SHERIDAN WASHINGTON (AFP) - The amount of harmful pollutants released in the process of recovering oil from tar sands in western Canada is likely far higher than corporate interests say, university researchers said on Monday.

Actual levels of polycyclic aromatic hydrocarbon (PAH) emissions into the air may be two to three times higher than estimated, said the findings in the Proceedings of the National Academy of Sciences, a peer-reviewed US journal.

The study raises new questions about the accuracy of environmental impact assessments on the tar sands, just days after a US State Department report said the controversial Keystone pipeline project to bring oil from Canada to Texas would have little impact on climate change or the environment.

Current estimates do not account for the evaporation of PAHs from wastewater pools known as tailing ponds, which are believed to be a major source of pollution, said researchers at the University of Toronto.

According to corporate interests which are responsible for projecting their environmental impact, the Athabasca oil sands beneath Alberta, Canada - which hold the third largest reserve of crude oil known in the world - are only spewing as much pollution into the air as sparsely populated Greenland, where no big industry exists.

Lead study author Frank Wania, a professor in the department of physical and environmental sciences, described the corporate estimates as "inadequate and incomplete." "If you use these officially reported emissions for the oil sands area you get an emissions density that is lower than just about anywhere else in the world," he told AFP.

"We need a better accounting of the contaminants being released from these operations," he added.

"Only with a complete and accurate account of the emissions is it actually possible to make a meaningful assessment of the environmental impact and of the risk to human health."

BEGAN AS A STUDENT PROJECT

The research began as a term paper project by his student, Abha Parajulee, and was funded only by internal resources at the University of Toronto, he said.

She examined emissions estimates from environmental impact assessments that corporations must file before any new projects can begin to coax oil from the Athabasca oil sands.

She compared them with measurements in the field by academic scientists and by the federal ministry of the environment, known as Environment Canada.

The estimates were way lower than the actual measurements, apparently because they did not include any escape of PAHs from tailing ponds, which are engineered dyke and dam systems built near mining operations in the oil sands to collect the water, sand, clay and residual oil left over from processing.

Until now, they were not expected to be a source of pollution.

Computerized modeling of the pollutant levels emitted by oil sands operations only came close to the observed measurements in the environment when Wania and his student added in the expected pollution from evaporation out of tailing ponds.

PAHs are dangerous, cancer-causing chemicals created in the burning of fossil fuels. They can also coat meats and other foods that are charcoal-grilled.

"If you think about it from an environmental chemist's point of view, it really shouldn't come as a surprise that these chemicals can evaporate especially from water bodies," said Wania.

"We were surprised that clearly unreasonable assumptions had been made in these emissions estimates." Wania said to his knowledge, the research marks the "first time these emissions have been put to any sort of plausibility test." Environment Canada was interested in the findings and has agreed to fund more research going forward, he said.

With the third largest crude oil reserves in the world after Venezuela and Saudi Arabia, Canada has predicted that oil sands development will bring in some two trillion dollars over the next two decades.

The US State Department's report on Friday raised no major objections to the controversial Keystone XL pipeline plan and said the pipeline would not in itself significantly increase greenhouse gases, blamed for climate change.

The Keystone XL project aims to carry some 830,000 barrels of heavy crude a day from Alberta's oil sands south to Nebraska refineries before joining an existing pipeline to be shipped to Texas.