| Hunan Province is well known for its abundant reserves of non-ferrous metals in China.The quality of agricultural soils,crops, including vegetables and rice,river sediments and river water is significantly affected by long-time mining and smelting activities for non-ferrous metals.In this study,the agricultural soils,vegetables,rice from nonferrous metals mining and smelting areas,sediments and river water in the middle-downstream of the Xiangjiang River were selected in order to study the distribution and environmental behavior of metal elements both in soil-vegetable system from nonferrous metals mining and smelting areas and in river sediment-river water system.The spatial distribution and interaction of extractable metal fractions in soils and transfer of metal elements in soil profiles were studied which is affected by the principal physico-chemical properties of soil,such as pH,organic matter,texture and oxides of iron and aluminum,etc.At the same time, the metal bioavailability,potential risk and migration characteristics of metal in the riverbank sediment profiles were also studied.The results show that the tested soils,vegetables and rice from nonferrous metals mining and smelting areas are mainly contaminated by As,Cd,Cu,Pb and Zn.The concentrations of As,Cd,Pb and Zn in agricultural soils are heavily higher than the Standard of Soil Environmental Quality of China(GradeⅡ)(GB 15618-1995),especially Cd(11.13 mg kg-1),Pb(742.24 mg kg-1) and Zn(966.42 mg kg-1).The average concentrations of Cd(0.37 mg kg-1),Pb(1.42 mg kg-1) and As (0.17 mg kg-1) in vegetables and of Cd(0.46 mg kg-1),Pb(6.04 mg kg-1) and As(0.58 mg kg-1) in rice significantly exceed the Maximum Levels of Contaminants in Foods(GB 2762-2005).The active fractions of Cd in vegetable soils mainly exist in acid-extractable forms,those of As,Cu and Pb mainly exist in reducible forms,and those of Zn mainly exist in acid-extractable and reducible forms.The ratios of total extractable fraction concentrations to the total concentrations of Cd,Cu and Pb in soils are 61.71%,43.14%and 48.84%,respectively.The combined pollution for active As,Cd,Cu,Pb and Zn in soils is significant.The relationships between total extractable concentrations of Cd,Cu and Zn in soils and total concentrations of those in vegetables are significant(P＜0.05).The relationships,which are between acid-extractable concentrations of Cd and of Ca,Cu,Fe and Zn,between those of Pb and of Cu,Zn and Fe,between residual concentrations of As and those of Fe and Mn,between those of Pb and of Fe and Mn in vegetable soils,are also significant(P＜0.05),respectively.The concentrations of extractable Cd is significantly affected by the pH of soil while those of extractable Pb in soils significantly increased with the contents reducing of organic matter and Fe-Al oxides in soil.The precentages of the concentrations of extractable Cd and Pb to those of total Cd and Pb in soil profiles are obviously higher than those of As and Zn in the soil profiles,suggesting the environmental availability of Cd and Pb in soil profiles are significantly higher than those of As and Zn,and have huge potential risk for human health and surrounding environment.The contamination of As,Cd,Pb and Zn in soil profiles from Zhuzhou district and Hengyang district is significantly influenced by the current and histrical sources related with mining and smelting activities.The higher concentrations of As,Cd,Pb and Zn in surface soils are,the stronger leaching of metals in the soil profiles is.The average concentrations of As,Cd and Pb in the river water of the section from Zhuzhou to Changsha slightly exceed the limit of Surface Water Environment Quality Standard(GB 3838-2002).The sediments from the mid-downstream of the Xiangjiang River are mainly concamanted by As,Cd,Pb and Zn.The concentrations of Cd(94.08 mg kg-1),Pb(1520.94 mg kg-1) and Zn(2122.48 mg kg-1) in riverbank sediments,and of As(582.27 mg kg-1),Cd(64.74 mg kg-1),Pb(1056.83 mg kg-1) and Zn(2272.77 mg kg-1) in riverbed sediments completely exceed the Control Standards for Pollutants in Sludge for agricultural use (GB 4284-84) in acidic soil(pH of soil is less than 6.5).The longitudinal distribution pattern of As,Cd,Cr,Cu,Fe,Mn and Zn concentrations in the riverbank sediments display a significantly increasing tendency with the flow from Zhuzhou to Changsha m of the Xiangjiang River,while those of Cd,Cu,Cr,Pb and Zn are stable along the watercourse in riverbed sediments.The fractions of extractable Pb and Zn in the sediments are mainly associated with acid-extractable and reducible forms,and those of extractable Cd are mainly existed in acid-extractable forms.The percentages of extractable Cd,Pb and Zn,including acid-extractable and reducible forms,are high,and vary from 31%to 80%.The potential health risk for the river sediments from the mid-downstream of the Xiangjiang River is mainly by Cd in sediments. The spatial distribution of metal concentrations in the riverbank sediment profiles from the Zhuzhou-Changsha section of the Xiangjiang River shows that the concentrations of As,Cr,Cd,Cu,Pb and Zn at sediment profiles from the downstream are higher than those from the middlestream.The concentration depth profiles of As and Cr have extensively changed,and the concentrations of As and Cr are significantly elevated in the upper zones of the sediment profiles from Xiangtan but slight changes were observed in Pb and Zn.
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