ATA News Release 2004

Various Levels of Perchlorate Exposure Found Not to Be Harmful to
Newborns, Pregnant Women, and Other Adults

(VANCOUVER, BC, Oct. 1, 2004)—A chemical, perchlorate, that is increasingly turning up in soil and water may not be as harmful as previously thought when people ingest it or are exposed to it, according to three new studies being presented on Sept. 30 and Oct. 1, 2004, at the 76th Annual Meeting of the American Thyroid Association in Vancouver, British Columbia, Canada.

Perchlorate is both a naturally occurring and man-made chemical. Most of the perchlorate manufactured in the United States is used as the primary ingredient of solid rocket propellant. Perchlorate is increasingly being found in the environment, at which certain levels are then passed on to people and animals through soil and water.

These discoveries have brought concern to communities and physicians, as well as the Environmental Protection Agency (EPA) because perchlorate interferes with iodide uptake into the thyroid gland. Perchlorate at sufficiently high doses can disrupt how the thyroid functions because iodide is an essential component of thyroid hormones. In adults, the thyroid helps to regulate metabolism. In children, the thyroid plays a major role in proper development and metabolism. Impairment of thyroid function in expectant mothers, in turn, may affect the fetus and newborn, resulting in behavioral changes, delayed development, and decreased learning capability. According to an EPA guidance, drinking water should not contain more than four to 18 parts per billion perchlorate. This amount is equivalent to a daily dose of .008 mg to .036 mg perchlorate for an adult.

There has been considerable debate as to what levels of perchlorate are tolerable for children, fetuses, pregnant women, and other adults, and the National Academy of Sciences is currently studying the question. Lewis Braverman, MD, of Boston University Medical Center, and colleagues undertook two studies on perchlorate exposure. In one (#31, Sept. 30, 8:00 a.m.), they recruited 13 volunteers to explore whether long-term ingestion of perchlorate would affect thyroid function. Five took 0.5 mg of perchlorate daily, four took 3 mg, and four took a placebo. Researchers reported that the daily ingestion of .5 mg or 3 mg of perchlorate for six months did not affect thyroid function in adults with normal thyroid levels. The researchers say that these findings suggest that the far lower concentrations of perchlorate found in drinking water would not adversely affect thyroid function.

In the second study led by Dr. Braverman (#119, Oct. 1, 8:00 a.m.), he and his colleagues examined the effect of perchlorate on thyroid function in workers exposed to perchlorate on the job. They monitored 29 workers who had worked at an ammonium perchlorate production plant in Utah between two to more than six years. The researchers conducted various thyroid function tests after three days off and during the last of three, 12-hour night shifts in the plant, as well as in 12 volunteers not working in the plant. Half of the workers absorbed 20 mg or more perchlorate during a single 12-hour shift.

They found that high perchlorate absorption during three nights of work exposure decreased the 14-hour thyroid radioactive iodine uptake (RAIU) by 38 percent in the workers compared to the RAIU after three days off. To have a normal RAIU test, the amount of radioactive iodine absorbed by the thyroid would be in a normal range. However, thyroid hormone levels in the blood and thyroid volume by ultrasound were not affected by perchlorate, suggesting that long-term, intermittent, high exposure to perchlorate does not cause hypothyroidism or goiter in adults.

In a third study (#125, Oct. 1, 8:00 a.m.), led by Rafael Téllez, MD, of Sótero del Río Hospital in Santiago, Chile, researchers conducted a longitudinal epidemiological study among 50–60 nonsmoking pregnant women from each of three cities in Northern Chile: Taltal with 113 ppb naturally occurring perchlorate in the public drinking water, Chañaral with 6 ppb, and Antofagasta with undetectable perchlorate. The researchers wanted to find out if chronic exposure to perchlorate may result in a situation similar to iodine deficiency. A lack of iodine, which alters thyroid hormone levels, in the mother during the early stages of pregnancy or in the newborn can cause slowed growth. They found, however, that naturally occurring perchlorate in drinking water at levels as high as 114 ig/L during pregnancy does not affect maternal thyroid status early in gestation or fetal thyroid status at birth. In addition, it does not reduce breast milk iodine concentrations.

“The perchlorate level in the municipal water in Taltal would result in a daily dose of approximately 0.2 mg a day,” said John P. Gibbs, MD, principle investigator of the study and Medical Director and Vice President of the Health Management Division at Kerr-McGee Shared Services LLC in Oklahoma City, “significantly lower than the doses studied by Dr. Braverman, yet substantially higher than any municipal sources of concern in the United States.”

# # #