The study on the chemical fractionation and bioavailability of heavy metals from non-contaminated and sewage-irrigated soils of Sizhuangding in Xinxiang showed that

total Cd

Ni

Zn

Cu and Cr concentrations of non-contaminated soils achieved the national standard for soils

and sewage-irrigated soil Cr concentration achieved the national standard for soil

while Cd

Zn

Ni and Cu concentrations were over the standard

with the average contents being 65.31

1196.64

2799.25

145.78 mg/kg.The average concentrations of Cd

Zn

Ni and Cu were 65.31

19.94

9.33

1.46 times of national standard for soil

respectively.Sequential extraction rusults showed that

Cd was dominated by iron-manganese oxides fraction

with the percentages being 56.84%.Ni was dominated by iron-manganese oxides fraction and residual bound fraction

with the percentage being 37.44% and 39.55%.Zn was dominated by residual bound fraction

with the percentage being 78.24%.Cu was dominated by organic fraction

with the percentages being 57.70%.Cr was dominated by organic fraction and residual bound fraction

with the percentages being 45.50% and 34.18%.Compared with the non-contaminated irrigation soils

percentage of Cd

Ni

Zn

Cu

Cr residual fractions in the contaminated soils reduced

which could increase the heavy metal mobility and bioavailability.For exchangeable fraction and bioavailability of Cd being higher than Zn

Ni

Cu with the percentages being 24.54%

we should pay attention to the mobility and phyto-toxicity of Cd.