Tom Neltner, J.D., is Chemicals Policy Director and Maricel Maffini, Ph.D., Consultant
On January 9, we described a new Food and Drug Administration (FDA) report showing that perchlorate exposure to infants and toddlers increased 34% and 23% respectively between the years around 2005 and 2010. Young children were the most exposed age groups. FDA compared the exposure to a “safe dose” established in 2005 and saw no cause for concern. We respectfully disagree and find the levels alarming. First, we now know that the 2005 “safe dose” is no longer sufficient to protect children’s brains from the irreversible harm that can result from even transient exposures to perchlorate. Second, many young children may be over the “safe dose.”
Perchlorate and the brain
Perchlorate interferes with the thyroid gland’s ability to use iodine from the diet, a critical element to make a thyroid hormone, known as T4. This hormone plays an important role in the body regulating metabolism and, most critically, fetal and infant brain development. Inadequate levels of T4 during pregnancy and in the first years of life are likely to affect a child’s ability to reach his or her full intellectual potential.
Organ development, including that of the brain, is a one-way street where a series of “tightly regulated and temporally coordinated events” take place to produce a functional structure. Simply put, there is only one chance to get it right. Because of the fundamental role of thyroid hormone in brain development, experts warn that drops in T4 could adversely affect the child’s brain during pregnancy and after birth.
Perchlorate is not the only chemical in the diet that disrupts the function of the thyroid gland. Nitrates, a very common additive in processed meats, and thiocyanate, a food contaminant, also affect the ability of the thyroid to use iodine. These three chemicals affect the thyroid cells in the exact same way: they inhibit the sodium/iodine symporter, a protein whose function is to mediate the entrance of iodine from the blood into the cells, thus reducing the amount of the essential element available to make T4. Of the three, perchlorate poses the highest health risk due to its stronger bond to the symporter. Nitrate and thiocyanate’s affinity to the protein are 250 and 15 times lower, respectively, compared to perchlorate.
The “safe dose” set in 2005 is no longer sufficient to protect children’s brains
A safe amount or reference dose (RfD) represents how much perchlorate can be consumed without developing adverse effects during a lifetime of exposure. It’s usually expressed as the amount of a chemical per kilogram of body weight a person can take in on a daily basis.
The current RfD is 0.7 micrograms (µg) of perchlorate per kilogram of body weight per day (µg/kg bw/d). It was developed by a National Academy of Sciences (NAS) committee and is used by regulatory agencies as the value against which exposure to perchlorate from, for instance, drinking water and food would be compared. It hasn’t been updated since 2005.
The RfD was based on a study where adult men and women were given different amounts of perchlorate every day for two weeks. The researchers then measured how much or how little perchlorate inhibits iodine from entering the thyroid gland. The NAS committee concluded that the lowest dose of 7 µg/kg bw/d did not have an adverse effect defined as hypothyroidism. This clinical disease is recognized for low T4 levels, which triggers a response by the pituitary gland to release thyroid stimulating hormone (TSH) to stimulate the gland to make more T4. Because the study subjects were adults, an uncertainty factor of 10 was applied to protect the most sensitive population: fetuses of pregnant women with hypothyroidism or iodine deficiency.
We knew almost four years ago that the current RfD for perchlorate was insufficient to protect the most vulnerable population. In 2013, the Environmental Protection Agency’s (EPA) Science Advisory Board (SAB) stated that when hypothyroidism occurs, it may be too late to protect fetal and infant brain development. They recommended that EPA used a more sensitive measure of thyroid dysfunction, such as low T4 levels, to ensure better protection. EPA is currently developing an updated safe dose based on the SAB recommendations and has convened a panel of experts to advise it.
Many young children may be over the “safe dose” and at risk of irreversible harm
FDA’s estimate of perchlorate consumption for infants and toddlers is troubling news. The agency reported on perchlorate levels found in foods purchased between 2008 and 2012 and calculated perchlorate exposure for 14 different age/gender groups. The agency’s experts found that the mean exposure for toddlers (2 year olds) was 0.43 µg/kg bw/d but could range from 0.31 to 0.80. In other words, there is a realistic chance that the mean exposure for toddlers was already over the “safe dose” of 0.7 µg/kg bw/d.
Other young children also had an upper limit of mean exposures close to the “safe dose.” For 6-11-month-old infants, it was 0.65 µg/kg bw/d, and for 6-year-old children it was 0.55 µg/kg bw/d.
These levels alone are alarming because of the risk of irreversible harm to brain development. Yet, the report did not address additional exposure factors that further contribute to our serious concern about the risks of perchlorate in food:
- Contribution of perchlorate from drinking water, a source that is significant enough that EPA is currently developing standards to protect people.
- Exposure to nitrates and thiocyanate in the diet, which can also impair the thyroid.
Further, the levels in food may have continued to increase in the four years since the samples were collected.
Efforts to protect thyroid health and brain development are lacking
Nearly all the food we eat is contaminated with perchlorate. Exposure is likely to be even higher for those individuals drinking water contaminated with perchlorate. Given this, our children are likely consuming unsafe amounts of perchlorate. We need the FDA and EPA to act to protect what many of us value the most—our children’s health and their ability to learn and thrive to their fullest potential.