S. Vedantam had a piece yesterday on research into lead poisoning, specifically relating the presence of lead in the environment to crime rates. The theory being lead is a neurotoxin that causes impulsivity and aggression, so infants exposed to lead, either in lead paint or in the atmosphere from gas additives, grew up more apt to be criminals.
It sounds good in the writeup, as such pieces often do. Over at Freakonomics today , they are open to the idea, but aren't convinced (particularly because the proponent of the theory questioned their theory that legalized abortion might have impacted US crime rates. They include references to other researchers.
It's a little personal to me, since lead contributed to my existence. My father graduated from U of Minnesota in chemical engineering, went to work in a paint factory in St. Louis, became sick and was told to get into the fresh air or die.