I was given to understand that based on forensics and historical data, that the extensive use of lead for carrying water and in eating/drinking utensils was a major contributor to the decline. Lead poisoning causes all sorts of nasty mental and physical problems.
:’) The lead poisoning claim emerged some years ago, and has never been accepted, except by various popular media scribblers. Oddly enough, someone just FReepmailed some questions about this just in the past couple of weeks. :’)