It’s no secret lead exposure is dangerous. Even low levels can affect a child’s brain.

It’s also no secret that airports are one of the last remaining sources of airborne lead in the U.S.

The U.S. Environmental Protection Agency attests to both these facts.

And yet, the EPA has yet to declare an “endangerment finding” for leaded aviation fuel. That means it hasn’t said whether those emissions pose enough of a threat to public health or welfare to trigger the long and complex process of regulating them.

Lead was removed from car fuel and paint in the U.S. decades ago. That drove levels of lead in the air down nearly 95 percent. The amount of lead in Americans’ blood dropped just the same.

Large, commercial planes use jet fuel, which is lead-free. But lead remains an additive to the aviation fuel still used by piston-engine aircraft, such as smaller airplanes and helicopters. About 230,000 of these aircraft are in use worldwide, and 167,00o are in the U.S.

Scientists now say no amount of lead exposure is safe for children. Lead paint in old homes is still the most likely source for children’s lead exposure. But aircraft are some of the only active polluters putting lead into the environment.

Environmental groups have petitioned or sued the EPA to force action on this issue three times since 2006. Each time the agency has denied them. It has most recently delayed until 2018 a decision on lead emissions from aircraft.

“How much more studying do we need to do?” asked Jim Lubischer, a pediatrician who lives near Hillsboro, Oregon. “We know this stuff is very toxic. We know it’s being emitted in the air, over our kids, over everybody. There should be regulations to stop it.”

Lubischer is part of Oregon Aviation Watch, a group whose frequent complaints about the airport in Hillsboro target concerns ranging from noise to national security.

It was a petition from Oregon Aviation Watch, Friends of the Earth and Physicians for Social Responsibility that triggered the EPA’s latest denial in late January.

“I think it’s kind of a no-brainer,” Lubischer said of removing lead from aviation gas.

Fuel use at the Hillsboro Airport emits roughly half a ton of lead per year, making it Oregon’s leading producer of airborne lead. It’s one of more than a thousand airports that produce nearly 80 percent of lead emissions throughout Oregon, Washington and Idaho, according to an analysis of EPA data.

Across the country, airports account for nearly half of all lead emissions.

Critics of the EPA, such as Marcie Keever, legal director at Friends of the Earth, say the EPA’s delays on lead mirror other stances by the agency that divorce science from politics, despite a pledge from the Obama administration to base its policies on science.

“With the pressure and the politics that EPA is under, it’s almost impossible to even get something as harmful and clearcut as lead taken out of this fuel stream,” Keever said.

One independent study in 2011 showed children living near airports had slightly higher concentrations of lead in their blood. It’s been widely cited by environmental groups. Combining that, estimates of aircraft emissions and the federal government’s advisory that lead is unsafe in children’s blood at any level, groups like Keever’s say the EPA has all the information it needs to declare lead fuels dangerous.

The EPA declined an interview request for this story. An agency spokeswoman said in an email that it takes the issue seriously and is currently collecting necessary data.

The EPA is currently tracking lead concentrations at 17 of the country’s nearly 20,000 airports. Two of those 17 did not meet the national air quality standard for lead. The agency estimates 16 million people live within one kilometer of an airport.

“Our investigation includes necessary data collection and analysis that will provide nationwide estimates of the contribution of aircraft lead emissions to lead air pollution concentrations as well as an analysis of the impacted population,” EPA spokeswoman Enesta Jones wrote.

Grounding aircraft

The Federal Aviation Administration has tried for years to develop an unleaded fuel. It, too, is targeting 2018. Its plan for implementing that fuel standard would take the better part of a decade.

Alternatives exist now, but they tend to be either expensive or not widely available.

In Hillsboro, the airport recently unveiled a plan to supply unleaded gasoline. Many planes flying with leaded fuel could use unleaded gasoline so long as it doesn’t have ethanol.

The airport hopes to reduce emissions by a tenth of a ton by introducing the fuel. But an airport study found that in addition to being costly and usable only for certain aircraft, many pilots are reluctant to use unleaded fuel regardless of price.

Mary Rosenblum, president of the Oregon Pilot’s Association, said safety is one factor.

“There are a lot of people who are understandably reluctant to go out and fly over the Rocky Mountains with a fuel that maybe will cause something to deteriorate,” Rosenblum said.

Rosenblum spends much of her day in the garage, working on her custom-built plane. Hers can actually use unleaded fuel, but she says there are very few places she can find it without ethanol.

Rosenblum doesn’t like the idea of leaded fuel. Still, she’d prefer not to see a regulation. The emissions are minimal, and the costs would be great.

A writer by profession, Rosenblum flies as a hobby. She worries more about what the loss of leaded fuel would mean for the crop dusting, surveying and transport planes she says are crucial to the rural economy.

“It would be a significant economic impact — an adverse economic impact — if we said ‘OK, no more leaded fuel right now,’” Rosenblum said. “You’re going to ground an awful lot of aircraft that are not out there because they’re somebody’s toy. They’re out there because they’re doing work.”

A lot more to know

Meanwhile, not much data in Northwest states exists to link airport lead emissions directly to effects on human health in the region.

“There’s a lot more to know about potential exposures at airports,” said Sarah Armitage, an air quality specialist with Oregon’s Department of Environmental Quality. “And we really need that information before we can say there’s no problem.”

DEQ does not monitor lead at the state’s 457 public- and private-use airports, though. What it knows about lead at the Hillsboro airport comes from an air toxics monitor stationed less than a mile away from the airport, which is not set up specifically for lead. Armitage said lead is one of several chemicals that could make the agency’s priority list for future monitoring.

DEQ also doesn’t have the authority to regulate aviation if it wanted to, Armitage said. That’s one more reason she and others were hoping to see federal regulation move faster.

“We were looking forward to their work on this and the potential regulation of lead because we still have concerns that it could be causing a problem,” she said.