Acetylcholinesterase inhibition in estuarine fish and invertebrates as an indicator of organophosphorus insecticide exposure and effects

The majority of insecticides currently in use are organophosphorus, carbama te, and synthetic pyrethroid compounds. Organophosphorus insecticides (OPs) produce toxicity by inhibiting the cholinesterase enzymes in the nervous s ystem,Monitoring of acetylcholinesterase (AChE) inhibition has been widely used in terrestrial and freshwater aquatic systems as an indicator of OP ex posure and effects. This review describes the use of AChE inhibition as a b iomarker in the estuarine environment, discusses the relationship between A ChE inhibition and other manifestations of OP toxicity, and highlights area s where additional research is needed. A variety of studies with estuarine fish have suggested that brain AChE inhibition levels of >70% are associate d with mortality in most species. Selected species, however, appear capable of tolerating much higher levels (>90%) of brain inhibition. Sublethal eff ects on stamina have been reported for some estuarine fish in association w ith brain AChE inhibition levels as low as 50%. Most studies suggest, howev er, that these effects are observed only when brain AChE inhibition is at n ear-lethal levels. A number of field studies have successfully used AChE in hibition in fish as a biomarker in the estuarine environment. The use of AC hE inhibition as a biomarker in estuarine invertebrates has been less well studied. Although AChE inhibition has been measured in the tissues of a var iety of invertebrate species following OP exposure, the relationship betwee n AChE inhibition and lethality is less distinct. Additional work is needed in both fish and invertebrates to better explain species-specific differen ces in the relationship between AChE inhibition and mortality and to invest igate other physiological perturbations associated with AChE inhibition.