Science Advisory Board Panel Considers Perchlorate Issues

The perchlorate panel of EPA’s Science Advisory Board (SAB) met this week in Washington, DC (and was attended by an ASDWA representative). As EPA works to develop a regulation for perchlorate, they have asked a special panel of the SAB to consider a number of questions that will help EPA craft a Maximum Contaminant Level Goal (MCLG) for perchlorate. The SAB will address questions related to four areas that EPA will consider in developing the MCLG:

• Issue I – Sensitive Life Stages
• Issue II – Physiologically-Based Pharmacokinetic Evidence
• Issue III – Epidemiological Evidence
• Issue IV – Integration of Information

The advice of this SAB panel and findings previously received from the National Research Council (NRC) will provide much of the scientific support for the development of the perchlorate rule. A 2005 NRC report (“Health Implications of Perchlorate Ingestion”) set the Reference Dose (RfD) for perchlorate of 0.7 ug/kg/day based on a precursor non-adverse effect (i.e. inhibition of iodine uptake). The RfD is the most scientifically defensible endpoint for assessing risk from perchlorate exposure. A Reference Dose is used to define risk for noncarcinogens. The NRC also considered that pregnant women with possible hypothyroidism or iodine deficiency (and their fetuses) are particularly sensitive populations. The SAB panel was not asked to reevaluate the RfD but consider questions that will help to clarify and expand on the NRC findings, taking into account studies published since 2005.

Using the NRC’s RfD, in January 2009, EPA issued an interim health advisory (15 μg/L perchlorate in drinking water) to provide guidance to state and local officials in their efforts to address perchlorate contamination. An EPA white paper, analyzing the perchlorate research since the NRC report, was provided as background for the SAB deliberations. In that white paper, EPA proposed possible MCLG’s ranging from 2 to 18 ug/l based on applying the RfD to different life stages.

The SAB panel will evaluate all the evidence and may or may not agree with the conclusions of EPA’s white paper. A number of industry groups have found fault with the EPA analysis. In public comments filed before the meeting AWWA, the American Chemistry Council, the Chlorine Institute and others objected to some of EPA’s conclusions and recommended the SAB examine these issues, including even the RfD from the NRC. Because perchlorate is a contaminant of sodium hypochlorite, the impact of a low MCL in a final rule could have a significant impact on selection of disinfectants in water systems (a principal AWWA issue). Some of the issues raised by the SAB were as follows:

• The RfD represents a No Observed Effect Level (NOEL) versus the traditional No Observed Adverse Effect Level (NOAEL). The NRC’s use of a precursor to an adverse effect (iodine uptake inhibition) in establishing a threshold for exposure represents a “more conservative, health-protective approach”. This means sensitive populations should be protected at the RfD.
• EPA omitted significant peer-reviewed studies which provide a significant weight of evidence finding that there is no adverse impact from exposure to perchlorate in drinking water in the subpopulations cited by the NRC.
• Recent, longer term, studies have indicated that the thyroid adapts and will compensate for the iodine uptake inhibition effects of perchlorate. EPA should use the available chronic human data to revise the existing RfD.

The SAB will consider EPA’s charge questions and the public comment in developing its final report. It is not yet known to what extent they will include these public comments in their discussion, although panel members had raised similar issues in their own pre-meeting comments.

Based on the date of their decision to regulate perchlorate (February 2011), EPA needs to publish a proposed rule by February 2013. The SAB perchlorate panel will meet again by teleconference in September to finalize their report so it can be submitted to EPA by the full SAB. Additional material including the EPA white paper and outside comments can be found on the meeting website. Reports by the panel will also be available here as they are produced.