[CPEO-MEF] Analysis of EPA's perchlorate determination

[Lenny Siegel <lsiegel@cpeo.org>]

EPA has made a preliminary determination that not enough people in the 
United States are exposed to significant levels of perchlorate in public 
drinking water systems to merit the issuance a national primary drinking 
water regulation. After it has a chance to review and respond to public 
comments, it expects to finalize that finding. At that time, it also 
plans to issue a health advisory for perchlorate, "to provide State and 
local public health officials with information that they may use in 
addressing local contamination."

It proposes, in that advisory, to specify a health reference level of 15 
parts per billion (ppb) based on its current reference dose of .7 
micrograms per kilogram per day and a calculation of dietary sources of 
perchlorate other than drinking water. It has determined that at any 
given time only 16,000 to 28,000 (fetuses of) pregnant women, what it 
considers the most susceptible subpopulation, in the U.S. are being 
exposed to perchlorate above that 15 ppb level. It has concluded that 
that's not sufficient exposure to merit the establishment of an official 
drinking water standard.

Above that 15 ppb level, EPA believes perchlorate has an observable 
effect - the inhibition of iodide transport to the thyroid. In an 
arguable percentage of cases, such iodide inhibition reduces the 
production of thyroid hormone, adversely affecting the nervous system 
development of fetuses and young children.

Before EPA completes its final determination, it plans to submit for 
peer review the adjustments that it made to its physiologically-based 
pharmacokinetic (PBPK) model. This model predicts radioactive iodide 
uptake (RAIU) inhibition in the thyroid for various sub-populations and 
drinking water concentrations.

The preliminary determination, like other recent EPA pronouncements on 
perchlorate, rests on the 2005 National Research Council (National 
Academy of Sciences) report. The NRC study, in turn, is based upon the 
2002 Greer study of 37 healthy adults. The NRC committee concluded that 
.7 micrograms per kilogram per day is protective because it applied a 
tenfold (1/10) uncertainty factor to ensure that the reference dose is 
protective of what it considered the most sensitive subpopulation, 
fetuses of pregnant women exposed to perchlorate. It also argued that 
this level is protective because the Greer study associated it with "no 
effects" on thyroid hormones, more protective than a standard of "no 
adverse effects."

When the NRC issued its report, scientists from environmental 
organizations, academia, and some states questioned it conclusions, 
arguing that the Greer study had serious problems and that the NRC had 
unreasonably ruled out other evidence. When EPA subsequently established 
its non-statutory drinking water equivalent level (DWEL) of 24.5 ppb, 
some of the critics suggested that young children would be exposed at 
levels above the reference does because they drink more water relative 
to their body weight, compared to adults.

The EPA announcement also considers the 2006 Blount biomonitoring study, 
which measured perchlorate, iodide, and thyroid hormones in the urine of 
over 1000 women and as many men throughout the United States. Blount 
found that women with low iodide levels (over a third of the population) 
experience decreased thyroid functions at low perchlorate levels 
characteristic of much of the U.S. population.

But EPA states that Blount did not establish a causal relationship. That 
is, other factors - such as exposure to nitrates or thiocyanate, might 
be influencing thyroid function. It wrote, "It is also not known whether 
the association between perchlorate and thyroid hormone levels is causal 
or mediated by some other correlate of both."

Relying on the Greer Study rather than the Blount Study, it's easy to 
see why EPA has concluded that not many children, and not many pregnant 
women, are exposed to perchlorate at levels that are a cause of concern.

This is NOT a protective approach. The best explanation of Blount's 
results is that perchlorate at low levels disrupts thyroid function for 
a substantial percentage of American women, but EPA doesn't want to 
protect such women because it might be that another, unknown, correlated 
factor - that EPA is also not addressing - is the source of the problem. 
There is always uncertainty in scientific studies of toxicity, but 
that's not a reason not to take protective action based upon the best 
science available.

Critics and others have only until November 10 to submit comments on 
this complex, controversial issue. People and groups with limited time 
to devote to preparing such comments must review EPA's assessment of the 
Greer, NRC, and Blount studies, water intake, perchlorate in food, 
drinking water surveys, and the pharmokinetic model. There is simply not 
enough time to respond.

After years of foot-dragging, EPA - prompted by its overseers in the 
White House - appears to be rushing out the door a decision not to 
regulate perchlorate and to establish an advisory level of acceptable 
exposure that ignores the most extensive study on the relationship of 
perchlorate to thyroid function and thus the health and development of 
hundreds of thousands, perhaps millions of American children.

I urge those who are concerned to write EPA to request that it extend 
the public comment period to 90 days. I suggest that those requests be 
e-mailed to the contact in the October 10 Federal Register notice, 
burneson.eric@epa.gov, with a copy to EPA administrator Stephen Johnson 
at johnson.stephen@epa.gov.

Note: EPA's Federal Register notice may be downloaded in HTML or PDF 
format from http://www.epa.gov/safewater/ccl/reg_determine2.html#.

Lenny

--


Lenny Siegel
Executive Director, Center for Public Environmental Oversight
a project of the Pacific Studies Center
278-A Hope St., Mountain View, CA 94041
Voice: 650/961-8918 or 650/969-1545
Fax: 650/961-8918
<lsiegel@cpeo.org>
http://www.cpeo.org



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