Trace elements: water-sediment interactions in tropical rivers.

This research aimed to determine the water-sediment interaction (partition coefficient Kd) of trace element (Cd, Cu, total Cr, Pb, and Zn) in tropical rivers of the Upper Paraná River basin, Central Brazil. Three trace elements (Cu, total Cr, and Zn) presented quantifiable concentration values in the water and sediment. Neither the element trace considered nor the rivers displayed a similar water-sediment interaction. The evaluation of Kd values indicates the tendency of total Cr to be adsorbed into the sediment (min Kd = 6.244, max Kd = 131.389), mainly in one sampling station (São Francisco River, Kd = 131.389) and the availability of Zn in the water column in all sampling stations (min Kd = 0.234, max Kd = 1.289). The sediment concentrations of Cr in the São Francisco sampling station (0.118 mg L-1) are above international reference values suggesting a risk of contamination for the biota, whereas in four rivers, Cr concentrations represent a risk. The water-sediment interaction of Cu is influenced by water temperature, whereas the pH influenced the Zn interaction.