UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON. O.C. 20460
30 1QQ3 OFPK^e€1>li ADMINISTRATOR
«SU» LWO SCeNqeADVtSORYBQAftO
EPA-SAB-EC-LTR-93-010
IJdnorable Carol M. Browner
'Administrator
U.S. Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
Re; SAB Review of Multimedia Risk and Cost Assessment of Eadon in
Drinking Water
Dear Ms, Browner:
The EPA Science Advisory Board (SAB) is pleased to comment on the
multimedia risk of exposure to radon and the cost of mitigation as required by
Public Law 102-389 (the Chafee-Lautenberg Amendments to EPA's FY 1993
Appropriation Bill enacted October 6, 1992). The Chafee-Lautenberg Amendment
states that "The Science Advisory Board shall review the Agency's study and
submit its recommendation to the Administrator on its findings," The study
report made available to the SAB is entitled "Multimedia Risk and Cost
Assessment of Radon in Drinking Water",1 This SAB report on the Agency's
study, prepared by the Chafee-Lautenberg Study Review Committee of the SAB,
complements previous detailed SAB comments transmitted to you on the
uncertainty analysis of radon risks (July 9, 1993) and on costs of mitigation of
risks from radon in water (July 30, 1993).
The issues of major concern in assessing risks of radon exposure and costs
of mitigation may be grouped into four categories: a) population exposure profiles;
b) risk estimation procedures; c) mitigation costs; and d) integration of these for
regulatory decision mak'."5 The EPA study considered each of these issues and,
in turn, they have been addressed by the SAB.
By way of background, ike SAB early in 1993 began, interactions with SPA, including receipt of background nw*mat on
thit study Bataeuer, the specific report remewnd by th* Cumnuttee inns not received until Jttfy 9, 1993, and £Au*t tiauttd fun*
was iwfulabit to review and comment on the rppon fyn'uus« of the July 31, 1993 deadline for submission to Con^mx
Continuing to the present itudy report, there has irr/i a xtsiuly improvement ui flat quality of the onolytet conducts! trj £PA_
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A. Population extioawe profiles
The Agency report estimates that 81 million people use water originating
from community groundwater supplies with a population-weighted average radon
activity of 246 picocuries per liter of water (pCi/L^^p. The Agency report
estimates that approximately 19 million people are served by water supplies with
radon concentrations in excess of 300 pCi/Lwataji> the Maximum Concentration
Level proposed by the Agency, It is the SAB's impression from information
provided by public commentera, that the Agency's estimates of population exposure
to radon in drinking water are rather uncertain and may seriously underestimate
the number of community water systems impacted by the proposed drinking water
standard. This uncertainty in exposure estimates ultimately impacts the costs of
mitigation. There is clearly a need for more information and a better presentation
of available data on the profile of population exposure to radon in drinking water,
including the distribution of radon in drinking water exposures for communities of
varying size,
B. Risk, estimation procedures
The risk estimation procedures used by the Agency address both the risks
from radon inhaled in air and ingested in water. The risk estimates from airborne
radon with lung cancer as an endpoint are based on strong epidemiological
evidence from studies of uranium miners, augmented by data on other
underground miners, and supported by data from laboratory animal studies.
However, there continues to be debate about the extrapolated lung cancer risk at
lower levels of exposure. This issue may be clarified during the next several years
when the results of several major epidemiological studies focusing on exposure to
radon in homes become available. However, even though there is a potential risk
at low levels of exposure to air borne radon, it must be recognised that the
populations available for epidemiological studies are relatively small, the majority
of residential exposures are not particularly high, and the postulated levels of risk
are sufficiently low that epidemiological studies might well be unable to identify
any increase in risk attributed to residential radon exposure if such a risk is
present.
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The situation is quite different for estimating the risks of ingested radon in
drinking water. In this case, there is no direct epidemiologieal or laboratory
animal evidence of cancer being caused by ingestkm of radon in drinking water.
Thus, the approach to estimation of cancer risk from raaon in drinking water is
more indirect than for radon in air. In the absence of direct evidence, it is not
possible to exclude the possibility of zero risk from ingssted radon.
The indirect risk estimation approach involves several steps. First, the dose
to various tissues has been calculated from models for the distribution of radon in
the body following ingestion of radon. The model calculation is based, in part, on
organ distribution information from an unpublished study with radio-xenon (as a
surrogate for radon, since both are noble gases) using human subjects. The
meager data base results in uncertainty in estimating tissue doses from ingested
radon in drinking water. This uncertainty could be reduced through further
research. In the next step, the calculated doses havt been used along with organ-
specific risk estimates per unit dose, derived from data on the Japanese atomic
bomb survivors, to calculate cancer risk to various organs. To a large extent, this
involves an extrapolation from the very acute, high dose rate, gamma (low Linear
Energy Transfer) exposure of the Atomic Bomb survivors to a very protracted,
very low dose rate, alpha particle (high Linear Energy Transfer) exposure with
ingested radon. The SAB is of the opinion that the estimates of risk from
ingested radon have additional uncertainty due to possible differences in the
distribution of dose, and resulting effects, from alpha particles from radon and
progeny. However, it should be noted that even at the upper bound of the
uncertainty analysis for ingested radon, for most situations the risk from radon
ingested in drinking water is still much lower than the risk from airborne radon
entering the house directly from the soil. Indeed, for many homes the risk from
the radon in water is even lower than that from radon in the outdoor air.
The available information on exposure and risk have been generally
integrated under a scientifically satisfactory framework by the Agency as evidenced
in the Agency's multimedia risk assessment for radon (BPA-SAB-RAC-93-OH, July,
1993), However, the uncertainties noted earlier in this report are carried forward
into most of the integrated analyses. However, the differences of opinion,
especially with regard to the extent of the exposed population, with interested
parties are not reflected in the Agency report or in the integrated analyses.
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The risk estimates are illustrated in Figures 1 and 2. The population risk
estimates for airborne radon indoors are the most certain, with the nominal
estimate of 13,600 lung cancer deaths per year (range of 6740 to 30,600 lung
rt
cancer deaths) from exposure to indoor air . Less than one percent of this lung
cancer risk is attributable to radon reaching homes via water. In contrast,
exposure to radon in outdoor air is estimated to produce 520 lung cancer deaths
o
per year (range of 280 to 1500 lung cancer deaths) . And finally it is estimated
that ingestion of radon in water is estimated to cause 46 cancers per year (range
of 11 to 212 cancers per year) . This latter estimate is the most uncertain of all
the estimates made. Airborne radon arising from water is estimated to result in
113 lung cancers per year (range of 40 to 408 lung cancers per year) which are
included in the estimate presented above for indoor residential air. These risk
estimates for radon can be placed in perspective by comparison with an estimate
of approximately 30,000 cancer deaths per year from all exposures to naturally
occurring radiation, including approximately 13,600 deaths from inhaled radon and
approximately 2,500 cancers estimated for naturally occurring radio-potassium in
the human body,
C. Mitigation costs
The costs of mitigation of radon in the water and indoor air are also
uncertain. Part of the uncertainty for mitigation costs of radon in water relates to
differences of opinion between the Agency staff and interested parties over the
cost of mitigation systems, For example, the Agency staff estimates capital costs
for mitigation of radon in water at less than $2 billion, while interested parties
have estimates of capital coats in excess of $10 billion. Similar differences exist
for recurring maintenance and operating costs. The other part of the uncertainty
for mitigation costs of radon in water relates to the representativeness of the data
base on the occurrence of radon in groundwater used by the Agency. These data
2
Report to the United StatM Congnw on BadioauelidM In Drinking Water Multimedia Riik and Cort Aiaexament
of Radon in DrSWriag Wnt*r. Prtpawd for PL 102-389, Offit* of Wat*r. US EwnrQwoantai Protection Agency. Jujy 9, 1993.
3-2,
, p. 3-3,
4
Ibid, Tabte 7-3 beta model estimate*.
Tabta 7-3.
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are the source for estimates of the number and size of communities that would
require radon mitigation depending on the level of the MCL finally selected for
regulation, In contrast to ths potential mandated regulation of radon in water,
mitigation of radon in indoor air involves voluntary actions by homeowners. Total
cost estimates of the latter are highly uncertain because the extent and cost of
testing for radon in homes and the extent of voluntary participation in mitigation
action in affected homes are unknown.
The SAB is of the opinion that the mitigation cost uncertainties for radon
in drinking water could be reduced by the EPA working with interested parties to
resolve issues related to the occurrence of radon in community systems of various
sizes, the cost of the various process treatment operations and processes for
various system sizes, and the frequency of the need for disinfection after aeration.
This may require reopening the comment period for this rulemaking. The SAB
recommends that EPA, if necessary, request from the Court and Congress
sufficient time to do this work to reduce uncertainties in the cost estimates and
the cost per cancer avoided. The public interest will be served if the Agency
carries out activities over several years which provide a better basis for deciding
how to most effectively mitigate riiks from radon exposure in drinking water.
0. Integration for regulatory decision-making
Because of uncertainties in both risk estimates and costs of mitigation there
is substantial uncertainty in the cost per cancer death avoided. This uncertainly
is especially large for mitigation of cancers related to ingestion of water. However,
even with this uncertainty, it is clear that the cost per lung cancer avoided from
mitigation of indoor air radon is substantially less than the cost per cancer death
avoided due to mitigation of exposure from radon in drinking water. This
difference appears to be at least a factor of 4 ($3,2 million per cancer death
related to drinking water and $0,7 million per cancer death related to airborne
radon) and may be substantially larger. The highest costs may be those associated
with mitigation of risks for radon in water for the smallest communities.
In summary, the SAB notes the extent of the uncertainties in the population
exposure profiles, the risk estimates for ingested radon in drinking water and the
costs of mitigation. In view of these large uncertainties for risk estimates for
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ingested radon in drinking water and knowledge of the substantially greater risks
associated with airborne radon indoors and outdoors directly from soil, the SAB
advises that EPA consider various options for mitigating radon ean^r risks. The
options all include continuing the Agency's efforts to encourage voluntary actions
to reduce indoor air radon in view of the cost effectiveness of this approach for
reducing risks,
With regard to water, as one option the Agency could promulgate a
standard at 300 pCi/Lwater as has been proposed. However, in doing so it must be
recognized that this involves selecting a risk reduction strategy for radon that is
the most costly in terms of costs per cancer death avoided; i.e., more than four
tiroes the cost of cancer risk avoidance for airborne radon indoors. Alternatively,
as another option a standard might be set at some higher level such as 1000 to
3000 pCi/Lwater, to initiate mitigation of the highest potential risks. For example,
setting a water standard at 3000 pCi/Lwater would result in water contributing no
more radon to indoor air than is present in outdoor air, (Keep in mind that the
radon in outdoor air arises by natural processes from soil gas and there is no way
to alter the outdoor radon levels.) At the same time it would be appropriate to
intensify research on radon ingestion and radon mitigation, data gathering on
radon occurrence for all media, and dialogue with interested parties. These
actions would serve to reduce the uncertainties in the risk estimates, the costs of
mitigation, and, ultimately, the estimates of cost per cancer avoided. We cannot
emphasize too strongly the SAB view that a relative risk orientation should be
applied to the decision making process. Comparative analysis of uncertainties on
the risks of various exposure scenarios and mitigation approaches should be
developed and provided to the risk managers.
The SAB strongly supports the use of a relative risk reduction orientation
as an important consideration in making risk reduction decisions on all sources of
risk, including those attributable to radon. Other important considerations include
legislative authorities, environmental equity, economics, and the like. In short, the
relative risk approach calls For giving the highest priority to mitigating the largest
sources of risks first* espfially when the cost-effectiveness of risk reduction of
such sources is high. The SAB recognizes that the large number of laws under
which EPA operates makes it difficult to implement a relative risk reduction
strategy uniformly across the Agency. Radon is an excellent example of the
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problem with radon in drinking water governed under one statute (Safe Drinking
Water Act) while radon in indoor air is not currently subject to regulation under a
specific statute. The SAB strongly encourages the Agency and the Congress to
work together to consider changes in existing statutes that would permit
implementation of relative risk reduction strategies in a more efficient and
effective manner.
The SAB appreciates this opportunity to advise you and the Congress on
this important matter, and we look forward to receiving a response on these
suggestions.
Sincere
Dr.' Raymond C. Loehr v~*"-H5p5£ger &!ilcCleua& c
Chair, Executive Committee Chair, Chafee-Lautenberg Study
Science Advisory Board Review Committee
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Figure 1. Estimated Annual Cancer Risk From
Exposure to Radon (in Cancer Deaths/Year}
Ration from
Soil Gas
Radon from
Drinking Water
fndoorAIr
13,600 ^
tia inhalation
113
vtamhaiation
*fVs* potential inpacttKf by
Water Standard
Range offfis/c Estimates Shown m Figure:
13.6QQ (6740 - 30,600)
DATA SOURCf: "Report to Congmss on fiafffonuctides in Drinking Water:
Mu&media ftis* and Cosl Assess/rteftl of ftedon in Drinking Water
Office of Walor, Juty 9. 1993.
113(40-408)*
46(11-203)*
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Figure 2, Estimated Annual Deaths From Exposure
to Radon (In Cancer Deaths/Year)
Estimated Cancer Deaths/Year
3S.OOQ
30,000
25,000
20,000
15,000
10,000
5,000 -
High
Met/
Low
13,600
520
Ingested DW Inhaled Outdoor Air Inhaled Indoor Air
Sources of Exposure
; 'Report to ffig (/,$, Congress on Ract/onuc/lctes in Drinking Water:
Multimedia Risk and Cost Assessment of Radon in Drinking
Office of Water, US EPA Juty 9, W93,
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U.S. ENVIRONMENTAL PROTECTION AGENCY
SCIENCE ADVISORY BOARD
CHAFEE-LAUTENBERG STUDY REVIEW COMMITTEE
CHAIRMAN
Dr. Roger O. McClellan
President
Chemical Industry Institute of Toxicology
P.O. Bo* 12137
Research Triangle Park, NC 27709
MEMBERS
Mr, Richard Conway
Senior Corporate Fellow
Union Carbide Corporation 770/341
P.O. Box 8361
South Charleston, WV 25303-0361
Dr, Morton Lippmaim
Professor
Institute of Environmental Medicine
New York University
Long Meadow Road
Tuxedo, NY 10987
Dr. Genevieve M. Matanoski
Professor of Epidemiology
School of Hygiene and Public Health
The Johns Hopkins University
601 Wolff Street, Room 6019
Baltimore, MD 21205
Dr. Verne Ray
Senior Technical Advisor
Medical Research Laboratory
Pfizer Inc,
Groton, CT 06340
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DESIGNATED FEDEHAL OFFICIAL
Dr. Edward S. Bender
Environmental Protection Agency
Science Advisory Board
401 M Street, S.W,» A-101
Washington, DC 20460
STAFF SECRETARY
Mrs, Marcia K. Jolly
Environmental Protection Agency
Science Advisory Board
401 M Street, S.W., A-101
Washington, DC 20460
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