SAB Considers Report on Perchlorate

EPA’s Science Advisory Board (SAB) this week considered a draft report from a special Perchlorate Advisory Panel that recommends changes in how EPA approaches deriving the Maximum Contaminant Level Goal (MCLG) for perchlorate.  The special panel was created to develop recommendations that the full SAB can provide to EPA.  This is not the first time EPA has sought advice from the scientific community on their long path to a perchlorate regulation.  In a 2005 report by the National Research Council (NRC), they determined that perchlorate could affect thyroid function by inhibiting iodide uptake and leading to a deficiency in thyroid hormone.  This can have an impact on sensitive populations including pregnant women, infants, and fetuses.  The NRC recommended a Reference Dose (RfD) of 0.7 ug/kg/day, which was subsequently adopted by EPA.  This RfD includes an uncertainty factor of 10 to account for differences in sensitivity between healthy adults and the most sensitive populations.  When EPA made the decision to regulate perchlorate in 2009, they recognized that there was new research published since the NRC work and they were especially interested in information on sensitive life stages.  EPA also wanted to examine the use of physiologically-based pharmokinetic (PBPK) models for perchlorate.  The charge to the special SAB panel addressed these issues.

In the draft Report prepared by the panel, the SAB recommends that EPA specifically consider sensitive life stages in the development of the MCLG for perchlorate.  Even without specific studies of adverse neurodevelopmental effects in infants and children, the mode of action of perchlorate on the thyroid hormone and the impact of thyroid hormone on brain development, indicates that there will be a risk to these sensitive populations.  The SAB recommends that EPA use PBPK modeling addressing sensitive life stages to develop the MCLG rather than their traditional approach of deriving the MCLG from the RfD using formulas that consider chemical exposure.  Recognizing that it will take many years to fully develop this new modeling approach, the SAB recommends an interim approach that uses an existing model and clinical data on iodide uptake inhibition.

During their March 29th meeting, the full SAB may make some recommendations for changes before the official transmittal to EPA.  These revisions will be made and a final report submitted to EPA within the next few weeks.  EPA will then take the report’s recommendations into account when they do the final development of the MCLG.  EPA is not required to follow the SAB’s advice but they always take it very seriously.  New OGWDW Director, Peter Grevatt has stated that EPA will delay the development of rules, if necessary, to “get the science right”.  This is one of those cases.

Even with the interim path outlined by the SAB, it is likely to take EPA significant time to develop the MCLG if they use this completely new approach.  EPA has already missed the deadline for the proposed perchlorate rule in the original determination to regulate, as they waited for the SAB to complete their work.  EPA’s current plan is for a proposed rule by the end of the year.  It remains to be seen whether EPA can meet this new deadline.

The draft report and all the other related SAB documentation can be accessed on the SAB website.