This February, the European Chemicals Agency (ECHA) in Helsinki published a proposal that could lead to the world’s largest-ever clampdown on chemicals production. The plan, put forward by environmental agencies in five countries — Denmark, Germany, the Netherlands, Norway and Sweden — would heavily restrict the manufacture of more than 12,000 substances, collectively known as forever chemicals.

These chemicals, per- and poly-fluoroalkyl substances (PFASs), are all around us. They coat non-stick cookware, smartphone screens, weatherproof clothing and stain-resistant textiles. They are also used in microchips, jet engines, cars, batteries, medical devices and refrigeration systems (see ‘‘Forever chemicals’ in Europe’).

PFASs are extraordinarily useful. Their fluorine-swaddled carbon chains let grease and water slide off textiles, and they protect industrial equipment from corrosion and heat damage. But their strong carbon–fluorine bonds cannot be broken apart by natural processes. So after PFASs escape from factories, homes and vehicles into the environment¹, they add to a forever-growing pollution problem. The February proposal estimates that tens of thousands of tonnes of these chemicals escape annually in Europe alone.

Several PFASs are now known to be toxic. They have been linked to cancers and damage to immune systems, and are now banned under national and international laws. Most PFASs, however, have not yet undergone toxicology assessments or been linked to health harms. But officials at the agencies that submitted the plan to the ECHA say their persistence means they will inevitably build up until as-yet unknown safe thresholds are crossed.

“We see that there is an unacceptable risk now,” says Richard Luit, a policy adviser at the Dutch National Institute for Public Health and the Environment in Bilthoven.

There’s no prospect of an instant ban. The ECHA is consulting on the idea before it takes a position. European legislators are unlikely to have a plan to vote on before 2025, and even the current proposal offers grace periods — of more than a decade in some cases — to allow manufacturers to develop alternative materials or systems. Several permanent exemptions are also offered (including for fluorinated drugs, such as Prozac, and for materials used to calibrate scientific instruments).

But taken as a whole, the idea is to shrink PFAS use to a minimum. “We are asking society to make quite a shift,” says Luit. “We are asking to reverse all of it, go back to the drawing table and invent alternative solutions.”

Change is already under way for consumer use of PFASs. The notoriety of the toxic examples has pushed more than 100 companies and brands, including Apple, to pledge to phase out PFASs, even before it’s clear whether other materials can do the same job.

For industrial users, however, the idea of life without PFASs is a more shocking prospect. So February’s proposal has ignited debate about which uses of fluorinated chemicals the world could leave behind — and which must stay.

Three forms of forever

A peculiarity with fluorinated compounds, researchers say, is that some kill, whereas others are safe enough for use in medical products. “Fluorine compounds are really, really, incredibly strange in this regard,” says Mark McLinden, a chemical engineer at the US National Institute of Standards and Technology in Boulder, Colorado. “Certain fluorine compounds are incredibly toxic. And then you have things like [the gas] R134a, which is benign enough that you’re shooting it directly into your lungs in asthma inhalers”.

Forever chemicals come in three distinct forms (see ‘Fluorinated world’). The notoriously toxic kinds are fluorosurfactants. These molecules resemble those in soap, made of two parts: carbon chains with fluorine atoms wrapped around them, that repel everything, and a water-loving portion at one end of the chains that allows the molecules to dissolve in water.

After some of these molecules were linked to serious health harms and widespread water pollution, individual substances were banned or severely restricted internationally: first PFOS (perfluorooctanesulfonic acid) in 2009, then PFOA (perfluorooctanoic acid) in 2019, and, last year, PFHxS (perfluorohexanesulfonic acid). Manufacturers have moved on to other fluorosurfactants, many of which lack toxicity studies.

The February proposal suggests phasing out all the fluorosurfactants at once to avoid “regrettable” substitutions, says Jona Schulze, a staff scientist at the German Environment Agency in Dessau-Roßlau.

But the proposal goes further than that. The five agencies behind it have adopted the Organisation for Economic Co-operation and Development’s definition of PFASs: any molecule with a carbon atom in a chain that’s bonded to two fluorine atoms (or, if at the end of the chain, three). Restrictions under this expansive definition cover the other two kinds of forever chemicals.

There are the fluoropolymers, the plastic-like form that most consumers encounter. The most famous example is Teflon, or polytetrafluoroethylene (PTFE), long carbon chains wrapped in fluorine atoms. A Teflon-based coating makes frying pans non-stick; in medical products, it helps catheters to glide through the body, safeguards implants from deterioration, and, coated on the inside of bottles and blister packs, prevents drugs from interacting with their glass or foil containers. Stain-resistant textiles use a variant of this structure, in which fluorine-wrapped side chains hang off a main carbon chain.

How the US will remove ‘forever chemicals’ from its drinking water

The third category of PFASs is made up of small, light fluorocarbon molecules that generally exist as gases or liquids. R134a, the asthma-inhaler propellant, is also a common refrigerant in refrigerators and mobile air-conditioning systems, for instance. Sensitive equipment that is prone to overheating, such as servers in a data centre, can be submerged in fluorocarbon fluids that cool the apparatus without shorting its circuits or running the risk of fire.

Although fluoropolymers and fluorocarbons haven’t been shown to harm consumers directly, the problems come when they’re produced and when their useful lives end. Fluoropolymers are created using toxic fluorosurfactants, which pollute water and soil around fluoropolymer plants worldwide. Some researchers also suspect that fluoropolymers might, during their long lifetimes, shed fragments small enough to be ingested, as is known to happen with microplastics (Nature 593, 22–25; 2021). As for the fluorocarbons, some are powerful greenhouse gases, and others break up into a small-molecule PFAS that is no