Integrated assessment of surface water and soil contamination by potentially toxic elements from gold mine tailings using a combined risk index: a case study of Matjhabeng Local Municipality, South Africa

A combined risk index (CRI) was applied to evaluate cumulative pollution risk from surface water and soil contamination by 12 potentially toxic elements (PTEs) associated with gold mine tailings in the Matjhabeng Local Municipality, South Africa. Surface water and soil samples (n = 15 each) were collected during the 2018 wet season at varying distances from tailings. PTEs were measured by inductively coupled plasma optical emission spectrometry, and pollution levels were quantified using single-factor and Nemerow indices for surface water and soil, subsequently integrated into the CRI. The CRI classified low to moderate pollution risk at 60% of the sites, mainly at locations further from mining activities. Sites close to intensive mining and tailings accumulation presented exceptionally high pollution risk (CRI > 200). Elevated risk was driven primarily by As and Se in surface water and by Cd, Cu, Zn, and Se in soils. These findings confirm that gold mine tailings are a significant source of PTE contamination in the MLM area and demonstrate the benefit of integrating surface water and soil assessments for cumulative environmental risk evaluation. The CRI provides a practical and transferable tool for identifying pollution hotspots and supporting environmental monitoring and management in mining-affected regions.