Assessment of Occurrence and Concentrations of Xenobiotics in Selected Fish Species from Lake Naivasha, Kenya

Aquatic organisms are good bio-indicators of the environmental health in freshwater lakes; Xenobiotics are foreign materials to the organisms’ body and do not occur naturally in nature. Xenobiotics accumulate in adipose tissues due to high affinity to fatty tissues. This paper reports the levels of Organochlorine pesticide (OCPs) residues, their metabolites and Polychlorinated Biphenyl (PCBs) congeners in selected fish species from Lake Naivasha, Kenya. PCBs and OCPs are persistent organic pollutants most of which are banned or under restricted usage. The levels of p, p’DDT, p, p’DDE, p, p’DDD, heptachlor, heptachlor epoxide, aldrin, dieldrin, CB28, CB52 and CB105 were determined in Tilapia, Oreochromis leucostictus, Common carp, Cyprinus carpio, and Mirror carp, Cuprinus spectacularlus, during the months of September December 2008. The concentrations ranged within Below Detection Limit (BDL) 0.29 for Heptachlor epoxide, 0.42 4.19 μg/Kg, for Heptachlor, 0.43 4.73 Aldrin, BDL 0.34 Dieldrin, p, p’ DDT, BDL 6.69 p, p’ DDE, BDL 27.15 p, p’ DDD, BDL 28.87 methoxychlor, 0.05 5.56 CB28, 0.012 13.91 CB52 and BDL 0.45 CB105. The OCPs and PCBs varied widely between and within species. C. spectacularlus showed high levels followed by C. carpio and O. leucostictus respectively. Trophic position, lipid contents, weight and age/size of fish were important parameters in Xenobiotics concentrations in specimens. The occurrences of the Xenobiotics in fish indicate recent use in the catchment. The mean values and ranges of residues found in fish were below the FAO/WHO maximum acceptable limits in fish and sea food however increased monitoring is recommended to detect any changes.