This new study, which looks at four specific chemicals in the class, suggests that levels of one PFAS in rainwater around the globe often "greatly exceed" US drinking water advisory levels.

Soil around the world is similarly contaminated, evidence suggests.

The study's findings lead the authors to conclude that a planetary boundary has been crossed - that there simply is no safe space on Earth to avoid these substances.

"We argue here that we're not within this safe operating space anymore, because we now have these chemicals everywhere, and these safety advisories, we can't achieve them anymore," said Prof Ian Cousins, the lead author from Stockholm University.