Systematic literature review of radionuclides, heavy metals, and organochlorine pesticides in Nigerian food crops: Assessment of carcinogenic and non-carcinogenic health risk

The persistence of chemical and radioactive contaminants in Nigeria's environment presents a critical public health issue, primarily due to their bioaccumulation potential and associated toxic effects on the country's growing population via food crop consumption. This systematic review consolidates studies that assess environmental contaminant levels, specifically radionuclides, pesticides, and heavy metals, in commonly consumed Nigerian food crops and evaluates the associated carcinogenic (CR) and non-carcinogenic (NCR) health risks using established health risk assessment models, including estimated daily intake (EDI), hazard quotient (HQ), hazard index (HI), hazard ratio (HR), and carcinogenic risk (CR). Reports of quantitative levels of metals and organochlorine pesticides (OCPs), as well as information on radionuclides in Nigerian food crops, were sourced from SCOPUS, DOAJ, PubMed, Web of Science, and Google Scholar. Of the 568 articles retrieved, 66 met the inclusion criteria. The reviewed studies indicate increasing levels of both natural and artificial radionuclides in food crops, with isotopes such as 226Ra and 232Th posing higher carcinogenic risks and genetic-related syndromes. Findings also show that, among the heavy metals and OCPs, Cd and lindane were present at the lowest average concentrations, while iron (Fe) and p,p'-DDT had the highest. The HQ-based NCR estimates for Pb, Cd, Cu, and Mn exceeded 1 in both adults and children, while 92% of OCPs had HQ >1 across both age groups. The estimated CR suggests that lifetime exposure to carcinogenic heavy metals and OCP through contaminated food crops could present a significant carcinogenic risk to both children and adults, as estimated values exceeded the acceptable risk threshold of 1x10-4.