Assessment of heavy metals and naturally occurring radioactive materials (NORM) from historical mine wastelands: a case study of Brakpan, South Africa

Abstract

Mining has contributed to South Africa’s development, but its legacy has left more than 6000 abandoned sites, with Brakpan in South Africa among the most affected areas. This study assessed heavy metals and naturally occurring radioactive materials (NORM) in the Brakpan mine wasteland in Gauteng Province, South Africa. Soil and water samples from the area were analysed using inductively coupled plasma mass spectrometry (ICP-MS) for heavy metals and high-purity germanium gamma-ray spectrometry (HPGe) was used for NORM analysis. The results showed elevated concentrations of several contaminants. In soils, chromium (103.98 mg/kg) and arsenic (47.75 mg/kg) were notably enriched, while uranium exhibited the highest mean concentration (7.14 mg/kg), exceeding the South African soil quality guidelines for contaminated land. Water samples showed high concentration of uranium (mean 1.64 mg/L) and nickel (12.78 mg/L) concentrations, exceeding guideline values for agricultural use and aquatic ecosystem protection value of 0.03 mg/L and 0.04 mg/L, respectively. Suggesting potential risks to downstream water users and ecological receptors. Radiological analysis revealed activity concentrations of 238U ranging from 12.78 to 409.73 Bq/kg (mean: 160 Bq/kg), with mean activity concentrations of 232Th and 40 K of 19.65 Bq/kg and 376 Bq/kg, respectively. The absorbed dose rate averaged 108.19 nGy/h exceeding the UNSCEAR global average background level (59 nGy/h). Localised hotspots exhibited radium equivalent activity of up to 492.49 Bq/kg and an external hazard index of 1.33, indicating elevated radiological risk near residential settlements. Overall, the findings highlight combined geochemical and radiological hazards, underscoring the need for integrated remediation and management strategies to protect affected communities.