When a London Underground train hits the brakes, its wheels grind against the tracks, throwing up tiny specks of metal and other particles. There’s concern that this ‘Tube dust,’ could be damaging the health of passengers and workers on the network.
Yesterday, the London Assembly’s environment committee met to discuss the issue, which first started gaining attention in the 1990s, but has been given new impetus by Sadiq Khan’s efforts to clean up the city’s air since taking over as Mayor in 2016.
Airborne particles are ranked according to their size, with those under 2.5 microns (classed as PM2.5) generally considered the most potentially damaging to health because they’re small enough to get deep into the lungs, and then into the bloodstream and internal organs. The levels of PM2.5 particles on the Tube are between 30 and 40 times higher than above ground, but that doesn’t necessarily mean it’s more dangerous.
Above ground, especially in London, the air is full of known carcinogens, nitrogen dioxide and carbon monoxide from exhaust fumes, which aren’t present below the surface. Down there, it’s more likely to be iron oxide – which may or may not be harmful. “It’s made of a very different substance,” says Dr Matthew Loxham, who researches air pollution at the University of Southampton. “Above ground it’s car exhausts, heating systems, industrial outputs. Underground it’s from the trains themselves – erosion from the wheels and brakes, and the rails. It’s chemically different so you would expect different effects.”
A report published in 2003 found no evidence of harm from Tube dust, but a new investigation – which was published in January, and which Loxham was a co-author on – concluded that there was not enough evidence to say whether Tube dust was or wasn’t harmful and that further research was needed. “The implication from 2003 was that it’s not really a problem, now they’re saying that they’re not sure whether it’s a problem,” says Simon Birkett, the founder and director of Clean Air in London.
Loxham says there’s a lack of evidence either way. Studies on the Stockholm underground have found that there are detectable effects on the levels of certain chemicals in the lung and blood after two hours underground, but no major health implications. Long-term studies of drivers, also in Stockholm, found that they were not more likely to suffer from lung cancer or heart disease than the general population. It’s worth noting that most studies that have been done on humans have been conducted on healthy people. It’s possible that Tube dust could have a more detrimental effect on the very young or old, or those with pre-existing conditions such as asthma or other respiratory problems.
“There’s no good evidence that it’s much more harmful than above ground pollution,” says Loxham. “What we do know is that their chemistry means that [these particles] are probably not particularly good to have in your body for a long time. What you’ve breathed in for your commute to work will be in your body for several months at least.” Studies of cells grown in petri dishes in the lab that are exposed to Tube dust have found increased levels of oxidative damage and inflammation when compared to surface air, although the latter is more likely to have bacterial contamination. “It’s a double-edged sword,” says Loxham, who stresses that very different results may be obtained from studies with real people.
Transport for London has commissioned new research into the long-term effects of Tube dust in conjunction with King’s College London. It’s looking through its pension records over the past 50 years to see if it’s staff are more likely to suffer from certain ailments, and has been measuring particulate levels across the network using fixed and wearable monitors. It is also carrying out testing on the Waterloo & City and Bakerloo lines to look at new ways of minimising the dust. “We spend around £60 million every year cleaning our trains, stations and tunnels and closely monitor dust levels on the Tube to ensure that particle levels are well within Health & Safety Executive guidelines,” says Jill Collis, TfL’s director of health, safety and environment.
It’s also attacking the dust problem (if it is a problem) in four different ways. It’s modifying its trains to run on AC motors instead of DC ones, which use carbon brushes that gradually wear down and produce dust; and fitting new braking systems that will reduce wear on pads and discs. It also changing the way it does construction work, by isolating maintenance areas to reduce the amount of dust released, and breaking up concrete using hydraulic splitters instead of jackhammers. It’s improving ventilation, which will have the added benefit of making the Tube more bearable in summer.
Finally, it’s working to stop particles being dredged up from tunnel floors and walls when trains go past. Tunnels are currently cleaned with vacuums and brushes, while those on the Waterloo & City line have been treated with a glue-like solution that suppresses and clumps dust together to make it easier to clean. TfL is also investigating electrostatic filters that could capture dust and metal particles. They’re more efficient, but expensive to install – they could be a good option for areas where there’s a particularly bad dust problem – generally the oldest stations on the deepest lines, such as the Northern Line.
Redesigning stations could help. The highest levels of particles are found where the trains meet the platforms, and there’s some evidence that having barriers between the platform and the track – as on the Jubilee line – can reduce the exposure to dust for passengers and staff. Until then, Birkett says people should “think twice” about using old, deep lines regularly if they’re susceptible to breathing difficulties. “I think there needs to be more advice, more information and more research really quite urgently,” he says.
This article was originally published by WIRED UK
