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4 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON ~ C 20460
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April 9, 1987 °" cto"
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The Honcrable Lee M. Thcnas.
Administrator
U.S. Environmental Protection Acer.cy
401 M. Street., S.W.
Washington, D.C. 20460
Dear Mr. Thomas:
The Science Advisory Board's Municipal Waste Ccnixistion Subcomrittee
has oorrpleted its review of a dccunerrt jointly- prepared by the Office of Air
Quality Planning and Standards and the Environmental Criteria and Assessment
Office entitled Methodology for the Assessment of Health Risks Associated
with Multiple Pathway Exposure to Municipal Waste Carbustor Qnissions, as
requested in the Subcommittee's charge. The review was requested by both
offices and was conducted on Noveriber 10, 1986 in Research Triangle Park,
H.C.
The Subccnmittee considered the proposed methodology to be a considerable
iroroverient over other multi-media risk assessment methodologies previously
developed by EPA and reviewed by the Science Advisory Board. The current
methodology was more corrprehensive in scene and, in general, provides a
ccnceptual frarawork that ought to be expanded to other environmental problems.
The Subccnndttee identified several areas in this methodology that
need further consideration, including: the applicability of the Hanpton
incinerator facility and associated data to represent typical nass burn,
technology; the failure to use data frcm current best available control techno-
logy facilities for rodel validation; separate treatment of particulate and
gaseous emissions and their fate, i.e. ccwrrwash; the need to use best available
kinetics in predicting soil degradation; exposure resulting from the land-
filling of ash; using the naxiraily exposed individual (MEI) concept; ar.d
the treatment of plant (and herbivore) e.rpcsure. These and other issues are
discussed in the attached report.
The Subcorrmittse1 s review cf this rethodolcgy is part of its larger
evaluation of the scientific knowledge and uncertainties related to municipal
waste ccrbustion. Because of EPA's need to meet a court deadline, the
Siicc.Tru.ttse is issuing this nethcdolocy reviev as a separate report. It
also plans to assess the Office of Research and Development' s municipal
waste ccrbustion research stratecy.
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The Subuumiittee appreciates the opportunity to conduct this
scientific review. We recjuest that the Agency formally respond to the
scientific advice transmitted in the attached report.
Municipal Waste Corbustion Subcoimittee
Science Advisory Board
(/!, \jJ (/t
Norton Nelson, Chairman
Executive Comnittee
Science Advisory Board
Enclosure
cc: A. Janes Barnes
Vaun New ill
J. Winston Porter
Craig Potter
Tterry F. Yosie
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SAB-EETFC-87-027
EPA'S RISK ASSESSMENT METHODOLOGY
FOR MUNICIPAL INCINERATOR EMISSIONS:
Key Findings and Conclusions
REPORT OF THE MUNICIPAL WASTE COMBUSTION SUBCOMMITTEE
Environmental Effects, Transport and Fate Camaittae
SCIENCE ADVISORY BOARD
U.S. ENVIRONMENTAL PROTECTION AGENCY
Washington, D.c.
April 1987
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U. S. ENVIRONMENTAL PROTECTION AGENCY
NOTICE
This report has been written as a part of the activities of
the Science Advisory Board, a public advisory group providing
extramural scientific information and advice to the Administrator
and other officials of the Environmental Protection Agency. The
Board is structured to provide a balanced expert assessment of
scientific matters related to problems facing the Agency. This
report has not been reviewed for approval by the Agency, and
hence, the contents of this report do not necessarily represent
the views and policies of the Environmental Protection Agency,
nor of other agencies in the Executive Branch of the Federal
government, nor does mention of the trade names or commercial
products constitute endorsement or recommendation for use.
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U.S. ENVIRONMENTAL PROTECTION AGENCY
SCIENCE ADVISORY BOARD
ENVIRONMENTAL EFFECTS, TRANSPORT AND FATE COMMITTEE
MUNICIPAL WASTE COMBUSTION SUBCOMMITTEE
Dr. Rolf Hartung
Professor of Environmental
Toxicology
School of Public Health
University of Michigan
Ann Arbor, Michigan 48109
Dr. Martin Alexander
Professor
Department of Agronomy
Cornell University
Ithaca, New York 14853
Mr. Allen cywin
1126 Arcturus Lane
Alexandria, Virginia 22308
Dr. Robert Huggett
Senior Marine Scientist
Virginia Institute of
Marine Science
School of Marine Sciences
College of William & Mary
Gloucester Point, Virginia
23062
Dr. Renate Kimbrough
centers of Disease Control
Center for Environmental
Health
1600 Clifton Road
Atlanta, Georgia 30333
Dr. William Lowrance
Senior Fellow and Oirector
Life sciences fc Public
Policy Program
Or. John Neuhold
Dept. wildlife Sciences
College of Natural Resources
Utah State University
Logan, Utah 84322
Mr. Charles Velzy
Charles R» Velzy Associates
3 55 Main street
Araonk, New York 10504
Dr. Terry F. Yoaie, Director
Science Advisory Board, A101
U.S. Environmental Protection Agency
401 M St., SW, Room 1145 WT
Washington, D.C. 20460
Ms. Janis C. Kurtz, Exec. Secretary
Science Advisory Board, A101F
U.S. Environmental Protection Agency
499 South Capitol St., S.W.,Room 508
Washington, D.C. 20460
Dr. Stanley Auerbach
Environmental Sciences Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37831
Dr. Walter Dabberdt
National Canter for Atmospheric
Research
3100 Marine Street
Research Laboratory
Boulder, Colorado 80307
Dr. Alfred Joensen
Associate Professor
Department of Mechanical
Engineering
Iowa State University
Ames, Iowa 50011
Dr. Raymond Klicius
Environment Canada
351 St. Joseph's Boulevard
Hull Quebec, Canada K1A0E7
Dr. Charles Norwood*
4958 Escobedo Drive
woodland Hill, California 91364
Dr. Adel Sarofim
Dept. of Chemical Engineering
Massachusetts Institute of
Technology
Cambridge, Massachusetts 02139
•Participated until November 11, 1936
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TABLE OF CONTENTS
Page Number
Introduction 1
General Comments and Methodology Overview 1
Technology and Emissions 3
Exposure Models 4
Industrial Source Complex (ISC) Model 4
Human Exposure Model (HEM) 5
Terrestrial Food Chain (TFC) Model 6
Exposure Pathways 7
Surface/Ground Water Models 7
Other Exposures Not Considered 8
Estimation of Risks to Humans 8
Ecological Effects 9
Appendices
Appendix 1: Glossary A-l
Appendix 2: Executive Summary of the A-2
Methodology
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ASSESSING EPA'S RISK ASSESSMENT METHODOLOGY
FOR MUNICIPAL INCINERATOR EMISSIONS:
Key Findings and Conclusions
Introduction
On November 10, 1986, the Municipal Waste Combustion
Subcommittee of the Environmental Effects, Transport and Fate
Committee of EPA*s Science Advisory Board reviewed a draft
document entitled "Methodology for the Assessment of Health Risks
Associated with Multiple Pathway Exposure to Municipal Waste
combustor Emissions" prepared by the Office of Air Quality
Planning and Standards (OAQPS) and the Environmental Criteria and
Assessment Office (ECAO). This document will be referred to
hereafter as the "methodology".
The purpose of the risk assessment and exposure methodology
developed in the document under review is to examine the
potential health and environmental effects exposed populations
are likely to experience as a result of municipal waste
combustion (MWC) technologies. This asessment allows comparison
of variations in the efficiency of combustor design and operation,
and is also intended to predict the effects resulting fronr
multiple exposures to emissions from more than one source.
OAQPS and ECAO requested the Subcommittee to evaluate the
scientific validity of the methodology for assessing health
risks associated with multiple pathway exposures to municipal
waste combustor emissions. Specifically, the Subcommittee was
asked to determine whether the methodology provides a reasonable
scientific approach to evaluating effects on public health given
the available data, the validity of exposure assessments, and the
appropriateness of transport and dispersion models. The
Subcommittee's key findings are reported in the following pages;
detailed comments and meeting transcripts have been provided to
appropriate Agency authors.
General Comments and Methodology Overview
Overall, the Subcommittee considers the proposed methodology
to be conceptually thorough, although it identifies a number of
areas where specific technical improvements are needed. Since
the methodology will be used as a technical support document cor
regulatory decision making, a thorough technical effort is
necessary. The approach also makes reasonably effective use of
existing scientific data and exhibits the
understanding needed for using models. The Subcommittee
consensus is that the methodology is a credible effort towards
developing a tool for assessing multiple media exposures from
this source category.
The Subcommittee commands the authors on b°th th« tcna and
the detail used in documenting tha assumptions that »»»«* "e,
methodology. The uncertainties and possible consequences .
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using the methodology are clearly presented in a number of
instances, such as limitations created by focusing on stack
pollutants rather than total pollutant loadings (e.g., ash
residues, aqueous residues, and staclc emissions). Another con-
cern is the unce-rtainty in identifying specific pollutants in
emissions from a municipal waste conbustor, since characterizing
emissions improves the ability to predict the physical and
chemical properties and effects of emitted substances. The
authors are clearly aware that the methodology they have deve-
loped is but a step in a development process to expand current
risk assessment methodologies to include other pathways, in
addition to atmospheric, exposures beyond inhalation and non-human
effects.
The Subcommittee has several recommendations for placing the
scientific issued raised by the use of this technology into
better perspective. These recommendations include:
° The methodology should attempt to predict the risk
posed from both combustion as a whole and from specific
activities, such as automobile use, industrial practices (e.g.,
coal combustion for energy production), and both hazardous
chemical and municipal incineration.
0 While individual scenarios are modeled in this
methodology, calculating dose from the source and dispersal
through various pathways does not lead the reader to understand
the entire risk perspective that incineration technologies
present.
0 In applying the models, the methodology utilizes
two separata sites as examples: 1) Hampton, Virginia, and 2) a
proposed, or hypothetical, state-of-the-art facility to be
located in Florida. Although both sites are individually
discussed and evaluated as to the risks they presumably pose,
they are not compared. Since risk assessment is a comparative
tool, the Subcommittee recommends that the chosen sites be
evaluated in comparison to one another, and for reasons to be
discussed later, recommends that facilities in addition to
Hampton be used tor this comparison.
°* The subcommittee believes that the most appropriate
data for monitoring KWCs may be derived from combining actual
field measurements with predictions from mathematical models. For
the field measurements, this presupposes that measurements have
been made in appropriate locations, at appropriate times, and
with appropriate methods. It also presupposes, for the
mathematical models, that they have been validated at least to
the extent that their limitations are understood and that the
range of divergence between model predications and reality can be
quantified. In this context it is important to consider both
statistical variability and its propagation through the model, as
well as conceptual biases which inherently result from making the
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simplifying assumptions required for the construction of models.
The Subcommittee recognizes that elements of this recommendation
are best carried out through a longer-term research program.
The document should definitely state that, even when models
are validated, actual data are preferable to results predicted by
models. Also, the methodology should caution that the existence
of a useful model should not substitute for or discourage the
collection of site specific data. In addition, the methodology
.should encourage the use of field data and model application in
concert.
The methodology appropriately states that much of the
information needed to further support its development does not
exist, and that some assumptions about non-existant data must be
made to make initial predictions. However, the specific choices
in such assumptions raise several questions for the Subcommitte
which are addressed in the sections to follow.
The Subcommittee recommends that uncertainties be identified
as to whether they are the result of limitations in the
understanding of the MWC process itself, or a result of the
predictive capability of the model.
Technology and Emissions
The document cover attempts to represent a broad perspective
of exposure patterns. However, the Subcommittee is concerned
that the drawing depicts a worst-case exposure scenario without
illustrating the problem-solving aspects of the technology. This
concern centers around the negative impression that may result
from the depiction of a particulate emissions plume. It was also
noted that the illustration represents a rural setting, and does
not depict the urban environment, where most incinerators may be
built.
The methodology reviews the state-of-the-art for existing
and projected municipal waste combustors, and provides useful
background information. However, various sections on existing
and projected facility sites are inconsistent with regard to
future location*. In addition, projections for California may be
misrepresa&tad* The Subcommittee believes that it is important to
distingulajt between tha number of facilities and the number oC
incinerator furnaces, since most facilities consist of several
incinerators that can be operated independently.
Using a combination of dry scrubber and fabric filter
technology for pollution control is reported to reduce mercury
emissions by 50 percent. Data actually demonstrate that at 140
degrees Celsius (C) or below, 95-97 percent collection is
achieved, while at 209 degrees C, no collection is achieved. The
average may be 50 percent, but averaging this type of data does
not accurately represent the performance of the control system.
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The methodology discusses many factors that nay influence
emissions. The apparent and ultimate conclusion is that the
efficiency of the air pollution control system determines the
emission level of particulate matter (PM) and associated
pollutants from the stack. This conclusion should be clearly
stated.
The Subcommittee disagrees with the use of the Hampton
facility to represent existing incinerators and their emissions.
Use of this inappropriate example will yield a gross overestima-
tion of emissions from new incinerators. The Hampton data set may
be extensive, but the technology used at the facility is hardly
representative of typical mass burn technology. The design and
operating practices used at Hampton should be explained, along
with the fact that this design is not in common use. This
facility provides a worst case scenario that is not representa-
tive of most recent installations. The results of modeling will
be very different when best available control technology (BACT)
is used. The Subcommittee recommends that EPA develop more
scenarios, including one for BACT, that can be used to evaluate a
more complete range of source and emission characteristics for
existing and proposed MWC facilities.
The methodology cites three reasons to explain the presence
of polychlorinated dibenzo-dioxins and furans (PCDDs and PCDFs,
respectively) in MWC flue gases. A fourth reason should be added,
since these organic compounds may be formed in the boiler during
cooling, in the presence of fly ash (post-combustion formation).
It should also be stated that little is known about reactions
that occur between gaseous species within.emission plumes.
The methodology recognizes that the available emissions data
are limited in both quantity and quality. Few specific chemicals
have been identified, although much of the total mass has been
characterized as silicates and forms of carbon. There is reason
to suspect that some of the chemical components of MWC emissions
that remain to be identified may be toxic. However, these
chemical components, such as polyaromatic hydrocarbons (PAHs),
may be contributed by sources other than municipal incinerators,
and background levels are not adequately established. Major data
gaps exist with regard to chemical identity, toxic potential, and
total eavironaental burden of MWC emissions, making the
assessment of risk posed by the technology itself, and in
comparison to other alternatives, difficult to predict.
Exposure Models
0 Industrial Source Complex (ISC) Model
The introduction to the ISC model would be improved by a
discussion of the likely uncertainties of the estimates for
models of gaseous dispersion, particle dispersion, and wet and
dry deposition of gases and particles. This discussion should
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address uncertainties that arise both as a result of limitations
in the understanding of the processes and those due to random
variation in deposition and dispersal processes.
Although some of the assumptions made in parameterizing wet
deposition may be rather crude (e.g., assumptions regarding the
3patial distribution of precipitation), they are not likely to
present a problem when annualized computations are made.
However, the parameterization of dry deposition, particularly for
•emission of chemicals for which loss mechanisms are not under-
stood, is not clear. The methodology seems to imply that gaseous
components are not considered. This point needs to be clarified.
The use of data concerning the size distribution of particles
obtained from the Braintree MWC may not be representative, and
the data on emission rates seem to be conservative.
The methodology for atmospheric dispersion and deposition
of emissions should separately consider particulate and gaseous
emissions and their fate. The contribution from chemicals in
different physical and chemical states should be evaluated with
respect to to direct and indirect routes of exposure. Variability
in the size and solubility of particles should be considered. The
biological availability of emitted materials is also affected by
the degree of sorbtlon to particles that occurs. The discussion
should specify the assumptions made about emission characteristics.
The effects of buildings on lateral and vertical dispersion
of emissions has been considered in the methodology. However,
careful consideration of downvash is also necessary. The
proximity of other structures in urban areas aud the potential
for downwash are not treated in the methodology. Since one of the
strengths of the ISC model is the ability to consider multiple
sources/ the document should also address the issue of the
proximity of other incinerator facilities.
The methodology does not consider the exposure of people who
do not reside at ground level. This factor could be significant
for urban residents, and is compounded by the likely concentra-
tion of incinerator* in urban settings.
° Huaan Exposure Model (HEM)
The BW Is used to estimate the carcinogenic risX posed to
population# by inhalation of predicted ambient air concentrations
of MWC eaissiona. The aodel assumes equivalency of indoor and
outdoor concentrations, an assumption that the Subcommittee finds
suspect for two reasonst 1) the finite length of typical
infiltration rates (> 1 hour, typically), and 2) the significance
of indoor sources of certain chemicals.
The HEM estimates do not consider the short or long-term
mobility of the population. It also assumes a 70-year lifetime
for Mwcs. In other parts of the methodology, a more realistic
30-vear estimate is utilized. The assumption of continuous
operation of MWC facility is also an unrealistic assumption.
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Specific aspects of the locality and siting of the MWC
facility need to be considered because of their significant
effect on concentration and dispersal of pollutants.
The document should refer to the discussion of quantitative
risk assessment modeling found in EPA's revised guidelines for
cancer in order to provide the reader with a better understanding
of the range of assumptions and models used in cancer risk
assessment.
0 Terrestrial Food Chain (TFC) Model
This model is used to predict the deposition of MWC
emissions on soil and vegetation. Its pathways assess the
exposure to humans, animals, soil biota and vegetation, and
associated effects on the food chain. The TFC model has separate
components for examining the potential for human exposure from
ingesting contaminated soil and from consuming vegetation and
animal tissues containing the contaminants. The potential foi
children to be exposed as a result of ingeeting soil is alsc
estimated. However, pathways of human exposure via consumption oi
herbivorous animals are not clearly explained. The assumption
that herbivores are exposed only by ingesting soil or by
consuming plants that have assimilated emitted materials
deposited on soil neglects consideration of the component
presenting the highest exposure potential. Herbivores are likely
to receive the highest exposure from ingesting leaves of plants
upon which particulate emissions have been deposited.
The subcommittee questions the appropriateness of using
sludge or pesticide amendment practices as surrogates for
predicting fallout from MWC emissions. The burden of toxic
compounds and metals that is created by applying sludges to soils
should be compared to that presented by the assumption that rates
of dioxin or furan emissions will equal or exceed 2.7 kg/ha over
SO km linear dimension as a result of MWC.
This model uses a hypothetical Florida MWC as an example for
making predictions, but the input factors, such as rates of
emissions, soil characteristics, and design and operation, are
not docu*«ated. It is not clear whether the Florida MWC
represent* ft beat or worst case illustration. More exposition is
needed vi&b respect to both input and output parameters. These
improvement® would greatly enhance the reader's understanding of
the methodology.
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° Exposure Pathways
The assumptions required for determining the maximally ax-
posed individual (MEI) need to be considered more carefully to
prevent the overconservatisa which nay result from combining the
basic MEI concept with those resulting Cram the multi-exposure
models. The MEI concept estimates the effect on only one
hypothetical human subject,* population effects and effects over
generations are not determined. The HEX concept also does not
¦consider acute exposure or exposures to other biota. These
oversimplifications result in conservative estimates of human
exposure. A new concept should also be developed which includes
the cumulative probability of HEX exposure.
Another flaw in the methodology is the assumption of flat
terrain. Urban or hilly settings may, in actuality, result in
greater levels of human exposure.
The methodology does give appropriate consideration to soil
type. Soils differ greatly, making the selection of a specific
standard soil density and penetration depth tenuous. Compounds
from Mwc emissions will be deposited at different concentrations
and will be found at varying depths in the soil, depending on
soil type. Assumptions that toxicants will be concentrated in
the upper centimeter of soil may be incorrect for some locations
because of differences in soil density, moisture and composition.
Some toxicants will be concentrated near the soil surface, while
ethers may move down from the surface and be dispersed.
Degradation of chemicals in soil is often assumed to be a
first-order reaction/ even when data for specific chemicals
indicate that the degradation rate is not first order. The best
available kinetics should be used, since first order kinetics may
often be inappropriate.
In the methodology, trace metal contaminants are assumed to
persist indefinitely unless loss constants are available. A
reasonable loss constant, which can be derived from soil pH
values, should be used instead of making a blanket assumption
that contaminants will persist.
Assuming that no degradation and no retardation takes place
for chemicsls in the plow depth layer is of concern when there is
a lack of dfit* to support this assumption. The fate of chemicals
is known to be altered in plow depth layers compossd of organic
clays as a result of biologic activity.
0 Surface/Ground Hater Models
Tier one of the surface/ground water methodology assumes
that all material deposited during a single year ia incorporated
into the water in ths same year. This model does not take into
account the potential for build-up over periods of more than one
year, or the potential for this large amount of material to be
released by a single storm event at sons future time. In drier
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climates (i.e., the Intermountain West and the Southwest deserts)
major storms or "gully washers" can occur as seldom as once in 10
years, rendering doubtful the assumption that all toxicants
adhering to particulates are flushed out in a one year period.
Furthermore, in wet climates the opposite may be true, as some
toxicants may not build up appreciably.
° Other Exposures Not Considered
As the authors point out, no consideration is given to
exposures from landfilling ash. Similarly, consideration is not
given to the potential for change in emission characteristics
that may result from incinerator upsets. These data gaps are
significant, but consistent with the Inadequate knowledge
regarding MWCs. The Subsommittee recommends that the methodology
address these issues.
Estimation of Rislc to Humans
The equation used to calculate the adjusted reference intake
(RIA) is logical for application, since the use of the acceptable
daily intake (ADI) is well established. Also, the use of excess
concentration over background in the equation is an established
measure of the potential for human health effects. However, the
definition of total background intake (TBI) of pollutants from all
existing sources needs some clarification.
Examples presented in the methodology use national averages
to define the TBI, although these values may not be
Representative of the particular sites where risk is to be
evaluated. The approach taken for risk assessment is based on
the location with the sir.imua RIA, although people at this
location may not be those with the maximum exposure to the
pollutant. The Subcommittee believes that the values selected may
not be valid for the particular sites being evaluated.
Defining the TBI as the sum of contributions from individual
sources assumes that no interactions, such as synergism or
antagonism, occur when sourees are combined and individuals are
exposed by multiple routes. There are many instances where this
concept i* not supported by the available data.
There? is inconsistency in the methodology's treatment of
exposure to background concentrations of different chemical
substanceo. For some chemicals, such as cadmium, contributions
from KWC omissions are added to contributions from all background
sources to give total exposure. For other substances, such as
benzo(a)pyrene, exposures to background concentrations are
ignored and assessment is conducted in terms of additional risk
posed by MWC contributions alone. The methodology should assess
exposure to chemical substances in a consistent manner.
The prediction of inhalation exposure, which assumes that
individuals are exposed to emissions only in gaseous form,
neglects the potential for particulate absorption and particle
8
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deposition. Pathways other than inhalation, such as dry
depositon of particulate emissions and related dermal absorption,
need to be considered.
The methodology postulates that some noncarcinogenic effects
that exhibit thresholds occur only after nearly an entire life-
time of exposure. This assumption does not reflect the actual
situation. For example, fibrotic lung diseases occur after less
than a full life span of exposure, and their onset is very
.gradual. For many chemicals, the reported latency periods tend
to be measured in terms of weeks or months, rather than years.
Relative effectiveness (RE) is used in the methodology to
standardize effects of exposure by one route to the effects of
exposure by another. There may not be scientific justification
for this conversion factor. However, the concept is useful as
long as users realize that the effect of an exposure does not
relate solely to absorption efficiency, but is also related to
difference* ill the sensitivity of absorption sites to damage, and
to difference* in toxicokinetics between exposure routes. The
methodology shoQld acknowledge the assumptions required for using
this approach.
Consumption of fish by the general population is discussed,
but the discussion does not take into account the fact that fish
may come from a variety of sources with varying degrees of
contamination. A similar situation exists for drinking water.
Drinking water obtained from any one tap may consist of water
from a local source, may contain water that originates outside of
the localized delivery area, or may be a mixture of both.
Alternatively, drinking water may be obtained from individual
wells drawing on ground water from a large source or deep aquifer.
Local contamination is not always represented in the localized
supply of drinking water.
With regard to water consumption, the amount of fluid
intake documented is low. It is not clear whether this amount
represents total fluid intake or the intake of water alone. It is
usually assumed that fluid intake for adults averages 2 liters
per day. It i« questionable, therefore, that females between the
ages of 14 and 16 would only take in 586 ml water per day, as
reported la the document.
Ecological Effects
The treatment of plant uptake as a linear function is
erroneous unless no other information is available. Many
toxicants, especially metal salts, are actively transported
across membranes or cell walls and, therefore, cannot be described
by a linear function.
The Subcommittee disagrees with the assumption that plants
are exposed to contaminants mainly through uptake from soil.
Greater exposure is likely to occur from foliar deposition.
Estimates of deposition can be obtained from acid deposition
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studias and also from studies of the nuclear energy industry,
e.g., deposition of radioiodine (I131).
The Subcommittee also questions the method used to average
bioconcentration data for aquatic species. Even when means are
calculated separately for bivalves and fin fishes, misleading
interpretations can result. The bioconcentration data should be
correlated with human dietary factors. For example, humans con-
sume more oysters than mussels, and oysters may accumulate
significantly more contaminants than mussels. Averaging biocon-
centration factors together for oysters and mussels may create a
significant source of error in calculating exposure to
bioaccumulated chemicals.
The document summary mentions measurement of adverse effects
on natural ecosystem vitality. The definition of ecosystem
vitality is unclear, as are the endpoints to be used in measure-
ment. Uptake from water is modeled, but few other environmental
endpoints are considered, one important component not treated is
the highest trophic level, predators. Predators play an
important role in community regulation. There is also a need to
consider the potential for concentration of materials in
sediment, since sediments may serve as a source of contamination
for overlying waters, and materials concentrated in sediment may
be biologically available to benthic organisms and organisms
dwelling in the water column. Assessments of exposure cannot be
derived from water quality concentrations for benthic dwellers,
since they are exposed in a totally different way*
In closing, the Subcommittee agrees that the methodology
represents an appropriate step towards modeling and predicting
exposure from MWC emissions. Some conceptual assumptions can be
strengthened by Closer examination of the~£omplexities associated
with pollutant emission to and interaction with the environment,
while others must await collection of actual field data to fill
in knowledge voids and elucidate environmental Interactions.
Finally, the methodology/ over time, must be validated with actual
data to evaluate and demonstrate its utility, and to guide its
further development and refinement.
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APPENDIX 1: Glossary
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Glossary
ADI Acceptable Daily Intake (mg/kg/day)
BACT Best Available Control Technology
C Celsius
HEM Human Exposure Model
ISC Industrial Source Complex (as in ISC model)
MEI Maximally Exposed Individual
MWC Municipal Waste Combustor
PAH Polyaromatic Hydrocarbon
PCDO Polychlorinated Dibenzo-Dioxii
PCOF Polychlorinated Dibenzo-Furan
PM Particulate Matter
RE Relative Effectiveness of ingestion exposure
RIA Adjusted Reference Intake (u/day)
TBI Total Background Intake (mg/day)
TFC Terrestrial Fate Complex (as in TFC model)
A-l
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APPENDIX 2J,
Executive of Document Under Review:
"Methodology for the Assessment of Health Risks Associated with
Multiple Pathway Exposure to Municipal Waste Combustor Emissions*
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Unittd State*
Enviranmanul Protection
A9#ocy
The Office of Air Ouality Planning and Standards. RTP Norm Carol,,,* »r
The Environmental Critarffand Aa«easfnent Office. C.nemnau ah'„
Octotof. 1986 '
Methodology for the Assessment of Health Risks
Associated with Multiple Pathway Exposure to
Municipal Waste Combustor Emissions
DRAFT
00 NOT QUOTE OR Cr
\
RUNOFF
PERCOLATION
DEPOSITION
ON FOOO
ANO FEED
IRRIGATION
- W/ir
EATING
VEGETABLES
SOIL
INGESTION
ORINKING
MILK 3
EATING
FISH
\ •••
vSXv;-
INHALATION
ORINKIN
WATER
DERMAL
ABSORPTION
UPTAKE
BY BIOTA
A Staff Paper Submitted for Review to the Science Advisory Boarc
A-2
-------
EXECUTIVE SUMMARY
Each year the collective social and commercial activity in trie urn tea
States produces >150 million tons of discarded waste. Commonly termed munici-
pal solid waste (MSW), this discarded material must somehow be managed to avoid
undesirable adverse consequences on human life, and the vitality of terrestrial
and aquatic life.
The age-old solution to the problem of managing MSW has been to dispose of
the waste in the ground in land areas dedicated to that purpose. Currently
about BOX of the MSW is disposed of by land burial in -10,000 landfills nation-
wide. If not properly sited, designed, and managed, these landfills can cause
serious damage to the environment. For example, gases can escape the landfill
and travel to residential areas potentially Impacting human health, or contami-
nated leachate can migrate off-site into sources of potable drinking water and
into sensitive natural ecosystems. Because of the possible adverse environmen-
tal impact posed by landfills, many States have imposed strict siting require-
ments, landfill cover requirements, leachate collection and treatment require-
ments, landfill gas capture and treatment requirements, and groundwater monitor-
ing requirements to the design and operation of landfills. These requirements
have significantly increased the cost of disposing MSW 1n landfills, and have
limited land areas suitable for landfill sites.
Meanwhile the amount of MSW needing disposal continues to increase with
the increase in the U.S. population. By the year 2000 U.S. society may be faced
with managing the disposal of >250 million tons of MSW each year. Methods of
waste management are limited by available technology. Coanun1t1es can continue
to only landfill MSW, or they can utilize technologies that will substantially
reduce tH« vol taw of waste that 1s ultimately landfllled, e.g., recycling of
waste and Incineration of waste. While recycling strategies are being encour-
aged and fostered, many communities are turning to municipal waste combustion
(MWCs) 1n order to Incinerate and reduce the volume of waste by 70-90%. Current
MWC technology is a distinct improvement 1n the design, combustion efficiency,
and pollution control over combustors planned and constructed a decade ago.
xi i
-------
They not only reduce the volume of waste, but have the added advantage of ther-
mally recovering energy from combustion in the form of steam or hotwatar that
can be used In industrial cogeneration, used to generate electricity, and used
to heat and cool residential and commercial properties.
The U.S. EPA predicts a substantial growth in MWC will occur over the next
10-20 years. Today 99 MWCs nationwide incinerate about 4% of the annual vol-
ume of MSW, whereas it is conceivable that by the year 2000 one-third of the
MSW will be incinerated in >300 MWCs. There is a definite trend moving toward
incineration of MSW, and away from exclusively landfilling the waste.
The U.S. EPA has a limited opportunity to prospectively evaluate the poten-
tial environmental and health impact that may result from a sudden proliferation
of municipal waste combustion. In this regard the agency has developed a
methodology for the evaluation of emissions of pollutants into the atmos-
phere from the stacks of MWCs during incineration. The methodology consists
of a series of environmental fate and transport models that utillie the known
physical and chemical properties of specific pollutants to predict the atmos-
pheric dispersion from stack emissions, the potential for surface deposition and
accumulation; the movement of the settled pollutants through and into various
environmental media; the potential bioaccumulation of pollutants into trophic
systems; the potential for adverse effects on the vitality of natural ecosy-
stems; and the potential for adverse effects on human health. With regard to
evaluating potential human health effects, the methodology will estimate health-
risks resulting from inhalation of predicted ambient air concentrations of pol-
lutants; ingestion of pollutants deposited on the ground an bioaccumulated into
the food chain; ingestion of potable water or aquatic organisms contaminated
by the surface runoff and the leaching and percolation of settled pollutants
into water supplies; and ingestion of soil particles contaminated by deposited
incinerator ealsslont.
The utility of the present methodology is limited by a number of gaps in
the available technical data and significant uncertainties in many of the major
analytical parameters. There is little question that the methodology can be
improved by further research. One major limitation is that the methodology
focuses only on pollutants emitted from the stacks of MWCs. Ideally the total
pollutant loading resulting from the incineration process should be evaluated,
xi l i
-------
e.g., ash residues, aqueous residues, and stack emissions. The evaluation of
stack emissions 1s further limited by the relatively small number of organic
and inorganic pollutants that have been measured In MWC emissions. A final con-
straint on the methodology is the limited amount of data regarding the physi-
cal and chemical behavior of specific pollutants in the natural environment,
and the adverse impact these pollutants may have on human health.
In the evaluation of the potential environmental impact of combustion
sources, the U.S. EPA has traditionally focused on air emissions from the
source, and on the human health risks from direct inhalation of predicted
ambient air concentrations of pollutants. The present methodology represents
an expansion of the analytical scope to include consideration of multiple
pollutants, multiple exposure pathways, carcinogenic and noncarcinogenic risks
posed to humans, and potential adverse effects to the natural environment.
Human exposure to incinerator emissions results from direct Inhalation of
ambient air concentrations of the pollutants and Indirectly from skin contact
of the pollutants, and Ingestion of contaminated soil particles, water and
food. Oetailed experimental evaluation of the environmental fate and transport
of MWC emissions have not been conducted under actual conditions. Therefore,
mathematical models of fate and transport are currently the most feasible
alternative to the assessment of exposure to MWC emissions. In addition to
estimating concentrations that will be inhaled, these models can also be used
to estimate the potential accumulation in soils of pollutants adverse to the
promotion of human, animal and plant life, and accumulation of pollutants into
the human and ecological food chain. The models specifically used in this
analysis of MQ emissions are: the Human Exposure Model (HEM), the Industrial
Source Complex Short-Term Air Dispersion Modal; tha Terrestrial Food Chain
Modal, tha Surfact Runoff Modal, the Groundwater Contaminant Model, and the
Dermal Exposure Modal.
Gtvan tha complexities of predicting tha environmental fate and transport
of specific chemicals emitted, as well as predicting multiple routes of human
exposure to specific chemicals, it is not currently feasible nor practical to
apply the models to every existing or planned MWC. Therefore, the methodology
employs a simplified modeling approach by using a hypothetical plant (in
xiv
-------
western Florida) to characterize the potential adverse -Impacts of emissions
from technologies typical of MWCs currently being planned or considered, and
the Hampton, Virginia MWC to represent a reasonable worst case of the potential
adverse impacts on air pollutant emissions from existing MWC technology.
The Industrial Source Complex Model (ISC)
The industrial source complex model is used to predict the dispersion of
smokestack emissions from the hypothetical plant and the Hampton facility
through the atmosphere, as well as to predict both wet and dry deposition of
pollutants onto the surface. Assessments of potential risk from air emissions
have primarily been concerned with health risks resulting from direct inhala-
tion of ambient air concentrations of pollutants. The ISC assists 1n extending
the risk evaluation to a consideration of their routes of population exposure
to environmental pollutants and allows the U.S. EPA to predict the rate of
deposition, ov*P"ttae, of pollutants believed to be adsorbed onto particulate
matter fn the smokestack exhaust gas, and attempt to calculate the spatial and
temporal accumulation of these pollutants on the soil, surface water, ground-
water and terrestrial food chain.
For purposes of exposure analysis from MWC emissions, the ISC Short-Term
(ISCST) model program is utilized. The program makes mathematical calculations
of dispersion and d«*y deposition and produces a printout of these value*. How-
ever, the ISCST model as originally developed had no provision for calculating
wet deposition of the emissions. Because this deposition pathway is considered
to be of potential significance, the present methodology included an algorithm
to estimate the effect of precipitation events on the rate of surface deposi-
tion.
Human Exposure Itodtl (HEM)
The ISCST output Is a concentration array for a total of 160 receptors, or
10 receptors along each of 16 wind directions, specified in concentric radial
distances from each facility of 0.2, 0.5, 1, 2, 5, 10, 20, 30, 40 and 50 kilo-
meters computed every 22.5° on a radius-polar grid pattern. This output is a
suitable format for utilization with HEM. HEM 1s a general model that has
been routinely used with the CPA's air regulatory progran to estimate the
carcinogenic risk to the population exposed by inhalation to predicted ambient
xv
-------
air concentrations of specified pollutants. The HEM also is capable of air
dispersion modeling, and is often used in nationwide analysis of source cate-
gories.
Terrestrial Food Chain Model (TFC)
Contaminants associated with emissions from MWC are subject to deposition
on surfaces downwind form the MWC. The fallout may be deposited on soil and/or
vegetation.
Humans in the vicinity of the MWC have the potential to ingest contaminated
soil directly or consume vegetation and animal tissues containing the contami-
nants. The TFC model has separate components for examining each potential expo-
sure pathway. These components describe methods for using empirical data on
contaminant uptake by plant or animal tissues to estimate tissue concentrations,
and for Integrating these estimates to give a picture of potential human dietary
exposure. Potential exposure of children resulting from soil ingestion ("pica")
is also estimated.
Surface Runoff Model
Contaminants associated with particulates emitted by MWCs are subject to
deposition on surfaces downwind from the MWC at rates determined by meteorology,
terrain, and particle physics. This fallout Is subsequently subject to dissolu-
tion and/or suspension on runoff after precipitation events. Runoff moves over
the surface of the earth to a surface water body where it mixes with other
waters. As a consequence, humans utilizing water from the surface water body
or aquatic life living therein may be exposed to runoff transported contami-
nants.
The methodology 1s formulated 1n three successive tiers that begin with
simple but very conservative estimates, and proceed to more detailed analyses
if the first tiers predict unacceptable risks. Both acute events and chronic
exposure are evaluated, using standard approaches to calculate runoff volume
and associated runoff potential. The methodology was originally developed to
evaluate impacts from the application of municipal waste-waters sludge to land.
xv i
-------
Groundwater Infiltration Model
Contaminants associated with particulate emitted from MWCs are subject to
deposition on surfaces downward from the facility. This fallout is subsequently
subject to dissolution in rain or meltwatar from precipitation events. The dis-
solved portion can follow one of two pathways: either move over the surface
as runoff to a surface water body or infiltrate Into the ground and recharge
the groundwater. As a consequence, persons using the groundwater nay be exposed
to groundwater transported contaminants. Aquatic life Inhibiting surface water
bodies fed by the contaminated aquifer could be exposed as well.
The methodology derived to calculate risks from the groundwater pathway
was originally developed to evaluate Impacts from the landfllling of municipal
sludge. As for surface runoff, this methodology 1s formulated in three succes-
sive tiers. Only chronic exposure is evaluated using standard approaches to
calculate leachate generation and associated groundwaters transport in the un-
saturated xono.
Qermal Exposure Model
The dermal exposure model refers to human skin contact with contaminants
from emissions of MWC deposited on the soil. The tissue of derual absorption
of deposited contaminants is very complex. There is a fundamental lack of data
for percutaneous absorption of chemicals in human skin from soil. Other factors
important for estimation of Nu&an "exposure to contaminants by the dermal route
also have many uncertaioties. The.model described in this document is offered
as a possible approach for the estimation of human exposure and risk associated
with a dermal exposure, but 1t is recognized that in most, if not all cases,
the available data will not provide a satisfactory basis for risk calculations.
Systemic toxic thresholds or carcinogenic potencies of chemicals by a dermal
route of exposure havo not been delineated by the U.S. EPA at the present time.
Ecological Effects from HWC Emissions
Methodi to assess risk to terrestrial organisms represent a follow-up to
the Terrestrial Food Chain (TFC) model. Components for assessing effects of
deposited pollutants on herbivores, soil biota, predators of soil biota, and
xvi i
-------
plants are included. Methods to assess risk to aquatic organisms and wildlife
preying on aquatic organisms follow from the surface runoff and groundwater
infiltration models. Surface water concentrations predicted by these models
are used to predict adverse effects on aquatic organisms or wildlife.
Example Calculations
Two chemicals have been selected to provide example calculations of risk:
benzo(a)pyrene [B(a)P] and cadniua (Cd). Both chemicals are used only as
examples for each methodology. The examples are shown for the Human Exposure,
Terrestrial Food Chain, Surface Runoff, Groundwater Infiltration and Dermal
Exposure models. The purpose of the examples are to assist the reader in the
functional operation of the calculations for each methodology.
xv i ii
-------
U.S. EUVTROfttEOTAL PSCTSCTION AGENCY
SCIENCE ADVISORY BOARD
ENVIRONMENTAL EFFECTS, TRANSPORT AND FAXE OOM4TTTEE
MUNICIPAL WASTE COMBUSTION REVIEW SUBCOMUTTEE
Dr. Rolf Hartung, Chairman
Professor of Envircrunantai Toxicology
School of Public Health
University of Michigan
Ann Arbor, Michigan 48109
Dr. Martin Alexander
Professor
Departnent of Agrcnaty
Cornell University
Ithaca, New York 14853
Mr. Allen Cywin
1126 Arcturus Lana
Alexandria, Virginia. 22308
Dr. Robert Huggett
Senior Marine Scientist
Virginia Institute of Marine
Science
School of Marine Sciences
College of William and Mary
Gloucester Point, Virginia 23062
Dr. Renate Kimbrough
Centers for Disease Control
Center for Environmental Health
1600 Clifton Road
Atlanta, Georgia 30333
Dr. William Lowranca
Senior Fellcw and Director
Life Sciences and Public Policy Program
The Rockefeller University
1230 York Avenue
s'aw York, New York 10021
Dr. John ^euhold
Department of Wildlife Sciences
College of Natural Resources
Utah State University
Logan, Utah 84322
Mr. Charles Velzy
G^arlea R. Velzy Associates
355 Main Street
Arrcrk, I'e* Ycrk 10504
Dr. Terry F. Yosie, Director
U.S. Environmental Protection Agency
Science -Advisory Board
401 M St., SW, Suite L14S WT - A101
Washington, D.C. 20460
Ms. Jams C. Kurtz, Executive Secretary
U.S. Environmental Protection Agency-
Science Advisory Board, A101F
499 South Captol St., S.W., Suite 508
Washington, D.C. 20460
Dr. Stanley Auerbach
Division Director
Bivircnasntal Sciences Division
Cakridge National Laboratory
Oakridge, Tennessee 37830
Dr. Walter Dabberdt
National Center for Atcrospheric
Research
3100 Marine Street
Research Lab
Boulder, Colorado 80307
Qr. Alfred Joensen
Associate Professor
Department of Mechanical Engineering
Iowa Stats University
Anas, Iowa 50011
Dr. Raymond Klicius
Bivircnsmnt Canada
351 St. Joseph's Boulevard
Hull Quebec, Canada K1A0E7
Dr. Charles Norwood
4958 Cscobedo Drive
Woodland Hill, California 9L364-
Dr. Adel Sarofim
Department of Chemcal Er.cir.eennc
Cartridge, Massachusetts C2L39
-------
Maka Umt«3 Siatas
IVtUA Environmental Prowerion
V)/UI ri Agtncy
"Hi# OHicb of Air Quality P'anning and Standards "TP Nonn Carolina jra
Hit environmental Cficana and A»a«sam»rt 0*fic« Cincinnati Cr»a
Oc:oo«f, 1986
Methodology for the Assessment of Health Risks
Associated with Multiple Pathway Exposure to
Municipal Waste Combustor Emissions
DRAFT
00 NOT QUOTE OS Ci
ssssrssssb^
\
RUNOFF
ON GROUND .. _
PERCOLATION
DEPOSITION
ON FOOO
AND FEED
IRRIGATION —
EATING
VEGETABLES
DRINKING
MILK
/
SOIL J*
INGESTION
EATING
FISH
INHALATION
DRINKIN
WATER
DERMAL
ABSORPTION
UPTAKE
BY BIOTA
A Staff Paper Submitted for Review to the Science Advisory Board
-------
EXECUTIVE SUMMARY
Each year the collective social and commercial activity in the United
States produces >150 million tons of discarded waste. Commonly termed munici-
pal solid waste (MSW), this discarded material must somehow be managed to avoid
undesirable adverse consequences on human life, and the vitality of terrestrial
and aquatic life.
The age-old solution to the problem of managing MSW has been to dispose of
the waste in the ground in land areas dedicated to that purpose. Currently
about 80% of the MSW is disposed of by land burial in ~10,Q00 landfills nation-
wide. If not properly sited, designed, and managed, these landfills can cause
serious damage to the environment. For example, gases can escape the landfill
and travel to residential areas potentially impacting human health, or contami-
nated leachate can migrate off-site into sources of potable drinking water and
into sensitive natural ecosystems. Because of the possible adverse environmen-
tal impact posed by landfills, many States have Imposed strict siting require-
ments, landfill cover requirements, leachate collection and treatment require-
ments, landfill gas capture and treatment requirements, and groundwater monitor-
ing requirements to the design and operation of landfills. These requirements
have significantly increased the cost of disposing MSW in landfills, and have
limited land areas suitable for landfill sites.
Meanwhile the amount of MSW needing disposal continues to increase with
the increase in the U.S. population. By the year 2000 U.S. society may be faced
with managing tha disposal of >250 million tons of MSW each year. Methods of
waste management art United by available technology. Communities can continue
to only land/111 MSW, or they can utilize technologies that will substantially
reducfr»th« vol lot of waste that is ultimately landfllled, e.g., recycling of
waste ami Incineration of waste. While recycling strategies are being encour-
aged and fostared, many communities are turning to municipal waste combustion
(MWCs) in order to Incinerate and reduce the volume of waste by 70-90%. Currar
MWC technology is a distinct improvement in the design, combustion efficiency,
and pollution control over combustors planned and constructed a decade ago.
xi i
-------
They not only reduce the volume of waste, but have the added advantage of ther-
mally recovering energy from combustion in the form of steam or hotwater that
can be used in industrial cogeneration, used to generate electricity, and used
to heat and cool residential and commercial properties.
The U.S. EPA predicts a substantial growth in MWC will occur over the next
10-20 years. Today 99 MWCs nationwide incinerate about 4% of the annual vol-
ume of MSW, whereas it is conceivable that by the year 2000 one-third of the
MSW will be incinerated in >300 MWCs. There is a definite trend moving toward
incineration of MSW, and away from exclusively landfilling the waste.
The U.S. EPA has a limited opportunity to prospectively evaluate the poten-
tial environmental and health impact that may result from a sudden proliferation
of municipal waste combustion. In this regard the agency has developed a
methodology for the evaluation of emissions of pollutants into the atmos-
phere from the stacks of MWCs during incineration. The methodology consists
of a series of environmental fate and transport models that utilize the known
physical and chemical properties of specific pollutants to predict the atmos-
pheric dispersion from stack emissions, the potential for surface deposition and
accumulation; the movement of the settled pollutants through and into various
environmental media; the potential bioaccumulation of pollutants into trophic
systems; the potential for adverse effects on the vitality of natural ecosy-
stems; and the potential for adverse effects on human health. With regard to
evaluating potential human health effects, the methodology will estimate health
risks resulting from inhalation of predicted ambient air concentrations of pol-
lutants; ingestion of pollutants deposited on the ground an bioaccumulated into
the food chain; ingestion of potable water or aquatic organisms contaminated
by the surfact runoff and the leaching and percolation of settled pollutants
into water supplies; and Ingestion of soil particles contaminated by deposited
incinerator eafssions.
The utility of the present methodology is limited by a number of gaps in
the available technical data and significant uncertainties in many of the major
analytical parameters. There is little question that the methodology can be
improved by further research. One major limitation is that the methodology
focuses only on pollutants emitted frcm the stacks of MWCs. Ideally the total
pollutant loading resulting from the incineration process should be evaluated,
-------
e.g., ash residues, aqueous residues, and stack emissions. The evaluation of
stack emission? is further limited by the relatively small number of organ-.c
and inorganic pollutants that have been measured in MWC emissions. A final con-
straint on the methodology is the limited amount of data regarding the physi-
cal and chemical behavior of specific pollutants in the natural environment,
and the adverse impact these pollutants may have on human health.
In the evaluation of the potential environmental impact of combustion
sources, the U.S. EPA has traditionally focused on air emissions from the
source, and on the human health risks from direct Inhalation of predicted
ambient air concentrations of pollutants. The present methodology represents
an expansion of the analytical scop* to Include consideration of multiple
pollutants, multiple exposure pathways, carcinogenic and noncarclnogenic risks
posed to humans, and potential adverse effects to the natural environment.
Hunan exposure to incinerator emissions results from direct Inhalation of
ambient air concentrations of the pollutants and Indirectly from skin contact
of the pollutants, and ingestion of contaminated soil particles, water and
food. Detailed experimental evaluation of the environmental fate and transport
of MWC emissions have not been conducted under actual conditions. Therefore,
mathematical models of fate and transport are currently the most feasiole
alternative to the assessment of exposure to MWC emissions. In addition to
estimating concentrations that will be inhaled, these models can also be used
to estimate the potential accumulation in soils of pollutants adverse to the
promotion of human, animal and plant life, and accumulation of pollutants into
the human and ecological food chain. The models specifically used in this
analysis of MWC emissions are: the Human Exposure Model (HEM), the Industrial
Source Complex Short-Term A1r Dispersion Model; the Terrestrial Food Chain
Model, th® Surface Runoff Model, the Groundwater Contaminant Model, and the
Dermal Exposure Model.
Given the complexities of predicting the environmental fate and transport
of specific chemicals emitted, as well as predicting multiple routes of human
exposure to specific chemicals, it is not currently feasible nor practical to
apply the models to every existing or planned MWC. Therefore, the methodology
employs a simplified modeling approach by using a hypothetical plant (in
xi v
-------
western Florida) to characterize the potential adverse Impacts of emissions
from technologies typical of MWCs currently being planned or considered, and
the Hampton, Virginia MWC to represent a reasonable worst case of the potential
adverse impacts on air pollutant emissions from existing MWC technology.
The Industrial Source Complex Modal (ISC)
The Industrial source complex model is used to predict the dispersion of
smokestack emissions from the hypothetical plant and the Hampton facility
through the atmosphere, as well as to predict both wet and dry deposition of
pollutants onto the surface. Assessments of potential risk from air emissions
have primarily been concerned with health risks resulting from direct inhala-
tion of ajntoient air concentrations of pollutants. The ISC assists in extending
the risk evaluation to a consideration of their routes of population exposure
to environmental pollutants and allows the U.S. EPA to predict the rate of
deposition, over time, of pollutants believed to be adsorbed onto particulate
matter in the smokestack exhaust gas, and attempt to calculate the spatial and
temporal accumulation of these pollutants on the soil, surface water, ground-
water and terrestrial food chain.
For purposes of exposure analysis from MWC amissions, the ISC Short-Term
(ISCST) model program is utilized. The program makes mathematical calculations
of dispersion and dry deposition and produces a printout of these values. How-
ever, the ISCST model » originally developed had no provision for calculating
wet deposition of the emissions. Because this deposition pathway is considered
to be of potential significance, the present methodology Included an algorithm
to estimate the effect of precipitation events on the rate of surface deposi-
tion.
Human gxoosur* Model (HEM)
The ISCST output fs a concentration array for a total of 160 receptors, or
10 receptors along each of 16 wind directions, specified In concentric radial
distances from each facility of 0.2, 0.5, 1, 2, 5, 10, 20, 30. 40 and 50 kilo-
meters computed every 22.5® on a radius-polar grid pattern. This output is a
suitable format for utilization with HEM. HEM is a general model that has
been routinely used with the EPA's air regulatory program to estimate the
carcinogenic risk to the population exposed by inhalation to predicted ambient
xv
-------
air concentrations of specified pollutants. The HEM also is capable of air
dispersion modeling, and is often used in nationwide analysis of source cate-
gories.
Terrestrial Food Chain Model (TFC)
Contaminants associated with emissions from MWC are subject to deposition
on surfaces downwind form the MWC. The fallout may be deposited on soil and/or
vegetation.
Humans in the vicinity of the MWC have the potential to ingest contaminated
soil directly or consume vegetation and animal tissues containing the contami-
nants. The TFC model has separate components for examining each potential expo-
sure pathway. These components describe methods for using empirical data on
contaminant uptake by plant or animal tissues to estimate tissue concentrations,
and for integrating these estimates to give a picture of potential human dietary
exposure. Potential exposure of children resulting from soil Ingestion ("pica")
is also estimated.
Surface Runoff Model
Contaminants associated with particulates emitted by MWCs are subject La
deposition on surfaces downwind from the MWC at rates determined by meteorology,
terrain, and particle physics. This fallout Is subsequently subject tb dissolu-
tion and/or suspension on runoff after precipitation events. Runoff moves ocer
the surface of the earth to a surface water body where it mixes with other
waters. As a consequence, humans utilizing water from the surface water body
or aquatic 11ft living therein may be exposed to runoff transported contami-
nants.
Th® mthodology Is formulated in thre* successive tiers that begin wittt
simple but very conservative estimates, and proceed to more detailed analyses
if th«» first tiers predict unacceptable risks. Both acute events and chronic
exposure art evaluated, using standard approaches to calculate runoff volume
and associated runoff potential. The methodology was originally developed to
evaluate impacts from the application of municipal waste-waters sludge to land
xv i
-------
Groundwater Infiltration Modal
Contaminants associated with particulate emitted from MWCs are subject to
deposition on surfaces downward from the facility. This fallout is subsequently
subject to dissolution in rain or meltwater from precipitation events. The dis-
solved portion can follow one of two pathways: either move over the surface
as runoff to a surface water body or infiltrate into the ground and recharge
the groundwater. As a consequence, persons using the groundwater may be exposed
to groundwater transported contaminants. Aquatic Ufa Inhibiting surface water
bodies fed by the contaminated aquifer could be exposed as well.
The methodology derived to calculate risks from the groundwater pathway
was originally developed to evaluate Impacts from the landfilling of municipal
sludge. As for surface runoff, this methodology 1s formulated 1n three succes-
sive tiers. Only chronic exposure 1s evaluated using standard approaches to
calculate leachatt generation and associated groundwatars transport in the un-
saturated zone.
Dermal Exposure Wodel
The dermal exposure model refers to human skin contact with contaminants
from emissions of MWC deposited on the soil. The tissue of dermal absorption
of deposited contaminants 1s very complex. There 1s a fundamental lack of data
for percutaneous absorption of chemicals In human skin from soil. Other factors
important for estimation of human exposure to contaminants by the dermal route
also have many uncertainties. The model described In this document 1s offered
as a possible approach for tha estimation of human exposure and risk associated
with a dermal exposure, but 1t 1s recognized that 1n most, If not all cases,
the available data will not provida a satisfactory basis for risk calculations.
Systemic toxic threshold* or carcinogenic potencies of chemicals by a dermal
route of exposal* hav# not ba«n delineated by th« U.S. EPA at tha present time.
Ecological Effects from WC Emissions
Methods to assass risk to terrestrial organisms represent a follow-up to
the Terrestrial Food Chain (TFC) modal. Components for assessing effects of
deposited pollutants on herbivores, soil biota, predators of soil biota, and
xv i i
-------
plants are Included. Methods to assess risk to aquatic organisms and wildlife
preying on -aquatic organisms follow from the surface runoff and groundwater
infiltration models. Surface water concentrations predicted by these models
are used to predict adverse effects on aquatic organisms or wildlife.
Example Calculations
Two chemicals have been selected to provide example calculations of risk:
benzo(a)pyrene [8(a)P] and cadmium (Cd). Both chemicals are used only as
examples for each methodology. The examples are shown for the Human Exposure,
Terrestrial Food Chain, Surface Runoff, Groundwater Infiltration and Oermal
Exposure models. The purpose of the examples are to assist the reader in the
functional operation of the calculations for each methodology.
xv i i i
------- |