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1L - Exposure Modelling (WEP/82) A Soot-Carbon Inclusive Multimedia Level IV Fugacity Model for the Fate of PCDD/Fs in the Marine Environment of the Grenlandsfjords, Norway. Persson, Johan1, Cousins, Ian1, Gustafsson, Örjan1, Mulvaer, Jarle2, Naes, Kristoffer2, Broman, Dag1, 1 Institute of Applied Environmental Research (ITM), Stockholm, Uppland, Sweden2 Norwegian Institute for Water Research (NIVA), Grimstad, Oslo, Norway ABSTRACT- The established paradigm for more than 30 years has been that hydrophobic organic compounds sorb primarily to the organic matter present in soils and sediments. For example, the relationship derived from the work of Karickhoff, namely Koc = 0.41Kow, is the most widely used in fate modelling for estimating soil-water and sediment-water partitioning. There is increasing evidence, however, to suggest that the existing organic-matter partitioning model paradigm is not sufficient alone to explain the sorption of hydrophobic organics to soils and sediments. Many laboratory sorption studies have found that sorption isotherms for soil-water and sediment-water systems can show substantial deviations from a linear partition model, especially at water concentrations significantly below a compound's water solubility. Furthermore, field-observed Kd's are often shown to be much higher than those estimated using the Karickhoff model. It has recently been postulated that the observed enhanced sorption is a result of adsorption to a strongly sorbing pyrogenic sub-fraction of the sediment termed soot-carbon. As a result of these findings, a revised soot-carbon inclusive sorption model for estimating Kd based on simultaneous sorption to both organic carbon and soot carbon has been proposed. In this study, this soot-inclusive sorption equation is used within a Level IV fugacity model used to describe the fate of PCDD/Fs in a marine fjord environment in Norway, the Grenlandsfjords. Model predictions are compared to monitoring data for PCDD/Fs in the water column, sediment solids and sediment pore-water. The soot-carbon inclusive sorption model is shown to give an improved description of sediment-water partitioning compared to the Karickhoff model. It is therefore recommended that this novel soot-inclusive model be considered for inclusion within environmental fate and exposure models, especially for estimating the sorption of planar compounds such as co-planar PCBs, PAHs, PCNs and PCDD/Fs, for which soot adsorption is particularly strong. Key words: soot, partitioning, model, sediment |
