Effect of plant root exudates on the desorption of hexachlorocyclohexane isomers from contaminated soils.

Plants and their associated microbiota can have a significant impact on the behaviour of soil contaminants. Particularly, root exudation is one of the most important plant-associated processes in this respect, as it may have a substantial effect on the bioavailability of soil contaminants, specially of hydrophobic contaminants strongly sorbed by soil. The aim of the present study was to evaluate the effect of root exudates (natural and artificial) on the desorption of α-, ß-, δ- and γ-isomers of hexachlorocyclohexane (HCH) from contaminated soil, using batch experiments. Natural root exudates were obtained from Holcus lanatus plants growing in the same (contaminated) area. Fifteen compounds (mainly organic acids and phenolic compounds) usually found in root exudates were also tested, individually or as mixtures (1 and 10 mM). Both natural and artificial exudates favoured the mobilization of sorbed HCH in soil. The effect was highly significant for α-, ß- and γ-HCH isomers, for which the desorption rates increased by 23.0, 26.8 and 15.5% in the presence of natural root exudates and by 40.1, 25.9 and 25.6% in the presence of the artificial mixture (at 10 mM). The δ-HCH desorption rates increased by less than 10%. The effect of individual exudate components was very variable, but increased with the carbon content, reflecting the significance of hydrophobic interactions between the exudates and HCH molecules in the desorption of these last from soil. These findings indicate that plants may significantly influence the bioavailability of persistent contaminants, with major implications for improving phyto- and bioremediation procedures.

Coupling of bioaugmentation and biostimulation to improve lindane removal from different soil types.

Lindane is an organochlorine pesticide that, due to its persistence in the environment, is still detected in different matrices. Bioremediation using actinobacteria consortia proved to be promising for the restoration of contaminated soils. Another alternative to remove xenobiotics is to use agricultural residues, which stimulates microbial activity, increasing its capacity to degrade organic pollutants. The present work studies the coupling of sugarcane bagasse biostimulation and bioaugmentation with the actinobacteria consortium composed of Streptomyces sp. A2, A5, A11 and M7 on lindane removal in different soil types. In this sense, factorial designs with three factors (proportion and size of sugarcane bagasse particles, and moisture content) were employed. A response optimizer identified the combination of factors levels that jointly allowed obtaining the maximum lindane removal in the evaluated conditions. In the optimal conditions, the effect of the bioremediation process on soil microbiota was studied by evaluating different parameters. The highest lindane removal percentages were detected in biostimulated microcosms bioaugmented with the microbial consortium, which were accompanied by a decrease in lindane half-life respect to the controls. Also, the bioaugmentation of biostimulated microcosms increased the microbial counts and enhanced soil enzymatic activities, corroborating the bioremediation process efficiency. The survival of the four actinobacteria at the end of the assay confirmed the ability of all Streptomyces strains to colonize amended soils. Bioremediation by simultaneous application of biostimulation with sugarcane bagasse and bioaugmentation with the actinobacteria consortium, in the optimized conditions, represents an efficient strategy to restore lindane contaminated soils.

Enhanced electrolytic treatment for the removal of clopyralid and lindane.

In this work, it is evaluated the more critical point of a new electrochemical technology for the removal of organic pollutants based on the regeneration of granular active carbon (GAC) (that can be used efficiently to concentrate aqueous wastes) with methanol and in the electrochemical treatment of methanol with conductive diamond electrochemical oxidation (CDEO). The system proposed was studied with lindane and clopyralid. Results show that it is possible the complete removal of the raw pesticides and intermediates formed by electrolyzing these species in methanol media and that both sodium chloride and sodium hydroxide can be used as supporting electrolyte to increase the conductivity of methanol. The cell voltages obtained are quite similar to those obtained during the electrolysis of aqueous wastes. The electrolysis of these dilute solutions does not generate significant concentrations of intermediates and the depletion of the raw pollutant fits well to a pseudo-first order kinetic model. Oxidants capable to oxidize iodide to iodine are produced during the electrolysis in methanol media and they have an important influence on the degradation of the pollutants. The new technology, based on the concentration of the pollutant before electrolysis, allows to remove completely pollutants from soil and soil washing fluids in a more efficient way, although the concentration of pollutant attained and, hence, the efficiency of the overall removal process depends on the adsorption equilibria of the pollutant in aqueous and methanol media.

Multi-resistant plant growth-promoting actinobacteria and plant root exudates influence Cr(VI) and lindane dissipation.

The aims of this study were (1) to isolate new multi-resistant actinobacteria from soil, rhizosphere and plant samples collected from an ancient illegal pesticide storage and (2) to elucidate the effects of these microorganisms developed with maize root exudates on lindane and Cr(VI) removal. Fifty-seven phenotypically different actinobacteria were isolated and four of them, belonging to the genus Streptomyces exhibit tolerance to a mixture of lindane and Cr(VI). Two rhizospheric strains named as Streptomyces sp. Z38 and Streptomyces sp. Z2 were selected to be grown with root exudates because they showed the highest Cr(VI) and lindane removal in co-contaminated medium. When root exudates were the only carbon source, metal dissipation increased significantly either as single or mixed contaminant, compared to metal dissipation with glucose. No significant differences were found on lindane removal with root exudates or glucose, so a higher lindane concentration was evaluated. Despite of this, lindane removal remained stable while metal dissipation was notoriously lower when lindane concentration was enhanced. In addition to a good performance growing with mixed contaminants, Streptomyces strains showed plant growth promoting traits that could improve plant establishment. The results presented in this study show the importance of the screening programs addressed to find new actinobacteria able to grow in co-contaminated systems. It was also evidenced that root exudates of maize improve the growth of Streptomyces strains when they were used as carbon source, being the dissipation of Cr(VI) considerably improved in presence of lower lindane concentration.

Streptomyces sp. is a powerful biotechnological tool for the biodegradation of HCH isomers: biochemical and molecular basis.

Actinobacteria are well-known degraders of toxic materials that have the ability to tolerate and remove organochloride pesticides; thus, they are used for bioremediation. The biodegradation of organochlorines by actinobacteria has been demonstrated in pure and mixed cultures with the concomitant production of metabolic intermediates including γ-pentachlorocyclohexene (γ-PCCH); 1,3,4,6-tetrachloro-1,4-cyclohexadiene (1,4-TCDN); 1,2-dichlorobenzene (1,2-DCB), 1,3-dichlorobenzene (1,3-DCB), or 1,4-dichlorobenzene (1,4-DCB); 1,2,3-trichlorobenzene (1,2,3-TCB), 1,2,4-trichlorobenzene (1,2,4-TCB), or 1,3,5-trichlorobenzene (1,3,5-TCB); 1,3-DCB; and 1,2-DCB. Chromatography coupled to mass spectrometric detection, especially GC-MS, is typically used to determine HCH-isomer metabolites. The important enzymes involved in HCH isomer degradation metabolic pathways include hexachlorocyclohexane dehydrochlorinase (LinA), haloalkane dehalogenase (LinB), and alcohol dehydrogenase (LinC). The metabolic versatility of these enzymes is known. Advances have been made in the identification of actinobacterial haloalkane dehydrogenase, which is encoded by linB. This knowledge will permit future improvements in biodegradation processes using Actinobacteria. The enzymatic and genetic characterizations of the molecular mechanisms involved in these processes have not been fully elucidated, necessitating further studies. New advances in this area suggest promising results. The scope of this paper encompasses the following: (i) the aerobic degradation pathways of hexachlorocyclohexane (HCH) isomers; (ii) the important genes and enzymes involved in the metabolic pathways of HCH isomer degradation; and (iii) the identification and quantification of intermediate metabolites through gas chromatography coupled to mass spectrometry (GC-MS).

Organochlorine pesticides accumulation and breast cancer: A hospital-based case-control study.

The aim of this study is to detect the accumulation status of organochlorine pesticides in breast cancer patients and to explore the relationship between organochlorine pesticides contamination and breast cancer development. We conducted a hospital-based case-control study in 56 patients with breast cancer and 46 patients with benign breast disease. We detected the accumulation level of several organochlorine pesticides products (ß-hexachlorocyclohexane, γ-hexachlorocyclohexane, polychlorinated biphenyls-28, polychlorinated biphenyls-52, pentachlorothioanisole, and pp'-dichlorodiphenyldichloroethane) in breast adipose tissues of all 102 patients using gas chromatography. Thereafter, we examined the expression status of estrogen receptor, progesterone receptor, human epidermal growth factor receptor-2 (HER2), and Ki-67 in 56 breast cancer cases by immunohistochemistry. In addition, we analyzed the risk of breast cancer in those patients with organochlorine pesticides contamination using a logistic regression model. Our data showed that breast cancer patients suffered high accumulation levels of pp'-dichlorodiphenyldichloroethane and polychlorinated biphenyls-52. However, the concentrations of pp'-dichlorodiphenyldichloroethane and polychlorinated biphenyls-52 were not related to clinicopathologic parameters of breast cancer. Further logistic regression analysis showed polychlorinated biphenyls-52 and pp'-dichlorodiphenyldichloroethane were risk factors for breast cancer. Our results provide new evidence on etiology of breast cancer.

Integral use of sugarcane vinasse for biomass production of actinobacteria: Potential application in soil remediation.

The use of living actinobacteria biomass to clean up contaminated soils is an attractive biotechnology approach. However, biomass generation from cheap feedstock is the first step to ensure process sustainability. The present work reports the ability of four actinobacteria, Streptomyces sp. M7, MC1, A5, and Amycolatopsis tucumanensis, to generate biomass from sugarcane vinasse. Optimal vinasse concentration to obtain the required biomass (more than 0.4 g L-1) was 20% for all strains, either grown individually or as mixed cultures. However, the biomass fraction recovered from first vinasse was discarded as it retained trace metals present in the effluent. Fractions recovered from three consecutive cycles of vinasse re-use obtained by mixing equal amounts of biomass from single cultures or produced as a mixed culture were evaluated to clean up contaminated soil with lindane and chromium. In all cases, the decrease in pesticide was about 50% after 14 d of incubation. However, chromium removal was statistically different depending on the preparation methodology of the inoculum. While the combined actinobacteria biomass recovered from their respective single cultures removed about 85% of the chromium, the mixed culture biomass removed more than 95%. At the end of the reused vinasse cycle, the mixed culture removed more than 70% of the biological oxygen demand suggesting a proportional reduction in the effluent toxicity. These results represent the first integral approach to address a problematic of multiple contaminations, concerning pesticides, heavy metals and a regionally important effluent like vinasse.

Removal of a mixture of pesticides by a Streptomyces consortium: Influence of different soil systems.

Although the use of organochlorine pesticides (OPs) is restricted or banned in most countries, they continue posing environmental and health concerns, so it is imperative to develop methods for removing them from the environment. This work is aimed to investigate the simultaneous removal of three OPs (lindane, chlordane and methoxychlor) from diverse types of systems by employing a native Streptomyces consortium. In liquid systems, a satisfactory microbial growth was observed accompanied by removal of lindane (40.4%), methoxychlor (99.5%) and chlordane (99.8%). In sterile soil microcosms, the consortium was able to grow without significant differences in the different textured soils (clay silty loam, sandy and loam), both contaminated or not contaminated with the OPs-mixture. The Streptomyces consortium was able to remove all the OPs in sterile soil microcosm (removal order: clay silty loam > loam > sandy). So, clay silty loam soil (CSLS) was selected for next assays. In non-sterile CSLS microcosms, chlordane removal was only about 5%, nonetheless, higher rates was observed for lindane (11%) and methoxychlor (20%). In CSLS slurries, the consortium exhibited similar growth levels, in the presence of or in the absence of the OPs-mixture. Not all pesticides were removed in the same way; the order of pesticide dissipation was: methoxychlor (26%)>lindane (12.5%)>chlordane (10%). The outlines of microbial growth and pesticides removal provide information about using actinobacteria consortium as strategies for bioremediation of OPs-mixture in diverse soil systems. Texture of soils and assay conditions (sterility, slurry formulation) were determining factors influencing the removal of each pesticide of the mixture.

Sequestration of HCHs and DDTs in sediments in Dongting Lake of China with multiwalled carbon nanotubes: implication for in situ sequestration.

Organochlorine pesticides (OCPs) in sediments could be released into water, posing great threats to human health and organisms. In this study, the treatment effectiveness of in situ sequestration of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethane (DDTs) in sediments was explored using multiwalled carbon nanotubes (MWCNTs) as adsorbents. Physicochemical tests (aqueous equilibrium concentrations, semipermeable membrane device (SPMD) uptake, and quiescent flux to overlying water) were conducted to evaluate the sequestration effectiveness of MWCNTs. Compared to the control, the MWCNT-treated sediments showed great reductions of HCHs and DDTs in aqueous equilibrium concentrations, SPMD uptake, and quiescent flux to overlying water. And the effects of dose of MWCNTs, diameter of MWCNTs, and contact time between MWCNTs and sediments on sequestration effectiveness were studied. Increased dose, decreased MWCNT diameter, and prolonged contact time resulted in a better sequestration effectiveness. The results indicated that the addition of MWCNTs to sediment could reduce the content of HCHs and DDTs released from sediments, reducing bioavailability of HCHs and DDTs and minimizing risks to ecosystem and human. MWCNTs have potential applications as adsorbents for in situ treatment of OCP-contaminated sediments.

Longitudinal study of pesticide residue levels in human milk from Western Australia during 12 months of lactation: Exposure assessment for infants.

The presence of pesticides in human milk (HM) is of great concern due to the potential health effects for the breastfed infant. To determine the relationships between HM pesticides and infant growth and development, a longitudinal study was conducted. HM samples (n = 99) from 16 mothers were collected at 2, 5, 9 and 12 months of lactation. A validated QuEChERS method and Gas chromatography-tandem mass spectrometry (GC-MS/MS) were used for the analysis of 88 pesticides in HM. Only p,p'-DDE, p,p'-DDT and ß-HCH were detected with a mean concentration (±SD) of 52.25 ± 49.88 ng/g fat, 27.67 ± 20.96 ng/g fat and 48.00 ± 22.46 ng/g fat respectively. The concentrations of the detected pesticides decreased significantly throughout the first year of lactation. No significant relationships between HM p,p'-DDE and infant growth outcomes: weight, length, head circumference and percentage fat mass were detected. The actual daily intake (ADI) of total DDTs in this cohort was 14-1000 times lower than the threshold reference and significantly lower than the estimated daily intake (EDI). Further, the ADI decreased significantly throughout the first 12 months of lactation.

Simultaneous Removal of Lindane, Lead and Cadmium from Soils by Rhamnolipids Combined with Citric Acid.

This study investigated the performance of rhamnolipids-citric acid mixed agents in simultaneous desorption of lindane and heavy metals from soils. The capacity of the mixed agents to solubilize lindane, lead and cadmium in aqueous solution was also explored. The results showed that the presence of citric acid greatly enhanced the solubilization of lindane and cadmium by rhamnolipids. A combined effect of the mixed agents on lindane and heavy metals removal from soils was observed. The maximum desorption ratios for lindane, cadmium and lead were 85.4%, 76.4% and 28.1%, respectively, for the mixed agents containing 1% rhamnolipidsand 0.1 mol/L citric acid. The results also suggest that the removal efficiencies of lead and cadmium were strongly related to their speciations in soils, and metals in the exchangeable and carbonate forms were easier to be removed. Our study suggests that the combining use of rhamnolipids and citric acid is a promising alternative to simultaneously remove organochlorine pesticides and heavy metals from soils.

Displacement and competitive sorption of organic pollutants on multiwalled carbon nanotubes.

Displacement of lindane presorbed on the pristine and OH-functionalized multiwalled carbon nanotubes (MWCNTs) by phenanthrene, naphthalene, and atrazine, and competition of these compounds with lindane on the aforementioned sorbents were investigated. Displacement of lindane presorbed on MWCNTs by atrazine, naphthalene, and phenanthrene, and competitive sorption effect of these chemicals with lindane on MWCNTs followed the same order: atrazine > naphthalene > phenanthrene. The lowest competition and displacement of lindane by phenanthrene were mainly because of the strong interactions between these two chemicals, whereas interaction of lindane with atrazine and naphthalene was quite low. The more pronounced displacement of lindane by atrazine than naphthalene and higher competitive sorption of lindane with atrazine than with naphthalene can be ascribed to the larger molecular volume of atrazine; thus, the steric hindrance effect is higher relative to naphthalene. This study is valuable for evaluating influence of the coexisting organic compounds on sorption of primary solute towards MWCNTs in the environment.

Quantitative solid phase microextraction - gas chromatography mass spectrometry analysis of the pesticides lindane, heptachlor and two heptachlor transformation products in groundwater.

This paper describes the development and validation of a method for the determination of lindane, heptachlor and two heptachlor transformation products (exo- and endo-heptachlor epoxide) in groundwater. Samples were extracted using a simple solid phase microextraction (SPME) method with a polyacrylate fibre prior to detection by gas chromatography mass spectrometry in electron impact ionisation mode (GC-EI-MS). The linearity of the method ranged from 0.015 to 5.0 µg L(-1), with correlation coefficients greater than 0.99. Recoveries ranged from 96 to 101% at several fortification levels with all coefficients of variation (CV%) less than 10.5%. The method was validated to the permitted limits laid down in the European Union drinking water directive (98/83/EC). The limit of quantitation (LOQ) was 0.015 µg L(-1) in groundwater samples. Samples had to be analysed within 24h of collection otherwise degradation occurred and disposable SPME polyacrylate fibres lasted up to 51 injections. Both endo-heptachlor epoxide and lindane were detected in groundwater samples with concentrations ranging between 0.033 and 0.048 µg L(-1).

Enzymatic conversion of ε-hexachlorocyclohexane and a heptachlorocyclohexane isomer, two neglected components of technical hexachlorocyclohexane.

α-, ß, γ-, and δ-Hexachlorocyclohexane (HCH), the four major isomers of technical HCH, are susceptible to biotic transformations, whereby only α- and γ-HCH undergo complete mineralization. Nevertheless, LinA and LinB catalyzing HCl elimination and hydrolytic dehalogenations, respectively, as initial steps in the mineralization also convert ß- and δ-HCH to a variety of mainly hydroxylated metabolites. In this study, we describe the isolation of two minor components of technical HCH, ε-HCH, and heptachlorocyclohexane (HeCH), and we present data on enzymatic transformations of both compounds by two dehydrochlorinases (LinA1 and LinA2) and a haloalkane dehalogenase (LinB) from Sphingobium indicum B90A. In contrast to reactions with α-, γ-, and δ-HCH, both LinA enzymes converted ε-HCH to a mixture of 1,2,4-, 1,2,3-, and 1,3,5-trichlorobenzenes without the accumulation of pentachlorocyclohexene as intermediate. Furthermore, both LinA enzymes were able to convert HeCH to a mixture of 1,2,3,4- and 1,2,3,5-tetrachlorobenzene. LinB hydroxylated ε-HCH to pentachlorocyclohexanol and tetrachlorocyclohexane-1,4-diol, whereas hexachlorocyclohexanol was the sole product when HeCH was incubated with LinB. The data clearly indicate that various metabolites are formed from minor components of technical HCH mixtures. Such metabolites will contribute to the overall toxic potential of HCH contaminations and may constitute serious, yet unknown environmental risks and must not be neglected in proper risk assessments.

Expression of a human cytochrome P4502E1 in Nicotiana tabacum enhances tolerance and remediation of γ-hexachlorocyclohexane.

Lindane (γ-hexachlorocyclohexane), a persistent organo-chlorine insecticide widely used in developing countries, has a negative effect as a polluting agent of soil and surface waters. Plants can be used for remediation of organic pollutants and their efficiency can be enhanced by introduction of heterologous genes. Mammalian cytochrome P4502E1 (CYP2E1), an important monooxygenase is involved in the degradation of a wide range of xenobiotics including environmental pollutants/herbicides and pesticides. Here, we report the development of transgenic tobacco plants expressing human CYP2E1 and the efficacy of plants for remediation of lindane. Transgenic tobacco plants with CYP2E1 showed enhanced tolerance to lindane when grown in hydroponic medium and soil compared to control plants. Remediation of (14)C-labeled lindane from hydroponic medium was higher in transgenic plants compared to that of control plants, with the best performing line showing 25% higher removal of lindane from solution than control plants. Similar results were seen in plants grown in soil spiked with lindane. The present study has shown that transgenic plants expressing CYP2E1 gene have potential use for remediation of lindane from contaminated solutions and soil.

Degradation of lindane contaminated soil using zero-valent iron nanoparticles.

Lindane, has been classified by the United States Environment Protection Agency as a potent carcinogen and teratogen. Zero-valent iron nanoparticles (nZVI) have been shown to effectively transform chlorinated hydrocarbons, organochlorine pesticides. An attempt has been made to explore the potential of nZVI for the remediation of Lindane contaminated soil. nZVI was synthesized by reducing FeCl3 with NaBH4. Lindane (10 microg/g) completely disappeared from spiked soil within 24 hours at nZVI concentration of 1.6 g/L, indicating its possible use in environmental cleanup. Reductive dehalogenation is the predominant mechanism for the removal of Lindane from spiked soil by nZVI. Dechlorination was further confirmed by the chloride ion release.

Remediation of lindane using engineered nanoparticles.

Organochlorine pesticides (OCPs; aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, toxaphene and hexachlorocyclohexane) are chemical pollutants found in all environmental media. There is an urgent need to stop the usage and develop innovative strategies for the remediation of contaminated soil and water. The present work was aimed to evaluate the (i) interaction of fullerene with lindane and its role in the remediation of lindane from contaminated systems and (ii) compare the interaction of fullerene with lindane and trichloroethylene. Strong molecule-surface bonding of fullerene-lindane complex than fullerene-TCE complex indicates that fullerene can be used as a potential nanoparticle for remediation of lindane. However, toxicity and fate of nanoparticles is under investigation and more studies are needed before utilization of fullerene and other nanoparticles for phytoremediation.

Effect of growing Sesamum indicum L. on enhanced dissipation of lindane (1, 2, 3, 4, 5, 6-hexachlorocyclohexane) from soil.

The effect of growing Sesamum indicum L. on the dissipation of lindane (gamma-HCH) was studied in spiked soil. For this, S. indicum was grown with four different concentrations of lindane (5, 10, 15, and 20 microg g(-1)). Plant growth, yield, photosynthetic pigments, soluble protein, microbial biomass carbon, lindane uptake, residual lindane concentration in soil and percentage dissipation of lindane from soil were analyzed at 25, 90, and 124 d. The accumulation of lindane in test plants was linearly related to the soil concentration (r2 = 0.897-0.979). At maturity, the accumulation of lindane in S. indicum grown with four spiked concentrations reached up to 7.98, 13.72, 23.71, and 33.29 microg g(-1) dry matter, respectively. There was a marked difference in the dissipation of lindane in vegetated and non-vegetated soils (p < 0.01). After final harvesting, the residual lindane concentrations in four spiked concentrations were reduced by 77.56, 70.12, 62.51, and 58.7%, respectively. Agronomic practice for the onsite application of this species is discussed. Based on the present study, it was calculated that S. indicum could accumulate 2237-2611 mg lindane per acre after 124 d cultivation. S. indicum could thus be used for the phytoremediation of lindane contaminated soil.

Fate of pesticides in the arid subtropics, Botswana, Southern Africa.

Despite a history of pesticide usage, few data exist on their concentrations in air and soil of Southern Africa. To add to the understanding of the processes controlling the fate of organic contaminants in arid regions, the levels, spatial trends, and seasonal variability of pesticides were studied in air and soil from Botswana. XAD resin-based passive air samplers (PAS) were deployed at 15 sites across the country from May 2006 to May 2007. Soil samples were collected from the vicinity of nine of the PAS sampling sites. In addition, 27 24-h high-volume air samples were collected in Maun, at the southeastern edge of the Okavango Delta, every two weeks for one year. Levels of pesticides in PAS were low, with α-endosulfan and lindane being most abundant. Concentrations in soils were extremely low and only soils with high organic carbon contained notable amounts of dieldrin and traces of other pesticides. In particular, air and soil from the Okavango Delta had very low levels even though the area had repeatedly been sprayed with DDT and endosulfan in the past. Air samples from Eastern Botswana, where the majority of the population lives, contained higher levels. Higher air concentrations of α-endosulfan occurred during summer and higher HCB levels occurred in winter. This seasonality was related with neither minor seasonal changes in temperature nor hydrological seasonal events such as the rainy season or the flooding of the Okavango Delta. Thus, the observed spatial and seasonal patterns are more likely related to pesticide usage pattern than to environmental factors or historical use. High temperature and low organic matter content limit the uptake capacity of most subtropical soils for pesticides. No evidence was found that sorption to dry mineral matter plays a major role. Arid soils in subtropical regions are therefore neither a major reservoir of organic contaminants nor do they constitute a significant long-term source of pesticides to the atmosphere.

Stable isotope fractionation of gamma-hexachlorocyclohexane (lindane) during reductive dechlorination by two strains of sulfate-reducing bacteria.

Carbon isotope fractionation factors were determined with the dichloro elimination of gamma-hexachlorocyclohexane (gamma-HCH) by the sulfate-reducing bacteria Desulfococcus multivorans DSM 2059 and Desulfovibrio gigas DSM 1382. Both strains are known for cometabolic HCH dechlorination. Degradation experiments with gamma-HCH in concentrations of 22-25 gammaM were carried out using benzoate (for D. multivorans) and lactate (for D. gigas) as electron donors, respectively. Gamma-HCH was dechlorinated by both bacterial strains within four weeks, and the metabolites gamma-3,4,5,6-tetrachlorocyclohexene (gamma-TCCH), chlorobenzene (CB), and benzene were formed. The carbon isotope fractionation of gamma-HCH dechlorination was quantified by the Rayleigh model, using a bulk enrichment factor (epsilon C) of -3.9 +/- 0.6 for D. gigas and -3.4 +/- 0.5 for D. multivorans, which correspond to apparent kinetic isotope effect (AKIEc) values of 1.023 +/- 0.004 or 1.02 +/- 0.003 for stepwise Cl-C bond cleavage. The extent and range of isotope fractionation suggest that gamma-HCH dechlorination can be monitored in anoxic environments by compound-specific isotope analysis (CSIA).