| With the acceleration of urbanization and industrialization,humans have released more and more heavy metal elements into the environment,which leads to continuous declines of soil environmental quality.As a new emerging steel industry city in Gansu Province,Jiayuguan City is rich in energy resources and has more heavy industry distribution,so the soil is seriously polluted by heavy metals.Studying the distribution of heavy metals in the soil has important scientific significance for the local ecological,social and economic development.First of all,the spatial distribution of heavy metal elements is studied.Collected126 surface soil samples and 46 soil samples from 5 profiles covering four functional areas: industrial area,agricultural area,human living area and Gobi.The contents of heavy metals Cd,Cr,Cu,Ni,Pb,and Zn in soil were determined by inductively coupled plasma mass spectrometry(ICP?MS)in this study.The average contents of heavy metals in topsoil were: 0.19 mg/kg,319.44 mg / kg,30.82 mg/kg,44.00 mg/kg,31.88 mg/kg,111.53 mg/kg.The spatial distribution of each heavy metal is very uneven.The sampling points of high soil heavy metal content in the top soil are mainly distributed in Jiabei Industrial Area,Gobi heavy metal content is higher than that in agricultural areas,the distribution of the Gobi heavy metal is greatly affected by the wind direction.The soil heavy metal content in the profile has an obvious law of decreasing with increasing depth.It is mainly concentrated in the shallow soil within 20 cm.Element migration mainly occurs in the surface soil of 0-10 cm and can migrate down to the depth of 30 cm.Secondly,the enrichment degree of surface soil was evaluated by Nemerow index method and geo-accumulation index method.The Nemero Index showed that6% soil samples in Jiayuguan City were polluted by heavy metal,Cr is heavily enriched.The order of enrichment of the elements shown by Nemerow index is:Cr>Zn>Cd>Ni>Pb>Cu.Geoaccumulation index shows that 60% of the samples haveat least one element meets or exceeds slight enrichment.6% of the samples have Cr content that meets or exceeds strong enrichment.The order of enrichment of each element shown by geoaccumulation index is: Cr>Cd>Pb>Zn>Cu>Ni.The rankings of heavy metal enrichment in each functional area by the two evaluation methods are:industrial area> living area> Gobi> agricultural area.Third,the chemical forms of soil heavy metals and the soil particle size and magnetic susceptibility were analyzed.According to the morphological analysis of heavy metals,Cr is not very mobile in the soil;Although the concentration of Ni element in Jiayuguan City is low,it has a certain degree of mobility in soil;Cd elements are relatively abundant in the soil,and are very easy to migrate.The particle size and magnetic sensitivity of the top soil were measured.The relationship between heavy metal content and particle size and magnetic susceptibility was analyzed,the results show that soil heavy metals are most easily concentrated in clay,followed by silt.There is a significant positive correlation between soil heavy metal content and magnetic susceptibility.Therefore,the concentration of heavy metals in the soil can be estimated by the index of magnetic susceptibility.Finally,the sources of major heavy metals were estimated by principal component analysis and element ratio.The results show that the heavy metals in the soil of Jiayuguan City are main anthropogenic sources.The element ratio method shows that the Cd in industrial and living areas is likely to be directly polluted by Cd-containing waste residues,while the Cd in agricultural areas and Gobi sampling points is mainly comes from atmospheric deposition in industrial areas.The principal component analysis showed that the sources of heavy metals in Jiayuguan were industrial production pollution sources mainly in the building materials industry sector,the steel industry sector,and traffic pollution sources. |
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