Enhanced biodegradation of hexachlorocyclohexane (HCH) isomers by Sphingobium sp. strain D4 in the presence of root exudates or in co-culture with HCH-mobilizing strains

Hexachlorocyclohexane (HCH) isomers are reported to persist in the environment long after their usage is discontinued. Pleurotus florida, a white rot fungus, was found to degrade not only γ-HCH but also its more persistent isomers individually as well as a mixture in a Raper’s complete medium. Within 30 days γ-HCH degraded completely, whereas other 3 isomers degraded 92-99%. The degradation rate was γ-HCH>β-HCH>α- and δ-HCH. The mycelium biomass was free from γ-HCH residues but accumulated about 3% residues of other 3 isomers. Presence of intermediate metabolites was not detected indicating complete mineralization of HCH isomers. Ability of P. florida to degrade HCH isomers was further studied in soil by amendment with spent mushroom substrate (SMS). SMS addition could marginally increase degradation of α-, β- and δ-HCH, but significantly increased degradation of γ-HCH. When the study was repeated similar trend was observed. The half-life of degradation of γ-HCH was 439-570 days in un-amended soil while 37-42 days in SMS amended soil. For other 3 stable isomers the half-life was reduced from 686-828 to 88-125 days by SMS amendments. These results indicate that SMS from P. florida cultivation can be utilized for bioremediation of HCH contaminated site.

The disposal of hexachlorocyclohexane (HCH) muck has created large number of HCH dumpsites all over the world from where the harmful HCH isomers are leaking into the environment. Bacteria have evolved at such contaminated sites that have the ability to degrade HCH. Degradation of various HCH isomers in bacterial strains is mediated primarily by two genes: linA and linB which encode dehydrochlorinase and haloalkane dehalogenase respectively. In this study we explored one such highly contaminated HCH dumpsite located in Lucknow, Uttar Pradesh, India. To assess the biostimulation potential of the contaminated site, microbial diversity study and real-time PCR based quantification of lin genes was carried out. The soil samples from dumpsite and surrounding areas were found to be highly contaminated with HCH residue levels as high as 1.8 × 10(5) mg kg(-1). The residues were detected in areas upto 13 km from the dumpsite. Sphingomonads, Chromohalobacter, and Marinobacter were the dominant genera present at the dump-site. Role of Sphingomonads in HCH degradation has been well documented. The highest copy numbers of linA and linB genes as determined using real-time PCR were 6.2 × 10(4) and 5.3 × 10(5), respectively, were found in sample from the dump site. The presence of Sphingomonads, linA, and linB genes from HCH contaminated soil indicates the presence of indigenous bacterial communities capable of HCH degradation.

Anaerobic biotransformation of hexachlorocyclohexane isomers in aqueous condition: Dual C[sbnd]Cl isotope fractionation and impact on microbial community compositions

The exposure to hexachlorocyclohexane (HCH) isomers has been a concern to public health, because of their persistence, toxicity and carcinogenicity.Blood of agrochemicals retailers were analyzed for HCH -isomers and metabolite in selected retail outlets in North and Southern senatorial district of Taraba, Nigeria.The retailers were group into five exposure duration based on their years of involvement in trade viz; 1-5years, 6-10years, 11-15years, 16-20years, ≥ 21years.The residues analyses shows that 45 (50) retailers had residues of α -HCH, β -HCH, γ -HCH, δ -HCH, chlordane and Heptachlor in their blood.90% of the retailers had α -HCH at mean concentration of 0.0087mg/l, ranged from n.d-0.0511mg/l.64%β -HCH(mean=0.0116mg/l,range=n.d-0.0411mg/l),74% γ -HCH(mean=0.0180mg/l,range=n.d-0.050mg/l),4%δ -HCH(mean=0.0002mg/l,range=n.d-0.050mg/l),54% chlordane(mean=0.0017mg/l,range=n.d-0.0017mg/l) and 2%Heptachlor(mean=0.0009mg/l,range=n.d-0.0059mg/l).The total content HCH isomers(sum of α, β , γ and δ HCH ) in the whole blood samples was 0.0382mg/l and ranged from 0.0100-0.1214mg/l.The observed trend for all the HCH isomers and metabolite were of no adverse and comparatively lower than the NOAEL and results from other findings.In conclusion, agrochemicals retailers in Taraba, Nigeria are occupationally exposed to and carry a body burden of pesticide, due to the sales, and handling of pesticide in stores.

Opposite effects of different hexachlorocyclohexane (lindane) isomers on cerebellar cyclic GMP: Relation of cyclic GMP accumulation to seizure activity

Biodegradation of α, β, γ and δ hexachlorocyclohexane (HCH) isomers was studied in broth medium and soil microcosm by Bacillus circulans and Bacillus brevis isolated from contaminated soil. Degradation of α and γ isomers by both the bacterial isolates was higher than thermodynamically stable β and δ isomers. However, B. circulans was found more effective than B. brevis for β and δ isomers. Maximum rate of degradation was recorded at 150 mg/L followed by 100 and 50 mg/L. Soil microcosm study revealed maximum degradation of HCH isomers in the treatment containing natural soil, pesticide and bacterial inocula than the treatment having sterilised soil, pesticide and bacterial isolates. Chloride release was positively co-related with HCH degradation in broth medium as well as in soil microcosm, suggesting that B. circulans and B. brevis hold promising potential by having efficient enzyme(s) required for dechlorination of HCH from contaminated sites.

Although the pesticide hexachlorocyclohexane (HCH) and its isomers have long been banned, their presence in the environment is still reported worldwide. In this study, we investigated the bioaccumulation potential of α, β, and δ hexachlorocyclohexane (HCH) isomers in black alder saplings (Alnus glutinosa) to assess their environmental impact. Each isomer, at a concentration of 50 mg/kg, was individually mixed with soil, and triplicate setups, including a control without HCH, were monitored for three months with access to water. Gas chromatography–mass spectrometry revealed the highest concentrations of HCH isomers in roots, decreasing towards branches and leaves, with δ-HCH exhibiting the highest uptake (roots—14.7 µg/g, trunk—7.2 µg/g, branches—1.53 µg/g, leaves—1.88 µg/g). Interestingly, α-HCH was detected in high concentrations in β-HCH polluted soil. Phytohormone analysis indicated altered cytokinin, jasmonate, abscisate, and gibberellin levels in A. glutinosa in response to HCH contamination. In addition, amplicon 16S rRNA sequencing was used to study the rhizosphere and soil microbial community. While rhizosphere microbial populations were generally similar in all HCH isomer samples, Pseudomonas spp. decreased across all HCH-amended samples, and Tomentella dominated in β-HCH and control rhizosphere samples but was lowest in δ-HCH samples.

The genotoxic potential of hexachlorocyclohexane (HCH) isomers (α-, β-, and γ-) which are organochlorine pesticides was tested in peripheral blood lymphocyte cultures from two donors by using the cytokinesis-block micronucleus assay. Micronucleus (MN) frequency, binucleated cells with micronucleus (BNMN), and cytokinesis-blocked proliferation index (CBPI) were determined as genotoxic and cytotoxic endpoints. At the concentration ranges tested (12.5–100 μg.L −1), all HCH isomers induced dose-dependent cytotoxic effects, γ-HCH being the most toxic. This isomer was also able to induce significant increase in MN frequency and BNMN cells indicating a genotoxic potential at 50 and 100 μg.L −1. The genotoxic test of β-HCH showed a positive induction of MN and BNMN cells at the highest concentration of 100 μg.L −1 and a significant cytotoxicity at 50 μg.L −1. Under the experimental condition used, α-HCH was unable to induce any significant increase in MN frequency confirming that α-HCH is a non-genotoxic agent.

Landfarming is a bioremediation technology in which contaminated soil is mixed with nutrients and amendments, and the material is periodically tilled for aeration. Contaminants are degraded, transformed and immobilised by means of biotic and abiotic reactions. In this study, a soil heavily contaminated (>5000 mg kg−1) with hexachlorocyclohexane (HCH) isomers derived from lindane production was treated using this technique. The combination of the physical disruption of HCH aggregates together with the biological degradation which is favoured by the improvement in the soil’s physical and chemical conditions, both contributed to a significant decrease of the α- and γ-HCH isomers (up to 89 and 82% of the initial concentration, respectively) at the end of the 11 month long experiment. In contrast, the most persistent β-isomer remained essentially unaffected. Flooded conditions did not improve HCH degradation. Degradation of α- and γ-HCH was quite rapid initially. Pentachlorocyclohexene (PCCH) and tetrachlorocyclohexene (TCCH) were identified as the main metabolites during the treatment period. The main variables that affected the process were: moisture content, temperature and especially the distribution and size of HCH aggregates, which limits HCH bioavailability. Aerobic landfarming appears to be an interesting and cost effective bioremediation treatment for soils contaminated with α- and γ-HCH isomers. However, complete sanitation of soil (total HCH < 2 mg kg−1), especially in the case of β-HCH, would require the application of other techniques, for example slurry system under anaerobic conditions.

Recent revelation of the evolution of Hexachlorocyclohexane (HCH) degrading sphingomonads and their acquisition of lin genes for the degradation of HCH isomers at the HCH dumpsites and HCH contaminated sites has lead us to consider that bacteria employ science and chemistry beyond scientific imagination. The HCH contamination of the environment portrays one of the best examples to highlight the evolution of catabolic genes and pathways leading to survival of these bacteria at HCH concentrations as high as 450 mg/g soil. While contamination of the environment with HCH has created several health related issues, this compound has not only enabled us to study the marvel of HCH degradation that sphingomonads employ but has also emerged as a good model to study the evolution of catabolic genes, especially the lin genes. The potential of HCH degradation by these sphingomonads can be tapped in order to create a phenomenal and large scale bioremediation technology. This review describes briefly the massive contamination of our environment by HCH isomers, along with the spontaneous evolution of the versatile HCH degradation pathways in sphingomonads and lin genes in response to HCH.

Hexachlorocyclohexane (HCH), a highly chlorinated pesticide, was used worldwide in the 1950s and 1960s. HCH toxic residues are still detected in environmental compartments. Thus, effective, viable and eco-friendly strategy is required for its remediation. In this study, degradation of four HCH isomers was evaluated by amending contaminated soil using four treatments of spent mushroom compost (SMC) of Pleurotus ostraetus. The soil was incubated for 5 weeks and was sampled every seven days. Quantitative attenuation in HCH was calculated using gas chromatography–electron capture detector (GC-ECD) and metabolite was identified using gas chromatography–mass selective detector (GC-MSD). Maximum reduction 58%, 26%, 45%, and 64% for α-, β-, γ- and δ-HCH isomers, respectively, using SMC and soil (both unsterilized) showed that this treatment was the best for bioremediation of HCH in soil. However, when one of the factors, either soil or SMC, was sterilized, a significant reduction in HCH degradation was noticed. The second most reduction of isomers was seen during treatment where unsterilized SMC was added in sterilized soil followed by treatment where SMC was sterilized but soil was not. Abiotic control did not remove any significant quantities of HCH. Simple first-order (SFO) kinetic confirmed that SMC reduced the half-live manifolds as compared to biotic control. Only one metabolite δ-PCCH was identified during the course of study.

The organochlorine pesticide Lindane is the gamma-isomer of hexachlorocyclohexane (HCH). Technical grade Lindane contains a mixture of HCH isomers which include not only gamma-HCH, but also large amounts of predominantly alpha-, beta- and delta-HCH. The physical properties and persistence of each isomer differ because of the different chlorine atom orientations on each molecule (axial or equatorial). However, all four isomers are considered toxic and recalcitrant worldwide pollutants. Biodegradation of HCH has been studied in soil, slurry and culture media but very little information exists on in situ bioremediation of the different isomers including Lindane itself, at full scale. Several soil microorganisms capable of degrading, and utilizing HCH as a carbon source, have been reported. In selected bacterial strains, the genes encoding the enzymes involved in the initial degradation of Lindane have been cloned, sequenced, expressed and the gene products characterized. HCH is biodegradable under both oxic and anoxic conditions, although mineralization is generally observed only in oxic systems. As is found for most organic compounds, HCH degradation in soil occurs at moderate temperatures and at near neutral pH. HCH biodegradation in soil has been reported at both low and high (saturated) moisture contents. Soil texture and organic matter appear to influence degradation presumably by sorption mechanisms and impact on moisture retention, bacterial growth and pH. Most studies report on the biodegradation of relatively low (< 500 mg/kg) concentrations of HCH in soil. Information on the effects of inorganic nutrients, organic carbon sources or other soil amendments is scattered and inconclusive. More in-depth assessments of amendment effects and evaluation of bioremediation protocols, on a large scale, using soil with high HCH concentrations, are needed.

Organochlorine pesticides air monitoring near a historical lindane production site in Spain

Stable isotope fractionation associated with the synthesis of hexachlorocyclohexane isomers for characterizing sources

Occurrence and distribution of hexachlorocyclohexane isomers in vegetation samples from a contaminated area