Assessment of stream bottom sediment quality in the vicinity of the caldas uranium mine

Abstract

An assessment of the river sediments quality was carried out in the vicinity of Caldas uranium mine (Minas Gerais State). The objective of this work was to verify if the sediments in water bodies downstream of the mine were impacted by effluents from the waste rock pile #4 (WRP4) and from the tailings Dam (TD). Twelve sampling stations were established: one inside the basin that receives effluents from the WRP4, and another one inside the tank that receives the effluents from TD; the others are located upstream (four) and downstream (six) of the mine. Four sampling campaigns were carried out between 2010 and 2011. The samples were analyzed for metals, metalloids and radionuclides by means of inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma atomic emission spectrometry (ICP-AES ), ultraviolet-visible (UV-Vis) spectroscopy and gamma-ray spectrometry. The results suggest that effluents from WRP4 and TD would be causing increases in concentrations of As, B, Ba, Mn, Mo, Pb, Zn, 238U, 226Ra, 210Pb and 228Ra in the downstream sediments. Considering the classification of sediment quality proposed by the Environmental Company of the State of São Paulo (CETESB), the elements As, Pb and Zn were the most critical from the environmental point of view, responsible for sediments with “REGULAR” and “BAD” quality class. All the radionuclides analyzed showed activities below levels at which harmful effects are expected on organisms living in freshwater sediments. It is recommended that an environmental remediation plan be prepared for areas impacted by the interference caused by the mine.