Assessment of heavy metals availability and its health risk on Zea mays and Sorghum grown on agricultural soil, Southern Borno, Nigeria

Heavy metals are deleterious due to their long biological half-lives, non-biodegradable nature, and their ability to accumulate in different body parts. Heavy metals emanating from anthropogenic sources are more dangerous because of their instability and solubility leading to high bioavailability. Heavy metals uptake by plants is generally the first step of their entry into the agricultural food chain. The present study aimed at assessing the availability of heavy metals on cereals crops (Zea mays and Sorghum) grown on agricultural soil hence their health risk index. Soil and cereals crops were digested analyzed for Cr, Cd, Cu, Pb, Ni and Zn using Atomic Absorption Spectroscopy (Buck scientific model 210GP) while transfer factor (TF), daily intake of metals (DIM) and health risk index (HRI) were evaluated. The concentration of Cd in all the three soil samples had mean values of 10.7±2.32 mg/kg while Zea mays and Sorghum had mean values of 2.12±0.09 and 2.75±0.03 mg/kg respectively. The decrease in concentrations of the metals in Zea mays and Sorghum samples across sampling locations followed this order Cd > Cu > Cr > Pb > Ni > Zn. The trend of heavy metal transfer factor from soil to Zea mays and Sorghum grown in Askira Uba, Southern Adamawa were in the order of Cd > Ni > Cu > Pb > Cr > Zn. The HRI values of Cd (1.00, 2.70) in both zea mays and sorghum were higher than other studied heavy metals. The finding of this study with respect to DIM and HRI showed that the consumption of  Zea mays and Sorghum grown in Askira Uba, Southern Borno were nearly free of risks at all sites for all assessed heavy metals except Cd. Even though the values of HRI for other metals were nearly one, the long term consumption of these crops may lead to serious health risk.