At least half the people in the US today have “meaningful cognitive loss because of lead exposure,” according to the study. These exposures show up decades later in a child’s income, health, and socioeconomic status. “Lead influences the trajectory of a person’s life,” McFarland warns. “Even relatively small deficits in achieved IQ…meaningfully predict a person’s educational and occupational attainment, health, wealth, and happiness.”

One long-term study that followed more than 500 children in New Zealand born between 1972 and 1973 found that cognitive impairment from lead was associated with nearly half of their downward social mobility as adults 38 years later.

Even modest exposure to lead can push someone below the range of average intelligence. The late John Rosen, a pediatrician who advocated for lead paint removal in the 1990s, said early lead exposure for a child with an IQ of 85 “could mean the difference between a menial job in a fast-food restaurant or a meaningful career.”

Putting a price on lead

Children don’t need to be exposed to lead to suffer from it. Claudia Persico, a policy researcher at American University,  found (pdf) that even the presence of lead-exposed peers in classrooms is associated with lower test scores, lower graduation rates, and more suspensions for all students.“Even kids who are not exposed to lead are being influenced by the behavior of lead-poisoned kids,” Persico tells Quartz. “Peer effects can have really long-run consequences. Lead poisoning is much more costly than we ever thought.”

Researchers have, in fact, put a number on it. One study concluded (pdf) that the cost per child for each microgram of lead in the blood was $50,000. For society, the cost is billions of dollars every year. Aaron Reuben, a PhD candidate in clinical psychology at Duke University and a co-author of the study led by McFarland, says the past 80 years represent trillions of dollars in lost earning potential alone—that’s before factoring in the heart disease, bone disease, dementia, ADHD, teen pregnancy, crime rates, and other ills associated with lead exposure.

The legacy of lead

Economists and epidemiologists do their best to calculate the social cost of lead by measuring what’s most measurable, like IQ, earnings, and special education programs. But that fails to capture the true cost in people’s lives: parents whose children can’t curb their aggression; students who never go on to college; the fallout of an unplanned teen pregnancy; adults whose careers falter when they fail to master complex skills.

“The legacy of lead continues to shape the health and wellbeing of the country in ways we do not yet fully understand,” McFarland concluded in his study noting millions of people are still exposed to lead around the world. “Our estimates provide a springboard to understand the global extent that populations were harmed, and continued to be harmed, by legacy lead exposures.”

Want to know more about lead exposure in your area?

Quartz has built maps, searchable by city and state, of neighborhoods surrounding 95 of the top lead-emitting general aviation airports in the US.

More stories in this series:

Leaded airplane fuel is poisoning a new generation of American children

Living with the risk of childhood lead exposure: A day in the life

This series was reported with grant support from:

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