The U.S. Court of Appeals for the District of Columbia Circuit has the latest word in the long-running saga concerning regulation of the contaminant perchlorate in its decision dated May 9, 2023, when it ruled the U.S. Environmental Protection Agency (EPA) must issue drinking water regulations setting a Maximum Contaminant Level (MCL) for perchlorate. This has been a long road since Massachusetts was one of the first states to regulate perchlorate in drinking water in 2006, as described by Holland & Knight in "Massachusetts Proposes First-in-the-Nation Drinking Water and Cleanup Standards of 2 ppb for the Chemical Perchlorate."
Beginning with the EPA's Unregulated Contaminant Monitoring Rule (UCMR) promulgated Sept. 17, 1999, EPA began collecting data from public drinking water suppliers on perchlorate, which is a highly soluble compound commonly used in solid rocket propellants, munitions, fireworks, signal flares and blasting materials. EPA and other federal agencies asked the National Research Council (NRC) to evaluate the health implications of perchlorate ingestion, which published its results in 2005. The NRC concluded that perchlorate exposure inhibits the transport of iodide into the thyroid, which may lead to decreases in thyroid hormone function and was especially concerning to pregnant women and their fetuses.
On May 1, 2007, EPA published the results of its analysis of the perchlorate data, concluding it was not making a statutorily authorized determination as to whether a national primary drinking water regulation is needed, but "the Agency has placed a high priority on making a regulatory determination for perchlorate and will publish a preliminary determination as soon as possible" (72 Fed. Reg. 24038). Thereafter, EPA established a reference dose (RfD) of 0.7 ug/kg/day for perchlorate consistent with the NRC recommendation. From that, EPA derived a Health Reference Level (HRL) of 15 micrograms per liter (ug/L). Despite this HRL, EPA published its Preliminary Regulatory Determination on Perchlorate on Oct. 10, 2008, indicating that "a national primary drinking water regulation would not provide a meaningful opportunity to reduce health risk" (73 Fed. Reg. 60265).
In response to comments on EPA's preliminary determination, including comments from the Massachusetts Department of Environmental Protection (DEP), EPA issued an Interim Drinking Water Health Advisory of 15 ug/L promulgated in December 2008. This Health Advisory is a non-regulatory (not legally enforceable) informal technical guidance identifying the concentration of perchlorate as a drinking water contaminant at which adverse health effects are not anticipated to occur over a specific exposure duration.
Thereafter, EPA once again sought comment on whether there is a meaningful opportunity for human health risk reduction of perchlorate through a national primary drinking water rule. In addition, EPA sought comment on its derived potential alternative HRLs for 14 different age groups, which ranged from 1 ug/L to 47 ug/L. EPA received approximately 39,000 comments from individuals and organizations. Massachusetts DEP once again filed comments urging EPA to set the HRL on the basis of the life stage(s) with the highest exposure and risk, which Massachusetts concluded would support an HRL of 2 ppb.
On Feb. 11, 2011, EPA issued its formal Regulatory Determination concluding that perchlorate meets the SDWA criteria for regulating a contaminant. Specifically, EPA concluded that perchlorate 1) may have an adverse health effect, 2) is known to occur or is at risk for occurring in public water systems with frequency and at levels of public health concern, and 3) regulation presents a meaningful opportunity for health risk reduction. EPA concluded that as many as 16 million people could be exposed to perchlorate at levels of concern. Having concluded that perchlorate meets the criteria for regulating a contaminant under SDWA Section 1412(b)(1)(A), EPA announced it would "initiate the process for proposing a NPDWA [National Primary Drinking Water Regulation] for perchlorate" (76 Fed. Reg. 7765).
Thereafter, EPA went about the regulatory process, including further evaluation of the scientific approach and modeling of adverse health effects. It sought the advice of the Science Advisory Board (SAB), which provided recommendations in its 2013 report and it conducted peer review studies of its modeling efforts. The SAB recommended a robust and transparent process by which to consider sensitive life stages explicitly because perchlorate was known to disrupt thyroid function, and interference with the thyroid and available thyroid hormones is known to produce adverse effects on neurodevelopment in humans, with fetuses and infants being most vulnerable. Specifically, the SAB recommended EPA address sensitive life stages through "physiologically-based pharmacokinetic/pharmacodynamic modeling based upon its mode of action" (also known as Biologically Based Dose Response or BBDR), rather than the default approach using the RfD. EPA undertook such studies developing a two-step approach combining the BBDR model results with epidemiology literature that relates incremental changes in maternal thyroid hormones to neurodevelopmental outcomes in children. Next, EPA evaluated the occurrence data collected from the UCMR and other monitoring, including the data generated by Massachusetts and California, which each had previously adopted their own, much lower MCLs of 2 ppb and 6 ppb, respectively.
Then, on the eve of a court-ordered deadline in June 2019, EPA sought comment whether it should withdraw its 2011 Regulatory Determination and issue no NPDWR for perchlorate based upon the available information that the benefits of establishing an NPDWR for perchlorate do not justify the associated costs.
A year later, and after more than 1,000 comments were filed in the docket, on June 18, 2020, EPA issued a press release indicating it determined that perchlorate does not meet the criteria for regulation as a drinking water contaminant under the Safe Drinking Water Act (SDWA) and thus is withdrawing the 2011 Regulatory Determination and is making a final decision to not issue a national regulation for perchlorate. Specifically, EPA determined that perchlorate does not occur "with a frequency and at levels of public health concern" within the meaning of the SDWA. In addition, in the judgment of the EPA Administrator, regulation of perchlorate does not present a "meaningful opportunity for health risk reduction for persons served by public water systems." This decision was reaffirmed on March 31, 2022, when EPA stated it did not intend to regulate perchlorate in drinking water, instead issuing a two-page plan to address perchlorate contamination.
EPA was once again sued. This time, the court ruled that EPA's withdrawal of its Regulatory Determination was improper. Two of the three judges found EPA lacked statutory authority to withdraw a Regulatory Determination once made under the SDWA, while the concurring judge found the "EPA's 2020 decision not to regulate perchlorate was arbitrary, capricious, and contrary to law because it was based on a MCLG that did not comply with a statutory directive, and relied on selectively updated data concerning the prevalence of perchlorate in drinking water."
It will be interesting to see what happens on remand, and whether this tortured history has any impact on EPA's long-awaited proposal to regulate per- and polyfluoroalkyl substances (PFAS) under the SDWA through issuance of a proposed NPDWR for six PFAS compounds. As described in Holland & Knight's previous alert, "EPA Publishes Proposed PFAS Drinking Water Regulation," March 29, 2023, comments on that proposal are still being accepted until May 30, 2023.