Photodegradation of UV filters oxybenzone and sulisobenzone in wastewater effluent and by dissolved organic matter

Organic UV-filters are key ingredients found in sunscreens, cosmetics and plastic goods. Concerns have been raised about potential ecological and human health effects of certain organic UV filters that are currently FDA approved for use in the United States. Here, we investigate the photochemical fate of two of these compounds, oxybenzone and sulisobenzone. Both oxybenzone and sulisobenzone have previously been detected in surface waters, seawater, and treated wastewater effluent. Direct photolysis is found to be unimportant for these compounds, however, enhanced photodegradation of oxybenzone and sulisobenzone was observed under simulated solar irradiation in solutions of International Humic Substance Society standards (Pony Lake fulvic acid and Suwannee River natural organic matter), filtered wastewater effluent (Southerly Wastewater Treatment Plant in Lockbourne, OH), and Scioto River water (Columbus, OH) at pH 7. Quenching experiments with isopropanol revealed that the main pathway for degradation appears to be reaction with the hydroxyl radical (OH). Observed degradation rates were 2-3 times slower than estimates calculated using literature reported second-order rate constants and measured hydroxyl radical steady-state concentrations for Suwannee River natural organic matter, Pony Lake fulvic acid and Scioto waters. The Southerly sample, however, exhibited nearly identical expected and observed rate constants, which we take to indicate the presence of unidentified reactive species that can react with oxybenzone and sulisobenzone. Values obtained in this work were used to calculate second-order rate constants for oxybenzone and sulisobenzone with the hydroxyl radical, as well as to estimate environmental half-lives for these compounds. Near surface 24-h averaged half-lives of 3.0 and 4.0 days were calculated for oxybenzone and sulisobenzone, respectively. When extrapolated to an environmentally representative water column, these same 24-h averaged half-lives increased to 2.4 and 3.5 years, respectively.