| Contents of heavy metals (Cu, Zn, Pb, Cd, Cr, Hg and As) in agricultural surface soils from Shanghai were analyzed. Different evaluation methods and assessment standards of heavy metals were also used for comparison. In addition, inverse distance interpolation (IDW) method was also applied to study the spatial variability of heavy metals pollution, based on GIS. The results show that mean concentrations of heavy metals in soils all exceeded their corresponding natural-background values, except for As. Compared mean concentrations of heavy metals with the National Standard, the soils were not contaminated. All the determined heavy metals excluding Pb in some regions, however, exceeded the critical values of national soil quality standard. Additionally, it is indicated that most of cropland soils were good, and the ratio of good soil, certified soil and disqualified soil were 71.4%, 94.9% and 5.1%, respectively. Most of the disqualified soils, which distributed in Jiading and Pudong, however, have been urbanized and covered with buildings and factories. Moreover, the soil quality was influenced by different heavy metals at different levels, thus the regional differentiation of soil pollution was obvious. Zn, Cd and Hg were the dominant elements causing soil heavy metal pollution in the study area. Furthermore, it was found there was a close relationship between the urban distribution and heavy metal pollution of the soils. Therefore, it is concluded that with the expanding of urbanization, a new polluted area may appear. |
