Concentration and Health Risk Assessment of Organophosphorus Pesticide Residues in Selected Grains: Maize (Zea Mays L.) And Beans (Vigna Unguiculata (L.) Walp.) Sold in Karu Market, Nasarawa State, Nigeria

Abstract

This study provides a comprehensive assessment of the concentration and potential health risks of organophosphorus pesticide (OPPs) residues in two widely consumed grains purchased from major trading centers (market) in Nasarawa State. For this study a total of twelve grain samples were collected using stratified random sampling to ensure market-level representation where homogenization and extraction using the QuEChERS method, followed by a dispersive solid-phase extraction SPE clean-up. Quantification and identification of nine target OPPs were performed using Gas Chromatography–Mass Spectrometry (GC–MS) calibrated with multilevel standard. The analytical results showed that OPPs residues were widespread across all samples, though concentrations varied markedly by grain type and market location. Notably, methyl parathion and azinphos-methyl pesticides banned or severely restricted due to their high toxicity were detected in several samples, indicating possible illegal application or improper storage practices. White and yellow maize recorded higher contamination than beans, with yellow maize from Orange Market containing the highest oxydisulfoton concentration (11.96 mg/kg) and white maize from Karu Market showing extremely elevated ronnel levels (50.63 mg/kg). Health risk assessment was conducted using Estimated Daily Intake (EDI) and Target Hazard Quotient (THQ) for both adults and children. Results revealed that multiple pesticides exhibited THQ values significantly greater than 1, signaling substantial non-carcinogenic health risks from chronic exposure. Maize particularly from Orange and Karu markets posed the highest risk burden, while beans showed moderate to high risk depending on pesticide type and concentration. In conclusion, the study findings highlight the urgent need for stricter enforcement of pesticide regulations, routine monitoring of pesticide residues in grain markets, and comprehensive farmer and trader sensitization on the dangers of banned and excessive pesticide use. Implementing these measures is essential to safeguard food safety and reduce long-term health risks associated with dietary pesticide exposure.