Contamination Levels, Source Apportionment and Human Health Risks Assessment of Toxic Elements from a Mining District.

Abstract

While artisanal and small-scale mining is important to local economies, their operations pose significant environmental and public health risks because they release potentially toxic elements (PTEs) into the ecosystem. This study examines the contamination, sources apportionment, and associated human health risks of PTEs at Manwe in the Wa East District of Ghana. An X-ray Ray Fluorescence (XRF) analyzer was used to measure PTE concentrations in sixty-five soil samples collected from key artisanal mining sites in the study area except mercury which was determined using Lumex mercury analyzer. Other parameters measured were pH, electrical conductivity, and organic matter content. The pH values in the samples ranged from 5.30 to 8.67, indicating that the soil varies significantly whereas some parts are slightly acidic, others are somewhat alkaline. The region has low organic content, with a mean organic matter content of 2.3% and an average electrical conductivity of 125.0 µS/cm, indicating moderate salinity levels. These parameters provide important context for the behaviour and mobility of PTEs in their environment. The mean PTE concentrations found in the soil samples were As (405.740 mg/kg), Pb (3.797 mg/kg), V (67.46 mg/kg), Ni (29.93 mg/kg), Cd (20.45 mg/kg), Co (104.83 mg/kg), Hg (40.46 mg/kg), Cr (40.46 mg/kg), Cu (27.28 mg/kg), Hg (0.35 mg/kg) and Zn (28.69 mg/kg). The results revealed that concentrations of As, Cd, Cr, Hg, and Co in the sampled areas were significantly higher than the crustal average, raising concerns about environmental contamination from mining activities. Environmental pollution indices were used to assess the degree of contamination using models such as the geochemical load index, enrichment factor, contamination factor (CF), and pollution load index, which revealed that the soils were heavily polluted by Cd, moderately polluted by Co, and unpolluted by other elements. EF showed the soil was significantly enriched by Cd (220.0), while As (10.36) and Co (15.40) are moderately enriched. The CF indicated low contamination for the majority of the metals studied, except As (3.06) and Co (5.52) which are significantly contaminated, while Cd (68.16) showed high contamination. The value of PLI > 1 (2.2) suggests the soil is polluted as a result of the mining activities. The principal component analysis (PCA) used to predict the sources of these PTEs revealed significant anthropogenic contributions of mercury, arsenic, cobalt, and cadmium, resulting in elevated PTE levels in the soil. These anthropogenic activities included mining, pesticide and phosphate-based fertilizer application, vehicular and grinding mills, auto mechanic workshops, with natural sources accounting for only a small portion. Using human health risk assessment models, the elements' total hazard index (HI) for ingestion and dermal contact in adults and children was greater than one, indicating a likely non-carcinogenic health risk effect. The cancer risk (CR) value for ingestion and dermal exposure pathways exceeded permissible limits (1 x 10−6 to 1 × 10−4), posing health risks to residents. The levels of these PTEs were discovered to pose a significant risk to both adults and children, with children being more susceptible to exposure, primarily through oral ingestion and skin contact. Arsenic and cadmium were identified as the most dangerous elements, with long-term exposure potentially leading to cancer, kidney damage, and neurological disorders. This study recommends that adequate attention be directed toward a thorough risk assessment of PTEs in the study area.