Concentration of ²²⁶Ra in soil, water, and sediment of active and abandoned quarries in southern Vietnam and environmental risk assessment: experimental and modeling studies

Open-pit mining disturbs the earth's surface, impacts geological characteristics, and releases many pollutants including heavy metals, radionuclides, and poisonous gases into the environment. This study investigated the difference between the activity levels of ²²⁶Ra radionuclide in the abandoned quarry region (region A) and the active quarry region (region B). In the surface soil, the mean values of activity concentrations were 40 Bq kg^-1 and 55 Bq kg^-1 in region A and region B, respectively. The statistical analysis shows that the obtained values of ²²⁶Ra concentrations in Region B are higher and more dispersed than those in Region A. For four study quarry lakes, the ranges of activity concentrations in water and sediment were (0-19.4 mBq L^-1) and (25-71 Bq kg^-1), respectively. The levels of ²²⁶Ra in lake water are within the recommended value of 0.74 Bq L^-1 of the United States Environmental Protection Agency (USEPA) for radiation safety. This water can be considered for drinking, agricultural irrigation, and fish farming. The Revised Universal Soil Loss Equation (RUSLE) estimated the soil loss due to soil erosion in the abandoned quarries. It was predicted that the soil erosion degrees in the study area were from very low class to moderately high class according to soil loss classification. The Quantitative Water, Air, Sediment Interaction (QWASI) was validated to predict ²²⁶Ra activity concentrations in the water and sediment of quarry lakes. Based on Student's t-test, the predicted values of ²²⁶Ra activity concentrations for study quarry lakes agreed with the measured values (confidence interval 95%).