London Underground has high levels of toxic air pollution

High levels of potentially toxic iron particles have been found in the air on London Underground, a new study by the University of Cambridge has found. The air pollution includes metal particles that are small enough to enter the human bloodstream.

Scientists looked at samples of air from ticket halls, platforms and train carriages on several Underground lines. Using magnetic detection technology, they found high concentrations of a form of iron oxide called maghemite. The submicroscopic particles had previously gone undetected, as their minuscule size of five nanometres (billionths of a metre) means they don’t show up on normal pollution-monitoring systems.

Hassan Sheikh, author of the paper showing the results of the study, said: ‘The abundance of these very fine particles was surprising.’

Although the research didn’t look into the health effects of maghemite particles on the tube, other studies suggest they could be harmful to passengers. Exposure to nanoparticles has been linked to serious health risks such as lung and heart disease, and brain damage. ‘The abundance of ultrafine particles identified could have particularly adverse health impacts as their smaller size makes it possible to pass from lungs to the bloodstream,’ the researchers said.

The tiny iron particles are created when trains’ wheels create friction with brakes and the rails. Most of the particles found were oxidised, meaning they could have been in the tunnels for a while before they were blown up in the air.

The good news is that the iron dust can be reduced by washing the tracks and tunnel walls, or TfL could even put magnetic filters in the ventilation systems, though this would require new expensive equipment. Putting screens between platforms and trains, as on the Jubilee line, could also help.

TfL said it was reviewing the study ‘to ensure it fully understands them and how to reduce the levels further’.

Lilli Matson, TfL’s chief safety, health and environment officer, said: ‘We periodically collect samples of tube dust and analyse its content to track levels of potentially harmful materials, including iron, chromium and nickel. Analysis has shown that quantities of these materials are well below the legal limits in environments such as the tube.

‘We are going further and have developed a number of innovative new cleaning regimes. This includes the use of industrial backpack dust cleaners, which are one part of our multimillion pound tube cleaning programme.’

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