ORGANOCHLORINE PESTICIDE RESIDUES IN FISH AND DAM WATER FROM OGBOMOSO, SOUTHWESTERN NIGERIA: SPATIAL DISTRIBUTION AND MATRIX-DEPENDENT CONTAMINATION

This study assessed pesticide residues in water and Nile tilapia (Oreochromis niloticus) from Ogbomoso Waterworks and Papa Abede Waterworks dams in Ogbomoso, Oyo State, Nigeria, focusing on their occurrence, concentrations, spatial distribution and compliance with applicable residue limits. Water samples were randomly collected from different sections of the waterbodies, while sixteen fish specimens were obtained, comprising six from each study dam and two from each of two privately managed control water bodies. Fish muscle tissues were extracted using the QuEChERS method, and pesticide residues were identified and quantified using gas chromatography–mass spectrometry (GC–MS). Data were analysed using descriptive statistics and analysis of variance, with Duncan’s Multiple Range Test applied at a 5% significance level. The results revealed organochlorine, organophosphate, carbamate and pyrethroid pesticide residues in the sampled water and fish. Among the organochlorines, p,p′-DDT recorded 3.60 mg/l in Ogbomoso Waterworks water and 0.64 mg/l in Papa Abede Waterworks water, while concentrations in fish were 0.73 and 0.75 mg/kg, respectively. The concentration of p,p′-DDD in water reached 2.34 mg/l. Among the organophosphates, dimethoate recorded 2.74 mg/l in water, while dichlorvos reached 2.61 mg/l in Ogbomoso Waterworks water and 0.86 mg/kg in fish from the same location. Carbaryl recorded 1.59 mg/l in water, whereas permethrin reached 0.69 mg/l in Ogbomoso Waterworks water. Overall, Ogbomoso Waterworks generally exhibited higher pesticide-residue concentrations than Papa Abede Waterworks, while the control locations recorded comparatively lower concentrations for many compounds. Statistical comparisons showed variations among compounds, locations and sample types, although not all differences were statistically significant. Comparison with the applicable benchmarks adopted in the study indicated that several residues exceeded the relevant limits, suggesting contamination of the investigated aquatic environments and non-compliance with applicable maximum residue limits in affected fish samples. The study recommends routine pesticide-residue monitoring, improved pesticide application practices and measures to minimise agricultural runoff into water bodies. The findings provide baseline information for environmental management and food-safety monitoring in Ogbomoso, Nigeria.