Solar Radiation Effect on the Complexation Capacity of Aquatic Humic Substances with Metals

Abstract

This study had as main objective to assess the effect of solar radiation on the capacity of the aquatic humic substances (AHS) to complex Al3+, Cr3+, CrO42- and Ni2+. Microcosms were prepared with AHS from Preto River containing 5.0 mg L-1 of dissolved organic carbon and different concentrations of metal species, being exposed to solar radiation, in situ. Conditional stability constants obtained for the AHS-Cr3+, AHS-Ni2+ and AHS-CrO42- complexes were 2.0 x 10(-2), 1.1 x 10(-5) and 2.6 x 10(-2), respectively. The results showed that solar radiation is responsible for decreasing capacity complexation in 15-26% for AHS-Al3+, 15-72% for AHS-Cr3+, 12-18% for AHS-CrO42- and 13-42% for AHS-Ni2+. We can conclude that solar radiation alters metals' availability previously complexed to AHS, making them available in the aquatic body.