Concentrations and chemical speciations of Cu, Zn, Pb and Cr of urban soils in Nanjing, China

About 150 soil samples from 20 urban and 3 non-urban soil profiles in Nanjing were analyzed for total concentrations of Cu, Zn, Pb and Cr using ICP spectrometry. The Cu, Zn, Pb and Cr of 23 urban and non-urban topsoils (A horizon soils) were sequentially extracted into 5 fractions according to the method of Tessier [Anal. Chem. 51 (1979) 844]. Total Cu, Zn, Pb and Cr concentrations of the urban soils were 84.7 (48.1-139.7), 66.1 (12.2-869.4), 162.6 (57.7-851.6) and 107.3 (36.3-472.6) mg kg(-1) respectively. The soils were polluted with Cu, Zn and Cr to some extent and heavily polluted with Pb. For 20 urban topsoils, the Cu, Zn, Pb and Cr were dominated by the residual fraction and were least present in exchangeable fraction. On average, the order of Cr, Cu in each fraction was residual (92.9%, 66.1%) much greater than organic (4.2%, 23.4%)>Fe-Mn oxide (2.7%, 5.4%)>carbonate (0.2%, 4.7%)>exchangeable (0.04%, 0.38%), Zn followed the order residual (60.0%)much greater thanFe-Mn oxides (19.1%)>carbonate (11.6%)>organic (8.8%)>exchangeable (0.5%), Pb was residual (56.8%)>Fe-Mn oxide (30.9%)much greater thanorganic (6.3%)>carbonate (5.2%)>exchangeable (0.8%). The percentage of residual Cu and Zn decreased with the increase of total Cu and Zn concentrations. The proportion of residual Pb increased with the increase of total P. The mobility and bioavailability of heavy metals were Pb>Zn>Cu>Cr. Cu, Zn and Pb were more mobile and bioavailable in the urban than in the non-urban soils; however, Cr was similar. (C) 2003 Elsevier Science B.V. All rights reserved.