Valuable oil sands environmental research raises several questions.

Kurek et al. (1) provide a valuable contribution concerning oil sands development. The authors should also be congratulated for not drawing irresponsible inferences about human cancer risks from polycyclic aromatic hydrocarbons (PAHs) and for accurately reporting substantially lower PAH contamination of sediments for their study lakes vs. popular Alberta recreational lakes:Wabamun, Pigeon, and Lac St. Anne. Kurek et al.’s finding of detectably elevated PAHs in sediments of five pothole lakes (four with depths of 1.5– 1.7 m; three with areas less than 5 ha; and dissolved organic carbon levels from 20.6 to 71.5 mg/L, mean 42.5 mg/L) (table S1 in ref. 1) close to oil sands development is not surprising. Lakes NE13 and NE20 are within ∼10 km (figure 1 in ref. 1). The most noteworthy findings relate to Namur Lake, reported as being 90 km northwest of the first major oil sands developments. Elevated PAHs in sediments at Namur Lake were described as expanding beyond the 50 km of higher PAH deposition previously identified (2). What Kurek et al. (1) fail to do is to discuss several features of the sediment PAH record at Namur Lake that are inconsistent with their main hypothesis. First, the authors do not discuss forest fire records for explaining widely fluctuating sediment PAHs while acknowledging that Namur has substantially lower apparent oil sands PAH input. Second, the authors do not discuss the striking fourfold oscillations in sediment PAH concentrations with the two most recent values back down to their predevelopment level. Certainly, scatter in environmental data and some anomalies are inevitable, but the six recurring peaks and valleys in Namur Lake ΣPAH sediment values (figure 1 in ref. 1) do not appear to be random. Third, the PAH flux values for Namur Lake exceed all lake sites except heavily influenced NE20 (figure S2 in ref. 1), a finding that is difficult to explain given that PAH levels in snow declined exponentially within 50 km of the expected oil sands source (2). Finally, the striking concordance between the rise in sediment PAH levels and the sediment chlorophyll levels at all five pothole lakes is only discussed by possibly attributing increased lake productivity to climate change. There was no attempt to falsify any possible relationship between sediment PAH and productivity, which tracked each other remarkably well at all five pothole lakes. Unfortunately, Kurek et al. (1) report no organic carbon levels for their sediment samples. Certainly, if they have such common data, reporting it may prove valuable toward improving our understanding of the behavior of these sediment PAH records. Finally, some of these authors will know that Canadian governments spent millions of dollars on oil sands environmental research between 1975 and 1997. Perhaps Kurek et al. can elaborate on the lack of focus they have attributed to all oil sands environmental research before 1997.