Link between lead and violent crime

Young adults exposed to high levels of lead as children are more likely to become aggressive and commit violent crimes resulting in death, a new Australian study shows.

It’s well known high-level exposure to lead is toxic. It builds up in teeth and bones and among other health problems, high levels of lead attack the brain and nervous system, resulting in neurological and behavioural changes, scientists say.

It is particularly harmful to developing children and environmental lead exposure during childhood is estimated to cost $50 billion a year in the US alone.

But despite Australia being one of the world’s largest lead producers and exporters, the majority of studies on lead exposure health effects have been carried out in the US. Now, Macquarie University researchers conducted the first Australian study linking lead exposure to aggressive criminal behaviour.

The team analysed air lead concentration measurements from six suburbs in New South Wales for which data was available from at least 30 years. They then linked the environmental lead levels to the impact on the rates of assault 15 to 24 years later, after adjusting the data for socio-demographic factors that affect criminal behaviour, such as age and household income.

The researchers found that, among the studied suburbs, exposure to lead in the environment was the strongest predictor of assault rates in adulthood.

In fact, the assault rates 21 years after exposure rose by 163 assaults per 100,000 people for every extra microgram of lead per cubic metre of air. That’s a speck less than a thousandth the weight of a snowflake in the volume of a large fridge.

The researchers found air lead concentrations accounted for nearly 30% of the variance in assault rates, a measure of deviation from the average rates, seen 21 years after exposure. And in New South Wales and Victoria over 32% of the variance in the rates of death by assault were linked to lead concentrations, 18 years after exposure.

The trend for lead exposure seems to be specific to violent crimes. When the researchers compared lead levels and fraud – a non-aggressive crime – they saw only 5.5% of the variance was accounted for by lead.

Good news is, the historic problem sources, such as lead paint and leaded petrol have been reeled back. Studies have shown that since removal of leaded petrol in 2002 and reduction of allowable lead levels in paint to 0.1% in 1997, blood levels in the Australian population have fallen.

But emissions from leaded petrol, as well as mining and smelting operations, have left a lasting legacy in the environment and lead paint poses a problem during renovations of older buildings.

“The results [of the study] indicate that measures need to be taken to lessen exposure to lead in areas where environmental air levels remains high, so as to avoid any long-term neurodevelopmental consequences,” study author Mark Taylor said.

The study was published in Environmental Health.

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