Prior to 1971, Monsanto marketed a series of polychlorinated biphenyl-(PCB)-containing heat transfer fluids designated as Therminol FR series in the United States and Santotherm FR series in Europe. FR series Therminol heat transfer fluids contained PCBs, which imparted fire resistance. Monsanto voluntarily ceased sales of these fluids in 1971. No form of Therminol heat transfer fluids have contained PCBs since that time. Polychlorinated biphenyl was banned by the United States Congress in 1979 and the Stockholm Convention on Persistent Organic Pollutants in 2001.