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Scientists are discovering that inhaled toxic particles may be able to reach and possibly damage the brain. Bloomberg Creative/Getty Images
  • While air pollution has often been shown to be harmful to the lungs and heart, new research suggests that airborne particulates may also be associated with brain disorders.
  • A new study has found fine particles of pollution in the cerebrospinal fluid of people diagnosed with brain disorders.
  • The authors of the study also tracked particles through the bodies of mice and assert that such particles in humans travel from lungs to blood, and through the brain-blood barrier.

Particulate matter in air pollution is known to cause problems for our lungs and hearts. However, the damage doesn’t stop there. A new study from researchers at the University of Birmingham in the U.K. and Chinese research institutions found that such pollution-borne toxic particles can also reach the brain.

The researchers examined the cerebrospinal fluid and blood of 25 patients with various mental disorders at a Chinese hospital and found a variety of toxic fine particulates in the cerebrospinal fluid of 32% of the patients as well, as in the blood.

Samples were also taken from 26 healthy people, and the researchers found particulate matter in only one individual.

The study was published in PNAS.

Study co-author Professor Iseult Lynch tells University of Birmingham News that our knowledge of the harmful effects of airborne fine particles on the central nervous system has been lacking. She says the study shines light on “the link between inhaling particles and how they subsequently move around the body.”

Particulate matter and air pollution

Particle pollution, also called particulate matter (PM), is ranked by size:

  • PM 10 — Particles up to 10 μm (microns). These include airborne viruses, bacteria, smoke, dust, and mold spores.
  • PM 2.5 — Particles up to 2.5 μm. These are likely to be particles from power plants, vehicle exhausts, wildfires, and other types of combustion.
  • PM 0.1 — Particles up to 0.1 μm. This is ultra-fine dust, largely from the same sources as PM 2.5 particles, but much finer. They are the most common indoor particles.

PM 0.1 particles are believed to be the most hazardous to human health since they are so infinitesimal they can evade the body’s defenses, internal barriers against intrusive foreign matter, and even the immune system’s sentinel cells.

Recent research suggests PM 0.1 particles are sources of oxidative stress and cardiovascular toxicity.

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Some particles the researchers found were typical of air pollution. They found calcium-based particles, such as calcite and aragonite, minerals often used in construction materials, abrasives, soil treatment, pigments, and as a pharmaceutical additive.

In addition, they also found iron and silicon particles, having reported finding iron in the brain in previous research.

“It appears actually that some of the metal ions are particularly bad. And the metal ions are common, like iron. You don’t need exotic metals to cause damage,” noted Dr. Zare.

Nonetheless, researchers also found some unusual particles: malayite, which is used as a pigment in ceramic glazes, particularly in China, and anatase, which is used in sunscreens and as pigment in paints.

There are theories as to how particulate matter may get into the brain, including through the nose’s olfactory bulb.

Dr. Zare’s study found:

“The olfactory bulb actually breaks down the [brain-blood] barrier, which helps [particles] get through. I have data showing that there’s stuff that’s given out that actually breaks the [endothelial] membrane that tries to protect you.”

Based on experiments with a mouse model, the new research demonstrated the means by which its authors believe most particulates travel to the brain: the bloodstream.

The researchers exposed mice to fine airborne particles of titanium oxide, and subsequently, gold, cerium oxide, and nanoscale quantum dots.

The experiments showed that such fine particulates in the lungs can traverse the oxygen-blood barrier to enter the bloodstream. Traveling to the brain, the particles “may cross from the bloodstream through the [brain-blood barrier] without visibly damaging it for final localization in the ventricles of the brain.”

The brain-blood barrier typically blocks the entry of such intruders but was unable to keep the tiny particles out.

“The data suggests that up to eight times the number of fine particles may reach the brain by traveling, via the bloodstream, from the lungs than pass directly via the nose — adding new evidence on the relationship between air pollution and detrimental effects of such particles on the brain,” says Professor Lynch.

The mouse model studies also indicated that particles are likely to remain in the brain longer than they do in other organs.

The new study follows other research suggesting that such particulate matter may cause a range of neurological issues.

These include dementia, Alzheimer’s disease and brain aging, and may increase the incidence of depression, ADHD, schizophrenia, and stroke.

Stanford chemistry professor Dr. Richard Zare was co-author of a 2020 paper that also observed fine particulates in the brain. He was not involved in the current study. Dr. Zare told Medical News Today that not enough people understand the damage air pollution can do to the brain:

“It is not well recognized, the danger of particulate matter in the brain. And I have been frustrated [that] I haven’t been able to get people to realize how important this is. The message needs to get to the policymakers,” he said.

Environmental journalist Beth Gardner also recently spoke about the effects of pollution on the brain.

“A neuropathologist examined puppies who’d lived in badly polluted Mexico City. She found the same markers in their brains that doctors use to diagnose Alzheimer’s disease in humans — plaques, twisted proteins, degenerating neurons. The same research team examined the brains of children and young people who’d been killed in accidents,” Gardner told NPR/TED Radio Hour.

“They found the red flags of Alzheimer’s in the brains of 40% of those who’d lived in polluted places and none who’d breathe cleaner air,” she said.

The findings are a promising start, with the authors writing that the research “opens up a new avenue via which to study the exposure and adverse effects of exogenous particles on CNS under environmental and occupational settings.”

Dr. Zare felt, however:

“[I]t’s not enough the doctors know this. It’s not important that research scientists know this, either. [T]he public needs to know this, and particularly the policymakers.”

Dr. Zare underscored that concrete steps would be more helpful than more research.

“[W]hat we need is action. We need public awareness and policymaking related to this,” he said.