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Magnetite pollution nanoparticles in the human brain
Proceedings of the National Academy of Sciences of the United States of America
vol. 113 no. 39 > Barbara A. Maher, 10797–10801, doi:
Barbara A. Maher a,1, Imad A. M. Ahmed b, Vassil Karloukovskia, Donald A. MacLaren c, Penelope G. Foulds d, David Allsop d, David M. A. Manne, Ricardo Torres-Jardón f, and Lilian Calderon-Garciduenas g, h
a Centre for Environmental Magnetism and Palaeomagnetism, Lancaster Environment Centre, University of Lancaster, Lancaster LA1 4YQ, United Kingdom;
b Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, United Kingdom;
c Scottish Universities Physics Alliance, School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom;
d Division of Biomedical and Life Sciences, Faculty of Health and Medicine, University of Lancaster, Lancaster LA1 4YQ, United Kingdom;
e Division of Neuroscience & Experimental Pyschology, School of Biological Sciences, University of Manchester, Manchester M6 8HD, United Kingdom;
f Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, Mexico City 04310, Mexico;
g Neurotoxicology Laboratory, The University of Montana, Missoula, MT 59812;
h Universidad del Valle de México, Mexico City, 04850, Mexico
Edited by Yinon Rudich, Weizmann Institute of Science, Rehovot, Israel, and accepted by Editorial Board Member A. R. Ravishankara July 25, 2016 (received for review April 13, 2016)
We identify the abundant presence in the human brain of magnetite nanoparticles that match precisely the high-temperature magnetite nanospheres, formed by combustion and/or friction-derived heating, which are prolific in urban, airborne particulate matter (PM). Because many of the airborne magnetite pollution particles are <200 nm in diameter, they can enter the brain directly through the olfactory nerve and by crossing the damaged olfactory unit. This discovery is important because nanoscale magnetite can respond to external magnetic fields, and is toxic to the brain, being implicated in production of damaging reactive oxygen species (ROS). Because enhanced ROS production is causally linked to neurodegenerative diseases such as Alzheimer’s disease, exposure to such airborne PM-derived magnetite nanoparticles might need to be examined as a possible hazard to human health.
Biologically formed nanoparticles of the strongly magnetic mineral, magnetite, were first detected in the human brain over 20 y ago Kirschvink JL, Kobayashi-Kirschvink A, Woodford BJ (1992) Proc Natl Acad Sci USA 89(16):7683–7687. Magnetite can have potentially large impacts on the brain due to its unique combination of redox activity, surface charge, and strongly magnetic behavior. We used magnetic analyses and electron microscopy to identify the abundant presence in the brain of magnetite nanoparticles that are consistent with high-temperature formation, suggesting, therefore, an external, not internal, source. Comprising a separate nanoparticle population from the euhedral particles ascribed to endogenous sources, these brain magnetites are often found with other transition metal nanoparticles, and they display rounded crystal morphologies and fused surface textures, reflecting crystallization upon cooling from an initially heated, iron-bearing source material. Such high-temperature magnetite nanospheres are ubiquitous and abundant in airborne particulate matter pollution. They arise as combustion-derived, iron-rich particles, often associated with other transition metal particles, which condense and/or oxidize upon airborne release. Those magnetite pollutant particles which are <∼200 nm in diameter can enter the brain directly via the olfactory bulb. Their presence proves that externally sourced iron-bearing nanoparticles, rather than their soluble compounds, can be transported directly into the brain, where they may pose hazard to human health.
brain magnetite magnetite pollution particles Alzheimer's disease combustion-derived nanoparticles airborne particulate matter
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