Studies On Distribution Of Organochlorine Pesticide Residues In A Tropical Marine Environment Along The Kenyan Coast

Abstract

A Study was conducted in which samples of seawater, seaweed, sediment and fish were collected from four sites: Sabaki, Kilifi, Ramisi and Mombasa along the Kenya coast between 1996 and 1997. The samples were: subjected to liquid extraction and subsequent analysis of aldrin, lindane, endosulfan, dieldrin, and p,p'-DDT and its metabolites p,p'-DDD and p,p'··DDE using gas liquid chromatography with election capture detection. Identification was done by matching the retention times of the

analytes with those of the standard compounds. The objectives of the work were to compare the concentrations of the chlorinated hydrocarbon insecticide residues both within' and between sites in order to assess the contamination level of the coastal

marine environment; and to establish their variation with season of sampling. The DDT metabolites p,p'-DDT, p,p'-DDE and p.p'-DDD (0.072-0.30 ppb), dieldrin ·(0.144-0.50 ppb), endosulfan (0.17-0.30 ppb), and aldrin (0.02-0.054 ppb) were detected in all water samples at all sites. But p,p'-DDT and lindane were not detected in Mombasa although they reached concentrations of 0.37 and 0.53 ppb in Kilifi, respectively. In Kilifi and Sabaki, lindane could not be detected in seaweed and sediment samples; but reached concentrations of 280 and 612 ppb ill fish from Ramisi and Sabaki, respectively. By contrast, aldrin, dieldrin, endosulfan and the p,p'-DDT metabolites were detected in all samples at 'all-sites, at concentrations ranging from 2.35-101, 5.85- 48.5, 2.94-40.3, and 0.95-70.8 pob, respectively. Concentrations of the residues were ·consistently high in fish samples from Sabaki and generally low in those from Ramisi. The analysis of data for seasona' effects shows that samples obtained during the wet weather has relatively higher residue concentrations than those collected during the dry season, and the differences are particularly significant for seaweeds and sediments.

Comparison of the concentration in ppb of organochlorine pesticides with those for other global coastal waters shows, Cor example, that in 1995 dieldrin (1.88), endosulfan (2.98) and p,p'-DDT (7.02) recorded ill waters from Kingston Harbour (Jamaica) were about four, ten and twenty time) higher than the maximum range values obtained in this study. This suggests that the coastal marine environment in Kenya is relatively unpolluted. These data provide a baseline for future work in determining the concentrations of chlorinated cyclic pesticides in marine samples along the coast of Kenya.