Re: [CPEO-MEF] EPA Sets Reference Dose for Perchlorate

[Lenny Siegel <lsiegel@cpeo.org>]

U.S. EPA's adoption of a 0.0007 mg/kg/day reference dose (RfD) for
perchlorate, the number recommended by a National Academy of Sciences
(NAS) committee last month, was anticipated. I think the reference dose
should be more protective, because of the limitations of the study upon
which it was based, but in the absence of new evidence no one expected
EPA to diverge from the NAS recommendation.

The establishment of the reference dose is significant, because it can
be plugged into risk assessments to generate site-specific cleanup
goals. This will make it harder for the Defense Department to assert
that it doesn't need to - or that it can't - spend money on perchlorate
because there is no promulgated standard. I don't believe that assertion
was ever true, but now there is an official standard.

I am troubled, however, by the language in the EPA press release that
the new RfD "translates to a Drinking Water Equivalent Level (DWEL) of
24.5 ppb [parts per billion]." That may be true for a healthy,
70-kilogram adult, but most Americans - regardless of ideology or
political party - believe that drinking water should be safe enough for
babies and pregnant women to drink. Without any further adjustments -
such as for the accumulation of perchlorate in the food supply - the new
RfD would translate to a drinking water exposure of 4 or 5 ppb, because
babies drink more for their body weights than healthy adults.

It's not enough that the Academy and EPA applied an uncertainty factor
of 10 to calculate the reference dose from the study of healthy adults.
That number compensates for the fact that babies (and others) react
differently than healthy adults to the same exposure levels. But once
the acceptable exposure level is determined (the RfD), the drinking
water standard should be calculated so that a typical baby will not be
exposed to more than that amount on a daily basis. That's why 24.5 ppb
is far from protective.

Given what I've been hearing from EPA staff as well as independent
scientists, I'm surprised that the EPA press release contains this
un-supported conversion. The DWEL isn't mentioned in the detailed
explanation of the reference dose at
http://www.epa.gov/iris/subst/1007.htm. The press release sentence on
the DWEL doesn't have force of law, but it reinforces a general
misinterpretation of the NAS report. NAS representatives have repeatedly
stated that going from the RfD to a drinking water level involves policy
choices beyond the NAS scope.

I'm wondering, who at EPA - or the White House or Defense Department -
inserted such policy choices into the press release.

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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