A new story calls into question the connection between lead and violent crime.
In a recent story published in Mother Jones, journalist Kevin Drum argues that the presence of lead is a driving force behind violent crimes' rise and fall.
"Ten years ago it was an intriguing idea, but the evidence wasn't all that solid," Drum told The Huffington Post. "Now the evidence is really strong. Criminologists should be taking it seriously."
He writes that research over the last decade provides compelling evidence that, as the presence of lead increases, so does crime; as it decreases, crime follows suit.
Much of the research hinges on the use of leaded gasoline, which became prominent in the 40s then gradually lessened in the mid-1970s.
From Mother Jones:
A 2000 paper ... concluded that if you add a lag time of 23 years, lead emissions from automobiles explain 90 percent of the variation in violent crime in America. Toddlers who ingested high levels of lead in the '40s and '50s really were more likely to become violent criminals in the '60s, '70s, and '80s.
Other research shows that states in which leaded gasoline use fell more quickly, crime also decreased more rapidly compared to states with continued use of leaded gasoline. The same trend was found in other countries -- those with higher lead concentrations had higher rates of crime and vice versa.
Exposure to lead has also been shown to damage brain function.
"Even moderately high levels of lead exposure are associated with aggressivity, impulsivity, ADHD, and lower IQ," Drum writes. "And right there, you've practically defined the profile of a violent young offender."
Drum told HuffPost he does not think lead is the only cause of crime, but the research he's seen suggests it's responsible for between 40 to 50 percent of violent crime over the last half-century or so.
"There's always gonna be a lot of factors," Drum said. "You never know if you're controlling for everything. That's as true of lead as anything else."
But Drum said lead likely has enough of an impact on crime that it merits further research and, that America should invest more in getting rid of lead in soil and in homes.
"The evidence is strong enough that Congress should commit a small amount of money to map lead soil and housing stock in every neighborhood in every big city in the country so we know where the problem is," Drum said. "There should be a serious, rigorous cost-benefit analysis so we know how much it would cost to clean up all this paint and what the fiscal benefits would be."