Environmental fate of multiple organic compounds, both natural and anthropogenic ones, is affected by their sorption and reactions at diverse interfaces present on soils, sediments, aerosols and, specifically, associated with natural organic matter (NOM) and clay minerals. In environment of variable humidity, water plays its own important role, by suppressing or cooperating in uptake and reactions of organic chemicals at interfaces. These processes are often monitored during relatively short time periods, which may not cover slow processes eventually leading to thermodynamically controlled endpoint. The current contribution presents a long-term study of interactions of mixed phenol-water vapors with model sorbents such as humic acid salt, leonardite and NOM- and clay-rich soils. Phenol is a representative of multiple organic compounds capable of polymerization at environmental interfaces, reactions with soil components, covalent binding to NOM and strong H-bond interactions. Gravimetric monitoring of phenol-water vapor uptake kinetics was performed during 4000 hrs by the sorbent materials prehydrated at different levels of water activity. Differences between mixed vapor uptake kinetics and those observed for control sorbent samples exposed to phenol-free humid atmospheres (at the same water activities) allowed to demonstrate that phenol-induced vapor deposition follows sigmoid kinetics typical for second-order autocatalytic reactions. Interestingly, long-term kinetics on interfaces of some essentially different sorbents, such as NOM-rich and clay-rich soils, were associated with significant rise in hydration thus suggesting that organic vapor deposition created new sorption sites for water. Abiotic oxidative coupling of phenol associated with its polymerization at surfaces was considered to control phenol-water deposition such that large portion of sorbed phenol became resisting to extraction. Since sigmoid uptake kinetics were developed with the significant delay, limited-time observations would not allow detecting the processes finally leading to significant changes in the system composition. The apparent rate constants were not influenced by sorbent nature, water activity or phenol concentrations, thus suggesting "universal" phenol deposition mechanisms and opportunity to predict long-term uptakes on various materials.

Phenol-water vapor deposition in long-term exposure: Different interfaces, similar sigmoid kinetics, and enhanced water retention

2019 Fall National Meeting

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