What if some per- and polyfluoroalkyl substances, known as PFAS, were not, in fact, PFAS? In a letter published on June 10 in the journal Environmental Science and Technology, a group of 20 scientists specializing in forever chemicals condemned efforts to change the definition of this family of synthetic, toxic, and persistent chemicals established by the Organisation for Economic Co-operation and Development (OECD).

The nature and, therefore, the number of PFAS captured by regulations depend on this chemical "identikit." The ongoing effort could weaken the many initiatives now targeting PFAS worldwide. "We are concerned that this effort is politically and/or economically, rather than scientifically, motivated," the researchers warned.

What is a PFAS? For a long time, the question was not simple for anyone, even specialists. The chemistry of PFAS is dizzyingly complex, and the devil lies in the smallest of atoms. In 2011, a group of experts proposed a first definition in a scientific article. Soon after, the OECD, which has been deeply involved with PFAS issues since the early 2000s, decided to take up the subject. In 2018, it published a definition covering 4,730 substances. Further work, led under its auspices by academic scientists, regulators, and industry representatives, resulted in 2021 in a definition identifying more than 10,000 PFAS.

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