Geochemical Mechanism Of Cadmium、Copper And Arsenic Availability In Paddy Soil In The Pearl River Delta

In this paper,191 samples were collected from Pearl River Delta in Guangdong province. The method of GIS spatial analysis was used to study the concentrations and forms of Cd, Cu, As and the physical and chemical properties of soil in this area. The pollution status and spatial variability of heavy metal as well as the spatial relationship between physic-chemical properties of soil in this area was studied. The paper studied the concentrations and forms of heavy metal in different physic-chemical properties soil as well as the influence of heavy metal forms in soil on the concentrations of heavy metal in rice. The results were as follows:(1) All of them exceed the normal levels, especially Cd which was already 2.5 times over background value 0.09. which indicated that the spatial correlation was strong. Respectively 22.51%,21.47% of Cd and As in rice of Pearl River Delta exceed the normal levels, which indicated that a quarter of rice was polluted in this area, the pollution of As could affect by natural conditions and human activity.(2) The spatial distribution characteristics of Cu, Cd, As in soil of Pearl River Delta was that the concentration in river network was higher than the others. The total quantity of Cu, Cd in rice had the same feature. But for As, the distribution in soil and rice was opposite.(3) The physical and chemical properties of soil could affect the heavy metal in soil. the soil organic, pH value and the content clay of soil makes the stable forms of heavy metals content increased.(4) The enrichment coefficient of heavy metal were different, it follows Cd>Cu>As, which indicated Cd was easy to migrate. The results of the different forms of heavy metal extracted in soil indicted that the heavy metal forms which could be extracted by HCl>CaCl2= NaHAOc>DCB were easy to be absorbed by rice.(5) The free and amorphous iron in soil had the ability to promote the absorption of Cu, Cd by different rice organs. Oppositely, the two forms iron would decrease the concentration of As in rice, rice husk and rice straw.