Tetrabromobisphenol A is considered as persistent, bioaccumulative and toxic compound and environmental endocrine disruptor, because it is the largest used brominated flame retardant and has the similar structure with thyroid hormone. The production, use and disposal of TBBPA have caused widespread concern because it may induce serious pollution problems and bioaccumulation which threaten the human life and health.
TBBPA was chosen as the model species in the work to investigate its photoreaction in aquatic environment under solar light irradiation. Focus on the pure water system and high saline system. The influence and reaction mechanism of common environmental factors on the phototransformation of TBBPA have been assessed. We wanted to thorough understand the phototransformation mechanism and environmental behavior of TBBPA in aquatic environment.
The major results of the study are as following:
(1) The reaction did not occur in the dark, but occurred after irradiation. The reaction kinetic follows the first-order reaction kinetics equation. The degradation rate of TBBPA was faster at high pH conditions. Chloride, nitrate, carbonate and sulfate ions restrained the degradation of TBBPA. The calculated light shielding factor of fulvic acid proved that fulvic acid compete more photons than TBBPA during photochemical process;
(2) In the pure water system, the photolysis products were identified: tribromobisphenol A, hydroxyl-tribromobisphenol A, hydroxyl-dibromobisphenol A, 4-isopropylene-2,6-dibromophenol, 4-(2-hydroxyisopropyl)-2,6-dibromophenol, 2,6-dibromophenol. Hydroxyl-tribromobisphenol A was the main product. The photodegradation mechamisms involve three pathways: debromination reaction, MIE-hydrolysis of TBBPA photolysis and singlet oxygen oxidation. The tests of radical provided the proof that singlet oxygen played a role in the reaction mechanism, while compound-specific isotope analysis (CSIA) of 13C has been first used to demonstrate the magnetic effect of hydrolysis as the main degradation path of TBBPA,which involving the change of excited states of TBBPA;
(3) In the high saline system, the photochlorination of TBBPA and other photochemical reaction occurred at the same time. There were two chlorinated products of TBBPA. They were 2,6-dibromo-4-(2-(3-bromo-5-chloro-4-hydroxyphenyl)propan-2-yl)phenol and 3-chloro-5-(2-(3,5-dibromo-4-hydroxyphenyl)propan-2-yl)benzene-1,2-diol. And the first was the main chlorinated product. We hypothesized that the reaction was related with the excited TBBPA*. Results show that photochlorination of TBBPA in aqueous seawater could occur at a low level, though, which suggest a natural source of chlorinated products in the environment.
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