None of the sediment cores in the study revealed ΣPAH trends similar to trends observed in remote lakes in north-central North America, where maximum PAH deposition typically occurred during the mid-20^th century and has declined toward modern times.

This study, published as an open access paper in the Proceedings of the National Academiesof the United States of America (PNAS), follows a pair of studies published in 2009 and 2010 that found oil sands development is a greater source of polycyclic aromatic compounds and heavy metals contamination to the Athabasca River and its tributaries than previously realized. (Earlier post.)

With stakeholders having polarized views on Canada’s oil sands development, attention is fixated on the region because of environmental and perceived public-health concerns, as well as the significant economic benefits and evolving governmental macro-economic and energy policies. Environmental concerns result primarily from the industrial activities associated with surface mining, in situ recovery, and upgrading of bitumen. Collectively, these industrial activities yield significant landscape disturbance and habitat loss and add to the controversy regarding water quantity and quality issues. The potential and realized emissions of pollutants, including greenhouse gases and mercury, are also contentious. Some of the controversy results from a lack of systematic environmental monitoring of industrial activities before the establishment of the industry-funded Regional Aquatics Monitoring Program (RAMP) in 1997. Furthermore, weaknesses highlighted by scientific reviews of RAMP, in its inability to recognize effects on freshwaters, leads to additional criticism by some stakeholders.

A paradox exists between the pace and scale of oil sands development after ∼1980 and the claims that development has minimal or no detectable impacts and that contaminants result mainly from natural sources. Of particular concern are the atmospheric loadings and distributions of contaminants associated with oil sands surface-mining and processing activities, many of which are carcinogens and rank in the top 10 hazardous substances on the US Agency for Toxic Substances and Disease Registry. Polycyclic aromatic hydrocarbons (PAHs) are one such example, with natural and anthropogenic pathways to ecosystems. PAHs are a diverse group of organic compounds with multiple aromatic rings and are produced by the incomplete combustion of fossil fuels and biomass. They are relatively insoluble in water and bind to organic particles in the water column, persist in lake sediments, occur in complex mixtures, and have the potential to impact aquatic organisms at several trophic levels, particularly in the presence of other stressors. With similar properties to PAHs, the sulfur-containing dibenzothiophenes (DBTs) are a related class of aromatic compounds. C₁-C₄–alkylated PAHs and DBTs are both recognized as prominent components of Athabasca oil sands bitumen.

Almost two decades of environmental monitoring within the oil sands region has failed to establish background concentrations of highly toxic contaminants....The lack of consensus among the few temporal-focused PAH studies to date, and the shortcomings of oil sands monitoring programs to adequately recognize the deposition patterns of atmospheric contaminants, leave justifiable cause for concern as to the ecological implications of oil sands development. Establishment of background PAH concentrations and historic loadings is essential and would allow the impacts of development, including industrial PAH contributions, to be compared with the natural range in variability and composition of these contaminants in lake sediments from the region.

—Kurek et al.

To solve the problem of the lack of monitoring data and the focus of previous studies using highly mobile river sediments, the researchers in this latest study used paleolimnological techniques to reconstruct PAH loadings, aquatic primary production, and zooplankton (Cladocera) assemblage shifts archived in a strategically selected set of study lakes.

Daphnia, the focal zooplankton indicator, is an established model organism used worldwide in toxicology assessments is a promising indicator for understanding multiple environmental stressors, including contaminants.

The researchers used paleolimnological records dating to at least the mid-19^th century to examine trends in atmospheric PAH deposition from five lakes near upgrading facilities and mining operations north of Fort McMurray, Alberta. To detect a wider signal of contaminant loading, a sediment core from remote Namur Lake, ∼90 km northwest of the upgrading facilities and outside of the recently identified zone of high atmospheric PAH deposition, was analyzed for PAHs.

Analyses of sediment cores from five lakes near major oil sands operations and remote Namur Lake demonstrate that modern ΣPAH concentrations and fluxes, including DBTs, are well above “natural,” predevelopment levels. Coincident with increased PAH deposition after the ∼1960s to 1970s, lake ecosystems must now also contend with 20^th century climatic changes, which are contributing to increased aquatic primary production and marked cladoceran assemblage shifts. Daphnia, a sentinel zoo-plankter, has not yet exhibited decreases in relative abundance associated with increased PAH loadings through time, despite potential toxicity enhancement of PAHs by other stressors. Rather, climate-driven primary production increases may have trumped some effects of oil sands-derived PAHs on at least Daphnia populations. Nonetheless, several striking PAH trajectories recorded in sedimentary profiles reflect the decades-long impacts of oil sands development on lake ecosystems, including remote Namur Lake. This temporal PAH pattern was not recognized previously by industry-funded oil sands monitoring programs. We conclude that lake sediments in the Athabasca oil sands region register a clear PAH legacy with the pace and scale of industrial development of the region’s tremendous bitumen deposits.

—Kurek et al.

While they found that Daphnia has not yet been negatively impacted by decades of high atmospheric PAH deposition, they concluded that coincident with increases in PAHs, climate-induced shifts in aquatic primary production related to warmer and drier conditions are the primary environmental drivers producing marked daphniid shifts after ∼1960 to 1970.

Because of the striking increase in PAHs, elevated primary production, and zooplankton changes, these oil sands lake ecosystems have entered new ecological states completely distinct from those of previous centuries.

—Kurek et al.

Funding for the research was provided by Environment Canada and the Natural Sciences and Engineering Research Council of Canada.

Resources

• Joshua Kurek, Jane L. Kirk, Derek C. G. Muir, Xiaowa Wang, Marlene S. Evans, and John P. Smol (2013) Legacy of a half century of Athabasca oil sands development recorded by lake ecosystems. PNAS doi: 10.1073/pnas.1217675110