The contribution of different carbonaceous material fractions to the sorption of hydrophobic organic contaminants to subsurface sediments

The fate and transport of hydrophobic organic contaminants (HOCs) in subsurface sediments is strongly affected by sorption to the carbonaceous materials (CMs). The importance of CM properties and mass in soils and sediments has been previously emphasized. However, the contribution of different CMs in HOC sorption to subsurface sediments is ambiguous. The primary objectives of this research are (1) to identify methods that can be used to obtain CM enrichments of groundwater sediments for sorption characterization, (2) to determine the amount of different types of CMs in reduced and oxidized sediments of glacially deposited groundwater sediments, (3) to characterize CM fractions that control HOC sorption and their structural and chemical properties, and (4) to determine the HOC sorption protective effects on condensed form CMs by soft form CMs and minerals.; Density separation and a series of chemical treatments evaluated using reference CMs were applied to glacially deposited subsurface sediments collected from oxidized and reduced zones of Chanute Air Force Base (AFB) in Rantoul, Illinois, in order to obtain fractions of these materials enriched in one or more of the CM fractions. The results indicate that water/acid soluble organic matters dominate total carbon mass, with kerogen/humin the next most abundant CMs. Isotherm results indicate that condensed form CMs, most likely kerogen and humin, control the sorption of TCE. Even though the KCM values for particulate carbonaceous materials (PCM) are higher than those of the other fractions, the sorption contributions of PCMs were relatively small because of the small amount of mass of these solids. Results show that reduced sediment and its fractions have higher HOC sorption capacity than oxidized sediment and its fractions. The spectroscopic results indicate that when the first few microns of CM surfaces of PCMs are considered, the oxidized sediment is more weathered than the reduced sediment. This is one reason K CM values for reduced sediments are greater than those of oxidized sediments. Results also indicate that there are HOC sorption protective effects on condensed form of CMs by minerals and soft form CMs, and the degree of protection is larger in oxidized sediments.