"Forever chemicals", technically known as per- and polyfluoroalkyl substances or PFAS, are everywhere.
The synthetic substances have been detected in various levels in cookware, building materials and cosmetics.
Now, Australia's National Health and Medical Research Council (NHMRC) has released a draft update to its 2018 guidelines around safe levels of PFAS in our drinking water.
It follows the US Environmental Protection Agency's National Primary Drinking Water Regulation in April this year, in which the agency set legally enforceable — and extremely low — limits on six types of PFAS.
So what are the draft guidelines, and how do they compare to the US?
PFAS chemicals were developed in the mid-20th century and resist water, stains, heat and flames.
They were commonly found in firefighting foam and waterproofing sprays, for instance.
But their durability also means they don't easily break down. They can hang around in the environment for decades.
They can also build up in living beings, including humans, over time — and concerns about how these chemicals may affect our health have intensified over the past few years.
(That said, the relationship between PFAS exposure and human health is not settled among scientists and public health experts.)
Of the thousands of types of PFAS available, the NHMRC's draft guidelines focused on four.
Their limits were based on the amount a person could consume in drinking water on a daily basis without any significant risk to their health.
Under the previous guidelines, the NHMRC recommended perfluorooctanoic acid (PFOA) levels be kept under 560 nanograms a litre (ng/L). The new draft recommends a limit of 200 ng/L.
Previously, safe levels of perfluorooctane sulfonic acid (PFOS) and perfluorohexane sulfonic acid (PFHxS) were capped at a combined total of 70 ng/L.
The new draft guidelines suggest PFOS levels be lowered to 4 ng/L and PFHxS limited to 30 ng/L.
The fourth and final PFAS included in the draft guidelines was perfluorobutane sulfonic acid (PFBS), which the NHMRC recommends limiting to 1,000 ng/L.
How does this compare internationally?
Different parts of the world have different accepted levels for each type of PFAS chemical.
The World Health Organization (WHO) maintains higher levels of some types of PFAS are safer in water than those in the new NHMRC guidelines, while in the US, acceptable levels of some chemicals, such as PFOA, are drastically lower.
NHMRC CEO Steve Wesselingh said this comes comes down to legislative differences in the US.
If a product is thought to be carcinogenic in the US — meaning it has the potential to cause cancer — "they have to reduce their levels down to zero, or as close to zero as they possibly can."
Australian guidelines, he said, were based on a threshold.
Safe levels are set at a point "where we believe there is no risk of that substance causing the problem identified, whether that be thyroid problems, bone marrow problems or cancer".
What do experts think?
The guidelines are now open for public consultation, with the final guidance due for release in April 2025. Until then, current guidelines remain in effect.
RMIT University chemistry researcher Oliver Jones said the proposed guidelines were "pretty sensible and within the ranges suggested by [most] other regulatory agencies around the world.
"While some PFAS have been linked to health effects, the concentrations needed to cause such effects are much, much higher than the levels typically found in Australian drinking waters."
He added that given the chemicals were so widespread, experts didn't know if water was the major source of PFAS exposure to most people.
For Denis O'Carroll, managing director of the UNSW Water Research Laboratory, the proposed guidelines don't include enough PFAS types.
"International organisations ... have serious health concerns about a much wider range of PFAS than those subject to Australian guidelines," he said.
While the NHMRC acknowledged in its guidelines "other PFAS of emerging concern may be present in Australian drinking water supplies", it stated it had a "defined scope for undertaking the review" with the potential for additional PFAS to be reviewed and revised in future.
It also advocated for the need for further research in the area, with which Professor O'Carroll agreed.
"Much more work is required to map out PFAS contamination in Australian source waters, and the government urgently needs to take a range of action," he said.
So what's next?
The new limits mean some of Australia's water supplies, which are currently considered safe, may not comply as of April next year if the draft guidelines stand.
That includes the Cascade water filtration plant in the NSW Blue Mountains, where PFAS was detected in levels that breach the proposed new standards.
University of Sydney water quality researcher Stuart Khan said many jurisdictions would be forced to take action to ensure their supplies were compliant.
"I think there will be lots of communities that are out of compliance with that, and we will need to put in solutions."
But he said there currently wasn't enough available data to know the extent of the problem.
The question now turns to who will wear the costs of implementing technology that removes the chemicals: the taxpayer, the companies who manufactured the chemicals, or both.
"It could well be a very expensive problem," Professor Khan said.
"We tend to talk about the 'polluter pays' principle, that whoever causes the pollution should be paying the cost of remediating that pollution and that would be a just outcome."
US-based companies such as 3M and DuPoint manufactured the product that was in everyday products and firefighting foam used in Australia for decades.
NSW water minister Rose Jackson said the government was looking at legal options.
"We do want to make sure that the cost to the community for the pollution is borne by the polluter."