Environ. Sci. Technol. IQ05, 19, 997-1003
(12) Mackay, D.; Yeun, A. T. K. Environ. Sci. Technol. 1983, 17, 211-217. (13) Lyman, W. J.; Reehl, W. F.; Rosenblatt, D. H. “Handbook of Chemical Property Estimation Methods”; McGraw-Hill: New York, 1982. (14) Wolff, C. J. M.; van der Heijde, H. B. Chemosphere 1982, 11, 103-117. (15) Atlas, E.; Foster, R.; Giam, C. S. Environ. sci. Technol. 1982,16, 283-286. (16) Roberts,P. V.; Dandliker, P. G. Environ. Sci. Technol. 1983, 17,484-489. (17) Liss, P. S.; Slater, P. G. Nature (London) 1974, 247, 181-184. (18) Kavanaugh, M. C.; Trussell, R. R. J.-Am. Water Works Assoc. 1980, 72, 684-692. (19) Mackay, D.; Shiu, W. Y.; Sutherland, R. P. Enuiron. Sci. Technol. 1979. 13., 333-337. - - - -(20) Hampton,-C. V.; Pierson, W. R.; Schuetzle, D.; Harvey, T. M. Enuiron. Sci. Technol. 1983, 17, 699-708. (21) Hampton, C. V.; Pierson, W. R.; Harvey, T. M.; Updegrove, W. S.; Marano, R. S. Environ. Sci. Technol. 1982, 16, 2a7-298. (22) Dietz, W. A. J. Gas Chromatogr. 1967, 5,68-71. (23) Meyer, W. C.; Yen, T. F. In “Science and Technology of Oil Shale”;Yen, T. F., Ed.; Ann Arbor Science: Ann Arbor, MI, 1976; pp 19-34. (24) Arbuckel, W. B. Environ. Sci. Technol. 1983,17,537-542. (25) Mackay, D.; Bobra, A.; Chan, D. W.; Shiu, W. Y. Environ. Sci. Technol. 1982, 16, 645-649. (26) Andon, R. J. L.; Cox, J. D.; Herington, E. F. G. J. Chem. SOC. 1954,3188-3196. 1935, (27) Butler, J. A. V.; Ramchandani, C. N. J . Chem. SOC. 952-955. (28) Buttery, R. G.; Ling, L. C.; Guadagni, D. G. J.Agric. Food Chem. 1969,17, 385-389. (29) Hawthorne, S. B. Ph.D. Thesis, University of Colorado, Boulder, CO, 1984.
methylphenol, 108-6&9; 2,3-dimethylphenol, 526-75-0; 3,4-dimethylphenol, 95-65-8; 2,4,6-trimethylphenol, 527-60-6; 2,3,6trimethylphenol, 2416-94-6; 2,4,5-trimethylphenol, 496-78-6; acetone, 67-64-1; butanone, 78-93-3; 2-pentanone, 107-87-9; 3pentanone, 96-22-0; 2-hexanone, 591-78-6; cyclopentanone, 12092-3; 2-methylcyclopentanone,1120-72-5;3-methylcyclopentanone, 1757-42-2; 2-heptanone, 110-43-0; cyclohexanone, 108-94-1; aisophorone, 78-59-1; thiophene, 110-02-1; 2-methylthiophene, 554-14-3;3-methylthiophene, 616-44-4; benzene, 71-43-2; toluene, 10888-3; a-pinene, 80-568; camphene, 79-92-5;@-pinene,127-91-3; A3-carene, 13466-78-9; limonene, 138-86-3; hexane, 110-54-3; heptane, 142-82-5;octane, 111-65-9; nonane, 111-84-2;decane, 124-18-5; undecane, 1120-21-4;dodecane, 112-40-3; tridecane, 629-50-5;tetradecane, 629-59-4:ethylbenzene,100-41-4;rn-xylene, 108-38-3;p-xylene, 106-42-3; o-xylene, 95-47-6.
Literature Cited
- I
Bates, E. R.; Thoem, T. L., Eds. “EnvironmentalPerspective on the Emerging Oil Shale Industry”; EPA Oil Shale Research Group: Cincinnati, OH, 1981; EPA-600/2-80-205a. Hester, N. E.; Mester, Z. C.; Wang, Y. G. Environ. Sci. Technol. 1983,17, 714-717. Peterson, K. K., Ed. “Oil Shale: The Environmental Challenges HI”; Colorado School of Mines Press: Golden, CO, 1982. Gary, J. H., Ed. Oil Shale Symp. h o c . 1983, 16th. Gary, J. H., Ed. 011 Shale Symp. h o c . 1982, 15th. Gary, J. H., Ed. Oil Shale Symp. h o c . 1981, 14th. Hawthorne, S. B.; Sievers, R. E. Environ. Sci. Technol. 1984, 18,483-490. Hicks, R: E.; Probstein, R. F.; Farrier, D. S.; Lotwala, J.; Phillips, T. E. “Proceedings of the 13th Annual Oil Shale Symposium, Colorado School of Mines”; Colorado School of Mines Press: Golden, CO, 1980; pp 321-334. Hicks, R. E.; Probsbin, R. F. In “Oil Shale: The Environmental challenges 111”;Peterson, K. K., Ed.; Colorado School of Mines Press: Golden, CO, 1982; pp 87-109. Proposal for oil shale development submitted to the United States Synthetic Fuels Corp. by Union Oil Co.of California, 1980. Mackay, D.; Shiu, W. Y.; Bobra, A.; Billington, J.; Chau, E. C.; Yeun, A.; Ng,’C.; Szeto, F. U S . EPA Report EDA 600/S3-82-019, 1982, NTIS PB 82-230-939.
~
Received for review July 6, 1984. Revised manuscript received April 22,1985. Accepted May 1,1985. This research was supported by US.Department of Energy Contract DE-ACO283ER60121.
Development of a Dosimeter for Personnel Exposure to Vapors of Polyaromatic Pollutants Tuan Vo-Dlnh
Advanced Monitoring Development Groyp, Health and Safety Research Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 A new personnel dosimeter based on molecular diffusion and direct detection by rmm temperature phosphorescence (RTP) has been developed to monitor vapors of polynuclear aromatic (PNA) pollutants. The dosimeter is a simple, pen-size device that requires no sample extraction for analysis. By proper calibration of the dosimeters, the time-weighted average exposure to the pollutants can be determined directly on the sample collection substrate. The dosimeters can detect a variety of PNA compounds such as pyrene, phenanthrene, and quinoline at 2.5, 0.5, and 0.75 ppb vapor concentrations, respectively, after 1 h of exposure.
Introduction Occupational exposure to airborne polynuclear aromatic (PNA) pollutants is of great concern because many PNA species have been found to be carcinogenic in laboratory 0013-936X/85/0919-0997$01.50/0
animal bioassays (1). One important pathway of exposure is via inhalation of air particulates, aerosols, or vapors. Whereas extensive studies have been devoted to the detection of particulates, fewer studies have dealt with the problem of aerosol and vapor emissions. Conventional monitoring devices for personnel exposure developed to date are usually active devices that utilize a pump to draw air through a sorbent material. After sampling,the sorbent has to be sent back to the laboratory where the analytes are thermally or chemically desorbed and characterized by chromatography. A real-time monitor using a chemical ionization mass spectrometer has been developed to detect PNA in the vapor phase (2). This instrument, however, is not a simple personnel monitor but a sophisticated instrument transportable in a van and is used as an area monitor. In the past few years, a variety of passive monitors for organic vapor have been developed for personnel dosimetry
0 1985 American Chemical Society
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( 3 ) ;many devices are based on the pioneering work by Palmes and Gunnison ( 4 ) . Some of these vapor monitors operate via gaseous diffusion by using activated charcoal to absorb organic compounds. The organic vapors must be subsequently extracted from the charcoal with a suitable solvent, and the resulting solution is concentrated and analyzed by chromatography using procedures similar to those with active samplers. This paper describes the operating principle and performance of a new personnel dosimeter developed at the Oak Ridge National Laboratory (ORNL) to detect vapors and aerosols of potentially hazardous PNA pollutants (5, 6). The PNA dosimeter described in this work is a passive monitor that differs from most of the previous organic vapor monitors in several aspects. Previously developed passive monitors have been used mainly for simple gases or for low molecular weight species such as the monocyclic aromatic molecules and halogenated species. Sensitivity problems limit the use of these monitors for multiring PNA compounds. High molecular weight species such as the multiring PNA compounds generally occur at low vapor concentrations and cannot be detected as vapors with sufficient sensitivity by traditional chromatographic methods with extracted samples. The PNA dosimeter is designed to detect vapor concentrations of various multiring compounds at partper-billion (ppb) levels. The device employs the room temperature phosphorescence (RTP) technique for direct measurement of the amount of pollutants collected on the dosimeter, requiring no desorption or wet-chemical extraction procedure. After exposure, the dosimeter is inserted into a spectrometer for direct determination of the integrated vapor concentration of the pollutants being monitored. In this paper, the characteristics and performance of the dosimeter are described. The detection of vapors for various PNA compounds such as carbazole, phenanthrene, pyrene, and quinoline is discussed. An example of field measurements is presented to illustrate the usefulness of the dosimeter.
Basic Operating Principles and Design of the Dosimeter Basic Principle. The operating principle of the PNA dosimeter is based on the combination of three processes: (1)sample collection via a diffusion-controlled process, (2) adsorption of the analyte molecule on a solid substrate, and (3) direct detection by RTP. Principle of Sample Collection Mechanism. Sample collection of the dosimeter is based on molecular diffusion. A solid sorbent material is placed at the closed end (x = 0) of the tube while the open inlet of the tube (x = L ) is exposed to the ambient concentration, CA,of analyte vapor molecules. The heart of the PNA dosimeter is the sample collection sorbent that consists of a cellulosic material treated with chemicals. One of the unique features of this dosimeter involves the integrated utilization of the sample substrate as a sample holder for in situ detection, a sorbent medium for diffusion, and a phosphorescence inducer for direct measurement. The sorbent material maintains the concentration of the PNA compounds at the collection surface at zero or near-zero concentration, C,, while the air outside the dosimeter is at ambient concentration. A concentration gradient is therefore maintained, which serves as a driving force inducing the diffusion of the PNA molecules from the outside of the dosimeter onto the sorbent surface. the diffusion process can be described by Fick's first law: J
998
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where D is the diffusion coefficient of the PNA compounds (m2&), J is the diffusion flux (kg.m-2.s-1), and acid2 is the concentration gradient along the diffusion path (kg. m-4). At steady-state conditions and for an efficient sorbent material (i.e., C, 0), the mass of PNA compounds collected at the sorbent surface is given by
M = D(A/L)CAt (2) where M is the mass of the analyte collected by the dosimeter (kg), A is the cross-sectionalarea of the dosimeter (m'), t is the exposure time (s), and L is the length of the diffusion path (m). In the above equation, the expression D ( A / L ) ,which has the dimension of m 3 d , is often referred to as the sampling rate of the dosimeter. With a typical PNA dosimeter m, the sampling having A = 2.5 X 10" m2and L = 5 X m 3 d for organic compounds that have rate is -5 X a typical diffusion coefficient D 1 X r n 2 d (7). This slow sampling rate of only a few cm3.min-l minimizes the effect of ambient air movement, which is discussed in a subsequent section. It should be emphasized that passive dosimeters provide the integrated exposure but cannot yield temporal information for short-term fluctuations of the analyte vapor concentrations. The time-dependent diffusion equation, known as Fick's second law, should be considered for non-steady-state conditions (8, 9). A t steady-state conditions, a h e a r concentration gradient is established inside the sample, ranging from zero concentration at the sorbent surface to the ambient concentration at the tube inlet of the dosimeter. The time period, T,required to establish this steady-state gradient is usually defined as
-
T = k(L2/D) (3) where k is a constant between 0.5 and 1.5, depending on the different definitions of the time period (10, 11). Equation 3 indicates that the response time, T , of a passive monitor varies inversely with the diffusion coefficient and linearly with the square of the diffusion length. For the dosimeter that has 0.005-m diffusion tube length, the response time is about 3 s for a PNA compound that has a m 2 d . A slow time typical diffusion coefficient of 1 X constant can be one source of error for monitors with longer response times when the devices are used in atmospheres with rapidly fluctuating concentrations. Sample Adsorption. The molecules that diffuse through the tube are collected and adsorbed onto a solid substrate that also serves as a direct sample medium for RTP detection. The sorbent material is a filter paper treated with various heavy-atom salts such as cesium iodide, sodium bromide, thallium acetate, and lead acetate. Ideally, with an efficient sorbent material, the analyte concentration, C,, directly above the surface of the substrate should be zero. If C, is not zero but is lower than the ambient analyte concentration, a concentration gradient (C,-C,) is still maintained, but the sampling rate is reduced. The effectiveness of the adsorption process and the validity of the diffusion principle for this dosimeter will be discussed further in subsequent sections. Direct-Reading Detection by RTP Spectroscopy. The unique feature of this dosimeter is the dual mode of the heavy-atom salts that serves both as a sorbent agent and as an RTP inducer. A variety of heavy-atom salts have been found to increase the phosphorescence emission of many PNA compounds by several orders of magnitude (12-14). In general, the phosphorescence signals of PNA compounds in solution or in the gas phase are extremely weak at ambient temperatures. Because of its long lifetime
fective collection area of the dosimeter but has negligible effect upon the diffusion characteristics of the analyte molecules. The use of a windscreen is effective in preventing artifacts caused by turbulent mass transport in windy environments. One type of diffusion used in later versions of the dosimeter consists of a Teflon honeycomb tube that consists of parallel cylindric holes of 0.01-m diameter and 0.04-m length. The honeycomb decreases the effective value of A , and, therefore, the sampling rate, but increases the reproducibility of the method of sampling. With the honeycomb tube, it is not necessary to cover the open end of the diffusion tube with a windscreen since the honeycomb geometry can effectively prevent disruption of the diffusion process by ambient air movements. Most of quantitative measurements were conducted by using the dosimeters equipped with honeycomb tubes.
5c
(TI Figure 1. Schematic diagram of the PNA dosimeter design.
(lom3to several seconds), the phosphorescence emission is almost completely quenched by collisions with surrounding molecules present in solutions or in the air. Intramolecular vibrational and rotational deactivation processes are other possible mechanisms for phosphorescence quenching. For these reasons, conventional phosphorimetric techniques require the use of low-temperature sample matrices in order to protect the analyte molecules from quenching mechanisms. Due to the requirement of cryogenic equipment and refrigerant, conventional low-temperature phosphorimetry has limited usefulness for routine applications or field measurements. Unlike conventional phosphorimetry, RTP is a technique based on the phosphorescence from organic compounds absorbed on solid substrates at room temperature (12-21). It has been show that the adsorbed state of the analyk molecule on the solid substrate results in increased molecular rigidity, thus reducing collisional and rotational deactivation. Although a variety of solid substrates such as silica, alumina, paper, and asbestos can be utilized, fiiter paper is normally used in this laboratory because of its convenience, low cost, and applicability to a large variety of PNA species. The RTP technique for detection of PNA species has been recently reviewed in detail (21). The RTP procedures developed for analyzing the dosimeters are extremely simple since the dosimeters can be inserted into a detector for direct reading of the integrated exposure immediately after exposure. Dosimeter Design. The PNA dosimeter is a self-contained, badge-size passive monitor. The device weighs about 50 g and can be conveniently worn by a person or placed at a stationary location. Figure 1shows a schematic illustration of the dosimeter. The monitor is designed such that it is compatible with the spectrophotometer currently used for measuring the RTP signal. The dosimeter shown in Figure 1basically consists of a badge-size sample holder (B),a filter paper substrate (S), an interchangeable diffusion tube (TI, and an interchangeable screen device (not shown in Figure 1). The dosimeter body is a 5 cm long and 1.2 cm wide pen-size badge made of aluminum. The sample collection area is a circle having 0.6-cm diameter. The screen device serves to prevent air turbulence from affecting the diffusion process within the dosimeter. Several screen types were used, including a grid and honeycomb device. One type of diffusion tube used in an earlier design has the open end covered with a mesh metal grid that serves as a windscreen. The grid has square holes m2. The windscreen decreases the efof about 5 X
Instrumentation and Procedure Instrumentation. A Perkin-Elmer spectrophotometer (Model MPF-44A) equipped with a special laboratoryconstructed sample holder was used to detect the RTP signal directly from the dosimeter. A PNA vapor generation system and an exposure chamber were set up to study the diffusion-controlled processes and to conduct vapor calibration experiments for various PNA compounds. The dynamic method was used for generating gas and vapor test atmospheres (22). Liquid solutions having known concentrations of analyk were injected, evaporated, and mixed into a carrier gas stream via a syringe injection device controlled by a moving synchronous motor. The vaporization of the liquid was controlled by use of a heating coil regulated by a transformer. A circular platform rotated by a stepping motor controlled by a microprocessor unit (AIM65, Rockwell International) was designed to conduct experiments for air velocity studies. The conditions for air movements were investigated by conducting exposure experiments with the dosimeter placed on the rotating platform. The details of these devices will be described elsewhere (22). Chemicals and Reagents. The filter paper used to prepare the sample collection material was purchased from Schleicher & Schuell (type 2043A). All chemicals were commercially available. Spectroscopic-grade ethanol was used as the solvent. The coal liquid material used to produce vapor was from the H-Coal Liquefaction Plant in Cattletsburg, KY. Field evaluations of the dosimeters were conducted at a coal liquefaction pilot plant operated by Ashland Synthetic Fuels, Inc., for the Department of Energy. Procedure for Preparing, Exposing, and Analyzing the Dosimeter. (1) Laboratory Experiments. The procedures for exposing and analyzing the dosimeter were simple since no extraction or desorption was required. The dosimeters were prepared by impregnating the filter paper disk with solutions of heavy-atom salt. The treatment consisted of spotting a 3-pL solution of heavy-atom salts on the filter paper substrate and letting the substrate dry under an infrared lamp. Only a 3-5-min drying time was required to dry the paper substrates on the dosimeters. In general, a saturated solution of ethanol-water (1/1v/v) containing lead acetate (1M) and thallium acetate (1M) was used to treat the substrates. These two heavy-atom salts have been found to be most effective in producing the strongest RTP signals for most PNA compounds investigated (21). Several studies of the effect of heavy-atom sdts for different polyaromatic hydrocarbons adsorbed on paper found that the RTP intensity increased in the following order of added heavy atoms: T1+ > Ag+ > Pb2+> Environ. Sci. Technol., Vol. 19, No. 10, 1985
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Figure 2. RTP spectrum of pyrene vapor (solid curve) detected on the dosimeter after 1-h exposure at 10 ppb. RTP background from fitter paper is shown as the dashed curve.
Hg2+(12,13,21). Silver nitrate was often used for spectroscopic studies but was found unsuitable for the dosimeters because this heavy-atom salt is often photochemically not stable and darkens the paper after the drying process. We have selected the mixture of thallium and lead acetate for this study because these two heavy-atom salts were found to provide the best results for a wide variety of PNA compounds investigated (12,21). Note that Hg2+salt was recently found to be very specific for nitrogen-containing PNA compounds (23). After being dried, the dosimeters were placed in a vapor generation chamber for exposure studies. After exposure, the dosimeters were inserted into a spectrometer for direct reading of the RTP signal. A flow of dry air is also flushed through the sample compartment during RTP analysis to keep the sample dried. The flow of dry air sufficiently removed moisture from the dosimeters after about 5 min. (2) Field Evaluations. For field evaluation, the dosimeters were prepared in this laboratory and kept enclosed in small plastic vials tightly closed by protective caps. Each monitor was numbered for identification. The dosimeters were generally sent by air mail to the agency or industry that had requested or agreed to the field study. The personnel at the field location were instructed to expose the monitors by attaching them to the workers or to place them in locations of interest. The beginning and ending times of exposure were recorded along with other relevant information including temperature, humidity, and wind velocity. For every field study, at least one set of three dosimeters was kept unexposed to serve as blank samplers. After exposure, the dosimeters were placed in their vials and mailed back to this laboratory for analysis. Upon receipt of the vials, the dosimeters were removed and inserted directly into a spectrphotometer for RTP detection of the dosimeter responses. In general, the dosimeters can be analyzed during the same day of their arrival at the 1000
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Figure 3. RTP signal detected by the dosimeter exposed to vapors emitted from an H-Coal product.
laboratory. The time interval between the time the sampling was concluded, and the time the dosimeters were actually analyzed was generally about 3 days. The dosimeter RTP signals were compared to preestablished calibration curves to obtain the total integrated exposure.
Results and Discussion Direct Detection of Polyaromatic Vapors by RTP. Measurements were conducted to detect vapors of a variety of PNA compounds, including acridine, chrysene, fluorene, phenanthrene, and pyrene. Figure 2 depicts the RTP spectrum of pyrene vapor detected from the dosimeter after an exposure of only 1 h in the exposure chamber containing pyrene at equilibrium vapor concentration of 10 ppb. The excitation wavelength used was 343 nm. The RTP spectrum of pyrene vapor is identical with that observed for pyrene from solutions spotted on filter paper after solvent evaporation. No spectral shift or structural changes were noticed. This feature is of great convenience for analytical studies since a wealth of spectral data on RTP from previous studies can be utilized as references for vapor detection investigations (21). Figure 3 shows the spectral response from the PNA dosimeter exposed for 1 h at ambient temperatures in the exposure chamber containing saturated vapor of an H-Coal coal liquefaction product. As shown in this figure, the presence of pyrene can be clearly detected in the vapors emitted by a complex sample such as a coal liquid product. This result opens the possibility of using the dosimeter to detect selected target compounds in a complex atmosphere such as vapor from a coal liquid product. Studies of the Dosimeter Response. Calibration measurements were conducted with a variety of PNA compounds such as pyrene, quinoline, and carbazole. The
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Flgure 4. Dependence of the dosimeter response upon the length of the diffusion path for pyrene vapor.
Figure 5. Experimental verification of the linear relationship between the sample uptake of the dosimeter and the inverse of the diffusion path for quinoline vapor.
results demonstrated that the dosimeter can be designed to produce a response linear to the exposure time for over 10 h under saturated equilibrium vapor conditions. This feature is important for industrial hygiene applications where daily occupational exposure of workers for 8-h workday shifts is generally monitored. The design of the dosimeter diffusion tube can be modified to increase or decrease the dynamic range of the dosimeter response curve. For example, for a compound that has a high vapor pressure, saturation of the dosimeter signal may occur, causing deviation in the linearity of the response curve. One cause for this nonlinearity may be the saturation of the adsorption sites on the collection substrate after extended exposure periods. Saturation occurs as fewer and fewer sites are available for adsorption. With the higher concentration gradient, the diffusion process becomes faster and the saturation will occur sooner. In such a situation, one possible means to extend the linear range of the dosimeter response is to decrease the concentration gradient by increasing the length of the dosimeter tube. The response time of the dosimeter, however, is increased with a longer diffusion tube. Verification of the Diffusion Law. One purpose of this work is to verify that the sampling rate of the dosimeter is diffusion controlled. Since mass transport of the analyte molecules through ambient air onto the dosimeter may also occur via natural convection or simple mass deposition rather than via a diffusion-controlled process, measurements were conducted to test the applicability of Fick’s first law of diffusion at steady-state conditions. Figure 4 shows the dosimeter response as a function of the length of the diffusion tubes used in various dosimeters exposed to identical conditions of pyrene vapor of 4 ppb vapor concentration. The results shown in this figure are in excellent agreement with the theoretical prediction expressed in eq 2 that states the amount of analyte collected on the dosimeter is inversely proportional to the diffusion path length. To further demonstrate the applicability of the diffusion principle, similar experiments were performed with quinoline as another model compound. Figure 5 is a graph of the dosimeter response plotted vs. the inverse of the tube length after 1 h exposure to 700 ppb of quinoline vapor. The results, which show the linearity between the inverse of the tube length and the dosimeter signal intensity, further underscore the applicability of the diffusion process occurring within the device. The straight line established in this graph is determined by a least-squares fitting
procedure and provides a correlation coefficient of 0.994, thus underscoring the validity of the diffusion process expressed by Fick’s first law. Sorption Properties and Stability of the Dosimeter Response. A unique feature of the dosimeter is the use of the heavy-atom salt on the filter paper substrate not only as a phosphorescence enhancer but also as a sorbent material for the analyte molecules. Whereas the phosphorescence enhancement properties of heavy-atom salts have been investigated (21,and references therein), there has been no study dealing with the role and stability of the heavy-atom salts to retain the analyte molecules. In many field tests, the dosimeters were prepared, then exposed at a given location, and finally sent back to the laboratory for analysis. For this reason, it is important to investigate the stability of the dosimeter signal with time before and after exposure. Several seta of dosimeters were prepared on different days over a period of 3 weeks and exposed to given vapor concentrations of pyrene under identical conditions of temperature and humidity. Before exposure the dosimeters were kept in light- and air-tight plastic vials. The responses measured from these different sets of dosimeters were found to be similar within the typical 15-25% relative standard deviation. To investigate the effect of storage time after exposure, several sets of dosimeters were exposed to pyrene vapors and stored over a period of 1week before analysis. These dosimeters were then analyzed at regular intervals to determine the temporal behavior of their response. Figure 6 illustrates the results obtained over a 2-day period for two sets of dosimeters exposed to 200 and 300 ppb X h of pyrene vapor. The data collected for a 2-week experiment indicate that the pyrene molecules were efficiently retained on the dosimeters over a time period of 2 weeks. The results of the retention studies show that the sorbent acts as an efficient collector for the analyte. This feature confirms that the dosimeters for pyrene are sufficiently stable for weeks and can be mailed, exposed, and returned to the laboratory for analysis within 2 weeks without special precautions. The stability of the dosimeters for longer time periods (6 months or longer) are under investigation for a variety of other PNAs. Effect of Air Movement. In general, the performance of passive dosimeters may be affected by the air movement or absence of air movement around the device. Whereas turbulent air movements may create non-ideal and nonsteady-state conditions, stagnant air may result in error of sampling due to creation of a depletion layer of the Envlron. Sci. Technol., Vol. 19, No. 10, 1985
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Table I. Limit of Detection (LOD) of the Passive Dosimeter for Vapors of Several Polynuclear Aromatic Pollutants
PYRENE RETENTION CURVE
compound carbazole phenanthrene pyrene quinoline
A’,
nm
nm 295 295
415 475
343 320
510
LOD,’ppb X h 0.5 0.5 2.5 0.75
598
A,, = excitation wavelength. * A.pl = emission wavelength. CTheheavy-atom salt used was a mixture of lead acetate and thallium acetate.
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Figure 6. Stability of the response to two sets of dosimeters exposed to 200 and 300 ppb X h of pyrene vapor.
analyte molecules in the air space adjacent to the inlet of the dosimeter tube. This depletion process has the effect of decreasing the actual analyte concentration in the ambient air, causing a decrease in the concentration gradient, which is the driving force of the diffusion process. This may result in an actual sampling rate lower than expected. To study the effect of air velocity, measurements were conducted by placing the dosimeters in the exposure chamber on a rotating platform at various distances from the central shaft. When the platform was rotated at a constant speed, the air velocity experienced by each dosimeter was determined by the circular distance traveled by the dosimeter over the rotation period. The results obtained with dosimeters exposed to 200 ppb X h of quinoline vapor at three different velocities (0.04,0.12, and 0.24 ms-l) indicated no significant effect on the sampling rate of the dosimeter within the 15-25% relative error limit. Depletion effects caused by low air velocity should, therefore, not significantly affect the performance of the dosimeter since air velocities normally encountered by personnel dosimeters are typically higher (-0.5 ms-l) (24). Specificity, Sensitivity, and Field Applications. The dosimeter can detect a variety of PNA species. Both the general applicability and the specificity of these monitors benefit from the versatility and selectivity of the RTP detection technique. As an emission technique, RTP offers the selection of both the emission and excitation wavelength. The RTP technique is also a very sensitive technique that can detect many PNA compounds at subnanogram levels. Since the dosimeters utilize a direct detection technique, no sample handling loss can occur. All these factors contribute to make the dosimeters suitable to detect PNA vapors that usually occur at low concentrations (ppb levels) not easily detected by other techniques. Table I gives some typical detection limits for several PNA compounds for 1-h exposure time. During the last 2 years, the PNA dosimeters have been evaluated during several field trips at various DOE synfuel production pilot plants. The dosimeters were able to detect a variety of airborne pollutants such as pyrene, phenanthrene, fluorene, and quinoline under actual field conditions. Figure 7 illustrates the results obtained during a field evaluation at a coal liquefaction plant. The figure shows the RTP signals of two sets of dosimeters exposed at two different locations inside the plant. Three dosim1002
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Figure 7. Detection of pyrene vapor by the dosimeters during a field test at a coal liquefaction plant.
eters were used per set; the variation of the dosimeter responses was typically 15%. The response of the dosimeters exposed in a clean room (location B) showed a broad RTP emission. This emission was similar to that of the paper substrate background emission of an unexposed dosimeter, thus indicating that the location exhibited no detectable levels of PNA compounds. In contrast, the dosimeters exposed at location A revealed the predominant presence of pyrene detected at 20 ppb vapor concentration level. This example illustrates the usefulness of the dosimeter for direct detection of PNA pollutants under real-life conditions.
Conclusions The use of personnel monitors is essential in the quantification of human exposure for health protection, epidemiological, and regulatory purposes. Whereas active samplers can provide real-time detection of hazardous pollutants, these devices often are not the most practical and economical choice for monitoring individual exposure to airborne pollutants. Passive dosimeters offer the advantages of lower capital expense, simplicity, and compactness. The dosimeter described in this work shows that the combination of molecular diffusion and phosphorescence processes provide a valuable tool for monitoring personal exposures to PNA pollutants that can provide critical information needed to assess the health implications of exposure to these compounds. The sensitivity and low cost of the device make it suitable for routine monitoring of PNA pollutants in the ambient atmosphere of workplace environments. The PNA monitors have recently
been field tested at an H-coal liquefaction plant in the and a synfuel process development unit United States (25) in England. The PNA monitor has also been evaluated side-by-sidewith several charcoal-basedpassive dosimeters commercially available, and the results indicate that the PNA dosimeter is at least 1 order of magnitude more sensitive for detecting quinoline. The detailed results of this study will be given in a forthcoming communication (26). Registry No. Lead acetate, 15347-57-6; thallium acetate, 15843-14-8;carbazole, 86-74-8; phenanthrene, 85-01-8; pyrene, 129-00-0;quinoline, 91-22-5.
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Environ. Scl. Technol., Vol. 19,
No. 10, 1985 1003
