Present And History Assessment Of Heavy Metal Pollution Of Soils In The Metallic Ore Area And Its Bioavailability Analysis

Domestic and foreign scholars have done a lot of researches on the heavy metal pollution caused by the development of mineral resources, but little researches on historical pollution and the bioavailability of heavy metals in Soil-plant system. The bioavailability of heavy metals is not only affected by the environment, but also affected by the organism itself, involving physical, chemical, and biological as well as other aspects. The research of the bioavailability of heavy metals in Soil-plant system directly reflects the extent of heavy metals pollution and potential hazards of heavy metals on ecosystems and human health, also, can provide a theoretical basis for the remediation of heavy metal contaminated soil and local agricultural production.The Puyu gold mine in the town of Mengyuan of Huayin were selected as the research object in the thesis. The studies consisted of on-site sampling, soil and plant analyses in the laboratory and correlation analysis. By comparing present and history status of the heavy metal pollution, and studying its bioavailability in metal mining, the main conclusions include: Evaluated heavy metals pollution of local soil based on heavy metals content and found that Cu, Zn, Pb, _Cd, Cr has far exceeded the standard in soil. The improved Nemerow pollution index shows that the minimum value is 5.81, the maximum value is up to 72.57 which means the soil is heavily polluted. Through the linear relationship between heavy metals in the tree rings and the corresponding soil, using Years sequence of the average content of Cu, Zn, Pb, _Cd, Cr in tree rings inverse corresponding heavy metal pollution history and time distribution. The bioavailability of heavy metals in this area was studied through the availability forms, geochemical facies, activity coefficient, migration coefficient and transfer coefficient. The availability forms of _Cd has the maximum ratio which is 30.79%, the minimum ratio is Cu which is 1.53%. MF_Cd=0.514,M_Cd=0.28,TF_Cd=0.93,shows that Cd has greatest potential pollution to the environment. MF_Cu=0.034,M_Cu=0.02,TF_Cu=0.015, shows that Cu is the highest stable, which caused the minimum potential harm to the environment. According the correlation analysis of impact factors,it is found that there is obvious antagonism or synergistic effect among heavy metals. There is little influence between heavy Metals of iron-manganese oxides,organic state and residual state. The Physicochemical properties of soil have little influence on the total content and different fractions of Cu. PH, moisture content, clay, total nitrogen, organic matter have direct effects on the total content of Zn, Pb, Cd, Cr, organic state and residual state. The principal component analysis about fourteen impact factors shows that the main controlling factors of heavy metals bioavailability in Soil-plant system are Zn, Pb, _Cd, moisture content, PH, clay, organic matter, total nitrogen and available potassium, which account for 51.945%.