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5
Basic Approaches to Regulating Radiation Exposures
of the Public
This chapter presents a general discussion of basic approaches to
regulating exposures of the public to radionuclides in the environment. These
approaches are applied without regard for whether the radionuclides of concern
are naturally occurring or human-made. The primary purpose of this discussion
is to provide information that would be useful in understanding the many
guidances and regulations regarding radionuclides in the environment discussed
in chapters 7-10. The guidances and regulations cited here as examples are
discussed in more detail in chapter 7.
The fundamental purpose of any standard for radionuclides in the
environment is to limit health risks to exposed individuals and populations.
Many standards for controlling radiation exposures of the public have been
developed by the Environmental Protection Agency (EPA) and other federal
agencies with responsibilities in radiation protection of the public, including the
Nuclear Regulatory Commission and the Department of Energy. Furthermore,
the EPA's guidances and regulations have been developed under the authority of
various environmental laws that mandate different approaches to health
protection of the public (Overy and Richardson 1995~. Nonetheless, any
standard is based on considerations of one of the following factors for the
particular exposure situations of concern:
· Judgments about whether particular magnitudes of health risk to
the public are acceptable.
.
Judgments about whether particular magnitudes of health risk to
the public are achievable.
89
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APPROACHES TO REGULATING EXPOSURES
In judging the acceptability of risks, radiation dose often is used as a
surrogate for risk. Similarly, judgments about the achievability of risks might be
represented by judgments about the achievability of releases of radionuclides to
the environment, amounts of radioactivity in the environment, exposures, or
doses.
JUDGMENTS ABOUT ACCEPTABILITY OF HEALTH RISKS
An important example of the use of judgments about acceptable health
risks to the public in developing standards for control of radiation exposures is
found in EPA's proposed federal guidance on radiation protection of the public
(EPA 1994d) discussed in chapter 7. This guidance would apply to all controlled
sources of exposure, including sources not associated with operations of the
nuclear fuel cycle, but excepting exposures to indoor radon and beneficial
medical exposures. Because the guidance would apply to nearly all sources of
exposure other than natural background, it embodies important statements of
principle about acceptable health risks to the public posed by radiation
exposure.
EPA's proposed federal guidance on radiation protection of the public
is based in large part on the traditional approach to radiation protection
embodied in recommendations of the International Commission on Radiological
Protection (ICRP 1991; 1977) and the National Council on Radiation Protection
and Measurements (NCRP 1993a; 1987c). An important element of these
recommendations, which is incorporated in EPA's proposed federal guidance, is
the specification of a maximum allowable individual dose from exposure to all
controlled sources combined. The specified primary dose limit for chronic
exposure of individual members of the public is 1 mSv (100 mrem) per year.
The primary dose limit of 1 mSv (100 mrem) per year for all controlled
sources combined was originally developed on the basis of considerations of
acceptable risk. Specifically, on the basis of a review of other involuntary risks
that the public has accepted in everyday life, ICRP (ICRP 1977) judged that an
increase in lifetime risk of about 10-3 was an upper bound on acceptable risk
posed by radiation exposure. The 1-mSv (100-mrem) limit on annual dose then
was derived from the upper bound on acceptable risk by assuming a risk of fatal
cancers of about 10-s per millisievert (10-7 per millirem)3 and continuous
3The current estimate of the risk per unit dose and its effect on the primary dose
limit for individual members of the public is discussed in chapter 7.
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GUIDELINES FOR EXPOSURE TO TENORM
91
exposure over a 70-y lifetime (ICRP 1977~. Consideration of whether the
primary dose limit was achievable was not an important factor in establishing its
value. However, on the basis of experiences with the nuclear industry, ICRP
expected that individual doses substantially below the limit were easily
achievable for nearly all controlled sources.
A second example of the use of judgments about an acceptable risk in
developing standards for controlling radiation exposures of the public is found
in EPA's current regulations for airborne emissions of radionuclides developed
under authority of the Clean Air Act and discussed in chapter 7. In contrast with
the proposed federal guidance on radiation protection of the public discussed
above, the regulations for airborne emissions apply only to particular sources
(that is, not all airborne releases of radionuclides are subject to the regulations)
and only to a single pathway of release to the environment.
In response to a lawsuit over standards for airborne emissions of vinyl
chloride, the court of appeals mandated that standards for airborne emissions of
hazardous air pollutants developed under the Clean Air Act must be based on a
determination by EPA of a safe or acceptable level of risk to individuals or
populations and an ample margin of safety below that level for protection of
public health, but that the standards could not be based on considerations of
technical feasibility or cost (for example, EPA 1989d). In response to the court's
mandate, EPA established standards for airborne emissions of radionuclides
(and other carcinogens) that would ensure that the lifetime cancer risk would not
exceed about 10 ~ for maximally exposed individuals and about 10-6 for average
exposures in the population.
A third example of the use of judgments about an acceptable risk in
developing standards for controlling exposures of the public is found in EPA's
current regulations for remediation of contaminated sites; the regulations were
developed under authority of the Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA) and are discussed in chapter 7. The
regulations, which apply to radionuclides and hazardous chemicals, specify that
a lifetime cancer risk of about 10-4 iS one of the criteria to be used in defining
acceptable risk when considering the need for site remediation. However, the
individual risk criterion of 10-4 in standards for remediation of contaminated
sites under CERCLA is fundamentally different in concept from the upper
bound on acceptable risk corresponding to the primary dose limit of 1 mSv
(100 mrem) per year in the proposed federal guidance on radiation protection of
the public and the limit on individual risk of 10-4 embodied in regulations for
airborne emissions of radionuclides. The primary dose limit and the regulations
for airborne emissions define limits on acceptable risk for the exposure
situations to which they apply, but the risk criterion for remediation of
contaminated sites defines a goal for acceptable cleanups that can be relaxed on
the basis of many considerations, including a determination that achieving the
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APPROACHES TO REGULATING EXPOSURES
goal is not cost-effective. In essence, the risk goal of 104 for remediation of
contaminated sites defines an upper bound on negligible (trivial) risk for a
particular exposure situation, but it does not define a limit on risk that must be
met regardless of other circumstances.
Thus, several EPA guidances and regulations for radionuclides in the
environment were based primarily on a priori judgments about acceptable health
risks to the public for the exposure situations of concern. However, it would be
misleading to assume that judgments about acceptable risk were the only basis
for those standards. The proposed federal guidance on radiation protection of
the public includes additional provisions, besides the primary dose limit of
1 mSv (100 mrem) per year for all controlled sources combined, that are based
on considerations other than a limit on acceptable risk. The standards for
airborne emissions of radionuclides also were cognizant of doses and releases
that were reasonably achievable, and the cancer-risk criterion for cleanup of
contaminated sites under CERCLA is only a goal that can be exceeded in
acceptable cleanups under many circumstances (see chapter 7~.
JUDGMENTS ABOUT ACHIEVABILITY OF HEALTH RISKS
Many EPA regulations that apply to specific sources or practices were
based primarily on judgments about the ability of available technologies to
control or reduce releases of radionuclides to the environment, levels of
radioactivity in the environment, exposures, or doses, rather than a priori
judgments about acceptable risks for the exposure situations of concern.
Regulations based primarily on judgments about the ability of technologies to
control or reduce radiation exposures of He public include standards for
operations of uranium fuel-cycle facilities, radioactivity in community drinking-
water systems, radioactivity in liquid discharges from particular mines or mills,
uranium and thorium mill tailings, and management and disposal of spent fuel,
high-level waste, and transuranic waste (see chapter 7~. The federal guidance on
indoor radon (see chapters 7 and 8) also was based in part on considerations of
the cost effectiveness of available technologies for reducing existing
concentrations of radon in homes. Finally, most cleanup decisions regarding
contaminated sites subject to remediation under CERCLA have been based
primarily on considerations of cost and feasibility, rather than compliance with
the cancer-risk goal described in the previous section (see chapter 7~. Thus, in
controlling radiation exposures of the public, the standards for airborne
emissions of radionuclides developed under the Clean Air Act are the only EPA
regulations for specific sources or practices that were based primarily on
judgments about acceptable risks.
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A second important element of ICRP (1991) and NCRP (1993a)
recommendations on radiation protection, which also is incorporated in the
proposed federal guidance on radiation protection of the public (EPA 1994d), is
the principle that exposures of individuals and populations should be as low as
reasonably achievable (ALARA). Thus, compliance with the primary dose limit
of 1 mSv (100 mrem) per year for all controlled sources combined does not, by
itself, provide acceptable radiation protection of the public, because doses also
should be reduced as far below the primary dose limit as practicable. Indeed, as
discussed in chapter 7, application of the ALARA objective often is the most
important consideration in radiation protection of the public (for example,
NCRP 1993a).
In essence, all EPA regulations or guidances listed above that were
based primarily on judgments about the achievability of releases of
radionuclides to the environment, levels of radioactivity in the environment,
exposures, or doses (and, therefore, risks) constitute an application of the
ALARA objective to standard-setting itself. The standards for particular sources
or practices represent risks that EPA judged reasonably achievable at any site,
that is, the standards specify minimally acceptable performance for the
particular sources or practices based on ALARA considerations. In each case,
however, the judgments necessarily were somewhat subjective; there are no
purely objective criteria for judging what is reasonably achievable, and
judgments about the achievability of particular doses or risks for a particular
exposure situation can be influenced by their magnitude in relation to doses or
risks that have been judged acceptable for other exposure situations.
OTHER CONSIDERATIONS IN DEVELOPING STANDARDS
As described in the previous two sections, judgments about the
acceptability of risks or the achievability of risks are fundamental to the
development of all standards for controlling radiation exposures of the public.
However, other considerations also can be important in developing radiation
standards for the public, including the justification of practices, the ability to
measure radioactivity in the environment at the levels of concern, and levels of
natural background radiation.
Justification of Practices
A third important element of ICRP (1991) and NCRP (1993a)
recommendations on radiation protection, which also is incorporated in the
proposed federal guidance on radiation protection of the public (EPA 1994d), is
the principle that all exposures should be justified, that is, that the benefits to
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APPROACHES TO REGULATING EXPOSURES
society from any practice that increases radiation exposure should outweigh the
overall societal costs. Justification of exposures is not an important concern for
any of the guidances or regulations discussed in chapter 7, either because
exposures cannot be avoided, as is the case with some exposures to naturally
occurring radionuclides, or because a societal decision was made that operations
of the nuclear fuel cycle for peaceful and defense purposes were, on the whole,
beneficial.
In some cases, however, the principle of justification has been
important in radiation protection of the public. For example, frivolous uses of
radioactive materials (such as incorporation into children's toys or costume
jewelry) have been banned by the Nuclear Regulatory Commission without
regard for the magnitude of the resulting doses and risks because there is no
overriding benefit.
Measurability of Radioactivity in the Environment
A standard for controlling radiation exposures of the public is useful in
practice only to the extent that compliance with the standard can be verified by
environmental measurements, including measurements of external radiation or
quantities of radionuclides in air, water, soil, foodstuffs, or other materials.
Therefore, the ability to measure radioactivity in the environment at particular
levels can be an important consideration in developing standards for specific
sources or practices. For example, current regulations for operations of uranium
fuel-cycle facilities, radium and gross alpha-particle activity in community
drinking-water supplies, radium in soil at uranium and thorium mill-tailings
sites, and management and storage of spent fuel, high-level waste, and
transuranic waste all took into account, to some extent, the ability to measure
radioactivity in the environment at levels corresponding to the specified
standards.
Although the ability to measure radioactivity in the environment is
important, the measurability of various environmental surrogates for risk
generally cannot be the primary basis for the standards. The difficulty with
basing standards only on considerations of measurability is that the levels at
which particular radionuclides can be measured in the environment do not
correlate well with doses and risks to the public; furthermore, radionuclides
posing the greatest risks might be the most difficult to measure at environmental
levels of concern. For example, radionuclides that are high-energy photon
emitters are the easiest to measure at low levels in the environment but often are
relatively short-lived and so might result in relatively low doses and risks,
whereas long-lived beta- or alpha-emitting radionuclides might be difficult to
measure at low levels but could result in relatively high doses and risks. An
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additional consideration here is that the environmental levels of concern should
be readily measurable with conventional and cost-effective techniques.
Natural Background Radiation
Radiation standards for the public generally have been developed in
full recognition of the magnitude and variability of natural background
radiation. The ubiquitous background of natural radiation, with its attendant and
largely unavoidable doses and risks, has influenced the development of radiation
standards in two ways.
First, geographic variations in natural background, excluding the large
variations in levels of radon in homes, provide a perspective on whether the
primary dose limit for the public of 1 mSv (100 mrem) per year for all
controlled sources combined discussed earlier is reasonable (NCRP 1993a;
ICRP 1991~. In particular, it is regarded as unreasonable to require reductions in
doses from all controlled sources combined to levels far below variations in
natural background on the basis only of considerations of acceptable risk
because, although the risk from natural background might not be welcome, the
variations in background can hardly be called unacceptable (ICRP 1991~.
Furthermore, there is no direct evidence of increased risks due to radiation
exposure at magnitudes of natural background (National Research Council
1990~.
Second, levels of naturally occurring radionuclides in environmental
media, including considerations of their bioavailability, can be important in
developing standards for particular sources or practices. For example, cleanup
standards for radium in soil at uranium and thorium mill-tailings sites were
based in large part on background levels of radium in surface soil in parts of the
United States where the mill tailings were produced. In this case, the maximum
allowable concentrations of radium in soil must be substantially above
background, so that the radium arising from mill tailings can be distinguished
from the radium in native soil.
The influence of natural background radiation on the development of
radiation standards is discussed further in chapter 7.
SUMMARY
This chapter has discussed the basic considerations that are important
in developing any standards for controlling radiation exposures of the public.
The main points of these discussions are summarized as follows.
First, all standards for radionuclides in the environment are based on
judgments about the acceptability of magnitudes of health risk to the public or
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judgments about the achievability of magnitudes of health risk to the public.
Those two considerations are applied without regard for any differences in
mandates in the various environmental laws that provide the authority for
regulations.
Second, other considerations also can be important in developing
standards for radioactivity in the environment, including the justification of
practices (positive net benefit), the ability to measure radioactivity in the
environment at levels corresponding to the standards and the magnitude and
variability of natural background radiation, and the levels of naturally occurring
radionuclides in various environmental media. However, these other
considerations usually do not provide the primary basis for standards for
controlling radiation exposures of the public.
Representative terms from entire chapter:
primary dose
