Power plants, like thisone in Tyumen, Russia, let off air pollutionthatcontainsmanynanoparticles, includingmagnetite. A new studyfindsthismagnetitecan make its way into human brains.

Sergei Butorin/iStockphoto

Industrial air pollutionleavesmagnetic waste in thebrain

ByMichael PriceSep. 5, 2016 , 3:00 PM

Ifyou live in anurban environment, chances are you’vegotnanomagnets on thebrain—literally. New research suggeststhat most magnetite found in the human brain, a magnetic iron oxide compound, comesfromindustrial air pollution. Andbecauseunusually high concentrations of magnetite are found in the brains of peoplewithAlzheimer’sdisease, thefindingsraisethespecter of analarming new environmental risk factor forthisandotherneurodegenerativediseases.Still, otherscientistscautionthatthe link remainsspeculative.

For decades, scientists have knownthebrainharborsmagneticparticles, but most assumedthattheyderivednaturallyfromthe iron used in normalbrainfunction. About 25 yearsago,geophysicist Joe Kirschvink atCalifornia Institute of Technology in Pasadenadetectedbiologicallyformedmagnetiteparticles in human brains, lendingevidencetotheirnaturalorigin.

The problemwithmagnetite is thatit’stoxic. It causesoxidative stress, disruptingnormalcellularfunctionandcontributingtothecreation of destructive free radicals—unstablemoleculesthatcandamageother important molecules. Previouswork has alsoshown a correlationbetween high amounts of brainmagnetiteandAlzheimer’sdisease, and recent studies suggestitincreasesthetoxicity of thedisease’s hallmark β amyloid plaques, clumpsof proteinthatcaninterferewithcellsignaling. Nothingdefinitively links magnetitetoAlzheimer’s, but the kinds of cellulardamageitcancause are consistent withwhat’sseen in thedisease.

Physicist Barbara Maher, co-director of the Centre forEnvironmentalMagnetismandPaleomagnetism at LancasterUniversity in the United Kingdom, wonderedwhetherallthemagnetite found in thebraincouldbetracedtobiologicalprocesses. As an expert in environmentalmagneticparticles, sheknewthatmany, includingmagnetite, are prevalent in air pollution let off by power plant smokestacks.

“The paradigmuntilnow has been thatmagnetitejustformsnaturally in thebrain,” Maher says. “Givenhowprolificmagnetiteparticles are in theatmosphere, I wonderedifthey had gained entry intothe human brain.”

So Maher and a team of U.K. andMexicanscientistslooked at postmortem samples of brain matter fromthefrontalcortexes of 37 human brains. Most camefrompeoplewholived in Mexico City, andotherscamefromformerresidents of Manchester, U.K. Using a variety of high-resolution imaging techniques, theresearchersexaminedthecharacteristics of thebrain samples’ magnetite.

Biologicalmagnetiteusuallyforms in tetrahedral or octahedralshapes, but the vast majority of magnetiteparticles found in thisstudywereinsteadroundnanospheres (like theone below). The researchersdetectedotherunexpected metallic nanoparticles in thebrain samples, too: platinum, nickel, andcobalt. None of these metalsoccursnaturally in thebrain, suggestinganenvironmentalorigin.

These magnetitenanospheres, found in pollutionfromthe United Kingdom'sDidcot power station, match themagnetiteresearchers found in human brain samples.

Barbara Maher

For Maher, themagnetite’snanosphereshape, combinedwiththepresence of theothermetals, was a tell-talesign. “Theyshowedallthepropertiessuggestingtheyformed in high temperatures,” shesays. Thosetemperaturesvarywiththefuelbeingburned, but they are muchhigherthanthose of the human body. “[The nanospheres are] combustionbyproducts, like what’s found in power station pollution.” Frictionalheating, like whathappensto a car’sbrakepads, canalso produce magnetitenanospheres, sheadds.

The researchers found biologicallyformedmagnetite, too, but foreveryone of thoseparticles, they found at least 100 pollution-derivedmagnetiteparticles, they report today in theProceedings of the National Academy of Sciences. Thatcomes out tomillions of magnetiteparticles per gram of brain matter, Maher says.

At 150 nanometers or less in diameter, these magnetitenanoparticles are small enoughtobeinhaledthroughthenoseand enter thebrainthroughtheolfactorybulb, Maher explains. Previous air quality studies in the United Kingdomand Mexico City have found thaturbanareas, especiallyalongroadsides, have abundant airbornemagnetite, sheadds, providing plenty of opportunity forpeopletosniff these toxicnanoparticlesintotheirbrain.

Otherenvironmental risk factors forAlzheimer’sandotherneurodegenerativediseases have been suggested, andit’snotclearhowmagnetite fits intothe overall risk picture, or whetherthere’san exposure thresholdthat’sespeciallydangerous. Still, theresultsdeserve special attention fromepidemiologistsand air quality policymakers, Maher says. “It’s anunfortunatelyplausible risk factor, andit’sworthtakingprecautions. Policymakers have triedto account forthis in theirenvironmentalregulations, but maybethoseneedtoberevised.”

Kirschvink, the first scientisttodetectbiologicallyderivedmagnetite in thebrain 25 yearsago, is convincedthattheresearchers have indeed found evidencethatmagnetitecanbeintroducedthrough air pollution. The especially high levels of magnetite found in thestudy’sbrain samples are shocking, he says, thoughnotnecessarilysurprisinggiventhattheylivedandworked in industrial environments withlots of air pollution.

Still, he’sconcernedthatresearchers found somuchenvironmentalmagnetite in thebrain. Suchmagnetite is more dangerousthanbiogenicversions of theparticle, he says. “Onceyou start gettinglarger volumes of [environmental] magnetite, thechemicalreactivitygoes way up,” he says. “Thatnanoparticles of industriallygeneratedmagnetite are ableto make their way intothebrain tissues is disturbing.”

Jennifer Pocock, a neurologist at University College London, says in a statement throughthe independent Science Media Centre thatalthoughsheagreestheevidence points topollution-bornemagnetite in thebrain, more work is neededbefore a solidconnectiontoAlzheimer’scanbedrawn. “Thereneedstobe a betterstudycarried out tocorrelatethemagnetiteconcentrations of patientswholivedprimarily in a city, forexample, comparedwithpatients living in relativelyunpolluted area, and analyses of theirAlzheimer’sdiseasebrainpathologycorrelatedwithmagnetiteconcentrations."

*Update, 6September, 7:07 a.m.:This story has been updatedtoadd a reactionfromJenniferPocock,a neurologist at University College London.

Posted in:

  • Brain & Behavior
  • Chemistry
  • Environment
  • Health

DOI: 10.1126/science.aah7262

Michael Price

Michael Price is a formerscientificemploymentand training writer at ScienceCareers.