Lead was once a common additive in fuels, paints, glasses, batteries, pipes, ceramics, and more.  As the health effects of lead exposure came to be better known, Congress and EPA began targeting lead pollution under a variety of laws and regulations governing air and water pollution, including the Toxic Substances Control Act, Residential Lead-Based Paint Hazard Reduction Act of 1992, Clean Water Act, the Safe Drinking Water Act, and the Clean Air Act (CAA), among various other non-statutory initiatives such as the 2018 Federal Lead Action Plan.  Lead exposure dropped dramatically as a result of these initiatives, but one industry still makes extensive use of lead-based products: aviation fuels for piston-engine aircraft which generate emissions that make up over half the country’s annual lead inventory.

On October 17, 2022, the United States Environmental Protection Agency issued a proposed finding that lead air pollution may reasonably be anticipated to endanger the public health and welfare within the meaning of Section 231(a) of the Clean Air Act, 42 U.S.C. § 7571, and further that engine emissions of lead from aircraft contribute to such pollution.  This is a two-pronged “endangerment” and “cause or contribution” finding which addresses both elements provided under Section 231 which provides that EPA shall “issue proposed emission standards applicable to the emission of any air pollutant from any class or classes of aircraft engines which in his judgment causes, or contributes to, air pollution which may reasonably be anticipated to endanger public health or welfare.”  An endangerment and contribution finding is therefore the first step in the process of regulating lead emissions from aviation fuels.  EPA often, but not always, combines these endangerment findings with the substantive regulations and emissions limitations but has not done so here.    

Aviation gasoline (avgas) is used in many piston-engine aircraft and it is the only leaded transportation fuel in use in the United States, using an additive called tetraethyl lead which helps boost fuel octane, prevents engine knock, and prevents valve seat recession.  This ultimately becomes brominated lead and lead oxybromides when the fuel is consumed and is emitted as submicron-sized particulate matter from the engine.  The FAA reports that there are 222,600 registered piston-engine aircraft consuming approximately 184 million gallons of leaded avgas per year with 160,000 private, non-commercial pilot licenses active as of 2021.  These aircraft are primarily owned by private pilots for recreational uses or “general aviation.”  By contrast, all commercial jet aircraft run on unleaded jet fuels.  Air taxi services also often use piston-engine aircraft which use leaded avgas.  EPA estimates that, in 2017, approximately 470 tons of lead were emitted by engines in piston-powered aircraft, which constituted 70 percent of the annual emissions of lead to air in that year.     

The proposed endangerment finding thus targets in the aggregate one of the largest remaining lead sources in the country.  In the proposed finding, EPA would categorize lead as “air pollution” and an “air pollutant” as defined by Section 231(a), a decision which would be consistent with past agency actions—EPA first listed lead as a “criteria air pollutant” in 1976 and has long regulated lead from other sources.  This decision would not have any immediate impact because an endangerment finding does not, itself, impose any requirements on regulated entities.  As noted above, EPA chose not to combine the proposed finding with proposed standards for regulated industry.  Standards will require another round of rulemaking, which are expected to take many months to propose, finalize and implement.  

However, once EPA has made that finding, CAA Section 231 requires EPA to issue proposed emissions standards for such pollutants.  Further, under 49 U.S.C. § 44714, the FAA is required to issue standards and regulations “for the composition or chemical or physical properties of an aircraft fuel” “to control or eliminate aircraft emissions the Administrator of the Environmental Protection Agency decides under Section 231 of the Clean Air Act endanger the public health or welfare.”  The endangerment finding will necessarily lead to new rulemaking from EPA and FAA on this issue, which is expected to dramatically reduce, if not eliminate, lead in avgas.  This would have significant effects on aircraft manufacturers and maintenance organizations, pilots, and others involved in general aviation and air taxi industries.  Although the course of rulemaking can be lengthy and difficult to forecast, industry participants should begin planning for a lead-free future.  Comments on the proposed finding are currently due January 17, 2023.  We are prepared to assist clients to identify proactive measures to mitigate this risk and to engage with EPA during this early comment period.