Article pubs.acs.org/est
Mercury Trends in Colonial Waterbird Eggs Downstream of the Oil Sands Region of Alberta, Canada Craig E. Hebert,*,† David Campbell,# Rhona Kindopp,§ Stuart MacMillan,§ Pamela Martin,‡ Ewa Neugebauer,† Lucy Patterson,# and Jeff Shatford§ †
Environment Canada, Science and Technology Branch, National Wildlife Research Centre, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada K1A 0H3 # Parks Canada Agency, Wood Buffalo National Park, Box 38, Fort Chipewyan, Alberta, Canada T0P 1B0 § Parks Canada Agency, Wood Buffalo National Park, Box 750, Fort Smith, Northwest Territories, Canada X0E 0P0 ‡ Environment Canada, Science and Technology Branch, 867 Lakeshore Road, Burlington, Ontario, Canada L7R 4A6 ABSTRACT: Mercury levels were measured in colonial waterbird eggs collected from two sites in northern Alberta and one site in southern Alberta, Canada. Northern sites in the Peace-Athabasca Delta and Lake Athabasca were located in receiving waters of the Athabasca River which drains the oil sands industrial region north of Fort McMurray, Alberta. Temporal trends in egg mercury (Hg) levels were assessed as were egg stable nitrogen isotope values as an indicator of dietary change. In northern Alberta, California and Ring-billed Gulls exhibited statistically significant increases in egg Hg concentrations in 2012 compared to data from the earliest year of sampling. Hg levels in Caspian and Common Tern eggs showed a nonstatistically significant increase. In southern Alberta, Hg concentrations in California Gull eggs declined significantly through time. Bird dietary change was not responsible for any of these trends. Neither were egg Hg trends related to recent forest fires. Differences in egg Hg temporal trends between northern and southern Alberta combined with greater Hg levels in eggs from northern Alberta identified the likely importance of local Hg sources in regulating regional Hg trends. Hg concentrations in gull and Common Tern eggs were generally below generic thresholds associated with toxic effects in birds. However, in 2012, Hg levels in the majority of Caspian Tern eggs exceeded the lower toxicity threshold. Increasing Hg levels in eggs of multiple species nesting downstream of the oil sands region of northern Alberta warrant continued monitoring and research to further evaluate Hg trends and to conclusively identify sources.
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INTRODUCTION
Athabasca approximately 200 km downstream from Fort McMurray (Figure 1). Enhanced monitoring programs are being implemented to better understand the impacts of oil sands development on the environment.5 Chemical emissions data for various sources in Canada are available through the National Pollutant Release Inventory (NPRI).6 The NPRI is Canada’s legislated, publicly accessible inventory of pollutant releases to air, water, and land. For example, for mercury emissions to air, the primary source in Alberta’s industrial sector during 2011 was the petroleum industry. It accounted for approximately 40% of total provincial industrial mercury air emissions. This was about 13% of the provincial total of Hg emissions to air from all sources in 2011 (Figure 2). Mercury emissions from all sectors in Alberta are predominately through the air (approximately 90%), and this is also true for oil sands operations in the vicinity of Fort
The Peace-Athabasca Delta was designated a wetland of international significance under the Ramsar Convention in 1982.1 It is also a defining feature of Wood Buffalo National Park, a UNESCO World Heritage Site. This region provides important nesting and staging habitat for millions of birds annually including the endangered Whooping Crane (Grus americana).2 The surrounding region also provides important habitat for nesting birds. For example, Egg Island in western Lake Athabasca was designated a provincial ecological reserve in 1992 as it harbors the largest breeding colony of Caspian Terns (Hydroprogne caspia) in Alberta.3 These examples highlight the ecological sensitivity of this region to growing human activities. Since 1967, when operations commenced, industrial exploitation of the bitumen-rich oil sands in northern Alberta has expanded greatly.4 Oil Sands activities are primarily centered in the region north of Fort McMurray, Alberta where the Athabasca River flows northwards. The river discharges into the Peace-Athabasca Delta and western Lake Published 2013 by the American Chemical Society
Received: Revised: Accepted: Published: 11785
June 10, 2013 September 5, 2013 September 5, 2013 September 26, 2013 dx.doi.org/10.1021/es402542w | Environ. Sci. Technol. 2013, 47, 11785−11792
Environmental Science & Technology
Article
greater than for earlier years (Figure 2). Evidence has emerged that links oil sands industrial activities to increased regional availability of organic and inorganic contaminants.7−9 These studies have primarily centered on the analysis of information from abiotic environmental compartments, e.g. sediments, water, snow. Information from biological monitoring is more limited and has relied significantly on the compilation of data from diverse sources.10 Here, we build on earlier research11 to assess mercury trends in wildlife. Mercury (Hg) levels are measured in colonial waterbird eggs collected from two sites in northern Alberta (located in receiving waters of the Athabasca River) and at a reference site located south of the oil sands region near Calgary. We also measure egg stable nitrogen isotope (15N/14N, expressed as δ15N) values to determine if changes in bird diets/trophic position may be contributing to trends in egg Hg levels. Top predators, such as the birds studied here, are effective indicators of change in levels of environmental contaminants.12 Gull and tern eggs are useful for gaining insights into local environmental conditions because they are composed primarily of constituents of local origin.13 Hence, the chemical composition of the egg reflects the chemical characteristics of prey captured in the region around the breeding colony. The diets of the bird species studied here are composed to a great extent of small prey fish. Mercury levels in small fish are known to respond rapidly to changes in levels of Hg in their environment, i.e. 1−2 years,14 likely reflecting the rapid cycling of recently deposited Hg into lake ecosystems.15 Hence, we expect that Hg levels in bird eggs will also respond rapidly to changes in Hg availability in the environment. Oil sands development is only one of the possible factors that could affect Hg levels in Alberta wildlife. Long-range atmospheric transport of Hg could be important as well. For example, combustion of coal to generate electricity and for industrial purposes in Asia is an important source of gaseous elemental Hg (Hg0) to North America.16 Deposition of Asian Hg0 may exhibit a relatively uniform distribution in receiving regions.17 Therefore, if long-range Hg sources were the primary factor regulating Hg levels in Alberta wildlife, then we might
Figure 1. Colonial waterbird egg collection locations in northern Alberta, Canada. Eggs were collected over multiple years from Egg Island (Lake Athabasca), Mamawi Lake (Wood Buffalo National Park), and Langdon Reservoir (Calgary).
McMurray (Figure 2). Total annual Hg releases to air in the province of Alberta exhibited a general decline after 2004. Total annual Hg emissions from oil sands operations increased in 2007 followed by a decline, but emissions after 2006 remained
Figure 2. Total annual mercury emission estimates (kg) to air from all sources in the Province of Alberta and to air and water from oil sands operations north of Fort McMurray, Alberta. Data are from Canada’s National Pollutant Release Inventory. Data for 2012 are preliminary and are subject to change. 11786
dx.doi.org/10.1021/es402542w | Environ. Sci. Technol. 2013, 47, 11785−11792
Environmental Science & Technology
Article
resulting in the complete pulverization of egg contents. Individual homogenized samples were stored frozen (−40 °C) in the National Wildlife Specimen Bank. Individual egg samples were used for mercury and stable nitrogen (N) isotope (15N/14N) analyses. At the time of processing, the stage of embryonic development was noted. Some eggs showed signs of embryonic development, i.e. they were not freshly laid. As incubation progresses, water and lipid content of eggs decline but not contaminant content.24,25 Hence, with development, chemical concentration data (both wet weight and dry weight) may be biased high. Egg contents mass was compared among years at each site to determine the importance of adjusting for this phenomenon. When differences in egg contents mass were found among years, all egg concentration data for that species and site were multiplied by an adjustment factor calculated for each egg (egg mass/egg volume). Volume (cm3) was calculated using the equation: egg volume = 0.489 (length * breadth2)/ 1000.26 Where appropriate, adjusted egg concentration data for Hg and PCDDs/PCDFs were generated. Eggs from all years and species were analyzed using identical, current methodologies. Total Hg analyses were completed at NWRC using the following methods. Egg samples were weighed into plastic, acid-washed vials, then freeze-dried, and dry mass recorded. Hg was quantified as follows: 10−25 mg of dried egg material were thermally and chemically decomposed within the decomposition furnace of an advanced mercury analyzer (AMA-254, Altec, Czech Republic) using EPA Method 7473 (Mercury in solids and solutions by thermal decomposition, amalgamation, and atomic absorption spectrophotometry. Rev. 1998). AMA-254 software calculated mercury concentrations. Quality control was maintained by using certified reference materials (DOLT-3, TORT-2, ERM-CE278 Mussel Tissue, BCR-463 Tuna Fish), sample replicates, and blanks. Limit of quantification for Hg was 0.006 μg/g (dry wt.). Recoveries of mercury for the certified reference materials ranged from 98.2 to 103.5%. PCDD/PCDF analyses were completed on selected egg samples (n = 32). Eggs were chosen to represent periods before and after the Richardson Backcountry Fire of 2011. PCDD/ PCDF analyses were conducted by AXYS Analytical Services Ltd. (Sidney BC) according to the following protocol (AXYS Method MLA-017 Rev 20 Ver 06). Briefly, 5−6 g samples were spiked with 13C-labeled surrogate standards prior to extraction. Soxhlet extraction was performed with 1:1 dichloromethane:hexane. Extracts were cleaned-up using florisil and alumina/ carbon/Celite columns. Instrumental analysis was conducted by gas chromatography (Agilent 6890N) using a DB-5 capillary column coupled to a high-resolution mass spectrometer (HRMS; Waters AutoSpec Premier). The HRMS was operated in voltage selected ion-recording mode (V-SIR). A second GC/ MS (HP 5890 Series II/VG Analytical AutoSpec V-Series Ultima) analysis using a DB-225 column was used to confirm 2,3,7,8-TCDF identification. Calibration was performed using a five point calibration series of solutions encompassing the working concentration range. Quantification of confirmed peaks was by isotope dilution. Target concentrations were determined with respect to labeled surrogate standards. Quality control involved the use of blanks, spiked reference samples, and certified reference materials. Reporting limit (RL) for all individual PCDD-PCDF congeners was
