Application of dual carbon-bromine stable isotope analysis to characterize anaerobic micro-degradation mechanisms of PBDEs in wetland bottom-water. (1st January 2022)

• Record Type: Journal Article
• Authors: Wang, Guoguang; Liu, Yu; Wang, Xu; Dong, Xu; Jiang, Na; Wang, Haixia
• Is Part Of: Water research. Volume 208(2022)
• Publication Date: 2022-01-01
• Subjects: Microbial reductive debromination -- Dual carbon-bromine isotope analysis -- Nucleophilic aromatic substitution -- Polybrominated diphenyl ethers -- Wetland bottom water; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2021.117854
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: Preferential removal of bromine in para position for anaerobic degradation of PBDEs. First report on pronounced Br isotope fractionation during PBDE biodegradation. First application of dual C-Br isotope analysis in reaction mechanism of PBDEs. Cleavage of C-Br bond as rate-determining step for reductive debromination of PBDEs. Stepwise debromination of PBDEs by nucleophilic aromatic substitution in anoxic water. Abstract: Polybrominated diphenyl ethers (PBDEs), one kind of persistent organic pollutants, were widely detected in coastal wetlands. Microbial reductive debromination is one of the most important attenuation processes for PBDEs in anaerobic environment, whereas the underlying reaction mechanisms remain elusive. Dual-element stable isotope analysis was recently recognized to distinguish different reaction mechanism for degradation of organic pollutants. In this study, the dual carbon-bromine isotope effects associated with the anaerobic microbial degradation were first investigated to characterize the reaction mechanisms for BDE-47 and BDE-153. Presence of lower brominated congeners indicated stepwise debromination as the main degradation pathway, with the preferential removal of bromine in para position > meta/ortho position. The pronounced isotope fractionation was observed for both carbon and bromine, with similar carbon ( ε C ) and bromine isotope enrichment factor (εBr ) between BDE-47 ( ε C = -5.98‰, ε Br = -2.44‰) and BDE-153 ( ε C = -5.57‰, ε Br = -2.06‰) during the microbial degradation. Compared to ε C and ε Br, the correlation of carbon and isotope effects (ΛC/Br = Δ δ 81 Br/Δ δ 13 C) was almost the same between BDE-47 (0.436) and BDE-153 (0.435), indicating the similar reaction mechanism. The calculated carbon and bromine apparent kinetic isotope effects ( AKIE C and AKIE Br ) were 1.0773 and 1.0098 for BDE-47 and 1.0716 and 1.0125 for BDE-153, within range reported for degradation of halogenated compounds following nucleophilic substitution. Combination analysis of degradation products, ΛC/Br and AKIE, all the results pointed to that the anaerobic reductive debromination of BDE-47 and BDE-153 followed the nucleophilic aromatic substitution, with the addition of cofactor to the benzene ring concomitant with dissociation of carbon-bromine bond via the inner-sphere electron transfer, and the cleavage of C-Br bond was the rate-determining step. This study contributed to the development of dual carbon-bromine isotope analysis as a robust approach to probe the fate of PBDEs in contaminated sites. Graphical abstract: Image, graphical abstract