| Hunan Province is well known for its abundant reserves of non-ferrous metals in China. The quality of flood plain soils and vegetables is significantly affected by long-time mining and smelting activities for non-ferrous metals. In this study, the flood plain soils and vegetables from the Changsha section of the Xiangjiang River were selected in order to study the environmental behavior and environmental risk of metal elements in soil-vegetable system. The principal physico-chemical properties of soil, such as pH, organic matter,were studied. At the same time,the potential ecological risk of the metal health risk of the vegetables were also studied.The results show that the tested soils from flood plain areas are mainly contaminated by Cu, Cd, Pb, Zn, As and Hg. The concentrations of Cd, Zn, As and Hg in flood plain soils are heavily higher than the Standard of Soil Environmental Quality of China(Grade Ⅱ)(GB15618-1995), and the content of Cd(12.87mg/kg) and Zn(431.21mg/kg) are43and2.16times of China Environmental Quality Standard for Soils(GB15618-1995,Grade Ⅱ), respectively. There are about100%of Cd,94.44%of Zn,100%of Hg and75%of As in all the collected soil samples from the investigated sites which have overran the contents for heavy metal of China Environmental Quality Standard for Soils(GB15618-1995,Grade Ⅱ). The soil heavy metals pollution index has already reached dangerous level and heavy metals contamination could be devided into four groups:negligible contamination,which is the case for Cu and Pb; low contamination, which is the case for As and Hg; moderate contamination, which is the case for Zn; and certain to severe contamination, which is the case for Cd, suggesting that the pollution characteristics of multi-metals in soils are mainly reflected by Cd. There are significantly positive correlations between the concentrations of Cd, Pb, Zn, Hg and Cu in soils, however only Zn had significant positive correlations with As. Principal component analysis demonstrated that Cu, Cd, Pb, Zn and Hg derived from non-ferrous metal mining and metallurgy, discharge of industrial wastewate and automobile exhaust, but Zn and As came from agricultural contamination.The active fractions of Cu in flood plain soils mainly exist in reducible and oxidizable forms, those Cd mainly exist in acid-extractable and reducible forms, and those of Pb mainly exist in reducible and residual forms.The ratios of total extractable fraction concentrations to the total concentrations of Cd, Cu, Zn and Pb are relatively high, but only Cd possessed higher mobility which indicated that Cd showed relatively higher potential risk. The modified potential ecological risk coefficients of heavy metal show that the risks are in the decreasing order of Cd>Pb>Cu>Zn. The overall risk indexes caused by the four toxic heavy metals were all far beyond1200, indicating very high ecological risk to the environment. Cd is the priority pollutant in the flood plain soils, and Cd contributed most (average98.21%) of the total overall ecological risk.The vegetables from flood plain areas are mainly contaminated by Cd and Zn and Chinese Cabbage is seriously contaminated by heavy metals. The average concentrations of Cd(0.78mg/kg) and Zn(20.23mg/kg) in Chinese Cabbage significantly exceed the Maximum Levels of Contaminants in Foods(GB2762-2005). The health risk values of vegetables in the flood plain areas exceeded the maximum acceptable levels set by US EPA. The health risk caused by Chinese Cabbage is far higher than the other three kinds of vegetables and the carcinogen risks of Cd is5to6orders of magnitude biger than the other three heavy metals. Therefore the pollution of Cd should be firstly taken into consideration of prevention in the flood plain. It is very necessary to focus on potential ecological risk and health risk of heavy metals for food safety and human’s health in flood plain soils and vegetables in the Changsha section of Xiangiiang River, Hunan Province of China. |
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