Pesticide (Cyhalothrin, Mancozeb, and Metalochlor) Residue Levels in Kales and Spinach in Water, Soil, and Plant Samples among Selected Farmers in Uasin Gishu, Kenya

Abstract

Purpose: Intensive insecticide use in smallholder horticultural systems presents growing concerns for food safety and environmental sustainability in Kenya, particularly for leafy vegetables that are consumed daily. This study assessed insecticide residue distribution across irrigation water, cultivated soils, and edible tissues of kale and spinach grown along River Moiben basin in Uasin Gishu County. Methodology: Samples were analyzed using HPLC, and accumulation dynamics were evaluated through statistical and multivariate approaches. Results: Mean insecticide concentrations were lowest in irrigation water (0.00199 mg L⁻¹), increased substantially in soils (0.08455 mg kg⁻¹), and reached the highest levels in crop tissues (0.20785 mg kg⁻¹), demonstrating a significant accumulation gradient (F = 68.83, p < 0.001). Spinach accumulated markedly higher residues (0.2887 mg kg⁻¹) than kale (0.1616 mg kg⁻¹), reflecting stronger bioaccumulation capacity. Soil concentrations were strongly correlated with tissue residues (r = 0.78–0.91), while irrigation water contributed minimally to plant contamination. Principal component analysis confirmed soil-mediated transfer as the dominant uptake pathway. Dietary risk assessment indicated low acute exposure (HQ = 0.027 for kale; 0.048 for spinach), although spinach presented elevated chronic exposure potential. Unique Contribution to Theory, Practice and Policy: These findings highlight cumulative soil contamination as the key driver of insecticide transfer into leafy vegetables and emphasize the need for improved pesticide management, soil remediation strategies, and strengthened residue monitoring to safeguard food safety and environmental health in intensive horticultural systems.