(0–10 cm) of reclaimed farmland are listed in Table 2. The average
heavy metal concentrations in seven vertical soil profiles are
presented in Fig. 1. The concentrations of heavy metals both in
surface soils and in vertical profile soils are in the same order
as Zn > Cr > Cu > Pb > Ni > Cd. The absolute deviations for Zn concentrations
in vertical soil profiles are high because of higher
concentration. However, the coefficients of variation for Zn concentrations
are similar to the other metals. The chemical speciation of
heavy metals in the selected surface soil samples of reclaimed farmland
is presented in Fig. 2. The predominant chemical partitioning
of six metals is residual fraction. The percentages of exchangeable
fraction of Cd and Pb are significantly higher than those of
Cu, Cr, Ni, and Zn, implying that Cd and Pb are more mobile and
phytoavailable.
Almost all heavy metal concentrations in all the soil samples are
higher than their background values of soil in Guangdong province
[20]. According to the Chinese farmland environmental quality
evaluation standard for edible agricultural products [21], reclaimed
farmland soil is contaminated with heavy metals significantly. The
pollution of Cd is the most serious. The percentages of samples that
exceeded the standard are in the order of Cd > Cu > Ni > Pb > Zn > Cr.