The joint study between scientists at Queens University and Environment Canada looked at core samples from five lakes close to the oilsands mining and upgrading operations in Fort McMurray, Alta. They also studied samples from Namur Lake, 90 kilometres northwest.
The authors focused on polycyclic aromatic hydrocarbons, or PAHs. These are cancer-causing chemicals that are released when things are burned. They can occur naturally — from forest fires, volcanic activity and geological deposits — but burning petroleum in the production of the oilsands leaves a particular fingerprint, so the scientists were able to trace where the PAHs in the core samples came from.
The study found that the levels of PAHs in all six lakes had increased anywhere from 2½ times to 23 times background levels in the early 1960s, before the start of oilsands mining in the region. The PAHs fall into the water from air pollution and are deposited in the mud over time.
The study's lead author, biologist John Smol from Queen's University, says these formerly pristine northern lakes now have the same chemical composition as lakes near urban areas.
"This is an early warning indicator of what is happening, he said. "These lakes are not pollution pits by any means, but these wilderness lakes are similar to your typical urban lake."
Smol says scientists were surprised to see that even Namur Lake, the furthest away, was being affected.
"The footprint of the tarsands is much further," he said. "Here we have effects 90 kilometres away."
The study warns the chemical deposits will increase as oilsands production in northern Alberta triples in size in the next 25 years.
Joint monitoring plan in place
The effect of the oilsands on the environment is highly controversial. There was little monitoring of the air and water in the region before the production started and there is a polarized debate about what is considered "natural" occurrence of petroleum deposits in lakes and rivers.
But other studies have warned of problems. A study in 2010 by University of Alberta scientist David Schindler discovered deformed fish in Lake Athabasca downstream from the oilsands. It caused a huge public outcry and eventually led to a federal-provincial environmental monitoring plan for the Alberta oilsands announced last February.
In a statement emailed to CBC News, a spokesman for Environment Canada said it was important to note that the results in the Queen's study came from field studies that were conducted before the announcement of the "scientifically rigorous, comprehensive, integrated and transparent" monitoring plan for the region.
"In fact, the [joint monitoring plan] was created, and implemented, to address the very concerns raised by such studies — it was designed to provide an improved understanding of the long-term cumulative effects of oilsands development," said Adam Sweet in the email.
Sweet said that only one lake in the study, which was "very close to the oilsands," showed a level of contaminants exceeding Canadian guidelines, and said overall the results were "low compared to urban areas," while noting there was no comparable data since this was the first study of its kind.
Monday's study concludes there is "little doubt of the unprecedented increases of PAHs" in northeastern Alberta's lakes, and warns of "striking contaminant increases consistent with the prevailing winds blowing across local upgrading facilities and surface-mining areas."
The scientists also took a look at how the chemicals from the oilsands are affecting zooplankton, which are sort of the canary in the coal mine in freshwater research. Zooplankton are tiny little organisms the size of a dot that float around in water and are eaten by fish.
So far, the study shows the zooplankton are doing fine, with numbers at an increasing level. Scientists think warmer temperatures caused by climate change are actually helping them to survive the effects of the chemicals. But that may only be short-term good news.
The study warns of the "unknown" long-term ecological effects of the PAHs, as increasing amounts of the chemicals occur in freshwater lakes and are absorbed by fish, birds and up the food chain to humans.