Dual C–Br Isotope Fractionation Indicates Distinct Reductive Dehalogenation Mechanisms of 1,2-Dibromoethane in Dehalococcoides- and Dehalogenimonas-Containing Cultures

Abstract

Brominated organic compounds such as 1,2dibromoethane (1,2-DBA) are highly toxic groundwater contaminants. Multi-element compound-specific isotope analysis bears the potential to elucidate the biodegradation pathways of 1,2-DBA in the environment, which is crucial information to assess its fate in contaminated sites. This study investigates for the first time dual C− Br isotope fractionation during in vivo biodegradation of 1,2-DBA by two anaerobic enrichment cultures containing organohaliderespiring bacteria (i.e., either Dehalococcoides or Dehalogenimonas). Different ε bulk C values (−1.8 ± 0.2 and −19.2 ± 3.5‰, respectively) were obtained, whereas their respective ε bulk Br values were lower and similar to each other (−1.22 ± 0.08 and −1.2 ± 0.5‰), leading to distinctly different trends (Λ C−Br = Δδ 13 C/Δδ 81 Br ≈ ε bulk C /ε bulk Br ) in a dual C−Br isotope plot (1.4 ± 0.2 and 12 ± 4, respectively). These results suggest the occurrence of different underlying reaction mechanisms during enzymatic 1,2-DBA transformation, that is, concerted dihaloelimination and nucleophilic substitution (S N 2reaction). The strongly pathway-dependent Λ C−Br values illustrate the potential of this approach to elucidate the reaction mechanism of 1,2-DBA in the field and to select appropriate ε bulk C values for quantification of biodegradation. The results of this study provide valuable information for future biodegradation studies of 1,2-DBA in contaminated sites.

Novel Insights into Uptake, Translocation, and Transformation Mechanisms of 2,2′,4,4′-Tetra Brominated Diphenyl Ether (BDE-47) in Wheat (Triticum aestivum L.): Implication by Compound-Specific Stable Isotope and Transcriptome Analysis

“…Meanwhile, the concentrations of 6-OH-BDE47 were higher than those of 3-OH-BDE47 and 5-OH-BDE47 in shoots (Figure S2), indicating that the hydroxyl group preferentially substituted at the ortho-positions of BDE-47. This similar phenomenon was also reported for the transformation of BDE-47 in maine . Based on the above results, the proposed metabolic pathways of BDE-47 in wheat shoots can be summarized in Figure S3.…”

“…This similar phenomenon was also reported for the transformation of BDE-47 in maine. 45 Based on the above results, the proposed metabolic pathways of BDE-47 in wheat shoots can be summarized in Figure S3. In addition, it was interesting that these OH-BDEs were also detected in exposure solutions, and the concentrations of OH-PBDEs showed no significant changes over time, with the values fluctuating at 5.7 ng/mL (Figure S4).…”

“…Thus, it was challenging to accurately characterize the plant transformation of organic pollutants based on concentrations and products alone. Compound-specific stable isotope analysis (CSIA) is a promising method to characterize the transformation of organic pollutants independent of concentration changes, and different transformation processes was associated with different isotope fractionation effects. – Chemical bonds with lighter isotopes in the reaction sites react slightly compared to those with heavier isotopes, leading to the enrichment in heavier isotopes in residual fractions, known as isotope fractionation. It was reported that distinct transformation processes comprised different modes of chemical bond cleavage and thus were associated with specific stable isotope effects. , In addition, the physical processes were unable to cause the detectable changes in stable isotope compositions of organic pollutant. , Therefore, CSIA was successfully applied to investigate the chemical and microbial transformations of PBDEs in the environment. ,, However, the information on the stable isotope effects of organic pollutants during the transformation in plants was very limited.…”

Assessing Biodegradation Processes of Atrazine in Constructed Wetland Using Compound-Specific Stable Isotope Analysis

“…This investigation focused on both the carbon and the nitrogen isotope, achieved through the simultaneous measurement of carbon (δ 13 C) and nitrogen (δ 15 N) during different operational phases, as graphically depicted in Figure 2. The effects of the non-fractionating processes and the masking effects can be minimized in the dual-isotope plot, under the assumption that both carbon and nitrogen will be affected similarly, thus, maintaining a constant ratio between carbon and nitrogen isotope fractionation [9]. A dual-isotope plot was constructed to show the relationship between the δ 13 C and δ 15 N values of atrazine at varying concentrations.…”

“…Compound-specific stable isotope analysis (CSIA) has emerged as a monitoring approach that offers distinct advantages over traditional tools by enabling the differentiation of competing environmental sinks [9]. CSIA takes advantage of the kinetic isotope effect (KIE), which results in faster bond breakage for lighter isotopes (e.g., 12 C) compared to heavier isotopes ( 13 C) during degradation.…”