Assessing the photodegradation potential of compounds derived from the photoinduced weathering of polystyrene in water

Benzoate (Bz(-)) and acetophenone (AcPh) are aromatic compounds known to be produced by sunlight irradiation of polystyrene aqueous suspensions. Here we show that these molecules could react with (OH)-O-center dot (Bz(-)) and (OH)-O-center dot + CO3 center dot-(AcPh) in sunlit natural waters, while other photochemical processes (direct photolysis and reaction with singlet oxygen, or with the excited triplet states of chromophoric dissolved organic matter) are unlikely to be im-portant. Steady-state irradiation experiments were carried out using lamps, and the time evolution of the two sub-strates was monitored by liquid chromatography. Photodegradation kinetics in environmental waters were assessed by a photochemical model (APEX: Aqueous Photochemistry of Environmentally-occurring Xenobiotics). In the case of AcPh, a competitive process to aqueous-phase photodegradation would be volatilisation followed by reaction with gas-phase (OH)-O-center dot. As far as Bz(-) is concerned, elevated dissolved organic carbon (DOC) levels could be important in protecting this compound from aqueous-phase photodegradation. Limited reactivity of the studied compounds with the dibromide radical (Br-2(center dot-), studied by laser flash photolysis) suggests that (OH)-O-center dot scavenging by bromide, which yields Br-2(center dot-), would be poorly offset by Br-2(center dot-)-induced degradation. Therefore, photodegradation kinetics of Bz(-) and AcPh should be slower in seawater (containing [Br-] similar to 1 mM) compared to freshwaters. The present findings suggest that photochemistry would play an important role in both formation and degradation of water-soluble organic compounds produced by weathering of plastic particles.