[Citation in PubMed] [Related Articles]

Breath Measurements as Volatile Organic Compound Biomarkers

¹Atmospheric Research and Exposure Assessment Laboratory, U.S. Environmental Protection Agency, Reston, Virginia
²Research Triangle Institute, Research Triangle Park, North Carolina
³Battelle Memorial Institute, Columbus, Ohio

• Introduction
• Basic Concepts
• Methods
• EPA Field Studies
• U.S. EPA Chamber Studies
• Results
• Discussion
• Future Directions

Key words: breath measurements, volatile organic compounds, benzene, aromatics, aliphatics, terpenes, halocarbons, chlorinated chemicals, TEAM Study

This paper was presented at the Conference on Air Toxics: Biomarkers in Environmental Applications held 27-28 April 1995 in Houston, Texas. Manuscript received 24 May 1996; manuscript accepted 5 June 1996.

Address correspondence to Dr. L. Wallace, Atmospheric Research and Exposure Assessment Laboratory, U.S. EPA, 11568 Woodhollow Court, Reston, VA 22091. Telephone: (540) 341-7509. Fax: (703) 860-0678. E-mail: wallace.lance@epamail.epa.gov

Abbreviations used: API, atmospheric pressure ionization; GC-MS, gas chromatography-mass spectroscopy; MS-MS, tandem mass spectroscopy; MTBE, methyl-tert-butyl ether; PBPKs, physiologically based pharmacokinetics; TEAM, total exposure assessment methodology; TLV, threshold limit value; U.S. EPA, U.S. Environmental Protection Agency; VOCs, volatile organic compounds.

Introduction

The use of breath analysis in environmental applications is recent and is not yet widespread. Nonetheless, in the short time of its use, a number of discoveries of importance have been made, and the future appears bright for this branch of analysis. In this paper, the basic concepts and methodology of breath analysis are briefy presented. The history of breath analysis as employed in the U.S. Environmental Protection Agency (U.S. EPA) studies (and a few studies sponsored by other organizations) is also summarized. New methods and future directions of research are described.

Basic Concepts

Having a reasonable estimate of the partition coeffcient allows us to estimate the arterial blood concentration from the breath measurement. Provided we have some model of the distribution of the chemical in the body, knowing the blood concentration then allows estimation of concentrations in other body tissues.

Pharmacokinetic models are all based ultimately on mass-balance considerations. Differential equations for different compartments (liver, other organs, muscle, fat, etc.) are developed and solved, usually numerically. Historically, a number of simplifying assumptions were made that allowed analytic solution of the equations for certain simple inputs (a single bolus, or a constant exposure at high concentrations); these solutions were generally in the form of exponential functions with different parameters for each compartment (12-13). For example, assuming someone without previous exposure to a particular VOC is suddenly exposed to a constant high concentration Cair, the alveolar breath concentration Calv is given by (14):

        Calv = fCair ai [1-exp(-t/_i)] [1]

where f=fraction of parent compound exhaled at equilibrium; _i=residence time in ith compartment; ai=fraction of breath concentration contributed by the ith compartment at equilibrium (t=(infinity)); t=time of exposure (t=0 at start of exposure); and ai=1.

One important parameter in these compartmental models is the residence time, _i, for the ith compartment. This is the time it takes for the chemical to decline to 1/e of its initial concentration in the compartment, assuming all other compartments are at zero concentration. A series of chamber studies sponsored by the U.S. EPA have provided estimates of _i for i=1...4 for a number of VOCs (14).

A second important parameter in the compartmental models is the fraction, f, of the chemical exhaled under steady-state conditions. This is particularly important for environmental considerations because it may often be the case that persons under normal conditions are at or near equilibrium with their chemical environments; in such a case, multiplying the breath measurement by 1/f is quite a good estimate of their long-term average normal exposure. Later we provide estimates of f for a number of chemicals obtained from the U.S. EPA-sponsored feld and chamber studies.

Recently, with the advent of more powerful computers, the equations have been solved numerically. This has allowed more realistic consideration of physiological processes and has led to a class of models known as physiologically based pharmacokinetic (PBPK) models (15). Although these models are powerful and have a number of successful applications, they require knowledge of a much larger number of parameters, some of which are diffcult to obtain quantitative information on; thus there is some question of how unique their parameter estimates are (16).

Methods

An improvement to this method was developed after completing the TEAM Studies and was used in a series of feld and chamber studies. The method (22-24) employs a charcoal face mask to allow breathing clean air without the need for a cylinder of clean air and a separate inhalation bag. Several (2-4) breaths are taken through the charcoal flter to fush the alveoli and bronchial tubes of ambient air before collecting the breath sample. The exhalation bag is replaced by an evacuated electropolished 1.8-liter stainless-steel cylinder with a critical orifce (although other suitable collecting devices such as Tenax or other sorbents could also be used). The subject exhales through a 1-m long perfuoroethylene tube, which retains the latter part of the breath (the alveolar portion) for a few seconds during the resting and inhalation parts of the respiration cycle, during which time the alveolar air in the tube is pulled into the cylinder through the critical orifce. The canister collects approximately 98% alveolar air. About 12 breaths are collected over an 80-sec period. The method is readily deployable in the feld; electrical power is not needed, and the entire set of equipment fts into a metal carrying case about the size of a suitcase. The cycle time (from beginning to collect one breath sample until readiness to collect another) can be as short as 3 min. A miniature version of the system was made and validated for use in space fight (25).

Recently, a single-breath method has been developed (26). The subject breathes directly into a 1-liter evacuated cylinder through a strawlike attachment; after wasting the frst (dead space) portion of the breath, the subject opens the valve on the cylinder to allow collection of the second (alveolar) portion. The cycle time is reduced to approximately 1 min. The new method allows for immediate collection following exposure, thus documenting the maximum breath (and therefore blood) concentration attained during the exposure period. Also, a much more fnely detailed picture of the decay curve during the frst few minutes of rapid decay can be achieved.

Together with the new sampling method, a three-step sequential analytical approach was developed (27). In the frst step, only the carbon dioxide level in the sample is quantifed. This allows an estimate of the amount of dead space air included in the sample. Since CO₂ in alveolar air is about 4 to 5%, compared to only 0.035% in outdoor air, a sample including a mixture of alveolar and dead space air will have an intermediate level of CO₂. Determining the CO₂ level allows a quantitative adjustment of the subsequent trace-level determinations to more nearly estimate the alveolar air concentration. Although CO₂ levels vary from person to person according to several factors (such as metabolic rates and the amount of time the breath is held before providing a sample), the CO₂ concentrations should be steady over any given series of breath measurements for a single subject. Deviations from the average established for each person permit correction of the measured VOC levels. In the second step, the sample is analyzed for volatile endogenous compounds such as acetone and isoprene, which are found at levels approaching 1 ppm by volume. This step is also capable of quantitating polar compounds such as methanol, ethanol, dimethyl sulfde, and 2-propanol at parts per billion levels. Finally, in the third step the sample is analyzed in detail for the remainder of the VOCs at subparts per billion levels.

A few years ago, Kelly and co-workers (28) developed a new exhaled breath interface that allows continuous real-time analysis of undiluted breath. The system takes advantage of the high sensitivity and specifcity of tandem mass spectrometry (MS-MS) by coupling the exhaled breath inlet to a direct air sampling source [e.g., atmospheric pressure ionization (API) or glow discharge ionization source] and an MS-MS instrument (e.g., triple-stage quadrupole or ion trap mass spectrometer) (29). The subject inhales clean air from a suitable source and exhales directly into the breath interface. The inlet requires no attention from the subject and provides a constant fow of exhaled air into the mass spectrometer. Trace chemicals in the breath are immediately ionized, and compounds of interest are isolated according to mass. The selected masses are dissociated, and the fragments are identifed and quantifed. This direct air sampling MS-MS technique thus offers a means of extracting the VOCs directly from the exhaled breath matrix and eliminates the preconcentration step that normally precedes exhaled breath analysis by GC-MS.

The method was tested in pilot studies to measure dimethyl sulfde (which has been shown to be elevated in breath levels of person with liver disease) in breath of healthy people; lactic acid in breath during physical exercise (28); and the elimination of 1,1,1-trichloroethane from breath of a machine shop worker, sampling at 5.5-sec intervals over a 20-min period immediately after exposure (29). The data from the latter experiment were evaluated in terms of a two-compartment model of the body. The residence time for the frst compartment was estimated to be 1.2 min and for the second compartment to be 17 min. The method is capable of analyzing both polar and nonpolar organics. Detection limits for certain compounds measured with the API source, such as dimethyl sulfde, are as low as 5 ppt. Most other VOCs exhibit detection limits in the low parts per billion range with either the API/triple quadrupole or glow discharge/ion trap system [(30,31); Gordon et al. unpublished results].

In a recent study designed to validate a PBPK model, Thrall and Kenny (32) developed a real-time technique to quantitatively measure the concentration of exhaled breath VOCs using laboratory rats. Breath samples are collected using a specially designed manifold in which up to four rats can be attached to the manifold via nose-only restraint tubes. The exhaled breath from the rats exits the nose ports and is driven into a common mixing chamber by a continuous fow of supplied breathing air. Samples for analysis by either API/triple quadrupole or glow discharge/ion trap tandem mass spectrometry are continually drawn from the contents of the mixing chamber. Detection limits for the target compound, carbon tetrachloride, are in the range of 2 to 10 ppb.

The highly compact Teledyne 3DQ Discovery ion trap mass spectrometer is expected to form the nucleus of a feld-deployable MS/MS system for real-time monitoring of VOCs in breath (and air) (30). The U.S. EPA's Atmospheric Research and Exposure Assessment Laboratory has instituted a cooperative agreement with Battelle Memorial Institute to refne the technique for applications in assessing human exposure.

EPA Field Studies

Several special TEAM studies were also undertaken, most of which included breath sampling. For example, breath and mothers' milk samples were analyzed for the target VOCs in a subsample of 17 nursing mothers selected from the Elizabeth-Bayonne, New Jersey, area (43-45). Breath samples were also collected at home and at work from workers in three dry cleaning shops (46-48).

The suitcase sampler was used (49) to evaluate total benzene body burden resulting from a 20-min shower using gasoline-contaminated groundwater. About 10 breath samples were collected during the 3 hr following the end of exposure.

More recently, the suitcase sampler was used in the Lower Rio Grande Valley Environmental Scoping Study (Buckley et al., unpublished data). However, due partly to using unsuitably high calibration standards, the detection limit was too high (on the order of 1 µg/m³) and yielded detectable levels in only 5 (2.6%) of the possible 189 breath samples.

U.S. EPA Chamber Studies

Later chamber studies (53-60) employed the suitcase sampler developed by Pellizzari. Persons were monitored immediately after leaving commercial establishments with expected high levels of some VOCs and were also exposed for controlled time periods (2, 4, or 10 hr) to high, constant levels of selected VOCs in a chamber. Decay periods of 2, 4, and fnally 24 hr were prescribed, during which up to a dozen or so breath samples were taken. This series of studies has resulted in estimates of f and _i for four compartments, including blood and fat as well as organs and muscle.

More recently, Buckley et al. (82) studied uptake and decay in breath during inhalation exposure to methyl-tert-butyl ether (MTBE). Two persons were exposed to constant levels of MTBE for 1 hr in a room-sized environmental chamber. Breath samples were collected using the suitcase sampler during uptake and decay for 7 hr following exposure.

Results

Daytime median 12-hr average personal exposures and subsequent breath concentrations are provided in Table 1 for 18 prevalent chemicals from four chemical classes. Because of the possible contamination of the Tedlar bags by van exhaust fumes during the frst (1981) New Jersey trip, the breath values for gasoline-related VOCs such as the aromatic compounds may be erroneously high for this frst visit. Also, during the second (summer 1982) trip to New Jersey, contamination of the Tenax cartridges during storage in a hotel that had been recently renovated may have affected the results for both air and breath values; blank values were unusually high and variable, and thus the estimated values are uncertain, although the direction of error cannot be determined.

Because all residents were visited at home in the evening to obtain their breath samples, and because more than 75% of them had been home for a number of hours before the sample was taken, it is likely that most were being sampled under normal or typical conditions. This makes it probable that the blood and breath concentrations for many of the residents were close to equilibrium with their surroundings. Even for those not close to equilibrium, it seems likely that for most chemicals roughly equal numbers of persons were either above or below their equilibrium breath concentrations. By this reasoning, the ratio of the median values for the breath and personal air concentrations of the participants should be close to the equilibrium value of f. The chamber studies provide an independent estimate of f, although for a much smaller population. The estimates of f obtained from the feld and chamber studies are compared in Table 2.

Perhaps the most striking evidence of the importance of making breath measurements was the discovery that the single most important source of exposure to both benzene and styrene for some 50 million Americans is active smoking. The personal monitor detected a modest increase of about 50% in personal air exposures, but the breath values documented a 6- to 10-fold increase in benzene and styrene concentrations in the breath of smokers (Figure 1).

Figure 1. Benzene and styrene concentrations in exhaled breath of smokers and nonsmokers. Data from the U.S. EPA TEAM Studies of 200 smokers and 300 nonsmokers (39).

In the benzene shower study described above, the decay curve was not at all similar to the decay curves previously noted for benzene and other aromatics, suggesting that a second pathway (presumably dermal) was contributing to the uptake and decay of benzene. By assuming an expected decay due to inhalation only and subtracting the expected breath levels from the observed values, Buckley et al. (unpublished data) derived an estimate of the contribution of dermal absorption to total body burden.

The chamber studies discussed above provide estimates (Table 3) of the residence times, _i, for nine VOCs drawn from three classes: aliphatic, aromatic, and halogenated hydrocarbons. Using the average values of f and _i for each of these three classes, the observed breath concentrations during the postexposure period for all fve subjects during the chamber studies can generally be predicted to within 30%, except at the very end of the decay curve, when concentrations approach the detection limit (Figure 2).

Figure 2. Residual errors from a four-compartment ft to observed breath concentrations of four aromatic chemicals in a chamber study of fve subjects. Subjects were exposed for 10 hr to a constant concentration of toluene, ethylbenzene, p-xylene, and o-xylene. The ft is to the subsequent 24-hr decay while the subjects were in a clean environment. Only one set of parameters (the residence time for each of the four compartments averaged over all four compounds and all fve subjects) was used in the model. Virtually all observed points are within 30% of the predicted values except for the fnal measurements, which are close to the detection limit of the method (81).

The more recent chamber study of MTBE mentioned above resulted in a three-compartment model ft to MTBE breath decay (Figure 3) yielding residence times for the frst compartment of 2 to 5 min, for the second compartment of 20 to 50 min, and for the third compartment of 5 to 12 hr. Thus, the residence times for MTBE appear to be roughly similar to those calculated for other (nonpolar) VOCs. Values of f for a 226-lb male and a 147-lb female were calculated to be 0.46 and 0.6, respectively. The blood-breath partition coeffcient was calculated to be in the range of 15 to 20, based on simultaneous blood measurements in both subjects; however, the likelihood that MTBE, a polar chemical, might be absorbed in the mucous membranes, resulting in larger differences than usual between the measured exhaled breath and the alveolar concentration, made this estimate uncertain.

Figure 3. A three-compartment ft to the observed breath values of methyl-tert-butyl ether (MTBE) for one subject during a 1-hr exposure followed by a 7-hr decay period. The residence times are on the order of 2 min, 17 min, and 4.5 hr for the frst three compartments. The "sawtooth" portion of the curve during the exposure period results from the subject breathing pure air for 2 min at a time while providing a breath sample (Buckley TJ, in preparation).

Discussion

It is relevant to note that breath sampling was initially selected for the TEAM Studies in preference to blood sampling for two major reasons: a) Breath sampling is more sensitive than blood sampling. A typical limit of detection for many VOCs in breath is 0.2 µg/m³. Depending on the partition coeffcient, this corresponds to part-per-trillion levels in blood, which are extremely diffcult to quantitate adequately. b) Breath sampling is more acceptable to people than blood sampling. The method is noninvasive and easily mastered by young and old. For population-based studies such as TEAM, it is particularly important to achieve a high response rate, and blood sampling would no doubt have depressed the response rates of 50 to 60% normally achieved in the TEAM Studies.

Having trustworthy estimates of the main breath parameters (f and ) is important in several ways. For example, in designing chamber studies, it is important to time the collection of the breath samples to gain maximum effciency in defning the decay curve. Typically, two measurements bracketing each expected residence time, _i, are about the minimum required to delineate the decay curve adequately. Also, knowing the expected value of f helps to determine the initial exposure concentration required to assure detectable concentrations at the end of the decay period.

The values of f estimated from the feld studies are generally similar to the values determined from the chamber studies; therefore it appears that they can be used with some confdence to estimate the relationship between airborne exposure and resulting body burden. In two cases (chloroform and limonene) f exceeds 1. Of course, the reason for this is that both chemicals have major routes of exposure other than the air. Chloroform is contained in drinking water, soft drinks, and dairy products (33,50,51); limonene in citrus fruits, soft drinks, and other foods. However, it appears that for all the other target chemicals, air provides 95 to 100% of the total exposure.

The residence times are quite similar from one chemical to another. It appears that for all these VOCs, an initial residence time on the order of 3 min, and a secondary one on the order of 30 min, is not a bad approximation. Fewer data are available for the third and fourth residence times, due partly to the diffculty of keeping subjects for 24 hr in a completely clean background. Thus, the residence time estimates for muscle and fat tissues of about 3 hr and about 3 days, respectively, are more uncertain than for the vessel-rich tissues.

An important use of breath sampling is in estimating dermal absorption of VOCs. In one study, breath samples were collected from volunteers who took showers with and without rubber suits to isolate the contributions of inhalation and dermal absorption of chloroform (64,65). The breath levels were about twice as high in persons who showered without the rubber suits, suggesting that dermal absorption accounted for about half of the total chloroform uptake during the showers.

More recently, a study of swimmers at an indoor pool in which the chloroform content of the water was regulated showed that breath concentrations after normal swimming were about 4 times higher than those after swimming with a scuba tank supplying pure air (66). The authors concluded that dermal uptake was thus responsible for about 25% of the total chloroform uptake during swimming. [The difference between their results and the earlier ones from the shower studies (64,65) was attributed to the hotter temperature of the shower water and possibly the permeability-affecting properties of the soap and shampoo used in the shower.] Other studies of chloroform exposure in showers or swimming pools have also utilized breath samples as an estimate of combined inhalation and dermal exposure (67-70).

An interesting recent hypothesis is that exhaled breath may not only refect exposure but also cause it. Using data from the TEAM Study of dry cleaners mentioned earlier, which found breath values of 10,000 to 25,000 µg/m³ in the workers and elevated home air values of about 100 µg/m³, Thompson and Evans (71) used a PBPK model to estimate that all or a portion of the increased home air levels could have been introduced from the workers' breath.

Another area where breath sampling could be useful is in relating compounds in breath to disease, perhaps as early warning markers for lung cancer (72,73). Related studies have identifed a marker of active smoking in smokers' breath: 2,5-dimethylfuran (74,75). This marker may even be useful in identifying exposure to environmental tobacco smoke (76). Other diseases for which breath sampling has been used as a diagnostic tool include malabsorption syndrome and pancreatic damage, both of which result in increased amounts of hydrogen in breath following a dose of certain sugars (77), and peptic ulcers and chronic gastritis due to Helicobacter pylori infections, which can create CO₂ in the breath by using the urease enzyme found in these bacteria to metabolize urea, which is otherwise not metabolized by the stomach (4). Breath sampling has also been used in identifying exposure to VOCs in confned spaces, such as submarines (78).

Unfortunately, few data are available on simultaneous measurements of blood and breath on the same subjects at environmental levels of exposure; such data would be extremely useful in determining how well the partition coeffcients obtained in chamber studies and occupational (high-exposure) situations apply to low-exposure environmental conditions. Some studies (10,11) suggest that blood-breath ratios at low concentrations may be 2 to 3 times the ratios at high concentrations. A possible explanation for this phenomenon is the sequestering of a portion of the inhaled chemical by proteins in the blood (79). If the capacity of the proteins is relatively small, they would become saturated as concentrations increased, and the laboratory values of the partition coeffcient would be approached.

In the absence of such simultaneous blood and breath measurements at environmental levels of exposure, it is possible to arrive at a rough estimate of blood-breath ratios at low levels by comparing the TEAM Study results on breath levels of representative subpopulations with the National Health and Nutrition Examination Survey study results on blood levels of a nationwide sample (80). Provided that the two populations are roughly comparable, this comparison (Table 4) suggests that the blood-breath ratio increases at the mean compared to the 95th percentile; the increase is greater at lower percentiles, such as the median.

Future Directions

We conclude that breath sampling is a fertile and developing scientifc discipline with much promise for providing useful data on scores or hundreds of VOCs of present or future interest.

1. Morgan A, Black A, Belcher DR. Studies on the absorption of halogenated hydrocarbons and their excretion in breath, using 38 Cl-tracer techniques. Ann Occup Hyg 15:273-282 (1972).

2. Hake CL, Stewart RD, Wu A, Graff SA. Experimental human exposure to perchloroethylene. Toxicol Appl Pharmacol 37:175 (1976).

3. Leung H-W, Paustenbach D. Application of pharmacokinetics to derive biological exposure indexes from threshold limit values. Am Ind Hyg Assoc J 49:445-450 (1988).

4. Phillips M. Breath tests in medicine. Sci Am 267(1):74-79 (1992).

5. Gargas ML, Burgess RJ, Voisard DE, Carson GH, Andersen ME. Partition coeffcients of low-molecular-weight volatile chemicals in various liquids and tissues. Toxicol Appl Pharmacol 98:87-99 (1989).

6. Sato A, Nakajima T. Partition coeffcients of some aromatic hydrocarbons and ketones in water, blood, and oil. Br J Ind Med 36:231-234 (1979).

7. Sato A, Nakajima T. A structure-activity relationship of some chlorinated hydrocarbons. Arch Environ Health 34:69-75 (1979).

8. Sato A, Nakajima T. Pharmacokinetics of organic solvent vapors in relation to their toxicity. Scand J Work Environ Health 13:81-93 (1987).

9. Berlin M, Gage JC, Gulberg B, Holm S, Knutsson P, Tunek A. Breath concentration as an index of the health risk from benzene. Scand J Work Environ Health 6:104-111 (1980).

10. Brugnone F, Perbellini L, Faccini GB, Pasini F. Benzene in the breath and blood of normal people and occupationally exposed workers. Am J Ind Med 16:385-399 (1989).

11. Perbellini I, Faccini GB, Pasini F, Cazzoli F, Pistoia S, Rosellini R, Valsecchi M, Brugnone F. Environmental and occupational exposure to benzene by analysis of breath and blood. Br J Ind Med 45:345-352 (1988).

12. Teorell T. Kinetics of distribution of substances administered to the body. I: The extravascular modes of administration. Arch Int Pharmacodyn 57:205-225 (1937).

13. Teorell T. Kinetics of distribution of substances administered to the body. II: The intravascular mode of administration. Arch Int Pharmacodyn 57:226-240 (1937).

14. Wallace LA, Pellizzari ED, Gordon SA. Linear model relating breath concentrations to environmental exposures: application to a chamber study of four volunteers exposed to volatile organic chemicals. J Expos Anal Environ Epidemiol 3(1):75-102 (1993).

15. Ramsey JC, Andersen ME. A physiologically based description of the inhalation pharmacokinetics of styrene in rats and humans. Toxicol Appl Pharmacol 73:159-175 (1984).

16. Bois F, Woodruff TJ, Spear RC. Comparison of three physiologically based pharmacokinetic models of benzene disposition Toxicol Appl Pharmacol 110:79-88 (1991).

17. Krotoszynski BK, Gabriel G, O'Neill H. Characterization of human expired air: a promising investigation and diagnostic technique. J Chromatogr Sci 15:239-244 (1977).

18. Krotoszynski BK, Bruneau GM, O'Neill HJ. Measurement of chemical inhalation exposure in urban populations in the presence of endogenous effuents. J Analyt Toxicol 3:225-234 (1979).

19. Michael LC, Erickson MD, Parks SP, Pellizzari ED. Volatile environmental pollutants in biological matrices with a headspace purge technique. Anal Chem 52:1836-1841 (1980).

20. Pellizzari ED, Zweidinger RA, Sheldon LS. Breath sampling. In: Environmental Carcinogens: Methods of Analysis and Exposure Measurement--Indoor Air, Vol 12 (Seifert B, Van de Wiel HJ, Dodet B, O'Neill IK, eds). IARC Scientific Publications No 109. Lyon:International Agency for Research on Cancer, 1993;228-236.

21. Barkley J, Bunch J, Bursey JT, Castillo N, Cooper SD, Davis JM, Erickson MD, Harris BSH III, Kirkpatrick M, Michael L, Parks SP, Pellizzari E, Ray M, Smith D, Tomer K, Wagner R Zweidinger RA. Gas chromatography mass spectrometry computer analysis of volatile halogenated hydrocarbons in man and his environment--a multimedia environmental study. Biomed Mass Spectrometry 7(4):139-147 (1980).

22. Pellizzari ED, Thomas KW, Raymer JH, Smith DJ, Cooper SD. Measurements of Exhaled Breath Using a New Portable Sampling Method. Final Report, Contract # 68-02-4544. Research Triangle Park, NC:U.S. Environmental Protection Agency, 1990.

23. Thomas KW, Pellizzari ED, Cooper, SD. A canister-based method for collection and gc/ms analysis of volatile organic compounds in human breath. J Anal Toxicol 15:54-59 (1991).

24. Raymer JH, Thomas KW, Cooper SD, Whitaker DA, Pellizzari ED. A device for sampling human alveolar breath for the measurement of expired volatile organic compounds. J Anal Toxicol 14:337-344 (1990).

25. Raymer JH, Thomas KW, Pellizzari ED, Whitaker DA, Cooper SD, Limero T, James JT. A breath sampling device for measuring human exposure to volatile organic compounds in microgravity. Aviat, Space Environ Med 65:353-360 (1992).

26. Pleil JD, Lindstrom AB. Collection of a single alveolar exhaled breath for volatile organic compounds analysis. Am J Ind Med 27:109-121.

27. Pleil JD, Lindstrom AB. Measurement of volatile organic compounds in exhaled breath as collected in evacuated electropolished canisters. J Chromatography B: Biomed Appl 665:271-279.

28. Kelly TJ, Kenny DV, Spicer CW, Sverdrup GM. Continuous analysis of human breath using atmospheric pressure ionization MS/MS with a novel inlet design. In: Proceedings of the 1989 EPA/AWMA International Symposium on Measurement of Toxic and Related Air Pollutants. VIP-13. Pittsburgh, PA:Air and Waste Management Association, 1989.

29. Gordon SM, Kenny DV, Kelly TJ. Continuous real-time breath analysis for the measurement of half-lives of expired volatile organic compounds. J Expos Anal Environ Epidemiol (Suppl 1):41-54 (1992).

30. Gordon SM, Callahan PJ, Kenny DV, Pleil JD. Direct trace analysis of volatile organic compounds in air using ion trap mass spectrometers with fltered noise felds. In: Proceedings, EPA/AWMA International Symposium on Field Screening Methods for Hazardous Wastes and Toxic Chemicals, 22-24 February 1995, Las Vegas, Nevada, Vol I. VIP-47. Air and Waste Management Assoc. Pittsburgh, PA. (1995).

31. Gordon SM, Callahan PJ, Kenny DV, Pleil JD. Direct sampling and anaylsis of volatile organic compounds in air by membrane introduction and glow discharge ion trap mass spectrometry with filtered noise fields. Mass Spectrometry 10:1038-1046 (1996).

32. Thrall KD, Kenny DV. Evaluation of a carbon tetrachloride physiologically based pharmacokinetic model using real-time breath-analysis monitoring of the rat. Inhal Toxicol 8:251-261 (1996).

32. Wallace LA, Pellizzari ED, Hartwell T, Rosenzweig R, Erickson M, Sparacino C, Zelon H. Personal exposure to volatile organic compounds. I: Direct measurement in breathing-zone air drinking water, food, and exhaled breath. Environ Res 35:293-319 (1984).

33. Wallace LA, Pellizzari ED, Hartwell T, Sparacino C, Sheldon L, Zelon H. Personal exposures, indoor-outdoor relationships and breath levels of toxic air pollutants measured for 355 persons in New Jersey. Atmos Environ 19:1651-1661 (1985).

34. Wallace LA, Pellizzari ED, Hartwell TD, Sparacino C, Whitmore R, Sheldon L, Zelon H, Perritt R. The TEAM study: personal exposures to toxic substances in air, drinking water, and breath of 400 residents of New Jersey, North Carolina, and North Dakota. Environ Res 43:290-307 (1987).

35. Wallace LA. The TEAM Study: Summary and Analysis. Vol I. 600/6-87/002a. Washington:U.S. Environmental Protection Agency, 1987.

36. Pellizzari ED, Perritt K, Hartwell TD, Michael LC, Whitmore R, Handy RW, Smith D, Zelon H. Total Exposure Assessment Methodology (TEAM) Study: Elizabeth and Bayonne, New Jersey; Devils Lake, North Dakota; and Greensboro, North Carolina. Vol II. Washington:U.S. Environmental Protection Agency, 1987.

37. Pellizzari ED, Perritt K, Hartwell TD, Michael LC, Whitmore R, Handy RW, Smith D, Zelon H. Total Exposure Assessment Methodology (TEAM) Study: Selected Communities in Northern and Southern California. Vol III. Washington:U.S. Environmental Protection Agency, 1987.

38. Entz R, Thomas K, Diachenko G. Residues of volatile halocarbons in food using headspace gas chromatography. J Agric Food Chem 30:846-849 (1982).

39. Wallace LA, Pellizzari ED, Hartwell T, Perritt K, Ziegenfus R. Exposures to benzene and other volatile organic compounds from active and passive smoking. Arch Environ Health 42:272-279 (1987).

40. Wallace LA, Pellizzari ED, Hartwell TD, Whitmore R, Perritt R, Sheldon LS. The California TEAM study: breath concentrations and personal exposures to 26 volatile compounds in air and drinking water of 188 residents of Los Angeles, Antioch, and Pittsburgh, CA. Atmos Environ 22:2141-63 (1988).

41. Wallace L.A. Major sources of exposure to benzene and other volatile organic compounds. Risk Analysis 10:59-64 (1990).

42. Wallace LA, Nelson WC, Ziegenfus R, Pellizzari E. The Los Angeles TEAM study: personal exposures indoor-outdoor air concentrations, and breath concentrations of 25 volatile organic compounds. J Expos Anal Environ Epidemiol 1(2):37-72 (1991).

43. Pellizzari ED, Hartwell TD, Harris BSH III, Waddell RD, Whitaker DA, Erickson MD. Purgable organic compounds in mother's milk. Bull Environ Contam Toxicol 28:322-328 (1982).

44. Sheldon LS, Handy RW, Hartwell TD, Leininger C and Zelon H. Human Exposure Assessment to Environmental Chemicals: Nursing Mothers Study. Final report. Washington:U.S. Environmental Protection Agency, 1983.

45. Wallace LA, Sheldon L, Hartwell TD, Zelon H, Perritt R, Sparacino C, Pellizzari ED. Personal exposures and body burdens of 34 environmental pollutants measured for 17 New Jersey nursing mothers. Presented at the Second International Conference on Total Exposure Assessment Methodology (TEAM), Atlanta, GA, 1991.

46. Pellizzari ED et al. Total Exposure and Assessment Methodology (TEAM): Dry Cleaners Study. EPA Contract 68-02-3626, Washington:U.S. Environmental Protection Agency, 1984.

47. Thomas KW, Pellizzari ED, Perritt RL, Nelson WC. Effect of dry-cleaned clothes on tetrachloroethylene levels in indoor air, personal air, and breath for residents of several New Jersey homes. J Expos Anal Environ Epidemiol 1:475-490 (1991).

48. Wallace LA, Sheldon LS, Pellizzari ED, Hartwell TD, Perritt R, Zelon H. Exposures of dry cleaning workers to tetrachloroethylene and other volatile organic compounds: measurements in air, water, breath, blood, and urine. Presented at the Second International Conference on Total Exposure Assessment Methodology (TEAM), Atlanta, GA, 1991.

49. Lindstrom AB, Highsmith R, Buckley TJ, Pate WJ, Michael LC. Gasoline-contaminated ground water as a source of residential benzene exposure: a case study. J Expos Anal Environ Epidemiol 4:183-196 (1994).

50. Buckley TJ, Lewis RG, Akland GG, Berry MR, Johnson L, Schwab M, Liddle J, Kendall D. Residential-based human exposure to metals, pesticides, PAH and VOCs: Results from the Lower Rio Grande Valley Environmental Pilot Study. (Abstract). Presented at Fourth Conference of the International Society for Exposure Analysis, 18-21 September 1994, Chapel Hill, NC.

51. Gordon SM, Wallace LA, Pellizzari ED, O'Neill HJ. Breath measurements in a clean-air chamber to determine 'wash-out' times for volatile organic compounds at environmental concentrations. Atmos Environ 22:2165-2170 (1988).

52. Gordon SM, Wallace LA, Pellizzari ED, Moschandreas DJ. Residence times of volatile organic compounds in human breath following exposure to air pollutants at near-normal environmental concentrations. In: Total Exposure Assessment Methodology--A New Horizon. VIP-16 247-256. Pittsburgh, PA:Air & Waste Management Association, 1990.

53. Raymer JH, Pellizzari ED, Thomas KW, Kizakevich P, Cooper SD. Kinetics of low-level volatile organic compounds in breath. II: Relationship between concentrations measured in exposure air and alveolar air. J Expos Anal Environ Epidemiol 2(Suppl 2): 67-83 (1992).

54. Raymer JH, Thomas KW, Pellizzari ED, Cooper SD, Smith DJ, Kizakevich P, Pugh D. Breath and Blood Measurements of Individuals Exposed to Volatile Organic Chemicals: Elimination from the Third Compartment. Final Report. Contract 68-02-4544. Research Triangle Park, NC:U.S. Environmental Protection Agency, 1992.

55. Raymer JH, Pellizzari ED, Cooper SD, Castillo NP Thomas KW. Evaluation of a Pharmacokinetic Model for Volatile Organic Compounds in Breath and of the Application of the Analytical Method to Polar VOCs. Final Report. EPA Contract 68-02-4544. Research Triangle Park, NC:U.S. Environmental Protection Agency, 1990.

56. Raymer JH, Pellizzari ED, Thomas KW Cooper S. Elimination of volatile organic compounds in breath after exposure to occupational and environmental microenvironments. J Expos Anal Environ Epidemiol 1:439-452 (1991).

57. Thomas KW, Pellizzari ED, Raymer JH, Cooper SD Smith D. Kinetics of low-level volatile organic compounds in breath. I: experimental design and data quality. J Expos Anal Environ Epidemiol 2:(Suppl 2):45-66 (1992).

58. Pellizzari ED, Wallace LA, Gordon SM. Elimination kinetics of volatile organics in humans using breath measurements. J Expos Anal Environ Epidemiol 2(3):341-356 (1992).

59. Pellizzari ED, Raymer JH, Thomas KW, Cooper SD, Wallace LA, Nelson WC. Breath measurements of volatile organic chemicals as an indicator of exposure. In: Indoor Air '90: Proceedings of the 5th International Conference on Indoor Air Quality and Climate, Vol 2. Ottawa, Ontario:Canada Mortgage and Housing Corp., 1990;133-138.

60. Wallace LA, Pellizzari ED, Gordon SM. The use of breath analysis to determine recent or long-term exposure to indoor sources of volatile organic chemicals. In: Indoor Air '90: Proceedings of the 5th International Conference on Indoor Air Quality and Climate, Vol 2. Ottawa, Ontario:Canada Mortgage and Housing Corp., 1990;127-132.

61. Entz RC, Diachenko GW. Residues of volatile halocarbons in margarines. Food Additives Contam 5:267-276 (1988).

62. Uhler AD, Diachenko GW. Volatile halocarbon compounds in process water and processed foods. Bull Environ Contam Toxicol 39:601-607 (1987).

63. Rose WP. Analysis of Foods for Benzene. Washington:American Petroleum Institute, 1992.

64. Jo WK, Weisel CP and Lioy PJ. Routes of chloroform exposure and body burden from showering with contaminated tap water. Risk Analy 10:575-580 (1990).

65. Jo WK, Weisel CP and Lioy PJ. Chloroform exposure and the health risk associated with multiple uses of chlorinated tap water. Risk Analy 10:581-584 (1990).

66. Levesque B, Ayotte P, Leblanc A, Dewailly E, Prud'Homme D, Lavoie R, Sylvain A, Levallois P. Evaluation of dermal and respiratory chloroform exposure in humans. Environ Health Perspect 102:1082-1087 (1994).

67. Weisel, CP, Jo WK. Variations in breath concentrations of volatile organic compounds after exposure from showers: estimates of their elimination from the body. In:Indoor Air '90: Proceedings of the 5th International Conference on Indoor Air Quality and Climate, Vol 2. Ottawa, Ontario:Canada Mortgage and Housing Corp., 1990;171-176.

68. Weisel CP, Jo WK, Lioy PJ. Routes of chloroform exposure from showering with chlorinated water. In: Measurement of Toxic and Related Air Pollutants: Proceedings of the 1990 EPA/Air & Waste Management Association International Symposium. VIP-17. EPA 600/9-90/026. Pittsburgh, PA:Air & Waste Management Association, 1990.

69. Weisel CP, Jo WK, Lioy PJ. Utilization of breath analysis for exposure and dose estimates of chloroform. J Expos Anal Environ Epidemiol (Suppl 1):55-70 (1992).

70. Aggazzotti G, Fantuzzi G, Righi E, Tartoni P, Cassinadri T, Predieri G. Chloroform in alveolar air of individuals attending indoor swimming pools. Arch Environ Health 48:251-254 (1993).

71. Thompson KM, Evans JS. Workers' breath as a source of perchloroethylene (PERC) in the home. J Expos Anal Environ Epidemiol 3:417-430 (1993).

72. O'Neill HJ, Gordon SM, O'Neill MH, Gibbons RD, and Szidon JP. A computerized classifcation technique for screening for the presence of biomarkers in lung cancer. Clin Chem 34:1613-1618 (1988).

73. Gordon SM, Szidon JP, Krotoszynski BK, Gibbons RD, O'Neill HJ. Volatile organic compounds in exhaled air from patients with lung cancer. Clin Chem 31:1278-1282 (1985).

74. Gordon SM. Identifcation of exposure markers in smokers' breath. J Chromatogr 511:291-302 (1990).

75. Gordon SM. Identifcation of unique volatile organic compounds in exhaled breath of smokers. In: Walkinshaw (ed) Indoor Air '90: Proceedings of the 5th International Conference on Indoor Air Quality and Climate, Vol 2. Ottawa, Ontario:Canada Mortgage and Housing Corp., 1990;177-182.

76. Ashley DL, Bonin MA, Hamar B, McGeehin M. Using the blood concentration of 2,5-dimethylfuran as a marker for smoking. J Expos Anal Environ Epidemiol (in press).

77. Perman JA. Clinical application of breath hydrogen measurements. Canadian J Physiol Pharmacol 69:111-115 (1991).

78. O'Neill HJ, Gordon SM, Brousek LM, Moschandreas DJ, Knight DR, Bowman JS. Submarine air quality: relationship to human body burden. In: Measurement of Toxic and related Air Pollutants: Proceedings of the 1993 US EPA/AWMA International Symposium. VIP-34. EPA/600/A93/024. Pittsburgh, PA:Air & Waste Management Association, 1994;237-243.

79. Travis CC, Bowers JC. Protein binding of benzene under ambient exposure conditions. Toxicol Ind Health 5(6): 1017-1024 (1989).

80. Ashley DL, Bonin MA, Carkinali L, McCraw JM, Wooten JV. Blood concentrations of volatile organic compounds in a nonoccupationally exposed US population and in groups with suspected exposure. Clin Chem 40:1401-1404 (1994).

81. Wallace LA, Nelson WC, Pellizzari ED, Raymer JH. A four compartment model relating breath concentrations to low-level chemical exposures: application to a chamber study of fve subjects exposed to nine VOCs. J Expos Anal Environ Epidemiol (1996).