Seventeen classic organochlorine pesticides in surface seawater were studied in terms of their composition pattern as well as their distribution pattern in the areas covering the Japan Sea, Okhotsk Sea, Bering Sea, Chukchi Sea and Arctic Ocean. Their concentrations varied, but roughly two levels were seen with one ranging between 0.1 and 1 ng L-1 for most HCH isomers and the other lower than 0.1 ng L-1 for other chemicals. Of the 17 target compounds, HCHs were dominant with a total concentration percentage generally more than 50%, and a relatively high concentration percentage of heptachlor and aldrine was also observed at scattered stations. The historical long-term trend of several target chemicals in the five sea zones considered was discussed in comparison with previous reports. Inter-sea zone comparison was carried out for individual chemicals by comparing the concentration variation in all five sea zones. A higher variation in concentration was generally found in the northern sea zones, namely the Bering Sea, Chukchi Sea and Arctic Ocean, for most target compounds. The sum concentration of the 17 target chemicals displayed a general trend of increasing northward from the Japan Sea to the Okhotsk Sea to the Bering Sea to the Arctic Ocean. Different latitudinal trends were found for alpha-HCH and gamma-HCH, and the reason of this difference was discussed by considering their divergence of thermodynamic properties, which could contribute to a slightly different fractionation effect during their northward transport driven by atmospheric long range transport. The source of the HCHs was identified by analyzing the alpha-HCH/gamma-HCH ratio, which was less than 4 without exception, indicating a component characteristic featuring a mixture of technical HCHs and lindane. In addition, the vertical distribution of alpha-HCH, gamma-HCH and their ratio at station B80 was discussed. Different patterns were found in the upper 300 m while in layers from 300 m downward to 3500 m the patterns were fairly comparable. The vertical profiles were used to correlate the water mass distribution, based on which four layers were tentatively classified at station B80.National Natural Science Foundation of China [40776040, 40306012, 40776003]; National High Technology Research and Development Program of China [2007AA09Z121]; Ocean Public Welfare Scientific Research Project ; State Oceanic Administration of China [200805095]; Fujian Provincial Department of Science Technology [2005Y021]; Chinese Arctic and Antarctic Administration, State Oceanic Administration of Chin

The Beibu Gulf (also named the Gulf of Tonkin), located in the northwest of the South China Sea, is representative of a bay suffering from turbulence and contamination associated with rapid industrialization and urbanization. In this study, we aim to provide the novel baseline levels of heavy metals for the research area. Concentrations of five heavy metals (i.e., Cu, Pb, Zn, Cd and Cr) were determined in surface sediments from 35 sites in the eastern Beibu Gulf. The heavy metal content varied from 6.72 to 25.95 mg/kg for Cu, 16.99 to 57.98 mg/kg for Pb, 73.15 to 112.25 mg/kg for Zn, 0.03 to 0.12 mg/kg for Cd, and 20.69 to 56.47 mg/kg for Cr, respectively. With respect to the Chinese sediment quality criteria, sediments in the eastern Beibu Gulf have not been significantly affected by coastal metal pollutions. The results deduced from the geoaccumulation index (Igeo) showed that the study area has been slightly polluted by Pb, which might be caused by non-point sources. Relatively high concentrations of Cu, Pb and Cd were found around the coastal areas of Guangxi province, the Leizhou Peninsula and the northwest coast of Hainan Island, whereas the highest concentrations of Zn and Cr were found on the northwest coast of Hainan Island. Spatial distribution patterns of the heavy metals showed that bioavailable fractions of Pb were higher than in the residual fractions, while Cu and Cd concentrations in exchangeable and carbonate fractions were relatively higher than those in the bioavailable fractions. Hierarchical clustering analysis suggested that the sampling stations could be separated into three groups with different geographical distributions. Accompanying their similar spatial distribution in the study area, significant correlation coefficients among Cu, Cd and Pb were also found, indicating that these three metals might have had similar sources. Overall, the results indicated that the distribution of these heavy metals in the surface sediments collected from the Beibu Gulf was complex.

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