The 2003 Perchlorate State-of-the-Science Symposium concluded Wednesday in Omaha, with leading scientists verbally presenting their consensus reports on some of the most recent scientific studies on perchlorate. The significance of these results is that it questions the basic assumptions of a number of recent and influential government efforts to assess the safe level of perchlorate exposure.
The University of Nebraska Medical Center in Omaha hosted a conference of independent experts from leading institutions in the U.S. and Canada who have expertise in scientific areas that are critically related to the study of perchlorate, including toxicologists, epidemiologists, risk assessors, clinicians, statisticians, neurodevelopmental scientists, thyroid endocrinologists and pharmacologists.
Scientists concluded that the neonatal rat brain analysis in a key animal study was conducted in a manner that rendered the rat brain data unreliable for concluding that perchlorate adversely affects the development of the central nervous system.
“It is the firm opinion of panel members that theses studies allow us to draw no conclusions with respect to the effects of perchlorate on rats,” said Harold L. Schwartz, Ph.D., professor of medicine at the University of California-Irvine and an expert in thyroid hormones who spoke for the scientific panel. “We recommend setting them aside and conducting new studies.”
A separate panel of independent scientists who examined recent animal behavior studies on perchlorate also recommended these studies not be used for estimating perchlorate’s effects on the developmental central nervous system. While noting the studies were carried out professionally and competently, the scientific experts offered seven specific criticisms of the studies’ design.
“These experiments are inadequate in demonstrating significant risks from exposure to perchlorate, and likewise they failed to demonstrate the absence of risks,” said Sam Sanderson, Ph.D., a UNMC professor who facilitated the module and presented the expert panel’s results. “The results are invalid and the conclusions of these studies should not be used in any way.”
A third panel of scientists and physicians concluded that there are a number of human studies that provide important information about the effect of perchlorate on humans. The scientists determined that the human studies offer greater insight than animal studies into the affects of perchlorate at high doses (doses that are far higher than what is found in U.S. drinking water supplies). Scientists also reported that more human research related to sensitive populations should be considered.
A fourth panel of scientists examined what constitutes an “adverse effect” to the thyroidal system, and concluded that the inhibition of iodide uptake clearly is not an adverse effect but is instead a mundane biochemical event. Further, they also concluded that changes in thyroid hormone levels by themselves are not harmful.
Perchlorate has now been detected in about two dozen states at levels as low as 4 ppb in water. Substantial public and private drinking water supplies now contain trace levels of perchlorate. Media reports allege that low-level perchlorate exposure may cause a host of thyroid disorders, while many scientists disagree. Federal and state regulatory agencies have issued draft risk assessments concluding that low-level exposure does indeed pose potential health risks. These documents have proved to be highly controversial.
The 2003 Perchlorate State-of-the-Science Symposium was structured to allow researchers who have conducted recent scientific studies on perchlorate to present their work, and leading independent scientific experts to evaluate those studies and develop consensus reports on the state-of-the-science as of 2003. The symposium was structured around the Office of Management and Budget’s Draft Peer Review Standards for Regulatory Science issued in August 2003. Four scientific issues were addressed: (1) Analysis and Interpretation of Developmental Rat Brain Morphometry Studies; (2) Analysis and Interpretation of Developmental Animal Studies; (3) Adequacy and Relevance of Human Data; and (4) Alternative Definitions of “Adverse” Effects.
The consensus reports were delivered verbally during the final session of the symposium, with final written reports from each of the four panels of experts due Oct. 31. Requests for videotapes of the symposium proceedings or the final written reports should be made via e-mail to Ercole Cavalieri, D.S.C., at scherek@unmc.edu. They also will be available at the conference Web site, www.perchloratesymposium.com.