General Publications July 20, 2020

“EPA’s Pass on Perchlorate Regulation Reduces Lawsuit Risk,”Law360, July 20, 2020.

Extracted from Law360

The U.S. Environmental Protection Agency has refused to regulate perchlorate in drinking water, in a decision that is supported by a wide range of scientific studies showing perchlorate exposure is not harmful.

Perchlorate is both a naturally occurring and manufactured chemical. Ammonium perchlorate, which is an oxidizer, has been used as the largest component in solid rocket engines for decades, and potassium perchlorate remains an important ingredient in road flares and fireworks.

In 1997, perchlorate was detected in water sources nationwide due to advances in groundwater testing. By 2011, perchlorate had been detected in 4% of water systems tested nationwide, exposing between 5 and 16 million people to the chemical.[1]

Perchlorate can block the thyroid's uptake of iodide, an essential dietary nutrient, if it is present in the bloodstream at high enough concentrations.[2] Intake of very high levels of perchlorate can be of concern for sensitive populations — in particular, pregnant women — because it can lower iodide uptake in such a way that it decreases production of hormones needed for fetal brain development.[3]

Since its initial widespread detection, government and private sector officials have battled over whether the EPA should establish a maximum contaminant level, or MCL, for perchlorate under the Safe Drinking Water Act and, if so, what level is safe to consume. An MCL is the maximum allowable level of a contaminant in water that is delivered to any user of a public water system.

Massachusetts and California hastily rushed to regulate perchlorate in drinking water, setting respective MCLs of 2 micrograms per liter in 2006[4] and 6 micrograms per liter in 2007,[5] in the face of multiple scientific studies showing that perchlorate in drinking water is harmless at those levels, and even at much higher levels. To this day, those are the only two states that have set MCLs for perchlorate, though 10 others have established guidance on acceptable amounts of perchlorate in drinking water.[6]

On June 18, the EPA formally announced it would not regulate perchlorate, and formally withdrew a 2011 Obama administration decision to regulate perchlorate in drinking water.[7] The EPA's decision likely means that no federal MCL will be established during the Trump administration, and deprives plaintiffs attorneys of the argument that consumption of perchlorate at levels above the MCL is de facto evidence of harm.

The EPA's decision to refrain from setting a nationwide MCL under the Safe Drinking Water Act for perchlorate evidences sound governance, which is fully supported by numerous scientific studies that show low-dose exposure to perchlorate presents no risk to human health. Study after study has found that perchlorate exposure in doses both similar to, and significantly greater than, the Massachusetts and California MCLs has no negative health effects.

For example, one Nevada study examined people who consumed drinking water that contained 4 to 24 micrograms of perchlorate per liter, and found "no evidence that perchlorate-containing drinking water at the given level increased the prevalence of acquired hypothyroidism or of any other thyroid condition."[8] Another study looked at adults who were given 3 milligrams per day of perchlorate for six months, and the dosage had "no effect on thyroid function."[9]

Multiple studies have also found that drinking water containing perchlorate is not harmful to mothers and infants, a particularly vulnerable population. A Boston University study of mothers and infants found that although perchlorate and thiocynate, another iodide inhibitor, were ubiquitous in the environment and present in breast milk, infants were not harmed: "[T]hese results do not support the concern that maternal and infant environmental perchlorate and thiocyanate exposures affect infant thyroid function."[10]

Another study analyzed 23,000 newborns in Nevada, comparing those living in areas with water that contained 9 to 15 micrograms of perchlorate per liter to those living in areas with no perchlorate in the water, and found no difference between the two groups.[11]

And yet another study looked at pregnant women living in Chilean cities with perchlorate in the drinking water ranging from 0.5 to 114 micrograms of perchlorate per liter, and found no differences among their babies at birth — and also found the infants to be consistent with norms in the U.S.[12] "Therefore, perchlorate in drinking water at 114 micrograms per liter did not cause changes in neonatal thyroid function or fetal growth retardation," the study found.

Still other studies have looked at workers who experienced prolonged exposure to perchlorate, and found no negative health effects. One study of manufacturing plant workers exposed to 0.004 to 167 milligrams of particulate perchlorate per day found that "thyroid function was not affected by these levels of absorbed perchlorate," and that "no clinical evidence of thyroid abnormalities was found in any exposure group."[13]

And a Nevada study looked at employees at an ammonium perchlorate production facility, where single-shift exposures ranged from 0.2 to 436 micrograms per kilogram. It found that "no perchlorate-attributable effects on thyroid, bone marrow, kidney or liver function were detected."[14]

There are also lingering questions about how people are even exposed to perchlorate. A 2008 EPA report noted that although the U.S. Department of Defense and defense contractors account for 90% of perchlorate use nationwide, perchlorate exposure is so widespread that it cannot be attributed to just those entities.[15]

The report also stated that although perchlorate can inhibit the uptake of iodide, the chemical thiocyanate occurs naturally in many common vegetables, and also inhibits the uptake of iodide, raising questions about the source of any iodide uptake issues.[16]

Taken together, these studies show that perchlorate exposures in line with the Massachusetts and California MCLs are actually harmless, and validates the EPA's decision not to regulate perchlorate in drinking water. They also call into question decision-making by Massachusetts and California regulators to heavily regulate this naturally occurring chemical at levels that are absurdly low, at a cost to the government and other stakeholders of billions of dollars.[17]

Establishment of an MCL for perchlorate could have far-reaching implications. The setting of an MCL, particularly at a low level, would have provided plaintiffs attorneys a baseline to argue that contamination beyond that level could cause negative health effects.

A low MCL could also force entities to either clean up groundwater or stop serving it to customers, and would almost certainly lead to a cascade of litigation against entities allegedly responsible for perchlorate contamination. Government entities such as the Department of Defense and NASA, as well as major defense contractors, would likely be ensnared in such lawsuits.

The federal government has taken a winding path on perchlorate regulation. Congress has considered, but never adopted, legislation mandating perchlorate regulation. All action thus far has been by the executive branch.

In 2008, President George W. Bush's administration declined to regulate perchlorate in drinking water after finding there was not "meaningful opportunity for health risk reduction" via an MCL. Then, in 2011, President Barack Obama's administration reversed that decision and announced that it intended to establish an MCL for perchlorate.

No MCL was set during the Obama administration, and the task fell to the Trump administration. In June 2019, the EPA sought public comment about perchlorate regulation, and presented three regulatory proposals:

  • Setting an MCL for perchlorate at 18 micrograms per liter;
  • Setting an MCL for perchlorate at 90 micrograms per liter; and
  • Withdrawing the agency's 2011 determination to regulate perchlorate in drinking water altogether and to not set an MCL.[18]

On June 18, the EPA formally adopted the third proposal, withdrawing the 2011 determination to regulate perchlorate and opting not to set an MCL. It is notable that scientific studies have found that perchlorate exposures at MCLs that the EPA considered are not harmful.

The agency's decision not to regulate perchlorate is "built on science and local success stories," EPA Administrator Andrew Wheeler said in a statement.[19] "State and local water systems are effectively and efficiently managing levels of perchlorate. Our state partners deserve credit for their leadership on protecting public health in their communities, not unnecessary federal intervention."

On May 14, before declining to regulate perchlorate in drinking water, Wheeler issued a statement touting a reduction in perchlorate contamination nationwide since 2011. "Because of steps that EPA, states and public water systems have taken to identify, monitor and mitigate perchlorate, the levels have decreased in drinking water," Wheeler said.[20] The reduction in perchlorate contamination is attributed to remediation activities nationwide, as well as the establishment of state MCLs in Massachusetts and California.

Moreover, the EPA released a fact sheet documenting the reductions of perchlorate in drinking water systems across the country.[21] The fact sheet surveys the water systems, catalogs reductions in perchlorate, documents the reason for the reductions and concludes that perchlorate no longer exists at levels that could harm public health.

"The EPA concludes that there is infrequent occurrence of perchlorate at the levels of public health concern," the fact sheet says.[22] "In addition, studies show that perchlorate occurrence in the environment has decreased over time, due to several mitigation actions taken by the EPA and others."

Although the EPA's refusal to regulate perchlorate likely stopped what could have been a cascade of litigation if a perchlorate MCL had been established, plaintiffs may still file perchlorate contamination lawsuits. The heart of those lawsuits will be the science behind perchlorate. It is imperative that defendants use expert testimony to demonstrate what the science has already proved: that current levels of perchlorate in drinking water are not harmful.

The EPA's decision to follow the science and not regulate perchlorate provides greater weight to the scientific findings. Moreover, in making its decision, the EPA also performed a new health impact analysis based on recommendations from the agency's Science Advisory Board. The new analysis showed that the concentrations at which perchlorate may present a public health concern are higher than the concentrations considered in the 2011 regulatory determination, according to an EPA statement.

[1] EPA, Reductions of Perchlorate in Drinking Water, at 2 (May 2020). Available at:

[2] EPA, Office of Inspector General Scientific Analysis of Perchlorate, Assignment No. 2008-0010, at 1 (External Reviews Draft Released Dec. 30, 2008).

[3] Id.





[8] F.X. Li, L. Squartsoff, S.H. Lamm, Prevalence of Thyroid Diseases in Nevada Counties with Respect to Perchlorate in Drinking Water, Journal of Occupational Environmental Medicine, 43:630–634 (2001).

[9] Lewis E. Braverman et al., Effects of Six Months of Daily Low-Dose Perchlorate Exposure on Thyroid Function in Healthy Volunteers, Journal of Endocrinology & Metabolism (August 2006).

[10] Angela M. Leung and Lewis E. Braverman, et al., Environmental Perchlorate and Thiocyanate Exposures on Infant Serum Thyroid Function, Thyroid, vol. 22, no. 9 (2012).

[11] Zili Li et al., Neonatal Thyroxine Level and Perchlorate in Drinking Water, Journal of Occupational and Environmental Medicine (February 2000).

[12] Rafael Téllez Téllez et al., Long-Term Environmental Exposure to Perchlorate Through Drinking Water and Thyroid Function During Pregnancy and the Neonatal Period, Thyroid, vol. 15, no. 9 (2005).

[13] S.H. Lamm et al., Thyroid Health Status of Ammonium Perchlorate Workers: A Cross-Sectional Occupational Health Study, Journal of Occupational Environmental Medicine (April 1999).

[14] J.P. Gibbs et al., Evaluation of a Population With Occupational Exposure to Airborne Ammonium Perchlorate for Possible Acute or Chronic Effects on Thyroid Function, Journal of Occupational Environmental Medicine (December 1998).

[15] EPA, Office of Inspector General Scientific Analysis of Perchlorate, Assignment No. 2008-0010, at 2 (External Reviews Draft Released Dec. 30, 2008).

[16] Id. at 1-2.

[17] Not to be stopped by mounds of scientific data that compels lifting the MCL for perchlorate in California, regulators there are doubling down, pushing to lower the existing MCL from 6 parts per billion to 1 part per billion, the equivalent of one drop of perchlorate in an Olympic-size swimming pool. Although the costs of making this change after many cleanup systems are already in place has not been calculated, it is certain to saddle government and other stakeholders with hundreds of millions, if not billions, of dollars in costs that will accomplish nothing toward protecting human health.




[21] EPA, Reductions of Perchlorate in Drinking Water (May 2020).

[22] Id. at 12-13.

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