Study On Environmental Geochemical Baseline Of Heavy Metals In Soils Of Taiyuan Basin

On the basis of summarizing and analyzing geochemical data from the project of Multi-purpose Geochemical Survey of Taiyuan Basin, the geochemical baseline of 8 heavy-metal elements Cd, Cr, Hg, Ni, Pb, Zn, As and Cu in the soil of the Taiyuan Basin were researched using standardized method, relative cumulative frequency method, and content-area method (C-A).Accordingly, the Geoaccumulation Index and Contamination Degree Index were adopted for assessing heavy metal pollution degree,and the sources of heavy metals were discussed.First of all, the spatial distribution characters of heavy metals were studied in detail, and the geochemical baselines were calculated by means of standardized method, relative cumulative-frequency method and C-A method. Determined by statistics of C-A method contrasting to other methods, the geochemical baselines of As, Cd, Cr, Cu,Hg, Ni, Pb, and Zn, which were regarded as the evaluating criteria of the heavy metal pollution degree, are 13.02×10-6,0.18×10-6,86.67×10-6,35.68×10-6,0.22×10-6, 38.07×10-6,30.25×10-6, and 88.46×10-6, respectively.Secondly, the pollution status of 8 heavy-metal elements were analyzed using Pollution Degree Index. Most of the surficial soil in Taiyuan Basin suffer no or slight pollution, and the pollution degree index of each element is smaller than 1,other than part over 1,suffering mid-pollution or strong pollution. According to the size of pollution degree index, the order of pollution degree is as follows:Hg> Cd> Zn> Pb> Cu> Cr> As> Ni.The study shows that the most polluted heavy metal elements are Hg and Cd, followed by Zn, Pb, Cu, Cr, etc. The most comprehensive polluted areas are Taiyuan, Fenyang-Xiaoyi zone and its vicinity.Finally, the sources of heavy metals were discussed by associating pollution status, geology and industrial and agricultural situation of the Taiyuan Basin. The natural source of Cd,Hg,Cu,Ni and Zn is mainly the strata in the mountains around the basin,usually Carboniferous System and Permian System. This kind of source has little impact on high contents of soil heavy metals,but the main factor is anthropogenic source. High contents of elements Cr,As,Pb are not related to the strata near the basin, and locally caused by human activities.