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Appendix B
Review of Acceptable Cancer Risk Levels
ORGANIZATIONAL USE OF ACCEPTABLE RISK LEVELS
Federal Agencies
In an evaluation of regulated chemicals, Travis and Hattemeyer-Frey
(1988) found that 70% of chemical carcinogens have a post-regulatory
added lifetime estimated risk greater than 1 × 10-6, and 30% have a post-
regulatory added lifetime estimated risk greater than 1 × 10-4. They con-
cluded that past regulatory decisions explicitly acknowledge that some
risks, in the range of 1 × 10-6 to 1 × 10-3, are acceptable in modern society.
In the case of benzene, high estimates of maximum individual risk (1 × 10-3)
are considered tolerable when the aggregate population risk (extra cancers
per year in the population) is insignificant. Similar levels of risk are ac-
cepted for emissions from zinc-oxide plants (3 × 10-3), secondary lead
smelters (3 × 10-3), elemental phosphorus plants (1 × 10-3), vinylidine chlo-
ride facilities (8 × 10-4), DOE facilities emitting radionuclides (7 × 10-4),
and uranium mill tailings emitting radon (5 × 10-4) (EPA 48 Fed. Reg.
33112 [1983]; 50 Fed. Reg. 5190 [1985]; 50 Fed. Reg. 32632 [1985]; 51
Fed. Reg. 6382 [1986]; Rodricks et al. 1987; Travis and Hattemeyer-Frey
1988).
Occupational Safety and Health Administration
In deciding on a level of acceptable risk associated with the workplace,
137
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138 APPENDIX B
the Occupational Safety and Health Administration (OSHA) used an ap-
proach similar to that of the U.S. Food and Drug Administration (FDA) by
not defining “safe” as the equivalent of risk-free, because many activities
considered safe by most people entail some risk of accident or health dam-
age. Workplace activities or exposures are not considered unsafe unless a
significant risk of harm exists. In addition, because of the benefits accrued
from employment (e.g., income), workers are presumed to be willing to
accept higher levels of risk than would someone to whom little or no benefit
accrues from accepting risk. Some studies have shown that salary is com-
mensurate with the level of risk inherent in an occupation (Starr 1969;
Whipple 1988).
Supreme Court action (Industrial Union Department, AFL-CIO v.
American Petroleum Institute et al. 448 U.S. 607 [1980]) was instrumental
in defining acceptable occupational risk for OSHA. The court suggests that
significant occupational risk be determined by comparing the risk in ques-
tion with other common occupational risks levels. The court suggested that
an occupational lifetime cancer risk of 1 × 10-3 is significant. On the basis
of actuarial data from 1984, the average lifetime (i.e., 45 years) risk of
work-related death in a private company with 11 or more employees was
2.9 per 1,000. Risks in high-hazard occupations, like mining, range be-
tween 7.6 and 18.6 per 1,000, and risks in low-hazard workplaces, like the
service industry, range between 0.9 and 1.8 per 1,000 (Cotter 1986;
Rodricks et al. 1987). These rates are measured, not estimated risks, and
show little variation from year to year.
OSHA as well as the U.S. Environmental Protection Agency (EPA) and
the Nuclear Regulatory Commission have used those lifetime risk values as
benchmarks to develop occupational acceptable risk levels. In developing
radiation protection guidelines, EPA selected 3 × 10-3 because it was com-
parable to the working lifetime risk of accidental death in the least hazard-
ous occupations (EPA 46 Fed. Reg. 7836 [1981]; Rodricks et al. 1987).
The Nuclear Regulatory Commission stated that the average annual mortal-
ity rate in “safe industries” does not exceed 1 × 10-4, which translates to a
worker 45-year lifetime risk of approximately 4 × 10-3. Like EPA, the
commission proposed occupational standards on the basis of the assumption
that worker risks due to radiation are acceptable if kept at or below the “safe
industry” risk level (Nuclear Regulatory Commission 1986; Rodricks et al.
1987).
For other workplace carcinogens, OSHA has not regulated below 1 ×
10-3, largely because of technical feasibility. Residual lifetime occupational
risks associated with permissible exposure levels (PELs) revised in the
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APPENDIX B 139
1980s range from a low of 0.2 per 1,000 to 6 per 1,000 for ethylene dibro-
mide and 39 per 1,000 for acrylonitrile (Table B-1). As with other federal
agencies, OSHA has not claimed that those health risks are insignificant,
but rather that they are “acceptable” (Rodricks et al. 1987).
National Institute for Occupational Safety and Health
Unlike OSHA, the National Institute for Occupational Safety and
Health (NIOSH) is not a regulatory agency, but it is engaged in research on
and interpretation of occupational health and safety issues. Its policy on
acceptable cancer risk is qualitative, as first stated in 1976, calling for “no
detectable exposure levels for proven carcinogens” (Fairchild 1976; NIOSH
2002). That statement represents a zero-risk policy similar to FDA’s
Delaney Clause of 1958 and the treatment of Category I potential carcino-
gens in the generic OSHA rulemaking on carcinogens (29 CFR 1990).
Under the policy, when carcinogen thresholds that would protect 100% of
the population have not been identified, nonquantitative recommended
exposure levels (RELs) labeled “lowest feasible concentrations” (LFCs) are
adopted for most carcinogens. The few quantitative RELs for carcinogens
(e.g., for asbestos, formaldehyde, benzene, and ethylene oxide) were set
based on limits of detection or technological feasibility. NIOSH also
adopted several quantitative RELs from OSHA’s 1989 PEL update (imply-
ing an acceptable risk limit consistent with that used by OSHA for category
II potential carcinogens).
TABLE B-1 Risk Considered Acceptable within OSHA Permissible
Exposure Limits
Chemical Residual Risk at PELs
8 × 10-3
Arsenic
1-2 × 10-3
Ethylene oxide
0.2-6 × 10-3
Ethylene dibromide
5-16 × 10-3
Benzene
39 × 10-3
Acrylonitrile
2 × 10-3
Dibromochloropropane
6.7 × 10-3
Asbestos
Source: Adapted from Rodricks et al. 1987.
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140 APPENDIX B
In the 20 years since NIOSH first set its policy, science and risk-assess-
ment techniques and management techniques have advanced to the point
that NIOSH has adopted a more inclusive attitude. NIOSH projects both
no-effect exposure levels for chemical or physical agents as well exposure
levels at which residual risks for all workplace hazards, including carcino-
gens, might be present. This approach is consistent with the 1970 OSH Act
(P.L. 91-596 Section 20(a)(3)) that charged NIOSH to “describe exposure
levels that are safe for various periods of employment, including but not
limited to the exposure levels at which no employee will suffer impaired
health or functional capacities or diminished life expectancy as a result of
his work experience.” However, no single acceptable risk level or range of
values has been set forth in policy to date.
U.S. Environmental Protection Agency
EPA has been at the forefront of the issue of acceptable risk in virtually
all of its programmatic areas, primarily as the result of court challenges to
its regulations. In response to the 1987 Section 112 Clean Air Act decision
(Natural Resources Defense Council v. U.S. Environmental Protection
Agency 824 F. 2nd 1146 [1987]), EPA decided it would base its regulatory
decisions on quantitative risk assessments using the general policy that a
lifetime added cancer risk for the most exposed person of 1 in 10,000 (1 ×
10-4) might constitute acceptable risk and that the margin of safety required
by statute and reinforced by the court should reduce the risk for the greatest
number of persons to an added lifetime risk of no more than 1 in 1 million
(1 × 10-6). However, EPA (along with the courts) has not viewed “safe” as
the equivalent of risk-free and has determined that standards should protect
against significant public health risks (EPA 49 Fed. Reg. 8386 [1984];
Rodricks et al. 1987; Industrial Union Department, AFL-CIO v. American
Petroleum Institute et al. 448 U.S. 607 [1980]). EPA has repeatedly re-
jected the opinion that it can establish a universal (i.e., brightline) accept-
able risk that should never be exceeded under any circumstances, and they
maintain that guidance provided under one statute might have little rele-
vance to others because of differing program goals. In practical terms, EPA
almost never regulates at a theoretical risk below 1 × 10-6 (de minimis) and
almost always regulates at a theoretical risk below 1 × 10-4 (de manifestis).
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APPENDIX B 141
U.S. Food and Drug Administration
The U. S. Food and Drug Administration (FDA) was the first federal
agency known to have encountered the issue of acceptable risk with the
adoption of the Delaney Clause in 1958. The clause states that no additive
that is deliberately included in food products during or after processing is
allowed to be in use if it causes cancer in animals (Federal Food, Drug, and
Cosmetic Act Sec. 409.[348](c)(3)(A); Sec. 512.[360b](d)(1)(I); and Sec.
721.[379e](b)(5)(B)). At the time, this zero-risk policy was based on the
presumption that no safe human exposures to animal (nonthreshold) carcin-
ogens could be identified the way that safe levels of compounds acting
through threshold mechanisms could (NRC 1994).
In 1973, FDA employed quantitative risk assessment using the Mantel-
Bryan methodology for estimating cancer risks (Mantel and Bryan 1961;
Rodricks et al. 1987) and defined the risks associated with the residues of
carcinogenic drugs used in food animals. The acceptable risk level pro-
posed at the time was 1 × 10-8, as suggested by Mantel and Bryan (Mantel
and Bryan 1961; FDA 38 Fed. Reg. 19226 [1973]; Rodricks et al. 1987).
The risk-assessment methodology was later modified to a linear-propor-
tional form, and the acceptable risk level changed to 1 × 10-6 in response to
public comment, the idea of risk assessment having become firmly en-
trenched by 1979 (FDA 44 Fed. Reg. 17070 [1979]; Rodricks et al. 1987).
FDA has since employed this technique for other substances regulated
under the federal Food, Drug, and Cosmetic (FD&C) Act. D&C Green No.
5 was listed with an estimated upper limit risk of 3 × 10-7, and lead acetate
also received approval as a colorant with a lifetime added risk of between
5 × 10-6 and 1.9 × 10-7 (FDA 45 Fed. Reg. 72112 [1980]; 47 Fed. Reg.
24278 [1982]; Rodricks et al. 1987). In neither instance was 1 × 10-6 de-
clared an agency-significant risk criterion, but the above risks were consid-
ered insignificant in terms of the public health as applied to food additives.
The same risk-assessment tools have been used to address the zero-risk
requirements of the Delaney Clause. In those cases, FDA has interpreted
“safe” in the context of food law to be defined as “reasonable [but not abso-
lute] certainty of no harm,” although at the same time, the benefits of an
additive cannot be considered in its decisions. The FDA position is that a
carcinogen is considered safe as long as exposure to it is restricted to levels
posing insignificant risks. Insignificant risk has been defined as 1 × 10-6 or
less in several agency decisions.
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142 APPENDIX B
Even though 1 × 10-6 has been used as the de facto brightline acceptable
risk level in several cases, FDA has also found that cancer risks above 1 ×
10-6 are acceptable for certain classes of contaminants (e.g., PCBs, dioxins,
and aflatoxins) given the technical difficulties and costs associated with
reducing exposure. In the case of fish contaminated with PCBs, FDA con-
sidered that an estimated risk of 1 × 10-4 provided adequate protection to the
public health on the basis of their PCB residue tolerance of 2 ppm. This
conclusion considered the ubiquity of the contaminant and the presumed
benefit from consuming fish proteins. FDA stopped short of labeling esti-
mated risks greater than 1 × 10-6 as insignificant (Rodricks et al. 1987).
Other Authoritative Sources
American Conference of Governmental Industrial Hygienists
The American Conference of Governmental Industrial Hygienists
(ACGIH), like NIOSH, develops recommended occupational exposure
limits to protect workers from injury. Their Threshold Limit Values (TLVs)
are not enforceable because ACGIH is a nongovernmental organization.
The TLVs are based on threshold toxicity events and include a designation
for the weight-of-evidence for carcinogenicity and other forms of toxicity
similar to that used by IARC and EPA. ACGIH has not to date identified
an acceptable risk for any carcinogen in the workplace, stating instead that
exposure to carcinogens must be kept to a minimum (ACGIH 2001). Work-
ers exposed to known human carcinogens that do not have a TLV should be
properly equipped to eliminate exposures to those carcinogens to the fullest
extent possible. For known human carcinogens that have a TLV or sus-
pected human carcinogens, worker exposures by all routes should be care-
fully controlled to levels as low as possible below the TLV.
National Commission on Radiologic Protection
The National Commission on Radiologic Protection (NRCP) proposed
an average cancer risk of 1 × 10-5 per year (not per worker lifetime or full
lifetime) for members of the public exposed continuously or repeatedly to
radiation sources other than medical and background. This translates to a
lifetime cancer risk of 7 × 10-4 and may be considered the de manifestis risk.
A negligible 1% of that risk (7 × 10-6) was suggested by Schiager et al.
(1986).
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APPENDIX B 143
World Health Organization
In developing drinking water guidelines, the World Health Organization
(WHO) employed an acceptable risk level of 1 × 10-5 (WHO 1996; Fiori
and Meyerhoff 2002) but did not indicate how that level of health protection
was selected. For its air quality guidelines, WHO provides only qualitative
guidance by specifying that the “acceptability of the risk and, therefore, the
standards selected, depends on the expected incidence and severity of the
potential effects, the size of the population at risk, the perception of the
related risk and the degree of scientific uncertainty that the effects will
occur at a specific level of air pollution” (WHO 2000).
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Representative terms from entire chapter:
exposure levels