UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C, 20460
April 11, 1984
OF
THE ADMINISTRATOR
Honorable William D. Ruckelshaus
Administrator
U. S, Environmental Protection Agency
401 M Street SW
Washington, n. C, 20460
Hear Mr, Ruckelshaus:
The Environmental Health Committee of the Science Advisory
Board has completed its review of a revised Draft Cancer Risk
Assessment Document for Coke Oven Emissions prepared by the
Agency's Office of Research and Development (ORD). The major
conclusion of the document was that coke oven emissions are
carcinogenic to humans. This conclusion is based on a number
of scientific studies including an extensive series of
occupational epidemiology studies of coke oven workers and
evaluation of individual coke oven constituent responses in
experimental animals. The Committee unanimously concurs with
this conclusion.
Several risk models were evaluated by ORD's Cancer
Assessment Group (CAG) staff to develop a quantitative risk
assessment for this pollutant. The dose-response relationship
in the epidemiological studies is non-linear in the range of
past occupational exposure. At the much lower levels that
characterize ambient exposures, the dose-response relationship
is highly uncertain and several forms of the dose-response
relationship can be validly hypothesized and defended. Because
the available scientific evidence does not permit rejection
of the hypothesis that the dose-response relations-hip is
dominated at low doses by a linear term, a linear nonthreshold
approach has therefore been used to estimate an upper bound
for the incremental cancer risk from unit exposure. Non-linear
weibull and multi-stage models have been used to calculate
both maximum likelihood estimates- and ranges' for the -•.'.'
un.it/ risk (one rticrogram of- pollutant per cubic meter of
air). Results from the two models were in the expected
directions and did not differ greatly. The Committee -was briefed
by CAR on its plans to carry out additional calculations on
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the modified linear non-threshold approach; it is the Committee's
expectation that it will receive the final results of such
analysis when they are completed. The Committee anticipates
that the modified linear nonthreshold approach will continue
to be the most protective to public health, and it is assumed
to be applicable in this report.
The revised Draft Cancer Risk Assessment for Coke Oven
Emissions has been reviewed by the Committee following exten-
sive briefings by Agency staff and participation by the public*
CAfi staff have proven responsive to previous Committee requests
for revisions, particularly in the development of a quantitative
risk assessment. The result has been beneficial in at least
three important respects: 1) the Committee is satisfied that
the September 1983 draft document presents a thorough and
balanced treatment of the available scientific evidence
associated with coke oven emissions; 2} the process of communi-
cation between Agency staff and the Committee has produced
cons itferah 1 e clarification regarding the development and use
of quantitative risk assessment by ORO; and 3} several recent
heilth assessment documents developed by ORD and reviewed by
the Committee, including those for acrylonitrile, carbon
tetrachloride and inorganic arsenic* have incorporated the
discussions regarding the use of mathematical models and
evolved from the review of the coke
These documents were of high scientific
the overall review process has been
quantitative methods that
oven emissions document.
quality and, as a result,
considerably shortened.
Additional Committee comments and recommendations for
the Draft Cancer Risk Assessment for Cok» Oven Emissions are
summarized in the attached report. The Committee recommends
that CAS provide a formal response to the recommendations
included in the attachment* The Environmental Health Committee
appreciates the opportunity to provide its scientific advice
on this important issue.
Hersehel
Chairman, £nvi r
Committee
ental Health
Norto eson
Chairman, Science Advisory Board
cc; Mr, Alvin Aim
Dr. Elizabeth Anderson
Mr, Joseph Cannon
Dr. Bernard Goldstein
Or, Terry Yosie
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Environmental Health Committee Key Findings,
Conclusions and Recommendations on the
Revised Draft Cancer Risk Assessment
for Coke Oven Emissions (September 1983)
I. Qualitative Assessment
Based upon an extensive review of epidemic!ogical studies
of coke oven workers in America, Britain, and Japan* as well
as tests in experimental animals and bacteria, the following
conclusions were drawn in the document?
" 1) coke oven workers have been found to be at an
excess risk of mortality from cancer at all sites,
lung cancer, prostate cancer, and kidney cancer as a
result of exposure to coke oven emissions. These
risks may possibly have been enhanced by smoking but
are not believed to have been confounded by smoking.
2) Sample extract from a coke oven main and coal tar,
a condensate of coke oven emissions, were found to be
carcinogenic in animal skin painting studies. Animals
exposed to coal tar aerosol developed lung tumors.
3) Simple extracts from coke oven topside and a coke
oven main initiated tumor formation in initiation-
promotion studies in mice. 4) Coke oven door emissions
were found to be mutagenic in bacteria. 5) Numerous
constituents of coke oven emissions are known or
suspected carcinogens. The Cancer Assessment Group
concluded that coke oven emissions are carcinogenic,"
The Committee unanimously agrees with these conclusions.
II. Quantitative Assessment
The Committee reviewed at length the quantitative
assessment section of the document and is pleased to report
that numerous changes, and improvements have been incorporated
as the result of the Committee's advice. The body ,of this
section of our report will address these changes.
1. Understanding of the significance of coke oven
emissions as i public health issue is enhanced by the
presentation of alternative quantitative estimates and the
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comparison of risk estimates against other known or suspected
carcinogens. This is a particularly useful means of communi-
cating to both the scientific community as well as the general
public the significance of the risk of this pollutant.
2. The Committee suggests an alternative definition of
unit risk which it believes will more thoroughly explain its
use in risk assessment when the linear nonthreshold model is
utilized. The alternative definition should read; unit
risk is defined as the maximum, lifetime incremental lung
cancer risk theoretically estimated to occur in a population
in which all individuals are assumed to be continuously exposed
from birth to death to i one microgram per cubic meter increase
of the agent in the air they breathe.
3. The discussion of the use of mathematical models in
risk assessment has been considerably clarified by placing
confidence limits on the estimates calculated through the use
of the Weibull model and the multistage model. Hore caution
should be exercised, however, in presenting a risk estimate to
two significant figures past the decimal point. This practice
implies a degree of certainty or precision which does not
exist. It is also desirable to present in tabular form the
results of all the models» giving at - least the most likely
estimator and upper confidence limits.
4* The issue of linearity vs. non-linearity in the dose
response relationship is a constant subject of discussion in
evaluating risk assessments. In the case of coke oven
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emissions there Is relatively clear evidence of rton-1 inearity
in cases of occupational exposure. This issue should be
stated more forcefully 1n the Summary of the document. A
proposed insert might read as follows:
At the much lower levels that characterize ambient
exposures, the dose-response relationship is highly
uncertain: the available scientific data do not
permit rejection of the hypothesis that the dose-
response relationship will be dominated by a linear
term. EPA therefore makes upper bound calculations
of risk using the conservative assumption that an
essentially linear nonthreshold dose-response relation-
ship function exists at low doses. The multistage model
is used to estimate, with an upper bound 95% confidence
limit, the largest linear term consistent with the
occupational data. Such estimates for different lag
times have been used in developing a plausible upper
bound estimate of the unit risk for coke oven emissions.
5, A more careful statement is needed in the document
to clarify that the cancer risk assessment for coke oven
emissions uses the benzene soluble organic (BSD) portion of
coke oven emissions as an indicator of the risk due to the
entire complex mixture. There is discussion of other car-
cinogenic agents in the coke oven emissions mixture, and
BSD serves as an indicator for estimating the cancer risk
of the entire mixture* including these other compounds.
6. The Office of Research and Development and the
Office of Air Quality Planning and Standards shoul d 'joi ntly
work to develop exposure assessment information for hazardous
air pollutants. The Committee recommends that data bases
related to exposure assessment be included in the risk
assessments submitted for the Committee's review.
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7, A statement is needed in the document with respect
to the radioisotope portion in coke oven emissions that would
*
theoretically contribute to lung cancer. This radiation
component from radon or other radioisotopes that have alpha
emissions has a linear term throughout the dose response
curve. There are numerous studies, among uranium miners for
example, for which a lung cancer incidence rate has been
calculated. There is also information available on alpha
emitted particles in coke oven emissions.
Ad d i t_i o n a 1 Re commendations
1. The ultimate credibility of the Cancer Assessment
Group's (CAS's) procedures in developing risk assessments
will rest upon their publication in the scientific, peer
reviewed literature. wany of the difficulties and confusions
that arise from the application of CAG's methods are the
result of not having this peer review. The Committee strongly
recommends that CAG submit its risk assessment procedures,
and the assumptions contained therein, for publication in
applied statistics and other journals.
2. CAG has undertaken a project to establish correlations
between quantitative responses in humans and in experimental
animals from selected pollutants, including coke oven emissions,
believed to cause cancer. The Committee has discussed this
project with Agency staff and strongly recommends that the
Office of Research and Development provide support to see
this work through to its completion.
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3. The Committee supports the CAG effort to extend the
coke oven worker study through 1984. CAG Intends to use data
on individual coke oven workers to improve the current risk
assessment model which is based on aggregate data from groups
of workers.
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