Some experts now claim that the trick to reducing crime has more to do with pollution, specifically exposure to lead, than just bolstering police forces.

During the 1990s criminologists were stunned to discover that crime rates were suddenly dropping after decades of rising homicides, rapes and other unlawful activity. By the end of the decade, the murder rate alone declined more than 40% throughout the United States.

Various theories were offered up to explain this change.

Traditionalists insisted more prisons and new police strategies, such as those employed in crime-ravaged New York City, brought criminals under control.

Others, like economist and “Freakonomics” coauthor Steven D. Levitt, made the case that the legalization of abortion in 1973 resulted in fewer unwanted children being born and growing up to become law breakers.

A third explanation also involved linkage between events in the 1970s and falling crime rates two decades later. But this one focused on lead.

The year 1973 was significant beyond the Roe v. Wade decision that made abortion legal. That year, gas stations began phasing out the sale of leaded gasoline, which was found to release heavy metals into the air.

Five years later builders ceased using lead-based paint in new homes.

“Because of these actions, children born in the mid- to late-1970s grew up with less lead in their bodies than children born earlier,” Lauren Wolf explained at Chemical & Engineering News. “As a result, economists argue, kids born in the ’70s reached adulthood in the ’90s with healthier brains and less of a penchant for violence.”

Researchers at the Centers for Disease Control & Prevention say the more lead a person has in their brain, the more likely they’ll have impaired neurological functions, including those predisposing them to committing violence.

Studies show the amount of lead in Americans’ bodies has declined significantly since the 1970s.

In 1976, the average person had a blood-lead level of 16 µg/dL, according to the National Health & Nutrition Examination Survey. By 1991, that average had plummeted to 3 µg/dL.

-Noel Brinkerhoff

To Learn More:

The Crimes of Lead (by Lauren K. Wolf, Chemical & Engineering News)

America's Real Criminal Element: Lead (by Kevin Drum, Mother Jones)

The Urban Rise and Fall of Air Lead (Pb) and the Latent Surge and Retreat of Societal Violence (by Howard W. Mielke and Sammy Zahran, ScienceDirect) (abstract)