the Science of the Total Jhhnment Am-,urul,“-~~ IutbEn-.WlD*Wk..UP”llht.lM ELSEVIER The Science of the Total Environment 1710995) 213-220 Enzymological differences of AChE and diazinon hepatic metabolism: correlation of in vitro data with the selective toxicity of diazinon to fish species Johannes Keizer”, Giuseppina D’Agostinoa, R. Nagel”, Teresa Volpeb, Paola Gnemid, Luciano Vittozzi”” aDepartment of Comparative Toxicology and Ecotoxicology, Istituto Superiore di Sarait&, Vile Regina Elena 299, I-00161 Rome, Italy bDepartment of Pharmacology, Istituto Superiore di Sanitri, Kale Regina Elena 299, I-00161 Rome, Italy ‘Johannes Gutenberg Universitiit Ma&, Fachbereich Biologic, Institut fiir Zoologie, Saarstr@e 23, D-6500 Mairu, Germuny dIstituto di Ricerche Biomediche ‘Antoine Malxer’, Iurea, Italy Received 29 September 1993; revision received 28 June 1994; accepted 17 January 1995 Abstract The in vitro hepatic metabolismof diazinon, as well as the sensitivity of the brain acetylcholine esterase, to diazoxon inhibitory action have been studied in order to explain the different toxicity of diazinon to Oncorhynchus mykiss (rainbow trout), Poecilia reticulata (guppy), Brachydanio rerio (zebrafish) and Cyprinus carpio (carp>. In spiteof a very sensitiveacetylcholine esterase the carp is very resistantto diazinon toxicity because of its very low rate of bioactivation and relatively high activity of detoxicating enzymes. The trout is very sensitive towardsdiazinon in spite of its low activity of bioactivation, because of its lack of detoxicating enzymesand a very sensitiveacetylcholine esterase. Diazinon is very toxic for the guppy,because this fish combines a relatively sensitive acetylchohne esterase with a high rate of bioactivation. The zebra fish has the most insensitive acetylcholme esterase, associated with a limited activation rate, thus resulting a rather resistant species. The resultsobtained indicate that diazinon toxicity differencesamong the fish species studied can largely be explained in relation to metabolicbalances in the liver and with the features of the target enzyme. Keywords: Enzymologicaldifference; Diazinon; Hepatic metabolism; Fish species; Detoxicating enzyme 1. Introduction The species specific acute toxicity of organophosphorous (OP) pesticides among fish * Corresponding author. often exceeds one or two orders of magnitude (Vittozzi and De Angelis, 1991; Nikunen, et al., 1991). The selective toxicity of OPs prevents a satisfactory assessmentof their impact for the aquatic environment on the basis of information on just few species.Also the classification of OPs hazards to the environment, which is often based 0048-9697/95/$09.50 0 1995 Elsevier Science BV. All rights reserved. SSDI 0048-9697(95)04687-V