Abstract

Although microporosity and surface area of natural organic matter (NOM) are crucial for mechanistic evaluation of the sorption process for nonpolar organic contaminants (NOCs), they have been underestimated by the N₂ adsorption technique. We investigated the CO₂–derived internal hydrophobic microporosity (V_o) and specific surface area (SSA) obtained on dry samples and related them to sorption behaviors of NOCs in water for a wide range of condensed NOM samples. The V_o is obtained from the total CO₂–derived microporosity by subtracting out the contribution of the outer surfaces of minerals and NOM using N₂ adsorption–derived parameters. The correlation between V_o or CO₂–SSA and fractional organic carbon content (f_OC) is very significant, demonstrating that much of the microporosity is associated with internal NOM matrices. The average V_o and CO₂–SSA are, respectively, 75.1 μL g⁻¹ organic carbon (OC) and 185 m² g⁻¹ OC from the correlation analysis. The rigid aliphatic carbon significantly contributes to the microporosity of the Pahokee peat. A strong linear correlation is demonstrated between V₀/f_OC and the OC-normalized sorption capacity at the liquid or subcooled liquid–state water solubility calculated via the Freundlich equation for each of four NOCs (phenanthrene, naphthalene, 1,3,5-trichlorobenzene, and 1,2-dichlorobenzene). We concluded that micropore filling (“adsorption”) contributes to NOC sorption by condensed NOM, but the exact contribution requires knowing the relationship between the dry-state, CO₂–determined microporosity and the wet-state, NOC-available microporosity of the organic matter. The findings offer new clues for explaining the nonideal sorption behaviors of NOCs.

Copyright © 2013. . Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.