Minute magnetic particles typically found in air pollution have been detected in “abundant” quantities in human brain tissue for the first time.
The tiny particles of iron oxide, known as magnetite, are toxic and it has been suggested they could play a role in causing or hastening the onset of Alzheimer’s disease.
The study, in which brain tissue samples from 37 people were collected from those who had lived in Mexico City and in Manchester in the UK, is the first to prove magnetite particles found in air pollution have made their way into the brain.
Magnetite naturally occurs in angular formations in the brain. But for every one natural angular particle, researchers found as many as 100 smooth, spherical particles.
The smooth shape of the observed magnetite particles is characteristic of high temperature formation, such as from vehicle (particularly diesel) engines, power stations or open fires, researchers said.
The toxic magnetite particles disrupt normal cellular functions in the brain by causing oxidative stress, and by the creation of unstable free radicals – particles which damage essential structures in brain cells.
Though no definite link between magnetite and Alzheimer’s has been established, previous studies have found a correlation between high quantities of the compound and the disease in the brains of Alzheimer’s sufferers.
The study was led by scientists at Lancaster University and published in the Proceedings of the National Academy of Sciences (PNAS).
The World Health Organisation warned as many as three million premature deaths every year were the result of air pollution.
In the UK it is thought as many as 50,000 people die each year due to air pollution. A further 520,000 are affected by Alzheimer’s, a common form of dementia.
Physicist Barbara Maher, co-director of the Centre for Environmental Magnetism and Paleomagnetism at Lancaster University said in a statement: “Our results indicate that magnetite nanoparticles in the atmosphere can enter the human brain, where they might pose a risk to human health, including conditions such as Alzheimer’s disease.
“The particles we found are strikingly similar to the magnetite nanospheres that are abundant in the airborne pollution found in urban settings, especially next to busy roads, and which are formed by combustion or frictional heating from vehicle engines or brakes.”
Speaking to the BBC she added: “It’s dreadfully shocking. When you study the tissue you see the particles distributed between the cells and when you do a magnetic extraction there are millions of particles, millions in a single gram of brain tissue – that’s a million opportunities to do damage.”
Professor David Allsop, a specialist in Alzheimer’s at the University of Lancaster and co-author of the study, said: “This finding opens up a whole new avenue for research into a possible environmental risk factor for a range of different brain diseases.”
Geophysicist Joe Kirschvink at California Institute of Technology in Pasadena, who first detected naturally formed magnetite particles in the brain 25 years ago, told the journal Science, he believes the presence of the particle in the brain is “disturbing”.
He said: “Once you start getting larger volumes of [environmental] magnetite, the chemical reactivity goes way up.
“That nanoparticles of industrially generated magnetite are able to make their way into the brain tissues is disturbing.”
Dr David Reynolds, chief scientific officer at Alzheimer's Research UK, told the Press Association: “Little is known about the role of magnetite nanoparticles in the brain and whether their magnetic properties influence brain function.
“It’s interesting to see further research investigating the presence of this mineral in the brain, but it’s too early to conclude that it may have a causal role in Alzheimer’s disease or any other brain disease.
“We know that air pollution can have a negative impact on certain aspects of human health, but we can’t conclude from this study that magnetite nanoparticles carried in air pollution are harmful to brain health.”
Policymakers should take note of the results, Professor Maher told Science.
“It’s an unfortunately plausible risk factor, and it’s worth taking precautions. Policymakers have tried to account for this in their environmental regulations, but maybe those need to be revised,” she said.
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