Determination of Organochlorine Pesticide Residues in Catfish and Tilapia from Oguta Lake, Imo State

The persistence of organochlorine pesticides in aquatic environments and their bioaccumulation in fish tissues represent significant food safety and ecological concerns, particularly in freshwater bodies adjacent to agricultural lands in South East Nigeria. This study determined the levels of organochlorine pesticide residues in muscle tissue of catfish and tilapia species harvested from Oguta Lake in Imo State. Samples were collected seasonally during the dry and rainy seasons over a twelve-month period. Pesticide extraction employed a liquid-liquid partitioning method followed by clean-up using Florisil column chromatography. Residues were quantified by gas chromatography with an electron capture detector. Fourteen organochlorine compounds were targeted, including DDT and its metabolites, aldrin, dieldrin, endrin, heptachlor, and lindane. Total DDT residues, expressed as the sum of p,p-DDT, p,p-DDE, and p,p-DDD, were detected in 82 percent of samples, with concentrations in catfish reaching 0.14 mg/kg wet weight. Endrin was detected in 45 percent of samples. Aldrin and dieldrin were present at low but detectable levels. Concentrations in catfish were consistently higher than in tilapia, reflecting differences in lipid content and feeding habits. Dry-season samples showed higher residue levels, attributed to concentration effects from reduced lake volume. Maximum residue limits set by the European Union were exceeded in 23 percent of catfish samples. These results indicate potential dietary risks for communities consuming fish from Oguta Lake and call for monitoring and regulatory attention.

Keywords: organochlorine pesticides, fish tissue, Oguta Lake, gas chromatography, Imo State