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Airborne Petcoke Dust is a Major Source of Polycyclic Aromatic Hydrocarbons in the Athabasca Oil Sands Region Yifeng Zhang, William Shotyk, Claudio Zaccone, Tommy Noernberg, Rick Pelletier, Beatriz Bicalho, Duane Froese, Lauren J. Davies, and Jonathan W. Martin Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b05092 • Publication Date (Web): 15 Jan 2016 Downloaded from http://pubs.acs.org on January 16, 2016

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Environmental Science & Technology

Airborne Petcoke Dust is a Major Source of Polycyclic Aromatic Hydrocarbons in the Athabasca Oil Sands Region Yifeng Zhang,† William Shotyk,‡ Claudio Zaccone,§ Tommy Noernberg,‡ Rick Pelletier,‡ ∥ ∥ Beatriz Bicalho,‡ Duane G. Froese, Lauren Davies, and Jonathan W. Martin*,† † Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, AB, Canada, T6G 2G3 ‡ Department of Renewable Resources, University of Alberta, 348B South Academic Building, Edmonton, AB, Canada, T6G 2H1 § Department of the Sciences of Agriculture, Food and Environment, University of Foggia, 71122, Foggia, Italy ∥ Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada, T6G 2E3 1

To whom correspondence should be addressed. Jonathan W. Martin, 10-102, Clinical Sciences Building, University of Alberta, Edmonton, AB, Canada, T6G 2G3; E-mail: [email protected]; Phone: (780) 492-1190

Keywords: Athabasca oil sands, polycyclic aromatic hydrocarbons, Sphagnum moss, peat, source apportionment The authors declare no competing financial interest.

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Abstract. Oil sands mining has been linked to increasing atmospheric deposition of

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polycyclic aromatic hydrocarbons (PAHs) in the Athabasca oil sands region (AOSR), but

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known sources cannot explain the quantity of PAHs in environmental samples. PAHs

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were measured in living Sphagnum moss (24 sites, n=68), in sectioned peat cores (4 sites,

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n=161), and snow (7 sites, n=19) from ombrotrophic bogs in the AOSR. Prospective

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source samples were also analyzed, including petroleum coke (petcoke, from both

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delayed and fluid coking), fine tailings, oil sands ore and naturally exposed bitumen.

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Average PAH concentrations in near-field moss (199 ng/g, n=11) were significantly

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higher (p=0.035) than in far-field moss (118 ng/g, n=13), and increasing temporal trends

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were detected in 3 peat cores collected closest to industrial activity. A chemical mass

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balance model estimated that delayed petcoke was the major source of PAHs to living

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moss, and among three peat cores the contribution to PAHs from delayed petcoke

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increased over time, accounting for 45-95% of PAHs in contemporary layers. Petcoke

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was also estimated to be a major source of vanadium, nickel, and molybdenum. Scanning

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electron microscopy with energy dispersive X-ray spectroscopy confirmed large petcoke

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particles (>10 µm) in snow at near-field sites. Petcoke dust has not previously been

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considered in environmental impact assessments of oil sands upgrading, but improved

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dust control from growing stockpiles may mitigate future risks.

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Introduction

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The Province of Alberta has proven bitumen reserves equivalent to 168 billion barrels of

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crude oil.1 In the Athabasca oil sands region (AOSR), surface mining operations extract

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bitumen from oil sands using a hot water process. The recovered bitumen subsequently

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undergoes on-site upgrading, including coking and catalytic hydrocracking to produce

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marketable synthetic crude oil. Overall, the industry is known to release polycyclic

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aromatic hydrocarbons (PAHs) and elements to the environment,2-8 but the major

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emission source(s) has (have) not been identified.

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PAHs are known mutagens and carcinogens, they are ubiquitous in the environment and

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can be found naturally in all hydrocarbon deposits, including in bitumen. PAHs are

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classified as toxic substances in Canada under Schedule 1 of the Canadian Environmental

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Protection Act (1999), and sixteen PAHs are listed as priority pollutants by the U.S.

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Environmental Protection Agency (EPA). PAHs in air may originate from natural

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processes such as volcanic eruptions, as well as forest and prairie fires,9 but they are also

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emitted from anthropogenic sources in urbanized or industrialized regions. Since the

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seminal study of Kelly et al.,2 who reported on the spatial distribution of PAHs in snow

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collected in the AOSR, it has become accepted that the surface mining oil sands industry

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(rather than just natural sources) contributes to the atmospheric deposition of PAHs in the

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region. Subsequent studies have confirmed that PAH concentrations decrease with

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distance from surface mining and upgrading operations,10-12 moreover that PAH

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deposition has increased during the past 30 years, particularly within 55 km of mining

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activity.3,13

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Possible suggested industrial sources include stack emissions from bitumen upgrading,

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diesel exhaust from mining and transportation equipment, or wind-blown particulate

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matter from the mines (e.g. oil sands ore), mine reclamation sites (e.g. fine tailings) or

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haul roads. Nevertheless, unique natural sources may also exist in the region, for example

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from naturally exposed bitumen outcroppings on the banks of the Athabasca River.14

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Parajulee and Wania15 noted that all known industrial PAH sources were not enough to

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explain the environmental burden of PAHs in the AOSR, and went on to suggest that

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atmospheric partitioning of PAHs from tailings ponds might be a significant additional

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source. This suggestion remains unresolved,16 and today there is still great uncertainty

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about the major industrial source of PAHs to the AOSR.17

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Petroleum coke (petcoke) is a carbonaceous residual product from the upgrading of crude

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petroleum. Delayed and fluid coking are two major coking processes in the AOSR. Both

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forms of petcoke derived from bitumen have high sulfur content (up to 8%),18 and cannot

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be used for fuel, thus most petcoke is currently stockpiled, and some is integrated into

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reclaimed landscapes.19 Despite that petcoke from upgrading of traditional crude oil

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products is generally known to contain PAHs, we are unaware of any PAH profiles

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reported for petcoke derived from Canadian oil sands. Large black stockpiles of petcoke

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from bitumen upgrading are visible on mine sites in the AOSR, presumably making them

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susceptible to wind erosion. Jautzy et al.20 showed isotopic evidence for phenanthrene -4-


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from petcoke in lake sediment in the Peace-Athabasca Delta, but the importance of this

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prospective source remains unknown around oil sands mining. Given the black color of

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snow filters presented by Kelly et al.,2 and results of environmental modeling by

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Parajulee and Wania,15 we hypothesized that wind-blown petcoke particles may be the

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missing industrial source of PAHs in the AOSR.

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Here we analyzed for priority PAHs and alkylated PAHs in living moss (Sphagnum

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fuscum), in peat cores and in snow from ombrotrophic bogs in the AOSR. Sphagnum

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moss has no root system, and in ombrotrophic bogs this moss receives its nutrients and

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contaminants exclusively from the atmosphere. Sphagnum peat is slowly formed over

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time by the accumulation of dead moss, partially preserved by the acidic and low oxygen

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conditions of ombrotrophic bogs. Peat cores have previously been validated as good

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environmental archives of PAH contamination.21-24 Prospective PAH source samples

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were also analyzed, and a chemical mass balance (CMB) model was used to quantify

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their contribution to moss and peat contamination. Scanning electron microscopy (SEM)

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with energy dispersive X-ray spectroscopy (EDS) was subsequently used to characterize

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particles in snow from selected bogs, thereby confirming results of the model.

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Materials and Methods

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Field Sampling.

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Sampling sites were selected in the vicinity of open pit mining, tailing pond zones and 4

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upgraders in the AOSR (Figure 1A). All detailed information on moss samples, peat

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cores, snow samples and authentic source samples can be found in Table S1. Triplicate

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moss samples (almost exclusively Sphagnum fuscum) were collected by hand using

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polyethylene gloves at each of 22 bogs in the AOSR in July and August, 2013, 3 bogs far

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from the AOSR (>250 km) in 2014, and two moss samples were cut from the living layer

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of Mildred and McKay peat cores, respectively. Peat cores were collected using a

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titanium Wardenaar monolith corer (15×15×100 cm) in August and October, 2013. Snow

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cores from some of the same locations as peat cores (sites 21-25) were collected using

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Prairie-type Sampler (7.8 cm diameter, model 3620, Figure S1) and reference snow

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samples from Edmonton were collected by hand using polyethylene gloves in winter of

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2015 prior to the spring melt (Figure 1).

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Laboratory.

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Melted snow was filtered using 0.4 µm glass fiber filters (Glass Fiber Store, 90 mm

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diameter). Moss, peat and snow filter samples were freeze-dried for 48 hours. Moss and

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peat were milled into fine powders using a titanium centrifugal mill (Retsch Ultra

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Centrifugal Mill, Germany). Accelerated solvent extraction was used for target analyte

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extraction for moss, peat and snow particles. Liquid-liquid extraction with

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dichloromethane (Optima™) was employed for melted snow filtrate. Solid phase

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extraction by Sep-Pak® silica cartridge (Waters, 1g/6cc) was used for cleanup for all

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samples. All the above pretreatment was performed in the ultraclean organics lab in the

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Faculty of Medicine and Dentistry at the University of Alberta.

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PAHs were determined using gas chromatography-mass spectrometry (Agilent, model

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6890N/5973N). Twenty of the 39 targeted analytes monitored in present study were

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below the method detection limits in all samples (Table S2). The recoveries of the

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measured PAHs are presented for moss, peat and snow meltwater (Table S3). The

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analytical procedure was evaluated by analyzing internal lab reference peat samples with

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most batches of experiments (Table S4), and commercially available certified reference

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material (Figure S2). We also participated in the “Alkyl-PAHs in Environmental

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Samples-Interlaboratory Study 2014”, led by Environment Canada, and most Z scores

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were in the range of -1 to 1 for water analysis.

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SEM-EDS measurements were performed at the University of Alberta Earth and

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Atmospheric Sciences SEM lab. Trace metals were determined in petcoke using the same

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ultraclean, metal-free SWAMP (Soils, Water, Air, Manures, and Plants) lab facilities and

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procedures described earlier for moss.5 Radiocarbon dates were measured using

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identifiable macrofossil remains picked from the peat cores (Table S5) according to

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methods described in SI Text, and the 14C ages for each site were used to construct age-

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depth models (Figure S3) using the Oxcal P_Sequence model with 1 year resolution.25

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Spatial Analysis of PAH Concentrations.

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Geographic Information System (GIS) analyses were performed by ArcGIS 10.3

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Geostatistical Analyst software (Esri, Redlands, California) to construct maps and to

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calculate distances between upgraders and sampling sites.

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Previous studies have examined the spatial measurement of contaminant concentrations

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change by correlating the environmental measurements with linear distance from a

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single point in the vicinity of the major mining activity,2,5,8,10 which is a reasonable proxy

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for general industrial PAH sources from these two major mine sites. Nevertheless,

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Syncrude and Suncor are not the only major surface mines in the AOSR, and there are

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actually four active upgraders producing synthetic crude from bitumen in the AOSR

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(Figure 1A). Moreover, data is available from the Government of Alberta on the annual

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synthetic crude oil production (SCOP) and petcoke inventory (PI) at each upgrader. Thus,

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in this exercise three arbitrary terms (Ax, 1/km; Bx, 1,000,000 m3/km and Cx, 1,000,000

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tonnes/km) were calculated for each moss collection site (x, sites 1-24). These terms were

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all inversely proportional to the distance between each sampling site and each upgrader,

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where n identifies each of the 4 upgraders (Eq. 1-4). For term Bx, this was directly

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proportional to the annual SCOP reported for each upgrader in 2013. For term Cx, this

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was directly proportional to the petcoke inventory in October, 2013. Given that the mean

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concentration of total PAHs in fluid petcoke (170 ng/g) was much lower than in delayed

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petcoke (26800 ng/g), we used the fluid petcoke inventory to multiply by a factor

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(170/26800=0.00634) to transform to the delayed petcoke inventory for the one

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upgrading site where fluid coking is used, and the term Dx was thereby adjusted to the

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petcoke inventory in October, 2013 (Eq. 3-4). Linear correlations between moss PAH

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concentrations and arbitrary terms (Ax, Bx, Cx and Dx) were then examined (Figure S4).

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For each site, we arbitrarily assigned A values that were lower than 0.125 as far-field

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sampling sites, and higher values were termed as near-field sampling sites (Figure 1A and

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S4A).

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[1]

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[3]

[2]

[4]

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CMB model

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The EPA CMB model is appropriate for quantitatively apportioning localized sources of

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contaminants,26 and detailed information on the analysis can be found in SI Text. Briefly,

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for separate analyses, moss and peat concentrations (ng/g) were used as the ambient

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environmental data, with relative uncertainty as the standard deviation of triplicate moss

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at each sampling site (site 1-22). Data from two moss sites (site 23 and 24) and all peat

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layers are for single samples, thus relative uncertainty was assumed to be 20%. Source

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profile data included data from our own analysis of authentic source samples, but also

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included data from the literature as detailed in Table S6. Among the profiles in Table S6,

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8 of these were used for the final CMB model in the current work, as indicated. As

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suggested by Li et al.,27 the relative uncertainty for all source profiles is set to 40 %, and

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when the fingerprint values for any individual PAHs are below the limit of detection, or

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not reported, an uncertainty of 0.001 was assigned.

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Results and Discussion

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PAH Spatial Trends in Moss.

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In the following sections, the sum concentrations of 13 detectable PAHs are referred to as

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∑13PAH (SI Text) while the sum concentrations of 4 detectable alkyl-PAHs are referred

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to as ∑alkyl-PAH. Finally, the sum combination of naphthalene, ∑13PAH, and ∑alkyl-

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PAH are referred to as “total PAHs”.

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Sample collection sites were categorized as either near-field or far-field sites, as shown

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spatially in Figure 1A. This categorization was based on the sum of the inverse distance

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(1/km) between each sampling site and each of the 4 bitumen upgraders (Eq. 1); a break-

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point in these values can be visualized in Figure S4A.

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∑13PAH concentrations in moss from the AOSR ranged from 28.7-389 ng/g, but

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concentrations were significantly greater (p=0.035) among near-field sites (199 ng/g)

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compared to far-field sites (118 ng/g). ∑13PAH concentrations were highest at two near-

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field sites (site 19 and 23) near the center of the sampling region (Figure 1A and Table

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S7), and concentrations here were 7-14 times higher than at far-field sites (sites 3 and 4,

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Figure 1B). Total PAH concentrations increased significantly with decreasing distance to

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the 4 known bitumen upgraders in the AOSR (r=0.701, p10 µm) (Figure 4 and S9) and

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would therefore not be observed by PM2.5 monitoring.

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The aerodynamic diameters of almost all particles (>99%) emitted from upgrader stacks

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has been reported to be 10 µm) is not

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clear and may depend on several factors. Second, the sample size for certain industrial

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prospective PAH sources is small (i.e. 1-2), which leads to some uncertainty in the

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quantitative CMB results. Additional samples were requested but could not be obtained.

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Nevertheless, in context of the current findings it was reassuring that the two distinct

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samples of delayed petcoke analyzed had very similar PAH profiles. Third, for the

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literature PAH profile used here to represent upgrader stack emissions, details of sample

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collection were not provided in the associated report,49 and it cannot be confirmed if this -22-


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data represents total emissions or rather just the gas phase or just the particle phase,49 thus

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it is possible that an important PAH source has still not been considered.

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Supporting information

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Detailed information on trace analytical methods and instrumentation, method recovery

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and detection limits, the U.S. EPA CMB model (v8.2), calibration of radiocarbon

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measurement and dating, PAHs data, and additional figures.

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ACKNOWLEDGEMENTS

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We acknowledge the financial support of Alberta Innovates-Energy and Environment

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Solutions. Drs Melanie Vile (Villanova University), Steve Larter (University of Calgary),

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and Daniel Alessi (University of Alberta) are gratefully acknowledged for moss, oil sands,

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and petcoke samples, respectively. Drs Kun Zhang, Alberto Pereira and Nathan J. Gerein

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from University of Alberta are thanked for their technical assistance. Drs Erin Kelly and

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David Schindler are sincerely thanked for providing congener-specific PAH data in snow

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from their previously published study.

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(39) Baker, L.F.; Ciborowski, J.J.H.; MacKinnon, M.D. Petroleum coke and soft tailings sediment in constructed wetlands may contribute to the uptake of trace metals by algae and aquatic invertebrates. Sci. Total Environ. 2012, 414, 177-186. (40) Alessi, D.S.; Alam, M.S.; M.C. Kohler. Designer biochar-coke mixtures to remove naphthenic acids from oil sands process-affected water (OSPW). The Oil Sands Research and Information Network (OSRIN) Report No. TR-57. 2014, 38 pp. (41) Meyer, T.; Lei, Y.D.; Wania, F. Measuring the release of organic contaminants from melting snow under controlled conditions. Environ. Sci. Technol. 2006, 40, 33203326. (42) Bari, M.; Kindzierski, W.B. Fifteen-year trends in criteria air pollutants in oil sands communities of Alberta, Canada. Environ. Int. 2015, 74, 200-208. (43) Wang, X.L.; Watson, J.G.; Chow, J.C.; Kohl, S.D.; Chen, L.-W.A.; Sodeman, D.A.; Legge, A.H.; Percy, K.E. Measurement of real-world stack emissions with a dilution sampling system. Elsevier Press: Oxford, UK, 2012; p 171-192. (44) Austen, I. A black mound of Canadian oil waste is rising over Detroit. The New York http://www.nytimes.com/2013/05/18/business/energyTimes. environment/mountain-of-petroleum-coke-from-oil-sands-rises-in-detroit.html (accessed June 9, 2015). (45) CBC News. Company appeals pet coke storage ban on Detroit River. http://www.cbc.ca/news/canada/windsor/company-appeals-pet-coke-storage-banon-detroit-river-1.2521340 (accessed Spetember 18, 2015). (46)

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TOC Artwork



Figure captions Figure 1. (A) Location of near-field and far-field sampling sites in relation to 4 bitumen upgraders and various tailings deposits. (B) Moss concentrations of ∑13PAHs (ng/g) at each site in summer 2013, and the respective contribution of various sources as estimated by chemical mass balance modelling (pie charts). The predicted spatial distribution is also shown by simple kriging. The wind rose diagram for Mildred Lake weather station was previously described in Shotyk et al.5 Figure 2. Concentrations of PAHs and retene with depth in four peat cores whose locations are shown in Figure 1A. Individual radiocarbon dated samples (dashed lines) are plotted with their modeled age range (Year, AD) based on 68% confidence intervals. Multiple age ranges are sometimes reported, particularly from the pre-bomb time interval (i.e. prior to the 1950s), due to the shape of the calibration curve (see SI Text). Figure 3. Profiles of PAHs (number of rings increasing left to right) and retene in moss, in prospective source samples and in summer air in the AOSR.12 *To avoid the influence of forest fires, the air data shown is from April 2 to June 11, 2012; naphthalene was not reported for air, and almost all acenaphthylene and acenaphthene are below detection limits. Figure 4. SEM images of snow filters (×1,000 and ×20,000 magnification) and associated EDS spectra of particles compared to authentic delayed petcoke. Letters in the SEM images indicate points at which EDS spectra were recorded. Additional EDS spectra (points C, D, E) appear in Figure S8.


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Figure 1. Location of near-field and far-field sampling sites in relation to 4 bitumen upgraders and various tailings deposits and moss concentrations of ∑13PAHs (ng/g) at each site in summer 2013, and the respective contribution of various sources as estimated by chemical mass balance modelling. 279x240mm (200 x 200 DPI)



Figure 2 PAHs in peat cores 296x209mm (300 x 300 DPI)


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Figure 3 Profiles of PAHs and retene in moss, in prospective source samples 296x209mm (300 x 300 DPI)



Figure 4 SEM images of snow filters and associated EDS spectra of particles compared to authentic delayed petcoke. 669x450mm (96 x 96 DPI)


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