Tiny magnetic particles called "magnetite nanoparticles" present in air pollution have, for the first time, been discovered in human brains, and researchers think they could be a possible cause of Alzheimer's disease.
Researchers at Lancaster University in the United Kingdom found abundant magnetite nanoparticles in the brain tissue from 37 individuals aged three to 92-years-old living in Mexico City and Manchester, a major city in England.
This strongly magnetic mineral is toxic. It's been implicated in the production of free radicals or "reactive oxygen species" in the human brain associated with neurodegenerative diseases, including Alzheimer's.
Prof. Barbara Maher from Lancaster Environment Centre and colleagues (from Oxford, Glasgow, Manchester and Mexico City) used spectroscopic analysis to identify the particles as magnetite.
Unlike angular magnetite particles that are believed to form naturally within the brain, most of the observed particles were spherical, with diameters up to 150 nanometers. Some of these particles had fused surfaces, all characteristic of high-temperature formation - such as from vehicle (particularly diesel) engines or open fires.
The spherical particles are often accompanied by nanoparticles containing other metals such as platinum, nickel and cobalt.
"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," said Prof. Maher.
Particles smaller than 200 nm are small enough to enter the brain directly through the olfactory nerve after breathing air pollution through the nose.
"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," she noted.
According to Alzheimer's researcher Professor David Allsop of Lancaster University's Faculty of Health and Medicine, this finding "opens up a whole new avenue for research into a possible environmental risk factor for a range of different brain diseases."
The results were published in the paper 'Magnetite pollution nanoparticles in the human brain' by the Proceedings of the National Academy of Sciences.
The paper's authors are Barbara Maher, David Allsop, Vassil Karloukovski and Penny Foulds from Lancaster University; Imad Ahmed from the University of Oxford; Donald MacLaren from the University of Glasgow; David Mann from the University of Manchester; Ricardo Torres-Jardon from the Universidad Nacional Autonoma de Mexico; and Lilian Calderon-Garciduenas from The University of Montana.
A YouTube video of the discovery can be viewed here.