Environmental occurrence, spatial distribution, and probabilistic dietary risk assessment of cypermethrin and glyphosate residues in agricultural ecosystems of southwestern Nigeria

Abstract

Pesticide use in vegetable production raises concerns regarding environmental contamination, food safety, and human health, particularly where pesticide stewardship is inadequate. This study investigated the occurrence, spatial distribution, environmental partitioning, and dietary health risks of cypermethrin and glyphosate in water, sediment, soil, and Amaranthus cruentus collected from 30 sampling sites across three major vegetable-producing settlements in Oyo State, southwestern Nigeria. A total of 240 matrix-season samples were analysed using validated chromatographic methods, generating 480 independent pesticide-specific sample-level observations after analytical duplicates were averaged. Residue data were evaluated using hierarchical mixed-effects modelling, principal component analysis, Moran’s I spatial autocorrelation analysis, deterministic dietary risk assessment, empirical Monte Carlo simulation with 10,000 iterations, and a structured survey of vegetable farmers. Glyphosate predominated in soil and sediment, whereas cypermethrin occurred at comparatively higher concentrations in A. cruentus. Significant spatial autocorrelation was detected specifically for glyphosate in sediment (Moran’s I = 0.783, p = 0.0003). Deterministic assessment indicated acceptable dietary risk for adults for both pesticides and for glyphosate in children, whereas cypermethrin exceeded the hazard threshold in children (HQ = 1.818). Monte Carlo simulation showed HQ > 1 in 15.09% of adult and 70.47% of child cypermethrin exposure scenarios, while no simulated glyphosate exposure exceeded this threshold. Despite substantial exceedance of selected EU spinach maximum-residue-limit benchmarks, farmer practices indicated limited pesticide stewardship and short pre-harvest intervals. These findings support strengthened pesticide stewardship, residue surveillance, farmer education, and regulatory oversight to improve food safety.