Assessment of Some Toxic Heavy Metals in Rice and Beans Sold in Benin City, Nigeria

Abstract

Rice and beans are staple foods for more than 50% of the world's population. They are prone to heavy metal contamination, with the global rise in heavy metal pollution, which causes harm and danger to the ecosystem and puts people and other living things in major health problems. This study aimed to determine the level of some heavy metals in local and foreign rice and white and brown bean samples obtained from an open market in Benin City. The samples were prepared and analysed using a standard method with the aid of an atomic absorption spectrophotometer (A.A.S.). The results of the analysis show the levels of heavy metals in the beans and rice ranged from 0.013–0.067 mg/kg for Pb, 0.02-0.043 mg/kg for Cr, 0.003-0.367 mg/kg for Mn, 0.263–1.017 mg/kg for Zn, 0.30–0.933 mg/kg for Fe, and 0.01–0.023 mg/kg for Cu, with Cd being the only metal below the detection limit. Statistical analysis using a t-test showed that there was no significant difference between the levels of the selected heavy metals analysed among the bean samples and those analysed among the rice samples. If these heavy metals are used as benchmarks for measuring the product's quality, local rice would be considered to be of higher quality than foreign rice, according to statistical analysis using a correlation matrix that showed a nearly identical heavy metal composition between local and foreign rice. The concentration of all the metals studied was observed to be present at tolerable levels lower than the maximum permissible limit as given by the World Health Organisation (WHO). Based on the research findings, the rice and bean samples studied were safe for human consumption.