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Sulphur-oxidising bacteria isolated from deep caves improve the removal of arsenic from contaminated harbour sediments

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Abstract

Acidophilic S-oxidising bacteria isolated from sulphur-rich deep caves (Frasassi, Italy), characterised by relatively low temperature, were tested for their ability to mobilise (semi-)metals from contaminated sediments. Sediment samples from two commercial Italian seaports were used to set up bioleaching experiments. The effect of different growth substrates was also investigated. Our experiments revealed that S-oxidising bacteria isolated from Frasassi caves have a high potential to remove As from contaminated marine sediments, as never reported before. Although As solubilisation efficiency was quite low (i.e. about 30%), only a small amount of As was associated with non-residual fractions of the sediment. On the contrary, the solubilisation efficiencies of Zn and Ni (20% and 10%, respectively) were lower than those previously obtained by the use of other acidophilic bacteria and mainly influenced by the experimental conditions rather than by the presence of the S-oxidising bacteria. Results presented here open new perspectives in bioleaching applications for the remediation of contaminated sediments. Indeed, microbial strains adapted to relatively low-temperature environments could improve sediment bioleaching at temperature regimes where mesophilic and thermophilic strains are not favoured. Such strains could be exploited for developing selective bioremediation procedures for sediments contaminated with As, to be applied in multistep biotreatment processes.

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... These microorganisms were determined to be used in the construction of bio-concretes, crack healing in concretes, and soil bioremediation. In addition, diverse enzyme activities revealed in cave isolates can serve industrial uses with low energy spending [11,22,24,25]. Wastes bioremediation potentials were detected also in cave isolates [5,25]. ...
... In addition, diverse enzyme activities revealed in cave isolates can serve industrial uses with low energy spending [11,22,24,25]. Wastes bioremediation potentials were detected also in cave isolates [5,25]. ...
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Pilot studies were carried out to evaluate different options for metal-polluted (Cd, Cr, Cu, Ni, Pb and Zn) sediment decontamination. Chemical and biological leaching tests were done in a 350-L capacity stirred-tank reactor. The use of short acidic sediment washing steps (pH 2.0-3.0) was not an efficient approach for metal removal. The addition of an oxidant agent during the first washing step resulted in a large increase of removal yields for Pb (53-76%), Cd (54-92%) and Zn (69-93%). However, other metals were not well leached from sediments: Cr (6-30%), Cu (0-34%) and Ni (1-16%). The bioleaching treatment, with or without chemical washing steps, allows very good removal yields for Cd (82-100%), Cu (44-70%) and Zn (80-87%). On the other hand, this method was not efficient to remove other metals like Cr (6-16%), Ni (12-21%) and Tb (14-33%). The metals solubilized by chemical and/or biological leaching techniques can be efficiently removed from solution by precipitation using lime.
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Sediment contamination in coastal areas with high anthropogenic pressure is a widespread environmental problem. Metal contaminants are of particular concern, since they are persistent and cannot be degraded. Microorganisms can influence metal mobility in the sediment by several direct and indirect processes. However, the actual fate of metals in the environment is not easily predictable and several biogeochemical constraints affect their behaviour. In addition, the geochemical characteristics of the sediment play an important role and the general assumptions for soils or freshwater sediments cannot be extended to marine sediments. In this paper we analysed the correlation between metal mobility and main geochemical properties of the sediment. Although the prediction of metal fate in sediment environment, both for ex-situ bioleaching treatments and in-situ biostimulation strategies, appears to require metal-specific and site-specific tools, we found that TOM and pH are likely the main variables in describing and predicting Zn behaviour. Arsenic solubilisation/increase in mobility appears to correlate positively with carbonate content. Cd, Pb and Ni appear to require multivariate and/or non-linear approaches.
Chapter
The microbial populations in stirred-tank, mineral-processing bioreactors and in ore leaching heaps generally comprise several species. The presence of sulfur and iron as energy sources from most of their mineral substrates and the existence of gradients (chemical and physical) in their environments underlie the diversity in these populations. Many of the important organisms are well known and their relative proportions in the bioreactor populations of some pilot plants and commercial operations have been estimated. Generally, two or three species, specific to a particular temperature range, predominate in the various mixed cultures that exist in the bioreactors. The description of populations in ore leaching heaps has so far been mostly qualitative. Reasons for the coexistence of different species in these mixed cultures or populations are clearer in some cases than in others. Similarly, some of the features that give individual species a competitive advantage over others in mixed cultures have been revealed but others, particularly at elevated temperatures, remain to be defined.
Article
A method for enumeration of viable numbers of Thiobacillus ferrooxidans using membrane filters on ferrous-iron agar is presented. Factors affecting colony production were the concentration and brand of agar, pH of the medium, and type of membrane filter. The results suggest that inhibition of T. ferrooxidans by agar is a result of the acid hydrolysis of agar, the main product of which is d-galactose. Colony development was suppressed by aged medium, by acid-hydrolysed agar and by 0.1% galactose. Sartorius and Millipore membrane filters were suitable for the experiments, whereas Oxoid MF-50 membranes virtually suppressed the production of colonies. The method was employed to follow growth of T. ferrooxidans in pH 1.3 medium. The viable cell numbers were correlated with 14CO2-fixation and ferrous iron oxidation. Generation time was 6 h 22 min with a yield of 2.2×1012 organisms/g atom Fe2+ oxidized. Growth of T. neapolitanus on thiosulphate medium was not affected by agar-type or membrane filters and yield of the organism was 1.5×1013 organisms/g molecule Na2S2O3 oxidized.
Article
Bioleaching Xiangjiang River alkaline sediment contaminated by multiple heavy metals was investigated. Multiple metals in alkaline sediment possess significant toxicity to aquatic organisms or humans and will greatly inhibit bioleaching. The bioleaching method using autotrophic bacteria mixed with heterotrophic bacteria can solve this problem successfully. The experiment results showed that bioleaching efficiencies of Zn, Mn, Cu, and Cd were 95.2 %, 94.2 %, 90.1 %, and 84.4 %, respectively. Moreover, the changes of heavy metal concentrations in different fractions in contaminated sediment before and after bioleaching were analyzed by selective sequential extraction, and it was discovered that the main fractions of Zn, Mn, Cu and Cd after bioleaching are Fe-Mn oxide, organic associated form and a residual form. Its biotoxicity decreased greatly. The bioleaching heavy metals from sediment using autotrophic bacteria combined with heterotrophic bacteria can effectively improve the bioleaching efficiency and reduce toxicity.
Article
The contamination of aquatic sediments with metals is a widespread environmental problem. Coastal aquatic ecosystems with low hydrodynamics need to be periodically dredged in order to maintain the navigation depth and facilitate sailing; consequently large volumes of contaminated sediments need to be managed. Conventional remediation strategies include in-place sediment remediation strategies (e.g. in situ-capping) and relocation actions; in particular, landfill disposal and dumping at sea are still widely applied. Both this options are becoming unsustainable, due to problems associated with contaminant transport pathways, the uncertainties about long-term stability under various environmental conditions, the limited space capacity, costs and environmental compatibility. Alternative approaches have received increased attention; treatment and reuse of contaminated sediments is politically encouraged, but its application is still very limited. Because of the potential human health and environmental impacts of contaminated sediment, different chemical treatments are conventionally applied for contaminated sediments before reuse in other environmental settings. Environmentally friendly techniques developed for soils and other environmental matrices have been investigated for applications with sediments. Biotechnological approaches are gaining increasing prominence in this field and they are often considered as a promising strategy for the eventual treatment of contaminated sediments. In this paper an overview of the main treatment strategies potentially available for sediment contaminated with metals is given, together with a brief overview of the issue associated with the problem of the sediment management.
Article
This work describes the effect of weathering of fresh quenched municipal solid waste incinerator (MSWI) bottom ash on the mobility and leaching behavior of zinc (Zn). A sequential extraction procedure (SEP) was used to characterize the fractionation of zinc in the fresh and weathered MSWI bottom ash samples. It showed that the stable fraction of Zn, including organic matter bound fraction and residual fraction decreased from 62.4% to 30.9% during the weathering treatment, while the mobile fraction, including exchangeable fraction, carbonate bound fraction and Fe–Mn oxides bound fraction, increased from 37.6% to 60.1%. Furthermore, two standard leaching procedures, synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP), were carried out on the fresh and weathered samples. The leaching of Zn was attenuated with the weathering treatment in the SPLP procedure, but enhanced in the TCLP procedure. The SEP and TCLP results suggested that the weathering treatment could enhance the mobility of Zn, which was distinct from previous work.
Article
Bioleaching strategies are still far from finding real applications in sediment clean-up, although metabolic mechanisms governing bioleaching processes have been deeply studied and can be considered well established. In this study, we carried out bioleaching experiments, using autotrophic and heterotrophic acidophilic bacteria strains, and worked with marine sediments characterized by different geochemical properties and metal concentrations and speciations. The solubilization efficiency of the metals was highly variable, with the highest for Zn (40%-76%) and the lowest for Pb (0%-7%). Our data suggest that the role of autotrophic Fe/S oxidizing bacteria is mainly associated with the production and re-cycling of leaching chemical species, mainly as protons and ferric ions. Metal solubilization appears to be more related to establishing environmental conditions that allow each metal or semimetal to remain stable in the solution phase. Thus, the maintenance of acid and oxidative conditions, the chemical behavior in aqueous environment of each metal species and the geochemical characteristics of sediment interact intimately to influence metal solubilization in site-specific and metal-specific way.
Article
The microbial consortium in continuous-flow, stirred tank processes used to treat gold-bearing arsenopyrite concentrates in South Africa has become adapted to high concentrations of arsenic over several years. The dominant microorganisms, Acidithiobacillus caldus and Leptospirillum ferriphilum, were found to contain two sets of arsenic-resistance genes. One set was present in all isolates of a species irrespective of whether they were highly arsenic resistant or not, while a second, transposon-located set was present in only those strains that had been adapted to high concentrations of arsenic.The arsenopyrite treatment tanks from Tamboraque (near Lima, Peru) have not been inoculated with an arsenic-adapted consortium from South Africa. Isolation of a Leptospirillum ferrooxidans from the Tamboraque consortium allowed us to determine whether these microorganisms had acquired similar arsenic-resistance mechanisms as contained on the transposons in the highly arsenic resistant South African cultures. Several isolates of both L. ferriphilum and L. ferrooxidans from Europe as well as a “Leptospirillum ferrodiazotrophum” were also screened to detect whether they contained similar arsenic-resistance transposons even though they had not been selected for enhanced arsenic resistance.Transposons containing arsenic-resistance genes that were identical or closely related to those from South Africa were found in both L. ferrooxidans and L. ferriphilum isolates from South America and Europe. The widespread occurrence of arsenic-resistance transposons suggests that it should be possible to select for highly arsenic resistant biomining microorganisms from many different sources and therefore, unnecessary to use pre-adapted arsenic resistant consortia.
Article
The solubility of arsenic (As) and heavy metals (Me) from two sediments with differing chemical characteristics and degrees of contamination was quantified by suspension leaching under both aerobic and anoxic conditions. Elemental sulphur (S°) was added as a substrate for the indigenous Thiobacillus spp. The objective of this study was to examine the effects of measures, which attempted to stimulateor to prevent the mobilization of the pollutants in the source material.By stimulating aerobic bioleaching with S°, up to 80% (660 mg/kg) of the As became soluble in a highly polluted lake sediment (Suesser See) in the form of arsenite and arsenate. Without the addition of S°, the As solubility ranged between 0.6 and 3.5 mg/kg. No toxic effects of As (III) on bacterial growth and microbial activity of the indige nous Thiobacillus spp. were observed. By comparison, the As solubility in an oxic sediment from the river Weisse Elster was low (max. 0.5 mg/kg), while the total Me solubility reached 60% (3.7 g/kg).The anaerobic leaching tests were performed under the conditions of a nitrogen atmosphere in a special vessel allowing the redox potential and the pH of the solution to be continuously recorded. In the lake sediment without adding S°, the As solubility increased temporarily; up to 9% of the total As became soluble, and As (III) was the dominant As soluble species (20 mg/kg). In the late leaching phase (—300 mV), the total soluble As decreased, and As (V) became the major soluble species (3.9 mg/kg). In the presence of S°, soluble As and Me were immobilized. The inhibition of As and Me release can be explained by fixation as insoluble sulphides, suggesting that immobilization was driven by dissimilatory sulphur reduction.The data indicatethat the availability of oxidizable sulphur and the oxidation state of the polluted material play an important role in assessing the release of arsenic and heavy metals, including anaerobic conditions. Attention has to be paid to the maintaining of strong anaerobic conditions in sulphur-rich materials in order to prevent the mobilization of pollutants.
Article
Bioleaching is one of the feasible methods for the treatment of sediments contaminated with heavy metals. Effects of solid content, substrate (sulfur) concentration and pH on the performance of bioleaching process were investigated in this study. It was found that rates of sediment acidification and metal solubilization decreased with increasing solid content. Besides, sulfur concentration greater than 5 g/l was found to be inhibitory to bacterial activity and metal solubilization from sediment. It was concluded that a substrate concentration of 5 g/l in reactor was the optimum concentration for bioleaching process. It was also observed that solubilization of heavy metal from the sediment was highly pH-dependent. For all values of solid content and sulfur concentration tested, the efficiency of metal solubilization from sediment followed the order Cu>Zn>Pb>Cr. Keywords Bioleaching; contaminated sediment; heavy metal; solid content; sulfur concentration; thiobacilli
Article
Phosphate and OH- are often used for the extraction of As and Se from soils, either as single extractants or as part of a sequential extraction scheme. However, the recovery of As and Se species and the integrity of the resulting solution speciation merit investigation. In this study the relative effectiveness of PO4 at 0.1 and 0.5 M and pH values of 3 and 6.7 and 0.1 M OH- to extract As(III), As(V), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), p-arsanilic acid (p-ASA), roxarsone (ROX), Se(IV) and Se(VI) sorbed to goethite and an amorphous Fe oxide were compared, and the speciation in the resulting extract was determined. The extent to which 0.1 M PO4 added to 0.25 M NH2OH·HCl or 0.175 M Na oxalate/0.1 M oxalic acid prevents readsorption of As(V) or Se(IV) to goethite during the dissolution of an amorphous Fe oxide was also assessed. Hydroxide was the most effective extractant for desorption of all species except As(III) from both oxide surfaces. Arsenite was extracted most efficiently by 0.5 M PO4 at low pH; however, amorphous Fe oxide exhibited a strong affinity for As(III) with a maximum of 18% of As(III) extracted by 0.5 M PO4 at pH 2.8. Partial oxidation of As(III) to As(V) occurred in all extractions where an Fe oxide solid phase was present, but only in the hydroxide extract in the absence of a Fe solid phase. Addition of 0.1 M PO4 to extractants used for the dissolution of the amorphous Fe oxide prevented the readsorption of As(V) and Se(IV) to goethite.
Article
A study was conducted to assess the retention form of arsenic in soil and to evaluate the use of phosphate for releasing it from the soil. In this study, a loam soil was artificially polluted with arsenate at pH 5.5, which is one of the pH values at which maximum arsenic adsorption occurred. The soil was kept for 2.5 months under wet conditions to allow for stabilization. The soil was maintained under aerobic condition and losses of arsenic by volatilization were determined to be minimal. The soil was then sequentially extracted with a series of chemicals to identify the soil fractions in which the arsenic was bound. The percentage of arsenic found in the Fe bound-exchangeable, reducible-residual, Al bound exchangeable, residual, calcium bound exchangeable, and easily exchangeable forms was 31.6, 27.3, 25.2, 5.5, 4.9, and 4.7%, respectively. A batch experiment showed that at 20°C, 80% of the bound arsenic was removed by phosphate in the pH range of 5 to 7. A power function model was found to fit the data with a desorption rate constant of 402 mg/kg As h−1.
Article
The presence of selected toxic heavy metals, such as cadmium (Cd), lead (Pb) and mercury (Hg), was investigated in fish and seafood products, namely, blue mussel, carpet shell clam, European squid, veined squid, deep-water rose shrimp, red mullet, European seabass, gilthead seabream, Atlantic cod, European hake, Atlantic bluefin tuna and swordfish so as to assess their human exposure through diet. Metals were detected by quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) and hydride generation atomic absorption spectrometry (Hg-AAS). Measurements of Cd, Pb and Hg were performed by means of analytical methods validated in compliance with UNI CEI EN ISO/IEC 17025 [2005. General requirements for the competence of testing and calibration laboratories. Milano (Italy): UNI Ente Nazionale Italiano di Unificazione]. The exposure assessment was undertaken matching the levels of Cd, Pb and total Hg with consumption data related to fish and seafood products selected for this purpose. In order to establish human health implications, the estimated weekly intakes (EWIs) for Cd, Pb and Hg were compared with the standard tolerable weekly intakes (TWI) for Cd and provisional tolerable weekly intakes (PTWIs) for Pb and Hg stipulated by the European Food Safety Authority (EFSA) and the Food and Agriculture Organization/World Health Organization (FAO/WHO) Joint Expert Committee on Food Additives (JECFA). The found metal concentrations were largely below the maximum levels (MLs) established at the European Union level with the exception of Cd. This metal exceeded the MLs in squid, red mullet, European hake and Atlantic cod. Squid and blue mussel showed the highest Pb concentrations which accounted for 60% and 10% of the MLs, respectively. Highest Hg levels were found in predatory fish. The concentrations of Hg in swordfish, Atlantic bluefin tuna and red mullet accounted for 50%, 30% and 30% of the MLs, respectively. The EWIs for Cd, Pb and Hg related to the consumption of fish and seafood products by the median of the Italian total population accounted for 20%, 1.5% and 10% of the standard TWI for Cd as well as PTWIs for Pb and Hg, respectively. Furthermore, the EWIs estimated using consumption data concerning Italian consumers did not exceed the standard TWI and PTWIs, except for Cd at 95th percentile.
Article
Des travaux pilotes ont été menés dans le cadre de cette recherche afin de tester différents scénarios de décontamination de sédiments pollués par plusieurs métaux lourds (Cd, Cr, Cu, Ni, Pb et Zn). Des essais de lixiviation chimique et biologique ont été réalisés en réacteur de 350 L. L'application de lavages acides (pH 2.0–3.0) des sédiments constitue une approche peu efficace pour l'enlèvement des métaux toxiques. L'ajout d'un agent oxydant lors du premier lavage augmente considérablement les rendements d'enlèvement du Pb (53–76 %), Cd (54–92 %) et Zn (69–93 %). Les autres métaux demeurent toutefois difficiles à extraire: Cr (13–30 %), Cu (11–34 %) et Ni (0–16 %). La biolixiviation seule ou en combinaison avec un ou deux lavages chimiques, représente une approche efficace pour l'élimination du Cd (82–100 %), Cu (44–70 %) et Zn (80–87 %). Par contre, cette technique présente peu d'intére̊t pour la réduction des teneurs en Cr (6–16 %), Ni (12–34 %) et Pb (14–33 %). Les métaux solubilisés par lixiviation chimique et/ou biologique peuvent être précipités efficacement lors de la neutralisation des effluents acides par une solution de chaux.
Article
Microbial life in extremely low pH (<3) natural and man-made environments may be considerably diverse. Prokaryotic acidophiles (eubacteria and archaea) have been the focus of much of the research activity in this area, primarily because of the importance of these microorganisms in biotechnology (predominantly the commercial biological processing of metal ores) and in environmental pollution (genesis of ‘acid mine drainage’); however, obligately acidophilic eukaryotes (fungi, yeasts, algae and protozoa) are also known, and may form stable microbial communities with prokaryotes, particularly in lower temperature (<35°C) environments. Primary production in acidophilic environments is mediated by chemolitho-autotrophic prokaryotes (iron and sulfur oxidisers), and may be supplemented by phototrophic acidophiles (predominantly eukaryotic microalgae) in illuminated sites. The most thermophilic acidophiles are archaea (Crenarchaeota) whilst in moderately thermal (40–60°C) acidic environments archaea (Euryarchaeota) and bacteria (mostly Gram-positives) may co-exist. Lower temperature (mesophilic) extremely acidic environments tend to be dominated by Gram-negative bacteria, and there is recent evidence that mineral oxidation may be accelerated by acidophilic bacteria at very low (ca. 0°C) environments. Whilst most acidophiles have conventionally been considered to be obligately aerobic, there is increasing evidence that many isolates are facultative anaerobes, and are able to couple the oxidation of organic or inorganic electron donors to the reduction of ferric iron. A variety of interactions have been demonstrated to occur between acidophilic microorganisms, as in other environments; these include competition, predation, mutualism and synergy. Mixed cultures of acidophiles are frequently more robust and efficient (e.g. in oxidising sulfide minerals) than corresponding pure cultures. In view of the continuing expansion of microbial mineral processing (‘biomining’) as a cost-effective and environmentally sensitive method of metal extraction, and the ongoing concern of pollution from abandoned mine sites, acidophilic microbiology will continue to be of considerable research interest well into the new millennium.
Article
Aquatic sediments are a known source of pollutants, but their impact on the quality of overlying waters is not easily quantified. Sediments are generally considered to behave as a sink for pollutants such as heavy metals in the aquatic environment, frequently acting as a source for their presence in waters, with implications for catchment management. This study aimed to calculate the contribution of sediments to metal levels in overlying waters, helping understand their role as a source of metals in river catchments. An aquivalence mass balance approach was modified to take into account both natural and anthropogenic influences and applied to assess sediment contribution in a reach of the River Yare in the UK. The rates of total metal transport from sediments to overlying waters were estimated to be 29.89 g d(-1) for cadmium (Cd), 1633.39 g d(-1) for lead (Pb), 8.29 g d(-1) for mercury (Hg) and 357.56 g d(-1) for nickel (Ni). The results from the case study demonstrated that sediments could be a significant source of metal emissions in river catchments. The calculations proposed in the paper could be useful in developing strategies for sediment management, not only to improve and/or maintain quality of sediments but also to inform the selection of measures of pollution control for the catchment.
Article
Environmental studies on soil and sediment analysis are often based on the use of leaching or extraction procedures (e.g. single or sequential extraction procedures) which enable broader forms or phases to be measured (e.g. `bioavailable' forms of elements) and which are, in most cases, sufficient for the purpose of environmental policy. However, the lack of uniformity in the procedures used often hampers comparison of the results, owing to their `operationally defined' character. This implies that the `forms' of metals are defined by the determination of extractable elements, using a given procedure and, therefore, the significance of the analytical results is highly dependent on the extraction procedures used. The comparability of results can hence only be achieved if similar procedures are applied, which justifies efforts towards standardization. This article describes case studies of standardization approaches for single and sequential extraction procedures applied to soil and sediment analysis. In particular, the strategy followed by the Standards, Measurements and Testing program (formerly BCR) is fully described (feasibility study, interlaboratory studies and establishment of standardized protocols based on the results of tests and participants' experience).
Article
Differential rates of plagioclase and K-feldspar weathering commonly observed in bedrock and soil environments are examined in terms of chemical kinetic and solubility controls and hydrologic permeability. For the Panola regolith, in the Georgia Piedmont Province of southeastern United States, petrographic observations, coupled with elemental balances and 87Sr/86Sr ratios, indicate that plagioclase is being converted to kaolinite at depths > 6 m in the granitic bedrock. K-feldspar remains pristine in the bedrock but subsequently weathers to kaolinite at the overlying saprolite. In contrast, both plagioclase and K-feldspar remain stable in granitic bedrocks elsewhere in Piedmont Province, such as Davis Run, Virginia, where feldspars weather concurrently in an overlying thick saprolite sequence. Kinetic rate constants, mineral surface areas, and secondary hydraulic conductivities are fitted to feldspar losses with depth in the Panola and Davis Run regoliths using a time-depth computer spreadsheet model. The primary hydraulic conductivities, describing the rates of meteoric water penetration into the pristine granites, are assumed to be equal to the propagation rates of weathering fronts, which, based on cosmogenic isotope dating, are 7 m/106 yr for the Panola regolith and 4 m/106 yr for the Davis Run regolith. Best fits in the calculations indicate that the kinetic rate constants for plagioclase in both regoliths are factors of two to three times faster than K-feldspar, which is in agreement with experimental findings. However, the range for plagioclase and K-feldspar rates (kr = 1.5 × 10−17 to 2.8 × 10−16 mol m−2 s−1) is three to four orders of magnitude lower than for that for experimental feldspar dissolution rates and are among the slowest yet recorded for natural feldspar weathering. Such slow rates are attributed to the relatively old geomorphic ages of the Panola and Davis Run regoliths, implying that mineral surface reactivity decreases significantly with time.Differential feldspar weathering in the low-permeability Panola bedrock environment is more dependent on relative feldspar solubilities than on differences in kinetic reaction rates. Such weathering is very sensitive to primary and secondary hydraulic conductivities (qp and qs), which control both the fluid volumes passing through the regolith and the thermodynamic saturation of the feldspars. Bedrock permeability is primarily intragranular and is created by internal weathering of networks of interconnected plagioclase phenocrysts. Saprolite permeability is principally intergranular and is the result of dissolution of silicate phases during isovolumetric weathering. A secondary to primary hydraulic conductivity ratio of qs/qp = 150 in the Panola bedrock results in kinetically controlled plagioclase dissolution but thermodynamically inhibited K-feldspar reaction. This result is in accord with calculated chemical saturation states for groundwater sampled in the Panola Granite. In contrast, greater secondary conductivities in the Davis Run saprolite, qs/qp = 800, produces both kinetically controlled plagioclase and K-feldspar dissolution. Faster plagioclase reaction, leading to bedrock weathering in the Panola Granite but not at Davis Run, is attributed to a higher anorthite component of the plagioclase and a wetter and warmer climate. In addition, the Panola Granite has an abnormally high content of disseminated calcite, the dissolution of which precedes the plagioclase weathering front, thus creating additional secondary permeability.
Article
The degree to which anions can affect As mobility in subsurface environments depends on As speciation and fractionation in the soil. In this study, the fine soil fraction of an acidic soil was deliberately contaminated with arsenate (As(V)) and adequately aged for more than 220 days. A selective sequential extraction (SSE) scheme was developed to fractionate As in the soil into 6 fractions, while the influence of various anions on As mobility was assessed by evaluating its extractability by various salts such as Na3PO4, Na2CO3, Na2SO4 and NaCl. The variables of the extraction experiment were type of salt, salt concentration and reaction time. Fractionations of As in soil samples after extraction with the salts were also examined and the results compared against the initial As fractionation. The SSE results showed that the majority of the As was strongly adsorbed via surface complexation in the fine soil. A considerable amount of As was also associated with the exchangeable fraction, amorphous Fe oxyhydroxides, and the residual fraction. Abilities of the anions in mobilizing As bound in the fine soil followed the order of . Arsenic mobilization by was believed to be due primarily to a ligand exchange mechanism, through which the strongly bound As was replaced by the anion. Anion exchange might also contribute to the mobilization of As in this study. Increase in the concentration of the anions tested did not further mobilize As from the soil, with the exception of . The kinetics of As release in the solution could be best described by the Elovich model, which represents an exponential decrease in As desorption rate as more As was extracted from the soil.
Article
In order to evaluate the effect of improved oxygen concentrations in overlying surface water on the redox status, sediment geochemistry and metal bioavailability in metal-polluted sediments a 54 days lab experiment with two different experimental treatments was conducted (90% and 40% O(2)). Changes in redox potential (Eh) in the sediment were monitored over time. At 6 different time points (after 0, 2, 5, 12, 32 and 54 days) and at 4 sediment depths (0-1, 1-4, 4-8 and 8-15 cm), acid volatile sulfides (AVS), simultaneously extracted metals (SEM) and total organic carbon (TOC) were measured and metal release to overlying surface water was determined. Labile metal species in both water and sediment were measured using Diffusive Gradients in Thin films (DGT). Our results showed that elevated oxygen levels in overlying surface water led to an Eh increase in the sediment of the 90% O(2) treatment from 0 to ± 200 mV while AVS concentrations in the upper sediment layer decreased by 70%. Following AVS oxidation metal availability in the pore water was highly elevated after 54 days. However, Cu remained strongly bound to the sediment during the whole experiment. Only a limited metal release to the overlying surface water was noticed, which was due to the fact that SEM(tot) concentrations in the sediment did not yet exceeded AVS levels ([SEM(tot) - AVS]/f(OC) = 0) after 54 days. Additionally, adsorption on Fe and Mn hydroxides and particulate organic carbon also slowed down any potential metal release. Our results indicated that increasing oxygen concentrations due to general water quality improvements can enhance the mobility of trace metals which may result in the leaching of sediment-bound metals to overlying surface water, even in undisturbed watercourses.
Article
We investigated the effects of Shewanella putrefaciens cells and extracellular polymeric substances on the sorption of As(III) and As(V) to goethite, ferrihydrite, and hematite at pH 7.0. Adsorption of As(III) and As(V) at solution concentrations between 0.001 and 20 μM decreased by 10 to 45% in the presence of 0.3 g L(-1) EPS, with As(III) being affected more strongly than As(V). Also, inactivated Shewanella cells induced desorption of As(V) from the Fe(III)-(hydr)oxide mineral surfaces. ATR-FTIR studies of ternary As(V)-Shewanella-hematite systems indicated As(V) desorption concurrent with attachment of bacterial cells at the hematite surface, and showed evidence of inner-sphere coordination of bacterial phosphate and carboxylate groups at hematite surface sites. Competition between As(V) and bacterial phosphate and carboxylate groups for Fe(III)-(oxyhydr)oxide surface sites is proposed as an important factor leading to increased solubility of As(V). The results from this study have implications for the solubility of As(V) in the soil rhizosphere and in geochemical systems undergoing microbially mediated reduction and indicate that the presence of sorbed oxyanions may affect Fe-reduction and biofilm development at mineral surfaces.
Article
Process water and effluents from mining operations treating sulfide rich ores often contain considerable concentrations of metastable inorganic sulfur compounds such as thiosulfate and tetrathionate. These species may cause environmental problems if released to downstream recipients due to oxidation to sulfuric acid catalyzed by acidophilic microorganisms. Molecular phylogenic analysis of the tailings pond and recipient streams identified psychrotolerant and mesophilic inorganic sulfur compound oxidizing microorganisms. This suggested year round thiosalt oxidation occurs. Mining process waters may also contain inhibiting substances such as thiocyanate from cyanidation plants. However, toxicity experiments suggested their expected concentrations would not inhibit thiosalt oxidation by Acidithiobacillus ferrivorans SS3. A mixed culture from a permanently cold (4-6 °C) low pH environment was tested for thiosalt removal in a reactor design including a biogenerator and a main reactor containing a biofilm carrier. The biogenerator and main reactors were successively reduced in temperature to 5-6 °C when 43.8% of the chemical oxidation demand was removed. However, it was found that the oxidation of thiosulfate was not fully completed to sulfate since low residual concentrations of tetrathionate and trithionate were found in the discharge. This study has demonstrated the potential of using biotechnological solutions to remove inorganic sulfur compounds at 6°C and thus, reduce the impact of mining on the environment.
Article
In the present study we have concerned ourselves with heavy metal pollution in aquatic systems, and found that a series of metals, many of which are toxic, have become accumulated in sediments associated with inland water bodies, estuaries and coastal zones. A comparison of the metal values found in the sediments, collected from various areas, reveals that in industrialized and urbanized areas, the metal enrichment must be ascribed to anthropogenic influences rather than to natural enrichment of sediments by geological weathering (as evidenced by the analyses of the lower sections of sediment profiles).
Article
This study deals with bioremediation treatments of dredged sediments contaminated by heavy metals based on the bioaugmentation of different bacterial strains. The efficiency of the following bacterial consortia was compared: (i) acidophilic chemoautotrophic, Fe/S-oxidising bacteria, (ii) acidophilic heterotrophic bacteria able to reduce Fe/Mn fraction, co-respiring oxygen and ferric iron and (iii) the chemoautotrophic and heterotrophic bacteria reported above, pooled together, as it was hypothesised that the two strains could cooperate through a mutual substrate supply. The effect of the bioremediation treatment based on the bioaugmentation of Fe/S-oxidising strains alone was similar to the one based only on Fe-reducing bacteria, and resulted in heavy-metal extraction yields typically ranging from 40% to 50%. The efficiency of the process based only upon autotrophic bacteria was limited by sulphur availability. However, when the treatment was based on the addition of Fe-reducing bacteria and the Fe/S oxidizing bacteria together, their growth rates and efficiency in mobilising heavy metals increased significantly, reaching extraction yields >90% for Cu, Cd, Hg and Zn. The additional advantage of the new bioaugmentation approach proposed here is that it is independent from the availability of sulphur. These results open new perspectives for the bioremediation technology for the removal of heavy metals from highly contaminated sediments.
Article
Thiobacillus ferrooxidans originally cultured on ferrous iron can adapt to grow on thiosulphate, tetrathionate, trithionate or sulphur in liquid media. In unneutralized cultures (initial pH 4–4.4) mean doubling times on thiosulphate were 8.5–13 h and on tetrathionate was about 10 h. In pH-controlled cultures, growth on thiosulphate commenced at pH values from pH 3.6–4.7, with no growth in media initially below pH 3.5 or above pH 4.8. On tetrathionate, growth commenced between pH 1.5–4.3, with no growth below pH 1.3 or above pH 4.4. Growth rate was maximal ( = 0.043 h-1) on thiosulphate at pH 3.6 and on tetrathionate at pH 2.5 ( = 0.05 h-1). Growth yields of about 5.9 g (210 mmoles CO2 fixed) and 9.8 g (350 mmoles CO2 fixed) dry wt per gram-molecule were obtained respectively on thiosulphate and tetrathionate. Bacteria grown on thiosulphate or tetrathionate could produce colonies on ferrous iron agar, but this ability declined on prolonged culture on sulphur compounds. All the cultures grown on various inorganic sulphur compounds were capable of re-adapting to growth on iron. This was investigated in detail. About 66–82% of iron-grown organisms readily produced colonies on tetrathionate, but only about 1 in 109 produced colonies on thiosulphate.