Regulation of Perchlorate at Low Levels in Drinking Water:
A High Stakes Decision
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. This level is consistent with the recommended reference dose included in the National Academy of Sciences' January 2005 report on the health implications of perchlorate.
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.
Next: State regulation: California
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