Research Product

Brain acetylcholinesterase (EC 3.1.1.7) activities were compared in groups of an estuarine fish Lagodon rhomboides (pinfish) exposed in seawater to sublethal and lethal concentrations of malathion (0,0-dimethyl S-(1,2-dicarbethoxyethyl) phosphorodithioate) to determine enzyme inhibition values for diagnosis of poisoning. Lethal exposures caused greater enzyme inhibition than sublethal exposures through 72 h. Consistent levels of enzyme inhibition (72-79% inhibition) occurred when 40-60% of replicate exposed groups were killed at 3.5, 24, 48 and 72 h at mean concentrations of 575, 142, 92 and 58 µg/liter, respectively. A mean concentration of 31 µg/liter was sublethal through 72 h exposure and caused a maximum enzyme inhibition of only 34%. The correlation of brain acetylcholinesterase inhibition with exposure and deaths is of value in diagnosing poisoning in fish populations and has been applied to actual environmental situations. Enzyme inhibition in fishes is positively correlated with spraying of an estuary with malathion.