It's that no-one knows how many there are, let alone the scope of their impacts on human and environmental health.

The Australian government, in its public health advice, talks about "more than 4000". The National Measurement Institute recently told a contamination conference it's more like 12,000.

Other researchers say it could be much higher because once PFAS chemicals are out in the world, they can create complex mixtures of intentionally-produced and unintentionally-generated PFAS compounds.

One certainty is that the man-made chemicals are now whirling around the planet and present in the bodies of pretty much every human, even those yet to be born.

Less than a fortnight ago, a team of researchers announced PFAS chemicals were detected in literally all of the 30,000 umbilical cord blood samples used in 40 different studies over the last five years.

After more than 50 years of broad use, in everything from food packaging and cookware to paint and industrial products, PFAS chemicals are now ubiquitous.

At a recent conference in Adelaide, distinguished veteran science writer Julian Cribb described a global chemical "tsunami" in which PFAS features heavily.

"They travel on the wind, in water, attached to soil particles, in dust, in plastic fragments, in wildlife, in food, drink and trade goods, in and on people.

"They combine and recombine with one another, and with naturally occurring substances, giving rise to generations of new compounds, some more toxic, others less so. Most totally unknown.

"They leapfrog around the planet in cycles of absorption and re-release known as the grasshopper effect."

With the genie out of the bottle, and no way to put it back, nations are left to figure out what the health consequences might be, how to manage existing contamination, and how to turn off the tap.

Within that context, the federal government has just released the third version of its national plan to manage environmental risks in Australia.

The draft opens with an acknowledgement of the PFAS family's unusual chemical properties, of the "uncertainties associated with potential risks", and the need for a precautionary approach.

The purpose of the document is to provide practical guidance on the management of PFAS, with a focus on preventing and managing contamination.

But when widely available analytical techniques generally only measure "up to 33 of the more than 4,700 PFAS compounds known to exist", and there are still thousands of PFAS that can't be measured, that's a tall order.

Scientists say the end game must be making sure PFAS chemicals are not in products to begin with.

Sarah Dunlop is head of plastics and human health at philanthropic Minderoo Foundation, which is pushing for the tighter regulation of chemical producers and plastic manufacturers.

She says the current situation is an "after-the-crime" approach that leaves scientists and governments scrambling to work out what's out there, in what concentrations, how dangerous it is, how to clean it up, and how to regulate it.

"It should be the other way around," she says. "They (chemical producers) should give a full disclosure at the time of the making of the product."

Crucially, she says, that must include the spectra of their chemicals, the fingerprints that allow substances to be traced back to their makers and the right regulatory settings to be held accountable for them.

"At the moment we have to hit in the dark," Professor Dunlop says.

"Often they don't provide the spectra ... because it's proprietary information.

"The other thing they don't do is provide the chemical standard, which you use in your measurement techniques to make sure you really know what you are measuring."

The real world consequences of passing the PFAS problem down the line were on full display at a recent panel discussion involving Australian water utility companies, who fear they will be among those left holding the baby.

For years, those companies have collected sewage sludge at their treatment plants, dried it, and trucked the nutrient-rich fertiliser to farms that feed the nation.

The problem is the material, called biosolids, contains traces of PFAS and some are readily taken up, and can build up, in the things humans eat.

And humans are poor at shedding PFAS.

The new plan has for the first time set strict limits for PFAS concentrations in biosolids, but researchers say they're about 75 per cent lower than average PFAS loads recently found in samples from 19 treatment plants.

One view is that the limits will effectively end disposal of the waste on agricultural land.

Geoff Latimer writes Hazardous Waste in Australia reports for the federal government and says the limits are courageous and world leading.

The wastewater industry says it's all for a precautionary approach and the jury is still out on whether the new biosolids limits can be met. But if they can't, the industry will face higher-cost solutions for its waste, despite having no hand in creating the problem.

"We're just copping these PFAS compounds at the end of a treatment plant and we don't seem to be looking at other sources that are coming into the country," says Kelly Hopewell, who chairs the Australian and New Zealand Biosolids Partnership Technical Committee.

She says the solution must focus on making sure PFAS chemicals are reserved for essential purposes and not in things like make-up. Consumers also need to know what's in the products they use every day.

"I try and look at what I buy and you can't even tell ... and I've done science. There are consumers that would probably prefer not to use PFAS products, but it's almost impossible to work out if you are or not."

In terms of human health risks, governments vary in their tone.

The European Union's environment agency says PFAS can lead to health problems such as liver damage, thyroid disease, obesity, fertility issues and cancer.

The US Environmental Protection Agency says certain PFAS are known to cause human health risks and points to studies showing certain exposure levels may heighten cancer dangers, hurt fertility and birth weights and accelerate puberty.

Australia appears more cautious, referencing "fairly consistent reports of an association with several health effects" but notes they're generally small and within normal ranges for the whole population.

It also says there's limited to no evidence of human disease or other clinically significant harm resulting from exposure at this time, and PFAS levels in food and water are at low, safe levels.

For Prof Dunlop, from the Minderoo Foundation, the fixation with causality is unhelpful and she says there's a convincing bank of evidence that demonstrates the need to act decisively.

"In an ideal world you'd have it so tightly regulated in the beginning that these sorts of chemicals would never have been used in the first place," she says.

"The problem is they are out there. They've all got this rearguard action to control them and stop the health impacts, which are significant."

The federal Department of Climate Change, Energy, the Environment and Water says it's working with the states and territories to implement a new standard for the management of industrial chemicals.

Australia is also working towards ratifying the listing of the most researched types of PFAS under the international Stockholm Convention, which seeks to guard against long-lived pollutants that accumulate in animals.

Australian Associated Press