Assessment of Radio-ecological Hazardous and Toxic Heavy Metal Contamination Associated With Artisanal Gold Mining in West Pokot County

Abstract

Artisanal gold mining in West Pokot County, Kenya, serves as a significant source of income for local communities, but it also poses potential environmental and health hazards due to contaminants such as dust particles, soil erosion, loss of biodiversity, radiation exposure, and toxic heavy metals. This study aimed to assess the radioecological hazards and heavy metal pollution resulting from such mining activities. Forty-six subsoil samples were collected from artisanal mines at various locations, including Weiwei, Nyangaita, Ortum, Turkwel, Porkoyo, Sekerr, and the Muruny River. These samples were prepared and analysed for their activity concentrations of 238U, 232Th, 40K, and toxic heavy metals (As, Cr, Hg, Pb) using gamma spectroscopy and EDXRF. The results revealed two distinct clusters of activity, indicating different geological origins. The activity concentrations in the soils ranged from 7.2 ± 1.1 to 78.4 ± 12.6 for 238U, 9.2 ± 0.3 to 89.7 ± 32.5 for 232Th, and 166 ± 79 to 1200 ± 326 Bq kg-1 for 40K. Compared with the mining samples, the control samples exhibited moderate activity levels. The internal and external hazard indices ranged from 0.12 to 1.32 and 0.10 to 1.25, respectively, with most sites below the recommended limit of 1 unit except in Turkwel. The ELCR ranged from 0.188 x10-3 to 0.482 x10-3, with the majority of the sites recording values above the acceptable limits, except for samples from the Sekerr and control areas. The Req ranges from 36.2 to 262, which is below the global limit of 370 Bq kg-1. All sites recorded values below the global limit of 1 except Turkwel for Iγ. Heavy metal concentrations were also assessed, with lead, chromium, and arsenic detected in some site samples. The concentration ranged from 13.6 to 4746 μg/g for lead, <60 to 664 μg/g for chromium, and <7 to 297 μg/g for arsenic. Mercury exceeded the detection limit of 10 μg/g in Turkwel and Porkoyo mines. In general, the soils at the sampling sites had low to moderate CFs for all the toxic metals, with few samples exhibiting considerable and very high CFs, particularly at the Turkwel site. These findings highlight the significance of the radioactivity and heavy metal contamination associated with ASGM in West Pokot County. This study emphasizes the need for further investigation and the development of strategies to mitigate negative impacts on both the environment and human health. This research provides crucial insights for informing policies and interventions by local and national governments, safeguarding community well-being and the environment, and serving as a reference for future research. It will also contribute significantly to the Kenya radiation data to meet the International Atomic Energy Agency's (IAEA) requirements for ASGM.