Soil Contamination Characteristic And Assessment In Suburb Of Taiyuan City

In recent years, with the rapid development of our society and economy, the problem of soil pollution is becoming more and more serious. It is a great threat to agricultural product quality, atmosphere, ecosystems and human health. This paper investigated the pollution situation based on the measured values of soil heavy metals, Organic chlorine pesticides (OCPs) and Polycyclic aromatic hydrocarbons (PAHs) from 171 soil samples collected in suburb area of Taiyuan City in 2013. Firstly, statistical characterization of each pollution index was explored. Then, correlation analysis, single factor index, Nemerow comprehensive pollution index and landscape index were applied to analyze the characteristics of soil heavy metals. At the same time, the composition characteristics of isomers of OCPs and PAHs were analyzed. Comparing the soil organic pollution level of Taiyuan with other regions, Random Forest (RF) model was used to assess the contamination status of soil heavy metals, OCPs, and PAHs and their comprehensive pollution status. The results were as follows:(1) The contents of soil heavy metals were higher than their corresponding background values in Shanxi, while belonged to the secondary level of national soil environmental quality standard. The concentrations of soil PAHs and OCPs were also between the primary and secondary standard values. Soil pollution in Suburb of Taiyuan city wasn’t quite serious.(2) The biggest coefficient of variation among the eight kinds of heavy metal elements was Hg, which reached 1.04. While the smallest coefficient of variation As has reached 0.33, which showed the soil heavy metal contamination was highly spatially heterogeneous in Suburb of Taiyuan.(3) By calculating and analyzing Single factor pollution index and Nemerow pollution index of heavy metals, the pollution of Cd and Hg were more serious, and single factor pollution index reached 2.4 and 4.72, respectively. The average comprehensive pollution index reached 3.59. The soil heavy metal pollution was more serious in Suburb of Taiyuan city.(4) The analysis of the spatial distribution of soil heavy metal pollution by landscape index showed that most of the soil heavy metal pollution belongs to the mild and moderate, and the plaque of different levels has good connectivity and high spatially heterogeneous.(5) Median of total OCPs was 70.43 μg/kg, variation coefficient was 1.05. By analyzing the isomers of OCPs, we found that α-HCH,β-HCH,γ-HCH and δ-HCH accounted for 13.88%,51.95%,11.47% and 14.79% of total HCH respectively.(6) The average of 16 PAHs was 3574.12 μg/kg. The coefficient of variation for each PAHs organic matter above 1, and ANY, ANT and PYR had reached 2.35,2.05 and 2.04 respectively. By analyzing the substance found that carcinogenic compounds accounted for a larger proportion in the total PAHs. The source of PAHs pollution was mainly from the incomplete combustion of fossil fuels.(7) The soil heavy metal pollution assessment results by random forest algorithm showed the samples belonging to grade 1,2,3,4 accounted for 4.68%,87.13%,8.19% and 0% of the 171 samples respectively, which showed soil heavy metal pollution most belong to 2 levels. The Sample number of soil heavy metal, OCPs, PAHs pollution level belongs to 1,2,3,4 respectively were 3,21 and 1,21,8 and 18,6,0 and 2,1,2 and 9.PAHs pollution was more serious in the 31 samples than OCPs and the most serious pollution of OCPs and PAHs was observed in the chemical industry enterprise zone in the West of Taiyuan.