I know that when fluoride began to be added to the water in the U.S. everyone was told that there would be no more cavities. I had never known that too much fluoride could poison you.

This sounds like a serious problem that this town and the site in Mexico has. Sounds like they are suffering from "too much of a good thing".

Check out this site to learn of other things you can have too much of ... http://www.gather.com/viewArticle.jsp?articleId=281474977207835