A phytoremediation approach to remove pesticides (atrazine and lindane) from contaminated environment

The present thesis is part of a project exploring new possibilities to remediate soils polluted by insecticide lindane and herbicide atrazine. It is the Indo-Swiss project entitled "Development of Phytoremediation Techniques Using Interactive Potential of Plant and Microbial Activities for Pesticides Hexachlorocyclohexane (HCH) and Atrazine". The purpose of this project was to address the problems of contamination of sites, agricultural soils, groundwater, surface water, and agricultural food products with recalcitrant pesticides, whose production and use are steadily increasing in India due to rapid economic development, industrialization and enhanced food production over the last 20 years. Preliminary experiments showed that vetiver was resistant to 20 ppm atrazine for 6 weeks, even with a maximum bioavailability created by the use of a hydroponic system. Atrazine resistance could be explained by plant metabolism, dilution of active ingredient into plant biomass, chloroplastic resistance, and sequestration of atrazine before it reaches its target site in leaves. It was found that vetiver thylacoids were sensitive to atrazine, excluding therefore chloroplastic resistance. Plants known metabolism of atrazine relies on hydroxylation mediated by benzoxazinones, conjugation catalyzed by glutathione-S-transferases and dealkylation probably mediated by cytochromes P 450. Therefore, these metabolic pathways were explored in vetiver to understand its resistance to atrazine and to evaluate benefits or risks of phytoremediation. Plant metabolism took place in vetiver: small amounts of dealkylated products were found in roots and leaves, and conjugated atrazine was detected mainly in leaves, confirming in vitro tests. No benzoxazinones were detected in plant extracts, in agreement with the absence of hydroxyatrazine in vetiver organs. Altogether, these metabolic studies suggest that hydroxylation was not an important metabolic pathway in vetiver: the plant behaved more like a related species, sorghum, where conjugation clearly dominates on dealkylation. Under transpiring conditions, conjugation in leaves was important, but under non-transpiring conditions, it is suspected that atrazine and its metabolites could be trapped in roots according to the partition-diffusion law. Over-concentration of atrazine was observed in oil from roots grown in soil, suggesting that during plant ageing, partition may play a non negligible role in retaining atrazine from agricultural runoff. Atrazine metabolism study was successfully conducted in entire vetiver plants thanks to hydroponic system. However, such a system had limitations for understanding plant effect on atrazine removal from a soil environment. Limitation of hydroponic system was also observed for the study of γ-HCH (lindane) disappearance from the medium by the species chilli and coriander, but for other reasons: persistence of lindane in soil is not easily transposed to persistence in water. Lindane was stripp