Nanoparticles Found in Brains Come From External Sources

Research indicates that nanoparticles found in the brain are not the product of the body but likely come from air pollution

Transmission electron micrographs of brain thin sections, identifying two distinct types of magnetite nanoparticles within frontal brain cells
Image: Lancaster University

An international team of researchers, led by Barbara Maher, a professor at Lancaster University, in England, has found evidence that suggests that the nanoparticles that were first detected in the human brain over 20 years ago may have an external rather an internal source.

In research described in the Proceedings of the National Academy of Sciences, the scientists leveraged electron microscopy and magnetic analyses to not only discover the abundant presence of magnetite nanoparticles in the brain, but also determine that these nanoparticles are consistent with high-temperature formation, which means that they were likely not produced inside the body but were manufactured outside of it.

These magnetite nanoparticles are an airborne particulate that are abundant in urban environments and formed by combustion or friction-derived heating. In other words, they have been part of the pollution in the air of our cities since the dawn of the Industrial Revolution.

However, according to Andrew Maynard, a professor at Arizona State University, and a noted expert on the risks associated with nanomaterials,  the research indicates that this finding extends beyond magnetite to any airborne nanoscale particles—including those deliberately manufactured .

“The findings further support the possibility of these particles entering the brain via the olfactory nerve if inhaled.  In this respect, they are certainly relevant to our understanding of the possible risks presented by engineered nanomaterials—especially those that are iron-based and have magnetic properties,” said Maynard in an e-mail interview with IEEE Spectrum. “However, ambient exposures to airborne nanoparticles will typically be much higher than those associated with engineered nanoparticles, simply because engineered nanoparticles will usually be manufactured and handled under conditions designed to avoid release and exposure.”

While the results do seem to confirm previous research that indicates that airborne nanoparticles can reach our brains if inhaled, Maynard cautions that we should be careful not to extrapolate the data too far. He says that the paper had insufficient evidence to establish a causal link between the nanoparticles and neurodegenerative disease.

“What is lacking is any indication of how much exposure is needed to lead to harmful effects, and how the severity and probability of possible effects increases with increased exposure,” explains Maynard.

The formula for determining the risk of any substance is Hazard x Exposure = Risk. In this formula you can see that a highly hazardous substance like an acid may have restricted access, limiting its exposure and in so doing reducing its risk. When this formula is applied to the difference between engineered nanoparticles and those found in the air because of air pollution, we can begin to put the risks into perspective.

“In most workplaces, exposure to intentionally made nanoparticles is likely be small compared to ambient nanoparticles, and so it’s reasonable to assume—at least without further data—that this isn’t a priority concern for engineered nanomaterial production,” said Maynard. 

While deliberate nanoscale manufacturing may not carry much risk, Maynard does believe that the research raises serious questions about other manufacturing processes where exposure to high concentrations of airborne nanoscale iron particles is common—such as welding, gouging, or working with molten ore and steel.

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IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.