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Photodegradation of tetrabromobisphenol S (TBBPS) in regional surface water: direct and indirect processes impacting by dissolved organic matter (DOM) and chloride
Summary
Researchers investigated the photodegradation of the flame retardant tetrabromobisphenol S (TBBPS) in surface water, finding that direct photolysis and indirect reactions with dissolved organic matter and chloride ions both contribute to degradation, with important implications for environmental persistence.
Abstract The photodegradation of Tetrabromobisphenol S (4,4 'Sulphonylbis(2,6-dibromophenol, TBBPS) in saline river determined the accumulation and potential harm to living organisms. With the inherent features of the absorption at longer wavelength and favorable intersystem crossing (ISC) process, TBBPS was prone to undergo direct photolysis with the main involvement of triplet-excited state (3TBBPS*). It turns out that the monoanionic form of TBBPS (TBBPS−) at pH = 5 had the fast degradation rate by advantage of the low excited energy. Furthermore, the impact of DOMs and chloride at the photolysis behavior was sufficiently investigated. Humic acid (HA) inhibited TBBPS photodegradation mainly by light shielding effect. In comparison with HA, fulvic acid (FA) exhibited janus effect on the photolysis rate at varied concentrations. The presence of chloride also contributed to the dual effect on TBBPS photolysis. To unveil the mechanism of photodegradation pathways, theoretical calculation were employed to prove the thermodynamic favored access. Electron transfer dominated the acceleration in the indirect photolysis promoted by FA. Higher oxidation potential ET of TBBPS over 3P* induced the formation of RHS through electron transfer between Cl− and 3P*. Furthermore, Apex model computations confirmed that the calculated t1/2 were 43.2 ~ 244.8 min in springtime and 7.2 ~ 42.0 min in summertime with the water depth from 0 to 1 m and DOC concentration from 0 to 50 mgC·L− 1. And t1/2 would increase with increasing water depth and DOC concentration. Even in natural water bodies, direct photolysis remained the primary pathway of photolysis in surface water. Due to the attenuated toxicity profiles of the available transformation products, these findings might suggest photodegradation as an important toxicity reduction process for TBBPS in surface saline waters.