Microscopic dust particles in the air in underground railways may be bad for people's health, a study suggests.
Research published in the journal Environmental Science and Technology suggests that the dust found in underground railways is different to that breathed in above-ground.
A team at the University of Southampton studied the particulate matter found in an underground station in Europe and found it to be unusually high in metals.
Working in steel mills and other environments that are rich in airborne metals has previously been shown to have a damaging effect on health and the latest findings suggest that sustained exposure to underground railways - such as by regular commuting or working below-ground - could also have implications for health.
Matt Loxham, a PhD student at the university, said: 'The high level of mechanical activity in underground railways, along with very high temperatures, is key in the generation of this metal-rich dust.
'These tiny dust particles have the potential to penetrate the lungs and the body more easily, posing a risk to someone's health.'
Mr Loxham added that more research is needed to determine the effects of this particulate matter on human health.