Lead based crime: petrol not bullets

In our Western democracy, elections are won and lost on the basis of multiple factors. Commonly, the economy is nearly always top of the agenda due to its trickledown effect on every facet of  society, including crime.

Crime rates are a major issue for any government. If crime is falling, history tells us that they will seek to use this to their political advantage; citing their policies and strategy as the primary factors in any perceived successes.  However, the explanation for any success can be completely unexpected and often of a more scientific nature.

Experts often suggest that crime resembles an epidemic. Karl Smith, a professor of public economics and government at the University of North Carolina-Chapel Hill had a rule to categorise epidemics. If the epidemic spreads along lines of communication the cause is information, if it travels along transportation routes the cause is microbial, if it fans out from a single place the cause is insects, or if it’s everywhere at once the cause is a molecule.

Thomas Midgley Jr. (1889-1944) was lauded for his scientific achievements, but his legacy leaves a bad taste in the mouth. He can be credited with two scientific discoveries that have had some of the most catastrophic effects on our environment over the last century. One of which was the use of CFCs in fridges and aerosols that have contributed to ozone layer depletion. The other being the creation of our molecule in question: tetraethyl lead.

Created in 1921, tetraethyl lead was mixed into petrol until it was gradually phased out 20 years ago due to its neurotoxicity and damaging effect on catalytic converters. It has a high octane rating – signifying it’s ability to withstand compression before detonating – a trait that can increase fuel economy and performance. Ethanol has the same effect. It is cleaner and more widely available, but tetraethyl lead was pushed as the ‘mixer’ of choice due to its profitability to patent holders.

Exposure to lead is predominantly through inhalation, or in the case of tetraethyl lead, through the skin. Lead has been known to be poisonous for a long time. In the 2nd century, Greek botanist Nicander wrote that lead makes the mind ‘give way’.


Lead in petrol is especially dangerous for children due to the simple fact that they spend more time closer to the ground than the average adult. This small difference in height can make all the difference in the quality of air they’re breathing; lead is heavy and heavy stuff sinks. Also the physiology of children means that lead lingers in their bodies longer. Children’s bones are continuously being remodelled as they grow, allowing the lead to be continuously re-introduced into the bloodstream.

But how does lead exposure affect a person’s psychology, and why can it cause a spike in criminal activity?

Lead interferes with neurotransmitters, chemicals used by neurons to send signals to other cells. It blocks certain receptors in the brain, and it’s the targeting of these receptors that is thought to be one of the main effects of lead’s toxicity.

Lead poisoning interferes with the normal development of a child’s brain and nervous system. Increased blood lead-levels in children have been shown to correlate with decreases in intelligence, nonverbal reasoning, short-term memory, attention and social engagement, amongst other things. Lead exposure has also been shown to increase aggression in countless studies.

From the 1920s onwards, crime in industrialised countries continued to rise as exasperated politicians and chiefs of police failed to reverse the trend. Any small victories in crime reduction seemed unable to stem the increase in violent crime, especially in cities such as New York, a hotbed for life-sapping traffic jams; perfect for the proliferation of lead.

In 1994, Rick Nevin of the US Department of Housing and Urban development, began investigating whether lead exposure had an effect on violent crime.

Nevin found that if you track the levels of lead in the atmosphere and compare them violent crime rates, the correlation is inescapable, almost perfect.  He published a paper on the subject in 2000, concluding that if by adding a time lag of 23 years (the time it takes from childhood to full-grown, criminal adulthood), lead emissions from cars explain 90 percent of the variation of violent crime in the US.

It is important to remember that correlation does not always equal causation, therefore something more concrete was needed, and a double whammy hit the criminology world in 2007.

Jessica Wolpaw-Reyes, a public health professor at Amherst of the University of Massachusetts, picked up Nevin’s gauntlet and released a paper that coincided with another of Nevin’s papers. She decided to investigate trends from state to state, and she discovered that the reduction in crime was far from uniform. Speaking to the BBC in 2013, she said ‘there is a substantial causal relationship, I can see it in the state-to-state variations. States that experienced particularly early or particularly sharp declines in lead experienced particularly early or particularly sharp declines in violent crime 20 years later.’

But then couldn’t it be argued that this trend is exclusive to the US, with its ridiculously high gun ownership and its poverty stricken inner-city ghettos, resulting from years of the ineffectual and detrimental ‘war on drugs’?

This is where Nevin’s second paper comes in; he took his study and applied it to other industrialised countries such as New Zealand and Canada – not exactly renowned for their crime rates – and found an identical pattern. He then applied it to the UK, France, Germany, Australia and Italy and found the exact same matched pattern. Nevin claims that he has never found a country where the correlation is absent. It has even been applied to individual neighbourhoods and the same pattern is found.

As with every theory, it is important to remember it is still only a theory. It would certainly be pretty evil to systematically subject thousands of children to lead exposure to test this theory, so it can never be confirmed under experimental conditions. For this reason we will never know if it’s lead bullets that cause crime, or the very lead itself.


Michael Owen

Feature Image: Wikimedia Commons

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