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(W/EH058) The rapid assessment of pesticide exposure in aquatic bivalves using combined esterase activities as biomarkers. Millward, Nicholas1, Carter, Alan1, Galloway, Tamara1, Depledge, Michael1, 1 ABSTRACT- Carboxylesterases in bivalve molluscs have shown higher sensitivity to organophosphorous and carbamate pesticides (OPs)than acetylcholinesterase and are present at high levels.The aim of this work was therefore to evaluate the utility of combining measurement of both acetylcholinesterase and carboxylesterase activities in the tissues of aquatic bivalves as a means of monitoring exposure to OPs. Three species indigenous to Devon were used:Mytilus edulis, Mya arenaria and Cerastoderma edule which inhabit sandy estuary muds where agricultural run off is at its highest. Enzyme activities were assayed in haemolymph and tissue homogenates in microtitreplate format using modifications to the method of Ellman, incorporating the substrate analogues acetylthiocholine or phenylthioacetate. in vitro exposure of enzyme preparations to eserine, DFP and chlorpyrifos confirmed the sensitivity of carboxylesterase with IC50 values an order of magniture lower than for acetylcholinesterase. However, in vivo 24h exposure to sublethal concentrations of either eserine or chlorpyrifos revealed a different spectrum of inhibition, with a large percentage of carboxylesterase activity resistant to inhibition. These results highlight the importance of carboxylesterase activity in the resistance of bivalves to the effects of OPs but do not support the suggestion that combined monitoring of both activities improves the utility of acetylcholinesterase monitoring as a biomarker of exposure in these organisms Key words: organophosphorous, biomarker, acetylcholinesterase, bivalve |
