BBC: Tiny particles of pollution have been discovered inside samples of brain tissue, according to new research.
Suspected of toxicity, the particles of iron oxide could conceivably contribute to diseases like Alzheimer's - though evidence for this is lacking.
The finding - described as "dreadfully shocking" by the researchers - raises a host of new questions about the health risks of air pollution.
Many studies have focused on the impact of dirty air on the lungs and heart.
Now this new research...