Companies making so-called “forever chemicals” knew they were toxic decades before health officials, but kept that information hidden from the public, according to a peer-reviewed study of previously secret industry documents.

The new study in the Annals of Global Health concluded that 3M and DuPont, the largest makers of per- and polyfluoroalkyl substances, or PFAS, actively suppressed evidence that the chemicals were hazardous since the 1960s, long before public health research caught up.

“The chemical industry took a page out of the tobacco playbook when they discovered and suppressed their knowledge of health harms caused by exposure to PFAS,” researchers claimed in a statement.

“These documents reveal clear evidence that the chemical industry knew about the dangers of PFAS and failed to let the public, regulators and even their own employees know the risks,” the paper’s senior author, Tracey Woodruff, said in a statement.

PFAS are a range of chemicals used for their slippery or lubricating properties. Teflon and ScotchGuard are the best known brands of this chemical coating, but there are more than 12,000 types of these chemicals, according to the paper. First commercially produced in the 1940s, PFAS were used widely in cookware, fabrics, food packaging and insulation — and today they are ubiquitous in human bodies.

The chemicals, now linked to cancer, birth defects and other illnesses were believed to be “biologically inert” until studies published in the late ’90s revealed their toxicity.

But for 40 years before then, the makers of PFAS-based products already knew that these chemicals could be toxic to animals and humans, but withheld that information in violation of public health laws, the study revealed. Internal “documents were all marked as ‘confidential,’ and in some cases, industry executives were explicit that they ‘wanted this memo destroyed’,” the report said.

A Teflon company report from 1961 found that low doses of the material made rats’ livers grow and advised that the substance “be handled ‘with extreme care’ and that ‘contact with the skin should be strictly avoided,'” the paper showed. 

Researchers at a DuPont-funded lab discovered by 1970 that C-8, an older name for the chemicals, was “highly toxic when inhaled and moderately toxic when ingested,” and a 1979 report found that dogs exposed to one dose of PFOA died two days later.

In 1980, DuPont and 3M learned of eight pregnant women who worked in the manufacturing of PFAS, two of whom gave birth to children with birth defects. The two companies not only hid that information from their workers, but DuPont sent an internal memo the following year saying, “We know of no evidence of birth defects caused by C-8 at DuPont.”

In a statement, DuPont said it could not comment on the findings because of a corporate reorganization.

“In 2019, DuPont de Nemours was established as a new multi-industrial specialty products company. DuPont de Nemours has never manufactured PFOA or PFOS,” spokesperson Dan Turner said. “DuPont de Nemours cannot comment on allegations contained in the UCSF paper that relate to historical E.I. du Pont de Nemours matters.”

3M noted that “The paper is largely comprised of previously published documents — as evidenced by the paper’s references section, which includes citations dating back as far as 1962.”

“3M has previously addressed many of the mischaracterizations of these documents in previous reporting,” the company said, without specifying what those were.

Some public health researchers said the evidence unearthed in this paper shows that companies can’t be trusted to monitor their own adherence to public health laws and safety standards, and that regulators need to take a harsher stance with makers of potentially dangerous products.

“Like Big Tobacco, the major chemical manufacturers have a vested financial interest in suppressing scientific evidence of the harms of their products, while maintaining the public perception that their products are safe,” the study’s authors wrote. “The U.S.’s failure to shift the burden of proof to the industry with respect to chemical policy means that we may always be chasing the devil they knew, rather than defending public health from the outset.”