Toxic magnetic nanoparticles from air pollution have been discovered in \u0022abundant\u0022 quantities in human brains, according to a new study.The study, published Monday in the Proceedings of the National Academy of Sciences (PNAS), is particularly alarming because other research recently raised the strong possibility of a link between such particles and Alzheimer\u0026#039;s disease.\u0022Magnetite in the brain is not something you want to have because it is particularly toxic there.\u0022—Professor Barbara Maher, Lancaster UniversityThis latest study \u0022suggests that most magnetite found in the human brain, a magnetic iron oxide compound, comes from industrial air pollution. And because unusually high concentrations of magnetite are found in the brains of people with Alzheimer’s disease, the findings raise the specter of an alarming new environmental risk factor for this and other neurodegenerative diseases,\u0022 writes Science.The researchers examined the brains of 37 people in Mexico City, Mexico, and Manchester, U.K., and discovered \u0022abundant\u0022 amounts of magnetite and other nanoparticles deemed toxic.The new research \u0022suggests the particles can be inhaled and enter the brain through the olfactory nerve, which takes information about smells to the brain,\u0022 according to the Telegraph.Professor Barbara Maher of Lancaster University, who headed the study, told the Guardian:\u0026nbsp; \u0022You are talking about millions of magnetite particles per gram of freeze-dried brain tissue—it is extraordinary.\u0022\u0022Magnetite in the brain is not something you want to have because it is particularly toxic there,\u0022 she added, explaining that the metal can create free radicals, which have been linked to Alzheimer\u0026#039;s. \u0022Oxidative cell damage is one of the hallmark features of Alzheimer’s disease, and this is why the presence of magnetite is so potentially significant, because it is so bioreactive.\u0022\u0022Abnormal accumulation of brain metals is a key feature of Alzheimer\u0026#039;s disease and a recent study showed that magnetite was directly associated with the damage seen in Alzheimer’s brains,\u0022 the Guardian notes.The Guardian reports on Maher\u0026#039;s further findings:\u0022Many of the magnetite particles we have found in the brain are very distinctive,\u0022 said Maher. \u0022They are very rounded nanospheres, because they were formed as molten droplets of material from combustion sources, such as car exhausts, industrial processes and power stations, anywhere you are burning fuel.\u0022\u0022They are abundant,\u0022 she said. \u0022For every one of [the crystal shaped particles] we saw about 100 of the pollution particles. The thing about magnetite is it is everywhere.\u0022 An analysis of roadside air in Lancaster found 200m magnetite particles per cubic metre.Furthermore, said Maher: \u0022We also observed other metal-bearing particles in the brain, such as platinum, cobalt and nickel. Things like platinum are very unlikely to come from a source within the brain. It is a bit of an indicator of a [vehicle] catalytic converter source.\u0022\u0022This is a discovery finding, and now what should start is a whole new examination of this as a potentially very important environmental risk factor for Alzheimer\u0026#039;s disease,\u0022 Maher said. \u0022Now there is a reason to go on and do the epidemiology and the toxicity testing, because these particles are so prolific and people are exposed to them.\u0022The negative health impacts of air pollution have recently come into stark relief, with the UN saying last week that it kills as many people as cancer.