Many cities around the world are afflicted with air pollution, leading to an early death for as many as 200,000 people each yeah in the U.S. alone. Now, there’s even more of a reason to be concerned. According to a recent study, toxic nanoparticles have been found in “abundance” in human brain tissue. Although researchers don’t have a causative link yet, it is possible that these toxins can contribute to growing instances of Alzheimer’s disease.
Found within open fires and engines, magnetite particles are small, less than the width of a human hair. This new research shows that they can also sometimes be found in the frontal cortex of the human brain, leading to mental health hazards.
Researchers at the University of Lancaster in the United Kingdom took brain samples of 37 people who had lived much of their lives in Mexico City or Manchester, UK, both of which are highly polluted areas.
Many of the brains tested had 2 kinds of magnetite within them. Firstly, many had magnetite that is made naturally within the human brain. However, more troubling is the second type of magnetite, which is spherical in shape and are formed in high temperatures, such as a car engine. 
Where Do These Toxic Nanoparticles Come From?
So how do these invaders get into the human brain? Doctors believe that they sneak in through the olfactory bulb, which is at the top of the nose. There is no blood-brain barrier at this entry point, so the body can do little to protect it from allowing small, foreign substances to enter into the brain.
The World Health Organization reports that air pollution is at a crisis level, and that it kills more people per year than malaria and AIDS combined. What’s more, new research indicates that it may now be associated with reduced intelligence, mental illness, and Alzheimer’s. 
A recent study yielded results showing that metal accumulated in the brain can result in Alzheimer’s disease, which is also associated with nanoparticle air pollution.
Professor Barbara Maher, lead researcher at Lancaster University, stated:
“We have not demonstrated a causal link between these particles and Alzheimer’s disease but when you consider that magnetite has been found in higher concentrations in Alzheimer’s brains and you know that magnetite is pernicious in its effect on the brain, then having a direct [air pollution] source of magnetite right up your olfactory bulb and into your frontal cortex is not a great idea.”
Maher hopes that her study will lead to further studies within the field and ignite policy changes on the subject of air pollution. With awareness growing, we can more easily make necessary changes to improve air quality breathed in by billions of people.
 The Guardian