I don't think anyone that has commented so far (or the article itself) really understands how problematic it really is. I don't either for sure, but it's a few 10s(?) of kgs of heavy metal. It's probably going to act like a rock in the glacier, eroding slowly over a long period of time. I don't know how much is problematic, but consider the concentration of naturally occurring Uranium as a point of comparison: https://en.wikipedia.org/wiki/Uranium_in_the_environment#Nat.... Even factoring in a few orders of magnitude for refined Plutonium vs. naturally occurring Uranium, it's still a relatively low concentration, and that assumes it erodes entirely and quickly, neither of which seems likely at all.