Carbon nanoparticles from vehicle exhausts can enter the bloodstream and sow seeds of disease, research suggests
Microscopic specks of soot from vehicle exhausts can enter the bloodstream through the lungs and sow seeds of disease in arteries, research suggests.
The carbon nanoparticles, a thousand times smaller than the width of a human hair, are coated with powerful toxins which increase the risk of heart attacks and strokes, scientists believe.
Air pollution, especially from traffic, is estimated to cause between 29,000 and 52,000 deaths per year in the UK and has been linked to an increased risk of heart and artery disease.
But while the effects of exhaust fume particles on public health are well known, less is understood about what they do in the body.
The new study, reported in the journal ACS Nano, shows for the first time how the smallest particles pass through the lungs and gather in the most vulnerable areas of blood vessels.
It suggests people who already suffer from artery damage are likely to be hit hardest by inhaled traffic pollution.
Because carbon particles are so hard to trace in the body, the scientists modelled them using non-reactive and harmless gold nanoparticles.
A series of trials in which volunteers were asked to inhale the gold dust showed within 24 hours they migrated from the lungs to the bloodstream, and were still detectable three months later.
Part of the study involved exposing surgical patients at high risk of stroke to the gold particles. Analysis of clogging material removed from the patients' arteries demonstrated that the nanoparticles accumulated in fatty deposits growing inside blood vessels.
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Lead researcher Dr Mark Miller, from the University of Edinburgh, said: "It's the smallest particles in air pollution that are harmful, but scientists don't fully understand the biological mechanism underlying this.
"Using gold as a model, we show that gold nanoparticles can get into the blood and that these particles appear to preferentially accumulate at sites of disease.
"These findings suggest that ultrafine nanoparticles in air pollution may well do the same thing. They will enter the blood and accumulate at sites of vascular disease. And while gold is not a very reactive particle, environmental particles are highly reactive.
"It doesn't take large amounts of these particles. If they reach these susceptible areas it can have serious health consequences."
Other work had shown, while not harmful in themselves, carbon pollution particles carried a large mixture of molecules on their surfaces some of which were highly toxic, he said.
One reason for the build-up in vulnerable areas could be because they were taken up by immune system cells, leading to a vicious cycle of inflammation.
All internal combustion engines produce nanoparticle pollution but levels are 50 times higher from diesel than from petrol-driven vehicles.
Current clean air regulations focus on larger particles such as PM10s, which are up to 10 micrometres across, rather than nanoparticles. Yet it is the really small particles that are the most dangerous, the scientists believe.
"We are potentially looking in the wrong place," said co-author Professor David Newby, from the University of Edinburgh.
While some commercial trucks and buses have "particle traps" that can filter out pollution dust, they reduce fuel efficiency and are not a standard feature in most vehicles.
Professor Jeremy Pearson, associate medical director at the British Heart Foundation, which co-funded the research, said: "There is no doubt that air pollution is a killer, and this study brings us a step closer to solving the mystery of how air pollution damages our cardiovascular health.
"Individual avoidance of polluted areas is not a solution to the problem. Government must put forward bold measures to make all areas safe and protect the population from harm."