London's Underground is still polluted, but the dust does not pose a serious risk to health
The study shows that although polluted and extremely dusty, London's underground transport system has much lower levels of more hazardous ultrafine particles than are found in the air near the capital's roads.
Instead, the system harbours larger and heavier particles that are made of iron, rather than carbon, while harmful minerals are well below levels permissible in the workplace.
The research team analysed the amount and size of dust particles at several different station platforms and in drivers' cabs on the London Underground. They calculated the likely levels of exposure to particulate matter by staff and passengers, and tested it for levels of toxicity.
They found that compared with outdoor air the dust levels were high in terms of mass, but low in terms of particle number, and were somewhat lower in drivers' cabs than on station platforms.
Two thirds (67%) of the dust comprised iron oxide, with a further 1 to 2% quartz, plus traces of other minerals, such as chromium, copper, zinc and manganese, which were too low to pose a health risk.
The researchers judged that, weight for weight, the risks from Underground dust are much more comparable to iron oxide welding fume than to particles in outdoor air. But the exposure is much lower than would be required to cause lung disease.
The safe occupational welding fume exposure level is set at 5000 ug/m3 and workers on the London Underground could expect to be exposed to maximum levels of 200 ug/m3 over an 8 hour shift.
Commuters using the Underground for two hours every day would boost their particulate matter levels by 17 ug/m3 over 24 hours, but this would comprise iron oxide rather than ultrafine particles.
The authors conclude that the risks of serious heart or lung disease are very low for those working or travelling on the London Underground, and that choice of travel should be based on cost and convenience, not on the risks to health from inhaling particles.. But they say that efforts to eliminate the dust should continue, "since the dust is not without toxicity."
[The London Underground: dust and hazards to health Occup and Environ Med 2005; 62: 355-62]
[The London Underground: time for a thorough clean-up? Occup and Environ Med 2005; 62: 334] (Editorial)
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