(ORDO NEWS) — The particles found are so small that they were probably underestimated in the works on the pollution of the world’s oldest subway system.
According to scientists from the University of Cambridge, the London Underground is polluted with ultra-fine metal particles, small enough to enter the human bloodstream.
The researchers conducted a new type of pollution analysis using magnetism to study dust samples from underground ticket offices, platforms and operator cabins.
Harm to health in the subway
The British team found that the resulting samples contained high levels of an iron oxide called maghemite.
Since iron takes time to oxidize to maghemite, the results show that the pollution particles are suspended for a long time due to poor ventilation in the subway.
Some particles are as small as five nanometers in diameter: small enough to be inhaled into the bloodstream, but too small to be captured by conventional pollution monitoring methods. It is still unclear exactly what health risk these particles pose.
It is assumed that periodic dust removal from underground tunnels, as well as magnetic monitoring of pollution levels, can improve air quality throughout the network.
Worth noting: The London Underground carries 5 million passengers a day.
“The abundance of these very small particles was amazing,” said lead author Hassan Sheikh from the Cambridge Department of Geosciences.
“The magnetic properties of iron oxides change dramatically as the particle size changes. In addition, the size range in which these changes occur is the same as when air pollution becomes a health hazard.”
“If you want to answer the question of whether these particles are harmful to health, you first need to know what these particles are made of and what their properties are,” Sheikh said.
“Our methods give a much more accurate picture of pollution in the metro, and standard pollution monitoring does not give a good picture of very small particles,” the study authors write.
The scientists reported that due to poor ventilation in subways, iron-rich dust can be re-weighed into the air as trains arrive at the platforms, making the air quality worse than in ticket halls or in driver’s cabs.
Given the magnetic nature of airborne dust, the researchers suggest that an effective removal system could be magnetic filters in ventilation, cleaning tracks and tunnel walls, or placing screen doors between platforms and trains.
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