I'll start and then allow some of my colleagues to jump in.
You compared the precautionary principle to risk management. The precautionary principle actually guides us throughout that entire cycle, and it guides us through the risk assessment phase. I'm sure my colleagues would be welcome to speak more on that aspect.
But as has been mentioned, many of these substances are quite ubiquitous. They're serving a purpose in society. For instance, we're still using mercury in instrument measurement. What we try to do is avoid future exposures. We try to control existing exposures. In some cases, that will be a ban--it's an appropriate tool--and in other cases, we look for phase-out over time. We also look for the precautionary principle even in terms of where our enforcement efforts come in. I think a precautionary principle applies throughout.
We do try to balance whether or not something is performing a useful purpose, if the risk can be controlled, and if there can be prevention of any releases to the environment and exposure to human health. Whether the substance has a useful value to society is something that we do have to demonstrate in our risk management. We have to compare the benefits and costs to get the appropriate instrument.
The other thing is that some of these substances are naturally occurring. With lead and mercury, you're always going to have some residual levels in the environment from natural sources. It's a matter of managing the exposures and trying to find the most cost-effective way to do that. That's where the precautionary principle does help us choose the appropriate measure.