PREDICTION OF INTERSPECIES DIFFERENCES IN THE TOXICITY OF ORGANOPHOSPHORUS PESTICIDES TO WILDLIFE - A BIOCHEMICAL APPROACH

The activation of organophosphorus pesticides and sensitivity of 'B' e sterases to inhibition (I-50) by the oxon metabolites were investigate d in brain, liver and serum as the basis for a model to predict the to xicity of organophosphorus pesticides to four avian species. There wer e statistically significant correlations between LD(50) and brain rate of activation of the OP (r = 0.68), brain acetylcholinesterase I-50 ( r = 0.88), and serum carboxylesterase I-50 (r = 0.60). A significant p roportion of the oxon produced within the liver is unlikely to reach t he brain, due to irreversible binding by 'B' esterases. The production of the active oxon form of the pesticide within the brain, and the se nsitivity of the brain AChE to inhibition, are probably the most impor tant factors in determining the avian toxicity of organophosphorus pes ticides.