I had a comment on the use of risk assessment for mixtures or groups of similar substances. I think cumulative exposure is an approach you can take on things like the organophosphate pesticides that have a similar mechanism of action.
I think, again going back to my arguments, that that's already being done by Environment Canada and Health Canada for things that have a common mechanism of action. Polycyclic aromatic hydrocarbons are being addressed as best they can be as a group, and dioxins and furans and those kinds of things. Sometimes the relationship, though, sort of falls apart. It holds up pretty well for dioxins and furans, but for PAHs it depends on the end point,sometimes, where it doesn't hold up quite so well for cancer and the effects on blue-green algae, and so on.