P16SOLID-STATE NMR METHOD FOR STUDY OF THE DISTRIBUTED REACTIVITY MODEL OF CONTAMINANT SORPTION TO SOIL ORGANIC MATTER |
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The sorption of hydrophobic organic contaminants to soil has been described by a "distributed reactivity model" (DRM) in which three distinct types of sorbents are present in soil (Weber et al., Environ. Sci. Technol. 1992, 26, 1955-1962). The DRM states that soils can be treated as a heterogeneous combination of inorganic and organic sorption matrices each with distinctly different sorptive properties.
The interaction of these different matrices with organic contaminants can be qualitatively described by a three-domain model involving an exposed inorganic mineral phase, an amorphous soil organic matter (SOM) phase, and a condensed SOM phase. Contaminants sorbed to each phase should have measurably different physical and chemical characteristics. Solid-state l9F NMR experiments will be developed to test for the existence of the different SOM domains predicted by the DRM using fluorinated analogs of PAHs and PCBs bound to SOM. If the DRM is valid, at least two distinct NMR resonances should be evident, a narrow signal from contaminant residing in the mobile amorphous SOM, a broad signal from the contaminant in the more rigid condensed SOM, and possibly a third signal from contaminant sorbed to the exposed inorganic mineral phase. Results of the development of the NMR experiments will be discussed in light of the usefulness of solid-state l9F NMR as a tool in the study of the fate of hydrophobic organic contaminants. Key words: 19F NMR, soil organic matter, PAH, PCBs
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