| Sulfides in the mine tailings are oxidized easily by air,water and microorganisms,to form the acid mine drainage（AMD）with considerable level of heavy metals.The AMD then flows into rivers and lakes,resultes in the acidification and potential heavy metal pollution of waters.In this study,surface sediments were collected from rivers of Shicao and Huangtun around the Zhongshan iron tailing,at Lujiang County,Anhui Province.The grain size,moisture content,total heavy metals of Mn,Ni,Cu,Zn,Pb,and Cd and their various chemical forms based on BCR extraction in sediments were analysed in order to study the heavy metals distribution and evaluate the level of pollution and ecological and health risks by using multi-methods.The results and conclusions listed as follows.The water in Shicao and Huangtun rivers is generally acidic,with the pH ranges of2.70-6.94 and 2.24-7.43,respectively.The grain compositions of sediments in Shicao and Huangtun were mainly of the powder-sand.The moisture content of the sediments in Shicao river was 38.97%-92.92%,with an average of 63.16%,while that of Huangtun river was43.08%-77.38%,with an average of 62.74%.The total Cu,Cd,Zn and Pb in the sediments of Shicao and Huangtun rivers exceeded the background values of the Yangtze River systems.The main chemical form of Ni,Zn and Pb is their residual fraction with little environmental harm.The mian form of Cu is its oxidable fraction,while that of Mn and Cd was the reduced and residual fraction;all of Cu,Mn and Cd in the river sediments in our study have high potential risks.In contrast to the high level of heavy metals in river sediments affected by AMD in Tongling city,those of Lujiang are relative low due to the low-level heavy metals in the mine tailings.The result of the indexes of geoaccumulation of Shicao river sediments indicated a pollution level of moderate,partial moderate and mild for Cu,Cd and Zn,respectively;For Huangtun river sediments,the pollution level of both Cd and Pb was mild.The results of the secondary phase versus primary value method indicated the level of serious pollution for Cu and Cd in these two rivers.The analyses of the potential ecological risk indicated a strong level for Cd,a medium level for Cu,and a slight level for other metals.The RAC risk indexes in Shicao river sediments indicated a level of low risk and risk-free for Ni,Cu,Zn and Pb;and a level of medium risk for Mn and Cd,which should be concerned.The RAC index of Pb in Huangtun river sediments below 1%indicated a level of risk-free;while that of Mn,Ni,Cu,Zn and Cd indicated a level of moderate risk.The HQ and HI indices from health risk assessment of the heavy metals in two river sediments were less than 1.0,indicated the non-carcinogenic health risk was negligible.The total cancer risk indexes of Ni and Pb in the two river sediments was less than 10-6 with no risk;while that of Cd indicated a tolerated cancer risk and should be concerned. |
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