Organochlorine pesticide residues in water, sediment, and fish of Gilgel Gibe Reservoir and tributaries, Ethiopia: Levels, distribution and risk assessment

Abstract

Levels, distribution, and risk assessment of organochlorine pesticides (OCPs) residues in water, sediment, and fish from Gilgel Gibe Reservoir and its tributaries were investigated. A total of 42 samples were analyzed, comprising 12 water samples, 12 sediment samples, and 18 fish specimens. OCPs were extracted from water using homogeneous liquid-liquid microextraction, while Soxhlet extraction was employed for sediment and fish samples, before being analyzed by gas chromatography-mass spectrometry detection. Among the detected OCPs, gamma-hexachlorocyclohexane (γ-HCH) was the most predominant in water samples, especially in Yadi River (YR) (10.97 µg/L) and Nada Guda River (NGR) (7.04 µg/L). However, its concentrations were lower at river mouths and reservoir sites. Dichlorodiphenyltrichloroethane (p,p’-DDT) and its metabolites dichlorodiphenyldichloroethylene (p,p’-DDE) and dichlorodiphenyldichloroethane (p,p’-DDD) were detected in all samples. The concentrations of the studied OCPs were highest in Nedi River Sediment (NRS), Yadi River Sediment (YRS), and NGR Sediment (NGRS), ranging from 53.75 ± 0.32 to 71.93 µg/kg, except heptachlor epoxide (HCE). Sediment samples from Nada Qala River (NQR), at its mouth and reservoir in its inflow side showed lower concentrations of the studied pesticides. African catfish from Unkure site had HCE levels (225.22 µg/kg) exceeding the maximum residue limit (MRL) set in Codex Alimentarius Commission (CAC) guidelines. However, other OCPs like α-HCH, γ-HCH, HC, and p,p’-DDT in African catfish and Nile tilapia remained below MRLs. The Health Risk Index (HRI) values for both fish species remained below the critical value of 1, indicating no significant health risks for human consumption.