It is an accepted fact in the medical community that any effect perchlorate may have on the human body is limited to the thyroid gland.

There are no measureable human health effects from low levels of perchlorate.

There are no measureable health effects when perchlorate is consumed at levels below 245 ppb. Any effects of high levels of perchlorate exposure are fully reversible once exposure declines or stops because perchlorate is not stored in the body. No studies show that environmental levels of perchlorate cause harm to human health.

The 2005 National Academy of Sciences report found that adverse effects of perchlorate exposure are only theoretical and have not been demonstrated in humans, and exposure to perchlorate over months and years must exceed levels above 14,000 ppb before there can be a risk of adverse effects.

To put this in perspective, more than 98% of perchlorate detections in U.S. water systems are below 10 ppb - that's 24 times lower than the recognized no effect level. At 10 ppb, a human would have to drink almost 740 gallons of water a day before a health risk could be possible.

Cancer Facts

The issue of whether perchlorate poses a cancer risk is a critical one, and one on which the science has been clear: perchlorate does not cause cancer.

Several national scientific and health organizations have reached this conclusion. Read below to learn more about each organization’s study of perchlorate and cancer.

The National Academy of Sciences

After careful review, the National Academy of Sciences (NAS) panel on perchlorate concluded that perchlorate is unlikely to cause cancer. Earlier studies of rats that had led to speculation about cancer in humans were dismissed by the NAS, which stated it is unlikely perchlorate poses a cancer risk to humans due to the species differences between rats and humans in thyroid function.


It is an accepted medical fact that any effects of perchlorate are limited to the thyroid gland. The U.S. Environmental Protection Agency (EPA) has stated there is no known chemical carcinogenic to the human thyroid. The EPA also acknowledges perchlorate is not mutagenic - that is, it does not cause permanent changes in the genetic material of cells that can be passed on when the cell divides. Genetic changes in the cell are often the precursor of cancerous conditions.

To be cautious, after reviewing data from a 1998 Argus Labs study, "Two Generation Reproduction Study of Ammonium Perchlorate in Rats," EPA stated in its risk assessment that perchlorate "may" pose a cancer risk to humans. The EPA is required to make this assumption based on its own Policy for Assessment of Thyroid Follicular Tumors.

In the Argus Labs study, perchlorate was given in various doses to different groups of pregnant rats. The effects were studied in two generations of those rats' offspring. Out of a total of 60, two offspring in the highest dose group developed adenomas of the thyroid gland. To equal the dose of perchlorate received by the mothers of those rats that experienced health effects, a human would have to drink 20,000 gallons of water containing 20 ppb of perchlorate every day.

The State of California

A peer-reviewed document produced for the University of California stated "no data are presented that show perchlorate, by itself, is a carcinogen." Likewise, California's Office of Environmental Health Hazards Assessment (OEHHA) stated "perchlorate does not pose a known cancer risk to the public." Read more.

Thyroid Facts

Though perchlorate may affect the thyroid gland at high doses, no actual adverse effect level for perchlorate has been identified.

In the human body at high doses, perchlorate can compete with iodine, which the thyroid gland uses to make hormones. This effect is called iodide uptake inhibition, or IUI, and this effect is not adverse. Notably, in its 2005 report, the National Research Council of the National Academies of Science (NAS) in the United States confirmed that IUI is not an adverse health effect, and that adverse effects of perchlorate exposure are only theoretical and have not been demonstrated in humans.

What else in our diet blocks iodine from the thyroid?

  •   Nitrates, thiocyanate and other compounds found naturally in everyday foods like broccoli, cauliflower, meats and leafy vegetables: 99%
  •   Perchlorate: less than 1%. Perchlorate is naturally found in organic fertilizer and in a variety of defense and industrial applications.

Source: Epidemiology of Environmental Perchlorate Exposure and Thyroid Function: A Comprehensive Review (Tarone, et al, June 2010)

The body already has natural defenses against reduced levels of thyroid hormone.
Even if iodide absorption is affected, most Americans consume at least twice the recommended daily allowance of iodide, which allows the human body to keep a substantial iodide reserve. When and if production of thyroid hormones is reduced, the pituitary gland responds by increasing production of Thyroid Stimulating Hormone (TSH), which stimulates the thyroid to make more thyroid hormones. This is a normal process that occurs naturally in the human body throughout the day to maintain optimal thyroid hormone levels.

We know how the body responds to prolonged periods of low levels of hormone.
If the need for thyroid hormones is great enough and continues for a long enough period of time, the human thyroid responds either by increasing the size of cells or by producing more cells that are capable of producing thyroid hormones.

Pregnant Women & Infants

A reference dose (RfD) is defined by the EPA as, "an estimate of a daily oral exposure to the human population, including sensitive subgroups such as children, that is not likely to cause harmful effects during a lifetime."

See the definition of reference dose on the EPA website »

The definition is based on the assumption that exposure could occur throughout the lifetime and takes into account all stages of life. Also, the definition takes into account "sensitive subgroups," such as pregnant women, infants, children, and fetuses. In the case of perchlorate, the weight of more than six decades of scientific evidence supports the conclusion that the most sensitive population to perchlorate exposure is the pregnant woman and her fetus.

Credible scientific and medical research shows that the low levels of perchlorate being detected in drinking water have no measurable effect on pregnant women or fetuses.

The basic science of perchlorate health effects, as reported by the National Academy of Sciences (NAS) are: Exposure to perchlorate at levels equivalent to 24.5 ppb would be safe for even the most sensitive population — the pregnant woman and her fetus. This was the scientific consensus noted by the NAS in 2005 — and remains the scientific consensus today.

Protecting the most sensitive population protects all populations

In 2004 and 2005, respectively, OEHHA and NAS identified the most sensitive population as the fetus of the pregnant woman. There is no scientific justification for basing regulation on any population other than the most sensitive population.

In its deliberations on the health effects of perchlorate in drinking water, the committee considered pregnant women and fetuses to be particularly sensitive populations.*

A reference dose of 24.5 ppb should protect the health of even the most sensitive populations.*

*The National Research Council Committee to Assess the Health Implications of Perchlorate