| Twenty-seven topsoil samples were collected from kindergartens in Kaifeng City,Henan Province,China.Tessier's sequential extraction procedure was used to extract five (exchangeable,carbonate,Fe-Mn oxides,organic and residual) chemical fractions of soil heavy metals (Pb,Zn,Ni,Cu and Cr).Soil metal concentrations in each fraction were determined by F-AAS (flame atomic absorption spectrophotometer).The pollution,chemical fraction distribution,mobility,bioavailability and potential ecological risks of soil heavy metals were discussed based on the mobility factors (MF) and ecological risk index (RI) presented by Hkanson.The results show as follows: ①Average concentrations of Zn,Cu,Cr,Pb and Ni in urban kindergarten soils were 138.13, 24.08, 132.03, 130.38 and 42.44 mg·kg-1 respectively,and 2.83, 2.27, 1.45, 1.33 and 0.98 times of the control soils respectively,indicating that Zn,Cu,Cr and Pb are the anthropogenic source metals because they enriched in urban kindergarten soils obviously.On the contrary,Ni is a natural source metal. ②There were significant differences between fraction distributions of five heavy metals in different soil samples.Zinc was mainly associated with the Fe-Mn oxides fraction,whereas other metals was predominantly bound to the residual fraction.The exchangeable fraction of the five metals was found to be the least among the chemical fraction distribution in most samples.The average MF value of Pb was the highest with 24.9%,indicating that Pb is the most mobile and bioavailable element among the selected metals.The average MF value of Ni and Zn were 18.4% and 16.4%,suggesting high mobility and bioavailability,while Cr and Cu are stable with the average MF values of 1.0% and 4.8%,respectively.In brief,soil Pb,Ni and Zn are main heavy metals that would have adverse effects on the ecosystem. ③Soil in most kindergartens showed moderate contamination degree and moderate ecological risk level.Lead is the main heavy-metal pollutant and ecological risk metal,because it made a main contribution as high as 56.0% to the contamination and 69.5% to the ecological risk,respectively. ④Ecological hazard of heavy metals was found to correspond with their bioavailability.Correlation analysis showed significantly positive correlation between potential ecological risk and contamination degree of heavy metals (p＜0.01). ⑤To assess potential ecological risk of pollutants,the standards for different levels ofEir and RI must be modified according to the numbers of pollutants studied and their toxic-response factors. |
