The Environmental Protection Agency (EPA) department responsible for protecting the public from toxic substances is working under a new definition of PFAS “forever chemicals” that excludes some of their widely used compounds. The new “working definition”, established by the Office of Pollution Prevention and Toxics, is not only at odds with much of the scientific world, but is narrower than that used by other EPA departments. Among other uses, the narrower definition excludes chemicals in pharmaceuticals and pesticides that are generally defined as PFAS. The EPA also cited the narrower definition in December when it declined to take action on some PFAS contamination found in North Carolina. PFAS, or per- and polyfluoroalkyl substances, are a class of about 12,000 compounds most frequently used to make products water-, stain- and grease-resistant. They are in thousands of products across dozens of industries, and have been linked to cancer, birth defects, decreased immunity, high cholesterol, kidney disease and a range of other serious health problems. They are dubbed “forever chemicals” due to their longevity in the environment. The discussion within the EPA comes as the agency faces increased pressure to largely restrict the entire chemical class, and critics say the change benefits chemical manufacturers, the Department of Defense and industry. “There’s a real difference in the definition that industry uses and what the international scientific community uses, and, unfortunately, the definition I see the EPA toxics office using is a lot more like industry’s,” said Linda Birnbaum, a former EPA scientist and head of the National Toxicology Program. An EPA official who spoke with the Guardian on the condition of anonymity said the new definition was developed about a year ago and discussions over it were ongoing. The issue comes to light as the EPA’s new chemicals division managers face whistleblower charges that allege management altered risk assessments to make PFAS appear less toxic. The EPA didn’t immediately respond to questions, but an agency document obtained by the Guardian states the new definition “focuses on PFAS believed to be of highest concern based on their persistence and potential for presence in the environment and human exposure”. Researchers say the international scientific community has been engaged in a debate over how to define PFAS that’s focused on chemical structure. PFAS are called “forever chemicals” because their fluorinated atoms prevent them from fully breaking down. The most widely used, inclusive definition, and that proposed by the Organization for Economic Cooperation and Development (OECD), defines any chemical with one fluorinated carbon atom as a PFAS. That could include tens of thousands of chemicals on the market. The EPA toxics office, however, wrote a “working definition” that calls for “at least two adjacent carbon atoms, where one carbon is fully fluorinated and the other is at least partially fluorinated”. It covers about 6,500 PFAS, and the EPA is using that definition in its recently introduced “national testing strategy”, which serves as a road map in its attempt to rein in PFAS pollution. Beyond chemicals in pesticides and pharmaceuticals, the narrower definition excludes some refrigerants and PFAS gases. Some of the excluded PFAS compounds turn into highly toxic chemicals, like PFOA and PFOS, as they break down in the environment or are metabolized by the human body. And the production of some excluded PFAS requires the use of other more dangerous PFAS compounds. “How do you say something is not PFAS when it becomes PFAS after it is metabolized by the body or undergoes changes in the environment – that just doesn’t hold with me,” Birnbaum said. The definition debate also partly centers on the chemicals’ “persistence”. The vast majority of chemicals with a fully fluorinated carbon atom will not fully break down, and some of those compounds are accumulating at concerning levels throughout the planet, noted Ian Cousins, a Stockholm University PFAS researcher who has co-authored papers on the topic. “The levels are increasing but toxicity is low, so should we be concerned?” he asked. “I say ‘Yes’, because we shouldn’t be releasing substances … that increase in the environment and eventually we may find a problem when it’s too late to reverse.” Cousins and other experts say a discussion over how to narrow the definition is warranted, but the toxic office’s approach is too restrictive. The EPA’s Office of Research and Development appears to have found a middle ground and is working from a definition that encompasses about 12,000 PFAS compounds. Meanwhile, the US congresswoman Deborah Ross introduced legislation that would establish one fluorinated carbon atom as law. The EPA official who spoke with the Guardian said they were not part of the discussion that preceded the definition change, but said chemists in the agency’s new chemicals division probably developed it. The employee said the chemists probably defined the compound solely on the chemicals’ structures, not the threats they present to human health and the environment. The employee said the exclusion of some PFAS compounds was “a problem”, but developing an appropriate definition was “tricky”. The definition change’s implications have already been seen in North Carolina’s Cape Fear basin, a region contending with decades of pollution from a PFAS manufacturing plant owned by chemical giant Chemours. A 2019 citizen group petition asked the EPA to conduct studies that would shed light on the health impacts of 54 PFAS compounds found in human blood and water in the region. In the agency’s December 2021 response, it declined to test for 15 chemicals it said “do not meet” the toxic’s office PFAS definition. The citizen groups are suing, and the justice department and EPA are coordinating with Chemours for their defense, said Bob Sussman, an environmental attorney for the groups. The EPA wrote in its response that some of the excluded chemicals “are expected to degrade in the environment”, and some will turn into TFA, which the office called a “well-studied substance”. But researchers say most substances, like TFA, don’t fully break down, and studies show it is accumulating in the environment and toxic during prolonged exposure. Critics also stressed that there was very little data on the toxicity of some excluded chemicals, and permitting the use of PFAS with little toxicological data has led to problems. The EPA in November reported GenX, PFOA and PFOS – three widely used compounds – are much more toxic than previously thought, noted Kyla Bennett, a former EPA scientist now with Public Employees for Environmental Responsibility. “That’s the biggest issue: the EPA just doesn’t know,” she said. “I would rather use the precautionary principle and capture chemicals that maybe don’t deserve to be regulated as strongly than miss [dangerous chemicals].”