NEWS THAT THE Environmental Protection Agency pressured the federal Agency for Toxic Substances and Disease Registry to suppress a study showing PFAS chemicals to be even more dangerous than previously thought drew outrage this spring. The EPA pressure delayed the study’s publication for several months, and a similar dynamic seems to have been in play this July in Michigan, where Robert Delaney, a state scientist who tried to raise alarms about the chemicals six years ago, was largely ignored. Delaney, who delivered a report to his superiors about high levels of the chemicals in fish and the dangers they presented to people, has been heralded as prophetic. And both delays are being lamented as missed opportunities for getting critical information to the public.

But the dangers presented by these industrial chemicals have been known for decades, not just a few months or years. A lawsuit filed by Minnesota against 3M, the company that first developed and sold PFOS and PFOA, the two best-known PFAS compounds, has revealed that the company knew that these chemicals were accumulating in people’s blood for more than 40 years. 3M researchers documented the chemicals in fish, just as the Michigan scientist did, but they did so back in the 1970s. That same decade, 3M scientists realized that the compounds they produced were toxic. The company even had evidence back then of the compounds’ effects on the immune system, studies of which are just now driving the lower levels put forward by the ATSDR, as well as several states and the European Union.

The suit, which the Minnesota attorney general filed in 2010, charges that 3M polluted groundwater with PFAS compounds and “knew or should have known” that these chemicals harm human health and the environment, and “result in injury, destruction, and loss of natural resources of the State.” The complaint argues that 3M “acted with a deliberate disregard for the high?risk of injury to the citizens and wildlife of Minnesota.” 3M settled the suit for $850 million in February, and the Minnesota Attorney General’s Office released a large set of documents — including internal studies, memos, emails, and research reports — detailing what 3M knew about the chemicals’ harms.