Environmentalists are demanding urgent investigations into air pollution on the Glasgow subway after a snapshot survey by the Sunday Herald's New Era magazine discovered passengers were breathing in tens of millions of tiny metallic particles that might damage their health.

The investigation found levels of pollution by microscopic particles on the subway – known in the city as the Clockwork Orange – up to 10 times higher than on the streets outside and up to eight times above the World Health Organisation's recommended daily limit.

Experts estimate passengers on the subway for 45 minutes could each inhale 60 million particles. Anyone spending the same amount of time at one of Scotland's busiest railway stations could breath in 10 million particles, or 2.5 million on a Glasgow-to-Edinburgh train journey.

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Because the particles in the electricity-powered subway are likely to be mostly iron oxide from the grinding of wheels against rails, they may not be as dangerous as the sooty particles emitted by trains or diesel-powered cars. But experts and campaigners agree the risks require serious examination.

Dr Richard Dixon, the director of Friends of the Earth Scotland, described the concentrations of particle pollution on the subway as alarming. He called on Strathclyde Partnership for Transport (SPT), which runs the subway, to take the results very seriously.

"This problem urgently needs further investigation. Confirmation of these results would require decisive action to reduce pollution."

Alison Johnstone MSP, environment spokeswoman for the Scottish Greens, urged SPT to respond urgently to New Era's findings. "They should ensure that Glaswegians don't find they escape polluted air on the streets only to suffer even more severe problems underground," she said.

Air pollution was measured on a 40-minute subway journey on the afternoon of Friday, May 10. A portable, state-of-the-art monitor detected concentrations of between 40 million and 80 million particles per cubic metre of air.

In Glasgow Central station levels peaked at just in excess of 40 million, and at Edinburgh Waverley station they just topped 10 million. In Glasgow city centre they once registered at more than 10 million, but were otherwise lower.

The air pollution expert who helped with the monitoring, Dr Sean Semple from the University of Aberdeen, agreed the high levels in the subway required investigation. Concentrations of tiny particles can be much higher in cars, trains, buses, railway stations and other enclosed spaces than outdoors, he pointed out. "These tend to be the places where we spend most of our time and yet they are the environments that we know least about in terms of air quality," he said.

Air pollution has been linked to asthma, heart attacks and strokes, and blamed by Government experts for causing 29,000 early deaths every year in the UK.

However, SPT described the Sunday Herald survey as sensational and alarmist. It complained it had not been shown the full scientific evidence, or details of how the survey was conducted.

"There are a huge array of factors during even the shortest journey which can impact on pollution monitors, and it is not clear from this snapshot if that has been taken into consideration," said an SPT spokeswoman.

"However, SPT takes both passenger and staff health very seriously and uses respected industry expertise to guide us on best practice in the subway."

This weekend, New Era also publishes the first ever maps revealing the most polluted streets in Glasgow, Edinburgh and Perth. Large parts of the city centres are shown to breach safety limits.

Local authorities have identified 13 urban areas across Scotland where air pollution is a problem. As well as Glasgow, Edinburgh, Dundee, Aberdeen and Perth, these include Bearsden, Paisley, Falkirk, Broxburn and Dunfermline.