Exposure to nanoparticles from air pollution significantly increases people's chances of getting brain cancer as these toxic particles have been discovered in human brains in "abundant" quantities, research has said.
As per the new study, the ultra-fine particles (UFPs) produced by fuel burning, particularly in diesel vehicles, get into the brain and carry carcinogenic chemicals. The study based on the analysis of medical records and pollution exposure of 1.9 million adult Canadians between 1991 and 2016 concluded the correlation between brain cancer and nanoparticles was "surprisingly consistent".
Cases of the deadly cancer are increasing across the globe, according to scientists, because an increase in pollution exposure roughly equivalent to moving from a quiet city street to a busy one leads to a single extra case of brain cancer for every 1,00,000 people exposed.
The study suggested that a one-year increase in pollution exposure of 10,000 nanoparticles per cubic centimetre -- the approximate difference between quiet and busy city streets -- increased the risk of brain cancer by more than 10 per cent.
"Environmental risks like air pollution are not large in magnitude â their importance comes because everyone in the population is exposed," author Scott Weichenthal from McGill University in Canada said.
"In a large city, it could be a meaningful number, particularly given the fact that these tumors are often fatal," he continued in the findings published in the journal Epidemiology.
The researcher said that the study provided strong evidence of the effect of toxic particles in the development of brain cancer, but it was important that other researchers replicated the findings in further experiments.
A study in 2016 established that carcinogens travelled through these toxic nanoparticles found in abundant quantity in human brains and damaged every organ, virtually every cell in the body.
Air pollution has also been linked with other effects on the brain, including reduced IQ, dementia, as well as, mental health issues in both adults and children, blamed for symptoms such as coughing, tearing, difficulty breathing, and angina immediately upon exposure. According to the World Health Organisation (WHO), air pollution is a "silent public health emergency" that affects over 90 per cent of the world's population.
The agency, terming air pollution a "bigger killer than tobacco", estimated over 8.8 million deaths â double than earlier estimated -- prematurely across the globe each year due to toxic air, more than malaria and HIV/Aids combined. Weichenthal said people living with pollution of 50,000/cm3 had a 50 per cent higher risk of brain cancer than those living with 15,000/cm3.
He said Toronto and Montreal, with pollution ranging from 6,000/cm3 to 97,000/cm3, were typical of major cities with harmful levels of air pollution. Professor Jordi Sunyer from the Barcelona Institute for Global Health, who was not involved in the research, said UFPs were directly emitted by combustion cars and several studies in animals showed UFPs were "more toxic than larger particles".
Professor Barbara Maher from the University of Lancaster in the UK said iron-rich nanoparticles called magnetite, an iron oxide, from traffic pollution were likely to be carcinogenic and were, therefore, a plausible possible cause of brain cancer.
"You are talking about millions of magnetite particles per gram of freeze-dried brain tissue - it is extraordinary," said Maher, adding that the substance could create reactive oxygen species called free radicals.
She continued that oxidative cell damage was one of the hallmark features of Alzheimer's disease, and the presence of magnetite was potentially significant because of its bioreactive nature.