SALT LAKE CITY — A new study shows air pollution particles can damage the cells of the heart's critical pumping muscles in children as young as 3 years old.

Iron-rich nanoparticles, produced by vehicles and industry, could be the underlying cause of the long-established link between dirty air and heart disease, according to the study, conducted by researchers at Lancaster University in England and published in the journal Environmental Research.

Environmental science professor Barbara Maher and her colleagues looked at the hearts of 72 deceased people with an average age of 25. Sixty-three of the subjects lived in Mexico City — ranked as the 30th worst capital city for air pollution in the world by the IQAir AirVisual 2018 World Air Quality Report. Nine control subjects lived in less polluted areas in the region.

The researchers found between 2 billion and 22 billion iron-rich nanoparticles per gram of dried tissue. The hearts of the Mexico City residents contained 2 to 10 times more nanoparticles than the control subjects. Even in the study's youngest subject, a 3-year-old, damage and abnormalities could be seen in the mitochondria of the heart's muscle tissue cells.

There is absolutely no reason to expect this would be different in any other city. – Environmental science professor Barbara Mahe

"Putting an abundance of iron-rich nanoparticles right into the sub-cellular components of the heart’s muscle tissue, that’s not where you want them to be sitting," said Maher. "Mitochondria are your energy source, making sure your heart pumps effectively.”

Maher told The Guardian that the results were relevant for all cities where more traffic, buildings and industry lead to higher levels of pollution, including particulate matter, ozone and nitrogen dioxide.

“There is absolutely no reason to expect this would be different in any other city,” she said.

More than 90 percent of the world’s population lives with toxic air pollution, according to the World Health Organization, which has declared the issue a global “public health emergency.” While countries like India and China have some of the world's most polluted cities, the United States is no stranger to dirty air.

The American Lung Association ranks California cities including Los Angeles, Bakersfield and Fresno among the worst in the U.S. when it comes to air pollution. The Salt Lake-Provo-Orem area is ranked 8th worst in the country for short-term particulate pollution, due to the high concentration of air pollutants during winter inversions. The same area in Utah is ranked 14th worst for ozone pollution, which is made worse by hot summers.

"We cannot pass this problem off to the next generation," said Jonny Vasic, executive director of Utah Physicians for a Healthy Environment, in response to the American Lung Association rankings released in April. "There are solutions, but it starts with awareness and needs the combined effort of the community with strong political will from our leaders.”

This year in Utah, legislators allocated more than $28 million towards improving air quality with funding for a wood stove exchange program, electric vehicle charging stations, free public transportation on bad air days and the replacement of old, polluting government vehicles like snowplows, among other things.

Elsewhere in the world, cities like Oslo and Paris have created no-car zones to reduce traffic in busy areas. Cities like Nanjing and Liuzhou in China are building urban forests on top of buildings. India, the U.K. and Norway are among countries that have made pledges to ban the sale of diesel and gas vehicles in the near future, and companies like German start-up CityTree and Dutch investment collective Evinity Group are investing in technology that can suck carbon dioxide and toxic pollutants from the air.

The Lancaster University study builds on a large body of research showing links between bad air quality and negative health outcomes, including heart disease. But prior to the study, little was known about the abundance of metal-rich nanoparticles in human heart tissue or what specific damage they could be causing, according to Air Quality News.

“For really young people, the evidence is now of very early-stage damage both in the heart and the brain,” Maher told The Guardian.

In a comprehensive review of air pollution's effects on health published earlier this year, the Forum of International Respiratory Societies' Environmental Committee concluded that air pollution may be damaging every organ and virtually every cell in the human body as tiny particles are inhaled, move into the blood stream and are transported around the body.

Other research suggests links between air pollution and Alzheimer's disease, cancer, miscarriages and stillbirths.

Four million children around the world develop asthma each year because of air pollution particles from road traffic, according to another recent study by researchers at George Washington University.

Exposure to nitrogen dioxide, largely from road transport, is thought to be behind 240,000 new cases in the U.S. each year, according to the research, which was reported in April.

The study ranked the U.S. as the 22nd worst out of 194 countries for the rate of children developing asthma from traffic pollution, and found that 19 percent of asthma cases in children can be attributed to unhealthy levels of nitrogen dioxide.

Samantha Walker of Asthma U.K., told the Daily Mail, "Worryingly, this study confirms existing research which shows children breathing in toxic air from traffic fumes have stunted lung growth and are at risk of developing asthma."

Mark Miller, an expert on the cardiovascular effects of air pollution, from the University of Edinburgh, told the Guardian that recent research highlights how important it is to understand the way air pollution impacts health.

“More effort is needed to reduce particle emissions from vehicles, especially to remove the number of vehicles on the road by encouraging people to walk and cycle for short journeys,” he said.