History of environmental contamination by oil sands extraction

The extraction and processing of Canada’s massive oil sands in the Athabasca region of northern Alberta have been marked by an ongoing controversy about the nature and extent of associated environmental impacts. Impacts include habitat destruction and fragmentation by surface mining and tailings disposal, depletion of water resources, greenhouse gas and chemical emissions, and the impacts of emissions on environmental and human health. The debate has been characterized by accusation, denial, emotion, and few reliable or appropriate data to clarify the issues. Thankfully, a paleolimnology study in PNAS by Kurek et al. (1) provides some badly needed perspective. They report the distribution of polynuclear aromatic hydrocarbons (PAHs) in sediment cores of lakes proximate to oil sands industries and as far as 90 km away.

A major point of contention has been the extent to which oil sands contaminants (PAHs, metals, airborne particulates; oxides of nitrogen and sulfur) are distributed downwind and downriver of mining and processing. Public concerns have not been allayed by images of large-scale industrial emissions (Fig. 1), frequent reports of deformities in commercial fish, and denials from industry associations and government officials. Their most frequent response was the assertion of no scientific evidence that industrial activities have elevated concentrations of oil sands-related chemicals beyond the background concentrations derived from the natural erosion of bitumen deposits (2). They referenced their case to the results of the Regional Aquatics Monitoring Program (RAMP), an industry-sponsored program that measures PAHs, mercury, and other contaminants in water, sediments, and fish tissues from the Athabasca River (AR) and its tributaries. Initiated in 1997, the RAMP program was roundly criticized by two successive program reviews (3, 4), which cited inadequacies in the questions being asked (e.g., a lack of attention to air emissions), the study designs and criteria needed to answer those questions, and a lack of public access to raw data.

Fig. 1.

Flare towers at an Athabasca oil sands processing plant. (Photograph reproduced with permission from Erin Kelly, Government of Northwest Territories, Yellowknife, NT, Canada.)

To test the hypothesis of “no-impact,” Kelly et al. (5, 6) executed an independent, synoptic survey of PAH and metal contamination in the AR and its watershed in the vicinity of the oil sands mining and processing. Their findings, also published in PNAS, were stunningly different than those of RAMP. Sampling in winter and summer of 2008 with a powerful survey design (main-stem AR; three industrially developed and three reference tributaries; stations upstream of the oil sands formation and processing, within the formation but upstream of processing, and within the formation and downstream of processing) demonstrated clear and consistent patterns of contamination by PAHs and metals as a result of mining and processing. Deposition of oil sands contaminants to snow exceeded background concentrations by 750 fold, and was evident as far as 50 km (PAHs) and 85 km (metals) from refineries. This new definition of the industrial footprint was enabled by integrative sampling and superior analytical sensitivities compared with RAMP surveys. Sensitivity was enhanced by sampling the March snow pack (4-mo composite of air fallout), and installing passive water samplers in rivers under ice in March (30-d signal; water emissions only) and in open water between June and August (30-d signal; surface erosion plus air and water emissions). Comparing sampling sites to successive Landsat photos discriminated chemical emissions from recent land disturbance from ongoing emissions by mining and processing (5, 6).

Although Kelly et al. (5, 6) resolved conflicting arguments about oil sands contaminants, their synoptic survey was not a comprehensive description of the area affected or duration of contamination. It did not account for mass transport of contaminants in river particulates, biotic transfer in migrating fish species, total annual emissions, or seasonal distributions of airborne contaminants by prevailing winds. Interpretation was also hampered by the absence of true baselines in an already contaminated landscape.

In response to one of the studies by Kelly et al. (5), sediment cores from lakes in the Peace-AR Delta, approximately 200 km north of oil sands industries, were analyzed by Hall et al. to integrate the history of PAH deposition to lakes over a period of 100 to 250 y (7). In a Delta lake isolated from the AR, the absence of petrogenic PAHs typical of the oil sands was consistent with the observed short-range transport of airborne PAHs from oil sands industries (<50 km) (5); the observed PAHs were pyrogenic, likely from forest fires (7). These data might suggest little threat of oil sands contaminants to downwind communities, but the snow study by Kelly et al. (5) was limited in scope to 4 mo, and the lake sediment study by Hall et al. (7) represented a single point on the regional wind rose, leaving significant uncertainty about the area influenced by oil sands emissions.

Kurek et al. (1) focus this picture considerably. By chemical and biological analyses of dated sediment cores, they link PAH contamination to the history of air emissions from oil sands industries, track the growth of oil sands activities since the 1960s, discriminate industrial from “natural” sources of PAHs, establish a predevelopment baseline of PAH fluxes to sediments, expand the area known to be affected by emissions, and raise new questions about potential impacts on freshwater ecosystems.

The key element of the study (1) was the choice of six pothole lakes (i.e., no streams flowing in or out) in undisturbed landscapes, five within 35 km of oil sands production sites and one 90 km away. These lakes are fishless and unaffected by erosion of bitumen deposits, and isotope dating provided a temporal series of each lake’s chemistry, biology, and sediment accumulation over the previous 100 to 200 y.

PAH fluxes calculated from sediment accumulation rates and PAH analyses of core slices demonstrated relatively constant loadings of 46 PAHs (ΣPAH) from 1910 to 1966. In contrast, standardized ΣPAH concentrations increased continuously and significantly from 1967 to 2010 by 2.5 to 23 fold, in parallel with increased oil sands production [15-fold since 1980 (1)]. The pre-1967 sediments provided the much-needed background loadings, independent of oil sands activities, and were dominated by pyrogenic PAHs typical of wood combustion, from forest fires. Post-1967, the PAH fingerprint was dominated by oil sands materials, as shown by increasing concentrations of dibenzothiophene, and increasing ratios of alkyl dibenzothiophenes to alkyl phenanthrenes and alkyl chrysenes typical of petrogenic PAHs. The greater contamination of lakes to the east and downwind of processing sites compared with upwind lakes to the west reinforced the connection between oil sands production and contamination of aquatic environments. Assertions that PAHs in the AR watershed are entirely caused by natural erosion of bitumen (2) are no longer tenable (1, 5, 6).

The finding of elevated PAH concentrations in Namur Lake sediments, 90 km northwest of oil sands industries (1), contradicts the 50-km limit of atmospheric transport of oil sands PAHs to snow (5). Namur Lake is not on the axis of prevailing winds, and accumulation of ΣPAH was more variable than in the other lakes and included pyrogenic PAH from forest fires. Nevertheless, the trend of increasing concentrations of petrogenic PAH since 1967 was sufficient to conclude an oil sands source, which demonstrates that air emissions of PAHs may travel as far as emissions of metals (85 km) (6).

Although Kurek et al. (1) confirm environmental contamination by PAHs, are concentrations sufficient to harm aquatic species? And are PAHs the only issue? The highest concentrations of ΣPAH in surface

Kurek et al. provide a clear warning of possible future problems if PAH inputs to lakes continue to climb in tandem with oil sands production.

(i.e., most recent) sediments were almost 10,000 ng/g dry weight (1), approximately 5% of the concentrations in bituminous sediments toxic to embryos of fathead minnow (Pimephales promelas), a species native to the region (8). In one lake [NE20 (1)], concentrations of seven PAHs exceeded Canadian Interim Sediment Quality Guidelines (9) but not probable effect levels. The guidelines limit pyrogenic unsubstituted PAHs, not petrogenic PAHs, which are dominated by alkyl derivatives (10) that are as much as 10 times more toxic than unsubstituted congeners [e.g., 7-isopropyl-1-methyl phenanthrene vs. phenanthrene (11)]. Given the 23-fold increase in sediment PAH concentrations over the past 50 y, and the projected 150% increase in oil sands production over the next 15 y, there is reason for concern.

The significance of parallel increases in concentrations of chlorophyll a (algal productivity) and in the relative abundance of the cladoceran Daphnia magna in sediment cores (1) is less obvious. Increasing algal productivity may be a signal of regional climate change interacting with nutrient cycling, and the change in the cladoceran assemblage was attributed to the increase in algal production (1). However, alternative hypotheses could include changes to the species composition of algae that favor one cladoceran over another, or selective toxicity of oil sands-derived PAHs or metals (5, 6) in aerial fallout. Given that each lake will receive a spring pulse of low alkalinity, low-pH melt water, laden with PAHs and metals, multiple stressors could interact with ecosystem structure and function in complex ways.

Kurek et al. (1) provide a clear warning of possible future problems if PAH inputs to lakes continue to climb in tandem with oil sands production. There are clear research needs related to the cumulative effects of oil sands contaminants on the function of lake ecosystems, assessment of effects on terrestrial ecosystems, forecasting contaminant loadings and effects on lakes of industrial expansion, and finer-scale sampling to define the geographic extent of oil sands contamination and potential ecological effects.