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.

Beyond Naphthenic Acids: Environmental Screening of Water from Natural Sources and the Athabasca Oil Sands Industry Using Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…There was similarity between the organic components detected in the groundwater samples and the OSPW samples from Company A. Similarities between groundwater and industrial samples are in line with recent findings by Ahad et al [53], Frank et al [37], and Barrow et al [54]. This demonstrates a degree of overlap and potential for future environmental screening, especially if included in a multilevel approach that integrates geochemistry and other factors [37].…”

Impacts and prognosis of natural resource development on water and wetlands in Canada’s boreal zone

“…However, Janfada et al (2006) found preferential sorption of the individual NAs in soil, which could be important from a toxicity standpoint because different NA species have varying degrees of toxicity. Ahad et al (2013) highlighted the need for accurate characterization of the diversity of NA species to quantify potential seepage from tailings ponds. Savard et al (2012) developed a new method of carbon isotopic analysis of carboxyl groups to distinguish mining-related contaminants from natural background organic acids.…”

Ozonation of Naphthenic Acids in Water: Kinetic Study

“…OSPW has demonstrated both acute and chronic toxicity to a number of species (Del Rio et al 2006;Wang et al 2013). The toxicity of OSPW is mainly due to the presence of a group of dissolved organic acids, known as Bnaphthenic acids^(NAs) which refer to a complex suite of alkyl-substituted acyclic and cycloaliphatic carboxylic acids (Clemente et al 2004;Ahad et al 2013). The Alberta government has posted a Bzero dischargep olicy for all OSPW (Government of Alberta 2010).…”