title: Methane production and isotopic fingerprinting in ethanol fuel contaminated sites.
abstract: Biodegradation of organic compounds in groundwater can be a significant source of methane in contaminated sites. Methane might accumulate in indoor spaces posing a hazard. The increasing use of ethanol as a gasoline additive is a concern with respect to methane production since it is easily biodegraded and has a high oxygen demand, favoring the development of anaerobic conditions. This study evaluated the use of stable carbon isotopes to distinguish the methane origin between gasoline and ethanol biodegradation, and assessed the occurrence of methane in ethanol fuel contaminated sites. Two microcosm tests were performed under anaerobic conditions: one test using ethanol and the other using toluene as the sole carbon source. The isotopic tool was then applied to seven field sites known to be impacted by ethanol fuels. In the microcosm tests, it was verified that methane from ethanol (δ¹³C = -11.1‰) is more enriched in ¹³C, with δ¹³C values ranging from -20‰ to -30‰, while the methane from toluene (δ¹³C = -28.5‰) had a carbon isotopic signature of -55‰. The field samples had δ¹³C values varying over a wide range (-10‰ to -80‰), and the δ¹³C values allowed the methane source to be clearly identified in five of the seven ethanol/gasoline sites. In the other two sites, methane appears to have been produced from both sources. Both gasoline and ethanol were sources of methane in potentially hazardous concentrations and methane could be produced from organic acids originating from ethanol along the groundwater flow system even after all the ethanol has been completed biodegraded.
authors.affiliation: Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W., Waterloo, Ontario, Canada N2L 3G1. jgardena@scimail.uwaterloo.ca
authors.forename: Juliana G
authors.initials: JG
authors.lastname: Freitas
authors.forename: Barbara
authors.initials: B
authors.lastname: Fletcher
authors.forename: Ramon
authors.initials: R
authors.lastname: Aravena
authors.forename: James F
authors.initials: JF
authors.lastname: Barker
mesh_terms: D000693:Anaerobiosis / Q000187:drug effects; D001673:Biodegradation, Environmental; D001938:Brazil; D002247:Carbon Isotopes / Q000737:chemistry / Q000378:metabolism; D004784:Environmental Monitoring; D000431:Ethanol / Q000737:chemistry* / Q000378:metabolism; D005742:Gasoline / Q000032:analysis; D008697:Methane / Q000737:chemistry* / Q000378:metabolism; D009864:Ontario; D010084:Oxidation-Reduction; D014865:Waste Disposal, Fluid; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D005742:Gasoline; D014874:Water Pollutants, Chemical; D000431:Ethanol; D008697:Methane