PFAS stands for "per- and polyfluorinated alkyl substances" - but if you're not a chemist, that probably doesn't help too much.

"Fluorinated" means that PFAS molecules contain the element fluorine, and the "per or poly" means that there are a lot of fluorine atoms. In organic chemistry, "alkyl" refers to a chemical group containing at least one carbon atom bonded to two or three hydrogens.

"PFAS resemble naturally occurring hydrocarbon chemicals, except that the halogen element fluorine is taking the place of multiple or all of the hydrogen atoms in the structure," explains Rolf Halden, a professor at the Biodesign Center for Environmental Health Engineering at Arizona State University, US.

PFAS are also fully synthetic - meaning they're not found in the natural world. Fluorinated chemicals in general are very uncommon in nature.

This quality was seen as an advantage in the past, says Mark Jones, a retired industrial chemist and industry consultant who formerly worked at the Dow Chemical Company.

"Forty years ago, when I first encountered fluorination in an organic chemistry class, it was talked about as an example of something that is fully synthetic ... therefore, they're going to be safe, because they will be non-interactive with biology," he recalls.

Since they were first synthesised in the 1940s, new PFAS have been invented over time and now number in the thousands. Perfluorooctanoic acid (PFOA) - which has been used in carpeting and upholstery, textiles and clothing, and fire fighting foam - and perfluorooctane sulphonate (PFOS) are two older PFAS that have been widely used and studied.

There's surprisingly little consensus on exactly which chemicals should be classified as PFAS, though. A 2022 study from Boston University highlighted how different US regulatory agencies and non-governmental organisations defined PFAS in different ways. For instance, some pharmaceuticals that contain fluorine are considered PFAS under some definitions, but not others.

"This issue of defining [PFAS] is really insidious," says Jones, who recently wrote about this topic for the American Chemical Society's Industry Matters newsletter. He describes a tension between defining PFAS as a list of specific chemicals, or more broadly based on the presence of particular chemical characteristics.

"It's kind of a fun game to play with chemistry friends: 'is 1,4-difluorobutane a PFAS or not?'" Jones jokes. "Most people don't get it right."

PFAS are versatile chemicals. They're found in consumer products like food packaging, cookware, clothing, furnishings, camping gear, dental floss, and stain removers.

A lot of this is down to their useful chemical properties. For example, PFAS' resistance to heat is handy for coating non-stick pots and pans. PFAS can make textiles and other products water- and stain-resistant too.

"We think of most molecules being either hydrophobic or hydrophilic - being attracted to water or to oils," explains Stuart Khan, a professor in the School of Civil and Environmental Engineering at the University of New South Wales (UNSW). "In fact, PFAS can repel both water and oil."

A US study published last week in the journal Environmental Science and Technology found that several children's apparel, bedding and furnishing products contained PFAS or molecules that could be converted to PFAS when oxidised in the body or in the environment. The study was partly funded by the Silent Spring Institute, an organisation that researches the links between chemicals in the environment and women's health.

Another well-known use of PFAS is in firefighting foams - particularly for liquid fuel fires.

"You don't want to spray water on a fuel fire, because it'll just splash more fuel and fire everywhere," says Khan. Instead, PFAS foams sit on top of fuel fires and smother them by blocking access to oxygen.

The hardiness of PFAS is a double-edged sword. They're very resistant to both chemical and biological degradation - hence the not-so-fond nickname of "forever chemicals". While the use of PFOA and PFOS has been phased out in many jurisdictions, these chemicals are still all around us, and will be for the foreseeable future.

"We all have PFAS in us," says Michael Manefield, also a professor in Civil and Environmental Engineering at UNSW. "It's everywhere in the environment ... it's just this slimy film that we've put over everything, really."

According to the US Environmental Protection Agency (EPA), PFAS can enter our bodies through food and drinking water, consumer products and packaging, and breathing air or dust.

Locations like airports and military bases that host firefighting training can have high levels of PFAS nearby.

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"Often the PFAS foams end up on the ground, and eventually after rainfall they soak into the ground and end up in the groundwater table," says Khan. "That's why we have lots of problems now with contaminated groundwater supplies in many parts of Australia."

But should we be worried about having PFAS in our bodies?

"There's still quite a lot unknown about the public health impacts, especially from environmental exposure," says Khan.

According to Manefield, PFAS are not as harmful as some other pollutants, such as dioxins - but they're not necessarily benign either.

Halden is more concerned. "We know enough about PFAS chemistry to understand that it is incompatible with our health and the health of the planet," he says.

PFAS haven't been shown to directly cause any specific diseases in humans. However, results from epidemiological studies and research in non-human animals have linked PFAS exposure to health problems like increased risk of certain cancers, increased cholesterol, and impaired immune function and vaccine response. Much of the strongest evidence comes from studies of PFOA and PFOS, which have been around for longer and studied more.

Recently, concerns have been raised that higher PFAS exposure may reduce vaccine efficacy and make people more vulnerable to COVID-19.

Ultimately, our overall understanding of the health and environmental impacts of PFAS is still relatively limited. Difficulties include the number of different PFAS, the challenges of pinning down causation when looking at epidemiological associations, and the fact that research in non-human animals may not translate to us.

However, many experts and government agencies take the precautionary view that we should reduce our exposure to PFAS where possible and limit their use.

While PFAS are difficult to break down, we do have ways to remove them from water and soils. Ion exchange water treatment plants, such as that soon to open in Katherine, in the Northern Territory, use a special resin that adsorbs the PFAS out of the water. We can also "wash" soils by separating out the soil components that PFAS are bound to. However, these methods don't destroy PFAS, but simply move it out of the environment.

"We're accumulating this ion exchange resin that's contaminated with PFAS, which one day is going to have to go somewhere," says Khan.

Manefield adds that PFAS-contaminated resin or soil can be incinerated, but this uses a lot of energy and is expensive. There's also ongoing research into immobilising PFAS in soils using activated carbon, which stops the PFAS from further spreading around the environment. Again, it's not a permanent solution.

Some scientists are working on better ways to actually degrade PFAS, using bacteria and chemical catalysts. The difficult first step is to break the very strong chemical bond between carbon and fluorine.

"Our focus is removing these fluorine atoms that are really, really tightly stuck onto the carbon backbone," says Manefield. "If you think about PFAS like a little armadillo, the fluorine atoms are the armour around an organic backbone."

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Interestingly, one of promising molecules that can catalyse the removal of fluorine is one you might have heard of: vitamin B12. Catalysts work by lowering the energy needed for a chemical reaction, such as breaking a bond.

Bacteria already use vitamin B12 to remove chlorine atoms from molecules. Because fluorine is just above chlorine in the periodic table, they share similar chemical properties.

"You can take a strong reductant like zinc, and get it to pass electrons to vitamin B12," explains Manefield. "Vitamin B12 then passes those electrons to the carbon-fluorine bond, which removes the fluorine."

Once the fluorine is gone, it's much easier for bacteria to degrade the resulting by-products of PFAS.

Other UNSW researchers are developing and testing new catalyst molecules that are chemically similar to vitamin B12, but more effective at breaking down PFAS.

PFAS are used widely because they're, well, useful. Can we learn to replace PFAS, or do without them?

"In many cases, it is difficult to find a one-on-one, drop-in replacement for them," says Jones. "For example, Teflon really has very unique properties that are difficult to reproduce."

On the other hand, he says, we could probably simply learn to live without greaseproof coatings on food packaging.

"And I think you'd have everything in between ... I believe that intelligent people will innovate and move away from these types of materials if they're recognised to be a hazard," Jones concludes.

According to Halden, we need to ask ourselves some tough questions about whether the benefits of continuing to use PFAS outweigh the risks.

"What is a legitimate use of this chemistry, and what is the carrying capacity of the planet and the biosphere for these chemicals?" he asks.

Both Khan and Manefield highlight that systemic changes are likely needed to prevent the current issues with PFAS from repeating themselves over and over.

"How do we put systems in place so that we don't end up with this problem again with the next group of chemicals?" asks Khan.

"We really need to get ahead and get better at planning for what some people call 'green chemistry' - producing chemicals that have all the useful properties that we need, but are either going to be benign in the environment or break down quickly."