Risk assessment of agricultural pesticides in water, sediment, and fish from Owan River, Edo State, Nigeria

The distribution of pesticides in water, sediments, Clarias gariepinus, and Tilapia zilli from the Owan River was investigated to evaluate the pollution status and potential hazard in the river system. A total of 16 pesticides were analyzed using gas chromatography (GC) equipped with electron capture detector (ECD). The concentration of pesticide residues ranged from ND to 0.43 mu g/l for water samples, 0.82 to 2.14 mu g/kg/dw for sediment, 0.04 to 2.34 mu g/kg/ww for C. gariepinus, and 0.02 to 1.73 mu g/kg/ww for T. zilli. High concentrations of organochlorine pesticides, specifically benzenehexachloride (alpha-BHC, gamma-BHC, and beta-BHC) observed in all environmental media, are an indication of the current illegal use of banned pesticides for agricultural activities in the region. Analysis of data showed a strong correlation (r(2)=0.7) between total organic carbon (TOC) and total pesticide residues in sediment samples. Meanwhile, risk quotient estimates for heptachlor epoxide, dieldrin, endrin, dichlorodiphenyltrichloroethane (4,4'-DDT), endosulfan I, endosulfan II, endosulfan aldehyde, and phosphomethylglycine showed potential risk to aquatic organism under observed mean concentrations (risk quotient (RQ)>= 1). Estimated average daily intake (EADI) for organochlorine pesticides (gamma-BHC, heptachlor epoxide, aldrin, dieldrin, and endrin) was above their respective acceptable average daily intake (ADI), while hazard quotient for each of these pesticides was above the unity value (1). This indicates that there is a potential cancer risk for the local residents with life time consumption of pesticidecontaminated fish.