The UK government has been underestimating lead pollution from by a significant amount, and has found that over 370,000 households could be at greater risk of exposure to lead than previously believed. A study from the says that homes within a four kilometer radius (2.5 miles) are exposed to lead levels that are 14,000 times higher than reported by the UK’s National Atmospheric Emissions Inventory (NAEI), as reports.

The toxic pollution is coming from piston-powered planes that burn a widely-available to operate; these are mostly small private planes flown for recreation or during airshows. To increase their engine power, the planes are commonly fueled by , which contains 0.56 grams of lead per liter.

Data from the NAEI reported that these small planes were responsible for 0.0003 percent of lead air pollution found in the UK between 1998 and 2020, or about 32 kilograms (68.3 pounds). But the University of Kent study found the lead air pollution coming from the planes could be as high as 455 tonnes (502 tons), which is 14,219 times higher than reported by the NAEI — an agency tasked with monitoring air pollutants and greenhouse gases, among others.

The findings of the study suggest that, contrary to previous reports, small planes are one of the UK’s largest sources of lead pollution going back to 1998, having emitted more heavy metal pollution than “all foundries, power stations, and lead dust created by car brake pads in towns and cities,” per .

The use of in cars was banned in 2000 after two decades of campaigning against the combustible, which has been linked to early death in adults and cognitive decline in . According to the NAEI, overall lead pollution in the UK fell from 529 tonnes (583 tons) in 1999 to 90 tonnes (99 tons) in 2020, thanks to the leaded gas ban, but this only applied to cars.

Small planes kept using leaded gasoline, presumably, under the assumption that private craft produced a negligible amount of lead air pollution. The study disproves this, and UK agencies will reportedly adjust the data to reflect more accurate findings by February 2023. Some officials and researchers say the new data should prompt the government to review its requirements for air pollution monitoring, because there are no stations watching for lead air pollution within the four kilometer radius of certain airports in the UK.

The monitoring stations use data from the NAEI, meaning they are woefully underestimating the risk of lead air pollution near thousands of homes. The authors of the study say the UK government should encourage the use of unleaded fuel in small planes, such as the “universal” high-octane fuel called G100UL, which is not as easily found as leaded AVGAS100LL. And researchers also said the government should “start actively monitoring blood lead levels in children” near the pollution sources found by the study.