Scientists have discovered the first direct evidence that PM2.5 particles attach themselves to red blood cells, providing a mechanism for how they spread throughout the human body.
The breakthrough research, led by Professor Jonathan Grigg and Dr Norrice Liu at Queen Mary University of London, demonstrates that particles from vehicle exhausts, brakes and tyre wear can latch onto red blood cells after entering the lungs.
While PM2.5 has previously been detected in the brain and heart, this study is the first to conclusively show how they get there.
The research involved 12 healthy volunteers who spent four hours in a London office building before standing within ten meters of a busy road for an hour, then returning to the office.
Each participant carried an aethalometer to measure pollution levels and researchers collected blood samples at three intervals to track particle accumulation on red blood cells.
It was found that roadside pollution levels were nearly five times higher than indoors and the volunteers showed two to three times more particulate matter stuck to their red blood cells after just one hour of exposure.
Interestingly, some participants’ levels decreased after returning indoors, while others remained elevated, suggesting individual differences in how bodies process inhaled pollution.
Although only about two or three in every thousand red blood cells carried particles, researchers calculated this translates to approximately 80 million affected cells circulating in the body’s five litres of blood after an hour near a main road.
Additionally, eight volunteers repeated the experiment wearing FFP2 masks. Despite identical pollution exposure, masked participants showed no increase in particles on their red blood cells, providing genuine evidence that FFP2 masks effectively prevent PM2.5 being inhaled.
Laboratory tests confirmed the findings, showing that diesel exhaust particles readily adhered to both human and mouse red blood cells, with attachment increasing proportionally to particle concentration.
Analysis revealed the PM2.5 contained metals including iron, copper, silicon, chromium and zinc from vehicle exhausts, plus silver, copper and molybdenum from brake and tyre wear.
Professor Grigg said: ‘In our bodies, red blood cells work by collecting oxygen from our lungs and delivering it throughout the body. With this set of experiments, we have shown that tiny air pollution particles are hijacking our red blood cells, meaning they can also travel almost anywhere in the body.
‘We’re finding more and more evidence that air pollution particles are making their way into many different organs of the body and now we have clear evidence of how that could be happening.
‘This technique means we now have a relatively simple way to measure the amount of pollution entering the body, so now we can test out which factors might increase or reduce the problem. We were surprised to find how well an FFP2 face mask prevents these very tiny particles from reaching and attaching to blood cells.’
Professor Ane Johannessen, chair of the European Respiratory Society’s expert group on epidemiology and environment, who was not involved in the research, said: ‘These tiny particles are produced by vehicles and industrial processes and released into the air we breathe. This study sheds light on how these dangerous particles might be infiltrating every part of the body via the bloodstream. It also suggests we could lower the risk with the right protective facemask. This could be beneficial for people who are vulnerable because they have a lung disease, or they cannot avoid spending time next to a busy road.
‘However, most of us cannot avoid being exposed to dangerously high levels of air pollution in our daily lives, so we need laws to dramatically lower air pollution and reduce the risk for everyone.’
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