Photodegradation of Pollutants in the Hydrophobic Cores of Dissolved Organic Matter: When Is It Important?
Elio Mondino, Luca Carena, Cheng Gu, Davide Vione
Abstract
High Resolution Image Download MS PowerPoint Slide In natural surface waters, hydroxyl radicals ( • OH) and singlet oxygen ( 1 O 2 ) are known to occur not only in the bulk aqueous phase but also within the hydrophobic cores of dissolved organic matter (DOM). In these DOM sites, • OH and 1 O 2 reach steady-state concentrations that are orders of magnitude higher than those in bulk water, which can enhance photodegradation of hydrophobic pollutants. In analogy with previous works, here, we use a two-phase reactivity model to address the importance of the phenomenon. The model requires much care to identify which variables are referred to the total solution volume (bulk water + DOM), the volume of the water bulk, and most importantly, that of the DOM phase. We suggest that DOM-phase partitioning could significantly affect the photodegradation of pollutants having an octanol–water partition coefficient log 10 K ow > 3. In the case of • OH, differences should be expected between irradiation of solutions containing organic matter alone as the only • OH source and irradiation of natural water samples where • OH would also be generated by photolysis of nitrate and nitrite.