Site Mitigation & Restoration Program

We protect and maintain California’s land and places
by setting strict standards for land restoration and cleanup

Human and Ecological Risk Office


What is Perchlorate?

Perchlorate (ClO4) is both naturally occurring and a man-made contaminant that is increasingly found in groundwater, surface water and soil. Most perchlorate manufactured in the U.S. is used as an oxidizer in solid fuel for rockets and missiles. In addition, perchlorate-based chemicals are also used in the construction of highway safety flares, fireworks, matches, pyrotechnics, explosives, common batteries, and automobile restraints. Perchlorate contamination has been reported in at least 20 states.

Perchlorate impacts human health by interfering with iodide uptake into the thyroid gland and the production of thyroid hormone. Thyroid hormone is needed for prenatal and postal growth and development, as well as for normal metabolism and mental function. Unlike adults, fetuses and infants have little to no reserve of thyroid hormone. Due to the increased needs of the developing fetus and infant, iodine deficiency is also more common in pregnant women.  Thus, there is concern is that fetuses, infants, children and pregnant women may be more susceptible to inhibition of thyroid hormone levels by perchlorate exposure.  Since thyroid hormone is required for development and function of many tissues in the body, including the brain, perchlorate is considered a serious threat to human health and water resources.

Note that other chemicals, including nitrate can also inhibit iodine uptake by the thyroid.  Co-exposure to perchlorate and nitrate has been shown to alter thyroid function in pregnant women.


The California Office of Environmental Health Hazard Assessment (OEHHA) published an updated public health goal (PHG) of 1 part per billion (ppb) for perchlorate in drinking water in February 2015. This updates the previous California PHG of 6 ppb perchlorate, which was set in 2004. The updated PHG is lower because it incorporates new research about the effects of perchlorate on infants.
The California Maximum Contaminant Level (MCL) for perchlorate is 6 micrograms per liter, while the US federal Maximum Contaminant Level Goal (MCLG) is 15 micrograms per literMCLG are defined by US EPA and refer to contaminant level in drinking water up to which no health risks are known or expected. MCLG’s are non-enforceable public health goals that allow for a minimum safety margin.

On June 26, 2019, US EPA proposed National Primary Drinking Water Regulation for perchlorate to establish a MCL and MCLG at 56 micrograms per liter.  EPA is also considering the alternatives of establishing a federal MCL and MCLG of 18 micrograms per liter perchlorate, 90 micrograms per liter perchlorate, or withdrawal of the agency’s 2011 determination to regulate perchlorate in drinking water EPA Proposed Rule for Perchlorate in Drinking Water.
As of November 2019, the US EPA Regional Screening Levels (RSLs) for soil are 55 mg/kg perchlorate for residential use and 820 mg/kg perchlorate for Industrial use.

Best Management Practices (BMPs)

What are DTSC’s Perchlorate Best Management Practices (BMPs)?

In addition to overseeing the cleanup of sites contaminated with perchlorate, AB 826, the Perchlorate Contamination Prevention Act of 2003 required DTSC to adopt regulations specifying best management practices for perchlorate and perchlorate-containing substances. The Perchlorate Best Management Practices were adopted on December 31, 2005 and became operative on July 1, 2006.

  • Perchlorate Containing Material – One-Time Notification By September 1, 2007, businesses that managed more than 500 lbs or 55 gallons of Perchlorate Containing Materials at their site must have submitted the notification.

If you are in the Department of Defense or you are in an industry centered on aerospace, fireworks, pyrotechnics, amusement parks, automobile air bag and safety restraint, lithium perchlorate batteries, or if you are in a public safety agency, the Perchlorate BMPs may apply to you. Others that may be affected by these regulations include farmers who use perchlorate-containing fertilizer, laboratories, bleach manufacturers and users, and Publicly Owned Treatment Works (POTWs). Even households may be affected. See the materials below for more information.

Perchlorate Fact Sheets and Other Information



 Contaminated Sites

 Analytical Methods

The EPA Technical Fact sheet – Perchlorate lists drinking water methods and SW-846 methods, including Method 6850 and Method 6860 for measuring perchlorate.  However, the DTSC Environmental Chemistry Laboratory indicates that drinking water methods 314.0, 314.1, and 314.2 for perchlorate should be avoided due to interference by sulfate that can potentially underestimate perchlorate.


On-Line Resources

Page Last updated January 23, 2020