Regulation of Perchlorate


In February 2005, the U.S. Environmental Protection Agency (EPA) established its official reference dose of perchlorate at 0.0007 milligrams per kilogram per day, and translated that number to a Drinking Water Equivalent Level (DWEL) of 24.5 parts per billion (ppb). This level is consistent with the recommended reference dose included in the National Academy of Sciences' ("NAS" or "NAS Committee") January 2005 report on the health implications of perchlorate.

Federal regulators will now need to determine whether to proceed with a national drinking water standard for perchlorate. California is already engaged in the process of developing its own enforceable drinking water standard, also known as a maximum contaminant level (MCL). The MCL is required under California law to be set as close as is economically and technologically feasible to the final PHG. U.S. EPA would follow a similar process if it determines an MCL is necessary. A closer look at the next steps in the standard setting process for U.S. EPA and California is set forth below:


EPA's 24.5 ppb DWEL may be used by officials throughout the agency to make site-specific cleanup or interim drinking water standard decisions involving perchlorate. States and private parties also may look to EPA's RfD and DWEL as they make similar decisions.

At this juncture, EPA is contemplating two regulatory decisions:

First, EPA may revise its 2003 Interim Guidance on perchlorate. That guidance recommended that EPA Regions use a range of 4 ppb to18 ppb for site-specific cleanup decisions or interim drinking water standards. Since EPA's guidance values of 4 ppb to18 ppb were based on older scientific studies and analyses, the agency might choose to change the guidance to reflect its new DWEL.

Second, EPA must decide whether to promulgate a Federal drinking water standard (MCL) for perchlorate. EPA will only proceed with a standard if it determines that perchlorate adversely affects human health, is known or likely to substantially occur in public water systems at frequencies and levels that would cause adverse health effects, and that setting a Federal standard for perchlorate presents a meaningful opportunity to reduce the risk from perchlorate exposure.


California has set a state Public Health Goal (PHG) for perchlorate of 6 ppb. This accounted for exposure from water as well as from other sources, such as farm products, breast milk and cow's milk.

The California Department of Health Services (DHS) has already begun the process for adopting an enforceable drinking water standard (the MCL) for perchlorate. State law requires that the MCL be set as close to the PHG as is economically and technologically feasible, but does not require the state to investigate the science any further.

Currently, if the level of perchlorate in drinking water exceeds 6 ppb - the "Action Level" set by the DHS as a temporarily acceptable level pending adoption of the MCL - water system operators are required to notify local government agencies. The DHS also recommends that consumers be notified, and that the drinking water source be removed from service, if perchlorate is found at levels 10 times the Action Level. Some drinking water purveyors have already stopped serving drinking water that contains any amount of detectable perchlorate, thereby preventing all potential exposures while the MCL is pending.


To best protect the public, regulatory standards should be based on the best available science.

It is clearly important that standards be set at a level sufficiently low enough to assure public health protection, including a margin of safety. It is also important that regulatory standards not be set at an unnecessarily low level.

Unnecessarily restrictive regulatory standards - that is, standards more restrictive than indicated by the best available scientific data - could result in a number of direct and indirect adverse consequences. The economic costs potentially could be staggering - especially in the Colorado River Basin states of California, Nevada, and Arizona - resulting in citizens incurring significant expenses in their capacities as taxpayers, ratepayers and consumers. Water purveyors and those who rely on them for personal and business usage have particular reason for concern.

Some people suggest that economic costs imposed by a standard that is more stringent than indicated by the best scientific data would nonetheless be justifiable; they assume that any reduction in pollution is beneficial. However, all risks are not equal; greater resources should be applied to greater risks. Regulatory decision makers routinely must choose between one risk and another, in the same way that legislatures, companies and families must set budget priorities. Moreover, additional increments of reduction tend to have dramatically increasing costs - inevitably diverting resources that would otherwise be available for more significant environmental and health challenges, or other needs (e.g., retrofitting of facilities for protection against terrorist incidents, pre-natal care, etc.).


Reference Dose (RfD): An estimate of the amount of a particular substance in drinking water that U.S. EPA considers "safe" if consumed every day over a lifetime.

Public Health Goal (PHG): California's version of the U.S. EPA's Reference Dose, it is the level of a particular substance in drinking water that Cal/EPA considers safe for daily consumption.

Maximum Contaminant Level (MCL): Drinking water standard, or how much of a particular substance is allowed in drinking water. The drinking water standard must be as close to the Drinking Water Equivalent Level (DWEL) as possible, while taking into account economic and technological feasibility.