RESIDUES OF ENDOSULFAN IN THE LIVERS OF WILD CATFISH FROM A COTTON GROWING AREA BARBARA NOWAK School of Biological Sciences, A08, The University of Sydney, N.S.W. 2006, Australia and Centre for Environmental Toxicology, State Pollution Control Commission and University o f Technology, N.S.W. 2001, Australia (Received December 1988) Abstract. Residues of endosulfan insecticide(a- and ~1- isomers, and endosulfan sulphate) were determined in the livers of catfish from a cotton growing area during the summer and winter of 1988. The concentration of total endosulfan residues found in the fish was up to 0.31 mg kg-1 wet wt. It decreased in winter with a maximum 0.02 mg kg- 1wet wt. The difference in endosulfan residues between seasons was statistically significant (ANOVA, p<0.01). 1. Introduction Endosulfan (Thiodan*, 1,4,5,6,7,7-hexachloro-8,9,10-trinorborn-5-en-2,3-ylenedi- methyl sulphite) is an insecticide possessing a relatively broad spectrum of activity (for review see Maier-Bode, 1968; Goebel et al., 1982). Although it belongs to the organochlorines, it has a short persistence time compared to other members of this group. Endosulfan was found to disappear completely during the four weeks after its application to river water whereas other organochlorines like DDT, dieldrin and endrin were still detected at initial concentrations (Eichelberger and Lichten- berg, 1971). Endosulfan is one of the most widely used pesticides in cotton growing areas in N.S.W. The application season begins in late November and ends in February. Aquatic organisms, particularly fish are highly sensitive to very low concentrations even when exposed for a short period of time (Schoettger, 1970; Fox and Matthies- sen, 1982). Fish have been shown to accumulate endosulfan directly from the surrounding water (Schoettger, 1970). The liver was reported as the main site of endosulfan detoxification in fish, having the highest residues of the insecticide (Schoettger, 1970; Herzberg, 1986). Australian freshwater catfish Tandanus tandan- us does not migrate thus forming local populations which may be more easily affected by local pollution (Davis, 1970; Reynolds, 1983). Residues of endosulfan in wild fish are rarely reported (Claeys et al., 1975; Pick et aL, 1981; Matthiessen et al., 1982). Experimental work has been carried out on the biological significance of endosul- fan residue levels. In this paper the range of endosulfan residues in livers of the Environmental Monitoring and Assessment 14:347-351, 1990. 9 1990 Kluwer Academic Publishers. Printed in the Netherlands.