Characteristics and evaluation of heavy metal pollution in soil around coal-fired power plants

According to the National Soil Pollution Status Survey Report, the overall soil environment in China was not optimistic. In some areas, soil pollution was heavy, and the quality of cultivated soil environment was worrying. In order to investigate and evaluate the pollution levels of heavy metals in the soil around the coal-fired power plants, according to the sector layout principle for point sources, the sampling sites were laid out at four different distances around the power plants A and B, with the area far away from the power plants was taken as the control point. A total of 32 soil samples were finally collected. The contents of 12 heavy metals such as Cr, Mn, Ni, Cu, Zn, As, Se, Ag, Cd, Sb, Hg, and Pb were analyzed. The results showed that 8 kinds of heavy metal elements including Mn, Ni, Cu, Zn, As, Se, Ag, and Cd in the soil around the two power plants were higher than the average background value of Anhui Province. The average concentration of Cd in the soil around power plants A and B was 0.230 and 0.172 mg/kg, respectively. Compared with the risk screening values under 6.5Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018), the average concentration was 1.79 and 1.49 times higher than the standard value, respectively, and the maximum over-standard points were located at 500 m downwind of 45° angle to the dominant wind and 500 m downwind of the sub-dominant wind direction. The contents of Cr and Cd in the downwind direction of its perennial dominant wind were higher than that of the control points, and the difference was statistically significant (P was 0.03 and 0.04 respectively). The heavy metal elements of Cr, Cd, Ni, As, Pb and Sb around the power plants had obvious spatial distribution differences, which were consistent with the point source distribution characteristics, while the distribution of other heavy metals was uniform, and the difference was not obvious. The pollution degree of heavy metal elements in the soil around power plant A was severe pollution, while that of power plant B was moderate or light pollution, with Nemerow comprehensive pollution index (PI) being 2.7-5.0 and 1.5-2.4, respectively for plants A and B. The comprehensive potential ecological risk index (RI) of various heavy metals around power plants A and B was 105.0-190.7 and 82.1-139.6, respectively, and the potential ecological risk was moderate or slight. The contribution rate of Cd, Hg and As to RI was large. Comprehensively considering the content and spatial distribution characteristics of heavy metals in the soil around the power plants and the results of correlation analysis and cluster analysis, the heavy metal elements in the soil around power plant A may have been affected by human activities, as the pollution degree and potential ecological risk of heavy metals in the soil were significantly higher than that of power plant B and the control points. The pollution orientation was also multi-faceted, not only limited to the downwind direction. Therefore, in the supervision of coal-fired power plants, comprehensive consideration should be given to their impact of various aspects on the environment, soil and population.