We know air pollution is linked to heart disease, stroke, lung disease, and early death. But scientists have long wondered how tiny pollution particles travel from the lungs to the rest of the body.

A new study offers an interesting clue. Researchers found evidence that traffic-related pollution particles can enter the bloodstream and attach to red blood cells. They also found that people wearing FFP2 masks had far fewer of these particles on their blood cells after being exposed to traffic pollution.

Pollution Particles on Red Blood Cells

Researchers recruited 12 healthy adults in London. Participants spent several hours indoors before standing next to a busy road for one hour. During that time, levels of black carbon, a common marker of traffic pollution, were nearly eight times higher than indoors.

The researchers collected blood samples before and after exposure. They then examined 3,000 red blood cells from each volunteer.

After spending an hour near traffic, participants had two to three times more pollution particles attached to their red blood cells. The levels remained elevated even an hour after they left the roadside.

Light microscopy images of particles adherent to red blood cells.

That may not sound like much, but we have 20–30 trillion red blood cells in our bodies, which means tens of millions of red blood cells could be carrying pollution particles through the bloodstream.

Think of red blood cells as tiny delivery vehicles. Pollution particles hitchhike on red blood cells, and they may be able to travel throughout the body after being inhaled.

What Happened When People Wore Masks?

To test the idea, eight volunteers repeated the experiment while wearing an FFP2 mask.

The results were very positive. The amount of pollution particle material attached to red blood cells was about 63% lower when participants wore the mask.

In other words, people wearing masks had roughly one-third as much particle material detected on their blood cells after spending time near traffic.

What’s in These Particles?

To confirm their findings, the researchers also exposed human blood cells and mice to diesel exhaust particles in the lab. In both cases, the particles readily attached to red blood cells.

The team analyzed some of the particles found on volunteers’ blood cells and detected metals, including iron, copper, silicon, chromium, and zinc. These are commonly associated with vehicle emissions, brake wear, and tire wear.