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

Abstract

A dual reactive domain model (DRDM) for sorption of hydrophobic organic contaminants by soils, sediments, and other geosorbents is described. The model is predicated on the hypothesis that heterogeneous natural sorbent organic 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 SOM domains is evidenced by observations of a glass transition for a soil-derived humic acid. Extensive examinations of phenanthrene sorption and desorption for a broad range of soils, sediments, shales, and kerogens reveal that sorption by condensed SOM matrices is nonlinear and hysteretic while sorption by amorphous SOM domains is linear and completely reversible. Semi-quantitative correlations between SOM oxygen/carbon (O/C) atomic ratios and isotherm linearity ( n), single-point K OC values, and degrees of sorption–desorption hysteresis indicate that the geochemistry of SOM determines binding and sequestration of organic contaminants by soils and sediments. The model reconciles observations of, and provides predictability for, various complex sorption phenomena associated with soils and sediments