Page 641
Index
A
Acceptable daily intakes (ADIs), 30-31, 62
Activity patterns, 5, 47, 53, 53-54, 114, 118, 119, 139
variability, 196, 199-200, 217
Age-dependent effects, 54-55, 141, 191, 219
Age-related differences, 200, 220, 511
Agency for Toxic Substances and Disease Registry, 10, 157
Aggregation, 6, 12-13, 79, 224-225, 240-242
chemical agents, 13, 89, 224-225, 226-229, 240
dose-response thresholds, 224-225, 228-229
exposure routes, 13, 41, 51-52, 119, 225-226, 240, 252
nonthreshold end points, 13, 225, 229-234, 240-241, 516-528
risk characterization, 234-240, 530-534
and variability, 13, 234, 237-240, 242, 530-534
Air-quality models, 50, 51-52, 86, 112, 114-119, 454-560, 544-545
complex terrain, 9, 115, 139, 199, 247, 249, 264, 378
Gaussian-plume models, 8, 9, 51, 52, 115, 116, 118, 119, 138-139, 140, 247, 249, 264, 376-378
industrial-source complex (ISC), 249, 377, 378, 482-483, 489, 565-566, 570-572
stochastic, 9, 52, 55, 116, 138-139
Ambient concentrations, 45, 86, 114, 150-151, 158
cadmium, 100-101
carcinogens, 1, 2, 16, 59, 92-94, 92-100, 102, 229-231, 393, 395, 406-409
dioxins, 102-103
extrapolation from, 2, 5, 32, 58-59, 88-89, 119-120, 142, 210, 220, 449-451
carcinogenicity, 86, 88, 92-104, 120-126, 134, 140-142, 397, 435-436
Page 642
methylene chloride, 94-96
nickel compounds, 101-102
trichloroethylene (TCE), 99-100
Area sources, 3, 37, 38-39, 322, 545-546
Armitage-Doll model, 123, 202-203
Atmospheric processes, see Air-quality models; Transport and fate
Average values, 173, 192-193, 194, 195-196
B
Benchmark dose (BD), 64
Benzene, 32, 33, 42n, 198, 199, 317-321
Bioaccumulation, 37, 40, 51, 52
Biological markers, 45, 151-152
Butadiene, 479
C
Cadmium, 100-101
Cancer and carcinogens, 1, 2, 16-17
animal studies, 92-100, 102, 229-231
extrapolation from, 86, 88, 92-104, 120-126, 134, 140-142, 397, 435-436
classification, 10-11, 58, 59, 60, 126-131, 142, 252, 421-427
dose-response relationship, 65-67, 85, 94-103, 236-237, 427-438
epidemiological studies, 1, 2, 16, 58, 88, 120, 207, 395, 398-404
individual species of suspect classes, 101-102
lifetime risk, 3, 19, 36, 250, 543, 552-553
mechanisms, 2-3, 9, 31, 98-99, 103, 104, 120-121, 123-126, 390-394
cell proliferation, 66-67, 99, 123, 228-229, 391-392, 415
multiple tumor risk, 13, 229-231, 240-241
regulatory approaches, 3, 17, 19, 31-33, 35, 36, 396
risk estimation, 69-70, 488-501, 552-553, 560-561, 567-568
guidelines, 34-35, 56, 87-88, 102, 236-237, 388-440, 600, 629
low-dose, 32, 85, 87, 228-229, 412-417
potency, 10, 102-103, 122-124, 126, 143, 265
unit risk estimate (URE), 10, 94, 103, 122, 124, 143, 314, 323, 543
sites of tumor formation, 121, 141
susceptibility, 200, 201-203, 207, 218-219, 505-512
synergistic interactions, 227-228, 511, 512
threshold doses, 29, 31, 65-66
Carbon monoxide, 198
Cell proliferation, 66-67, 99, 123, 228-229, 391-392, 415
Censuses of population, 113, 114
Central-tendency estimates (CTEs), 172-173, 618-621, 622, 635
Chemical Manufacturers Association (CMA), 111
Chemicals inducing alpha-2-93-94, 621
Children, 11, 210-211, 220, 252, 511
Cigarette smoke, 227-228
Clean Air Act, 3, 21, 36, 89, 91. See also Clean Air Act Amendments of 1990
Clean Air Act Amendments of 1990 (CAAA-90)
Section 112
charge to NRC study committee, 4, 17-20, 82, 599-600
on environmental effects, 39-40
Page 643
listed substances, 3, 36, 38, 84, 92, 145, 146, 148-149, 226, 250-251, 252, 541-542
margin-of-safety approach, 31, 37, 89, 609
on offsetting emissions, 38, 324
on role of risk- and technology-based standards, 3, 21, 28, 36-37, 38, 245, 294, 318-319, 321
Section 303
Risk Assessment and Management Commission, 19, 82, 600
Communication, see Risk characterization and communication
Comparison of risk estimates, 12, 166, 183, 185-186, 260-261, 268. See also Hazard ranking; Risk ranking
Complex terrain, 9, 115, 139, 199, 247, 249, 264, 378
Concentration models, see Air-quality models
Continuous emission monitors (CEMs), 109
Convolution model, 380
Criticisms of risk assessment, 5-6, 40-42, 256, 258
Cumulative distribution function (CDF), 167-168
D
Data availability and quality, 9, 106, 137-138, 333-434
emissions, 9, 110, 138, 147-149
pollutant transport and fate, 150
population data, 112-114
toxicity assessment, 154
Data bases
activity patterns, 114
literature reviews, 10, 253, 265
validation, 106, 107, 254, 255
see also Integrated Risk Information System; Toxic Release Inventory
Data collection priorities, 10-11, 145-146, 154-158, 344-348
exposure, 145, 150-152, 155, 156
pollutant transport and fate, 149-150, 155, 156
toxicity assessment, 145, 153-154, 155, 156
Data needs, 6, 10-11, 79, 115, 144-145, 157-159
activity patterns, 114
emissions, 147-149, 158, 253, 591, 592
exposure, 150-152, 158, 594-596, 635
toxicity assessment, 152-154, 253, 265, 596-597
transport and fate, 149-150, 591, 593-594
see also Data availability and quality; Data collection priorities
Database on Toxic Interactions, 227
Default options, 5, 7, 28-29, 32, 80-81, 85-87, 137-138
articulation of, 7, 8, 81, 87, 88-89, 104, 252, 254-255
criteria and principles, 6, 7, 8, 34, 79, 81-83, 87-90, 195
plausible conservatism, 7, 82, 83, 89, 601-626, 632-634
policy bases, 8, 81, 82, 87, 89, 104
scientific bases, 7, 8, 28-29, 82, 83, 87, 104, 610, 629-640
departures from, 6, 7, 8, 28-29, 34, 79, 90-91, 105
criteria, 7, 8, 81, 90-91, 105, 254-255, 615-617, 629, 632-633
examples of, 92-104
petitioning, 267
scientific consensus for, 7, 8, 91, 105
Page 644
in iterative risk assessment, 243-244, 246-247
recommendations, 8, 14, 104-105, 263, 613-617
susceptibility, 11, 207-209, 219-220, 222n, 252
see also Linearized multistage model; Maximally exposed individual
Detoxifying enzymes, 227, 508, 510
Developmental toxicity, 8, 234, 241
assessment guidelines, 35, 56-57, 63-64
Dibenzofurans, 103
Dioxins, 102-103
Discrete variability, 503
Distribution of exposure, 5, 9, 53, 77, 204-205, 355
Dose-response assessment, 4-5, 26, 60, 152-153, 363-364
carcinogens, 65-67, 85, 94-103, 236-237, 427-438
modeling, 26, 31, 103-104, 122-126, 133, 134
variability issues, 192-193, 221-222n
noncancer endpoints, 60-64, 76
uncertainty issues, 62-63, 71, 163, 236-237, 241-242
see also Linearized multistage model; Potency estimates
Dosimeters, 49
E
Early-reduction program, 38
Elderly persons, 511
Electric Power Research Institute (EPRI), 116
Emission characterization, 5, 9, 23, 27, 47-48, 138
data availability and quality, 9, 110, 138, 147-149
data needs, 147-149, 155, 156, 158, 253, 591, 592
estimation methods, 5, 8, 48-49, 107-112
uncertainty analysis, 8, 9, 110, 112, 138, 453
itemization by chemical constituent, 111, 148
measurement methods, 5, 48-50, 109, 110-111
plant operation and disruptions, 48, 110-111, 197-198
Emission factors, 48, 107, 109, 110, 111-112
Emission standards and limits, 3, 19, 20, 36
for area sources, 3, 37, 38-39, 322
reporting requirements, 109, 110, 112, 148
technology-based, 3, 21, 28, 36-37, 38, 245, 294, 318-319, 321
see also Residual risk evaluation
Environmental Defense Fund v. EPA, 89
Environmental effects, 38, 39-40, 226
Epidemiological studies, 26, 30, 32, 57-58, 104, 113-114, 136-137, 143, 153-154, 212, 220
cadmium, 100-101
carcinogens, 1, 2, 16, 58, 88, 120, 207, 395, 398-404
multiplicative interactions, 227-228
susceptibility, 210
Ethyl Corp. v. EPA, 38, 89, 609
Ethylene oxide (ETO), 233, 233-234
Exponential models, 107-109, 110
Exposure, see Aggregation; Dose-response assessment; Exposure assessment; Routes of Exposure; Threshold dose hypotheses; Toxicity assessment; Variability, in exposure
Exposure assessment, 3, 5, 26-27, 43-45, 48-49, 329-331, 364
Page 645
maximally exposed individual (MEI), 9, 45, 46-47, 203-206, 217
criticisms of, 41
data needs, 145, 150-152, 155, 156, 158, 328, 594-596, 635
estimation methods, 44-45
biological markers, 45, 151-152
environmental monitoring, 26, 44-45, 150-151, 152, 158
guidelines, 44, 45, 68, 69-70, 76, 308-310
modeling, 5, 9, 44, 45, 50-55, 117-119, 139, 252, 330, 332, 376-381
activity patterns, 5, 47, 53, 53-54, 114, 118, 119, 139
Human-Exposure Model (HEM), 9, 117-119, 139, 140, 247, 319, 378-379
long-term, 54-55, 544, 547, 549-554, 558-561, 564-569
population data, 112-114, 117, 118, 139-140, 379
short-term, 55, 380-381, 544, 547, 554-557, 562-563, 569-574
and variability, 6, 11, 20, 79, 189, 196-200, 203-206, 216, 217-218
see also Air-quality models; Emission characterization; Routes of exposure; Transport and fate
Exposure Factors Handbook, 195
Exposure-response relationship, see Dose-response assessment
Extensive-hydroxylator phenotype, 200, 508
Extrapolation of data, 88, 90, 113, 220
among exposure routes, 134, 141, 450
animal to human, 2, 5, 32, 58-59, 88-89, 119-120, 142, 210, 220, 449-451
carcinogens, 86, 88, 92-104, 120-126, 134, 140-142, 397, 435-436
see also Linearized multistage model
F
Food Additive Amendments of 1958, Delaney clause, 17, 31
Food additives and contaminants, 30, 32
Food and Drug Administration (FDA), 32
Food chain accumulation, see Bioaccumulation
Formaldehyde, 96-99, 133, 198, 199
Fugitive emissions, 47, 108-109, 111, 545-546
G
Gaussian-plume models, 8, 9, 51, 52, 115, 116, 118, 119, 138-139, 140, 247, 249, 264, 376-378
Genetic mutation, 231-234, 241
Genetic susceptibility, 11, 201-203, 219, 505-511
Geographic information systems (GIS), 140, 330
Glutathione-S-transferase (GST), 95-96, 508, 510
Great Waters Study, 322-323
Guidance on Risk Characterization for Risk Managers and Risk Assessors, 20
Guidelines for risk assessment, 87, 90, 637
California, 35
carcinogens, 34-35, 56, 87-88, 102, 236-237, 388-440, 600, 629
developmental toxicity, 35, 56-57, 63-64
of EPA, 5, 34-35, 68, 104, 306-307
exposures, 44, 45, 68, 69-70, 76, 308-310
Interagency Regulatory Liason Group (IRLG), 32
Office of Science and Technology Policy (OSTP), 34, 35
Superfund sites, 35, 68, 70, 72, 73-74, 161, 226
toxicity, 56-57
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uncertainty analysis, 12, 70, 72-75, 175-179, 185, 255-256, 257-258
see also Default options; Red Book
H
Habicht memorandum, 68, 76-78, 351-374
Harmonization of risk assessments, 183-184, 186
Hazard assessment, see Hazard identification; Toxicity assessment
Hazard Assessment Documents (HADs), 251, 307-308, 314
Hazard identification, 4, 26, 27, 57, 152, 362-363
carcinogens, 1, 2, 16, 59, 92-94, 393, 395, 406-409
and carcinogen classification, 58, 59, 60, 126-127, 128, 421-427
epidemiological studies, 26, 32, 57-58
carcinogens, 1, 2, 16, 58, 88, 120, 395, 398-404
Hazard index, 69, 70, 250, 544, 557, 561, 563, 569, 572-574
Hazard ranking, 27, 37, 295, 315, 324-325
Heterogeneity dynamics, 202-203
High-end exposure estimate (HEEE), 9, 46, 47, 204-206, 217, 218, 369-370
Homeostasis, 131-132
Human-Exposure Model (HEM), 9, 117-119, 139, 140, 247, 319, 378-379
I
Identifiability, 196, 213, 216-217, 503
Individual risk, 11, 69-70, 207-209, 218, 368-371
uncertainty and variability, 237-239, 532-534
Indoor sources, 9, 10, 49, 199-200, 262, 268, 379
Industrial-source complex (ISC) models, 249, 377, 378, 482-483, 489, 565-566, 570-572
Industrial Union Department, AFL-CIO v. American Petroleum Institute (Benzene decision), 33, 36
Inference guidelines, see Default options
Ingestion, 226
Integrated Risk Information System (IRIS), 250-251, 261-262, 265, 323, 363-364, 583-590
Interagency Regulatory Liason Group (IRLG), 32
International Agency for Research on Cancer (IARC), 32, 58, 59, 126, 129
Iterative risk assessments, 14, 84, 89, 146, 154, 155, 157-158, 253-254, 634
emissions characterization, 147, 247, 249-250
environmental fate and transport, 149-150
exposure, 150-152, 247-250, 540-576
recommendations, 14-15, 263, 264, 266, 267
L
Lagrangian models, 52, 118, 138
Lead, 8
Lesser quantity emission rates (LQERs), 325-326
Lifetime cancer risk, 3, 19, 36, 250, 543, 552-553
Linearized multistage model (LMS), 9, 28, 65, 90, 103, 123, 124-125, 141-142, 613-614
departure from, 10, 28-29, 87-88, 98, 102, 142
and uncertainty analysis, 176-177
Page 647
M
Major point sources, 3, 37, 545
and central-tendency estimates, 618-619
under Clean Air Act, 3, 31, 36, 37, 89, 609
Mass balances, 1-7, 48, 107, 111
Material balances, see Mass balances
Maximally exposed individual (MEI), 9, 37, 45, 46-47, 195, 203-206, 217
Maximum achievable control technology (MACT), 3, 37, 118, 321
Maximum tolerated dose (MTD), 120
Measurement methods, 5, 48-50, 107, 109, 110-111
Metabolic processes, 59, 94-96, 121, 122, 133-134, 411-412, 505-510
Meteorological variability, 198-199
Methylene chloride, 94-96
Microenvironments, 49, 53-54, 114, 199-200, 375-376
Missing defaults, 81, 105, 195, 207
Mixed-function oxidase (MFO) enzymes, 95-96
Mobile sources, 10, 20, 262, 268
Mobility and migration, 45, 54, 113, 118, 119, 139, 205, 217-218
Models and modeling, 9, 107-112, 137-138. See also Air-quality models; Animal studies; Default options; Dose-response assessment, modeling; Exposure assessment, modeling; Linearized multistage model; Model uncertainty; Parameter uncertainty; Pharmacokinetic models; Validation and evaluation
Model uncertainty, 7, 11-12, 80, 83, 86, 87, 90, 165-166, 171-175, 185, 239
Molecular toxicology, 11, 143, 207, 219
Monitoring programs and methods, 26, 44-45, 109, 110-111, 150-151, 152
personal dosimeters, 44, 49, 151, 158
Monte Carlo models, 52, 177, 206, 330, 500
Moolgavkar-Venzon-Knudson model, 123, 195, 211
Multimedia risk assessment model, 453-461
Multiple exposure, see Aggregation
Multiplicative models, 107, 109, 111
N
N-acetylation polymorphism, 200, 508
National Ambient Air Quality Standard (NAAQS) Exposure Model (NEM), 117, 118, 247, 379
National Emission Standards for Hazardous Air Pollutants (NESHAPS), 42n, 72, 74-75, 166, 233
National Institute for Occupational Safety and Health, 143
National Institutes of Health (NIH), 34, 207, 219
National Research Council (NRC), see Red Book
National Toxicology Program (NTP), 10, 122, 141, 157, 231-232, 251, 521, 522-523
Natural Resources Defense Council (NRDC) v. EPA, 3, 36, 37, 89, 317, 320, 609
New York, 137
Nickel, 101-102
Noncancer risks, 10, 39-40, 41, 58, 59, 61, 69-70, 76, 131-132, 142
dose-response assessment, 60-64, 76
Noninhalation exposures, 10, 44, 119, 140, 226
Nonthreshold end points, 225, 229-234, 240-241, 516-528
No-observed-adverse-effect level (NOAEL), 30, 39, 61-64, 132, 142, 323
Page 648
No-observed-effect level (NOEL), 30, 41, 61
Numerical integration, 177
O
Occupational exposure and regulation, 30, 32, 33, 143
Occupational Safety and Health Administration (OSHA), 32, 33
Office of Air Quality Planning and Standards (OAQPS), EPA, 261, 268, 307-308, 309, 311, 329-330, 579
Office of Research and Development (ORD), EPA, 261, 268, 307
Office of Science and Technology Policy (OSTP), 34, 35
Offsetting emissions, 38, 260, 324
P
Parameter uncertainty, 74-75, 86, 165, 172, 173-175, 185, 187n, 238-239, 256, 454, 457-459, 614
Pathways of exposure, see Routes of exposure
Peak-concentration sampling, 151
Peer review, 8, 91, 105, 261, 296-297, 617
Permissible exposure level (PEL), 62
Peroxisome proliferation, 100
Personal activity, see Activity patterns
Personal monitors, 44, 49, 151, 158
Pharmacokinetic models, 95, 125-126, 220-221
physiologically based (PBPK), 66, 95, 96, 122, 165, 211-212, 431, 449-451, 617
in toxicity assessment, 2-3, 9-10, 66, 132-136, 141-142
Pharmacodynamics, 66, 125, 141-142
Photochemical air-quality models, 115, 118, 138
Physiologically based pharmacokinetic models (PBPK), 66, 95, 96, 122, 165, 211-212, 431, 449-451, 617
Plant operations and disruptions, 48, 110-111, 197-198
Plant Organization Software System (POSSEE), 111
Plausible conservatism, 7, 82, 83, 89, 237, 601-626, 632-634
aggregation of, 235-236, 241-242
and risk management, 12, 41, 166-167, 179-181, 184-185
Pollutant transport and fate, see Airquality models; Transport and fate
Polycyclic aromatic hydrocarbons (PAHs), 506-507, 508
Polymorphic phenotypes, 200, 505-510
Population data and models, 112-114, 117, 118, 139-140, 379
mobility, 45, 54, 113, 118, 119, 139, 205, 217-218
Population risk, 70, 209-210, 218, 371-372
children, 11, 210-211, 220, 252, 511
subgroup exposure and susceptibility, 11, 114, 191, 205, 253, 372-373
uncertainty and variability, 239-240, 531-532
Potency estimates, 10, 27, 38, 102-103, 122-124, 126, 143, 265
uncertainty analysis, 10, 143, 162
unit cancer risk, 10, 103, 122, 124, 143
variability, 189, 193, 218-219
Probability density function (PDF), 167-168, 171-175, 184, 186
Probability distributions, 161, 167-178, 180, 184, 454
generation of, 175-177, 465-467
subjective, 83, 170-171, 177, 178
Process-vent emissions, 47, 109
Public criticisms, see Criticisms of risk assessment
R
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Radon, 227-228
Red Book (1983 NRC report), 25, 33-34, 160
on default options, 85, 86-87, 90-91
risk assessment framework, 4-5, 23-24, 26-27, 306, 396, 637
on risk management, 5, 34, 41, 260
Reference concentrations (RfCs), 39, 70, 250, 265, 323, 543
Reference dose (RfD), 62, 63, 70, 142, 311-312
Regulatory policy and decision-making, 2, 3, 5, 7, 17, 18, 28, 36-39, 258-259
and carcinogens, 17, 31-33, 35, 396
and public perception, 262-263
resource allocation, 2, 19, 28, 246, 631
see also Default options; Emission standards and limits; Risk management
Reproductive toxicity, 8, 63, 234, 241
Research activities and agendas, 27-28, 261-262, 268, 611-612, 617-618, 630, 638, 640
Residual risk evaluation, 3, 21, 37, 101, 118, 180, 245, 321, 327, 329, 540, 542
Resource Conservation and Recovery Act (RCRA), 35
Risk Assessment and Management Commission, 19, 82, 600
Risk Assessment in the Federal Government: Managing the Process, see Red Book
Risk characterization and communication, 5, 23, 27, 68, 78, 80, 181, 183, 439-440, 630-631
and aggregation, 234-240, 530-534
EPA (Habicht) memorandum, 68, 76-78, 351-374
full disclosure, 77, 352-353, 355, 361-367
to managers, 13, 78, 80, 83-84, 310-312, 614-615, 630-632
presentation of estimates, 69-70, 76-78, 83-84, 351-374, 624-625
professional judgment, 77, 354
to public, 78, 144-145, 194, 252
uncertainty analysis, 12, 15, 20, 27, 41, 70-75, 78, 83-84, 174, 180, 235-240, 263, 310-312, 362, 365-366
use of multiple descriptors, 77, 353-354, 355, 367-374
of variability, 11, 194, 212-213, 214-215, 221
Risk management, 18, 19, 28, 32, 41-42, 349-350, 360-361, 630-632
communication of risk to, 13, 78, 80, 83-84, 310-312, 614-615, 630-632
risk-reduction strategies, 196, 262
safety-factor approach, 30-31
separation from risk assessment, 5, 34, 77, 259-260, 267-268, 355, 358-360, 623
and uncertainty analysis, 41, 166-167, 171-175, 179-183
Risk ranking, 27, 37, 171, 183, 186-187, 296, 315, 325-326, 617
Routes of exposure, 10, 26-27, 43-44, 119, 140
extrapolation among, 134, 141, 450
multiple, 13, 41, 51-52, 119, 225-226, 240, 252
noninhalation, 10, 44, 119, 140, 226
and site of tumor formation, 121
S
Safety-factor method, 30-31, 62-63, 224
Science Advisory Board (SAB), EPA, 7, 8, 91, 105, 617
Screening assessments, 9, 14, 84, 156, 159, 217, 242, 245-246, 263, 326-327, 544, 549-563
Simulation of Human Air Pollution Exposure (SHAPE) Model, 117, 118, 379-380
Single point estimates, see Point estimates
Page 650
Source Category Ranking System (SCRS), 325
Sources of hazardous pollutants, 3, 37, 47-48, 54, 545
area sources, 3, 37, 38-39, 322, 545-546
indoor, 9, 10, 49, 199-200, 262, 268, 379
Spatial variability, 191-192, 197-198
State Activity Pattern Study, 114
State government, 10, 42, 152, 157
State implementation plans (SIPs), 147-148
Stochastic modeling, 9, 52, 55, 116, 138-139
Storage-tank emissions, 47-48, 111
Strength of evidence, 10, 126-127, 128, 129
Structured activity relationships (SARs), 410-411
Subjective probability distributions, 83, 170-171, 177, 178
Subpopulation exposures and risk, 11, 114, 191, 205, 253, 372-373
Superfund Amendments and Recovery Act (SARA), 147, 148, 158, 313
Superfund-site risk assessment, 35, 68, 70, 72, 73-74, 161, 226
Susceptibility, 11, 30, 207-209, 219-220, 222n, 252
to cancer, 200, 201-203, 207, 218-219, 505-512
genetic, 11, 201-203, 219, 505-511
identification of high-risk individuals, 196, 213, 216-217, 503
variability in, 6, 11, 40, 79, 196, 206-210, 213, 216-217, 218-221
Synergistic interactions, 40, 227-228, 511, 512
Systematic bias, 165
T
Targeted fixed-point monitoring, 151
Technology-based regulation, 3, 21, 28, 31, 33, 36-37, 38, 245, 294, 318-319, 321
Temporal variability, 191, 197-198
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), 102-103
Theoretical upper-bound exposure (TUBE), 9, 46-47, 204
Threshold dose hypotheses, 8, 29-31, 39, 62-64, 131-132
multiple chemical exposure, 224-225, 228-229
Threshold limit values (TLVs), 30
Tiered modeling approach, 243-244, 326-327, 329. See also Iterative risk assessments
Time-activity patterns, 47, 53, 114
Total Exposure and Assessment Methodology (TEAM), 49, 114, 117
Toxic-equivalency factor (TEF) method, 103
Toxicity assessment, 2-3, 23, 56-57, 295, 314, 323-324
carcinogen classification, 10-11, 126-131, 142, 252
carcinogens, 397-427
animal studies, 120-126, 140-142, 397
data needs, 145, 152-154, 155, 156, 253, 265, 596-597
extrapolation of animal studies, 119-120, 120-126, 140-142, 142
noncancer endpoints, 10, 131-132, 142
pharmacokinetic models, 2-3, 9-10, 66, 132-136, 141-142
see also Dose-response assessment; Hazard identification; Potency estimates
Toxic Release Inventory (TRI), 147-149, 158, 313
Toxic Substances Control Act (TSCA), 35
Transfer emissions, 48
Page 651
variability, 189, 197, 198-199
see also Air-quality models; Exposure assessment
Trichloroethylene (TCE), 99-100
U
Uncertainty, 11-12, 27, 28, 70, 137, 160-166, 252
communication of, 12, 15, 20, 27, 41, 70-75, 78, 83-84, 174, 180, 235-240, 263, 310-312, 362, 365-366
in dose-response assessment, 62-63, 71, 163, 236-237, 241-242
in emissions estimation, 8, 9, 110, 112, 138, 453
EPA approach, 6, 70, 72-75, 79, 166-167
in exposure assessment, 71, 163
guidance on analysis, 12, 70, 72-75, 175-179, 185, 255-256, 257-258
in hazard identification, 71, 163
in population data, 113-114
probability distributions, 161, 167-178, 180, 184, 454
generation of, 175-177, 465-467
recommendations, 12, 167, 168, 184-187
in Superfund-site assessments, 70, 72, 73-74, 161
and variability, 11, 162, 164, 180-181, 187n, 213, 221, 237-240, 242
see also Default options; Model uncertainty; Parameter uncertainty
Uncertainty-factor approach, 39, 62-63, 142, 224
Unit risk estimate (URE), 10, 94, 103, 122, 124, 143, 314, 323, 543
Unleaded gasoline, 92
V
Validation and evaluation, 6, 8-10, 79, 106-107, 136-143, 254-255
air-quality models, 114-119, 138-139
data bases, 106, 107, 254, 255
exposure models, 49-50, 114, 139-140, 264
extrapolation of animal studies, 119-136, 140-142, 212
Variability, 11, 188-191, 189, 195, 196, 221n
in biological characteristics, 211-212, 220
communication of, 11, 194, 212-213, 214-215, 217-221
in exposure, 6, 11, 20, 79, 189, 196-200, 203-206, 216, 217-218
activity patterns, 196, 199-200, 217
management strategies, 191-196
in susceptibility, 6, 11, 40, 79, 206-210, 216-217, 218-221
to cancer, 200, 201-203, 207, 218-219, 505-512
defaults, 11, 207-209, 219-220, 222n, 252
distributions and dichotomies, 201-203, 206-210, 503
identifiable, 196, 213, 216-217, 503
and uncertainty, 11, 162, 164, 180-181, 187n, 213, 221, 237-240, 242
use of averages, 192-193, 194, 195-196
use of high end values, 193, 195-196, 217
Variance-component model, 380-381
Vinyl chloride, 42n, 133-134, 317, 320
Volatile organic compounds (VOCs), 111, 148, 149, 150