Assessment of heavy metal contamination and associated health risks in processed cowhides from Nigerian markets

Heavy metals are well-established contributors to carcinogenesis, and chronic dietary exposure constitutes a significant, yet under-recognised route of intake in many developing regions. In Nigeria, cowhide (“ponmo”) is a widely consumed delicacy; however, its safety remains insufficiently investigated, despite potential contamination from environmental sources, animal husbandry practices, and processing methods such as singeing. Hence, this study was designed to investigate the concentrations of heavy metals and associated health risks in different processed cowhides sold in major markets in Ewekoro Local Government Area, Ogun State, Nigeria. A total of 100 cowhide samples were collected and sampled from four major markets, with a total of five processing types; fresh, dried, wet, white, and fried. Heavy metal concentration was determined using Atomic Absorption Spectrophotometry (AAS). Zinc (Zn) recorded the highest concentration among all metals, followed by Lead (Pb), Arsenic (As), Copper (Cu), and Chromium (Cr) in descending order. Dried and wet samples consistently contained higher metal concentrations than fresh, white, and fried samples, suggesting that dehydration and processing intensity contribute to metal accumulation. Additionally, the health risk assessment, based on the Estimated Daily Intake (EDI), Hazard Quotient (HQ), and Hazard Index (HI), indicated that Cu and Zn were within acceptable limits, whereas As, Cr, and Pb exceeded safety thresholds in several samples. As and Cr showed HQ values greater than 1 in dried and fried cowhides from Arigbajo and Wasinmi, indicating potential chronic toxicity with prolonged intake. The HI values ranged from 1.844 ± 1.544 in Obada-Oko to 2.618 ± 1.709 in Arigbajo, surpassing the recommended limit of 1.0, signifying possible additive effects of multiple metals. More so, the carcinogenic risk (CR) analysis further revealed that As ranged from 0.000713 ± 0.000602 in Obada-Oko − 0.000853 ± 0.000666 in Arigbajo and Cr ranged from 0.000129 ± 0.000104 in Obada-Oko − 0.000796 ± 0.001413 in Arigbajo, while Pb presented lower CR values. The total carcinogenic risk (TCR) ranged from 0.000847 ± 0.000708 to 0.001654 ± 0.001436, indicating potential lifetime cancer risk from habitual consumption of contaminated cowhide. Cowhide samples are rich in trace elements such as Cu, Zn, and Cr; however, the elevated concentrations of Pb and As, which exceed maximum permissible limits, indicate that their consumption poses potential human health risks likely linked to environmental contamination, animal rearing, and singeing practices. Therefore, routine monitoring, stricter regulatory enforcement, and adoption of safer processing and handling methods are strongly recommended to mitigate exposure risks and safeguard public health.