Actress and activist Darryl Hannah was arrested this week in Washington D.C during a protest against extending TransCanada's Keystone XL pipeline, which would carry oilsands crude from Alberta through six U.S. states to refineries in Texas.

On Wednesday, Hannah appeared on CBC's Power & Politics to debate Alykhan Velshi, founder of Ethicaloil.org, a website devoted to defending Canada's oil industry.

During the debate, Hannah made claims about the oilsands, some of which CBC News investigated:

Claim 1.: "It's well-documented that the tar sands itself is one of the world's largest ecological atrocities and disasters."

The Royal Society of Canada (RSC) released a 414-page report last year entitled Environmental and Health Impacts of Canada's Oil Sands Industry. It was written by scientists and academics and targeted oil companies, the federal and provincial government and environmentalists.

The report addressed the question of whether the oilsands is "the most environmentally destructive project on earth."

The report compares the oilsands to a number of other industries. In terms of toxic emissions, for example, it says the oilsands industry ranks fifth for mercury, sixth for cadmium, eighth for lead and eighth for four carcinogenic pollutants.

The industry would have to increase its emissions by five-fold to become the first ranked industrial emitter of air pollutants and toxic emissions, the RSC said, something "no foreseeable oilsands growth scenario" would lead to.

The academic group also found that no evidence had been demonstrated that the industry is a major polluter of surface waters, although groundwater is less certain.

They did note the substantial impact of open pit surface mining and a need for more rapid reclamation of disturbed areas. But they said "the claim by some critics of the oil sands industry that it is the most environmentally destructive project on earth is not supported by the evidence."

Claim 2.: "The contribution to the carbon in the atmosphere is unprecedented."

The report acknowledges reducing greenhouse gas emissions from the oil sands poses a challenge to Canada and that the industry is the country's fastest growing source.

But it said the oilsands makes up about five per cent of the country's total emissions, compared with 16 per cent for fossil fuel-fired powered generation and 27 per cent for transportation, based on 2008 data.

In terms of global emissions, the oilsands contributes .08 per cent. the report found.

Claim 3: "I've been hearing about how many people have cancer that live downstream from the tar sands project"

Hannah is referring to the residents of Fort Chipewyan who live downstream from the oilsands. Concerns were first raised in 2006 by a local doctor about supposed elevated cancer rates in the town. In 2009, the Alberta Cancer Board said cancer rates were 30 per cent higher than expected.

But the RSC report noted that the doctor was later criticized by the College of Physicians and Surgeons of Alberta for making "a number of inaccurate and untruthful claims."

International experts who looked at the Alberta Cancer Board study also found that the increase in cancer incidence was not evidence that an environmental exposure was the cause.

"There is currently no credible evidence of environmental contaminant exposures from oilsands reaching Fort Chipewyan at levels expected to cause human cancer rates."

However, the Alberta government has said it will further study the issue.

Claim 4: "It has poisoned every one who's lived downstream from it."

The report found that "environmental contaminants at current levels of exposure are unlikely to cause major health impact for the general population." It added that projected emissions from expanded operations are not likely to change that expectation.

Claim 5. "TransCanada, who's building this pipeline has told people in [the U.S.] that they're going to be taking their land through eminent domain if they don't agree to the terms."

Hannah is referring to TransCanada's threat to go to court to expropriate parts of U.S. land from landowners who oppose the Keystone XL pipeline on their property.

While the company has said it's trying to work out agreements with the landowners, it has admitted it would go to court as a "last resort" to force a deal.

TransCanada spokesman Terry Cunha told the Associated Press in April that landowners who agree to easements with TransCanada will receive payment when they sign the agreement, and Cunha said landowners would keep the money even if the project isn't approved. Plus, the ranchers and farmers retain ownership of the land.