Pesticides are used all around the world in agriculture, having a huge impact on non-target species. In Argentina, the most used pesticide is the organophosphate azinphos-methyl which is related to the inhibition of the acetylcholinesterase enzyme. Exposure to organophosphate insecticides is generally evaluated by the measuring of cholinesterase activity, but in recent years carboxylesterases have also been postulated as good biomarkers. Water contamination by pesicides used in agriculture is a world wide problem and as consequence of the considerable decrease in the diversity of mollusk noticed, several studies with invertebrates species have been started to be performed. Particularly, freshwater gastropods represent about 20% of the recorded mollusk extinctions. Chilina gibbosa is a gastropod found in freshwater habitats in some regions of Argentina, and an important item in the diet of some fishes, but till now there was not toxicological studies performed with contaminants on these organisms.