The diluted oil sands bitumen Enbridge proposes to send by pipeline across northern B.C. poses much greater spill risks than conventional oil, a trio of environmental groups argued in a report released Tuesday.

Whether that's actually the case is the subject of intense debate.

But invoking those fears to fight Enbridge's Northern Gateway proposal shows an evolution in strategy for Canada's environmental movement.

It suggests Canadian campaigners may now be taking cues from the highly-publicized, and ostensibly successful, U.S. battle against TransCanada's Keystone XL pipeline.

"Diluted bitumen is not the same as conventional oil," reads Tuesday's report, authored by researchers from the Living Oceans Society, Pembina Institute and U.S.-based Natural Resources Defense Council. "It is more likely to cause corrosion in the pipelines through which it flows, as well as in the tankers that carry it through marine ecosystems."

This argument was first made by the Natural Resources Defense Council in a brief, but explosive, report last February.

The gist of it was that the diluted bitumen TransCanada wants to ship from Alberta's oil sands to the Texas Gulf Coast contains high concentrations of sulphur, acid and other contaminants, magnifying the likelihood of spills.

An Alberta government report this week questioned whether these qualities actually make bitumen more corrosive than conventional oil.

Yet there's been no independent, peer-reviewed study on the controversy to date. And as an insideclimatenews.org investigation concluded in early November: "There is little information to support either side," oil industry or environmental.

Still, worries about corrosion loomed large enough last June to cause top Democrat Congressman Henry Waxman and others to call for an inquiry.

Those types of concerns likely played a role in President Barack Obama's recent decision to delay Keystone XL by up to 13 months.

Canada's environmental movement, with the release of Tuesday's report, is now evoking similar worries.

"This report shows why the Northern Gateway pipeline is not worth the risk for the communities, rivers and Pacific coastline of British Columbia," senior Pembina Institute policy analyst Nathan Lemphers said in a statement.

Will Prime Minister Stephen Harper, like his American counterpart, actually take those concerns to heart? Don't hold your breath for now.

Geoff Dembicki reports on energy and climate issues for The Tyee.