Since the mid-1990s, there has been an increasing amount of research effort aimed at evaluating the potential human health risk of perchlorate (ClO4) because of its presence at trace levels in some water systems. Concern over potential effects on the thyroid gland in humans from perchlorate exposure and whether environmental levels pose a risk to human health have surfaced recently. In response to this concern, a broad collaborative effort spanning both private and government sectors has been engaged in extensive toxicological testing of perchlorate to add to our knowledge about how and under what exposure conditions perchlorate may cause effects in laboratory animals and in humans. The collaboration between the U.S. Environmental Protection Agency (EPA), the Department of Defense (Air Force) and an inter-industry Perchlorate Study Group (PSG) is unique in its focus on development of state-of-the art science for accurately determining what constitutes a safe level for humans.
Because of its mission to identify significant public health threats and to bring sound scientific analysis to environmental health concerns, the American Council on Science and Health (ACSH) has (a) evaluated the allegations of health risk from perchlorate as alleged by the Environmental Working Group (EWG); (b) reviewed the current regulatory process that is ongoing with respect to the establishment of a safe environmental exposure level; and (c) highlighted some of the recent scientific studies that have further characterized the toxicity of perchlorate in both animals and humans.
With respect to the EWG's Report entitled "Rocket Science" which alleges human health risk from perchlorate in drinking water, ACSH concludes the following:
- The EWG report encompasses a selective and limited use of the scientific data for perchlorate and does not represent the totality of our current knowledge regarding its toxicity.
- Many of the claims of health risk are not supported through the inclusion of scientific references and as such cannot be construed to represent the scientific facts.
- The EWG report mischaracterizes the current regulatory efforts underway aimed at defining a safe exposure level and fails to recognize the scientific process at work.
- The EWG report has prematurely forecast what it believes to be a safe environmental exposure level without consideration of the significant amount of toxicological data that have been generated in the last few years or without regard for the scientific process at work.
In reviewing the history of the regulatory response in establishing a safe level for perchlorate in the environment, the ACSH concludes the following:
- Over the course of the last 10 years, the EPA has worked to define a safe exposure level for perchlorate in the environment, although a final value has not been established owing to data gaps for perchlorate.
- There has been a concerted effort to identify those studies and data gaps that would facilitate the establishment of a safe exposure level and significant testing has resulted in a much improved toxicological database for perchlorate.
- There has been a cooperative strategy and effort amongst both government and industry groups aimed at improving the scientific database for perchlorate for the protection of public health.
- As a result of the extensive toxicological testing, the EPA is expected to release its proposed Reference Dose (RfD, the safe exposure level for humans) in 2002, at which time all interested parties and stakeholders can publicly comment on the level.
In reviewing the recent scientific studies that have enhanced our knowledge of perchlorate's toxicity, ACSH concludes that:
- Both animal and human studies have appreciably contributed to our understanding of dose-response relationships for perchlorate such that the process of defining a protective RfD will be accompanied by less uncertainty and increased confidence.
- Both animal and human studies have contributed to our knowledge about the mechanism of action by which perchlorate exerts toxicity and under what exposure conditions. This knowledge will aid in the identification of sensitive subpopulations and in our increased ability to set a safe level for all humans.
- Because the number and types of toxicological studies that have been conducted for perchlorate has increased significantly, there is less uncertainty that accompanies the establishment of a safe exposure level and as such, the need for conservatism in the absence of knowledge has been reduced.
It is the intent of this ACSH report to provide readers with a perspective on how the concern over perchlorate arose, what the regulatory response has been over the last 10 years, and how the scientific process can be extremely beneficial in establishing safe exposure levels for humans in order to safeguard public health.