EPA/600/R-18/109 | August 2018
www.epa.gov/homeland-security-research
United States
Environmental Protection
Agency
oEPA
Exposure Assessment During a
Chemical Attack: Livestock
Carcass Management
Office of Research and Development
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EPA/600/R-18/109
August 2018
Exposure Assessment During a
Chemical Attack: Livestock Carcass
Management
by
Sandip Chattopadhyay, Ph.D.
Threat and Consequence Assessment Division
National Homeland Security Research Center
Cincinnati, OH 45268
Interagency Agreement HSHQPM13X00157
Contract No. EP-C-14-001 to ICF
U.S. Environmental Protection Agency Project Officer
Office of Research and Development
Homeland Security Research Program
Cincinnati, OH 45268
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Disclaimer
The U.S. Environmental Protection Agency (EPA) through its Office of Research and
Development), in collaboration with the United States Department of Homeland Security funded
and managed the research described here under Interagency Agreement HSHQPM13X00157 and
contract No. EP-C-14-001 to ICF under WA 24. It has been subjected to the Agency's review
and has been approved for publication. Note that approval does not signify that the contents
necessarily reflect the views of the Agency. Numeric results in this assessment should not be
interpreted as "actual" risks. No official endorsement should be inferred. Any mention of trade
names, products, or services does not imply an endorsement by the U.S. Government or EPA.
The EPA does not endorse any commercial products, services, or enterprises.
Questions concerning this document or its application should be addressed to:
Sandip Chattopadhyay, Ph.D.
National Homeland Security Research Center
Office of Research and Development
U.S. Environmental Protection Agency
26 W. Martin Luther King Drive, MS NG16
Cincinnati, OH 45268
Phone: 513-569-7549
Fax: 513-487-2555
E-mail: chattopadhyay.sandip@epa.gov
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Table of Contents
Disclaimer i
List of Tables v
List of Figures vii
Acknowledgements viii
Executive Summary ix
Acronyms and Abbreviations xiii
1. Introduction 1
1.1 Purpose and Scope 1
1.2 Report Organization 2
2. Problem Formulation 3
2.1 Scenario Description 3
2.2 Chemical Hazards 4
2.2.1 Dioxins 4
2.2.2 Diazinon 5
2.2.3 Other Potential Chemical Hazards 8
2.3 Livestock Carcass Management Options and Assumptions 8
3. Exposure Estimation 13
3.1 Estimation of Releases 13
3.1.1 On-site Open Burning (Pyre) 13
Air-curtain Burning 21
3.1.2 Burial 26
3.1.3 Composting 30
3.2 Fate and Exposure Estimation Methods 35
3.2.1 Air Dispersion Modeling 36
3.2.2 Concentrations in Surface Soil 43
3.2.3 Soil to Groundwater Transport Modeling 45
3.2.4 Surface Waters and Sediment 50
3.2.5 Bioaccumulation in Fish 51
3.2.6 Terrestrial Plants and Livestock 53
3.2.7 Terrestrial Plants 53
3.2.8 Livestock 54
3.3 Exposure Estimation 54
3.3.1 Characterization of Exposed Individuals 55
3.3.2 Description of Exposed Persons 55
3.3.3 Exposure Durations 55
3.3.4 Human Exposure Factor Values 56
3.3.5 Exposure Estimation 57
4. Results and Discussion 64
4.1 Exposure Assessment 65
4.1.1 Tier 1 Comparison of the Seven Carcass Management Options 65
4.1.2 Tier 2 Ranking of On-site Carcass Management Options 65
4.2 Uncertainty Analysis 75
4.2.1 Chemical Selections 75
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4.2.2 Scale of Mortality 76
4.2.3 Contamination Level 81
4.2.4 Distance from Source 87
4.2.5 Air-curtain Burning Fuel Ratio 88
4.2.6 Chemical Degradation 90
4.3 Uncertainty Summary 91
4.4 Summary of Findings 102
5. Quality Assurance 107
6. Literature Cited 108
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List of Tables
Table ES. 1. Tier 1 Ranking of Livestock Carcass Management Options - Off-site versus On-site
Management Options xi
Table ES. 2. Tier 2 Ranking of Livestock Carcass Management Options xii
Table 2-1. Documented Chemical Emergencies Involving Livestock 6
Table 2-2. Livestock Carcass Management Options Considered for the Exposure Assessment 9
Table 2-3. Containment of Releases from Management Options 10
Table 2-4. Scoping Assumptions for the Chemical Emergency Assessment 11
Table 3-1. Source and Exposure Pathway Assumptions for On-site Open Burning Management Option. 14
Table 3-2. Dioxin Emission Profiles for Carcasses and Woody Fuels 17
Table 3-3. Dioxin Emission Rates from Combustion-based Management Options 18
Table 3-4. Mercury Emission Rates and Bottom Ash Mercury Content for a Coal-fueled Pyre for 100
Cattle Carcasses 19
Table 3-5. Pyre Design Assumptions for the Uncertainty Analysis for Greater Numbers of Carcasses ....21
Table 3-6. Assumptions for On-site Air-curtain Burning of Livestock Carcasses 23
Table 3-7. Air-curtain Burning Assumptions for the Uncertainty Analysis for Greater Numbers of
Carcasses 25
Table 3-8. Assumptions for the On-site Burial of Livestock Carcasses 28
Table 3-9. Assumptions for the Uncertainty Analysis for Burial with Greater Numbers of Carcasses 30
Table 3-10. Assumptions for the Composting Management Option 32
Table 3-11. Estimated Loading of Chemicals to Soil with Compost Application 34
Table 3-12. Assumptions for the Uncertainty Analysis for Composting with Greater Numbers of
Carcasses 35
Table 3-13. Toxicity Equivalency Factors for Dioxins/Furans 38
Table 3-14. Estimated Dioxin/Furans in Air by Distance from Center of Source, Base Case 39
Table 3-15. Estimated Mercury Concentrations in Air by Distance from Center of Source, Base Case.... 40
Table 3-16. Comparison of Dioxin/furan Emissions by Emergency Scenario, Management Option, and
Combustion Material 42
Table 3-17. Chemical Concentrations in Soil from Air Deposition 45
Table 3-18. Chemical Concentration in Soil from Application of Finished Compost 45
Table 3-19. Estimated Diazinon Concentrations in the Groundwater Pathway for the Base-case 47
Table 3-20. Summary of Precipitation Data Used in This Assessment3 49
Table 3-21. Estimated Mercury Concentrations in the Groundwater Pathway for the Base-case 50
Table 3-22. Estimated Total Concentrations of Chemicals in Surface Water 51
Table 3-23. Estimated Chemical Concentrations in Fish from the On-site Lake 52
Table 3-24. Chemical Transfer Pathways for Produce 53
Table 3-25. Chemical Transfer Pathways for Livestock 54
Table 3-26. Mean Exposure Factors for Children and Adults 58
Table 3-27. Typical and High-end Exposure Factor Values for Infant Water Consumption 59
Table 3-28. Ingestion Exposure Estimates for Open Burning, Coal Fueled 61
Table 3-29. Ingestion Exposure Estimates for Air-curtain Burning, Wood and Diesel Fueled 62
Table 3-30. Ingestion Exposure Estimates for Burial 62
Table 3-31. Ingestion Exposure Estimates for Composting — Windrow 63
Table 3-32. Ingestion Exposure Estimates for Composting - Compost Application 63
Table 3-33. Ingestion Estimates for Infants with Formula Made Using Well Water3 for Open Burning,
Burial, and Composting Options 63
Table 4-1. Tier 1 Ranking of Livestock Carcass Management Options - Off-site vs. On-site Management
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Table 4-2. Human Exposure Pathways for Livestock Carcass Management 67
Table 4-3. Toxicity Reference Values 70
Table 4-4. Ranking Ratios for Dioxin Inhalation 70
Table 4-5. Ingestion Exposure Estimates for the Base Case 71
Table 4-6. Mercury Background Concentrations in Soil and Surface Water 73
Table 4-7. Ingestion Ranking Ratios for Infants with Formula Made Using Well Water 73
Table 4-8. Tier 2 Ranking of Livestock Carcass Management Options 74
Table 4-9. Dioxin and Mercury Inhalation Exposure with Increased Numbers of Carcasses 76
Table 4-10. Ingestion Exposure with Increased Numbers of Carcasses 77
Table 4-11. Inhalation Exposure with Varied Levels of Dioxin Contamination 83
Table 4-12. Ingestion Exposure to Dioxin with Varied Levels of Dioxin Contamination 84
Table 4-13. Ingestion Exposure with Varied Levels of Diazinon Contamination 86
Table 4-14. Exposures from Air-curtain Burning with Varied Fuel Ratios and Dioxin Contamination .... 89
Table 4-15. Exposures from Air-curtain Burning with Varied Fuel Ratios and Numbers of Carcasses .... 89
Table 4-16. Percentage of Diazinon Remaining in Finished Compost by Time and Compost pH 90
Table 4-17. Moderate to High Natural Variation in Parameter—Potential Bias from Selected Values 92
Table 4-18. Uncertainty in Parameter Value(s) Selected 95
Table 4-19. Simplifying Assumptions—Effects on Exposure Estimates 98
Table 4-20. Summary of Livestock Carcass Management Options and Mitigation Measures for a
Chemical Emergency Scenario 104
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List of Figures
Figure 3-1. Conceptual model of exposure pathways from on-site open burning of livestock carcasses... 16
Figure 3-2. Conceptual model for exposure pathways from on-site air-curtain burning of livestock
carcasses 22
Figure 3-3. Conceptual model for exposure pathways from on-site burial of livestock carcasses 27
Figure 3-4. Conceptual model of exposure pathways from livestock carcass composting 31
Figure 3-5. Modeled, annual-total deposited mass of chemicals emitted from open-pyre and air-curtain
burner units, using hourly meteorology 37
Figure 3-6. Peak event average dioxins concentrations in air with distance from source 41
Figure 3-7. Peak 1-hour average dioxins concentrations in air with distance from source 41
Figure 4-1. Ranking ratios for base case exposure 72
Figure 4-2. Inhalation exposure to dioxin with increasing numbers of carcasses 78
Figure 4-3. Ingestion exposure to dioxin with increasing numbers of carcasses 78
Figure 4-4. Ingestion exposure to diazinon with increasing numbers of carcasses 80
Figure 4-5. Inhalation exposure to dioxin with varied levels of contamination 83
Figure 4-6. Ingestion exposure to dioxin with varied levels of contamination 85
Figure 4-7. Ingestion exposure to diazinon with varied levels of contamination 87
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Ack i
The following individuals and organization have been acknowledged for their contributions
towards the development and/or review of this document.
United States Environmental Protection Agency (EPA), Office of Research and Development,
National Homeland Security Research Center (NHSRC)
Sandip Chattopadhyay, Ph.D. (Principal Investigator)
Sarah Taft, Ph.D.
Paul Lemieux, Ph.D.
United States Department of Agriculture (USD A), Animal and Plant Health Inspection Service
(APHIS)
Lori P. Miller, P.E.
United States Department of Homeland Security (DHS) Science and Technology Directorate,
Chemical and Biological Defense Division
Michelle M. Colby, D.V.M., M.S.
ICF
Joshua Cleland
Kaedra Jones
Margaret McVey, Ph.D.
Acknowledgements also are due to the following workshop attendees at the International
Symposium on Animal Mortality Management in Lancaster, Pennsylvania:
Robert DeOtte, Ph.D., P.E., P.G., West Texas A&M University
Gary Flory, Virginia Department of Environmental Quality
Mark Hutchinson, University of Maine Extension
Mark King, Maine Department of Environmental Protection
Mike Brown, Ph.D., West Texas A&M University
N. Andy Cole, Ph.D., PAS, ACAN.
Acknowledgements are extended to reviewers who provided many helpful comments on the
report, including:
Scott Wesselkamper, Ph.D., National Center for Environmental Assessment (NCEA), USEPA
Amy Delgado, D.V.M., Ph.D., USD A/National Animal Health Monitoring System (NAHMS)
Kevin Garrahan, Ph.D., NHSRC, USEPA.
Marti Sinclair (CSRA) is acknowledged for technical editing; and quality assurance reviewer
Eletha Brady-Roberts (USEPA) is acknowledged for contributions to this report.
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ExeCU ; .ii-:'"": 'j' /
This exposure assessment does not address a specific emergency scenario, but includes
chemicals of concern representing two categories that have been involved in past events. These
are diazinon, an organophosphate pesticide, and dioxins/furans, which are persistent organic
pollutants. Potential chemical emergency scenarios affecting livestock could include intentional
criminal or terroristic acts such as chemical poisoning of food supplies or sabotage of
agricultural production or commodity markets. The contamination could be unintentional as
well. Examples of unintentional chemical emergencies include industrial accidents, accidental
contamination of feed or other agricultural supplies, and transportation-related accidents (e.g.,
tanker truck or rail car spillage).
The livestock carcass management options included in this exposure assessment are seven well-
established methods with sufficient capacity for large-scale carcass management: on-site open
burning (pyre), on-site air-curtain burning, on-site unlined burial, on-site composting, off-site
fixed-facility incineration, off-site landfilling, and off-site carcass rendering.
With the three off-site options, all releases to the environment (e.g., incinerator emissions to air,
rendering facility discharge to surface water) are restricted by, and are assumed to comply with,
applicable U.S. federal regulations. Therefore, chemical releases from off-site commercial
facilities are assumed to be adequately controlled. Because the chemical exposures with the off-
site options are not quantitatively assessed, they are not individually ranked with the on-site
options.
As shown in Table ES.l, the off-site options, collectively, are compared with the on-site options
in the first tier of a two-tier assessment. The first column of Table ES.l shows that the off-site
options are ranked higher (i.e., Rank 1) than the on-site options (i.e., Rank 2) because of their
greater level of pollution control under applicable regulations. The top section of Table ES.2
shows that off-site options are not ranked further relative to each other, because they are not
quantitatively assessed.
In the Tier 2 assessment, for the on-site management options, rankings are based on a
quantitative assessment in which different methods are applied to estimate combustion releases
to air and subsequent deposition to ground level, and to assess fate and transport in surface and
subsurface soils, groundwater, and an on-site lake. The assessment is based on carcass
management at a hypothetical site, using a standardized set of environmental conditions (e.g.,
meteorology), assumptions about the scale of mortality, and how the carcass management
options are designed and implemented.
The findings for the Tier 2 chemical assessment are summarized in the bottom section of Table
ES.2. Potential exposures are ranked relative to one another based on ratios of exposure
estimates to applicable toxicity reference values. As shown in Table ES.l and ES.2, the
exposures and relevant exposure pathways for each management can differ by chemical. This is
due to chemical-specific fate properties, such persistence and mobility in different media. In
addition, site-specific circumstances (e.g., the presence of a drinking water well) can affect
which exposure pathways are relevant at a site. For these reasons, there is not "best" carcass
management option for every event.
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This report provides information to compare options and support decision-making in the event of
actual chemical emergencies. It provides a scientifically based understanding of the potential
environmental releases and exposure pathways for each option, and information to evaluate the
likely relative contribution of specific exposure pathways based on chemicals of concern, site
settings, and steps in carcass management processes. The assessment also can aid selection and
priority setting for mitigation and best management practices.
Because well-informed carcass management decisions are site-specific, the exposure estimates
presented in this report should not be interpreted as "actual" exposures associated with the
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1. Introduction
Proper management of livestock carcasses following large-scale livestock mortalities protects
humans, livestock, and wildlife from chemical and biological hazards; maintains air, water, and
soil resources; protects ecological resources and services; and enhances food and agricultural
security. In support of the National Response Framework, the U.S. Department of Homeland
Security Science and Technology Directorate funds research in collaboration the U.S.
Environmental Protection Agency's (USEPA's) Office of Research and Development, Homeland
Security Research Program (HSRP) and the U.S. Department of Agriculture's (USDA's) Animal
and Plant Health Inspection Service (APHIS) to support the proper management of animal
carcasses following major environmental incidents. Mass livestock mortalities can result from a
natural disaster, foreign animal disease (FAD) outbreak, chemical or radiological incident, or
other large-scale emergencies. As a product of the collaborative research between USEPA and
USD A, this report evaluates livestock carcass management options following a chemical
emergency through a comparative exposure assessment. This assessment helps to inform a
scientifically-based selection of environmentally protective methods in times of emergency.
Preceding phases of this project assessed exposures following natural disaster and foreign animal
disease outbreaks. A separate report examines exposures following radiological incidents.
Established by the Department of Homeland Security, the National Response Framework is a
single comprehensive approach to domestic incident management.1 The Framework provides a
context for Department of Homeland Security and other federal agencies to work with each other
and with communities to prevent, prepare for, respond to, and recover from hazards such as
natural disasters, acts of terrorism, and pandemics.
In support of the National Response Framework, the Department of Homeland Security is
funding research in collaboration with the United States Environmental Protection Agency's
(USEPA's) Homeland Security Research Program and the United States Department of
Agriculture's (USDA's) Animal and Plant Health Inspection Service (APHIS) to assure the
proper management of animal carcasses following major environmental incidents such as a
natural disaster, foreign animal disease (FAD) outbreak, chemical or radiological contamination
incident, or other large-scale emergencies. Proper management of livestock carcasses following
such emergencies is needed to protect humans, livestock, wildlife, and the environment, and to
enhance food and agricultural security.
1.1 Purpose and Scope
This report focuses on relative exposures and hazards for different livestock carcass management
options in the event of a chemical emergency. Selection of chemical agents for the assessment is
described under Problem Formulation in Section 2.
1 Information about the National Response Framework is available at https://www.fema.gov/national-response-
framework
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2. Problem Forimi
Problem formulation for the exposure assessment defines the scope of the assessment including
the chemical emergency scenario, scale of mortality, carcass management activities, and
chemical hazards. Problem formulation for this assessment builds on and uses many of the same
methods and assumptions as the previous assessments of managing livestock carcasses following
a natural disaster (USEPA 2017) and foreign animal disease (FAD) outbreak (USEPA 2018).
2.1 Scenario Description
As in exposure assessments for the natural disaster and FAD scenarios, the base case for this
assessment assumes 100 cattle carcasses weighing 50 U.S. tons (45,359 kilograms [kg]) for all
management options. Because some cattle ranches have more than 100,000 head, the number and
total weight of carcass could be much higher than the base case. An uncertainty analysis
presented in Section 4.2 examines how exposures would differ with 500, 1000, and 10,000
carcasses.
To focus the assessment on outcomes of carcass management, the carcasses are assumed to be
intact when promptly collected for management (i.e., within 48 hours [hr]), and management of
the carcasses is not impeded by other impacts (e.g., damage to or availability of resources and
equipment) of the emergency scenario.
To be consistent with the previous assessments, this assessment uses the same site setting and
exposed individuals. The humans potentially exposed include adult and child onsite (farm)
residents and workers participating in carcass management. The farm includes agricultural fields
and a home garden that supplies the farm residents' fruits and vegetables. The residents also
produce their own livestock food products at home, including beef, dairy, pork, poultry, and
eggs; fish for consumption are caught in an on-site lake. Farm residents obtain drinking water
from an on-site groundwater well. Further description of these assumptions is provided in the
natural disaster assessment report (USEPA 2017).
Potential chemical emergency scenarios could include intentional criminal or terroristic acts such
as chemical poisoning of food or water supplies, sabotage of agricultural production or
commodity markets, or use of a chemical warfare agent. The contamination could be
unintentional as well. Examples of unintentional chemical emergencies include industrial
accidents, accidental contamination of feed or other agricultural supplies, and transportation-
related accidents (e.g., tanker truck or rail car spillage).
Kosal and Anderson (2004) reviewed past incidents of livestock feed poisonings and concluded
that feed security is a vulnerable target for terrorism. For example, a small amount of a very
toxic chemical (e.g., a bag of pesticide) added at a single point in in the feed supply can lead to
very rapid and wide distribution of the chemical with potentially severe health or economic
consequences.
Table 2-1 describes 10 incidents in which livestock have been contaminated with chemicals.
These incidents include contamination from an industrial accident, accidental contamination of
livestock feed, and intentional poisoning of livestock through contaminated drinking water or
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feed. Three of the incidents in Table 2-1 resulted in large numbers of cattle deaths from toxic
chemical exposure.
The scenario for this assessment does not necessarily require a specific type of emergency - if
the assessment begins after the chemical emergency has killed the livestock or contaminated
animals are culled, the event itself has no bearing on the exposure modeling approach. By this
same logic, natural disaster assessment (USEPA 2017) did not include a specific disaster
scenario. However, information on livestock contamination from actual chemical emergencies is
relevant to selecting chemicals of concern.
2.2 Chemical Hazards
Virtually any toxic compound could affect livestock through a conceivable chemical emergency
scenario. Considerations used to choose chemicals for this assessment included:
¦ Availability of chemical property and other data (i.e., biotransfer factors) needed for fate
and transport modeling;
¦ Availability of toxicity reference values (TRVs) with which to assess the potential for
exposure to result in adverse health effects;
1 Relative toxicity as indicated by comparing TRVs among chemicals;
¦ Environmental persistence as indicated by media half-life values; and
¦ For pesticides, current registered pesticide uses (i.e., not banned).
Some or all of these criteria are met by all of the chemicals involved in the ten incidents
described in Table 2-1. Of these ten chemicals, four involved dioxins, three involved pesticides,
two involved polychlorinated or polybrominated biphenyls, and one involved cyanide.
2.2.1 Dioxins
Dioxins, unless separately identified in this report, include polychlorinated dibenzo-p-dioxin
(PCDD) compounds and polychlorinated dibenzofurans (PCDFs). Collectively, these groups of
similarly structured compounds, called congeners, are among the so called "dirty-dozen"
persistent organic pollutants (POPs) subject a 2001 United Nations treaty. The United States and
other signatories to the Stockholm Convention agreed to reduce or eliminate the production, use,
and/or release of these chemicals.
Dioxins are hydrophobic (also called lipophilic), resistant to metabolism, and persistent in the
environment (USEPA 1994, 2012). Their toxicity depends on the degree of chlorination and
which functional sites on the molecule are substituted with chlorine (i.e., the congeners with
chlorine substituted at the 2,3,7, and 8 positions are the toxic isomers), and 2,3,7,8-
tetrachlorinated dibenzo-p-dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD]) serves as the
index chemical for relative toxicity factors (USEPA 2010).
In air, dioxins can travel long distance and deposit to soils and surface waters. Because they
generally have very low solubility and a high affinity for organic matter, in surface water they
tend to either volatilize to air or adsorb to suspended particles that eventually settle to the
bottom. Dioxins can bioaccumulate in the fatty tissues of fish and other animals and can be of
concern in milk products from exposed cattle and goats because of the high lipid content of milk.
In aquatic communities, dioxins can bioaccumulate through successive steps in the food web,
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resulting in higher concentrations in the top trophic level fish. Also because of their low
solubility and tendency to sorb to organic material, dioxins do not travel far in subsurface soil
and are not generally associated with groundwater contamination. Based on these properties,
human exposures to dioxins/furans from carcass management options are expected to occur
primarily through air transport and deposition pathways and not through leaching from storage
piles, burial trenches, or compost windrows.
The level of dioxin/furan contamination in carcasses assumed for the assessment is based on the
maximum level observed in beef during the 2008 contamination incident in Ireland described in
Table 2-1. That level was 400 times the applicable European Union dioxin limit of 0.2 ng toxic
equivalency quotient [TEQ]/g fat, or 80 ng[TEQ]/g fat (Pogatchnik 2008). Assuming that a
1,000-kg adult beef carcass is 30% fat (Topel and Kauffman 1988) and that dioxins are found
only in the fat, the total body burden of dioxin based on the 2008 incident in Ireland is 24 mg per
carcass. This is the base-case level of contamination assumed for the assessment. Contamination
levels one order of magnitude higher and lower than the base-case level are evaluated in the
uncertainty analysis presented in Section 4.2.
2.2.2 Diazinon
Because most dioxin congeners have very low mobility in soil and groundwater, the assessment
also includes a chemical that might be expected to leach to groundwater and meets criteria listed
above. Based on the incidents included in Table 2-1, the assessment includes a pesticide,
specifically diazinon. Diazinon is organophosphate insecticide (other organophosphate pesticides
include chlorpyrifos, fenamiphos, malathion, disulfoton, and ethyl parathion). These are among
the most widely used pesticides, with USEPA registered uses in agriculture, homes, gardens, and
veterinary practices. All organophosphate insecticides can cause acute and subacute toxicity by
affecting the functioning of the nervous system (Roberts and Reigart 2013). Considering the
selection criteria above, the specific organophosphate insecticide for the assessment is diazinon.
Diazinon has been limited to agricultural uses since 2004. It is considered to be of moderate
toxicity compared to other organophosphates. It is found in all environmental media without a
pronounced tendency for any particular one (ATSDR 2008). Spray applications and
volatilization can release diazinon to the air, making inhalation exposure is possible. It is
moderately mobile in soils and groundwater under certain conditions. In surface water, it does
not bioconcentrate significantly in aquatic food webs (ATSDR 2008). It is not considered a
persistent organic pollutant because it is degraded in time by abiotic and biotic processes.
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Persistence varies by medium and environmental conditions. For example, diazinon half-lives in
sandy loam soil are 66, 209, and 153 days at pH values of 4, 7, and 10, respectively (Schoen and
Winterlin 1987).
The base-case level of diazinon contamination for the assessment is a body burden of 5 g per
carcass. This is based on a lethal dose of 20-25 mg/kg (Junquera 2017). For a 1,000-kg cow, the
body burden associated with the upper bound lethal dose would be 25,000 mg (25 g). A sublethal
dose of 5 g per carcass (20% of the lethal dose) is selected as the base-case body burden. Body
burdens of 0.5, 50, and 500 g per carcass are included in the uncertainty analysis (Section 4.2).
2.2.3 Other Potential Chemical Hazards
When coal is used as a fuel for combustion-based carcass management, naturally present
mercury will be emitted. Although coal combustion was included in the natural disaster
assessment, mercury was not included in the emissions data used for the assessment. Data to
include mercury now have been obtained and are included in this assessment. Exposures to
mercury estimated in this report would apply equally to the previously assessed scenarios.
The exposure assessment does not include chemicals (e.g., trace metals) that are naturally present
in livestock, veterinary drugs, or other chemicals unrelated to the chemical emergency. Human
exposure to chemicals naturally present in cattle was evaluated in the exposure assessment for
the natural disaster scenario (USEPA 2017), and exposure to those chemicals would not differ
when the carcasses are in the chemical emergency scenario.
The natural disaster assessment also evaluated exposure to chemicals produced as combustion
products from carcasses and fuels, specifically dioxins, polycyclic aromatic hydrocarbons
(PAHs), and various metals. Production of, and exposure to, the combustion products would not
differ with the natural disaster and chemical emergency scenarios, and it is not necessary to
repeat the assessment for those chemicals. However, dioxins from combustion are included in
this assessment because the chemical emergency scenario includes contamination with dioxins,
as discussed further in Section 2.2.1. As a result, the assessment examines the total exposure to
dioxins following the chemical emergency scenario.
This assessment does not include exposure to microbes. The natural disaster scenario assessment
(USEPA 2017) evaluated exposures to microbes that are typically found in healthy cattle, and the
findings of that assessment would apply equally to the chemical emergency scenario.
2.3 Livestock Carcass Management Options and Assumptions
The carcass management options included in this assessment are the same seven well-established
methods included in the exposure assessments for the natural disaster and FAD outbreak
scenarios. These options, which are listed in Table 2-2, can be distinguished as occurring on-site
or off-site. The on-site management options (i.e., open burning, air-curtain combustion, burial,
and composting) typically are performed on the livestock owner's property if a suitable location
is available. Therefore, residues from carcass management including from carcasses and fuels,
woodchips, or other management materials could remain on-site after the carcass management
operation is complete.
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)sure Estimation
Section 3.1 describes the approaches used to estimate chemical releases to air and to soil for all
management. Section 3.2 describes the modeling methods employed for specific environmental
media for these scenarios. Section 3.3 describes how the estimated concentrations of chemicals
in exposure media (e.g., air, drinking water, fruits and vegetables) are used to estimate exposure
doses for adults and children.
3.1 Estimation of Releases
This section describes estimated chemical release rates from the four on-site management
options: open-pyre burning (Section 3.1.1), air-curtain burning (Section 3.1.2), unlined burial
(Section 3.1.3), and composting (Section 3.1.4).
In-slte Open Burning (Pyre)
The conceptual model for the on-site open burning (pyre) management option is presented in
Figure 3-1, and further assumptions for open burning are provided in Table 3-1. With this option,
the carcasses are burned in a single pyre resulting in release of gases and particles. When
constructed according to USD A standard operating procedures (USD A 2005), combustion
should be complete within 48 hours. Ash could be managed on site or removed to an off-site
landfill. For this exposure assessment, the ash is managed on site, specifically by being buried or
covered with clean soil in place (i.e., over the area of ground on which the pyre burned). The
fuels used to promote burning of the carcasses also will release some chemicals in vapor and
particulate-phase to air while leaving other chemicals in the residual ash. Further details about
the pyre design, including fuel types and quantities and ash management, are provided in the
report for the natural disaster assessment (USEPA 2017).
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550°C (1022°F), the pyre will decompose diazinon, which has a flash point of 82.2° C (180° F)
(NIOSH 2016), to various aliphatic organophosphates, substituted pyrimidines, and hydrogen
cyanide, phosphorus oxides, sulfur oxides, and nitrogen oxides. Because incineration destroys
dioxins only at temperatures above 982°C (1800°F) (NRC 2000), none of the dioxin body burden
is destroyed by the pyre. Dioxins are highly lipophilic and all of the dioxin contamination in the
carcasses is assumed to be in fat, which burns completely leaving no ash. With these
assumptions, all of the dioxin contamination in the carcasses is emitted to air from the pyre.
Rates of dioxin emission to air (in g/sec) are estimated separately for carcasses and woody
materials (i.e., timbers, kindling, straw) used to build and fuel the pyre. For each of these,
particulate and vapor phase emissions are estimated separately, and the total emissions of each
phase is divided among 17 dioxin/furan congeners. The emissions are separated by phase and
congener using congener emissions profiles from the literature. The dioxin profile for the woody
materials, shown in Table 3-2, was developed for the natural disaster scenario assessment and is
further documented along with emission rates in Appendix B USEPA (2017).
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Natural Disaster
Mortalities
On-site Transportation
Combustion
. ¦
Open Burning
r
Burial of ash
in place
Air
Particle
Deposition,
Stomatal Uptake
Wet & Dry Particle
Deposition;
Diffusive Vapor
Exchange
Sedimentation,
Resuspension, &
Diffusive Exchange
Wet & Dry
Deposition
Erosion
& Runoff
Terrestrial
Plants
Root uptake
Leaching
Surface Water
Recharge
Inha ation
Incidental
Ingestion
Ingestion
Livestock
Ingestion
Water
Ingestion &
Inhalation
u m a nT^) -
Ingestion
Ingestion
Inhalation
Uptake,
bioaccumulation
Aquatic
Life
Uptake,
bioaccumulation
Figure 3-1. Conceptual model of exposure pathways from on-site open burning of livestock carcasses.
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concentrations of combustion-produced dioxin in bottom ash (i.e., ash remaining on the ground)
from open burning of livestock carcasses. Consequently, dioxin concentrations in bottom ash are
estimated by combining concentrations known to be present as combustion products from each
of the different fuel types. The resulting concentration of total dioxins in fuel ash 7.8E-02 (J,g/kg
and 1.2E-02 (J,g/kg in all pyre ash. Further details about dioxin contamination in combustion ash
are available in USEPA (2017).
Uncertainty Analysis Design for Open Burning
The uncertainty analysis varies the open-burning base-case scenarios by (1) varying the level of
dioxin and diazinon contamination in the carcasses and (2) varying the number of carcasses.
To vary the level of dioxin contamination, the base-case body burden of 24 mg per carcass (see
Section 2.2.1) is decreased to 2.4 mg per carcass an increased to 240 mg per carcass. All other
attributes of the base-case are unchanged in the uncertainty analysis. Diazinon contamination is
not varied of the combustion-based options because it is entirely consumed by combustion.
To evaluate how exposures vary with the scale of mortality, the base-case number of carcasses
(i.e., 100) is increased to 500 and 1,000 carcasses. Increasing the scale of mortality increases the
size of the pyre, contaminant emission rate, amount of ash and ash disposal area. Table 3-5
summarizes the sizes and orientation of the pyres for each number of carcasses evaluated.
Management of 10,000 carcasses is evaluated for burial and composting, but not for the
combustion-based options (i.e., open-burning and air-curtain burning). Feasibility at this scale is
unlikely based on the land area and the resources that would be required. For example, pyre
construction would require 5,000 U.S. tons of coal and 30,000 timbers. Although mortality at
this scale, or greater, is possible, carcass management probably would require a combination of
management options.
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Natural Disaster
Mortalities
I On-site Transportation
Combustion
Air Curtain Burning
Air
Particle
Deposition,
Stomatal Uptake
Terrestrial
Plants
Root uptake
Ingestion
Inhalation
Livestock
Wet & Dry Particle
Deposition;
Diffusive Vapor
Exchange
Burial of ash
in place
Wet & Dry
Deposition
I Erosion
I.& Runoff
Incidental
Ingestion
Ingestion
Leaching
Uptake,
bioaccumulation
Surface Water/
Recharge
Sedimentation,
Resuspension, &
Diffusive Exchange
Aquatic
Life
Groundwater
Ingestion &
Inhalation
Water
Uptake,
bioaccumulation
Ingestion f Ingestion
Human
Inhalation
Figure 3-2. Conceptual model for exposure pathways from on-site air-curtain burning of livestock carcasses.
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Releases of Combustion Products to Air from Air-curtain Burning
Releases to air from air curtain burning are estimated using the same approach as described
above for open burning. Differences in determining emission rates for the two combustion
options are fuel types and amounts, combustion temperatures, and the size and configuration of
the combustion sources. Emissions rates for fuels for the base-case scenario are the same as used
for the natural disaster assessment (USEPA 2017). Air-curtain burning is fueled with scrap wood
at a 4:1 ratio with the carcasses by weight. Dioxin emissions from the wood fuel are calculated
with the congener profile included in Table 3-2. Dioxin emission from carcass contamination are
the same as for open burning because the amount of contamination and burn duration are the
same, and the combustion temperature is below the temperature at which dioxins are destroyed
(NRC 2000). Emission rates, including dioxins from carcasses and fuel combustion, are provided
in Table 3-3.
No mercury is emitted from air curtain burning because coal is not used as a fuel, and no
diazinon is emitted because it is consumed by combustion. The combustion temperature and the
size and configuration of the air-curtain burner processing chemical-impacted carcass are the
same as developed for the natural disaster assessment and are summarized in Table 3-6.
Leachii n Air-curtain Burner Ash
Exposures are not expected from leaching from air-curtain burning combustion ash. Dioxins
have very low mobility in soil due to their low solubility and their tendency to partition to
organic matter. Modeling of contaminant release, including leaching from ash, showed
essentially negligible dioxin reaching groundwater(USEPA 2017). Neither diazinon nor mercury
are present in the air curtain burner ash as discussed previously.
Uncertainty Analysis for Air-curtain Burning
Uncertainty analyses in Section 4.2 examine varying levels of dioxin contamination and scales of
mortality as discussed above for open burning. The uncertainty analysis for the level of dioxin
contamination uses the same range of body burden values used for open burning.
The uncertainty analysis for the scale of mortality affects assumptions about the duration of
combustion and the size and orientation of air release sources. Like the related sensitivity
analysis for open burning, the sensitivity analysis considers air-curtain burning of 100, 500, and
1,000 carcasses. As described above, the base-case includes 100 carcasses burned over 48 hours
in a single air-curtain burner unit. Managing larger number of carcasses could be accomplished
by a using a single unit for a longer time, using multiple units simultaneously, or a combination
of these options. Longer durations are limited by the progressive decomposition of the carcasses.
As reported by Ellis (2001), within 7 to 10 days after death the decomposed carcasses lose
structural integrity making them difficult to move. Based on this, burn durations greater than 10
days are considered infeasible for this assessment.
Assuming the base-case burning rate, (i.e., 48 hr to burn 100 carcasses with a single unit), some
options for managing 500 carcasses include a single unit operating for 10 days, 2 units operating
for 5 days, 5 units operating for 2 days, and ten units operating for a single day. Options with
multiple units become increasingly infeasible as the number of units increases due to cost and
-------
An additional sensitivity for air-curtain burning analysis examines the wood fuel to carcass ratio.
For the base-case, four tons of wood fuel are burned for each ton of carcasses (i.e., a 4:1 ratio).
This assumption represents the conservative upper bound of values identified from the literature
(USEPA 2017). However, available sources (e.g., NABCC 2004; SKM 2005) indicate that lower
fuel ratios are more typical. Therefore, the uncertainty analysis examines exposures with a fuel
ratio of 2:1.
3.1.2 Burial
Figure 3-3 provides an overview of the conceptual model for the on-site livestock carcass burial
option. In this option, livestock carcasses are placed in an unlined, excavated pit or trench in a
suitable location on site.3 The carcasses are covered with clean fill creating a mound over the site
that will flatten over time as the carcasses lose fluids and other mass during decomposition.
Although access to the site is not restricted, it will not be used in the relatively near future for
crop farming or raising livestock; it will be seeded over for soil stabilization.
3 Mass livestock burial trenches might be created off-site following some natural disasters. It is assumed that in those cases, state
and federal representatives would participate in selection of location(s) with appropriate conditions (e.g., high over
groundwater, far from any groundwater wells).
-------
Natural Disaster
Mortalities
Terrestrial
Plants
Diffusion through raw sOH
Stpmwfff'UpfaJkif
On-site Burial
leaching from to
subsurface sort and
Groundwater
Motown
Ingestion
Subsurface Soil
tesKfong
Surface Water
Recharge
Groundwater
Livestock
ItiQeviQft
Uptake,
bbacctimuiation
Sedimentation,
Remapemkm, &
Diffusive Exchange
pi;
m
A
Uptake,
Aquatic
life
bfaocCttrmrfOlktn
tngeftioft &
bthaknkm tnbatatkm
tfiQtXkm /
—-—H Humans
Water
ingestion
Figure 3-3. Conceptual model for exposure pathways from on-site burial of livestock carcasses.
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the abdomen in a livestock carcass typically bursts 3 to 4 days after death, with leachate releases
occurring 3 to 7 days after death. Before the abdomen bursts, liquid matter unrelated to
decomposition (e.g., feces, urine, blood, ingesta, serum, saliva) can be released (UM-CAHFS
2014). Because liquids could be released at varying but unknown rates throughout the first post-
mortem week, the total amount released during the first week is averaged to calculate a daily
rate. For 100 carcasses, 7,500 L/week divided by 7 days is 1,070 L per day. This equates to 10.7
L/day per carcass. For the remaining duration of the first two months (i.e., days 8 through 60),
the average volume of leachate is 1.4 L per day per carcass.
Exposure is calculated based on chemical leaching from the carcasses during the first two
months. Because the fluid release is highest during the first week after death, contributions to
exposure are calculated separately for leaching during the first week and for weeks 2 through 8.
Daily average chemical concentration in leachate during each period are calculated by dividing
the total amount of chemical released per day during each period divided by the daily leachate
volumes described above. Chemical releases per day per carcass are calculated by multiplying
the body burden of contaminant by the percentage of carcass mass released as fluid per day
during the time period. For the base-case, an estimated 117.9 mg of diazinon are released per
carcass per day during the first week, and 15.6 mg of diazinon are released per carcass per day
during weeks 2 through 8. Throughout the first two months, the concentration of diazinon in
fluid released is 11 mg/L.
The chemical release from burial the burial trench is estimated only for diazinon; mercury from
coal is not present for air-curtain burning and dioxin leaching is not estimated due to its low
mobility in subsurface soil and water.
Uncertainty Analysis for Burial
Sensitivity analyses for the burial option evaluate varied diazinon body burdens and scales of
mortality. As discussed in Section 2.2.2, the base-case diazinon body burden is 5 g. The
uncertainty analysis evaluates leaching to groundwater from burial of 100 carcasses with body
burdens of 0.5, 5, 50, and 500 g per carcass per carcass.
The uncertainty analysis evaluates burial of 100, 500, 1,000, and 10,000 carcasses, all with the
base-case body burden (i.e., 5 g diazinon per carcass). Table 3-9 summarizes the assumptions for
this uncertainty analysis.
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On-site Transportation
Diffusion from Compost
Windrows
Leaching from
Compost Windrows
Stomatal
Uptake
Application of Finished
Com post to Soil
Terrestrial
Plants
Root uptake
Uptake,
bioaccumulation
Erosion & Runoff
Aquatic
Life
Sedimentation,
Resuspension, &
Diffusive Exchange
Surface Water
Recharge
Leaching
Uptake,
bioaccumulation
Inhalation
Incidental
ingestion
Ingestion
Livestock
Ingestion
Ingestion &
Inhalation
Ingestion
Ingestion
Humans
Inhalation
Air
Well
Water
Composting
Natural Disaster
Mortalities
Figure 3-4. Conceptual model of exposure pathways from livestock carcass composting.
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plan. Transport of chemicals from the compost application site can occur by runoff/erosion to the
lake.
Leaching to Groundwater from the Windrow
The approach to estimating leaching to the ground from the windrow is similar to the approach
described in Section 3.1.3 for leaching from the burial trench. For the same number of carcasses
and level of contamination, the amount of liquid released and the concentration of diazinon in the
leachate is the same for buried and composted carcasses. While all of the leachate from burial
seeps into the soil below the burial trench, most of the leachate from composting is absorbed by
bulking material. As an absorbent, the bulking material allows water to evaporate while the bulk
of the minerals and non-volatile organic and inorganic compounds remain in the bulking
material, which later is mixed into the finished compost.
Using corn stalks as the sorbent bulking material, researchers including Glanville et al. (2006)
and Donaldson et al. (2012) found the volume of leachate from experimental compost windrows
to be no more than 5% of precipitation falling (500-600 mm) on the windrows (i.e., the bulking
material facilitated evaporation of water back into the air for 95% of the rainfall). Based on these
findings, the assessment assumes that 5% of the liquid released from the carcasses seeps to the
ground below the windrow. Contaminants in the remaining 95% of the leachate remain in the
windrow.
Using the approach and data described above, the windrow releases 0.53 L per day per carcass
during the first week after death and 0.07 L per day per carcass during weeks 2 through 8. The
amounts of diazinon released per carcass per day are 5.9 mg and 0.8 mg during the first week
and weeks 2-8, respectively. Throughout the first two months the concentration of diazinon in
leachate released from the windrow is 11 mg/L.
Application of Compost to Soil
The determination of the appropriate rate of finished compost application to soil (i.e., tons of
compost per acre) and the total area of soil receiving compost assume the nitrogen (N) content of
the compost is at an agronomic rate, ostensibly following the farm's nutrient management plan.
An agronomic rate of application occurs when the nutrient content added to the soil does not
exceed the uptake capabilities of crops to be planted at the site, nor does it result in fertilizer
"burn" (i.e., leaf and root damage) (NABCC 2004). Agronomic fertilization rates also help to
protect air, soil, and water quality. For example, nutrients supplied in excess of the agronomic
rate can run off or leach to surface water, causing eutrophication, or to groundwater, degrading
its quality.
Compost volume and agronomic application rate calculations for the compost of 100 cattle
carcasses were performed for the exposure assessment for the chemical attack scenario, and the
details of those calculations are presented in the assessment report (USEPA 2017). Based on
those calculations, the estimated area over which the finished compost can be applied is about 4
hectares (ha) (-40,000 m2 or 10 acres [ac]). This amounts to an application rate of about 24 dry
tonnes of compost per hectare. In the compost application area, the resulting loading rates (g/m2)
and soil concentrations (mg/kg) for dioxins and diazinon are shown in Table 3-11.
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3.2 Fate and Exposure Estimation Methods
The methods described in this section simulate processes that occur between the carcass
management units and the locations where people are exposed. These processes determine
chemical concentrations in air, soil, groundwater, surface water, aquatic biota, and agricultural
products.
3.2.1 Air Dispersion Modeling
Dispersion of airborne chemicals is modeled with the AMS/USEPA Regulatory Model air
dispersion model (AERMOD) (version 14134).5 AERMOD calculates air concentrations and
rates of wet, dry, and total deposition to the ground resulting from particle and vapor phase
chemical releases from the combustion management options. The assessment assumes emissions
originate at the height of the pyre or air-curtain burner and that emissions occur at a continuous
rate throughout the duration of combustion. Emission rates for dioxins and mercury are provided
in Tables 3-3 and 3-4, respectively. However, air curtain burning is not in Table 3-4, which
details mercury emissions, because coal is not used as a fuel.
AERMOD calculates average hourly air concentrations and deposition rates for each hour during
the full year of meteorological data (described in USEPA 2017). All estimated air concentrations
are in units of ng/m3, and deposition rates are in units of g per m2 per hour. Concentrations and
deposition rates are calculated at 304 locations on a radial grid centered on the source: each of
the 16 radial lines is separated by 22.5° and includes 19 locations (at 0.1 km intervals from the
source to 1 km, and at 1 km intervals thereafter to 10 km). The radial grid is shown in Figure 3-5.
Dioxins and furans emitted from open burning and air-curtain burning include 17 compounds
(i.e., congeners) with similar chemical structures and toxic health effects. The compounds are
modeled individually and then totaled to present results as total dioxins. Although similar, the
individual compounds differ in their toxic potency. Previous researchers developed relative
toxicity equivalency factors (TEF) that express the toxicity of each compound relative to an
index compound (2,3,7,8-TCDD). The compound-specific concentrations are multiplied the
TEFs, which are presented in Table 3-13, before totaling to a single 2,3,7,8-TCDD equivalent
(TEQ) concentration (i.e., total dioxins/furans).
Because the base-case combustion options are assumed to last 48 hours, the hourly results are
processed to find the highest 48-hour average air concentrations during the year for each
location. For comparison purposes, all results are also recorded for 1-hour averaging periods.
These results are presented in Table 3-14 for dioxins and for mercury in Table 3-15. Peak 48-
and 1-hour average dioxin concentrations in air are plotted in Figures 3-6 and Figure 3-7, at
distances from 100 m to 10 km from the source.
5 Complete documentation of AERMOD and related tools, including AERMOD, AERMET, and AERSURFACE, is available at
.
-------
48-hour Total Dioxin (TEQ)
Deposition (mg/m2)
¦
4.4E-11 - 8.7E-09
¦
8.8E-09 - 2.9E-08
¦
3.0E-08 - 6.2E-08
¦
6.3E-08 - 1.2E-07
¦
1.3E-07 - 2.2E-07
2.3E-07 - 3.5E-07
3.6E-07 - 5.3E-07
¦
5.4E-07 - 9.1E-07
¦
9.2E-07 - 2.0E-06
¦
2.1E-06 - 6.1 E-06
¦¦¦V
"/!
¦
¦
C
V-:.
¦ ¦
W
¦
¦
5 10 km
i , i I
0 500 1,000 m
Figure 3-5. Modeled, annual-total deposited mass of chemicals emitted from open-pyre and
air-curtain burner units, using hourly meteorology.
-------
M
3 1.6E-06
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8.0E-07
6.0E-07
4.0E-07
Open Burning
-Air-curtain Burning
Distance from Source (Km)
Figure 3-6. Peak event average dioxins concentrations in air with distance from source.
C
o
u
c
'x
o
5
t-i 2.0E-06
^-Open Burning
^Air-curtain Burning
Distance from Source (km)
Figure 3-7. Peak 1-hour average dioxins concentrations in air with distance from source.
-------
soil with Equation 3.1 (below) from USEPA's (2005)HHRAP for Hazardous Waste Combustion
Facilities 6 This Human Health Risk Assessment Protocol (HHRAP) is a peer-reviewed
environmental modeling framework developed, refined, and used by USEPA's Office of
Resource Conservation and Recovery (formerly the Office of Solid Waste) to estimate chemical
transport of chemicals released to air from a point source and their subsequent fate and transport
in soil, surface water, and terrestrial plants and animals. In Equation 3.1, the total chemical
deposition or addition with compost is mixed with the surface soil layer. The resulting estimate,
Cs, is the concentration of chemical per kg bulk soil at the deposition location.
("s = (vDpt) / (Zs * BD) (Eqn. 3.1)
where:
Cs = Concentration of chemical in surface soil, from deposition, mg/kg
vDpt = Total chemical deposition or addition, mg/m2
Zs = Soil mixing zone depth (m)
BD = Soil bulk density, kg/m3
Soil parameter values used in these calculations are HHRAP default assumptions. Specifically,
HHRAP provides default assumptions for bulk-soil density at 1,500 kg per m3 (93.6 pounds [lb]
per ft3) (surface soil, unsaturated) and mixing depth assumptions. For deposition form air,
HHRAP assumes that deposited particles mix with the top 0.02-meter (m) (0.79 inches [in]) soil
layer. Compost is assumed to be tilled into the soil to a depth of 20 cm. Tables 3-17 and 3-18,
respectively, present the estimated chemical concentration in soil from air deposition (i.e., from
the combustion-based options) and compost application.
The exposure assessment does not include direct exposure by humans to contaminants in soil.
However, the soil contaminants are taken up by plants and livestock products consumed by farm
residents. In addition, a portion of the soil eroded from the compost application site reaches the
on-site lake where it may enter the aquatic food web, including recreationally caught fish
included in the residents' diet. Except for leaching to groundwater, which is discussed in Section
3.2.3, chemical losses from soil (e.g., runoff, erosion, plant root uptake) are calculated with
equations from HHRAP (USEPA 2005). Further details about HHRAP formula and assumptions
used for this assessment are provided in Appendices D through G of USEPA (2017).
6 Further information on HHRAP is available at: https://archive.epa.gov/epawaste/hazard/tsd/td/web/html/risk.html.
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¦ Compost windrows leaking leachate from the carcasses that is not absorbed by the bulking
material; and
¦ Buried combustion ash that leaches chemicals to infiltrating precipitation.
The conceptual models for all four on-site management options include groundwater recharge to
the on-site lake, followed by chemicals from groundwater entering the aquatic food web. This
pathway is not included in the assessment because the groundwater modeling approach used to
estimate well water concentrations is not designed to enable estimation of groundwater
recharge. See Section 3.2.4 for further discussion of this issue.
Leaching from Burial Trenches and Composting Windrows
After seeping into the ground beneath the burial trench or composting windrow, leachate first
passes downward through unsaturated soil until it reaches the water table where it is carried in
the direction of the ambient groundwater flow. The leachate is diluted as it moves through these
two subsurface zones, and the leached chemicals may be affected by the physical, chemical, and
biological process that tend to further reduce concentrations with distance from the source
(USEPA 1996). The combined effect of these processes is complex and dependent on site-
specific soil and hydrodynamic properties.
To support regulatory analyses, the USEPA (1996) created th qEPA Composite Model for
Leachate Migration with Transformation Products (EPACMTP). The model simulates physical,
chemical, and biological processes in both the unsaturated and saturate zones and has been found
by the USEPA's Science Advisory Board to be suitable for generic applications (USEPA 1996).
One such application was a background study supporting for Soil Screening Level guidance for
USEPA's Superfund program. Using Monte Carlo simulations with EPACMTP and nationwide
site data (e.g., soil properties at contaminated sites, well location and depth), USEPA estimated
chemical concentrations in soil that correspond to safe drinking benchmark concentrations at
downgradient wells. One of the products of this application was a set of Dilution Attenuation
Factors (DAFs), ratios of the original soil leachate concentration to the concentration in water at
a downgradient well. With a DAF of 1, chemical concentrations at the well would equal
concentrations at the source. DAFs greater than 1 indicate dilution and attenuation before
contaminants reach the well.
EPA prepared DAFs for six well-placement scenarios. Distances from the source to the well in
these scenarios were 100 m, 25 m, or 0 m from the source, or randomly selected from a
distribution of nationwide data. The well's horizontal offset distance from the plume center line
was randomly selected, either within the plume's width or half the width. Well depths were
randomly selected from nationwide data for most scenarios.
Because sensitivity analyses determined that soil types and the size of the contaminated area
have the greatest effect on the DAFs, USEPA developed DAFs for sources ranging in size from
1,000 to 5,000,000 ft2 (93 to 464,515 m2). With further analysis, USEPA prepared a default
nationwide DAF for sources up to 0.5 acres (0.2 hectares).
The EPACMTP modeling effort described above included simplifying assumptions that make
the estimated DAFs conservative. For example, retardation due to absorption/desorption kinetics
were excluded by assuming that soil and porewater concentrations are at equilibrium. In
-------
where:
mgs = mg [solid-phase contaminant]
mga = mg [aqueous phase contaminant]
kgs = kg [dry weight of solids]
La = L [volume of water]
To estimate chemical concentrations in precipitation after it passes through the ash, Equation 3.4
is rewritten as follows:
Kd = (mginit - mga / kgs)/(mga / La) Eqn. 3.4
Where mginit is the initial concentration of chemical in the ash, as presented in Section 3.1.1.
Equation 3.5 is then solved for mga, to estimate the mass of chemicals carried with water
percolating through the ash.
mda (^a * m-dinit)/(Hgs * Kd ^a) Eqn. 3.5
Kgs is the weight of ash, which for the base case is 3,235 kg for open burning (see Section 3.1.1)
and 3,220 kg for air-curtain burning.
In these calculations, the amount of infiltrating water (La) is calculated by multiplying the total
rainfall (in m/yr) during the first year after carcass management by the area (m2) of the ash
disposal. At the hypothetical site, there were 168 "precipitation events" in 2014, with at total
amount of 38.1 in (0.968 m) (see Table 3-20). The area of ash disposal, 223 m2 and 41 m2 for
open burning and air-curtain burning, respectively (see Section 3.1.1.). For example, the total
volume of water seeping through the pyre ash for the base case is 0.968 m/yr * 223 m2 = 216
m3/yr = 216,000 L/yr.
Chemicals with high Kd values have a high affinity to solids and lower mobility than chemicals
with lower Kd values. A modeling study by the New Jersey Department of Environmental
Protection (NJDEP 2008) found that, over a 100-year simulation period, chemicals with a Kd
value greater than 100 L/kg moved vertically 11 inches or less in sandy loam. Chemicals with a
Kd value greater than 200 L/kg moved 3.6 inches or less.
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Ingestion exposure is assessed for drinking water consumption, incidental soil ingestion, fish
ingestion, and ingestion of the ten types of agricultural products identified in Tables 3-24 and 3-
25. Ingestion exposure is evaluated relative to exposure-dose health benchmarks (i.e., mg
chemical per kg body weight per day). Therefore, the chemical concentrations in abiotic and
biotic media discussed in Section 3.2 are used to calculate ingestion exposure doses for adults
and children. These calculations are made by MIRC with the following inputs:
¦ Total concentration of the chemical in the air;
¦ Fraction of the chemical in the air in the vapor-phase;
1 Wet and dry deposition rates for particle-phase chemical;
¦ Concentration of the chemical in drinking water;
¦ Concentration of the chemical in soil; and
1 Concentration of the chemical in upper trophic-level fish.
Inputs to MIRC also include chemical-specific parameters values, the exposure scenario (e.g.,
which foods are eaten and at what rate), and assumptions about the potentially exposed adults
and children. Section 3.3.1 describes the approach to characterizing the adult and children
exposure receptors including exposure factors (e.g., body weight) used to estimate their
exposures. Section 3.3.2 presents the chemical exposure estimates for each of the onsite
management options.
3.3.1 Characterization of Exposed Individuals
This section discusses who the assessment assumes is exposed to the chemical, as well as
characteristics about them (e.g., age) and their levels of exposure (e.g., how much home-grown
food they eat).
3.3.2 Description of Exposed Persons
Exposure is estimated for three types of farm residents: infants who consume drinking water in
their formula, young children (age 1-2 years old), and adults who live on the farm near the
carcass management unit for at least one year after carcass management. A young child (e.g., age
1 to 2 years) consumes more food per unit body weight on a daily basis than older children and
adults. For the young child, exposure is calculated from estimated concentrations of chemicals in
a limited diet of foods produced on the farm, using assumptions about a small body weight, and
higher metabolic rates (ingestion and inhalation rates). For the adult, exposure is calculated from
estimated concentrations of chemicals in the drinking water and food items using mean values
for various exposure factors (e.g., body weight, ingestion rates for different foods and water,
inhalation rates).
3.3.3 Exposure Durations
The assessment includes two exposure routes and durations: inhalation over the duration of
combustion (i.e., 48 hours for the base case) and ingestion (i.e., of drinking water, home-grown
food products, and fish) over one year. Inhalation exposures are assessed only for the
combustion-based management options. Inhalation exposure concentrations in mg chemical/m3
air are estimated as event-average concentrations. For the base case, that means the assessment
uses average chemical concentration present in the air during that 48-hour period (at the location
of maximum air concentrations).
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Ingestion exposures are evaluated for a one-year period starting with the beginning of the carcass
management actions. The one-year exposure periods for the various ingestion sources do not
necessarily coincide with one another. For example, drinking water exposure begins when the
chemicals in groundwater reach the well. Ingestion of home-grown foods begins for the
combustion-based options after chemicals are deposited from air to soil and plants, and for the
composting option after finished compost is applied as a soil amendment.
All ingestion exposures are assumed to be constant and uniform throughout the one-year periods.
Chemical concentrations in drinking water, home-grown produce, and fish based on the total
chemical released during the first year to an environmental medium after accounting for
chemical movement to other environmental media (e.g., from surface soil to the lake) are
assumed to represent the average daily exposure concentrations for one year. The exposure
assumptions, such as the availability and consumption of home-grown food products, are
assumed to be consistent throughout the year (i.e., data for seasonal changes not available).
3.3.4 Human Exposure Factor Values
This assessment uses mean life-stage-specific exposure-factor values that are included in MIRC.
Those values are from the most recent version of USEPA's Exposure Factors Handbook
(USEPA 2011), its Child-specific Exposure Factors Handbook (USEPA 2008), and its Child-
Specific Exposure Scenarios Examples (USEPA 2014). These handbooks include a thorough
review of relevant original data and list the USEPA-recommended values for use in exposure
assessments. The handbooks provide mean, median, and percentile (e.g., 75th, 90th, 99th
percentiles) values to allow the user to determine the degree of conservatism appropriate for each
factor as used in their particular type of exposure assessment (e.g., screening, ranking, refined).
The purpose of this assessment is to compare the management options by their exposure
potential relative to each other, not to estimate possible real-world maximum individual or
population exposures or risks for any of the options. Consequently, the most appropriate value to
select for each exposure factor is the mean value, not an upper percentile value as often is
selected for screening-level risk assessments to represent most exposed individuals. Mean
exposure factor values are preferred for several reasons:
¦ Mean values are the most robust (i.e., have the narrowest confidence limits) of the statistical
descriptors of parameter distributions. The more extreme values (i.e., values near the "tails")
in a natural distribution of parameter values, such as a 95th or 99th percentile value, are more
uncertain (i.e., and have much wider confidence limits). Upper percentile values (i.e., upper
tail of a distribution) can be highly skewed by outlier values in the data set.
¦ The expected value, or mean, of the sum of two random variables is the sum of the means
(additive law of expectation).
* The mean of the product of two parameters (with any type of distribution of values) is the
product of the mean values if (and only if) the two parameters are not correlated with one
another.
¦ If the variables are correlated (e.g., body weight positively correlates with daily quantities of
food ingested), then the product of the mean values for each parameter will likely be smaller
than the mean of the product of the values (e.g., the same individual). To avoid this error,
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original data on food ingestion rates for each individual should be expressed as kg food
ingested per kg of body weight per day. The mean of that distribution should be a more
accurate measure than taking the mean of food ingestion rates (kg/day) across all adults and
dividing by the mean body weight of all adults (in kg).
¦ Percentiles for random variables generally are not additive or multiplicative whether the
variables are correlated to some degree or not. Instead, reasonably accurate estimates of a
percentile (e.g., 90th percentile) for the sum, product, or ratio of two (or more) random
variables generally requires a Monte Carlo simulation in which the distribution of each
variable and its correlation with the others are well defined. For example, multiplication of
upper percentile values for two independent parameters (e.g., 95th percentile for exposure
concentration in water in mg/L multiplied by the 95th percentile water ingestion rate in L/kg
body weight/day) yields a much more conservative (i.e., higher) percentile value (e.g.,
99.9th) than the original percentile value (e.g., 95th). Moreover, using the percentile requires
knowledge of the shape of the original distributions and their variances even if the two
parameters are completely uncorrelated.
To compare the livestock carcass management options based on their relative exposure potential,
mean values for adult and child body weight, and food and water ingestion rates are used. These
values are shown in Table 3-26 and are further documented in Appendix K of USEPA (2017).
For infants, exposures are considered from well water used to mix with formula, with both mean
and high-end exposure factor values as listed in Table 3-27.
3.3.5 Exposure Estimation
This section describes the methods used to estimate chemical exposures for each carcass
management option. Separate estimation methods are used for human inhalation and ingestion
exposures.
inhalation
Inhalation exposures are calculated for adult farm residents at a location of maximum
concentrations of the chemicals in air as estimated by AERMOD on a date for which
meteorological conditions resulted in the highest-event-average concentration. These exposure
concentrations are presented in Tables 3-13 and 3-14 for dioxin/furans and mercury,
respectively. In Section 4, the average inhalation exposure concentrations are compared to
health-based benchmark concentration. Separate exposure estimates are not made for adults and
children because evaluation of inhalation exposures occurs on an air-concentration basis and not
an exposure-dose basis.
For dioxins, compound-specific concentrations in air are multiplied by the TEFs (see Table 3-13)
for conversion to 2,3,7,8-TCDD equivalent (TEQ) concentration. The 17 TEQ concentrations are
then added and presented as total dioxins/furans.
The conceptual models for each of the onsite management options includes inhalation of
aerosolized chemicals from home uses of well water (specifically showering as the worst-case
home-use scenario). However, given the low mobility of the assessed chemicals in soil and
groundwater, this inhalation exposure pathway is considered negligible, and is not estimated.
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medium, and receptor age group. All the ADDs for a given carcass management option are then
summed for each combination of receptor age group and chemical.
For fish ingestion, the assessment assumes that farm residents catch and consume both water-
column game fish (e.g., walleye, northern pike) and pan fish (e.g., yellow perch, bluegill). The
fish ingestion rates are mean values for the general population developed by USEPA's Office of
Air Quality Planning and Standards for use in multimedia risk assessments in support of
USEPA's Risk and Technology Review program. In particular, the USEPA's Office of Air
Quality Planning and Standards estimated the values of 7 g/person/day for adults and 1.4
g/person/day for children age 1 to 2 years from data presented in USEPA's (2002) Estimated Per
capita Fish Consumption in the United States and the Agency's (2008) Child-Specific Exposure
Factors Handbook. Subsistence fish ingestion rates are not used because the farm residents also
rely on home-grown plants and livestock for food. Further details are available in USEPA 2017,
Appendix K.
All ingestion ADDs are calculated assuming one year of exposure to the chemicals {ED of 1 yr),
exposure that every day during the year (i.e., exposure frequency of 365 days/yr), and that all of
the food or drinking water ingested is from potentially contaminated food and drinking water
obtained on site (i.e., the fraction from the contaminated area is 1.0). The averaging time in the
equation above {AT of 1 yr) is the period of time over which the average daily chemical exposure
is averaged. Only the first year following management of the carcasses on site is assessed,
because that is the year in which chemical concentrations will be highest in environmental
media. Chemical concentrations in subsequent years will be lower as various loss processes (e.g.,
diffusion, dispersion, degradation, movement of chemicals to other environmental media)
continue over time. Thus, exposures will continue, but decrease at a rate that is difficult to
calculate across carcass management options.
For each carcass management option, chemical-specific ingestion exposures, expressed as
ADDs, for each age group (i.e., adult and child aged 1-2), are summed across ingested drinking
water, soil, fish, five types of home-grown produce, and five types of home-raised animals or
animal products. Total ADD for a particular age groups (ADDm) is estimated as the sum of a
given chemical ingested from all pathways from which the chemical could be consumed. The
ADDs for dioxins are totaled using the TEQs described in Section 3.2.1.
Ingestion exposure estimates (i.e., ADDs) for adults and young children associated with each
management option are presented in Tables 3-28 through 3-32. These tables include ADDs for
each food ingested, drinking water, and incidental soil ingestion, which are added to calculate the
total ingestion exposure for each chemical. The tables show "np" where a chemical is not present
in the exposure medium. For example, diazinon is combusted and is not present in any pathway
for the two combustion-based options, and mercury is present only for open burning because its
only source is coal used as pyre fuel. Including the "not present" pathways in Tables 3-28
through 3-32 helps to show how potential exposure pathways differ among the management
options.
The tables show "na" if where exposure is not assessed. Reasons for not assessing particular
chemicals and pathways are discussed in Sections 3.1 and 3.2. For example, dioxins are not
assessed in the drinking water ingestion because their low mobility. Mercury exposure is not
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4. Results i mission
This section compares options for managing dioxin- and diazinon-contaminated carcasses
relative to each other in terms of potential exposures to onsite residents and workers. In Section
4.1 the carcass management options are evaluated in a two-tiered approach. Tier 1 (Section
4.1.1) groups the seven carcass management options in two categories of potential exposure
based on the level of regulatory pollution controls that limits releases of chemicals to the
environment. Tier 1 is qualitative because the off-site options are not included in the quantitative
exposure assessment.
In Tier 2 (Section 4.1.2), the four on-site management options are evaluated further based on the
quantitative exposure assessment. Specifically, the exposure estimates presented in Sections 3.2
and 3.3 are normalized to chemical-specific Toxicity Reference Values (TRVs) to allow a
relative comparison of the management options in terms of their potential for exposures at levels
of concern for human health.
The quantitative assessment presented in Section 4.1 uses a "base-case" set of reasonably
conservative values identified from available literature and previously developed default
assumptions for the hypothetical farm site. Section 4.2 examines how assumptions such as the
scale of mortality and level of chemical contamination affect the magnitude of exposure and the
relative exposures for the on-site management options. Section 4.3 discusses the uncertainties
and limitations of the assessment to help readers understand and use the findings of this
assessment, including how these findings may relate to site-specific circumstances in the event of
an actual chemical emergency.
All of the on-site management options include preceding carcass transportation and handling
steps. Chemical exposures from these steps are not included in this assessment. However, they
were included, either qualitatively or quantitatively, in the chemical and microbial exposure
assessments for the natural disaster (USEPA 2017) and foreign animal disease (FAD) outbreak
(USEPA 2018) scenarios. The FAD assessment concluded that temporary carcass storage, if
employed as part of the overall carcass management response, can be the primary source of
potential exposure. This finding applies to the foot and mouth disease, the subject of the FAD
assessment, but not necessarily to other microbial hazards. For chemical hazards, the natural
disaster assessment concluded that exposures from temporary carcass storage are well below
exposures from the combustion-based options and roughly comparable in magnitude to the
exposures from burial and the composting windrow. Based on these findings, the handling and
transportation steps were not re-examined in this assessment. For this assessment, the on-site
carcass transportation and handling steps, and their resulting chemical exposures, are assumed to
be the same for all management options, and therefore do not affect the relative levels of
chemical exposure across the options.
Readers of this document should recognize that the exposures estimated for the hypothetical base
case scenario might differ from those of the different carcass management options in specific
locations and under various conditions. This document does not replace the need for county or
statewide planning for chemical or other disasters with mass livestock mortality based on
availability of off-site management options and suitability of on-site options for the region.
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4,1 Exposure Assessment
This section compares the livestock carcass management options relative to each other in a two-
tiered approach. Tier 1 (Section 4.1.1) groups the seven carcass management options in two
categories of potential exposure based on the level of regulatory pollution controls that limits
releases of chemicals and microbes to the environment. Tier 1 also considers the number of
potential exposure pathways identified in the conceptual models for each management option
(Appendix C) and describes why the three off-site carcass management options present minimal
to negligible relative risks. In Tier 2 (Section 4.1.2), the four on-site management options are
evaluated further based on the quantitative exposure assessments presented in Sections 3 through
6.
4.1.1 Tier 1 Comparison of the Seven Carcass Management Options
As discussed in Section 2, this assessment considers seven well-established carcass management
options with documented use following chemical emergencyies or with sufficient capacity for
large-scale carcass management. With the three off-site options, releases to the environment
(e.g., incinerator emissions to air, rendering facility discharge to surface water) are restricted by,
and are assumed to comply with, applicable regulations. Therefore, chemical releases from off-
site commercial facilities are assumed to be adequately controlled. The on-site management
options all include uncontrolled or minimally controlled chemical releases to air, soil, or water,
for which exposures are modeled as described in Section 3. Moreover, the on-site management
options tend to have more potential exposure pathways than the off-site options. Acknowledging
the distinction between off-site and on-site options based on regulatory pollution control
constitutes the first tier ranking of the seven carcass management options. Table 4-1 presents that
ranking and lists the numbers of conceptual model pathways for chemicals. Table 4-1 also
describes controlling legislation and technologies to limit releases to permitted levels or below.
The table shows that the three off-site options are ranked higher (i.e., less potential for exposure
and risk) than the four on-site options based on these considerations.
4.1.2 Tier 2 Ranking of On-site Carcass Management Options
In Tier 2, the four on-site carcass management options are compared using the exposure
estimates presented in Section 3.3. In particular, ranking ratios are calculated and compared for
each combination of management option, chemical, exposure route (i.e., inhalation or ingestion),
and health effect (i.e., cancer or noncancer) for which exposures are estimated. Some exposure
pathways were not quantified for one or more reasons (e.g., the chemical is not present). These
reasons are noted in in general categories in Table 4-2 and explained more specifically in
Sections 3.1 and 3.2.
By itself, an exposure concentration does not indicate whether adverse effects on human health
or environmental quality are possible or likely. To support a risk-based comparison of the
exposure estimates, they are normalized to inherent toxicity using toxicity reference values
(TRVs). A TRV is a concentration- or dose-based estimate of the exposure level below which
adverse health effects are not expected for individual humans in the population evaluated. TRVs
are chemical-specific and are developed by various agencies (e.g., USEPA, ATSDR) using
agency- or program specific-methods and definitions. TRVs also are developed for various
exposure durations, and the TRVs for this assessment are those most appropriate, as available,
for the exposure durations of the exposure estimates. Table 4-3 presents the TRVs used in the
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The selected TRVs are referred to by the general term "benchmarks," because they include
values for cancer and non-cancer endpoints, are developed by various agencies for various
exposure durations, and differ for inhalation and oral exposures. As described below, exposure
estimates for each management option, chemical, and exposure route are compared to the cancer
and non-cancer benchmarks for purpose of comparing or ranking the management options
relative to one another.
The benchmarks for inhalation exposure are expressed as air concentrations (i.e., (|ig
[chemical]/m3[air]) that can be compared directly to the concentrations estimated at a receptor
location (e.g., 100 m from the source). The exposure concentrations are presented in Section
3.2.1 as peak 1-hour concentrations during combustion and averages over the duration of
combustion, which is 48 hours for the base case. Because these concentrations are short-term
(i.e., hours to days), the preferred TRVs for the inhalation benchmarks are acute toxicity
reference concentrations (RfCs). The benchmarks are based on sub-chronic or chronic RfCs
(unadjusted) when acute RfCs are unavailable.
Benchmarks for ingestion exposure are expressed as the ingested dose (i.e.,
mg[chemical]/kg[human body weight] per day). As discussed in Section 3.3, ingestion exposures
are assumed to occur over the first year of maximum exposures. Accordingly, the preferred
TRVs for evaluating non-cancer health effects from ingestion exposures are subchronic oral
reference doses (RfDs), which are developed for periods up to 7 years (USEPA 1989). Chronic
oral RfDs (unadjusted) are selected when subchronic RfDs are unavailable.
The TRVs for evaluating cancer health effects from ingestion are oral slope factors in units of
per mg/kg-day (i.e., (mg/kg-day)"1), based on lifetime exposure. The slope factors require a
transformation for direct comparison to exposure estimates, which are in units of mg/kg-day.
Specifically, a target individual risk level of 1E-04 (one in 10,000) is divided by the oral slope
factor to calculate the corresponding risk-specific dose (RSD), that is, the dose that corresponds
to a target risk level of 1E-04 over a lifetime of exposure. This risk target is selected because, in
general, USEPA considers excess cancer risks above 1E-04 to be sufficiently large that some
response action is merited (USEPA 1991). Because the RSD represent cancer risk based on a
lifetime of exposure, the estimated average daily exposure dose for the first year (i.e., the ADD)
is divided by 70 years to calculate the lifetime average daily dose (LADD).
Even in comparative or relative risk assessments, cancer and non-cancer endpoints generally are
not grouped into one category. There are no consensus guidelines at USEPA by which risk
assessors can combine estimates of cancer risk (a probability or incidence rate) with a hazard
quotient (ratio of a point estimate of exposure to the appropriate benchmark, either >1.0
indicating adverse effects are possible or <1.0 indicating adverse effects are unlikely). Severity
of effects is also a complicating factor for comparisons. Some health effects upon which non-
cancer toxicity RfCs or RfDs are based are more severe than others. Some types of cancer are
associated with limited expected future survival whereas others have better prognoses.
For the relative risk comparison of the four on-site carcass management options, the estimated
exposures (Section 3.3.2) are compared with the relevant benchmarks (Table 4-3) by calculating
the ratios of exposure to benchmarks. These ratios, which normalize each of the exposure
estimates to inherent toxicity, are referred to as "ranking ratios." Risk managers and the public
should not interpret risk ratios as "actual likely" exposures or risks, particularly given the data
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limitations and generic assumptions of this assessment. However, the ranking ratios can be
compared to evaluate the relative exposure among management options within the base case (this
section) or when certain base case assumptions are changed (Section 4.2).
Mercury originating from coal combustion is included in the assessment, but only pertains to the
open burning option. Therefore, mercury exposures are discussed separately in the sections
below.
inhalation Exposure
Ranking ratios for base-case inhalation exposure are presented in Table 4-4. The table includes
dioxins only, because diazinon is not present in the combustion emissions and mercury is
discussed separately below. Considering either peak 1-hour or event average concentrations,
open burning produces dioxin inhalation exposure that is similar to, but greater than, inhalation
exposures from air-curtain burning. As discussed in Section 3.2.1, dioxin emissions, and
exposures, from the two management options are more similar in this assessment than they were
in the previously completed assessments (USEPA 2017). A reason for this is that dioxin from the
contaminated carcasses, which are assumed to be equivalent with the two management options,
contribute 48% or more of the total dioxin emissions with the base case. As the amount of dioxin
contamination becomes greater relative to the dioxins formed as fuel combustion products, their
contribution to total dioxin emissions increasingly outweighs the difference between the options
due to the fuels alone.
With both open burning and air-curtain burning, the estimated exposures for the base case are
below the dioxin inhalation benchmark. Diazinon exposure is not included in the inhalation
assessment because it would be decomposed and fumes might ignite during combustion.
For the open burning option, base case inhalation exposure to mercury is well below the
reference concentration (i.e., 0.6 |ig/m3). For example, the highest peak 1-hour concentration at
the closest receptor location (100 m) is 4.9E-4 |ig/m3 as shown in Table 3-14.
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well) can affect which exposure pathways are relevant at a site. For these reasons, there is no
"best" carcass management option for every event.
4.2 Uncertainty Analysis
The exposure estimates presented in Sections 4.1.2 are affected by several scoping decisions
about the chemical emergency (e.g., chemicals present, contamination levels, number of
carcasses) and about the design and use of the carcass management options (e.g., configuration,
type and amount of combustion fuels). In addition, several parameter values are likely to vary
substantially across locations and by season, and available input data and models are subject to
limitations. Although the assessment approach generally uses conservative values for parameters
that vary substantially in the real world, parameter values assumed when preferred types of data
are not available might over- or under-estimate exposures. Sources of uncertainty are discussed
further in Section 4.3.
This section examines how changes to various aspects of the base case scenario affect the
magnitude of the estimated exposures, and resulting differences in exposures among the options,
pathways, and chemicals. The aspects evaluated include the following:
¦ Chemical selections
¦ Scale of mortality
¦ Contamination level
1 Distance from source
¦ Air-curtain burner fuel ratio
¦ Chemical degradation
4,2.1 Chemical Selections
This assessment evaluated just two of thousands of chemicals that could contaminate livestock in
the event of a chemical emergency. As discussed in Section 2.2, the two chemicals (i.e., dioxins
and diazinon) represent two categories, halogenated organics and pesticides, respectively,
involved in past livestock contamination events. In addition, data required for the assessment
(e.g., TRVs) are available for both chemicals.
Another reason for selecting dioxin and diazinon is their distinct environmental fate
characteristics. The effects of these differences are discussed throughout Sections 3 and 4. For
example, the partitioning behavior of dioxins causes them to have low mobility through the
groundwater pathway and a strong tendency to bioaccumulate in the aquatic food web. Dioxins
are persistent and will not degrade significantly during composting, and are not likely to be
destroyed at the combustion temperatures of on-site open burning or air-curtain burning. In
contrast, diazinon is destroyed at these combustion temperatures. Diazinon also is moderately
mobile in the groundwater pathway and not strongly bioaccumulative. In addition, diazinon is
subject to degradation processes that would decrease exposure. These processes are not included
in the environmental fate modeling because they are dependent on many location specific factors
(e.g., temperature) as well as time. Thus, diazinon exposures are likely to be overestimated in
this assessment. This issue is examined further in Section 4.2.6.
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For open burning, inhalation and ingestion exposure at a distance of 100 m is estimated to be
greater with 500 carcasses than with 1,000 carcasses. Two factors contribute to this finding.
First, as described above the size and configurations of the combustion sources change as more
carcasses are managed. Because the 100 m distance is measured from the center of the
management units, the distance from the nearest edge is not necessarily the same with different
configurations. These differences affect the concentration unequally, particularly at distances
close to the sources. In addition, with more carcasses, the air-curtain burning duration increases
from two to five days, while open burning remains 48 hours.
A second factor that affects dioxin concentrations and exposures is the emission profile, which
includes the relative proportions of the 17 individually modeled congeners, the proportions of the
emission in vapor and particular phases, and the size distribution of particles. From available
literature, the assessment uses separate congener profiles for dioxins from carcass contamination
and formed as combustion products of the woody fuels. In addition, the transport of each
congener is affected by chemical-specific properties (e.g., Henry's law constants). Differences
between the emissions profiles, along with differences in emission rates and the sizes and shapes
of the sources affect the air concentration and depositional patterns.
For mercury, emissions are modeled separately for vapor and particulate divalent mercury and
vapor phase elemental mercury. All of the mercury comes from coal used to fuel the pyre.
Consequently, all the pyre emissions have the same mercury profile and total mercury inhalation
and ingestion exposures are approximately proportional to the scale of mortality.
Burial and Composting
The burial and composting options are evaluated for the management of 100 (base case), 500,
1,000, and 10,000 carcasses. In the event of a chemical emergency with diazinon contamination,
only the burial and composting options would pose potential exposures; diazinon would be
eliminated by the combustion-based options. In an emergency with dioxin contamination
exposures might occur from compost application, as well as the combustion options, but
exposures are unlikely from the burial option and leaching from the compost windrow due to low
mobility in the relevant pathways.
In this assessment, the only exposure pathway evaluated for the burial option is the ingestion of
drinking water from an on-site well contaminated by leachate from the burial trench. A number
of site-specific factors might eliminate this pathway at actual sites. For example, the well, if
present, might be located away from the direction of groundwater flow or draw from a deeper
aquifer. This assessment assumes that a drinking water well intersects contaminated groundwater
100 m from the source as discussed in Section 3.2.3. Exposures estimates for this scenario are
included in Table 4-10 and Figure 4-1.
Drinking water exposure to diazinon increases with the number of carcasses. However, the
increase in exposure is not in proportion to the number of carcasses managed. For example, with
10,000 carcasses the exposure is 69 times greater than with 100 carcasses (an increase in
carcasses of 100 times). This pattern is attributable to the DAFs used in the assessment, which
are based on EPACMTP modeling and the areal extent of the burial trench. In the EPACMTP
modeling, increasing the source area increases the infiltration rate, which lowers the DAF, but
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emergency, the finished compost might be managed as a residual product of the emergency
response, and either buried or managed off site, and farm residents might avoid eating
agricultural products grown on site and fish caught from the lake.
Given the scenarios assumed for this assessment, incidental soil ingestion accounts for about 1%
of the exposure, of either dioxins or diazinon, resulting from compost application. With diazinon
contamination, more than 98% of the exposure from compost application comes from home-
grown vegetables, fruits, and livestock products, with less than 2% coming from fish ingestion.
Fish ingestion is larger source of exposure in a dioxin contamination emergency. In particular,
the dioxin contributions from the ingestion of fish and home-grown foods are 31% and 68%,
respectively for adults and 7% and 92%, respectively, for young children. As discussed in
Section 3.1.4, this assessment assumes that 50% of the contaminated soil eroded from the
compost application is captured by a buffer area before it reaches the lake. Without this
assumption, the contributions of fish ingestion to total exposure is 47% and 13% for adults and
children, respectively.
4,2.3 Contamination Level
As discussed in Section 2.2, the base case level of dioxin contamination in cattle (0.024
g/carcass) is based on a past contamination event, and the base case level of diazinon
contamination (5 g/carcass) is based on toxicity data. In actual chemical emergencies involving
these chemicals, the average amount of contamination in the carcasses could be higher or lower
than the base case. For this reason, this assessment may under- or over-estimate exposures in
those actual emergencies. As noted elsewhere, the purpose of this assessment is not to estimate
absolute levels of exposure or risk that would occur in an actual emergency. It is to compare the
management options relative to each other in terms of exposure levels and exposure pathways.
For a simple exposure scenario, one would expect exposure to change in direct proportion to the
level of contamination. To test this hypothesis, the levels of dioxin and diazinon contamination
are varied from the base case by powers of ten. Specifically, dioxin and diazinon are both
evaluated for 1/10th to 10 times the base case level. Diazinon is also evaluated at 100 times the
base case level.
Table 4-11 shows how dioxin and mercury exposures from open burning and air-curtain burning
change with increasing levels of dioxin contamination in the cattle. Mercury exposure with open
burning is unaffected, which is expected because the amount of coal burned is not affected by the
dioxin contamination level. The slight increase in mercury exposure at the highest dioxin
contamination level is attributable to differences in the hourly meteorological data that can occur
between modeling runs.
Dioxin inhalation exposures are similar with the two combustion-based options, and
concentrations in air are below the non-cancer reference concentration with all levels of dioxin
contamination evaluated. With open burning, dioxin inhalation exposure increases in direct
proportion (i.e., by factors of 10) to the initial level of contamination as shown in Figure 4-5.
With air-curtain burning, however, the dioxin exposures increase approximately 5 times when
the carcass contamination increases 10 times from 0.0024 g/carcass to 0.024 g/carcass. The
likely cause for this is that at the lowest contamination level, wood burning, which does not
increase, accounts for a larger share of the total dioxins emitted. At the two higher contamination
levels, the dioxin exposure increases by a factor of 10. This pattern is not seen with open burning
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because the amount of woody fuel per carcass is about one-fourth of that used for air-curtain
burning.
Ingestion exposure with increasing dioxin contamination is shown in Table 4-12 and Figure 4-6.
Overall, dioxin exposures are highest with compost application followed by similar levels of
exposure with open burning and air-curtain burning. Exposures increase in direct proportion to
contamination levels with open burning and compost application, and slightly less than
proportionally with air curtain burning due to the larger contribution of dioxins from wood
burning with this option and assumed fuel ratio.
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The base case assessment assumes that diazinon leached from the burial pit and compost
windrow reaches a drinking water well 100 m away. This is a conservative scenario that is
unlikely to exist at an actual chemical emergency site where contaminated carcasses are
managed. Several conditions must be met for a drinking water well to be contaminated. For
example, the drinking water well must draw from the same shallow aquifer affected by leachate,
and the well must be in the direction of groundwater flow. A complete drinking water pathway
also requires that any chemicals of concern are mobile in soil and groundwater and that they are
not subject to rapid degradation. The movement of contaminants through soil and groundwater
can be very slow, particularly over large distances, and dilution and degradation processes can
reduce chemical concentrations before contamination reaches the well. In the event of an actual
chemical emergency, site managers can first determine whether a complete drinking water
pathway exists based on these conditions.
Fish are contaminated in this assessment by deposition of airborne chemicals to the lake and its
watershed, or by erosion of soil from a compost application site near the lake. For air deposition,
the lake is assumed to be downwind from the source and within one kilometer. The potential for
fish ingestion exposure at an actual carcass management site is likely to be lower than estimated
for this assessment if the lake is either not downwind or is not nearby (e.g., within a kilometer),
or if fish are not consumed or are consumed infrequently. In addition, fish ingestion exposure
will be lower with chemicals that are not as strongly bioaccumulative as dioxins/furans.
Soil erosion from a compost application site to surface water can be reduced with erosion control
practices or by applying compost away from the lake. Erosion to the lake will be reduced if there
is an uncontaminated "buffer" between the application site and the lake. For this assessment
there is no assumed distance; however, it is assumed that 50% of the contaminated soil eroded
from the compost application site reaches the lake.
4,2.5 Air-curtain Burning Fuel Ratio
Emissions from air-curtain burning for the base case are calculated with a 4-to-l ratio of wood
fuel to carcasses by weight. In practice, the fuel ratio may vary depending on factors such as the
quality and moisture of woody fuels used (Peer et al. 2006) and the rate at which fuel and
carcasses are place in the burner. Various fuel ratios have been reported in the literature, and the
base-case assumption is at the upper end of the range. Lower ratios around 2-to-l have been
cited by multiple authors (e.g., NABCC 2004; SKM 2005). To evaluate the effect of the fuel
ratio assumption on exposure, the air-curtain burning base case was run with the fuel ratio is
reduced to 2:1. In addition, the reduced fuel ratio was run with increased numbers of carcasses,
as in Section 4.2.2, and varied levels of dioxin contamination, as in Section 4.2.3.
Table 4-14 compares dioxin exposures from air-curtain burning with 4:1 and 2:1 fuel ratios and
varied levels of dioxin contamination. Overall, halving the amount of wood fuel reduces dioxin
exposures by less than half. This is expected because the amount of dioxin from the carcasses is
the same with both fuel ratios. As seen in the ingestion results, the difference between the
exposures with the two fuel ratios is greatest with the lowest level of carcass contamination. As
the contamination level increases, the carcass contamination contributes a larger share of total
dioxins emissions and the effect of the fuel ratio is less significant. Inhalation exposures are
lower when there is less wood burned. However, the inhalation exposure differs in a more than
ingestion exposure with varied contamination levels. This might be because ingestion exposure
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4,3 Uncertainty Summary
In addition to the parameters varied in Section 4.2, this exposure assessment includes
uncertainties and assumptions about the emergency scenario, response activities, and
environmental conditions that might differ from those of an actual chemical emergency. This
section identifies a number of those factors and discusses how the exposure assessment might
over- or underestimate exposures in the event of an actual chemical emergency.
Tables 4-17 through 4-19 on the following pages summarize three types of "uncertainties" in the
exposure assessment:
1 Parameters with Moderate to High Natural Variation
¦ Uncertain Parameter Values
¦ Simplifying Assumptions
Table 4-17 describes parameters for which substantial variation exists across the United States,
and the base case assessment uses value selected either to be nationally representative, to be
health protective (i.e., overestimate exposure), or for another reason. The table lists the expected
magnitude (low, medium, high) and direction (under- or overestimate) of bias in the exposure
estimates for each one.
Table 4-18 describes parameters for which limited data were available to calculate a central
tendency value or to estimate likely variation across conditions possible in the country.
Uncertainty is characterized as low, medium, or high. By definition, the direction of bias is
unknown.
Finally, Table 4-19 includes several "simplifying assumptions" that are required to compare
management options relative to each other within a reasonable level of effort. As for Table 4-17,
the expected magnitude (low, medium, or high) and direction (under- or overestimate) of bias
introduced by the assumption is summarized.
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4.4 Summary of Findings
This assessment is meant to support selection of environmentally protective livestock carcass
management methods in the event of a chemical emergency in which livestock are intentionally
or unintentionally contaminated. Examples of intentional livestock contamination include
criminal or terroristic acts such as chemical poisoning of food or water supplies, sabotage of
agricultural production or commodity markets, or use of a chemical warfare agent. Examples of
unintentional livestock contamination include industrial accidents, accidental contamination of
feed or other agricultural supplies, and transportation-related accidents.
Based on documented past livestock contamination events, this assessment evaluates exposures
for two chemicals with distinct environmental fate properties. Dioxins are chemically stable and
not readily degraded (e.g., by sunlight or microbes). They persist for years in the environment
and can travel long distance in air, but have very low mobility in soil and groundwater. Dioxins
are hydrophobic and may bioaccumulate in in the fat of animals that consume contaminated
prey, feed, or food. Diazinon is an organophosphate pesticide that does not strongly partition to
any particular environmental medium, is moderately mobile in soil and groundwater, and is
degraded by biotic and abiotic processes. These are just two of thousands of chemicals that could
contaminate livestock in conceivable scenarios.
Exposures are assessed for these chemicals using generally conservative scenarios and
assumptions that would overestimate exposures at most actual carcass management locations.
For example, the assessment is designed to assess exposure for reasonably anticipated exposure
pathways from carcass management. Therefore, the conceptual models and site layout were
intentionally designed to include all feasible complete exposure pathways. The purpose of the
assessment is to compare the management options by their exposure potential relative to
each other, not to estimate the level of exposure that can be expected in any real event.
In Tier 1 of a two-tier assessment, the three off-site livestock carcass management options,
collectively, are ranked above the on-site options. This is because off-site commercial facilities
are assumed to be adequately controlled under applicable pollution control regulations. The on-
site management options all include uncontrolled or minimally controlled chemical releases to
air, soil, or water.
In Tier 2, the on-site options are ranked relative to each other based on estimated exposures to
dioxins and diazinon. When exposures are compared among the management options,
differences are evident due to the environmental fate properties of the two chemicals. Diazinon
exposures are greater with burial and composting than the combustion-based options, which
destroy the chemical. Dioxins is resistant to combustion, but has low mobility in soil and
groundwater pathways from burial and composting. While diazinon is reduced by degradation
processes during months in the compost windrow, dioxins persist and become more concentrated
in the compost as carcass decomposition progresses. Because chemical-specific environmental
fate characteristics greatly influence the relative potential for exposure from the carcass
management options, there is no "best" option across all chemicals.
Several site-specific factors also affect which option will best protect human health and the
environment in the event of an actual chemical emergency. Examples include proximity to
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residential areas and surface water bodies; availability of land area, resources, and equipment;
and depth to groundwater and the presence of potentially affected wells.
Additional findings of the assessment are presented in the bullets below and in Table 4-20.
¦ The three off-site management options could be more protective than on-site options. The
off-site treatment facilities expected to have applicable and appropriate pollution prevention
technologies in place to comply with U.S. federal regulations. Thus, the off-site facilities
and infrastructures might be capable to contain contaminants and environmentally more
protective than a resource-limited on-site setting. The on-site management options all
include uncontrolled or minimally controlled chemical releases to air, soil, or water.
¦ In general, options that destroy contaminants (e.g., combustion) are more effective than
those that contain them. However, metals are not destroyed by combustion and some
organic chemicals (e.g., dioxins, polycyclic aromatic hydrocarbons) are resistant to
combustion or are formed as combustion products. Based on available information (USEPA
2017), this assessment assumes that the combustion temperatures of open burning, air-
curtain, burning, and off-site incineration are 550°C, 850°C, and >1,000°C, respectively.
Some chemicals may be degraded over time while in containment (e.g., burial, compost
windrow).
¦ Comparing on-site options at a specific site will benefit from understanding all of the
potential exposure pathways identified in the conceptual models provided in Section 3.
Considering the site and contaminants of concern, determine which pathways are and are
not relevant at the site.
¦ Chemical-specific environmental fate properties that should be considered in the event of an
actual chemical emergency include partitioning and mobility in soil, surface water, and
groundwater. Persistence, as indicated by degradation half-lives in relevant media,
flammability at incineration temperatures, and bioaccumulation potential, also should be
considered.
¦ Although chemical releases are minimal from properly constructed compost windrows,
consideration should be given to the use of the finished compost. If carcasses are
contaminated with persistent chemical pollutants, using the compost as a soil amendment
might result in remobilization and exposure.
¦ Each of the on-site management options can be designed and implemented to avoid or
reduce potential exposures (see Table 4-20).
This assessment cannot identify which option would be most protective in every situation.
However, this report provides information to managers can use in site-specific decision-making.
In addition to the exposure-based rankings, it provides conceptual models and environmental
fate and effects concept for scientifically based understanding of potential chemical releases and
exposure pathways. Site managers can use this report with site-specific information to identify
possible exposure pathways, determine whether complete exposure pathways exist, which
carcass management options are compatible at their site, and to determine how exposures can be
avoided.
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5, Quality Assurance
This report used scientific information extracted from sources of secondary data including
journal articles, publications in the open literature, and government reports both published and
non-published, including distribution limited reports. Data and information were gathered from
published reports to identify the significant pathways by which pathogens might reach
individuals and estimate how many microorganisms an individual is likely to be exposed to
through each pathway. A targeted literature review was performed to identify the most highly
relevant data to inform an exposure assessment. Scientific and technical information from
various sources were evaluated using the assessment factors below:
Focus: The extent to which the work not only addresses the area of inquiry under
consideration, but also contributes to its understanding; it is germane to the issue at hand.
Verity: The extent to which data are consistent with accepted knowledge in the field, or if
not, the new or varying data are explained within the work. The degree to which data fit within
the context of the literature and are intellectually honest and authentic.
Integrity: The degree to which data are structurally sound and present a cohesive story.
The design or research rationale is logical and appropriate.
Rigor: The extent to which work is important, meaningful, and non-trivial relative to the
field. It exhibits sufficient depth of intellect rather than superficial or simplistic reasoning.
Soundness: The extent to which the scientific and technical procedures, measures,
methods, or models employed to generate the information is reasonable for, and consistent with,
the intended application.
Applicability and Utility: The extent to which the information is relevant for the intended
use.
Clarity and Completeness: The degree of clarity and completeness with which the data,
assumptions, methods, QA, and analyses employed to generate the information are documented.
Uncertainty and Variability: The extent to which variability and uncertainty (quantitative
and qualitative) related to results, procedures, measures, methods, or models are evaluated and
characterized.
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