Variation Characteristics and Potential Ecological Risk Assessment of Heavy Metals in the Surface Sediments of Bohai Bay
渤海湾表层沉积物各形态重金属的分布特征与生态风险评价

The geochemical characteristics of eight heavy metals (Cd, Co, Cr, Cu, Ni, Pb, V and Zn) in two sediment cores from Bohai Bay, North China, were studied. Sediment samples were collected from 27 stations in spring 2008.A sequential extractions, procedure was used to gain their fractionation information. Five operationally defined fractions were obtained by this protocol, i.e. exchangeable (L1), bound to carbonates (L2), bound to Fe/Mn-oxides (L3), bound to organic matter and sulphides (L4), and residual fraction (R5). Combined with ecological risk in total contents and fraction, a series of results and viewpoints with regard to distribution characteristics of heavy metals were presented, as well as ecological risk and controlling factors. Heavy metals in sediments were mainly concentrated in the middle region with fine particle. The distributions of V, Ni, Cu, Pb, Co, Cd were mainly controlled by nature source, while Zn and Cr can be easily impacted by environment or human input. Coming from atmospheric deposition and riverine, Pb was different with other heavy metals. Sequential extractions suggested that V, Zn, Cr were mainly composed with residual fractions, while Co, Ni, Cu were dominated by labile fractions. The percentage of labile Co increased from inner to outside, labile Ni reached maximum at station A3, labile Cu and Pb concentrated in the middle of Bohai Bay, while Cu achieved maximum at station D1 near Yellow River. Labile heavy metals were enriched near the estuary of Haihe River. The order of enrichment factors (EF) of heavy metals was Pb>Cd>Zn>Cr>V>Co>Cu>Ni. And the EF of Pb, Cd and Zn were above 1, suggesting that they could be polluted by exterior input, while the sediment quality was relatively good in general. The ratios of labile and residual fraction showed that V and Cr were clean, Zn was partly in slightly polluted, Co was mostly slightly polluted, Cu was from clean to moderately polluted, Ni was polluted from slightly to heavy, and Pb was polluted heaviest in all heavy metal. In conclusion, V, Cr and Co were clean, Cu and Zn may be polluted, while Pb was polluted heaviest.