Environ. Scl. Technol. 1994, 28, 363-363
Gas/Particle Partitioning of Polycyclic Aromatic Hydrocarbons and Alkanes to Environmental Tobacco Smoke James F. Pankow,' Lorne M. Isabelle, Donald A. Buchholz, Wental Luo, and B. Douglas Reeves
Department of Environmental Science and Engineering, Oregon Graduate Institute, P.O. Box 9 1000, Portland, Oregon 9729 1-1000 Introduction General. Since environmental tobacco smoke (ETS) has been implicated as a cause of human cancer (1-41, there is a need to understand the physical-chemical behavior of the carcinogenic and toxic organic compounds present in ETS. These compounds include the polycyclic aromatic hydrocarbons (PAHs) and a variety of substituted PAHs. One very important physical-chemical process governing the behavior of organic compounds in air is partitioning between the gas and aerosol particulate phases. Such gas/particle (G/P) partitioning determines the distribution of a given compound between the gas and particulate phases. With pure compound liquid vapor pressures (p:) in the range 10-6-100.0Pa (-10-8--10-2 Torr), semivolatile organic compounds (SOCs) (which include many of the PAHs and substituted PAHs) are of special interest in the G/P partitioning context because their intermediate volatilities permit them to be present to significant degrees in both phases. Volatile compounds (e.g., benzene) are usually almost exclusively in the gas phase, and low-volatility organic compounds (e.g.,organic diacids) are usually almost exclusively in the particulate phase. Understanding G/P partitioning for ETS is important because dose/response relationships are strongly related to the physical forms in which the compounds are present when exposure occurs. Although a fair amount is known about the composition of ETS (1,5-15), there has been little study of G/P partitioning in indoor air contaminated with ETS. As a result, currently available epidemiologic studies on the effects of ETS do not have adequate dose/ response documentation (1,2,6). In addition to affecting compound toxicity, G/P partitioning is important in predicting the (1)behavior of tracers used to apportion indoor air pollution among the different possible sources (5, 6); (2) deposition of gases and particles (e.g., see refs 1, 11, and 16) on indoor surfaces in models of indoor air quality; and (3) effectiveness of air filters and electrostatic particle precipitators in removing air toxics from indoor air. Partition Constant Kp, G/P partitioning has been examined to a considerable extent in the outdoor environment under both urban and rural conditions (e.g.,refs 17-25). An equation that has been used successfully to parameterize partitioning in the urban environment is (18, 20, 24, 25):
where K , (m3/pg) is a compound- and temperaturedependent partitioning constant; F (ng/m3) and A (ng/ m3)are the particle-associated and gaseous concentrations, respectively; TSP (pg/m3) is the level of total suspended particulate matter in the air. Since (FITSP) gives the ~
~~
~~
* Corresponding author. 0013-936X/94/0928-0363$04.50/0
0 1994 American Chemical Society
concentration on/in the particulate matter (in units of ng/pg), the constant K , represents the sorbed/gaseous concentration ratio. Decreasing TSP causes the G/P equilibrium to shift toward the gas phase and vice versa. K , values decrease with increasing temperature. With urban particulate matter (UPM) at a given temperature, it has been found that a given SOC will exhibit K , values that are surprisingly similar from city to city. Equating a measured value of (F/TSP)/A with the thermodynamic constant K , carries with it the assumption that equilibrium was present in the air a t the time of sampling and that all of the measurements were made without error. In this paper then, the group (F/TSP)/A will be used to refer to measured values of (F/TSP)/A; usage of the symbol K , will be reserved for discussions of the underlying thermodynamics. Dependence of log Kpon log pi. Equation 1does not, by itself, indicate whether the partitioning is primarily adsorptive to surfaces, primarily absorptive to the portion of the TSP that is organic phase, or some combination of adsorption and absorption. Nevertheless, for any combination of the two sorption mechanisms, theory predicts (26) that log K , values will be correlated (negatively) with log pi according to an equation of the type log K p = m, log p:
+ b,
Theory predicts that m, will usually be close to -1 (26). When we correlate the entire Yamasaki et al. (18)data set for Osaka UPM (179 points, excluding 5 points for phenanthrene + anthracene due to breakthrough) against logpi, we obtain m, = -1.02 and b, = -8.09 (see Figure 1). As noted above, in the urban environment, measured K , values have been found to be quite similar from city to city. K , values measured by Yamasaki et al. (18) in Osaka, Japan have been used to successfully predict the G/P partitioning of PAHs in Chicago and in a highlycontaminated roadway tunnel where TSP levels can exceed 1000 pglm3 (21, 25). This type of predictive accuracy suggests that G/P partitioning might be as reproducible in other settings, e.g., in the indoor environment wherein the health effects of toxic organic compounds are of increasing interest. In this paper, we seek to test whether G/P partitioning to indoor ETS follows the general behavior observed for UPM, as represented by eqs 1and 2. Experimental Section Sampling. Sampling was carried out at a local business that provides a form of social recreation. Fire regulations limit occupancy in the -38 m by 33 m by 5 m high hall to about 300 people at any one time; 200 people are commonly present, with perhaps 30 5% smoking a t any one time. A smoky, blue haze is often clearly visible in the air. Beside tobacco smoke, no other significant forms of indoor air pollution were apparent in the hall. Although some grilling of food occurs, the cooking area is quite small and Envlron. Sci. Technol., Vol. 28, No. 2, 1994 363
Table 1. Mean log ( F / T S P ) / A(m3/fig) Values (= log Kp at Equilibrium) for ETS for Three Sampling Eventse
O i
compound
-Ij -5
I
-6 1 -8
fluorene phenanthrene anthracene fluoranthene pyrene chrysene ETS
-1.00
-6.84 0.93
UPM
-1.02
-8.09
0.96
I
1
I
I
I
-7
-6
-5
-4
-3
6-7
c16 c17
-2
CZO CZl cz2
Figure 1. (NTSP)/A vs log p: for PAHs sorbing to urban particulate matter (UPM) (based on data of ref 18) and to environmental tobacco smoke (ETS) particles at 25 O C . ETS error bars are f 1 SD for three sampling events.
-
is vented. The overall building ventilation allows the air to become substantially cleaner within about 1h after the patrons leave. Therefore, the samples taken may be considered to be “fresh” rather than “aged” ETS. The sampler involved a 90-mm-diameter glass fiber filter followed by two parallel gas sampling trains. One train employed polyurethane foam (PUF) plugs to collect the PAHs, and the second employed Tenax-GC to collect the more volatile compounds. The flow rates were as follows: filter, -70 L/min; PUF train, -70 L/min; Tenax train, 0.25 L/min. Sampling durations were short (-4 h) so volatilization losses from the filter due to reductions in concentration during sampling are expected to have been minimal; the high TSP levels are expected to have prevented gas adsorption by the filter from being important relative to sorption by the TSP collected. Sample Workup and Analysis. Each filter and PUF was Soxhlet-extracted for 3.5 h using 125 and 400 mL, respectively, of methylene chloride. Each extract was reduced to -4 mL using a Kuderna-Danish apparatus, dried on a column of NazSOs/silica gel (0.5 g/0.5 g), blown down with Nz gas to a final volume of 0.2 mL, and then analyzed by capillary GUMS. Internal and external standards were used throughout to monitor for recoveries. Each Tenax cartridge was thermally desorbed as described elsewhere (27, 28). Results and Discussion
General. Data from three sample events a t -25 “C were obtained. For samples 1 and 3, the PUF data were used; for sample 4, the Tenax data were used. [For many compounds, PUF and Tenax trains have been shown to give essentially the same concentrations (27)l. The TSP levels for samples 1 , 3 , and 4 were 414,578, and 701 pg/m3. An average TSP of -570 pglm3 has been found in the Baltimore Harbor Tunnel (21). PAHs. Figure 1 and Table 1 give measured values of log (F/TSP)/A vs log p i for PAHs sorbing to ETS. Each ETS point is an average; the error bars represent f l standard deviation ( f l SD) for the three samplings. Variability in the sorption properties of the ETS (e.g., as due to variations in composition and relative humidity) was one likely source of variability in the data. The effects 364
Environ. Sci. Technol., Vol. 28,No. 2, 1994
ClS c19
log (F/TSP)/A
f l SD
logp;
PAHs -5.09 -3.66 -3.35 -2.76 -2.59 -1.55
0.30 0.52 0.67 0.21 0.23 0.67
-2.24 -2.98 -3.01 -4.07 -4.24 -5.42
n-Alkanes -4.93 -4.35 -3.95 -3.49 -3.01 -2.52 -2.24
0.17 0.14 0.13 0.16 0.09 0.18 0.67
-3.16 -3.27 -3.72 -4.36 -4.84 -5.18 -5.70
0 f l SD for those values, and log pi (Torr) values, all for for selected PAHs and n-alkanes.
-25
‘C
of relative humidity on sorption to UPM have been examined by Pankow et al. (29). The temperature (2“) dependence of log K , values is due largely to the T dependence of log p : (19,26),and so plots of log K , vs log p i are independent of T over small ranges in T. Thus, in Figure 1, although the ETS line was obtained a t -25 “C, and the data underlying the UPM line were obtained over a range of temperatures (18),the two lines can be compared directly. In particular, the ETS line indicates that G/P partitioning to ETS is characterized by the same type of dependence on p i that is seen for UPM. The difference in the two slopes is not statistically significant. However, the line for ETS is significantly (99.9+ % confidence level) higher than that for UPM, indicating stronger sorption (factor of 17) of PAHs to these ETS samples. (The possibility of encountering UPM that is more sorptive of PAHs than the ETS sampled here is not ruled out.) One possible reason for the difference might be a higher specific surface area for the ETS particles, making them more adsorptive. Alternatively, it seems quite possible that a higher fraction of available organic matter (as from cigarette “tar”) could make the ETS particles very absorptive. Pankow (26) provides a framework for understanding the relative importance of the adsorption and absorption mechanisms. Alkanes. The precision in the measured log (F/TSP)/A values for the alkanes (Table 1 and Figure 2) was found to be very high, with an average fl SD value of only 0.22. As with the PAHs, the log (F/TSP)/Avs logp; correlation line was found to have a slope very close to the theoretically predicted value of -1. Also, the degree of correlation was very high. Comparing Figures 1 and 2, the alkanes are seen to be less strongly sorbed by the ETS particles than the PAHs. This type of difference between compound classes is not unexpected; for G/P partitioning to UPM, it has been found that the PAHs are more strongly sorbed than are organochlorines (20). Data for sorption of alkanes to UPM is also available (30, 31). It is likely that the tobacco bases (e.g., nicotine, the substituted pyridines, etc.) will follow their own log (F/TSP)/A vs log p i correlation line for sorption to ETS.
-
Conclusions
The good linearities in Figures 1and 2, the slope values that are very near the predicted value of -1, and the
"I
'alkanes
T
slope E TS
*6-
-0.99 I
-8
-7
ETS
int
r8
-7.77
0.97
1
-6
I
I
-6
m I
-4
I
-3
i
-2
log Pi Figure 2. Measured values of log (F/TSP)IA vs log p: for alkanes sorbing to environmental tobacco smoke (ETS) particles at -25 O C . ETS error bars are f l SD for three sampling events.
reasonable to excellent event-to-event reproducibility observed here indicate that predictive G/P partitioning calculations can be made for organic compounds in indoor air contaminated with ETS. Much-improved compounddependent dose estimates that differentiate between the gaseous and particle-associated fractions can therefore be incorporated into studies of human exposure to ETS. In order to permit that incorporation, study is needed into (1)the underlying reproducibilities of the measured Kp values; (2) the temperature and relative humidity dependence of those Kp values; and (3) the effects of aging on the sorption properties of ETS. Our laboratory is currently engaged in such research because of the importance of ETS and because we hope to improve our understanding of the general G/P partitioning process as it relates to ambient, outdoor particulate matter. Acknowledgments
The authors are grateful for support provided by the
U.S.EPA Office of Exploratory Research (USEPA/OER) under Grant R-816353-01-0. We are deeply appreciative to Terri Jo Bonbright and the Columbia Empire Volleyball Association for assistance in the sampling. The technical assistance of A. James Tesoriero is also gratefully acknowledged. Literature Cited (1) National Academy of Sciences. Environmental tobacco
smoke. Measuring exposure and assessing health effects; National Academy Press: Washington, DC, 1989. (2) Report of the Surgeon General. The Health Consequences of Involuntary Smoking. U.S. Department of Health and Human Services: Washington, DC, 1986. (3) Balter, N.; Schwartz, S. L.; Kilpatrick, S. J.; Witorsch, P. Proceedings of the 79thAnnual Meeting of the AirPollution
Control Association; Air Pollution Control Assoc.: Minneapolis, MN, 1986; Paper 86-80.9. Kuller, L. H.; Garfinkel, L.; Correa, P.; Haley, N.; Hoffman, D.; Preston-Martin, S.; Sandler, D. EHP, Environ. Health Perspect. 1986, 70, 57-69. Eatough, D. J.; Benner, C. L.; Bayona, J. M.; Caka, F. M.; Richards, G.; Lamb, J. D.; Lewis, E. A.; Hansen, L. D. Environ. Sci. Technol. 1989, 23, 679-687. Eatough, D. J.; Benner, C. L.;Tang, H.; Landon, V.; Richards, G.; Caka, F. M.; Crawford, J.; Lewis, E. A.; Hansen, L. D.; Eatough, N. L. Environ. Znt. 1989, 15, 19-28. Chamberlain W. J.; Stedman, R. L. The Chemistry of Tobacco and Tobacco Smoke; Schmeltz, I., Ed.; Plenum Press: New York, 1972; pp 99-105. Chuang, J. C.; Mack, G. A.; Kuhlman, M. K.; Wilson, N. K. Atmos. Environ. 1991, 25B, 369-380. Heavner, D. L.; Ogden, M. W.; Nelson, P. R. Environ. Sci. Technol. 1992,26, 1737-1746. Ishizu, Y.; Kaneki, K.; Okada, T. J.Aerosol Sci. 1987, 18, 123-129. Lofroth, G . Mutagen Res. 1989,222, 73-80. Lofroth, G.; Burton, R. M.; Forehand, L.; Hammond, S. K.; Seila, R. S.; Zweidinger, R. B.; Lewtas, J. Enuiron. Sci. Technol. 1989,23,610-614. Nelson, P. R.; Heavner, D. L.; Collie, B. B.; Malolo, K. C.; Ogden, M. W. Environ. Sci. Technol. 1992,26,1909-1921. Sakuma, H.; Shimojima, N.; Sugawara, S. Agric. Biol. Chem. 1978,42, 359-363. Tang, H.; Richards, G.; Benner, C. L.; Tuominen, J. P.; Lee, M. L.; Lewis, E. A.; Hansen, L. D.; Eatough, D. L. Environ. Sci. Technol. 1990, 24, 848-852. Repace, J. L.; Lowrey, A. H. Science 1980,208, 464-472. Junge, C. E. In Fate of Pollutants in the Air and Water Environments; Suffett, I. H., Ed.; Wiley: New York; pp 7-26. Yamasaki, H.; Kuwata, K.; Miyamoto, H. Environ. Sci. Technol. 1982,16, 189-194. Pankow, J. F. Atmos. Environ. 1987,22, 2275-2283. Pankow, J. F.; Bidleman, T. F. Atmos. Environ. 1992,26A, 1071-1080. Benner, B. A.; Gordon, G. E.; Wise, S. A. Environ. Sci. Technol. 1989,23,1269-1278. McVeety, B. D.; Hites, R. A. Atmos. Environ. 1988,22,511536. Manchester-Neesvig, J. B.; Andren, A. W. Environ. Sci. Technol. 1989,23, 1138-1148. Pankow, J. F. Atmos. Environ. 1991,25A, 2229-2239. Pankow, J. F. Atmos. Environ. 1992,26A, 2489-2497. Pankow, J. F. Atmos. Enuiron. 1994,28, 185-188. Ligocki, M. P.; Pankow, J. F. Anal. Chem. 1985,57,11381144. Hart, K. M.; Isabelle, L. M.; Pankow, J. F. Environ. Sci. Technol. 1992,26, 1048-1052. Pankow, J. F.; Storey, J. M. E.; Yamasaki, H. Environ. Sci. Technol. 1993,27, 2220-2226. Hart, K. M. Ph.D. Dissertation, Oregon Graduate Institute, Portland, OR, 1989. Foreman, W. T. Ph.D. Dissertation, University of South Carolina, Columbia, SC, 1986. Received for reuiew August 3, 1993. Revised manuscript received October 25, 1993. Accepted November 5, 1993." Abstract published in Advance ACS Abstracts, December 15, 1993.
Envlron. Sci. Technol., Vol. 28, No. 2, 1994 365
