You are absolutely correct about the levels of poisons being a critical piece of information. Also that costs need to be assessed as well as benefits, when addressing clean-up issues.

I would like to bring up an additional and separate point though.

The fact of the matter is that we don't know much about the long-term effects of anything, until we study them. We still don't have much of a clue about what causes Alzheimer's, for instance. Could it be trace amounts of an elemental or chemical contaminant over a long period of time? Nobody knows. Why the jump in cancer rates in the 20th century? Can it be traced to just a few trace contributors? Nobody knows.

So the point I would like to make is this: the reverse of "environmental hysteria" (whatever you want to call it) could keep us from figuring out puzzles like these. And having a large population of "environmental hysterics" could drive us to find out what we need to know.