Accumulation,release potential and spatial variation of heavy metals in urban soils of Hangzhou City.

Total concentrations,chemical fractions and release potential of heavy metals in topsoil samples collected at 82 locations in Hangzhou City were measured to: i) assess their distribution in urban environments;ii) understand their differentiation as related to land use;and iii) assess their environmental risk.Results showed that heavy metals were anthropogenically accumulated in the urban soils to a different extent,about 8.5%,1.2%,3.6%,11.0% and 30.3% of the soil samples had Cd,Cr,Cu,Pb,and Zn concentrations,respectively,above their allowable limits for public and private green areas and residential use.The concentrations of soil heavy metals decreased generally in order of industrial area commercial area scenic area residential area agricultural area.The concentrations of Cu,Pb and Zn of soils in residential sites increased with ages of the residential sites.Most of Cd,Co,Cr,and Ni in the soils were found in residual fractions and soil Cu,Pb and Zn mainly as extractable fractions.Land uses also had significant influence on forms of the metals in the soils.Amounts of the heavy metals dissolved in dilute acid(pH 2.5) increased with decreasing pH in equilibrium solution.Low potential solubility of the heavy metals in the dilute acid was due to their low percentage of acid-extractable fraction of the heavy metals in the soils.Measured data indicated a low environmental health hazards for heavy metals from the urban soils in the Hangzhou City.The high-level polluted soils were mainly distributed in the northwest-southeast orienting areas of the city,which included most of the north,center regions and part of the southeast regions of the city.Industrial and commercial activities were the most important factors affecting accumulation of heavy metals in the soils.