I would say that we see all of the toxins I mentioned. There's a wide suite of polycyclic aromatic hydrocarbons, including several known carcinogens; some related compounds that have one of the carbons substituted by a sulphur, known as dibenzothiophenes; and then a suite of toxic trace metals that are bound up in this bitumen matrix too. Basically, any water that runs through those wetlands leaches small amounts of those pollutants out.
That being said, some odd times the overlying vegetation can be helpful. For example, wetlands with peat as a base are known to retain mercury very strongly. But I think it's also fair to say that if you go in and disturb either the geology or the ecosystem in those areas, you expose fresh surfaces to weathering by air and rainfall, so that the amount of those things that are mobilized, either by water or airborne, is increased. That's something you can find 40 or 50 years of studies to show, pretty well all over North America and Europe.
So in this case, it isn't a surprise that materials tied up in this bitumen are mobilized and it isn't a surprise that some are there naturally either. I think the situation is that there are natural levels, as industry and Alberta Environment have correctly stated, but those amounts are clearly enhanced by digging up the watershed of the Athabasca and its tributaries.