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Abstract
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.
Highlights
In Brazil (Caldas, Minas Gerais State) there is a uranium ore-mining area (Ore Treatment Unit of the Brazilian Nuclear Industries - UTM/INB), the main environmental problem of which is the generation of acid mine drainage (AMD) containing high concentrations of fluoride, sulfate, manganese, zinc, aluminum and uranium
Before being discharged into the environment (Antas reservoir), this uranium mine effluent is treated with slaked lime, contributing to the high hardness values registered in the water samples taken from the Antas reservoir[9,10]
Much attention has been paid to the degradation of aquatic ecosystems downstream from mine sites affected by AMD12–15
Summary
In Brazil (Caldas, Minas Gerais State) there is a uranium ore-mining area (Ore Treatment Unit of the Brazilian Nuclear Industries - UTM/INB), the main environmental problem of which is the generation of acid mine drainage (AMD) containing high concentrations of fluoride, sulfate, manganese, zinc, aluminum and uranium. AMD is frequently observed in mine sites that contain sulfide rocks, being caused by the oxidation of metal sulfides (mainly pyrite) to produce sulfuric acid and discharge metals, with potential toxicity[11] This represents an important source of water quality degradation throughout the world[12], since its continuous release into the environment is related to a severe pollution problem associated with these mining activities. According to Goulet et al.[19], more toxicity studies with water chemistry downstream from U mines and mills are necessary, to support predictive assessment of the impacts of U discharge into the environment In this context, the present study was designed to evaluate the relation between the chemical and ecotoxicological approaches, taking seasonal and spatial samples from the reservoir under the influence of treated effluents coming from the uranium mine and containing AMD. Acute 48 h toxicity tests were carried out with Ceriodaphnia silvestrii and Daphnia magna, to assess possible risks caused by the uranium mine effluents discharged into the tropical freshwater systems
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