Pesticide Residues and Health Risks of Lambda-Cyhalothrin, Mancozeb, and Metolachlor in Irrigated Agroecosystems of Kenya

Background . Intensive horticultural production in sub-Saharan Africa relies heavily on pesticides, often without adequate regulation, raising concerns about food safety and environmental contamination. This study quantified pesticide residues in tomato fruits ( Lycopersicum esculentum ), soils, and irrigation water on cultivated farms and evaluated associated dietary-exposure risks in the Moiben irrigation corridor, western Kenya. Methods . Samples of tomato fruits ( Lycopersicum esculentum ), surface soils (0–15 cm), and irrigation water were collected from six cultivated farms and analysed for lambda-cyhalothrin, mancozeb, and metolachlor using validated HPLC-UV methods. Descriptive statistics, one-way ANOVA, Pearson correlation, and translocation factors (TF = C_tomato/C_soil) were computed. Estimated Daily Intake (EDI) and Hazard Quotient (HQ = EDI/ADI) were calculated to assess human-health risks. Results . Mancozeb was the dominant residue in tomatoes (mean = 0.93 mg kg⁻¹), followed by lambda-cyhalothrin (0.24 mg kg⁻¹) and metolachlor (0.04 mg kg⁻¹). Soil residues were lower (0.096–0.14 mg kg⁻¹), while irrigation water contained trace amounts of lambda-cyhalothrin (0.003 mg L⁻¹) and mancozeb (0.06 mg L⁻¹). ANOVA revealed no significant differences among farms (p > 0.05). Strong soil–water–tomato correlations (r > 0.97) indicated shared contamination pathways, and TF values ranked mancozeb > lambda-cyhalothrin > metolachlor. Dietary-risk assessment showed HQ = 1.03 for mancozeb, exceeding the safety threshold, while other pesticides posed low or negligible risk. Conclusions . The findings demonstrate diffuse pesticide contamination in the Moiben irrigation system, largely driven by over-application and poor compliance with pre-harvest intervals. Strengthened residue monitoring, farmer education, and adoption of integrated pest-management practices are recommended to mitigate health risks.