Toxic Airborne Particulates Cross the Brain-Blood Barrier

It has long been known that airborne contaminants can do serious damage to the lungs and heart. New research confirms what has become increasingly apparent in recent years: that polluted air is toxic for the brain, as well.

Last month a team of British and Chinese researchers published a study in PNAS that concluded airborne toxic particles can and often do cross the brain-blood barrier, causing a range of chronic and debilitating conditions.

When the researchers examined 25 patients who were suffering from mental disorders, they found that 32 percent of the group had particulates in both the blood and cerebrospinal fluid. Among a healthy control group, only one in 26 patients had toxic fine particulates in these fluids.

The research team identified a range of airborne contaminants, including viruses, bacteria, smoke, dust, mold spores; particles from power plants, vehicle exhaust and wildfires; calcium-based particles, such as calcite and aragonite; minerals from construction materials, abrasives, soil treatments and pigments; as well as silicon particles and anatase, which is used in sunscreens and paints.

These toxic particles are small enough to slip past the body’s defenses and barriers, including the immune system’s sentinel cells. One suspected pathway to the brain is the olfactory bulb of the nose. Once past the endothelial membrane, the particulates travel in the bloodstream to the brain. 

Professor Iseult Lynch of the University of Birmingham in the United Kingdom is a co-author of the study. She explained the significance of the findings: “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.”

There is a growing awareness that airborne contaminants may play a role in an array of neurological disorders, including: dementia, Alzheimer’s disease, brain aging, depression, ADHD, schizophrenia and even stroke. Compounding the problem is the clinical observation that particulates tend to remain in the brain longer than they linger in the heart or lungs.

Commenting on the study’s findings, journalist Beth Gardner noted: “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. 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 breathed cleaner air.”

Stanford chemistry professor Dr. Richard Zare has also been studying this phenomenon intensely. He welcomed the new research, but cautioned: “It’s not enough that doctors know this. It’s not enough that research scientists know this, either. The public needs to know this, and particularly the policymakers. What we need is action. We need public awareness and policymaking related to this.”