The basic properties and heavy metal pollution of urban soils in Nanjing

Samples were collected by selecting different functional zones from Nanjing city. Analysis of physico-chemical properties including soil-forming parent material constituent, structure of profile, pH, soil texture, soil organic matter, the total and extractable heavy metals of the soils were conducted. The results indicated that the source of the parent material of the urban soils is complicated and the profiles were disordered. Compared with soils from conservation zone, the urban soils showed an trend of increasing soil pH, coarse particle contents, soil organic matter. The pollution by heavy metals in the urban soils was dramatic with the industrial zone being the worst. The overall pollution degree, as indicated by the pollution index calculated from the different heavy metal accumulation, is higher for the industrial zone and old residential zone plus the concentrated commercial zones. However, the extractable content of heavy metals seemed no significant variation among the functional zones. Both the soil properties and the content of heavy metals exhibited a very remarkable spatial variability. Some “islands” with extremely polluted soil with heavy metals might exist in some locations with emission impacts. This should be taken into account of the environmental concerns for the urban society.