Dunedin is a pretty clean place, but even here most children born in the early 1970s absorbed enough lead to lower their intelligence and life prospects. Byvalet/Shutterstock

If you grew up near a busy road during the era of leaded gasoline, you're probably not as smart as you could have been. Moreover, you may also make less money. A long-term study has confirmed what health researchers have suspected – exposure to lead as a child may damage the brain in ways from which it never recovers.

The harm lead does to the developing brain is old news, but proving the effects last is harder. Professor Terrie Moffitt of Duke University took advantage of the fact that New Zealand has been tracking the development of 1,037 children born in the city of Dunedin in 1972-73. This is now one of the world's longest and most comprehensive cohort studies, allowing detailed investigations of how childhood influences affect adult outcomes.

Lead can be absorbed from (now banned) paints, factory pollution, or corroded pipes, but in the 1970s, children absorbed it primarily from car emissions.

With a population of just 120,000 and exposure to the roaring forties, Dunedin is an unlikely place to study the consequences of air pollution. However, participants in the Dunedin study had their blood tested for lead concentrations at age 11. Since then, their social and economic status has been recorded every few years, along with other factors that might have influenced these things. This provides a rare resource for measuring lead's effects.

On average, the Dunedin children had 11 mictograms of lead per deciliter of blood. Historically, 10 μg/dlL was considered the “level of concern”, but this has now been lowered to 5 μg/d as evidence has emerged of just how damaging lead can be.

In the Journal of the American Medical Association, Moffitt reports that for every 5 ug/dL in their 11-year-old blood, the study's participants lost 1.5 IQ points at the age of 38. Comparing those above the traditional 10 μg/dL level with those below, the gap was 4.25 points.

"This is historical data from an era when lead levels like these were viewed as normal in children and not dangerous, so most of our study participants were never given any special treatment," Moffitt said in a statement.

Moffitt contrasted this with more recent cases, such as Flint, where intervention is taking place to try to offset the damage, which is just as well because the consequences went far beyond a few IQ points. Dunedin children with high lead concentrations were more likely to end up earning less money and in lower status jobs, relative to their parents, than those who avoided breathing in too much car exhaust. The findings indirectly support the hotly debated theory that lead exposure is a major cause of crime.

Considering how clean Dunedin's air is, the implications are frightening for bigger cities. Maybe gutting the EPA is a bad idea, huh?