DDT RESIDUES AND MERCURY LEVELS IN REED CORMORANTS ON LAKE KARIBA: A HAZARD ASSESSMENT

Summary Douthwaite, R.J., Hustler, C.W., Kruger, J. & Renzoni, A. 1992. DDT residues and mercury levels in Reed Cormorants on Lake Kariba: a hazard assessment. Ostrich 63: 123–127. Samples of liver and visceral fat from 86 cormorants Phalacrocorax africanus collected at the eastern end of Lake Kariba between January and October 1986 were analysed for 22 organochlorine compounds. Residues of four insecticides were detected but concentrations of hexachlorobenzene, Hch and lindane in liver did not exceed 0.3 mg kg−1 extractable lipid. Unaltered DDT, or its metabolites DDD and DDE, were found in every sample, almost all as DDE. Levels varied seasonally, with the highest found between May and September. Risk of increased mortality in full-grown birds was negligible but visceral fat of adult females contained DDE levels associated elsewhere with eggshell thinning and breeding failure in a related species. In a separate study, tissues from ten birds were analysed for mercury. Up to 13.6 mg mercury kg1 dry weight...