Environmental assessment of toxic heavy metals and natural radionuclides in irrigation water from Rustenburg, South Africa

Water is a transparent, tasteless and odourless inorganic compound, essential for life and sustainable development. It is important for food and energy production, socio-economic growth, healthy ecosystems and human existence. Global attention is given to water quality monitoring due to the role it plays in human exposure to different kinds of contaminants, including radioactive and toxic contaminants from industrial, agrochemicals, mining and other anthropogenic activities. This work presents the results of measured natural radionuclides and toxic heavy metals in Rustenburg, and their associated non-carcinogenic and carcinogenic risk. The average concentrations of Cd, Cu, Co, Fe, Ni, Mn, Pb and Zn are 0.00007 mg/l, 0.0087 mg/l, 0.0033 mg/l, 0.0636 mg/l, 0.0052 mg/l, 0.0217 mg/l, 0.0003 mg/l and 0.0047 mg/l respectively and are below the safe limit of toxic heavy metals in water. The activity concentration of ⁴⁰K and ²³⁸U ranges from 7.07 Bq/l to 13.2 Bq/l and 1.24 × 10⁻⁰⁴ Bq/l to 1.09 × 10⁻⁰² Bq/l, with a mean activity concentration of 11.6 Bq/l and 2.78 × 10⁻⁰³ Bq/l respectively. ²³²Th was not found in all measured water samples. The estimated average committed effective dose from ingestion of natural radionuclides was observed to be below 170 μSv/yr for ⁴⁰K, 120 μSv/yr for ²³²Th and ²³⁸U, and a total of 290 μSv/yr reported by the United Nations Scientific Committee on the Effects of Atomic Radiation. The assessment of human health risks resulting from exposure to toxic heavy metals shows negligible carcinogenic and non-carcinogenic health risks to the exposed population, making the water sources from which the sample was collected, safe for agricultural and domestic use. The obtained results will also serve as reference data for future environmental studies.