Distribution and Speciation Analysis of Heavy Metal Elements in Urumqi Urban Soils

A selective sequential extraction method developed by Tessier et al was used to study the speciation of heavy metal elements, Cr, Cu, Zn, and Pb, in soils taken from six different functional areas in Urumqi. The results showed that the contents of Pb, Zn, Cr, and Cu were significantly above their average background values, as high as 3.6 times, 2.3 times, 2.1 times, and 1.9 times, respectively. In urban soils, Pb existed mainly as residual fraction and Fe-Mn oxides, accounted for 45.4% and 38.9% totally. Cr and Zn elements were mostly in residual fraction as 94.9% and 52.7%, respectively. In the soil of Industrial Area, Cu element dominated as organic form of 58.2% among the four elements. In other functional areas, Cu contents reached the highest proportion of 71.7% ~ 78.7% in residual fraction. The activity of the heavy metal elements in soil was assessed by the activation of the elements. The activation sequence was obtained as Pb > Zn > Cu > Cr. It indicates that the Pb and Zn contents in Urumqi urban soils have potential ecological risks, and should be in strict control.