A number of studies are linking the use of leaded petrol during the 1980s and the 1990s with increase in violent crimes which dropped steeply in the 2000s after the use of leaded petrol fell down.
High lead levels have been tied to birth defects, lower intelligence and hearing problems. But now researchers are linking it to high levels of aggression.
Tulane University toxicologist Howard W. Mielke says high levels of lead exposure in children in the 1960s and 1970s resulted in a dramatic surge in crime two decades later. But crime rates dropped off with declining use of leaded gasoline, the Daily Mail reported.
Each metric tonne of lead released into the atmosphere, Mielke calculated, resulted in an increase of 1.59 aggravated assaults per 100,000. The results were millions more shootings, stabbings and beatings, the professor said.
The data was able to explain 90 percent of the rise and fall of crime rates in the cities studied. The link between lead and violence is relative new, as well.
Herbert Needleman, University of Pittsburgh researcher, conducted a 1996 study that showed that children with high lead levels were much more likely to exhibit aggressive behaviour than those with normal levels.
A 2002 study showed that arrested youths had far higher levels of lead in their bones, on average, than their non-delinquent peers.
Leaded fuel is still in use - but only in race cars, piston-powered airplanes and some off-road vehicles.