How many nanoparticles? Artur Debat /Getty

You won’t breathe easy after reading this: a few of the nanoparticles in the air you are inhaling are entering your bloodstream and building up in the diseased areas of your arteries.

This finding could help explain why air pollution raises the risk of heart disease and strokes. But what’s really worrying is that it suggests that current laws and efforts to regulate air pollution are focusing on the wrong particles.

“We are potentially looking in the wrong place,” says David Newby at the University of Edinburgh, UK.


Numerous studies have shown that air pollution leads to millions of premature deaths worldwide each year. Even in Europe, with its relatively clean air, air pollution is blamed for 400,000 premature deaths a year.

Most of these deaths are due to the raised risk of cardiovascular disease: simply being exposed to high pollution for short periods can trigger heart attacks and strokes, while long-term exposure causes vascular damage. The big question is why.

It has long been suspected that some of the nanoparticles we breathe in could get into the bloodstream and damage blood vessels, but until now, this had never been shown. These nanoparticles are mostly carbon compounds, and finding them inside carbon-based lifeforms like ourselves is extremely difficult.

Artery plaques

So the team instead got volunteers to breathe air filled with harmless gold nanoparticles. Within 15 minutes the nanoparticles began to show up in the volunteer’s blood – and they could still be found in blood and urine three months later.

“We were really surprised that levels were so high three months afterwards,” says team leader Mark Miller, also at Edinburgh.

Next the team got a few people who were due to undergo surgery to breathe in the gold nanoparticles. They found that when nanoparticles get into the body, they accumulate in the fatty plaques that can grow inside arteries, causing heart attacks and strokes.

While gold nanoparticles are inert, the reactive compounds found in air pollution could have all sorts of harmful effects, from impairing the contraction of blood vessels to promote clotting, Miller says.

The study goes a long way towards explaining how air pollution causes vascular injury and disease, says Frank Kelly at King’s College London. “If these findings with gold particles reflect the movement of exhaust-generated carbon particles, then the increased production of very small particles by modern engines is a cause for further concern,” he said in a statement.

Next the team will investigate whether gold nanoparticles get into the brain. Air pollution seems to increase the risk of brain disorders such as dementia, Alzheimer’s and Parkinson’s, and one recent study found tiny iron particles in people’s brains that may have come from vehicle exhausts.

Difficult to measure

Air quality laws in the European Union and elsewhere set a limit on particulate matter smaller than 2.5 micrometres – so-called PM2.5. However the limit is on the total mass of these particles in a cubic metre of air, rather than the total number.

The thing is, thousands of ultrafine particles can weigh far less in total than a few relatively large ones. Over the past few decades the mass of PM2.5 per cubic metre has fallen in most wealthy countries, suggesting air pollution is improving. But because of the increasing numbers of diesel vehicles on European roads, Newby thinks the number of ultrafine particles has risen over this time.

So should the laws be changed? The trouble is that measuring the numbers of ultrafine particles is very difficult and cannot be done using the roadside devices widely used to monitor air pollution.

“Ideally we would measure numbers,” says Miller. “But the technology is not there.”

The UK government is currently seeking to delay releasing its latest plan for tackling air pollution – a plan it was ordered to produce after losing a series of lawsuits brought by environment group ClientEarth.

The ClientEarth cases revolve around wild violations of the EU limits for the gas nitrogen dioxide rather than particulates. However, some of the measures needed to reduce nitrogen dioxide levels – such as getting diesel vehicles off the roads – should also help reduce particulate levels.

Journal reference: ACS Nano, DOI: 10.1021/acsnano.6b08551