There are forty-five million different chemicals which are currently commercially available around the world, and many of them have never been tested. In the interview with Professor Patricia Hunt linked below, she reveals that there are 12,000 new substances registered every day.
Of greatest concern may be the ones that act like hormones in your body, especially high-volume chemicals that you likely encounter on a daily basis. The standard set of guidelines toxicologists use for testing doesn't work very well for chemicals that mimic the actions of hormones.
According to Hunt, as reported by Living on Earth:
"There are hundreds of studies looking at the effects of bisphenol A -- most of them using experimental animals. And when the regulatory panels sit down and look at them, quite frankly, they don't know what to do with a lot of the research ... And the problem with these chemicals is, there are so many of them and some of them are present in our daily lives at pretty significant levels. And so, if these are having effects, and if they're having effects on our developing babies and infants, it may take us a couple of generations to actually get that proof -- that definitive proof -- in humans."