Investigating Controls on Variation in Isotopic Fractionation during Biodegradation of Chlorinated Ethenes and Ethanes

Kinetic isotope effects occur due to different reaction rates for light and heavy isotope-containing molecules, and are controlled by the bonds broken during degradation. For many primary pollutants, stable carbon, hydrogen, and chlorine isotope effects have been found to fit a Rayleigh model, indicating a single rate-limiting step. This thesis examines biodegradation pathways where additional controls and rate-limiting steps may affect observed isotope fractionation. Two haloalkane dehalogenases catalyzed aerobic 1,2-dichloroethane (1,2-DCA) dechlorination with very different enzyme affinities and turnover rates. However, carbon isotope enrichment factors were the same for both enzymes, reflecting the intrinsic kinetic isotope effect associated with C-Cl bond breakage. Carbon isotope fractionation was also largely constant during anaerobic 1,1,1-trichloroethane (1,1,1-TCA) biodegradation, even when the rate of biodegradation was inhibited by trichloroethene (TCE) co-contamination. This finding provided the basis for carbon isotope-based assessment of 1,1,1-TCE biodegradation at a TCE co-contaminated field site. The wide range of carbon isotope fractionation observed for anaerobic tetrachloroethene (PCE) biodegradation has been a matter of longstanding controversy. This work found the magnitude of carbon isotope fractionation for PCE biodegradation is related to the phylogenetic relationships between PCE-degrading organisms, which may allow for better selection of enrichment factors when assessing PCE biodegradation at field sites. Unexpectedly large variations in carbon isotope fractionation have also been observed for anaerobic TCE biodegradation. During C-Cl bond breakage, slopes of dual element carbon and chlorine isotope effects are typically constant for a given reaction because additional rate-limiting steps affect both elements in a similar way. Hence, characteristic combinations of C/Cl isotope effects can be used to investigate the underlying mechanistic details of a reaction. For TCE biodegradation, C/Cl isotope slopes indicate different reductive dehalogenases may catalyze different reductive dechlorination reaction pathways. This thesis advances the application of compound specific isotope analysis for assessing bioremediation of chlorinated ethenes and ethanes, as well our understanding of the enzymatic degradation mechanisms that catalyze biodegradation.

Department dc:contributor.department

Earth Sciences

Year dc:date.issued

2015

Author dc:creator

• Douglas, Lisa Marie

Advisor dc:contributor.advisor

• Sherwood Lollar, Barbara

• Biodegradation
• Bioremediation
• Chlorinated ethanes
• Chlorinated ethenes
• Compound specific isotope analysis

Handle dc:identifier.uri

http://hdl.handle.net/1807/77746

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/77746