From Flying magazine…

“The aviation community was expecting the announcement and points to progress on unleaded fuel in the market.

On Friday, the Environmental Protection Agency (EPA) released its proposed finding on leaded aviation fuel, triggering a response from the consortium of general aviation associations that have been working on the removal of lead from avgas with the FAA and industry partners. Under the EAGLE (Eliminate Aviation Gasoline Lead Emissions) initiative, the collective has demonstrated in recent months its commitment to sunsetting 100LL in a safe, deliberate manner.

The Proposed Endangerment Finding for Lead Emissions from Aircraft Engines that Operate on Leaded Fuel does not call for any immediate ban on avgas containing lead. It’s simply the initial step required for the agency to exercise its authority to “address this source of lead pollution,” which is well known to the GA industry.”

EPA Releases Proposed Finding on Leaded AvGas

“The performance-enhancing additive prevents engine knock that can lead to sudden engine failure.  But its toxicity has been known since the 1920s, when scientists and health experts warned the federal government in public hearings of the dangers of using it in gasoline fuel.”

Getting the lead out — at long last

“She discovered lots of not great news, with studies showing higher instances of everything from asthma to heart disease to preterm births for those who live and work near airports. But one fact she found stopped her in her tracks.

Shepler learned that, while leaded gas has been fully banned in automobiles due to health concerns since 1996, it’s still widely used by many small planes and helicopters. And out of more than 20,000 airports nationwide, data from the Environmental Protection Agency shows Long Beach Airport ranks No. 2 in country for lead pollution, with planes there emitting nearly 1,600 pounds of lead each year into neighborhoods like the one where Shepler’s twins attend school.”

Lead spews from some Southern California airports; cleaner fuel is coming

“That’s because Reid-Hillview is one of 13,000 so-called general aviation airports, from which leaded-fuel piston-engine aircraft fly. While leaded gasoline was fully phased out in 1996 with the passage of the Clean Air Act, it still fuels a fleet of 170,000 piston-engine airplanes and helicopters. Leaded aviation fuel, or avgas, now makes up “the largest remaining aggregate source of lead emissions to air in the U.S.,” according to the Environmental Protection Agency.”

https://www.nbcnews.com/business/business-news/leaded-gas-was-phased-out-25-years-ago-why-are-n1264970