The more we learn about exposure to toxic metals, the worse it becomes. While we know a fair bit about acute
poisoning, we actually know next to nothing about chronic
exposure to low grade amounts. My boy had lead toxicity
and we saw amazing improvements in behavior and cognition when we treated him for it. Although we knew he had been exposed to mercury, it was not testable thru standard blood testing. However, he did not begin using expressive language until after we began treating him for mercury along with the lead.
http://www.newswise.com/articles/2003/4/LOWLEAD.CNS.html