Scientific Studies


Health Implications of Perchlorate Ingestion is the most comprehensive and authoritative source of scientific information on human health issues relating to perchlorate. This landmark report was published by the National Academy of Sciences (NAS) National Research Council (NRC) in 2005.

The NRC select panel on perchlorate comprised 15 world-renowned experts in toxicology, thyroid endocrinology, pediatric endocrinology, epidemiology and other areas of science directly related to perchlorate. The panel was engaged by U.S. EPA to review perchlorate science in response to significant questioning and criticism of the scientific basis for EPA’s 2002 draft risk assessment for perchlorate. In 2005, EPA adopted the NRC-derived Reference Dose (RfD), which remains in effect today.

The NRC panel focused on the perchlorate dose-response relationship. The panel’s review concluded that below a threshold equal to 245 ppb in water, no measurable effects were reported. The NRC estimated that a dose 50 times greater than this threshold must be ingested on a daily basis for several months or years for an adverse effect to occur (such as hypothyroidism). NRC further concluded that a perchlorate exposure 10-fold less than this threshold dose —equivalent to 24.5 parts per billion (ppb) — would be safe for even the most sensitive population, identified as the pregnant woman and her fetus (all others being less sensitive).

It is important to underscore NRC’s scientific logic in providing a level of safety far exceeding customary regulatory practice. NRC chose to base its RfD on a No Observed Effect Level (NOEL) of a non-adverse effect, rather than the no observed adverse effect level (NOAEL) or lowest observed adverse effect level (LOAEL), which EPA has traditionally used as the point of departure. The NOEL is the dose at which no effect occurs, adverse or otherwise, and results in a substantially more conservative RfD than the traditional and also conservative approach using the NOAEL or LOAEL.

Equally important, no new scientific information has been published in the peer-reviewed literature since the NRC report refuting the NAS panel’s conclusions relating to the fundamental knowledge of perchlorate and its effects on human health.