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Analysis of a humic acid by differential scanning calorimetry has revealed the existence of a glass transition point. Glass transition temperatures, T g, of water-wet and desiccator-dry specimens were found to range from 43 °C for water-wet humic acid to 62 °C for dry samples. Phenanthrene sorption isotherms for these and other natural and synthetic organic matrices having known glass transition tempera tures were determined to exhibit linearity and nonlinearity corresponding respectively to the rubbery (expanded) and glassy (condensed) states of the sorbent. Invoking a limiting case of the distributed reactivity model based on polymer sorption theory, we explain the observed sorption behavior as comprised in each case by a linear phase-partitioning component and a Langmuir-like nonlinear adsorption component. We conclude that polymer sorption theory provides a useful context in which to assess sorption phenomena associated with soil and sediment organic matter, providing more accurate projections of contaminant behavior in environmental systems and better informed specifications of appropriate remediation measures.
LeBoeuf et al. (Thu,) studied this question.