Perchlorate has been used for decades in healthcare and industrial capacities. During this time, a wide array of institutions and organizations has intensively studied perchlorate and its effects. Use the timeline below to learn more about the evolution of the use of perchlorate over the past 60 years.


  • Military begins using ammonium perchlorate as an ingredient in solid rocket propellant (not "rocket fuel").
  • Medical community begins using perchlorate at very high levels (equal to 70,000 to 300,000 parts per billion in drinking water) to treat hyperthyroidism.


  • U.S. Environmental Protection Agency (EPA) proposes "provisional" Reference Dose (safe exposure level) for perchlorate of 4 parts per billion (ppb) in drinking water.


  • Aerospace, defense and chemical companies form Perchlorate Study Group join with government agencies to fund studies on health effects of perchlorate.


  • Full-scale development of perchlorate removal and treatment technology gets under way.


  • EPA raises "provisional" perchlorate Reference Dose to 4-18 ppb.


  • In California, monitoring technology is developed enabling perchlorate detection at levels as low as 4 ppb. California Department of Health Services (DHS) sets "provisional" Action Level (level at which water companies or districts must report presence of perchlorate) at 18 ppb.


  • Based on results of eight new studies on humans and animals, U.S. EPA proposes "draft" Reference Dose of 32 ppb.


  • An EPA peer review panel concludes a "draft" Reference Dose of 32 ppb level is probably overly cautious and recommends additional study.


  • New studies show humans — even sensitive sub-populations — can consume perchlorate at levels up to 200 ppb in drinking water with no risk of adverse health effects.


  • EPA relies primarily on animal studies, particularly a scientifically flawed and controversial rat study, to propose a new "draft" Reference Dose of 1 ppb.
  • In response to EPA's "draft" Reference Dose, the California Department of Health Services lowers the "provisional" Action Level from 18 ppb to 4 ppb.
  • California proposes a "draft" Public Health Goal of 2 ppb for children and 6 ppb for adults in drinking water. Controversy around this decision leads California to call for a peer review by a panel of scientists convened by the University of California.


  • EPA puts "draft" Reference Dose of 1 ppb on hold until completion of peer review by the National Academy of Sciences.
  • California puts Public Health Goal on hold pending completion of peer review by scientists acting under auspices of University of California.


  • University of California peer reviewers submit three separate reports regarding the risk assessment used to develop California's draft Public Health Goal. All three disagreed with California, and one another, on what the science says and how the state should proceed.
  • California issues perchlorate Public Health Goal of 6 ppb in drinking water. This accounted for exposure to perchlorate in water, farm products and cow's milk.
  • California, in issuing its Public Health Goal for perchlorate, states that perchlorate does not pose a known cancer risk to the public
  • Massachusetts Department of Environmental Protection establishes a draft toxicity value for perchlorate at 1 ppb.


  • National Academy of Sciences releases its report "Health Implications of Perchlorate Ingestion," which recommends a reference dose of perchlorate at 0.0007 milligrams per kilogram per day.
  • EPA establishes its official reference dose of perchlorate at 0.0007 milligrams per kilogram per day and translates that number to a Drinking Water Equivalent Level of 24.5 ppb.


  • California enacts a maximum contaminant level (MCL) for perchlorate in drinking water of 6 ppb.


  • U.S. EPA issues a preliminary determination not to regulate perchlorate. Public comments are sought to assist the agency in making a final determination.


  • U.S. EPA’s Office of the Inspector General issues a report concluding, among other findings, that the perchlorate RFD of 24.5 ppb protects against all human biological effects from exposure and that further reducing the perchlorate exposure below the RFD does not effectively lower risk.


  • California’s Office of Environmental Health Hazard Assessment within the California Environmental Protection Agency releases a draft public health goal of 1 ppb for perchlorate.
  • U.S. EPA announces its decision to move forward with the development of a national perchlorate standard.
  • OEHHA posted external scientific peer review comments from three academicians on OEHHA’s January, 2011, draft PHG. Two of three reviewers are generally supportive of OEHHA’s proposal to adopt a revised PHG at a more stringent level (1-2 ppb).
  • The Perchlorate Study Group held an initial meeting with state and federal perchlorate MCL stakeholders in Washington DC in November, 2011. Follow-up meetings are ongoing.


  • Discussions with stakeholders on potential development of a white paper examining benefit-cost analysis of perchlorate regulation to inform HRRCA evaluation by USEPA. This work may be jointly funded by a group of stakeholders or involve coordination of individual stakeholder work products and can be used with other affected government entities.
  • U.S. EPA’s perchlorate Science Advisory Board (SAB) meeting with stakeholder participation and comment. USEPA deadline for comments and statements from SAB is August 9, 2012, and USEPA is expected to issue a draft SAB report during the week of September 11, 2012.
  • U.S. EPA perchlorate MCL public stakeholder meeting to discuss the state of the science, the basis for its decision to regulate perchlorate, its review and response to comments regarding that decision, next steps in the regulatory process and the status of the HRRCA, and to receive public input.
  • National Drinking Water Advisory Council (NDWAC) meeting in Chicago to review USEPA’s perchlorate timeline.
  • U.S. EPA’s Science Advisory Board Perchlorate Advisory Panel discusses the scientific and technical bases for the approaches being considered in developing a maximum contaminant level goal for perchlorate.
  • Public teleconferences on USEPA Perchlorate Science Advisory Panel’s revised draft report.
  • OEHHA issues revised draft PHG at 1 ppb. Comment deadline is January 22, 2013.


  • SDWA statutory deadline for USEPA to sign a proposed MCL and HRRCA. Publication and start of comment period is likely to be several weeks after signature. Signature may be delayed at least 90 days without legal implications for EPA. If longer than 60 days, EPA may be sued by environmental groups for failure to meet statutory deadline. Based on past practice in numerous rulemakings, the likely implication is that USEPA would settle litigation by signing a consent decree to issue the proposal at a later date.
  • Completion of PSG-sponsored “white paper” on cost-benefit analysis for journal submittal and future use with USEPA, Cal-EPA, other affected agencies and offices and perchlorate stakeholders.


  • OEHHA adopts revised PHG at 1 ppb. Responses to public and peer review panel comments (on both 2011 and 2012 draft technical support documents) posted with final PHG.
  • Earliest timeframe by which the State Water Resources Control Board (SWRCB) is expected to begin its informal MCL review process. During this period SWRCB will collect occurrence data, treatment efficacy and cost information. This process typically takes about 18-24 months, assuming drinking water program transfer does not result in policy changes that truncate or expand the informal review process, SWRCB can allocate sufficient staff resources and is not overwhelmed by competing regulatory priorities. See Attachment #2 for more detail.

February 2016

  • Earliest timeframe by which USEPA is expected to open public comments on proposed draft of PBPK model.

March 2016

  • First of 2 phase peer review of the draft PBPK model (first phase on mechanics of the model.) Three month review to run until December, 2016.