An Environmental Working Group (EWG) analysis of recently published data from scientists at the Centers for Disease Control (CDC) and Boston University (BU) shows that infants are being exposed to dangerous levels of the rocket fuel component perchlorate. The CDC/BU study, which examined breast milk from 49 Boston area women, found that the average infant in this study is being exposed to more than double the dose of perchlorate that the Environmental Protection Agency (EPA) considers safe; highly exposed babies are ingesting up to 10 times this amount. [1,2]
Boston area infants are exposed to unsafe levels of perchlorate in breast milk
At the 95th percentile perchlorate dose level in women with lower iodide intake, CDC found a 20% drop in thyroid hormone levels
Calculations based on 4kg infant and average daily infant intake of 0.78 liters breast milk.
Sources: 1, 3.
If this weren't troubling enough, in September of 2006, the CDC published a study showing significant changes in thyroid hormone levels in women who were exposed to far less perchlorate than babies drinking breast milk in this study, and less than the EPA "safe" dose.  Since it is also well known that infants are at much greater risk for thyroid hormone disruption than adults, taken together, the findings of these two studies show that the perchlorate levels found in the breast milk of ordinary American women could be threatening the normal development of their exposed infants. 
Perchlorate, the explosive ingredient in solid rocket fuel, has leaked from military bases and defense and aerospace contractors' plants in at least 22 states, contaminating drinking water for millions of Americans. The chemical has also been found to contaminate dairy milk, produce, and many other foods and plants. [5-12] In a related 2006 study, the CDC found perchlorate in the urine of every one of 2,820 people tested, suggesting that food is a key route of exposure in addition to drinking water.  Boston's tap water is not known to be contaminated with perchlorate; the 49 women in this study were likely exposed through food. 
Infants are at greater risk for thyroid disruption by perchlorate than adults for several reasons. Perchlorate acts by inhibiting the thyroid gland's ability to take up the nutrient iodide, a key building block for thyroid hormone. Unlike adults, infants have minimal stores of thyroid hormones and must rely instead on their own daily production (breast milk does not contain significant quantities of thyroid hormone). Therefore, while adults may be able to use hormone stores to make up for temporary shortages related to chemical insults, infants can only do this to a very small degree. 
While thyroid hormones regulate metabolism in adults and long-term deficiencies can lead to chronic health problems, the consequences for thyroid disruption in infants are much more serious. Normal thyroid hormone levels are critical for normal brain and organ development, and recent research has shown that infants can suffer permanent neurological deficits from even short-term thyroid hormone insufficiency. [15,16,17]
On average, babies drinking breast milk in the Boston study would be exposed to 19 times more perchlorate than the September, 2006 CDC study found would depress thyroid hormone levels by 20 percent in adult women with lower iodide intake (thirty-six percent of women in the U.S. have urinary iodide levels in this "lower" range). 
To make matters worse, the Boston study found that 47 percent of the babies tested were not getting adequate levels of iodine from breast milk. Since the effects of perchlorate are compounded by insufficient iodide consumption, these babies are at even greater risk for thyroid hormone disruption. 
Notably, the Boston study also found that even moms who ingested extra iodine by using iodized salt or taking multivitamins containing iodine didn't always have sufficient iodine in their breast milk.  This finding is important because it underscores the need for the government to act to reduce perchlorate contamination of food and drinking water, rather than just simply pointing to iodized salt and multivitamins as quick fixes to the perchlorate problem.
Earlier research confirmed—health protections still lacking
The CDC/BU study confirms earlier research that found high levels of perchlorate in breast milk. [18,19] One study, for example, found perchlorate in every one of 36 samples of breast milk from nursing mothers in 18 states at levels as high as 92 parts per billion (ppb).  The Boston study found even higher levels of perchlorate among its 49 women, with a maximum concentration of a startling 411 ppb. The median perchlorate level in CDC/BU study was 9 ppb. 
The Boston study also measured perchlorate concentrations in the mother's urine, finding a median level of 3.0 ppb. More important than the actual values, however, is the fact that these concentrations are remarkably similar to the levels of perchlorate that the CDC found in its much larger study of perchlorate exposure that tested the urine of more than 2,800 individuals.  In that study, the median urinary perchlorate concentration was 3.6 ppb. Since the perchlorate exposures in the two studies are so closely aligned, one can assume that the high levels found in the Boston women's breast milk are, unfortunately, probably typical of the general U.S. population.
CDC's large study of urinary perchlorate levels also raises concerns about fetal exposures. CDC found that in the 36 percent of U.S. women with low iodine intake, almost any amount of perchlorate exposure was linked to a significant change in levels of thyroid hormones.  For about 1 in 10 of these women, exposure to perchlorate in drinking water at 5 ppb would result in subclinical hypothyroidism; this is a condition that requires treatment if these women become pregnant because it may negatively impact the brain development of their fetus if left untreated.  EWG estimates that there are more than 2.2 million women who fall into this latter category. 
Taken together, the weight of the evidence from these studies strongly support the conclusion that perchlorate is a major public health threat that needs to be addressed. Yet, there are still no federal safety standards for perchlorate in drinking water or food. Under pressure from the Pentagon and the defense industry, EPA has delayed setting a drinking water standard for perchlorate. California is in the final stages of adopting a perchlorate drinking water standard of 6 ppb, recommended by state scientists before release of the September, 2006 CDC study. The proposed standard in New Jersey is 5 ppb. Last July, Massachusetts adopted 2 ppb as the nation's first legally enforceable drinking water standard.
Senators Boxer, Feinstein, and Lautenberg and Representative Solis from California have introduced legislation in the U.S. Senate and House of Representative that seeks to improve perchlorate monitoring and regulation to better protect public health.
Breast milk is by far the healthiest food for infants. However, the perchlorate levels found in breast milk in this CDC/BU study are alarming. The doses of pechlorate that infants are getting from ingesting this food are far higher than doses that have been shown to cause significant disruptions of thyroid hormone levels in many adult women. We also know that infants are more vulnerable than adults to the health effects of perchlorate exposure.
The level of perchlorate found in breast milk in this study suggests a serious threat to the normal development and health of potentially all American infants.
To protect public health:
EPA must adopt a maximum contaminant level for perchlorate in drinking water based on the most recent science, including the 2006 CDC study and the Boston study described above. The 2006 CDC study showed convincingly, with statistically valid data from a large human population, that perchlorate levels well below the EPA's "safe" dose cause significant thyroid hormone depression in adult women of childbearing age.
With the CDC study showing that even less than 1 ppb perchlorate in water may pose health risks to women, fully protective drinking water standards must be set as low as possible—at no more than 1 ppb—and revised downward as detection and cleanup technology improves. The Food and Drug Administration must also adopt an action level for perchlorate in food that is designed to protect the fetus, infants and children from the adverse effects of these exposures.