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() Variations in soot carbon-water distribution coefficients with different soot types.

Thorsen, W1, Cope, W1, Shea, D1, 1 North Carolina State University, Raleigh, NC, USA

ABSTRACT- Sorption of hydrophobic organic contaminants, such as PAHs, to organic carbon and soot carbon phases of sediment in the aquatic environment drives contaminant availability and resultant organism exposure and effect(s). Therefore, to better understand the mobility and fate of PAHs in the aquatic environment, it is important to elucidate the influences of these sediment sorptive phases on PAH availability. Previously, we reported that pyrogenic PAHs exhibit lower bioavailability than petrogenic PAHs, as measured by Biota-Sediment Accumulation Factors (BSAFs). The Pyrogenic PAH bioavailability appeared to be influenced by the presence of soot carbon and the source of the PAHs, whereas petrogenic PAH bioavailability was not greatly impacted by either. Few studies have been conducted to measure soot carbon-water distribution coefficients (Ksc) for PAHs for different types of soot, and to observe how these values change with competition for active sites (e.g., presence of organic matter and native versus added PAHs). In this study, we report empirically derived Ksc values for 8 PAHs and use these values to evaluate the sorption strength of different types of soot. Three different types of soot were used, including activated carbon, traffic soot and oil soot. The Ksc values are largest for highest combustion temperature soot, in some cases demonstrating Ksc values 5,000 times greater than the corresponding Kow value, and lowest for the lower combustion temperature (and less weathered) oil soot, where Ksc values are nearly equivalent to Kow. Sorption of PAH to all three types of soot carbon decreased (i.e., lower Ksc values) with organic carbon addition, and this effect was greatest for the activated carbon, with decreases in log Ksc of at least one log unit. Competition and saturation of active sites are likely the reasons for the decreased sorption of PAHs to soot carbon treated with organic carbon. However, uncertainty remains with the use of activated carbon data to estimate real environmental sites where soot carbon is a prevalent adsorptive phase.

Key words: soot carbon, polycyclic aromatic hydrocarbons, bioavailability, soot carbon-water distribution coefficient

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