Acetylcholinesterase Inhibition in the CrayfishProcambarus clarkiiExposed to Fenitrothion

Laboratory and field studies were conducted to evaluate the effects of fenitrothion (O,O-dimethylO-4-nitro-m-tolyl phosphorothioate) on the crayfishProcambarus clarkii.Acetyl- and butyryl-cholinesterase activities were measured in the muscle ofP. clarkiiexposed to different doses of fenitrothion (4, 20, and 100 μg/liter) for different times (up to 48 hr). A positive correlation was found between both cholinesterases, and acetylcholinesterase (AChE) was selected as a biomarker of exposure to this compound. Significant AChE depression (20%) was detected 2 hr after exposure to 20 μg/liter of fenitrothion, reaching a maximum at 48 hr (47%), followed by a slow recovery. Reactivation techniques using the nucleophilic reagent pyridine 2-aldoxime methiodide were assayed in fenitrothion-poisoned specimens, and the results suggested the utility of this method to diagnose exposure, particularly when control animals are not available. Finally, AChE inhibition was used to test a field population ofP. clarkiipotentially exposed to high concentrations of the organophosphorus pesticide fenitrothion, and a 55% inhibition was detected.