Dostie Farm, an organic dairy in Fairfield, Maine, was thriving until one day in October 2020 when owner Egide Dostie Jr. got a call from Stonyfield, his exclusive buyer. Something was off with the farm’s milk: Tests had found that it contained three times the state’s allowable level of perfluorooctanesulfonic acid, one of the class of “forever chemicals” known as PFAS. “We called bullshit,” Dostie remembers. PFAS contamination had recently been…