A team involving Oxford University scientists has, for the first time, discovered tiny magnetic particles from air pollution lodged in human brains – and researchers think they could be a possible cause of Alzheimer's disease.Researchers led by Lancaster University found abundant magnetite nanoparticles in the brain tissue of 37 individuals aged three to 92 who lived in Mexico City and Manchester. This strongly magnetic mineral is toxic and has been implicated in the production of reactive oxygen species (free radicals) in the human brain, which are associated with neurodegenerative diseases including Alzheimer's disease.The results have been published in the journal Proceedings of the National Academy of Sciences.