Abstract: The sediments from Yellow River were collected in 2004. Their heavy metals (Cu, Zn, Pb, Cd, Cr, As, and Hg) concentrations were determined, chemical forms were analyzed with BCR sequential extraction method, and pollution level and ecological risk were evaluated by the methods of geological index (I_geo) and ratio of secondary to protogenic (RSP). The results showed that the overall characteristics of the heavy metals concentrations in the sediments basically accorded with the abundance trend of the heavy metals in the shale at global scale. However, in parts of heavier polluted regions, there existed definite geographical diversity. From the viewpoint of concentration level, the contamination status of the heavy metals was not very serious. The Cu, Zn, Cr and As in the sediments were mainly in residual form, suggesting that they had better environmental stability; while Pb, Hg and Cd were more in highly active form, suggesting that they had greater environmental effects. Pb, Hg and Cd had high ecological risk index, and especially, the potential risk of Pb should be attached more importance to.

Key words: Soil-rice system, Heavy metal, Soil enzyme