Perchlorate can interfere with iodide uptake by the thyroid gland, reducing thyroid hormone production and interfering with normal growth and neurological development.
Perchlorate (ClO4–) is both a natural product and a synthetic chemical with numerous uses including in rocket fuel, fireworks, flares and explosives. It is also present in some fertilizers.
It has been used as a pharmaceutical to treat Graves’ disease (hyperthyroidism) because it depresses thyroid activity.
Perchloric acid (HClO4) forms salts, such as potassium perchlorate (KClO4), ammonium perchlorate (NH4ClO4) and sodium perchlorate (NaClO4).
Occurrence:
Perchlorate has been found in some surface and ground waters around military operations, defense manufacturing facilities and areas where blasting agents have been used. It is found naturally in subsurface soil, especially in the southwest U.S. and in deposits in Chile, and it has also been found at low levels in some groundwaters where no anthropogenic source is apparent.
Perchlorate is generated in small amounts from chlorate (ClO3–) in hypochlorite that is stored for some time at warm temperatures.
Perchlorate has been found at ppb levels in just over 4 percent of public water systems in the U.S. It was analyzed as part of the Unregulated Contaminant Monitoring Regulation 1 (UCMR 1) program.
Perchlorate is highly mobile in water and can persist for many decades under typical ground and surface water conditions.
Health effects:
Perchlorate is very slightly metabolized after ingestion and is excreted unchanged with a half-life around eight-12 hours. At sufficiently high doses, perchlorate can interfere with iodide uptake by the thyroid gland, reducing thyroid hormone production and interfering with normal growth and neurological development.
Perchlorate dosages used in treatment of Graves’ disease are typically in the 400 to 700 mg/day (about 6 to 10 mg/kg/day) range taken in four or five doses for three to eight weeks. Minimal side effects were noted.
A 2005 National Academy of Sciences (NAS) review recommended a perchlorate reference dose (RfD) of 0.7 µg/kg/day (micrograms per kilogram) of body weight from a No Observed Effect Level (NOEL) of 7 µg/kg/day. It was based upon reduced uptake of radioactive iodine, which is not an adverse effect per se (serum hormone levels were not significantly altered at the NOEL).
The U.S. Food and Drug Administration (FDA) estimated lowest intake levels at 0.08 to 0.11 µg/kg/day for 25- to 30-year-old men and the highest intakes at 0.35 to 0.39 µg/kg/day for two-year-olds. It concluded that no adverse health effects were expected at those levels.
The American Thyroid Association reported that there were no effects on thyroid function for women in early pregnancy at typical environmental exposures, even for mildly iodine deficient individuals.
In 2011, the WHO/FAO Joint Expert Committee on Food Additives (JECFA) calculated a provisional Tolerable Daily Intake (TDI) of 10 µg/kg/day. It estimated total perchlorate daily exposures of 0.7 µg/kg/day body weight (highest) and 0.1 µg/kg/day body weight (mean) from food and water and concluded they were well below the provisional maximum Tolerable Daily Intake. The JECFA committee concluded that those estimated dietary exposures were not of health concern.
Regulation:
There is considerable disagreement between the WHO/FAO JECFA assessment and the California and Massachusetts assessments.
The California drinking water standard is 6 µg/L and the Massachusetts standard is 2 µg/L micrograms per liter. In January 2011, the California OEHHA, recommended a reduction of the current state standard (MCL) from 6 µg/L to 1 µg/L.
If the EPA will announce its decision to regulate perchlorate under the Safe Drinking Water Act (SDWA) it would reverse a 2008 preliminary determination.
Water treatment:
ANSI/NSF Standard 58 requires a reverse osmosis (RO) unit to be able to reduce water containing 130 ppb of perchlorate to 4 ppb or less. Additional industry standards for other devices are under consideration.
In addition to RO, anion exchange and carbon adsorption will reduce perchlorate to some extent.
Sources: Agency for Toxic Substances and Disease Registry, American Thyroid Association, Joint FAO/WHO Expert Committee on Food Additives, NSF International, U.S. Environmental Protection Agency, U.S. Food and Drug Administration, U.S. Geological Survey.
Water Technology would like to thank Dr. Joseph Cotruvo for reviewing this information and providing additional content. Dr. Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He is a former director of the U.S. EPA Drinking Water Standards Division.
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