| This thesis focuses on environmental geochemistry of heavy metal in sewage-irrigated paddy soil in two areas of 4000 acres in Guixi, Jiangxi Province. The author not only analyzed the total concentrations of heavy metals, such as Cu, Zn, Cd, Pb, Cr, Co, Ni, Fe and Mn in paddy soil, but also analyzed the fractions of Cu, Zn, Cd and Pb by the means of sequential extraction. The transformation relation of their fractions is analyzed, which is related to the physical-chemical conditions of paddy soils and the pollution source. At the same time, the author defines the environment geochemical indicators, which are used to distinguish the influence of the human being from that of nature, and suggests the assessment system of potential ecological risk. On the base of above, assessment of heavy metal pollution in paddy soil is made. The main researching results are as follows:1.The concentrations of Cu, Pb and Cd accumulate in topsoil (A layer) in Sumen and Shuiquan. And the activity ratio of all heavy metal elements, Cu, Zn, Cd, and Pb, decrease with increase of the depth of paddy soil profile.2. There are significantly positive co-relations between Cu, Zn, Cd and Pb in paddy soil in Sumen, where the fag ends are the main pollution source, but Shuiquan is not. The cause, which results the Cu, Zn, Cd and Pb not to be co-related, may be the different irrigated water and different irritating modes, which disturbs the co-relation between them.3. The cause that result in obvious differences between Sumen and Shuiquan in the distribution of faction of Cu, Zn, Cd and Pb, especially Zn, is the different pollution source. The former is fag ends and the latter is wastewater. There are obvious differences in the distribution of faction of Cu, Zn, Cd and Pb in the different section of paddy soil profile.4.The concentrations of residue fraction of Cu, Zn, Cd and Pb in A Layer are larger than that of B layer, which demonstrates that the concentrations of the heavy metals of residue fraction of soil polluted by the fag ends and the wastewater from Guixi Copper Ore Melting could not represent these background concentrations of soil.5.The fractions of all these metals of Cu, Zn, Cd and Pb have positive and/or negative co-relation each other in paddy soil in Sumen and Shuiquan, which shows that the fractions can be transformed into each other. There are positive Co-relation between the sum of five fractions of water solution, exchangeable, carbonate, Fe-Mn oxide and org-sulfide fraction of Cu, Zn, Cd and Pb, and their total concentrations respectively, which showed that the total concentrations of Cu, Zn, Cd and Pb control the distributions of their fractions. The fractions, the water solution, exchangeable, carbonate, Fe-Mn oxide and org-sulfide fraction of Cu, Zn, Cd and Pb, have negative Co-relation with their residue fraction respectively.6. The linear regression analysis showes that the concentration of Fe-Mn oxides has significant positive co-relation with the concentrations of Fe-Mn oxide fraction of Cu, Zn and Cd, but there isno relationship between the concentration of Fe-Mn oxide and Pb concentration of the Fe-Mn oxide fraction in the soil, Sumen, and neither between that of the Fe-Mn oxide fraction and concentrations of Cu, Zn ,Pb and Cd in Shuiquan paddy soil.7. The quality of polluted soil is evaluated by three means: Contamination Degree (CD), the Index of Geoaccumalation (Igeo) and the potential ecological Risk Index (RI). The results show that the sewage irrigated soils in Guixi region have been contaminated by heavy metals of Cu, Zn, Cd, Pb and As, but have not been by Cr, Co and Ni, and that the degree of pollution is Sumen> Shuiqui.8.The best evaluation methods in the region are Contamination Degree, which the valuation standard is soil environmental standard and the background, and Potential Ecological Risk Index.
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