The Environmental Behavior Of Heavy Metals In Wetland Sediments At The Pearl River Estuary

This article studied the heavy metal pollution condition in the sediments of the coastal wetlands at the Pearl River estuary. The total concentrations of heavy metals were extracted by digesting the samples using HC1, HClO₄ and HF. The different geochemical speciations of heavy metals were extracted by Tessier's method of sequential extracting process. The concentration of heavy metals was tested by AAS method. The article analyzed the distribution, source and the factors affecting bioavailability of heavy metals. It also assessed the heavy metal pollution condition by Hakanson's potential ecological risk index method.The study results showed that in the study area the order of heavy metal concentration is as follows: Zn>Ni>Cr>Cu>Pb>Cd. According to the standard of Marine Sediment Quality, the heavy metals contamination is serious except for the element of Pb. The order of the seriousness is Cd>Zn>Cu>Cr. The heavy metals distribution differences between different sampling sites are significant. Due to the hydrodynamic force, heavy metal concentrations increase as the sampling site shifts from low-tide area to high-tide area. The distribution of heavy metals is mainly controlled by clay particles and the direct waste water discharge. The sources of heavy metals are similar except for element Pb.In farmland sampling sites, the significance of chemical forms that are available to plants follows the order of Zn>Pb>Cd>Cr. And that in Qi'ao Island follows an order of Cd>Zn>Pb>Cr>Ni>Cu. The main heavy metal pollutants in Qi'ao Island are Cd, Pb and Zn. Some of the heavy metals concentrations are related to the salinity of the area. The bioavailability is higher in the areas that covered by plantation, and the potential bioavailability and the forms not available to plants are higher in the areas without plantation. Some heavy metals have high bioavailability, that probably because the pollution time is relatively short. Potential Ecological Risk Index assessment result showed that the potential ecological risk is extremely high in the study area and the main pollution element is Cd.