Tar sands oil development in the province of Alberta is releasing increasing levels of cancer-causing toxins into surrounding freshwater sources, according to a new study commissioned by the Canadian government.

The study, published Monday, counters claims that the carcinogens are naturally occurring and found that levels of polycyclic aromatic hydrocarbons, or PAHs, in six lakes surrounding tar sands surface mining sites were rising at a rate roughly proportional to the increase in development of such projects.

The Canadian research team analyzed layers of sediment dating back 50 years to determine the historical increase in levels of PAHs, which have been found to cause lung, skin, and bladder cancer in humans.

“One of the biggest challenges is that we lacked long-term data,” John P. Smol, a professor of biology at the University of Kingston who led the research, said in an interview with the New York Times. “So some in [the] industry have been saying that the pollution in the tar sands is natural, it’s always been there.”

Others in the scientific community said the study should put to rest any claims that tar sands development has no correlation to rising levels of pollution.

“I think it’s pretty convincing evidence,” David Schindler, a University of Alberta biologist who co-authored a 2010 study that revealed contaminants, such as mercury and lead, in the Athabasca River near the tar sands site, said, the Globe and Mail reported. “Hopefully, this will kill the all-the-pollutants-are-natural theory once and for all.”

"We have, in some ways, a smoking gun here," Smol told the Reuters news agency. "We can show the amount of PAHs, only one of the many contaminants that are out there, are increasing in lockstep with the tar sands developments starting in the 1960s."

The team’s findings showed that current levels of pollution did not pose a serious health threat but that it should raise concerns about its future impact.

“We’re not saying these [lakes] are poisonous,” Professor Smol told the Times. “But it’s going to get worse. It’s not too late, but the trend is not looking good.”

The Canadian government has indicated that it intends to implement a monitoring program for tar sands development in Alberta, while emphasizing what it considers a limited environmental impact in the area.

“All the lakes studied are remote and not easy to access,” wrote Adam Sweet, press secretary for the government ministry Environment Canada, in an email response to the International Business Times.

“Given their remoteness, the lakes are not likely accessed or used for recreation by local populations. Environment Canada does not have information that the lakes are used as a source of freshwater for human consumption,” he added.

Sweet said the ministry has begun implementing a “scientifically rigorous, comprehensive, integrated and transparent environmental monitoring program for the region” since February 2012.

“That’s just not good enough,” said Dr. Keith Stewart, Climate and Energy Campaign Coordinator at Greenpeace Canada.

“They’ve announced this monitoring program, and yet they keep approving new projects. If they’re serious about assessing the environmental impact of these contaminants, then they need to stop approving new projects.”

Canada currently produces roughly 2 million barrels of oil from tar sands per day, Stewart said, but the government has already approved an increase in production up to 5 million with an additional 4 million in pending projects.

“It’s growing rapidly,” he said. “The level of contamination is increasing in step with production, so you can see it’s going to multiply.”

Responding to the government’s claim that the lakes are remote and therefore unlikely to affect human populations, Stewart pointed out that indigenous populations in the area are being negatively affected.

“It is absolutely affecting human health and human ecosystems,” he said. “If the fish in that lake consume those contaminants and people consume that fish, you will see a concentration and buildup of those contaminants over time.”

The study has also drawn further criticism of the petroleum industry, which had previously claimed that tar sands mining activities did not have a negative impact on local water sources.

Environmental advocates criticize the development of tar sands due to the energy-intensive process it requires to produce oil, thus increasing carbon levels in the atmosphere through both the extraction and subsequent usage of fossil fuels, which has been linked to climate change.

They also condemn the deforestation resulting from tar sands mining, including both the immediate destruction of the environment and the exacerbation of climate change through the removal of natural carbon filters.

Tar sands development has also become a major environmental issue in the U.S. with the construction of the controversial Keystone XL pipeline, which may eventually transport tar sands oil from Canada through the Midwest down to the Gulf Coast for export.