International pollution regulators are moving to control the use of toxic chemical compounds in motor vehicle tyres.
Modern tyres are a cocktail of chemicals that end up as shed tyre dust. These tiny particles spread to waterways, and potentially the lungs of people on, or close to, roads.
Many tyres are manufactured with a chemical called 6PPD-quinone, which helps resist degradation and cracking.
But the discovery that a compound called 6PPD is responsible for the collapse of salmon populations on the US west coast set alarm bells ringing.
Now the US Environment Protection Agency (EPA) has signalled that it is investigating the toxicity of 6PPD, a step that could lead to a ban on the substance.
Until recently regulators were focused only on the harm from tailpipe emissions.
The European Union's upcoming Euro 7 emission regulations will set standards for tyres for the first time.
Manufacturers Michelin, Continental and Pirelli are pursuing alternatives to 6PPD but want higher tyre standards so that US and Chinese tyre makers are forced to comply with any new pollution controls.
One manufacturer, Enso, is making tyres for EVs that are designed to shed less rubber/plastic.
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