Ecotoxicological Assessment of Organochlorine and Organophosphate Pesticide Residues in Fishes of the Hadejia River, Jigawa State, North West Nigeria

This study assesses organochlorine (OC) and organophosphate (OP) pesticide residues in commercially important fish species from the Hadejia River, Jigawa State, North West Nigeria. The Hadejia River catchment encompasses extensive irrigated agricultural areas where pesticide use is intensive, and the downstream bioaccumulation of persistent pesticide residues in fish poses unquantified food safety and ecotoxicological risks. Fish samples (muscle, liver, and gonad) were collected from five species representing different trophic guilds at three stations along the river over two sampling periods. Organochlorine residues (aldrin, dieldrin, DDT and metabolites, endosulfan, and heptachlor) were determined by GC-ECD and organophosphate residues (chlorpyrifos, malathion, dimethoate) by GC-FID following lipid extraction and clean-up procedures. A bioaccumulation factor was calculated relative to measured sediment concentrations. OC residues were detected in all five species, with mean total OC concentrations in liver ranging from 28 to 142 ng/g wet weight. DDT and its metabolites dominated the OC pattern, suggesting continuing recent inputs despite DDT's restriction. Carnivorous species showed significantly higher OC concentrations than herbivores, confirming trophic biomagnification. OP residues were highest immediately downstream of irrigation drainage points. Estimated daily intake of OC residues through fish consumption exceeded acceptable daily intake thresholds for three OC compounds for regular consumers of large-bodied piscivorous species. The study recommends regular pesticide monitoring of Hadejia River fish and a policy review of agricultural pesticide use in the catchment. Keywords: organochlorine pesticides, fish residues, Hadejia River, bioaccumulation, ecotoxicology.