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OCR for page 204
10
Comparison of Current Guidances for TENORM in
the Environment
INTRODUCTION
Chapters 7-9 of this report discussed guidances for naturally occurring
radionuclides and TENORM in the environment developed by regulatory
authorities in the United States and other countries and by national and
international advisory organizations, such as the National Council on Radiation
Protection and Measurements (NCRP), the Health Physics Society (HPS), the
International Commission on Radiological Protection (ICRP), and the
International Atomic Energy Agency (L\EA). For consistency with the purpose
of this study, guidances developed by the Environmental Protection Agency
(EPA) were considered separately from guidances developed by other
organizations.
This chapter presents summary comparisons of EPA guidances specific
to TENORM with the guidances for TENORM developed by other regulatory or
advisory organizations. As discussed in chapter 1, TENORM refers to naturally
occurring radioactive materials (NORM) not regulated under the Atomic Energy
Act whose radionuclide concentrations or potential for exposures of individuals
or populations have been increased by human activities.
In comparing EPA guidances for TENORM with guidances developed
by other organizations, indoor radon is considered separately from other
TENORM. This distinction is based on historical precedents in developing
guidance on radiation protection. As described in chapter 1, it has been
maintained essentially because the relationship between the increased risk of
lung cancer and exposure to short-lived radon decay products in air can be
estimated, with some uncertainty, directly from epidemiological studies in
various groups of miners (ICRP 1993b; National Research Council 1988)
204
OCR for page 205
COMPARISON OF CURRENT GUIDANCES FOR TENORM
205
without the need to estimate the dose to radiosensitive tissues of the lung from
irradiation by alpha particles following inhalation intakes and the risk per unit
dose from alpha particles. The availability of epidemiological data which
directly links cancer risk with concentrations of short-lived radon decay
products in air bypasses the need to consider the complexities and attendant
uncertainties in describing physical and biological processes in the lung
following inhalation of radionuclides, which are particularly important for alpha
emitters (ICRP 1994~. A dosimetric approach to estimating lung cancer risks
from radon also requires assumptions-for example, the deposition of radon
decay products in the respiratory tract and the particular target cells at risk-that
may be difficult to verify. Thus, both the BEIR IV Committee (National
Research Council 1988) and UNSCEAR (1993) did not endorse the use of
dosimetric models for calculating risks of lung cancer from exposure to radon.
Radon is unique because for no other radionuclides, including other naturally
occurring alpha emitters (radium, uranium, and thorium), can a complete
characterization of cancer risk be obtained without estimating the dose per unit
exposure and the risk per unit dose.
INDOOR RADON
Guidances for mitigation of exposures to indoor radon developed by
EPA, regulatory authorities in other countries, and national and international
advisory organizations are discussed in chapters. This section presents a
summary comparison of EPA guidances for indoor radon with those developed
by other organizations.
Guidances for mitigation of radon in homes are summarized in
table 10.1. This summary indicates that EPA's recommended mitigation level
lies toward the lower end of the range of values encompassed by the guidances
developed by other regulatory and advisory organizations. Some of the reasons
for the differences are as follows.
All regulatory or advisory organizations that have developed guidance
for radon in homes have assumed about the same risk per unit exposure to short-
lived radon decay products. As summarized in chapter 8, on the basis of the
assumption of a relative-risk model, there are some differences in the risk per
unit exposure assumed by various organizations, arising from such factors as
differences in the time at which the data were evaluated (that is, differences in
the observed number of lung cancers in study populations) and differences in
the models for projecting future risks in study populations for people who are
still alive. However, those differences are not large, and the differences among
the various guidances do not reflect substantial differences of scientific opinion
about risks posed by exposure to indoor radon. Rather, the differences among
OCR for page 206
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COMPARISON OF CURRENT GUIDANCES FOR TENON
207
the guidances result primarily from such factors as differences in average radon
levels in homes in various countries, in judgments about maximum tolerable
risks posed by exposure to indoor radon or levels of indoor radon that are
reasonably achievable with available technologies for mitigating exposures, and
in the population groups of concern in establishing the guidances.
The differences between EPA guidance for radon in homes and NCRP
and ICRP recommendations are of particular interest. As noted above, these
differences do not result from substantial differences in assumptions about the
risk posed by exposure to indoor radon. NCRP and ICRP recommendations
were based primarily on judgments about the maximum tolerable risk or dose to
individuals, and the intent was mainly to mitigate exposures of the relatively
few individuals who experience the highest risks (ICRP 1993b; NCRP 1984c).
NCRP's recommended mitigation level was based on an assumption that lifetime
risks of fatal lung cancers greater than 0.02 from exposure to radon in homes
should be avoided. NCRP also recommended that levels of indoor radon be
reduced below the mitigation level in accordance with the ALARA objective (as
low as reasonably achievable). Therefore, actions to reduce levels of indoor
radon, once undertaken, should result in radon exposures substantially below the
recommended mitigation level. ICRP's recommended mitigation level was based
on the assumptions that the annual effective dose from exposure to indoor radon
should not exceed about 10 mSv, which corresponds to a lifetime risk of fatal
cancers of about 0.04, and that the optimized annual effective dose, based on
application of the ALARA objective, should be in the range of about 3-10 mSv,
taking into account the various situations in different countries.
The EPA guidance also is concerned with protection of individuals
who experience the highest exposures to indoor radon. However, the EPA
guidance was based for the most part on considerations of average levels of
radon in homes and a cost-benefit analysis of reducing these levels with
available technologies (EPA and DHHS 1994~; that is, the guidance reflected a
greater emphasis on reducing exposures to radon in the greatest number of
homes. Thus, the difference between EPA's mitigation level and the values
recommended by NCRP and ICRP is explained in part by a difference in
emphasis reducing risks to individuals versus reducing risks to whole
populations.
Many regulatory or advisory organizations also have developed
separate guidance on mitigation of indoor radon in above-ground workplaces
(excluding workplaces involving operations of the nuclear fuel cycle) and
schools. These guidances are summarized in table 10.2. With the notable
exception of EPA guidance for radon in schools, the guidances for workplaces
or schools usually are substantially higher than the corresponding guidance for
OCR for page 208
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COMPARISON OF CURRENT GUIDANCES FOR TENORM
209
homes. The increase is based on consideration of the lower residence times in
workplaces and schools than in homes. Although EPA recognized the difference
in residence times, the guidance for radon in homes was applied to schools
primarily on the basis of a judgment that the mitigation level in homes is
reasonably achievable in schools, taking into account the existing levels of
radon in schools and a cost-benef~t analysis of reducing these levels (EPA and
DHHS 1994~. It is also possible, although not yet demonstrated, that children,
who are the primary population group of concern in schools, experience
substantially higher radon risks than adults.
TENORM OTHER THAN INDOOR RADON
This section presents a summary comparison of EPA guidances for
TENORM other than indoor radon with relevant guidances developed by other
federal agencies (the Nuclear Regulatory Commission and the Department of
Energy, DOE), state organizations, and advisory organizations (NCRP, HPS,
and ICRP). As noted above, this comparison does not consider guidances for
naturally occurring radionuclides that apply to operations of the nuclear fuel
cycle or the management and disposal of uranium or thorium mill tailings,
which are regulated by EPA, the Nuclear Regulatory Commission, and DOE
under the Atomic Energy Act. EPA guidances for TENORM other than indoor
radon are discussed in chapter 7, and the relevant guidances developed by other
organizations are discussed in chapter 9.
For consistency with the presentations in chapter7, guidances for
TENORM other than indoor radon are divided into two categories: those which
apply to multiple sources of exposure combined, including sources other than
TENORM, and those which apply only to specific sources or practices involving
TENORM.
Guidances on Radiation Protection of the Public Applicable to TENORlVi
Guidances for TENORM other than indoor radon that apply to multiple
sources of exposure combined are summarized in table 10.3. These guidances
generally have been developed in the context of radiation-protection standards
for the public (see chapter 7~. The following points should be noted in
comparing them.
OCR for page 210
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COMPARISON OF CURRENT GUIDANCES FOR TENORM
211
First, this committee has assumed that the annual dose limit of 1 mSv
(100 mrem) in EPA's proposed federal guidance on radiation protection of the
public (EPA 1994d), rather than the annual dose limit of 5 mSv (500 mrem) in
the existing federal guidance (FRC 1960), represents EPA's current views on the
maximum tolerable dose from exposure to all controlled sources combined,
even though the proposed revision of the guidance has not been issued in final
form.
Second, the annual dose limit of 1 mSv (100 mrem) for all controlled
sources combined, including TENORM and human-made radionuclides but
excluding indoor radon and medical exposures, in EPA's proposed federal
guidance on radiation protection of the public (EPA 1994d) is the same as the
dose limit for all human-made sources combined recommended by the ICRP
(1991) and NCRP (1993a). However, the NCRP and ICRP recommendations do
not apply to TENORM and so are not given in table 10.3.
Third, the NCRP recommendation in table 10.3 applies only to natural
sources (including natural background radiation), TENORM as defined in this
study, and presumably uranium and thorium mill tailings, but it does not apply
to human-made radionuclides. Therefore, the Federal Radiation Council and
EPA guidances in table 10.3 that apply to TENORM other than indoor radon
and to human-made radionuclides but not to natural background are not directly
comparable with NCRP's recommended remedial-action level for natural
sources. However, given that the average annual dose from natural background
excluding radon is about 1 mSv (100 mrem) (see table 2.10), NCRP's remedial
action level of 5 mSv (500 mrem) normally would allow considerably higher
exposures to TENORM than EPA's proposed primary dose limit of 1 mSv (100
mrem).
Finally, as emphasized in chapter 7, acceptable radiation protection of
the public is not defined solely in terms of compliance with a dose limit from
exposure to all controlled sources combined. Rather, a basic principle of
radiation protection is that the ALARA objective should be applied in reducing
doses below the limit, and the ALARA objective is an integral part of all
guidances listed in table 10.3.
Guidances for Specific Sources or Practices Involving TENORM:
Guidances that apply only to specific sources or practices involving
TENORM other than indoor radon are summarized in table 10.4. As discussed
in chapter 7, standards for specific sources or practices are an important means
of ensuring compliance with radiation-protection standards for all controlled
sources combined, including the primary dose limit and the ALARA objective.
The guidances summarized in table 10.4 differ from those listed in table 10.3 in
OCR for page 212
212
GUIDELINES FOR EXPOSURE TO TENORM
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COMPARISON OF CURRENT GUIDANCES FOR TENORM
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214
GUIDELINES FOR EXPOSURE TO TENORM
that they do not apply to human-made radionuclides or to natural sources other
than TENORM.
Guidances specifically for TENORM have been developed only by
EPA, DOE, and state organizations. However, this committee also considers that
the Nuclear Regulatory Commission guidance on natural uranium and thorium
in soil and the HPS recommendation on cleanup standards for radium and
thorium in soil are relevant to TENORM. In current ICRP (1991) and NCRP
(1993a) recommendations, exposures to specific sources or practices involving
TENORM other than indoor radon are considered only in the context of
guidances on radiation protection of the public, which were considered in the
previous section and summarized in table 10.3. The following points should be
noted in comparing the guidances in table 10.4.
First, as noted in chapters 6 and 7, EPA's current approach to
regulating TENORM other than indoor radon is rather fragmentary because no
standard or set of standards applies to all potentially important exposure
situations. However, in addition to requirements for complying with any
applicable regulations including those developed under the Safe Drinking
Water Act, Clean Water Act, and Clean Air Act (table 10.4 - this committee
has assumed that an annual dose constraint of 0.15 mSv (15 mrem) (Luftig and
Weinstock 1997) represents EPA's current views on acceptable exposures to
TENORM from any source.
Second, it is difficult to compare EPA guidance (Luitig and Weinstock
1997) expressed in terms of dose with standards for radium-226 expressed in
terms of activity per unit mass developed by other organizations (see table
10.4), because the dose from exposure to materials containing a given
concentration of 226Ra can depend on the volume of the source. For example, for
large volumes of contaminated surface soil, the annual dose from external
exposure corresponding to the state and Conference of Radiation Control
Program Directors (CRCPD) standards for 226Ra expressed in terms of activity
concentrations would be about 0.6 mSv (60 mrem) or greater for continuous
occupancy (see chapter 7~. Therefore, for large-volume sources, the annual dose
constraint of 0.15 mSv (15 mrem) in EPA guidance should be considerably
more restrictive than the state or CRCPD standards, with the exception of the
standard in New Jersey. However, for much smaller sources, the external dose
corresponding to a given concentration of 226Ra could be reduced considerably.
For example, at the outer surface of a steel pipe that contains 226Ra
contamination at 0.6 Bq/g (15 pCi/g) on the inside wall, Bernhardt and others
(1996) estimated that the exposure rate would be about 2 pR/h. If the
contamination is assumed to be represented by a line source, for which the dose
varies inversely with the distance from the source, and if the outer surface of the
pipe is assumed to be about 1 cm from the source, the exposure rate at a nominal
distance of 1 m would be 0.02 ,uR/h, and the annual dose equivalent for
OCR for page 215
COMPARISON OF CURRENT GUIDANCES FOR TENORM
215
continuous exposure at this distance, taking into account that 1 R is about 7 mSv
(0.7 rem) (ICRP 1987a), would only be about 1 pSv (0.1 rurem). Similar
comparisons with EPA's dose constraint would apply to the Nuclear Regulatory
Commission, DOE, and HPS guidances in the form of activity concentrations.
Third, in regard to EPA guidance for cleanup of Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA) sites
(Luttig and Weinstock 1997), this committee again emphasizes that the annual
dose constraint of 0.15 mSv (15 mrem) from exposure to TENORM
a/contaminated sites subject to remediation under CERCLA is a goal, rather
than a regulatory limit, and the goal may be exceeded if compliance is not
feasible. That consideration compounds the difficulties in comparing EPA
guidance with the various state standards for cleanup of 226Ra, which are
interpreted as regulatory limits. The dose criterion in EPA guidance essentially
may be regarded as an upper bound on de minimis (negligible) dose, rather than
a limit that must be met for specific sources or practices (see chapter 7~.
Fourth, some state regulations for 226Ra include both cleanup standards
and exemption levels, and the two usually are essentially the same. Thus, in
effect, these regulations specify that acceptable exposures to TENORM other
than indoor radon can be no higher than exposures that do not warrant
regulatory control.
Finally, the proposed Part N of the suggested state regulations (CRCPD
1997) also specifies conditions, not shown in table 10.4, for unrestricted release
of facilities and equipment contaminated with TENORM, including limits on
surface contamination for alpha and beta or gamma activity and limits on
external radiation due to surface contamination. As described in chapter 9, such
contamination limits also are specified in DOE requirements for unrestricted
release of facilities and equipment contaminated with TENORM (DOE 1990~.
However, those criteria, especially the limits on surface contamination, are not
clearly related to dose and so are not easily compared with the dose constraint in
EPA guidance.
Bases For Differences In Guidances
The information discussed in the previous two sections and
summarized in tables 10.3 and 10.4 indicates that current EPA guidances for
TENORM other than indoor radon often are substantially more restrictive than
similar guidances developed by other organizations. That is especially the case
if one compares EPA's dose limit for all sources combined with NCRP's
remedial action level for natural sources (table 10.3) or EPA's preferred dose
constraint for individual sources with other guidances in the form of activity
concentrations of radionuclides (table 10.4~. However, as in the case of indoor
radon discussed previously, all regulatory or advisory organizations that have
OCR for page 216
216
GUIDELINES FOR EXPOSURE TO TENORM
developed guidances for TENORM other than indoor radon assume essentially
the same risk per unit dose from uniform exposure of the whole body on the
basis of estimates by expert groups (ICRP 1991; National Research Council
1990~.
As discussed in chapter 11, EPA has developed methods of risk
assessment for exposure to radionuclides other than radon that differ from the
approaches normally used by other organizations, and the differences in
estimated risks are particularly important for internal exposure to some naturally
occurring radionuclides. However, the differences between EPA guidances for
TENORM other than indoor radon, especially the annual dose limit of 1 mSv
(100 rurem) for all controlled sources combined and an annual dose constraint
of 0.15 mSv (15 rurem) for specific practices or sources, and the guidances
developed by other organizations do not result from differences in methods of
risk assessment for radionuclides. That is, EPA's approach to risk assessment, as
it differs from the approach normally used by other organizations, was not an
important factor in developing the current EPA guidances.
Thus, the differences between EPA guidances for TENORM other than
indoor radon and the guidances developed by other organizations are not based
on the differences of opinion about risks posed by exposure to TENORM.
Rather, the differences between the guidances result in part from differences in
judgments about acceptable risks from exposure to TENORM and differences in
judgments about levels of TENORM in the environment that are reasonably
achievable (see chapter 5~. In addition, the guidances for TENORM in the form
of concentration limits for radium and thorium in contaminated soil and other
materials often were based primarily on existing EPA standards in 40 CFR
Part 192 for cleanup of contaminated soil at uranium or thorium mill tailings
sites (see chapter 9~.
SUMMARY
This chapter has presented summary comparisons of guidances for
controlling exposures of the public to TENORM developed by EPA with similar
guidances developed by other organizations, including the Nuclear Regulatory
Commission, DOE, state organizations, other countries, NCRP, HPS, ICRP, and
IAEA. Guidances for indoor radon have been considered separately from
guidances for TENORM other than indoor radon.
EPA's current mitigation level for indoor radon is somewhat lower than
the values developed in most other countries or recommended by NCRP and
ICRP. However, the differences in the guidances do not result from substantial
differences of scientific opinion about the risks posed by exposure to indoor
radon. Rather, they result primarily from such factors as differences in average
OCR for page 217
COMPARISON OF CURRENT GUIDANCES FOR TENORM
217
radon levels in homes, differences in judgments about maximum tolerable risks
to individuals or levels of radon that are reasonably achievable after mitigation,
and differences in whether a guidance focuses primarily on reduction of risks to
individuals receiving the highest exposures or on reduction of risks in the whole
population.
In many cases, the current EPA guidances for TENORM other than
indoor radon also appear to be more restrictive than the relevant guidances
developed by state organizations, other federal agencies, NCRP, and HPS.
However, direct comparisons of the various guidances are difficult and
potentially misleading because of differences in whether exposures to natural
background are included, the difference in concept between a regulatory goal
and a limit, and the use of dose criteria in some guidances and activity
concentrations of radionuclides in others. The differences between guidances do
not reflect the differences in approaches to risk assessment for radionuclides
used by EPA and other organizations. Rather, the differences in the guidances
for TENORM other than indoor radon result primarily from differences in
judgments about acceptable risk, differences in judgments about risks that are
reasonably achievable, and judgments about the transferability of standards
from one exposure situation to another.
An additional consideration of importance in comparing the guidances
for TENORM summarized in this chapter is that the specified quantitative
criteria usually are not the most important factor in determining doses and risks
that would be experienced in any exposure situation. Rather, as discussed in
chapter 7, actual doses and risks usually are determined primarily by application
of the ALARA objective, largely without regard for any limits or goals for
exposure to TENORM that might be specified in guidances.
Representative terms from entire chapter:
epa guidances
