Reports that the EPA may not set national drinking water limits for perchlorate have already resulted in outcries from various groups.
The EPA has not issued any new drinking water regulations since revised disinfection and filtration rules about 15 years ago, so perchlorate seemed to be the most likely next candidate.
The EPA has produced several Drinking Water Health Advisories (DWHA) for algal toxins, perfluorocompounds, and perchlorate. It has been examining the perchlorate regulatory question for more than 15 years. Perchlorate is present in some locations from natural or synthetic sources, including in some fertilizers from solar UV oxidation, fireworks and explosives manufacture, and some solid rocket fuels.
It is present at low parts per billion (ppb or micrograms/liter) levels in some groundwaters, and the diet. It had been used therapeutically to treat Graves Disease, significantly overactive thyroid, with doses as high as 600 to 1000 mg per day (600,000 to 1,000,000 micrograms).
The concern for exposure to perchlorate is for pregnant women and infants who are deficient in iodine intake, because of risks of neurological effects from deficient thyroid function. Perchlorate, as well as other common anions, competes with iodide transport to the thyroid by the sodium-iodide symporter (NIS) protein. Its binding is stronger than other anions.
Based upon data from 2001-2005, EPA (2011) estimated that about 3 percent of U.S. water supplies would be affected by a Maximum Contaminant Level of 4 ppb, and about 0.5% by an MCL of 15 ppb. There are a few states where most of the national perchlorate detections have occurred. Since then, EPA reported (Proposal, May 2020) that substantial reductions had occurred and that the current estimate was that 0.03% would exceed 18 ppb.
The EPA said its latest analysis of perchlorate monitoring data shows that the chemical is showing up infrequently at levels of public health concern. The EPA, however, stopped short of saying whether it will move ahead with its plans to set actual drinking water limits for the chemical in its final regulation that the White House Office of Management and Budget is currently reviewing.
The EPA in 2019 had proposed four options, which included varying drinking water limits for the chemical and the option to withdraw its 2011 decision to regulate this chemical. State officials say the EPA report indicates that the agency is moving from its decision to set national drinking water standards, and here’s why.
Health Basis for Potential Drinking Water Regulations
Perchlorate is essentially not metabolized and is excreted unchanged with a half life of ingested perchlorate of about 8 to 12 hours, so it also rapidly disappears when dosing ceases.
There are several controlled perchlorate dose studies with human volunteers. One example of the human studies found no difference in thyroid status in pregnant women in a city in Chile with 110-115 ppb in the drinking water plus 20-30 micrograms in their diets, and urinary iodide of 269 micrograms per liter, compared to two other cities with less than 0.5 or 6 ppb in the drinking water.
The National Research Council (NRC) independent review (2005) concluded that iodide deficiency in the US population was mild, if it exists, and they (and the EPA’s Integrated Risk Information System, IRIS) applied a safety (uncertainty) factor of 10 to the human data in the most sensitive population, and concluded it was “conservative and health protective.”
They also concluded that perchlorate was not carcinogenic in humans. The NRC recommended No Observed Adverse Effect Level (NOAEL) was 400 micrograms per kg body weight. IRIS calculated an oral reference dose of 0.0007 mg/kg/day from a No Observed Effect Level (NOEL) of 0.007 mg/kg/day (also the NRC NOEL) applying that factor of 10 to controlled human studies. IRIS concluded that it had High confidence in the Reference Dose.
The EPA (2008) issued a Drinking Water Health Advisory (DWHA) of 15 micrograms/liter based upon the NRC report. The WHO/FAO Joint Expert Committee on Food Additives (2015) calculated a provisional tolerable daily intake of 10 micrograms/kg/day and estimated highest exposures were around 0.7 micrograms/kg/day with a mean of 0.1 micrograms/kg./day, and concluded that it was not a health concern. The World Health Organization Guidelines for Drinking Water Quality (2017) established 70 ppb as the guideline value in drinking water with margins of safety.
Safe Drinking Water Act Criteria for National Regulation
The Safe Drinking Water Act specifies three criteria that the EPA must apply to the regulatory determinations for potential drinking water standards.
- The contaminant may have an adverse effect on the health of person.
- The contaminant occurs in public water systems with a frequency and at levels of public health concern.
- In the judgment of the EPA Administrator, regulation presents a meaningful opportunity for health-risk reduction.
As with most or all chemicals, perchlorate may have an adverse health effect if the dose is sufficiently high. As of EPA 2011 and 2020, based upon the low occurrence frequency and reported concentrations, and the several noted guidelines and DWHA, meeting the second criterion is debatable, and thus the third criterion is also not likely to be met.
States have the authority to establish state standards to address their situations. Many states have utilized the EPA DWHA value of 15 ppb as their decision rule, and a few have chosen lower values.
National regulations have economic consequences. In this case the most efficient approach is for states to individually decide how to proceed, and most already have done so.
The Food and Drug Administration did not suggest alterations of drinking water and dietary patterns for the general public, but recommended that infant formulas be prepared from water with less than 15 ppb perchlorate, based upon the EPA DWHA. The EPA’s inspector general issued a review in 2010, concluding that the DWHA was conservative and that assuring that pregnant women received iodine supplements to reduce risks for fetuses and infants would be the most effective approach to assure that they had adequate daily iodine intake and reducing their risk.
In sum, it appears that there is little to be gained in health risk reduction by issuing a national regulation for perchlorate in drinking water. Given the numerous occurrence and toxicology assessments, and existing guidelines recommendations from several institutions, including the EPA DWHA of 2008, states are in the best position to determine whether their circumstance warrants drinking water maximum contaminant levels, and most, if not all, have done so.
This column does not necessarily reflect the opinion of The Bureau of National Affairs, Inc. or its owners.
Joseph A. Cotruvo PhD, BCES was director of EPA’s Drinking Water Standards Division after passage of the Safe Drinking Water Act of 1974, and director of the Risk Assessment Division in the Toxics Substances office. Since his retirement from the EPA, he consults on water, environment, and public health issues and has been a member for more than 20 years of the WHO group that produces the Guidelines for Drinking-water Quality.