Here's a great article stating that 'poison' is oozing by the barrel-full into Lake Ontario, but never stating exactly how much. Might be one atom per year, for all we know! Yet, our nasty rivers dump a heck of a lot of natural uranium, mercury, lead, whathaveyou, into the lake every year. Lucky for us, the zebra mussels eat all this up, and they're very healthy for doing so!
Sometimes we forget that 'the dose makes the poison'. And remember the song: "A spoonful of uranium makes the medicine go down" la, la, la!