Comparison of the biodegradability of naphthenic acids from commercial sources with
those in Athabasca oil sands tailings waters
Angela C. Scott† and Phillip M. Fedorak,
Department of Biological Sciences, University of Alberta,
Edmonton, Alberta, T6G 2E9 Canada.
† Corresponding
author; phone: (780) 492-4434; fax: (780) 492-9234;
e-mail: ascott@ualberta.ca.
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Abstract
Naphthenic acids (NAs) are natural constituents in many petroleum sources, including bitumen
in the oil sands of Northern Alberta, Canada. NAs are complex mixtures of predominately alkylsubstituted cycloaliphatic carboxylic acids (containing cyclopentane and cyclohexane rings) and
small amounts of acyclic acids (Brient et al. 1995). They are described by the general chemical
formula CnH2n+ZO2, where n indicates the carbon number and Z is zero or a negative, even
integer that specifies the hydrogen deficiency resulting from ring formation.
Commercial NA preparations, obtained via extraction of petroleum distillates, have numerous
applications including wood and textile preservation, as well as promoting vulcanization of
rubber used to manufacture tires (Brient et al. 1995). In the Athabasca oil sands operations,
bitumen extraction processes produce tailings waters that contain NAs. These waters cannot be
discharged to the environment because NAs are acutely toxic to aquatic species. However, a
study using laboratory cultures of microorganisms indigenous to tailings waters found evidence
of detoxification following aerobic incubation with extracted oil sands NAs (Herman et al.
1994). It has also been observed that the toxic character of commercial NAs is reduced following
their biodegradation in laboratory cultures (Clemente et al. 2004). Based on these findings it was
hypothesized that NAs in the oil sands tailings waters would be readily biodegraded and that
tailings waters could be effectively detoxified by biological treatment.
The purpose of our recent studies was to characterize four commercial NAs preparations and the
NAs in oil sands tailings waters from two sources, Syncrude Canada Ltd. and Suncor Energy
Inc., using gas chromatography-mass spectrometry (GC-MS). These NAs were also incubated
with microorganisms from the tailings waters under aerobic, laboratory conditions.
Biodegradation was monitored by following changes in the NAs concentration via high-
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performance liquid chromatography (Yen et al. 2004). This method does not resolve individual
NAs but quantifies NAs based on integration of a “hump” corresponding to the NAs mixture.
Similarly, the GC-MS method generates a hump-shaped total ion chromatogram (TIC) that can
provide qualitative information useful for comparing NAs samples. GC-MS data can also be
used to develop three-dimensional plots of ion intensity versus carbon number and Z-value
(Clemente et al. 2004).
NAs in the commercial preparations had lower molecular masses than the NAs in the tailings
waters. Commercial NAs were biodegraded within 14 days, but only about 25% of the NAs
native to the tailings waters were removed after 40-49 days. These results show that low
molecular mass NAs (C ≤ 17) are more readily biodegraded than high molecular mass NAs (C ≥
18). Moreover, the results indicate that biodegradation studies using commercial NAs alone will
not accurately reflect the potential biodegradability of NAs in the oil sands tailings waters.
Because of the demonstrated recalcitrance of the high molecular mass NAs in tailings waters,
alternative methods, such as ozonation, are being considered for removing the toxicity associated
with these compounds. We are also pursuing better analytical techniques and characterization
methods in order to facilitate the study of these complex NAs mixtures.
Keywords: naphthenic acids, biodegradation, toxicity reduction, tailings waters, Athabasca oil
sands
References:
Brient, J. A., Wessner, P. J., and Doyle, M. N. 1995. Naphthenic acids. In Encyclopedia of
Chemical Technology, 4th ed.; Kroschwitz, J. I., Ed.; John Wiley&Sons: NewYork, 1995; Vol.
16, pp 1017-1029.
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Clemente, J. S., MacKinnon, M. D., and Fedorak, P. M. 2004. Aerobic biodegradation of two
commercial naphthenic acids preparations. Environmental Science and Technology, 38: 10091016.
Herman, D. C., Fedorak, P. M., MacKinnon, M., and Costerton, J. W. 1994. Biodegradation of
naphthenic acids by microbial populations indigenous to oil sands tailings. Canadian Journal of
Microbiology, 40: 467-477.
Yen, T.-W., Marsh, W. P., MacKinnon, M. D., and Fedorak, P. M. 2004. Measuring naphthenic
acids concentrations in aqueous environmental samples by liquid chromatography. Journal of
Chromatography, A, 1033: 83-90.
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