Photo-induced degradation of tracer phenols added to marine surface microlayers

Investigating the Mechanism of Phenol Photooxidation by Humic Substances

“…The photosensitized oxidation of phenols in natural waters by the chromophore-containing constituents of dissolved organic matter (CDOM) and humic substances (HS) has been the focus of numerous studies over the last twenty years. − In early work, attention was centered on photoproduced reactive oxygen species (ROS), namely peroxy radicals (RO 2 ), ,− the hydroxyl radical (·OH) − and singlet dioxygen ( 1 O 2 ), − ,− as the intermediates initiating oxidation. However, radical trapping experiments showed little evidence of a major photochemical source of RO 2 . − Further, both RO 2 and 1 O 2 have rate constants for reaction with undissociated phenols that are relatively small, of the order 10 3 to 10 6 M –1 s –1 for RO 2 and 10 6 to 10 8 M –1 s –1 for 1 O 2 , − depending on the phenol ring substituent(s). − , Although the rate constants for the reaction of ·OH with phenols are much larger, the very low steady state concentrations of this intermediate found in most natural waters appeared to preclude this species as a dominant sink as well. , Based on estimates of the steady-state concentrations of these ROS produced photochemically from CDOM in natural waters, the measured loss rates of many phenols at environmentally relevant concentrations appeared significantly larger than could be produced by these ROS …”

Transformation Kinetics of Phenols in Water: Photosensitization by Dissolved Natural Organic Material and Aromatic Ketones

“…Numerous substituted phenols hardly absorb light in the solar spectral region, but in natural waters their phototransformation is strongly promoted by the presence of dissolved natural organic material (DNOM). Photosensitized transformation half-lives of several hours were determined for alkyl phenols in summer noon sunlit waters at the surface [1,2). Such a photosensitization by DNOM is not surprising since phenols are readily oxidizable compounds that may be attacked by the various photooxidants steadily produced in sunlight (for reviews see refs 3 and 4).…”

Electron-Rich Phenols for Probing the Photochemical Reactivity of Freshwaters

“…These photooxidants are nevertheless important as it has been shown that DOM-derived photooxidants other than the hydroxyl radical or singlet oxygen dominate the photosensitized transformation of various substituted phenols in fulvic and humic acid solutions (8,9). Such photosensitized transformations also occurred in lake waters (8)(9)(10) and in seawater (11). Thus, substituted phenols have the potential of being used as probe molecules to characterize and quantify the reactivity of such DOM-derived photooxidants occurring in natural waters.…”