What the study found
Researchers report the first direct evidence that tiny air pollution particles can attach to red blood cells, potentially enabling them to travel throughout the body. The team, led by Professor Jonathan Grigg and Dr Norrice Liu at Queen Mary University of London, studied healthy volunteers and found that particles from vehicle exhausts and brake/tyre wear can cling to red blood cells after exposure to busy urban air. The implications are significant because red blood cells routinely ferry oxygen around the body, and if pollutants hitch a ride, they could reach organs such as the heart and brain more readily than previously shown.
How the study was conducted
The study involved 12 adult volunteers who spent four hours in an office setting before and after a one‑hour exposure near a busy London road, separated by a return to the office. Each participant carried an aethalometer to gauge ambient particle pollution in real time. Eight of the volunteers repeated the experiment on another day wearing an FFP2 mask to test whether reducing inhaled particles would affect the outcome. Blood samples were taken at three points: after the initial office period, immediately after roadside exposure, and after returning to the office. Using microscopes, researchers quantified how many pollution particles were attached to red blood cells.
Key findings in numbers
Ambient roadside pollution levels were nearly five times higher than in the office. After spending time by the road, participants showed a noticeable increase in red blood cells bearing pollution particles compared with the baseline. On average, the study found two to three times as many particles attached to red blood cells following roadside exposure. Although the proportion of red blood cells carrying particles remained small (roughly two or three per thousand), the researchers estimated that in a typical 5‑litre circulating blood volume, about 80 million red blood cells could be transporting particles after an hour near a major road.
The protective effect of masks and what the lab showed
When the same participants were exposed to roadside air while wearing a protective mask, there was no increase in particles stuck to red blood cells. This suggests that an effective mask can significantly reduce the dose of inhaled pollution particles reaching blood components. To corroborate the human data, the researchers exposed purified human red blood cells—and also mouse cells—to diesel exhaust in the lab. They found that particles readily attached to both human and mouse red blood cells, with attachment rising as particle numbers increased. This lab work supports the idea that red blood cells can act as transport vessels for inhaled pollutants in living organisms.
What the particles are made of and why this matters
Analysis of pollution particles found on blood cells revealed common constituents: iron, copper, silicon, chromium, and zinc—elements associated with vehicle exhaust—along with silver, copper, and molybdenum linked to brake and tyre wear. The particles were in the PM2.5 size range (2.5 micrometres or smaller), a category routinely monitored because it can penetrate deep into the lungs and enter circulation. The team’s discovery provides a plausible mechanism for how pollutants could reach organs such as the heart and brain, aligning with growing evidence that air pollution contributes to cardiovascular and neurodegenerative risks.
Implications for health and policy
Professor Grigg said the findings show red blood cells can be hijacked by tiny air pollutants, enabling movement through the body. “We now have a relatively simple way to measure the amount of pollution entering the body, so we can test factors that might increase or reduce the problem,” he noted. The researchers highlighted how effective masks appear in limiting the dose of particles entering the bloodstream, a finding with immediate public health relevance for people who cannot avoid roadside exposure. Dr Ane Johannessen, though not involved in the study, emphasized that while laws to curb pollution are crucial, individual protections such as quality face coverings could offer meaningful risk reduction for vulnerable groups.
What comes next
The study adds a tangible mechanism to a broader conversation about how air pollution affects health and why reducing exposure matters. The team plans to refine their measurement technique to explore which factors—such as pollution composition, duration of exposure, and individual physiology—most strongly influence particle attachment to red blood cells. In the meantime, the findings support continued advocacy for cleaner air policies and practical protective measures for urban dwellers facing persistent pollution near busy roads.
About the researchers
The work was conducted by scientists at Queen Mary University of London and appears in ERJ Open Research. While the study uses human volunteers, it also incorporated controlled lab experiments with animal tissue to strengthen the evidence that pollution particles readily adhere to red blood cells.
