During a March 29 teleconference, EPA's Science Advisory Board (SAB) gave preliminary approval of the path forward for setting a Maximum Contaminant Level Goal (MCLG) for perchlorate as recommended by the SAB Perchlorate Advisory Panel. Based on a draft report from the Advisory Panel, the SAB will recommend using an enhanced physiologically based pharmacokinetic (PBPK) model to derive an MCLG that would ultimately underpin a perchlorate regulatory decision.
In addressing the SAB, Dr. Stephen Roberts, chair of the Perchlorate Advisory Panel, stressed that its report lays out recommendations at "the 5,000-foot level" for EPA to consider as it moves forward, but leaves it up to EPA to decide how far it needs to go in carrying out those recommendations before the science is deemed strong enough to support a policy decision. In the accompanying discussions with SAB members, timeframes ranging from one to 10 years were mentioned for revision of the PBPK models underlying any policy decision, with the ultimate timeframe dependent on the amount of change made to the modeling approach.
However, the SAB's and, ultimately, EPA's decision on how to proceed in setting a perchlorate MCLG has been significantly complicated due to the publication, just days before the SAB's March teleconference, of a newly revised perchlorate model in the journal Toxicological Sciences. The published article, "Evaluation of Perturbations in Serum Thyroid Hormones during Human Pregnancy due to Dietary Iodide and Perchlorate Exposure using a Biologically Based Dose Response Model," presents a revised perchlorate model that incorporates many of the recommendations in the Perchlorate Advisory Panel report. Of particular potential significance to the perchlorate regulatory development process, the model indicates that EPA's current reference dose for perchlorate (0.7 micrograms per kilogram bodyweight per day) is adequately protective of public health, a finding that appears to back EPA's original 2009 decision not to regulate perchlorate.
Though the revised model and its findings have been submitted to the SAB for consideration as it finishes its report to EPA, it is not yet clear if the SAB will significantly change its recommendations or specifically endorse the use of the newly published modeling approach. EPA has independently indicated that it is looking closely at the revised model as it continues to evaluate the perchlorate regulation.
As a result of these new developments, the timeline for proposal of a perchlorate regulation, already delayed past the February 2013 statutory deadline, appears to be facing even further delays, most likely well into 2014. EPA should be able to provide additional clarification on a new schedule in the coming months after it receives the SAB's final report and has additional time to evaluate the potential implications of using the newly published modeling approach. The latest draft of the Advisory Panel's report and other information on the SAB review process are available at the SAB Perchlorate Advisory Panel webpage.