Translocation of Trace Metals in Selected Crops Grown At Rimin Zayam Mining Area – Toro, Local Government, Bauchi State, Nigeria

Abstract

Most farmlands close to mining sites are susceptible to pollution due to the activities of miners, which result 
in both natural and anthropogenic pollution. Soil–bound heavy metals are of great concern for human health 
due to potential exposure via food chain transfer. This research aimed to determine the concentration of Cr, 
Cu, Fe, Mn, Ni, Pb and Zn in the soil of the farmland Rimin Zayam at Toro Local government of Bauchi 
State, Nigeria and to investigate heavy metals in the soil-crop transfer coefficient based on their total and 
bio-concentration in the soils. Three different crops were collected from the farmland, Zea maysmaise), A. 
Hypogeal (groundnut) and A. esculentus (Okra), together with the soil in the vicinity, were prepared and 
analysed for the heavy metals using standard methods. The heavy metals in the soil and crops were 
determined using Micro–Plasma Atomic Emission Spectroscopy (OMP-AES 4200 Model). The trend of a 
bio-concentration factor of the heavy metal accumulations in Z. mays collected from farms around the active 
mining area is in the order: copper (1.600) > zinc (0.800) > chromium (0.106) > manganese (0.031) > nickel 
(0.013) > iron (0.004). A. Esculentus are in the order: copper (2.375) > zinc (0.800) > manganese (0.091) > 
chromium (0.070) > nickel (0.014) > iron (0.004). The trend of biological concentration factor (BCF) of 
heavy metal accumulations in A. hypogea is in the order: copper (0.615) > chromium (0.357) > zinc (0.256) 
> manganese (0.063) > iron (0.001). Iron had the highest BCF values and the lowest value of the three crops 
investigated. The soil-plant transfer coefficient values for chromium, copper, iron, lead, manganese, nickel, 
and zinc accumulated by crops obtained from the active mining site were 10.60, 160.00, 0.400, 3.10, 1.30, 
0.00 and 30.90, respectively for Z. mays. In A. esculentus, these were 7.00, 23.75, 0.90, 9.10, 1.40, 0.00 and 
80.00, respectively. For A. hypogea, the soil plant transfer coefficient values were 35.70, 66.50, 0.10, 6.30, 
0.00 and 25.60 for chromium, copper, iron, manganese, nickel and zinc, respectively. The soil-plant transfer 
coefficients of the crops from the non-mining sites (control) were 6.80, 108.30, 0.70, 100.00, 11.60, 0.00 
and 61.50, respectively, for Z. mays. In A. esculentus, TF values are 13.70, 183.30, 1.60, 200.00, 25.60,0.00 
and 105.00, respectively. For A. hypogea, TF values were 10.60, 133.30, 0.40, 50.00, 6.20, 1.90 and 68,00 
mg/kg for chromium, copper, iron, lead, manganese, nickel and zinc, respectively. The trend of biological 
concentration factors of heavy metal accumulations in all the crops collected from both locations showed 
that it was highest with copper and least with iron, same with the trend of soil-plant transfer coefficient, 
thus indicating that there was no bioaccumulation of toxic heavy metals in the plant's tissues. The study 
indicated that metal pollution at the site does not occur. However, a study of the health risks of long-term 
consumption of the crops should be carried out, and monitoring of mining activities to avert pollution is 
recommended.