantitatively explain able through the extended, soot-partioning inclusive, distribution model. The importance of the soot phase for PAHs in the environment has implications for how we perceive (and should test) in situ bioavailability and, consequently, also for the development of sediment quality criteria.
As they persist, or age, in soil, organic compounds become progressively less available for uptake by organisms, for exerting toxic effects, and for biodegradation and bioremediation by microorganisms. This declining bioavailability is not reflected by currently used methods for the chemical analysis of soils for determining concentrations of organic pollutants. As a result, such methods overestimate exposure, and thus risk, from toxic chemicals in contaminated sites.
In this study, temporal changes in extractability of [14C]pyrene were followed in two soils with differing organic matter contents under sterile and nonsterile conditions over 24 weeks. The nonsterile pasture soil was the only incubation to show significant loss of [14C]pyrene-associated activity over the 24-week incubation. Sequential extraction using methanol:water (1:1), followed by 1-butanol and finally dichloromethane−Soxhlet showed changes in the relative proportions of extractability with increased soil−PAH contact time. Significant decreases in methanol:water and 1-butanol extractability were recorded over the 24-week incubation. The nonsterile pasture soil exhibited the greatest decrease in 1-butanol extraction. Significant nonextractable residues were formed with increased soil−pyrene contact time in all soils, with the largest increase found in the nonsterile pasture soil. These residues were investigated by the alkaline extraction of the humic material and saponification of the resultant humin. After 24-week soil−pyrene contact time, the bioavailability of the added [14C]pyrene was assessed by bacterial mineralization. A comparison was made between bioavailability and the amount of 14C activity extracted by the sequential scheme of solvents. Methanol:water significantly underestimated the bioavailable fraction, whereas 1-butanol overestimated the bioavailability of the [14C]pyrene-associated activity.
The fate of radiolabeled ([14C]) phenanthrene, pyrene, benz[a]anthracene, chrysene, and benzo[a]pyrene was examined in five soils, four of which had previous exposure to polycyclic aromatic hydrocarbons (PAHs). The soils and [14C]PAHs studied represent a range of characteristics (fraction of soil organic carbon [foc] and PAH solubility) that can potentially impact contaminant fate. Fates of [14C]PAHs examined in slurry microcosms included mineralization, production of water-soluble metabolites and their polarity, cellular incorporation, and the association of [14C]PAHs with soils, all compared to an abiotic control. The soils all contained active heterotrophic communities and the contaminated soils had sizable populations of PAH-degrading microorganisms, measured by the [14C]-most probable number assay. All [14C]PAHs, except [14C]benzo[a]pyrene, were readily mineralized in most of the preexposed soils, whereas in the uncontaminated soil, less than 5% of each [14C]PAH was mineralized. In the adapted soils, mineralization, after 8 weeks of incubation, accounted for 30 to 60% of [14C]phenanthrene, 10 to 55% of [14C]pyrene, 5 to 40% of [14C]benz[a]anthracene, 10 to 50% of [14C]chrysene, and 2 to 9% of [14C]benzo[a]pyrene added to the microcosms. Metabolite production and cellular incorporation usually accounted for less than 10% of the added [14C]PAH. The fate of PAHs was usually not related to measurements of microbial community size, characteristics of the PAH (water solubility and Kow), and many characteristics of soils (soil foc and PAH concentration). The fraction of silt and clay in the soils for each soil–PAH combination, however, was negatively related to the extent of added [14C]PAH mineralized and the amount solvent extractable from the soil, and positively related to the amount of [14C]PAH remaining in soils after extraction.
Soils contaminated with organic chemicals are now widespread in industrialized and developing countries, and the risk assessment and remediation of such contaminated sites is a priority. However, containment and remediation strategies are complicated in many cases by the range of contaminants present and the historical nature of the contamination. Research has increased our understanding of the behaviour of organic contaminants in soil and the factors that control their behaviour. There is a fundamental need to understand and, where possible, quantify the bioavailable fraction as well as the total concentration of contaminant present in soil: the bioavailable fraction is key to toxicity or biodegradation. To quantify these fractions, a large number of techniques have been employed, ranging from organic and aqueous based solvent extractions to the use of biota. Many studies have been carried out investigating the use of chemical techniques to describe bioavailability, which could be used in the assessment and remediation of contaminated land. The aim of this review is to consider the behaviour of organic contaminants in soil, highlighting issues of bioavailability, and then to discuss the relevance of the various methods for assessing risk and potential remediation of organic contaminants in soil.
Soils represent a major sink for organic xenobiotic contaminants in the environment. The degree to which organic chemicals are retained within the soil is controlled by soil properties, such as organic matter, and the physico-chemical properties of the contaminant. Chemicals which display hydrophobic and lipophilic characteristics, as well as a recalcitrant chemical structure, will be retained within the soil, and depending on the ‘strength’ of the association may persist for long periods of time. This review describes the behaviour of hydrophobic organic contaminants in soils, focusing on the mechanisms controlling interactions between soil and contaminants. The bioavailability of contaminants in soil is also discussed, particularly in relation to contact time with the soil. It considers the degradation of organic contaminants in soil and the mechanisms microbes use to access contaminants. Finally, the review discusses the ‘pros’ and ‘cons’ of chemical and biological techniques available for assessing bioavailability of hydrophobic organic chemicals in soils, highlighting the need to quantify bioavailability by chemical techniques. It concludes by highlighting the need for understanding the interactions between the soil, contaminants and biota which is crucial to understanding the bioavailability of contaminants in soils.
This paper describes the validation and application of a simple flask-based 14C-respirometer system designed to assess mineralisation of 14C-labelled substrates under defined conditions. Validation of this respirometer system indicated stoichiometric CO2 trapping up to a maximum of 400 μmol of CO2 (in a single trap). Polycyclic aromatic hydrocarbon (PAH)-degrading bacteria were used to measure growth-linked biodegradation of [14C]naphthalene to 14CO2. A 14C activity balance of 101.7±8.9% (n=6), after 74 h incubation time and 10 respirometer-opening events, indicated the suitability of the system for monitoring substrate mineralisation. This respirometric apparatus was then successfully applied to assess: (i) the PAH catabolism of microbes in a field contaminated soil, where naphthalene and phenanthrene were rapidly mineralised and (ii) soil-associated organic contaminant bioavailability, where increased soil–phenanthrene contact time resulted in a reduction in phenanthrene mineralisation in the soil. The described respirometer system differs from existing respirometer systems in that the CO2 trap can be removed and replaced quickly and easily. The system is efficient, reproducible, adaptable to many situations, easy to construct and simple to use, it therefore affords advantages over existing systems.
A study was conducted to determine factors affecting the sequestration and changes in bioavailability as phenanthrene persists in soils. Phenanthrene became sequestered in seven soils differing appreciably in organic matter and clay content as measured by earthworm uptake, bacterial mineralization, or extractability. Phenanthrene also became sequestered as it aged in soil aggregates of various sizes as measured by decline in availability to a bacterium, a mild extractant, or both. Wetting and drying a soil during aging reduced the amount of phenanthrene recovered by a mild extractant and the rate and extent of bacterial mineralization of the hydrocarbon. After biodegradation of phenanthrene added to the soil, more of the compound remained if it had been aged than if it had not been aged. Wetting and drying the soil during aging further increased the amount of phenanthrene remaining after biodegradation. The rate and extent of bacterial mineralization of phenanthrene were less in leached than in unleached soil. Aging/sequestration is thus markedly affected by soil properties and environmental factors.
Studies were conducted to examine the adaptation response of aquifer microbial communities to xenobiotic compounds and the influence of chemical preexposure in the laboratory and in situ on adaptation. Adaptation and biodegradation were assessed as mineralization and cellular incorporation of 14C-radiolabeled substrates. For some compounds, such as ethylene dibromide, aniline and m-nitrophenol, biodegradation and adaptation rates were not influenced by chemical concentration over the range tested. Biodegradation rates increased with concentration for p-chlorophenol, and a gradient of adaptation and biodegradation responses was observed for p-nitrophenol up to a threshold concentration. Acclimation to laboratory conditions decreased but did not eliminate the adaptation period to p-nitrophenol. Laboratory adaptation studies and examination of uncontaminated and contaminated field samples from a single aquifer indicated that adaptation was accompanied by shifts in the metabolic fate of the substrate. The increased metabolism associated with adapted communities was predominantly the result of increased mineralization. Cellular incorporation represented a significantly smaller fraction of total metabolism in the adapted versus the unadapted communities. The results indicate that the adaptation response in aquifer solids is due to a complex set of interactions that are influenced by the physiology and growth of the degrading populations.
Contamination of soil by polycyclic aromatic hydrocarbons is frequently associated with non-aqueous-phase liquids. Measurement of the catabolic potential of a soil or determination of the biodegradable fraction of a contaminant can be done using a slurried soil respirometric system. This work assessed the impact of increasing the concentration of transformer oil and soil:water ratio on the microbial catabolism of [14C]phenanthrene to 14CO2 by a phenanthrene-degrading inoculum. Slurrying (1:1, 1:2, 1:3 and 1:5 soil:water ratios) consistently resulted in statistically higher rates and extents of mineralisation than the non-slurried system (2:1 soil:water ratio; P<0.01). The maximum extents of mineralisation observed occurred in the 1:2–1:5 soil:water ratio microcosms irrespective of transformer oil concentration. Transformer oil concentrations investigated displayed no statistically significant effect on total mineralisation (P>0.05). Soil slurries 1:2 or greater, but less than 1:5 (soil:water), are recommended for bioassay determinations of total contaminant bioavailability due to greater overall mineralisation and improved reproducibility.
A technique using Tenax TA® beads as “sink” for desorbed solute was employed to measure the kinetics of desorption of chlorobenzenes, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons from laboratory-contaminated sediment. First-order rate constants of rapid and slow desorption were in the order of 10−1/h and 10−3/h, respectively. The rate constants of slow desorption correlate well with the molecular volumes of the compounds used and decrease between 2 and 34 d of equilibration. Slowly desorbing fractions increase with both increasing solute hydrophobicity and increasing equilibration time.
Soot-associated PAHs were exposed to simulated sunlight to investigate disappearance rates under environmental aging conditions and to examine the robustness of diagnostic ratios for PAH source apportionment. Naphthalene, acenaphthylene, acenaphthene, and fluorene showed an obvious two-phase disappearance in all experiments while phenanthrene and anthracene exhibited this behavior for all but the highest soot loading. The first phase loss is 5–40 times faster than the second phase loss and occurred within 3 h for naphthalene, acenaphthylene, acenaphthene, and fluorene and within 10 h for phenanthrene and anthracene. Two-phase disappearance was not observed for any of the higher molecular weight PAHs with 4–6 rings. Each PAH has a unique loss rate via photodegradation and volatilization and these rates of some PAHs were affected by soot loadings; phenanthrene and anthracene showed similar rates in the first phase and increased loss rates in the second phase as soot loading increased. In the absence of light, the loss of PAHs was related to both temperature and molecular characteristics. Due to differences in disappearance rates of individual PAHs under illumination over extended times, prolonged exposure to sunlight could change the interpretation of some diagnostic ratios used previously for PAH source identification. This result indicates that more consistent and accurate methods that take into consideration the longevity of particulate PAHs are needed for reliable source apportionment.
Plant litter and the microbial biomass are the major parent materials for soil organic matter (SOM) formation. Plant litter is composed of complex mixtures of organic components, mainly polysaccharides and lignin, but also aliphatic biopolymers and tannins. The composition and relative abundance of these components vary widely among plant species and tissue type. Whereas some components, such as lignin, are exclusively found in plant residues, specific products are formed by microorganisms, e.g. amino sugars. A wide variety of chemical methods is available for characterizing the chemical composition of these materials, especially the chemolytic methods, which determine individual degradation products and solid-state 13C NMR spectroscopy, that gives an overview of the total organic chemical composition of the litter material. With the development of these techniques, an increasing number of studies are being carried out to investigate the changes during decay and the formation of humic substances. An overview is given on the amount of litter input, the proportion of various plant parts and their distribution (below-ground/above-ground), as well as the relative proportion of the different plant tissues. Major emphasis is on the organic chemical composition of the parent material for SOM formation and thus this paper provides information that will help to identify the changes occurring during biodegradation of plant litter in soils.
The adsorption of dysprosium ions onto activated charcoal from aqueous solution has been investigated in relation to pertinent variables, such as shaking time, pH, concentration of dysprosium ions, and temperature. The conditions leading to maximum adsorption have been established. The adsorption of dysprosium ions obeys the Langmuir and the Dubinin-Radushkevich isotherm equations. Thermodynamic quantities, namely AH and AS, have been calculated from the slopes and intercepts of plots of In (KD) versus . The results indicate that the adsorption of dysprosium ions on activated charcoal is an endothermic process. The influence of different cations and anions on the adsorption of dysprosium ions has been examined. The adsorption of other metal ions on activated charcoal has been measured under specified conditions to evaluate their selectivity. Approximately 98% of the dysprosium adsorbed on the activated charcoal was recovered using 40 ml of 3M HNO3 solution.
This review highlights the major progress over the last decade on characterization of geochemically heterogeneous soil/sediment organic matter (SOM) and the impacts of SOM heterogeneity on sorption and desorption of hydrophobic organic contaminants (HOCs) under equilibrium and rate limiting conditions. Sorption and desorption by soils and sediments are fundamental processes controlling fate and transport of less polar and nonpolar organic pollutants in surface aquatic and groundwater systems. Recent studies have shown that soils and sediments exhibit an array of HOC sorption phenomena that are inconsistent with an early partition model based on an assumption of homogeneous gel-like SOM. Increasing data have revealed that isotherm nonlinearity, varied sorption capacity, sorption–desorption hysteresis, and slow rates of sorption and desorption are characteristics for HOC sorption by soils and sediments. These phenomena have been shown to result from different types of condensed SOM that exhibit capacity limiting sorption processes. Recent findings of glass transition phenomena and the nonlinear HOC sorption by humic acids provide a scientific foundation for drawing an analogy between humic acids and synthetic organic polymers that supports a dual mode model for sorption by soils and sediments. Humic acid is glassy or rigid at temperatures lower than its glass transition temperature and exhibits relatively nonlinear sorption isotherms for HOCs. Fractionation and quantification of SOM indicate that soils and sediments contain significant amounts of black carbon and kerogen of different origins. These particulate organic materials have rigid 3-dimensional structures and are often less polar compared to humic substances. Limited studies show that black carbon and kerogen exhibit nonlinear sorption for HOCs and may dominate the overall nonlinear sorption by soils and sediments.
Assessments of the hazard of toxic chemicals in soil are made without concern about the possibility that their bioavailability may change with time. The patterns of disappearance of persistent compounds in the field and laboratory studies show a declining availability to microorganisms with residence time in soil. Changes in extractability with residence time and the kinetics of sorption and desorption suggest that the compounds are becoming sequestered in inaccessible microsites within the soil matrix. Diminishing toxicity as chemicals age in soil is evident in a limited number of assessments. Such findings suggest that the hazard and risk from toxic chemicals diminish as the compounds persist in soil.
A study was conducted to determine whether the time that a compound remains in a soil affects its biodegradability and the ease of its extraction. Phenanthrene and 4-nitrophenol were aged in sterilized loam and muck, and bacteria able to degrade the compounds were then added to the soils. increasingly smaller amounts of phenanthrene in the muck and 4-nitrophenol in both soils were mineralized with increasing duration of aging. Aging also increased the resistance of phenanthrene to biodegradation in nutrient-amended aquifer sand. The rate of miner- alization of the two compounds in both soils declined with increasing periods of aging. The amount of phenanthrene and 4-nitrophenol added to sterile soils that was recovered by butanol extraction declined with duration of aging, but subsequent Soxhlet extraction recovered phenanthrene from the loam but not the muck. The extents of mineralization of phenanthrene previously incubated for up to 27 days with soluble or insoluble organic matter from the muck were similar. Less aged than freshly added phenanthrene was biodegraded if aggregates in the muck were sonically disrupted. The data show that phenanthrene and 4-nitrophenol added to soil become increasingly more resistant with time to biodegradation and extraction.
Biotransformation is controlled by the biochemical activity of microorganisms and the mass transfer of a chemical to the microorganisms. A generic mathematical concept for bioavailability is presented taking bath factors into account. The combined effect of mass transfer of a substance to the cell and the intrinsic activity of the cell using the substance as primary substrate, is quantified in a bioavailability number (Bn). The concept can easily be extended to secondary substrates. The approach has been applied to explain the observed kinetics of the biotransformation of organic compounds in soil slurries and in percolation columns. The model allowed us to predict threshold concentrations below which no biotransformation is possible. Depending on the environmental system and the chemical involved, predicted threshold concentrations span a range of 11 orders of magnitude from nanograms to grams per liter and match with published experimental data. Mass transfer-and not the intrinsic microbial activity-is in most cases the critical factor in bioremediation.
Black carbon in sediment, present natively or added as a treatment amendment in the form of activated carbon, reduces contaminant bioavailability. Field evaluation of activated carbon effectiveness in reducing contaminant bioavailability requires accurate methods to measure the amendment in sediments. The most commonly used method to separate black carbon from natural organic matter in soils and sediments is low temperature (375 degrees C) thermal oxidation which resulted in significant losses of activated carbons. A method was developed to isolate activated carbon using a solution of concentrated sulfuric acid and potassium dichromate to oxidize the natural organic matter while preserving the activated carbon. The chemical oxidation method was applied to assess the delivery of activated carbon to sediments in a pilot-scale demonstration project carried out in Grasse River, NY. Using this method on sediment from the Grasse River, over 98% of the natural organic matter was removed while preserving at least 95% of the activated carbon. The method was also demonstrated on other carbonaceous geosorbents and native black carbon in several sediment samples.
We studied the mineralization of pyrene, carbazole, and benzo[a]pyrene in soils obtained from three abandoned coal gasification plants in southern Illinois. The soils had different histories of past exposure to hydrocarbon contamination and different amounts of total organic carbon, microbial biomass, and microbial activity. Mineralization was measured by using serum bottle radiorespirometry. The levels of indigenous mineralization of 14C-labeled compounds ranged from 10 to 48% for pyrene, from undetectable to 46% for carbazole, and from undetectable to 25% for benzo[a]pyrene following long-term (greater than 180-day) incubations. Pyrene and carbazole were degraded with short or no lag periods in all soils, but benzo[a]pyrene mineralization occurred after a 28-day lag period. Mineralization was not dependent on high levels of microbial biomass and activity in the soils. Bacterial cultures that were capable of degrading pyrene and carbazole were isolated by enrichment, grown in pure culture, and reintroduced into soils. Reintroduction of a pyrene-degrading bacterium enhanced mineralization to a level of 55% within 2 days, compared with a level of 1% for the indigenous population. The carbazole degrader enhanced mineralization to a level of 45% after 7 days in a soil that showed little indigenous carbazole mineralization. The pyrene and carbazole degraders which we isolated were identified as a Mycobacterium sp. and a Xanthamonas sp., respectively. Our results indicated that mineralization of aromatic hydrocarbons can be significantly enhanced by reintroducing isolated polycyclic aromatic hydrocarbon-degrading bacteria.
A study was conducted of possible reasons for acclimation of microbial communities to the mineralization of organic compounds in lake water and sewage. The acclimation period for the mineralization of 2 ng of p-nitrophenol (PNP) or 2,4-dichlorophenoxyacetic acid per ml of sewage was eliminated when the sewage was incubated for 9 or 16 days, respectively, with no added substrate. The acclimation period for the mineralization of 2 ng but not 200 ng or 2 micrograms of PNP per ml was eliminated when the compound was added to lake water that had been first incubated in the laboratory. Mineralization of PNP by Flavobacterium sp. was detected within 7 h at concentrations of 20 ng/ml to 2 micrograms/ml but only after 25 h at 2 ng/ml. PNP-utilizing organisms began to multiply logarithmically after 1 day in lake water amended with 2 micrograms of PNP per ml, but substrate disappearance was only detected at 8 days, at which time the numbers were approaching 10(5) cells per ml. The addition of inorganic nutrients reduced the length of the acclimation period from 6 to 3 days in sewage and from 6 days to 1 day in lake water. The prior degradation of natural organic materials in the sewage and lake water had no effect on the acclimation period for the mineralization of PNP, and naturally occurring inhibitors that might delay the mineralization were not present. The length of the acclimation phase for the mineralization of 2 ng of PNP per ml was shortened when the protozoa in sewage were suppressed by eucaryotic inhibitors, but it was unaffected or increased if the inhibitors were added to lake water.(ABSTRACT TRUNCATED AT 250 WORDS)
This paper describes the validation and application of a simple flask-based (14)C-respirometer system designed to assess mineralisation of (14)C-labelled substrates under defined conditions. Validation of this respirometer system indicated stoichiometric CO(2) trapping up to a maximum of 400 micromol of CO(2) (in a single trap). Polycyclic aromatic hydrocarbon (PAH)-degrading bacteria were used to measure growth-linked biodegradation of [(14)C]naphthalene to (14)CO(2). A (14)C activity balance of 101.7+/-8.9% (n=6), after 74 h incubation time and 10 respirometer-opening events, indicated the suitability of the system for monitoring substrate mineralisation. This respirometric apparatus was then successfully applied to assess: (i) the PAH catabolism of microbes in a field contaminated soil, where naphthalene and phenanthrene were rapidly mineralised and (ii) soil-associated organic contaminant bioavailability, where increased soil-phenanthrene contact time resulted in a reduction in phenanthrene mineralisation in the soil. The described respirometer system differs from existing respirometer systems in that the CO(2) trap can be removed and replaced quickly and easily. The system is efficient, reproducible, adaptable to many situations, easy to construct and simple to use, it therefore affords advantages over existing systems.
The importance of mass transfer relative to the intrinsic microbial activity was examined in a laboratory system using Mycobacterium sp. LB501T and poorly soluble anthracene as sole carbon source. M. sp. LB501T was grown on various amounts of solid anthracene in batch cultures, and microbial biomass formation was compared to independently determined dissolution fluxes. Provision of only a few anthracene crystals (< or = 2 g L(-1)) resulted in pseudolinear growth due to low dissolution fluxes, whereas exponential growth was only obtained when high amounts of solid anthracene (30 g L(-1)) were provided. The influence of substrate bioavailability on microbial growth was predicted successfully by a dynamic, flux-based approach (Best-Equation), which combines substrate dissolution from crystals into solution, substrate uptake by microorganisms from solution, and concurrent biomass formation.
This study reports results of sediment bioslurry treatment and earthworm bioaccumulation for polycyclic aromatic hydrocarbon (PAH) contaminants found in sediment dredged from Milwaukee Harbor. A significant finding was that bioslurry treatment reduced PAHs on the sediment clay/silt fraction but not on the sediment coal-derived fraction and that PAH reduction in the clay/silt fraction correlated with substantial reduction in earthworm PAH bioaccumulation. These findings are used to infer PAH bioavailability from characterization of particle-scale PAH distribution, association, and binding among the principal particle fractions in the sediment. The results are consistent with work showing that the sediment comprised two principal particle classes for PAHs, coal-derived and clay/silt, each having much different PAH levels, release rates, and desorption activation energies. PAH sorption on coal-derived particles is associated with minimal biodegradation, slow release rates, and high desorption activation energies, while PAH sorption on clay/silt particles is associated with significant potential biodegradability, relatively fast release rates, and lower desorption activation energies. These characteristics are attributed to fundamental differences in the organic matter to which the PAHs are sorbed. Although the majority of the PAHs are found preferentially on coal-derived particles, the PAHs on the clay/silt sediment fraction are more mobile and available, and thus potentially of greater concern. This study demonstrates that a suite of tests comprising both bioassays and particle-scale investigations provide a basis to assess larger-scale phenomena of biotreatment of PAH-impacted sediments and bioavailability and potential toxicity of PAH contaminants in sediments. Improved understanding of contaminant bioavailability aids decision-making on the effectiveness of biotreatment of PAH-impacted sediments and the likelihood for possible reuse of dredged sediments as reclaimed soil or fill.
This paper describes the induction of phenanthrene-catabolism within Phase II mushroom compost resulting from its incubation with (1) phenanthrene, and (2) PAH-contaminated soil. Respirometers measuring mineralization of freshly added 14C-9-phenanthere were used to evaluate induction of phenanthrene-catabolism. Where pure phenanthrene (spiked at a concentration of 400 mg kg(-1) wet wt.) was used to induce phenanthrene-catabolism in compost, induction was measurable, with maximal mineralization observed after 7 weeks phenanthrene-compost contact time. Where PAH-contaminated soil was used to induce phenanthrene-catabolism in un-induced compost, induction was observed after 5 weeks soil-compost contact time. Microcosm-scale amelioration of soil contaminated with 14C-phenanthrene (aged in soil for 516 days prior to incubation with compost) indicated that both induced (using pure phenanthrene) and uninduced Phase II mushroom composts were equally able to promote degradation of this soil-associated contaminant. After 111 days incubation time, 42.7 +/- 6.3% loss of soil-associated phenanthrene was observed in the induced-compost soil mixture, while 36.7 +/- 2.9% loss of soil-associated phenanthrene was observed in the uninduced-compost soil mixture. These results are notable as they indicate that while pre-induction of phenanthrene-catabolism within compost is possible, it does not significantly increase the extent of degradation when the compost is used to ameliorate phenanthrene-contaminated soil. Thus, compost could be used directly in the amelioration of contaminated land i.e. without pre-induction of catabolism.
The development of pyrene catabolic activity was assessed in two similar soils (pasture and woodland) amended with 100 mg pyrene kg(-1) In the pasture and woodland soils, significant mineralisation of 14C-pyrene was observed after 8 and 76 weeks soil-pyrene contact times, respectively. In both soils, there were significant decreases (P<0.05) in the lag times and significant increases (P <0.05) in the maximum rates and extents of 14C-pyrene mineralised with increasing soil-pyrene contact time. A microbial inoculum was added to the woodland soil to assess if the previously added, but undegraded 14C-pyrene was bioavailable at 16 and 24 weeks. This resulted in the immediate mineralisation of the previously added 14C-pyrene, indicating that it was bioavailable but that the microbial community in the woodland soil had not developed the ability to mineralise pyrene. The relative contributions of the indigenous microflora to 14C-pyrene mineralisation were assessed by the addition of celective inhibitors, with bacteria seeming to be responsible for the mineralisation of pyrene in both soils. It is suggested that the rate of pyrene-transfer from the soil to the microorganisms was lower in the woodland soil due to its higher organic matter content.
Soot contains high levels of toxic compounds such as polycyclic aromatic hydrocarbons (PAHs). Extraction of PAHs from soot for quantitative analysis is difficult because the compounds are extremely tightly bound to the sorbent matrix. This study was designed to investigate the effect of solvent type on PAH extraction yield, to identify the most optimal solvent for PAH extraction from soot, and to gain insight into the mechanism of PAH sorption to soot in aquatic environments. To that end, different types of soot as well as coal, charcoal, and sediments containing soot-like material were extracted with seven organic solvents. Large differences in extraction recoveries were observed among solvents, with relative values as low as 16% as compared to the best extracting solvent. These differences were much larger for soot than for sediments. Dichloromethane, which to date is the most widely used solvent for soot and sediment extractions, appeared to be the overall worst extractant, whereas toluene/methanol (1:6) gave the best results. Based on extraction yields and solvent properties, extraction of PAHs from soot was explained by a two-step mechanism involving swelling of the sorbent matrix and subsequent displacement of sorbates by solvent molecules. Due to the low displacement capacity of water, desorption of PAHs from soot in the aquatic environment will be strongly limited. Moreover, a certain fraction of the total PAH mass on soot is suggested to be physically entrapped, making it unavailable for partitioning to the aqueous phase.
We hypothesized that the sorption of polycyclic aromatic hydrocarbons (PAHs) to natural sediments and soils should consider both absorption into a biogenic/diagenetic organic carbon (OC) fraction and adsorption onto a combustion-derived, black carbon (BC) fraction. Here, two sets of literature data were reevaluated to illustrate that an OC absorbent and a BC adsorbenttogether can (1) account for sediment--pore-waterdistribution coefficients observed in the field that are greater than predicted by a simple f(OC)K(OC) partitioning model and (2) explain a group of nonlinear phenanthrene isotherms observed in the laboratory with a single value for the BC-normalized distribution coefficient (log K(BC) = 6.1 i 0.04) and a Freundlich exponent (n approximately 0.6 if log K(OC) = 4.0) that is strongly dependent on the K(OC) value selected.
Laboratory based studies on the fate of organic contaminants in soil typically requires the test compound(s) to be spiked into the test medium. Consequently, such studies are inherently dependent on the homogeneity of the contaminant within the spiked soil. Three blending methods were compared for the addition of a phenanthrene-transformer oil mixture into field-wet soil. Spiking homogeneity, reproducibility and artefacts were assessed based on dichloromethane and hydroxypropyl-beta-cyclodextrin chemical extractability, and bacterial mineralization. Spiking using a stainless-steel spoon, consistently produced good spike homogeneity as determined by sample oxidation, chemical extraction and mineralization, and was consistently more reliable than either the Waring blender or modified bench drill. Overall, neither transformer oil-concentration nor blending method influenced chemical extractability or mineralization of the PAH following 1 day equilibration. In general, spiking procedures require validation prior to use, as homogeneity cannot be assured.
Desorption and biodegradation of pyrene (PYR) were investigated and their relationships to soil characteristics were addressed. The results indicated that maximum achievable desorption was 30.2, 10.4, and 1.0 mg/kg for soils that had 1.7, 2.2, and 4.4 wt.% of expandable clays (smectite and vermiculite), respectively. Neither dissolved organic matter (DOM) nor total clay amounts made a good prediction of the desorption trend. Subsequently, the ease of desorption facilitated a faster aqueous biodegradation rate. The slowest aqueous biodegradation rate, 0.02 l/h, was achieved for the soil system that had the greatest amount of expandable clays, whereas the soil containing 1.7% expandable clays only achieved 0.73 l/h. The soil with 2.2% expandable clays depicted 0.41 l/h of aqueous biodegradation rate. A good linear correlation was obtained between maximum achievable desorption and aqueous biodegradation rate (R(2)=0.92). Soil analysis revealed that the total (soil+water) biodegradation reached was 65%, 78.3%, and 81.8% of the initial concentration (100 mg/kg) for the sandy clay loam (Colombian), sandy loam (Ohio), and silty loam (New Mexico) soils, respectively. This biodegradation extent was also in good agreement of expandable clay amount. Although aqueous PYR bioavailability was limited due to the strong association with the expandable clays, microbial movement and adhesion to those clays seemed to result in a great extent of the soil-phase biodegradation.
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants frequently associated with light non-aqueous-phase liquids (LNAPLs) in soil. Microbial degradation comprises a major loss process for PAHs in the environment. Various laboratory studies, using known degraders, have shown reduced or enhanced mineralisation of PAHs when dissolved in different LNAPLs. Effects due to the presence of LNAPLs on indigenous micro-organisms, however, are not fully understood. A pristine pasture soil was spiked with [14C]phenanthrene and transformer oil to 0, 0.01 and 0.1%, and incubated for 180 days. The catabolic potential of the soil towards phenanthrene was assessed periodically during ageing. The extent of the lag phase (prior to >5% mineralisation), maximum rates and overall extents of mineralisation observed during the course of a 14-day bioassay appeared to be dependent upon phenanthrene concentration, the presence of transformer oil, and soil-contaminant contact time. Putatively, transformer oil enhanced acclimation and facilitated the development of measurable catabolic activity towards phenanthrene in a previously uncontaminated pasture soil. Exact mechanisms for the observed enhancement, longer-term fate/degradation of the oil and residual phenanthrene, and effects of the presence of the oil on the indigenous microbes over extended time frames warrant further investigation.
Strong sorption to soot- and charcoal-like material (collectively termed black carbon or BC) in soils and sediments is possibly the reason for recent observations of elevated geosorbent-water distribution ratios, slow desorption, limited uptake, and restricted bioremediation. We evaluated the role of environmental BC in the sorption of phenanthrene (PHE) to a polluted lake sediment from a Rhine River sedimentation area. Sorption isotherms were determined over a wide concentration range (0.0005-6 microg/ L) for the original sediment (with organic matter or OM, native sorbates, and BC), sediment from which we had stripped > 90% of the native sorbates (only OM and BC), and sediment combusted at 375 degrees C (only BC). The sorption isotherms of the original and stripped sediments were almost linear (Freundlich coefficient or n(F) > 0.9), whereas the isotherm of the BC remaining after the sediment combustion was highly nonlinear (n(F) = 0.54). At low concentrations (ng/L range), PHE sorption to BC in the combusted sediment was found to exceed the total PHE sorption in the original and stripped sediments. This implies that it may not be possible to use a BC-water sorption coefficient measured in combusted sediment to estimate total sorption to the original sediment. This "intrinsic" BC-water sorption coefficient after combustion was calculated to be 9 times larger than the "environmental" one in the untreated sediment. Competition between the added PHE and the native PAHs and/or OM may explain this difference. It appears that, at low aqueous PHE concentrations (ng/L and below), BC is the most important geosorbent constituent with respect to sorption. At higher concentrations (microg/L), BC sorption sites become saturated and BC sorption is overwhelmed by sorption to the other OM constituents. Because sorption is a central process affecting contaminant behavior and ecotoxicity, understanding this process can strongly contribute to risk assessment and fate modeling.
The bioavailability of 38 individual polycyclic aromatic hydrocarbon (PAH) compounds was determined through calculation of biota-sediment-accumulation factors (BSAF). BSAF values were calculated from individual PAH concentrations in freshwater mussel, marine clam, and sediment obtained from field and laboratory bioaccumulation studies. Sediment that was amended with different types of soot carbon (SC) was used in some of the bioaccumulation experiments. BSAF values for petrogenic PAH were greater than those for pyrogenic PAH (e.g., 1.57 +/- 0.53 vs 0.25 +/- 0.23, respectively), indicating that petrogenic PAH are more bioavailable than pyrogenic PAH (p < 0.05). This trend was consistent among marine and freshwater sites. Increased SC content of sediment resulted in a linear decrease in the bioavailability of pyrogenic PAHs (r2 = 0.85). The effect of increasing SC content on petrogenic PAH was negligible. SC was considered as an additional sorptive phase when calculating BSAF values, and using PAH-SC partition coefficients from the literature, we obtained unreasonably large BSAF values for all petrogenic PAH and some pyrogenic PAH. This led us to conclude that a quantitative model to assess bioavailability through a combination of organic carbon and soot carbon sorption is not applicable among field sites with a wide range of soot carbon fractions and PAH sources, at least given our current knowledge of PAH-SC partitioning. Our data offer evidence that many factors including analysis of a full suite of PAH analytes, PAH hydrophobicity, sediment organic carbon content, sediment soot carbon content, and PAH source are importantto adequately assess PAH bioavailability in the environment.
The sorption of polycyclic aromatic hydrocarbons (PAHs) to soot carbon in marine sediments has been hypothesized to reduce PAH bioavailability. This hypothesis was tested for eight species of marine benthic invertebrates (four polychaete worms, Clymenella torquata, Nereis virens, Cirriformia grandis, and Pectinaria gouldii, and four bivalve mollusks, Macoma balthica, Mulinia lateralis, Yoldia limatula, and Mya arenaria) that span a wide range of feeding behavior, ability to metabolize PAHs, and gut chemistry. Organisms were exposed for 20 d to two PAH-spiked sediments, one with soot and one without soot. The soot treatment generally resulted in lower bioaccumulation than the no soot treatment, though the differences between treatments were not significant for all species. All but one species accumulated significant PAH concentrations in their tissues from the soot treatment, indicating that soot-bound PAH cannot be dismissed as unavailable to infaunal benthic biota. Bioaccumulation factors were correlated negatively to both the organisms' ability to metabolize PAHs and the gut fluid contact angle, supporting the hypotheses that high PAH metabolism results in lower bioaccumulation factors and bioavailability of PAHs may be limited partially by PAH solubilization in the gut lumen. The variability in bioaccumulation due to the soot treatment was much less than the variability between species and between PAH analytes. Comparatively low bioaccumulation was observed in Nereis virens, a species commonly used in bioaccumulation tests. These results suggest that more effort is needed in understanding the salient characteristics of species present in a threatened environment, rather than focusing solely on the sediment geochemistry (e.g., soot and organic carbon content) and contaminant characteristics when predicting ecological risk of PAH-contaminated sediments.
Soot, soot-amended sediment, and unamended sediment spiked with hydrophobic organic contaminants (HOC) were subjected to laboratory desorption and assimilation efficiency experiments in an effort to assess and compare the importance of soot in controlling HOC desorption and deposit-feeder assimilation efficiency. Three contaminants, naphthalene (NAP), benzo[a]pyrene (BaP), and hexachlorobenzene (HCB) were sorbed to sediments, sediments amended with soot (2-4% dry wt), and soot for a period of 34 d. Desorption of all three contaminants into seawater from the three prepared sorbates was then monitored, and Nereis succinea assimilation efficiency experiments on the BaP- and HCB-contaminated sorbates were conducted. Both NAP and BaP desorption rates for soot and soot-amended sediments were reduced by at least a factor of two relative to unamended sediment. Hexachlorobenzene desorption rates were similar for both the soot-amended and the unamended sediments. Results of N. succinea assimilation efficiency experiments indicate a trend similar to the desorption experiments: higher assimilation of BaP from unamended relative to soot-amended sediment and little difference in assimilation between treatments for HCB. However, soot was more effective in reducing BaP desorption than assimilation efficiency, which would be consistent with the hypothesis that the gut fluid dissolution by deposit feeders may partially decouple biological availability from chemical availability.
Bioaccumulation of hydrophobic organic chemicals from sediments containing soot or sootlike materials has been hypothesized to be limited by strong sorption of the chemicals to the soot matrixes. To test this hypothesis, we quantified bioaccumulation of 11 polychlorinated biphenyls (PCBs) into the aquatic oligochaete Limnodrilus sp. exposed to spiked sediment with and without the sootlike materials coal and charcoal. In addition, sorption experiments with sediment containing varying amounts of coal or charcoal were performed to elucidate the accumulation mechanism. Results showed that coal and charcoal (at realistic levels of 1.5% on a dry-wt basis) reduced PCB accumulation in worms 1.2 to 8.5 times when expressed on a mass basis. Moreover, whereas bioaccumulation from pure sediment increased with molecular planarity of the PCBs (toxic potency), it decreased in case of sediments containing coal and charcoal. In contrast to this advantageous effect, it was hypothesized that coal and charcoal had an adverse influence on the habitat quality of oligochaetes: Organisms inhabiting sediment containing coal or charcoal had significantly reduced lipid contents as compared to organisms from pure sediment. Because of these reduced lipid contents, lipid-normalized PCB concentrations in worms and biota-to-sediment accumulation factors (BSAFs) for most PCBs were higher in sediments containing the sootlike materials as compared to those for reference sediment. Also, measured BSAFs for coal- and charcoal-containing sediments appeared to be much higher than estimated on the basis of equilibrium partitioning theory. Sorption experiments revealed that this was caused by much weaker sorption to the sediment-coal/charcoal mixture than calculated assuming linear additivity of sorption capacities of the distinct phases. It was hypothesized that this weaker sorption resulted from competition between PCBs and dissolved organic carbon molecules for sorption sites on coal/charcoal. This points to a sorption process that is much more complicated than generally assumed.
The aim of this paper was to estimate the contribution to total phenanthrene sorption from unburned coal and black carbon (BC; soot and charcoal) in sediment. We determined sorption isotherms for five Argonne Premium Coal standards over a wide concentration interval (0.01-10 000 ng/L). The coals showed strong and nonlinear sorption (carbon-normalized K(F) = 5.41-5.96; nF = 0.68-0.82). Coal sorption appeared to become more nonlinear with increasing coal maturity. The coal's specific surface area appeared to influence K(F). On the basis of the current coal sorption observations combined with earlier petrographic analyses and BC sorption experiments, we calculated for one particular sediment that coal, BC, and "other" OC were all important to PHE sorption in the environmentally relevant nanogram per liter range. This indicates that it is important to consider strong sorption to coal in the risk assessment of coal-impacted geosorbents (e.g., river beds) where coal is mined/shipped and manufactured gas plant sites.
The influence of pyrene added in a single application (0, 50, 100 and 200 mg kg(-1)) was investigated in multiple applications (1 x 50, 2 x 50 and 4 x 50 mg kg(-1)) on the evolution of catabolic activity in a pristine pasture soil. The microbial community's ability to degrade pyrene was assessed at 0, 4, 8 and 12 weeks by the mineralization of added 14C-pyrene. Significant mineralization (>5%) of added 14C-pyrene only occurred after 4 weeks soil-pyrene contact time in most of the pyrene-amended soils. Pyrene-amended soils showed statistically significantly shorter (P<0.05) lag times compared to the control soil after 8 and 12 weeks soil-pyrene contact time. Further, the rates of degradation increased in the presence of pyrene, peaking at 8 weeks. In terms of the overall extents of pyrene mineralization, there were statistically significant increases (P<0.05) between 4 and 8 weeks, with little difference between 8 and 12 weeks, with the general trend that an increase in pyrene concentration resulted in higher levels of mineralization. Increasing the concentration and number of pyrene additions can have a significant impact on the adaptation of the soil microflora to degrade pyrene over time.
The aim of this study was to investigate the influence of diesel on the loss and bioavailability of soil-associated [14C]phenanthrene with time. In addition, the temporal development of phenanthrene catabolic activity and the impact of co-contaminant mixtures on the soil microflora were also assessed. With respect to compound fate, the results suggested that competitive effects between dissimilar co-contaminants did influence [14C]phenanthrene loss. Where diesel was present at a concentration of 0, 20, 200 and 2000 mg kg(-1), increased phenanthrene loss was observed with increasing diesel concentrations. In the 20,000 mg kg(-1) diesel treatment, however, a significantly higher amount of the initial [14C]activity remained after 225 days. Furthermore, initial degradation of phenanthrene in this treatment was retarded as a result of repressed phenanthrene catabolic activity. These results were complemented by a 4-fold increase in total culturable bacterial cell numbers in the 20,000 mg kg(-1) treatment when compared with the 2000 mg kg(-1) after 225 days of incubation time.
Evidence is accumulating that sorption of organic chemicals to soils and sediments can be described by "dual-mode sorption": absorption in amorphous organic matter (AOM) and adsorption to carbonaceous materials such as black carbon (BC), coal, and kerogen, collectively termed "carbonaceous geosorbents" (CG). Median BC contents as a fraction of total organic carbon are 9% for sediments (number of sediments, n approximately 300) and 4% for soils (n = 90). Adsorption of organic compounds to CG is nonlinear and generally exceeds absorption in AOM by a factor of 10-100. Sorption to CG is particularly extensive for organic compounds that can attain a more planar molecular configuration. The CG adsorption domain probably consists of surface sites and nanopores. In this review it is shown that nonlinear sorption to CG can completely dominate total sorption at low aqueous concentrations (<10(-6) of maximum solid solubility). Therefore, the presence of CG can explain (i) sorption to soils and sediments being up to 2 orders of magnitude higher than expected on the basis of sorption to AOM only (i.e., "AOM equilibrium partitioning"), (ii) low and variable biota to sediment accumulation factors, and (iii) limited potential for microbial degradation. On the basis of these consequences of sorption to CG, it is advocated that the use of generic organic carbon-water distribution coefficients in the risk assessment of organic compounds is not warranted and that bioremediation endpoints could be evaluated on the basis of freely dissolved concentrations instead of total concentrations in sediment/soil.
Black carbon (BC; soot and charcoal) can be an extremely strong sorbent for organic compounds. In a previous study, sorption of d(10)-phenanthrene (d(10)-PHE) to BC in an unmodified contaminated sediment was found to be nine times less than that for BC isolated from this sediment. To find out the mechanism of this sorption attenuation (competition for BC sites between d(10)-PHE and native PAHs or blocking of BC sites by natural organic matter), we determined the effect on d(10)-PHE-BC sorption isotherms of additions of either PAHs or precipitated humic acid. Addition of humic acid did not significantly decrease BC sorption, whereas PAH additions (equal to the native PAH content in the original sediment) did, by about one order of magnitude. Therefore, competition between d(10)-PHE and the native PAHs could explain the whole attenuation of sorption to BC in unmodified sediments.
The emission of black carbon is known to cause major environmental problems. Black carbon particles contribute to global warming, carry carcinogenic compounds and cause serious health risks. Here, we show another side of the coin. We review evidence that black carbon may strongly reduce the risk posed by organic contaminants in sediments and soils. Extremely efficient sorption to black carbon pulls highly toxic polycyclic aromatic hydrocarbons, polychlorinated biphenyls, dioxins, polybrominated diphenylethers and pesticides into sediments and soils. This increased sorption is general, but strongest for planar (most toxic) compounds at environmentally relevant, low aqueous concentrations. Black carbon generally comprises about 9% of total organic carbon in aquatic sediments (median value of 300 sediments), and then may reduce uptake in organisms by up to two orders of magnitude. This implies that current environmental risk assessment systems for these contaminants may be unnecessarily safe.