title: Photosensitizing and Inhibitory Effects of Ozonated Dissolved Organic Matter on Triplet-Induced Contaminant Transformation.
abstract: Dissolved organic matter (DOM) is both a promoter and an inhibitor of triplet-induced organic contaminant oxidation. This dual role was systematically investigated through photochemical experiments with three types of DOM of terrestrial and aquatic origins that were preoxidized to varying extents by ozonation. The inhibitory effect of DOM was assessed by determining the 4-carboxybenzophenone photosensitized transformation rate constants of two sulfonamide antibiotics (sulfamethoxazole and sulfadiazine) in the presence of untreated or preoxidized DOM. The inhibitory effect decreased with the increasing extent of DOM preoxidation, and it was correlated to the loss of phenolic antioxidant moieties, as quantified electrochemically, and to the loss of DOM ultraviolet absorbance. The triplet photosensitizing ability of preoxidized DOM was determined using the conversion of the probe compound 2,4,6-trimethylphenol (TMP), which is unaffected by DOM inhibition effects. The DOM photosensitized transformation rate constants of TMP decreased with increasing DOM preoxidation and were correlated to the concomitant loss of chromophores (i.e., photosensitizing moieties). The combined effects of DOM preoxidation on the inhibiting and photosensitizing properties were assessed by phototransformation experiments of the sulfonamides in DOM-containing solutions. At low extents of DOM preoxidation, the sulfonamide phototransformation rate constants remained either unchanged or slightly increased, indicating that the removal of antioxidant moieties had larger effects than the loss of photosensitizing moieties. At higher extents of DOM preoxidation, transformation rates declined, mainly reflecting the destruction of photosensitizing moieties.
authors.affiliation: †Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.|‡Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätstrasse 16, CH-8092 Zürich, Switzerland.
authors.forename: Jannis
authors.initials: J
authors.lastname: Wenk
authors.affiliation: ‡Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätstrasse 16, CH-8092 Zürich, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Aeschbacher
authors.affiliation: ‡Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätstrasse 16, CH-8092 Zürich, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Sander
authors.affiliation: †Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.|‡Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätstrasse 16, CH-8092 Zürich, Switzerland.|§School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: Urs
authors.initials: U
authors.lastname: von Gunten
authors.affiliation: †Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.
authors.forename: Silvio
authors.initials: S
authors.lastname: Canonica
mesh_terms: D001577:Benzophenones / Q000737:chemistry; D004583:Electrons; D007700:Kinetics; D009930:Organic Chemicals / Q000737:chemistry*; D010084:Oxidation-Reduction; D010126:Ozone / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry; D055668:Photochemical Processes; D012995:Solubility; D013411:Sulfadiazine / Q000737:chemistry; D013420:Sulfamethoxazole / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: C530484:4-carboxybenzophenone; D001577:Benzophenones; D009930:Organic Chemicals; D010636:Phenols; D014874:Water Pollutants, Chemical; D013411:Sulfadiazine; D010126:Ozone; D013420:Sulfamethoxazole