Leaded gasoline may trigger violent behaviour: study

Tulane University toxicologist Howard W Mielke said high levels of lead exposure in children in the 1960s and 1970s resulted in a dramatic uptick in crime in the US two decades later.

When the use of leaded gasoline declined in the 1980s, crime rates dropped off at corresponding rates, the 'Daily Mail' reported.

Mielke found that in all six cities - Atlanta, Chicago, Indianapolis, Minneapolis, New Orleans, and San Diego - every one per cent increase in the number of tonnes of lead released into the atmosphere resulted in a half percentage point increase in the aggravated assault rate 22 years later.

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, Mielke said.

The data was able to explain 90 per cent of the rise and fall of crime rates in the cities studied.

Dr Herbert Needleman, a 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 youths had been arrested had far higher levels of lead in their bones, on average, than their non-delinquent peers.

Mother Jones writer Kevin Drum reported that the leaded gasoline theory is the only explanation for the dramatic rise and fall of violent crime across US.

Politician Rudy Giuliani is credited with lowering crime rates in New York thanks to aggressive policing and revolutionary tactics.

Crime rates in the city dropped 75 per cent between the 1990s and 2010.

But, Drum points out, it dropped by similar rates all over the nation - 70 per cent in Dallas, 74 per cent in Newark, 79 per cent in Los Angeles.

All of those cities stepped up enforcement, but never had 'revolutionary' leaders to combat crime, Drum said.

Leaded gas was phased out by the 1980s. It was banned for use in vehicles on US roadways in 1996.

It is still in use - but only in race cars, piston-powered airplanes and some off-road vehicles.

The study was published in the journal Environmental International.