Per- and polyfluorinated alkyl compounds (PFAS) are considered »indestructible« chemicals. They are practically not degraded and accumulate in humans and the environment. The presumed health consequences include asthma, cancer and changes in the reproductive organs – and how to get rid of PFAS was previously completely unclear. Now there are first approaches to destroy the resistant molecules.
The most important ingredient for breaking the carbon-fluorine bonds characteristic of this class of substances is heat. In a study published in the Journal of Environmental Engineering, the US Environmental Protection Agency (EPA) found that a technique called "supercritical water oxidation" destroyed 99 percent of the PFAS contained in a water sample.
PFAs have a combination of properties that makes it unique and is suitable for many technical applications. At the same time, they are oil and water repellent and resistant to high temperatures and chemicals. They therefore appear in many consumer goods as well as in applications such as fire foam for fire fighting. That's why you can find them almost everywhere. In Germany, too, soil and groundwater are contaminated in several counties, in Rastatt in 2019 Pfas made the drinking water unusable. Studies show measurable concentrations in blood and breast milk among the entire European population.
The first attempts with new methods to destroy the "indestructible" substances at least give hope. In the recently published study by the US Environmental Protection Agency (EPA), the experts mixed PFAS-contaminated water with oxidizing substances and heated it at a pressure of more than 220 bar above its critical temperature of 374 degrees Celsius. The water becomes supercritical, it is neither gas nor liquid. In this state, even water-repellent substances such as PFAS dissolve much better, at the same time the condition accelerates chemical reactions.
The EPA used procedures from three companies that differ slightly in the chemicals and processes used. Nevertheless, all procedures delivered the desired result, reports the team led by EPA researcher Max J. Krause. The amount of PFAS contained in the water decreased by more than 99 percent in each case. It also turned out that the PFAS previously identified in the water accounted for less than a quarter of those substances in the water. On the one hand, this shows that previous analysis techniques only cover a part of the PFAS – the variety of industrially used representatives of this class of substances is so great that many of the substances are hardly known.
On the other hand, the finding demonstrates that the technology also reduces the "invisible" stress due to the enormous number of previously hardly described representatives of the fabric class. Nevertheless, experts advocate restricting the use of the PFAs to absolutely necessary applications. On the one hand, the technology is relatively complex due to the high temperatures and pressures and therefore expensive. And on the other hand, it is simply unrealistic to clean contaminated soils and basic water in this way.
