Defendant 3M conducted studies in the 1950s and early 1960s that showed its perfluorooctanesulfonate (PFOS) accumulates in the human body and is toxic,” stated U.S. Magistrate Judge John C. Nivison, in his written opinion for the court. “By the 1970s, additional 3M studies revealed that its PFOS products were ‘even more toxic’ than previously believed.