[Distribution Characteristics and Risk Assessment of Heavy Metals in the Sediments of the Estuary of the Tributaries in the Three Gorges Reservoir, SW China]

To investigate the pollution status of sediments at the junction of the Three Gorges Reservoir area, sediment samples were collected over four seasons from the junction of the estuary located at a tributary of the Ruxi River and the Yangtze River. The content of eight heavy metals (HMs), including Cr, Zn, Mn, Ni, Cu, As, Cd, and Pb, in sediments was determined by ICP-MS. The results showed the average levels of investigated HMs (in mg·kg^-1) were Cr (45.24), Zn (46.46), Mn (406.14), Ni (20.885), Cu (12.49), As (7.02), Cd (0.253), and Pb (11.042). The distribution analysis indicated that the levels of HMs at the river mouth were higher than that of the tributaries of the middle reaches and the two sections nearby. The seasonal distribution shows that the heavy metal content in the spring sediment is higher than in summer, autumn and winter. In addition, the correlation analysis indicated that the eight HMs possessed similar homologous characteristics and had common exogenous inputs. The assessment of the Geo Accumulation Index showed slight Cd pollution in the estuary of Ruxi River, and the Potential Ecological Risk index showed that Cd presented moderate ecological risks. The toxic effect of benthonic organisms was possibly correlated to Ni contamination at the intersection of the tributary and main stream, which was supported by the evidence from the sediment quality criteria. In conclusion, the rating of ecological risk at the mouth of the Ruxi River tributary is slight.