Characteristics of Soil Heavy Metal Pollution and Its Ecological Risk Assessment in South Jining District

Many methods, including single factor index method, Nemero comprehensive index method, potential ecological risk index method and geoaccumulation index method, have been employed to evaluate soil heavy metal pollution. However, no well-developed or standard method has yet been established. Herein, 77 samples of farmland soil in south Jining were collected and analyzed. The results show that average concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn in the samples were 16.7, 0.270, 88.4, 33.0, 0.050, 40.4, 29.3 and 89.1 mg/kg, respectively. The values of Hg and Cd were 1.50 and 1.39 times higher than the benchmark value of the Huang-Huai-Hai Plain and values of other elements were 0.26-0.52 times higher than the benchmark value. All of the samples were evaluated by bivariate correlation analysis method, and the results show that soils are polluted by Hg. The enrichment coefficient method and geoaccumulation method were employed to evaluate the pollution level of 8 elements (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) in the target area soil. Both results show that there was light accumulation of Hg and Cd, while other elements were at normal levels. Combining heavy metal concentration in the selected area, the biotoxicity index of heavy metals, ecological effect and environmental effect, and the potential biological hazard index method were applied to evaluate the biological risk. The results show that the potential hazard sequence is as follows: Hg>Cd>As>Cu>Pb>Ni>Cr>Zn with obvious differences to the accumulation level. Although there was only light accumulation of Hg and Cd, their potential hazards contributed up to 81.26% of the total contribution of potential ecological risk index. The result was schematized by using MapGIS. It showed that about 6.83% of the selected area had the problem of strong or very strong potential ecological risk, and the remainder was at the medium level. Despite the junction of Fuxing River, Yaolou River and Jinghang canal faced the problem of very strong potential biological risk. According to the investigation on the anthropogenic emission sources in the research area, it was found that the risk had positive correlation with coal mining activities. Therefore, taking effective measures to remedy the polluted soil, especially the remediation of the Hg and Cd pollution, will be of great significance to prevent the further deterioration of the soil environment.