Heavy metal fractionation in sediments from the Tinto River (Spain)

Seventeen sediment samples from the Tinto and its main tributaries were analyzed for this study. For each of these samples, the association of metals (Cu, Zn, Cd, Pb, Fe, Ni, Cr and Co) was determined in four fractions: acid soluble, reducible, oxidizable and residual. The total metal content was also determined. Results showed high mean concentrations of Fe (109,000 mg/kg), Pb (2330 mg/kg), Zn (901 mg/kg), Cu. (805mg/kg), and Cd (2.7 mg/kg) in the sediments studied. However, the mean values found for Co (21 mg/kg), Cr (56 mg/kg) and Ni (17 mg/kg) are comparable to those in unpolluted areas. Heavy metal fractionation of the Tinto River sediments showed that the metals with the greatest mobility (i.e., metals that could pass easily into the water under changing environmental conditions) are Cd and Zn. These are the metals that showed the highest percentages in the first two fractions (the most labile) and the lowest percentages in the residual fraction. However, the percentage of metal present in the fourth fraction (residual) was high for Cr (78%), Ni (71%), and Co (66%), which implies that these metals are strongly linked to the sediments.