title: Environmental photochemistry of fenamate NSAIDs and their radical intermediates.
abstract: Fenamates are a class of nonsteroidal anti-inflammatory drugs (NSAIDs) that are not fully removed during wastewater treatment and can be released to surface waters. Here, near-surface photochemical half-lives were evaluated to range from minutes to hours of four fenamates and the closely related diclofenac. While quantum yields for direct photochemical reactions at the water surface vary widely from 0.071 for diclofenac to <0.001 for mefenamic acid, all fenamates showed significant reactivity towards singlet oxygen and hydroxyl radical with bimolecular reaction rate constants of 1.3-2.8 × 107M-1s-1and 1.1-2.7 × 1010M-1s-1, respectively. Photodecay rates increased in the presence of dissolved organic matter (DOM) for diclofenac (+19%), tolfenamic acid (+9%), and mefenamic acid (+95%), but decreased for flufenamic acid (-2%) and meclofenamic acid (-14%) after accounting for light screening effects. Fast reaction rate constants of all NSAIDs with model triplet sensitizers were quantified by laser flash photolysis. Here, the direct observation of diphenylamine radical intermediates by transient absorption spectroscopy demonstrates one-electron oxidation of all fenamates. Quenching rate constants of these radical intermediates by ascorbic acid, a model antioxidant, were also quantified. These observations suggest that the balance of oxidation by photoexcited triplet DOM and quenching of the formed radical intermediates by antioxidant moieties determines whether net sensitization or net quenching by DOM occurs in the photochemical degradation of fenamates.
authors.affiliation: Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, 8092 Zurich, Switzerland. kris.mcneill@env.ethz.ch.
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Davis
authors.forename: Paul R
authors.initials: PR
authors.lastname: Erickson
authors.forename: Kristopher
authors.initials: K
authors.lastname: McNeill
authors.forename: Elisabeth M L
authors.initials: EML
authors.lastname: Janssen
mesh_terms: D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000032:analysis* / Q000737:chemistry / Q000528:radiation effects; D052918:Environmental Restoration and Remediation; D054361:Fenamates / Q000032:analysis* / Q000737:chemistry / Q000528:radiation effects; D005618:Fresh Water / Q000737:chemistry; D006812:Humic Substances / Q000032:analysis*; D017665:Hydroxyl Radical / Q000737:chemistry; D008027:Light; D008962:Models, Theoretical; D010084:Oxidation-Reduction; D010777:Photochemistry; D026082:Singlet Oxygen / Q000737:chemistry; D013057:Spectrum Analysis; D062065:Wastewater / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry / Q000528:radiation effects
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D054361:Fenamates; D006812:Humic Substances; D017665:Hydroxyl Radical; D026082:Singlet Oxygen; D062065:Wastewater; D014874:Water Pollutants, Chemical