The phenomenon of 'tyre mountains', where used car tyres are piled up awaiting either landfill or incineration, has given any process that aims to recycle or repurpose our synthetic rubber cast-offs a green tint.
One use for the tyres that has been widely promoted is to shred them and use them as a mulch, either in horticulture or for children's play areas.
But now the US Environmental Protection Agency has launched an investigation into whether using chipped tyres in playgrounds is safe.
Made from crude oil, tyres naturally contain heavy metals such as cadmium, chromium, lead and mercury, as well as arsenic and an array of hydrocarbons.
The new EPA research will examine whether children are at risk of either inhaling or ingesting the compounds from the chippings.
'Where we are right now is, we just don't have a recommendation,' an EPA spokesman told Waste and Recycling News. 'I wish we did.'
News of the study was released by the advocacy group Public Employees for Environmental Responsibility, which claims that government bodies are issuing contradictory advice on the safety of the tyre chippings.
The tyre recycling industry maintains that previous scientific studies have shown the chippings to be safe.