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Giam, C. S.; Atlas, E.; Chan, H. S.; Neff, G. S. Atmos. Environ. 1980, 14, 65-9. Tanabe, S.; Hidaka, H.; Tataukawa,R. Chemosphere 1983, Bidleman, T. F. Environ. Sci. Technol. 1988, 22, 361-7. Safe, S. CRC Crit. Rev. Toricol. 1984, 13, 319-93. Poland, A.; Glover, E. Mol. Pharmacol. 1977,13,924-38. Doskey, P. V.; Andren, A. W. Anal. Chim. Acta 1979,110,
Burkhard, L. P.; Armstrong,D. E.; Andren, A. W. J. Chem. Eng. Data 1984,29, 248-50. Junge, C. E. Tellus 1974,26,477-87. Junge, C. E. In Advances in Environmental Science and Technology; Suffet, I. H., Ed.; John Wiley & Sons: New York, 1977; Part 1, Vol. 8, pp 7-25. Andren, A. W. In Physical Behavior of PCBs in the Great Lakes; Mackay, D., Paterson, S., Eisenreich, S. J., Simmons,
129-37.
M., Eds.; Ann Arbor Science: Ann Arbor, MI, 1983; pp
12, 277-88.
Hunt, G.; Pangaro, N. Anal. Chem. 1982,54, 369-72. Bidleman, T. F.; Burdick, N. F.; Westcott, J. W.; Billings, W. N. In Physical Behavior of PCBs in the Great Lakes; Mackay, D., Paterson, S., Eisenreich, S. J., Simmons, M., Eds.; Ann Arbor Science: Ann Arbor, MI, 1983; pp 15-48. Bouchertall, F.; Duinker, J. C. Anal. Chim. Acta 1986,185,
127-40.
Eisenreich, S. J. In Sources and Fates of Aquatic Pollutants; Hites, R. A., Eisenreich, S. J., Eds.; Advances in Chemistry 216; American Chemical Society: Washington, DC, 1987; pp 393-469. Swackhamer, D. L.; Armstrong, D. E. Environ. Sci. Technol.
369-75.
1986,20,879-83.
Bidleman, T. F.; Matthews, J. R.; Olney, C. E.; Rice, C. P.
Strachan, W. M. J.; Eisenreich, S. J. Mass Balancing of Toxic Chemicals in the Great Lakes: The Role of Atmospheric Deposition. International Joint Commission workshop report, Scarborough, Ontario, Canada, 1986. Murphy, T. J.; Formanski, L. J.; Brownawell, B.; Meyer, J. A. Environ. Sci. Technol. 1985, 19, 942-6. Lambert, G.; Sanak, J.; Polian, G. In Precipitation Scavenging, Dry Deposition, and Resuspension;Pruppacher, H. R., Semonin, R. G.; Slinn, W. G. N., Eds.; Elsevier: New York, 1983; Vol. 2, pp 1352-8.
J. Assoc. Off. Anal. Chem. 1978, 61, 820-8. Mullin, M. D.; Pochini, C. M.; McCrindle, S.; Romkes, M.; Safe, S. H.; Safe, L. M. Environ. Sci. Technol. 1984, 18, 468-76.
Albro, P. W.; Parker, C. E. J. Chromutogr. 1979,169,161-6. Albro, P. W.; Corbett, J. T.; Schroeder,J. L. J. Chromatogr. 1981,205, 103-11.
Onuska, F. I.; Kominar, R. J.; Terry, K. A. J. Chromatogr. 1983, 279, 111-8.
Manchester,J. N. M.S. Thesis, Water Chemistry Program, University of Wisconsin-Madison, 1988. Burkhard, L. P.; Weininger, D. Anal. Chem. 1987, 59, 1187-90.
Bidleman, T. F.; Christensen, E. J.; Harder, H. W. In Atmospheric Pollutants in Natural Waters; Eisenreich, S. J., Ed.; Ann Arbor Science: Ann Arbor, MI, 1981; pp 481-508.
Hites, R. A. University of Indiana-Bloomington, personal communication.
Received for review August 26,1988.Revised munuscript received April 25,1989. Accepted May 15,1989. This research was funded by the University of Wisconsin Sea Grant Program under grants from the National Sea Grant Program, National Oceanic and Atmospheric Administration, US.Department of Commerce, and from the State of Wisconsin. Federal Grant NABOO-AAD-ooo86, Project RIMW-28. We also acknowledge the Wisconsin Department of Natural Resources for allowing us the use of the observation tower.
Collection and Determination of Solanesol As a Tracer of Environmental Tobacco Smoke in Indoor Air Michael W. Ogden" and Katherlne C. Malolo R. J. Reynolds Tobacco Company, Research and Development, Winston-Salem, North Carolina 27 102
Methodology for the gas chromatugraphic determination of solanesol in the particulate fraction of environmental tobacco smoke (ETS) aerosol is presented. Sampling is performed by drawing air through Fluoropore membrane filters with personal sampling pumps. Samples are prepared by extracting filters, evaporating the extract to dryness, and derivatizing the residue with N,O-bis(trimethylsily1)trifluoroacetamide (BSTFA) followed by analysis on short, thin-film capillary columns with either flame ionization or mass spectrometric detection. Limit of detection is estimated at 0.2 pg/m3 for 2-h sample duration a t 2 L/min. Results obtained from sampling in an environmental chamber indicate that solanesol is 2-3 % by weight of respirable suspended particles (RSP) attributable to ETS from commercial cigarettes. Consequently, the solanesol/RSP weight ratio can be used to apportion total RSP into ETS and non-ETS contributions. This approach was used to correctly predict the ETS contribution to a mixture of RSP from cigarette, candle, and oil lamp sources with an error of 10%. Introduction
Environmental tobacco smoke (ETS) is an aged, dilute mixture of sidestream and exhaled mainstream smoke from combustion of tobacco products such as cigarettes 1148
Environ. Sci. Technol., Vol.
23, No. 9, 1989
and cigars. Since ETS has been implicated as one of a number of sources impacting on indoor air quality, there exists a need to develop methods that estimate the concentration of ETS in the indoor environment. In the past, a variety of tracers of environmental tobacco smoke have been used, including nicotine, carbon monoxide, respirable suspended particulate matter (RSP), nitrogen oxides, nitrosamines, and aromatic hydrocarbons (1). With the exception of nicotine, all of these potential tracers suffer from either a lack of specificity or extremely low concentrations, which makes their detection and quantitation difficult, unreliable, or expensive. Although total RSP concentration can be reliably determined, it too is not specific to tobacco smoke. Nicotine, however, is very characteristic of all Nicotiana species and should enter the indoor environment only from tobacco sources. As a result, the most reliable current estimates of ETS concentration are based on measurements of vapor-phase nicotine and RSP, and numerous methods have been developed for these determinations. The methods developed and currently in use in our laboratory have been described (2,3), tested ( 4 ) ,and are in routine use in a number of laboratories. Attempts to estimate the contribution of ETS to indoor air quality through the use of these two parameters are not
0013-936X/89/0923-1148$01.50/0
0 1989 American Chemical Society
without difficulty. Nicotine in ETS aerosol, although 90+% in the vapor phase (5-7), is removed from the environment at a faster rate than the particulate fraction of the aerosol due to adsorptive and chemical interactions. On the other hand, studies have shown that as much as half of the RSP collected in an indoor environment where smoking occurs may be attributable to sources other than ETS (8-10). As a result, total RSP overestimates ETS concentration, although the magnitude of this bias can be reduced by determining a quantity identified as ultraviolet particulate matter (W-PM) ( 3 , I I ) .Based on an empirical relationship between RSP and its UV absorption established on particulate matter collected in an environmental chamber containing only ETS, the contribution of ETS to RSP in indoor environments can be estimated. Since this procedure relies on measuring the total absorbance at 325 nm of the methanol extract of filters used to collect RSP, the tendency is still toward overestimating the contribution of ETS to RSP. Previously, there existed no chemical constituent that could be used as a reliable tracer of the particulate fraction of ETS aerosol. In experiments designed to elucidate the particulate-phase composition of ETS aerosol, we identified the presence of solanesol in relatively large quantities (12). Reported here are the results of additional experimenta, which demonstrate that solanesol appears to be well suited as a sensitive, unambiguous tracer of environmental tobacco smoke particles in indoor environments. Experimental Section Materials. Fused silica capillary tubing (0.53-mm i.d.) was obtained from Polymicro Technologies, Inc. (Phoenix, AZ). Octamethylcyclotetrasiloxane(D4) and OV-1 from Ohio Valley Specialty Chemical Co. (Marietta, OH) and azo-tert-butane (ATB) from Fairfield Chemical Co. (Blythewood, SC) were used in column preparation. Solanesol (13190-97-1) and l-triacontanol (593-50-0) from Sigma Chemical Co. (St. Louis, MO) and N,O-bis(trimethylsily1)trifluoroacetamide (BSTFA) with and without 1% added trimethylchlorosilane (TMCS) from Pierce Chemical Co. (Rockford, IL) were used for sample/ standard preparation. Fluoropore filter pads (1.0-pm pore size, 25- and 37-mm diameter) from Millipore Corp. (Bedford, MA) were used for sample collection in conjunction with personal sampling pumps from SKC, Inc. (Appomattox, VA) operated at either 1 or 2 L/min flow rate. Impactors with a 3.5-pm cutoff at 2 L/min (stainless steel nozzle and body) were obtained from Craft Assoc. (Atlanta, GA), while impactors with a 3.5-pm cutoff at 1 L/min (Delrin body and aluminum nozzle) were manufactured internally. Sorbent tubes containing XAD-4 resin, Catalogue no. 226-30-11-04-GWS from SKC, Inc., were used for collecting nicotine and also for verifying the absence of solanesol in the vapor phase of ETS aerosol. Gas Chromatography. Analyses were performed on Hewlett-Packard Model 5890A gas chromatographs equipped with on-column injectors and Model 7673A autosamplers with either flame ionization or mass spectrometric (HP 5970A Mass Selective Detector) detection. MS detection was accomplished in the selected ion mode by monitoring ions at m/e 496 from 8 to 16 min (l-triacontanol) and m/e 69 from 16 to 20 min (solanesol). Gas Chromatography Columns. Fused silica tubing was hydrothermally treated with 20% HN03,deactivated with D4,statically coated with a 0.05-pm film of OV-1 (0.0004 g/mL in pentane), and cross-linked with ATB as described previously (13). Commercially available capillary columns (0.53 mm i.d. X 15 m) coated with a 0.15-pm film of DB-1 (100% methylpolysiloxane, equivalent to OV-1)
C (H ,O ,
CH3-C=CH
-t
MW=631)
r
?3 CH2-CH2 -C=CH
1
r
CH2 -OH
Figure 1. Structure of solanesol (3,7,11,15,19,23,27,31,35-nonamethyl-2,6,10,14,18,22,26,30,34-hexatriacontanonaen-l-ol).
were obtained from J&W Scientific (Folsom, CA) and cut into 3-m sections prior to use. Calibration Standard Preparation. Standards covering the range of 0.5-30 ng/pL solanesol were prepared by adding the appropriate volume (1-60 pL) of a stock solution of solanesol (0.1 pg/pL in methyl ethyl ketone, MEK) to a 1-mL conical-bottom reaction vial followed by 20 pL of a stock solution of 1-triacontanol (internal standard, 0.1 pg/pL in MEK). Standards were evaporated to dryness at 70 "C under a nitrogen purge, and 100 pL of pyridine and 100 pL of BSTFA were added to each. Vials were capped, shaken briefly, and heated at 70 "C for 30 min, after which the contents were transferred to an autosampler vial for analysis. Sample Preparation. After sampling and gravimetric determination of RSP, filter pads were transferred from their cassette holders to 1-mL reaction vials, spiked with 20 pL of internal standard solution, and covered with 0.75 mL of pentane. Vials were capped and placed in an ultrasonic bath at 37 "C for 30 min after which the filters were removed, the pentane was evaporated, and derivatization was performed as described above. Analysis. Instrumental parameters were as follows: initial oven temperature, 100 "C; oven temperature program rate, 10 "C/min; final oven temperature, 300 "C; FID temperature, 350 "C; MS transfer line temperature, 310 "C; carrier gas, He at 0.5 psig (ca. 7 mL/min at 100 "C); injection, 1 pL (FID) and 3-5 pL (MS) on-column. Results and Discussion Solanesol, a primary terpenoid alcohol, was first isolated from flue-cured tobacco in 1956 by Rowland et al. (14)and was tentatively assigned a pentaterpenoid structure, which was later corrected to a trisesquiterpenoid structure (15-18). The structure of solanesol, composed of all trans isoprene units, is shown in Figure 1. Numerous authors (14,19-27) have investigated both the free and esterified solanesol content of tobacco and found concentrations ranging up to 4% of the dry leaf weight for the free alcohol, thus making solanesol the most abundant constituent of the tobacco lipid fraction. On the other hand, relatively little work has been directed toward determining solanesol in tobacco smoke, with the majority being done on mainstream smoke by Rodgman and coworkers (28-30) and others (31). The first report of solanesol determination in either sidestream or environmental tobacco smoke appeared only recently (12). Insufficient data exist to indicate a difference in solanesol leaf content of the major commercial tobacco types (flue-cured, Burley, Oriental, and Maryland). However, significant correlations have been made for other variables of tobacco growing and processing. Both flue-curing and aging have been shown to increase solanesol concentrations (21, 23), while close-growing practices (24), selective breeding (251, and ozonization (26, 32) have resulted in solanesol decreases. Furthermore, solanesol has been shown to be present in the laminae of tobacco leaf while absent from the stem and stalk (22)and also in increasing concentration from lower to upper leaf stalk position (23). Such findings seem to indicate that solanesol is associated Environ. Sci. Technol., Vol. 23, No. 9, 1989
1149
pretation of ETS chromatograms difficult due to the presence of solanesenes, which are formed by pyrolysis of solanesol/solanesyl esters during smoking. Therefore, attempts to determine solanesol by GC without derivatization were abandoned. Since the absolute minimum elution temperature was no longer necessary, we began increasing the thickness of the stationary-phase film from 0.05 pm to improve resolution. During this time, 0.53 mm i.d. fused silica columns with thin stationary-phase films (0.15 pm) became commercially available and were evaluated and found to be well suited for this application. However, these columns have a limited lifetime, and their performance must be routinely monitored and maintained to ensure the utmost reliability of results. For sample preparation, we initially used BSTFA containing 1% TMCS as catalyst and obtained rapid and complete derivatization of both solanesol and l-triacontan01 (internal standard). However, chromatograms on the commercially available columns began to indicate the presence of solanesenes in the analysis of standards after 10 injections. These degradation products would subsequently increase until column performance was unacceptable. Rinsing the column would temporarily restore the initial level of performance, but degradation again became apparent after only 2 or 3 additional injections. After visualizing crystalline deposits in the column inlet and attributing them to a buildup of pyridinium chloride, we switched derivatizing reagents to BSTFA without TMCS and experienced dramatically improved column performance. However, degradation of standards still becomes apparent after 40-50 injections, at which time the column is removed, rinsed with approximately 20 mL each of methanol, acetone, and pentane (in that order), and dried overnight in an oven at 60 OC under helium flow. When treated in this manner, the column performance level can be maintained through two or three washing sequences (representing 150-200 injections) before the columns are discarded. Preliminary experiments using hexane as derivatizing solvent instead of pyridine showed no appreciable differences in column longevity. Recent analyses with a 15 m X 0.32 mm i.d. capillary column coated with a 0.1-pm film of methylpolysiloxane connected to a 1 m X 0.53 mm i.d. retention gap with an all-glass “press-fit” butt connector show continued improvement in the chromatography and elution of derivatized solanesol without degradation. Retention gaps with nonpolar deactivation treatment (D4) exhibit poor performance after only a few injections, whereas those with polar deactivation treatment (Carbowax) perform extremely well for 30 or more injections. This observation is consistent with prior experiencesthat polar precolumns are more resistant to destructive contamination than nonpolar ones. With this combination, the retention gap effectively protects the analytical column and need only be replaced when solanesol shows signs of decomposition. For quantitation of free solanesol concentrations in ETS, the internal standard method utilizing 1-triacontanol as standard was used. The requirements for a good internal standard make 1-triacontanolan ideal choice. Being a high molecular weight primary alcohol, it tracks solanesol extremely well from filter extraction and derivatization through GC analysis. Additionally, it is a stable compound, is available pure, fits into an open window in the chromatogram, has never been identified in tobacco smoke, and is not likely to occur in an indoor environment. As a result, complete recovery of solanesol from filter samples is not a necessity; the only requirement is that the recovery of solanesol and 1-triacontanol be equivalent.
-
0
5
10
15
20
Time (min)
Figure 2. Chromatogram of 500 pg of solanesol and 1-triacontanol (internal standard) as their TMS derlvatives.
with chloroplasts in the leaf and also explain the lower concentration of solanesol in reconstituted tobacco sheet, which is fabricated from a large proportion of stems. These various correlations may be useful in explaining variations in ETS solanesol delivery for different cigarette blends. The first published gas chromatographic method for determining solanesol in tobacco by Severson et al. (20) utilized trimethylsilyl derivatization and analysis on short, packed columns following earlier work on polyisoprenoid alcohols reported by Wellburn and Hemming (33). Direct analysis of underivatized free solanesol was impossible due to thermal degradation to solanesenes. Additional methods have been described using trimethylsilylation (34) and perhydrogenation (23) followed by GC analysis. The first determinations of solanesol by GC with capillary columns reported here and previously (12)represent a marked improvement due to the inherent advantages of open tubular columns over packed columns. These advantages combine to enable the elution of derivatized solanesol from the short, 3-m capillary columns at temperatures 20-40 “C below those reported with packed columns while at the same time realizing roughly a 5-fold increase in column efficiency. Also, this increased efficiency, combined with superior inertness, enables a reduction in minimum detectable quantities of solanesol resulting in improved sensitivity. A chromatogram of 500 pg of derivatized solanesol on a 3 m X 0.53 mm i.d. fused silica capillary column coated with a 0.15-pm film of DB-1 is shown in Figure 2. In initial experiments with solanesol (12),we prepared capillary columns of customized dimensions, which were not commercially available, in an attempt to chromatograph underivatized solanesol without thermal degradation to solanesenes. Although we were successful with standard solutions, this performance could not be maintained after a few injections of ETS samples and could not be routinely regenerated by column washing. In addition, underivatized solanesol was not well resolved from solanesenes on these short, extremely thin-film columns, which made inter1150 Environ. Sci. Technol., Vol. 23, No. 9, 1989
Table I. Recovery of Solanesol from Spiked Fluoropore Filter Pads Determined by Second-Order Polynomial Regression’ % recovery
solanesol, pg/mL 0 0.5 5.1 15.3 mean
*
n n = 5 at each concentration. ND. not detected. Table 11. Solanesol Method Development Results from Environmental Chamber with ETS from KlR4F Reference Cigarettesn sample
RsP, pg/m3
KlR4F blank
851 (31) 12 (10)
solanesol, pg/m3 GC/FID GC/MS
danesol/RSP wt % GC/FID GC/MS
34 (13) NDb
4.0 (1.6) 0
46 (8) ND
day
5.3 (0.9) 0
3 candles 3 candles oil lamp 4 oil lamp 5 lKlR4F 6 lKlR4F 7 combination 8 combination 9 2 full-flavor 10 2 low-tar 11 4 ultra-low-tar 12 2KlR4F 13 2 UK full-flavor’
186 128 48 132 328 353 698 655 925 544 1449 737 1050
188 178 55 38 345 373 753 701 1063 601 1563 824 1123
6 3 2 2 23 22 23 21 41 34 100 56 55
’United Kingdom product containing 100% flue-cured tobacco. Table IV. UV-PM and Solanesol/RSP Weight Ratio Results for Apportionment Study
’Results presented as mean (SD). * ND, not detected. Calibration curves are generated by plotting the solanesol/ 1-triacontanol peak area ratios versus solanesol concentration. The data are then fit to either a linear or second-order polynomial least-squares regression model, whichever is deemed more appropriate. Second-order regressions were used in this study since calibration results from both GC/FID and GC/MS showed slight, but significant curvature near the origin. Typical recovery data from solanesol-spiked filter pads are shown in Table I. After spiking, the pads (five at each concentration) were stored in the dark in a freezer for 24 h prior to analysis. Clearly, the recovery of solanesol from the Fluoropore filter pads is 100% even at the limit of quantitation, which is 0.5 pg/mL. The limit of detection for this method is estimated to be 0.2 pg/mL for flame ionization detection, which corresponds to approximately 0.2 pg/m3 for 2-h sample duration at 2 L/min. For solanesol to be a reliable tracer of ETS particulate matter (ETS-PM), it must be in a constant proportion to the particulate fraction of ETS aerosol for a variety of smoking products and environmental conditions. To study the relationship of solanesol to ETS-PM, environmental tobacco smoke was generated in an 18-m3environmental test chamber operated at 23 “C and 50% relative humidity in the static mode (i.e., no air exchanges) with recirculating fans on. A more detailed description of this chamber and associated instrumentation is available (35). Cigarettes were “human-smoked”in the chamber at 1 puff/min and samples were collected at 2 L/min for 2 h. In initial experiments, two University of Kentucky 1R4F (KlR4F) reference cigarettes were smoked on each of 5 days with duplicate samples taken each day for analysis. In addition, duplicate blank samples were obtained at the same flow rate and duration on 5 separate days in the chamber. The results of these experiments are given in Table 11. Limits of detection in this early phase of method development were determined to be 0.1 and 0.2 pg/filter and 0.4 and 0.8 pg/m3 for GC/FID and GC/MS analysis, respectively. The solanesol/RSP ratio range of 4-5% reported previously for ETS from KlR4F cigarettes (12) represents a composite of the GC/FID and GC/MS analyses. After additional experiments, these two techniques have been demonstrated to be internally consistent, with results by GC/MS always slightly higher than those obtained by GC/FID. Since we do not have GC/MS data for all samples obtained, and for the sake of brevity, fur-
gravimetric piezobalance nicotine, RSP, pg/m3 RSP, pg/m3 pg/m3
experiment
1 2 3
NDb 110 92 109 104 10
* SD
Table 111. Results from Environmental Chamber Sampling
day 1 2 3 4 5 6 7 8
UV-PM, pg/m3 8 9 8 3 337 314 450 422
solanesol/RSP ratio, wt % 0 0 0 0
3.5 3.6 1.6 1.6
ther discussion is restricted to GC/FID results. A typical chromatogram of environmental tobacco smoke from a KlR4F cigarette collected on a Fluoropore filter pad is shown in Figure 3, revealing solanesol as the most abundant component of ETS-PM when collected and analyzed in this manner. (The off-scale peak near 8 min is a filter-related artifact.) These experiments revealed that the solanesol/RSP ratio is constant at ca. 4% for the KlR4F reference cigarette. Additional experiments were then designed and conducted to investigate the accuracy of both the solanesol and UV-PM procedures for correctly apportioning the ETS-PM contribution to RSP under controlled conditions and also to assess the solanesol composition of ETS from several commercial cigarettes. For the apportionment phase of the study, three separate combustion sources of RSP were introduced in the chamber individually and collectively. These sources consisted of three ordinary wax dinner candles, an oil lamp, and one KlR4F cigarette. Since the cigarette requires approximately 10 min to smoke under “normal”conditions (1puff/min), the other sources were ignited, allowed to burn for 10 min, and then extinguished. The chamber was operated in the static mode with sample flow rates and durations as before. In each case, the experiment was duplicated on succeeding days. Data from pertinent determinations from these tests are given in Table 111. With the exception of the gravimetric determination of RSP on day 4, all results replicated extremely well. The presence and decline of vapor-phase nicotine in the chamber during the combustion of the candles and oil lamp is attributable to a nicotine background in the chamber (a characteristic of virtually any closed environment with a history of substantial smoking activity). Solanesol/RSP ratios and results of UV-PM determinations for the apportionment study are listed in Table IV. The UV-PM method was developed and calibrated Environ. Sci. Technol., Vol. 23, No. 9. 1989
1151
Table V. Solanesol/RSP Weight Ratios for All Cigarette-Only Experiments
i;
Y 2
4
$
I
d
1
1
0
5
10
w z w
Yz 4
8
d 1 20
Time (min) Flgure 3. Chromatogram of RSP fraction of ETS generated from KlR4F cigarettes in an environmental chamber.
by using ETS-PM from KlR4F cigarettes. As a consequence, when ETS-PM is the only source of RSP in the chamber, the results for UV-PM and RSP should agree. As evidenced by the data in Tables I11 and IV for days 5 and 6, this agreement is excellent with UV-PM/RSP ratios being 1.0 and 1.1, respectively. The ratios, then, of UVPM/RSP for days 7 and 8 represent the percentage of the RSP attributable to ETS-PM as estimated by UV-PM. These calculations result in the estimation that 64% of the RSP from the candle/lamp/cigarette combination is attributable to the cigarette. The estimation of apportionment using solanesol results is a bit more straightforward. From Table IV, the solanesol/RSP ratios are 3.5 and 3.6%, respectively, for days 5 and 6 (KlR4F cigarette only). Accordingly, when solanesol constitutes 3.5% of RSP, this indicates that all RSP collected is from ETS. Any reduction from 3.5% indicates the presence of respirable particles that do not contain solanesol, i.e., non-ETS-PM. Results from days 7 and 8 show this ratio to be 1.6%; therefore, the ratio of these two percentages (1.613.55) represents the fraction of RSP attributable to ETS-PM. This calculation results in the estimation that 45% of the RSP from the candlellamplcigarette combination is attributable to the cigarette. An estimate of the true contribution of ETS-PM to RSP for this combination of sources is obtained from the data in Table 111. With RSP concentrations determined gravimetrically, the average of days 5 and 6 (cigarette only) divided by the average of days 7 and 8 (combination)yields a calculated apportionment of 50%. (A similar calculation using RSP concentrations determined by the piezobalance predicts 49% .) Consequently,the errors in apportionment resulting from RSP, W - P M , and solanesol determinations in this study are +loo, +28, and -lo%, respectively. The ability of the UV-PM procedure to predict the correct apportionment of ETS-PM in RSP for these conditions is quite good, while that of solanesol is excellent. As expected, the UV-PM method slightly overestimates 1152
day
KlR4F KlR4F KlR4F full-flavor low-tar ultra-low-tar UK full-flavor
(see Table 11) 5 and 6 12 9 10
11 13
chamber mode
solanesol/RSP ratio, % f SD
normaln normal lights onb normal normal normal normal
4.0 f 1.6 3.5 f 0.8 2.3 f 0.1 3.0 f 0.3 2.1 0.8 2.0 f 0.6 2.2 f 0.5
*
One 8-ft, 215-W fluorescent light on during smoking (10 min) and then off for remainder of sample duration. fluorescent light on during smoking and two 215-W fluorescent lights and three 60-W incandescent lamps on for the remainder of sample duration. United Kingdom product containing 100% flue-cured tobacco.
v)
I 15
product
Envlron. Sci. Technol., Vol. 23, No. 9, 1989
the contribution while total RSP is a gross overestimation. Although most scientists recognize the inappropriateness of using RSP as an indicator of ETS, some continue to use this parameter without qualification. In addition to demonstrating the applicability of solanesol determination for correctly apportioning RSP into ETS and non-ETS components, this example also illustrates the significant contributions to RSP from other potential indoor sources. The data in Table I11 for days 9-11 and 13 represent ETS generated from commercial cigarettes, while that collected on day 12 utilized the KlR4F cigarette with alternate lighting conditions in the chamber. Solanesol/RSP ratios are listed in Table V for all cigarette-only experiments conducted to date in the environmental chamber. These results, although statistically inconclusive, suggest several trends that are currently under investigation. Comparison of the first two table entries reflects improvements in the analysis and quantitation of solanesol from our initial experiments as evidenced by the improved precision. Some effect of chamber lighting on the solanesol/RSP ratio is indicated for the KlR4F cigarette. Of more interest than the apparent reduction in ratio is the improved precision. Further experiments that will be conducted will have lights on for the duration of sampling. The data for commercial products seem to indicate a trend in reduced solanesol/RSP ratio upon going from the “full-flavor” product, to the “low-tar” product, to the “ultra-low-tar” product, which is not altogether unexpected. The full-flavor UK product was of interest because of the correlation of increased solanesol content with fluecuring of tobacco leaf. Containing 100% flue-cured tobacco, the UK cigarette has a solanesol ratio that is apparently smaller than that for the KlR4F cigarette, which contains only 33% flue-cured tobacco (36). Obviously, other parameters, or combinations thereof, are more influential in determining the solanesol content of ETS-PM. As an illustration of the potential utility of this method, the results of several field trials are listed in Table VI. All samples were collected during the last week of November 1987 in Cambridge, MD, or in transit (automobile) from Cambridge to Winston-Salem, NC. Data reported for the home are for samples collected on 2 separate days in the kitchen. Typically, no smoking activity occurs on the sales floor of the department store although, occasionally, customers enter the store with a lit cigarette and extinguish it once inside. This, or recirculation of air from a break room, could explain the minute quantity of nicotine detected. Although no smoking occurred in the automobile
Table VI. Results of Field Trials’ location
sample duration, h
approx no. of cigarettes smoked
billiard parlor home home department store automobile blank
2 4 4 4 8
346 6c 6c 0 0
RSP 355 187 212 55 18
(concn,d in gg/m3) nicotine solanesol
19.4 12.1 14.4 0.6 0.4 ND
12.8 6.4 6.6 ND ND ND
Sol/RSP ratio, wt%
3.6 3.4 3.1 0 0 0
Samples acquired at 1 L/min for time indicated. bActual count, 30 cigarettes, 4 cigars. Kitchen only. ND, not detected.
during sampling, the small amount of nicotine detected here is most likely attributable to desorption from the clothes, contents, or upholstery in the car‘. Assuming the weight percent relationships between solanesol and RSP shown in Table V are representative of commercially available smoking products, the results in Table VI indicate that, in the first three instances, the majority of RSP measured is attributable to tobacco smoke. Such a conclusion is not surprising considering the substantial amount of smoking activity in each of these sampling situations. The solanesol/RSP ratio obtained in the billiard parlor is apparently higher than the average result of values reported in Table V. This may, in part, be attributable to a significant portion of the ETS arising from cigar smoke. In the two results from home sampling, the only product smoked was a full-flavor menthol cigarette with essentially the same blend content as the fullflavor product listed in Table V. The agreement of these field results with experimental chamber data is excellent. The solanesol/RSP ratios for the department store and automobile samples indicate the exact opposite effect. Here, none of the RSP measured can be attributed to tobacco smoke, as would be expected. The particular sampling situations chosen here were intended to illustrate the two extremes of RSP apportionment with regard to ETS contributions, and the results indicate excellent performance of the solanesol/RSP ratio approach. Of more interest are environments with “moderate” smoking activity and better ventilation, such as restaurants, offices, and public conveyances where a realistic apportionment of RSP sources is needed. Clearly, more work needs to be done before solanesol can be used as a routine tracer of ETS. As demonstrated here, there apparently are measurable differences in the solanesol percentage of RSP delivered to the environment from different smoking products. More thorough investigations of the effect of various cigarette construction parameters and environmental conditions on solanesol delivery are required and are in progress. Like nicotine, it is anticipated that the only measurable contribution of solanesol to an indoor environment would be from tobacco sources. Solanesol is, of course, characteristic of plants in the Solanaceae family, a member of which is the Nicotiana genus. Many other members of this family that contain solanesol are also those that contain traces of nicotine, e.g., tomato, potato, eggplant, and pepper. Outside of a remote possibility arising from cooking sources, the potential for interference is extremely minute. However, unlike nicotine, solanesol is not expected to shift equilibrium between vapor and particle phases of the ETS aerosol under any normal conditions encountered in an indoor environment. Additionally, because of its high molecular weight and extreme nonvolatility, solanesol is truly associated only with the particle phase of ETS and will not be lost from filter pads used for collection due to
evaporation (as can happen with nicotine, neophytadiene, and other major tobacco smoke constituents). In chamber experiments using various combinations of filter pads and XAD-4 sorbent tubes connected in series, we have verified these intuitively obvious phenomena. As a result, of all the potential tracers that have been suggested for quantifying ETS particulate concentrations in indoor environments, solanesol appears to be the best suited candidate.
Acknowledgments We gratefully acknowledge the assistance of David Heavner, Barbara Collie, and Paul Nelson in operating the environmental test chamber and associated instrumentation. Registry No. Solanesol, 13190-97-1.
Literature Cited (1) National Research Council, Committee on Passive Smoking Environmental Tobacco Smoke. Measuring Exposures and Assessing Health Effects; National Academy Press: Washington, DC, 1986;Chapter 5. (2) Ogden, M. W. J. Assoc. Off.Anal. Chem., in press. (3) Conner, J. M.; Oldaker, G. B., III; Murphy, J. J. submitted for publication in Environ. Technol. Lett. (4) Ogden, M. W. Presented at the lOlst Annual International Meeting of The Association of Official Analytical Chemists, San Francisco, CA,September, 1987;Poster 239A. (5) Eudy, L. W.; Thome, F. A.;Heavner, D. L.; Green, C. R.; Ingebrethsen, B. J. Presented at the 39th Tobacco Chemists’ Research Conference, Montreal, Canada, October 2-5,1985. (6) Eudy, L. W.; Thome, F. A.;Heavner, D. L.; Green, C. R.; Ingebrethsen, B. J. In Proceedings of the 79th Annual Meeting of the Air Pollution Control Association; June 22-27, 1986, Minneapolis, MN, Paper 86-38.7. (7) Eatough, D.J.; Benner, C.; Mooney, R. L.; Bartholomew, S.; Steiner, D. S.; Hansen, L. D.; Lamb, J. D.; Lewis, E. A. In Proceedings of the 79th Annual Meeting of the Air Pollution Control Association, June 22-27,1986,Minneapolis, MN, Paper 86-68.5. (8) Spengler, J. D.; Treitman, R. D.; Testeson, T. D.; Mage, D. T.; Soczek, M. L. Environ. Sci. Technol. 1985,19,700. (9) Spengler, J. D.;Dockery, D. W.; Turner, W. A.; Wolfson, J. M.; Ferris, B. G. Atmos. Enuiron. 1981, 15, 23. (10) Dockery, D. W.; Spengler, J. D. Atmos. Enuiron. 1981,15, 335. (11) Oldaker, G. B., 111; Perfetti, P. F.; Conrad, F. W., Jr.; Conner, J. M.; McBride, R. L. Int. Arch. Occup. Enuiron. Health, in press. (12) Ogden, M. W.; Maiolo, K. C. HRC CC, J. High Resolut. Chromatogr. Chromatogr. Commun. 1988, 11, 341. (13) Ogden, M. W.; McNair, H. M. HRC CC, J. High Resolut. Chromatogr. Chromatogr. Commun. 1985,8, 326. (14) Rowland, R. L.; Latimer, P. H.; Giles, J. A.J. Am. Chem. SOC.1956, 78, 4680. (15) Erickson, R. E.; Shunk, C. H.; Trenner, N. R.; Arison, B. H.; Folkers, K. J . Am. Chem. SOC.1959, 81, 4999. (16) Kofler, M.; Langemann, A.;Ruegg, R.; Gloor, U.; Schwieter, U.; Wuersch, J.; Wiss, 0.;Isler, 0. Helu. Chim. Acta 1959, 42, 2252. Environ. Sci. Technol., Vol. 23, No. 9, 1989 1153
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Meeting of the Air Pollution Control Association; June 22-27, 1986, Minneapolis, MN, Paper 86-37.9. (36) Tobacco and Health Research Institute The Reference and Research Cigarette Series; The University of Kentucky Printing Services: Lexington, KY, 1984. Received for review January 6,1989. Accepted M a y 15, 1989. This work was presented, in part, at the Indoor and Ambient Air Quality Conference, 13-15 J u n e 1988 in London, England, and at the 42nd Tobacco Chemists’ Research Conference, 2-5 October 1988 i n Lexington, KY.
Human Exposures to Chemicals through Food Chains: An Uncertainty Analysis Thomas E. McKone”
University of California, Lawrence Livermore National Laboratory, P. 0. Box 5507, L-453, Livermore, California 94550 P. Barry Ryan
Harvard School of Public Health, 665 Huntington Avenue, Boston, Massachusetts 02115 Using models that link human ingestion exposures to chemical concentrations in air and soil, we assess the amount and source of uncertainties in model predictions. We use pathway exposure factors (PEFs) to convert environmental concentrations to human exposures for the air/plant/food- and soil/ plant/food-ingestion pathways. Input data are presented as probability distributions, which are used to construct output probability distributions for child and adult exposures associated with arsenic and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Our analysis reveals that, without information on the distribution and variance of input parameters, one can underestimate the mean value of exposure distributions by using only mean or median values of the input parameters. We also find that much of the overall uncertainty in exposure is attributable to uncertainty in biotransfer factors and that uncertainties in the input data limit the precision of exposure predictions to a 90% confidence range of roughly 2 orders of magnitude. Introduction
The EPA ( 1 ) defines exposure as “the contact with a chemical or physical agent”. This implies that, when we perform an assessment of human exposure to environmental contaminants, we translate environmental concentrations into quantitative estimates of the amount of contaminant that passes through the lungs, across the gut wall, and through the skin surfaces of individuals within a specified population. The quantity of chemical daily crossing these boundaries provides the basis for assessing health detriment within the population. This process of 1154
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estimating exposure with limited data and extrapolating to large and diverse populations requires many assumptions, inferences, and simplifications. How well these exposure estimates reflect actual exposures is still largely an unanswered question. There are many uncertainties and some defy quantification. Nonetheless, only by examining exposure data and proposing exposure models can we gain the insight needed to manage the potential hazards of environmental contaminants. An exposure assessment can be most valuable when it provides a comprehensive view of exposure routes and identifies major sources of uncertainty and what impact this will have on the decisionmaking process. Yet, the common practice in exposure evaluations has often been to use single exposure routes and mean or point estimates for most parameters. Human exposures to ambient airborne pollutants is an area where uncertainty is particularly important. Much of the uncertainty is attributable to ignorance about the values of particular process parameters. Inhalation is typically the pathway given the most attention even though food-chain pathways, which are less well understood, could be the dominant contributor to total exposure. Consider for example the chemical 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the trace metal arsenic, which are found in ambient air attached to suspended dust or combustion particles. These contaminants can be found in the air as a result of hazardous waste incineration or as a result of land disposal of municipal or industrial wastes. In order to assess the contribution to lifetime risk of ingestion exposure relative to inhalation exposures, it is useful to construct steady-state models that allow comparison of lifetime average exposures. A risk assessment
0013-936X/89/0923-1154$01.50/0
0 1989 American Chemical Society
