Human Health Risks Associated With Radioactivity and Heavy Metals Around Mrima Hill and the Kwale Heavy Mineral Sand Mine, Kenya

Abstract

This study addresses global health concerns from heightened environmental radioactivity and heavy metal exposure. Despite extensive research on the dynamics and health risks of heavy metal pollution from various mining activities, a significant knowledge gap persists, particularly in understanding the impact on human health from heavy mineral sand (HMS) mining. This research focuses on the ecological and human health risk assessment resulting from exposure to heavy metals and naturally occurring radioactive materials in soil and drinking water around Mrima Hill and the Kwale HMS deposit, utilizing the Agilent 7700s ICP-MS technique. Water quality indices were used to evaluate the quality of drinking, while the geo-accumulation index (Igeo), enrichment factor (EF), and pollution index (PI) were used to evaluate the extent of soil pollution. The USEPA model was used to evaluate the non-carcinogenic (NCR) and carcinogenic (CR) health risks. The total effective dose equivalent (TEDE) and the incremental lifetime cancer risk (ILRC) from exposure to environmental radioactivity were assessed using the RESRAD OFFSITE code. Cr and Cd in water samples exceeded the maximum contaminant levels of 0.1 and 0.005 mg/L in drinking water, with Cd contributing the highest percentage to the WQI. However, the soil was strongly polluted by Cr, As, and Cd. Mean Cr, As, and Cd concentrations in soil samples from Mrima Hill were ~500, ~7, and ~9 times higher than the maximum allowable concentration (MAC) of 200 mg/kg Cr, 20 mg/kg As, and 5 mg/kg. The EF of Cr, As, and Cd for soil samples from Mrima Hill were ~700, ~5, and ~224 higher than the EF threshold value of 1.5. The NCR assessment showed that the population was more susceptible to the effects of As in soil and Cr in drinking water. As contributed ~67% to the hazard indices (HI) from exposure to soil, while Cr contributed ~60% to the HI in drinking water. The CR assessment showed that both As and Cr values from ingestion and dermal exposure to water and soil were above the threshold value of 10-4. The TEDE assessment showed that the dose values for inhabitants from the Kwale HMS deposit and Mrima Hill environs were highest (67.72 μSv and 504.7 μSv, respectively) in the 74th year of exposure. The ILCR values from external exposure to 228Ra and 228Th in the soil were above the regulatory limit of 10-4. However, the ILCR from ingesting soil particles was within the tolerable limit of 10-6 to 10-4, while the ILCR from inhaling the soil particles was below the recommended value

of 10-6. Thus, the populations in the surveyed areas are prone to health risk from exposure to natural radioactivity and heavy metals. There is therefore need for stringent mechanisms to monitor, control, and mitigate soil pollution from future mining activities. Epidemiological studies from exposure to these metals could be done to assess the occurrence and distribution of the health risks from exposure to these metals.