Phototransformation of the sunlight filter benzophenone-3 (2-hydroxy-4-methoxybenzophenone) under conditions relevant to surface waters

The UV filter benzophenone-3 (BP3) has UV photolysis quantum yield BP3 F = (3.1±0.3)×10−5 and the following second-order reaction rate constants: with •OH, BP OH k • 3, = (2.0±0.4)×1010 M−1 s−1; with the triplet states of chromophoric dissolved organic matter (3CDOM*), 3, * 3BP CDOM k = (1.1±0.1)×109 M−1 s−1; with 1O2, 2 1 BP3, O k = (2.0±0.1)×105 M−1 s−1, and with CO3 −•, −• 3 BP3,CO k < 5×107 M−1 s−1. These data allow the modelling of BP3 photochemical transformation, which helps filling the knowledge gap about the environmental persistence of this compound. Under typical surfacewater conditions, direct photolysis and reactions with •OH and 3CDOM* would be the main processes of BP3 phototransformation. Reaction with •OH would prevail at low DOC, direct photolysis at intermediate DOC (around 5 mg C L−1), and reaction with 3CDOM* at high DOC. If the reaction rate constant with CO3 −• is near the upper limit of experimental measures (5×107 M−1 s−1), the CO3 −• degradation process could be somewhat important for DOC < 1 mg C L−1. The predicted half-life time of BP3 in surface waters under summertime conditions would be of some weeks, and it would increase with increasing depth and DOC. BP3 transformation intermediates were detected upon reaction with •OH. Two methylated derivatives were tentatively identified, and they were probably produced by reaction between BP3 and fragments arising from photodegradation. The other intermediates were benzoic acid (maximum concentration ~10% of initial BP3) and benzaldehyde (1%).