Distribution and pollution assessment of heavy metals in surface sediments in the central Bohai Sea, China: a case study

The Bohai Sea is a semi-enclosed sea affected by intense industrial and maritime activities which may lead to heavy metal contamination. The major objective of this study was to reveal the distribution, and assess the potential risk of heavy metals in the sediments of the central Bohai Sea (CBS). Eight metals (Pb, Cd, Cu, Fe, Ni, Mn, Zn, and Co) in sediments obtained at 29 sites in summer and winter, 2011 were analyzed by inductively coupled plasma-mass spectrometry. The pollution assessments were carried out with three methods including marine sediment quality, the geoaccumulation index and Hakanson potential ecological risk index. Results showed that higher concentrations of heavy metals (except for Mn) were generally found in the northwest of the CBS, near the Luanhe Estuary, and higher concentrations of Mn were found in the north of the CBS. The distribution of heavy metals was mainly affected by contents of total organic carbon and clay percentage in sediment. In terms of pollution assessment, Cd was the major pollutant in the CBS. The CBS was moderately contaminated in summer and uncontaminated in winter. The most contaminated zone was near the Luanhe Estuary, and anthropogenic sources from the Luanhe Estuary might be the main contributor. The results of three assessment methods were similar. Hakanson potential ecological risk index is more useful for the risk assessment of trace metals as it considers both potential ecological risks and biological effects. The combination of several pollution assessment methods is suggested in practice to obtain comprehensive and accurate results.