Environ. Sci. Technoi. 1992, 26, 1737-1746
Multisorbent Thermal Desorption/Gas Chromatography/Mass Selective Detection Method for the Determination of Target Volatile Organic Compounds in Indoor Air Davld L. Heavner,” Michael W. Ogden, and Paul R. Nelson R. J. Reynolds Tobacco Company, Research and Development, Wlnston-Salem, North Carolina 27 102
A thermal desorption/gas chromatography mass selective detection method using Tenax and Larhotrap multisorbent cartridges for the determination of 28 target volatile organic compounds (VOCs) is described. Techniques used for method validation include determination of limit of detection, limit of quantitation, repeatability, room temperature storage stability, breakthrough volume, and sampler collection efficiency. In addition, 3ethenylpyridine (3-EP), a pyrolysis product of nicotine, is investigated as a suitable marker for environmental tobacco smoke (ETS). Experiments conducted in an environmental chamber at five different ventilation rates are used to determine 3-EP ratios to selected VOC analytes. These ratios are used to apportion the contribution of ETS to indoor air VOCs. Field results from four smoking and four nonsmoking homes are presented to illustrate the ETS apportionment technique. Selected analyte apportionment indicates that ETS contributes a fraction of the target VOCs in homes with smoking activity. Introduction Interest in analytical methods for the quantitation of volatile organic compounds (VOCs) in nonindustrial indoor air environments has increased dramatically in the last 5 years due to several factors: (1)a heightened awareness of emissions from sources such as gas stoves and furnaces, kerosene heaters, oil furnaces, environmental tobacco smoke (ETS), new clothing, cleaning products, deodorizers, pesticides, cosmetics, perfumes, building materials, carpet, new furniture, and automobile exhaust; (2) a trend toward reducing uncontrolled infiltration and controlled ventilation rates in order to curb rising energy costs; and (3) general public concern regarding long-term exposure to chemicals at home and at work. This interest has resulted in the publication of numerous analytical methods, chamber studies, and field studies to identify and quantify VOCs in indoor air environments (1-22). Because the concentration of VOCs found in public buildings and private homes is generally 2-3 orders of magnitude lower than that found in industrial environments, more sensitive sampling and analytical techniques are required. Historically, most sample collection and analytical techniques are based on liquid impinger collection (23),passivated canister collection (9,10,24), and passive or active sorbent collection with solid adsorbents such as Tenax (1-4, 6, 8, 11-18, 20-221, Carbotrap (4), activated carbon (3,6-8,19), or graphitized carbon (3,4, 6,B). The most popular method used today for monitoring VOCs in ambient indoor air is active sorbent sampling with thermal desorption preconcentration prior to analysis. Glass or stainless steel cartridges are packed with a solid adsorbent and connected to small, portable, battery-operated pumps for personal or area air sampling. For years, the adsorbent of choice for active VOC sampling has been Tenax GC or, more recently, Tenax TA. Tenax is a well-characterized, general purpose porous polymer based on 2,6-diphenyl-p-phenyleneoxide (5,25, 26). Unfortunately, Tenax collection efficiencies for low 0013-936X/92/0926-1737$03.00/0
molecular weight, volatile compounds less than or equal to C6 are often unacceptable for quantitative purposes. Therefore, researchers have turned to the use of “multisorbent”cartridges containing Tenax and other solid adsorbents suitable for collecting the more volatile compounds in indoor air (3, 4, 6, 8). The purpose of this study is threefold: (1)to validate the use of a multisorbent sampler (Tenax and Carbotrap) and thermal desorption/gas chromatography/mass selective detection (TD/GC/MSD) for the collection and quantitation of 28 target VOCs in indoor environments; (2) to evaluate the potential of 3-ethenylpyridine (3-EP) as a vapor-phase ETS marker; and (3) to investigate application of the technique for apportionment of selected ETS VOCs in indoor air. The validation includes experimenb for determining room temperature storage stability, breakthrough volumes, collection efficiencies, limits of detection and quantitation, and repeatability. Application of the sample collection and analysis techniques is demonstrated in a chamber study where environmentaltobacco smoke (ETS) is the sole source of VOCs. Results from the chamber study are used to generate 3-EP/VOC ratios that provide the capability of apportioning the contribution of ETS to target VOC levels.
Experimental Methods Materials and Chemicals. Stainless steel cartridge tubes (3.5 in. X 0.25 in. 0.d.) were obtained from PerkinElmer Corp. (Norwalk, CT). Each cartridge was packed with 160 mg of Tenax TA 60/80 mesh (Alltech Associates, Deerfield, IL) followed by 160 mg of Carbotrap 20/40 mesh (Supelco Inc., Bellefonte, PA). Therefore, each cartridge contained a total of 320 mg of adsorbent. Three stainless steel wire mesh screens were inserted into the cartridge: one between the two adsorbent beds and one on either end of the cartridge. A piece of silanized glass wool and a stainless steel spring were inserted behind the Carbotrap bed in order to maintain sorbent bed integrity during sampling. After preparation, the sorbent cartridges were conditioned in a 14-tube thermal conditioner, obtained from Nutech Corp. (Durham, NC), at 280 “C overnight (approximately 16 h) with a helium flow of 10-30 mL/min per cartridge. After conditioning, the cartridges were capped with Perkin-Elmer aluminum O-ring storage caps and placed in individual 25 X 150 mm glass culture tubes fitted with Teflon-lined screw caps. Thus, all cartridges were double-sealed in order to prevent contamination prior to use. The multisorbent sampler was prepared for sample collection by connecting two identical Tenax/Carbotrap cartridges in series with a modified outer-flanged analytical end cap (screen and ball removed) purchased from Perkin-Elmer Corp. Therefore, each multisorbent sampler contained a totalof 640 mg of adsorbent. Air flow through the multisorbent sampler was generated by a Model 222-4 “low-flow” diaphragm pump (SKC South, Appomattox, VA) at 50-80 mL/min such that the sample made contact with Tenax and Carbotrap in order on the “front” cartridge followed by Tenax and Carbotrap in order on the “back” cartridge.
0 1992 American Chemical Society
Environ. Sci. Technol., Vol. 26, No. 9, 1992
1737
All chemicals for preparation of analytical standards were obtained from Aldrich Chemical Co. (Milwaukee,WI) with the exception of the n-alkanes (Polyscience Corp., Niles, IL) and 1,2-dichloroethane(Sigma Chemical Co., St. Louis, MO). Stock VOC target standard solutions (w/v) were prepared by dilution with n-hexane (Burdick & Jackson, Muskegon, MI). Six concentration levels of working standard solutions were prepared, ranging nominally from 10 to 400 ng/pL. The internal standard (ISTD), 1-undecene, was added to each working standard solution at a concentration of 245 ng/pL. A separate internal standard working solution for spiking field and chamber sample cartridges was prepared at a concentration of 245 ng/pL. Stock and working standards were stored at -10 "C when not in use. Also, field and chamber sample cartridges were stored at -10 "C prior to spiking with the internal standard and subsequent GC/MSD analysis. Apparatus. Cartridges used for calibration were fitted to a Hewlett-Packard Co. (Palo Alto, CA) Model 5880 GC 1/4-in.injection port held at 150 "C with a helium flow of 50 mL/min. A Hamilton Co. (Reno, NV) Model 7101 syringe equipped with a Chaney adaptor was used to inject 1.0 pL of each VOC target standard solution with internal standard onto individual cartridges. Chamber and field sample cartridges were treated in a similar manner with 1.0 pL internal standard solution spikes. After 1min, the cartridges were removed and fitted with Perkin-Elmer outer and inner analytical end caps. To prevent order effects during analysis, all sample and standard cartridges were placed in random order onto the thermal desorption unit sample carousel. Thermal desorption was achieved with a Perkin-Elmer Model ATD-50 automatic thermal desorption unit capable of processing 50 cartridges sequentially in an unattended mode of operation. The ATD-50 was fitted with a multiple splitter assembly to provide cold trap inlet and outlet splitting capabilities. Cartridges were thermally desorbed in the reverse direction to sample flow. The ATD-50 conditions were as follows: desorption temperature, 250 "C; transfer line/box temperature, 150 "C; U-tube trap temperature (low),-30 "C; U-tube trap temperature (high), 300 "C; U-tube trap adsorbent, 40 mg Tenax TA (60/80 mesh); column head pressure, 30 psig; desorption flow, 50 mL/min; desorption time, 10 min; inlet split vent, closed; outlet split vent, closed 50 s during trap fire then 10 mL/min; outlet purge vent, closed. The ATD-50 desorber was coupled to a Hewlett-Packard Model 59940A MS Chemstation (HP-UX series) consisting of a Model 5890A gas chromatograph and a Model 5970B mass selective detector. The thermal desorber, the gas chromatograph, and the mass selective detector were interfaced with remote "ready* and remote "start" cables in order to fully automate the system for complete, unattended operation. The GC conditions were as follows: carrier gas, helium grade 5.0; linear velocity, 29 cm/s at 100 "C; flow, 0.80 mL/min at 100 "C;capillary column, 60 m X 0.25 mm DB-WAX fused silica column with a 0.5-pm film thickness (J&W Scientific, Rancho Cordova, CA); oven temperature, 40 "C (hold 6 min), then 3 "C/min to 142 "C, and 30 "C/min to 240 "C (hold 10 rnin). The MSD conditions were as follows: interface temperature, 250 "C; interface type, capillary direct; solvent delay, 7 min; electron multiplier, 2000-2400 V; total ion scan range, m/z 40-250; acquisition mode, 2.28 scans/s; manual tune masses, m / z 69, 131, and 219. Characteristic ions for "postrun" selected ion monitoring (SIM) were chosen for each target compound based upon relative abundance, individuality, and GC retention time. Characteristic ions 1738 Envlron. Scl. Technol., Vol. 26, No. 9, 1992
Table I. Selected Ion Monitoring (SIM) Characteristic Ions and Summary Experimental Results for Repeatability, Limit of Detection (LOD), and Limit of Quantitation (LOQ) for 28 Target VOCe compound n-nonane benzene n-decane trichloroethylene tetrachloroethylene toluene 1,2-dichloroethane n-undecane ethylbenzene p-xylene m-xylene isopropylbenzene o-xylene pyridine n-dodecane limonene n-propylbenzene 2-picoline 1,3,54rimethylbenzene styrene n-tridecane 3-picoline 4-picoline n-butylbenzene 1,2,3-trimethylbenzene 3-ethylpyridine 1,4-dichlorobenzene 4-ethenylpyridine 1-undecene
charac ion, % RSD LOD, LOQ, (pooled) ngfsample ng/sample mlz 43 78 57 130 166
4.99 5.35 3.59 5.14 3.96
1.09 1.26 1.25 1.59 0.91
3.65 4.20 4.17 5.30 3.05
91 62 57 91 91 91 105 91 79 57 68 91 93 105
5.46 5.55 3.62 1.37 1.60 1.83 1.52 1.71 10.25 6.25 3.00 1.67 2.71 1.41
2.12 3.12 1.47 0.57 0.11 1.04 0.09 0.27 0.93 3.37 1.73 0.36 1.41 0.18
7.05 10.40 4.90 1.90 0.35 3.45 0.30 0.90 3.10 11.24 5.75 1.20 4.70 0.60
104 57 93 93 91 105
2.08 5.50 3.51 4.56 1.30 1.49
0.81 0.59 1.58 2.04 0.47 0.78
2.70 1.97 5.25 6.80 1.55 2.60
92 146
4.40 2.12
3.21 0.78
10.70 2.60
105 55
5.11
2.46
8.21
(ISTD)
chosen for each analyte are listed in Table I.
Results and Discussion Ideally, any method for VOC determinations should include calibration for all compounds present in indoor air, however, this would be prohibitively time consuming and expensive, if not impossible. Instead, most researchers select a representative list of target VOC compounds for routine analysis. For this work, target VOC selection criteria were based on several factors: (1)the prevalence of a compound in indoor air environments; (2) the frequency that a compound has been used as a target analyte by other investigators; (3) the potential for a compound to act as a tracer for specific consumer products such as petroleum-based solvents, deodorizers and air fresheners, cigarettes, paints, lacquers, varnishes, etc.; and (4) the presumed potential for a compound to induce health effects upon long-term exposure (1-4,6,8,9,11-19,21-24, 2 7-30). A typical chromatogram of a VOC target standard solution (level six) is presented in Figure l. The baseline rise between 16 and 18 min is due to the desorption of a small amount of water vapor trapped by the Tenax/ Carbotrap adsorbent bed. Although several compounds are coeluting, the characteristic ions for these compounds are deconvoluted by the SIM analysis technique. In the standard solution chromatogram, 4-ethenylpyridine is found a t a retention time of approximately 38 min; however, 3-ethenylpyridine is the predominant nicotine pyrolysis product found in ETS (31,32). For calibration purposes, 3-ethenylpyridine is not commercially available; therefore, 4-ethenylpyridine is used as the calibrant since
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Figure 1. Total ion chromatogram of a thermally desorbed VOC target standard solution cartridge spike.
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Flgure 2. Total Ion chromatogram of a 9.0-L thermally desorbed sample from a smoker's home. The inset scan at 38.15 mln demonstrates the presence of 3-ethenylpyrldineas a vapor-phase marker for ETS.
the mass fragmentation patterns are similar (32). A typical chromatogram of an air sample from a smoker's home is presented in Figure 2. The peak at
approximately 15 min is toluene and is the predominant VOC found in this home. The inset scan from the peak at 38.15 min illustrates the mass fragmentation of 3Environ. Scl. Technol., Vol. 26, No. 9, 1992 1730
ethenylpyridine. As a potential marker of vapor-phase ETS, 3-ethenylpyridine is found in this sample at a concentration of 2.9 hg/m3. In our laboratory, 3-ethenylpyridine (as well as pyridine and other substituted pyridines) has been used as a vapor-phase marker of ETS for several years. An atmospheric pressure chemical ionization mass spectrometer and XAD-4 sorbent tubes coupled to an environmental chamber have been used to routinely monitor the concentration and decay behavior of 3ethenylpyridine in ETS (32-34). LOD, LOQ, and Repeatability. Summary experimental results for determining limit of detection (LOD), limit of quantitation (LOQ), and repeatability (RSD) of the 28 target VOCs are reported in Table I. In practice, LOD is defined as the lowest amount of a compound that a method can reliably detect, whereas LOQ is defined as the lower limit for precise quantitative measurements; repeatability is defined as the within run relative precision of the measurements (35,36). In order to determine LOD, LOQ, and RSD for the VOC method, the procedure of Taylor (37) was used, where a sufficient number of replicates (in this case, eight) at various concentrations (in this case, six) are required to calculate these parameters. For this experiment, all six levels of VOC target standard solutions were selected for cartridge spikes (1.0 pL/cartridge) with eight replicate cartridge spikes per level. All 48 cartridges were randomly placed in the ATD-50 carrousel, desorbed, and analyzed. With the Taylor procedure, the LOD is further defined as 3s0, and the LOQ is defined as lOsowhere so is the standard deviation at zero amount of analyte or the minimum detectable limit (MDL) at 95% confidence. The mean amounts at the four lowest levels are plotted versus their respective standard deviations to obtain so by extrapolation of the least squares regression line. Only the four lowest levels are used to determine so in order to maintain the extrapolation distance near the zero amount. If the extrapolation distance becomes too great, then significant error may be introduced into the measurement since the higher levels have a greater effect on the y-intercept of the regression line. The RSD is further defined as lOOs/x, where s is the standard deviation and x is the mean of the eight replicates at a given amount level. The "pooled" RSD for each VOC is then defined as the mean of the RSDs determined at each amount level. In Table I, all of the 28 target VOCs demonstrate good precision with RSDs less than 7%, with the exception of pyridine (10.3%). The LODs and LOQs reported in Table I as nanograms per sample may be converted to micrograms per cubic meter by dividing with the sample volume in liters. Therefore, for n-nonane, a 3.65 ng/sample LOQ is equivalent to 0.37 hg/m3 for a 10-L sample volume. Room Temperature Storage Stability. In order to maintain sample integrity, chamber sample tubes are routinely stored in a laboratory freezer at -10 "C immediately following collection. Field samples are placed in a freezer at the site or kept on dry ice upon receipt of the sample and during transport to the laboratory. Therefore, under ideal conditions, sample cartridges are kept at reduced temperatures to prevent VOC loss; however, samples may occasionally remain at room temperature for some time. In order to evaluate the room temperature storage stability of samples, an experiment was designed to determine the magnitude of VOC sample loss that might occur over abnormally long periods of time at room temperature conditions. For this experiment, four levels of VOC target standard solutions (levels 2,4,5, and 6) were selected for cartridge 1740
Environ. Sci. Technol., Vol. 26, No. 9, 1992
Table 11. VOCs with Significant ANOVA p Values in Test for Linear Trends from 4-Week, Room Temperature Storage Stability Experiment
compound
parameter
VOC target std soln cartridge spike level 2 level 4 level 5 level 6
n-nonane
slope y-intercept p value n-undecane slope y-intercept p value p-xylene slope y-intercept p value o-xylene slope y-intercept p value 1imonen e slope y-intercept p value 2-picoline slope y-intercept p value 1,3,5-trimethylslope benzene y-intercept p value n-tridecane slope y-intercept p value slope 3-ethylp yridine y-intercept p value 4-ethenylpyridine slope v-intercerd p value
1.75 113.03 0.0315 2.08 133.4 0.0177 0.207 22.09 0.0258 0.245 23.52 0.0102 -0.598 -1.043 -2.027 -2.153 23.07 45.99 115.05 185.97 0.0391 0.0015 0.0014 0.0024 0.483 27.46 0.0127 0.256 25.01 0.0011
2.264 3.777 2.937 17.72 33.53 94.79 0.0035 0.0194 0.0003 -0.523 54.47 0.0300 -3.553 293.92 0.0144
spikes (1.0 pL/cartridge). Three replicate cartridges were spiked for each level and each week (weeks 0-4) for a total of 60 sample cartridges. The cartridges were capped, placed in Teflon-lined screw-cap tubes, and stored in the laboratory at room temperature (approximately 22 "C). Twelve sample cartridges were desorbed and analyzed each week from week 0 to week 4. Using SAS software (SAS Institute Inc., Cary, NC), a one-way analysis of variance (ANOVA) was performed at each level for each VOC to test for linear trends. VOCs with significant slopes are reported in Table I1 with corresponding y-intercepts and ANOVA p values. Three patterns emerge: (1) 18 of the VOCs demonstrate no statistically significant effect of room temperature storage at any of the four levels; (2) 7 of the VOCs demonstrate a significant increase in amount from week 0 to week 4 for at least one of the levels; and (3) 3 of the VOCs demonstrate a significant decrease in amount from week 0 to week 4 for at least one of the levels. By referring to Table 11, the loss or gain of VOC mass per week for a specific VOC level may be found from the slope parameter; the starting concentration at week 0 may be found from the y-intercept parameter. For example, limonene mass loss for each week at the four levels is 0.6, 1.0, 2.0, and 2.2 ng, respectively. In relative terms, this amounts to 4-week losses of 10.4, 9.1, 7.0, and 4.6%, respectively, for the four levels. Since the other VOCs do not demonstrate consistent storage effects at all levels, positive or negative, the overall storage stability for these compounds is acceptable. However, any long-term elevated temperature storage would affect limonene results and should be considered problematic. The 4-week room temperature storage experiment presented here is designed to represent a "worst-case" situation; routine procedure calls for immediate placement of cartridges into a freezer or on dry ice. It is unlikely that any sample cartridge
would remain at elevated temperatures for periods greater than 1-2 days. However, should that situation occur, corrections may be made based on the experimentally determined storage loss or gain. Breakthrough Volumes. Adsorption on Tenax is due to localized negative charges from the aromatic 7r electrons and the lone pair of electrons at the ether oxygen. Tenax is widely accepted as an adsorbent for thermal desorption techniques in air and water analyses due to its relatively high thermal stability, its ability to trap a broad range of compound classes, its adsorption and desorption efficiencies, its hydrophobicity, and its ability to be reused for subsequent multiple collections after thermal desorption and conditioning (26). However, the main drawback to Tenax is the relatively low breakthrough volumes exhibited for low molecular weight VOCs. Carbotrap is a graphitized carbon black without localized charges; therefore, Carbotrap’s entire surface is available for interaction. Carbotrap is also relatively hydrophobic, free of contaminants, and amenable to thermal desorption (38). In order to evaluate the acceptability of these adsorbents in a multisorbent sampler, the breakthrough volume must be considered. Breakthrough volume is normally determined by either of two methods, frontal analysis or elution analysis (25). In frontal analysis, the adsorbent is challenged with a steady-state concentration of the adsorbate; therefore, the sample introduction is presented over a long period of time. In elution analysis, the adsorbate is injected onto the adsorbent, followed by passage of a gas through the adsorbent to simulate sampling. The breakthrough volume in either analysis is normally defined as Vg,the volume of gas per gram of adsorbent at the experimental temperature corresponding to the elution of 50% of the adsorbate. Breakthrough volumes are often reported by the manufacturer or vendor of a particular adsorbent (26,39);however, interlaboratory comparison of adsorbent combinations is difficult. Therefore, on-site breakthrough volume determinations for specific multisorbent configurations are preferable to relying on results determined elsewhere. A modified elution analysis technique was used to evaluate breakthrough volumes for the multisorbent sampler (two cartridges in series) in this experiment. Instead of challenging the adsorbent bed with a one-component adsorbate, the front cartridge was injected with 1.0 pL of a VOC target standard solution (level five) in the gas phase. A back cartridge was connected to the front cartridge as described in the experimental section, and a “low-flow” pump was attached to simulate sampling. Then, the multisorbent sampler was connected to a 10-port stainless steel manifold through which approximately 2 L/min of clean, dry air was flowing. With 10 sample trains connected at flows of 60-80 mL/min each, excess manifold flow was 1200-2000 mL/min. Glass fiber filters were placed a t either end of the manifold to provide pressure drop resistance to diffusion of volatiles from the laboratory surroundings. All pumps were started simultaneously, and throughout the remainder of the experiment, multisorbent samplers were removed from the manifold at elapsed times of 60,120,180,240,300,360,450,540,630,and 720 min. As a sampler was removed, the empty port was capped immediately with a Teflon Swagelok cap (Crawford Fitting Co., Solon, OH). The front and back cartridges were capped and stored a t -10 “C in Teflon-lined screw-cap tubes prior to analysis. This procedure was repeated on three consecutive days in order to generate three samples at each of the 10 time periods. Sample pump flows were not perfectly matched from day to day at each time period
Table 111. Comparison of Laboratory Breakthrough Volume Retention Efficiency with Chamber and Field Collection Efficiencies for 28 Target VOCs
compound n-nonane benzene n-decane trichloroethylene tetrachloroethylene toluene 1,2-dichloroethane n-undecane ethylbenzene p-xylene m-xylene isopropylbenzene o-xylene pyridine n-dodecane limonene n-propylbenzene 2-picoline 1,3,5-trimethylbenzene styrene n-tridecane 3-picoline 4-picoline n-butylbenzene 1,2,3-trimethylbenzene 3-ethylpyridine 1,4-dichlorobenzene 3-ethenylpyridine
breakthrough chamber study” studyb field study” retentn collectn collectn effic, % effic, % effic, % 100.0 0.0
89.3 98.4
100.0
100.0
0.0
NDd NDd 99.6 NDd 92.0 100.0 99.5 99.5 100.0 99.6 100.0 100.0 100.0 100.0 100.0 100.0 100.0 90.8
100.0 98.9 53.9 96.1 100.0 100.0
100.0 100.0
100.0 95.1 96.3 100.0
100.0 98.9 100.0 100.0 92.5 99.0 99.3 100.0
100.0
100.0 100.0
100.0 100.0 100.0
NDd
100.0
100.0
100.0 100.0
92.7 89.8 91.2 100.0 100.0 87.5 NDd 96.9 90.1 84.8 89.3 95.8 84.9 NAe 100.0 65.9 97.2 100.0 86.3 62.3 97.7 95.3 100.0
97.0 83.4 100.0 96.8 100.0
“Mean sample volume (L): 49.5 f 1.0 (n = 3). bMean sample volume (L): 8.0 rl: 0.7 (n = 22). Mean sample volume (L):11.9 & 2.1 (n = 8). ND. none detected. e NA. not audicable (see text).
so that true replication was not achieved. Thus, 30 discrete total flow conditions were obtained. In Table 111,breakthrough volumes expressed as retention efficiences are reported as the mean volume of the three 720-min intervals (49.5 L). For a given volume, retention efficiency is defined as the percentage of VOC mass remaining on the front cartridge of a multisorbent sampler. Seventeen of the 28 VOCs exhibit retention efficiencies of 100%. Thus, at the maximum total volume tested (49.5 L) there is no detected breakthrough to the back cartridge. For eight of the VOCs, acceptable retention efficiencies range from 92.5 to 99.3%. However, for benzene, 1,2-dichloroethane, and trichloroethylene, the retention efficiencies are 0.0,53.9, and 0.070, respectively. In Figure 3, the VOC mass determined on each of the front and back cartridges is plotted versus the total sample volume for benzene, 1,2-dichloroethane, trichloroethylene, and tetrachloroethylene. The plot for tetrachloroethylene is typical of the 25 VOCs with efficiencies greater than 92.5%; the VOC mass charged to the front cartridge fails to break through to the back cartridge even at total volumes approaching 50 L. Benzene and trichloroethylene exhibit undesirable, but not unexpected, breakthrough patterns with greater than 50% loss from the front cartridge at total volumes less than 10 L; at total volumes approaching 50 L, benzene and trichloroethylene have broken through the back cartridge as well. Thus, the retention efficiency is reported as 0.0% at 49.5 L. The pattern for 1,2-dichloroethaneis more unusual as the VOC mass is lost rapidly from the front cartridge similar to the previous pattern; however, the back cartridge appears to efficiently collect the material and retain it for total volumes approaching 50 L. The experimental breakthrough results observed here are consistent with those published Environ. Sci. Technol., Vol. 26, No. 9, 1992
1741
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Flgure 3. Effect of sample volume on the recovery of selected VOCs from spiked tandem multisorbent cartridges (front tube only). Twenty-fhm of the VOCs demonstrated no breakthrough for volumes less than 50 L, slmllar to tetrachloroethylene. Benzene and trichloroethylene demonstrated identical patterns with 100% loss from the back cartrklge at volumes greater than 40 L. Only 1,2dichloroethanedemonstrated a pattern of inltlal 50% loss from the front cartridge wlth subsequent efficient collection by the back cartridge.
by vendors of Tenax and Carbotrap, where benzene, 1,2dichloroethane, and trichloroethylene have low breakthrough volumes (less than 13 L/g of adsorbent) while the remaining target VOCs have breakthrough volumes greater than 50 L (26, 39). Collection Efficiencies. In order to further evaluate the ability of adsorbents to collect and retain an adsorbate, the collection efficiency of a sampler must be determined (40). The collection efficiency, e, of a sampler is defined as (1) e = (xl - xb/xl where x1 is the amount of analyte found on the front cartridge, and x 2 is the amount of analyte found on the back cartridge. The amount entering the front cartridge of a sampler, t, is defined as t =xl/e (2) In practice, the collection efficiency correction factor of a sampler may be applied to any data set where front and back cartridge results are determined. Two sets of experiments in an environmental chamber and in four "smoking" and four "nonsmoking" homes were conducted to evaluate sampler efficiencies. The chamber study was conducted in an 18-m3environmental chamber that has been described elsewhere (41). Fresh makeup air entering the chamber was filtered with 1742 Environ. Sci. Technol., Voi. 26, No. 9, 1992
a charcoal filter and a high-efficiency particle filter. Five nominal fresh air makeup conditions were selected as follows: 0,0.5,1.0,1.5, and 2.0 air changes per hour (ACH). For each of these conditions, five replicate runs were obtained for a total of 25 runs. Temperature and relative humidity were maintained nominally at 72 O F and 50%, respectively. Environmental tobacco smoke (sidestream smoke only), the sole source of VOCs in the chamber, was generated by the simultaneous smoking of two University of Kentucky 1R4F reference cigarettes on a Borgwaldt (Hamburg, Germany) Model RM 4/CS 4-port smoking machine. Mainstream smoke was vented from the chamber. VOC multisorbent samplers were inserted through l/&. Teflon bulkhead unions that provided sampling port access through the chamber wall. A typical chamber run consisted of a 12-min "background" period, followed by an ll-min "smoke" period, followed by a 97-min "decay" period for a total run time of 120 min. The VOC multisorbent sampler was operated for the entire 2-h experiment. Due to ATDdO and GC/MSD instrument problems, data from three of the back cartridges were lost; therefore, 22 samples were obtained from the study. On average, the mean sample volume for all 22 samples was 8.0 f 0.7 L. Collection efficiencies were calculated as described above. For the purpose of comparison to breakthrough volume retention efficiencies, the values are expressed as percentages in Table 111. As expected, the four halogenated
VOCs were not detected in ETS: trichloroethylene, tetrachloroethylene, 1,2-dichloroethane, and l,4-dichlorobenzene. For the remaining 24 VOCs, only n-nonane demonstrated a mean collection efficiency less than 90.0% (89.3%). Fifteen of the VOCs demonstrated mean collection efficiencies of 100.0%. Surprisingly, the mean benzene collection efficiency is 98.4%. From Figure 3, for a sample volume of 8.0 L, one would predict a benzene breakthrough retention efficiency of approximately 35%. Although, breakthrough volume retention efficiencies and collection efficiencies are calculated somewhat differently, a discrepancy of this magnitude would not be predicted. The field study was conducted in eight homes, four “smoking” and four “nonsmoking.” Subjects wore a VOC multisorbent sampler for 3 h during a typical night and recorded the number of cigarettes that they observed being smoked. Subjects returned samplers the next day; the cartridges were removed, capped, and placed in Teflonlined screw-cap tubes. The tubes were placed in cardboard containers, stored over dry ice in a foam-insulated container, and transported to the laboratory. Upon receipt in the laboratory, the tubes were removed from the containers and stored at -10 OC prior to analysis. On average, the mean sample volume for the eight field samples was 11.9 f 2.1 L. Collection efficiency results for the field samples are reported in Table 111. Overall, the field collection efficiencies are acceptable but not as high as the chamber collection efficiency results predict. Fifteen of the VOCs have lower field efficiencies than chamber efficiencies, five are identical, and three are higher. Trichloroethylene has a field efficiency of 100%. From Figure 3, for a sample volume of 13.9 L, one would predict a trichloroethylene breakthrough retention efficiency of approximately 20%. Benzene has a field efficiency of 89.9%. From Figure 3, one would predict a benzene breakthrough retention efficiency of 20%. Results for limonene, styrene, and pyridine are somewhat more discouraging. Limonene and styrene demonstrate field efficiencies of 65.9% and 62.3%, respectively, compared to breakthrough retention efficiencies and chamber efficiencies of 100%. Pyridine field efficiency results are negative since more pyridine was found on the back cartridges than on the front cartridges. If equal amounts were found on each cartridge, the collection efficiency would be 0%. For pyridine, front and back cartridge amounts are combined in order to obtain the total pyridine amount with the understanding that absolute pyridine concentrations are likely to be understated. For the remaining VOCs, collection efficiency correction factors are applied in order to determine the amount entering the front cartridge. Therefore, with the exception of pyridine, collection efficiencies are acceptable with the caveat that the correction factor be applied in order to obtain the amount entering the front cartridge. The disparity between chamber- and field-determined collection efficiencies may be explained by several factors: leaks, channeling, relative humidity, elevated collection temperatures, exceeded capacity, poorly conditioned cartridges with high VOC backgrounds, or VOC migration between the front and back cartridges after sampling (prior to separation and storage). However, based on the results, none of these factors adequately explain the observed inconsistency. ETS Apportionment. For characterization of any indoor air environment with respect to volatile organic compounds, two factors must be considered: (1)the concentration of specific VOCs, and (2) the source of those VOCs. In order to apportion sources in any complex mixture of analytes, a marker or tracer for a given source
must be identified. According to the National Research Council (42),a tracer or marker for ETS should meet four criteria: (1)it should be unique or nearly unique to tobacco smoke; (2) it should be present in sufficient quantities to permit detection at low smoking rates; (3) it should be emitted a t similar rates across cigarette brands; and (4) it should maintain a constant ratio to the contaminant of interest for a wide range of cigarette brands and environmental conditions. Historically, nicotine has been used as a marker for ETS; however, a recent study has demonstrated problems associated with its use (34). More recent studies have suggested that 3-ethenylpyridine, a major pyrolysis product of nicotine, would be a more suitable marker of ETS (31,431. Using analytical results from the previously described chamber study, ratios of 3-ethenylpyridine and selected analytes (benzene, styrene, pyridine, 2-picoline, 3-picoline, and 3-ethylpyridine) were calculated. These ratios were determined across a broad range of air exchange rates (ACH) for one cigarette type, the University of Kentucky 1R4F reference. Summary resulta for the determination of 3-ethenylpyridine (3-EP) ratios are presented in Table IV. Mean 3-EP ratios and standard deviations for each analyte are reported a t the bottom of the table with the results of one-way ANOVA tests for the null hypothesis that the difference between the ratio means for each group of nominal ACHs (0,0.5,1.0,1.5, and 2.0) is no greater than the difference within groups. For three of the analytes (pyridine, 2-picoline, and 3-ethylpyridine) there is no significant effect of ACH on the ratios. For three of the analytes (benzene, styrene, and 3-picoline), a statistically significant effect of ACH is observed. This effect may be further evaluated with a Bonferroni-normalized multiple comparison test using Stata software (Computing Resource Center, Santa Monica, CA) to identify the source and magnitude of the effect. For these three analytes, the significant differences (p I0.05 experimentrwise error rate) are found to occur between the 0 ACH condition and the 1.5-2.0 ACH conditions. For benzene, styrene, and 3picoline, the differences between the 3-EP ratios for the 0 and 2.0 ACH conditions are 21, 18, and 12%, respectively. In fact, the 0 ACH condition is unique and is unlikely to be found in any field situation. In a study of 189 homes in the Suffolk, NY, area and 197 homes in the Onondaga, NY, area, Leaderer et al. (44) reported mean ACHs of 0.58 and 0.50, respectively. In another study of 312 homes in North America, Grimsrud et al. (45) found a median value of 0.5 ACH. Finally, in another study of 266 low income homes in North America, Grot and Clark (46) observed median ACHs of 0.9. Therefore, although significant differences in 3-EP ratios across the experimental ACH conditions are found for several of the analytes, these differences are encountered between ACHs that are not likely to be found in any field situation, particularly private residences. By comparison, differences between the mean ratios at the nominal 0.5 ACH condition and the mean ratios at all ACH conditions for each selected analyte are minimal and demonstrate excellent agreement: benzene (1.29 a t 0.5 ACH versus 1.30), styrene (3.23 a t 0.5 ACH versus 3.32), 2-picoline (4.57 at 0.5 ACH versus 4-47), 3-picoline (2.32 a t 0.5 ACH versus 2.32), and 3-ethylpyridine (9.70 at 0.5 ACH versus 8.97). Thus, the overall mean ratios are more representative of the conditions at 0.5 ACH than at 0 ACH, and personal residences are more likely to have ventilation rates nearer to 0.5 ACH than 0 ACH. Using analytical results from the previously described field study, ETS apportionment of selected analytes may Envlron. Scl. Technol., Vol. 26, No. 9, 1992
1743
Table IV. Effect of Air Exchange Rate (ACH) on 3-Ethenylpyridine (3-EP) Ratios for Kentucky Reference 1R4F Cigarettes in Environmental Chamber at Nominal 0,0.5, 1.0, 1.5, and 2.0 ACHs
run
ACH
3-EPIbenzene
1.52 1.90 0.39 0.05 1.03
1 2
3 4 5 6 7 8 9
1.27 1.45 1.36 1.19 1.34 1.28 1.39 1.17 1.33 1.37 1.45
1.82
0.61 0.04 1.63 1.13 1.47 0.04 1.45 1.42 1.17
10 11 12
13 14 15 16 17 18 19 20 22 23 24 25 mean SD ANOVA D value
3.34 3.53 3.26 2.84 3.40 3.40 3.24 2.95 3.45 3.23 3.67 3.05 3.99 3.78 3.32 3.84 3.22 3.11 3.03 3.47 2.89 2.87 3.26 3.58 3.33 3.32 0.30 0.0002
1.11
1.52 1.52 1.25 1.57 1.20
2.11
21
3-EPIstyrene
0.49 0.53 1.54 1.09 0.05 0.05 1.06 2.03 0.50
1.26 1.26 1.07 1.07 1.21
1.32 1.22
1.30 0.14 0.0015
3-EPlpyridine
3-EP/2picoline
3-EP/3picoline
3-EP/3ethylpyridine
4.09 3.95 4.44 3.92 4.33 4.09 4.52 4.36 4.25 4.21 4.60 4.36 5.67 5.10 4.74 4.97 4.63 4.78 4.24 4.80 3.94 3.99 4.41 4.96 4.46 4.47 0.42 0.2933
2.52 2.61 2.30 2.09 2.27 2.01 2.26 2.20 2.24 2.44 2.56 2.26 2.54 2.44 2.27 2.47 2.24 2.37 2.25 2.53 2.03 2.08 2.28 2.58 2.26 2.32 0.18 0.0270
6.20 5.84 9.19 9.34 8.31 6.33 9.76 9.99 7.73 7.68 8.32 9.94 11.04 8.83 9.22 9.85 9.13 10.52 7.71 10.40 9.81 9.97 9.58 9.54 9.92 8.97 1.38 0.1222
1.36 1.40 1.25 1.19 1.33 1.02 1.46 1.30 1.04 1.30 1.43 1.40 1.53 1.54 1.46 1.56 1.42 1.56 1.41 1.20 1.03 1.22
1.07 1.51 1.11
1.32 0.18 0.5544
Table V. Apportionment of Selected Indoor Air Analytes in Four “Nonsmoking”and Four ’Smoking” Homes”
home smoking status no. of cigarettes smoked
0
benzene styrene pyridine 2-picoline 3-picoline 3-ethylpyridine
2.0 0.5 1.0 ND ND ND
benzeneETs styreneETs pyridineETs 2-picolineETs 3-picolineEw 3-ethylpyridineETs
0.0 0.0 0.0
3
2
1
NS
S 6
NS 0
Compound 5.7 1.8 5.2 0.7 1.0
0.3
4 S 2
Concentration, pg/m3 2.7 13.2 1.6 7.0 0.1 2.1 ND 0.4 ND 0.1 ND ND
Compound Apportionment, % 39.0 0.0 0.2 49.2 0.0 1.6 41.6 0.0 12.4 89.0 22.2 100.0 100.0 94.1
5
6
7
8
NS
S
NS
5
0
12
0
1
3.0
4.5 1.9 2.9 0.5 0.7 0.3
12.1 1.2
4.0 2.4 0.1 ND 0.3 ND
1.1 1.1
ND ND 0.2 0.0 0.0 0.0 0.0
25.6 24.9 39.3 73.9 94.2 65.4
1.4 0.4 ND ND 0.0 0.0 0.0 0.0
9.2 5.8 100.0 80.8
“NS, nonsmoking; S, smoking; ND, none detected.
be determined by calculating their 3-EP ratios. Then, the percentage of any analyte attributable to ETS is given by the expression % analyteETs =
F3-EP
/
x 100
CI-EP/ Canalyte
(3)
where Fsw/Fanalyte is the ratio of 3-ethenylpyridine to any analyte determined from field measurements, and C3-EP/Canalyte is the ratio of 3-ethenylpyridine to the same analyte determined in the chamber study (Table IV). In Table V, absolute concentrations of these selected analytes and their respective ETS apportionment are reported. The proposed ETS marker, 3-ethenylpyridine,was not detected in any of the nonsmoking homes; therefore, all of these homes demonstrate percent analyteETsvalues of 0% for the selected analytes. For smoking homes, the percent 1744 Environ. Sci. Technol., Voi. 26, No. 9, 1992
benzeneETs ranges from 0.2 to 39.0% and the percent styreneEw ranges from 1.6 to 49.2%. Without the ability to apportion results, one might be prediposed to assign the total amount to smoking activity. For example, in nonsmoking home 3 and smoking home 4, the benzene concentrations are 2.7 and 13.2 pg/m3, respectively. Without apportioning, one might assume that the elevated benzene concentration is a consequence of smoking activity; however, only 0.2% of the benzene in the smoking home is attributable to ETS. Obviously, activities during the sampling period other than smoking are predominant contributors to the elevated benzene concentration. Apportionment resulta for the “tobacco bases” (pyridine, 2-picoline, 3-picoline, and 3-ethylpyridine) indicate that these compounds originate predominately from ETS, but other sources also contribute to their total concentration. Pyridine and many of the pyridine derivatives have been
found at trace levels in foods such as fish, meat, vegetables, cereals, dairy products, and alcoholic beverages (47,481. Also, a number of these compounds are used as chemical intermediates in the manufacture of adhesives, acrylic fibers, resins, and pesticides (49). Therefore, it is reasonable to observe these compounds in indoor air environments in the absence of smoking activity. For example, all of the homes have a measurable amount of pyridine regardless of smoking activity, and two of the nonsmoking homes have measurable amounts of 3-ethylpyridine and 2-picoline. The proposed ETS apportionment technique augments VOC target analysis in providing the capability to characterize complex chemical mixtures in indoor air environments. Conclusions
The laboratory validation of VOC multisorbent collection and TD/GC/MSD analysis indicates that the LOD, LOQ, and RSD for each of the compounds is satisfactory. Excellent long-term room temperature storage stabiilty is exhibited for all analytes with the exception of limonene. Breakthrough volume retention efficiencies, chamber collection efficiencies, and field collection efficiencies are contradictory for some of the VOCs and demonstrate the importance of using an efficiency correction factor in order to determine the amount of analyte entering the front cartridge. Field collection efficiency results for pyridine are discouraging and limit application of the method for its determination. The target volatile organic compound mix selected for this method includes analytes that are ubiquitous and useful for characterizing indoor air environments. One of the target compounds, 3-ethenylpyridine, is a pyrolysis product of nicotine and meets the criteria of an acceptable ETS tracer. Ratios of 3ethenylpyridine to selected analytes demonstrate the utility of ETS apportionment in analyzing a complex mixture of multisource VOCs. In general, 3-EP ratios for the selected analytes are unaffected by ventilation at rates commonly encountered in home situations. Additional research is required in order to determine 3-EP/VOC ratios across a large number of commercial cigarette brands. Selected analyte apportionment indicates that ETS contributes a fraction of the target VOCs in homes with smoking activity. Registry No. n-Nonane, 111-84-2;benzene, 71-43-2; n-decane, 124-18-5;trichloroethylene, 79-01-6;tetrachloroethylene,127-18-4; toluene, 108-88-3; 1,2-dichloroethane, 107-06-2; n-undecane, 1120-21-4; ethylbenzene, 100-41-4;p-xylene, 106-42-3;m-xylene, 108-38-3;isopropylbenzene, 98-82-8; o-xylene, 95-47-6; pyridine, 110-86-1; n-dodecane, 112-40-3; limonene, 138-86-3; n-propylbenzene, 103-65-1; 2-picoline, 109-06-8; 1,3,5-trimethylbenzene, 108-67-8; styrene, 100-42-5; n-tridecane, 629-50-5; 3-picoline, 108-99-6; 4-picoline, 108-89-4; n-butylbenzene, 104-51-8; 1,2,3trimethylbenzene, 526-73-8; 3-ethylpyridine, 536-78-7; 1,4-dichlorobenzene, 106-46-7;4-ethenylpyridine,536-75-4; 1-undecane, 821-95-4.
L i t e r a t u r e Cited Brunnemann, K. D.; Cox, J. E.; Kagan, M. R.; Hoffmann, D. Proceedings of the CORESTA Smoke Study Group, Kallithea, Greece, 1990; CORESTA Paris, France, 1990; pp 100-107. Wolkoff, P. Enuiron. Technol. 1990, 11, 339-344. Chan, C. C.; Vainer, L.; Martin, J. W.; Williams, D. T. J. Air Waste Manage. Assoc. 1990, 40, 62-67. Higgins, C. E.; Thompson, C. V.; Ilgner, R. H.; Jenkins, R. A.; Guerin, M. R. Presented at the 41st Tobacco Chemists’ Research Conference, Greensboro, NC, Oct 1987. Hillenbrand, L. J.; Riggin, R. M. Proceedings: National Symposium on Recent Advances in Pollutant Monitoring of Ambient Air and Stationary Sources, Raleigh, NC, Jan
1984; U.S. Government Printing Office: Washington, DC, 1984; EPA-600/9-84-001; pp 344-357. (6) Hodgson, A. T.; Girman, J. R.; Binenboym, J. Proceedings of the 79th Annual Meeting of the Air Pollution Control Association, Minneapolis, MN, June 1986; Air Pollution Control Association: Pittsburgh, PA, 1986; Paper 86-37.1. (7) Cocheo, V.; Bombi, G. G.; Silvestri, R. Am. Ind. Hyg. Assoc. J. 1987,48, 189-197. Chan, C. C.; Martin, J. W.; Pond, P. J.; Williams, D. T. Proceedings of the 1986 EPA f APCA Symposium on Measurement of Toxic Air Pollutants, Raleigh, NC, April 1986; APCA Pittsburgh, PA, 1986; pp 71-85. Hsu, J. P.; Miller, G.; Moran, V., I11 J. Chromatogr. Sci. 1991,29,83-88. (10) Michael, L. C.; Pellizzari, E. D.; Perritt, R. L.; Hartwell, T. D.; Westerdahl, D.; Nelson, W. C. Environ. Sci. Technol. 1990,24,996-1003. (11) Proctor, C. J.; Warren, N. D.; Bevan, M. A. J.; Baker-Rogers, J. Environ. Int. 1991, 17, 287-297. (12) Proctor, C. J. In Indoor and Ambient Air Quality, 1st ed.; Perry, R., Kirk, P. W., Eds.; Selper Ltd.: London, U.K. 1988; Chapter 2. (13) Proctor, C. J. Proceedings of the Air and Waste Management Association Annual Meeting, Anaheim, CA, June 1989; AWMA Pittsburgh, PA, 1989; Paper 89-80.4. (14) Proctor, C. J.; Warren, N. D.; Bevan, M. A. J. Environ. Technol. Lett. 1989,10, 1003-1018. (15) Wallace, L. A.; Pellizzari, E.; Hartwell, T. D.; Perritt, R.; Ziegenfus, R. Arch. Environ. Health 1987, 42, 272-279. (16) Wallace, L. A. Proceedings of a n APCA International Specialty Conference, Chicago, IL, Apr 1986; APCA Pittsburgh, PA, 1986; pp 14-24. (17) Wallace, L. A. Tox. Environ. Chem. 1986, 12, 215-236. (18) Miksch, R. R.; Hollowell, C. D.; Schmidt, H. E. Environ. Int. 1982,8, 129-137. (19) Weechler, C. J.; Shields, H. C.; Rainer, D. Am. Ind. Hyg. ASSOC.J. 1990, 51, 261-268. (20) Bayer, C. W.; Black, M. S. Biomed. Environ. Mass Spectrom. 1987,14,363-367. (21) Bayer, C. W.; Black, M. S. Proceedings of the ASHRAE Conference IAQ’86, Atlanta, GA, Apr 1986; ASHRAE: Atlanta, GA, 1986; pp 281-291. (22) Winberry, W. T.; Forehand, L.; Murphy, N. T.; Ceroli, A.; Phinney, B.; Evans, A. Compendium of Methods for the Determination of Air Pollutants in Indoor Air: Method IP-1B US. Environmental Protection Agency, Atmospheric Research and Exposure Assessment Laboratory: Research Triangle Park, NC, Sept 1989. (23) Brown, V. M.; Crump, D. R.; Gardiner, D. Environ. Int. 1990,16,283-289. (24) Lagrone, F. S. Environ. Sci. Technol. 1991, 25, 366-368. (25) Gallant, R. F.; King, J. W.; Levins, P. L.; Piecewicz, J. F. Characterization of Sorbent Resins for Use in Environmental Sampling; U.S. Government Printing Office: Washington, DC, Mar 1978; EPA-60017-78-054. (26) Chrompack News Special 1982,82-03, 1-8. (27) Hileman, B. Chem. Eng. News 1991, July 22, 26-42. (28) Girman, J. R.; Hodgson, A. T.; Newton, A. S. Environ. Int. 1986,12, 317-321. (29) Mmlhave, L. Environ. Int. 1982,8, 117-127. (30) McKone, T. E.; Knezovich, J. P. J. Air Waste Manage. ASSOC.1991, 40, 282-286. (31) Nelson, P. R.; Ogden, M. W. Proceedings of the 38th ASMS Conference on Mass Spectrometry and Allied Topics, Tucson, AZ, June 1990; ASMS: East Lansing, MI, 1990; pp 677-678. (32) Ogden, M. W. In Capillary Chromatography-The Applications, 1st ed.; Jennings, W. G., Nikelly, J. G., Eds.; Huthig: Heidelberg, Germany, 1991; Chapter 5. (33) Thome, F. A.; Heavner, D. L.; Ingebrethsen, B. J.; Eudy, L. W.; Green, C. R. Proceedings of the 79th Annual Meeting of the Air Pollution Control Association, Minneapolis, MN, June 1986; APCA Pittsburgh, PA, 1986; Paper 86-37.6. (34) Nelson, P. R.; Heavner, D. L.; Oldaker, G. B., I11 Proceedings of the 1990 EPA fA&WMA International Symposium: Measurement of Toxic and Related Air PolluEnviron. Scl. Technol., Vol. 26, No. 9, 1992
1745
Environ. Scl. Technol. 1992, 26, 1746-1752
tants, Raleigh, NC, Apr 1990; AWMA Pittsburgh, PA,
(43) Eatough, D. J.; Benner, C. L.; Tang, H.; Landon, V.;
1990; 550-555.
ACS Committee on Environmental Improvement. Anal. Chem. 1980,52,2242-2249. Miller, J. C.; Miller, J. N. Statistics for Analytical Chemistry, 2nd ed.; John Wiley and Sons: New York, 1988; Chapter 5. Taylor, J. K. Quality Assurance of Chemical Measurements; Lewis: Chelsea, MI, 1987; pp 79-82. Betz, W. R. Proceedings of the 1986 E P A I A P C A Symposium on Measurement of Toxic Air Pollutants, Raleigh, NC, Apr 1986; APCA Pittsburgh, PA, 1986; pp 882-892. Supelco GC Bull. 1986,No. 8464,1-4. Caka, F. M.; Eatough, D. J.; Lewis, E. A.; Tang, H.; Hammond, S. K.; Leaderer, B. P.; Koutrakis, P.; Spengler, J. D.; Fasano, A.; McCarthy, J.; Ogden, M. W.; Lewtas, J. Environ. Sci. Technol. 1990,24,1196-1203. Heavner, D. L.; Thome, F. A.; Eudy, L. W.; Ingebrethsen, B. J.; Green, C. R. Proceedings of the 79th Annual Meeting of the Air Pollution Control Association, Minneapolis, MN, June 1986; APCA: Pittsburgh, PA, 1986; Paper 86-37.9. Committee on Passive Smoking, Board on Environmental Studies and Toxicology, National Research Council. Environmental Tobacco Smoke: Measuring Exposure and Assessing Health Effects; National Academy Press: Washington, DC, 1986; pp 63-100.
(44)
(45)
(46)
(47) (48) (49)
Richards, G.; Caka, F. M.; Crawford, J.; Lewis, E. A.; Hansen, L. D. Environ. I n t . 1989,15, 19-28. Leaderer, B. P.; Koutrakis, P.; Briggs, S.; Rizzuto, J. Proceedings of the 5 t h International Conference on Indoor Air Quality and Climate, Toronto, ON, Aug 1990; International Conference on Indoor Air Quality and Climate, Inc: Ottawa, ON, 1990; Vol. 2, pp 269-274. Grimsrud, D. T.; Sherman, M. H.; Sonderegger, R. C. Calculating Infiltration: Implications for a Construction Quality Standard; LBL-9416, Lawrence Berkeley Laboratory: Berkeley, CA, 1983. Grot, R. A.; Clark, R. E. Proceedings of the DOEIASHRAE Conference on Thermal Performance of External Envelopes of Buildings, Orlando, FL, Dec 1979; ASHRAE: Atlanta, GA, 1980. Vernin, G. Perfum. Flau. 1982,7, 23-26. Jori, A.; Calamari, D.; Cattabeni, F.; Di Domenico, A.; Galli, C. L.; Galli, E.; Silano, V. Ecotoxicol. Environ. Saf. 1983, 7, 251-275. The Merck Index; Windholz, M., Ed.; Merck Rahway, NJ, 1976; p 7207.
Received f o r review December 13, 1991. Revised manuscript received March 19,1992. Accepted April 17, 1992.
Effects of Consecutive Pulsing of an Inhibitory Substrate on Biodegradation Kinetics Mehmet S. Okaygun, Lynda A. Green, and Aydin Akgerman"
Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843
A series of long-term batch studies were performed by consecutively pulse feeding an inhibitory substrate, phenol, to mimic the response of an activated sludge system to consecutive shock loads of a toxic chemical. For each batch study, the phenol and biomass concentrations were continuously measured and the dominant microbial species were determined as Pseudomonas spp. and Klebsiella spp. There was a remarkable decrease in specific substrate removal rates with increasing number of consecutive phenol pulses. The values of half-saturation coefficient, K,, and of the maximum specific growth rate, pm,remained constant through pulse feeding, but the value of the inhibition coefficient, KI, decreased with each consecutive phenol pulse. A lumped parameter, called the inhibition factor, was introduced into the Haldane equation to explain and model the decreasing trend of KI with phenol pulse frequency. W
Introduction There is very limited information in the literature on the effecta of exposing activated sludge systems to multiple consecutive toxic shock loads. When an activated sludge system is exposed to consecutive toxic shock loads, there may be changes in the values of kinetic parameters and the microbial composition that may be due to substrate inhibition and accumulation of toxic intermediates. If exposure to subsequent toxic shock loads is prolonged, the bacterial cells may be deactivated, resulting in a decrease in degradation rates. Eventually, the instability in the system may yield to total system failure unless necessary precautions in operation are taken. Therefore, when the operational safety limits for activated sludge processes are being determined, it is imperative to understand and 1746 Environ. Scl. Technol., Vol. 26, No. 9, 1992
quantify the phenomena occurring in activated sludge systems exposed to consecutive shock loads of inhibitory chemicals. In general, at high concentrations of an inhibitory substrate, the bacterial growth is modeled by the Haldane equation given by 9=
qms
K, + S
+ S2/KI
or
p
=
PInS
K, + S
+ S2/KI
(1) where S is the soluble substrate concentration (mg/L), q the specific substrate removal rate (h-l), p the specific growth rate (h-l), qm the maximum specific substrate removal rate (h-l), pm the maximum specific growth rate (h-l), K, the half-saturation constant (mg/L), and KI the inhibition constant (mg/L). Among different inhibitory chemicals, there is much interest in phenolic compounds since they are discharged at high concentrations in industrial wastewater streams. Many investigators have reported satisfactory use of the Haldane equation to quantify substrate inhibition at high toxic phenol concentrations. D'Adamo et al. (1) and Pawlowsky and Howell (2) used heterogeneous populations in their studies to investigate phenol biodegradation at concentrations ranging from 50 to 1000 mg/L by measuring the initial specific growth rates in batch experiments. They fitted the biodegradation data to the Haldane equation and to ita modified forms classified by Edwards (3) and reported average values for pm,K,, and KI for the Haldane equation as 0.26 h-l, 25.4 mg/L, and 173.0 mg/L, respectively. Szetela and Winnicki ( 4 ) reported values of the Haldane equation constants, pm,K,, and KI as 0.33 h-l, 19.2 mg/L, and 229.0 mg/L, respectively, for phenol.
0013-936X/92/0926-1746$03.00/0
0 1992 American Chemical Soclety
