Advances in microbial and enzymatic degradation of lindane at contaminated sites

Lindane is a chemical within the organochlorine group of insecticides. About 800,000 tons were used throughout the world from the 1940s to the 2010s to control a wide range of agricultural, horticultural, and public health pests. Despite increasing concerns about its nontarget toxicity and stability in the environment, it is still being manufactured in India for domestic and export purposes, and hence, residual problems have continued for many decades. In humans, chronic toxicity demonstrates itself as effects on the gastrointestinal tract and the cardiovascular and musculoskeletal systems. Microbial diversity provides eco-friendly options for the mineralization of lindane. Aerobic degradation of lindane was found to be best with two bacterial strains, Sphingomonas paucimobilis strain UT26 and S. paucimobilis RP5557T. The pathway for aerobic hexachlorocyclohexane (HCH) degradation in S. paucimobilis showed that lin genes are involved in encoding the HCH biodegradation pathway. Understanding lin genes and their expression systems will provide the structural and functional relationships to support the degradation mechanism. The anaerobic pathway for HCH degradation has been poorly understood. Biostimulation and bioaugmentation approaches to remediation of HCH-contaminated soils have met with some success. A large-scale land cleanup situation is still a realistic option.