Studies of organochlorine pesticide residues in some freshwater and estuarine fish in Kenya

Abstract

Organochlorine pesticides persist in the environment and accumulate in aquatic organisms. Although the chemicals have been used in Kenya since the 1940's, information on the occurrence of their residues in fish is still scanty. The main objective of the present study was to identify and quantify organochlorine residues in freshwater and estuarine fish from selected areas in Kenya and evaluate the toxicological implications of the findings. A total of 275 fish samples were collected from five locations in Kenya between October, 1988 and October, 1989. The samples were obtained from Tana River at Masinga Darn, Garsen and Tarasaa, the estuary of Athi (Sabaki) River at Malindi and Lake Naivasha in the Great Rift Valley. The fish were caught with gill nets, line and hook or fishing baskets. The liver, eggs and fillet (muscle) from each fish were analysed separately using a Packard gas liquid chromatograph, fitted with a 63Ni electron capture detector. Nine· organochlorine pesticide residues were detected in 22.5% of the samples in the following order of frequency: p,p' DOE (20.4%), p,p' DDT (12.7%), Lindane (4.7%), o,p'DOT (4%), p,p' ODD (3.6%), f3-HCH (2.5%), a-HCH (1.8%), heptachlor (0.7%) and o.p' DDD (0.4%). Polychlorinated biphenyls (PCB's) and hexachlorobenzene (HCB) were not detected in the fish. The residues with the highest levels were p,p'DDE and p,p'DDT with ranges of 0.027 to 1.241 and 0.011 to 2.674mg/kg on wet weight basis respectively. Sum DDT levels ranged from 0.03 to 3.148mg/kg. The range for residue levels of lindane and o.p' DOT were 0.004 to 0.295 and 0.031 to 0.133mg/kg respectively. The results showed locational differences in the occurrence of the pesticide residues in the fish but no significant difference (p> 0.1) in the means of the residue levels. Out of the 67 samples from Malindi and 40 samples from Masinga Darn, 72.7% and 39.5% respectively had one or more of the 9 pesticide residues detected. Only one out of the 65 samples from Garsen had p,p' DOE at a low level of 0.033mg/kg. No residues were detected in the 65 samples from Tarasaa and 40 samples from Lake Naivasha. There was a difference in the distribution of organochlorine pesticide residues in the fish body. Cornman carps obtained from Masinga Darn had lindane, p.p' DDE and p,p' DOT in fillet while fish from Malindi rarely had the pesticide residues in fillet. Lindane was only detected in fish from Masinga Darn and was more common than DDT and its metabolites in the fish. p,p' DOT was more frequent than p,p' DDE and other DDT metabolites in the fillet of common carps. This indicated a recent exposure of the fish to p,p' DDT or a slow degradation rate of the compound in this species. Common carps had significantly higher residue levels of lindane (p= 0.008) than catfish in Masinga Darn. There was a positive correlation (r= 0.74) of sum DOT to weight in the seven species of fish with detectable levels of the residue. Sharks had significantly higher mean level of sum DDT (p< 0.0001) than catfish, common carps and breams. No difference was observed between males and females of various fish species and betwen different organs in the levels of the various pesticide residues detected in the fish. Nonetheless, the residues were most common in the liver and eggs (ovaries). The residue levels found in the present study are generally below the maximum residue limits (MRL), for the respective organochlorine pesticide residues, set by the National Food Administration (NFA) of Sweden. This indicates that the pesticide residues do not pose a health risk to the consumers of fish from the areas studied.