Mechanism investigation and stable isotope change during photochemical degradation of tetrabromobisphenol A (TBBPA) in water under LED white light irradiation

Light driven degradation is very promising for pollutants remediation. In the present work, photochemical reaction of tetrabromobisphenol A (TBBPA) under LED white light (λ > 400 nm) irradiation system was investigated to figure out the TBBPA photochemical degradation pathways and isotope fractionation patterns associated with transformation mechanisms. Results indicated that photochemical degradation of TBBPA would happen only with addition to humic acid in air bubbling but not in N2 bubbling. For photochemical reaction of TBBPA, singlet oxygen (1O2) was found to be important reactive oxygen species for the photochemical degradation of TBBPA. 2,6-Dibromo-4-(propan-2-ylidene)cyclohexa-2,5-dienone and two isopropyl phenol derivatives were identified as the photochemical degradation intermediates by 1O2. 2,6-Dibromo-4-(1-methoxy-ethyl)-phenol was determined as an intermediate via oxidative skeletal rearrangement, reduction and O-methylation. Hydrolysis product hydroxyl-tribromobisphenol A was also observed in the reductive debromination process. In addition, to deeply explore the mechanism, carbon and bromine isotope analysis were performed using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) and gas chromatography-multicollector inductively coupled plasma mass spectrometry (GC/MC/ICPMS) during the photochemical degradation of TBBPA. The results showed that photochemical degradation could not result in statistically significant isotope fractionation, indicated that the bond cleavage of C-C and C-Br were not the rate controlling process. Stable isotope of carbon being not fractionated will be useful for distinguishing the pathways of TBBPA and tracing TBBPA fate in water systems. This work sheds light on photochemical degradation mechanisms of brominated organic contaminants.