DuPont has agreed to provide residents near its plant in Washington, WV, with clean water should perfluorooctanoic acid (PFOA) reach 0.5 parts per billion (ppb) in the area's drinking supplies. The deal replaces a similar agreement in 2002 with the EPA in which DuPont agreed to give residents bottled water or install water-treatment equipment should PFOA reach 150 ppb. The stricter rules follow studies that show people who live near the plant have a median PFOA level in their bloodstreams dozens of times higher than the average found in the general population. The company said it has already begun to implement the agreement but said the threat to humans posed by PFOA, used in the production of Teflon, is unproven. The EPA, however, has said that new studies have demonstrated various kinds of toxic effects on experimental animals.