Public enemy #1?

Recently I came across the lead crime hypothesis. According to this hypothesis, proposed by Rick Nevin, crime rates are related to the exposure to lead. More precisely Nevin argues that the crime bulge seen in multiple Western countries could be related by the use of leaded gasoline.

From the 1950s the number of cars using leaded gasoline increased and from the 1960s crime rates rose as well. On the other when leaded gasoline was outphased, soon crime rates started to decline. Well, this might be just a spurious relations and on its face it does not prove much.

However, Nevin found that as different countries have a slighty different of crime rates and leaded gasoline use, in all investigated countries there was a similar relation between crime statistics and lead exposure. But again correlation is not causation.

Nevertheless I would not have written this piece if there were no reason that lead might be a key factor in explaining criminal behavior. The fact is that lead is a known neurotoxin.

In an article by Kevin Drum, we can read:

Neurological research is demonstrating that lead’s effects are even more appalling, more permanent, and appear at far lower levels than we ever thought. For starters, it turns out that childhood lead exposure at nearly any level can seriously and permanently reduce IQ. Blood lead levels are measured in micrograms per deciliter, and levels once believed safe—65 μg/dL, then 25, then 15, then 10—are now known to cause serious damage.Neurological research is demonstrating that lead’s effects are even more appalling, more permanent, and appear at far lower levels than we ever thought. For starters, it turns out that childhood lead exposure at nearly any level can seriously and permanently reduce IQ. Blood lead levels are measured in micrograms per deciliter, and levels once believed safe—65 μg/dL, then 25, then 15, then 10—are now known to cause serious damage.

The same article has a graph which shows that blood-lead level of 65 μg/dL is associated with a loss of IQ of 20 points. The lower level of 10 μg/dL has an average loss of IQ of 7 points. Though that does not sound as much, but for those at the lower IQ spectrum it is critical.

The Wikipedia article on the Intelligence Quotient has several tables, which illustrates the meaning of different IQ levels. For instance unskilled work requires an IQ of 87, elementary school drop-outs have an average IQ of 80 to 85 and people with an IQ of 75 have a 50% change to finish elementary school.

The social impact of a “low” decrease of IQ of 7 points are huge. A few percent of the population won’t be able to perform even the simplest jobs. In a society where more and more jobs are automated this is even worse.

And IQ loss is even the greatest problem, as we read further:

even moderately high levels of lead exposure are associated with aggressivity, impulsivity, ADHD, and lower IQ. And right there, you’ve practically defined the profile of a violent young offender.even moderately high levels of lead exposure are associated with aggressivity, impulsivity, ADHD, and lower IQ. And right there, you’ve practically defined the profile of a violent young offender.

This is because lead causes damage to the production of myelin, which is responsible for neural connections in the brain, and causes a loss of grey matter in the prefrontal cortex, associated with aggression control. And even low levels of lead exposure increases the risk for children to develop ADHD.

An issue not discussed in Drum’s article but nevertheless important, is that lead exposure increases the probability of developing dementia. Dementia is a growing problem around the world as it increases the pressure on an already overloaded healthcare system.

Though lead exposure is not the sole cause of crime, behavioral disorders and dementia, it is a preventable one. Governments can and should implement policies to reduce the amount of lead in our environment. And space settlements in particular should prohibit the use of lead and lead-compounds in homes, consumer goods and at the workplace.

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