Seasonal variability of persistent organochlorine pesticide residues in marine fish along the Indian Ocean coast of Kenya

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Organochlorine pesticide residues were analyzed in samples of fish taken from four different locations along the Indian Ocean coast of Kenya. Considering all the four sampling sites in the two sampling seasons, the ranges of concentrations of residues detected in the fish samples (in µg kg−1 wet weight) were: lindane 16.1 (in sample from Mombasa)–1445 (Sabaki), aldrin 1.55 (Kilifi)–323 (Kilifi), dieldrin 4.81 (Ramisi)–109 (Sabaki), endosulfan 5.91 (Mombasa)–54.6 (Sabaki), p,p′-DDT 9.11 (Mombasa)–29.3 (Kilifi), p,p′-DDE 1.94 (Kilifi)–97.5 (Sabaki) and p,p′-DDD 1.68 (Mombasa)–98.9 (Kilifi). The concentration ranges obtained in fish in this study indicate that Mombasa Old Town was least contaminated by organochlorine residues as higher residues were detected near Malindi, at Funzi Lazy lagoon and at Kilifi creek which were near the confluences of Rivers Sabaki, Ramisi and Goshi at the Indian Ocean coast, indicating that the sources of the residues in fish the Indian Ocean coast were through discharge from the rivers. Seasonal variation in concentration of residues detected in fish samples was clear, with higher residue levels being recorded in the rainy season in May compared with those detected in the dry season in January. This seasonal variation was particularly observable in p,p′-DDT residues which were only detected in samples taken in the rainy season but none in the dry season in all the sampling sites. The high DDT/DDE and aldrin/dieldrin concentration ratios also indicated that the sources of these residues were recent. This conclusion was also supported by high BCF values of lindane in fish sampled in Sabaki and of aldrin sampled from Kilifi and Ramisi. Overall, the concentration ranges of some of the residues such as DDT, DDE, and DDD were comparable with those reported earlier for fish samples from Lake Kariba in Zimbabwe but concentration ranges of lindane and aldrin were much higher than those reported in fish from Lake Kariba. The concentration ranges of the residues of dieldrin, lindane and DDE were comparable with those obtained in fish from Tana River in Kenya but the other residues of aldrin, endosulfan, DDD, and DDT were much higher than those detected in fish from River Tana.