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EPA Cincinnati EPA 600/R-06/087 June 2006 Exposures and Internal Doses of Trihalomethanes in Humans: Multi-Route Contributions from Drinking Water National Center for Environmental Assessment Office of Research and Development U.S. Environmental Protection Agency Cincinnati, OH 45268 NOTICE The U.S. Environmental Protection Agency through its Office of Research and Development funded and managed the research described here under Purchase Order no. 3C-R3350WASX to Wilkes Technologies, Inc. It has been subjected to the Agency’s peer and administrative review and has been approved for publication as an EPA document. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. ABSTRACT The concentrations of the four commonly-identified trihalomethanes (THM; chloroform, bromodichloromethane, chlorodibromomethane and bromoform) in U.S. drinking water systems are regulated as a group. This report develops, applies and communicates a method to estimate internal exposures to these simultaneously- exposed chemicals. Because they are present in water used for drinking, bathing and other household uses, and because they are highly volatile, this work evaluated the development of internal doses via the oral, dermal and inhalation routes following residential exposures. This was accomplished by integrating several data sets that characterize human activity patterns, water use behavior, household volumes and ventilation, and THM concentration in drinking water. Physiologically based pharmacokinetic modeling was used to translate external exposures to internal doses for the simulated adult male and female and the 6-year-old child. Results indicated that inhalation exposures predominated and that children developed higher internal doses (mg/kg body weight) than adults in the same household. This report demonstrates the technical feasibility of combining stochastic and deterministic models and modeling approaches with “real-world” concentrations of drinking water contaminants (here, THMs) to estimate internal doses for risk evaluation and for the examination of toxicokinetic interactions among mixtures of chemicals. Preferred citation: U.S. EPA. 2006. Exposures and Internal Doses of Trihalomethanes in Humans: Multi- Route Contributions from Drinking Water. Office of Research and Development, National Center for Environmental Assessment, Cincinnati, OH. EPA 600/R-06/087. ii TABLE OF CONTENTS Page TABLE OF CONTENTS ..................................................................................................iii LIST OF TABLES............................................................................................................vi LIST OF FIGURES..........................................................................................................xi LIST OF ABBREVIATIONS......................................................................................... xviii PREFACE .....................................................................................................................xix AUTHORS, CONTRIBUTORS AND REVIEWERS ........................................................xx EXECUTIVE SUMMARY.............................................................................................. xxii 1. PROJECT OVERVIEW AND OBJECTIVES......................................................... 1 1.1 OVERVIEW OF EXPOSURE AND PBPK MODEL APPROACH AND LINKAGE........................................................................................... 4 1.1.1. Modeling Theory and Numerical Methods....................................... 5 1.1.2 Simulating Water Uses.................................................................... 5 2. MODEL PARAMETERS ....................................................................................... 8 2.1. VOLATILIZATION MODEL PARAMETERS............................................... 9 2.1.1. Literature Review of Chemical Properties ..................................... 11 2.1.2. Estimating Chemical Properties .................................................... 11 2.2. BEHAVIORAL CHARACTERISTICS ....................................................... 16 2.2.1. Activity Patterns ............................................................................ 17 2.2.2. Water-use Behaviors for Groups of Interest.................................. 21 2.3. INGESTION CHARACTERISTICS .......................................................... 27 2.3.1. Available Data Sources................................................................. 28 2.3.2. Ingestion Behavior for the Three Populations: Results of Analysis......................................................................................... 29 iii TABLE OF CONTENTS cont. Page 2.4. BUILDING CHARACTERISTICS ............................................................. 30 2.4.1. Representation of Household Volumes......................................... 30 2.4.2. Representation of Whole House Air Exchange Rates and Interzonal Airflows......................................................................... 32 2.4.3. Model Representation of Building ................................................. 35 2.5. CONCENTRATIONS IN WATER SUPPLY.............................................. 35 2.5.1. Water Concentrations Selected as Model Inputs .......................... 38 2.5.2. Estimated Concentrations in Consumed Tap Water ..................... 39 2.6. UPTAKE AND SOLUBILITY PARAMETERS........................................... 42 2.6.1. Breathing Rates by Activity and Demographic Group ................... 42 2.6.2. Skin Permeability Coefficients for Each Chemical......................... 42 2.6.3. Partition Coefficients for Each Chemical ....................................... 42 2.7. UPTAKE CALCULATIONS ...................................................................... 42 2.7.1. Dermal Uptake Calculations .......................................................... 43 2.7.2. Inhalation Uptake Calculations ...................................................... 44 3. PHYSIOLOGICALLY BASED PHARMACOKINETIC (PBPK) MODEL............... 46 3.1. MODEL STRUCTURE............................................................................. 46 3.2. MASS BALANCE EQUATIONS............................................................... 47 3.3. RELATIONSHIP BETWEEN THM METABOLISM AND TOXICITY......... 49 3.4. METABOLIC INTERACTIONS ................................................................ 50 4. TRANSFER FILE DEFINITIONS........................................................................ 54 4.1. BREATHING RATE FILES ...................................................................... 54 4.2. DERMAL DATA FILES ............................................................................ 55 4.3. INGESTION DATA FILES........................................................................ 55 4.4. INHALATION DATA FILES...................................................................... 56 iv TABLE OF CONTENTS cont. Page 5. RESULTS........................................................................................................... 58 5.1. EXPOSURE TO THE THMs THROUGH WATER USAGE...................... 58 5.1.1.` Water Concentrations ................................................................... 58 5.2. INTERNAL DOSES OF THE THMs FROM WATER USAGE: AN ILLUSTRATIVE CASE RESULTS ........................................................... 59 5.3 INTERNAL DOSES OF THE THMs FROM WATER USAGE: POPULATION-BASED RESULTS........................................................... 60 5.3.1. Population Results for Chloroform ................................................ 60 5.3.2. Population Results for BDCM ....................................................... 61 5.3.3. Population Results for DBCM ....................................................... 61 5.3.4. Population Results for Bromoform ................................................ 61 5.4. METABOLIC INTERACTIONS BETWEEN THE THMs ........................... 61 5.5. INFLUENCE OF WATER-USE PATTERNS ON INTERNAL DOSIMETRY FOR THE THMs ................................................................ 62 5.6. LIMITED SENSITIVITY ANALYSIS OF THE PBPK MODEL ................... 64 6. DISCUSSION ..................................................................................................... 67 7. CONCLUSIONS ................................................................................................. 71 8. MODEL ASSUMPTIONS AND DATA QUALITY ................................................ 73 8.1. DATA QUALITY....................................................................................... 73 8.2. ACTIVITY PATTERN DATABASE OVERVIEW....................................... 73 8.3. OTHER ASSUMPTIONS ......................................................................... 76 9. REFERENCES................................................................................................... 78 APPENDIX: PBPK Model Code .................................................................................... 86 v LIST OF TABLES No. Title Page 1 Location Codes Recorded in the National Human Activity Pattern Survey (NHAPS)................................................................................................T-1 2 Activity Codes Recorded in the National Human Activity Pattern Survey (NHAPS)................................................................................................T-2 3 List of Chemicals for Exposure Assessment......................................................T-3
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