They are in the outdoor jacket as well as in the carpet, the coated pan, the fire-fighting foam or the ski wax. They protect pizza boxes from soaking through, electronic cables from catching fire and make car seats insensitive to stains: per- and polyfluoroalkyl substances, PFAS for short. These chemicals consist of hydrocarbon chains in which at least one carbon atom has all of the hydrogen atoms replaced with fluorine.
They are so seductive for the consumer goods industry because they are water, grease and dirt-repellent, fire-retardant, extremely stable and therefore very durable on surfaces. But unfortunately they retain these properties even when no one needs them anymore, when they get into nature from everyday objects or from industrial plants.
The OECD has identified 4,730 substances from this family and authorities such as the European Food Safety Authority EFSA or the Federal Institute for Risk Research (BfR) lower the permissible limit values for PFAS in drinking water, surface water and soil at regular intervals. Various experts even see the group of substances in the same category as DDT or PCB.
Where everywhere PFAS have already been found
As early as 2015, Greenpeace detected PFAS in the most remote places in the world – in untouched snow at 5,000 meters or in mountain lakes. A recent study by Stockholm University and ETH Zurich, published in the journal Environmental Science & Technology, now suggests that PFAS have already exceeded the planetary carrying limit.
“Based on the latest US guidelines for PFOA in drinking water, rainwater would be classified as non-potable anywhere. Although we don’t often drink rainwater in the industrial world, many people around the world expect it to be safe to drink, and it provides care many of our sources of drinking water,” says Ian Cousins, the lead author of the study and a professor at Stockholm University’s Department of Environmental Sciences.
The team from the Swedish university has been studying the transport of PFAS in the atmosphere for the past decade. The researchers found that the concentrations of the investigated PFAS in the atmosphere are not declining noticeably, although 3M, for example, one of the major producers, stopped producing the chemicals two decades ago.
Until now, the chemicals were considered to be virtually indestructible. They are also not degraded in nature. The “Washington Post” therefore gave them the nickname “Forever Chemicals” in 2018. As awareness of PFAS has increased in recent years, the research landscape has also become concerned with their degradation. Many of the processes are complex, energy-intensive and, neither technically nor for cost reasons, are suitable for comprehensive renovations. But now researchers at Northwestern University in Evanston, USA, have developed a simple method. Using a mixture of lye and solvent, they managed to destroy at least some of the PFAS compounds.
The kryptonite of the PFAS: They are organic acids
They combined the solvent dimethyl sulfoxide (DMSO) with sodium hydroxide in water, brought the mixture to a boil and observed that a PFAS subgroup degraded in this solution. The PFAS group that the researchers studied is one of the most significant from an environmental perspective. It represents about 40 percent of all PFAS. They are found in fire-fighting foams and non-stick coatings. The decisive criterion for the degradation of these PFAS is that they are organic acids. The DSMO splits off the acid group and then the entire molecule breaks down.
According to the researchers, all that remains are easily trapped fluorine ions and a mixture of harmless, naturally occurring by-products containing carbon and oxygen. The researchers suggest filtering the chemicals out of drinking water or waste water in a conventional way and subsequently destroying them.
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