Abstract: Transformation of chemical forms of extrogenous heavy metals in the wetland soil collected from the Pearl River Estuary were studied using laboratory incubation and the Tessier chemical fractionation method to explore effects of salinity on their chemical forms in the soil.Results show that extrogenous heavy metals existed in the wetland soil mainly in available or potentially available form,but after eight months of incubation,very little remained to be in residual form.With increasing loads of heavy metals in the soil,the percentage of residual form decreased,while the percentages of the other four fractions increased.Ni,Zn,Cu,Cr and Pb tended to be bound with Fe-Mn oxides,while Cd to be transformed into exchangeable form or bound into carbonate.Soil salinity did not have much impact on Cu,Zn,Ni and Cr in fractionation,but did on Pb and Cd,particularly their exchangeable forms.Exchangeable forms of Cd and Pb in the soil increased with increasing soil salinity until soil salt reached 80 g·kg^-1.

Key words: extrogenous heavy metal, fraction transformation, salinity, soil, wetland