An international team of experts from the University of Birmingham in the UK and research institutions in China discovered that inhaled particles can enter the bloodstream after crossing the air-blood barrier, eventually reaching the brain, and leading to damage of the brain-blood barrier and surrounding tissues as they do so. Once in the brain, the particles were hard to clear and were retained for longer than in other organs.

For the study, published in the journal PNAS, the team analysed various fine particles in human cerebrospinal fluids taken from patients who had experienced brain disorders, uncovering a process which may result in toxic particulate substances ending up in the brain.

"There are gaps in our knowledge around the harmful effects of airborne fine particles on the central nervous system. This work sheds new light on the link between inhaling particles and how they subsequently move around the body," said Professor Iseult Lynch, from the University of Birmingham.

"The data suggests that up to eight times the number of fine particles may reach the brain by travelling, 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," Lynch added.

Air pollution is a cocktail of many toxic components, but particulate matter (PM, especially ambient fine particles such as PM2.5 and PM0.1), are the most concerning in terms of causing detrimental health effects. Ultrafine particles, in particular, are able to escape the body's protective systems, including sentinel immune cells and biological barriers.

Recent evidence has revealed a strong link between high levels of air pollution and marked neuroinflammation, Alzheimer's-like changes and cognitive problems in older people and even in children.

While the findings offer new evidence in proving the risks from particulate pollution to the central nervous system, the researchers recommend that more investigation is needed into the mechanics of how inhaled ambient fine particles reach the brain.