Pesticide residues in cowpea production in Nigeria (2018–2024): a systematic review of health risks and sustainable management

Cowpea (Vigna unguiculata) is vital for food security in Nigeria, but reliance on synthetic pesticides increases the risk of residue contamination. This review synthesises literature from 2018 to 2024 on pesticide types, residue levels, and associated health risks in Nigerian cowpea production. A systematic review approach was applied, including database searches, predefined inclusion/exclusion criteria, and PRISMA-style selection to ensure comprehensive and unbiased evidence synthesis. Frequently reported pesticides include organochlorines (DDT, aldrin, dieldrin, lindane), organophosphates (DDVP, chlorpyrifos), pyrethroids (cypermethrin), and glyphosate. Residue concentrations often exceeded regulatory limits: DDVP reached 0.02 µg/g (WHO limit: 0.01 µg/g), 18.2% of glyphosate samples exceeded WHO/FAO CODEX thresholds (15.0 mg/kg), and banned organochlorines persisted above EU standards, e.g., endrin ketone 0.0663 mg/kg (limit: 0.050 mg/kg). Documented human health effects include carcinogenicity, neurotoxicity, endocrine disruption, and acute poisoning. Integrated Pest Management (IPM) consistently reduced pesticide use and residue levels across studies. Additional interventions such as hermetic storage, solar drying, natural insecticides, and biopesticides (e.g., NSPRIDUST) showed potential to improve grain safety. The evidence indicates that pesticide residues in Nigerian cowpea remain a public health concern. Systematic implementation of evidence-based management strategies, particularly IPM and validated post-harvest interventions, is critical to minimizing exposure risks and ensuring grain safety.