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Clinical Chemistry 43:5 723–730 (1997)

Drug Monitoring and Toxicology

Exhaled human breath measurement method for assessing exposure to halogenated volatile organic compounds Joachim D. Pleil* and Andrew B. Lindstrom The organic constituents of exhaled human breath are representative of blood-borne concentrations through gas exchange in the blood/breath interface in the lungs. The presence of specific compounds can be an indicator of recent exposure or represent a biological response of the subject. For volatile organic compounds (VOCs), sampling and analysis of breath is preferred to direct measurement from blood samples because breath collection is noninvasive, potentially infectious waste is avoided, and the measurement of gas-phase analytes is much simpler in a gas matrix rather than in a complex biological tissue such as blood. To exploit these advantages, we have developed the “single breath canister” (SBC) technique, a simple direct collection method for individual alveolar breath samples, and adapted conventional gas chromatography–mass spectrometry analytical methods for trace-concentration VOC analysis. The focus of this paper is to describe briefly the techniques for making VOC measurements in breath, to present some specific applications for which these methods are relevant, and to demonstrate how to estimate exposure to example VOCs on the basis of breath elimination. We present data from three different exposure scenarios: (a) vinyl chloride and cis-1,2-dichloroethene from showering with contaminated water from a private well, (b) chloroform and bromodichloromethane from high-intensity swimming in chlorinated pool water, and (c) trichloroethene from a controlled exposure chamber experiment. In all cases, for all subjects, the experiment is the same: preexposure breath mea-

surement, exposure to halogenated VOC, and a postexposure time-dependent series of breath measurements. Data are presented only to demonstrate the use of the method and how to interpret the analytical results. INDEXING TERMS:

exhaled breath sampling

•

exposure

assessment The presence of specific compounds in human blood can indicate a recent exposure (or biological response) to a drug or an environmental pollutant, or indicate a disease state of the individual. The direct measurement of blood for various substances and biomarkers is one of the primary medical diagnostic tools in current use. Because the organic constituents of exhaled human breath are representative of their blood-borne concentrations through gas exchange in the blood/breath interface in the lungs, a breath measurement could conceivably replace a direct blood measurement. A classic example of this is the “breathalyzer” test for inebriation from ethanol [1]. A more recent example is an automated clinical instrument developed for assaying carboxyhemoglobin in blood through measurement of carbon monoxide in end-tidal breath [2]. For volatile organic compounds (VOCs), sampling and analysis of breath is preferred to direct measurement from blood samples because breath collection is noninvasive, potentially infectious waste is avoided, and the measurement of gas-phase analytes is much simpler in a gas matrix rather than a complex biological tissue such as blood.1 To exploit these advantages for the assessment of exposure to environmental pollutants, the US Environmental Protection Agency (EPA), academic research institutions, and the medical community have been studying

National Exposure Research Laboratory (MD-44), US Environmental Protection Agency, Research Triangle Park, NC 27711. *Author for correspondence. Fax 919-541-3527; e-mail PLEIL.JOACHIM@ EPAMAIL.EPA.GOV. The information in this document, funded by the EPA, has been subjected to Agency review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. Received September 25, 1996; revised December 20, 1996; accepted December 24, 1996.

1 Nonstandard abbreviations: VOCs, volatile organic compounds; EPA, Environmental Protection Agency; GC-MS, gas chromatography–mass spectrometry; SBC, single breath canister; QA, quality assurance; and QC, quality control.

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exhaled breath with a variety of sampling and analytical methods. An overview of such work is available in recent review articles by Wallace et al. [3, 4]; a more general history of the use of breath measurement in medicine has been written by Phillips [5]. For a given scenario or human activity, a pre- and postset of breath samples is sufficient to confirm the occurrence of an exposure to specific VOCs. To quantify the exposure and to glean additional information regarding residence time in the body, a series of postexposure breath samples can describe the time-dependent elimination of the VOC from the subject and thus be used to infer total body burden and the distribution of target chemicals in the blood and other body tissues. Some examples of this approach and the attendant theory can be found in the literature [6 –9]. Clearly one of the critical issues in the use of elimination kinetics is the collection of samples in an appropriate time frame. For example, the residence times of VOCs in blood are on the scale of a few minutes, so to properly model this behavior requires a series of samples collected rapidly after an exposure. Second, the sample should preferably consist of alveolar air, i.e., expired breath involved in the blood gas interface deep in the alveoli with minimal contribution from the tracheal dead volume. To address these concerns, we have developed a simple, direct collection method for individual alveolar breath samples and adapted conventional gas chromatography–mass spectrometry (GC-MS) analytical methods for trace-concentration VOC analysis. The “single breath canister” (SBC) sampling method is based on direct exhalation of alveolar air into a 1-L volume stainless steel canister with an internally passivated surface. The SBC technique requires minimal instruction for an untrained subject, is self-administered, and can (in theory) be used to collect individual samples of adjacent breaths; a 30-s sample-to-sample time frame was found to be the practical limit. Subsequent analysis is performed in the laboratory with GC-MS methods especially modified to accommodate the 1-L samples and the high concentrations of water and carbon dioxide in breath. Refs. 10 and 11 present the detailed sampling and analytical procedures (which are beyond the scope of this paper) as well as brief discussions and listings of other relevant studies concerning exhaled breath measurement. Here we briefly describe the sampling method and present some examples of exhaled breath measurement as a diagnostic tool for determining exposure to microenvironmental pollutants. Specifically, we use the same experimental procedures to explore three different scenarios. The SBC method is used to objectively demonstrate the occurrence and relative magnitude of a recent exposure and to show how the resulting breath concentration vs elimination time data can be interpreted to estimate the magnitude and duration of the resulting blood-borne dose. Individual demonstrations of different scenarios were performed on a few subjects in the realm of methods

development for sampling and analysis. As such, no generic interpretation of typical exposures can (or should) be made, nor can we interpret biological responses in context of body type, sex, or age. The intent is to demonstrate the SBC breath measurement method as a tool for exposure assessment, and, by inference, to future clinical applications.

Materials and Methods human subjects In each scenario, the breath component was a part of a larger study and affected a subset of all human subjects. Subjects were volunteers who gave informed consent and were recruited and selected under institutional procedures by the respective lead organizations: 1) Rockford scenario (exposure to vinyl chloride and cis-1,2-dichloroethene from contaminated well water): Illinois Department of Public Health, Springfield, IL; contact: Ken McCann 2) Montana scenario (exposure to chloroform and bromodichloromethane from high-intensity swimming in chlorinated pool water): University of Montana, Missoula, MT; contact: Brent Ruby 3) Chamber scenario (exposure to trichloroethene from a controlled exposure chamber experiment): US Air Force, Wright Patterson AFB, OH; contact: Jeff Fisher; Research Triangle Institute, Research Triangle Park, NC; contact: Paul Kizakevich In total, we collected a variety of breath samples from 17 healthy adult subjects who were exposed in the various scenarios (9 men, 8 women, ages 22 to 42). Detailed elimination studies were performed on a subset of 10 subjects for demonstration of the SBC techniques.

sampling equipment and procedures The sampling apparatus consists of an evacuated 1-L canister fitted with a small Teflon tube used as a mouthpiece as shown in Fig. 1. The subject closes her lips on the tube, and as she exhales, she opens the canister valve and the breath is collected, filling the evacuated volume. The subject is instructed and trained to begin sample collection at the “bottom” (or end) of a normal resting tidal breath to achieve an alveolar sample. The tracheal dead volume is expelled before the canister sample valve is opened. We note that the typical “at rest” tidal volume is ;500 mL and the typical dead volume is ;150 mL; as such, the expiratory reserve volume that is collected is as close as possible to purely alveolar. An investigation of the alveolar nature of an SBC sample in contrast to other techniques is available in ref. 10. Fig. 2 depicts a subject self-administering a sample collection. The SBC method can be used to collect a timed series of samples easily with 30-s sample-to-sample resolution as described in detail in ref. 10. The canisters used were from two commercial manufacturers, Scientific Instrumentation Specialists, Moscow, ID, and Biospherics, Hillsboro, OR. They are constructed of 306 stainless steel with internal surfaces

Clinical Chemistry 43, No. 5, 1997

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Fig. 1. Diagram of an evacuated 1-L alveolar breath sampling canister equipped with a disposable Teflon tube mouthpiece.

passivated with an electropolishing technique generally referred to as the “SUMMAy” process. Although the breath samples were all collected in 1-L volume canisters, microenvironmental samples (where volume is noncritical) were collected in a variety of canister types including 1.8-, 2.8-, 3-, and 6-L volumes, subject to availability. Both “integrated” whole-air samples (averages over a specific time period) and “grab” whole-air samples were used to assess the inspired air during and after the exposures.

Fig. 2. Diagram of a subject self-administering a breath collection. Note that the hand of the arm supporting the canister is pinching off the flow through the nose while the other hand is operating the canister valve.

analytical equipment and procedures Although subsequent laboratory analysis can be performed with any of a variety of GC-MS methods for air, for our purposes here, the standard EPA Method TO-14 [12] and the concentrator equipment were somewhat modified to accommodate some of the more reactive species found in exhaled breath; this is described in detail in ref. 11. For some quality-assurance (QA) analyses, where the compound(s) of interest allowed, the standard TO-14 method and commercially available instrumentation were also used. Briefly, each breath sample is transported to the laboratory, pressurized with a neutral gas, and a dilution factor is calculated on the basis of pre- and postpressurization absolute pressure. The analytical instrumentation is fully automated to extract an aliquot from the canister, cryogenically concentrate, thermally desorb/inject onto a capillary column, and then analyze with a mass spectrometer. Samples of microenvironmental air from the exposure area and control samples of inspired air after the exposure were also collected and analyzed with the same equipment. Carbon dioxide as-

says of breath samples were performed also by GC-MS; however the injection technique was adjusted to use only a tiny (typically 50-mL) aliquot via injection loop, or with a short cycle of the “valveless concentrator” as described in ref. 11. For the Rockford scenario, microenvironmental samples were analyzed with TO-14 methodology with a Nutech 320 – 01 cryoconcentrator (Graseby-Nutech, Smyrna, GA) and a Hewlett-Packard GC-MS system GC5880 and MS5970 (Hewlett-Packard, Avondale, PA and Palo Alto, CA, respectively). The GC column was an SPB-1 60 m 3 0.32 mm (i.d.) 3 1.0 mm film thickness (Supelco, Bellefonte, PA). Exhaled breath samples were analyzed with a prototype “valveless concentrator” (patent #5447556) developed under a cooperative research and development agreement (CRADA #0026 –92) between Graseby-Nutech and the EPA that was interfaced to an ITS40 (Magnum) GC-MS ion trap instrument (Finnigan MAT, San Jose, CA). The analytical column was an XTI-5

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30 m 3 0.25 mm (i.d.) with 1.0 mm stationary phase (Restek Corp., Bellefonte, PA). Preliminary microenvironmental and exhaled breath samples for the Montana study were analyzed with the valveless concentrator interfaced to a Saturn II GC-MS ion trap instrument (Varian, Walnut Creek, CA) by using an RTX-5 30 m 3 0.25 mm (i.d.) with 1.0 mm stationary phase (Restek). For the main body of the Montana samples and all of the Chamber samples, analyses were performed with a Graseby-Nutech 3550A cryoconcentrator with a 16-canister autosampler. This was interfaced to the Finnigan ITS40 instrument detailed above. Quantification was achieved with external calibrators prepared for each sample set for all analytes. System linearity was always confirmed over the sample range with five-point calibration. Daily response factors and system integrity were determined via single-point calibration and canister blanks. A minimum of 25% replicate analyses (of real samples) was performed to continually assess system precision. Calibrators were independently prepared and assessed by our on-site contractor, ManTech Environmental Technology, by using certified calibrators from Alphagaz, Morrisville, PA, and Scott Specialty Gases, Plumsteadville, PA.

data postprocessing and interpretation Raw GC-MS extracted ion peak area data for analytes of interest were corrected to reflect current calibration response factors. Measurements of carbon dioxide concentrations were then used to assess a subject’s data set and used to normalize to a nominal 5% for alveolar breath to assure internal consistency for that subject. For the healthy adult subjects studied in this work, 5% was a reasonable normalizing factor for the “true” alveolar concentration, although this technique may require revision in the case of ill or impaired subjects with pulmonary disorders. Because each subject was seated, calm, and at rest during the sample collection, there was no variability due to exercise or hyperventilation; we used the carbon dioxide correction only as a method to account for slight variations from the sample pressurization step in the laboratory and from the subject’s technique in filling the canister. We found through many trials that even the most experienced subject can occasionally entrain some ambient air into the sample, or prematurely close the valve, both of which would result in a dilution of alveolar air in the finally processed sample. In either case, the assay of carbon dioxide provides an accurate correction factor for the overall “alveolar” nature of an individual sample and thus is used to scale the concentration of the analyte to correctly reflect the breath concentration. Issues concerning the assay of carbon dioxide in breath, exercise- and breathing technique-related perturbations, and the consistency of data sets from one individual are discussed in refs. 10 and 11. Time after exposure vs analyte concentration data were modeled to generate a mathematical approximation of the

breath elimination of VOCs. We chose a multiterm exponential decay model by Wallace et al. [7] and applied it to the data with GraphPad Prism (GraphPad Software, San Diego, CA), a nonlinear modeling program optimized for a least-squares fit (no weighting). Specifically, the model takes the form: Calveolar(t) 5 A1e 2 k1t 1 A2e 2 k2t 1 . . . 1 Ane 2 knt 1 iCair

(1)

where Calveolar(t) is the alveolar breath concentration (mg/ m3)at any time t (min) during the elimination (t 5 0 denotes the end of the exposure); the coefficients Ai (mg/m3) indicate capacities or contributions from bodily compartments that have elimination time coefficients of kn (1/min); and iCair (mg/m3) is the contribution of the inspired air during elimination (in our experiments, iCair 5 0). The resulting equation is integrated from time 5 0 to infinity, then multiplied by the alveolar breathing rate R (m3/min) to establish the mass of contaminant Mcont (mg) eliminated via exhalation. The resulting quantity takes the form: Mcont 5 R*Calveolar(t)dt 5 RSAi/ki

(2)

which is considered a lower-bound estimate of the total absorbed dose. Note that there may be other mechanisms of elimination such as metabolism, urinary excretion, and dermal losses that are not represented by Mcont. Additionally, if Eq. 1 is evaluated at time t 5 0, and we have access to the blood/breath partition coefficient P (m3/1000 L), we can generate an estimate of the lower bound of the highest blood concentrations caused by the exposure as follows: Cblood(max) 5 P 3 Calveolar(0) 5 PSAi

(3)

This assumes that the exposure is nondecreasing. Finally, the estimated parameters ki from Eq. 1 are used to estimate the half-life t ⁄ i (min) of the contaminant in the “ith” modeled bodily compartment by: 12

t ⁄ i 5 (ln2)/ki 12

(4)

Although detailed pharmacokinetics would be required to legitimately assign the “ith” term of Eq. 1 to a specific biological system or compartment, we generally consider the 1st term to represent the blood, the 2nd “highly perfused tissues” (liver, other organs, some muscle), the 3rd “moderately perfused tissues” (muscle, organs, liquid reservoirs), and the 4th “poorly perfused tissues” (adipose and connective tissue). Some well-known examples of pharmacokinetic modeling of VOCs and interpretations of bodily compartments are listed in the references [8, 9, 13–15].

Results and Discussion In all cases the instrumentation performed better than 6% replicate precision (CV) on synthetic breath calibrators and working calibrators across a dynamic range that included the real data. For the Rockford and Montana

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Table 1. Exposure parameters. Exposure Experiment scenario

Trial no.

Compound

Avg. air, mg/m3

Time (min)

Avg. water, mg/L

Rockford

1 Vinyl chloride 10 25.3 2 Vinyl chloride 10 15.8 1 cis-1,2-Dichloroethene 10 125 2 cis-1,2-Dichloroethene 10 83.9 Montana 1,2 Bromodichloromethane 120 2.7 1,2 Chloroform 120 147 Chamber 1–7 Trichloroethene 480 550 000 Conversion factors: 1 mmol/L 5 x mg/L 5 1000 x mg/m3; vinyl chloride 62.5; cis-1,2-dichloroethene 96.9; bromodichloromethane chloroform 119.4; trichloroethene 131.4; ND, not detected; NA, not applicable.

4.03 3.82 28.4 20.4 ND 70.5 NA 163.8;

mmol/L and mg/L for the compounds of interest for reference. Table 2 presents the numeric values for the parameters that result in the best nonlinear least-squares fit for each data set for the exponential elimination function as described in Eq. 1. Each data set is identified by the experiment name, subject/experiment identification code, and compound measured; the number of measurements and elimination times are given to assist interpretation of the model parameters. The number of compartments (or exponential terms) most appropriate to the data set was empirically determined with a “residuals runs” analysis to set the lower limit, and occurrence of redundant terms to set the upper limit. For these data, a time frame .2 h is necessary to be able to mathematically discern the elimination from the 3rd compartment. In all cases the model fit to the concentration data was excellent, with most R2 test limits .0.99. Graphs of representative data of VOC elimination from each experiment are presented in Fig. 3. Fig. 3A–C shows data and model for R1ABL1 (vinyl chloride) and R1ABL2

sample sets, carbon dioxide assays resulted in a typical replicate precision of 2–3%. Because of unavoidable instrument changes, controlled QA/quality-control (QC) tests resulted in a CV of 4 –5% for carbon dioxide measurements for the Chamber experiment. Analyses of ambient (inspired) air during the elimination portion of each experiment confirmed concentrations of halogenated VOC analytes below the concentration of quantification for each experiment. For the Rockford and Montana scenarios, the subjects were physically removed from the exposure area; for the “Chamber” work, hospital-grade air and individual free-flowing masks were used for inspired air until the chamber had been cleared. Exposure parameters for the three experiments are given in Table 1. These include the compound name, the duration of the exposure, the measured average values for the air concentration, and the water concentration. Note that a variety of sequences are represented: short-term, low-concentration; moderate-term, low- and moderateconcentration; and long-term, high-concentration. Also, we have included conversion equivalency between

Table 2. Data model parameters for breath elimination. Experiment

Subject

Compound

Rockforda R1ABL1 Vinyl chloride R2ABL1 Vinyl chloride R1ABL2 cis-1,2-Dichloroethene R2ABL2 cis-1,2-Dichloroethene Montanaa M1MLS1 Bromodichloromethane M1FMS1 Bromodichloromethane M1MLS2 Chloroform M1FMS2 Chloroform Chamberb C1F108 Trichloroethene C1M208M Trichloroethene C2F109 Trichloroethene C2M209 Trichloroethene C3F110 Trichloroethene C3M210 Trichloroethene C3MCON Trichloroethene a b

Concentration units in mg/m3. Concentrations units in mg/m3.

No. data pts.

Time range, min

Nonlinear least-squares fit parameters (see Eq. 1 in text) A1

7 8 7 8 15 16 15 16 9 8 10 10 16 15 14

(1.1–30) (1.3–30) (1.1–30) (1.3–30) (1–150) (1–180) (1–150) (1–180) (1–599) (1–600) (1–724) (1–719) (1–956) (1–842) (0.55–45)

6.5415 44.6472 12.9447 11.7014 1.3152 4.9795 111.4434 152.5953 58.7921 104.7996 155.7683 114.0761 146.1714 156.7775 36.2579

k1

A2

k2

A3

k3

0.3791 5.1367 0.0463 1.9188 4.8805 0.0464 0.8495 12.0130 0.0774 0.2925 6.9615 0.0236 1.0928 1.4975 0.0743 1.4384 0.0079 1.5290 1.9511 0.0673 1.0964 0.0060 0.5094 107.3954 0.0273 46.8321 0.0035 0.7274 105.0416 0.0411 47.0217 0.0051 1.3763 26.6843 0.0468 11.1236 0.0037 0.7155 21.2056 0.0231 4.3226 0.0017 0.9040 53.6358 0.0258 6.2721 0.0014 0.2586 36.9623 0.0324 10.1509 0.0026 0.1696 8.6465 0.0111 7.4664 0.0021 0.6743 31.4732 0.0172 6.4739 0.0006 0.1996 53.6502 0.0168

Model fit parameter R2

0.995 0.995 0.998 0.997 0.979 0.958 0.993 0.987 0.999 0.999 0.999 0.999 0.949 0.997 0.943

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Fig. 3. (A) Short-term, low-concentration exposure; (B) moderate-term, low- and moderate-concentration exposure; and (C) long-term, highconcentration exposure. Example breath elimination data and models from (A) Rockford experiment for 10-min-long shower exposure to cis-1,2-dichloroethene and vinyl chloride; (B) Montana experiment for 2-h-long swimming pool exposure to bromodichloromethane and chloroform; and (C) Chamber experiment for 4-h-long “occupational” exposure to trichloroethene.

(cis-1,2-dichloroethene) as an example of a short-term, low-concentration exposure; M1FMS1 (bromodichlo-

romethane) and M1FMS2 (chloroform) as an example of moderate-term, low- and moderate-concentration exposure; and C3F110 and C3M210 (trichloroethene) as examples of long-term, high-concentration exposure, respectively. Table 3 documents the calculated biological parameters as described in Materials and Methods. For the lowerbound estimate of the total dose, Mcont, as described in Eq. 2, we used a conservative breathing rate estimate of 0.007 m3/min (7 L/min). For the estimates of the highest blood concentration generated by the exposure (see Eq. 3), we used blood/breath partition coefficients published by Gargas et al. [16]: 1.16 for vinyl chloride, 9.85 for cis-1,2dichloroethene, 6.85 for chloroform, and 8.11 for trichloroethene. Though unavailable in the literature, we estimated the partition coefficient for bromodichloromethane at 29.9 through interpolation of coefficient vs boiling point for trihalomethanes. Note that even for a brief 10-min shower exposure of 25 mg/m3 (inhalation) and 4 mg/L (dermal contact in water), we calculate 0.9 mg absorbed dose of vinyl chloride and a blood concentration of 0.01 mg/L. The 2-h swimming pool exposure (for trained athletes) resulted in an estimated dose of 100 mg and a blood concentration of ;2 mg/L. The 4-h exposure to 100 ppmv (550 000 mg/m3) of trichloroethene,which (for comparison) represents half of the integrated Occupational Safety and Health Administration permissible exposure limit of 100 ppm for occupational exposure for an 8-h workshift [17], resulted in estimated absorbed doses from 23 to 90 mg with peak blood concentrations averaging ;1200 mg/L. Calculated half-lives (as defined in Eq. 4) in the 1st compartment (blood) were calculated from 0.5 to 4 min, the 2nd compartment (highly perfused tissues) from 8 to 62 min, and the 3rd compartment (moderately perfused tissues) from 1.5 to 19 h across all subjects and all types of exposures to halogenated VOCs. Overall, these experiments gave reasonable estimates of absorbed dose and blood concentrations in line with the cited literature. Critical examination of the timedependence of the elimination curves as graphed in Fig. 3 and the model results in Tables 2 and 3 show that the first few minutes after the exposure are critical in estimating the dose and peak blood concentration because the breath concentration is decreasing by half in the first 1–2 min. Gathering representative data during this time is complicated by several factors. First, it is experimentally difficult to assign a precise time (t 5 0) for when the elimination begins because some time does elapse during the transition of the subject from exposure to “clean” air. Second, the physical movement of the subject and the increased activity associated with sample collection tend to affect the ventilation rate during this time and may perturb the “alveolar” nature of the sample. Finally, the logistics of collecting a quick series of samples in a few minutes require some coordination of effort in sample container handling and records keeping. The behavior of the “slow-

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Table 3. Breath elimination results. Half-life, min Experiment scenario

Rockford

Montana

Chamber

Compound

Mcont, mg

Blood (max), mg/L

Blood (1st comp)

Highly perfused (2nd comp)

Vinyl chloride Vinyl chloride cis-1,2-Dichloroethene cis-1,2-Dichloroethene Bromodichloromethane Bromodichloromethane Chloroform Chloroform Trichloroethene Trichloroethene Trichloroethene Trichloroethene Trichloroethene Trichloroethene Trichloroethene

0.90 0.90 1.19 2.34 1.42 1.50 121.54 83.86 25128.99 24747.18 46699.03 37938.55 36551.94 89341.96 23568.47

0.01 0.06 0.25 0.18 0.13 0.24 1.82 2.09 783.43 1056.96 1749.13 1307.25 1316.13 1579.22 729.15

1.83 0.36 0.82 2.37 0.63 0.45 1.36 0.95 0.50 0.97 0.77 2.68 4.09 1.03 3.47

14.98 14.94 8.96 29.33 9.33 10.30 25.39 16.87 14.80 29.99 26.83 21.42 62.44 40.30 41.15

Subject

R1ABL1 R2ABL1 R1ABL2 R2ABL2 M1MLS1 M1FMS1 M1MLS2 M1FMS2 C1F108 C1M208 C2F109 C2M209 C3F110 C3M210 C3MCON

Moderately perfused (3rd comp)

87.20 115.18 195.53 135.83 185.53 396.31 488.82 261.96 332.44 1145.70

For conversion factors, see Table 1.

er” tissues (2nd and 3rd compartments) is more easily deduced because accurate sample timing is not as critical. On the basis of the results from these experiments, we are investigating modifications to our techniques to get a more accurate representation of the 1st-compartment elimination. We will experiment with the use of a portable clean-air supply and “on-demand” breathing regulators (modified scuba diving gear) to precisely decouple the exposure period from the elimination period. Second, we will attempt to extend the model into a hypothetical “zeroth” compartment that could be considered a very fast, low-capacity compartment comprising the mucous membranes of the mouth and tracheal airway by collecting adjacent breaths during the first 30 s of the elimination time. The analysis of exhaled breath is an excellent exposure assessment tool for halogenated VOCs that can unambiguously demonstrate that an exposure has occurred, and with a time series of samples after the exposure, gives the possibility of modeling the washout of the contaminant from the body. The appropriate multiterm exponential decay model has been used to establish approximate residence times for pollutants in the body, and also to estimate minimum blood concentrations and integrated dose, all without an invasive medical procedure. The techniques presented here could be extended to the broader clinical setting where the analyte could be a volatile bioresponse marker for a disease state, for an administered drug or anesthetic, or for changes subsequent to a medical procedure. Future work should focus on individual differences among a statistically significant number of subjects sorted by body type, sex, and age to further develop the method for eventual mainstream clinical use.

Portions of this work were performed under a Cooperative Research and Development Agreement, CRADA #0026 –92, between the US EPA and Graseby-Andersen (Nutech) Corp., and CRADA #0114 –94 with Restek Corp. Samples and analytical confirmation for QA/QC standards were provided by ManTech Environmental Technology under contract 68-D0 – 0107. We acknowledge the expert advice throughout these experiments of Sydney Gordon of Battelle Memorial Institute, Lance Wallace and Timothy Buckley of the US EPA, David Shelow of Restek Corp., and Sharon Reiss of Graseby-Andersen Corp. We thank the anonymous subject volunteers for their generous participation in the exposure scenarios. We thank the following participants in the fieldwork from the various collaborative organizations for providing subjects and arranging/controlling the exposures: Ken McCann and Mike Moomey of the Illinois Department of Public Health, Brent Ruby and David Berkoff of the University of Montana, Jim Bowyer of ManTech Environmental Technology, Paul Kizakevich and Linda Voorhees of Research Triangle Institute, Jeff Fisher of US Air Force, and Kenneth Hudnell of US EPA. Special thanks go to the QA/QC and researchers from ManTech Environmental, Karen Oliver, Jeff Adams, Ron Bousquet, Hunter Daughtrey, Keith Kronmiller, and Chris Fortune, for their ongoing expert support.

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