It’s 8:30am. I am setting off for my daily commute to work. I jump on the bike. A bulky GPS watch is squeezing my wrist. A thin black tube sticks up from behind the collar of my jacket. In the breast pocket sits a black box as thick as five smartphones.
This week, I am a guinea pig in a King’s College London study trying to assess how much air pollution the city’s residents inhale. Each of the study’s eight volunteers uses a different mode of transport to get to and from their offices in the city. I am the cyclist in the group. Another person rides a motorbike. The rest use a combination of buses, Overground and Underground trains, and walking.
“The detectors are measuring black carbon – a type of particulate matter which generally comes from diesel exhaust. It’s mostly related to exposure to traffic, but we can also find it on the Underground as it can come from brake wear,” explains Andrew Grieve, King’s College air quality analyst, who leads the study. “The participants are also wearing a GPS watch, which will allow us to tie their exposure exactly to their location so we can build a picture of how exposure on routes differs.”
The study runs over two weeks. During the first week the volunteers use their regular routes. After that, Grieve will analyse our data and propose a different, quieter and less polluted route to see how much we could reduce our exposure by avoiding the worst air hotspots.
Air pollution has been making headlines lately. According to a King’s College study published in 2015, some 9,500 Londoners die every year due to health complications triggered by inhaling nitrogen oxides and toxic microscopic particles less than 2.5 micrometres in diameter (PM2.5). A recent study by the US-based Health Effects Institute concluded that in 2015 over 4.2 million people around the world died prematurely because of fine particulate matter alone.
In urban areas, diesel engine exhaust is the number one source of nitrogen oxides and particulate matter, and many UK cities struggle to keep both in check.
With every breath they take, residents of London, Glasgow and Leeds suck in a dangerous cocktail of toxic chemicals and invisible particles containing cadmium, mercury, nickel or ammonium. Combustion engines spew out some particles directly, while others arise in reactions of various precursor pollutants. Some particles are so tiny they escape the body’s natural protection mechanisms and penetrate deep into the lungs.
“There is no doubt that particles get taken up when they are inhaled,” explains Professor Jonathan Grigg from Queen Mary University of London, a leading expert on effects of air pollution on human health. “They are taken up by B cells like macrophages and that would stimulate cells to produce inflammation cytokines and inflammatory mediators. That’s one explanation for the effect in the lung and also at distant sites of the body, because the mediators can get across into the bloodstream.”
Air pollution worsens allergies. Those with heart disease, asthma or lung cancer are more likely to experience complications or die during high air-pollution spells. Evidence is mounting that polluted air can contribute to a wide range of health problems with no direct link to breathing such as diabetes or neurological disease. A recent study by the University of Birmingham found every extra 10 micrograms of PM2.5 per cubic metre of air increases the risk of dying of any type of cancer in elderly people by 22 per cent. Pregnant women breathing highly polluted air are more likely to go into labour prematurely.
In addition to the monitored PM10s and PM2.5s, there is a large amount of the so-called ultra-fine particles, which air-quality networks do not regularly measure. Less than 100 nanometres in diameter (you could fit more than 25 across the width of a human hair), the ultra-fine particles make up a relatively low proportion of total particulate matter mass. If counted by particle, however, these are the most abundant.
The macrophages rid the body of some particles, but some stay in the lungs for the long haul.
“If you look at the lungs of people who are non-smokers, you can see accumulation of carbon in the tissues,” says Grigg, who recently founded Doctors Against Diesel, a campaign representing medical professionals calling for the abolition of diesel-powered vehicles in the UK’s cities.
Yet the lungs are probably not the only dumpsite for air pollution particles. Worryingly, multiple studies have indicated that ultra-fine particles might be able to cross from the alveoli to the bloodstream.
In September last year, a study published in the journal PNAS by Lancaster University Professor Barbara Maher and her team stirred up the scientific community. Maher set out to find whether magnetic air pollution particles could penetrate into the most important human organ – the brain.
“Wherever you have particles formed by combustion processes, heating or by friction from braking, you always produce some strongly magnetic particulates,” Maher explains.
“We can make magnetic measurements of airborne pollution and we can identify where air pollution is highest because of magnetic particles. Wherever you have more particulate pollution, you also have more magnetic particulate pollution.”
The connection between magnetic air pollution and the human brain intrigued Maher for one particular reason – she knew that deposits of magnetite could be found in brains of Alzheimer’s disease sufferers.
The widely accepted hypothesis that this magnetite is produced in the brain as a result of the organ’s chemistry going awry didn’t fully satisfy her.
“Knowing that there was so much magnetite available in the atmosphere in urban locations, my question was – could it be that some magnetite in human brains is not forming inside the brain, but is coming from external pollution sources?” says Maher.
“Many of these pollution particles are less than 150 nanometres in size so I thought it would be difficult for the body not to actually take up some of them.”
The Lancaster University professor ordered a set of brains from the Manchester Brain Bank and another bunch from Mexico City, which has struggled with extreme air pollution for years.
In the brains, Maher and her team found two types of magnetite particles – geometric crystalline particles corresponding with the metabolic hypothesis, but also a large amount of smooth spherical magnetite.