The water quality of the Antas reservoir, under the influence of treated effluents from a uranium mining area Ore Treatment Unit (UTM) with acid mine drainage, was investigated. Samples were collected every 3 months from the Antas reservoir (CAB, P41-E and P14) and from the UTM (P41-S). Chemical and acute 48 h toxicity tests using Ceriodaphnia silvestrii and Daphnia magna analyses were carried out to determine the potential environmental risks due to discharging the uranium mine effluents into this reservoir. All the water samples taken from the treated effluent (P41-S) were positively correlated with elevated concentrations of uranium, manganese, aluminum, zinc and fluoride and with high electrical conductivity and pH values, being considered toxic. In November 2014 water samples taken from the reservoir showed chemical concentrations above the legislation limits for fluoride (4.5 mg L−1) uranium (0.082 mg L−1), sulfate (662.4 mg L−1), manganese (1.125 mg L−1) and aluminum (1.55 mg L−1), and in July 2015 for fluoride (2.55 mg L−1), uranium (0.01 mg L−1) and manganese (0.36 mg L−1). The extremely high average value for hardness (543.55 mg L−1) possibly reduced the toxicity potential of this chemical species mixture with respect to the bioindicators. The influence of the variation in water hardness on the toxicity of the cladocerans was discussed.

The first uranium mine that had its deposit explored in Brazil is located in the region of the Poços de Caldas Plateau (Minas Gerais) and currently, mining activities no longer take place there. Still, a serious environmental problem occurs at the site: acid mine drainage. An alternative to monitor such environments is through the analysis of the microalgae community, as this can provide information about species with biotechnological potential for remediation actions. In the present study, an analysis of the composition of the microalgae community found in the UDC/INB uranium mine pit (point CM) and in the Antas Reservoir (point 14) was carried out, and a comparison was made between these points in order to identify the present species that play important roles in the biotechnology area. The expected result was to find a much lower microalgae diversity in CM than in P14. However, the results were very similar: in both sampling sites, a taxonomically diverse microalgae flora was found, dominated by the Bacillariophyceae and Chlorophyceae classes. In addition, at both sites, microalgae were recorded which are widely used in biotechnological processes of environmental remediation, removal of contaminants from wastewater, production of biofuels, pigments, medicines, among others, showing that the use of microalgae for various purposes is a very promising and environmentally sustainable path.