Guidelines for Exposure Assessment - US EPA

EPA/600/Z-92/001 May 1992

Guidelines for Exposure Assessment

Published on May 29, 1992, Federal Register 57(104):22888-22938 These guidelines replace the previously issued final Guidelines for Estimating Exposures (September 24, 1986), Federal Register 51(185):34042-34054, and the Proposed Guidelines for Exposure-Related Measurements (December 2, 1988), Federal Register 53(232):4883048853.

Risk Assessment Forum

U.S. Environmental Protection Agency

Washington, DC

DISCLAIMER This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

Note: This document represents the final guidelines. A number of editorial corrections have been made during conversion and subsequent proofreading to ensure the accuracy of this publication.

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CONTENTS

Lists of Tables and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Federal Register Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

Abbreviations and Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii

Part A: Guidelines for Exposure Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1. Intended Audience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2. Purpose and Scope of the Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3. Organization of the Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. General Concepts in Exposure Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1. Concepts of Exposure, Intake, Uptake, and Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.1.1. Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.1.2. Applied Dose and Potential Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1.3. Internal Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1.4. Exposure and Dose Relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.1.4.1. Calculating Potential Dose for Intake Processes . . . . . . . . . . . 10

2.1.4.2. Calculating Internal Dose for Uptake Processes . . . . . . . . . . . 14

2.1.4.3. Calculating Internal Dose for Intake Processes (Especially via

Respiratory and Oral Routes) . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.1.5. Summary of Exposure and Dose Terms with Example Units . . . . . . . . . 18

2.2. Approaches to Quantification of Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.2.1. Measurement of Exposure at the Point of Contact . . . . . . . . . . . . . . . . . 22

2.2.2. Estimates of Exposure from Scenario Evaluation . . . . . . . . . . . . . . . . . . 22

2.2.3. Exposure Estimation by Reconstruction of Internal Dose . . . . . . . . . . . . 24

2.3. Relationships of Exposure and Dose to Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2.3.1. Individual Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2.3.2. Population Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.3.3. Risk Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3. Planning an Exposure Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.1. Purpose of the Exposure Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.1.1. Using Exposure Assessments in Risk Assessment . . . . . . . . . . . . . . . . . . 33

3.1.2. Using Exposure Assessments for Status and Trends . . . . . . . . . . . . . . . . 34

3.1.3. Using Exposure Assessments in Epidemiologic Studies . . . . . . . . . . . . . 35

3.2. Scope of the Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

3.3. Level of Detail of the Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

3.4. Determining the Approach for the Exposure Assessment . . . . . . . . . . . . . . . . . . . . 36

3.5. Establishing the Exposure Assessment Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.5.1. Planning an Exposure Assessment as Part of a Risk Assessment . . . . . . 38

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CONTENTS (continued)

3.5.2. Establishing the Sampling Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.5.2.1. Data Quality Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.5.2.2. Sampling Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.5.2.3. Quality Assurance Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

3.5.2.4. Background Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

3.5.2.5. Quality Assurance and Quality Control . . . . . . . . . . . . . . . . . . 43

3.5.2.6. Quality Assurance and Quality Control for Previously Generated

Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

3.5.2.7. Selection and Validation of Analytical Methods . . . . . . . . . . . . 44

3.5.3. Establishing the Modeling Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

3.5.3.1. Setting the Modeling Study Objectives . . . . . . . . . . . . . . . . . . . 45

3.5.3.2. Characterization and Model Selection . . . . . . . . . . . . . . . . . . . 45

3.5.3.3. Obtaining and Installing the Computer Code . . . . . . . . . . . . . . 46

3.5.3.4. Calibrating and Running the Model . . . . . . . . . . . . . . . . . . . . . 46

3.5.3.5. Model Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

3.5.4. Planning an Exposure Assessment to Assess past Exposures . . . . . . . . . 48

4. Gathering and Developing Data for Exposure Assessments . . . . . . . . . . . . . . . . . . . . . . . . . 49

4.1. Measurement Data for Point-of-contact Assessments . . . . . . . . . . . . . . . . . . . . . . . 49

4.2. Obtaining Chemical Concentration Information . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

4.2.1. Concentration Measurements in Environmental Media . . . . . . . . . . . . . . 50

4.2.2. Use of Models for Concentration Estimation . . . . . . . . . . . . . . . . . . . . . . 56

4.2.3. Selection of Models for Environmental Concentrations . . . . . . . . . . . . . . 57

4.3. Estimating Duration of Contact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

4.3.1. Observation and Survey Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

4.3.2. Developing Other Estimates of Duration of Contact . . . . . . . . . . . . . . . . 60

4.4. Obtaining Data on Body Burden or Biomarkers . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

4.5. Obtaining Data for Pharmacokinetic Relationships . . . . . . . . . . . . . . . . . . . . . . . . . 61

4.6. Obtaining Data on Intake and Uptake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

5. Using Data to Determine or Estimate Exposure and Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

5.1. Use of Data in Making Inferences for Exposure Assessments

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

5.1.1. Relevance of Data for the Intended Exposure Assessment . . . . . . . . . . . 64

5.1.2. Adequacy of Data for the Intended Assessment . . . . . . . . . . . . . . . . . . . . 64

5.1.2.1. Evaluation of Analytical Methods . . . . . . . . . . . . . . . . . . . . . . . 65

5.1.2.2. Evaluation of Analytical Data Reports . . . . . . . . . . . . . . . . . . . 65

5.1.2.2.1. Evaluation of Censored Data Sets. . . . . . . . . . . . . . . . 66

5.1.2.2.2. Blanks and Recovery. . . . . . . . . . . . . . . . . . . . . . . . . . 68

5.1.3. Combining Measurement Data Sets from Various Studies . . . . . . . . . . . 68

5.1.4. Combining Measurement Data and Modeling Results . . . . . . . . . . . . . . . 69

5.2. Dealing with Data Gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

5.3. Calculating Exposure and Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

5.3.1. Short-term Versus Long-term Data for Population Exposures . . . . . . . . . 71

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CONTENTS (continued)

5.3.2. Using Point-of-contact Data to Calculate Exposure and Dose . . . . . . . . . 72

5.3.3. The Role of Exposure Scenarios in Exposure Assessment . . . . . . . . . . . . 72

5.3.3.1. Scenarios as a Means to Quantify Exposure and Dose . . . . . . . 73

5.3.3.2. Exposure Scenarios and Exposure Estimators as Input to Risk

Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

5.3.3.3. Exposure Scenarios as a Tool for Option Evaluation . . . . . . . . 75

5.3.4. General Methods for Estimating Exposure and Dose . . . . . . . . . . . . . . . 76

5.3.4.1. Preliminary Evaluation and Bounding Estimates . . . . . . . . . . . 76

5.3.4.2. Refining the Estimates of Exposure and Dose . . . . . . . . . . . . . . 78

5.3.5. Using Estimates for Developing Descriptors . . . . . . . . . . . . . . . . . . . . . . 79

5.3.5.1. Individual Exposure, Dose, and Risk . . . . . . . . . . . . . . . . . . . . . 79

5.3.5.2. Population Exposure, Dose, and Risk . . . . . . . . . . . . . . . . . . . 86

6. Assessing Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

6.1. Role of Uncertainty Analysis in Exposure Assessment . . . . . . . . . . . . . . . . . . . . . . 90

6.2. Types of Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

6.2.1. Scenario Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

6.2.2. Parameter Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

6.2.3. Model Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

6.3. Variability Within a Population Versus Uncertainty in the Estimate . . . . . . . . . 97

7. Presenting the Results of the Exposure Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

7.1. Communicating the Results of the Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

7.1.1. Exposure Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

7.1.2. Risk Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

7.1.2.1. Integration of Hazard Identification, Dose-response, and Exposure Assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

7.1.2.2. Quality of the Assessment and Degree of Confidence . . . . . . . 102

7.1.2.3. Descriptors of Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

7.1.2.4. Communicating Results of a Risk Assessment to the Risk Manager

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

7.1.3. Establishing the Communication Strategy . . . . . . . . . . . . . . . . . . . . . . . 103

7.2. Format for Exposure Assessment Reports . . . . . . . . . . . . . . . . . . . . . . . . . 104

7.3. Reviewing Exposure Assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

8. Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

9. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

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