Science of the Total Environment 447 (2013) 337–344

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Is there widespread metal contamination from in-situ bitumen extraction at ColdLake, Alberta heavy oil field?

Elliott K. Skierszkan, Graham Irvine, James R. Doyle, Linda E. Kimpe, Jules M. Blais ⁎Department of Chemical and Environmental Toxicology, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5

H I G H L I G H T S

► In-situ bitumen production is not causing regional metal contamination at Cold Lake.► Sediment cores show post-industrial increases of Cd, Pb and Hg concentrations.► These increased concentrations level off prior to large-scale bitumen extraction.► One core demonstrated Cu and V increases concurrent with Cd, Pb and Hg increases.► Soil samples collected near the oil field had minor metal enrichment.

⁎ Corresponding author at: 30 Marie Curie, DepartmentOttawa, Ontario, Canada K1N 6N5. Tel.: +1 613 562 5800x

E-mail addresses: e.skierszkan@gmail.com (E.K. Skiegrahammirvine@gmail.com (G. Irvine), jamiedoyle@symlinda.kimpe@uottawa.ca (L.E. Kimpe), jules.blais@uottaw

0048-9697/$ – see front matter © 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.scitotenv.2012.12.097

a b s t r a c t

a r t i c l e i n f o

Article history:Received 14 October 2012Received in revised form 27 December 2012Accepted 28 December 2012Available online 5 February 2013

Keywords:Alberta oil sandsMetalsPaleolimnologySoil contaminationAirborne contamination

The extraction of oil sands by in-situ methods in Alberta has expanded dramatically in the past two decadesand will soon overtake surface mining as the dominant bitumen production process in the province. Whileconcerns regarding regional metal emissions from oil sand mining and bitumen upgrading have arisen,there is a lack of information on emissions from the in-situ industry alone. Here we show using lake sedimentrecords and regionally-distributed soil samples that in the absence of bitumen upgrading and surface mining,there has been no significant metal (As, Cd, Cu, Hg, Ni, Pb, V) enrichment from the Cold Lake in-situ oil field.Sediment records demonstrate post-industrial Cd, Hg and Pb enrichment beginning in the early TwentiethCentury, which has leveled off or declined since the onset of commercial in-situ bitumen production atCold Lake in 1985.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Environmental scrutiny of Alberta's oil sand industry has increasedin recent years, given the 9-fold increase in annual bitumen productionbetween 1980 and 2010 (Burrowes et al., 2011). Bitumen production byin-situmethods, involving the injection of superheated steam intowellsdrilled into deep (>70 m) oil sand formations, has steadily grown andwill soon overtake surface strip mining to become the dominant oilsand extraction method in Alberta (Moorhouse et al., 2010). In-situextraction of oil sands has increased 80-fold over the past three decadesand now accounts for over 47% of province-wide bitumen extraction(Burrowes et al., 2011) (Fig. 1).

To date, the few available studies on contaminant emissionsfrom oil sand production have focused largely on surface miningand bitumen upgrading. Kelly et al. (2010) identified metal emissions

of Biology, University of Ottawa,6650; fax: +1 613 562 5486.rszkan),patico.ca (J.R. Doyle),a.ca (J.M. Blais).

rights reserved.

as a source of potential concern for the Athabasca watershed innorthern Alberta. They reported increased Ag, As, Cd, Cr, Cu, Pb, Hg,Ni, Sb, Tl and Zn concentrations in rivers downstream of oil sanddevelopment, and found elevated deposition of metals to the snow-pack adjacent to bitumen mining and processing facilities. Guéguenet al. (2011) found Cu, Pb and Cd concentrations in excess of environ-mental quality guidelines associated to oil sandmining in the AthabascaRiver, and Timoney and Lee (2011) also found elevated polycyclicaromatic hydrocarbons (PAH) in sediments in the same river down-stream of the oil sand development near Fort McMurray. However,there has been an ongoing debate regarding the source of contaminantrelease in the region, with several reports providing strong evidencethat elevated contaminant levels in the Athabasca watershed are atleast in part due to natural releases from the erosion of outcroppedbituminous soils (Akre et al., 2004; Evans et al., 2002; Headley et al.,2001). One suggested approach to separating anthropogenic and natu-ral signals has been to use lake sediment cores to evaluate long-termdeposition of contaminants (Dowdeswell et al., 2010; EnvironmentCanada, 2011). Most recently, Wiklund et al. (2012) followed thisapproach and reported in this journal that Pb, Sb, As and Hg emissionshave been decreasing in recent years in a lake 200 km north of the

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Cold Lake Peace River Athabasca

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men

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Pilot projects

Fig. 1. Historical in-situ bitumen production in Alberta at the Cold Lake, Peace Riverand Athabasca oil sand deposits. Bitumen production by oil sand deposits prior to1998 was extrapolated using data from Alberta's Energy Resources ConservationBoard (Burrowes et al., 2011) because prior to 1998 only total province-wide in-situbitumen production data were available.

338 E.K. Skierszkan et al. / Science of the Total Environment 447 (2013) 337–344

Athabasca oil sand development, suggesting decreasing contaminationin the airshed despite the increased output of the oil sand industry.

The Cold Lake oil field of eastern Alberta, located approximately300 km southeast of the Athabasca oil field, provides an ideal settingto study emissions from in-situ oil sand extraction in the absence of asignal from surface mining and natural bitumen erosion. At this loca-tion the bituminous formations lie between 415 and 470 m belowgrade (Stancliffe and van der Kooij, 2001) and there are no bitumenupgraders or oil refineries within a radius of 150 km, making thisstudy the first to evaluate emissions from the in-situ extraction pro-cess alone. In order to produce the required steam for in-situ bitumenextraction, large amounts of hydrocarbons are combusted in thermalplants. These are comprised of approximately 85% natural gas importedto the site and 15% produced gas recovered as a by-product of bitumenproduction (Imperial Oil, 2002). Gas flaring can occur when the bitu-men collection process is over-pressurized with the produced gasesemanating from the boreholes (Imperial Oil, 2002). A regional airshedsurvey conducted prior to 2002 for Imperial Oil's environmentalassessment found an average industrial emission of 1.2 tonnes perday of PM2.5 including thermal plant releases and vehicle emissions(Imperial Oil, 2002).We could find no information on themetal contentof aerial emissions.

The Cold Lake First Nations (CLFN) territory is located immediatelyadjacent to the oil field and CLFN band members face increasedexposure to contaminated soils due to traditional lifestyle practices, inparticular wild food gathering and processing (Doyle et al., 2012).Thus, environmental monitoring is warranted to ensure that any re-leases of heavy metal from the in-situ facilities are not accumulatingat harmful levels.

In this study, we used spatial and temporal analyses of metal con-centrations to characterize the impact of in-situ oil sand extraction onregional metal enrichment in soil and sediment. The Cold Lake studysite allows us to assess in-situ emissions in the absence of mining andnatural erosion of surficial bitumen, which previous studies in theAthabasca region have examined (Akre et al., 2004; Headley et al.,2001; Evans et al., 2002; Kelly et al., 2009, 2010; Timoney and Lee,2011; Wiklund et al., 2012). We examined historical variations ofseven trace elements (Hg, Cd, Cu, Pb, Ni and V) that have been asso-ciated with the oil sands elsewhere (Cao, 1992; Kelly et al., 2010)using sediment cores from two lakes located in the immediate vicin-ity of the oil field, and analyzed surficial soil samples collected in the

region to investigate whether regional metal contamination from thein-situ industry is occurring.

2. Study site and history

The Cold Lake in-situ oil installations are located in central-easternAlberta, approximately 25 km west of the Alberta–Saskatchewanborder. The local bedrock geology is predominantly marine shale ofthe Lea Park Formation from the Upper Cretaceous (Alberta GeologicalSurvey, 1999) overlain by various fluvial sediments and glacio-fluvialtills (Fenton and Andriashek, 1983). The predominant local wind pat-terns are in theWNWandESE directions (Imperial Oil, 2002). Followingpilot projects in the late 1960s by Imperial Oil, commercial productionbegan in 1985 and Canadian Natural Resources Ltd. and Cenovus FosterCreek Commercial launched operations over the course of the followingdecade. Currently, there are more than twenty companies operating atCold Lake, producing approximately 54,600 m3 of bitumen per day(Burrowes et al., 2011).

The two lakes in which sediment cores were collected are HildaLake (54°31′N, 110°25′W) and Ethel Lake (54°31′N, 110°21′W)(Fig. 2), located adjacent and immediately south of the most devel-oped portion of the oil field. Both lakes are mesotrophic and develophypoxic to anoxic hypolimnia during summer stratification (AlbertaAtlas of Lakes, 2007; Alberta Lake Management Society, 2007)which limits bioturbation and thus better preserves the sedimentarymetal archives (Carignan et al., 2003). The lakewater pH of HildaLake is 8.9 and the alkalinity is 325–431 mg CaCO3/L (Alberta LakeManagement Society, 2007). Ethel Lake is slightly less alkaline witha pH between 8.3 and 8.4 and an alkalinity of 160 mg CaCO3/L(Alberta Atlas of Lakes, 2007). The relatively high pH of both lakesreduces the potential for post-depositional mobilization of severaltrace metals which can occur under more acidic conditions (Calmanoet al., 1994; Gambrell et al., 1980, 1991; Schindler et al., 1980;Schindler, 1988; Schindler and Wageman, 1980). Other physical andchemical characteristics of the lakes are summarized in supplementaryinformation Table S1.

3. Methods

Field sampling was completed in August 2011. For lake sedimentsampling in Hilda and Ethel Lakes, cores were completed to depths of42–50 cm using a 6 cm Plexiglas gravity corer and were subsequentlysub-sectioned on-site into 1 cm intervals for the upper 24 cm, andthen 2 cm intervals thereafter using a Glew (1989) extruder. Intervalswere placed in pre-labeled Whirlpacks™ and kept frozen until labora-tory analyses.

210Pb dating of the sediment cores was completed by measuring210Pb and 226Ra activities using a high purity germanium detector in agamma spectrometer (DSPec spectrometer linked toMaestro II Softwareby Ortec, Tennessee, USA), using the methods of Appleby (2002). Inorder to date the sediments, unsupported 210Pb was measured bysubtracting supported 210Pb (measured as 226Ra activity) from total210Pb. 137Cs and 241Am activities were also measured as independentchronostratigraphic markers, which are known to have increased dra-matically due to nuclear arms testing circa 1954, and peaked in 1963prior to the Nuclear Test Ban Treaty signed that year.

Total organic carbon (TOC) of sediments was measured by massspectrometry using a Vario EL III Elemental Analyzer (Elementar,Germany). Prior to mass spectrometry, inorganic carbon was re-moved by acid digestion. A small amount (5–10 mg) of freeze-driedsediment from each sampling interval was wetted using ultra-pureHPLC water and placed in an acid desiccator containing concentratedHCl for 48 h. Following acid digestion, sample vials were filled withHPLC water, centrifuged (3000 rpm for 10 min) three times, withthe supernatant discarded between centrifugation steps to remove

Hilda Lake

City of Cold Lake

Ethel Lake

Fig. 2. Map of the Cold Lake in-situ oil field showing locations of most intense in-situ development, soil samples, and Ethel and Hilda Lakes, where sediment cores were collected.

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Fig. 3. Age–depth relationship in Hilda and Ethel Lake sediment cores using theConstant Rate of Supply model (Appleby, 2002).

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all dissolved inorganic carbon. Samples were then freeze-dried onceagain and re-weighed for TOC analysis.

Sediment metal analysis was completed by SGS minerals (Lakefield,Ont.), which is accredited formetal analysis of soils and sediments underthe Canadian Association for Laboratory Accreditation. The analysis wasdone by inductively-coupled plasma mass spectrometry followingdigestion of samples usingmicrowave-assisted aqua regia. For this anal-ysis, 0.5 mg of freeze-dried sediment was collected at 14 to 16 intervalsthroughout each sediment core. Approximately 10% of sampleswere an-alyzed as blind duplicates, yielding a precision of 5.4% as measured bythe relative percent difference (RPD), which is given by Eq. (1);

RPD ¼ x1−x2j j0:5� x1 þ x2ð Þ � 100% ; ð1Þ

where x1 and x2 are the concentrations of a given metal that were mea-sured in the sample and its duplicate.

Mercury analysis of sediments was performed by Cold VapourAtomic Absorption Spectroscopy (CVAAS) using a Nippon SP-3DMercury Analyzer (Nippon Instruments, College Station, Texas).Mercury samples were run in triplicate and instrument accuracywas verified using MESS-3 Marine Sediment 91±9 ng Hg/g, NationalResearch Council of Canada. The average relative standard deviationwas 4.4%.

Soil samples were collected at sites shown in Fig. 2 by removingthe uppermost layer of vegetation and sampling the superficial soilhorizon into Whirlpacks™ using a pre-rinsed plastic spatula. Soilsamples were kept frozen until laboratory analyses. Soil sampleswere sieved to reduce the variability between samples caused bysoil heterogeneity among sites. Freeze-dried samples were sievedthrough US Standard Test Sieves (ASTM E-11 Specification, FisherScientific, USA) at 2 mm, 250 μm and 63 μm using an automatedsieve-shaker (Soil Test Engineering Model Cl-592B, SoilTest, Evanston,IL, USA) that was operated for 10 min per sample. Samples wereweighed post-sieving to obtain the relative proportions in each grainsize fraction. For the purpose of brevity, only the b63 μm fraction isdiscussed in depth here. All soils that were analyzed were fine to medi-um sands and TOCwas generally quite low (i.e. 0.7–3.6%) except S21 at14% TOC. TOC andmetal analysis in soil samples followed the same pro-cedure as for sediments, with the exception that Hg was not measured

in soils. One soil sample was analyzed for metals in triplicate andyielded an average relative standard deviation of 3%. In order to evalu-ate geospatial trends in metal concentrations, interpolations betweensoil sampling locations by ordinary spherical kriging were completedusing ArcGIS software (v.10, ESRI, Redlands, CA). All concentrationdata for soils and sediment are reported in μg/g dry weight.

4. Results and discussion

4.1. Sediment 210Pb geochronology

The sedimentation rate was low in both lakes and CRS-derivedgeochronology placed the area corresponding to the start of commer-cial production at Cold Lake (i.e. 1985) at approximately 5 cm depth(Fig. 3.). The onset of industrialization of western North Americacirca 1900–1940 was identified at approximately 9–16 cm in EthelLake and 9–23 cm in Hilda Lake. However dating resolution waspoor for Hilda Lake due to low and variable 210Pb activity (Fig. S1)which resulted in high uncertainty around CRS dates deeper inthe core (Fig. 3). The resulting age-depth profile of Hilda Lake was

340 E.K. Skierszkan et al. / Science of the Total Environment 447 (2013) 337–344

smoothed between 9 and 15 cm at a date corresponding to 1937,making it difficult to accurately date sediments in those intervals.The exponential rise in 137Cs, which corresponds to nuclear armstesting in the 1950s, began in both cores at 8 cm and was in goodagreement with CRS dates placing the 1950s at that depth. 137Cspeaks corresponding to 1963 were found at ~4 cm in Hilda Lakeand ~7 cm in Ethel Lake, which in both cases somewhat overestimatethose sediment interval ages when compared to CRS dates. However,because of the tendency of 137Cs to be mobile in sediments (Blais etal., 1995; Davis et al., 1984; Kirchner, 2011), the CRS-model (Fig. 3)was retained for dating interpretations.

4.2. Sediment geochemistry

In each sediment core we observed pronounced Hg, Pb and Cdenrichment occurring at a consistent depth while there was noevidence for major anthropogenic enrichment of As, Cu, Ni and Vbased on concentration profiles (Fig. 5). In Hilda Lake concentrationsof Hg, Pb and Cd increased from pre-industrial background levelsaround 19 cm (~1930s), accompanied by a subtle increase in V at13 cm. The increasing trend for all of these elements leveled offabove 5–7 cm (~1970s–1980s) and concentrations either remainedconstant or decreased slightly in the subsequent shallow sedimentintervals. Arsenic concentrations remained relatively constant through-out the Hilda core. In Ethel Lake, the Hg, Pb and Cd concentrationincreases occurred starting at a depth of 12 cm (~1920s), leveling offabove 5–7 cm (~1970s–1980s), and As concentrations decreasedslightly in more recent sediments relative to pre-industrial levels. Niand V concentrations exhibited little variation in the Ethel core. A slightrise in Cu concentrations occurred between 12 and 5 cm (~1930s to~1970s), although they did not increase beyond those found inpre-industrial sediments.We also computed flux rates of metals to sed-iments in the shallowest portion of the Ethel Lake core, which revealeda continued increasing trend in flux above 6 cm (~1980s), suggestingthat the plateaus observed in the concentration profiles in recent sedi-ments may have been in part caused by dilution from increased sedi-mentation rates in recent decades. However, because the uncertaintyassociated with sedimentation rates is much greater relative to concen-tration data alone (Boyle, 2001), and given the consistency of metalconcentrations between both profiles and within other publishedstudies (e.g. Carignan et al., 2003; Hermanson, 1993; Landers et al.,

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Fig. 4. Total organic carbon, total iron and manganese profiles in Hilda and Ethel Lakesediment cores.

1998; Mast et al., 2010; Renberg et al., 1994; Schwikowski et al., 2004;Weiss et al., 1999; Wiklund et al., 2012,), we took the concentrationprofiles as being the most reliable indicators of metal input to thestudied lakes.

We used enrichment ratios, defined as the concentration of agiven metal at a certain depth divided by the average pre-industrialconcentration, to look for anomalies in the sediment record. Pre-industrial conditions were defined as those intervals prior to anyobserved Cd, Hg and Pb increases, corresponding to intervals below20.5 cm in both cores. Cd, Pb and Hg enrichment began circa ~1920in Ethel Lake, with concentrations peaking distinctly prior to com-mercial in-situ bitumen production at Cold Lake in 1985 (Fig. 6).The increasing Cu concentrations observed in the Ethel Lake sedimentprofile between ~1930 and 1985 did not yield enrichment ratios sig-nificantly greater than 1 due to comparably high concentrations indeep pre-industrial sediments. The enrichment ratio was strongestfor Hg, reaching 2.9, while Cd and Pb were enriched by ~1.5–2.3 atthe height of anthropogenic emissions.

In Hilda Lake, Pb, Hg and Cd enrichment began in approximatelythe 1930s and leveled off following the mid-1980s, similar to trendsfor those elements in Ethel Lake. Peak V enrichment occurred be-tween ~1970 and 1985 before leveling off and decreasing in theuppermost sediment interval. Lead demonstrated the greatest enrich-ment ratio, reaching 6.6, and Cd and Hg were enriched by 2.0–2.4following industrialization. The small V enrichment stabilized at 1.3.However, because the CRS-derived dates for Hilda Lake remain nearlyconstant at ~1937 between 9 and 17 cm (Fig. 3), it is difficult to accu-rately date the beginning of enrichment at Hilda Lake, which the CRSmodel suggests occurred circa 1930. Based on the proximity and sim-ilar physical and chemical properties of both lakes, it is expected thatany post-industrial metal enrichment would have occurred at thesame time. The lag indicated by CRS-derived dates for the timingof this enrichment may be an artifact of greater uncertainty surround-ing the Hilda Lake dating model. However, without a more high-resolution dating profile of Hilda Lake, we stress that the exact timingof the observed enrichment cannot be determined to a high degree ofprecision in that sediment core. Nonetheless, our data clearly suggestit occurred well before large-scale in-situ bitumen extraction thatbegan in 1985.

While the Cd, Hg, Pb and slight Cu enrichments coincided withincreasing TOC in Ethel Lake and TOC was significantly correlated withHg, Cd and Pb (r2=0.68, 0.62 and 0.70; pb0.00003, b0.002 andb0.0007, respectively), there was no significant correlation with TOCin the Hilda Core. Because the metal profiles were highly consistentamong both cores and there was no significant TOC–metal relationshipin Hilda Lake, we infer that TOC correlation was not responsible forthese observed increases. Fe and Mn, which can scavenge metalswhen present as oxyhydroxides, were not correlated to other metalsexcept for a negative relationship with Hg in Ethel Lake (r2=0.46,pb0.008). Fe and Mn profiles did not correlate significantly with eachother nor did they present any major spikes that would suggest thatactive redox gradients were taking place at the moment of sedimentsampling (Fig. 4).

Sediment concentrations were also compared to Canadian Councilof Ministers of the Environment sediment quality guidelines for As,Cd, Cu, Hg and Pb (CCME, 1999a). The CCME and Alberta have nosediment quality guidelines for Ni; therefore, the Ontario sedimentstandard for Ni was used for comparison (MOE, 2009). No federalor provincial guideline exists for V. All metal concentrations werebelow regulatory guidelines with the exception of As. Arsenic concen-trations throughout the Hilda Lake core exceeded both the CCMEInterim Sediment Quality Guideline and the CCME Probable EffectsLevel Guideline (5.9 μg/g and 17 μg/g, respectively) and four SedimentQuality Guideline exceedences occurred in deeper intervals (20–21 cm,24–26 cm, 30–32 cm and 36–38 cm) in the Ethel Lake core. However,despite the high As concentrations, there was no evidence for recent

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Fig. 5. Metal profiles in Hilda (white dots) and Ethel Lake (black dots) sediment cores. Gray shaded area corresponds to sediments deposited from 1985 to 2011 based on CRSradiometric dating.

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enrichment as concentrations fairly remained consistent in Hilda Lakeand decreased in shallower sediment intervals at Ethel Lake (Fig. 5).Other investigations have demonstrated that As is regionally enrichedin local groundwaters due to As-rich till deposits (Andriashek, 2000).Groundwater discharge is known to contribute a significant proportionof the lake budget in Hilda Lake, (Alberta Lake Management Society,2007), providing an alternative explanation for high As concentrationsin sediments.

Based on evidence from sediment profiles, there is no evidence forstrong metal enrichment attributable to the in-situ oil sand facilities.

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Fig. 6. Calculated enrichment ratios (concentration at depth i/average pre-industrial conceenrichment ratio of 1. Panels on right indicate approximate in-situ bitumen production at CBitumen production data from Burrowes et al. (2011).

Rather, Cd, Pb and Hg are likely enriched as a result of widespreadTwentieth Century industrialization, with concentrations peakingwell before the start-up of commercial operations at Cold Lake in1985, and leveling off or decreasing thereafter. Furthermore, our pro-files are typical for regions that are not subjected to major point-source anthropogenic emissions and are in good agreement withother profiles of lake sediments in remote areas such as the Arctic(Hermanson, 1993; Landers et al., 1998), the US Rockies (Mastet al., 2010) and northern Sweden (Renberg et al., 1994). Pb increasesin sediment cores that have been linked to the combustion of leaded

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~1985

ntration) for metals in Hilda and Ethel Lake sediment cores. Vertical line indicates anold Lake.

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fuels between the 1920s and 1970s have been widely reported else-where (Carignan et al., 2003; Mast et al., 2010; Renberg et al., 1994;Schwikowski et al., 2004; Weiss et al., 1999; Wiklund et al., 2012),with subsequent reductions in emissions following the introductionof unleaded gasoline. Our Hg and Pb records resemble those ofWiklund et al. (2012) for a remote northern Alberta lake located~200 km from the Athabasca oil sand region. While our As profiledoes not follow Wiklund et al.'s observed post-industrial increase,this may be a result of influx of local As-enriched groundwaters,given the enrichment in deep, pre-industrial sediments. Enrichmentratios ranging 1.2–6.6 (Pb), 1.85–2.85 (Hg), 1.03–1.53 (Cd) and0.85–.59 (Cu) at Cold Lake compare well with values recorded byHermanson (1993) in a pristine Arctic lake in the Hudson Bay'sBelcher Islands, who found post-WWII sediment flux enrichmentsof 3.5 for Pb, 3.2 for Hg, 1.8 for Cd, and 1.6 for Cu.

4.3. Soil geochemistry

Geospatial analysis of metals in soil corroborated the absence ofmajor in-situ associated enrichment found in the sediment cores. All

Fig. 7. Metal concentrations in surficial soil samples (b63 μm grain-siz

of the samples that were analyzed were selected from a similar soilclass (sandy soils), sieved to a uniform grain size (b63 μm) and sam-pled on an area of similar surficial geology (Alberta Geological Survey,1999; Fenton and Andriashek, 1983), reducing variability due to soilheterogeneities. Cu was highly enriched in samples S15 and S12 rela-tive to other locations, although there was no link with proximity tothe oil field as variability was high throughout the studied area, in-cluding among samples collected directly around the oil installations(Fig. 7 and Fig. S4, supplementary information). We observed a trendfor slightly enriched concentrations of As, Cd, Ni, and V in the vicinityof the in-situ oil installations (Fig. 7 and Figs. S2, S3, S6 and S7,supplementary information). Arsenic concentrations were elevatedwithin ~20 km of the oil field, although there was also a high concen-tration measured at sample S12, which was the furthest from the areaof interest. In addition, sample S21 located directly adjacent to the oilinstallations did not contain any measurable As. Cadmium followedsimilar trends of general but very minor enrichment closer to the oilfield but with some exceptions to this trend. Cadmium and Pb con-centrations at samples S25 and S12 were lower than those founddirectly onsite, though only marginally so (Fig. 7 and Figs. S3 and

e fraction) around the Cold Lake oil field. All data μg/g dry weight.

Table 2Comparison of relative percent difference (RPD) of metal concentrations betweenadjacent soil sample pairs S4/S8 and S3/S21. If the metal concentration in a samplewas below detection limits (DL), 1/2DL was used for the RPD calculation. All concentra-tions units μg/g dry weight.

S4 S8 RPD (%) S3 S21 RPD (%)

As 2.2 1.4 44 2.2 b0.5 89Cd 0.09 0.14 43 0.12 0.2 50Cu 36 58 47 43 82 62Ni 14 7.7 58 13 10 26Pb 6.1 5.1 18 7.9 11 33V 24 15 46 24 16 40

Average 42.6 Average 50

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S5, supplementary information). These samples were collected atthe furthest distance from the Cold Lake oil field as well as urban/agricultural areas to the south and are expected to be the most repre-sentative of natural conditions. Pb at sample S14, also >50 km fromthe oil field, had the second highest observed concentration, poten-tially reflecting inputs from the nearby city of Cold Lake and CanadianForces Base Cold Lake, about 12–15 km NW. In addition, some sam-ples collected directly adjacent to the oil field (S5, S9, S6) had lowerPb concentrations than those found at S25 and S12. Nickel and Vexhibited a relatively consistent enrichment moving closer from theoil installations with distinctly lower Ni concentrations measured atsamples >50 km from the site (S25, S12 and S14).

These relationships were further explored by grouping all sampleslocated within a 20 km radius of the most intense in-situ operationsand comparing average metal concentrations to samples located atdistances greater than 50 km. Only As, Cd, Ni and V were slightlyenriched within 20 km of the oil facilities, by factors of 1.51–1.97(Table 1). The mean concentration in this group was only marginallygreater for As (pb0.04, Welch two sample t-test, one-tail) and signif-icantly greater for Ni (pb0.006) and V (pb0.002). Concentrations forPb, Ni and Cd at Cold Lake were 17–79 times less elevated than thoseobserved in b63 μm soils in the vicinity of a Jordanian oil refinery(Banat et al., 2006).

We also observed spatial heterogeneity among proximate samplesthat was of a similar magnitude to the variability between near-site(b20 km from the oil field) and far-field (>50 km from the oilfield) samples, as assessed by comparing the relative percent differ-ence (RPD) between neighboring samples S4/S8 and S3/S21 to theRPD between the grouped near-site and far-field samples. The aver-age RPD between sample pairs S4/S8 and S3/S21 ranged 42.6–50%(Table 2), compared to an average RPD of 39.9% between near-fieldand far-field sample, which suggests that the difference betweenmetal concentrations over the whole study area did not surpass dif-ferences within more localized spatial scales.

Correlation analysis betweenmetals and TOC/iron in soil indicatedthat TOC had no significant relationship to As, Cd, Cu, Ni, Pb and Vconcentrations but there was a very high and significant relationshipbetween Fe and As, Ni and V. Thus we cannot discount the possibilitythat the slight enrichment of these metals was due to a higher ironcontent in the soils, given the high capacity for Fe oxyhydroxides insoils to sorb trace metals (Banat et al., 2006; Bright et al., 2006).This is important because apart from Cd, these were the only metalsthat were significantly more enriched near the oil field. Without fur-ther investigation we cannot identify why Fe was found at higherconcentrations near the oil field, though it could be due to increasedsoil erosion from road and building construction, or simply due tonatural variability in soil geochemistry.

Finally, soil data were also screened against federal and provincialguidelines, namely Canadian Council of Ministers for the EnvironmentSoil Quality Guidelines (CCME, 1999b) and Alberta Tier 1 Soil Remedia-tion Guidelines (Alberta Environment, 2010), and no exceedenceswerefound for the bulk soil samples (Table S2, supplementary information).The b63 μm fraction was consistently enriched in metals relative tocoarser grain-size fractions, as would be expected due to the higher

Table 1Comparison of metal concentrations (μg/g dry weight) in soil samples collected near (b20

>50 km from oil field b20 km from oil field

Mean SD Min Max Mean SD M

As 1.2 0.7 0.7 2.0 2.4 0.7Cd 0.1 0.1 0.1 0.2 0.2 0.1Cu 88.7 52.0 36.0 140.0 72.8 60.9 3Ni 6.1 2.2 3.7 8.1 12.3 3.5Pb 8.5 3.3 6.3 12.3 8.4 335.7V 13.3 3.8 9.0 16.0 21.0 5.4 1

a Compiled by Wedepohl (1995).

surface area to mass ratio in finer fractions. Cu concentrations in fiveout of twelve samples in the b63 μm fraction exceeded the federalguideline of 63 μg/g; however, there was no apparent relationship ofCu spikes with proximity to the Cold Lake oil field, given that two ofthese exceedences were found at sites furthest from the installations(S12 and S15) while several samples collected immediately adjacentto the installations had lower concentrations (S3, S4, S5 and S8), andthat the average concentration in samples collected within a radius of20 km from the oil field was less than that of samples collectedb50 km from the oil field (Table 1).

5. Conclusion

The oil sand industry in northern Alberta has been associated withheavy metal contamination (Kelly et al., 2010) and the close proxim-ity to local aboriginal groups that practice traditional lifestyles mayplace them at a greater risk of exposure to contaminants via the inad-vertent ingestion of soil. However, sediment cores from Hilda andEthel lakes indicate that metal enrichment from the in-situ oil sandindustry is not detectable at the Cold Lake oil field. Furthermore,post-industrial emissions of Cd, Hg and Pb have likely been decreasingor stabilizing concurrently with the recent development of in-situ oilsand extraction. Soil samples indicated only a minor enrichment ofmetals that was significant for Cd, As, Ni and V, although the latterthree may have been driven by adsorption to Fe oxyhydroxides. Allsoil and sediment samples contained concentrations of metals wellbelow applicable Canadian regulatory guidelines, with the exceptionof localized enrichment of Cu in soils that was not spatially linked tothe oil field, and As in sediments that was not associated to sedimentsdeposited since the start of industrial oil extraction at Cold Lake.Because the sediment and soil records do not indicate significantmetal enrichment, we conclude that in the absence of bitumenupgrading and refining, surface mining the in-situ extraction processhas not constituted a major source of metal emissions at Cold Lakesince the beginning of commercial production. As in-situ oil extractionexpands at Cold Lake and elsewhere in the province, it would be pru-dent to continue rigorous environmental monitoring given the smallamount of information available on emissions from the in-situ industryand the scale of the industry's growth, in particular in areas wherepost-extraction bitumen upgrading is occurring.

km) and far (>50 km) from the Cold Lake oil field.

Mean crustal concentrationa Mean0–20km/Mean>50km

in Max

1.4 3.4 1.7 2.00.1 0.2 0.1 1.53.0 230.0 25.0 0.87.7 19.0 55.0 2.05.1 13.0 14.8 1.05.0 32.0 98.0 1.6

344 E.K. Skierszkan et al. / Science of the Total Environment 447 (2013) 337–344

Acknowledgments

This research was supported by a grant from Health Canada'sNational First Nations Environmental Contaminants Program to JMBand a Natural Sciences and Engineering Research Council of Canadagrant to EKS. Field work was coordinated by Tribal Chiefs VenturesInc. with support from the Cold Lake First Nation. E. Yumvihozeassisted with mercury analysis.

Appendix A. Supplementary data

Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.scitotenv.2012.12.097.

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