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 the office of Ercole Cavalieri,
D.S.C., at UNMC at scherek@unmc.edu. They also will be available at the conference
Web site, www.perchloratesymposium.com.
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