The Study On Heavy Metal Pollution Of Baogang Tailings Dam

Soil is an important component of ecological environment, and it is also one of important natural resources for the subsistence and development of mankind. Heavy metal pollution of the soil becomes more and more serious due to the development of industrialization and municipal pollution. The soil fertility and crop yields and quality are decreased because of the heavy metal in soil. Most of all, it not only deteriorates the environment, but also endangers human life and health through food chain.In this work, the soil around Baogang Group Tailing Dam was studied. The characteristics of its combined pollution of heavy metals were examined and evaluated. The results indicate that the heavy metal pollution degree varies in Baogang Group Tailing Dam and its neighboring regions. It also shows the latent ecological risk indexes from high to low can be seen as followings: Pb, As, Cu, Cr, Zn. Among them, the pollution risk index of Pb is the highest and then As. At the same time, the soil samples in Baogang Group Tailing Dam and its neighboring regions have the possibility of ecological risks.Different chemical forms of the same element have different activities. They largely determine the elements of mobility, bioavailability and toxicity. Tessier morphology analysis was used in this study to analyze the element form of heavy metals in the soil of tailing dams, which have high potential ecological risk in Baogang Group. The results show that the Zn²⁺ mainly is distributed in sulfide and organic combination patterns in the sample, which accounts for 50% of the total and the exchangeable state accounts for about 25%. Pb²⁺ is mainly distributed in the exchangeable state, which accounts for about 50% of the total and this form can be utilized by living beings directly, so it has harm potentially. Besides, an investigation of heavy metal pollution on tailing dam was carried out with the method of bioleaching. The leaching results demonstrate the highest leaching rate is Zn²⁺ followed by Cu²⁺ and Pb²⁺ and the leaching rate is about 55%, 41% and 5.9%, respectively. Compared with adding soil sample in the logarithmic period of the bacteria, the leaching effect of adding soil sample in the early growth of the bacteria is a little bit better.The maximum tolerated concentrations of Acidithiobacillus ferrooxidans on metal Zn²⁺, Cd²⁺, Pb²⁺ were investigated. They were 750mmol/L, 35mmol/L and 10mmol/L, respectively. Compared with the tolerance concentration of Escherichia coli, this tolerance concentration was 750 times,175 times and twice respectively. Therefore, the mechanism of its resistance to heavy metals was prompted to be explored. An interesting protein── Cd(â…¡)-Pb(â…¡)-responsive transcriptional regulator (CmtR)was obtained. The gene CmtR from A. ferrooxidans was cloned and expressed in E. coli. The soluble protein was purified by one-step affinity chromatography to apparent homogeneity. Cadmium binding to apo-CmtR by measuring changes in the absorption spectrum was directly monitored in the ultraviolet, which showed formation of the Cd(â…¡)-CmtR complex resulted in a single strong absorption envelope with a maximum absorption at ca. 240-280 nm. The sequence alignment and molecular modeling show the crucial residues for cadmium binding may be Cys53, Cys77, Cys112, Cys121.