Occurrence and human health risk assessment of organochlorine pesticides in irrigated and non-irrigated agricultural soils of Wondogenet District, Ethiopia

Abstract

Organochlorine pesticides (OCPs) persist in agricultural soils and pose potential environmental and public health concerns, particularly in intensive cash-crop systems such as khat ( Catha edulis ). This study quantified OCP residues and assessed associated human exposure and risk in irrigated and non-irrigated khat farmlands in Wondogenet District, Ethiopia. We collected 30 surface soil samples from irrigated and non-irrigated farms during the 2024 growing season. We analyzed 20 OCPs using gas chromatography–mass spectrometry following USEPA Method 3540. The method showed strong performance (R² = 0.995–0.9999; recovery: 98.7–103.9%; LOD as low as 0.004 µg kg −1 ). We estimated chronic daily intake (CDI), hazard quotient (HQ), hazard index (HI), and total carcinogenic risk (TCR) using USEPA models. We detected all target OCPs except α-BHC and endrin ketone, with generally higher concentrations in irrigated soils. Dieldrin, endosulfan isomers, and DDT metabolites dominated, indicating both legacy persistence and possible recent inputs. Soil ingestion was the main exposure pathway, and adolescents showed slightly higher CDI values than adults. Non-carcinogenic risk estimates remained below threshold levels (HQ, HI < 1). Carcinogenic risk estimates for heptachlor and p, p′-DDD in adults fell within the upper range of the USEPA benchmark (10⁻⁶–10⁻⁴), indicating relatively elevated model-based risk. OCP residues persist in Wondogenet soils, with higher concentrations and exposure estimates in irrigated systems. While non-cancer risks appear low, the findings highlight spatial differences in potential long-term exposure. Continued monitoring and improved pesticide management are needed to reduce environmental contamination and exposure.