Spatial distribution and partitioning of heavy metals in surface sediments from Yangtze Estuary and Hangzhou Bay, People's Republic of China.

摘要

Two neighbouring areas, Yangtze estuary and Hangzhou Bay, were investigated to establish the planar distribution patterns and fractionation of heavy metals, viz., Cu, Pb, Zn, Cd, Ni, Cr, MnO and Fe2O3, in the surface sediments. X-ray diffraction analysis showed that the mineralogical compositions of the sediments in both water bodies were similar. The average values of heavy metals in the sediments decreased in the order of Fe > Mn > Zn > Cr > Ni > Cu > Pb > Cd. The concentration of heavy metals decreased from the inner reach to the river mouth of the Yangtze estuary. In Hangzhou Bay, the concentrations of heavy metals were higher in the east than in the west. There were significant positive correlations among all metal concentrations except for Fe-Cr and Fe-Cd, while Cu and Pb were highly correlated with other metals. The distributional patterns of the 8 metals were divided into two groups according to the degree of their association with the residual fraction. Cu, Cr, Zn, Fe and Ni were assigned to a group that were mainly found in the residual fraction, while Cd, Pb and Mn were in a group with their residual fraction less than 50% of the total levels. The percentages of five fractions for Cu, Fe, Ni and Zn in the sediments followed the order as residual > Fe-Mn oxides > organic > carbonate > exchangeable, while those of Cr followed the order as residual > organic > Fe-Mn oxides > carbonate > exchangeable. A considerable proportion of Cd and Mn were found in all of the five fractions, while Pb was not detected in the exchangeable fraction. In the non-residual fraction, Cd was mainly presented in exchangeable, carbonate fraction and Fe-Mn oxides while Pb was mainly retained in Fe-Mn oxides fraction. Mn was mainly dominated in carbonate and Fe-Mn oxides. Among the five fractions, the heavy metals in exchangeable and carbonate fractions can be easily remobilized by changes in environmental conditions. The results derived from the study indicate that the study area had Cd and Mn pollution risks..