Article

Freely Dissolved Concentrations and Sediment-Water Activity Ratios of PCDD/Fs and PCBs in the Open Baltic Sea

Department of Applied Environmental Sciences (ITM), Stockholm University, 10691 Stockholm, Sweden.
Environmental Science and Technology (Impact Factor: 5.33). 01/2009; 42(23):8733-9. DOI: 10.1021/es8018379
Source: PubMed

ABSTRACT

Aqueous concentrations of polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) as well as polychlorinated biphenyls (PCBs) in the open sea have heretofore been measured by filtering and extracting large amounts of water. Measurement of freely dissolved concentrations with this technique is difficult because of corrections for sorption to dissolved organic matter. In this study we use a novel, more economic technique using equilibrium passive samplers consisting of 17-microm thin polyoxymethylene (POM-17), capable of measuring freely dissolved aqueous concentrations (Cw) in pristine (i.e., background) locations. POM-17 was employed in an extensive field campaign at five stations in the open Baltic sea to obtain Cw at two depths (1 m above the seafloor and 25 m below the surface). Median Cw in the overlying water was 2.3 pg toxic equivalents (TEQ)/m3 PCDD/Fs and 15 pg/L sum 7-PCB, with generally less than a factor two variation among sites and depths. Also freely dissolved concentrations of native compounds in the surface sediment porewater (C(PW)) were determined in laboratory batch experiments. The data were used to derive sediment-water activity ratios, which indicate the diffusive flux direction. It was found that the PCDD/Fs and PCBs were in close equilibrium between the sediment porewater and the overlying water. Comparison of C(PW) with total sediment concentrations indicated that more than 90% of the compounds were sorbed to sedimentary black carbon.

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    • "The average activity ratio for all sampled stations increased significantly with increasing hydrophobicity ((p b 0.00001 and p = 0.0004); linear regression) with hydrophobicity from 1 ± 1 for PCB 77 and PCB 81, to 3 ± 2 for PCB 126 and 12 ± 4 for PCB 169. A similar trend of increasing activity ratio for PCBs with increasing hydrophobicity was observed in offshore areas (Cornelissen et al., 2008). Lower activity ratios for low K ow PCBs are probably the result of the more water-soluble PCBs being more mobile between pore water and bottom water. "
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    Full-text · Article · May 2014 · Science of The Total Environment
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