The problem of PFAS – solutions for substitution and elimination

Per- and polyfluoroalkyl substances, or PFAS for short, play a key role in numerous branches of industry due to their properties and wide range of applications. The downside is that they are not degradable and accumulate in the environment, animals and humans. Since some PFAS substances have been proven to be harmful to our health, politicians are discussing an EU-wide ban. Researchers at Fraunhofer IGB are working on harmless alternatives that can be used to substitute PFAS. In addition, the institute is developing various solutions to remove PFAS from water.

These were also the focus of the 22nd Wastewater Colloquium at Fraunhofer IGB “PFAS und Spurenstoffe im Brennpunkt” (PFAS and Trace Substances in the Spotlight) in September 2023. Experts from the Fraunhofer Chemistry Alliance, including Dr. Michaela Müller from Fraunhofer IGB, discussed possibilities for PFAS substitution as well as material and technical development goals in a dialog with user industries in October 2023.

Whether it's pans, rain jackets, food packaging or firefighting foam – numerous everyday products contain per- and polyfluoroalkyl substances, or PFAS for short. This is a group of versatile organic chemical compounds in which the hydrogen atoms have been replaced by fluorine atoms, either completely (perfluorinated) or partially (polyfluorinated). This gives them uniquely combined properties, such as water, grease and dirt repellent, which makes them interesting for numerous industries and products. PFAS plastics such as polytetrafluoroethylene (PTFE, trade name TeflonTM) are very stable both chemically and thermally: surfaces treated with them also have friction-reducing and non-stick properties. This makes PFAS versatile – as sealing materials, corrosion protection coatings, additives for lubricants, but also as ingredients in cosmetics.

But where does their bad reputation come from? Some PFAS representatives can now be detected in groundwater and humans, among other things. This requires a differentiated view of the different PFAS.

Smaller PFAS molecules such as perfluorooctane sulfonic acid (PFOS) have been shown to be toxic to humans and the environment. The low-molecular PFAS can accumulate in animal tissue and thus also end up on the dinner table in humans. The chemicals enter the human body through food or drinking water, with significant health effects ranging from damage to organs to cancers or developmental disorders.

For this reason, many countries already have limit values for certain PFAS in drinking water. With the amendment to the German Drinking Water Ordinance, which came into force in mid-2023, the limit values for PFAS in water will be reduced in two stages over the next few years. Specific bans also illustrate stricter regulations: for example, for perfluorooctane sulfonic acid (PFOS), the use of which is limited to a few essential areas of application in accordance with the Stockholm Convention on the Control of Persistent Organic Chemicals in the Environment.

In the case of higher-molecular plastics such as PTFE, their stability and thus non-degradability in the environment is the biggest problem. At present, it is simply not known or foreseeable what will happen to these materials in the environment in a hundred years' time, and whether they will perhaps be converted into toxic substances after all.

In order to comply with the precautionary principle prevailing in Germany and the EU, further regulation of such persistent materials is being discussed. It must be taken into account that low-molecular PFAS are used in the production of fluoroplastics, which can also be released into the environment.

In view of the threat of a PFAS ban or massive restrictions on the production, use and supply of industrial chemicals, manufacturers and users alike are faced with an acute need for action. Fraunhofer IGB supports companies in the search for suitable substitute materials for their products, in the development of tailor-made coatings, and in the evaluation of new substances and materials with regard to possible effects harmful to the environment and health.

Fraunhofer IGB also offers a wide range of technical solutions for the elimination of PFAS and other micropollutants from wastewater in order to reduce harmful health effects, for example via drinking water. In addition to membrane adsorbers and adsorber particles for concentration and separation, the institute is researching various advanced oxidation processes (AOP) to achieve a degradation of the persistent substances.

Fluorine-free membrane materials and coatings

The institute conducts research on several technologies and processes for the substitution of PFAS, especially in the field of coatings. These include plasma technology, in which water-repellent coatings, for example on single-use items, are realized with fluorine-free gases that are harmless to humans and the environment.

We have also been able to successfully achieve a water-repellent finish for textiles using modified biobased chitosan or certain fungus-produced proteins, hydrophobins.

There is also a need for action and current research work at Fraunhofer IGB in membrane materials, for example for filtration and the energy transition. In doing so, the institute supports companies in material development as well as in the adaptation or conversion of their manufacturing and processing processes.

Efficacy-based testing of PFAS alternatives

.In the case of PFAS, environmental and health effects only became apparent decades after they were approved. This shows how important it is to carry out a comprehensive and specific ecotoxicological and human toxicological assessment of new substances at a very early stage, ideally already in the development phase. 

Based on its expertise in the field of in vitro cell and tissue models, Fraunhofer IGB has therefore set itself the goal of developing screening test procedures that can be used during development to evaluate possible PFAS alternatives.

Cell-based assays established at the IGB can be used to test new substances for classic toxicological endpoints such as effects on cell proliferation or toxicity. With specific, specially developed and patented reporter cell assays as well as complex 3D in vitro tissue models, especially of the skin, targeted adverse effects on metabolic processes in cells and tissues can also be detected, and thus, for example, immunomodulating, sensitizing, cell stress-inducing or pro-inflammatory effects can be detected.

The department of Cell and Tissue Technologies, headed by Dr. Burger-Kentischer, is currently working on the establishment of specific reporter cells, for example for the targeted detection of the effect of PFAS on lipid metabolism or for the detection of endocrine (hormone-like) effects. 

But what about the PFAS that are already in circulation and can be detected in soils, waters and groundwater? As already mentioned, PFAS are released into the environment during the production of fluorine-containing plastics or the use of extinguishing foam. To a not inconsiderable extent, PFAS are also introduced into the environment through abrasion of plastic products and coated textiles. One problem is PFAS-containing waste in landfills, where the fluorinated substances are leached into the leachate.

This calls for water treatment processes that can be used to purify contaminated water. However, filtering with activated carbon is a common process that binds harmful PFAS but does not eliminate them, so that the remains must be disposed of or stored as hazardous waste. 

Goal: Complete degradation of micropollutans

With its expertise, Fraunhofer IGB therefore prefers to pursue strategies or technologies that not only remove PFAS (and other trace or micropollutants) from water, but in the best case completely dismantle them. In principle, this is possible with various AOP (Advanced Oxidation Processes) methods, including plasma-based or photocatalytic methods. 

Technologies for the degradation of the chemicals, which have already been successfully demonstrated on a laboratory and pilot plant scale, including with real water samples, now need to be scaled up and evaluated with partners under the real conditions of industrial sites and further developed for widespread use in acute damage cases or in production plants.