What does this research mean for the field?

Organochlorine pesticide residues, including γ-HCH and DDT, are widely distributed in the water, sediment, and fish of the Gilgel Gibe Reservoir system, but currently pose no significant health risk for human consumption. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

May 16, 2026Open Access

Organochlorine Pesticide Residues in Water, Sediment, and Fish of Gilgel Gibe Reservoir and Tributaries, Ethiopia: Levels, Distribution and Risk Assessment

Key Points

This research aims to analyze the levels and distribution of organochlorine pesticide residues in water, sediment, and fish from Gilgel Gibe Reservoir and its tributaries.
42 samples analyzed: 12 water, 12 sediment, and 18 fish specimens.
Organochlorine pesticides were extracted using liquid-liquid microextraction for water and Soxhlet extraction for sediment and fish.
Analysis conducted using gas chromatography-mass spectrometry.
Gamma-hexachlorocyclohexane was highest in Yadi River water at 10.97 µg/L.
Health Risk Index for fish species remained below critical value of 1, indicating no health risk for human consumption.
African catfish exceeded maximum residue limit for heptachlor epoxide at 225.22 µg/kg.

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.

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