Assessment of bioavailability and human bioaccessibility in surface soil at Bama Zinc-Lead mine, using single extraction methods

Measuring total metal concentration of heavy metals cannot be a suitable indicator to evaluate their danger and human health risk. Their toxicity depends on their mobility and bioavailability. In the present study, sixty-five surface soil samples in the Bama zinc-lead mining and residential area were collected to assess metal bioavailability. Since the mine is near to the metropolitan area (Isfahan) and a village is located in vicinity of the mine, assessing potential adverse effects of the surface soil on human health is a crucial issue. Firstly, total concentration of metals, using acid digestion method (Pb, Zn, Cu, Mn, Fe and Cd) as well as L.O.I and carbonate contents were determined for precisely understanding on pollution condition. Enrichment factor was used to determine the accumulation or non-accumulation of metals at Bama mining area and its residential area, using Fe and Mn as references elements. Single extraction tests were conducted to reveal bioavailability and human bioaccessibility of metals, using EDTA and glycine as extractants. Moreover, Bioavailability risk assessment index (BRAI) was used to assess the risk of metal bioavailability/bioaccessibility. Based on BRAI, qualitative mapping of health risk distribution was presented, using ordinary kriging method. High concentrations and enrichment factor of Pb, Zn and Cd were determined at mining area. Their high concentrations in mining area may be due to Bama host rocks where significant contents of mentioned metals were accumulated. The amount of L.O.I was higher in mining area, indicating the ability of its soils to carry more polluted metals. Cu created no pollution and health risk due to its low total and bioavailable contents at study area. Based on single extraction methods, the absorption percent for the toxic metals were different. The highest percent of bioavailability and human bioaccessibility was allocated to Cd and the lowest was for Pb. Further, it was found that glycine extracted more amounts of metals in comparison with EDTA,Since pH is in lower values using glycine solution, greater amount of metals can be changed into solution forms due to acidic pH of glycine. So the single extraction test exhibited higher bioaccessible fraction of metals. Bioavailable and bioaccessible percent of toxic metals was higher in residential area as mineral soils are in poor condition. Pearson correlation coefficient showed that Pb, Zn, Cd and carbonate contents were highly correlated at residential area. This is expressing that the metals probably are bonded with carbonate at residential area, which may increase the possibility of their mobility and release under changing conditions. Based on EDTA extractant, BRAI index was calculated 3.46 and 4.2 for mining and residential area, respectively. Further, on the base of glycine extractant, result of BRAI was calculated 4.2 and 4.6 for mining and residential area, respectively. The calculated BRAI represent a high risk for human beings and plants in both the mining and residential areas. Moreover, results revealed that higher degree of bioavailability/bioaccessibility for the residential area in comparison with the mining area. It could be concluded the higher potential health hazard for the residence beside the mining area.