I have a comment in terms of what Mr. Smith is saying.
It's very hard for us to study all the different possibilities of mixtures and combinations that can happen.
From looking at some of the studies, we know there is something called “synergy”. One substance will have a certain effect and another substance will have a certain effect, but when you put the two substances together, it's greater than the sum of its parts and you get an enhanced effect. A simple example of that is when ozone, smog, and pollens affect people with asthma. When you put them together, you get an expanded effect in terms of what those things can do.
It's part of the reason we seek a more precautionary approach to assessments of chemicals and to getting rid of them. It's going to be impossible for us to know all the possible combinations and synergies that can occur among the chemicals we're exposed to.