Application of radiological assessment as water quality criterion for effluent release in a Brazilian uranium mine

Uranium mining causes several radiological impacts on the surrounding environment, notably in the water bodies, mainly due to the release of long half-life radionuclides from the U-238 and Th-232 series. The Ore Treatment Unit, an old uranium mine undergoing decommissioning, has three points of liquid effluent release (# 014, #025, and # 076). For current study, 78 samples of water were collected at #014, 33 samples at #025, and 63 samples at # 076. The radionuclides were analyzed by gross alpha count, gross beta count, and by arsenazo spectrophotometry. Analyses were carried out using the radiological water quality criterion established by World Health Organization and other organizations, together with the Brazilian legislation, to assess if the released effluents may be used unrestrictedly by the individuals of the public. At #014, the mean values of activity concentration (AC), in Bq.L-1, were as follows: U-nat = 0.107, Ra-226 = 0.035, Pb-210 = 0.031, Th-232 = 0.007, and Ra-228 = 0.049. At #025 the mean values of AC, in Bq.L-1, were as follows: Unat = 0.086, Ra-226 = 0.015, Pb-210 = 0.028, Th-232 = 0.006, and Ra-228 = 0.032. Finally, at point #076, the mean AC values, in Bq.L-1, were as follows: U-nat = 3.624, Ra-226 = 0.074, 210Pb = 0.054, Th-232 = 0.013, and Ra-228 = 0.069. The current study showed that natural radionuclides were not in secular equilibrium. Despite uranium presented its values outside the limits of guidance levels, it can be state that the unrestricted use of effluents released in the three water bodies is authorized from the radiological point of view. In terms of dose rate, the releases at three points were within the radiological limits of potability. On the other hand, in an additional analysis, #76 presented chemical toxicity above the authorized value, pointing the need of restricted use of water from the point of view of chemical toxicity.

Automated summary

Uranium mining has significant radiological impacts, especially on water bodies, due to the release of long half-life radionuclides. A study analyzed water samples collected from three liquid effluent release points at an old uranium mine undergoing decommissioning. The results showed that the released effluents met the radiological water quality standards established by various organizations and legislation.