Geosorbent organic matter and its relationship to the binding and sequestration of organic contaminants

A dual reactive domain model (DRDM) for sorption of hydrophobic organic con taminants by soils, sediments, and other geosorbents is described. The mode l is predicated on the hypothesis that heterogeneous natural sorbent organi c matter (SOM) comprises two principal chemostructurally different domains; a highly amorphous domain and a relatively condensed domain. The existence of two chemically and phenomenologically different SQM domains is evidence d by observations of a glass transition for a soil-derived humic acid. Exte nsive examinations of phenanthrene sorption and desorption for a broad rang e of soils, sediments, shales, and kerogens reveal that sorption by condens ed SOM matrices is nonlinear and hysteretic while sorption by amorphous SOM domains is linear and completely reversible. Semi-quantitative correlation s between SOM oxygen/carbon (O/C) atomic ratios and isotherm linearity (n), single-point K-oc, values, and degrees of sorption-desorption hysteresis i ndicate that the geochemistry of SOM determines binding and sequestration o f organic contaminants by soils and sediments. The model reconciles observa tions of, and provides predictability for, various complex sorption phenome na associated with soils and sediments (C) 1999 Elsevier Science B.V. All r ights reserved.