San Francisco Frontiers - Forever chemicals and pesticides: what to know

But the Environmental Protection Agency has an alternative definition of per- and polyfluoroalkyl substances that excludes the pesticides, and says they pose no threat to human health.

The last three approvals were made without the customary press statements, surfacing only when nonprofits publicized them this month.

Critics say the chemicals may pose hidden risks, and many of them break down into trifluoroacetic acid (TFA), now abundant in global drinking water and potentially linked to serious health harms, including fetal and reproductive damage.

"If we want to do something about this class of chemicals, then you need to draw boundaries," Cindy Hu, an environmental scientist at George Washington University told AFP.

- Damning history -

PFAS are defined by the carbon-fluorine bond, the most stable in organic chemistry, whose strength and liquid repelling properties made the chemicals prized firefighting foam, nonstick pans, raincoats and more.

But evidence linking them to cancers, immune conditions and reproductive harms has triggered billion-dollar settlements, new laws and corporate phase-outs.

The Organization for Economic Co-operation and Development adopted a broad definition in 2021: any molecule with a single fully-fluorinated carbon atom. Roughly half of US states, Congress and the Pentagon have upheld it, as did 150 scientists in a 2024 consensus statement.

In 2023, the EPA under then-president Joe Biden went its own way, narrowing the definition to only include chemicals with two or more adjacent fully-fluorinated carbon atoms, which it deemed less likely to persist.

Using that definition, the EPA approved one such pesticide during Biden's term. Trump's second term has added five more.

Trump's EPA says pesticides are essential for food abundance, that all are reviewed, and that single-fluorinated ones can be less toxic than alternatives. It notes they are also registered or proposed in the European Union, Canada and Australia.

- 'Getting worse' -

That is not good enough for many scientists and activists, who fear a growing threat to the food supply and to farm workers.

Trifludimoxazin, one of the new herbicides, has "suggestive evidence of carcinogenic potential," the EPA's own review found.

And the new approvals are just the tip of the iceberg: a 2024 retrospective analysis revisited hundreds of pesticide ingredients approved in the past and found 66 would have met the OECD definition of PFAS.

"It's an issue that most administrations have kind of conveniently swept under the rug," Nathan Donley of the Center for Biological Diversity, who led the study, told AFP. "But it's definitely getting worse."

"If you were to buy 10 peaches or plums at random in the US, chances are nine of them are going to have at least residues of highly toxic PFAS pesticides," Varun Subramaniam, an Environmental Working Group scientist who conducted an analysis of produce samples, told AFP.

Many such pesticides break down into TFA, which is now found extensively in water, and the EU's food safety agency last week sharply cut the acceptable daily intake.

- Ex-lobbyists -

Criticism has focused on former lobbyists in senior EPA posts, including Kyle Kunkler, formerly of the American Soybean Association and Nancy Beck, formerly of the American Chemistry Council.

A Freedom of Information Act request led by Donley found those officials, alongside EPA chief Lee Zeldin, coordinated edits last November to the agency's webpage on PFAS and pesticides, stripping out any acknowledgment of the more widely-accepted definition.

The edit came the same day CropLife America, the pesticide industry's trade association, submitted a paper arguing against further regulation that cited the revised page. Neither the EPA nor CropLife America responded to an AFP query asking whether they had coordinated over the changes.

For researcher Hu, the debate echoes an earlier chapter in the PFAS story. When first-generation PFAS were phased out in the 2000s, industry replaced them with shorter-chain molecules marketed as safer -- one of which, GenX, caused a drinking water contamination crisis in North Carolina.

"It's a continuation of the same storyline," she said, advocating the "precautionary principle" that would presume such chemicals as harmful until proven otherwise.

K.Gray--SFF