Decades before the toxic chemicals used in products like Scotchgard and Teflon would be found running through the drinking water and groundwater of dozens of communities nationwide — including in Bucks and Montgomery Counties — the companies producing the substances had evidence the chemicals might be unsafe for humans, according to a compilation of internal documents released Wednesday by an advocacy group.

DuPont and 3M employees raised concerns about how toxic PFAS could be, found high levels of the chemicals in workers’ blood, and later discovered elevated cancer rates among workers, the records show. They also include a 3M discussion of how to minimize alarm about the chemicals.

In 1999, a 3M scientist quit over the company’s handling of the environmental risks of PFAS, saying it had waited too long to tell customers about the danger to humans and the environment.

“I have worked within the system to learn more about this chemical and to make the company aware of the dangers associated with its use," Rich Purdy wrote in his resignation letter. "But I have continually met roadblocks, delays, and indecision.”

The compilation of 3M and DuPont records released by the Environmental Working Group comes as executives from both companies prepare to testify at a Sept. 10 House subcommittee hearing on per- and polyfluoroalkyl substances.

The documents have previously been made public and reported on by various news outlets, but the advocacy group collected hundreds of pages together and created a timeline. Many of the documents are exhibits in a lawsuit brought against 3M by the State of Minnesota in 2010.

A spokesperson for 3M, Fanna Haile-Selassie, said the materials released “portray an incomplete and misleading story that distorts the full record regarding 3M’s action [in] respect to PFOA and PFOS." The documents highlighted by the advocacy group, which seeks strict regulation of PFAS, are only some of thousands in the public domain about the company’s work related to PFAS, she said.

Haile-Selassie said “3M has a long track record of collaborating with the experts at the U.S. EPA on a variety of environmental and chemical issues, and we support appropriate science-based regulation of PFAS.”

A spokesperson for DuPont did not respond to a request for comment about the documents. But on Wednesday, the company announced the a list of “commitments related to its use of the substances.” They include continuing remediation at DuPont sites, eliminating the purchase and use of firefighting foams made with PFAS, and having external experts review company processes.

Several states, including New Jersey and New Hampshire, have sued 3M, DuPont, or both, alleging that the companies knew of the dangers of PFAS. Earlier this year, the New Jersey attorney general also ordered the companies to pay for PFAS cleanup.

“DuPont and 3M knew of the health and environmental impacts of PFAS for decades but continued to use them in products and to release them into the environment,” said a directive from the New Jersey Department of Environmental Protection, citing data including 3M studies done as early as the 1970s.

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Other documents in the collection released Wednesday show the companies also knew about studies that showed adverse health effects of PFAS on lab animals.

PFAS were in products manufactured by 3M and DuPont as well as other companies. Firefighting foam used on military bases also contained PFAS; the chemicals seeped into drinking-water wells near bases across the country, including near former bases in Horsham and Warminster Townships.

“The manufacturers, EPA, and [the Department of Defense] have known about some of the dangers related to these chemicals for a long time,” U.S. Rep. Madeleine Dean (D., Pa.) said at a discussion in Upper Dublin in May. “In the early 2000s, it was clear that PFAS was contaminating drinking water.… Yet the public in the area was not notified until years later.”

The contamination has caused concern and inconvenience among thousands of Americans who question whether it could affect their health. The federal government and some states, including Pennsylvania, say they are working on developing safe drinking water standards.

By 1975, according to the documents, 3M had been informed by a university researcher that PFAS were in human bloodstreams. The company speculated in an interoffice memo that Teflon cookware and Scotchgarded fabrics could be a possible source.

That memo discussed ways to “clarify” the findings with a new interpretation and to bring 3M analysts into the discussion, then asked whether PFAS could have beneficial medical properties. One employee suggested experiments “to see just how much of these materials can, in fact, be tolerated in the bloodstream.”

Other highlights from the documents include:

  • A 3M technical manual advised “due care” in handling the chemicals in 1963, saying they ranged from slightly to moderately toxic.

  • In 1975, DuPont told 3M it was concerned about possible toxic effects of one of the chemicals if in contact with food products and asked whether 3M would provide DuPont with “defensive information” about its toxicity.

  • Over the course of 1976, tests of four different groups of employees working with PFAS showed that they had between 50 and 1,000 times the normal level of the chemicals in their blood.

  • But 3M said in a memo that year on the status of the compounds in blood that there was “no evidence now of related health problems.”

  • In 1981, employees “of childbearing potential” at a 3M plant were reassigned so they would not be exposed to PFAS after the company discovered one of the chemicals caused birth defects in rats.

  • PFAS in workers’ blood was documented again in 1984, when 3M said the chemicals were not decreasing but rising in their blood over time. The trend should be viewed “with serious concern,” the documents said.

  • Between 1989 and 1997, 3M and DuPont studies found elevated rates of cancer among people who worked with perfluorinated chemicals. One study found that working in production of one PFAS chemical for 10 years was associated with increasing the risk of prostate cancer by three times.