UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
16 DEC 198
OFFICE OF
SOLID WASTE AND EMERGENCY RESPONSE
MEMORANDUM
SUBJECT: ffjCDD,.Emissions for Municipal Waste. Combustors
FROM: Michael B. Cook
Dioxin Management C
TO: Addressees
We have recently completed an assessment of
tetrachlorodibenzo-p-dioxin (TCDD) emissions from another
municipal waste combustion (MWC) facility sampled early
this year. This is the sixth MWC plant sampled by the
Agency in its continuing program to evaluate the health risks
associated with emissions of TCDD from combustion facilities.
EPA assessed TCDD emissions from the first five MWC
facilities sampled in a report dated November, 1981, entitled
"Interim Evaluation of Health Risks Associated with Emissions
of Tetrachlorinated Dioxins from Municipal Waste Resource
Recovery Facilities", The report concluded that ". . . the'
levels of TCDD's from the five municipal waste combustors . .
do not present a public health hazard for residents living
in the immediate vicinity."
The emissions of TCDD from the sixth plant were higher
than had previously been found. We have nonetheless concluded
(p. 11) that ". . . in light of: . . . conservative assump-
tions . . . steps being taken . . ., the Agency does not
believe that this most recently sampled MWC represents.a
significant health concern ..."
I have attached a copy of the November 1981 interim
evaluation and the recent assessment for .your use. These
assessments may be shared, with interested members of the
public^ .
Atta.ciime.nfcs
Addressees:
Regional Dioxin Coordinators
Regional Solid Waste Branch Chiefs
"^gional Division Directors
ffice of Pesticides and Toxic Substances
:ate of Virginia
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12/8/83
ASSESSMENT OF EMISSIONS FROM A RECENT MUNICIPAL WASTE COMBUSTOR
Background
In the late 1970's concern was raised in the United
States regarding the possible emission of trace amounts of
highly toxic organic pollutants as a consequence of large
scale combustion. Following suggestive findings in this
country, which essentially confirmed reports from overseas
where emissions testing had first identified the presence
of chlorinated dibenzo-p-dioxins (CDDs)/ particular atten-
tion was directed to municipal waste combustors (MWCs).
In response, the Environmental Protection Agency (EPA)
conducted a program which performed sampling and analysis
at five separate MWCs. The focus of these studies was the
emission of tetrachlorodibenzo-p-dioxins (TCDDs), with an
'emphasis on the specific isomer, 2,3,7,8tetrachlorodiben2o-p~
dioxin ( 2,3,3, 8-TCDD).. This latter compound is known to
be quite toxic, even at very low doses, as demonstrated in
animal studies. Documented evidence of its presence in
emissions evoked special concerns.
In November, 1981, the Agency published a report entitled
"Interim Evaluation of Health Risks Associated with Emissions
of Tetrachlorinated Dioxins From Municipal Waste Resource
Recovery Facilities". (EPA, 1981) The report presented
upper limit estimates of what the health risks might be to
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people living in the vicinity of the MWCs and concluded:
"These estimates suggest that the present emissions
levels of TCDDs from the five municipal waste
combustors described in this report do not present a
public health hazard for residents living in the
immediate vicinity. In addition, the health risk
estimates presented in the assessment indicate that
as long as emission levels of TCDDs do not greatly
exceed the emissions measured at the five US sites
evaluated in this interim assessment, there should
be no reason for concern. This conclusion is valid
for all toxicological effects (including reproductive
and cancer) for which the available animal and human
data have been analyzed."
In the pasc few months, data have been generated by the
Agency on the emission of TCDDs (and other pollutants) from
a sixth MWC. These data and the supporting contractor report
on the sampling and analysis are currently undergoing the normal
review procedure within the Agency.
The existence of these "data and their qualitative indi-
cation of the presence of TCDDs in the emissions from this
MWC, however, have raised public concerns. Therefore, in
order to give some perspective to these findings, the Agency
is issuing this assessment employing the same procedures used
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in the November, 1981 document. These procedures incor-
porate a series of conservative assumptions which the
Agency believes tend to overestimate the risks due to TCDD
emissions. If this "worst case" assessment projects risks
which are so low as to not present a health concern to people
living in the vicinity, then there is additional assurance
that the actual risk from the TCDD emissions should not form
a health concern to nearby residents.
In sum, the purpose of this document is to project the
results from a sixth MWC on the scale generated by the results
from the five MWCs which were assessed in 1981, thereby providing
a basis for interpreting the significance of the new data and
'the efforts already underway to modify conditions at the plant.
Note that the present document is being issued before the
final report on the sampling and analysis that underlie this
effort have been thoroughly reviewed. Consequently, the
conclusions of this assessment are subject to changes that
might be necessitated by changes in the final report.
Overv Jew
This document presents an assessment of the health
implications associated with the emission of TCDDs from a
recently sampled MWC. The assessment is based on stack
emission data which were used to estimate the level of exposure
that people living near this facility might encounter, and
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on estimates of the health hazards that might be associated
with these emissions.
Exposure information on the TCDDs was obtained by field
sampling of stack emissions, followed by chemical analysis
using gas chromatography and mass spectrometry (GC/MS). The
actual amount of TCDDs from the stacks that would reach people
living in the areas surrounding the plant was expected to be
so small that it would not be detectable by available
analytical techniques. Therefore, the Agency used a mathema-
tical air dispersion model to estimate the ground level
concentration levels of TCDDs to which people were likely to
be exposed.
Estimates of the risk to human health from these TCDDs
emission were obtained by extrapolating from animal data on
the carcinogenic and reproductive effects of 2,3,7,8-TCDD.
While the toxicity information on the other isomers of TCDD
is limited, there is reason to believe that none of. the other
isomers are as toxic as 2,3,7,8-TCDD.
Hazard Assessment
The reader is referred to other sources which discuss
the toxic properties of TCDDs in detail (Huff, 1980). The
present document makes use of the same hazard assessment as
was used in the November, 1981 document.
Dose~Response Assessment
The reader is referred to other sources for a discussion
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of the dose-response assessment that the Agency associates with
2,3,7,8-TCDD (EPA, 1980), based on a lifetime feeding study in
rats (Kociba, et al, 1978). The present document makes use
of the same dose-response assessment as was used in the
November, 1981 document.
Exposure Assessment
Table I contains information on the MWC facility and the
TCDD emissions detected there.
In the present estimates, the relation between the emission
data and the maximum concentration to which people in the
surrounding area are likely to be exposed has been obtained
through a theoretical air dispersion model, PTMAX (EPA, 1977).
This computer program calculates the location and magnitude of
the maximum short term (1 hour) concentration in the area around
the stack. The necessary input data are contained in Table I.
In order to obtain a maximum annual average ground level con-
centration, a reasonable assumption was made that the maximum
annual average concentration is 1/40 of the maximum hourly
concentration (Tikvart, 1981). These results are found in
Table II.
Toxicity and Exposure Assumptions
Ideally, there would be sufficient information compiled
during the Hazard, Dose-Response, and Exposure Assessments to
directly combine the data in a Risk Characterization step
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(Rational-Research Council, 1983). However, many unanswered
questions relating to the toxicity of and exposure to these
TCDD emissions remain. Since there are insufficient data to
answer these questions definitively, and because some type
of answers is needed in order to characterize the risk to
people breathing the emissions, the Agency has adopted a
series of assumptions which are designed to represent
"reasonable worst cases". These are the same assumptions
used in the November, 1981 document. Some of these un-
answered questions and related assumptions are presented
be low:
Question 1
What are the toxicological properties of the 21 TCDD
isomers, other than 2,3,7,8-TCDD?
Assumption 1
The carcinogenic properties and reproductive
effects of all TCDDs are taken to be the same
as that of 2,3,7,8-TCDD.
Question 2
How can the toxicological effects in humans be assessed
in the absence of data in humans?
Assumption 2
The Agency has established methods (EPA, 1978) to
address this question which include the following:
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a. Use of the no-threshold assumption for
carcinogenicity.
b. Use of the most sensitive/ valid animal study.
c. Use of the linearized multi-stage model to
generate an estimate of the upper limit of
the excess cancer risk at low doses. The
actual risk could be nearly any number
between this upper limit and some lower
number (possibly zero).-
d. Conversion of animal dose to human equivalent
dose by. use of relative body surface area.
Question 3
Given the concentration and composition of TCDDs
measured in emissions from the stack, what are
the resulting air concentrations and compositions
at ground level to which people would be exposed?
Assumption 3
The computerized PTMAX air dispersion model and
the factor used to convert to the annual con-
centration is assumed to adequately represent
the transport of the emissions to ground level.
In lieu of a definitive analysis of atmospheric
conditions, the result from the worst of six
atmospheric classes modeled by the computer is
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assumed to be applicable. The composition of
emission products found at ground level is
taken to be identical to the composition (but
not the concentration) in the stack.
Question 4
How do the TCDD contaminants in the air behave when
they are breathed by humans? (The TCDDs in the
stack gases are generally associated with parti-
culate matter from which they are difficult to
remove in the laboratory).
Assumption 4
Seventy-five percent of the inhaled particulates
are assumed to be retained in the body (ICRP,
1968). Further, 100% of the TCDDs (gaseous
or particulate-bound) are treated as being
biologically available to exhibit a toxic
response.
Question 5
How often, for how long, and at what level will people
be exposed?
Assumption 5
People are assumed to be exposed continuously to
the maximum annual average ground level con-
centration 24 hours/day, under the worst
atmospheric conditions, for a 70 year lifetime,
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Health Risk Characteration
Within the limitations of the assumptions discussed in
the previous section/ Table III contains the results of the
health risk characterizations for the upper limit of excess
cancer and for reproductive effects resulting from lifetime
exposure to the maximum annual average concentration of TCDDs
which are likely to be generated at the MWC. The details of
these calculations are contained in the Appendix.
The cancer risk is characterized by an "estimated
upper limit of excess cancer risk", which is expressed as a
probability. For example, the upper limit of excess cancer
risk for the MWC, based on maximum total TCDDs, is 4.6 x 10~6,
This figure can be interpreted as the upper limit of the
excess cancer risk (probability) for an individual living
at the point of maximum annual average concentration of TCDDs
(resulting from emissions from the MWC) for 24 hrs/day, under
the worst atmospheric conditions, for a 70 year lifetime.
Alternatively expressed, this is a upper limit of risk of
46 in a 1,000,000 or 1 in 22,000. That is, based upon the
assumptions above, the excess risk of contracting cancer is
likely to be something less than 1 in 20,000. Again,
this is not a prediction of the risk but simply a
statement that the risk is not likely to exceed this level.
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For comparison, the highest upper limit of excess cancer
risk reported in the November, 1981 document for total TCDDs
was 8 x 10~6.
The reproductive effects risk is characterized in this
assessment by a "confidence ratio", which is the ratio of
the lowest level tested in animals divided by the anticipated
exposure level in humans. Note that if this lowest dose
tested is seen as a "no effect level" (this point is currently
the subject of some scientific dispute), then the confidence
ratio would become the more familiar "margin of safety".
For comparison, the lowest confidence ratio reported
in the November, 1981 document was total TCDDs was 30,000.
Conclusion
The information in Tables I and II indicates that
compared to the situations at the five MWCs evaluated in
1981, the roost recently sampled MWC, when sampled, was emitting
greater amounts of TCDDs, resulting in higher ground level
exposures at the point of maximum impact (approximately .6
km from the stack under the worst atmospheric conditions).
Table III shows that, under the conditions prevailing at the
time of the test, the emissions represented a risk approx-
imately 6-fold greater than that seen at any of the MWCs
included in the 1981 survey.
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A preliminary inquiry, into the design and operation of
this MWC has revealed a number of conditions that could be
contributing to the increased level of emissions. Discussions
are already underway with responsible parties in the public ,
and private sectors to determine appropriate corrective
measure that will likely lead to reduction into the emissions
of TCDDs. In light of:
a. the conservative assumptions made in this
current assessment,
b. the steps being taken to ameliorate the situation, and
•c. the relatively short time span anticipated before these
corrective measures are in place, the Agency does not
believe that this most recently sampled MWC represents
a significant health concern to people living in its
vicinity.
The Agency will continue to work with all parties concerned
to see to it that the planned changes in the facility and its
operations are carried out expeditiously and that a subsequent
re-sampling and analysis of the emissions is conducted
effectively and efficiently.
11
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TABLE I
PLANT PARAMETERS AND EMISSION RATES FOUND AT
A MUNICIPAL WASTE COMBUSTOR IN 1983
Parameters
Stack height 27.4 meters
Stack diameter 1.22 meters
Stack temperature 271 °C
Flue gas flow rate^3) 12 m-Ysec
Flue gas velocity 11.4 m/sec
Ambient temperature 4 °C
Average Emission Rate
Total TCDDs 2.9 x 10~6 gram/sec
(2,3,7,8-TCDD constitutes 21% of the total)
(a) total from both stacks averaged over four tests
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TABLE II
MAXIMUM ANNUAL AVERAGE GROUND LEVEL CONCENTRATION
OF TCDDs CALCULATED1 AT A MUNICIPAL WASTE COMBUSTOR (MWC)
IN 1983.
Facility Pollutant Concentration
MWC Total TCDDs 5.1 x 10~4 nanograms/m3
1 These values were generated through the air dispersion
model PTMAX (EPA, 1977) with a correction factor of
1/40 to convert to maximum annual average. [Acknowledge-
ment of the assistance by OPTS (Kinerson) and OANR
(McGinnity)].
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TABLE III
HEALTH RISK CHARACTERIZATION1 AT A MUNICIPAL WASTE COMBUSTOR
IN 1983, BASED ON TOTAL TCDDs IN STACK EMISSIONS.
UPPER LIMIT OF CONFIDENCE RATIO
FACILITY EXCESS CANCER RISK2 FOR REPRODUCTIVE EFFECTS3,
Municipal Waste
Combustor 4.6 x 10~5)
1 These results cannot be effectively interpreted indepen-
dent of the underlying conservative assumption upon
which they are based. (See text for further details)
a. All of the 22 possible TCDD isomers are assumed to
have carcinogenic and reproductive effects properties
equal to those of 2, 3 ,7,8-TCDD.
b. The established procedures for extrapolating from
high dose to low dose and from animals to man are
assumed to be appropriate.
c. The air dispersion model (with worst atmospheric
assumptions) is assumed to be an effective method
for extrapolating from concentrations in the stack
emissions to concentrations to which people will be
exposed.
d. The majority of inhaled particulate matter is assumed
to be retained in the body and all of the particulate
bound TCDD is assumed to be bioavailable.
c. Exposure to the annual maximum average ground
level concentration is assumed to occur continously
for 70 years.
2 Using linearized multi-stage extrapolation model (EPA, 1978).
Lowest dose tested = 1 ng/kg-d
3 Confidence Ratio = Estimated human dose Estimated human dose
a For comparison, the highest value from the five previously
tested MWCs was 8 x 10~6.
b For comparison, the lowest value from the five previously
tested MWCs was 30,000.
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APPENDIX
DETAILS OF CALCULATIONS
(using MWC maximum data as an example)
The PTMAX model was run using the input parameters in
Table I. For general purposes, however, the emission
rate entered into the model was 1 g/s. This permitted easy
scaling to whatever specific emission rate might be of interest,
since the model is linear in mass emission rate.
Specifically, for the MWC:
a. PTMAX showed that with 1 g/s the maximum hourly con-
centration of 7 x 10"^ g/m3 was obtained for atmospheric
stability class I (or A); that is, "unstable".
b. Applying the correction factor to estimate the annual
maximum average concentration, we obtain
7 x 10~6 g/m3 / 40 = 1.75 x 10~7 g/m3
c. Table I indicates that a total of 2.9 x 10"^ g/s was
the observed emission rate at the MWC. Applying
the factor from b, we obtain as annual maximum
average concentration:
(2.9 x 10~6 g/s) (1.75 x 10~7 g/m3)=5.1 x 10~13 g/m3 = 5.1 x 1CT4 ng/ro3
(See Table II)
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The estimated upper limit of excess risk of cancer was
obtained using the unit risk factor developed by th'e Agency's
Cancer Assessment Group (GAG) for 2,3,7,8-TCDD (EPA, 1981).
d. Upper limit of excess cancer risk = (unit risk factor) (cone.)
= [.091 (ng/m3)-1] [5.1 x 10~4 ng/m3]
= 4.6 x 10-5 (See Table III)
The confidence ratio makes use of the data from the three-
generation reproduction study in the rat conducted by Murray
(Murray, 1979) and compares the lowest dose in that study (1
ng/kg-d) to the estimated human dose derived from breathing
the dispersed emissions.
f. Estimated human dose =
(Cone) x (Breathing rate) x (75% retention) /
(Body mass)
= (5.1 x 10~4 ng/m3) (20 m3/d) (.75) / (70 kg)
= 1.1 x lO-4 ng/kg-d
g. Therefore, using results from f,
Confidence Ratio =
(Lowest dose in animals) / (Estimate human dose)
= (1 ng/kg-d) / (1.1 x 10~4 ng/kg-d)
= 9,100 (See Table III)
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References
EPA, 1977. Guidelines for Air Quality Maintenance Planning
and Analysis. Vol. 10 (Revised): Procedures for Eval-
uating Air Quality Impact of New Stationary Sources",
Pub. No. 450/4-77-001.
EPA, 1978. Water Quality Criteria Development Guidelines,
Cancer Assessment Group.
EPA, 1980. "Risk Assessment on 2,4,5-T, 2,4,5-Trichlorophenoxy
Acid, and 2,3,7,8-TCDD", Cancer Assessment Group, Sept. 12,
EPA, 1981. "Interim Evaluation of Health Risks Associated with
Emissions of Tetrachlorinated Dioxins from Municipal Waste
Resource Recovery Facilities," Office of the Deputy Admini-
strator, November.
Huff, J.E., J.A. Moore, R. Saracci, and L. Tomatis, 1980.
"Long Term Hazards of Polychlorinated Dibenzodioxins and
Polychlorinated Dibenzofurans", Env. Health Perspectives
26, 221-240.
ICRP (International Commission on Radiation Processes), 1968.
Report of Committee IV, Publication No. 10.
Kociba, R.J., et al, 1978. Tox. Appl. Pharm., 46, 279-303.
Murray, F.J. et al, 1979. Tox. Appl. Pharm. , _5£, 241-252.
National Research Council, 1983. Risk Assessment in the
Federa1 Government; Managing the Process, National
Academy Press.
Tikvart, J. 1981. Office of Air, Noise and Radiation,
personal communication to Randolph Chrismon, 1981.
17
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