Research On The Heavy Metal Pollution And The Sources In Topsoil Around The Power Plant

Atmospheric deposition of the waste emission from fossil fuel combustion is one of the major sources of soil heavy metal pollution.To comprehensively study the situation of the topsoil heavy metal pollution,research on three power stations located in different areas has been conducted in this paper.Soil samples were collected for the test of the pH value,cation exchange capacity and the content of eight heavy metal elements,i.e.Zn,Cu,Pb,Hg,Ni,Cr,Cd,As.Two-dimensional spatial distribution maps of the heavy metal content were plotted.The corresponding pollution degree was evaluated compared to local soil environmental background value and National Soil Environmental Quality Standard Value,and the pollution source was analyzed and predicted.The As content in No.3 power station is slightly lower than the background value,about as 0.9 times.The Hg content in No.1 power station is as 25.4 times as the background value,ranking the first among all the eight elements in the three power stations.The result of One-Sample K-S test shows that Cu and Hg in No.1 power station,Zn and Cd in No.2 power station and Hg in No.3 obey common logarithm normal distribution and the other elements obey standard normal distribution.The results of geo-accumulation index method indicate that Hg is the most serious pollution element among the three power stations.Nemerow index method and pollution load index method evaluate No.1 power station the most seriously comprehensively polluted,with No.2 station being the second and No.3 the least.The regional pollution load index of No.1 power station is 2.8,achieving a strong pollution level with the No.2and No.3 being 1.8 and 1.7 respectively at a medium level.Potential ecological risk index method evaluates Hg and Cd with the most serious risk and Ni and Zn the least.Hg is the most ecologically harmful among the eight elements.The potential ecological risk index of No.1 power station is 1152.92,indicating strong ecological hazard with No.2 being 187.46 and No.3 190.03,medium.Taking the background value and standard value,element content and toxicity coefficient into consideration at the same time,based on the current major comprehensive evaluation theory,a new model was established to evaluate the pollution degree,which was conducted through two paths with weighted mean.Located in the urban area,No.1 power station has the largest pollution index,1.85.No.3 station locates in the rural area with a pollution index of 0.91 and No.3 in the countryside at a level of0.69.The eight elements in No.1 and No.3 power stations are generally significantlycorrelated,both divided into four categories with No.2 less correlated and five categories.Agricultural production,industrial waste emission,road transportation and residents daily activities are all considered to be the pollution source of the eight heavy metal elements,some of which are basically affected by single source while others by a combined effect.