"We are being sold a bill of goods by this government," New Democrat environment critic Megan Leslie said Monday.
"If this report has been around since 2013 and not been released, then it makes me think they must be trying to hide something."
Francois Poirier, president of TransCanada's Energy East pipeline project, downplayed such concerns.
"There have been a number of studies by reputable third-party and scientific organizations ... that demonstrate that diluted bitumen behaves just like any other type of crude oil product that's transported through our pipeline," he said.
In an emailed statement, Phillipe Reicher of the Canadian Energy Pipeline Association made a similar point.
"Generally speaking, we have no operational evidence that indicates that diluted bitumen behaves differently than other forms of crude oil," he said.
But the unpublished report on environmental threats from oil and bitumen pipelines says little is known about potential toxic effects of oilsands products in oceans, lakes or rivers.
"In particular, research on the toxicology of bitumen is lacking," says the draft report, which was commissioned in response to concerns raised at the Northern Gateway pipeline hearings.
The document comes as Canada debates pipeline proposals for moving large amounts of diluted bitumen from Alberta's oilsands to refineries and ports on both coasts and into the United States. It was obtained by Greenpeace under freedom-of-information legislation.
A spokesman for the department of Fisheries and Oceans said a more complete, peer-reviewed version of the report is to be published in the coming months.
Canadians need that information now, said Keith Stewart of Greenpeace. He said Prime Minister Stephen Harper's Tories approving Northern Gateway in spite of important knowledge gaps shows a dangerous lack of caution.
"The fact they're saying full speed ahead even though they know it's a lot more dangerous than they've been letting on publicly should be a cause for concern," he said. "It throws into question the regulatory approvals process when they withhold this kind of information."
An early draft of the report lays out 10 specific "knowledge gaps" about bitumen and various substances used to dilute it when it's pumped through pipelines.
"Very little information is available on the physical and chemical characteristics of oilsands-related products following a spill into water," it says. "Research on the biological effects of oilsands-related products on aquatic organisms is lacking.
"A better understanding of the fate and behaviour of these products is critical for assessing the potential risk to aquatic organisms."
The draft finds that Orimulsion, a Venezuelan product about two-thirds bitumen and one-third water, is "highly toxic to fish" — 300 times more toxic to embryos than heavy fuel oil.
The 61-page draft includes 14 pages of references to peer-reviewed academic studies as well as to government and industry publications. They date from 1976 to 2013 and include articles from a wide variety of scientific journals.
The government spokesman said funding has already been provided for five research projects on possible bitumen effects on fish and shellfish.
A federal report released Jan. 14 echoes many of the concerns from the unreleased review. It concluded little can be said about how bitumen changes as it weathers, how it interacts with sediments or whether it would float or sink.
"Research regarding how bitumen products will further biodegrade in the environment is insufficient," it concludes.
Reicher added that industry is sponsoring a literature review of its own into how a "broad range" of industry products behave in water. That study is to be set by the Royal Society of Canada — an association of many of Canada's most senior scientists — and is expected to be published this fall.