title: Characterization and quantification of mining-related "naphthenic acids" in groundwater near a major oil sands tailings pond.
abstract: The high levels of acid extractable organics (AEOs) containing naphthenic acids (NAs) found in oil sands process-affected waters (OSPW) are a growing concern in monitoring studies of aquatic ecosystems in the Athabasca oil sands region. The complexity of these compounds has substantially hindered their accurate analysis and quantification. Using a recently developed technique which determines the intramolecular carbon isotope signature of AEOs generated by online pyrolysis (δ(13)Cpyr), natural abundance radiocarbon, and high resolution Orbitrap mass spectrometry analyses, we evaluated the sources of AEOs along a groundwater flow path from a major oil sands tailings pond to the Athabasca River. OSPW was characterized by a δ(13)Cpyr value of approximately -21‰ and relatively high proportions of O₂ and O₂S species classes. In contrast, AEO samples located furthest down-gradient from the tailings pond and from the Athabasca River were characterized by a δ(13)Cpyr value of around -29‰, a greater proportion of highly oxygenated and N-containing compound classes, and a significant component of nonfossil and, hence, non-bitumen-derived carbon. The groundwater concentrations of mining-related AEOs determined using a two end-member isotopic mass balance were between 1.6 and 9.3 mg/L lower than total AEO concentrations, implying that a less discriminating approach to quantification would have overestimated subsurface levels of OSPW. This research highlights the need for accurate characterization of "naphthenic acids" in order to quantify potential seepage from tailings ponds.
authors.affiliation: Geological Survey of Canada, Natural Resources Canada, Québec City, QC G1K 9A9, Canada. jason.ahad@nrcan.gc.ca
authors.forename: Jason M E
authors.initials: JM
authors.lastname: Ahad
authors.forename: Hooshang
authors.initials: H
authors.lastname: Pakdel
authors.forename: Martine M
authors.initials: MM
authors.lastname: Savard
authors.forename: Angus I
authors.initials: AI
authors.lastname: Calderhead
authors.forename: Paul R
authors.initials: PR
authors.lastname: Gammon
authors.forename: Alfonso
authors.initials: A
authors.lastname: Rivera
authors.forename: Kerry M
authors.initials: KM
authors.lastname: Peru
authors.forename: John V
authors.initials: JV
authors.lastname: Headley
mesh_terms: D002250:Carbon Radioisotopes / Q000032:analysis; D002264:Carboxylic Acids / Q000032:analysis*; D008401:Gas Chromatography-Mass Spectrometry; D060587:Groundwater / Q000737:chemistry*; D008906:Mining
chemical_list: D002250:Carbon Radioisotopes; D002264:Carboxylic Acids; C046170:naphthenic acid