WASHINGTON — The Environmental Working Group (EWG) on Wednesday released 20 3M documents as part of a timeline that the activist organization said shows the company knew about and hid the dangers of PFAS, a family of chemicals now at the center of a national pollution controversy.

Among other things, the documents and timeline released by EWG suggest that 3M was aware for decades that PFAS built up in the bodies of humans exposed to them. The earliest document dates to 1950.

A 1963 3M study included in the report rated company “fluoro­chemical surfactants” as “mildly toxic” or “slightly toxic” and warned: “Due care should be exercised in handling these materials until further information is available on their physiological properties.”

In a statement Wednesday, 3M said it has tried to increase understanding of PFAS by placing “thousands of documents in the public domain.”

“Much of the 3M-related documents shared by EWG reflect a small batch of documents released by the Minnesota Attorney General,” the company added. “They portray an incomplete and misleading story that distorts the full record regarding 3M’s action with respect to PFOA and PFOS, as well as who we are as a company.

“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.”

Minnesota Attorney General Lori Swanson sued 3M for $5 billion over PFAS pollution in the southeastern area of the Twin Cities. Without admitting guilt, the company settled the suit in 2018 for $850 million.

The company has denied human health risks in response to public and private lawsuits, though it has collectively paid hundreds of millions of dollars to settle several legal actions without admitting guilt. The company also has said it discontinued use of the most toxic PFAS more than a decade ago and that newly developed substitute PFAS are safe.

For more than half a century, manufacturers such as 3M and DuPont have used per- and polyfluoroalkyl substances — or PFAS — to waterproof shoes, stainproof clothes and carpets, make nonstick cookware and as an active ingredient in military firefighting foams.

PFAS are now present in water systems, groundwater and soil at roughly 700 sites in 49 states. Meanwhile, the U.S. Food and Drug Administration has linked PFAS to human health problems including cholesterol buildup and autoimmune problems. Animal tests also suggest links to liver disease and cancer.

The U.S. House of Representatives is expected to include new stringent PFAS restrictions in a defense funding bill. The Senate already has passed its own defense bill with PFAS restrictions.

The Environmental Working Group document release comes ahead of scheduled testimony by 3M executives at a Sept. 10 hearing on PFAS by the environment subcommittee of the House Oversight Committee.

“The long history of corporate deception is important,” said Scott Faber, EWG’s senior vice president for government affairs. “Most legislators are just learning about it.”

In addition to pollution suits, 3M now faces class-action suits by stockholders seeking damages for drops in share prices because of the company’s mishandling of PFAS problems.

More potentially bad news for the Maplewood-based corporation comes in a new peer-reviewed article in Chemical Engineering Journal. In the article, Auburn University researchers determined that new alternative PFAS — so-called “short-chain” versions — “are more persistent and mobile” than older versions that have been deemed toxic.

“Overall, this review reveals an urgent need for developing more cost-effective treatment technologies for short-chain PFAS in drinking water, for advancing our knowledge on the environmental fate, transport and impacts of short-chain PFAS in the environment, and for developing science-based regulations for short-chain PFAS,” the researchers wrote.