Environmental Risk and Bioremediation of Hexachlorocyclohexane Isomers

Pesticide residues in Indian agricultural soils due to extensive and sometimes indiscriminate use still pose a serious problem for the production and export of agricultural goods. Residues of pestcides including HCH (hexachlorocyclohexane) have even been detected in popular soft drinks such as CocaCola and Pepsi. In addition, at pesticide production sites, soils of the surrounding area are often heavily polluted. The proposed project deals with the technology for the decontamination of pesticide-contaminated soil developed in the previous ISCB-project entitled “Bioremediation of HCHand PNP-contaminated soils by bioaugmentation: Proof of concept at pilot scale” (BR3). The technology is based on bioaugmentation of soil with the pesticidedegrading bacterial strains. Microcosm, soil plot, and pilot-scale field experiments with HCHand PNPcontaminated soil have demonstrated the feasibility of using the pesticide-degrading strains for bioaugmentation. Although the concept developed during the previous project has been proven to be feasible even at pilotscale with agricultural soil contaminated due to pesticide applications, there are different issues that have to be investigated further concerning HCH-contamination. Mass cultivation on cheap carbon and energy sources of Sphingobium indicum B90A has been very difficult and the fate or the toxicity of the metabolites produced from β-HCH and δ-HCH are still unsolved aspects of degradation of HCH isomers. In the framework of another project carried out at the University of Delhi, several Sphingobium-like strains have been isolated that degrade all HCH-isomers very efficiently. Since microbial mixed cultures are more promising for application in the field due to their normally higher resistance to fluctuations of environmental parameters such as soil humidity, pH, and temperature, an HCH-degrading consortium will be constituted from the different available pure cultures and tested for mass cultivation and HCH-degradation in soil microcosms. Hydroxylated metabolites of β-HCH and δ-HCH have been detected in groundwater from an aquifer where HCH-production waste has been stored above at the production site in Switzerland. We therefore establish a survey of the presence of such metabolites at different HCH-contaminated site in soil and the aquifer underneath. In addition, we study the fate of these metabolites in HCH-degrading cultures in order to be able to fully understand the fate of all HCH-isomers. Furthermore, to at least guarantee transformation into harmless products, the toxicity of the degradation products will be elucidated with commercially available toxicity tests. The work in the Indian laboratories will mainly be done by PhD students. Detailed studies of the reconstituted bacterial consortium will be carried out. These studies will be done with modern molecular approaches in order to understand the importance of the different strains in HCH-degradation and will be partially carried out at the laboratories of the Swiss partners. One postdoc will investigate in detail the unresolved problems of the degradation of β-HCH and δ-HCH. Metabolites analysis will be done in collaboration with ACW (Agroscope Changin-Wädenswil) on the basis of sub-contracting this laboratory. The benefit of this project will be a relatively cheap technology to remediate soils contaminated with HCH, a problem of still worldwide concern. However, there is a risk that the metabolites of β-HCH and δ-HCH are not further degraded and that they are toxic. In order to optimally disseminate the results obtained, an international conference on HCH contamination and remediation will be organized in Delhi at the end of the project. In addition, the results obtained will be published in peer reviewed journals as it has been done successfully in the previous project phases.