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(051) Modeling HOC Sorption to Heterogenous Carbonaceous Matter in Sediments, Soils and Rocks.
Allen-King, Richelle*,1, Grathwohl, Peter2, Ball, William3, 1 Washington State University, Pullman, WA, USA2 University of Tübingen, Tübingen, Germany3 Johns Hopkins University, Baltimore, MD, USA
ABSTRACT- This presentation will link observations of the heterogeneity of naturally occurring carbonaceous materials (CM, non-carbonate carbon-containing matter) to the sorption behavior of hydrophobic organic compounds (HOCs). In particular, a model that simulates HOC sorption as the combined effect of adsorption to thermally altered CM and more linear solvation-driven absorption into gel-like CM will be presented. Examples of model fits to sediment samples that contain identified thermally altered CM illustrate the link between sorption processes and sorbent material properties. Whether adsorption is a dominant process within a particular soil/sediment-pollutant system is shown to depend on both the solute concentration of interest and the relative distribution of carbon among different CM types. The fact that both sorption processes (adsorption and partition) are scalable by compound solubility explains the observation that nonlinear sorption isotherms measured for different compounds and the same sediment collapse near each other with solubility normalization, compared to a much larger spread observed without normalization. The model is extended to suggest a means by which nonlinear sorption isotherms for a wide range of compounds may be estimated based on one or a few experimental measurements for a particular soil or sediment. Given that thermally altered CMs are widely distributed in the environment, and that environmentally relevant concentrations are often very low, we expect that the sorption modeling refinements presented in this work will have wide applicability as a step towards improving estimates of risk associated with contaminated soils and sediments.
Key words: sorption, hydrophobic organic compounds, adsorption, partitioning
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