Inhibition of Esterases of the Freshwater Snails Helisoma duryi and Lymnaea natalensis by Mixtures of Pesticides

Pesticides indirectly reach aquatic reservoirs via aerial drifts and as runoffs where they affect aquatic organisms. Aquatic reservoirs receive different pesticides from the different fields which usually surround them. However, studies investigating effects of pesticide mixtures on aquatic biota is limited. The effects of six pesticides and their mixtures on esterase activity of two freshwater snail species were investigated. Groups of snails were exposed to individual as well as mixtures of the pesticides for 96 hours before analysing for esterase activity. All pesticides inhibited esterase activity in exposed snails. Binary mixtures of pesticides caused additive or synergistic inhibitions of esterase activities when compared to effects of individual pesticides. The results indicated the importance of chemical interactions on the overall effects of pesticides on aquatic organisms.This research was supported by the International Foundation for Science (IFS), Stockholm, Sweden, and the Organization for the Prohibition of Chemical Weapons', The Hague, the Netherlands, through a grant to Dr Yogeshkumar S.Naik, the International Programme in Chemical Sciences (IPICS), Uppsala University, Sweden and the Research Board, NUST, Bulawayo, Zimbabw