Using a paleoecological framework, Joshua Kurek, John Smol and their collaborators showed that polycyclic aromatic hydrocarbons (PAHs) have increased within lake sediments conicident with the development of Athabasca oil sands. The signature of bitumen extraction was even found in a lake some 90 kms removed from the source. The paper was published in and can be downloaded from the Proceedings of the National Academy of Sciences.
The work received wide media coverage. See John speak about this work on As It Happens.