Scientists Question Basis of Most Recent Perchlorate Safety Studies
University of Nebraska Medical Center
Scientists questioned the assumptions behind several recent perchlorate studies at a symposium sponsored by the Department of Defense and the Center for Environmental Toxicology at the University of Nebraska Sept. 29 - Oct. 1 in Omaha.
At the end of the 2003 Perchlorate State-of-the-Science Symposium, panels of leading scientists presented their consensus reports on some of the most recent scientific studies on perchlorate.
These results question the basic assumptions used in a number of recent government efforts to assess the safe level of perchlorate exposure.
Independent experts from leading institutions in the United States and Canada brought their knowledge of scientific areas critically related to the study of perchlorate. They included toxicologists, epidemiologists, risk assessors, clinicians, statisticians, neurodevelopmental scientists, thyroid endocrinologists and pharmacologists.
The way neonatal rat brains were analyzed in a key study made the data from that study an unreliable basis for concluding that perchlorate adversely affects the development of the central nervous system, according to the participants.
“It is the firm opinion of panel members that these studies allow us to draw no conclusions with respect to the effects of perchlorate on rats,” said Dr. 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 recommended against using recent animal behavior studies on perchlorate to estimate its effects on the developmental central nervous system, after examining these studies. 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 University of Nebreska Medical Center 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 number of existing human studies provide important information about the effect of perchlorate on humans, a third panel of scientists and physicians concluded. The human studies offer greater insight than did the animal studies into the effects of perchlorate at high doses (doses that are far higher than what is found in U.S. drinking water supplies), the scientists determined. More human research related to sensitive populations should be considered, they said.
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 at levels as low as 4 parts per billion in water. Substantial public and private drinking water supplies now contain trace levels of perchlorate. Media reports allege low-level perchlorate exposure may cause a host of thyroid disorders, but 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 proven 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.
| For more information, visit the following Web site: The 2003 Perchlorate State-of-the-Science Symposium. |
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