PFAS: Danger spotted - now what?

PFAS chemicals increase the risk of cardiovascular disease. This is the result of a study published in February 2024 by the German Center for Neurodegenerative Diseases (DZNE). Since several European countries applied for a ban in January 2013, there has been an increasing amount of news about “eternity chemicals”. “Eternal” because they are extremely persistent and accumulate throughout the environment, particularly via water cycles. However, the issue is not entirely new: The first PFAS substance was banned in 2009, followed by further bans on individual substances in the group. Now, however, the aim is to ban the entire group of substances, which comprises up to 10,000 compounds.

The abbreviation PFAS stands for per- and polyfluorinated alkyl substances. They consist of a carbon skeleton whose hydrogen atoms are either completely or only partially replaced by fluorine atoms. They are very different, for example, in terms of the number of carbon atoms, which is why they are referred to as long-chain and short-chain PFAS. Long-chain PFAS in particular accumulate strongly in living organisms. In 2010, perfluorooctanoic acid (PFOS), a long-chain compound of the PFAS group, was added to the Stockholm Convention’s list of banned substances. Since then, PFOS has only been used in exceptional cases. However, some manufacturers have replaced the substance with shorter-chain PFAS. Such substances are still found in certain fire extinguishing foams and are used in the electroplating industry, i.e., in metal finishing processes such as chrome plating.

PFAS weaken the immune system

Whether short-chain or long-chain, what all PFAS have in common is that they either cannot be degraded or are converted into other PFAS in the environment, which in turn are not degradable. And they can be found everywhere. According to a study from 2020, every person in Germany is exposed to PFAS. “We are constantly exposed to PFAS,” says Gunda Herberth from the Helmholtz Center for Environmental Research – UFZ. The environmental immunologist researches the effects of environmental pollution on the immune system. The substances are associated with liver and kidney diseases, arteriosclerosis, cancer and asthma, diseases that can also have an immunological background.

In their experiments with human immune cells, Herberth and her team saw that the immune cells were inhibited in their function after coming into contact with PFAS. “Our experiment showed that the T helper cells and the MAIT cells were most affected in their activity,” says Herberth. MAIT cells are found in the mucous membranes and are therefore the first barrier for invading germs. T helper cells play a central role in the immune system and, as the name suggests, have a helper function: They support the immune response. A disruption of this function could lead to increased infections or reduced antibody production, for example, after a vaccination.

The effect on the immune system is perhaps the most important health effect of PFAS, because a dysregulated immune system is the basis for many diseases. “Unfortunately, the effect on the immune system has been the least studied so far,” says Herberth. One reason for this is that manufacturers have so far only had to show whether a substance is carcinogenic, teratogenic or neurotoxic. They do not have to test the effect of a chemical on the immune system. Gunda Herberth would therefore like to see manufacturers working more closely with researchers in future to test new substances for their immunological effects before they are used. “We have the tests and methods,” she says.

Special analysis techniques detect unknown substances

Environmental chemists can hardly cope with the task of detecting and evaluating all the unknown PFAS. “We alone cannot carry out tests for every single one of the thousands of substances,” says environmental analyst Hanna Joerss. “That would keep us busy for decades.” To make matters worse, manufacturers have repeatedly brought new PFAS onto the market. “As soon as a substance was banned, the industry switched to a substitute substance with a small change in the molecule, which was not banned at the time but was just as problematic in some cases,” says Joerss. “You can keep playing the game, but that doesn’t solve the basic problem.” At the Helmholtz-Zentrum Hereon in Geesthacht, Hanna Joerss is researching methods to identify as yet unknown PFAS. She considers a ban on the entire PFAS substance class to be very important. “This is very relevant because otherwise you always end up with the problem of substitute substances,” says Joerss.

Joerss uses high-resolution mass spectrometry to detect the substitute substances. “With this method, we examine molecular masses in a sample with high accuracy, which we then try to assign afterwards,” says Joerss. “This allows us to detect PFAS that we have not discovered using conventional analysis methods.” Another approach is to use certain parameters to determine a sum of PFAS in the sample. This makes it possible to recognize whether there is a large or small PFAS load. “With our methods, we can detect 2,000 PFAS. With the classic method, it’s 40,” says Joerss. "In routine laboratories, between ten and 30 PFAS are usually analyzed.”

Based on the patterns of the substances, she can trace them back to a specific source, for example, to hotspots such as chemical parks, electroplating industries and fire training grounds. “If I take a sample from a river and see high values for one PFAS substance and low values for another PFAS substance in the analysis, I can draw conclusions as to whether the pollution is coming from a municipal sewage treatment plant or an electroplating plant or a chemical plant that uses specific PFAS,” says the researcher. She and her colleagues are in close contact with environmental authorities and, in some cases, with state authorities that do not have the same analytical methods. “If we know the source, we work with the authorities so that emissions can be reduced. If it’s an old case of damage, for example, via fire extinguishing foams, we try to understand it and work towards remediation,” says Joerss.

New filter technologies for PFAS

This is where Anett Georgi’s field of research comes in. The chemist conducts research into remediation processes and wastewater treatment at the Department of Technical Biogeochemistry of the Helmholtz Center for Environmental Research (UFZ) in Leipzig. In the FABEKO project, she is working with other scientists and remediation experts to develop processes to clean PFAS from contaminated soil and water directly on site. To do this, she uses activated carbon, the most commonly used adsorbent in water purification. It filters long-chain PFAS out of water well but is less effective at retaining short-chain PFAS, which is why the carbon filters have to be replaced very often. Anett Georgi and her team have therefore developed a process with which the activated carbon can be easily regenerated with the help of electricity.

“You could call this electrosorption for short,” says Georgi. “The typical short-chain PFAS are negatively charged ions. If we also charge the activated carbon negatively, these PFAS anions are repelled and we can rinse them out of the activated carbon with a small amount of regeneration solution,” explains Georgi. She treats the remaining concentrate with a special process that breaks down the PFAS into completely harmless products. “We use electro-oxidation for this. This process completely destroys the PFAS, leaving behind carbon dioxide, fluoride and water. The fluoride can be separated by adding calcium ions,” says Georgi. A typical application for this process is groundwater contaminated with PFAS from fire extinguishing foams. It is also suitable for the treatment of drinking water.

Mineral sponges in the filter test

Together with her colleague Ariette Schierz, Anett Georgi is also looking for alternatives to activated carbon. “Activated carbon can do a lot, but it also has the disadvantage that we continue to import large quantities from Asia,” she says. “In addition, activated carbon production and regeneration through to incineration have a considerable CO₂ footprint.” Zeolites are a promising, more environmentally friendly candidate. These are volcanic rocks with sponge-like structures that can also be produced on an industrial scale from readily available minerals.

A major advantage of the zeolite method is that oxidizing agents such as persulfate can be used to destroy pollutants in the remaining filter concentrate. Persulphate can also be produced electrochemically. “This means that we can use renewable energy to regenerate the adsorbers,” says Georgi. The regeneration of activated carbon, on the other hand, requires high temperatures and the consumption of fossil raw materials. The UFZ team is currently testing the zeolite method in collaboration with an electroplating company that chrome-plates plastic parts. Such companies use a substance for occupational safety that is still classified as PFAS. The electroplating company is now working on equipping its water treatment plant so that no more PFAS are discharged with the wastewater in future.

Some manufacturers seem to realize that something has to happen, and many outdoor manufacturers are also trying to do without PFAS. The products may be less efficient than before in terms of certain requirements, but is that even a problem?

This question also concerns chemist Michaela Müller. She is head of the Functional Surfaces and Materials department at the Fraunhofer Institute for Interfacial Engineering and Biotechnology. Her research there includes PFAS-free coatings. She is certain that the PFAS ban will come. “Everyone has to come to terms with it. And I first have to ask myself whether I even need PFAS for my product,” says Müller. Many manufacturers come to her looking for environmentally friendly alternatives for their products, including coatings for outdoor clothing. “That’s where we come in, to scrutinize whether an application only needs to be water-repellent, for example. Fluoropolymers have a great performance for this, but there used to be alternatives,” says Müller. Alternative solutions are often based on silicones. Although these are not as problematic as PFAS, they are also not easily degradable. This is why many manufacturers who turn to Michaela Müller are increasingly looking for silicone-free solutions.

Chitosan - a bio-based PFAS alternative

The researcher and her team are therefore working on purely bio-based textile coatings made from chitosan. This substance is obtained from crab shells, which would actually end up as a waste product. Chitosan is water-repellent, breathable and antistatic, so it has good properties for textile processing. However, the researchers have to chemically modify the chitosans to make them water-repellent. “The modification is bio-based, but even bio-based substances can be toxic,” Müller points out. This means that bio-based alternatives must also be tested for environmental, human and animal toxicity. “Otherwise, in the worst case scenario, we will have the same problems in the future as with fluoropolymers,” says Müller. At the moment, the substance does not yet come close to the performance of PFAS or silicones. “We are working on making them even better,” says Müller. “But you also have to ask yourself when performance is sufficient. We don’t always need the maximum solution, but we would have a coating with certain ecological advantages.”