Aqueous photochemical degradation of BDE-153 in solutions with natural dissolved organic matter

Abstract

The compound 2,2′,4,4′,5,5′-hexabrominated diphenyl ether (BDE-153) is an intermediate photolytic product in the degradation of highly brominated diphenyl ethers to lower brominated forms. Herein, we report the effects of two natural organic matter (NOM) sources, Suwannee River fulvic acid (SRFA) and Pony Lake fulvic acid (PLFA), on BDE-153 photolysis in water. The rate constant (k) and half-life of BDE-153 was 2.26 × 10−2 min−1 and 30.72 min under UV–Vis irradiation (direct photolysis at λ > 290 nm). The k value for BDE-153 decreased markedly in the presence of NOM with a larger decrease in the presence of PLFA than SRFA. Electron spin resonance (ESR) demonstrated generation of free radicals in the photolytic process that mainly involved 1O2 and OH. The biomolecular k values for reaction of 1O2 and OH with BDE-153 were 3.65 × 106 and 7.70 × 108 M−1 s−1, respectively. The contribution of OH (28.7–31.0%) to the indirect photolysis of BDE-153 was higher than for 1O2 (12.9–14.9%). The photolytic rate of BDE-153 in oxygen-rich (aerated) solution was much slower than in oxygen-poor (nitrogen-sparged) conditions, demonstrating that 3NOM* is a more effective reagent for degradation of BDE-153 than 1O2. Addition of sorbic acid (a 3NOM* quencher) significantly reduced the photolytic rate of BDE-153 confirming the important role of 3NOM* in indirect photolysis. In the presence of NOM, BDE-153 indirect photolysis was facilitated mainly by reaction with 3NOM* and OH. To the best of our knowledge, this is the first comprehensive investigation of indirect photolysis of BDE-153 in water containing NOM.