Assessment of Levels and Health Risks of Trace Metals in Soils and Food Crops Cultivated on Farmlands Near Enyigba Mining Sites, Ebonyi State, Nigeria

Abstract

In most developing countries, mining is one of the major sources of toxic heavy metals, some of which are a major health concern to the surrounding populace through soil pollution and food contamination. We investigated the levels of Ti, Mn, Ni, Cu, Zn, Pb, Rb, Sr, Se, Nb, and V in 64 soil samples, 320 samples of regularly consumed staple food crops and vegetables (Manihot esculenta [cassava] tubers, Dioscorea rotundata [white yam], Arachi hypogea [groundnut] seed, Telfariria occidentalis [fluted pumpkin leaf]), and leaves of the medical plant Zanthoxulum zanthoxyloides on farmlands near Enyigba mining sites in Ebonyi state, Nigeria. We also examined the possible health risks due to consumption of these staple foods. Energy dispersive X-ray fluorescence was used to determine the metals present in the samples. The mean levels of metals, except for Mn, Pb, and Zn, were below the threshold limits recommended by various institutions for agricultural soils. Our data also showed that food crops cultivated near these sites bioaccumulated toxic levels of these metals above the proposed values set by the World Health Organization, National Agency for Food and Drug Administration and Control, and Codex Alimentarius Commission, especially for Pb, Zn, Cu, Ni, Se, and Rb. These findings may have potential health implications for the local dwellers. The estimated daily intakes of the toxic metals through the consumption of the crop samples were below the maximum tolerable daily intakes, except for Pb and Ni, by eating groundnut, cassava, and white yam. Furthermore, the target hazard quotient, computed based on the estimated daily intake of the heavy metals, was above unity for the metals for cassava, white yam, and groundnut consumption, suggesting significant health risk. Elevated amounts of heavy metals in cassava and groundnut samples, as revealed by their metal extraction coefficient computed in this study, hint that they may be used as bioindicators of ecological and health hazards and phytoremediators of Mn, Zn, Cu, and Pb.