We had a test flight once, for a report of smoke coming from a bleed air source, when thick white smoke indeed began to appear about halfway through the takeoff roll. (I seem to recall that it was a bad seal on the engine, but it might have been a bad seal on the pack.) Anyway, yes, something obviously had gone "seriously wrong" there so that I just killed the bleed supply for the affected pack, when we made an emergency return and left it for the engineers to sort out.
We had our masks with goggles on; the engineers observing the test flight got to sit in a cabin full of white smoke for a little while, That was for just a few minutes, but longer than anyone could hold his breath as it slowly dissipated. The real risk then was thick smoke leaving us unable to see the flight displays.
It's easy to imagine that there could be some problem with a pressurization system that puts a certain small amount of contaminant into the air supply, when it would be the flight crew and the cabin crew who get the most exposure.
For one thing, yes, there's a pressure differential between the oil supply and the bleed air supply, but what happens after shut-down? There is no pressure differential, when I assume that a tiny amount of oil could then leak across to the side we get our breathing air from. The 146, of course, has four engines, so that any such effect would be doubled compared to similar aircraft with only two engines. Another thing is that some particular engine design might have less effective seals than another. Too, engines do need to have oil added, even when that is merely a matter of one liter per every ten flight hours or whatever, when we have no real idea where that missing oil went, either safely out the exhaust or perhaps a little bit into the cabin air supply.
Part of the problem is that the basic design for almost all pressurization systems is from a time when we were not sensitive to risks from organophospates. (The Boeing 787 is the only airliner that does not use bleed air for pressurization.) It loosely was taken to be so that if you could not smell it, where was the problem?