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RELATIONSHIP BETWEEN PCB PLANERITY AND INTERACTIONS WITH SOOT CARBON
Citation:
Burgess, R M., S Ryba, M Cantwell, AND J Gundersen. RELATIONSHIP BETWEEN PCB PLANERITY AND INTERACTIONS WITH SOOT CARBON. Presented at Society of Environmental Toxicology and Chemistry Annual meeting, Baltimore, MD, November 11-15, 2001.
Description:
There is increasing interest in the role of soot carbon in the strong partitioning of organic contaminants to sediments. Primary interest has been focused on PAHs which have been shown to be affected by the presence of soot carbon in both their geochemical and bioavailability behaviors. One explanation for the strong association of PAHs with soot carbon is the theory that the planar conformation of PAHs allows greater interaction with the planar soot carbon molecular structures. Consequently, molecules must be able to assume a planar conformation to interact with soot carbon. If this explanation is correct, it may be assumed that other planar molecules like planar PCBs would also demonstrate strong associations with soot carbon. In this study, we explored the interaction of planar and non-planar PCBs with two coal power plant fly ashes, C18 and activated carbon. Using the Hyperchem? molecular modeling program, the change in heats of formation were calculated for ten PCBs (three of which were non-ortho substituted) indicating the energy necessary to bend the molecule into a planar conformation from an initial energy minimum conformation. Non-ortho substituted PCBs required very little energy to assume a planar conformation while mono-ortho substituted and di-ortho substituted PCBs required r" approximately 8 and 25 kcal/mol, respectively, to assume a planar conformation. These values were moderately to strongly correlated with the magnitude of association of PCBs to soot carbon with r2 values of 0.37, 0.31 and 0.75 for two fly ashes and the activated carbon, respectively. Association of PCBs to the non-planar C18 was not well correlated (r2 = 0.09). These data indicate the association of organic molecules to soot carbon is a direct function of the molecular conformation of the pollutant.