[Evaluation of the heavy metals contamination and its potential ecological risk of the sediments in Beijiang River's upper and middle reaches].

In order to find out the heavy metals concentrations and their potential ecological risks of the sediments in Beijiang river's upper and middle reaches, 25 sediments specimens were sampled from both the trunk stream and tributaries for analyzing Cu, Pb, Zn, Cd, Ni, Cr, As and Hg. The Index of Geoaccumulation and the Potential Ecological Risk Index were then employed to evaluate the pollution degree of heavy metals in the sediments. The results indicate that the sediments in Beijiang River have been severely contaminated by many heavy metals. The descending order of pollution degree of various metals is: Cd >> Hg > Zn > As > Pb approximately to Cu > Ni > Cr; and similarly the potential ecological risk intensity caused by different metals is: Cd >> Hg > Pb approximately to As > Cu > Zn > Cr, and Cd is the predominant element among them. In general, because the trunk stream receives huge waste discharge, the pollution degree of heavy metals is stronger in the trunk stream than that in the tributaries due to long time accumulation. The Maba River is the worst polluted among the tributaries, and the Zhengshui River and Wongjiang River are next to it.