Heavy metal contamination and potential health risks from soils around a stone quarry in Tzaneen, South Africa

Abstract

Heavy metals exist naturally in the earth’s crust as part of the composition. Their contents vary between regions resulting in spatial variations of background concentration. The concentration of heavy metals in the environment can increase to high levels through anthropogenic sources. Stone quarrying is one of the anthropogenic sources responsible for increase of heavy metals in the environment. Hence, the study aimed at assessing the contamination level and human health risks caused by heavy metals from soils around Tzaneen stone quarry. A total of 46 samples were collected and analysed for Cr, Pb, Cu, Co, Ni, Zn, Mn and Fe using AAS. The pollution level of the heavy metals in the study area was estimated using Pollution Index (PLI), Enrichment Factor (EF) and Geo-accumulation Index (Igeo). Non-carcinogenic and carcinogenic health risks were assessed for inhalation, ingestion and dermal absorption routes for infants, children and adults based on the hazard quotient (HQ), hazard index (HI), average daily intake and carcinogenic slope factor. Concentration of Mn and Fe were highest in the soil samples whereas Ni had the lowest concentration. Metal loading trends revealed a general decreased with distance from the quarry site. The PLI of heavy metals in the soil from the community ranged from 0.55 to 0.75 with an average value of 0.66 suggesting an unpolluted status. Metal enrichment at the quarry was in the order: Mn>Co>Pb>Cu>Ni>Cr>Zn while in the nearby community, it ranged from Co>Pb>Cr>Mn>Cu>Ni>Zn. The values for HQ and HI showed that infants, children, and adults in the study are exposed to potential non-carcinogenic health risks through dermal absorption compared to inhalation and ingestion. Children were the most at-risk population exposed to non-carcinogenic risk. Values for the incremental lifetime carcinogenic risk (ILCR), were lower than the US EPA tolerable range (10-6 – 10-4), suggesting no immediate carcinogenic risks. However, prolonged exposure to quarry dust may still remain a potential health threat to the surrounding communities. It is recommended that quarry workers and residents in the study area should take protective measures against long-term exposure to heavy metals in the area.