Unravelling the complexity of pollution by the oil sands industry.

Parajulee and Wania (1) make an important contribution to understanding the origin and magnitude of pollution caused by the massive oil sands industry in northeastern Alberta. Until recently, the oil sands industry and government officials have claimed that all pollutants carried by the lower Athabasca River system were the result of soil erosion, forest fires, and other natural phenomena. This claim was challenged by two earlier papers in PNAS (2, 3), which showed that the oil sands industry contributed substantial amounts of organic and inorganic pollutants to the watershed and river. Although these conclusions were first denied by industry and governments, expert panels appointed by provincial and federal governments supported the results, concluding that industry’s and government’s monitoring programs were incapable of assessing the extent of the pollution problem (4, 5). As a result, monitoring of the river was greatly upgraded by Environment Canada (6). The improved monitoring uncovered more mysteries. Kelly et al. (2, 3) had found that pollutants emitted by the upgraders that convert bitumen to synthetic crude oil were detectable in the winter snowpack of the area to a distance of about 50 km. These results were verified by Environment Canada’s studies of snowpack chemistry (7). However, analyses of lake sediments showed that a much larger area has been contaminated with airborne polycyclic aromatic compounds (PACs). PACs emanating from the oil sands industry were found in lakes at distances up to 95 km from known sources at bitumen upgraders, and to have increased over time in proportion to bitumen production. The “fingerprint” provided by analysis of multiple PACs showed that the oil sands industry, not natural sources such as forest fires, was responsible for the increases (8). Parajulee and Wania (1) demonstate a plausible explanation for the discrepancy between the magnitude of pollution reported by ref. 8 and that of refs. 2, 3, and 7. In warmer months, emissions of volatile PACs from the oil sands industry’s vast tailings ponds (>170 km in area, containing 720 million m of “process water”) (Fig. 1) are a major source of PACs to the atmosphere, whereas in winter, cold temperatures and ice McClelland Lake