Summary of Scientific Studies

Overly Strict Standards Would Create Unnecessarily High Costs to Consumers, Society

Perchlorate has a long, 50-year history of use as a medicine to treat certain thyroid gland disorders and because of this much is known about how it works in the human body. For example, the most up-to-date scientific studies show perchlorate is not carcinogenic (cancer-causing) in humans.

Even more has been learned in the last six years since new technology led to detection of perchlorate in drinking water. This finding led to new research into the health effects of perchlorate that shows perchlorate at low levels (under 245 parts per billion in drinking water) has no measurable health effects.

The body of scientific and medical knowledge about perchlorate includes 16 studies conducted between 1998 and 2002 specifically to determine any health effects of perchlorate at varying levels in water. Ten of these studies looked at perchlorate's effects on humans, and the other six studied its effects in animals. These studies on adults, newborns and children, together with new research completed in 2004 provide reason to believe that low levels of perchlorate also have no measurable effect on pregnant women or fetuses.

The National Academy of Sciences (NAS) spent nearly two years reviewing and analyzing the most recent scientific studies, research and data on perchlorate. Based on this review, 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 - the fetuses of pregnant women who might have hypothyroidism or iodide deficiency.

Key findings:

  1. Data from human studies shows that low levels of perchlorate being detected in some drinking water supplies have no adverse health effects on adults, children and newborns. >>Read about these studies.

    • Tellez et al. study. This study found no impacts from perchlorate on pregnant women during the critical period between the late first and early second trimesters, and no effect on fetal development or thyroid levels in newborns. The study examined pregnant women and babies from three cities in Chile, where perchlorate levels range from non-detect to 110 parts per billion (ppb), and daily intake of dietary iodide is equivalent with the U.S.
    • Kelsh et al. study. This study evaluated whether newborns had higher rates of primary congenital hypothyroidism (PCH) or elevated concentrations of thyroid-stimulating hormone in a community where perchlorate was detected in groundwater wells. The findings, according to the Journal of Occupational and Environmental Medicine, suggest that residence in a community with potential perchlorate exposure has not impacted PCH rates or newborn thyroid function.
    • Lamm and Doemland study. The actual number of cases of congenital hypothyroidism was compared to the expected number in seven counties in Nevada and California where perchlorate is present in water at levels of 4 ppb to 16 ppb. The study determined that perchlorate in drinking water at these low levels has no measurable effect on thyroid development of newborns.
    • Li et al (2000a). This study examined the thyroid function of more than 23,000 newborns in Las Vegas, where perchlorate is found in water up to 15 ppb, and Reno, which has no perchlorate in drinking water. It compared the thyroid hormone levels of newborns in each city and found no difference.
    • Li et al (2000b). This study, similar to the one above, examined the thyroid function of more than 540 newborns in Las Vegas and Reno. Scientists looked for changes in thyroid stimulating hormone (TSH) as evidence that the Las Vegas newborns were compensating for decreased levels of thyroid hormones. There was no difference in TSH levels in newborns in the two cities.
    • Li et al (2001). The study compared the prevalence of thyroid disease in Medicaid-eligible residents of Clark County, Nevada, which has perchlorate in drinking water up to 24 ppb, to Medicaid-eligible residents in other Nevada counties where perchlorate is not present in drinking water. It found no evidence of a higher rate of any thyroid disease in Clark County.
  2. Perchlorate has no measurable effect on the body until it reaches levels of approximately 245 ppb or greater in drinking water, at which point it may begin to block some of the thyroid's iodide uptake. Below this "no-effect" level of 245 ppb, perchlorate has no measurable biochemical or biological impact on people. Adverse effects are not seen at perchlorate levels of 14,000 ppb or less >>Read about these studies.

    • Greer study. Healthy adult volunteers, including both men and women, consumed perchlorate in drinking water at various dose levels for 14 days. At the low dose, equivalent to 180 ppb to 220 ppb, there was no detectable inhibition of iodide uptake by the thyroid. (The thyroid uses iodine to produce hormones essential to growth and metabolism.) There was no adverse change in thyroid hormone levels associated with any dose level.
    • Crump study. This study of children and newborns shows "no health-effect" at levels of about 110 ppb.
    • Braverman study. Healthy male volunteers consumed perchlorate equivalent to either 1,500 ppb or 5,000 ppb in drinking water for 14 days. There was approximately 10 percent and 38 percent inhibition of iodide uptake at the lower and upper levels, respectively. No adverse changes in thyroid hormone levels were observed at either level.
    • Braverman (2004). The study found that long-term, intermittent high exposure to perchlorate does not induce hypothyroidism or goiter in adults. The study examined 29 healthy adult males in Cedar City, Utah, who had been working in perchlorate production for at least two years, with 50 percent of the subjects having worked in perchlorate production for more than six years. Exposure to perchlorate was through ingestion and inhalation, and median exposure levels were equivalent to 10,000 ppb.
    • PBPK (Pharmocokinetic) Model Studies. These studies, conducted in rats, were designed to describe and predict the movement and effects of perchlorate in the body. Among other things, they showed that the threshold for iodide uptake inhibition in rats was equivalent to 350 ppb perchlorate in drinking water for humans.
  3. In healthy adults, perchlorate causes no adverse effects on the body at levels of 14,000 ppb or less. >>Read about these studies.

    • Lamm et al. and Gibbs et al. These studies examined employees who worked with perchlorate and were exposed to it in the air for several years. Breathing perchlorate is the same as drinking perchlorate in terms of its health effects. Workers in the highest exposure category absorbed doses of perchlorate equal to drinking two liters of water per day containing an average of 17,000 ppb of perchlorate. No differences in blood chemistry or thyroid hormones were found in the workers, nor was evidence of thyroid abnormalities observed in any group. The Lamm data showed that the lowest dose of perchlorate that could possibly cause an adverse effect to thyroid hormone levels, if ingested regularly for years, was 20,000 ppb.
  4. Even in rats, which are much more sensitive than humans to perchlorate, it takes extremely high doses of perchlorate (above 14,000 ppb) - beyond what would ever be found in nature or drinking water - to generate an adverse health effect. >>Read about these studies.

    • York et al. This study looked at whether perchlorate causes birth defects in rats. No adverse effects were found in either rat mothers or fetuses at doses of perchlorate equivalent to 1,050,000 ppb in water. The study confirms perchlorate is not a reproductive toxicant.
    • Bekkedal study. This study tested the motor activity of baby rats whose mothers were exposed to varying doses of perchlorate equal to 3,500 ppb to 350,000 ppb. The study found no significant differences between rat pups whose mothers were treated with perchlorate and those whose mothers weren't. It confirms the findings of an earlier neurobehavioral development study of perchlorate's effects in rats.
  5. Other studies.

    • Dasgupta et al. This study looked at how atmospheric processes can cause naturally occurring perchlorate. >>Read about this study.

In February 2005, the U.S. Environmental Protection Agency 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 ppb. This level is consistent with the recommended reference dose included in the NAS report.