dourson's organization tera has studied many substances whose use has been the matter of public debate, including chlorpyrifos (a pesticide), diacetyl (a food additive), ammonium perchlorate (a rocket fuel), 1-bromopropane (an industrial solvent), and perfluorooctanoic acid (pfoa) (a plastics production chemical). the determinations of safe occupational exposure limits, safe water standards, threshold limit value, recommended exposure limit and safe dose may vary by a factor of ten, even among equally qualified investigators.