Environmental Fate of Chiral Pesticides in Soils

Abstract

Chirality has received progressive attention in the field of pesticides. Enantiomers of chiral pesticides have identical physicochemical properties but, commonly, they exhibit stereoselective response with chiral host systems and, therefore, enantioselectivity against the target pest. Despite this, approximately 30% of the pesticides in current use are formulated as mixtures of enantiomers or racemic mixtures. This has engendered new environmental problems, which demand exhaustive knowledge regarding the enantioselectivity of the processes that chiral pesticides may undergo in the soil environment. Changes in the enantiomer composition of chiral pesticides are caused mainly by biological interactions and, consequently, factors affecting the biodegradation of pesticides can also alter the enantioselectivity of the biotransformation of chiral pesticides in soils. Accordingly, soil parameters such as pH, redox conditions, texture, or agronomic practices have been reported to indirectly influence the final enantioselective behavior of these pesticides in soils, although there is limited knowledge in this regard. Hence, predicting the environmental behavior of chiral pesticides in soil turns challenging. This chapter summarizes the most recent enantioselective studies on chiral pesticide transfer and transformation processes in soils. Future research needs scientific foundations to establish under which agricultural and environmental conditions it is appropriate to replace racemic chiral pesticide mixtures with the biologically active purified enantiomers, the underlying mechanisms of enantioselective interactions, and the relationships between the soil microbial diversity and the biotransformation of chiral pesticides, which remain largely unknown.