Geochemistry

Charting Sorption Variations

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Science  21 Sep 2007:
Vol. 317, Issue 5845, pp. 1651
DOI: 10.1126/science.317.5845.1651b

The extraordinary diversity of organic matter in soil and aquatic environments has posed a considerable challenge to researchers seeking to predict the fate of specific molecular contaminants. As a starting point, the enormous array of functionalized hydrocarbons has traditionally been divided into three broad classes of material: humin, humic acids, and fulvic acids. Even within these categories, however, chemical and physical properties can vary from place to place. Niederer et al. have undertaken a systematic survey of the differing sorption properties of 10 distinct terrestrial and aquatic humic and fulvic acids. Using inverse gas chromatography, they measured the air/sorbent partition coefficients characteristic of these materials for ~100 small organic molecules of widely varying polarities. The coefficients varied by as much as a factor of 10, but somewhat surprisingly, the changes were manifested as constant shifts. This result implies that despite the chemical diversity of the samples, sorption is primarily a function of the abundance of available binding sites. The authors rationalize this finding by invoking the high degree of cross-linking tying up functional groups beneath the surface of the material. A series of parametrized linear free-energy relations derived from the data shows promise for predictive applications. — JSY

Environ. Sci. Technol. 41, 10.1021/es0709932 (2007).

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