Health Risk Assessment of Pesticide Residues in Soil and Rice From Rainfed Floodplains of Anambra State, Nigeria

The use of organochlorine (OCP) and non-organochlorine pesticides in paddy soils is widespread in wetland and lowland rice systems, with implications for soil health and food safety. This study assessed pesticide residues in soils (0-15 and 15-30 cm) collected from uphill, hill-wash, and valley-bottom locations during pre-sowing and post-harvest periods, as well as in rice sampled at five post-harvest stages: harvested, dried, stored, dehusked, and parboiled. Gas chromatography revealed that before sowing, dichlorophenyltrichloroethane (0.7600 mg/kg) was significantly higher (p < 0.05) in valley-bottom subsoil, while post-harvest glyphosate (1.1562 mg/kg) was similarly elevated. In rice, dichlorvos (0.3899 mg/kg) peaked in dehusked grains. Detected residues included OCPs (e.g., lindane, hexachlorobenzene, aldrin, heptachlor, and DDT derivatives) and non-OCPs (glyphosate, 2,4-D, carbofuran, profenofos, and dichlorvos). Health risk assessment showed hazard quotients and indices below unity for most pesticides, indicating negligible non-carcinogenic risks, except for OCPs. However, lifetime cancer risks for aldrin, heptachlor, and γ-chlordane exceeded the USEPA's acceptable range (10^-6-10^-4) emphasizing long-term concerns from persistent OCPs. Comparisons with other tropical regions confirm modern pesticides rarely exceed Codex MRLs, but legacy OCPs persist. The findings highlight the need for integrated pest management and continuous monitoring to ensure soil health, rice safety, and consumer protection.