History of environmental contamination by oil sands extraction.

T he 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 industrysponsored 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. 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 shortrange 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 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.)