Radioecological evaluation (spatial and temporal variation) of the planktonic microorganisms in the Antas Reservoir, Caldas, Minas Gerais, Brazil

The Antas Reservoir (AR) receives treated effluents coming from the acid drainage of uranium ore from the Ore Treatment Unit?Brazilian Nuclear Industries (UTM-INB) plant located in Caldas, Minas Gerais, Brazil. This study was conducted in order to determine the possible radioecological impact caused by discharges of the treated liquid effluent from the UTM into the reservoir. Biological and physicochemical variables were evaluated in the present study. Sampling in the AR (Cab, P41, P14S and P14F points) took place during the dry winter (July 2006) and rainy summer seasons (February 2007). Each day, samples were collected four times (6:00 am, 12:00 noon, 6:00 pm and 12:00 midnight). The average trophic state index values obtained for samples in the dry and rainy periods allowed the areas to be classified as oligotrophic and mesotrophic, respectively. Chemical parameters indicated failures in the nuclear facility effluent treatment system, showing that effluents discharged at P41 do not agree with the standards that have been established by the Brazilian current legislation for Class II water. These results agreed with biological analyses, since P41 has the lowest density values for ciliated protozoa, indicating possible environmental impacts on the ecosystem due to the release of effluents by the mining company.