Concentration and distribution of 17 organochlorine pesticides (OCPs) in seawater from the Japan Sea northward to the Arctic Ocean

Abstract

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 α-HCH and γ-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 α-HCH/γ-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 α-HCH, γ-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.