Radiological health risk assessment of drinking water and soil dust from Gauteng and North West Provinces in South Africa

摘要

Long-lived natural radionuclides such as ( U) uranium-238, ( Th) thorium-232, ( Ra) radium-226 and ( K) potassium-40 and heavy metals are normally exposed to the surface during mining activities. They enter the human body when inhaled (as dust) or ingested (by drinking contaminated water). An intake of large concentrations of these radionuclides and heavy metals can lead to health effects such as development of cancers. The aim of this work was to assess the radiological health risk due to intake of radionuclides in dust and drinking water from the West Rand gold mining area and Modiri Molema Municipality (MMM) water treatment plant. The dust samples were analyzed for radionuclides of interest using the well-type high purity Germanium detector. Water samples were collected before and after purification from the Modiri Molema Municipality water treatment plant and analyzed using the ultra-low level Liquid Scintillation Counter (LSC), to evaluate the gross alpha and beta radioactivity dose levels of the radionuclides in water. An Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to evaluate the heavy metal concentrations in the drinking water after purification at the treatment plant. The total inhalation effective dose obtained in this study was (2.71 × 10 and 1.31 × 10 ) μSv.y for adults and infants respectively, which is below the prescribed dose range of 5–10 μSv.y . The mean activity concentrations of the radionuclides in air dust were found to be; Ra, (2.14 ± 0.82) × 10 (Bq.m ), U (6.08 ± 2.17) × 10 (Bq.m ) and Th (2.65 ± 1.1) × 10 (Bq.m ). The activity concentration of Ra obtained exceeded the world average by 2 times. The Ra , the external hazard (H ) and internal hazard (H ) indices were calculated and the values obtained from soil were lower than the world average. However, the absorbed dose rate in air was higher than the world averages of 60 nGyh . The minimum and maximum gross alpha activity obtained was 0.0041 (Bq.L ) and 0.0053 (Bq.L ) respectively, while the minimum and maximum gross beta activity obtained for water samples was 0.0083 (Bq.L ) and 0.0105 (Bq.L ) respectively. More heavy metals were detected in the first two stages of the water treatment than on the last two stages, nevertheless, their concentrations did not exceed recommended limits. The results for soil dust indicates that the windward areas might pose health risks for human population staying in the area and the activity concentration for drinking water indicate that the specific activity in the water supply after purification is below the WHO guideline limit of 0.5 (Bq.L ) for gross alpha and 1 (Bq.L ) for gross beta. The results obtained were also within the range of the South Africa Department of Water Affairs and Forestry target water quality limit of (0–1.38) (Bq.L ) for gross beta activity. Heavy metals concentrations in drinking water did not exceed the stipulated limits by USEPA and DWAF. Therefore, this water after treatment is radiologically and toxicologically safe for the members of the public.