Toxicity assessment of an effluent derived from an inactivated uranium mine: the Poços de Caldas (Brazil) example

Uranium mines can cause environmental impact because of acid mine drainages can reaches the surrounding water bodies. In this work we tested effluent samples from an inactivated uranium mine located in Pocos de Caldas city (Minas Gerais, Brazil) for acute and chronic toxicity. Untreated effluents were acutely toxic to Daphnia similis, with EC50 (48 h) varying from <0.01% to 38%. Both treated and untreated effluent samples presented chronic toxicity to Ceriodaphnia dubia. Vibrio fischeri acute toxicity tests were negative for all tested samples. Adjustment of pH performed in samples was not sufficient to remove acute toxicity indicating that not only pH was responsible for the observed effect. The physical-chemical treatment applied was not able to remove the chronic toxicity to C. dubia. V. fischeri, although a rapid test and easy to handle, was not sensitive to the level of toxicants present in the effluent from the mine. To determine the actual impact of the discharge of effluent into receiving waters, both the flow of the effluent and river should be considered. Nevertheless chronic toxicity tests with C. dubia could be included in the monitoring program of this facility to provide more information about the impact of this discharge.