Distribution. fractionation and mobility of trace elements in stream sediments

The gold and iron mining activities in the Velhas River yield considerable amounts of suspended solids as well as metals to the hydrological system of the region. The risks were assessed by sequential extraction procedures. They were carried out in sediment samples, aiming to evaluate the presence of Co, Cr. Cu, Ni, Zn and As. Although being at high levels in some parts of the river (e.g. As 527 mg g(-1) and Cr 475 mg(-1)) they are associated with the residual fraction. Mobility factors were also calculated and show that these species are enriched along the river, e.g. for As 0.02 at the spring and 0.33 at the high course of the river.