A 2007 study of the effects of lead on behavior found significant increases in aggressiveness correlated with increases in lead levels in children. The study also suggested that blood lead levels might produce such an effect not only in the early years of life (on development) but on concurrent behavior of seven year olds.
For every increase of 10 micrograms per deciliter of blood, children scored about five points worse on a 100-point scale that measures “externalizing” behavior problems, such as aggression and acting out.
Also, for every 10-microgram increase, the children were nearly 11/2 times more likely to exhibit these types of problems. (Source)
The study was published in Pediatrics and is available through NIH public access. (Link)