Environmental impact assessment due to the intake of uranium contained in surface waters in a semi-arid region in Brazil.

In Santa Quitéria City, part of the population uses surface water for potation. These waters do not undergo any treatment before consumption. As the region has a deposit of uranium, assessing water quality becomes important. In the present study, the uranium activity concentration (AC) in becquerels per liter was determined in water samples from six points. Univariate statistics showed differences between the soluble and the particulate fraction (soluble AC > particulate AC). The particulate fraction showed no variation in AC among the six points. On the other hand, the soluble fraction and the total fraction presented different ACs between them. The multivariate statistics allowed to separate the soluble from the particulate fraction of the points. The same tools applied to the total fraction made it possible to differentiate the sampling points, grouping them ((#1, #2); (#3, #4), and (#5, #6)). The maximum mean value of AC found was 0.177 Bq∙L-1, corresponding to 25% of the chemical toxicity limit (0.72 Bq∙L-1). The maximum mean dose rate, 2.25 µSv∙year-1, is lower than the considered negligible dose rate (> 10 µSv∙year-1). The excess lifetime cancer risk was 10-6, two orders of magnitude smaller than the threshold considered for taking action. The assessment parameters used in this work indicate that the risk due to the uranium intake by the local population is negligible.

Internal dose rate due to intake of uranium and thorium by fish from a dam reservoir associated with a uranium mine in Brazil.

Uranium mining can cause environmental impacts on non-human biota around mine sites. Because of this, the reduction in non-human biota exposure becomes an important issue. Environmental radioprotection results from the evolution of human radioprotection; it is based on dose rate to non-human biota and uses, as a biological target, and has harmful effects on populations. In the present study, a flooded impoundment created following dam construction in a uranium mine plant undergoing decommissioning was investigated. Internal dose rates due to activity concentration of natural uranium (Unat) and 232Th in omnivorous, phytophagous, and carnivorous fish species were estimated. Radionuclide activity concentrations were obtained by spectrophotometry with arsenazo III in the visible range. The dose rate contribution of 232Th was lower than that of Unat. There were no differences between the internal dose rates to studied fish species due to 232Th, but there were differences for Unat. A dose rate of 2.30·10-2 µGy∙d-1 was found due to the two studied radionuclides. Although this value falls below the benchmark for harmful effects, it is important to acknowledge that the assessment did not account for other critical radionuclides from uranium mining, which also contribute to the internal dose. Moreover, the study did not assess external doses. As a result, the possibility cannot be excluded that dose rates at the study area overcome the established benchmarks for harmful effects.

Evaluation of the radiological quality of water released by a uranium mining in Brazil.

A mine in an area of naturally occurring radioactive materials (NORM), characterized by acid mine drainage, generates effluents with natural radionuclide concentrations, usually above the limits authorized by the regulator. The plant exploiting NORM controls the water quality and discharges it into the aquatic environment after meeting technical requirements. Downstream, water usage is unrestricted. In order to reach activity concentrations in the released effluents below the authorized values, the facility applies a chemical treatment to the effluent. Then, to ensure the effectiveness of the treatment, the facility performs sampling of treated effluent and determines the activity concentration of natural radionuclides (Unat, 226Ra, and 210Pb from the uranium series and 232Th and 228Ra from the thorium series). In the current study, the proportion and distribution of these radionuclides between the soluble and particulate fractions were determined. The measured activity concentrations were compared with the values proposed by the World Health Organization and Brazilian legislation, as well as other authorities, as regards the potable use from the radioprotection point of view. It was observed that the radionuclides are not in secular equilibrium. The fractions contribute differently to the total release of radionuclide, and there is no linear relationship between the fractions. The average activity concentrations did not result in radiological restrictions to water use, and the committed effective dose due to ingestion was estimated at 0.06 mSv y-1. Therefore, there is no radiological restriction to water use, since the dose which was found was below the constraint value for the public.

Assessment of uranium release to the environment from a disabled uranium mine in Brazil.

The Ore Treatment Unit (in Portuguese Unidade de Tratamento de Minérios - UTM) located in Caldas, MG, Brazil is a disabled uranium mine. Environmental conditions generate acid drainage leaching metals and radionuclides from the waste rock pile. This drainage is treated to remove the heavy metals and radionuclides, before allowing the release of the effluent to the environment. To validate the treatment, samples of the released effluents were collected at the interface of the installation with the environment. Sampling was carried out from 2010 to 2015, and the activity concentration (AC, in Bq·l-1) of uranium in the liquid effluent was analyzed by arzenazo UV-Vis spectrophotometry of the soluble and particulate fractions, and of the sum of both fractions. Descriptive statistics, Z test and Pearson R2 correlation among the fractions were performed. Then, the data were organized by year and both ANOVA and Tukey test were carried out to group the means by magnitude of AC. The annual mean ranged from 0.02 Bq·l-1 in 2015 to 0.11 Bq·l-1 in 2010. The soluble fraction showed a higher AC mean when compared to the mean of the particulate fraction and no correlation of the data could be observed. Concerning the magnitude of the release, the ANOVA associated with the Tukey test, identified three groups of annual means (AC2010> AC2011 = AC2012 = AC2013 = AC2014 > AC2015). The mean values of uranium release at the interface installation-environment checking point (point 014) were within the Authorized Annual Limit (AAL) set by the regulator (0.2 Bq·l-1) indicating compliance of treatment with the licensing established for the unit. Finally, the data showed a decreasing tendency of U release.