Evaporative emissions from tailings ponds are not likely an

LETTER
LETTER
Evaporative emissions from tailings ponds are
not likely an important source of airborne
PAHs in the Athabasca oil sands region
In their paper, Parajulee and Wania (1) use
a multimedia fate model to argue that emissions of polycyclic aromatic hydrocarbons
(PAHs) in environmental impact assessments conducted to approve developments
in the Athabasca oil sands region (AOSR)
are likely underestimated. The discrepancy
between their model and reported emissions was mainly attributed to indirect evaporative releases of PAHs from tailings
ponds (TPs).
With the exception of naphthenic acids,
dissolved concentrations of most organic
contaminants in TPs and in adjacent shallow
groundwater are very low (2–4). Recently,
Wang et al. (3) reported concentrations
<0.8 μg/L for total US Environmental Protection Agency PAHs in two unspecified
TPs. In another study, dissolved concentrations of phenanthrene (PHE), pyrene (PYR),
and benzo(a)pyrene (BaP)—the three proxy
PAHs used in the model—in two different
TPs measured in summer 2011 were each
<2.0 μg/L (4). These values ranged from
around 10 to several hundred times lower
than the simulated summer 2009 concentrations reported by Parajulee and Wania (1).
A reason for the very large discrepancy between simulated and measured dissolved
PAH concentrations in TPs was not provided. Clearly the model is unable to accurately simulate what has been measured in
the field and underestimates the role of
sorption in tailings sediments, the most
likely process for removal of PAHs, even
those with relatively higher KAW values
(e.g., PHE).
Using lichens as a tool for receptor modeling of air pollution in the AOSR, Studabaker
et al. (5) found significant correlations between concentrations of total PAHs and
metals deriving from lithogenic sources
in samples located up to around 200 km
www.pnas.org/cgi/doi/10.1073/pnas.1403515111
away from the main area of mining activities.
In conjunction with the observation that
PAH concentrations drop off sharply as the
distance from the mines increases, these data
pointed to mine dust as an important source
for airborne PAHs. Another study used diagnostic ratios and compound-specific δ13C
signatures to delineate historical sources of
PAHs in sediment cores from two lakes located 40 and 55 km east of the main area of
mining operations (6). An increasingly larger
input of petroleum-derived PAHs over the
last 30 y was attributed to the deposition
of bitumen in dust particles associated with
wind erosion from open pit mines. Although Parajulee and Wania hint that dust
could be an important source of atmospheric PAHs with relatively low KAW values
(e.g., BaP), it was the δ13C signatures of
PAHs with relatively higher KAW values
(C1-fluorene and dibenzothiophene) that
provided evidence for a fugitive dust origin in recent sediments (6). Emissions
from upgrading facilities have also been
suggested as a principal source of PAHs
to the surrounding AOSR environment
(7, 8). Evaluating the relative importance
of these two sources should be a goal of
future research.
The capacity for multimedia fate models to
closely simulate the transport and fate of
PAHs relies on an accurate identification of
the major source inputs. With their model,
Parajulee and Wania miss the significance
of a previously reported important source of
mining-related PAHs in the AOSR—fugitive
dust—and likely overstate the importance of
evaporative releases from TPs. Such an oversight does not support informed oil sands
management strategies.
Jason M. E. Ahada,1, Paul R. Gammonb,
Charles Gobeilc, Josué Jautzyc, Sagar
Krupad, Martine M. Savarda,
and William B. Studabakere
a
Geological Survey of Canada, Natural Resources
Canada, Quebec, QC, Canada G1K 9A9;
b
Geological Survey of Canada, Natural Resources
Canada, Ottawa, ON, Canada K1A 0E8; cInstitut
national de la recherche scientifique (INRS),
Centre Eau Terre Environnement, Quebec, QC,
Canada G1K 9A9; dDepartment of Plant
Pathology, University of Minnesota-Twin Cities,
St. Paul, MN 55108; and eRTI International,
Research Triangle Park, Durham, NC 27709
1 Parajulee A, Wania F (2014) Evaluating officially reported polycyclic
aromatic hydrocarbon emissions in the Athabasca oil sands region
with a multimedia fate model. Proc Natl Acad Sci USA 111(9):
3344–3349.
2 Oiffer AAL, et al. (2009) A detailed field-based evaluation of
naphthenic acid mobility in groundwater. J Contam Hydrol
108(3-4):89–106.
3 Wang Z, et al. (2014) Forensic source differentiation of petrogenic,
pyrogenic, and biogenic hydrocarbons in Canadian oil sands
environmental samples. J Hazard Mater 271(0):166–177.
4 Savard MM, et al. (2012) A Local Test Study Distinguishes Natural
from Anthropogenic Groundwater Contaminants Near an
Athabasca Oil Sands Mining Operation (Geological Survey of
Canada, Natural Resources Canada, Ottawa), p 140.
5 Studabaker WB, Krupa S, Jayanty RKM, Raymer JH (2012)
Measurement of polynuclear aromatic hydrocarbons (PAHs) in
epiphytic lichens for receptor modeling in the Athabasca Oil
Sands Region (AOSR): A pilot study. Alberta Oil Sands: Energy,
Industry and the Environment, ed Percy KE (Elsevier, Oxford), pp
391–425.
6 Jautzy J, Ahad JME, Gobeil C, Savard MM (2013) Century-long
source apportionment of PAHs in Athabasca oil sands region lakes
using diagnostic ratios and compound-specific carbon isotope
signatures. Environ Sci Technol 47(12):6155–6163.
7 Kelly EN, et al. (2009) Oil sands development contributes polycyclic
aromatic compounds to the Athabasca River and its tributaries. Proc
Natl Acad Sci USA 106(52):22346–22351.
8 Kurek J, et al. (2013) Legacy of a half century of Athabasca oil
sands development recorded by lake ecosystems. Proc Natl Acad
Sci USA 110(5):1761–1766.
Author contributions: J.M.E.A., P.R.G., C.G., J.J., S.K., M.M.S., and
W.B.S. wrote the paper.
The authors declare no conflict of interest.
1
To whom correspondence should be addressed. E-mail: jason.
[email protected].
PNAS | June 17, 2014 | vol. 111 | no. 24 | E2439

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