A boy throws a frisbee in Birmingham, Alabama, in 1973. (Source: Leroy Woodson | EPA)
A boy throws a frisbee in Birmingham, Alabama, in 1973. (Source: Leroy Woodson | EPA)

About 170 million Americans, or half the population, have lower intelligence due to early childhood lead exposure from leaded gasoline, according to a new study.

The report, published this week in the Proceedings of the National Academy of Science, estimated a net population-wide IQ loss of 824 million points, or about 2.6 points per person.

While in many individual cases that is a nominal loss, at a population-wide level, it's concerning, because the whole bell curve shifts, epidemiologist Sung Kyun Park told NBC News.

For individuals at the low end of normal, the loss could be enough to lead to significant impairment, principal study author Michael McFarland told NBC.

Age cohorts who were children in the 1960s and 1970s were affected more strongly, as were populations in poorer urban areas, which are disproportionately non-White.

There is no safe level of exposure to lead, and the effects are permanent and irreversible. Though leaded gasoline was banned in 1996, lead exposure risks remain, due to legacy infrastructure including lead pipes and lead-based paint.

Locally, Penn Medicine Lancaster General Health and Lancaster's city government are both working to mitigate the latter risk. LG Health's Lead-Free Families initiative aims to abate lead hazards in at least 2,800 Lancaster County homes over the next decade, while Lancaster city's Lead Hazard Control Program has received federal funding to remove lead in four south-side census tracts.

Cars crowd the Hollywood Freeway in May 1972. (Source: Gene Daniels | EPA)
Cars crowd the Hollywood Freeway in May 1972. (Source: Gene Daniels | EPA)
Tim Stuhldreher