Research Of Ecological Risk Assess For Soil Heavy Metal In Taiyuan Sewage Irrigation District

In this paper, the pollution degree of soil heavy metals in Taiyuan sewage irrigation was investigated, collected soil samples include 150 topsoil and 60 section soil samples which layout according to GPS positioning technology and grid distribution. National standard methods (GB/T 17137-17139, GB/T 17138-17139, GB/T 17139-17139, GB/T 17141-1997) have been used to determine the contents of Pb, Zn, Cu, Mn, Ni, Cr, As, Hg.The present polluted degree and the potential ecological risk of heavy metals were evaluated by the Nemerow index and the potential ecological risk index (RI). At last, the grade diagram of heavy metals contents were drawn by using of ARCGIS technical. The results were as followed:According to the determined results of topsoil heavy metals full content, compared with soil background values of Taiyuan, the results of heavy metals content showed that there were no significant difference in the contents of Hg and Ni, oppositely, significantly different (p<0.05) in the content of Zn,and extremely significant different (p<0.001) in the contents of Pb, Cu, Mn, Cr, As, Cd. The normal distribution test results showed, Pb, Cu, Zn, Ni, Mn, Cr, As were agree with normal distribution; the distribution tendency of Hg and Cd were right-skewed.The determined heavy metals enriched in the topsoil (0-20cm), and the enrichment tendency of heavy metals gradually weakened as the depth increased. The statistical test results showed that there were no significant difference in the contents in depth of 20-40cm of Cu, Ni, Mn, As compared with surficial layer soil; very significant different (p<0.01)in the contents of Pb, Cr, Cd extremely significant different (p<0.001)in the contents of Zn and Hg. Because of the different heavy metal characters and soil textures, the vertical distributions were different. The Nemerow index evaluation results showed that the integrated pollution index of 9 kinds of heavy metals was 2.13, the degree of pollution was middle pollution. The ranking order of the heavy metals pollution indexes in different areas was:Jinyuan District (P= 3.01)> Jiancaoping District (P=2.58)> Xiaodian District (P=2.56)> Qingxu County (P =2.04).The ecological risk assessment of heavy metals results showed that, the degree of potential ecological risk of Cu, Pb, Zn, Mn, Cr, Ni, As were slight risk Cd was moderate risk, Hg was stronger risk. The rank of multi-factor potential ecological risk index (RI) was:Jinyuan District (RI=260.9)> Jiancaoping District (RI=235.3)> Xiaodian District (RI=227.6)> Qingxu County (RI=170.9), the degrees of multi-factors potential ecological risk in four districts were moderate hazard.In summary, based on polluted characteristics and variation tendency of heavy metal, in Taiyuan sewage irrigation, the following suggestions of soil were proposed:Xiaodian District and Jinyuan District should be considered as the main repaired region, the main remediation elements are mercury and cadmium, the remediation depth was 0-20cm, adopting mainly chemical methods to improve soil properties, at the same time, combined with the bioremediation by planting crops which have strong tolerance on mercury, cadmium.