EPA/600/R-05/095
February 2003
Inhalation Exposure to Methyl terf-Butyl
Ether (MTBE) Using Continuous
Breath Analysis
by
Sydney M. Gordon
Atmospheric Science and Applied Technology
Battelle Memorial Institute
Columbus, Ohio 43201
Task Order No. 0009 (ORD-99-202)
EPA Contract 68-D-99-011
EPA Project Officer
Ellen W. Streib
National Exposure Research Laboratory (MD-56)
Research Triangle Park, North Carolina 27711
Task Order Project Officer
Lance A. Wallace
National Exposure Research Laboratory
Reston, Virginia 20192
National Exposure Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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EPA Disclaimer
The information in this document has been funded wholly or in part by the United States
Environmental Protection Agency under Contract 68-D-99-011 to Battelle Memorial Institute. 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.
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Foreword
The mission of the National Exposure Research Laboratory (NERL) is to provide
scientific understanding, information, and assessment tools that will quantify and reduce the
uncertainty in EPA's exposure and risk assessments for environmental stressors. These stressors
include chemicals, biologicals, radiation, and changes in climate, land use, and water use. The
Laboratory's primary function is to measure, characterize, and predict human and ecological
exposure to pollutants. Exposure assessments are integral elements in the risk assessment
process used to identify populations and ecological resources at risk. The EPA relies
increasingly on the results of quantitative risk assessments to support regulations, particularly of
chemicals in the environment. In addition, decisions on research priorities are influenced
increasingly by comparative risk assessment analysis. The utility of the risk-based approach,
however, depends on accurate exposure information. Thus, the mission of NERL is to enhance
the Agency's capability for evaluating exposure of both humans and ecosystems from a holistic
perspective.
The National Exposure Research Laboratory focuses on four major research areas:
predictive exposure modeling, exposure assessment, monitoring methods, and environmental
characterization. Underlying the entire research and technical support program of the NERL is
its continuing development of state-of-the-art modeling, monitoring, and quality assurance
methods to assure the conduct of defensible exposure assessments with known certainty. The
research program supports its traditional clients - Regional Offices, Regulatory Program Offices,
ORD Offices, and Research Committees - and ORD's Core Research Program in the areas of
health risk assessment, ecological risk assessment, and risk reduction.
Monitoring techniques for volatile organic compounds (VOCs) in air or exhaled breath
are constantly evolving as the needs of the exposure assessment and health effects communities
change. The continuous real-time breath analyzer provides a unique means of collecting
abundant data with which to track the uptake, distribution in the body, and decay of numerous
compounds of interest to NERL. The purpose of the present study was to better understand the
uptake and disposition of methyl r-butyl ether (MTBE) and dibromochloromethane (DBCM)
within the human body as a result of inhalation exposure.
Gary J. Foley
Director
National Exposure Research Laboratory
in
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Abstract
The oxygenate methyl tert-buty\ ether (MTBE) has been added to gasoline to meet
national ambient air quality standards in those parts of the U.S. that are non-compliant for carbon
monoxide. Although MTBE has provided important health benefits in terms of reduced
hazardous air pollutants, the increasing occurrence and detection of MTBE in drinking water
sources in California, New Jersey, and elsewhere has raised concerns about potential exposures
from water usage and resulting health effects. In addition to MTBE, disinfection byproducts can
be present in the water people use for showering, bathing, or drinking, as a result of the reaction
of disinfection agents with organic material already present in water. Chlorine reacts with humic
acids to form the trihalomethanes, which are the most common and abundant byproducts in
chlorinated water. Besides chloroform, which has been widely studied, the byproduct
dibromochloromethane (DBCM) occurs as a result of the chlorination process in those areas that
naturally have bromide in their ground water. Relatively little information on exposure to this
chemical is available.
This study was designed to determine the uptake by humans of MTBE and DBCM as a
result of controlled, short-term inhalation exposures. Our approach made use of continuous real-
time breath analysis to generate exhaled-breath profiles, and evaluate MTBE and DBCM kinetics
in the body. Seven subjects were exposed continuously via face mask to 2,217 |ig/m3 (542 ppbv)
MTBE-di2 and 728 |ig/m3 (85.6 ppbv) DBCM, except for several brief (~2-min) intervals during
which breath measurements were taken. Total exposure time was -30 min, followed by
exposure to clean air for a further 30 — 60 min. Exhaled breath was sampled and analyzed with
the real-time breath technology; blood samples were simultaneously collected from the subjects
(3-4 samples during exposure; 2-5 samples post-exposure). The real-time technology was
specially modified with a biofeedback exposure control system to allow us to make uptake
measurements during the exposure period; breath measurements were taken continuously
throughout the post-exposure period.
The exposures resulted in an increase in the measured breath concentration of MTBE-di2
from pre-exposure levels of 10 - 20 |ig/m3 (2-5 ppbv) to 200 - 450 |ig/m3 (50 - 110 ppbv)
following exposure. MTBE-di2 blood concentrations increased from the limit of detection, 0.30
|ig/L, to -0.9 - 2.5 |ig/L at the end of the ~30-min exposure period.
The time-course measurements of both exhaled breath and venous blood are well-
described by the linear compartmental uptake and elimination models, the interpretation of
which provides important information on the residence times of the compound in the body, the
relative capacity of each compartment, and the fraction of the chemical exhaled unchanged at
equilibrium. The breath uptake data were consistent with a one-compartment model. The mean
IV
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value for the one-compartment uptake residence times Tiuptake was 5.7 ± 2.4 (SD) min (range 3.3
- 9.8 min). In contrast, the breath decay phase data gave satisfactory two-compartment fits. The
mean value for the first compartment decay residence times TI decay was 3.8 ± 1.9 (SD) min (range
2.4 - 7.8 min); for the second compartment, the mean decay residence time Tuecay was 61 ± 11
(SD) min (range 46 - 73 min). The blood uptake data were also consistent with a one-
compartment model and were convergent in almost all cases. The average blood uptake
residence time was essentially the same as that for the breath. The quality of the blood decay
data were such that we were only able to extract meaningful information from 2 or 3 data sets.
The mean MTBE-di2 total absorbed ("internal") dose was 149 ± 34 jig for the average 30-
min exposure and a mean total ("applied") dose of 209 jig. The mean fraction of MTBE-di2
absorbed, or relative uptake, was 0.73 ± 0.04. The mean value for/ the fraction of the MTBE-di2
exposure concentration exhaled unchanged was 0.29 ± 0.04. This value is in good agreement
with the value recently reported by Lee et al. Using linear regression analysis, the mean
blood/breath ratio for MTBE-di2 was found to be 6.7 ± 3.4. This value is significantly lower than
values obtained in previous studies. The reason for this discrepancy is not clear.
By and large, background levels for DBCM in the exhaled breath were below the limit of
detection, and the signal measured for this compound at m/z 129, the most abundant ion in the
glow discharge mass spectrum, was exceptionally "noisy". The average signals during the
uptake phase provided initial (pre-exposure) breath concentrations that ranged from 70 to 160
|ig/m3 and rose to between 130 and 250 |ig/m3 after 30 minutes. The high initial breath
concentrations suggest that the measured signal at m/z 129 was probably elevated due to an
unknown contaminant with fragment ions at the same mass. For TEA, all of the blood
measurements were below the detection limit.
The work reported herein was performed by Battelle Memorial Institute under U.S.
Environmental Protection Agency Contract 68-D-99-011, and covers the period from February
2000 to February 2002. Work was completed as of January 31, 2002.
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Contents
Foreword iii
Abstract iv
Figures vii
Tables xiii
Acknowledgments xiv
Chapter 1 Introduction 1
Chapter 2 Conclusions 3
Chapters Recommendations 5
Chapter 4 Experimental Procedures 6
Experimental Procedures 6
Data Analysis 17
Quality Control 23
Chapters Results 27
Exhaled Breath Data 27
Breath and Blood Data 30
Total Absorbed Dose 49
Fraction of Compound Exhaled Unchanged at Equilibrium 49
Empirical Modeling of Uptake and Decay Breath and
Blood Concentrations 49
Relationship Between Breath and Blood Concentrations 61
Quality Control Data 62
Chapter 6 Discussion 65
Breath and Blood Concentration/Time Profiles 65
Breath and Blood Residence Times 66
Total Absorbed Dose and Fractional Uptake ofMTBE 68
Fraction/Exhaled at Equilibrium and Respiratory Fraction
Eliminated Post-Exposure 68
Linear Compartment Coefficients 68
Blood/Breath Ratios 69
References 71
Appendices
A: Questionnaire and Summary of Responses Received
B: EOHSI Calibration Data for Analysis of Blood and Urine Field Samples
VI
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Figures
4-1 Closed delivery system to (i) provide subject wearing full face mask with
precisely metered amount of chemical(s) for inhalation (from pressurized
gas cylinder and dry gas meter); and (ii) to measure amount of chemical
exhaled unchanged (via dry gas meter attached to breath interface and
(glow discharge/ion trap mass spectrometer) breath analyzer) 7
4-2 Continuous real-time breath analyzer (RTBA), consisting of breath inlet
(breath holding volume) attached to direct breath sampling interface
(glow discharge ionization source) and ion trap mass spectrometer
(GD/ITMS) 9
4-3 Diagram of instrumentation to measure target contaminant breath
concentration continuously in real time during inhalation exposure
to the contaminant. Schematic shows initial configuration of Valves
A, B, and C at time t = 0 min. The breath inlet (breath holding volume)
and breath analyzer are shown in greater detail in Figure 4-2 9
4-4 Graphical user interface for inhalation exposure data acquisition and
control program 12
4-5 Modeled (solid line) and measured (asterisks) inhalation uptake of
1,1,1-trichloroethane in exhaled breath of a subject exposed to 50 ppbv
(270 |ig/m3) 1,1,1-trichloroethane in air. For the curve calculated from
the linear compartment model, we assumed/= 0.87; TI = 9.0 min;
72 = 41 min; and 7j = 288 min (from Wallace et al.45) 15
4-6 Step function exposure to a constant air concentration Cair for time T 18
4-7 Plot showing rapid increase in alveolar breath concentration Caiv as a result
of step function exposure to a constant air concentration Cair, followed
by a rapid decrease in breath concentration as a result of exposure to
clean air 19
5-1 Continuous uptake and decay profiles of MTBE-di2 (upper plot) and DBCM
(lower plot) in breath for female Subject IF02 exposed to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for
29.3 minutes (effective exposure period) 31
vn
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Figures (continued)
5-2 Continuous uptake and decay profiles of MTBE-di2 (upper plot) and DBCM
(lower plot) in breath for male Subject IM03 exposed to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for
30.6 minutes (effective exposure period) 32
5-3 Continuous uptake and decay profiles of MTBE-di2 (upper plot) and DBCM
(lower plot) in breath for male Subject IM04 exposed to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for
30.3 minutes (effective exposure period) 33
5-4 Continuous uptake and decay profiles of MTBE-di2 (upper plot) and DBCM
(lower plot) in breath for male Subject EVI05 exposed to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for
30.6 minutes (effective exposure period) 34
5-5 Continuous uptake and decay profiles of MTBE-di2 (upper plot) and DBCM
(lower plot) in breath for male Subject EVI08 exposed to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for
30.6 minutes (effective exposure period) 35
5-6 Continuous uptake and decay profiles of MTBE-di2 (upper plot) and DBCM
(lower plot) in breath for female Subject IF06 exposed to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for
30.7 minutes (effective exposure period) 36
5-7 Continuous uptake and decay profiles of MTBE-di2 (upper plot) and DBCM
(lower plot) in breath for male Subject EVIOl exposed to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for
30.5 minutes (effective exposure period) 37
5-8 Discrete uptake and continuous decay profiles of MTBE-di2 (upper plot) and
DBCM (lower plot) in breath for female Subject IF02 exposed to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for 29.3
minutes (effective exposure period). LOD designates limit of detection for
target compound 38
5-9 Discrete uptake and continuous decay profiles of MTBE-di2 (upper plot) and
DBCM (lower plot) in breath for male Subject EVI03 exposed to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for 30.6
minutes (effective exposure period). LOD designates limit of detection for
target compound 39
Vlll
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3
Figures (continued)
5-10 Discrete uptake and continuous decay profiles of MTBE-di2 (upper plot) and
DBCM (lower plot) in breath for male Subject IM04 exposed to 2,217 |ig/m
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for 30.3
minutes (effective exposure period). LOD designates limit of detection for
target compound 40
5-11 Discrete uptake and continuous decay profiles of MTBE-di2 (upper plot) and
DBCM (lower plot) in breath for male Subject IM05 exposed to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for 30.6
minutes (effective exposure period). LOD designates limit of detection for
target compound 41
5-12 Discrete uptake and continuous decay profiles of MTBE-di2 (upper plot) and
DBCM (lower plot) in breath for male Subject EVI08 exposed to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for 30.6
minutes (effective exposure period). LOD designates limit of detection for
target compound 42
5-13 Discrete uptake and continuous decay profiles of MTBE-di2 (upper plot) and
DBCM (lower plot) in breath for female Subject IF06 exposed to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for 30.7
minutes (effective exposure period). LOD designates limit of detection for
target compound 43
5-14 Discrete uptake and continuous decay profiles of MTBE-di2 (upper plot) and
DBCM (lower plot) in breath for male Subject EVI01 exposed to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv) of DBCM in air for 30.5
minutes (effective exposure period). LOD designates limit of detection for
target compound 44
5-15 Uptake and decay of MTBE-di2 in breath and blood for female Subject IF02
exposed to 2,217 |ig/m3 (542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv)
ofDBCMin airfor29.3 minutes 45
5-16 Uptake and decay of MTBE-di2 in breath and blood for male Subject EVI03
exposed to 2,217 |ig/m3 (542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv)
ofDBCMin airfor 30.6 minutes 45
5-17 Uptake and decay of MTBE-di2 in breath and blood for male Subject EVI04
exposed to 2,217 |ig/m3 (542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv)
ofDBCMin airfor 30.3 minutes 46
IX
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Figures (continued)
5-18 Uptake and decay of MTBE-di2 in breath and blood for male Subject IM05
exposed to 2,217 |ig/m3 (542 ppbv) of MTBE-di2 and 728 |ig/m3 (85.6 ppbv)
ofDBCMin airfor 30.6 minutes 46
5-19 Uptake and decay of MTBE-di2 in breath and blood, and of TEA in blood,
for male Subject IM08 exposed to 2,217 |ig/m3 (542 ppbv) of MTBE-di2
and 728 |ig/m3 (85.6 ppbv) of DBCM in air for 30.6 min 47
5-20 Uptake and decay of MTBE-di2 in breath and blood, and of TEA in blood,
for female Subject IF06 exposed to 2,217 |ig/m3 (542 ppbv) of MTBE-di2
and 728 |ig/m3 (85.6 ppbv) of DBCM in air for 30.7 min 47
5-21 Uptake and decay of MTBE-di2 in breath and blood, and of TEA in blood,
for male Subject EVI01 exposed to 2,217 |ig/m3 (542 ppbv) of MTBE-di2
and 728 |ig/m3 (85.6 ppbv) of DBCM in air for 30.5 min 48
5-22 Measured and modeled uptake of MTBE-di2 in exhaled breath and venous
blood for female Subject IF02 exposed to 2,217 |ig/m3 (542 ppbv) of
MTBE-di2 in air for 29.3 minutes 52
5-23 Measured and modeled elimination of MTBE-di2 from exhaled breath
and venous blood for female Subject IF02 after exposure to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 in air for 29.3 minutes. Breath data smoothed
using 5-point moving average 52
5-24 Measured and modeled uptake of MTBE-di2 in exhaled breath and venous
blood for male Subject EVI03 exposed to 2,217 |ig/m3 (542 ppbv) of
MTBE-di2 in airfor 30.6 minutes 53
5-25 Measured and modeled elimination of MTBE-di2 from exhaled breath
and venous blood for male Subject EVI03 after exposure to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 in air for 30.6 minutes. Breath data smoothed
using 5-point moving average 53
5-26 Measured and modeled uptake of MTBE-di2 in exhaled breath and venous
blood for male Subject EVI04 exposed to 2,217 |ig/m3 (542 ppbv) of
MTBE-di2 in airfor 30.3 minutes 54
5-27 Measured and modeled elimination of MTBE-di2 from exhaled breath
and venous blood for male Subject EVI04 after exposure to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 in air for 30.3 minutes. Breath data smoothed
using 5-point moving average 54
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Figures (continued)
5-28 Measured and modeled uptake of MTBE-di2 in exhaled breath and venous
blood for male Subject IM05 exposed to 2,217 |ig/m3 (542 ppbv) of
MTBE-di2 in air for 30.6 minutes 55
5-29 Measured and modeled elimination of MTBE-di2 from exhaled breath
and venous blood for male Subject EVI05 after exposure to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 in air for 30.6 minutes. Breath data smoothed
using 5-point moving average 55
5-30 Measured and modeled uptake of MTBE-di2 in exhaled breath and venous
blood for male Subject EVI08 exposed to 2,217 |ig/m3 (542 ppbv) of
MTBE-di2 in air for 30.6 minutes 56
5-31 Measured and modeled elimination of MTBE-di2 from exhaled breath
and venous blood for male Subject EVI08 after exposure to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 in air for 30.6 minutes. Breath data smoothed
using 5-point moving average 56
5-32 Measured and modeled uptake of MTBE-di2 in exhaled breath and venous
blood for female Subject IF06 exposed to 2,217 |ig/m3 (542 ppbv) of
MTBE-di2 in air for 30.7 minutes 57
5-33 Measured and modeled elimination of MTBE-di2 from exhaled breath
and venous blood for female Subject IF06 after exposure to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 in air for 30.7 minutes. Breath data smoothed
using 5-point moving average 57
5-34 Measured and modeled uptake of MTBE-di2 in exhaled breath and venous
blood for male Subject EVI01 exposed to 2,217 |ig/m3 (542 ppbv) of
MTBE-di2 in air for 30.5 minutes 58
5-35 Measured and modeled elimination of MTBE-di2 from exhaled breath
and venous blood for male Subject EVIOl after exposure to 2,217 |ig/m3
(542 ppbv) of MTBE-di2 in air for 30.5 minutes. Breath data smoothed
using 5-point moving average 58
5-36 Measured breath MTBE-di2 concentrations vs. venous blood MTBE-di2
concentrations for male Subject EVI03 61
5-37 Plot of average ion signal (and standard deviation) at m/z 55 as a function
of time, obtained from constant source of 2-butanone in glass chamber
at a concentration of 866 |lg/m3 in zero-grade air 62
XI
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Figures (continued)
5-38 GC/MS ion signal response as a function of spike level of target compounds
in blood 63
5-39 GC/MS ion signal response as a function of spike level of target compounds
in urine 64
6-1 Dependence of mean peak blood concentration for MTBE-di2 on total
("applied") dose from this study compared to literature values 69
xn
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Tables
4-1 Characteristics of subjects who participated in inhalation exposure study
atEOHSI, and associated exposure conditions
4-2 Mass spectral parent and product ions used to monitor inhalation exposure
to MTBE-di2 and DBCM 10
4-3 Cycle processes and their high and low signal states that are controlled by
the inhalation exposure software program 13
4-4 Battelle standard containing the target compounds, trichloromethane,
and benzene in nitrogen 24
4-5 Comparison of measured and certified concentrations of MTBE in certified
reference standard, and chloroform and benzene in NIST SRM 1804a 24
5-1 Summary of blood and breath sample collection times (min) in each
exposure experiment 28
5-2 Total absorbed dose of MTBE-di2 as a result of inhalation exposure 50
5-3 Theoretical calculations of MTBE-di2 model parameters 59
5-4 Theoretical calculations of DBCM model parameters 60
5-5 Correlation between blood and breath concentrations and average
blood:breath ratio for each participant 61
5-6 Limits of detection for MTBE-di2 and DBCM in exhaled breath, blood,
and urine, and for TEA in blood and urine 63
6-1 Summary of results obtained in current and previous MTBE exposure studies 67
Xlll
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Acknowledgments
We thank Dr. Lance A. Wallace of U.S. EPA for his expert advice and suggestions
throughout this investigation. Major contributions to the research effort were made by Battelle
personnel Marielle C. Brinkman and Jan Satola.
xiv
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Chapter 1
Introduction
Methyl fert-butyl ether (MTBE) was first introduced in the U.S. as a synthetic gasoline
additive in the 1970s. The federal Clean Air Act requirements for oxygenates in wintertime
gasoline made MTBE, which has oxygen-containing properties, a popular choice of refineries
manufacturing reformulated gasoline. Added to gasoline at levels of up to 15% by volume,
MTBE reduces automotive emissions of carbon monoxide.
A survey of ground water throughout the United States by the U.S. Geological Survey
has indicated that MTBE is one of the most frequently detected compounds in ground water.1
MTBE is highly water-soluble and appears to be resistant to chemical and microbial degradation
in water.2 When MTBE, which has a very unpleasant taste and odor,3 began appearing in
groundwater and some public drinking water systems throughout the U.S., environmental
agencies, state governments, and regulatory groups became concerned. Issues of toxicology and
exposure during automobile refueling also pointed to the need for information on the exposure
levels and distribution of MTBE in the human body.
Besides MTBE, the trihalomethanes (chloroform, bromodichloromethane, dibromochloro-
methane, bromoform) can be present in the water people use for showering, bathing, or drinking,
if the water supply was disinfected with chlorine and contaminated with MTBE. The most
common method of disinfecting water in the U.S. is by adding chlorine directly to the water.
Disinfection byproducts (DBFs) result from the reaction of disinfection agents with organic
material already present in water. Chlorine reacts with humic acids to form the trihalomethanes,
the haloacetic acids, and many other halogenated compounds. Of the many classes of
disinfection byproducts that occur, trihalomethanes are the most common and abundant in
chlorinated water. The DBF, dibromochloromethane (DBCM) occurs in the chlorination process
in those areas that naturally have bromide in their ground water. Dibromochloromethane has
been reported to occur at about 40 ug/L at the 90l percentile in Los Angeles, CA4.
Exposure to MTBE can occur by inhalation, dermal contact, or ingestion.5 Vehicle
refueling activities lead to the highest potential exposures by inhalation, with breathing zone
levels ranging from 0.1 to 4 ppm for 1 - 2 min durations and peaks occasionally exceeding 10
ppm.6'7'8 The health effects of exposures to gasoline or water containing MTBE are not well-
established, although acute effects such as headaches, nausea or vomiting, nasal and ocular
irritation, and sensations of disorientation, have been associated with exposure to gasoline
containing MTBE.9'10 In those areas of the U.S. that use MTBE as a gasoline oxygenate, doses
from non-occupational exposure are between 0.4 and 6 |ig/kg-day, and roughly 1.4 |ig/kg-day as
a result of exposure via contaminated water.11
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The uptake of MTBE by inhalation has been measured in exhaled breath under controlled
conditions using integrated sampling techniques.7'12'13'14'15'16 Several studies, including some
based on the analysis of exhaled breath, have demonstrated significant dermal absorption of
chloroform and trichloroethylene while showering or bathing, and the dose is roughly
comparable to that resulting from inhalation.17'18'19'20'21'22'23'24 Because of the dynamic
equilibrium between the concentration of a VOC in the blood and its concentration in exhaled
breath,25 breath measurements can be used to estimate body burden and to detect changes in
r\r r\ri r\r\ nQ
body burden with time. ' ' ' Most previous measurements of human breath concentrations of
VOCs to determine the dose resulting from inhalation exposure to the pollutant in air have,
however, relied on the use of integrated sampling methods and subsequent batch analysis. This
has limited the number of samples that are typically collected in such exposure studies to about
four during the uptake phase and usually no more than about twelve during the decay phase, thus
reducing the reliability of data designed to address these issues.30
Several recent studies conducted at Battelle under the auspices of the U.S. Environmental
Protection Agency (EPA) have demonstrated the value of using continuous breath measurements
to determine exposure to volatile organic compounds (VOCs). °'31'32 This monitoring technology,
based on direct breath sampling coupled with mass spectrometry, offers a powerful means of
extracting VOCs directly from the breath matrix and eliminates the pre-concentration step that
normally precedes exhaled air analysis by conventional gas chromatography/mass spectrometry
(GC/MS).27'33 The real-time breath measurement method provides abundant data, and thus better
time resolution over the uptake and elimination periods of an exposure episode, compared to
91 97 9X ^ 1 ^9 '^ \A. ^ S ^f\
previous discrete time-integrated breath sampling methods. '>>'>>>'
We have used the breath analysis technology to measure dermal absorption to chloroform
while bathing or showering, as well as exposure to the chemical by inhalation.21'37 Showering or
bathing in water contaminated with chloroform gives rise to a measurable dose of chloroform
through dermal exposures. We showed that water temperature has a powerful effect on dermal
absorption of chloroform while bathing, with about a 30-fold increase in absorbed chloroform
occurring over a 10°C increase in bath water temperature.21 The inhalation measurements
provided important information on the residence times of the compound in the body, the relative
capacity of each compartment, and the fraction of the chemical exhaled unchanged at
equilibrium.37
The purpose of the present study was to use the real-time breath measurement technology
to determine more precisely than previous studies the residence times in various physiological
compartments for MTBE in blood and breath. The study was also designed to provide analogous
data on DBCM and on the blood/breath ratios for MTBE and DBCM. A secondary purpose was
to analyze the data in an attempt to develop a model for MTBE that allows for the inclusion of a
mucous membrane component, if appropriate, since previous work has suggested that this may
be an important component of MTBE distribution in the body.12
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Chapter 2
Conclusions
The oxygenate methyl tert-buty\ ether (MTBE) has been added to gasoline to meet
national ambient air quality standards in those parts of the U.S. that are non-compliant for carbon
monoxide. Although MTBE has provided important health benefits in terms of reduced
hazardous air pollutants, the increasing occurrence and detection of MTBE in drinking water
sources in California, New Jersey, and elsewhere has raised concerns about potential exposures
from water usage and resulting health effects. In addition to MTBE, disinfection byproducts can
be present in the water people use for showering, bathing, or drinking, as a result of the reaction
of disinfection agents with organic material already present in water. Chlorine reacts with humic
acids to form the trihalomethanes, which are the most common and abundant byproducts in
chlorinated water. Besides chloroform, which has been widely studied, the byproduct
dibromochloromethane (DBCM) occurs as a result of the chlorination process in those areas that
naturally have bromide in their ground water. Relatively little information on exposure to this
chemical is available. The purpose of this study was to measure directly the uptake by humans
of MTBE and DBCM as a result of controlled, short-term inhalation exposures. Simultaneous
blood samples were also collected and analyzed as part of the study.
Seven subjects were exposed continuously via face mask to 2,217 |ig/m3 (542 ppbv)
MTBE-di2 and 728 |ig/m3 (85.6 ppbv) DBCM, except for several brief (~2-min) intervals during
which breath measurements were taken. Total exposure time was -30 min, followed by exposure
to clean air for a further 30 — 60 min. Exhaled breath was sampled and analyzed with the real-
time breath technology; blood samples were simultaneously collected from the subjects (3-4
samples during exposure; 2-5 samples post-exposure) and analyzed separately for MTBE-di2 and
DBCM, as well as for the MTBE metabolite, ^-butyl alcohol. The real-time technology was
specially modified with a biofeedback exposure control system to allow us to make uptake
measurements during the exposure period; breath measurements were taken continuously
throughout the post-exposure period. The uptake and decay of the target chemicals in the blood
was estimated by fitting the exposure and post-exposure breath and blood data to a linear multi-
compartmental model that estimated residence times. The measurements also provided
information on blood:breath concentration ratios, as well as the fraction of breath MTBE and
DBCM exhaled unchanged at equilibrium. The exposures resulted in an increase in the
measured breath concentration of MTBE-di2 from pre-exposure levels of 10 - 20 |ig/m3 (2-5
ppbv) to 200 - 450 |ig/m3 (50 - 110 ppbv) following exposure. MTBE-di2 blood concentrations
increased from the limit of detection, 0.30 |ig/L, to -0.9 - 2.5 |ig/L at the end of the ~30-min
exposure period.
The time-course measurements of both exhaled breath and venous blood are well-
described by the linear compartmental uptake and elimination models, the interpretation of
-------
which provides important information on the residence times of the compound in the body, the
relative capacity of each compartment, and the fraction of the chemical exhaled unchanged at
equilibrium. The breath uptake data were consistent with a one-compartment model. The mean
value for the one-compartment uptake residence times Tiuptake was 5.7 ± 2.4 (SD) min (range 3.3
- 9.8 min). In contrast, the breath decay phase data gave satisfactory two-compartment fits. The
mean value for the first compartment decay residence times TI decay was 3.8 ± 1.9 (SD) min (range
2.4 - 7.8 min); for the second compartment, the mean decay residence time T2decay was 61 ± 11
(SD) min (range 46 - 73 min). The blood uptake data were also consistent with a one-
compartment model and were convergent in almost all cases. The average blood uptake
residence time was essentially the same as that for the breath. The quality of the blood decay
data were such that we were only able to extract meaningful information from 2 or 3 data sets.
The mean MTBE-di2 total absorbed ("internal") dose was 149 ± 34 jig for the average 30-
min exposure and a mean total ("applied") dose of 209 jig. The mean fraction of MTBE-di2
absorbed, or relative uptake, was 0.73 ± 0.04. The mean value for/ the fraction of the MTBE-di2
exposure concentration exhaled unchanged was 0.29 ± 0.04. This value is in good agreement
with the value recently reported by Lee et al.
Using linear regression analysis, the mean blood/breath ratio for MTBE-di2 was found to
be 6.7 ± 3.4. This value is significantly lower than values obtained in previous studies. The
reason for this discrepancy is not clear.
By and large, background levels for DBCM in the exhaled breath were below the limit of
detection, and the signal measured for this compound at m/z 129, the most abundant ion in the
glow discharge mass spectrum, was exceptionally "noisy". The average signals during the
uptake phase provided initial (pre-exposure) breath concentrations that ranged from 70 to 160
|ig/m3 and rose to between 130 and 250 |ig/m3 after 30 minutes. The high initial breath
concentrations suggest that the measured signal at m/z 129 was probably elevated due to an
unknown contaminant with fragment ions at the same mass. For TEA, all of the blood
measurements were below the detection limit.
-------
Chapter 3
Recommendations
The real-time breath analyzer is a powerful technique for obtaining unique data on VOCs
in human exhaled breath in situations in which the concentrations of the constituents change
rapidly. In the present study, it was used to determine the uptake by humans of MTBE-di2 and
DBCM as a result of controlled, short-term inhalation exposure.
Analysis problems experienced at EOHSI prevented us from obtaining reliable data for
the target compounds in blood and urine. These biological measurements are important,
complementary information which serve to provide a more complete picture of the uptake,
distribution, and elimination of the pollutants from the body than is available from an analysis of
the exhaled breath data alone. It is recommended that careful attention be paid in future studies
to first ensuring that the analytical techniques for the characterization of target analytes in blood
and urine are reliable and can be applied without difficulty before embarking on similar studies.
-------
Chapter 4
Experimental Procedures
In this scenario, subjects wore a full face mask and were exposed by inhalation only to a
precisely measured amount of isotopically-labeled MTBE and dibromochloromethane (DBCM).
Following exposure, the subjects inhaled pure air and the exhaled breath was monitored for a
period to obtain residence times of chloroform in the body compartments. Pre-exposure,
exposure, and post-exposure blood samples were drawn at the same time as the breath was being
monitored, and the blood samples were analyzed separately for MTBE and DBCM. All
inhalation experiments were conducted in a bathroom at the Environmental and Occupational
Health Sciences Institute (EOHSI), Rutgers University, in Piscataway, NJ.
Experimental Procedures
Subject Selection and Recruitment
Volunteers for the study were sought from amongst the student population at Rutgers
University, in Piscataway, NJ by means of notices placed in buildings around the University
campus and local newspaper advertisements. Respondents with any of the following medical
conditions were excluded: neurologic disease or brain injury, significant exposure to other
neurotoxicants, chronic fatigue syndrome or multiple chemical sensitivity, stroke or cardio-
vascular disease, serious pulmonary disease, liver or kidney disease, serious gastrointestinal
disorders (e.g. colitis), claustrophobia, and major psychiatric conditions including psychoses,
manic depression, alcoholism, or drug abuse. No pregnant or lactating women were included.
The subjects were healthy, young nonsmoker adults of average weight and height.
Information on the subjects is provided in Table 4-1 along with a summary of the exposure
conditions. Information was collected from each subject on his/her age, height, weight, respiration
rate (using a dry gas meter), and percent body fat (from body circumferences and height). The
study protocol was reviewed and approved by both the Battelle Human Subjects Committee and
the EOHSI Institutional Review Board (IRB), then was approved by the EPA Human Subjects
Committee. Informed written consent was obtained from each subject before participation. Each
subject received financial compensation on completion of the exposure experiments.
Exposure Conditions
OO
According to the Integrated Household Exposure Model, a water concentration of 200
ug/L would be expected to result in a shower air concentration of 0.5 ppm for a fifteen minute
shower. For the U.S. population, the 90th percentile duration for showering is 30 minutes.39
-------
Table 4-1. Characteristics of subjects who participated in inhalation exposure study at EOHSI,
and associated exposure conditions
Subject
IF02
IM03
IM04
IM05
IM08
IF06
IM01
Sexa
F
M
M
M
M
F
M
Height
(cm)
163
185
173
175
173
163
170
Weight
(kg)
58.1
90.7
61.2
83.9
79.4
52.6
77.1
Age
(yr)
21
36
21
54
26
19
22
Expt.
Date
02/19/01
02/20/01
02/21/01
02/21/01
02/22/01
02/22/01
02/23/01
MTBE-d12/DBCM
Concn. in Air
^g/m3)
2,217/728
2,217/728
2,217/728
2,217/728
2,217/728
2,217/728
2,217/728
Exposure
Duration
(min)
33.5
36.7
33.5
33.9
35.8
33.8
34.2
RTBA Sample ID
IF02; IF02b
IM03; IM03b; IM03c
IM04; IM04b; IM04c
IM05; IM05b
IM08R; IM08Rb; IM08Rc
IF06; IF06b
IM01; IMOlb
Calibration File ID
ca!0219a
ca!0220a
cal0221a; ca!0221b;
ca!0221c; ca!0221d
ca!0222a; ca!0222b
ca!0223a
Abbreviations: M, male; F, female.
-------
The subjects were, consequently, exposed for 30 minutes to a mixture of 2,217 |ig/m (542 ppbv)
MTBE-di2 and 728 |ig/m (85.6 ppbv) DBCM in humidified zero-grade air. In previous work
done at EOHSI, subjects were exposed to 1 ppm MTBE in a gasoline mixture for 15 minutes to
simulate exposures that occur during fueling of automobiles.15'16 The nominal exposure of 0.5
ppm MTBE for 30 minutes was selected here to represent an equivalent dose.
Gas mixtures for inhalation exposure were prepared in pressurized aluminum gas
cylinders and consisted of 0.5 ppm isotopically-labeled MTBE-di2 (>99.8 atom % D; Lot No.
F65P1; C/D/N Isotopes; CAS No. 29366-08-3) and 0.12 ppm DBCM in humidified zero-grade
air. In order to ensure that the subject was exposed to a precisely metered amount of the
chemical, the cylinder containing the gas mixture was attached to the closed delivery system
shown schematically in Figure 4-1. The inlet tube to the full face mask (Hans Rudolph Model
8932) was attached to the cylinder and discrete amounts of MTBE-di2 and DBCM in the air
stream flowed to the subject with each inhalation through the full face mask on a demand basis.
The amounts of the chemicals inhaled with each inspiration were registered incrementally by
means of a dry gas meter (Model DTM-115, American Meter Co.), which was attached to the
vent of the breath inlet system via wide-bore flexible tubing. The dry gas meter also recorded
the total amount inspired over the entire exposure period and the respiration rate of each subject
was monitored. The total amount of the chemical exhaled unchanged was obtained from the area
under the breath concentration/time curve. The MTBE-di2 and DBCM concentrations in the
Ar Supply
Buffer Volume
Face
Mask
Breath Inlet
Buffer Volume
-CDOTP
One-way Valves
GD/ITMS
Khowi Concentration
of Test Oonpound in
1-bspitaJ-GradeAr
Dry Gas
Meter
Figure 4-1. Closed delivery system to (i) provide subject wearing full face mask with precisely
metered amount of chemical(s) for inhalation (from pressurized gas cylinder and dry
gas meter); and (ii) to measure amount of chemical exhaled unchanged (via dry gas
meter attached to breath interface and (glow discharge/ion trap mass spectrometer)
breath analyzer).
-------
cylinder were monitored by taking 6-L samples from the cylinder in evacuated stainless steel
canisters and analyzing them by a modified U.S. EPA Method TO-14.40
At the end of the exposure, the subject was switched to a pure air supply, and real-time
breath measurements continued uninterruptedly for a further 30 to 60 minutes. Then,
periodically during the next hour, the subject provided further breath samples for periods of 5-10
minutes each until the concentrations approached the pre-exposure levels.
Sampling and Measurement Procedures
Breath
To conduct these studies and ensure that the uptake of the target chemicals could be
monitored in real time, we developed an automated system for use with the real-time breath
analyzer (RTBA).
The breath analyzer, shown schematically in Figure 4-2, consists of a Battelle-patented
breath inlet unit, a direct breath sampling interface (glow discharge ionization source), and an ion
trap mass spectrometer (ITMS). A face mask (Hans Rudolph Model 8932) equipped with a two-
way non-rebreathing valve set is attached to the breath inlet. As shown in Figure 4-3, the inlet to
the face mask is connected to the MTBE-di2/DBCM standard exposure source (gas cylinder) or a
source of hospital grade breathing air through a 3-way wide-bore pneumatic solenoid valve. The
outlet from the face mask is attached to the holding volume of the breath inlet through a second
3-way wide-bore pneumatic solenoid valve. When the breath holding volume is connected to the
analyzer through the third 3-way solenoid valve, the breath sample is vacuum-extracted at a
constant rate by the vacuum pump of the glow discharge source and flows into the ion trap
without any attention from the subject.
The volume of the breath inlet (in Figure 4-2) is normally less than 100 mL, or roughly
one-fifth the mean value of the adult tidal volume. Under these conditions, each breath
exhalation effectively displaces the previous breath sample while a steady gas flow is maintained
into the analyzer. This ensures that unit resolution is achieved between individual breath
exhalations while at the same time producing a constant and undiluted sample for analysis. A
dry gas meter (Model DTM-115, American Meter Co.), attached to the vent of the breath inlet
system via wide-bore flexible tubing, was used to record the respiration rate and total exhaled
volume from each subject.
The direct breath sampling interface is a glow discharge ionization source, which is
attached to the ITMS. The operation of this system has been described in detail elsewhere.41'42'43
For this study, we used a Teledyne Electronic Technologies (Mountain View, CA) 3DQ™
Discovery ion trap MS as the analyzer.44 The 3DQ is a compact, field-deployable instrument
with high sensitivity and specificity. The breath analyzer was set up to measure the MTBE-di2
and DBCM target analytes both in the single MS as well as the MS/MS mode. The ions selected
for this purpose are listed in Table 4-2. Calibration measurements conducted in our laboratory
showed that MTBE-di2 can be determined in humidified air with high sensitivity and specificity.
-------
Glow
Discharge
Source
Teflon Tubing
Quartz Fiber Filter
x^
/ ^rr^
',., Teflon T-Piece Teflon Tubin9
One-Way
Valve
One-Way
Valve
r I
JT
Ion Trap
Analyzer
Figure 4-2. Continuous real-time breath analyzer (RTBA), consisting of
breath inlet (breath holding volume) attached to direct
breath sampling interface (glow discharge ionization source)
and ion trap mass spectrometer (GD/ITMS).
3-way
Solenoid
Valve A
N \
^ V X
Laptop Computer
with PCMCIA
Data Acquisition Card
Key
Air Flow
Data Flow
Digital Control
Pulse
Figure 4-3. Diagram of instrumentation to measure target contaminant breath
concentration continuously in real time during inhalation exposure to
the contaminant. Schematic shows initial configuration of Valves A, B,
and C at time t = 0 min. The breath inlet (breath holding volume) and
breath analyzer are shown in greater detail in Figure 4-2.
-------
Table 4-2. Mass spectral parent and product ions used to monitor
inhalation exposure to MTBE-dn and DBCM.
Compound
MTBE-d12
DBCM
TBA-d10
MW
100
208
84
Parent Ion
82
129
82
Product Ion
46,50
—
62
To calibrate the real-time breath analyzer in the laboratory, gas standards containing
MTBE-di2 and DBCM were prepared in high-pressure aluminum gas cylinders. As indicated
earlier, the concentrations of the standards were confirmed by taking samples from the cylinders
in evacuated 6-L stainless steel canisters, which were analyzed by a modified U.S. EPA Method
TO-14.40 The gas chromatograph/flame ionization detector/quadrupole mass spectrometer
(GC/FID/MS) system, in turn, was calibrated by analyzing aliquots taken from a gravimetrically-
prepared standard. Calibration of the breath analyzer itself was accomplished by connecting a
gas cylinder containing the standards to the glow discharge source inlet and measuring the
resultant ion signals of the target ions at the known concentrations. The instrument was
calibrated each day before experiments began.
Instrument calibrations were checked by first dynamically diluting a standard six-
component cylinder (LL 17298), which contains the target chemicals MTBE, MTBE-di2, and
DBCM, as well as chloroform, benzene, and 2-methyl-2-propanol. From the known
concentrations of these compounds in the cylinder (8-13 ppbv), we were able to generate average
response factors. The cylinders that were taken to the field for the exposure study were similarly
diluted, and the concentrations determined by GC/MS, based on the measured concentrations of
the components in standard cylinder LL 17298. These values were checked, in turn, by applying
the generated response factor for MTBE to the measurement of the concentration of MTBE in a
Scott Specialty Gas MTBE Certified Standard. Our measured values of 54.25 ppbv and 52.67
ppbv divided by the dilution factor of 0.0495 gave an estimated cylinder concentration of 1,080
ppbv versus a certified value of 1,030 ppbv. This agreement is regarded as satisfactory and
allowed us to use the generated response factors to determine concentrations of the target
compounds in the exposure experiments.
A CCh monitor (Pryon Model No. SC-300), equipped with an external infrared
sensor, is used to continuously monitor the subjects' breath CC>2 levels. The monitor is equipped
with a digital-to-analog converter (Pryon Model No. D2A-8000) with a 10 ms update response
time for the CC>2 waveform. The CC>2 analog waveform ranges from 0-10 Vdc, corresponding
to 0 - 7% CCh (automatically corrected for water vapor). The CCh analog waveform data are
collected using a PCMCIA data acquisition card (National Instruments Model No. DAQCard
1200), installed in a Dell laptop computer. A graphical user interface (GUI) was developed and
tested, using Lab View (Ver. 4.0.1) software, to acquire the relevant CC>2 data, count the number
of breaths the subject takes of the exposure standard or clean air, and control the three valves that
regulate the flow of the exposure standard to the subject, and subject's breath into the analyzer.
10
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The CCh analog waveform data, and the digital pulses that control the solenoid valves, are also
collected in a comma-delimited format for later analysis using spreadsheet software.
To measure the uptake of the target compounds during an inhalation exposure episode,
the exposure time is divided into a number of discrete exposure/clean air cycles. For a single
cycle, at t = 0 min, Valve A (in Figure 4-3) is set to allow flow of the MTBE-di2/DBCM
standard for a fixed period (say, 3 min) from the supply cylinder to the subject via the face mask,
while Valve B vents the exhaled flow from the face mask and Valve C permits the analyzer to
sample clean air. At t = 3n min, where n = 1, 2, 3, ..., Valve A switches to allow flow of clean
air to the face mask, in order to clear the tracheal dead volume of residual MTBE-di2/DBCM
standard, while Valve B continues to vent the flow of the first exhalation from the face mask and
Valve C continues to direct clean air into the breath analyzer. After completing two full breath
inhalation/exhalation cycles of clean air, Valve B switches to allow the next two clean air breath
exhalations into the 200-mL tube of the breath interface device ("holding volume") and Valve C
switches so that the analyzer samples from the breath holding volume for a set period of time
(say 0.5 min). After the fourth clean air breath is exhaled into the holding volume, Valve B
switches to prevent flow from the face mask into the holding volume, and Valve A is switched so
that the subject resumes breathing the MTBE-di2/DBCM standard to begin another exposure/-
clean air cycle. After the analyzer has sampled from the breath holding volume, Valve C is
switched so that the analyzer resumes sampling clean air.
The GUI that allows the operator to input parameters that control the inhalation exposure
scenario, and then monitor subject exposure parameters and CCh levels in breath, is shown in
Figure 4-4. Before conducting an inhalation exposure experiment, the user inputs the following
parameters.
a) Inhale/Exhale Cycle Time - the time(s) it takes the subject, when at rest and breathing
normally, to inhale and exhale one breath. This value is used to provide the subject with
on-screen "Inhale" and "Exhale" prompts in order to help him/her maintain steady,
symmetrical breathing rates. The value to be used for this time is determined empirically
by monitoring the subject's breath CCh levels prior to the start of the inhalation exposure
experiment, and measuring the time (distance) between two adjacent peaks.
b) MTBE Exposure Time - the time period(s), in a single exposure/clean air cycle, during
which the subject breathes the MTBE-di2/DBCM standard.
c) GDMS Sampling Time - the time period(s), in a single exposure/clean air cycle, during
which the breath analyzer (GDMS) samples from the breath holding volume.
d) CO2 Max Threshold - the level of the analog signal (Vdc) above which an inhalation is
counted.
e) CO2 Min Threshold - the level of the analog signal (Vdc) below which an exhalation is
counted.
11
-------
Exposure to MTBE
Figure 4-4. Graphical user interface for inhalation exposure data acquisition and control program.
12
-------
Once these parameters have been entered, the operator launches the program. The
program prompts the operator to provide a filename for the file in which the data will be stored.
Once the filename is entered, the program then generates the digital pulses that control the
solenoid valves, monitor the CO2 analog data, and count the subject's breaths. The CO2 analog
data and the digital pulses are collected, plotted on the screen, evaluated, and written to a file
continuously while the program runs. Timing and logic determine when digital pulses are sent to
control the flow of the MTBE-di2/DBCM standard, the flow of the subject's breath into the
breath holding volume, and the flow of the sample from the breath holding volume into the
breath analyzer. These cycle processes occur automatically without the need for operator
attention, and are summarized in greater detail, along with their high and low signal states, in
Table 4-3.
While the inhalation exposure software program runs, the operator can monitor the
progress of the experiment by observing the additional program output windows in Figure 4-4.
f) Subject Exhale/Inhale Coach - this window prompts the subject to inhale or exhale in
order to help the subject maintain a steady, symmetrical breathing rhythm. For example,
if the Inhale/Exhale Cycle Time [see a) above] is 8 sec, then the subject will be
"coached" to inhale for 4 sec, exhale for 4 sec, inhale for 4 sec, etc.
g) Exposure Source - this window indicates whether the subject is being exposed to the
MTBE-di2/DCBM standard or the clean air supply.
h) Analog Input - this window plots all of the data being collected and stored in a file, e.g.,
breath CO2 levels, cycle process digital pulse states, etc.
i) Digital Signal LED cluster - this window shows a series of 8 LEDs. Currently, only 3 of
the 8 LEDs are being used to indicate control of cycle processes. The LED states and the
cycle processes they represent are fully described in Table 4-2.
Table 4-3. Cycle processes and their high and low signal states that are controlled by
the inhalation exposure software program.
Cycle Process
Inhalation source
Exhalation source
GDMS analyzer source
High State (+5 Vdc)
Subject breathes MTBE-d12/DBCM
standard
(STD LED = red)
Subject's breath is vented to waste
(HVol LED = red)
GDMS analyzer samples from the
breath volume
(GDMS LED = red)
Low State (0 Vdc)
Subject breathes clean air
(STD LED = green)
Subject's breath is collected in
the breath holding volume
(HVol LED = green)
GDMS analyzer samples from
hospital grade clean air
(GDMS LED = green)
13
-------
j) Breath Count - total number of breaths taken by the subject since the inhalation exposure
experiment started. A breath is defined as one inhalation and one exhalation cycle.
k) Clean Air Breath Count - total number of clean air breaths taken by the subject for a
single exposure/clean air cycle. This value is reset to zero at the end of the GDMS
sampling portion of each exposure/clean air cycle.
Initial tests conducted with the system indicated that the breath holding volume (-95 mL)
was too small and the sample was being depleted during the sampling period, since the breath
levels following exposure first increased, then abruptly leveled off at much lower levels than
expected. To address this issue, as well as several others that were indicated by the initial tests,
several modifications were made to the inhalation exposure system and software program. The
changes included:
(1) The breath holding volume was increased to 500 mL by incorporating a long Teflon
sampling loop (754 cm long, 0.92 cm i.d.). The front end of the sampling loop was fitted
with a 2-way solenoid relief valve such that, when the breath analyzer is permitted to
sample from the back end of the sampling loop, clean air is able to enter the front of the
loop through the relief valve, thus avoiding the formation of a vacuum and keeping the
sampling loop at atmospheric pressure. The on/off switching of this relief valve was also
placed under automatic control by including its operation in the software program. This
change resulted in stable breath analyzer sampling periods of up to 4 min from the loop
when filled with 500 mL of a test gas standard (1,1,1-trichloroethane).
(2) The time period (s) for which the subject is exposed to the exposure standard was
modified to be user-selectable so that it could be varied for each individual exposure
cycle. Each exposure cycle consists of three separate periods: the time for which the
subject is exposed to the standard; the time it takes the subject to complete 4 clean-air
breaths; and the time for which the breath analyzer samples from the breath holding
volume. Each exposure experiment can consist of 10-15 cycles. Prior to this change, the
exposure standard time period was user-selectable, but its duration could not be varied
between cycles. The time periods that are selected for each cycle for a given inhalation
exposure experiment are attached to the end of the comma-delimited data file when the
experiment is halted (i.e., the STOP button is clicked).
(3) The subject's inhalations and exhalations were programmed to be counted separately,
beginning with the subject's first inhalation. This change was made to ensure that a
single breath is more accurately defined as an inhalation followed by an exhalation. The
clean air and exposure-standard inhalations and exhalations are shown in four separate
program output windows (see lower right hand corner of Figure 4-4). The clean air
inhalations and exhalations are each reset to zero at the beginning of a new exposure
cycle.
(4) A switch was included in the program to allow the user to choose between running the
inhalation exposure experiment, and stopping the experiment and sampling from the
14
-------
breath holding volume for any period of time. This change was made to allow the
collection of a baseline breath sample prior to running the inhalation exposure
experiment, and to allow continuous monitoring of the breath during the post-exposure
decay period. In addition to the inhalation exposure phase, the CC>2 levels are monitored
throughout the pre- and post-exposure phases, and are all recorded in a single comma-
delimited file.
The effects of all these changes were tested by conducting several inhalation exposure
measurements, using a standard of 50 ppbv (270 |ig/m3) 1,1,1-trichloroethane in humidified air.
The results obtained are shown in Figure 4-5, where the experimentally generated data points are
compared with a curve generated from the linear compartment model, using values for the
residence times for 1,1,1-trichloroethane reported earlier by Wallace et al.4
o
u>
n
•s <"
n Q
i c
c o
«0
§1
n
o
m
40
30
20
10
Measured 1,1,1-Trichloroethane Data
Modeled 1,1,1-Trichloroethane Data
10 20
Exposure Time (min)
30
Figure 4-5. Modeled (solid line) and measured (asterisks) inhalation uptake
of 1,1,1-trichloroethane in exhaled breath of a subject exposed
to 50 ppbv (270 u£/m3) 1,1,1-trichloroethane in air. For the
curve calculated from the linear compartment model, we
assumed/= 0.87; TI = 9.0 min; ?2 = 41 min; and Zj = 288 min
(from Wallace et al.45)
Blood and Urine
All blood and urine samples were analyzed by a purge-and-trap method using Tenax
(Supelco Inc., PA) as an adsorbent (0.25 g in each trap) and zero grade helium (Air Products and
Chemicals Inc., PA) as the purge gas.15'16'46 The sampling traps were conditioned by continuous
flushing with zero-grade nitrogen while being heated at 270°C for 3 hours. The trap was
15
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repacked with fresh Tenax sorbent after twenty uses. Newly packed traps were conditioned by
flushing with zero-grade nitrogen while being heated at 270°C for 6 hours. To evaluate
breakthrough, two traps were connected in series and each was analyzed for all of the
experiments. Calibration curves were prepared using only the first trap in the series as well as
the sum obtained from both traps.
Blood
Multiple blood samples were taken from each subject over several hours, using a Jelco
Winged IV Catheter (Johnson & Johnson, NJ), which remained in the subject's arm for the
duration of the experiment. Blood samples were drawn by a trained phlebotomist, who verified
that the catheter was not causing undue discomfort or other problems while it remained in the
arm.
The samples were collected into 10 mL Vacutainers® (Benton Dickson, NJ) with 20 mg
of potassium oxalate and 25 mg of sodium fluoride, and stored at 4°C until analysis. A 10 mg/L
disodium-EDTA solution (Baker Analyzed ACS Reagent, JT Baker, Phillipsburg, NJ) was
prepared with HPLC-reagent water (JT Baker, Phillipsburg, NJ), which had non-detectable levels
of MTBE. An 8-mL aliquot of the blood sample was transferred to a 250-mL gas bubbler vessel
containing 100 mL of the disodium-EDTA solution. One mL of antifoaming solution (Dow
Corning Antifoam® 1510-US Emulsion, Midland, MI) was added to prevent foaming. The gas
bubbler containing the sample was first immersed in a water bath at 40°C for 3 minutes before
purging to allow it to reach temperature equilibrium. Then, the blood-disodium-EDTA mixture
was purged with helium gas at 100 mL/min for 10 minutes at 40°C to collect MTBE-di2 and
DBCM. Next, the gas bubbler was transferred to a water bath at 90°C, allowed to come to
temperature equilibrium over 4 minutes, and the sample was further purged for an additional 10
minutes at 90°C to collect TEA.
Recovery tests were run with standards (24 ng of each compound) using both EDTA
mixed with 10 mL of Bacteriostatic sodium chloride injection solution 0.9% (Abbott
Laboratories, IL) and EDTA mixed with blood. The blood was obtained from individuals not
exposed to MTBE or DBCM. No difference in recovery between the two matrices was
observed. Consequently, the EDTA-sodium chloride matrix was used to prepare spiked
standards for generation of calibration curves and system evaluation rather than spiked EDTA-
blood matrices.
Urine
A 200-mL urine sample was transferred to a 250 mL gas bubbler. One drop of
antifoaming solution (Dow Corning Antifoam® 1510-US Emulsion, Midland, MI) was added to
the 200-mL urine sample to prevent foaming during purging. The gas bubbler containing the
urine sample was first immersed in a water bath at 40°C for 3 minutes before purging to allow it
to reach temperature equilibrium. Then, the urine was purged with helium gas at 150 mL/min
for 10 minutes at 40°C to collect MTBE-di2 and DBCM on the Tenax traps. Next, the gas
bubbler was transferred to a water bath at 90°C, allowed to come to temperature equilibrium over
16
-------
4 minutes, and the urine sample was further purged for an additional 10 minutes at 90°C to
collect TEA.
GC/MS Analysis
Target compounds were analyzed and quantified using a gas chromatograph (Hewlett
Packard 5890) coupled to a quadrupole mass spectrometer (Hewlett Packard 5971 A Mass
Selective Detector). Analytes were stripped from the Tenax trap and transferred to the GC/MS
system by thermal desorption (Perkin-Elmer, Inc, Model ATD-400). A 60 m, 5% diphenyl-95%
dimethyl polysiloxane capillary column (DB-5, 0.25 mm ID, 1 jim film thickness; J & W
Scientific, Folsom, CA) was used.
The GC temperature conditions were: injector 250° C; oven held at 35°C for 8 min, then
ramped at 10°/min to 170°C, ramped at 50°/minto 220°C, and held for 5 min. The target ions
for deuterated MTBE and TEA were m/e = 82 and 68, respectively, and their retention times
were 9.5 and 7.9 minutes, respectively. Ion intensity-area data were used to determine relative
response factors (RRF) for the compounds on each day the instrument was operated. This was
accomplished by injecting bromofluorobenzene (BFB) and 13C-benzene, using amounts similar
to those obtained from the purged samples.
The detection limit (DL) for each compound in the blood and urine samples was
determined by estimating the standard deviation of the blank (OB) and the level of the analytical
noise (VB). The standard error of the regression line was used as an estimated standard deviation
of the blank, and the intercept of the regression line was used as an estimate of the analytical
noise. The method detection limit (MDL) were calculated from
where OB = standard error of the regression line; ys = intercept of the regression line; andyoi
signal level. When y =yni, DL has the value of x.
Questionnaire
A brief questionnaire (shown in Appendix A) was administered to each participant to
assess the participant's potential exposure to MTBE and DBCM during the previous 24 hours.
Data Analysis
The data from the inhalation exposure uptake and decay of MTBE-di2 and DBCM were
evaluated in terms of a linear multi-exponential compartment model, developed by Wallace et
90
al., which allowed us to estimate the total ("applied") dose, the "unmetabolized mass", and the
total absorbed dose in addition to the distribution and residence times of the chemicals in breath
and blood corresponding to different body compartments.
17
-------
Total ("Applied") Dose
The total ("applied") dose to the subject is determined from the product of the total
exposure and the subject's average alveolar ventilation rate. Figure 4-6 depicts the form of the
model for exposure to a constant high concentration for a time T. For this condition,
Total Exposure, Etotal = Cair • T (//g.min/m3)
(4-1)
c
o
^
2
+j
0)
o
o
o
Total Exposure
Time
Figure 4-6. Step function exposure to a constant air concentration
C^ for time T.
and Total ("Applied") Dose = (Total Exposure) • (Alveolar Ventilation Rate) (jig)
= Etotai -AYR
= (CairT)-AVR
(4-2)
where Cair = constant exposure concentration (|ig/m3); T= total duration of exposure to the
constant concentration Cair (min); andAVR = alveolar ventilation concentration (L/min).
Total Absorbed Dose
The total absorbed (internal) dose to the subject is defined as the amount of the chemical
that passes through an absorption barrier or exchange boundary. It is given by the difference
between the total ("applied") dose and the "unmetabolized mass."47'48'49
"Unmetabolized Mass "
The "unmetabolized mass" is the total mass of the chemical that leaves the body via
exhalation.47 It is obtained by multiplying the sum of the areas under the exhaled breath uptake
and decay curves by the alveolar ventilation rate.
18
-------
For the situation in which an exposure at relatively high concentrations is followed
immediately by exposure to clean air, as depicted in Figure 4-7, it follows that the value of the
alveolar breath concentration at the beginning of the exposure to clean air, i.e., at time t = T, is
largely determined by the previous exposure. Then, in the case of a single compartment, for the
uptake phase:
= fC (l-e~t/T]
alv J^air\l ^ I
for t < T
and for the elimination phase, we have:
for t > T
(4-3)
(4-4)
O
c"
o
^5
re
o
o
c
o
o
re
o
m
Uptake
Elimination
Time
Figure 4-7. Plot showing rapid increase in alveolar breath concentration
Caiv as a result of step function exposure to a constant air
concentration Cair, followed by a rapid decrease in breath
concentration as a result of exposure to clean air.
where Caiv = exhaled alveolar breath concentration of the component; /= fraction of inhaled
breath concentration exhaled at equilibrium; and t = time from the start of the exposure.
Then, the area under the uptake curve, AUCuptake, is given by:
19
-------
AUCuptake=\Calvdt
(4-5)
Since Equation (4-5) contains the parameter/that is to be determined from this area, AUCuptake is
estimated instead by integrating under the exponentially increasing curve used to model the data,
i.e.,_y = a(l - e"6x), using the trapezoidal rule in SigmaPlot (Version 5.0, SPSS, Chicago, IL).
The area under the decay curve, AUC 'decay, is given by:
AUCdecay=]calvdt
(4-6)
(For the two-compartment case, the expression for AUC decay is:
A UCdecay = fCair a, r, (l - e-T* )+ fCair a2 T2 (l - e~T^ } (4-7)
where the coefficient at is the fractional contribution of the /'th compartment to the breath at
equilibrium; and TI is the residence time of the chemical in the /'th compartment.)
Since Equation (4-6) again contain the parameter/that has not yet been determined, we
have adopted an alternative approach for the practical determination ofAUCdecay. For the post-
exposure decay period, the model may be written in the form:29
(4-8)
20
-------
where, now, t = 0 denotes the time exposure ends; and/Ca;r, the fraction of the inhaled air
concentration of the chemical that is exhaled, is zero during elimination. It follows then, in
49
general, that:
AUCdeccy=]calvdt
(4-9)
.-.-
Thus, AUC 'decay may be estimated in practice from the best-fit parameters obtained from the
exponentially decreasing multi-compartment curve used to model the decay data, i.e., y = 'Late x.
For the one-compartment case, the total area under the uptake and decay curves, AUCtotai,
follows from Equations (4-5) and (4-6):
AUCtotal=fCair-T (4-10)
and the "unmetabolized mass" (i.e., total amount (jig) exhaled during uptake and decay) is given
by:
"Unmetabolized Mass"= AUCtota, • AYR
total , .
The fraction /of the chemical exhaled unchanged at equilibrium may be estimated from
the ratio of the "unmetabolized mass" to the total ("applied") dose, i.e.,
/(Total Dose) = "Unmetabolized Mass" (4-12)
It follows then that the total absorbed dose (jig) may be estimated from:
Total Absorbed Dose = (Total Dose) - (" Unmetabolized Mass")
= Cair-T-AVR-fCair-T-AVR (4-13)
= Cajr-T-AVR(\-f]
The fraction of the chemical absorbed (i.e., "relative uptake"16) is calculated from:
21
-------
pr —A Tjr
Fraction of Chemical Absorbed = -*& ^L = i _ / (4_i4)
^ total
Finally, the fraction of the chemical eliminated through expiration after exposure (i.e.,
"exhaled post-exposure"16) is estimated from:
_ . „_, . ,„ . . ,n ^ „ Amount Exhaled Post-Exposure
Fraction or Chemical Exhaled Post - Exposure =
Total Absorbed Dose , ,
AUCdecay-AVR (~ }
Total Absorbed Dose
Empirical Modeling of Uptake and Decay Breath and Blood Concentrations
90
The linear multicompartment model has the following solution:
(4-16)
where: C = exhaled breath or blood concentration of the component; at = capacity of the f
compartment at equilibrium (Ea; =1); t = time from the onset of exposure; and ^ = residence
time of the chemical in the ith compartment. Pleil et al.50 have pointed out that, when Equation
(4-16) is applied to blood data, the term for the exposure concentration Catr is, in fact, a
composite parameter that includes an adjustment for the effective transfer of the gas phase to the
blood (the blood/breath partition coefficient/1) that accounts for Henry's Law.
The fraction/of the compound exhaled unchanged at equilibrium, i.e., t = °°, follows
from Equation (4-16) as:
During the post-exposure decay phase, the concentration declines exponentially:
ie-^' (4-18)
where, now, t is measured from the time exposure ends. In the experiment conducted here, the
air concentration Ca;r was set to zero, i.e.,/Ca;r.= 0. In Equation (4-18), the first exponential term
(compartment) is generally associated with blood, the second with "highly perfused tissues," the
third with "moderately perfused tissues," and the fourth with "poorly perfused tissues." For a
broad range of VOCs, it has been found that the residence times for these compartments are roughly
similar, namely, 3-11 min for the first compartment, 0.4-1 .6 h for the second, 3-8 h for the third, and
several days for the fourth compartment.45 For the exposure times used in the present study, we
22
-------
apply a two-compartment decay model to evaluate the contributions to the breath levels during the
decay period.
The residence time is defined as the time it takes for the compound to decay to lie of its
initial concentration in the compartment, assuming all other compartments are at zero
concentration. The biological half-life ty2 of the compound in the body is related to the residence
time Tthrough the relation:
T=t%/ln2 (4-17)
All of the parameters are determined empirically using the Marquardt-Levenberg
(nonlinear regression) algorithm in SigmaPlot (Version 5.0, SPSS, Chicago, IL), which
minimizes the differences in the sum of squares between the assumed model and the
experimental data. This analysis provides values for the a, r, and ty2 terms.
The model may also be used to estimate the concentration of the component in the blood
at any time during the elimination phase from the relation: Cbiood = CaivP, where Cbiood is the
concentration of the component in the blood and P is the blood/breath partition coefficient. The
modeled breath values at t = 0, i.e., when exposure ceases, together with the relation for Cbiood,
provide an estimate of the maximum blood levels of the component attributable to the exposure.
Quality Control
Four types of samples were collected in this study: exhaled breath, room air, blood, and
urine. Exhaled breath samples were collected and analyzed simultaneously using the real-time
breath analyzer; whole-air samples were collected in stainless steel canisters and analyzed by
cryogenic preconcentration followed by GC/MS, using a modified U.S. EPA Method TO-14.
Blood and urine samples were analyzed using purge and trap procedures.15'16'46 For each of these
analyses, calibration curves were first prepared from at least four standards. The curves are
checked on a daily basis, using a standard prepared separately from the calibration standard. The
tune settings on the respective analytical mass spectrometers were verified daily. Holding times
for the air samples were less than one week. Laboratory blanks were analyzed on a regular basis
by the respective laboratories. Reproducibility was estimated from duplicate analyses. The
respective instrument minimum detection limits were determined from multipoint calibrations.
Exhaled Breath and Whole Air
The 3DQ ion trap mass calibration was established and checked each day, using routine
operating procedures and internal 3DQ software designed for that purpose. Specific 3DQ
operating parameters and diagnostic checks were also evaluated daily.
Calibration of response of the real-time breath analyzer to the target breath components
was performed, as described earlier (cf Chapter 4, Breath Measurements), using gas standards
prepared in cylinders. Samples of the cylinder contents were collected in canisters and analyzed
23
-------
using GC/MS. The concentrations of the MTBE, MTBE-di2, DBCM, fert-butyl alcohol (TEA),
and benzene in the canister samples were determined using a dynamic dilution of a
gravimetrically-prepared in-house standard (Battelle standard LL-17298). This calibration
mixture contains MTBE, MTBE-di2, DBCM, trichloromethane, TEA, and benzene prepared at
ppbv levels in nitrogen. Table 4-4 lists the target compounds and their concentrations in the
standard. These concentrations were derived from a knowledge of the original amount injected
and the pressure of the cylinder. The MTBE concentration was validated by analyzing a certified
reference gas (Scott Specialty Gas), which was also dynamically diluted under the same
conditions as the calibration standards.
Table 4-4. Battelle standard containing the target
compounds, trichloromethane, and benzene in nitrogen.
„ , Concentration
Compound , , ,
(ppbv)
MTBE 9.31
MTBE-d12 8.17
DBCM 12.9
Trichloromethane, CHC13 14.0
TEA 11.6
Benzene, C6H6 12.5
The accuracy of the Battelle standard LL-17298 was assessed, in turn, by analyzing
standard LL-17305 and the MTBE certified reference gas. Using the automated GC/MS system
described earlier, the resulting peak areas were used to quantify the target compounds in the
MTBE reference gas and Battelle standard. Then, the concentrations of MTBE, trichloro-
methane, and benzene in the standards were calculated from the peak areas using the average
response factor (concentration/average peak area) obtained from Battelle standard LL-17298.
Table 4-5 compares the certified and measured concentrations for the Battelle in-house and
Table 4-5. Comparison of measured and certified concentrations of MTBE in
certified reference standard, and chloroform and benzene in NIST SRM 1804a.
Compound
MTBE
Chloroform
Benzene
Certified
Concentration
(ppbv)
51.0a
16.9b
14.8b
Measured
Concentration*
(ppbv)
53.5±1.1
16.6 ±0.6
15.6±0.8
% Difference
4.9
1.8
5.4
a Certified reference gas (Scott Specialty Gas).
b With respect to Battelle LL-17298 standard.
24
-------
certified standards. These results indicate that the values obtained for the concentrations of
MTBE, chloroform, and benzene in Battelle standard LI-17298 are reliable.
The calibration standard for the real-time breath analyzer was prepared in-house by static
dilution in a 15.7 L cylinder. To prepare the standard, an intermediate standard consisting of 360
|lL of pure DBCM (Aldrich, 98% purity) was diluted to a final 2.0 mL volume with methanol.
To prepare the 3DQ calibration standard, 1.2 |iL of the intermediate standard and 0.6 |iL of pure
MTBE-di2 (C/D/N Isotopes, >99.8% atom % D) were injected into a 15.7 L cylinder through a
heated syringe injection port attached to the cylinder. The cylinder then was pressurized to 1,000
psig using medical grade breathing air (Praxair). A canister sample was collected and analyzed
in duplicate using the modified EPA TO-14 method and the automated GC/MSD/FID system
described earlier. The measured FID peak areas were used to quantify the MTBE-di2 and
DBCM in the sample. Then, as before, the concentrations of MTBE-di2 and DBCM in the
canister were calculated from the FID peak area using the average response factor
(concentration/average peak area) obtained from Battelle standard LL-17298. The concentration
of MTBE-di2 estimated in this way was 119.7 ppbv compared with the concentration injected,
viz., 100.0 ppbv, which represents a 19.7 percent difference. The concentration of DBCM
estimated in this way was 53.9 ppbv compared with the concentration injected, viz., 57.3 ppbv,
which represents a 5.9 percent difference. The good agreement obtained between the measured
and injected concentrations validates the accuracy of the spiking method, which has been used
extensively in our laboratory.28 The concentrations of MTBE-di2 and DBCM injected into the
cylinder (100.0 and 57.3 ppbv, respectively) and the average MTBE-di2 and DBCM peak areas
obtained for the canister sample were used to quantify the concentrations of MTBE-di2 and
DBCM in the breath sample data acquired continuously with the real-time breath analyzer. As
noted earlier, we were unable to calibrate the breath analyzer for the target compound TEA
because of its apparent adsorption onto the inner surfaces of the ion trap. Consequently, the
cylinders were only used to calibrate the instrument for MTBE-di2 and DBCM.
Blood and Urine
Quality control measures undertaken for the collection and analysis of the blood and
urine samples included the following:
• All glassware used was first cleaned with 10% HC1 and rinsed with de-ionized water,
then baked at 300°C for 12 h before use.
• Soon after collection, all blood and urine samples were stored in a cold room at 4°C until
analysis.
• Before purging a sample, helium gas was sparged through the entire system for 5 minutes
to remove any MTBE contamination. In addition, to avoid DBCM contamination, the
Tygon tubing connecting the purge vessel to the trap was replaced between samples.
• The operation and performance status of the GC/MS system was checked daily by
analyzing 50 ng of BFB (bromofluorobenzene) and 31.6 ng of 13C-benzene standards.
25
-------
• Blank traps were checked for contamination by GC/MS before use in the purge-and-trap
analysis. These blank traps were analyzed with each set of samples to ensure that neither
the traps nor the analytical system were contaminated.
• External QC standards were prepared on Tenax traps by directly injecting the BFB/-
benzene standard into a flash evaporator and flushing the vapors onto the trap with zero-
grade nitrogen. The QC standards were analyzed after every sixth sample to verify the
stability of the GC/MS response.
26
-------
Chapter 5
Results
A number of practical difficulties were experienced while conducting the inhalation
exposure experiments at EOHSI. The bathroom in which the experiments were carried out was
unventilated and had no temperature control. Heat emitted by the electronics of the real-time
breath analyzer and ancillary equipment during the day, along with the heat from the bodies of
the operators and the subjects in the room, caused the mass scale of the breath analyzer to drift in
an unexpected and unpredictable fashion, necessitating frequent and time consuming
recalibrations and additional operational checks. Additionally, serious problems were
subsequently encountered at EOHSI in the analyses of the blood and urine samples for the target
compounds. As a result, all of the blood and urine data presented here are regarded as suspect
and must be viewed with caution.
A total of seven subjects participated in the inhalation exposure experiments. Before
each experiment, the subject was fitted with a venous catheter and a face mask which was
connected to two gas cylinders such that the subject breathed either hospital-grade air from one
of the cylinders or air containing a mixture of 2,217 |ig/m3 (542 ppbv) MTBE-di2 and 728 |ig/m3
(85.6 ppbv) DBCM from the second cylinder. Pre-exposure blood, breath, and urine samples
were collected, followed by the exposure (uptake) period, which was of-30 minutes duration.
During the exposure period, we made an effort to collect paired blood and discrete breath
samples using various time sequences. A typical sequence was: t = -5 to 0 min (pre-exposure
baseline sample), then 3, 5, 20 (duplicate blood draw), and 29 min. At the start of the
elimination period (at t = -30 min), the subject's breathing tube was automatically switched to
the second cylinder so that he/she breathed only hospital-grade air. Breath measurements were
taken for an additional -30 min (until t = -60 min). After a rest period of about 25 min, an
additional 5-min breath sample was taken and all monitoring terminated at t = -90 min. In three
cases, a third continuous breath sample was taken, 15 minutes later in two of these cases, and 20
minutes later in the third case. During each elimination period, three or four blood samples were
taken, typically at 35, 45, and ending at either 60 or 90 min. Table 5-1 provides a summary of
the collection times for the breath and blood samples in the MTBE-di2/DBCM inhalation
exposure experiments.
Exhaled Breath Data
All of the Lab View CCh-in-breath and valve switching data were converted to
spreadsheet format; the CCh waveforms were converted into %CO2 based on the calibration of
the CO2 monitor with a 5% CC>2 gravimetric standard.
27
-------
Table 5-1. Summary of blood and breath sample collection times (min) in each exposure experiment.
MTBE-d12/DBCM Cone (jig/m3)
Activity
Pre-Exposure
Exposure Start
Exposure uptake monitored3
Exposure uptake monitored3
Exposure uptake monitored3
Exposure uptake monitored3
Exposure uptake monitored3
Exposure uptake monitored3
Exposure uptake monitored3
Exposure uptake monitored3
1st Continuous Post-Exposure Start0
Exposure decay monitored
Exposure decay monitored
Exposure decay monitored
1st Continuous Post-Exposure Stop
2nd Continuous Post-Exposure Start0
Exposure decay monitored
2nd Continuous Post-Exposure Stop
Subject IF02
2,217/728
Breath
-3.3
Blood
-5
0.00
2.45
5.99
9.35
12.98
17.52
22.61
27.69
33.32
—
5.0
—
15.0
—
—
29.0
—
33.51
V
35.0
45.0
60.0
62.11
83.67
V
90.0
91.21
Subject EVI03
2,217/728
Breath
-2.5
Blood
-5
0.00
2.42
6.49
10.34
14.12
18.95
23.85
29.59
36.45
—
5.0
—
15.0
—
—
29.0
—
36.68
32.0
—
60.0
60.45
85.32
V
90.0
90.54
Subject EVI04
2,217/728
Breath
-2.9
Blood
-5
0.00
2.34
5.85
9.14
12.72
17.18
21.64
27.27
—
—
5.0b
—
15.0
—
—
29.0
—
33.49
35.0
45.0
60.0
64.42
90.42
V
90.0
94.73
Subject EVI05
2,217/728
Breath
-2
3
Blood
-5
0.00
2.55
5.92
9.58
13
17.
16
69
22.96
—
—
—
5.0b
—
15.0
—
—
29.0
—
33.85
i
r
35.0*
45.0
60.0
64.27
89.15
^
r
—
94.74
Subject EVI08
2,217/728
Breath
-4.3
Blood
-5
0.00
1.74
4.45
7.24
12.90
18.71
25.28
32.98
35.69
—
5.0
10.0
—
—
28.0
—
—
35.84
35.0b
—
60.0
66.10
91.10
V
90.0
96.45
Subject IF06
2,217/728
Breath
-4.6
Blood
-5
0.00
1.43
3.84
6.18
9.57
15.97
22.60
31.12
33.53
3.0
5.0
—
—
—
20.0
29.0
—
33.75
35.0b
45.0
60.0
64.34
89.34
V
—
94.17
Subject EVI01
2,217/728
Breath
-5
0
Blood
-5
0.00
1.56
4.24
6.48
11.
17.
24
24
64
72
—
—
—
5.0
—
—
15.0
—
29.0
32.0b
34.23
i
r
35.0
45.0
60.0
60.08
90.08
^
r
90.0
95.18
-------
MTBE-d12/DBCM Cone (jig/m3)
Activity
3rd Continuous Post-Exposure Start0
3rd Continuous Post-Exposure Stop
Subject IF02
2,217/728
Breath
Blood
Subject EM03
2,217/728
Breath
115.7
1
120.7
Blood
Subject EM04
2,217/728
Breath
118.7
1
124.0
Blood
Subject EM05
2,217/728
Breath
Blood
Subject EM08
2,217/728
Breath
125.1
1
130.2
Blood
Subject IF06
2,217/728
Breath
Blood
Subject EM01
2,217/728
Breath
Blood
a Breath concentration during exposure period monitored at discrete times by temporarily interrupting the exposure to collect the exhaled breath sample.
See text for details.
b Duplicate samples taken.
0 Breath concentration during post-exposure (decay) period monitored continuously in real time (indicated by vertical arrow).
-------
For the inhalation exposure experiments, CO2-in-breath and valve switching data workup
included:
• Preparing a summary of clean air breaths taken by, and respiration rates of, each subject
during each exposure cycle
• Determining the following parameters for the three distinct periods of each inhalation
experiment; i.e., pre-exposure (baseline) breath, exposure period, and post-exposure
(decay) period:
> number of inhalations
> number of exhalations
> total volume of air expired
> average tidal volume
> respiration rate
Figures 5-1 to 5-7 show the continuous uptake and elimination breath profiles obtained
for MTBE-di2 and DBCM from the seven subjects. Buckley et al.12 have pointed out that to
characterize the breath uptake profile during inhalation exposure, it is necessary to temporarily
interrupt the exposure to the target pollutants with inhalations of pure air. Otherwise, the
collected breath samples would be masked, especially in the early stages of the exposure, by the
residual high levels of the target chemicals from the supply source. To circumvent this problem,
at fixed times during the exposure period (see Table 5-1), the biofeedback system shown in
Figure 4-3 was used to automatically switch the subject from the MTBE-di2/DBCM supply
source to inhalation of pure air from a separate cylinder for 1 - 2 min while continuing to exhale
into the breath monitoring system. At the end of each of these brief breath sampling periods, the
supply was switched back to the MTBE-di2/DBCM supply source and the exposure uptake
resumed until the next measurement sequence. Figures 5-8 to 5-14 show the uptake and
elimination breath profiles obtained after averaging the measurements taken during the uptake
phase using this procedure.
Breath and Blood Data
As indicated by the summary of experiments in Table 5-1, paired blood data for MTBE-
di2 were obtained for the uptake and elimination periods for all of the subjects who provided
breath samples. Measurable concentrations for TEA in blood were also obtained for three of the
seven subjects who participated, but blood levels for DBCM were below the limits of detection
in all cases.
Figures 5-15 to 5-21 show the uptake and elimination concentrations of MTBE-di2 in the
breath and the blood for all seven subjects. The results obtained for TEA in blood are also
included in Figures 5-19 to 5-21 for Subjects EVI08, IF06, and EVI01, respectively.
30
-------
^ 600 -
re
o>
TJ
111
00
500 -
O)
c
O
'^
re
•S 400 -
c
0)
O
O
O
300 -
m 200 -
100
JlJUnUll. I I lini
20
30
40 50 60
Time (min)
70
80
90
10 20 30 40 50 60 70 80 90
Figure 5-1. Continuous uptake and decay profiles of MTBE-di2 (upper plot)
and DBCM (lower plot) in breath for female Subject IF02 exposed
to 2,217 jig/m3 (542 ppbv) of MTBE-d12 and 728 ug/m3 (85.6 ppbv)
of DBCM in air for 29.3 minutes (effective exposure period).
-------
E 400 -
O)
c
O
o>
o
c
o
o
re
o>
m
TJ
111
m
re
o>
m
o
00
Q
MTBE-d12: Subject IM03
Post-Exposure
2 soo :
MTBE-d12 Breath Profile
200 -
100 -•
0 10 20 30 40 50 60 70 80 90 100 110 120
Time (min)
300
250 r
O)
o
~ 200 r
re
•4-i
C
0)
o
c
o
o
150
100
10 20 30 40
50 60 70
Time (min)
80 90 100 110 120
Figure 5-2. Continuous uptake and decay profiles of MTBE-di2 (upper plot)
and DBCM (lower plot) in breath for male Subject IM03 exposed to
2,217 jig/m3 (542 ppbv) of MTBE-d12 and 728 ug/m3 (85.6 ppbv) of
DBCM in air for 30.6 minutes (effective exposure period).
32
-------
400 -
re
o>
m
TJ
LJJ
00
O)
c
O
re 300 -
0)
o
c
o
O
Post-Exposure
MTBE-d12 Breath Profile
200 -
100 -
0 10 20 30 40 50 60 70 80 90 100 110 120 130
Time (min)
0 10 20 30 40 50 60 70 80 90 100 110 120 130
Time (min)
Figure 5-3. Continuous uptake and decay profiles of MTBE-di2 (upper plot)
and DBCM (lower plot) in breath for male Subject IM04 exposed to
2,217 jig/m3 (542 ppbv) of MTBE-d12 and 728 ug/m3 (85.6 ppbv) of
DBCM in air for 30.3 minutes (effective exposure period).
33
-------
Exp( sure ^-•> Post-Exposure
10
20
30
40 50 60
Time (min)
70
80
90
100
10
20
30
40 50
Time (min)
60
70
80
90
100
Figure 5-4. Continuous uptake and decay profiles of MTBE-di2 (upper plot)
and DBCM (lower plot) in breath for male Subject IM05 exposed to
2,217 jig/m3 (542 ppbv) of MTBE-d12 and 728 ug/m3 (85.6 ppbv) of
DBCM in air for 30.6 minutes (effective exposure period).
34
-------
MTBE-d12: Subject IM08
0 10 20 30 40 50 60 70 80 90 100 110 120 130
Time (min)
0 10 20 30 40 50 60 70 80 90 100 110 120 130
Time (min)
Figure 5-5. Continuous uptake and decay profiles of MTBE-di2 (upper plot)
and DBCM (lower plot) in breath for male Subject IM08 exposed to
2,217 jig/m3 (542 ppbv) of MTBE-d12 and 728 ug/m3 (85.6 ppbv) of
DBCM in air for 30.6 minutes (effective exposure period).
35
-------
cT* 600
E
1
c
o
•4-i
500
400
o>
o
o
O 300
re
S!
m 200
100
MTBE-d12: Subject IF06
10 20 30 40 50 60
Time (min)
70
80
90
100
10 20 30 40 50 60 70 80 90 100
Time (min)
Figure 5-6. Continuous uptake and decay profiles of MTBE-di2 (upper plot)
and DBCM (lower plot) in breath for female Subject IF06 exposed
to 2,217 jig/m3 (542 ppbv) of MTBE-d12 and 728 ug/m3 (85.6 ppbv)
of DBCM in air for 30.7 minutes (effective exposure period).
36
-------
400
O)
c
O
'*s
2
•4-i
C
0)
O
c
O
O
re
o>
m
TJ
111
m
O)
c
O
'^
re
•4-i
C
0)
O
c
O
O
re
o>
m
O
m
Q
300
200
100
MTBE-d12: Subject IM01
Exposure
Post-Exposure
MTBE-d12 Breath Profile
20
30
40 50 60
Time (min)
70
80
90 100
400
300 -
200 -
100
DBCM: Subject IM01
40 50 60
Time (min)
70
80
90 100
Figure 5-7. Continuous uptake and decay profiles of MTBE-di2 (upper plot)
and DBCM (lower plot) in breath for male Subject IM01 exposed to
2,217 jig/m3 (542 ppbv) of MTBE-d12 and 728 ug/m3 (85.6 ppbv) of
DBCM in air for 30.5 minutes (effective exposure period).
37
-------
I 50°
o
'•re 40°
c
0)
o
o
o
re
g> 200
m
LJJ
m
100
MTBE-d12: Subject IF02
^ Exposure ^.^•.
Pos'f -Ex p 6 s'u re"
Discrete Breath Uptake Profile
Continuous Breath Decay Profile
0 10 20 30 40 50 60 70 80 90
LOD
£ 500
.2 400
re
•4-i
0)
o
c
o
o
re
o>
m
O
m
Q
300
200
100
DBCM: Subject IF02
•Exposure ^-^ Post-Ex-posur-e-
Discrete Breath Uptake Profile
Continuous Breath Decay Profile
LOD
20
30
40 50 60
Time (min)
70
80
90
Figure 5-8. Discrete uptake and continuous decay profiles of MTBE-di2 (upper
plot) and DBCM (lower plot) in breath for female Subject IF02
exposed to 2,217 ug/m3 (542 ppbv) of MTBE-di2 and 728 jig/m3
(85.6 ppbv) of DBCM in air for 29.3 minutes (effective exposure
period). LOD designates limit of detection for target compound.
38
-------
§ 400
c
o
^
n
•| 300
o
u
c
o
o
£ 200
n
o
^
CO
CM
"? 100
UJ
CO
0)
o
c
o
O
re
e
00
o
tn
Q
MTBE-d12: Subject IM03
••Expos-tire-
••Post-Exposure-
Discrete Breath Uptake Profile
Continuous Breath Decay Profile
0 10 20 30 40 50 60 70 80 90 100 110 120
Time (min)
300
E 250
1
.1 200
150
100
50
DBCM: Subject IM03
..Exposure ^.^. Po.st.TExpo.sure...
Discrete Breath Uptake Profile
Continuous Breath Decay profile
LOD
10 20 30 40
50 60 70
Time (min)
80 90 100 110 120
Figure 5-9. Discrete uptake and continuous decay profiles of MTBE-di2 (upper
plot) and DBCM (lower plot) in breath for male Subject IM03
exposed to 2,217 ug/m3 (542 ppbv) of MTBE-d12 and 728 jig/m3
(85.6 ppbv) of DBCM in air for 30.6 minutes (effective exposure
period). LOD designates limit of detection for target compound.
39
-------
400
o>
2 300
o>
o
c
o
O
re
o>
m
LJJ
00
200
100
0
MTBE-d12: Subject IM04
Exposure ^
Post-Exposure
Discrete Breath Uptake Profile
Continuous Breath Decay Profile
If!
LOD
0 10 20 30 40 50 60 70 80 90 100 110 120 130
Time (min)
o>
o
+«i
re
o>
o
c
o
O
re
o>
m
o
CO
Q
400
300
200
100
DBCM: Subject IM04
Exposure
Post-Exposure
Discrete Breath Uptake Profile
Continuous Breath Decay Profile
LOD
0 10 20 30 40
50 60 70 80
Time (min)
90 100 110 120 130
Figure 5-10. Discrete uptake and continuous decay profiles of MTBE-di2
(upper plot) and DBCM (lower plot) in breath for male Subject
IM04 exposed to 2,217 ug/m3 (542 ppbv) of MTBE-d12 and 728
jig/m3 (85.6 ppbv) of DBCM in air for 30.3 minutes (effective
exposure period). LOD designates limit of detection for target
compound.
40
-------
o>
300
250
2 200
o>
o
c
o
O
150
re
2
CO
100
LJJ
CO
50
MTBE-d12: Subject IM05
Exposure
Post-Exposure
Discrete Breath Uptake Profile
Continuous Breath Decay Profile
LOD
10 20 30 40 50 60
Time (min)
70
80
90
100
o>
c
o
'^
re
+-i
c
0)
o
c
o
O
re
o>
^
00
o
CO
Q
300
250
200
150
100
50
rT
DBCM: Subject IM05
Exposure
><:
Post-Exposure
Discrete Breath Uptake Profile
Continuous Breath Decay Profile
LOD
10 20 30 40 50 60
Time (min)
70
80
90
100
Figure 5-11. Discrete uptake and continuous decay profiles of MTBE-di2
(upper plot) and DBCM (lower plot) in breath for male Subject
IM05 exposed to 2,217 ug/m3 (542 ppbv) of MTBE-d12 and 728
jig/m3 (85.6 ppbv) of DBCM in air for 30.6 minutes (effective
exposure period). LOD designates limit of detection for target
compound.
41
-------
O)
o
'^
re
•4-i
0)
o
c
o
o
re
o>
m
LLI
m
500
A nn
onn
oUU
onn
1 nn
l
c
• MTBE-d12: Subject IM08
^ Exposure Post-Exposure ^
ii • Discrete Breath Uptake Profile
• " "l
: •' | :
wL
' "™ 1 i :
r -* %- -
. 1 1 1 i . . 1 1 i . . 1 1 i . 1 1 1 1 . . 1 1 i . . 1 1 i . . 1 1 1 . . 1 1 1 . . 1 1 1 . . . 1 1 . . . 1 1 . . . 1 1 1 . 1 1 1 1 .
) 10 20 30 40 50 60 70 80 90 100 110 120 130
Time (min)
c
o
+J
re
o>
o
c
o
O
re
o>
m
o
m
Q
400
300
200
100
DBCM: Subject IM08
Exposure
Post-Exposure
Discrete Breath Uptake Profile
Continuous Breath Decay Profile
LOD
0 10 20 30 40
50 60 70 80
Time (min)
90 100 110 120 130
Figure 5-12. Discrete uptake and continuous decay profiles of MTBE-di2
(upper plot) and DBCM (lower plot) in breath for male Subject
IM08 exposed to 2,217 ug/m3 (542 ppbv) of MTBE-d12 and 728
jig/m3 (85.6 ppbv) of DBCM in air for 30.6 minutes (effective
exposure period). LOD designates limit of detection for target
compound.
42
-------
O)
c
O
700
600
•= 500
re
+«i
o>
o
c
o
O
re
o>
m
LJJ
m
MTBE-d12: Subject IF06
Exposure
Post-Exposure
E
^>
5
4-1
C
0)
o
c
o
O
re
£
m
s
o
m
Q
400
300
200
100
0
C
400
350
300
250
200
150
100
50
0
Discrete Breath Uptake Profile
Continuous Breath Decay Profile
TT--1LOD
10 20 30 40 50 60
Time (min)
70
80
90 100
DBCM: Subject IF06
Exposure
-X-
Post-Exposure
Discrete Breath Uptake Profile
Continuous Breath Decay Profile
LOD
10 20 30 40 50 60
Time (min)
70
80
90
100
Figure 5-13. Discrete uptake and continuous decay profiles of MTBE-di2
(upper plot) and DBCM (lower plot) in breath for female Subject
IF06 exposed to 2,217 jig/m3 (542 ppbv) of MTBE-d12 and 728
ug/m3 (85.6 ppbv) of DBCM in air for 30.7 minutes (effective
exposure period). LOD designates limit of detection for target
compound.
43
-------
O)
c
O
0)
O
O
O
re
m
w
•o"
ill
oo
O)
400
350
300
250
200
150
100
50
0
300
250
MTBE-d12: Subject IM01
Exposure
Post-Exposure
Discrete Breath Uptake Profile
Continuous Breath Decay Profile
-.LOD
0 10 20 30 40 50 60 70 80 90 100
Time (min)
'•E 200
c
o>
o
c
o
O
re
o>
m
O
00
Q
150
100
50
DBCM: Subject IM01
Exposure
Post-Exposure
Discrete Breath Uptake Profile
LOD
10 20 30 40 50 60
Time (min)
70
80
90
100
Figure 5-14. Discrete uptake and continuous decay profiles of MTBE-di2
(upper plot) and DBCM (lower plot) in breath for male Subject
IM01 exposed to 2,217 ug/m3 (542 ppbv) of MTBE-d12 and 728
jig/m3 (85.6 ppbv) of DBCM in air for 30.5 minutes (effective
exposure period). LOD designates limit of detection for target
compound.
44
-------
.
CO
500
_i
I 4°°
re
% 300
c
o
O
.n
re 200
o>
m
CN|
2 1°°
m
; MTBE-d12: Subject
IF02 -_
£. Exposure ~9 Post-Exposure ^ -
-
'.'•"• \
•
•
• Discrete Breath Uptake Profile :
• Measured Blood Profile J
• • :
"
Su i
- . '1WIW| ion ;
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
CD
m
a.
o
o
Q.
O
o
3
o
OJ
i«*
5'
(Q
10
20
30
40 50
Time (min)
60
70
80
90
Figure 5-15. Uptake and decay of MTBE-di2 in breath and blood for female
Subject IF02 exposed to 2,217 jig/m3 (542 ppbv) of MTBE-di2 and
728 ug/m3 (85.6 ppbv) of DBCM in air for 29.3 minutes.
^ 400
c
o
+J
re
•£ 300
0)
o
c
o
o
£ 200
re
0)
m
LU
m
100
MTBE-d12: Subject IM03
••Exposure-
••PesHExposttre-
0
Discrete Breath Uptake Profile
Continuous Breath Decay Profile
Measured Blood Profile
3 J
ro
o
o
Q.
O
o
3
O
(D
D)
p+
5'
0 10 20 30 40 50 60 70 80 90 100 110 120
Time (min)
Figure 5-16. Uptake and decay of MTBE-di2 in breath and blood for male
Subject IM03 exposed to 2,217 jig/m3 (542 ppbv) of MTBE-di2 and
728 ug/m3 (85.6 ppbv) of DBCM in air for 30.6 minutes.
45
-------
MTBE-d12 Breath Concentration (|j,g/m3)
->• M CO -fc.
O O O O
3 O O O O
C
Figure
300
-------
MTBE-d12 Breath Concentration (^g/m3)
->• M co j^ en CD
o o o o o o
3 O O O O O O
kH
(
Figure 5-
700
co~*
E
"01 600
c
~ 500
re
+-
g 400
c
o
O
j= 300
+-
re
0)
% 200
T3~
111
m 100
MTBE-d12 and TBA: Subject IM08
", Exposure _^ Post-Exposure _^
_ & -
[ • Discrete MTBE Breath Uptake Profile
' * • Measured MTBE Blood Profile
Jj A Measured TBA Blood Profile
• "*"ll
: •" | »
;•" /MJiL •
i » w i
., A i 1 i i i i 1 i < < < 1 < i < i 1 i < i < 1 < i < i 1 i < i < 1 1 i i i i 1 i i i i 1 i i i i 1 i i i i 1 i
MTBE-d12/TBA Blood Concentration (^ig/L)
o LO o LO c
CN t- t- CD C
) 10 20 30 40 50 60 70 80 90 100 110 120 130
Time (min)
-19. Uptake and decay of MTBE-di2 in breath and blood, and of TBA in
blood, for male Subject IM08 exposed to 2,217 ug/m3 (542 ppbv) of
MTBE-d12 and 728 ug/m3 (85.6 ppbv) of DBCM in air for 30.6 min.
I MTBE-d12 and TBA: Subject IF06 •_
~
- Exposure Post-Exposure
^» ^: *^ ^
-
£ A • Discrete MTBE Breath Uptake Profile
• Measured MTBE Blood Profile
• I ^ Measured TBA Blood Profile
; • " * 1 * :
: " • ^ l|]j[| •
>* * » w4|ul :
: « ff :
1 AA 1
MTBE-d12/TBA Blood Concentration (^ig/L)
LO o LO o LO c
C\i C\i t- t- CD C
0 10 20 30 40 50 60 70 80 90 100
Time (min)
Figure 5-20. Uptake and decay of MTBE-di2 in breath and blood, and of TBA in
blood, for female Subject IF06 exposed to 2,217 jig/m3 (542 ppbv) of
MTBE-di2 and 728 ug/m3 (85.6 ppbv) of DBCM in air for 30.7 min.
47
-------
CO
I
C
O
O
O
O
£ 150
re
£
m
T3
111
m
350
300
250
200
100
MTBE-cL, and TBA: Subject IM01
Exposure
Post-Exposure
Discrete MTBE Breath Uptake Profile
Continuous MTBE Breath Decay Profile
Measured MTBE Blood Profile
Measured TBA Blood Profile
1.5
1.0
00
m
o.
00
>
pa
o
o
Q.
O
o
o
CD
3
0.5 3
5'
0.0
10
20
30
40
50
60
70
80
90
100
Time (min)
Figure 5-21. Uptake and decay of MTBE-di2 in breath and blood, and of TBA in
blood, for male Subject IM01 exposed to 2,217 ug/m3 (542 ppbv) of
MTBE-dn and 728 ug/m3 (85.6 ppbv) of DBCM in air for 30.5 min.
48
-------
Total Absorbed Dose
The MTBE-di2 total absorbed dose to each subject was calculated from Equations 4-1 to
4-10. Results are presented for all seven subjects in Table 5-2. The mean MTBE-di2 total
absorbed dose was 148.5 ± 34.4 jig [mean ± standard deviation (SD)] for the ~30-min exposure.
We were unable to derive total absorbed dose values for DBCM from the exhaled breath
profiles obtained for this target analyte (see Figures 5-8 to 5-14). In most cases, the measured
signals were barely above the limit of detection, giving rise to considerable uncertainty in the
curve fitting phase. In addition, the decay portions of the profiles appeared to decrease unusually
slowly, suggesting that the measured signal may, in fact, have been affected by an unknown
contaminant. This slow decrease during elimination had the effect of greatly increasing the
estimated areas under the decay curves such that the resultant values were effectively
meaningless.
Fraction of Compound Exhaled Unchanged at Equilibrium
The fraction of MTBE-di2 eliminated through respiration at equilibrium was estimated as
the ratio of the "unmetabolized mass" to the total ("applied") dose (Equation (4-12)). The
"unmetabolized mass" was calculated from the product of the total area under the uptake and
decay curves with the alveolar ventilation rate (Equation (4-11)). Finally, the total dose was
determined from the product of the total exposure and the subject's average alveolar ventilation
rate (Equation (4-1)). Results for the value off obtained in this way for MTBE-di2 are
summarized in Table 5-2; the mean value of/was 0.29 ± 0.04. As explained above, we were
unable to estimate a value of/for DBCM from the exhaled breath data in Figures 5-8 to 5-14.
Empirical Modeling of Uptake and Decay Breath and Blood Concentrations
The linear compartment model developed by Wallace et al.29 was used to model the
MTBE-di2 uptake and decay concentrations in the breath and blood of the participants.
Equations (4-16) and (4-18) were fitted to the observed data. Curve fitting to estimate the
coefficients in the equations was accomplished using SigmaPlot. The results for MTBE-di2 are
shown in Figures 5-22 to 5-35, and values obtained for the calculated uptake and elimination
parameters are presented in Table 5-3. For the breath and blood uptake phase, a one-
compartment model was assumed; for the elimination phase, we used a two-compartment model
for the breath data and a one-compartment model for the blood data.
The results obtained by applying the linear compartment model to the breath and blood
uptake and decay data for DBCM are summarized in Table 5-4. As already noted, in most cases
for DBCM, the measured signals were only slightly above the detection limit, which resulted in
considerable uncertainty in the curve fitting. This uncertainty is clearly reflected in the data
presented in Table 5-4.
49
-------
Table 5-2. Total absorbed dose of MTBE-dn as a result of inhalation exposure.
Parameter
Cair (ug/m3)
Total Elapsed Exposure Time, T (min)
Total Interrupted MTBE Uptake Period (min)
Effective Exposure Time, T' (min)
Total Exposure, Etotal ((ig.min/m3)
Uptake Ventilation Rate (L/min)
Uptake Alveolar Ventilation Rate, AYR (L/min)a
Total ("Applied") Dose (ug)
Uptake Period, T (min)
Uptake AVR(L/mm)a
Area Under Uptake Curve ((ig.min/m3)
Total Amount Exhaled During Uptake (|ig)
Subj.
IF02
2,217
33.3
3.97
29.3
64,958
3.49
2.34
152.0
Total
33.3
2.34
9789
22.9
Subj.
IM03
Total
2,217
36.7
6.08
30.6
67,840
5.97
4.00
271.4
Subj.
IM04
Exposure
2,217
33.5
3.25
30.3
67,175
4.90
3.28
220.3
Subj.
IM05
2,217
33.9
3.26
30.6
67,840
4.74
3.18
215.7
Subj.
IM08
2,217
35.8
5.20
30.6
67,840
4.56
3.06
207.6
Subj.
IF06
2,217
33.8
3.14
30.7
68,062
5.56
3.73
253.9
Subj.
IM01
2,217
34.2
3.68
30.5
67,619
3.08
2.06
139.3
Mean
2,217
34.5
4.08
30.4
67,333
4.61
3.09
208.6
Std Dev
0
1.3
1.13
0.5
1,084
1.04
0.69
48.6
Amount Exhaled During Uptake Period
36.7
4.00
8216
32.9
Total Amount
Monitored Decay Period (min)
Decay Ventilation Rate (L/min)
Decay Alveolar Ventilation Rate, AYR (L/min)a
a, ((ig/m3)b
ti decoy (min)b
a2 ((ig/m3)b
t2decoy (min)b
Area Under Decay Curve ((ig.min/m3)0
Total Amount Exhaled During Decay (|ig)
57.4
3.69
2.47
111.8
2.39
148.7
45.7
7063
17.5
83.5
6.13
4.11
225.5
3.91
123.4
70.9
9631
39.6
33.5
3.28
8132
26.7
33.9
3.18
5816
18.5
35.8
3.06
9679
29.6
33.8
3.73
12615
47.1
34.2
2.06
7041
14.5
34.5
3.09
8755
27.4
1.3
0.69
2201
10.7
Exhaled During Decay Period
90.4
5.70
3.82
154.0
3.81
122.5
72.5
9468
36.2
60.8
4.45
2.98
73.0
7.82
77.0
161.3
12991
38.7
94.2
7.02
4.70
229.6
3.41
143.4
64.1
9975
46.9
60.1
4.49
3.01
247.9
2.68
182.7
50.8
9946
29.9
60.6
4.27
2.86
141.9
2.73
102.8
63.3
6895
19.7
—
5.11
3.42
169.1
3.82
128.6
75.5
9424
32.6
—
1.20
0.80
66.5
1.86
34.0
39.1
2054
10.8
-------
Table 5-2. Total absorbed dose of MTBE-dn as a result of inhalation exposure (continued).
Subj.
Parameter IF02
Subj. Subj.
IM03 IM04
Subj.
IM05
Subj.
IM08
Subj.
IF06
Subj.
IM01
Mean
Std Dev
Total Absorbed Dose
Total Exhaled During Uptake + Decay (ug) 40.4
Total Absorbed ("Internal") Dose = Total Dose - , , , fi
Unmetabolized Mass (fig)
Fraction/Exhaled at Equilibrium 0.27
Fraction Absorbed (= 1 -/) 0.74
Fraction Eliminated Post-Exposure (0-90 min) 0.3 1 1
Average Uptake/Decay AYR (L/min) 2.4 1
From Model: Total Absorbed Dose 1 1 s n
AVR.Cair.T.(l-J) 11XU
72.4 62.8
199.0 157.5
0.27 0.29
0.74 0.74
0.391 0.461
4.06 3.55
201.9 170.5
57.2
158.5
0.27
0.72
0.300
3.08
153.5
76.5
131.1
0.37
0.71
0.743d
3.88
166.2
77.0
176.9
0.30
0.67
0.387
3.37
159.8
34.2
105.1
0.25
0.79
0.346
2.46
125.5
60.1
148.5
0.29
0.73
0.366
3.26
156.1
17.2
34.4
0.04
0.04
0.060
0.65
29.0
a Alveolar ventilation rate assumed to be 67% of ventilation rate.
b Determined from nonlinear curve fit to exponential decay model (see Table 5-3).
c Estimated from Equation (4-9) :49 AUCdecay = |Ca;v(t)dt = T.a,T,.
d Excluded from calculation of the mean.
-------
450
MTBE-d,,: Subject IF02
Measured Breath Uptake
Modeled 1-Compartment Breath Uptake
Measured Blood Uptake
Modeled 1-Compartment Blood Uptake
0.0
30
10 20
Exposure Time (min)
Figure 5-22. Measured and modeled uptake of MTBE-di2 in exhaled breath
and venous blood for female Subject IF02 exposed to 2,217 jig/m3
(542 ppbv) of MTBE-dn in air for 29.3 minutes.
_, 300 P MTBE-d12: Subject IF02
250
c
o
is
•5 200 -i
I
O
o
.c
4-*
03
m
LU
00
Measured Breath Decay Profile
Measured Blood Decay Profile
Modeled 2-Compartment Breath Decay
Modeled 1-Compartment Blood Decay
150 -
100 -
1.8
1.6
1.4
1.2
1.0
0.8
0.6
30
Time (min)
DO
m
h.
ro
DO
Q.
O
O
D
O
0>
Figure 5-23. Measured and modeled elimination of MTBE-di2 from exhaled
breath and venous blood for female Subject IF02 after exposure
to 2,217 jig/m3 (542 ppbv) of MTBE-di2 in air for 29.3 minutes.
Breath data smoothed using 5-point moving average.
52
-------
o
D
f+
i-
o
D
CQ
Exposure Time (min)
Figure 5-24. Measured and modeled uptake of MTBE-di2 in exhaled breath
and venous blood for male Subject IM03 exposed to 2,217 ug/m3
(542 ppbv) of MTBE-d12 in air for 30.6 minutes.
- 3.0
MTBE-d,,: Subject IM03
Measured Breath Decay Profile
Modeled 2-Compartment Breath Decay
Measured Blood Decay Profile
Modeled 2-Compartment Blood Decay
40 50
Time (min)
Figure 5-25. Measured and modeled elimination of MTBE-di2 from exhaled
breath and venous blood for male Subject IM03 after exposure
to 2,217 jig/m3 (542 ppbv) of MTBE-di2 in air for 30.6 minutes.
Breath data smoothed using 5-point moving average.
53
-------
o
is
o'
- 1 f
10
20
Exposure Time (min)
30
Figure 5-26. Measured and modeled uptake of MTBE-di2 in exhaled breath
and venous blood for male Subject IM04 exposed to 2,217 ug/m3
(542 ppbv) of MTBE-dn in air for 30.3 minutes.
350
- MTBE-d12: Subject IM04
300
1
c
1 250'
o
c
o
o
re
£
m
?
LU
m
• Measured Breath Decay Profile
Modeled 2-Compartment Breath Decay
• Measured Blood Decay Profile
Modeled 2-Compartment Blood Decay
3.5
3.0
CD
m
2.5
2.0
CD
o
o
Q.
o
o
3
o
CD
p*
3
1.5 S-.
1.0
10 20 30 40
50 60 70
Time (min)
80 90 100 110 120
Figure 5-27. Measured and modeled elimination of MTBE-di2 from exhaled
breath and venous blood for male Subject IM04 after exposure
to 2,217 jig/m3 (542 ppbv) of MTBE-di2 in air for 30.3 minutes.
Breath data smoothed using 5-point moving average.
54
-------
300
MTBE-d12: Subject IM05
• Measured Breath Uptake
Modeled 1-Compartment Breath Uptake
• Measured Blood Uptake
3.0
2.5
2.0
1.5
1.0
0.5
CD
m
CD
O
a
o
o
o
0>
!•*
3
^
o'
0.0
10
20
Exposure Time (min)
30
40
Figure 5-28. Measured and modeled uptake of MTBE-di2 in exhaled breath
and venous blood for male Subject IM05 exposed to 2,217 ug/m3
(542 ppbv) of MTBE-dn in air for 30.6 minutes.
3.
c
g
IE
"c
ro
0.45 CD
O
a
0.40 O
0.35 |
o'
3
0.30 £
0.25
10
20
30 40
Time (min)
50
60
Figure 5-29. Measured and modeled elimination of MTBE-di2 from exhaled
breath and venous blood for male Subject IM05 after exposure
to 2,217 jig/m3 (542 ppbv) of MTBE-d12 in air for 30.6 minutes.
Breath data smoothed using 5-point moving average.
55
-------
MTBE-d,,: Subject IM08
Measured Breath Uptake
Modeled 1-Compartment Breath Uptake
Measured Blood Uptake
Modeled 1-Compartment Blood Uptake
_ 400 -
350 -
.g
+•»
ns
0.0
10
20
Exposure Time (min)
30
40
Figure 5-30. Measured and modeled uptake of MTBE-di2 in exhaled breath
and venous blood for male Subject IM08 exposed to 2,217 ug/m3
(542 ppbv) of MTBE-d12 in air for 30.6 minutes.
450
-§ 400
1
c 350
g
| 300
c
-------
600
500 -
c
o
ro 400 -
c
0.5 :=•
0.0
10
20
Exposure Time (min)
30
40
Figure 5-32. Measured and modeled uptake of MTBE-di2 in exhaled breath
and venous blood for female Subject IF06 exposed to 2,217 jig/m3
(542 ppbv) of MTBE-dn in air for 30.7 minutes.
600
,i
c
g
is
500 ,r
MTBE-d12: Subject IF06
Measured Breath Decay Profile
Modeled 2-Compartment Breath Decay
Measured Blood Decay Profile
1.5
1.4
CO
>
to
1.3 "
O
Q.
O
1.2
o
0)
1.1 a
o'
3
1.0 S
0.9
10
20
30 40
Time (min)
50
60
Figure 5-33. Measured and modeled elimination of MTBE-di2 from exhaled
breath and venous blood for female Subject IF06 after exposure
to 2,217 jig/m3 (542 ppbv) of MTBE-d12 in air for 30.7 minutes.
Breath data smoothed using 5-point moving average.
57
-------
_ 300 -
E
"3)
250 -
c
g
is
i 200 -
c
-------
Table 5-3. Theoretical calculations of MTBE-dn model parameters.
Matrix
Parameter
Cmr ((ig/m3)
Exposure Time (min)
Subj.
IF02
2,217
29.3
Subj.
IM03
2,217
30.6
Subj.
IM04
2,217
30.3
Subj.
IM05
2,217
30.6
Subj.
IM08
2,217
30.6
Subj.
IF06
2,217
30.7
Subj.
IM01
2,217
30.5
Mean
2,217
30.4
Std Dev
0.5
Uptake Models
Breath
Blood
fC^i (= Max. Breath
Concn.) ((ig/m3)
"1 uptake
Adjusted R2d
JCaita,
*1 uptake
Adjusted R2d
338a
4.58b
0.908
2.13e
(51.6e)
0.962
303a
9.76C
0.849
2.51C
5.41e
0.907
295a
5.94b
0.926
nch
nch
nck
190a
3.26b
0.951
1.92e
4.54e
0.658
347a
8.05a
0.970
1.63b
o.ir
0.850
440a
5.06b
0.885
1.92e
11.046
0.810
246a
3.41b
0.967
0.91C
6.32e
0.499
308
5.7
1.84
5.5
79
2.4
0.54
3.9
Elimination Models
Breath
a
a
Blood
a
Max. Breath Cone, ((ig/m3)
;
2
"1 decay
"2decay
Adjusted £2d
;
2
"1 decay
*2decay
Adjusted R2A
260
112a
149a
2.39a
45.7a
0.884
1.23b
(74.6e)
0.791
349
226a
123a
3.91a
70.9a
0.982
1.23a'f
1.27a'f
7.78a'f
114a'f
>0.999
277
154a
123a
3.81a
72.5a
0.947
1.26a'8
1.77a'8
5.50a'8
83. 3a'8
>0.999
150
73.0a
77.0a
7.82a
(161.3C)
0.802
i
i
i
i
i
373
230a
143a
3.41a
64. la
0.965
i
'
i
'
'
431
248a
183a
2.68a
50.8a
0.949
i
i
i
i
i
245
142a
103a
2.73a
63.3a
0.943
0.63C
—
19.1e
—
0.916
298
169
129
3.8
61
1.1
—
10.8
—
94
67
34
1.9
11
0.3
—
7.3
—
^Highly significant (p <0.0005j value.
b Significant (p <0.005j value.
0 Significant (p <0.05j value.
d Adjusted R2 is the adjusted coefficient of determination,
which takes into account the number of independent variables.
e Not a significant (p >0.05j value.
f Based on only three measured values.
8 Based on only four measured values.
h nc = no convergence.
1 Only two measured blood values available.
-------
Table 5-4. Theoretical calculations of DBCM model parameters.
Matrix Parameter
Cmr ((ig/m3)
Exposure Time (min)
Breath
*1 uptake
Adjusted £2d
Max. Breath Cone. (|ig/m3)
Breath
;
2
"1 decay
"2decay
a Adjusted £2d
Max. Breath Cone. (|ig/m3)
Subj.
IF02
728
29.3
92
80
1
0.
173
.Ob
.8a
.55C
086
Subj.
IM03
Subj.
IM04
Subj.
IM05
728 728 728
30.6 30.3 30.6
Uptake Models
127a — 171a
1.36C — 1.59C
0.000 — —
127 — 171
Elimination Models
46.2a
69.4a
3.42b
303b
0.341
116
80.0a
102a
6.54a
833C
0.583
182
43
81
9
0
125
,2b
,7a
,24C
.199
Subj.
IM08
728
30.6
187a
2.27C
187
145a
72.0a
1.86a
333b
0.671
217
Subj.
IF06
728
30.7
222a
2.16b
0.700
222
90
72
3
222
0
163
.6a
.r
.48a
C
.614
Subj.
IM01 Mean Std Dev
728 728
30.5 30.4 0.5
146a
0.84C
146
66
76
0
714
0
143
.6a
.r
.62C
C
.200
a Highly significant (p <0.0005) value.
b Significant (p <0.05) value.
0 Not a significant (p >0.05) value.
d Adjusted R2 is the adjusted coefficient of determination, which takes into account the number of independent variables.
-------
Relationship Between Breath and Blood Concentrations
As indicated earlier, in three cases (for Subjects IM03, IM05, and IM01, Figures 5-16, 5-
18, and 5-21) we found that the blood levels for MTBE-di2 closely track the breath
concentrations, indicating strong correlation between the blood and breath measurements. In
these cases, the correlation coefficient^2 ranged from 0.76 to 0.90. Figure 5-36 presents the plot
of the breath MTBE-di2 versus the blood MTBE-di2 concentrations for Subject EVI03 along with
the linear regression-fitted curve, whose slope provides an estimate of the average venous blood-
to-breath ratio. Two of the remaining four data sets yielded coefficients of 0.56 and 0.57, but for
the last two, the values were only 0.29 and 0.07. Table 5-5 summarizes the correlation
coefficients and blood-to-breath ratios established from the plots.
o
ro
01
o
o
o
(VI
•c"
LJJ
00
00
MTBE-d12:
Subject IM03
100
200
300
400
Breath MTBE-d12 Concentration (\iglm )
Figure 5-36. Measured breath MTBE-di2 concentrations vs.
venous blood MTBE-di2 concentrations for male
Subject IM03.
Table 5-5. Correlation between blood and breath concentrations and average
blood:breath ratio for each participant.
Subject
IF02
IM03
IM04
IM05
IM08
IF06
IM01
Correlation Coefficient R2
0.07
0.90
0.57
0.76
0.56
0.29
0.77
Average Blood:Breath
—
6.6
8.5
11.4
3.8
—
3.0
Ratio
Average: 6. 7 ±3. 4
61
-------
Quality Control Data
Exhaled Breath and Whole Air
The determination of the precision of a continuous real-time system, such as the breath
inlet/glow discharge/ion trap combination, is not well defined but, using a reasonably constant
source such as an environmental chamber, the variation in ion signal with time can be measured.
By averaging the results over a suitable time period, values of the means and standard deviations
for the target compounds can be found, to provide an overall measure of system stability and
reproducibility. Figure 5-37 shows the time course of the average signal for the MS/MS
fragment ion at m/z 55, obtained from a calibration standard of 2-butanone that was prepared in a
186-L glass chamber at a level of 866 |ig/m3 in zero-grade air. The ion current was sampled
every 6 s and, at fixed intervals, the signal was averaged for 5 min. The ion intensity is almost
constant over a 3!/2-h period, with a relative standard deviation of only 2.2%.
Quality control measures implemented in this study also included determining
background levels and limits of detection for the compounds of interest. Background levels were
estimated for the real-time breath measurements by passing humidified ultra-high purity air
through the entire breath analyzer and measuring the signals at the masses used to monitor the
target compounds. For the inhalation exposure study, the mean background levels for MTBE-di2
at m/z 82 and DBCM at m/z 129 were below the limits of detection, which were estimated by
taking three times the standard deviation of the background (blank) mean concentration.51 For
40000
~ 35000
o 30000
25000
20000
50
100
Time (min)
150
200
Figure 5-37. Plot of average ion signal (and standard deviation) at m/z
55 as a function of time, obtained from constant source of
2-butanone in glass chamber at a concentration of 866
|0.g/m3 in zero-grade air.
62
-------
Table 5-6. Limits of detection for MTBE-dn and DBCM in exhaled breath, blood, and urine,
and for TEA in blood and urine.
Breath (jig/m3) Blood (ug/L)
Subject
IF02
IM03
IM04
IM05
IM08
IF06
IM01
Average
SD (%RSD)
MTBE-d12
22.5
14.5
16.9
17.4
23.5
18.0
16.4
18.5
3.3 (18)
DBCM MTBE-d12 DBCM
106.6
44.8
55.4
47.8
44.3
41.3
42.5
46.0a 0.30 0.52
5.1 (ll)a
Urine (ug/L)
TEA MTBE-d12 DBCM TEA
0.25 0.017 0.035 0.032
Excludes value obtained for Subject IF02.
MTBE-di2, the detection limits averaged 18.5 ±3.3 (SD) ng/m ; for DBCM, the average
detection limit was 46.0 ±5.1 |ig/m3. The detection limits for the real-time breath analyzer as
well as for the blood and urine measurements are summarized in Table 5-6.
1200000
1000000
800000
~ 600000
ni
CO
400000
200000
• MTBE (R2=0.998)
• DBCM (R2=0.996)
A TBA (R2=0.992)
10 15
Blood Spike Level (ng)
20
25
Figure 5-38. GC/MS ion signal response as a function of spike level of
target compounds in blood.
63
-------
o
.a
ro
gi
in
400000
300000
200000
100000
• MTBE (R2=0.995)
• DBCM (R2=0.996)
A TBA (R2=0.988)
20 30
Urine Spike Level (ng)
40
50
Figure 5-39. GC/MS ion signal response as a function of spike level of
target compounds in urine.
Blood and Urine
Figures 5-38 and 5-39 show the calibration curves obtained for the target compounds in
blood and urine, respectively. Blank blood samples were spiked at 4 levels, 3, 6, 12, and 24 ng;
urine samples were spiked at five levels, namely, 3, 6, 12, 24, and 48 ng.
64
-------
Chapter 6
Discussion
Breath and Blood Concentration/Time Profiles
For MTBE-di2, the plots in Figures 5-15 to 5-21 show that exposure of the subjects to a
constant level of 2,217 |ig/m3 (542 ppbv) for 30 minutes resulted in a rapid increase in the
measured breath concentration from pre-exposure levels of 10 — 20 |ig/m3 (2 — 5 ppbv) to 200
— 450 |ig/m3 (50 — 110 ppbv). After exposure cessation, excretion resulted in a somewhat
slower decrease in the breath levels, coming close to pre-exposure baseline levels after about 60
minutes. Background levels for MTBE-di2 in the exhaled breath were below the limit of
detection, which was estimated by taking three times the standard deviation of the background
concentration. For MTBE-di2, the detection limits averaged 18.5 ±3.3 (SD) |ig/m3 (range 14.5 -
23.5 |ig/m3).
As explained earlier, uptake concentrations in the breath were determined by interrupting
the exposure for brief periods and measuring the breath levels while the subjects breathed pure
air. To minimize the deleterious effects of the signal noise, the breath data in the elimination
phase were first smoothed using a 5-point (22.6-sec) moving average.
Subjects also were exposed to 728 |ig/m3 (85.6 ppbv) of DBCM for 30 minutes.
Detection limits for DBCM were much higher than for MTBE-di2, averaging 46.0 ±5.1 |ig/m3
(range 41.3 - 55.4 |ig/m3, excluding Subject IF02). By and large, background levels for DBCM
in the exhaled breath were below the limit of detection, and the signal measured for this
compound at m/z 129, the most abundant ion in the glow discharge mass spectrum, was
exceptionally "noisy". The average signals during the uptake phase provided initial (pre-
exposure) breath concentrations that ranged from 70 to 160 |ig/m3 and rose to between 130 and
250 |ig/m3 after 30 minutes. The high initial breath concentrations suggest that the measured
signal at m/z 129 was probably elevated due to an unknown contaminant with fragment ions at
the same mass. As noted earlier, we were unable to measure DBCM in the MS/MS mode
because none of the precursor masses examined (m/z 127, 129, and 131) fragmented by
collision-induced dissociation in the glow discharge/ion trap mass spectrometer.
Generally, the measured MTBE-di2 blood concentrations followed the same behavior as
the measured breath profiles, but in a few cases, the correlation between blood and breath values
was found to be quite poor, probably the result of significant and ongoing problems that were
experienced at EOHSI with the analyses of the blood samples from this study.. As a result, we
cannot place great store by the results obtained for the blood samples. Interestingly, the general
shapes of the uptake portions of the blood and breath concentration/time plots for MTBE-di2 do
65
-------
not suggest a slower response in the blood compared with the breath; however, the decay curves
for the blood appear to return towards the baseline at a slower rate than do the breath curves.
The mean background level for MTBE-di2 in pre-exposure breath was 18.5 ±3.3 (SD)
|ig/m3 (range 14.5 - 23.5 |ig/m3), which was below the limit of detection of the real-time breath
analyzer. This concentration is higher than that obtained in studies that made use of batch
collection and analysis techniques to collect breath samples. In the single breath canister study
conducted by Lindstrom and Pleil,7 the pre-exposure breath levels ranged from 5.6 to 7.8 |ig/m3,
whereas in the study conducted by Buckley et al.,12 the background breath levels for one female
and one male were 3.6 and 12.6 |ig/m3, respectively. In the more recent inhalation study
reported by Lee et al.,15'16 the mean pre-exposure breath level was 2.9 ± 4.3 |ig/m3. The mean
pre-exposure blood concentrations of MTBE-di2 and TEA were 0.30 and 0.25 |ig/L,
respectively. Similar levels were measured by Moolenaar et al.9 and Lee et al.15'16
Breath and Blood Residence Times
The models were fitted to the breath and blood uptake and decay data for MTBE-di2 for
each subject. The results are shown in Figures 5-22 to 5-35, and values obtained for the
calculated model parameters are summarized in Table 5-3.
The breath uptake data were consistent with a one-compartment model, the adjusted
coefficients of determination (Adjusted,/?2) associated with the model fits ranging from 0.85 to
0.97. The mean value for the one-compartment uptake residence times Tiuptake was 5.7 ± 2.4
(SD) min (range 3.3 - 9.8 min). In contrast, the breath decay phase data gave satisfactory two-
compartment fits; in this case, the adjusted R2 values lay between 0.80 and 0.98. The mean
value for the first compartment decay residence times TI decay was 3.8 ± 1.9 (SD) min (range 2.4 -
7.8 min); for the second compartment, the mean decay residence time Qdecay was 61 ± 11 (SD)
min (range 46 - 73 min). Table 6-1 shows that these breath decay values are generally consistent
with values for the decay half-lives reported in previous studies. As noted earlier, it has been
found that the residence times for many VOCs for the first two compartments are roughly
similar, namely, 3 — 11 min for the first compartment, and 24 — 96 min for the second
compartment. Our values fall within these ranges and are also in very good agreement with
values reported in the literature (Table 6-1).
The blood uptake data were also consistent with a one-compartment model and were
convergent in almost all cases. The associated adjusted R2 ranged from 0.50 to 0.96 for the
blood data, and the average blood residence time was essentially the same as that for the breath.
The quality of the blood decay data were such that we were only able to extract
meaningful information from 2 or 3 data sets. Consequently, the results presented in Tables 5-3
and 6-1 must be treated with caution. Our values listed for the first and second blood residence
times are similar to the values reported by Buckley et al.12 The values reported by Lee et al.15'16
for the first blood compartment and the second breath compartment prompted them to speculate
that the second breath compartment rather than the first breath compartment is associated with a
66
-------
Table 6-1. Summary of results obtained in current and previous MTBE exposure studies.
Tvrui ' A i 13,14 ,-, . , , 52 Lindstrom and „ , , , , 12 T , , is,i6
Nihlen et al. Cam et al. p, .,? Buckley et al. Lee et al.
Scenario Chamber Chamber Gas station
Chamber Chamber
Exposure 5-50 ppm, 2 h 1.7 ppm, 1 h 0.1 14 ppm, 2 min 1.39 ppm, 1 h 1.7 ppm, 15 min
No. of Subjects & Gender 10 males 4 2
Total Absorbed Dose (|ig)
Fraction/Eliminated Unchanged -0.7
Fraction Absorbed 0.42 - 0.49
Fraction Exhaled Post-Exposure 0.32 - 0.47
Tiuptake (breath) (min)
T^^ (breath) (min) 4.2
^decaj (breath) (min) 49
T^coy (breath) (min)
Tiuptake (blood) (min)
?weca>, (blood) (min) 1.2-1.6 58
t2decay (blood) (min) 12-17
^decay (blood) (min) 121-139
feay (blood) (min) 1,472-1,818
Blood/Breath Ratio 17.7
1 male, 1 female 3 males, 3 females
160 ±50
0.60; 0.46 0.33 ± 0.06
0.66 ±0.06
0.40a
3.3; 1.7 3.0; 3.0
53; 14 40; 35
815; 190 421; 444
5.2; 16 25; 54
61; — 82; 107
1,904; 190 2,871; 1,284
18; 18 23.4; 23.6
This Study
Gas cylinder & face
mask
0.542 ppm, 30 min
5 males, 2 females
148 ±34
0.29 ±0.04
0.73 ± 0.04
0.37±0.06b
5.7 ±2.4
3.8 ± 1.9
61± 11
5.5 ±3.9
5.5- 19
83; 114
6.7 ±3.4
a Exhaled in 60 min after exposure.
b Exhaled in 90 min after exposure.
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1 9
blood compartment. Neither our data nor that of Buckley et al. provide support for this
suggestion.
As noted earlier, the overall quality of the breath and blood uptake and decay data for
DBCM adversely affected the results obtained for the residence times by applying the linear
compartment model (cf Table 5-4). In the case of the uptake residence time, Tuptake, only one
sample set (for Subject IF06) yielded a meaningful result, viz., Tuptake = 2.2 min. For the decay
phase, meaningful results were obtained from three sample sets (for Subjects EVI04, EVI08, and
IF06); the mean first-compartment residence time, Tidecay, was 4.0 ± 2.4 min (all values highly
significant). However, only one of the values obtained for the second compartment, Qdecay, was
significant, viz., 333 min (with/? < 0.05 for Subject EVI08).
Total Absorbed Dose and Fractional Uptake of MTBE
The total absorbed (internal) dose to a subject, defined as the amount of the chemical that
passes through an absorption barrier or exchange boundary, is obtained from the difference
between the total ("applied") dose and the "unmetabolized mass" (see Equation (4-10)). The
mean MTBE-di2 total absorbed ("internal") dose was 149 ± 34 jig for the average 30-min
exposure and a mean total ("applied") dose of 209 jig. The mean fraction of MTBE-di2
absorbed, or relative uptake, was 0.73 ± 0.04. For comparison, the 15-min exposure conducted
by Lee et al.15'16 resulted in a similar relative uptake of 0.66 ± 0.06.
Fraction /"Exhaled at Equilibrium and Respiratory Fraction Eliminated Post-Exposure
The mean value for/ the fraction of the MTBE-di2 exposure concentration exhaled
unchanged was 0.29 ± 0.04. This value is in good agreement with the value reported by Lee et
al.,15'16 and both are significantly lower than the values reported by Lindstrom and Pleil7 and
Buckley etal.12
The fraction of MTBE-di2 eliminated through expiration post-exposure was calculated
from the ratio of the amount exhaled post-exposure (i.e., product of decay curve and alveolar
ventilation rate) to the total absorbed dose. The mean fractional amount expired 90 minutes after
exposure for all seven subjects was 0.37 ± 0.06. For comparison, Lee et al. 5'16 reported a mean
value of 0.40 for 60 minutes after exposure.
Linear Compartment Coefficients
The coefficients of the exponential terms in Equation (4-15) determined from the MTBE-
di2 breath decay data for the subjects are summarized in Table 5-3. For a constant exposure
concentration, they provide a measure of the fraction of body burden in each compartment at
equilibrium. This fractional contribution from each compartment depends upon the exposure
period.29'50 Thus, a relatively short exposure (e.g., 15 — 30 minutes) would not be expected to
68
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result in significant transfer to the slower compartments, and most of the contribution would be
from the first and, to a lesser extent, the second compartment. In this study, the exposure
duration was 30 min, and post-exposure monitoring was limited to 60 — 90 min. Consequently,
we assume that compartments 1 and 2 were fully equilibrated.
•th
For the post-exposure period, the contribution of the im compartment is given by a;/£a;.
The mean value for a/ across the seven subjects was 0.57, and it was 0.43 for ct2, i.e., about 57%
of the exhaled MTBE-di2 was associated with the blood compartment.
Blood/Breath Ratios
By and large, the measured blood MTBE-di2 concentrations correlated reasonably well
with the breath concentrations, and the overall trends observed were generally consistent with
previous studies.12'15'16 However, peak levels, which ranged from about 0.9 — 2.5 |ig/L, were
significantly lower than those reported in other studies. Lee et al.15'16 exposed 6 subjects to 1.7
ppm MTBE for 15 minutes and observed peak levels at the end of exposure which ranged from 4
to 10 ng/L. For two subjects exposed to 1.39 ppm for 1 h, Buckley et al.12 observed peak blood
levels of 8.7 and 15 |ig/L. Much higher peak MTBE levels were reported by Nihlen et al.,1
who exposed 10 subjects to 5 — 50 ppm for 2 h and obtained levels between 123 and 1,144
|ig/L. Despite the low applied dose used in this study, the plot in Figure 6-1 shows a strong
13,14
10000
o
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linear relationship (R2 = 0.987) between mean peak blood concentration and total ("applied")
dose (exposure) from the different studies, including this one, over almost three orders of
magnitude.
An example of the relation of blood to exhaled breath measurements of MTBE-di2 is
shown in Figure 6-1 for Subject IM03, and summary statistics for all seven subjects are
presented in Table 5-5. Using linear regression analysis, the mean blood/breath ratio was found
to be 6.7 ± 3.4. Nihlen et al.1 '14 obtained a blood/breath partition coefficient of 17.7, Buckley et
al.12 reported a ratio of 18, and Lee et al.15'16 found a ratio of 23.5. The reason for the
significantly lower value calculated in the present study is not clear. We speculate that it may
have been due to a number of problems that were experienced in the course of the analysis of the
blood samples in the laboratory. Because of these problems, the analyses took more than 6
months to complete, a period that was far in excess of the normally accepted storage period for a
VOC such as MTBE in blood samples. The low measured blood concentrations may well have
been due to losses of MTBE that occurred during this period.
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