A radiological index for evaluating the impact of an abandoned uranium mining area in Salamanca, Western Spain

The establishment of a screening index would be a powerful tool to decide whether abandoned uranium mining areas should be rehabilitated or decommissioned. Thus, in this work we established a radiological index which uses the activity concentrations of different groups of gamma emitters from the natural radioactive series of 238U, 235U, and 232Th, as well as 40K and 137Cs. These activity concentrations were calculated by using the absorbed gamma radiation dose value of 175 nGy h−1 specified in the U.S. Code of Federal Regulations. We studied our index in an abandoned uranium mining area in Salamanca, Western Spain, and found that the most influential factors in this area were the presence of organic matter in the soil and the possible effect that plants and fungi may have on the retention of these aforementioned radionuclides. In addition, the results showed that contaminants are migrating in an easterly direction in line with the prevailing wind direction and we were able to identify areas in which the radiological risk is likely high. The mean effective dose rate was 2.51 ± 0.98 mSv y−1 which was equivalent to the levels obtained in previous works. [Display omitted] •Organic matter, plants and fungi are the principal factors on the retention of U.•Anaerobic conditions are the principal cause of Ra sorption onto soils.•The natural effective dose of the analyzed soils was higher than the world average.•The proposed index establishes whether U mining dump sites should be rehabilitated. Main finding of the work: The proposed index can help establish whether uranium mining dump sites should be rehabilitated and decommissioned.