UNITiD STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
January 9» 1992
OFFICE OF
THE ADMINISTRATOR
EPA-SAB-RAC-92-009
Honorable William K. Reilly
Administrator
U.S. Environmental Protection Agency
401 M Street SW
Washington, DC 20460
Subject: Review of Draft Criteria Documents for Radionuclides in Drinking Water
(Drinking Water Criteria Document for Uranium^ November 1989; External Review
Draft for the Quantification, of Tbxicological Effects Document on, Radium, (TR-
1242-67), 10 July 1990; Quantitative Risk Assessment for Radon in Drinking
Water, May 1990; and Quantitative Risk Assessment jbr Beta Particle and Gamma
Emitters in Drinking Water, May 1990.
Dear Mr. Reilly:
At the request of the Office of Drinking Water (ODW), the Radiation
Advisory Committee of the Science Advisory Board established a subcommittee to
review draft criteria documents and related reports that were the basis for new
drinking water standards for uranium, radium, radon and man-made beta-gamma
emitting radionuclides. The documents reviewed had been developed during the
period November 1989-July 1990, Revised background documents have subse-
quently been prepared by the Office of Drinking Water.
The Subcommittee conducted the review using a series of publicly an-
nounced conference call meetings and the exchange of written comments during
the period June 4~August 29, 1990. At the first meeting the Office of Drinking
Water asked, .that the Subcommittee determine whether the criteria documents
were scientifically sound. Later the Office of Drinking Water provided a formal
charge identifying five specific issues. By this time the Subcommittee meetings
and exchange of draft reports had already provided the Office of Drinking Water
and the Office of Radiation Programs with early advice to facilitate revisions of
the documents. The Subcommittee's findings, conclusions, and recommendations
appear in the enclosed report, which was approved by the Radiation Advisory
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Committee. • The charge also requested that the Subcommittee review the draft
notice to be published in the Federal Regis|gr,. That request will be handled as a
separate review when the draft notice is received.
The overall quality of the four draft criteria ^documents was not food.
Taken as a set, the documents are inconsistent in approach and with Agency
practice in the derivation of drinking water criteria such as those for volatile
organic contaminants. The Subcommittee found that recommendations from a
1987 Science Advisory Board report on its review of the basis for standards for
radionuclidee in drinking water (SAB-RAC-87-035) had not been addressed. Nor
did the new criteria documents address recommendations from other available SAB
reports that are directly relevant (such as SAB-RAC-88-026 and SAB-EEC-89-Q12),
Technical decisions contrary to those recommended by the SAB were presented
without justification and without acknowledgement of the existence of the SAB
recommended alternatives. Relevant recommendations of the National Research
Council's Committee on the Biological Effects of lonking Radiation were ignored
or selectively adopted without explanation or rationale. Uncertainties associated
with the selection of particular models, specific parameters used in the models, and
the final risk estimates are not adequately addressed in any of the documents.
The Subcommittee's responses to the Office of Drinking Water's five specific
questions on uranium metabolism, risk from ingested radon, the basis for estimat-
ing the risks from radon in water, the use of epidemiologic data and modeled risk
estimates in evaluating radium risks, and methodology for risks from man-made
radionuclides follow.
a. The estimates of the absorption, distribution, and excretion of urani-
um when ingested are not appropriate or supported by the data. The
basis for the metabolic model chosen and the value of the gut-to-blood
absorption factor (fj) have not been adequately discussed. Further-
more, the chosen value of fj appears to have been arbitrarily selected
from among the highest of all reported values. The uncertainties
associated with parameter and model selections are not discussed.
b. The methqds employed in the radon document do not form an appro-
priate basis for assessing the risks of directly ingesting water contain-
ing radon. The assumption of a tap water consumption rate of 0.66
liters per day conflicts .with other Agency practice as does .the as-
, sumption of a 20% volatilization loss between the tap and container.
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, The basis for and uncertainty associated with the assumed values are
not adequately addressed,
c. The appropriate basis for estimating risks from radon in water
requires that both the direct (ingestion) and indirect (inhalation)
exposure routes be carefully assessed. The EPA draft document
treats both pathways; however, possible inhalation exposures to high
concentrations at the point of use have not been addressed. Assess-
ment of uncertainties is an essential component of the evaluation of
both pathways. The' risk estimate for exposure to airborne radon
presented in the document disagrees with an Agency position paper
previously submitted to the SAB for review (EPA-SAB-Ltr-91-001).
d. For radium, the available human epidemiologic data should most
definitely be used to determine risk, rather than a mathematical
model. This recommendation reaffirms the previous response (SAB-
RAC-87-035).
e, The methodology for assessing risk from man-made radionuclides
(both individually and collectively) is incomplete because there is not
a criteria document for man-made alpha-emitters. The draft docu-
ment employs a set of ad hoc risk factors that have not been re-
viewed. Instead of providing the basis for selection of a guide value,
the level of 4 millirem per year was assumed. The document does
not employ the effective dose equivalent concept and does not ade*
quately address uncertainties in the input parameters and risk esti-
mates.
The Board is troubled over the failure of the Agency to address the Board's
earlier comments and recommendations and also relevant recommendations of the
National Research Council's Committee on the Biological Effects of Ionizing
Eadiation (198S, 1990). The EPA 1990 documents reflect technical decisions
contrary to those specifically recommended by the SAB, selectively adopt material
from other technical consensus reports, and present decisions concerning the risks
of radionuclides in drinking water without justification or acknowledgement.
Given this pattern, particularly the inattention to uncertainties and previous BEIR
Committee and SAB recommendations, it is difficult for the Board to understand
the scientific basis for the selection of maximum contaminant levels, . .
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We believe that the specific technical issues identified in the review and the
broader issue of the relationship between the SAB and the Agency are quite
important and request appropriate action by the Agency to address them. We look
forward to a written response from the Agency,
Sincerely,
Raymond C. Loehr, Chairman
Executive Committee
Science Advisory Board
Oddvar F. Nygaard, Chairman
Radiation Advisory Committee
Science Advisory Board
Paul G. Vbilleque, Chairman
Radionuclides in Drinking Water
Subcommittee
Radiation Advisory Committee
Enclosure
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