Dynamic interactions of natural organic matter and organic compounds

Purpose

This article reviews our current understanding about how organic chemicals and water interact dynamically with, and therefore coevolve with, soil and sediment natural organic matter (NOM). NOM can be regarded as a polymer-like phase that responds to the input of organic compounds in ways analogous to synthetic polymers.

Methods

Sorption selectivity of organic compounds is shown to result in part from the three-dimensional microstructure of NOM related to its glassy character. Sorption to NOM conforms to polymer theory by exhibiting isotherm shape and irreversible behaviors characteristic of the glassy organic physical state. The glassy state is a metastable state characterized by the presence of excess free volume (holes).

Results

In polymers and NOM, incoming molecules preferentially occupy holes due to the absence of a cavitation penalty. Incoming molecules can enlarge existing holes and create new holes that do not relax completely when the molecules leave. The physical changes in NOM induced by sorption result in hysteresis in the isotherm that persists indefinitely at ambient temperature.

Conclusions

Sorption selectivity and hysteresis have important implications for the fate and bioavailability of contaminants.