Article

Impact of two contrasting biochars on the bioaccessibility of 14C-naphthalene in soil

Authors:
  • Federal University Oye-Ekiti Nigeria
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Abstract

This study investigated the impact of two different wood biochars (BioC1 and BioC2) on the extractability and biodegradation of C-naphthalene in soil. Both biochars had contrasting properties due to difference in feedstocks and pyrolytic conditions (450–500 C and 900–1000 C, designated as BioC1 and BioC2, respectively). This study investigated effects of biochar on the relationship between C-naphthalene mineralisation and calcium chloride (CaCl ), hydroxypropyl- -cyclodextrin (HPCD) or methanol extraction in soil amended with 0%, 0.1%, 0.5% and 1% BioC1 and BioC2 after 1, 18, 36 and 72 d contact times. Total extents of C-naphthalene mineralisation and extraction were reduced with increasing concentrations of biochar; however, BioC2 showed greater sorptive capacity. Good linear correlation existed between total extents of C-naphthalene mineralisation and HPCD extractions in BioC1 (slope 0.86, r 0.92) and BioC2 (slope 0.86, r 0.94) amended soils. However CaCl and methanol extractions underestimated and overestimated extents of mineralisation, respectively. These results indicate that biochar can reduce the bioaccessibility of PAHs and the corresponding risk of exposure to biota, whilst HPCD extraction estimated the bioaccessible fraction of PAHs in soil. Bioaccessibility assessment is vital in evaluation of biodegradation potential and suitability of bioremediation as a remediation option.

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... The sorptive properties of biochars have been widely studied, however few studies have also reported their biodegradative potential for PAHs in soils, owing to their stimulation for substrate bioavailability for microbial degradation through the formation of microhabitat (bacteria and fungi) for actively growing autochthonous soil microflora through electrostatic attraction and attachment to biochar's porous surfaces (Anyika et al., 2015;Ogbonnaya et al., 2016;Zhang et al., 2018). For example, a recent study showed that microbe-biochar interaction enhanced mass transfer of PAHs (making the contaminant more bioavailable) to immobilised cells, thus resulting to higher PAH degradation when compared to uninoculated biochar in a sorbent-amended system (Xiong et al., 2017). ...
... The addition of external nutrient supplies and organic materials to soil would influence the indices of quantifying biodegradation, such as lag phases, fastest rates and overall extents of organic contaminant biodegradation (Jablonowski et al., 2013;Oyelami et al., 2013;Ogbonnaya et al., 2016). In this current study, the immobilised inoculum on the EbioC could have provided an additional support for the indigenous microbial population than NEbioC which led to shorter lag phases, increases in fastest rates and extents of 14 C-phenanthrene mineralisation in amended soil. ...
... The application of larger amounts (1.0% > 0.5%) of both biochar types reduced 14 C-mineralisation in soil. Even though biochar has been reported to have intrinsic ability to biodegrade organic contaminants (Anyika et al., 2015), the sorptive properties of black carbon, including biochars, can reduce mass transfer and bioaccessibility of PAHs to soil microorganisms (Rhodes et al., 2008(Rhodes et al., , 2012Anyika et al., 2015;Ogbonnaya et al., 2016). This further suggests the likely effect that is seen in this investigation occurs in soils with higher biochar amendments. ...
... The sorptive properties of biochars have been widely studied, however few studies have also reported their biodegradative potential for PAHs in soils, owing to their stimulation for substrate bioavailability for microbial degradation through the formation of microhabitat (bacteria and fungi) for actively growing autochthonous soil microflora through electrostatic attraction and attachment to biochar's porous surfaces (Anyika et al., 2015;Ogbonnaya et al., 2016;Zhang et al., 2018). For example, a recent study showed that microbe-biochar interaction enhanced mass transfer of PAHs (making the contaminant more bioavailable) to immobilised cells, thus resulting to higher PAH degradation when compared to uninoculated biochar in a sorbent-amended system (Xiong et al., 2017). ...
... The addition of external nutrient supplies and organic materials to soil would influence the indices of quantifying biodegradation, such as lag phases, fastest rates and overall extents of organic contaminant biodegradation (Jablonowski et al., 2013;Oyelami et al., 2013;Ogbonnaya et al., 2016). In this current study, the immobilised inoculum on the EbioC could have provided an additional support for the indigenous microbial population than NEbioC which led to shorter lag phases, increases in fastest rates and extents of 14 C-phenanthrene mineralisation in amended soil. ...
... The application of larger amounts (1.0% > 0.5%) of both biochar types reduced 14 C-mineralisation in soil. Even though biochar has been reported to have intrinsic ability to biodegrade organic contaminants (Anyika et al., 2015), the sorptive properties of black carbon, including biochars, can reduce mass transfer and bioaccessibility of PAHs to soil microorganisms (Rhodes et al., 2008(Rhodes et al., , 2012Anyika et al., 2015;Ogbonnaya et al., 2016). This further suggests the likely effect that is seen in this investigation occurs in soils with higher biochar amendments. ...
Article
Biochar is a by-product from the pyrolysis of biomass and has a great potential in soil amendment due to its carbon and nutrient-rich properties. The aim of this study was to investigate the impact of increasing amounts (0, 0.01, 0.1, 0.2, 0.5 and1.0%) of two types of biochar (so-called enhanced and non-enhanced) to soil on the biodegradation of14C-phenanthrene. Enhanced biochar contains inoculants which are designed to potentially stimulate microbial activity and promote biological function in soil. After 100 d of incubation, the addition of 0.5% and 1% enhanced (EbioC) and non-enhanced biochars (NEbioC) led to longer lag phases, reduced rates and extentsof14C-phenanthrene in amended soil. However, in soils amended with 0.01%, 0.1% and0.2% amendments, extents of mineralisation of14C-phenanthrene increased and were found to be higher in the EBioC — as compared to the NEbioC-amended soils. Increasing soil-phenanthrene contact time also increased14C-phenanthrene mineralisation in soil which had received smaller amounts of EBioC. Application of both EbioC and NEbioC also enriched the soil microbial populations during the incubation. However, it was found that phenanthrene-degrading microbial populations declined as soil contact time increased; this was particularly true for soils receiving larger amounts due to reduction in the mobile/bioaccessible fraction of the phenanthrene in soil. The findings revealed theimportance of the type and amount of biochar that may be added to soil to stimulate or enhance organic contaminant biodegradation.
... The highest percentages were 0.3, 4, and 18% for PAHs with two, three, and four rings, respectively. These values were lower than those found in the literature (Rhodes et al. 2008;Ogbonnaya et al. 2016). However, it was shown that the percentage of extracted PAHs varied according to the initial concentrations, the physicochemical parameters of the soil studied, and the duration of the experiments (Puglisi et al. 2007;Rhodes et al. 2008;Ogbonnaya et al. 2016). ...
... These values were lower than those found in the literature (Rhodes et al. 2008;Ogbonnaya et al. 2016). However, it was shown that the percentage of extracted PAHs varied according to the initial concentrations, the physicochemical parameters of the soil studied, and the duration of the experiments (Puglisi et al. 2007;Rhodes et al. 2008;Ogbonnaya et al. 2016). Whatever raw materials were used (e.g., woody, miscanthus), the biochars significantly decreased the extractability of PAHs with three and four rings from soil in absence of ryegrass. ...
... Whatever raw materials were used (e.g., woody, miscanthus), the biochars significantly decreased the extractability of PAHs with three and four rings from soil in absence of ryegrass. Thus, biochars immobilized PAHs in soil, probably via sequestration processes, including sorption phenomena and a physical trap facilitated by the aromatic structure of biochars, their substantial porosity, their specific surface area, and their carbon content (Ogbonnaya et al. 2014(Ogbonnaya et al. , 2016Cao et al. 2016;Bielská et al. 2017;Song et al. 2017b). These results are consistent with those obtained in several studies in which the authors showed a decrease of extractable PAH concentrations after adding biochars made from wood, demolition wood waste, bamboo, corn straw, and wheat straw (Ogbonnaya et al. 2014(Ogbonnaya et al. , 2016Ni et al. 2017;Song et al. 2017b). ...
Article
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The present study experimented five biochars, one made from wood (400 °C, 12 h) and four made from miscanthus cultivated on contaminated soils (temperature 400/600 °C, duration 45/90 min). They were used as amendments at a 2% application rate on soil, cultivated or not cultivated with ryegrass, contaminated with (i) metals (Cd, Pb, and Zn), (ii) eight polycyclic aromatic hydrocarbons (PAHs), and (iii) a mix of metals and PAHs. The objectives were (i) to compare the effectiveness of the five biochars on soil parameters and pollutant availability and (ii) to determine the influence of soil multicontamination and ryegrass cultivation on biochar effectiveness. The results showed that biochar application did not necessarily lead to lower pollutant extractability and metal bioaccessibility. However, differences were highlighted between the biochars. The miscanthus biochars produced at 600 °C (BM600) showed higher effectiveness at decreasing metal extractability than the miscanthus biochars produced at 400 °C (BM400) due to its better sorption characteristics. In addition, ryegrass cultivation did not impact pollutant availability but modified metal bioaccessibility, especially for the soil amended with the BM600 and the woody biochar. Moreover, the presence of PAHs also negatively impacted the metal bioaccessibility in the soil amended with the BM600, and, on the contrary, positively impacted it in the soil amended with the BM400. Complementary studies are therefore necessary to understand the mechanisms involved, particularly in a context where soils requiring remediation operations are often multicontaminated and vegetated.
... However, to date it is not clear whether AC could facilitate biodegradation of sediment-associated PAHs carried out by indigenous HC degraders. Earlier works on the effects of AC and biochar on PAH degradation show contrasting results leading either to enhanced bioremediation (Chen et al., 2012) or acting as an impediment to microbial degradation (Ogbonnaya et al., 2016). A recent in situ study showed that AC amended with bacteria decreased polychlorinated biphenyls (PCBs) concentrations in the sediment by up to 52% (Payne et al., 2019). ...
... A previous work using biocharda carbonaceous material similar to AC produced from pyrolyzed biomassdshowed opposing results on PAH degradation compared to ours. At increasing biochar concentrations, the mineralization of naphthalene by indigenous microorganisms in sandy soils decreased (Ogbonnaya et al., 2016). Those experiments, however, were conducted in aerobic conditions. ...
Article
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Biodegradation by microorganisms is a useful tool that helps alleviating hydrocarbon pollution in nature. Microbes are more efficient in degradation under aerobic than anaerobic conditions, but the majority of sediment by volume is generally anoxic. Incubation experiments were conducted to study the biodegradation potential of naphthalene—a common polycyclic aromatic hydrocarbon (PAH)—and the diversity of microbial communities in presence/absence of activated carbon (AC) under aerobic/anaerobic conditions. Radio-respirometry experiments with endogenous microorganisms indicated that degradation of naphthalene was strongly stimulated (96%) by the AC addition under anaerobic conditions. In aerobic conditions, however, AC had no effects on naphthalene biodegradation. Bioaugmentation tests with cultured microbial populations grown on naphthalene showed that AC further stimulated (92%) naphthalene degradation in anoxia. Analysis of the 16S rRNA gene sequences showed that sediment amendment with AC increased microbial community diversity and changed community structure. Moreover, the relative abundance of Geobacter, Thiobacillus, Sulfuricurvum, and methanogenic archaea increased sharply after amendment with AC under anaerobic conditions. These results may be explained by the fact that AC particles promoted direct interspecies electron transfer (DIET) between microorganisms involved in PAH degradation pathways. We suggest that important ecosystem functions mediated by microbes—such as hydrocarbon degradation—can be induced and that AC enrichment strategies can be exploited for facilitating bioremediation of anoxic oil-contaminated sediments and soils.
... The behaviour of a biochar as amendment for contaminant removal depends on its properties and current state of aging/weathering (Semple et al., 2013). Biochar reduces PAHs extractability, bioaccessibility, bioavailability, and toxicity in soils and these effects increase with rise in biochar application rate (Bielska et al., 2017;Jimenez et al., 2018;Ogbonnaya et al., 2016). Biochar reduced water soluble fraction of phenanthrene hence indicating biochar as a suitable amendment to prevent PAHs leaching and bioaccessibility (Ogbonnaya et al., 2014;Jimenez et al., 2018). ...
Article
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Heavy metals (HMs) contamination raises the expression of antibiotic resistance (AR) in bacteria through co-selection. Biochar application in composting improves the effectiveness of composting and the quality of compost. This improvement includes the elimination and reduction of antibiotic resistant genes (ARGs). The use of biochar in contaminated soils reduces the bioaccessibility and bioavailability of the contaminants hence reducing the biological and environmental toxicity. This decrease in contaminant bioavailability reduces contaminants induced co-selection pressure. Conditions which favour reduction in HMs bioavailable fraction (BF) appear to favour reduction in ARGs in compost and soil. Biochar can prevent horizontal gene transfer (HGT) and can eliminate ARGs carried by mobile genetic elements (MGEs). This effect reduces maintenance and propagation of ARGs. Firmicutes, Proteobacteria, and Actinobacteria are the major bacteria phyla identified to be responsible for dissipation, maintenance, and propagation of ARGs. Biochar application rate at 2-10% is the best for the elimination of ARGs. This review provides insight into the usefulness of biochar in the prevention of co-selection and reduction of AR, including challenges of biochar application and future research prospects.
... Chemical treatment by NaOH and coal composite with microorganisms can present greater efficiency in the removal of PAHs. Besides, the microorganisms present in the soil can be stimulated in the biochar's presence, promoting the contaminant's microbial degradation (Zama et al. 2018;Ogbonnaya et al. 2016). ...
Chapter
Increased industrial growth in the world serves a significant role in the water contamination with heavy metals. Heavy metals such as arsenic, copper, lead, chromium, mercury, nickel, and cadmium impart several health hazards to humans, plants, and animals. Moreover their accumulation potential disturbs the food chain. Freshwater demand is higher in the world which may lead to a severe water crisis in the upcoming years. Hence feasible water treatment technologies must be identified and its efficiency must be concentrated. Heavy metals bear the risk of biodegradation and transformation. Hence adsorption is found to be an attractive method nowadays for sequestration of such metals. It is an economically feasible and eco-friendly method. Biochar is advantageous over other adsorbents such as activated carbon, graphene, silica, etc. It is the product of a thermochemical process which possesses better adsorption capacity. It reduces the production time and in addition provides fuel. Different pyrolysis conditions influence the quantity and yield of char. The degree of biochar adsorption is mainly focused on the type of biomass used, metal species concentrated, functional groups, and surface area of the biochar. Regeneration of biomass is also an important phenomenon to be considered as the adsorbed biochar may cause secondary pollution if not disposed in a proper manner. In order to improve the surface properties, physical structure, and regeneration capacity of biochar, various modification technologies have been adopted. It will also pave way for the effective utilization of waste biomaterials in wastewater treatment. The modification may be carried out before pyrolysis or after pyrolysis. It is categorized under physical, chemical, magnetic, and mineral impregnation methods. This review focuses on the mechanism and improvements of the treated biochar in comparison to the pristine biochar for heavy metal sequestration.
... Biochar possesses porous structure, high internal surface area, and high adsorptive capability (organic compounds, gases, inorganic nutrients) (Zhang et al. 2010;Ogbonnaya et al. 2014Ogbonnaya et al. , 2016Takaya et al. 2016), which can suitably provide attractive sites for microbial colonization. Material scientists classify the total pore volume of biochar materials based on the internal width diameter of distinct pores: micropores (< 2 nm), mesopores (2-50 nm), and macropores (> 50 nm) (Rouquerol et al. 1999;Downie et al. 2009). ...
Article
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Literature shows that biochar can potentially retain nutrients in agricultural soils, avoiding significant nutrient losses. Furthermore, biochar porosity and functional groups have been shown to enhance physico-chemical properties of soil when amended, which in turn has the ability to encourage inhabitation of specific microorganisms as biofertilizers or to enhance soil remediation. It supports scale-dependent parameters and provides both ecosystem services and soil-vegetation solutions relevant to nature-based solutions. However, detailed researches on the mechanisms of soil microbial interactions with biochar porous properties are required, along with the microbial attachment factors, sustenance, and detachment when applied to soils. Recent valuable works have impregnated plant growth-promoting bacteria unto biochar and have observed inconsistent results. Firstly, biochar intrinsic properties alter the fate of impregnation by inhibiting quorum sensing signals, and the macropore requirements for adsorption and/or biofilm formation have not been well considered. Additionally, the nutrient and supplement requirements for each microorganism as well as the adsorption capacity have not been well understood for biochar surfaces. Substantial information is required to understand the mechanisms of microbe adsorption and factors that influence the process, as well as sustenance of the matrix even when deployed in soils. Research directions should focus on determining molecular and chemical mechanisms responsible for the biochar–microbe interaction process and fate of microbe on biochar while expressing plant growth-promoting properties, which needs to be done in laboratory and field trials. Graphical abstract
... 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). ...
Article
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.
... The NMR measurements have been shown to be consistent with the combination of pore size distributions from N 2 and CO 2 adsorption in shales [10]. However, NMR measurements show advantage in measuring much higher levels of macropores (10 μm diameter) compared to N 2 and CO 2 adsorption methods [11]. Based on these findings, the interactions between biochar and a common plant nutrient such as ammonium ion (NH 4 ...
Article
Biochar produced from moderately slow pyrolysis of oilseed rape and mixed softwood at 550 and 700 °C were studied through NMR relaxation and cryoporometry analysis to determine the pore size distribution (micro-, meso-, macro-pores), surface area and liquid hydrocarbon content resident within the pores. In addition, the surface properties were also investigated to determine ability to adsorb aqueous ammonium ion. The micropore volume was always the lowest amongst pore diameters, but increasing pyrolysis temperature remarkably increased micropore volume in concentration by 1000 folds when temperature was raised to 700 °C. This supported the surface area increase with associated loss of surface functional groups. It was also accompanied with 50% and 33% reduction in condensable liquid hydrocarbon content in OSR and SWP biochars, respectively. This further reflected on the reduction in liquid hydrocarbon content and total PAH content from 0.5 to less than 0.1 mg Kg⁻¹ in OSR and from 4.4 to 0.2 mg Kg⁻¹ in SWP biochar, Nevertheless, OSR showed higher surface functionality compared to SWP biochars by adsorbing higher concentrations of ammonium ion within the mesopore region. This study revealed the relationship between temperature and feedstock on pore size distribution, liquid hydrocarbon content and ammonium adsorptive nature with NMR cryoporometry and relaxation analysis.
... However, these removal efficiencies are affected by some biochar and soil properties including the nature of pyrolysis, particle size (Chen and Yuan, 2011), and microbial community (Waqas et al. 2015). For example, Ogbonnaya et al. (2016) investigated the efficiency of wood-derived biochar made by slow pyrolysis and gasification and observed that biochar produced by slow pyrolysis was better at immobilizing 14 C-naphthalene in soil than biochar produced by gasification. This could be attributed to the presence of a larger amount of pores and organic functional groups on slowly pyrolysed biochar 450-500°C (ramped at 10°C min −1 ) compared to gasified biochar at 900-1000°C. ...
Article
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Purpose Soil contamination mainly from human activities remains a major environmental problem in the contemporary world. Significant work has been undertaken to position biochar as a readily-available material useful for the management of contaminants in various environmental media notably soil. Here, we review the increasing research on the use of biochar in soil for the remediation of some organic and inorganic contaminants. Materials and methods Bibliometric analysis was carried out within the past 10 years to determine the increasing trend in research related to biochar in soil for contaminant remediation. Five exemplar contaminants were reviewed in both laboratory and field-based studies. These included two inorganic (i.e., As and Pb) and three organic classes (i.e., sulfamethoxazole, atrazine, and PAHs). The contaminants were selected based on bibliometric data and as representatives of their various contaminant classes. For example, As and Pb are potentially toxic elements (anionic and cationic, respectively), while sulfamethoxazole, atrazine, and PAHs represent antibiotics, herbicides, and hydrocarbons, respectively. Results and discussion The interaction between biochar and contaminants in soil is largely driven by biochar precursor material and pyrolysis temperature as well as some characteristics of the contaminants such as octanol-water partition coefficient (KOW) and polarity. The structural and chemical characteristics of biochar in turn determine the major sorption mechanisms and define biochar’s suitability for contaminant sorption. Based on the reviewed literature, a soil treatment plan is suggested to guide the application of biochar in various soil types (paddy soils, brownfield, and mine soils) at different pH levels (4–5.5) and contaminant concentrations (< 50 and > 50 mg kg⁻¹). Conclusions Research on biochar has grown over the years with significant focus on its properties, and how these affect biochar’s ability to immobilize organic and inorganic contaminants in soil. Few of these studies have been field-based. More studies with greater focus on field-based soil remediation are therefore required to fully understand the behavior of biochar under natural circumstances. Other recommendations are made aimed at stimulating future research in areas where significant knowledge gaps exist.
... The microorganisms must be in the same environment as the PAH and the PAH must be able to be physically transferred to the site of metabolism in the microorganism . Bioavailability is also important and depends on the physicochemical properties and concentration of the PAHs (Guo et al., 2010;Sayara et al., 2010), the properties of the soil (mainly organic matter content, moisture content/water activity and temperature), microorganisms present Ogbonnaya et al., 2014aOgbonnaya et al., , 2016, length PAHsoil contact time (Leonardi et al., 2007;Rhodes et al., 2010;Ogbonnaya et al., 2014a) and presence of co-substrate (Sayara et al., 2011). So, how do microorganisms develop the ability to degrade PAHs? ...
Article
The aim of this study was to investigate the biodegradation of phenanthrene in five Antarctic soils over 150 days at various temperatures and under slurry conditions. The development of catabolic activity was measured over time (1, 30, 60, 150 days) by the addition of 14C-phenanthrene and measuring changes in the lag phases, rates and extents of 14C-phenanthrene degradation. As the temperature increased (4 oC, 12 oC, 22 oC, 22 oC slurry), the highest extents of 14C-phenanthrene mineralisation increased significantly (0.46%, 12.21%, 24.82%, 60.81%), respectively. This was due to changes in the water availability and 14C-phenanthrene dissolution in aqueous phase, thus enhancing bioaccessibility of the contaminant to indigenous microorganisms within the soil. High catabolic activities can develop in Antarctic soils where appropriate conditions are ensured. However, further studies are however needed to explore the changes in microbial community structure that occur at different incubation temperatures.
... However, the 1% and 3% SWP BC-700 showed significantly higher (P < 0.05) Cd accumulation in shoot zone (Figure 1) compared to control soil due to the presence of Cd and Zn (Table 1) in the SWP biochars. SWP BC-700 also exhibited significantly higher (P < 0.05) carbon content and surface area compared to OSR BC-700, indicating a much preferred property for sorption of organic compounds (Ogbonnaya et al. 2016). Nevertheless, SWP biochars was shown to enhance phytoextraction of Cd from such soils (Figures 1&2).In contrast, OSR BC-700 significantly reduced (P < 0.001) accumulation of Cd by 70% to the root zone (13.9 mg kg-1 ) (Figures 1&2) compared to control and other amendments due to immobilisation and reduced bioavailability in the soil. ...
Article
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The influence of biochar (pyrolysed organic matter) on cadmium (Cd) (10 mg kg-1) bioaccumulation in Amaranthus viridis (amaranth) was investigated. In the pot experiment, Cd spiked-soils were amended with and without oilseed rape biochar (OSR BC-700) and softwood pellet biochar (SWP BC-700) at 1% and 3% levels. After six weeks incubation, Amaranthus viridis was harvested and analysed for Cd in root and shoot separately. In control soil, Cd bioaccumulated in the root zone (47.7 mg kg-1) compared to shoot (24.8 mg kg-1). OSR BC-700 drastically immobilised Cd in the soil and reduced bioavailability owing to higher pH and phosphate (P) but SWP BC-700 increased phytoextraction of Cd. Biochars with higher pH and P mitigates bioaccumulation of heavy metals in soil.
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The content of PAHs in surface soils of northeastern China is high, which causes long-term soil pollution and potential harm to human health. Influenced by the temperature, the soil in the northeast region is characterized by a long-term freeze–thaw seasonal climate, which greatly affects the process of soil remediation work. Therefore, it is necessary to study the remediation strategies of PAHs in low-temperature soils. Our group discovered that the combination of cold-tolerant fungi and bacteria was effective in degrading soil PAHs. However, we are required to further explore the choice of immobilization vector. In this study, four different types of biochar (C300, C500, B300, B500) were prepared at 300 °C and 500 °C using corn cob and wheat straw of industrial and agricultural waste as precursors. We then used the cross-mixing of these four types of biochar as the carrier for Pseudomonas sp. S4 and Mortierella alpina J7, which are bacteria capable of degrading PAHs. We used the adsorption immobilization method to prepare the repair materials for PAHs degradation mixed bacteria. Through comparison, the low-temperature and high-temperature mixed biochar (C300 + B500) was selected as the carrier. The results showed that mixed biochar immobilized degrading bacteria are the most effective in degrading Phe and Pyr in soil and their degradation effect was related to the mixing ratio. After 30 days of remediation at 15 °C, the best remediation effect was add immobilized mixed fungicide agent, mix biochar 1:2 using 0.67% C300 and 1.34% B500 (CBJ 1:2). Studies have shown that a mixture of low- and high-temperature biochar is a more promising strategy when used in combination with PAHs-degrading bacteria.
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Polycyclic aromatic hydrocarbons (PAHs) are known as a hazardous group of pollutants in the soil which causes many challenges to the environment. In this study, the potential of biochar (BC), as a carbonaceous material, is evaluated for the immobilization of PAHs in soils. For this purpose, various bonding mechanisms of BC and PAHs, and the strength of bonds are firstly described. Also, the effect of impressive criteria including BC physicochemical properties (such as surface area, porosity, particle size, polarity, aromaticity, functional group, etc., which are mostly the function of pyrolysis temperature), number of rings in PAHs, incubation time, and soil properties, on the extent and rate of PAHs immobilization by BC are explained. Then, the utilization of BC in collaboration with biological tools which simplifies further dissipation of PAHs in the soil is described considering detailed interactions among BC, microbes, and plants in the soil matrix. The co-effect of BC and biological remediation has been authenticated by previous studies. Moreover, recent technologies and challenges related to the application of BC in soil remediation are explained. The implementation of a combined BC-biological remediation method would provide excellent prospects for PAHs-contaminated soils.
Chapter
Bioremediation by biochar can occur by immobilizing, stabilizing, and reducing contaminants’ bioavailability such as toxic metals, polycyclic aromatic hydrocarbons (PAHs), phthalic acid esters, polychlorinated biphenyls (PCBs), and pesticides. Biochar characteristics depend on the biomass used, on the pyrolysis conditions, changing material characteristics and influencing the contaminants’ sorption capacity and affinity. In addition to immobilization, the degradation of organic contaminants in the soil can stimulate specific microbial groups. The aim is to synthesize the methods used in the production of biochar and the recent advances in the application of biochar in the remediation of different contaminants in the soil, summarizing the main methods used to improve the structural and physicochemical properties of biochar to increase its potential for remediation. Also, consideration was given to the biological and abiotic processes that can alter the physical and chemical properties of the biochar, and the main applications were presented as in soil amendment and composting, carbon sequestration, wastewater treatment, and bioenergy, relating the use of the biochar with the sustainable development goals.
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This study investigated the use of a hydrophobic resin, amberlite XAD, as a tool for assessing the biodegradation potential of 14C-phenanthene in soil. The method was optimised in terms of soil/XAD ratio, shaking, extraction time and eluting solvent. The most effective method was then tested on selected XADs, and the performance compared with cyclodextrin (HP-β-CD) and dichloromethane (DCM) extractions suitability to predict phenanthrene biodegradation in soil over 100 d. Results showed that the optimum conditions for the XAD extraction technique are a 2:1 soil/XAD ratio, 100 rpm mixing for 22 h and elution using a DCM:methanol solution (1:1). Mineralisation of 14C-phenanthrene was accurately predicted by HP-β-CD (r2=0.990, slope = 0.953, intercept = 1.374) and XAD-4 extractions (r2=0.989, slope = 0.820, intercept = 6.567), while DCM overestimated the bioaccessibility of 14C-phenanthrene (r2=0.999, slope = 1.328, intercept =−49.507). This investigation showed that XAD extraction can be considered a suitable non-exhaustive technique for estimating biodegradability of phenanthrene in soil.
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In this study, the indigenous microbial mineralisation of 14C-phenanthrene in seven background soils (four Norwegian woodland and three UK (two grassland and one woodland)) was investigated. ∑PAHs ranged from 16.39 – 285.54 ng g-1 dw soil. Lag phases (time before 14C-phenanthrene mineralisation reached 5%) were longer in all of the Norwegian soils and correlated positively with TOC, but negatively with ∑PAHs and phenanthrene degraders for all soils. Phenanthrene mineralisation in the soils varied due to physic-chemical properties. Results show that indigenous microorganisms can adapt to 14C-phenanthrene mineralisation following diffuse PAH contamination. Considering the potential of soil as a secondary PAH source, these findings highlight the important role of indigenous microflora in the processing of PAHs in the environment.
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The presence of biochar in soils through natural processes (forest fires, bush burning) or through application to soil (agriculture, carbon storage, remediation, waste management) has received a significant amount of scientific and regulatory attention. Biochar alters soil properties, encourages microbial activity and enhances sorption of inorganic and organic compounds, but this strongly depends on the feedstock and production process of biochar. This review considers biochar sources, the production process and result of pyrolysis, interactions of biochar with soil, and associated biota. Furthermore, the paper focuses on the interactions between biochar and common anthropogenic organic contaminants, such as polycyclic aromatic hydrocarbons (PAHs), pesticides, and dioxins, which are often deposited in the soil environment. It then considers the feasibility of applying biochar in remediation technologies in addition to other perspective areas yet to be explored.
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Traditionally, soil extraction techniques have been concerned with the determination of “total” organic contaminant concentrations, following an “exhaustive” extraction. However, in light of the increasing body of knowledge relating to organic contaminant availability and aging, such methods have little relevance to the amount of contaminant that may pose an ecological risk i.e., the “bioavailable” portion. Less exhaustive techniques have therefore been the subject of more recent approaches in the hope that they may access the “labile” or bioavailable pool. The use of an aqueous-based extraction technique utilizing hydroxypropyl-β-cyclodextrin (HPCD) is presented here for the extraction of PAHs from soil. The optimization of the method is described in terms of HPCD concentration, extraction time, and solution buffering. The procedure is then tested and validated for a range of 14C-labeled PAHs (phenanthrene, pyrene, and benzo[a]pyrene) added at a range of concentrations to a range of soil types. The amounts of soil-associated phenanthrene mineralized by catabolically active microorganisms were correlated with total residual phenanthrene concentrations (r 2 = 0.889; slope of best fit line = 0.763; intercept = −5.662; n = 24), dichloromethane (DCM)-extractable phenanthrene concentrations (r 2 = 0.986; slope of best fit line = 0.648; intercept = 0.340; n = 24), butan-1-ol (BuOH)-extractable phenanthrene concentrations (r 2 = 0.957; slope of best fit line = 0.614; intercept = 0.544; n = 24), and HPCD-extractable phenanthrene concentrations (r 2 = 0.964; slope of best fit line = 0.997; intercept = 0.162; n = 24). Thus, in this study, the microbially bioavailable concentrations of soil-associated phenanthrene were best predicted using the optimized HPCD extraction technique. In contrast, the DCM Soxhlet extraction and the BuOH shake extraction both overestimated phenanthrene bioavailability by, on average, >60%.
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Application of organic fertilizers and charcoal increase nutrient stocks in the rooting zone of crops, reduce nutrient leaching and thus improve crop production on acid and highly weathered tropical soils. In a field trial near Manaus (Brazil) 15 different amendment combinations based on equal amounts of carbon (C) applied through chicken manure (CM), compost, charcoal, and forest litter were tested during four cropping cycles with rice (Oryza sativa L.) and sorghum (Sorghum bicolor L.) in five replicates. CM amendments resulted in the highest (P<0.05) cumulative crop yield (12.4Mgha−1) over four seasons. Most importantly, surface soil pH, phosphorus (P), calcium (Ca), and magnesium (Mg) were significantly enhanced by CM. A single compost application produced fourfold more grain yield (P<0.05) than plots mineral fertilized in split applications. Charcoal significantly improved plant growth and doubled grain production if fertilized with NPK in comparison to the NPK-fertilizer without charcoal (P<0.05). The higher yields caused a significantly greater nutrient export in charcoal-amended fields, but available nutrients did not decrease to the same extent as on just mineral fertilized plots. Exchangeable soil aluminum (Al) was further reduced if mineral fertilizer was applied with charcoal (from 4.7 to 0mgkg−1). The resilience of soil organic matter (SOM) in charcoal amended plots (8 and 4% soil C loss, mineral fertilized or not fertilized, respectively) indicates the refractory nature of charcoal in comparison to SOM losses over 20months in CM (27%), compost amended (27%), and control plots (25% loss).
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Maintaining an appropriate level of soil organic matter and biological cycling of nutrients is crucial to the success of any soil management in the humid tropics. Cover crops, mulches, compost, or manure additions have been used successfully, supplying nutrients to crops, supporting rapid nutrient cycling through microbial biomass, and helping to retain applied mineral fertilizers better (Goyal et al., 1999; Trujillo, 2002). The benefits of such amendments are, however, often short-lived, especially in the tropics, since decomposition rates are high (Jenkinson and Ayanaba, 1977) and the added organic matter is usually mineralized to CO2 within only a few cropping seasons (Bol et al., 2000). Organic amendments therefore have to be applied each year to sustain soil productivity. Management of black carbon (C) — increasingly referred to as bio-char — may overcome some of those limitations and provide an additional soil management option. This is a highly aromatic form of organic matter that is present in most soils to varying extents (Schmidt and Noack, 2000; Skjemstad et al., 2002). Interest in and application of biomass-derived black carbon — using incompletely combusted organic matter such as charcoal (Glaser et al., 2002) — was prompted by studies of soils found in the Amazon Basin, referred to as Terra Preta de Indio (Lehmann et al., 2003c). These Amazonian Dark Earths are anthropic soils that were created by Amerindian populations between 500 and 2500 years ago. They have maintained high amounts of organic carbon, and their high fertility, even several thousand years after they were abandoned by the indigenous population, contrasts distinctly with the low fertility of the adjacent acid upland soils (Lehmann et al., 2003b). The reasons for these soils’ high fertility are multiple, but the source of the large amounts of organic matter and their high nutrient retention has been attributed to the extraordinarily high proportions of black carbon (Glaser et al., 2001). Such large amounts of black carbon can only originate from incompletely combusted biomass carbon, such as wood from kitchen fires or possibly from in-field burning (Smith, 1980; Hecht, 2003). This chapter considers the beneficial effects of this bio-char soil management system and discusses opportunities for applying such management within a sustainable system that can be called “slash-and-char,” as well as within other smallholder agricultural systems.
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The application of bio-char (charcoal or biomass-derived black carbon (C)) to soil is proposed as a novel approach to establish a significant, long-term, sink for atmospheric carbon dioxide in terrestrial ecosystems. Apart from positive effects in both reducing emissions and increasing the sequestration of greenhouse gases, the production of bio-char and its application to soil will deliver immediate benefits through improved soil fertility and increased crop production. Conversion of biomass C to bio-char C leads to sequestration of about 50% of the initial C compared to the low amounts retained after burning (3%) and biological decomposition (∘C common for pyrolysis). Existing slash-and-burn systems cause significant degradation of soil and release of greenhouse gases and opportunies may exist to enhance this system by conversion to slash-and-char systems. Our global analysis revealed that up to 12% of the total anthropogenic C emissions by land use change (0.21 Pg C) can be off-set annually in soil, if slash-and-burn is replaced by slash-and-char. Agricultural and forestry wastes such as forest residues, mill residues, field crop residues, or urban wastes add a conservatively estimated 0.16 Pg C yr−1. Biofuel production using modern biomass can produce a bio-char by-product through pyrolysis which results in 30.6 kg C sequestration for each GJ of energy produced. Using published projections of the use of renewable fuels in the year 2100, bio-char sequestration could amount to 5.5–9.5 Pg C yr−1 if this demand for energy was met through pyrolysis, which would exceed current emissions from fossil fuels (5.4 Pg C yr−1). Bio-char soil management systems can deliver tradable C emissions reduction, and C sequestered is easily accountable, and verifiable.
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Rapid turnover of organic matter leads to a low efficiency of organic fertilizers applied to increase and sequester C in soils of the humid tropics. Charcoal was reported to be responsible for high soil organic matter contents and soil fertility of anthropogenic soils (Terra Preta) found in central Amazonia. Therefore, we reviewed the available information about the physical and chemical properties of charcoal as affected by different combustion procedures, and the effects of its application in agricultural fields on nutrient retention and crop production. Higher nutrient retention and nutrient availability were found after charcoal additions to soil, related to higher exchange capacity, surface area and direct nutrient additions. Higher charring temperatures generally improved exchange properties and surface area of the charcoal. Additionally, charcoal is relatively recalcitrant and can therefore be used as a long-term sink for atmospheric CO, Several aspects of a charcoal management system remain unclear, such as the role of microorganisms in oxidizing charcoal surfaces and releasing nutrients and the possibilities to improve charcoal properties during production under field conditions. Several research needs were identified, such as field testing of charcoal production in tropical agroecosystems, the investigation of surface properties of the carbonized materials in the soil environment, and the evaluation of the agronomic and economic effectiveness of soil management with charcoal.
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In this study, the suitability of biochar and activated carbon (AC) for contaminated soil remediation is investigated by determining the sorption of pyrene to both materials in the presence and absence of soil and before as well as after aging. Biochar and AC were aged either alone or mixed with soil via exposure to (a) nutrients and microorganisms (biological), (b) 60 and 110 °C (chemical), and (c) freeze-thaw cycles (physical). Before and after aging, the pH, elemental composition, cation exchange capacity (CEC), microporous SA, and sorption isotherms of pyrene were quantified. Aging at 110 °C altered the physicochemical properties of all materials to the greatest extent (for example, pH increased by up to three units and CEC by up to 50% for biochar). Logarithmic K(Fr) values ranged from 7.80 to 8.21 (ng kg(-1))(ng L(-1))(-nF) for AC and 5.22 to 6.21 (ng kg(-1))(ng L(-1))(-nF) for biochar after the various aging regimes. Grinding biochar to a smaller particle size did not significantly affect the sorption of d(10) pyrene, implying that sorption processes operate on the subparticle scale. Chemical aging decreased the sorption of pyrene to the greatest extent (up to 1.8 log unit for the biochar+soil). The sorption to AC was affected more by the presence of soil than the sorption to biochar was. Our results suggest that AC and biochar have a high sorption capacity for pyrene that is maintained both in the presence of soil and during harsh aging. Both materials could therefore be considered in contaminated land remediation.
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Biochars are anthropogenic carbonaceous sorbent and their influences on the sorption of environmental contaminants need to be characterized. Here we evaluated the effect of Pinus radiata derived biochars on soil sorption and desorption of phenanthrene. Two biochars separately produced at 350 degrees C and 700 degrees C and three soils were tested. Biochar amendment generally enhanced the soil sorption of phenanthrene. The biochar produced at 700 degrees C generally showed a greater ability at enhancing a soil's sorption ability than that prepared at 350 degrees C. The single-step desorption measurement showed an apparent hysteresis in biochar-amended soils. After 28 d equilibration, the sorptive capacity of biochar-amended soil (with an organic carbon content of 0.16%) significantly decreased. This study clearly suggested that biochar application enhanced soil sorption of hydrophobic organic compounds, but the magnitude of enhancement depended on the preparation of biochars, the indigenous soil organic carbon levels, and the contact time between soil and biochar.
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Microbial activity patterns at buried coal-tar disposal sites have been under investigation for several years to determine the response of naturally occurring microflora to polycyclic aromatic hydrocarbons (PAHs) at the sites. At one site in upstate New York, data have shown enrichment of PAH-degrading bacteria in subsurface contaminated zones but not in uncontaminated zones. Similar work at a midwestern site showed that the same trends existed in a heterogeneous disposal site except that a borehole outside the plume showed some PAH-mineralization activity. Polymerase chain reaction amplification of DNA extracted from sediment samples from the New York site indicated the presence of naphthalene metabolism genes nahAc and nahR, similar to those found on the NAH7 plasmid of Pseudomonas putida G7. Significant sequence polymorphism was observed in amplified nahAc products, indicating that divergent homologs of nahAc were present in the native community. Protozoan numbers were elevated in sediment samples displaying relatively high PAH-degrading activity, suggesting that a food chain was established based on PAH-degrading bacteria. Removal of the coal-tar source at the site occurred in 1991. In 1992, sampling of three key borehole stations revealed that mixing and backfilling operations had introduced soil microorganisms into the source area and introduced 14C-PAH-mineralization activity into the previously inactive pristine area. Thus removal of the source of the contaminants and restoration at the site have altered the microbial activity patterns outside the contaminant plume as well as in the source area.
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In the review noncovalently bound cyclodextrin (CD) dimers, i.e. CD host-guest 2:1 complexes as well as CD self-assembled inclusion oligomers are briefly characterized, showing methods of their investigations; properties and possible applications of these species are also described.
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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.
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The objective of this study was to investigate the effect of biochar application (CA) on soil physical properties and grain yields of upland rice (Oryza sativa L.) in northern Laos. During the 2007 wet season, three different experiments were conducted under upland conditions at 10 sites, combining variations in CA amounts (0–16 t ha−1), fertilizer application rates (N and P) and rice cultivars (improved and traditional) in northern Laos.CA improved the saturated hydraulic conductivity of the top soil and the xylem sap flow of the rice plant. CA resulted in higher grain yields at sites with low P availability and improved the response to N and NP chemical fertilizer treatments. However, CA reduced leaf SPAD values, possibly through a reduction of the availability of soil nitrogen, indicating that CA without additional N fertilizer application could reduce grain yields in soils with a low indigenous N supply. These results suggest that CA has the potential to improve soil productivity of upland rice production in Laos, but that the effect of CA application is highly dependent on soil fertility and fertilizer management.
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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.
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Agricultural activities and soils release greenhouse gases, and additional emissions occur in the conversion of land from other uses. Unlike natural lands, active management offers the possibility to increase terrestrial stores of carbon in various forms in soil. The potential to sequester carbon as thermally stabilized (charred) biomass using existing organic resource is estimated to be at least 1 Gtyr−1 and “biochar,” defined by its useful application to soil, is expected to provide a benefit from enduring physical and chemical properties. Studies of charcoal tend to suggest stability in the order of 1000 years in the natural environment, and various analytical techniques inform quantification and an understanding of turnover processes. Other types of biochar, such as those produced under zero-oxygen conditions have been studied less, but costs associated with logistics and opportunity costs from diversion from energy or an active form in soil demand certainty and predictability of the agronomic return, especially until eligibility for carbon credits has been established. The mechanisms of biochar function in soil, which appear to be sensitive to the conditions prevailing during its formation or manufacture, are also affected by the material from which it is produced. Proposed mechanisms and some experimental 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 is important to ensure safety and regulatory compliance.
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The observed strong sorption of polycyclic aromatic hydrocarbons (PAHs) to black carbon (BC) presents potential implications for PAH bioaccessibility in soils. The effects of BC on the desorption kinetics and mineralisation of phenanthrene in four soils was investigated after 1, 25, 50 and 100d soil-PAH contact time, using sequential hydroxypropyl-β-cyclodextrin (HPCD) extractions in soils amended with 0, 0.1, 1 and 5% (dry wt. soil) activated charcoal (AC, a form of BC). The Rrapidly (%Frap) and slowly (%Fslow) desorbing phenanthrene fractions and their rate constants were determined using a first-order two-compartment (biphasic) desorption model. A minimum 7.8-fold decrease in %Frap occurred when AC was increased from 0-5%, with a corresponding increase in %Fslow. Desorption rate constants followed the progression krap(% h-1) > kslow(% h-1) and were in the order of 10-1 to 10-2 and 10-3 to 10-4, respectively. Linear regressions between %Frap and the fractions degraded by a phenanthrene inoculum (% Fmin) indicated that slopes did not approximate 1 at concentrations greater than 0% AC; %Fmin often exceeded %Frap, indicating a fraction of sorbed phenanthrene (%Fslow) remained microbially accessible. Therefore, sorption-HPCD-desorption kinetics alone may not be an adequate basis for the prediction of the bioaccessibility of PAHs to microorganisms and/or bioremediation potential in AC amended soils.
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13C-NMR spectroscopy was applied to the evaluation of soil-bound residues of the fungicide cyprodinil (4-cyclopropyl- 6-methyl-2-phenylaminopyrimidine). A mixture of the 13C- and 14C-labeled fungicide was used to obtain structural information as well as information on the quantitative distribution in the various fractions. Bound residues were accumulated by a 6-month incubation of the labeled compound with a clay loamy soil. Depending on the concentration of [13C]cyprodinil (500, 250, 80, and 3 mg/kg), binding ranged from 18% to 54% of the initial radioactivity. After methanol extraction of soil (10 g dry weight) treated with 500 mg/kg (5.0 mg) of the fungicide, the amount of unextracted bound material was equivalent to 0.9 mg of 13C-labeled cyprodinil. Upon fractionation, 0.21 mg of the bound fungicide was found in the dialyzed humic acid, 0.13 mg in fulvic acid (after extraction with CH2Cl2), and 0.24 mg in humin. The methylene chloride extract from fulvic acid mainly contained unchanged cyprodinil (0.21 mg) that was apparently sequestered in soil by physical forces. The humic acid fraction was dissolved in a 1% solution of NaOD and examined by 13C-NMR. The NMR spectrum of the material from the control sample exhibited all the characteristic features of a typical humic acid. When the control humic acid was spiked with cyprodinil labeled uniformly with 13C at the phenyl ring, four additional signals at 121.9, 124.4, 131.8, and 143.4 ppm could be distinguished in the NMR spectrum. However, when humic acid originated from the soil that was incubated with the phenyl-labeled fungicide, only two strong NMR signals, at 122.5 and 131.8 ppm, and two less significant signals around 142 and 162 ppm were observed. The difference in the signal pattern indicated cleavage of the cyprodinil molecule between the aromatic rings and independent binding of the phenyl and pyrimidyl moieties to humic acid.
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This is part of a larger study that addresses the question of whether site-specific sorption of organic compounds takes place in soil organic matter (SOM). Competitive sorption is one indication that such interactions may take place. Competitive sorption was tested between atrazine (AT) and other co-solutes in water suspensions of natural and model sorbents. The co-solutes included several s-triazine analogs, a substituted benzene analog (5-chloro-1,3-dimethoxybenzene), and a dissimilar compound, trichloroethene (TCE). The sorbents included a mineral soil (3% OM), a peat soil (93% OM), soil humic acid particles (99% OM), rubbery polymers (polyethylene, cellulose, chitin), a glassy polymer [poly(2,6-diphenyl-p-phenylene oxide)], and a mesoporous silica gel. The rubbery polymers afforded linear single-solute isotherms and no competition, both consistent with ideal (Henry's law) partition sorption. The other sorbents, including the glassy polymer, gave nonlinear single-solute isotherms and significant competition between AT and its analogs and weak or no competition between AT and TCE. A thermodynamic model, ideal adsorbed solution theory (IAST), was incapable of consistently simulating competition or lack thereof. For the SOM-containing materials, the results indicate that, like glassy polymers, SOM is a dual-mode sorbent. Sorption occurs by a partition mechanism and a hole-filling mechanism. The holes are conceptualized as specific sites inside the matrix where complexation follows the Langmuir isotherm and where a degree of specificity is exhibited. In the mineral and peat soils, from one-third to one-half of AT sorption occurs in the hole domain. Combined with previous data, it appears that dual-mode sorption in SOM is applicable to polar and nonpolar compounds alike. For silica, the results suggest that the spatial sorption domain of TCE is distinct (possibly further from the surface) than that of the s-triazines.
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The use of equilibrium expressions for sorption to natural particles in fate and transport models is often invalid due to slow kinetics. This paper reviews recent research into the causes of slow sorption and desorption rates at the intraparticle level and how this phenomenon relates to contaminant transport, bioavailability, and remediation. Sorption kinetics are complex and poorly predictable at present. Diffusion limitations appear to play a major role. Contending mechanisms include diffusion through natural organic matter matrices and diffusion through intraparticle nanopores. These mechanisms probably operate simultaneously, but the relative importance of each in a given system is indeterminate. Sorption shows anomalous behaviors that are presently not well explained by the simple diffusion models, including concentration dependence of the slow fraction, distributed rate constants, and kinetic hysteresis. Research is needed to determine whether adsorption/desorption bond energies may play a role along with molecular diffusion in slow kinetics. The possible existence of high-energy adsorption sites both within the internal matrix of organic matter and in nanopores is discussed. Sorption can be rate-limiting to biodegradation, bioavailablity, and subsurface transport of contaminants. Characterization of mechanism is thus critical for fate and risk assessment. Studies are needed to measure desorption kinetics under digestive and respiratory conditions in receptor organisms. Conditions under which the constraint of slow desorption may be overcome are discussed, including the addition of biological or chemical agents, the application of heat, and the physical alteration of the soil.
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Carbonaceous soil amendments are applied to contaminated soils and sediments to strongly sorb hydrophobic organic contaminants (HOCs) and reduce their freely dissolved concentrations. This limits biouptake and toxicity, but also biodegradation. To investigate whether HOCs sorbed to such amendments can be degraded at all, the desorption and biodegradation of low concentrations of (14)C-labelled phenanthrene (⩽5μgL(-1)) freshly sorbed to suspensions of the pure soil amendments activated carbon (AC), biochar (charcoal) and compost were compared. Firstly, the maximum abiotic desorption of phenanthrene from soil amendment suspensions in water, minimal salts medium (MSM) or tryptic soy broth (TSB) into a dominating silicone sink were measured. Highest fractions remained sorbed to AC (84±2.3%, 87±4.1%, and 53±1.2% for water, MSM and TSB, respectively), followed by charcoal (35±2.2%, 32±1.7%, and 12±0.3%, respectively) and compost (1.3±0.21%, similar for all media). Secondly, the mineralization of phenanthrene sorbed to AC, charcoal and compost by Sphingomonas sp. 10-1 (DSM 12247) was determined. In contrast to the amounts desorbed, phenanthrene mineralization was similar for all the soil amendments at about 56±11% of the initially applied radioactivity. Furthermore, HPLC analyses showed only minor amounts (<5%) of residual phenanthrene remaining in the suspensions, indicating almost complete biodegradation. Fitting the data to a coupled desorption and biodegradation model revealed that desorption did not limit biodegradation for any of the amendments, and that degradation could proceed due to the high numbers of bacteria and/or the production of biosurfactants or biofilms. Therefore, reduced desorption of phenanthrene from AC or charcoal did not inhibit its biodegradation, which implies that under the experimental conditions these amendments can reduce freely dissolved concentration without hindering biodegradation. In contrast, phenanthrene sorbed to compost was fully desorbed and biodegraded.
Article
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.
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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.
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The versatile pharmaceutical material cyclodextrin’s (CDs) are classified into hydrophilic, hydrophobic, and ionic derivatives. By the early 1950s the basic physicochemical characteristics of cyclodextrins had been discovered, since than their use is a practical and economical way to improve the physicochemical and pharmaceutical properties such as solubility, stability, and bioavailability of administered drug molecules. These CDs can serve as multi-functional drug carriers, through the formation of inclusion complex or the form of CD/drug conjugate and, thereby potentially serving as novel drug carriers. This contribution outlines applications and comparative benefits of use of cyclodextrins (CDs) and their derivatives in the design of novel delivery systems like liposomes, microspheres, microcapsules, nanoparticles, cyclodextrin grafted cellulosic fabric, hydrogels, nanosponges, beads, nanogels/nanoassemblies and cyclodextrin-containing polymers. The article also focuses on the ability of CDs to enhance the drug absorption across biological barriers, the ability to control the rate and time profiles of drug release, drug safety, drug stability, and the ability to deliver a drug to targeted site. The article highlight’s on needs, limitations and advantages of CD based delivery systems. CDs, because of their continuing ability to find several novel applications in drug delivery, are expected to solve many problems associated with the delivery of different novel drugs through different delivery routes.
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Purpose Polycyclic aromatic hydrocarbon (PAHs) are ubiquitous pollutants in agricultural soils in China. Biochar is the charred product of biomass pyrolysis, which is widely applied to soils to sequestrate atmospheric carbon dioxide and guarantees a long-term benefit for soil fertility. Knowledge about the impacts of various biochars on soil sorption affinity remains obscure. In this study, we evaluated the effects of various biochars on PAHs sorption to biochar-amended agricultural soil. Materials and methods Biochar of pine needle were produced under different pyrolytic temperatures (100°C, 300°C, 400°C, and 700°C, referred as P100-P700) and inputted into a paddy soil with various content. A batch equilibration method was used to determine sorption of PAHs (naphthalene, phenanthrene, and pyrene) in biochar amendment treated and untreated soil. The effects of biochar on PAHs sorption in biochar-amended soil were discussed. Results and discussion Biochars impose different effects on PAHs sorption by biochar-amended soil. P100 added to soil increased the linearity of sorption isotherm due to the linear-type isotherm of P100. While the nonlinearity of sorption isotherm for P300, P400, and P700 amended soil were increased with the increase of biochar content in soil. Biochar produced under high pyrolytic temperature demonstrated high efficiency in improving the sorption affinity of biochar-amended soil, and the total sorption were largely controlled by biochar when P300 content was larger than 0.5%, and P400 and P700 content above 0.1%. The predicted sorption of soil amended with P100 and P300 was consistent with their experimental values. However, for P400 and P700 amended soil, the actual sorption was lower than the predicted. Conclusions The results shown that added biochar into soil may enhance the sorption of PAHs to soil, thus provide a theoretical reference to apply biochar to mitigating the PAHs-contaminated soils through transferring PAHs from soil to biochar.
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In the review noncovalently-bound cyclodextrin (CD) dimers, i. e., CD host-guest 2:1 complexes as well as CD self-assembled inclusion oligomers, are briefly characterized, showing methods of their investigations; the properties and possible applications of these species are also described.
Article
There is considerable current interest in using biochar (BC) as a soil amendment to sequester carbon to mitigate climate change. However, the implications of adding BC to agricultural soil for the environmental fate of pesticides remain unclear. In particular, the effect of biochars on desorption behavior of compounds is poorly understood. This study examined the influence of BC on pesticide chemical and biological accessibility using the herbicide isoproturon (IPU). Soils amended with 1% and 2% BC showed enhanced sorption, slower desorption, and reduced biodegradation of IPU. Addition of 0.1% BC had no effect on sorption, desorption or biodegradation of IPU. However, the mineralization of (14)C-IPU was reduced by all BC concentrations, reducing by 13.6%, 40.1% and 49.8% at BC concentrations of 0.1%, 1% and 2% respectively. Further, the ratio of the toxic metabolite 4-isopropyl-aniline to intact IPU was substantially reduced by higher BC concentrations. Hydroxypropyl-β-cyclodextrin (HPCD) extractions were used to estimate the IPU bioaccessibility in the BC-amended soil. Significant correlations were found between HPCD-extracted (14)C-IPU and the IPU desorbed (%) (r(2)=0.8518, p<0.01), and also the (14)C-IPU mineralized (%) (r(2)=0.733; p<0.01) for all BC-amended soils. This study clearly demonstrates how desorption in the presence of BC is intimately related to pesticide biodegradation by the indigenous soil microbiota. BC application to agricultural soils can affect the persistence of pesticides as well as the fate of their degradation products. This has important implications for the effectiveness of pesticides as well as the sequestration of contaminants in soils.
Article
Apricot stone, hazelnut shell, grapeseed and chestnut shell are important biomass residues obtained from the food processing industry in Turkey and they have a great importance as being a source of energy. In this study, the characteristics of bio-oil and biochar samples obtained from the carbonization of apricot stone, hazelnut shell, grapeseed and chestnut shell were investigated. It was found that the biochar products can be characterized as carbon rich, high heating value and relatively pollution-free potential solid biofuels. The bio-oil products were also presented as environmentally friendly green biofuel candidates.
Article
Biochars, derived from biomass, are increasingly recognized as an environmental-friendly sorbent to abate organic pollutants. Sorption variations of biochars with their pyrolytic temperatures are evaluated. Nine biochars of orange peels with different pyrolytic temperatures (150–700 °C, referred as OP150–OP700) were characterized via elemental analysis, BET-N2 surface area, and Fourier transform infrared spectroscopy. Sorption of naphthalene and 1-naphthol by the biochars in water are compared. Sorption isotherms varied from linear to Freundlich with increasing pyrolytic temperature. The respective contributions of adsorption and partition to total sorption were correlated with biochars’ structural parameters. For OP150–OP600, sorption of 1-naphthol was significantly larger than naphthalene due to the former owning additional specific interactions. For 1-naphthol with high concentrations, the OP200 exhibited the maximal sorption capacity due to its largest partition and high adsorption among nine biochars. For 1-naphthol with low concentrations and naphthalene, the OP700 displayed the maximal sorption capacity. These observations provide a reference to the use of biochars as engineered sorbents for environmental applications.
Article
Five activated carbons (ACs) and two biochars were tested as amendments to reduce the availability of aged polychlorinated dibenzo-p-dioxin/dibenzofurans (PCDD/Fs) in two soils. All sorbents (ACs and biochars) tested substantially reduced the availability of PCDD/Fs measured by polyoxymethylene (POM) passive uptake and earthworm (E. fetida) biouptake. Seven sorbents amended at a level of 0.2 × soil total organic carbon (0.2X) reduced the passive uptake (physicochemical availability) of total PCDD/Fs in POM by 40% to 92% (or toxic equivalent by 48% to 99%). Sorbents with finer particle sizes or more macropores showed higher reduction efficiencies. The powdered regenerated AC and powdered coconut AC demonstrated to be the most effective and the two biochars also performed reasonably well especially in the powdered form. The passive uptake of PCDD/F in POM increased approximately 4 to 5 fold as the contact time between POM and soil slurry increased from 24 to 120 d while the efficacy of ACs in reducing the physicochemical availability remained unchanged. The reduction efficiencies measured by POM passive uptake for the regenerated AC were comparable to those measured by earthworm biouptake (bioavailability) at both dose levels of 0.2X and 0.5X. The biota-soil accumulation factor (BSAF) values for unamended soil ranged from 0.1 for tetra-CDD/F to 0.02 for octa-CDD/F. At both dose levels, the regenerated AC reduced the BSAFs to below 0.03 with the exception of two hexa-CDD/Fs. The reduction efficiencies measured by earthworm for coconut AC and corn stover biochar were generally less than those measured by POM probably due to larger particle sizes of these sorbents that could not be ingested by the worms.
Article
Qualitative identification of sorbed volatile organic compounds (VOCs) on biochar was conducted by headspace thermal desorption coupled to capillary gas chromatographic-mass spectrometry. VOCs may have a mechanistic role influencing plant and microbial responses to biochar amendments, since VOCs can directly inhibit/stimulate microbial and plant processes. Over 70 biochars encompassing a variety of parent feedstocks and manufacturing processes were evaluated and were observed to possess diverse sorbed VOC composition. There were over 140 individual chemical compounds thermally desorbed from some biochars, with hydrothermal carbonization (HTC) and fast pyrolysis biochars typically possessing the greatest number of sorbed volatiles. In contrast, gasification, thermal or chemical processed biochars, soil kiln mound, and open pit biochars possessed low to non-detectable levels of VOCs. Slow pyrolysis biochars were highly variable in terms of their sorbed VOC content. There were no clear feedstock dependencies to the sorbed VOC composition, suggesting a stronger linkage with biochar production conditions coupled to post-production handling and processing. Lower pyrolytic temperatures (⩽350°C) produced biochars with sorbed VOCs consisting of short carbon chain aldehydes, furans and ketones; elevated temperature biochars (>350°C) typically were dominated by sorbed aromatic compounds and longer carbon chain hydrocarbons. The presence of oxygen during pyrolysis also reduced sorbed VOCs. These compositional results suggest that sorbed VOCs are highly variable and that their chemical dissimilarity could play a role in the wide variety of plant and soil microbial responses to biochar soil amendment noted in the literature. This variability in VOC composition may argue for VOC characterization before land application to predict possible agroecosystem effects.
Article
Sorption of hydrophobic organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) to black carbon (BC) particles has been the focus of numerous studies. Conclusions on sorption mechanisms of PAH on BC were mostly derived from studies of sorption isotherms and sorption kinetics, which are based on batch experiments. However, mechanistic modeling approaches consider processes at the subparticle scale, some including transport within the pore-space or different spatial pore-domains. Direct evidence based on analytical techniques operating at the submicrometer scale for the location of sorption sites and the adsorbed species is lacking. In this work, we identified, quantified, and mapped the sorption of PAHs on different BC particles (activated carbon, charcoal and diesel soot) on a 25-100 nm scale using scanning transmission X-ray microscopy (STXM). In addition, we visualized the pore structure of the particles by transmission electron microscopy (TEM) on the 1-10 nm-scale. The combination of the chemical information from STXM with the physical information from TEM revealed that phenanthrene accumulates in the interconnected pore-system along primary "cracks" in the particles, confirming an adsorption mechanism.
Article
The supramolecular assemblies based on polysaccharides modified by cyclodextrins (CDs) and/or hydrophobic guest molecules have inspired interesting developments in the biomedical, pharmaceutical and cosmetic fields. This review will update the recent progress in the design, synthesis and study of such supramolecular structures. Preliminary studies demonstrated that such systems, based on the physical cross-linking of biopolymers through CD inclusion complexation, have potential as injectable hydrogels for the controlled release of drugs. Their nanoscale association also lead to the formation of original particles and films which pave the way to new applications in drug delivery and tissue engineering.
Article
Applying amendments to multi-element contaminated soils can have contradictory effects on the mobility, bioavailability and toxicity of specific elements, depending on the amendment. Trace elements and PAHs were monitored in a contaminated soil amended with biochar and greenwaste compost over 60 days field exposure, after which phytotoxicity was assessed by a simple bio-indicator test. Copper and As concentrations in soil pore water increased more than 30 fold after adding both amendments, associated with significant increases in dissolved organic carbon and pH, whereas Zn and Cd significantly decreased. Biochar was most effective, resulting in a 10 fold decrease of Cd in pore water and a resultant reduction in phytotoxicity. Concentrations of PAHs were also reduced by biochar, with greater than 50% decreases of the heavier, more toxicologically relevant PAHs. The results highlight the potential of biochar for contaminated land remediation.
Article
Conversion of waste products into biochar (BC) is being considered as one of several waste disposal and recycling options. In this study, we produced BC from dairy manures by heating at low temperatures (500 degrees C) and under abundant air condition. The resultant BC was characterized for physical, chemical, and mineralogical properties specifically related to its potential use in remediation. The BC from all manures behaved similarly. Surface area, ash content, and pH of the BC increased as temperature increased, while yield decreased with increasing temperature. The BC was rich in mineral elements such as N, Ca, Mg, and P in addition to C, and concentrations of C and N decreased with increasing temperature as a result of combustion and volatilization; while P, Ca, and Mg increased as temperature increased. For example, C significantly decreased from 36.8% at 100 degrees C to 1.67% at 500 degrees C; whereas P increased from 0.91% to 2.66%. Water soluble P, Ca, and Mg increased when heated to 200 degrees C but decreased at higher temperatures likely due to increased crystallization of Ca-Mg-P, as supported by the formation of whitlockite (Ca,Mg)(3)(PO(4))(2) following 500 degrees C treatment. The presence of whitlockite was evidenced by X-ray diffraction analysis. Quartz and calcite were present in all BC produced. The BC showed appreciable capability of adsorption for Pb and atrazine from aqueous solution, with Pb and atrazine removal by as high as 100% and 77%, respectively. The results indicated that dairy manure can be converted into biochar as an effective adsorbent for application in environmental remediation.
Article
The desorption of polycyclic aromatic hydrocarbons (PAHs) often exhibits a biphasic profile similar to that observed for biodegradation whereby an initial rapid phase of degradation or desorption is followed by a phase of much slower transformation or release. Most investigations to-date have utilised a polymeric sorbent, such as Tenax, to characterise desorption, which is methodologically unsuitable for the analysis of soil. In this study, desorption kinetics of (14)C-phenanthrene were measured by consecutive extraction using aqueous solutions of hydroxypropyl-beta-cyclodextrin (HPCD). The data indicate that the fraction extracted after 24 h generally approximated the linearly sorbed, rapidly desorbing fraction (F(rap)), calculated using a three-compartment model. A good linear correlation between phenanthrene mineralised and F(rap) was observed (r(2) = 0.89; gradient = 0.85; intercept = 8.20). Hence HPCD extraction (24 h) and first-order three-compartment modelling appear to provide an operationally straightforward tool for estimating mass-transfer limited biodegradation in soil.
Article
Desorption of pyrene and phenanthrene, from two charcoals and humic acid preloaded charcoals were studied. Desorption occurred obviously in two fractions, with rapid and slow desorption rate constant ranging from 0.18 to 0.71 d(-1), and from 6.3 x 10(-5) to 7.4 x 10(-3) d(-1), respectively. Both the kinetics and percentage extent of desorption were influenced greatly by the properties of chemical and charcoal. Generally, slower and less desorption is related to larger chemical at lower level, and occurred from charcoal with greater aromaticity and polarity. Both rapid and slow desorption rates of pyrene decreased after the two charcoals were preloaded with humic acids. This demonstrates that the size and surface property of charcoal micropores exhibit great influence on the combination state of sorbed chemicals. Aging caused a greater reduction in desorption of phenanthrene compared to pyrene, which supports the mechanism of the transferring of chemical molecules from fast-desorbing sites to slowly-desorbing sites during aging.
Article
Despite numerous reviews suggesting that microbial biosensors could be used in many environmental applications, in reality they have failed to be used for which they were designed. In part this is because most of these sensors perform in an aqueous phase and a buffered medium, which is in contrast to the nature of genuine environmental systems. In this study, a range of non-exhaustive extraction techniques (NEETs) were assessed for (i) compatibility with a naphthalene responsive biosensor and (ii) correlation with naphthalene biodegradation. The NEETs removed a portion of the total soil naphthalene in the order of methanol > HPCD > betaCD > water. To place the biosensor performance to NEETs in context, a biodegradation experiment was carried out using historically contaminated soils. By coupling the HPCD extraction with the biosensor, it was possible to assess the fraction of the naphthalene capable of undergoing microbial degradation in soil.
Article
The aim of this study was to investigate the prediction of (14)C-phenanthrene and (14)C-hexadecane biodegradation in the presence of other hydrocarbons in soil using beta- and alpha-cyclodextrin (CD) solutions, respectively. Prediction of the biodegradation of (14)C-phenanthrene using the beta-CD extraction was robust under single, co-contaminant and multiple contaminant conditions (r(2)=0.92, slope of best fit line=0.87, intercept=7.24, n=84). Prediction of (14)C-hexadecane using the alpha-CD extraction was robust under single and co-contaminant conditions (r(2)=0.92, slope of best fit line=0.97, intercept=1.24, n=60); however, the alpha-CD could not accurately predict (14)C-hexadecane biodegradation in the presence of multiple contaminants. The presence of multiple contaminants enhanced (14)C-hexadecane mineralisation, but did not enhance extractability. The results from this study provide further evidence for the application of HPCD extractions for the measurement of microbial accessibility in soil.
Article
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.
Article
A study was conducted to investigate whether cyclodextrins and surfactants can be used to predict polycyclic aromatic hydrocarbon (PAH) bioavailability in contaminated sediments. Two sediment samples were extracted with aqueous solutions of hydroxypropyl-beta-cyclodextrin (HPCD) and Triton X-100. PAH removal during extraction was compared with PAH removal during biodegradation and solid-phase extraction. The latter two methods were used as reference methods to establish which part of the PAHs could be biodegraded and to what extent biodegradation was governed by bioavailability limitations. It was demonstrated that HPCD extraction followed solid-phase extraction and removed primarily readily bioavailable PAHs, while Triton X-100 extracted both readily and poorly bioavailable PAHs. Moreover, HPCD did not affect the degradation of PAHs in biodegradation experiments, while Triton X-100 enhanced the degradation of low molecular weight PAHs. It was concluded that HPCD extraction may provide a good method for the prediction of PAH bioavailability. Triton X-100 extraction is unfit for the prediction of PAH bioavailability.
Article
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.
Article
Non-exhaustive extraction techniques (NEETs) have been shown to measure the putatively bioavailable fraction of hydrophobic compounds in soil. To date, these studies have only considered bioavailability in a single soil type. In this study, naphthalene was amended into five different soil types and mineralisation, bacterial biosensor response and the number of indigenous microbial naphthalene degraders were determined. Two NEETs were used to extract the naphthalene from soil; hydroxypropyl-beta-cyclodextrin (HPCD) and XAD-4. The HPCD extractable fraction correlated closely (R2 = 0.917) with the portion that was mineralised, but the XAD-4 extract did not (R2 = 0.044). HPCD may be ideal for the rapid assessment of the fraction of a hydrophobic organic contaminant that is available for biodegradation. A NEET that complements environmental microbial analysis will enhance our understanding of soil pollution interactions and equip us better in designing risk assessment models that integrate biological parameters. This application, although refined for soil samples, should be transferable to other environmental matrices.
Article
A certain amount of wood char or soot in a soil or sediment sample may cause the sorption of organic compounds to deviate significantly from the linear partitioning commonly observed with soil organic matter (SOM). Laboratory produced and field wood chars have been obtained and analyzed for their sorption isotherms of a model solute (phenanthrene) from water solution. The uptake capacities and nonlinear sorption effects with the laboratory wood chars are similar to those with the field wood chars. For phenanthrene aqueous concentrations of 1 microg l(-1), the organic carbon-normalized sorption coefficients (log K(oc)) ranging from 5.0 to 6.4 for field chars and 5.4-7.3 for laboratory wood chars, which is consistent with literature values (5.6-7.1). Data with artificial chars suggest that the variation in sorption potential can be attributed to heating temperature and starting material, and both the quantity and heterogeneity of surface-area impacts the sorption capacity. These results thus help to corroborate and explain the range of logK(oc) values reported in previous research for aquifer materials containing wood chars.