The clash pits President Donald Trump's pro-industry instincts against the Make America Healthy Again (MAHA) movement -- a diverse coalition of holistic-health moms, medical-freedom advocates and health-and-wellness influencers who envision a cleaner, less toxic world.

At the heart of the matter is the Environmental Protection Agency's recent decisions to green light new pesticides that critics -- including many scientists -- class as toxic "forever chemicals" known as PFAS, or perfluoroalkyl and polyfluoroalkyl substances.

Under Trump's second term, the EPA has approved two such new substances -- insecticide isocycloseram and fungicide cyclobutrifluram -- with proposals to approve several more.

MAHA views that as a deep betrayal and has launched a pressure campaign, including an online petition that has drawn more than 7,000 signatures calling for the removal of EPA administrator Lee Zeldin.

"We're calling him out because he is making a liar out of Trump," Zen Honeycutt, the founder and executive director of the Moms Across America advocacy group, told AFP, recalling the president's promise to protect Americans from harmful chemicals.

- 'Really concerning' -

Zeldin, for his part, lashed out in a sarcastic post on X, writing, "not everything on the internet is true," and arguing that molecules with a single fluorine-carbon bond are not in fact "forever chemicals."

That narrow definition was adopted by the EPA in 2021 under then-president Joe Biden, but it conflicts with those used by the Organization for Economic Co-operation and Development and by independent academic institutions.

"We were equally as critical of the definition when used by the previous administration," David Andrews, a chemist and acting science officer at the nonprofit Environmental Working Group, told AFP.

While these compounds don't build up in the body the way better-known PFAS chemicals do -- such as those used in nonstick cookware -- they break down into trifluoroacetic acid (TFA), which is highly toxic to reproductive systems and "is increasingly being detected in people, crops and waterways around the globe," Andrews said.

"As someone who myself is on a fertility journey, this is something that's really concerning for the increase of infertility rates in the United States," MAHA influencer Iliriana Balaj and CEO of Live Healthillie, told AFP.

- 'Excellent job' -

The petition was started by Kelly Ryerson, who co-founded American Regeneration to help farmers move away from pesticides, and who has admired Kennedy since his years as an environmental lawyer fighting Monsanto.

"I supported Kennedy during his independent presidential run, and supported him over to the Trump administration as well," she told AFP, adding that she believes he is doing an overall "excellent job."

She highlighted his pledge to close a loophole that lets companies self-affirm food ingredients as safe, while Honeycutt pointed to Kennedy's pressure on food companies to remove synthetic colorings.

Both praised a recommendation by a panel appointed by Kennedy -- a longtime vaccine skeptic -- that newborns no longer receive the hepatitis B shot at birth.

Yet Ryerson said she found it "incredibly disappointing" to see Trump's EPA -- which Zeldin has vowed to use as a vehicle "to unleash American prosperity" -- appoint two former chemical-industry lobbyists to key roles.

For now, tensions may be cooling. Ryerson met with Zeldin personally Tuesday, calling it an "excellent first step."

Asked by AFP at a regenerative farming event Wednesday about the schism, Kennedy said: "We're in discussions with Lee Zeldin at EPA, and we're very, very confident of his commitment to make sure to reduce toxic exposures to the American people."

Whatever happens next, Ryerson said she was heartened that pesticides are now more on the public's mind than ever.

"We're done now with having this poison in our food supply. So what are we going to do about it? And I think that now it's up for grabs as to which party really wants to run with it."