Yes, they appear to be able to follow the pathway used by smell neurons and thus pass directly from the olfactory membrane into the brain, i.e. not going via the lung and bloodstream. Experiments in rodents using radio-labelled nano-particles show that very small particles really can penetrate directly through the roof of the nose and pass into the brain along olfactory neurons. Here these particles set in motion an inflammatory process, which activates micro-glia (brain type macrophages), which attack neurons and lead to amyloid deposits – the hall mark of dementia. People who are exposed to particles have a high risk of dementia, and animals randomised to be exposed (or not) to pollution particles acquire brain amyloid and manifest cognitive decline. So there you have it – there is growing and quite compelling evidence that pollution particles are bad news for humans and other animals. It is time to act – phase out diesel cars, incentivise car manufacturers to clean up emissions, gradually increase tax on cars/lorries/fuels, incentivise cycling in cities (and make it safer), and build rail lines. But none of this will happen without public support so proselytise and increase susceptibility to the message by increasing science teaching in schools. In the end, lots of things come back to the intellectual sophistication of the average citizen. In the meantime I suspect that an increasing proportion of people will adopt face masks, although I do not know how effective they are in trapping particles.
— Richard Lilford, CLAHRC WM Director
- Underwood E. The Polluted Brain. Science. 2017; 355(6323): 342-5.
- Chen H, Kwong JC, Copes R, et al. Living near major roads and the incidence of dementia, Parkinson’s disease, and multiple sclerosis: a population-based cohort study. Lancet. 2017; 389(10070): 718-26.