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

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.

Organochlorine Pollutants in Western Antarctic Peninsula Sediments and Benthic Deposit Feeders

“…The total organic carbon percentages (f TOC %) in the bottom sediments were fairly low in the five locations (0.5-1%, Table 1), which were similar to f TOC found in the marine tidal sediments (0.04-1.71%) on James Ross Island, Antarctica (63.8°S, 57.8°W), but lower compared to the f TOC in other oceanic sediments (Baltic Sea 2.4-5.9%) (40) . The black carbon concentrations (f BC %) were independent of locations averaged around 0.1%.…”

“…Passive sampling has been shown by previous studies to be a reliable and robust approach to obtain porewater concentrations of POPs (35)(36)(37)(38)(39)(40) . The detailed methods have been described elsewhere (37) .…”

“…Passive samplers have been proven to be a robust sampling device to determine truly dissolved porewater concentration of POPs (35)(36)(37)(38)(39)(40) . The importance of black carbon for reducing bioavailability in the porewater thus can be assessed using passive sampler (35)(36)(37)(38)(39)(40) .…”

“…The importance of black carbon for reducing bioavailability in the porewater thus can be assessed using passive sampler (35)(36)(37)(38)(39)(40) .…”

Recent advances in the field measurement of the diffusion flux of hydrophobic organic chemicals at the sediment-water interface

“…In this case, sediment often acts as a sink of chemicals, thereby exerting a settlement flux into sediment (designated as ''negative flux''). Also, there are cases where chemical concentrations were nearly identical in sediment porewater and overlying water {e.g., polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) in the Baltic Sea [18] and hexachlorobenzene (HCB) in Delfzijl Harbor [15]}, so that no net diffusion flux was observed.…”