As public concern grows about the health and environmental impacts of so-called forever chemicals, a new investigation by ProPublica and The New Yorker reveals that 3M, the American manufacturing giant, discovered and concealed the risks of these toxic substances for decades. PFAS are used in everyday products, from nonstick cookware to food packaging, but take decades or longer to break down in the body and environment. They have been found in the blood of almost every person in the United States and are linked to serious health effects. Investigative reporter Sharon Lerner says 3M knew as early as the 1970s that forever chemicals were dangerous even in small amounts, but kept those findings secret and “gaslit” one of its own scientists, Kris Hansen, who later raised concerns about forever chemicals in human blood samples. “Her direct bosses had been aware of the presence of this chemical in blood, even though they … appeared to act surprised when she brought her findings,” says Lerner. “They knew all along that what she was finding was true.”