Assessment Of Heavy Metals Pollution In Soil At A Closed Smelting Plant In Tongguan

Nowadays, heavy metal pollution in soil has obtained more and more attention. Due to the disordered mining and smelting, there is a heavy pollution in Tongguan County, which is located in the Xiaoqinling vein. Thus, this study was conducted an assessment of heavy metal pollution based on a closed lead smelting plant-Hengfa Smelting Plant, in the Qindong Town, Tongguan County, Shaanxi Province, where is the intersection of Yellow River and Wei River. In this study, the Single Factor Pollution Index, Potential Ecological Risk Index and Health Risk Assessment Act were used to evaluate the pollution status. The results about this study were as follows:1. In the0～120cm soil, the content of Pb, Cd, As and Ni were higher than the second standard of Environmental quality standard for soils and Cd almost existed in all the samples. With the increase of the sample depth, the content of As and Ni showed little change. Although the average content of Pb was also changing little, the higher content of it showed a significant decreased tendency and its horizontal distribution tended to be uniform.2. Single Factor Index evaluation of heavy metal pollution in soil indicated that in0～120cm soil, the Pi of Cd was higher than1and the over-standard rate was100%; the Pi of As was>1in the57samples; in0-20cm and20～40cm soil, the number of samples whose Pi of Pb, Hg, Zn, Cu and Ni were>1among30samples were8,7,4,8and4, respectively, and the over-standard rate were26.7%、23.3%、13.3%、26.7%and13.3%accordingly.3. The results of potential ecological risk assessment of soil heavy metal pollution showed that:(1) The potential ecological risk assessment of individual metal was that the frequency distribution of more than potential ecological risk of Cd was71.8%, which had strong potential ecological risk; the potential ecological risk of As, Hg, Ni and Cu were lower;93.5%Pb distributed in a slight potential ecological risk,4.4%in the middle potential ecological risk, and2.2%in the strong potential for ecological risk.(2) Soil potential ecological risk index indicated that the range of it was38.9-21129.2and the average value was1684.2. There were39.3%soil samples in a slight ecological risk,16.7%in a middle ecological risk,17.9%in a strong ecological risk, and26.2%in a very strong ecological risk.4. Health risk evaluation of soil heavy metal contamination showed that:(1) In0-20cm soil, the average value of non-carcinogenic risk of Cd, As and Pb was higher than1×10-3, and this value of Hg, Ni, Zn and Cu was lower than1×10-3. For Cd, only one sample’s non-carcinogenic risk value was higher than1×10-3and other samples were lower, which meant that Cd had a higher non-carcinogenic risk. Cd, Pb and As all had a higher non-carcinogenic risk and the order was Pb> Cd> As> Hg> Ni> Cu> Zn.(2)In0-20cm soil, the average value of carcinogenic risk of Cd and As were39.951×10-6and1.384×10-6, respectively. And the maximum and minimum values of carcinogenic risk of Cd were141.093×10-6and0.608×10-6. These values of As were1.716×10-6and1.218×10-6. The carcinogenic risk of Cd and As were in the threshold value of10-6～10-4, which meant they did not show significant carcinogenic risk.