Ecological risk assessment of heavy metals in polluted sediments of sewage river

The object of this paper is to analyze the ecological risk of heavy metals,such as Zn,Cu,Cr,Pb and Ni in the sediments of a sewage river in Tianjin.As we know,heavy metals are often regarded as important parameters that reflect the sediment quality,and,needless to say that the river sediment is an essential component of water environment.The sediment samples were taken and collected from a total of 6 loci of the river from the original source to the downstream,and the concentrations of heavy metals were analyzed by using AAS.Hakanson Potential Ecological Risk Index and Geoaccumulation Index were used to evaluate pollution levels and ecological risk of heavy metals in the sediments.According to the background values of the sediments of Haihe river basin and Luanhe river basin,the results prove that the sediments were severely polluted by the heavy metals.As the result of our investigation,the concentrations of Cu,Zn and Cd turned out much higher than the background values with their major pollution factors reaching the hazard degree.Among the seven heavy metals,the concentration of Zn proves to be the highest(1 061.2 mg/kg) whereas that of Cd was the lowest(4.8mg/kg).The results of our study indicate that the contamination hazards of Cu and Cd are very great in all the six samples after being tested by Igeoand RI index.According to the assessment of the heavy metal contamination hazards,there is a little difference between the two methods.Such difference can be ascribed to different foci and means of calculation in the two evaluating methods,though they seem to be coincided on the whole.And,perhaps,the application of the two evaluation methods are likely to be able to compensate for the disadvantages of each method.In conclusion,heavy metal contamination risk can be well evaluated by Hakanson Potential Ecological Risk Index and Geo-accumulation Index,which can be used to obtain accurate results in assessing the heavy metal pollution risks in a variety of ways.