Potentially Toxic Elements (PTEs) in Surface Soils of Gemstones and Lead Mining Communities: Differential Mineral Phases and Exposure Risks

Abstract

Proper human health risk assessments are rarely conducted for mining communities, consequently when there is need for remediation to be conducted and compensation to be paid to impacted population they are typically done, assuming equal exposure risks from varying mining activities. This study was conducted to compare the distribution of potentially toxic elements in surfaces soils of gemstone and lead mining towns in Nigeria, and their anticipated exposure risks. To achieve this thirty-two surface soil samples were collected from Eggon, a gemstone mining town in Nasarawa State and Enyigba, a lead mining town in Ebonyi State. The samples were air dried, disaggregated and sieved through a 2000 μm mesh with the <2000 fraction retained for aqua regia digestion. Potentially toxic elements bound in the samples were quantified with Agilent Technologies 4210 (MP-AES). Mineral phases were identified and quantified using using a inXitu’s portable transmission XRD/XRF instrument (Terra) with a miniature X-ray tube and a CCD detector for collection both XRD signatures. The PTEs, As, Cd, Mn, Pb and Zn were higher in surface soils of lead mining town. At the gemstone mining town most the PTEs indicated similar concentrations at both mine site and residential areas, while at the lead mining town of the PTEs indicated higher concentrations at mine sites and mine road. At the lead mining town the estimated daily exposure doses for Pb were above threshold values irrespective of the exposure scenario. Mineralogy data indicated most of the PTEs in mineralized phases.