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guidelines corresponding to risks greater than one in a thousand are similarly
puzzled; how can such high absolute, risks be tolerated?

Given this situation, some resolution of the discordance between the two
paradigms is needed.. The resolution could simply be to assert that radiation and
chemicals are fundamentally different and should be assessed and managed differ-
ently, or some synthesis could be reached that takes into account both background
issues and absolute risk levels. As an example of the latter approach, Koeher and
Hoffman (1991) have recently proposed a specific risk management strategy that
may be applied to both radiation and chemicals. The following sections describe the
radiation and chemical paradigms in more detail and suggest some possible ap-
proaches to resolve the discordance between them.

The Radiation Paradigm

Current risk assessment approaches for radiation, whether from radionuclides
or from other sources, developed out of the atomic energy program. It both served
as a framework for radiation protection for atomic workers (and later for the gener-
al public) and, tinder the rubric of "damage assessment," was used to predict fatal-
ities and residual health impacts from the radioactive fallout from nuclear weapons.
In assessing risk, health physicists, radiobiologists, and radiation epidemiologists
have been able to make risk estimates of relatively high precision from human data.
While cancer risk estimates for radiation entail substantial uncertainties, especially
at low doses and dose rates, they are seen as being'Sufficient to justify making a best
estimate of risk within a statistical uncertainty factor of about 2 for all cancers com-
bined for whole-body external radiation if the dose is known accurately (NGRF,
1989).2 These best estimates of risk are used directly without further, safety factors
of any kind.' Because best estimates are used and the degree of uncertainty is only
moderate, risk assessment results'for radiation can be compared with risk criteria
for control decisions with some confidence.

Radiation risk assessment was heavily influenced by the thinking of physi-
cists; in fact, "health physicists" are more likely to be involved in the. practice of
radiation protection than are the "radiobioftrgikts" who study the fundamental bio-
logical aspects of radiation. Topically, the description of radiation risks emulated
the mathematical treatments of physical systems, often using phenomenologic .

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For coBftndoa to tha l*tt«r nnitt »fl wimwiral «r« djvjd»d ty am kmdiwL

2

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models with consideration of biological theory only as a secondary factor. The fit of
curves to cancer data from radiobiological experiments were interpreted as reflecting
linear, simple quadratic, or linear-quadratic dose-response relationships, and the un-
derlying mechanisms were described by "target theoiy" as, "one-hit" or "two-hit" and
so on. Later, it was postulated that radiation created breaks in DNA which, if not
repaired, could result in somatic mutations and eventually in cancer. While it is
now believed that additional mechanisms - e.g., radiation effects on oncogenes -
may play a role, the mutation hypothesis for radiation carcinogenesis still heavily
influences radiation risk assessment and management (NCRP, 1989).

The analysis of epidemiologic information followed similar models, whether
the data were from acute doses of whole-body gamma irradiation (Hiroshima and
Nagasaki), fractionated X irradiation (tuberculosis patients, for example), or
protracted irradiation from internally deposited radionuclides (the radium dial
painters and the uranium miners). Issues arose about the existence of thresholds
for radiation carcinogenesis (e.g., in the dial painters) or at least "practical thresh-
olds" (e.g., the idea that cancer latency was inversely related to dose such that
manifestation of risks at low doses could be delayed so long that no cancers would
occur during a normal lifetime).

Underlying all this development was the knowledge that "background expo-
sures to radiation in the range of about 70 to 250 millirem per year (mrem/jr) and
averaging perhaps 100 mremfrear dose equivalent (NCRP, 1987) were inescapable.
At least initially, these background exposures were generally assumed not to confer
significant risks. Thus, as recommended radiation standards became more strin-
gent with the discovery of adverse effects at ever lower levels of protracted exposure,
the radiation scientists kept in mind the difficulty of separating excess exposures
from natural exposures when the former did not substantially exceed the latter.
Consequently, cancer risk-reduction strategies for excess radiation exposures have
very probably included comparison to background radiation in addition to the
comparison of risks and benefits "resulting from radiation-producing technologies,
even though the background exposure issue has usually not been explicitly presented
in such decisions.

When in the early days the critical endpoints for radiation protection were
effects seen only at what are now considered to be high (e.g.» eiythema) doses, the
allowable excess doses were easily separable from normal variability in background
radiation. The standards have been tightened as the assumption of no threshold for
radiation carcinogenesis and the possibility of a linear dose-response relationship
have taken hold among most radiation risk assessors. These assumptions have been

3

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employed in the development of radiation protection policy. Scientists have also
learned, however, that many people are experiencing exposures to the lungs from
radon and its progeny that confer risks several times that from the 100 mrem/year
that arises from cosmic radiation, terrestrial gamma radiation, and internal potassi-
um-40 radiation, averaging perhaps 200 mrem/yr (NCRP, 1987). And, at least for a
time, medical diagnostic and therapeutic radiation increased the average radiation
dose about 100 mrem/year on the average.

The International Commission on Radiological Protection (ICRP) currently
recommends limiting excess environmental radiation exposures to a total of 100
mrem#r for the general population (ICRP, 1991). In addition, the ICRP requires
that there be a net positive benefit and that the ALARA principle be adhered to that
is, that exposures should be kept M Low As Reasonably Achievable when economic
and social factors have been taken into account. The ALARA concept appears to be
the radiation protection community's equivalent of feasible technology-based
standards for chemicals.

The potential cancer burden from 100 wremfyr exposure is not always made
explicit in radiation protection guidance. If continued over a lifetime, however, 100
mrem/yr is calculated with EPA's current risk coefficient for radiation carcinogen#'
sis,to cause cancer risks of almost 3 in a thousand (3 x 10"3) (NAS/NRC, 1990).

Some analyses would predict risks up to three times higher, Le., close to one in one
hundred.

The Chemical Paradigm

For chemicals, the paradigm is different. Most cancer risk assessments are
based on the results of bioassays in animals dosed with chemicals at lewis thou-
sands of times those expected in the environment, not from human data of high
reliability. To deal with the uncertainty, SPA''in particular has adopted the use of
the upper confidence limit on the slope of the linearized multistage model to project
risks at low doses and has used a conservative procedure - the surface area, scaling
rule - to project from animal bioassays to assumed human responses, loth of these
procedures are widely believed to produce risk estimates that are more likely to
overestimate than underestimate human risk (EPA 1986; 1989), Thus risk esti-
mates for chemicals are biased high (even though such may not be the case with
every chemical). This conservative method of dealing with uncertainty ensures that
in the vast majority of cases, the actual risk level achieved will be lower than the
risk criterion used in a control decision.

4

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Furthermore, the prototype chemical carcinogens were synthetic substances
with no or limited natural sources. In calculating excess risk from human sources of
a chemical, background levels, if any, are therefore frequently seen as irrelevant,
even though. in actuality background levels from either natural sources or anthropo-
genic sources other than the one being considered often exist.

Risk assessment for chemicals developed from the ideas of medical epidemi-
ologists, biostatisticians, experimental biologists, and - perhaps most importantly -
public health regulators. Again the idea was to protect people from the adverse
effects of chemicals on health, most particularly potential carcinogenicity. Here the
tradition was chemical safety, deriving from the early food and drug protection ideas
to keep chemical exposures low enough to protect health with a substantial margin
of safety. This was typically accomplished by finding some "no-effect level" and then
dividing by "safety factors" with the goal of achieving nearly absolute safety. This
approach is still used for non-carcinogenic chemicals.

The idea that some chemicals might be a little dangerous at any level of
exposure (the no-threshold idea, applied especially to what were then called "radio-
mimetic chemicals") came as quite a shock to the regulators. Congress responded in
1958 by attaching the "Delaney Clause" to the amendments for the Food, Drug, and
Cosmetics Act, which prohibited the addition to the human food supply of any
chemical that can cause cancer in humans or animals. The idea remained to provide
absolute protection against cancer risk.

From the start, however, FDA scientists and others realized that assuring
complete absence of carcinogens in the food supply was impossible, particularly in
view of the rapidly advancing ability of the analytic chemists to detect ever lower
levels of chemicals in food, and the abundance of naturally occurring carcinogens.
Almost from the outset of the Delaney era, therefore, the FDA was looking for the
practical equivalent to absolute safety in a world where thresholds for carcinogenesis
could not be assured. FDA and NIH scientists soon proposed that if risks calculated
under the no-threshold assumption were below some small value, the carcinogen was
effectively not present in the food and the Delaney Clause would be satisfied The
first proposal for a "virtually safe dose" was "to limit cancer risk to one in 100 million
(10*) over a lifetime of exposure (Eodricka et ai, 1987), The idea was clearly tied to
the assumption that all the people in the United States could be exposed at or near
the virtually safe dose; at the then-current population of about 150 million, only one
or two people currently alive could be affected even if all the conservative assump-
tions about exposure and potency proved to be true.

5

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Shortly thereafter, it' was realized that the 10"* criterion itself put an almost
mpossible burden on' the regulator for assuring the safety of food additives with
considerable benefits. Almost as a .reflex, the- idea arose that one in a million (10"6)
was a l-'fetime risk that most people would find negligible. At that level, everyone in
the na -ion could be exposed and only about 3 excess cancer cases per year would be
incurred, again even if the risk estimates were accurate and not conservative. Given
that everyone would not be so exposed if one calculated the risk for a reasonably
highly exposed person, the resulting cancer toll would elearly.be invisible and, for
most people, the risk insignificant

Although quasi-scientific arguments have been offered to justify the one-in»a-
million criterion for acceptable risk, we must not forget that it originated as a
number of convenience. Nevertheless, it became institutionalized over the next
several years and, when cancer risks from environmental exposures became recog-
nized in the late.'SOs tod early '70s, the concept of negligible risk at 10 was
applied there. Early on, the types of risks of most concern were widespread ones
such as exposures to PCBs or pesticide residues in the environment. Later, the
same risk criteria began to be applied to much less widespread risks such as around
industrial facilities or hazardous waste disposal areas.

Eventually, it became evident that 104 was a very stringent criterion when
relatively few people were exposed. Studies of EPA decisionmaking show that EPA
often has chosen not to require reductions in exposure when the calculated risks
were as high as 10 or even 10 when the population exposed was small (Travis et
al, 1987; Rodricks et al., 1987).

Moreover, some of the statutes that govern chemical regulation by EPA and
other agencies allow or even require a balancing of the risks against the benefits of
the technologies involved and the cost of control strategies in determining what risk
is acceptable in a specific situation, Others simply demand action whenever risks
are determined to be "substantial" or "significant," arid many judicial battles have
been fought over the meaning of these directives. For example, in the VInyt ,
Chloride case Etigated under the Clean Air Act, the court ruled that chemical safety
did not imply a complete and unambiguous -freedom from risk, but also that the

* Thi# Wv*i of risk limitation m not,' u4 ct3l"» not, r*quirtd in th*. «Eup«±ioo»l fcM&t ana* wbn* Vifetaa «f
azgrnb^ wtoteiy ead ly precedeit irea aoiwaHicw s totime ritit eiteim cf dMut cm $s s ihflwai $b

(S« Rodiricfei it «L, 19S?, pp. 314). Bwnlatfc* wiqwrtaori
ana*, lwwtwr, mdiattai «po«uj* limit* I*w mine*!** ia tiaktmu than ax* dsamieal «pa»nrt latt*. 'Qamstfy
*llow»bk radiation do* if actaaQf iacumi weald 'toad to alifctis* riak of w*l am em fa * tomdrtd, pwhaja mckiBf e»
w taa (3*4 JfASUNBG, 1993. pp. 172).

6

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primary safety decision had to be made without considering benefits and control
costs (Whipple, 1989), Later, risk/benefit balancing could be applied in determining
an adequate margin of safety. Such risk-benefit balancing is conducted in the same
spirit as the optimization principle in the radiation community, but at a different
balance point, mill -radiation protection requiring lower expenditures per cancer
avoided.

Recently, Don R. Clay, EPA's Assistant Administrator for Solid Waste and
Emergency Response (which includes the Superfund program) has indicated that
remediation at hazardous waste sites need not be undertaken when cancer risks for
lifetime exposures are calculated to be below 10"4 (Clay, 1991). Cancer risk levels at
or above 1CT* are also accepted in setting Maximum Contaminant Levels (MCLs) for
carcinogens in drinking water (e.g., for chloroform from water disinfection) when
limiting them further is not technically or economically feasible. Even so, many
EPA programs still apply a risk criterion in the 10" to 10"* range to a (sometimes
only hypothetical) "maximally exposed individual" or "reasonable maximum expo-
sure." This "individual risk" focus does not place as much weight on the overall
protection of public health (individual risk times number of people exposed at that
risk level) as does a "population risk" focus. Whether the Agency's judgment is
focused on individual risk or on population risk for a specific situation depends on
the provisions of the enabling legislation and the traditions of the EPA office imple-
menting it. Risk-based legislation is more likely to result in an individual risk focus,
whereas technology-based standards to some extent skirt the individual risk issue
and implicitly favor a population risk approach.

Some chemical regulators and environmentalists are convinced that risk
levels above one in a million are not acceptable for any person, invoking arguments
regarding equity: why should any person bear a cancer risk for the benefit of other
people? Why should all people not be afforded equal protection? Why should
carcinogens be allowed in the environment at all? And everyone would agree that
all opportunities to reduce risk should be seized as long as the costs - economic,
social, or other - are not too high.

Progress toward such goals is much'easier to measure when there is no
natural background exposure. Synthetic organic chemicals often would not be
observed in the environment at all if not for human activities; even when natural

7

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sources cart be identified, the risk levels for the natural levels of exposure are often
not high when calculated with the linearized multistage model or an equivalent,4

. Notwithstanding these similarities to the radiation paradigm, the chemical
carcinogen paradigm tends to view any risk levels above 10"*, even to a very few
individuals, as potentially excessive and therefore requiring action to reduce
exposure and' risk.	'

Discordance between the Paradigms

Although similarities and differences in risk assessment techniques for
chemicals and radiation have been discussed, (NCRP, 1980) and although the
difference in the risk-reduction strategies between these two paradigms has been
recognized by some scientists and regulators for several years, the provinces of tie
health physicists- and the chemical risk managers stayed relatively distinct until
recently. As the EPA. gradually took on greater and greater responsibility for
regulating radiation sources as well as chemical ones, the discordance became more
visible.

The difficulty became evident in several EPA program areas. When EPA had
to promulgate National Emissions Standards for Hazardous Air Pollutants
(NESHAFs) for radionuclides, it needed to harmonize the residual risk levels with
those allowable for other-carcinogenic air pollutants such as benzene. In the course
of analyzing sources of airborne radionuclides, more stringent controls were pro-
posed for them than would have been thought necessary to keep radiation doses to
100 mremJyr or somewhat less. Furthermore, EPA had to wrestle with the fact that
prior emissions from (or other practices of) these facilities may have left residual.
radioactivity in communities across the country producing radiation doses with
calculated risks greater than one in ten thousand. The Radiation Advisory Commit-
tee (SAB, 1992a) recently commented on the Idaho Radionuclides Study, in which
some people may have received excess gamma radiation of the same magnitude as
typical background radiation levels, ie., about 100 mremfrr, from uranium-series
radionuclides in elemental phosphorus slags distributed in their community.
Elsewhere, EPA is dealing with radon emanations from phosphogypsum stacks or
with radionuclides from processing of rare earths for radium, thorium, or non-
radioactive materials.

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that tb«r» |i no www npomai if m—lnrid copcutratiopi «x« not b«yond th» ttnfltkiy Baiti qn tin diatribctkn qf

8

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A second area of discordance pew out of the recognition of waste problems -
involving radioactive materials that were under the purview of EPA or state
environmental t gencies rather than the Nuclear Regulatory Commission or the
nuelear/radiatio' i safety agencies in agreement states. The most striking of these
are the radioactive or mixed waste problem at sites that have been placed on the
National Priority List for attention by the Superfund Program, Here the wastes of
most concern are often the radionuclides of she uranium or thorium series that are
also found in nature, and which have for the most part been "technologically
enhanced" by human activities, rather than created by them.

The facilities of the Department of Energy that are part of the nuclear
weapons complex form another group of problem sites where radionuclides are a
significant or even dominating part of the cancer risk equation. Whether these
facilities are treated as Superfund (CERCLA) problems or current waste disposal
sites under the Resource Conservation and Recovery Act (RCKA), the treatment of
radioactive materials is seen as necessarily being subject to the same types of risk
analyses and remedial responses that EPA has used for chemicals. The document
"Risk Assessment Guidelines for Superfund" (RAGS), for example, contains a section
on how to assess the cancer risks from exposure to radionuclides, but does not
suggest any different risk-reduction strategies than for carcinogenic chemicals. The
implication is that remediation is expected if the lifetime risks' from radionuclides
are calculated to exceed about 10 (or lower in some proposals for radiation sites).

The differences in the radiation and chemical paradigms have also become
apparent in EPA's actions with respect to radon in homes. The current EPA
guidance ("action level") for home remediation is 4 pCi/L of radon in air in the
lowest lived-in area, which by current EPA risk assessment methods translates to a
lifetime risk of over 1 in 100 or 10,000 in a million (1 x 10**) for an average person
(smokers and nonsmokera combined) (EPA, 1991a). The Agency is clearly not
implying that such a level of risk is acceptable in an absolute sense, but appears to
be applying a rule of practicality based on the difficulty of reducing exposure levels
much below 4 pCi/L within a reasonable budpt, EPA also must work on the radon
issue without a clear legislative mandate encouraging the Agency to regulate
homeowners' choices.

EPA has reacted differently to the legislative requirement to control levels of
radon in drinking water. Using an approximation of the chemical paradigm, the
Office of Drinking Water has proposed that public water utilities must treat water
that contains radon above 300 pCi/L (EPA, 1991b), a level yielding a risk in the
vicinity of one in ten thousand (1 x 10"4), even though this level of risk is two orders

9

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of magnitude.lower than what is recommended for radon in air and the cost per
calculated life saved is substantially greater than for remediation of radon in '
household air (SAB, 1992a).

It can be argued that thediscordance between radiation and chemical risk-
reduction strategies is simply another manifestation of necessary differences in
regulatory choices in different situations. Indeed, good reasons exist to make all
risk-reduction decisions within a framework intended to reduce overall risk levels
„ without excessive attention to keeping the risks from any one situation within ¦
inflexible guidelines. Clearly, the requirements of the various statutes enabling
EPA's regulatory activities force the Agency to formulate and apply some discordant
and seemingly inconsistent policies. Nevertheless, the Committee believes that the
differences between the chemical and radiation paradigms are more troublesome
than the variation within each area of regulation.

In each new case of radiation risk management, EPA can follow the chemical
tradition of regulating risks to the vicinity of 1Q4 or lower or the radiation tradition
of tolerating (where inexpensive remedies are not readily available) an approximate
doubling of the risks from natural background radiation, which are in the vicinity of
3 " 10*3 for background exclusive of radon and nearly one in a hundred (10*2) when
radon is included. This disparity can and has led to considerable lack of under-
standing and conflicts between health physicists and chemical risk managers. Even
the existence of an analogy In the chemical world to the radionuclide problem - the
background levels of carcinogenic inorganic substances such as arsenic and the
existence of substantial quantities of natural organic carcinogens in foods (Ames and
Gold., 1990)- has not brought about any resolution of this discordance.

Need for Harmonization

Clearly, EPA needs to adopt policies that will allow its staff, the regulated
community, scientific consultants-to both parties, and the general public ail to know
what to expect in EPA's regulation of residual radioactivity and other radiation
issues. The Radiation Advisoiy Committee does not claim any special insight in how
the resolution should be accomplished, but dSi$ emphasise the importance of .
achieving such harmonization. Interest in the comparative risks of radiation and
chemicals has a substantial history (NCRP, 1989) and is now becoming more
widespread (Kocher and Hoffman, 1991),

One approach could be to assert that radiation and chemical regulations are
fundamentally different, perhaps because of the unavoidability of background

10

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radiation. The guidance of the ICRP on dose limitation (currently, 100 mrem/yr
whenever the ALARA principle does not result in lower levels) could become the
explicit policy of the Office of Radiatio i Programs (ORP), and other branches of
EPA could explicitly defer to ORP on i adiation and radioactivity issues.

A second set of alternative approaches would strive for clear consistency
between the radiation and chemical risk*reduction strategies. The two extreme
cases are;

a.	Use the optimization principle along with background risks from
radiation as guidance for how much excess risk can be tolerated from
any source, be it chemical or radiation. Excess risks in the range of
10 or a bit higher would be used as a criterion for remedial actions or
regulations where remediation is expensive arid not easily achieved.
Use the ALAKA principle whenever it applies, that is, when risks can
be reduced without excessive penalties in terms of social or economic
costs. Make provisions for dealing with hazards in those cases where
exposures even at the calculated 1Q"3 risk level are not detectable or
distinguishable from background (Is., ALARA should apply whenever
risk reduction can be reasonably anticipated even though it cannot be
measured).

b.	Regulate radiation risks exactly as chemical risks are now regulated.
Use 10 as a standard criterion for remediation or regulation, regard-
less of how the corresponding standards compare with background
levels of exposure. Use the absolute value of risk in excess of back-
ground risk as a criterion, not the fractional increment relative to
background risk. Make practical exceptions for the inability to detect
some of the regulated exposures at the selected level of risk, just as is
done for chemical substances when the detection limit exceeds the
target for regulation, as is the case for dioxin in water. Take costs and
benefits into account where the applicable legislation provides for that
possibility.

The Radiation Advisory Committee recognizes that neither of these latter
options may be practicable given the history of how the two paradigms developed.
Probably more likely to be accepted would be a third option that seeks a compromise
risk-reduction strategy with an intermediate risk acceptance criterion or criteria.

11

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As a third option, the Agency could determine that, because the physical
characteristics of the two types of agents are so,different and because the approach-"
es to monitoring and regulating'them have developed so differently, bringing the two
areas into rigid conformity in the near term is very likely not possible, however
societaHy or ethically desirable as s long-term goal. The Radiation Advisor;.-
Committee strongly suggests in this case that the two approaches be harmonized-
that is, fitted into a common policy framework aimed at aggregate risk reduction but
not necessarily achieving such reductions in identical ways or with identical risk
criteria in every case (see Deisler, 1084, for an example of harmonization in tha
chemical safety field). The harmonization between chemical and radiation risks of
different types could occur by clearly and explicitly taking into account the differenc-
es in risk-reduction criteria or strategies between hazards that have natural sources
(rather than, or in addition to, anthropogenic sources) and those that have only
anthropogenic sources. For example, risk criteria for substances with no natural
sources (including radionuclides such as plutonium or americium) could be different
from those used for substances that have natural sources (including carcinogenic
inorganic substances and organic materials with significant natural sources).

Whatever the nature of harmonization between, the radiation and chemical
paradigms, it will need to incorporate as well the differences among ambient
environmental and indoor and occupational exposures, and the distributions of risks
and benefits among exposed individuals and the sources of the exposure.

Clearly, the choice among these options — and others that may exist — is a
policy choice that transcends scientific analysis. The leadership of the Environ-
mental Protection Agency has the authority and the responsibility to make the
choice. We urge the choice to be articulated clearly so that the scientists who assess
the risks of radiation and chemicals can understand the basis for subsequent
decisions about risk reduction. . '

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REFERENCES

Ames, B.N., and L.S. Gold, 1990. Too Many Rodent Carcinogens: Mitogenesis
Increases Mutagenesis, Science 249:970-971,

Clay, D.R., 1991. Role of the Baseline Risk Assessment in Superfund Remedy Selec-
tion Decisions, Environmental Protection Agency Memorandum, April 22, 1991, p, 1

Deisler, P.F. Jr., 1984, Reducing the Carcinogenic Risks in Industry, Marcei-
Dekker, pp. 135-158.

EPA, 1986, Environmental Protection Agency, Guidelines for Carcinogen Risk
Assessment, Fed', Beg, 51:33992-34003, September 24,1986..

EPA, 1989. Environmental Protection Agency, Risk Assessment Guidance for
Superfund, Vol. 1, Human Health Evaluation Manual (Part A), EPA/540/1-89/002,
pp. 8*6.

EPA, 1991a. Environmental Protection Agency, Proposed Revisions in EPA Esti-
mates of Radon, Risks and Associated Uncertainties.

. *

EPA, 1991b. Environmental Protection Agency, National Primary Drinking Water
Regulations; Radionuclides;"Proposed Rule, Fed. Reg. 56:53050-33127, July 18,
1991, pp. 33051.

ICRP, 1991. International Commission on Radiological Protection, Radiation
Protection: 1990 Recommendations of the International Commission on Radiological
Protection, ICRP Publication 60, Pergamon Press.

Kocher, D.C., and F.O. Hoffman, 1991. Regulating Environmental Carcinogens:
Where Do We Draw the Line?, Env. ScL TechnoL 25:1986-1989.

NAS/NRC, 1990, National Research Council, Health Effects of Exposure to Low
Levels of Ionizing Radiation (BEIR V). Report of the Committee on the Biological
Effects of Ionizing Radiations, National Academy Press, pp. 172-173.

NCRP, 1987. National Council on Radiation Protection and Measurements, Expo-
sure of the Population of the United States and Canada from Natural Background
Radiation, NCRP Report 94.

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NCRF, 1989, National Council on Radiation Protection and Measurements, Com-
parative Carcinogenicity of Ionizing Radiation and Chemicals, NCRP Report No, 96,
pp.2.

SAB, 1992a; Science Advisory Board, Radiation Advisory Committee, Idaho Radionu-
clide Study, EPA-SAB-RAC-LTR-92-004, January 21,1992.

SAB, 1992b: Science Advisory Board, Radiation Advisory Committee, Reducing
Risks from Radon; Drinking Water Criteria Documents, EPA-SAB-RAC-COM-92-
003, January 29,1992.

Rodricks, J.V., S.M. Brett, and G.C. Wrenn, 1987, Significant Risk Decisions in
Federal Regulatory Agencies, Reg. Toxicol Pharmacol, 7:307-320,1987, p. 308, 310-
313

Travis, C.C., et al., 1§87. Cancer Risk Management, Bnv-Sci. TechnoL 21:415420.

Whipple, C„ 1939. Courts Speak on Risk issue, Forum Appi. Research PubL Policy,
4:96-99.

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Administrator
Deputy Administrator
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Director, Office of Health and Environmental Assessment, ORD
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EPA Headquarters Library
EPA Regional Libraries
EPA Laboratory Libraries

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