Seasonal differences in organochlorine pesticide concentrations of zooplankton and fish in the Arabian Sea

Zooplankton and fish samples taken from different locations in the northern Arabian Sea before and during the southwest monsoon were examined for residues of DDT, its metabolites and aldrin. In the monsoon, the concentrations of total DDT (DDT + DDE + DDD) and aldrin in zooplankton were, respectively, 4 and 5 times higher than the pre-monsoon concentrations while the corresponding increases in fish were 10 to 30 times and 3 to 40 times, respectively. The presence of considerable amounts of primary DDT in samples obtained during the monsoon, coinciding with peak agricultural activity on land, indicated that (a) the pesticide residue levels in these organisms were determined by the pattern of use on land and (b) the pesticide compounds entering this environment were rapidly disseminated. Also, pesticide accumulation by fish was apparently dictated by their feeding habits. As observed from the lipid-normalised values, pelagic varieties accumulate more residues than the demersal ones during the pre-monsoon season white the opposite is true for the monsoon season. DDD was the major DDT metabolite present in all the samples. (C) 1997 Elsevier Science Limited.