PISTON-ENGINED AIRCRAFT, WHICH TAKE OFF FROM AIRPORTS LARGE AND SMALL IN EVERY STATE, STILL RUN ON L

Mark Grisco fuels a small airplane at DuPage Airport in West Chicago, Ill., on May 9, 2014. Though not used in cars in the U.S., fuel containing lead is still used in some small, private aircraft.

CHICAGO — Leaded gasoline is such a well-known scourge that automobile fuel made with the brain-damaging additive is still sold in only six countries: Afghanistan, Algeria, Iraq, Myanmar, North Korea and Yemen.

Shifting to unleaded fuel in the U.S. — the last drop of leaded gas was sold here in 1995 — has paid huge dividends. The amount of lead churned into the air by cars and factories has declined by more than 90 percent since the 1970s. Average concentrations of the toxic metal in children have plummeted almost as dramatically.

But one industry stubbornly remains a holdout in the decades-long push for a lead-free America.

Piston-engined aircraft, which take off from airports large and small in every state, still run on leaded aviation fuel known as avgas. As pollution from other sources has sharply declined, the general aviation fleet of 167,000 aircraft has become the nation’s top source of airborne lead, emitting nearly 500 tons a year, according to the U.S. Environmental Protection Agency.

Lead particles from airplane exhaust tend to be concentrated close to airports, but they also fall widely during flight. About 16 million people live and 3 million children go to school within a half-mile of an airport where leaded avgas is sold, the EPA estimates. Most are from low-income, minority households that already face increased health risks from exposure to lead paint.

“For years the federal government has been telling us there is no safe level of lead,” said Marcie Keever, a lawyer for Friends of the Earth, a Washington-based environmental group that petitioned the EPA last month to ban leaded aviation fuel. “We are well past the time for them to do something about this.”

Illinois ranks sixth in the nation for lead emissions from airports, according to a review of EPA data, with O’Hare International Airport topping the state list. Others on the list include Midway Airport, Lewis University Airport in Romeoville, DuPage County Airport in West Chicago, Chicago Executive Airport in Wheeling and Aurora Municipal Airport in Sugar Grove.

The EPA announced plans four years ago to phase out leaded aviation fuel with regulations similar to the ban on leaded gasoline. But the agency held back on filing rules after the aviation industry and members of Congress objected.

Representatives from aviation and oil companies say adding lead is a necessary safety measure because it boosts the octane of fuel high enough to prevent engine failure during flight. They say the government shouldn’t ban avgas until a lead-free alternative is widely available.

Industry executives acknowledge that at least 75 percent of the piston-engined aircraft in the U.S. already can operate safely on high-octane gasoline made without ethanol, which is readily available and has the added benefit of being less expensive than avgas.

But the market is so small that most airports sell only two types of fuel: leaded avgas for piston-engined aircraft and jet fuel for everything else. In the Chicago area, only Joliet Regional Airport sells unleaded aviation fuel, according to a website created by a pilots group.

Airport executives and fuel suppliers say there isn’t enough demand to merit installing extra fuel tanks for unleaded gas.

“Our avgas sales have been on the decline for about 20 years,” said David Bird, executive director of DuPage County Airport, which saw more than 40,000 general aviation takeoffs last year. “If there’s a change in EPA rules, we will certainly comply.”

The chief barrier to lead-free alternatives is the relatively small fleet of planes that can fly only on avgas. Industry groups estimate that up to 70 percent of the leaded fuel sold in the U.S. is used by 25 percent of the piston-engined aircraft, many of which are operated by charter airlines or companies that fly people and supplies to remote parts of Alaska.

“Premature regulation, before viable fuel alternatives are available, is simply untenable and irresponsible,” the Alaska Air Carriers Association wrote in a 2011 letter urging EPA officials to give the aviation industry up to 30 years to phase out leaded fuel.

In another letter to the EPA, a bipartisan group of 27 U.S. senators led by Republican John Thune of South Dakota and Democrat Mark Begich of Alaska said banning avgas would result in an “incredible cost to aircraft owners, operators and the consumers who rely on their service.”

An EPA spokeswoman declined to make someone available to answer questions. In an emailed statement, the agency said it intends to make a final decision about avgas regulations by mid-2015.

Fuel suppliers already have reduced the amount of lead added to aviation fuel, which combined with a decline in the number of piston-engined aircraft has steadily cut emissions during the past three decades. Aviation emitted 484 tons of lead in 2011, the last year for which figures are available, down from 74,000 tons in 1980.

The question is whether any continued use of lead is acceptable given the well-documented health hazards. Each of the 522,000 gallons of avgas sold daily in the U.S. last year contained 2 grams of tetraethyl lead, the same highly toxic substance added to automobile gasoline during most of the last century.

Unlike many other pollutants, lead doesn’t break down over time and can linger for years in the top few inches of soil. Children are most commonly exposed when they ingest lead paint dust in older houses or dirt contaminated with the toxic metal.

Studies show that lead is even more dangerous than previously thought. Even tiny amounts in young children can trigger learning disabilities, aggression and criminal behavior later in life, findings that are drawing closer scrutiny of the last sources of lead and raising new concerns about the thousands of pounds deposited into the environment during the last century.

Researchers from the National Oceanic and Atmospheric Administration have found that airborne lead particles tend to spike on weekends, likely from recreational flights.

The EPA has been monitoring lead emissions at 17 airports, none of which are in the Chicago area. Two airports — San Carlos and McClellan-Palomar in California — have violated the federal lead limit of 1.5 micrograms per cubic centimeter of air, according to preliminary test results reported last year.

Other studies highlight the potential health risks.

In 2000, the Illinois Environmental Protection Agency found that airborne lead pollution was significantly higher downwind from O’Hare than upwind. There are no signs that the agency followed up on the study with a more detailed investigation.

More recently, Duke University researchers reported in 2011 that children had higher levels of lead in their blood if they lived downwind from airports in North Carolina. Lead levels were highest in kids who lived within a third of a mile of an airport, the peer-reviewed study found.

“Lead is a known neurotoxin, and children are especially vulnerable,” said the study’s lead author, Marie Lynn Miranda, now the dean of the School of Natural Resources and Environment at the University of Michigan. “We’ve seen huge public health benefits from the elimination of lead in our environment, but there are other sources that need to be addressed.”

As the dangers of lead became more broadly understood during the middle part of the last century, the auto and oil industries fiercely resisted attempts to ban leaded gasoline. The federal government didn’t move to start phasing it out until the 1970s, after determining that lead damaged catalytic converters installed on cars to reduce lung-damaging smog pollution.

Aviation poses unique challenges, industry representatives say.

“Unlike the transition away from leaded gas in automobiles, performance issues in aircraft have life-and-death consequences for pilots and passengers,” says the General Aviation Avgas Coalition, a trade group representing aircraft manufacturers, pilots, charter businesses and fuel suppliers.

For its part, the Federal Aviation Administration has created a task force of government and industry officials to study alternative fuels. After a decade of legal and political pressure from green groups, Congress earmarked $5 million a year for the program, which according to the FAA website is expected to certify lead-free aviation fuel in 2018.

In a statement, the FAA said it “may not be technically feasible” to develop an unleaded fuel that could be used without overhauling aircraft engines.

Three companies have announced they intend to submit lead-free fuel for FAA review. In documents filed with the EPA, one of the contenders, Indiana-based Swift Enterprises estimated it would take just two years for the industry to shift to a fuel derived from agricultural waste.

“We’re taking this very seriously,” said Rob Hackman, vice president for regulatory affairs at the Aircraft Owners and Pilots Association. “We have a plan. We are going to transition to an unleaded fuel.”

