Distribution of Heavy Metals in Soils of Fast-Urbanizing Regions—With Kunshan as a Case Study

Distribution characteristics of heavy metals in soils of fast-urbanizing regions are discussed with Kunshan as a case for study.Results indicate that with the upper limits of the background values as indices for evaluation,about 25%,24%,22%,21%,18%,18%,14% and 4% of the 100 soil samples collected from farmland in Kunshan were exceeding the upper limit of soil content of Zn,Cu,Pb,Hg,As,Cd,Cr and Ni,respectively,suggesting external contaminants are entering the fields.According to norms of Grade Ⅱ of GB 156181995 "Standard for Soil Environment Quality",about 5%,（4%,）3% and 2% of the soil samples exceeded the limits of soil contents of Hg,Cd,Cr（dry land） and Zn,respectively.The maximum Cd content in the soil samples even reached up to 5.74 mg·kg^-1.Correlations between heavy metals varied with the soil parent material.It is held that for control of soil pollution, it is essential to give priority to prevention rather than remediation.At the same time,pollution control should be intensified in areas heavy with Cd and Hg point pollution sources,and measures taken to remediate the polluted soil.