A Current Research On Heavy Metal Pollution To The Soil And Rice In The Farmland In Tonglin Mining District

The heavy metal elements pollution has become the main factors that destroy the soil environment of farmlands, and it also endangers human bodies directly or indirectly. Being the main mining cities of China, the city of Tonglin in Anhui Province has been polluted badly. The tailings , slag and smelting of the polymetallic deposits, such as Cu and Au has become an important source of the heavy metal pollution to the soil of the farmland in Tonglin Mining District.This paper is based on many subjects, such as pedology, ecology, environmental geochemistry and so on. Through careful field work and laboratory analysis, we give a systematic analysis in the paper on the current conditions and spatial distribution features of the content and form of the heavy metal in top soil and deep soil in the farmland of Tonglin mining district and do research to the content of the heavy metal in crops (rice) that growing in the soil.In the paper, I use the FIS of the Matlab software for the first time to evaluate the heavy metal pollution to the top soil of the farmland in Tonglin mining district. The result shows that the top soil of the farmland in this area has been polluted by heavy metal for different degrees, and in the coasts of Xinqiao River, Shun'an River and Yang River, some top soil has been polluted badly. This proves that polluted water irrigation has been the main cause of the heavy metal pollution in this area. Different elements cause different degrees of pollution: Cd pollution is the most serious and its average content has reached to 20.21 times of its background values for reference; the next is Cu, it is also up to 4.04 times. And the pollution degrees of the other elements are Pb, As, Zn and Hg in turns.The research on the changes of the heavy metal content of the soil in the mining area in the vertical direction shows that the elements of Hg, Cd, Cu, and Pb enrich evidently in the top soil and the total contents of all the elements in different depths are all above the natural background values in soil. The contents of Hg, Cd, Cu, Pb and Zn show a claw back trend in the vertical direction, and in transverse direction, the contents of these elements also show a claw back trend from the Yang River, Shun'an River and Xinqiao River to all sides. The changes of the contents of As and Cr mainly reflect in the transverse direction. As to the speciation residues of every elements, almost all the elements exist in carbonate species in all depths, except Cd, which mainly exist in ion-exchange above the depth of 90 cm. And the percentages of every pattern change with the depth. The research on rice and the heavy metal content of the soil shows that the main exceeding element in the rice samples is Cd, and the main polluted places are the valleys of Xinqiao River, Shun'an River and Yang River. It is identical to the polluting rules of the corresponding soil. Pb and As in some samples exceed quota, but Hg, Cu, Zn and Cr haven't affected the growing of the crops (rice) till now. The content of the heavy metal in rice is not only related to the contents of each elements in the soil, but also affected by the pH of the soil, the forms of the elements in the soil, the distribution of each elements and other physical and chemical properties. Comparatively speaking, the elements of Zn, Cd and Cu in the soil are more easily to be absorbed by the rice seed, the elements of Pb and Cr are difficult to be absorbed.The turns of the potential ecological risks of each heavy metal elements in the soil of the evaluated district are: Cd〉As〉Cu〉Pb〉Hg〉Cr〉Zn. The high potential district with ecological risk is in the basin of the Xinqiao River (ATI-28, ATI-30, ATI-31, ATII-18, ATII-25) . It agrees with the evaluation results of the soil pollution.Through careful analysis on the correlation of the contents of each heavy metal in the soil of the farmland and correlation between the total content and availability, we can infer that the total contents of each heavy metal are related in high degrees, and this correlation shows the similarity of the polluted degrees of each elements or shows that every polluting elements has a similar source. And in Tonglin mining district, this source mainly refers to polluted water irrigation.