[CPEO-MEF] NAS Perchlorate report - A second look

[Lenny Siegel <lsiegel@cpeo.org>]

When it announced its report, "Health Implications of Perchlorate
Ingestion," earlier this week, the National Research Council (a branch
of the National Academies) explained that its panel of experts had
recommended a reference dose (the amount of perchlorate that a person
can ingest safely per day) twenty times the reference dose proposed by
U.S. EPA in 2002. Most of us believed that this statement implied that
the NRC was essentially recommending a drinking water standard of around
23 parts per billion (ppb).

After listening to the NRC webcast briefing, reviewing the report, and
discussing several aspects of the NRC report with experts, I have
concluded that the federal drinking water standard may still end up in
the range being proposed by the two states currently in the process of
promulgating their own standards, 1 ppb by Massachusetts and 6 ppb by California.

When a reporter referred to the "23 ppb standard," an NRC Committee
representative responded:  "I'm not sure where the 23 parts per billion
comes from in that particular question. There's a factor of 23 one might
think about that comes from what our potential reference dose would be
and what EPA had released in their 2002 recommendation. There's a factor
of 23 between where EPA was and where this committee ended up. That's
not the same as a drinking water level of 23 parts per billion."

In fact, NRC Committee members made it clear that it was well beyond
their scope to recommend a drinking water standard. I know, from the NRC
committees in which I have participated, that Academy officials
carefully monitor the work of all committees to ensure that they don't
overstep their statements of task. That's because the Academy selects
each panel to address the particular questions it is being asked to
review. Thus, the perchlorate committee did not include the full range
of expertise necessary to take the reference dose the next step -
developing a drinking water standard.

There are three factors that could drive down the drinking water
standard below the 23 ppb that many of us incorrectly inferred from the
recommended reference dose: 1) the higher ingestion rates of sensitive
populations; 2) the widespread presence of perchlorate in the American
food supply; and the 3) the uncertainty based on the short duration of
the study of healthy adults - the Greer study - that served as the
linchpin of the NRC's analysis. I know of no factors that are likely to
drive the drinking water standard above that level.

1. INGESTION RATES

Infants typically drink much more water, compared to body weight, than
adults. In fact, an NRC spokesman said, "If it's a 3-kilogram baby, you
adjust it down." As one expert explained to me that the concentration of
perchlorate in the baby's fluid required to deliver the reference dose
of .0007 milligrams per kilogram per daily is 4.35  ppb. Because
drinking water standards must protect sensitive populations, this
adjustment alone would bring the standard down to somewhere around 4 or
5 ppb. There might be countervailing influences, such as an adjustment
of the uncertainty factor that was based upon pregnant women and
fetuses, but it appears from the report that the Committee considers
infants more like fetuses than healthy adults, in their response to
perchlorate ingestion.

2. RELATIVE SOURCE CONTRIBUTION

At the public briefing, a Committee spokesperson said, "A reference dose
is the total amount that you can take in orally, regardless of where it
comes from ? food, milk, water, you name it." Therefore, drinking water
standards are typically made more stringent if people are likely to
ingest the same contaminant from other sources. For most age groups in
the U.S., this is clearly true for perchlorate, which has been found in
lettuce and other vegetables, milk, and even meat and fish. Under
certain assumptions, this could bring the drinking water standard below
1 ppb (when combined with the first factor). However, this will take
careful analysis, because the populations that ingest the most
perchlorate from other sources are probably not those that are most
susceptible to perchlorate.

3. DURATION UNCERTAINTY

The one dissenting opinion expressed in the NRC report stated, "An
uncertainty factor of 3 could account for the uncertainty surrounding
the small number of subjects and the absence of a long-term study." A
Massachusetts Department of Environmental Protection analysis went
further, explaining "However, perchlorate accumulation in the thyroid at
low doses has not been ruled out and the downstream effects of
perchlorate may themselves be cumulative (e.g. depletion of stored
thyroid hormones). In fact, a recent US EPA analysis of the Greer study
itself indicates that perchlorate effects were greater at later time
points in that study, supporting a duration of exposure effect over a
relatively short period of 2 weeks." 

However, the NRC majority insisted that the adverse effect - the
inhibition of iodide uptake by the thyroid - takes place at initial
exposure, so there is no need to consider long-term ingestion. This is a
two-edged sword, because if they're right, risk managers (environmental
regulators) would need to set the drinking water standard to protect
against the maximum exposure, not a long-term average. That is, if they
accept the reference dose without the uncertainty factor of three for
duration, they may still need to lower the drinking water standard to
account for the asserted "instant" impact.

IN CONCLUSION

Overall, upon careful review, the NRC's report seems to raise as many
questions as it purports to answer. It has launched a new round of both
scientific and political debate. All parties agree that there is a need
for continuing scientific study, leading up to and even following the
promulgation of drinking water standards.

It is essential that such studies be controlled by institutions that do
not have a significant financial stake in the outcome. The polluters
didn't like the results of the rat-brain study, so they funded another
study to call it into question. They liked the results of the short-term
study of healthy adults, so - it appears - they didn't fund another
study to address the charge that the short exposure period might have
hidden long-term effects.

Academy committees and the regulatory agency offices that develop
standards do not do their own original scientific research. They review
such studies. To protect the millions of children and children-to-be who
are exposed to low concentrations of perchlorate every day, there must
be a body of science that is beyond the manipulation of those who stand
to pay for the cleanup and treatment likely to be required if stringent
standards are imposed.

Lenny
-- 


Lenny Siegel
Director, Center for Public Environmental Oversight
c/o PSC, 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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