Heavy metal speciation in the surface water dissolved fraction of the low watershed and plume of the Manzanares River, Sucre State, Venezuela

Abstract

 This paper reports on the speciation of heavy metals (Cd, Pb, Cr, Cu, Ni, Mn, Fe, and Zn) in the surface water dissolved fraction of the low basin and plume of the Manzanares River, in the state of Sucre, Venezuela, based on data taken at 22 stations from July 1996 to June 1997. The total metal concentrations in the dissolved phase ranged from below detection levels to 0.01, 0.02, 0.02, 0.10, 0.10, 1.03, 2.56, and 5.13 µmol L^–1 for Cd, Pb, Cr, Cu, Ni, Mn, Fe, and Zn, respectively. Overall, the metals studied revealed a nonconservative behavior with removal at low salinities, likely due to anthropogenic contributions and to flocculation on account of Fe- and Mn-oxyhydroxide formation resulting from the shifts in pH and ion forces that ensue when the fresh waters of the river meet the marine water mass of the Gulf of Cariaco. The heavy metals in the dissolved fraction, in both free and hydrated form, had a composition in which the largest proportions were associated with humic acids, thus being more readily available to organisms.