After holding off on a proposed endangerment finding on piston-aircraft emissions from leaded fuel for most of the past decade, the U.S. Environmental Protection Agency (EPA) this week laid out a timeline for such action. The agency said such a proposal could be released this year, with a final finding in 2023.

A determination that emissions from leaded fuel contribute to air pollution that endangers public health and welfare lays the groundwork for an outright ban on leaded fuel. “Protecting children’s health and reducing lead exposure are interlocking priorities at the core of EPA’s agenda,” said EPA administrator Michael Regan in announcing the timeline on Wednesday.

“EPA has been investigating the air quality impact of lead emissions from piston-engine aircraft near airports for years, and now we’re going to apply that information to determine whether this pollution endangers human health and welfare,” he added. The EPA points out that although airborne lead in the U.S. has dropped 99 percent since 1980, piston-engine aircraft operating on leaded fuel are the largest remaining source of leaded emissions.

For years, environmental groups such as Friends of the Earth have pushed the EPA to issue an endangerment finding. The EPA had initially planned on 2018 for such a finding as the general aviation community in concert with the FAA had collaborated on a Piston Aviation Fuel Initiative (PAFI) that had targeted the development of a new unleaded standard.

While PAFI had also hoped to achieve progress on a standard in the 2018 timeframe, the program suffered a series of setbacks on the initial fuels identified as a baseline for a standard. Research has continued on finding a drop-in replacement. However, the FAA has signed off on an approved list of aircraft models for the 100-octane unleaded avgas developed by General Aviation Modifications Inc. (GAMI).

AOPA has estimated that the approval from last fall covered about 70 percent of the piston aircraft fleet, but the GAMI fuel still needs to be widely distributed.

Meanwhile, environmental groups and certain local communities have ramped their efforts back up to push for an endangerment finding, last year sending a renewed call to the EPA after it changed leadership under the Biden Administration. The agency responded this week that it has collected necessary data on aircraft lead emissions and has “completed these analyses and their subsequent peer review.”

The EPA stressed the dangers of lead exposure and said “no safe blood lead level in children has been identified. Even low levels of lead in blood have been shown to affect IQ, ability to pay attention, and academic achievement.”

While environmental groups continue to push the EPA, some communities are moving ahead with their own leaded-fuel bans. In California, for example, Santa Clara County is banning 100LL at Reid-Hillview Airport and San Martin Airport in a move that has spurred the FAA to open an investigation of violations of grant assurance agreements.