POLLUTION OF HEAVY METALS IN THE SEDIMENTS FROM RIVER AND ITS POTENTIAL ECOLOGICAL RISK ASSESSMENT--FOCUS ON THE TIANSHA RIVER OF THE PEARL RIVER DELTA REGION

The surface sediments from the Tiansha River were sampled and the contents of six heavy metals including Cr,Ni,Cu,Zn,Cd and Pb were measured.The pollution characteristics and ecological risk of heavy metals sediments containing were respectively evaluated by means of Nemerow index,geo-accumulation index,Hakanson's ecological risk index and Sediment Quality Guidelines(SQGs) for freshwater ecosystem.Meanwhile,the comparison of the evaluation methodology was fulfilled.The results showed that the characteristics of heavy metal pollution evaluated by Nemerow index and Hakanson's ecological risk index reached agreement to each sampling site.The pollution of Duruan,Baisha River basin and the upper reaches of the Tiansha River was more serious than that of the middle and down reaches of the Tiansha River.Besides,the evaluation on pollution risk of each heavy metal acquired general consistence by geo-accumulation index and Hakanson's ecological risk index.Cd and Cu possessed the highest risks,followed by Zn,Ni,Pb,Cr.The consequences deduced by SQGs assessment showed slight differences compared with other approaches,mainly because SQGs index was more susceptible to biotoxicity,and other methods focused on pollution effect of single heavy metal or comprehensive pollution effect of various heavy metal.