Correspondence/Rebuttal pubs.acs.org/est
Comment on “Sphagnum Mosses from 21 Ombrotrophic Bogs in the Athabasca Bituminous Sands Region Show No Significant Atmospheric Contamination of ‘Heavy Metals’” he recent article by Shotyk et al.1 contests the findings of previous studies2,3 that demonstrated metal contamination in the vicinity of open pit mining and upgrading in the Athabasca bituminous sands (ABS) of Alberta, where over 1 million barrels per day of synthetic crude oil are produced.4 Shotyk et al.1 measured metals in Sphagnum moss in ombrotrophic peat bogs within the ABS region, and concluded that there is no significant atmospheric contamination of a broad range of metals, including Mo, Pb, Ni, Ba, and only a slight enrichment of V. We take exception to these authors’ assertion that there is no evidence of atmospheric contamination of metals in ombrotrophic peat bogs or other environmental media in the ABS region due to problems identified in their analysis and interpretation. Their first line of evidence is based on calculating average metal concentrations in handfuls of living Sphagnum moss collected in an area that extends well beyond the known range of the ABS major impact zone. A surface sample of Sphagnum moss may represent growth spanning months or years, and differences in exposure times, accumulation rates, species composition and other site-specific factors result in variable metal concentrations.5,6 Kempter et al.5 also concluded that at least 25 Sphagnum samples from each bog are necessary to use metal accumulation by moss as an indicator of atmospheric metals deposition, versus the three samples per bog that Shotyk et al. relied upon.1 Because of uncertain exposure times, intersite differences in moss species, and variability in Sphagnum spp. productivity, the concentrations measured by Shotyk et al.1 are likely not an accurate measure of atmospheric loading rates in the ABS region.5 There are also problems with the spatial analysis of their study. Previous studies using seasonal accumulation of contaminants in snow and lichen2,3,7 demonstrated that upgraders and mining activities in the ABS region were the major source of regional airborne contaminants. The greatest amount of contaminant deposition was found within 20 km of the upgraders near the center of the industrial activity,2 though enrichment was detectable as far as 50 km. Shotyk et al. reached their conclusions by averaging data from 22 sites, of which only 5 were within 20 km of the midpoint of the upgraders. It is therefore not surprising that an average metal concentration calculated in this way appears low relative to deposition from populous and industrial Europe. Moreover, average concentrations calculated in this manner are inappropriate because the distribution of elements around the ABS development is not random: the average metal concentration in snow2,7 and lichen3 is exponentially related to the distance from upgraders, with more distant sites contributing to a lower average. This is the very reason why geospatial statistics, like Kriging, are being applied to quantify aerial deposition of metals within the ABS region,7 rather than a simple comparison of averages with Germany and Ontario sites as references. Although Shotyk et al.1 developed geospatial maps in
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their article (their Figure 5 and S1), they used them only to show similarities among elements. Their second line of evidence involves comparison of elements to Th, a conservative, lithophilic element, from which they concluded that metal inputs may simply be attributed to “mineral dust particles” and therefore do not represent contamination. The premise of these calculations is that the contribution of a natural trace element is proportional to the lithophilic tracer, and “unpolluted” or “unenriched” deposits will therefore have trace element concentrations that vary in tandem with the tracer. This approach may be problematic where the source of contamination is largely clastic or minerogenic, for example, where bituminous sands and other particles are major sources of atmospheric contamination. For example, the ABS operations release over 110 000 tonnes of fly ash and 1390 tonnes of PM 2.5 annually.8,9 The fly ash is mainly a composite of kaolinite, illite, gypsum, anhydrite, and other mineral phases,10 but also includes a small portion of very toxic metals, organic constituents, and acidic anions that are present in a highly exchangeable11 and bioavailable form. Some of these toxic and bioavailable metals may be masked in a full metal extraction by the large quantities of metals associated with the mineral lattices. PM 2.5 has recently been classified by IARC as a Group 1 human carcinogen,12 and its toxicity is attributable in part to its surface metal complexation properties.13 Fly ash particles have been shown to be highly toxic and mutagenic to humans and test animals and have been shown to cause inflammation, oxidative stress, and are linked to diabetes, cardiovascular disease, and cancer.12−15 It is the toxicity of these constituents that ultimately determines the severity of atmospheric contamination that has taken place. Given that the particles themselves (bitumen, fly ash, PM 2.5) contribute significantly to the airborne contamination in the ABS, ratios of total element concentrations to Th are misleading and may lead to serious errors when conducting assessments of environmental exposure and risk. For example, a recent analysis of the elemental composition of ABS emissions, including byproducts of petroleum coke, road dust, tailing sand, and overburden, showed extensive overlap or colinearity among sources.3 These authors concluded that the major sources of airborne particles in the ABS region are essentially different mixtures of these components. However, ombrotrophic bogs that have received considerable amounts of toxic fine particle bitumen, PM 2.5, or fly ash deposition appear to have been interpreted as “unpolluted” or “unenriched” according to the authors’ definition of enrichment that is based simply on the proportion of total metal concentrations to a lithophilic tracer. The title of the Shotyk et al.1 study, which states there is no atmospheric contamination of metals in the ABS region, is misleading. In ecotoxicology terms, “contamination” refers to Published: May 5, 2015 6352
DOI: 10.1021/acs.est.5b00475 Environ. Sci. Technol. 2015, 49, 6352−6353
Environmental Science & Technology
Correspondence/Rebuttal
(3) Landis, M. S.; Pancras, J. L.; Graney, J. R.; Stevens, R. K.; Percy, K. E.; Krupa, S. Receptor Modeling of Epiphytic Lichens to Elucidate the Sources and Spatial Distribution of Inorganic Air Pollution in the Athabasca Oil Sands Region. Dev. Environ. Sci. 2012, 11, 427−467. (4) Canadian Association of Petroleum Producers. CAPP’s 2013 Crude Oil Forecast, Markets & Transportation. http://www.capp.ca/ aboutUs/mediaCentre/NewsReleases/Pages/2013-OilForecast.aspx (accessed January 3, 2015). (5) Kempter, H.; Krachler, M.; Shotyk, W. Atmospheric Pb and Ti Accumulation Rates from Sphagnum Moss: Dependence upon Plant Productivity. Environ. Sci. Technol. 2010, 44, 5509−5515. (6) Kempter, H.; Frenzel, B. The Geochemistry of Ombrotrophic Sphagnum Species Growing in Different Microhabitats of Eight German and Belgian Peat Bogs and the Regional Atmospheric Deposition. Water Air Soil Pollut. 2007, 184, 29−48. (7) Kirk, J. L.; Muir, D. C. G.; Gleason, A.; Wang, X. W.; Lawson, G.; Frank, R. A.; Lehnherr, I.; Wrona, F. Atmospheric deposition of mercury and methylmercury to landscapes and waterbodies of the Athabasca Oil Sands Region. Environ. Sci. Technol. 2014, 48, 7374−7383. (8) Holloway, P. Vanadium Recovery from Oil Sands Fly Ash. M.Sc. Thesis, University of Alberta, Edmonton, Alberta, Canada, 2002. (9) Gosselin, P.; Hrudey, S. E.; Naeth, M. A.; Plourde, A.; Therrien, R.; Van Der Kraak, G.; Xu, Z. Environmental and Health Impacts of Canada’s Oil Sands Industry: The Royal Society of Canada Expert Panel. The Royal Society of Canada: Ottawa, ON, 2010. (10) Jang, H.; Etsell, T. H. Mineralogy and Phase Transition of Oil Sands Coke Ash. Fuel 2006, 85, 1526−1534. (11) Henke, K. R. Trace Element Chemistry of Fly Ashes from CoCombusted Petroleum Coke and Coal, Paper no. 45. Presented at the International Ash Utilization Symposium, Center for Applied Energy Research, University of Kentucky, Lexington, Kentucky, 2005. www. flyash.info (accessed 3/1/2015). (12) IARC (International Agency for Research on Cancer). Outdoor Air Pollution. IARC Monogr. Eval. Carcinog. Risks Hum. 2015, in press. (13) IARC (International Agency for Research on Cancer). Arsenic, Metals, Fibres and Dusts. A Review of Human Carcinogens. IARC Monogr. Eval. Carcinog. Risks Hum. 2012, 100C, 1−501. (14) Potera, C. Toxicity beyond the Lung: Connecting PM2.5, Inflammation, and Diabetes. Environ. Health Perspect. 2014, 122, A29. (15) Miller, K. A.; Siskovick, D. S.; Shepard, L.; Sheppard, K.; Sullivan, J. H.; Anderson, G. L.; Kaufman, J. D. Long-Term Exposure to Air Pollution and Incidence of Cardiovascular Events in Women. N. Engl J. Med. 2007, 356, 447−458. (16) Moriarty, F. Ecotoxicology. The Study of Pollutants in Ecosystems; Academic Press, Inc.: London, 1983. (17) Newman, M. C. Fundamentals of Ecotoxicology, 3rd ed.; CRC Press: Boca Raton, FL, 2010; 541 pp. (18) Schindler, D. W. Water Quality Issues in the Oil Sands Region of the Lower Athabasca River, Alberta. Geosci. Can. 2013, 40, 202−214. (19) Headley, J. V.; Crosley, B.; Conly, F. M.; Quagraine, E. K. The Characterization and Distribution of Inorganic Chemicals in Tributary Waters of the Lower Athabasca River, Oilsands Region, Canada. J. Environ. Sci. Health 2005, A40, 1−27. (20) Fischer, J. M.; Robbins, S. B.; Al-Zoughool, M.; Kannamkumarath, S. S.; Stringer, S. L.; Larson, J. S.; Caruso, J. A.; Talaska, G.; Stambrook, P. J.; Stringer, J. R. Co-mutagenic Activity of Arsenic and Benzo[a]pyrene in Mouse Skin. Mutat. Res., Genet. Toxicol. Environ. Mutagen. 2005, 588, 35−46. (21) Fleeger, J. W.; Gust, K. A.; Marlborough, S. J.; Tita, G. Mixtures of Metals and Polynuclear Aromatic Hydrocarbons Elicit Complex, Nonadditive Toxicological Interactions in Meiobenthic Copepods. Environ. Toxicol. Chem. 2007, 26, 1677−1685. (22) Parrott, J. L. Larval Fish Responses to Environmental Samples from Oil Sands Areas. Presented at SETAC North America 35th Annual Meeting in Vancouver, BC, Nov. 9−13, 2014.
any substance released to the environment by human activity.16,17 This contamination would include the fly ash and PM 2.5 from bitumen processing and fine bitumen particles released from the open pit mines, to which these metals are adsorbed. Public concerns about these emissions relate to the potential harm they may cause. The suggestion that these airborne particles should be of little concern does not conform to what we know about these particle emissions and their toxicity. There is a vast body of literature on the toxicity and effects of atmospherically deposited heavy metals, and one does not need to look far to find evidence of significant toxicological risk associated with atmospheric heavy metals contamination from ABS operations. Concentrations of Cd, Cu, Pb, Hg, Ni, Ag, and Zn in melted snow and water from the Athabasca River and its tributaries exceeded guidelines for the protection of aquatic life to the greatest extent at sites near oil sands development, while only Cd exceeded guidelines at sites far from oil sands development.2 Strong acid anions deposited in snow near the ABS operations produce acid pulses in spring which further exacerbate the effects of these metals.18 Exceedances of environmental guidelines were also observed during the spring freshet in 1999, including from the Ells River, when low water hardness enhanced heavy metal toxicity.19 Synergistic toxicological effects of mixtures of heavy metals and organic contaminants have also been identified, including increased toxicity of PAHs with coexposure to As, Cd, Pb, and Hg.20,21 Recently, a study in the ABS region demonstrated that melted snow collected near-field from the upgraders that contained elevated metals and other constituents were acutely lethal to embryo-larval fathead minnows within a few hours of exposure, whereas far-field snowmelt had no toxicological effect on the fish.22 Clearly the toxicology does not conform to the notion that there is nothing to see when it comes to atmospheric contamination from the ABS region, of which the “heavy metals” are an indelible part. There is mounting evidence that atmospheric contamination from the ABS development is not only present, but also toxic to the receptor ecosystem, and current and ongoing research continues to show the effects of this atmospheric contamination.
Jules M. Blais*,† William F. Donahue‡ †
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Centre of Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada ‡ Water Matters Society of Alberta, P.O. Box 8386, Canmore, Alberta T1W 2 V2, Canada
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Shotyk, W.; Belland, R.; Duke, J.; Kempter, H.; Krachler, M.; Noernberg, T.; Pelletier, R.; Vile, M. A.; Wieder, K.; Zaccone, C.; Zhang, S. Sphagnum Mosses from 21 Ombrotrophic Bogs in the Athabasca Bituminous Sands Region Show No Significant Atmospheric Contamination of “Heavy Metals”. Environ. Sci. Technol. 2014, 48, 12603− 12611. (2) Kelly, E. N.; Schindler, D. W.; Hodson, P. V.; Short, J. W.; Radmanovich, R.; Nielsen, C. C. Oil Sands Development Contributes Elements Toxic at Low Concentrations to the Athabasca River and Its Tributaries. Proc. Natl. Acad. Sci. U. S. A. 2010, 107, 16178−16183. 6353
DOI: 10.1021/acs.est.5b00475 Environ. Sci. Technol. 2015, 49, 6352−6353
