Brian
Everything you point out is true. Still, I don't think Listerine is going to turn out (like in the Woody Allen film Sleeper)to be a health elixir. I'm glad you raised the "volume of exposure" since that has always been a problematic issue that underlays the EPA's many failures to protect the public. The level of "no harm" is set far too high IMHO. Each time they reassess mercury or lead levels or some other toxic chemical lower, it's only after documented studies instead of being safe not sorry.
Good thing I'm not a homeopathic healer or else you would have hurt my feelings and questioned the entire basis of my life's work. Since homeopathic potions often average a 1 part to 1,000,000 of the original substance ratio, they obviously have a diiferent take on volumes of exposure. Let me be clear that I have zero idea of what the proper exposure level is for any of these chemicals. What's frustrating is that there is often no actual need for these additives.