A Cincinnati-based study found that low levels of lead can permanently damage the brain. 
The study followed lead-exposed children from before birth into adulthood and concluded that even relatively low levels of lead can permanently damage the brain and are linked to higher number of arrests, particularly for violent crime.
Researchers have long known that lead exposure reduces IQ by damaging brain cells in children during their early years. It also increases children’s distractibility, impulsiveness and restlessness and shortens their attention span, all factors researchers say are precursors of aggressive or violent behavior. 
About 38 million U. S. homes or 40 percent of the nation’s housing still contain lead-based paint, according to the U. S. Department of Housing and Urban Development, particularly in homes built before 1978. Paint in such houses contain as much as 50 percent lead. Even if covered by newer, lead-free paint, it still flakes or rubs off. The problem is particularly acute in urban areas, which typically have older housing that has not been renovated.
Cincinnati researchers found that by measuring blood levels of lead before birth and during the first seven years of life and then correlating the levels with arrest records and brain size produced the strongest evidence yet that lead plays a major role in crime.
What was even more surprising is that the link between criminal behavior and lead exposure was found among even the least-contaminated children in the study, who were exposed to amounts of lead similar to what the average U.S. child is exposed today.
The lead study enrolled 376 pregnant women in Cincinnati’s inner city between 1979 and 1984 and measured their blood lead levels during pregnancy and the children’s levels during their first seven years of life.
Environmental health researcher Kim N. Dietrich of the University of Cincinnati College of Medicine studied 250 of the original group, correlating their lead levels with adult criminal arrest records from Hamilton County, Ohio.
He and his colleagues found that 55 percent of the subjects (63 percent of the males) had been arrested and that the average was five arrests between the ages of 18 and 24.
The study found that the higher the blood level at any time in childhood, the greater the likelihood of arrests. “The strongest association was with violent criminal activity--murder, rape, domestic violence, assault, robbery and possession of weapons,” Dietrich said.