zoeschlanger:

Bitumen—the stuff extracted from tar sands—is nothing like its conventional crude counterpart. It’s thick and sticky, and has to be diluted to flow through pipelines. The chemical mixture used to dilute it is a trade secret, but often includes the human carcinogen benzene.

It’s nasty stuff. And now it has a NYT op-ed from my former boss at InsideClimate News, which heavily reported this particular aspect of the tar sands question before anyone was paying attention. From the op-ed:

[…]But this oil is no ordinary crude oil, and it carries with it risks that we’re only beginning to understand. Its core ingredient — bitumen — is not pumped from wells but is strip-mined or boiled loose underground.

[….]The nation’s pipeline network was designed to handle conventional crude oil and is governed by laws and regulations that were written long before the unique risks and hazards associated with dilbit began to emerge. In fact, dilbit is exempt from an excise tax that pays for oil spill cleanups, because the 1980 law that created the tax did not consider bitumen from the “tar sands” to be crude oil.

This is all very relevant to Enbridge—here’s some background on that.