University of Toronto
Camille Malcolm is a Master's of Science student in geochemistry at the University of Toronto, Canada. Under the supervision of Professor Barbara Sherwood-Lollar, Ms. Malcolm's research examines the isotopic signatures of CFCs in groundwater. A junior fellow of Massey College, Ms. Malcolm is also interested in global environmental politics and how modern governments approach environmental problems. Ms. Malcolm has worked in the environmental consulting and mining industries, and holds a B.Sc.H from Dalhousie University
Determining the pure-phase δ13C signatures for different CFC compounds for use in environmental remediation studies
Chlorofluorocarbons (CFCs) are anthropogenically-produced chlorinated compounds used in refrigerants, propellants and a variety of solvents. Notwithstanding the decrease of atmospheric CFCs following the Montreal Protocol, there is a growing need to mitigate CFC contamination in groundwater that is a legacy of past production and storage.
Over the past few decades, several studies have shown the potential to use compound specific isotope analysis (CSIA) to identify the source of contamination of chlorinated compounds, mainly ethenes and ethanes (Hunkeler et al., 2008). The carbon isotopic variability between different compounds from different sources can be related to different manufacturing processes and differences in source feedstock materials. Stable isotopes can also be used to identify and quantify biodegradation in the field, as biodegradation of chlorinated compounds has been associated with a δ13C enrichment trend among daughter products (Hunkeler et al., 2008). To date little work has been done to extend this approach to CFCs.
This study examines the isotopic variability of CFCs to build a database of expected source δ13C signatures for different CFC compounds that can be used in conceptual site model development. The δ13C signatures for CFC-11, CFC-12, CFC-113, CFC-114 and HCFC-22 were measured using dual inlet isotope ratio mass-spectrometry, following offline sealed-tube combustion preparation. Results suggest that most CFC compounds are associated with a distinct δ13C signature. These values are within a range consistent with petroleum hydrocarbon feedstock and consistent with other non-degraded hydrocarbon contaminants investigated. This information with be important for the interpretation of isotope data from field sites. Considering that the anaerobic biodegradation of CFCs is significant, the implications of this study are particularly relevant to remediation projects involving mixed contaminant plumes.