Well, ginnie.... there is a NEW villain on the horizon. It is called nano particle poisoning. This comes from fumes from diesel and auto emissions and other forms of pollution.

The tiny nano particles have shown in some studies done in Mexico City on children to damage the brains. This is very
frightening and really very new. What it amounts to is very small particles containing heavy metals get into the brain and really
damage things there.

http://www.ncbi.nlm.nih.gov/pubmed/21222367

I am not finding the most recent articles, but I did see them in Science News recently... regarding young children who died in Mexico City and showed damage in the brain tissue.

This is pretty scary and with time we will find out more. But
suffice it say, there are lots of things we don't address here on PN, that may be the real culprits.