The environmental fate via natural phototransformation of fenamate-based non-steroidal anti-inflammatory drugs (NSAIDs) was investigated. Specifically, this study focused on diclofenac, and tolfenamic, meclofenamic, mefenamic and flufenamic acids. These pharmaceuticals are not readily biodegradable and are incompletely removed during wastewater treatment. Currently, direct photodegradation and advanced oxidation by UVC irradiation have mostly been studied with particular emphasis on diclofenac. Here, the focus was on indirect photochemical pathways under environmentally relevant conditions for all five fenamate drugs. UVA irradiation (365 nm) was employed in the presence of natural dissolved organic matter (DOM). In environmental waters, DOM is omnipresent and upon interaction with light, gives rise to several reactive intermediates. It was observed that triplet excited DOM (3DOM) reacts readily with the fenamates. Reactions with reactive oxygen species represent only minor pathways. The degradation kinetics of fenamates slowed when 3DOM was quenched by sorbic acid and increased when the 3DOM lifetime was enhanced by removing oxygen. Laser flash photolysis further demonstrated that photosensitization occurs via an electron-transfer mechanism from fenamates to the photosensitizer. Here, the formation of the fenamate radical cation transients was observed and quenching rates of triplet model sensitizers transient by fenamates were collected. Carbazole derivatives are proposed to be among the phototransformation products, as suggested by high-resolution mass spectrometry data.

Aquatic phototransformation of fenamate-based NSAIDs

251st National Meeting (2016)

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