Assessment of the concentrations and health risk of some heavy metals in cowpea (Vignus unguiculata) in Gwagwalada, Nigeria

Cowpea (Vignus unguiculata) is a source of plant protein that is widely consumed by the Nigerian populace. The aim of the study was to evaluate the health risk of heavy metals in two cowpea types sold in Gwagwalada Market, Nigeria. The concentrations of five heavy metals nickel (Ni), cadmium (Cd), manganese (Mn), cobalt (Co), and chromium (Cr) were assessed in the cowpea types. Samples of each type were randomly purchased and the heavy metal concentrations (mg/kg) were analyzed with an atomic absorption spectrophotometer. The concentrations of the heavy metals in mg/kg dry weight of the brown type were as follows: Ni (2.45 +/- 0.87), Cd (0.26 +/- 0.10), Mn (9.11 +/- 1.80), and Co (1.67 +/- 0.20), while the concentrations for the white type were: Ni (4.55 +/- 1.21), Cd (0.27 +/- 0.13), Mn (9.17 +/- 1.50), and Co (1.09 +/- 0.15). The level of Cr was below detection in all the samples analyzed. However, the levels of Ni, Mn, and Co investigated were all below the permissible limits set by FAO/WHO. The Cd concentrations of both cowpea types exceeded the FAO/WHO permissible limit of 0.2 mg/kg for cowpea. Determined heavy metal concentrations were used for potential health risk assessment in adults and children. The target hazard quotient and hazard index were >1 for Co, while the target cancer risk of Ni subsulfide for the cowpea types exceeded 10(-4), and these results are causes for concern. It is recommended that the concentrations of the heavy metals in cowpea sold in Nigerian markets should be monitored regularly in order to avert their detrimental effects on consumers.