Fractionation of heavy metals in sediments from Dianchi Lake, China

Fractionation of heavy metals in sediments can help in understanding potential hazards of heavy metals. The present study analyzed total concentrations and fractions of selected heavy metals (Cd, Cr, Cu, Pb, and Zn) in surface sediments from Dianchi Lake, Yunnan Province, China, as well as factors that may affect distributions of the various heavy metal fractions. Total concentrations of the heavy metals decreased in the order Zn > Cu > Pb > Cr > Cd. These heavy metals except Cr, were much higher than their background levels, indicating that Dianchi Lake was polluted by Cd, Zn, Pb, and Cu. Cadmium occurred mainly as the non-residual fraction (sum of the HOAc-soluble, reducible, and oxidizable fractions) (97.6%), and Zn (55.7%) was also predominantly found in the non-residual fraction. In contrast, most of the Cr (88.5%), Pb (81.8%), and Cu (59.2%) occurred in the residual fraction. Correlation analysis showed that total heavy metal concentrations, organic matter and reducible Fe were the main factors affecting the distributions of the various heavy metal fractions. In the Waihai section of Dianchi Lake (comprising 97% of the lake area), the concentrations of Cd, Zn, Pb, and Cu in the non-residual fraction were significantly lower (P < 0.01 or 0.05) than those of the Caohai section (3% of the lake area). This indicated that potential heavy metal hazards in the Caohai section were greater than the Waihai section.