If you follow the scientific news, you will probably see research on PFAS (where they are found, where they come from, and their impacts on health and the environment) every week. But what are these chemicals actually, and why is there so much interest in them?
What are PFAS?
PFAS stands for “Perfluorinated and Polyfluorinated Alkyl Substances,” but if you’re not a chemist, that probably won’t help you much.
“Fluorinated” means that PFAS molecules contain the element fluorine, and “per or poly” means there are many fluorine atoms. In organic chemistry, “alkyl” refers to a chemical group that contains at least one carbon atom bonded to two or three hydrogens.
“PFAS resemble natural hydrocarbon chemicals, except that the halogen element fluorine is replacing several or all of the hydrogen atoms in the structure,” explains Rolf Halden, a professor in the Center for Biodesign for Environmental Health Engineering at UCLA. Arizona State University. US.
PFAS are also fully synthetic, meaning they are not found in the natural world. Fluorinated chemicals in general are very rare in nature.
This quality was considered an advantage in the past, says Mark Jones, a retired industrial chemist and industry consultant who previously worked at the Dow Chemical Company.
“Forty years ago, when I first came across fluoridation in an organic chemistry class, it was talked about as an example of something that is completely synthetic…so they will be safe, because they will not interact with biology. . ”She remembers.
Since they were first synthesized in the 1940s, new PFASs have been invented over time and now number in the thousands. Perfluorooctanoic acid (PFOA), which has been used in carpet and upholstery, textiles and clothing, and firefighting foam, and perfluorooctane sulfonate (PFOS) are two older PFASs that have been widely used and studied.
However, there is surprisingly little consensus on exactly which chemicals should be classified as PFAS. A 2022 Boston University study highlighted how different US regulatory agencies and non-governmental organizations defined PFAS in different ways. The study found that some fluoride-containing pharmaceuticals are considered PFAS by some definitions, but not by others.
“This question of defining it is really insidious,” says Jones, who recently wrote on the subject for the American Chemical Society’s Society. industry affairs 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 a fun game to play with chemistry friends: ‘Is 1,4-difluorobutane a PFAS or not?’” jokes Jones. “Most people don’t get it right.”
What do we use PFAS for?
PFAS are versatile chemicals. They are found in consumer products such as food packaging, cookware, clothing, furniture, camping gear, dental floss, and stain removers.
Much of this is due to its useful chemical properties. For example, the heat resistance of PFAS is useful for coating nonstick pots and pans. PFAS can also make textiles and other products resistant to water and stains.
“We think of most molecules as being hydrophobic or hydrophilic, attracted to water or 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.”
An American study published last week in the journal Environmental Science and Technology found that several children’s clothing, bedding, and furniture contained PFAS, or molecules that could become PFAS when oxidized in the body or in the environment. The study was funded in part by the Silent Spring Institute, an organization that investigates 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 will just splash more fuel and catch fire everywhere,” says Khan. Instead, PFAS foams sit on fuel fires and smother them by blocking access to oxygen.
Why are people worried about PFAS?
PFAS resistance is a double-edged sword. They are highly resistant to chemical and biological degradation, hence the not-so-affectionate nickname “chemicals forever.” 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 of Civil and Environmental Engineering at UNSW. “It’s everywhere in the environment… it’s just this slimy film that we’ve put on 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 by breathing air or dust.
Places like airports and military bases that host firefighting training may have high levels of PFAS nearby.
“Oftentimes, PFAS foams end up on the ground, and eventually, after rain, they soak into the ground and end up in the water table,” says Khan. “That’s why we now have a lot of problems with contaminated groundwater supplies in many parts of Australia.”
But should we be concerned about having PFAS in our bodies?
“Much is still unknown about public health impacts, especially from environmental exposure,” says Khan.
According to Manefield, PFAS are not as harmful as other pollutants, such as dioxins, but they are not necessarily benign either.
Halden is more concerned. “We know enough about the chemistry of PFAS to understand that it is incompatible with our health and the health of the planet,” he says.
PFAS have not been shown to cause specific diseases in humans. However, results from epidemiological studies and research in non-human animals have linked PFAS exposure to health problems such as increased risk of certain types of cancer, 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 the longest and have been studied the most.
Recently, concerns have been raised that increased exposure to PFAS may reduce the effectiveness of the vaccine and make people more vulnerable to COVID-19.
Ultimately, our general understanding of the health and environmental impacts of PFAS is still relatively limited. Difficulties include the number of different PFASs, the challenges of pinning down causality by 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 perspective that we should reduce our exposure to PFAS and limit their use where possible.
Can we remove PFAS from the environment?
Although PFAS are difficult to break down, we have ways to remove them from water and soils. Ion-exchange water treatment plants, like the one soon to open in Katherine, Northern Territory, use a special resin that adsorbs PFAS out of the water. We can also ‘wash’ soils by separating the soil components to which PFAS are bound. However, these methods do not destroy PFAS, they simply remove it from the environment.
“We are stockpiling this ion-exchange resin that is contaminated with PFAS, which is going to have to go somewhere one day,” says Khan.
Manefield adds that PFAS-contaminated resin or soil can be incinerated, but this is energy-intensive and expensive. There is also ongoing research into immobilizing PFAS in soil using activated carbon, which prevents PFAS from spreading further into the environment. Once again, it is not a permanent solution.
Some scientists are working on better ways to actually break down PFAS, using bacteria and chemical catalysts. The difficult first step is to break the very strong chemical bond between carbon and fluorine.
“Our goal is to remove these fluorine atoms that are very, very attached to the carbon backbone,” says Manefield. “If you think of PFAS as a little armadillo, the fluorine atoms are the armor around an organic backbone.”
Interestingly, one of the promising molecules that can catalyze fluoride removal is one you may have heard of: vitamin B12. Catalysts work by reducing 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 on the periodic table, they share similar chemical properties.
“You can take a strong reductant like zinc and have it pass electrons to vitamin B12,” explains Manefield. “Vitamin B12 then passes those electrons onto the carbon-fluorine bond, which removes the fluorine.”
Once the fluoride is gone, it is much easier for bacteria to break down the resulting PFAS byproducts.
Other UNSW researchers are developing and testing new catalyst molecules that are chemically similar to vitamin B12, but more effective at breaking down PFAS.
A future free of PFAS?
PFAS are widely used because they are, well, useful. Can we learn to replace PFAS or do without them?
“In many cases, it’s hard to find a direct, individual replacement for them,” says Jones. “For example, Teflon really has unique properties that are difficult to reproduce.”
On the other hand, he says, we could probably just learn to live without greaseproof coatings on food packaging.
“And I think you would have everything in between… I think smart people will innovate and move away from these types of materials if they are recognized as being 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 for this chemical and what is the carrying capacity of the planet and the biosphere for these chemicals?” he asks.
Both Khan and Manefield stress that systemic changes are likely to be needed to prevent current problems with PFAS from repeating themselves over and over again.
“How do we put systems in place so that we don’t end up with this problem again with the next group of chemicals?” Khan asks.
“We really need to move forward and get better at planning for what some people call ‘green chemistry’: making chemicals that have all the useful properties we need, but are either environmentally benign or break down quickly.”