MONTPELIER, Vt. — Some environmentalists may be overstating fears about the corrosive effects of tar sands oil on pipelines like the one across northern New England, a new study published by the National Academy of Sciences says.

Possible pipeline corrosion by tar sands oil has been cited by opponents both of a possible reversal of flow in the northern New England pipeline and the Keystone XL pipeline proposed to carry tar sands oil from western Canada to refineries in Texas.

Opponents say moving the oil through the aging pipeline would be a threat because it is thicker and more corrosive than the regular crude it now carries, making it more likely to spill and cause an environmental disaster. They also say that when burned, the fuel contributes more greenhouse gas emissions than lighter crude.

In Vermont, environmental official Kirsten Sultan ruled in April that a plan to reverse the flow of the New England pipeline, which now flows east to west from Maine to Montreal, would require a new permit under state law.

The pipe’s owner, the Portland Pipe Line Corp. is asking Sultan to reconsider. On Tuesday, its lawyer, Peter Van Oot, wrote to Sultan and asked her to take into account a study released June 26 by the Transportation Research Board, an affiliate of the National Academy of Sciences. The NAS is a private, nonprofit organization chartered by Congress to advise the federal government on scientific matters.

The study said there did not appear to be increased risk from shipping tar sands oil on pipelines that otherwise would carry traditional crude oil.

“The committee does not find any causes of pipeline failure unique to the transportation of” tar sands oil, the study said. The committee also said it found no aspects of the oil that would make it more likely than other crude oils to affect its transportation.

The American Petroleum Institute welcomed the findings, noting that Canadian crude oils have been transported safely in the U.S. for 40 years.

“All crude oils have to meet the same criteria when put in a pipeline, which protects the pipeline and communities along its route, as well as the quality of all transported crudes,” the API’s pipeline director, Peter Lidiak, said in a statement.

One person outspoken about perceived dangers of shipping tar sands oil over pipelines is Jim Murphy, senior attorney with the National Wildlife Federation’s Northeast regional office in Montpelier.

Murphy wrote in a blog post on Monday that the study “is no surprise and provides no comfort.” He said the study did not consider several key issues, one being that when tar sands oil does leak, it sinks to the bottom rather than floating on the surface of water, making cleanup much more difficult.

“The study did not look at how this substance behaves after it spills,” Murphy wrote.

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