Fulvic acid mediated photolysis of ibuprofen in water

Abstract

Photolysis of the non-steroidal anti-inflammatory drug ibuprofen was studied by exposure to a solar simulator in solutions of fulvic acid (FA) isolated from Pony Lake, Antarctica; Suwannee River, GA, USA; and Old Woman Creek, OH, USA. At an initial concentration of 10 μM, ibuprofen degrades by direct photolysis, but the presence of FA significantly increases reaction rates. These reactions proceeded up to 6× faster in FA solutions at lower ibuprofen concentrations (0.1 μM), but the rates are highly dependent upon DOM composition. Incomplete quenching of the reaction in the presence of isopropanol suggests that the hydroxyl radical is only partially responsible for ibuprofen’s photodegradation in FA solutions, and other reactive transients likely play an important role. Liquid chromatography-quadrupole time-of-flight mass spectrometry and NMR spectroscopy reveal the formation of multiple photoproducts, with three byproducts identified as 1-(4-isobutylphenyl)ethanol, isobutylacetophenone, and a phenol derivative. Pony Lake FA significantly increases the production of the major byproduct relative to yields produced by direct photolysis and the other two FA. Thus, the photolytic fate of ibuprofen in sunlit waters is affected by its initial concentration and the source of dissolved organic matter present.