The U.S Environmental Protection Agency (EPA) on Friday said it was proposing to declare emissions from piston-engine aircraft operating on leaded fuel pose a danger to public health.

Emissions from the 190,000 U.S. general aviation airplanes operating on leaded fuel account for about 70% of the lead entering the atmosphere, according to U.S. government estimates.<

Lead is not in jet fuel, which is used by commercial aircraft.

The EPA said if the proposed "endangerment finding" is finalized, it would subsequently propose regulatory standards for lead emissions from aircraft engines.

Reuters first reported in January that the EPA was again reviewing whether emissions from piston-engine aircraft operating on leaded fuel contribute pose a danger to public health.

While levels of airborne lead in the United States have declined 99% since 1980, piston-engine aircraft are the largest remaining source of lead emissions into the air.

Children's exposure to lead can cause irreversible and lifelong health effects, the EPA said.

"When it comes to our children, the science is clear, exposure to lead can cause irreversible and life-long health effects,” EPA Administrator Michael Regan said in a statement on Friday. "Aircraft that use leaded fuel are the dominant source of lead emissions in the country."

In 2006, the EPA received a petition asking for regulations of lead emissions from general aviation airplanes. The agency opened a proceeding in 2010 to review the issue and in 2015 said it had planned to issue a final endangerment finding in 2018.

The majority of aircraft that operate on leaded aviation gasoline are small piston-engine aircraft that typically carry two to 10 passengers.

The Federal Aviation Administration in February announced a new initiative outlining how to safely eliminate the use of leaded aviation fuel by the end of 2030 without adversely affecting the existing piston-engine fleet.