Heavy metals in tributaries of Pampulha Reservoir, Minas Gerais.

A great amount of heavy metals enter Pampulha Reservoir via it's main tributaries (Sarandi and Ressaca). Although no water quality classification has been carried out for these tributaries, the reservoir is expected to be in class 2 of the CONAMA-86 system. As part of a monitoring scheme of the Pampulha Watershed, heavy metals (Zn, Pb, Cd, Ni, Cu, Cr, Mn and Fe) were investigated in the water at a control site (considered free from direct human influence) and at potential sites of toxicity and contamination during August (dry season) and November (wet season) of 1998. The results for the first sampling period showed relatively high concentrations of zinc (0.22 mg.L-1) in the upper portion of the reservoir. The highest values of nickel and chromium (0.19 and 0.89 mg.L-1, respectively) were found in the initial portion of the Sarandi Stream, while the highest concentrations of lead (0.05 mg.L-1), cadmium (0.014 mg.L-1), manganese (0.43 mg.L-1) and iron (15.25 mg.L-1) were detected in the Ressaca Stream by the landfill dump of Belo Horizonte. A relatively high concentration of cadmium was also detected at the confluence of the two streams. During the second sampling period, there was an increase in the concentrations of zinc at all sampling sites except the control, with values varying from 0.71 mg.L-1 (the Sarandi Stream) to 2.50 mg.L-1 (the Ressaca Stream). Lead, cadmium, nickel and chromium concentrations were also higher in the Ressaca Stream, but not detected at the other sampling sites. Copper values were higher than in the first period: 0.10 mg.L-1 at the control up to 0.38 mg.L-1 at the confluence of the streams. Similar results were found for manganese and iron, with values reaching up to 19.30 and 125 mg.L-1, respectively. Moreover, all values recorded in the second sampling period were much higher than recommended for class 2 waters. These results emphasize the need for such monitoring in relation to better water quality management of this reservoir.