Occurrence and Human Health Risk Assessment of Pesticide Residues in Staple Cereals Sold in Northern Nigeria

Abstract

Pesticide contamination of cereal grains has become a growing food safety concern because cereals constitute a major component of the human diet and represent an important route of dietary exposure to agrochemical residues. This study investigated the occurrence of pesticide residues in commonly consumed cereals marketed in northern Nigeria, determined their compliance with maximum residue limits (MRLs), and evaluated the associated non-carcinogenic health risks to adults and children. Composite samples of beans, sorghum, maize, wheat, local rice, and imported rice were collected from representative markets and analysed using high-performance liquid chromatography (HPLC). Exceedance factors (EFs) were calculated by comparing measured concentrations with established MRLs, comparing pesticide residue concentrations among cereal types using one-way analysis of variance followed by Tukey’s Honestly Significant Difference (HSD) post hoc test where appropriate, and assessing the associated non-carcinogenic health risks for adults and children through ingestion, inhalation, and dermal exposure pathways. Four pesticide residues, imidacloprid, acetamiprid, pendimethalin, and propiconazole, were detected at concentrations ranging from 0.06 to 0.90 mg kg⁻¹. All detected residues exceeded their respective MRLs, with exceedance factors ranging from 1.2 to 18.0. Pendimethalin exhibited the highest contamination in maize (0.90 mg kg⁻¹; EF = 18.0), followed by local rice (0.86 mg kg⁻¹; EF = 17.2) and sorghum (0.85 mg kg⁻¹; EF = 17.0), whereas wheat contained the highest imidacloprid concentration (0.73 mg kg⁻¹; EF = 14.6). One-way analysis of variance (ANOVA) indicated significant differences in imidacloprid concentrations among the cereal types (p < 0.05). Tukey’s Honestly Significant Difference (HSD) post hoc test further revealed that wheat contained significantly higher imidacloprid concentrations than beans, sorghum, maize, and local rice (p < 0.001). Despite these exceedances, all estimated HQ and HI values for adults and children remained below the acceptable safety threshold of 1.0, indicating negligible non-carcinogenic health risks under the current exposure scenarios. Children consistently exhibited higher exposure estimates than adults due to lower body weight and greater intake relative to body mass. The widespread occurrence of pesticide residues above regulatory limits highlights the need for strengthened pesticide management, routine surveillance, and improved compliance with good agricultural practices. Continuous monitoring remains essential to minimise dietary exposure and ensure consumer safety.