Potentially Toxic Magnetic Nanoparticle Pollution Found in Human Brains

A woman wears a protective mask to guard her from air pollution as she walks on a street in Mexico City, March 16. A new study using subjects from Mexico City and Manchester found high levels of magnetic nanoparticle pollution in the brain. Reuters

Researchers have discovered significant quantities of potentially toxic magnetic nanoparticles in human brains, sparking fears they could lead to brain diseases.

The particles, made of a form of iron called magnetite, are produced during combustion and can reach high levels in polluted areas. A study published Sep. 5 in the journal Proceedings of the National Academy of Sciences suggests these pollutants can make their way into the brain when inhaled, either through the lungs or more likely directly through the olfactory bulb, where smell is processed.

In the paper, scientists examined the brains of people who lived in Mexico City and Manchester, England, and who were subject to high levels of particulate pollution during their lives. Some of the people also had Alzheimer's disease or dementia, and researchers are concerned these particles may increase the risk for such brain diseases, says Barbara Maher, a scientist at the University of Lancaster, and the study's first author.

"The recognition that nanoparticles of industrially-generated magnetite are able to make their way into the brain tissues is disturbing," says Joe Kirschink, a researcher at Cal Tech, who wasn't involved in the paper. In 1992, Kirschink discovered that magnetite can be naturally produced inside the brain, where it serves as-yet unknown functions. Magnetite has also been found in the neural tissues of other animals such as birds and bumblebees, where it may be involved in navigation and recognizing the Earth's magnetic fields.

A microscopic image shows magnetic nanoparticles in the human brain. Barbara Mayer

But this internally produced material is contained within cells. Spectroscopic imaging of the particles has found them to be very small and spherical, and different in appearance from naturally-produced magnetite. These externally derived nanoparticles are however likely to be toxic to the brain, Maher says. Magnetite is a particularly concerning pollutant because it forms destructive chemicals called reactive oxygen species, which lead to damage and inflammation, she notes. The fact that it's also magnetic could cause interactions with external magnetic fields, which may cause further problems.

Magnetite is commonly produced when combustion takes place in the presence of hot iron, as is the case in vehicle engines, stoves and in other industrial processes.

The study is a continuation of work done by Lilian Calderon-Garciduenas, who has studied the effect of particulate pollution on the brains of Mexico City residents. Her research has shown that some residents of the city exposed to high levels of particulates present in the air can have Alzheimer-like changes in the brain, as young as the teenage years.

George Perry, a prominent researcher with the University of Texas at San Antonio, says that his own work has shown that there are higher levels of magnetite within amyloid plaques characteristic of Alzheimer's disease. These appear to be internally produced. But this study, showing that magnetite can also make it into the brain from air pollution, is "some of the strongest [evidence] yet suggesting how the environment may have an impact" on the brain.

However, all researchers emphasized that it's as yet unclear yet if the magnetite could cause or increase the risk for Alzheimer's disease, but Maher says it should be studied in the future.