Effects of chlorpyrifos on acetylcholinesterase activity in two freshwater fish species (Cnesterodon decemmaculatus and Gambusia affinis)

Abstract

Chlorpyrifos (CPF) is a widely used organophosphate insecticide. The effect of chlorpyrifos exposure on acetylcholinesterase activity (AChE, biomarker of neurotoxicity) was evaluated in two freshwater fish species (Cnesterodon decemmaculatus and Gambusia affinis). The animals were exposed to sublethal concentrations (1 and 5 µg CPF × L-1) or remained in control water for 96 h. AChE activity was inhibited 48% and 69% in C. decemmaculatus and 27% and 36% in G. affinis for 1 and 5 µg CPF × L-1, respectively. In vitro assays showed no differential sensitivity of the enzyme to CPF between species. However, the IC50 for in vitro exposure to chlorpyrifos-oxon (CPF-oxon, a product of the natural oxidative desulfuration of CPF) were 10.2 nM and 54.2 nM for C. decemmaculatus and G. affinis, respectively. Therefore, a different sensitivity of the enzyme between both species could explain the dissimilar behaviour of AChE after in vivo exposure to CPF.