Safe Exposure Levels

At the request of the U. S. Environmental Protection Agency (EPA), the National Academy of Sciences (NAS) convened a world-class panel of experts to review the scientific database on perchlorate. Fortunately, at the time there was more than 50 years of research available; dating back to when perchlorate was used as a medicine at levels thousands of times higher than those now found in the environment.

After nearly two years of review and study, the NAS issued its report on the health implications of perchlorate in January 2005. The NAS committee concluded that a reference dose of perchlorate at 0.0007 milligrams per kilogram per day is appropriate and protective for all populations, including the most sensitive population: fetuses of pregnant women who might have hypothyroidism or iodide deficiency.

In February 2005, EPA established its official reference dose of perchlorate at 0.0007 milligrams per kilogram per day, and translated that number to a Drinking Water Equivalent Level of 24.5 parts per billion (ppb). Subsequently, EPA issued a Health Reference Level of 15 ppb to account for potential exposure to perchlorate from food.

Perchlorate in Perspective

Massive quantities of perchlorate are necessary over an extended period of time to create any risk of adverse effect in humans. As the example below illustrates, the National Academy of Sciences (NAS) reference dose for perchlorate exposure is already thousands of times lower than that level. There is no need to further reduce the reference dose for perchlorate.

14,000 ppb
The dose NAS estimates would be necessary to pose a risk of adverse effects if exposure was sustained for months or years.

245 ppb


The identified No Observed Effect Level (NOEL). Limiting exposure below the NOEL provides no additional health benefit.

24.5 ppb

1/10 of NOEL

Conservative reference dose level recommended by the NAS, taking into account the most sensitive populations.

6 ppb

1/40 of NOEL

Maximum Contaminant Level for perchlorate in California.

1 ppb

1/245 of NOEL

California’s Perchlorate Public Health Goal.