EPA uses standard default conversion factors for body weight (70 kilograms) and tap water consumption (2 liters per day) to translate RfDs to drinking water equivalents in ppb. For most people in a population, these assumptions are conservative as most people do not drink this much water each day (84 percent of the population drinks less than this amount each day). The following ppb equivalents correspond to various perchlorate doses:


No Observed Adverse Effect Level (NOAEL) [0.4 mg/kg per day] 14,000 ppb
No Observed Effect Level (NOEL) [0.007 mg/kg per day] 245 ppb
NAS Committee recommended reference dose [0.0007 mg/kg per day] 24.5 ppb

The NAS Committee based its RfD on the NOEL instead of the NOAEL and applied an additional 10-fold safety factor to account for sensitive populations.