Sidestream tobacco smoke constituents in indoor air modelled in an experimental chamber— Polycyclic aromatic hydrocarbons

Environntent International, VoL 15, pp. 57- 64, 1989 Printed in the U.S.A. All rights reserved.

0160-4120189 $3.00 +.00 Copyright 01989 Pergamon Press plc

SIDESTREAM TOBACCO SMOKE CONSTITUENTS IN INDOOR AIR MODELLED IN AN EXPERIMENTAL C H A M B E R POLYCYCLIC AROMATIC HYDROCARBONS Trinh Vu-Duc and Cong-Khanh Huynh Institute of Medicine and Occupational Hygiene, University of Lausanne CH-1005 Lausanne, Switzerland E1 87-626 (Received4 November 2987; Accepted 4 April 2989) Exposure to sidcstream tobacco smoke is concerned with constituents in suspension in the indoor atmosphere. The natural dissipation of sidestream tobacco smoke has been investigated in a static atmosphere in a I0 m3 experimental chamber, and the rate of dissipation is expressed as T0.s, the half-life of residence in the air. Respective T0j of smoke components are calculated from the various sample data points, assuming a kinetic equation of the first-order process. Sidestream smoke has been generated by a smoking machine according to the Coresta standard protocol and then left to age over an 8-hour period, with subsequent sampling at defined time intervals. The experiments have been repeated over five days, and eight data point samples are obtained for each experiment. Besides nicotine, CO, and smoke particulate matter, interest has been focused on polycyclic aromatic hydrocarbons (PAH). The initial concentrations, Co for smoke particulate matter and nicotine (gas and particulate phases) are found to be 13.8 mg and 92 J4g per cigarette per cubic meter, with T0.s being 2.6 and 2.1 hours, respectively. Low-molecular-weight PAH have T0.s up to 20 hours, explainable only by their high concentrations in the gas phase, while the 3- to 7-ring PAH have T0.s of about 2 hours. The contribution of CO to ambient concentration is 91 mg per cigarette per cubic meter. The data can be useful in mathematical modvllization studies regarding ventilation or exposure to sidestream smoke.

INTRODUCTION

indoor sources appear overlapped in the presence of tobacco smoke (Girman et al. 1982; Good et al. 1982), with the exception of the emissions by the combustion of fossil fuels from gas appliances, kerosene burners, space heaters, or wood burning likely to be used indoors (Spengler and Cohen 1985). The degree of pollution, and therefore the degree of health risk to occupants, depends on the type and the amount of pollutants entering the occupied space and the rate of removal by processes such as deposition, chemical reactions, and mechanical ventilation. Passive smoking is related to the exposure to indoor air contaminated by smoke components in the gaseous and particulate phases. The major source of

With regard to the emission levels of pollutants and the various nature and number of chemical substances in the smoke, tobacco smoke is, along with other combustion appliances, one of the predominant sources of air pollution in indoor atmosphere (NAS 1981). The incomplete pyrolysis of cigarette tobacco generates elevated concentrations of air contaminants (IARC 1986). Moreover, the smoke that is released into the ambient atmosphere between puff-drawing is known to contain higher amounts of pollutants than that inhaled by the smoker (Brunnemann et al. 1980; Klus and Kuhn 1982; Neurath and Ehmke 1964; Sakuma et al. 1984). In comparison, the emissions from other 57

58

environmental tobacco smoke (ETS) is the sidestream smoke (SS), which is emitted from the burning end of a cigarette in between puffs, and the exhaled smoke from the smoker (NAS 1986). Smoke that escaped during the puff-drawing from the burning cone and components in the vapor phase that diffused through the cigarette paper also contribute to ETS in minor amounts. Although initially complex because of the great varieties of compounds present in the smoke, the composition and physicochemical characteristics of ETS are different from those of SS and many more of the mainstream upon dilution. Passive smoking is concerned more or less with smoke components having long residence time in the air. Data coming from SS collected in a close smoking system, especially for analytical purposes, can hardly be assimilated to ETS. The fate of SS constituents following their emission and their dissipation in air over the course of time needs to be documented. The effects of chemical transformations and smoke aging on the persistence and concentrations of various constituents are to be established in order to establish what should be measured for the characterization of an exposure to ETS. Since the reported deposition of inhaled smoke in the respiratory tract is inconsistent (Dalhamm et al. 1968; Hinds et al. 1983), First (1984) estimated the contribution of exhaled smoke to be between 10% to 50%. It can be considered that the aged SS is close to ETS, with the exception of the contribution of exhaled smoke. A preliminary investigation of the chemical composition of ETS should be the study of the fate of SS in indoor air disregarding the participation of exhaled smoke. Besides the classical CO, particulate matter, nicotine, and a few other organics measured in real situations (Sterling et al. 1982) with no control of the nature of emission sources, systematic investigations on the time of residence of a smoke compound or group of components have only recently been undertaken (Eatough et al. 1987; Tang et al. 1988). The purpose of this work is to investigate in an experimental model the decay of physical and chemical SS constituents, with particular emphasis on the polycyelic aromatic hydrocarbons (PAH) and their methylated derivatives, since they are well known for their carcinogenic activities in animals and represent an important category. More precisely, the residence time of the constituents in the air and the effect of aging on their concentration levels are examined. Data on PAH in ETS for modelization studies on indoor air pollution by tobacco smoke are scanty.

T. Vu-Duc and C. K. Huynh

MATERIALS AND METHODS

Generation of sidestream smoke Commercial filter cigarettes (85 mm long, 0.6 mg nicotine, 7 mg tar) were conditioned at constant relative humidity (RH) in a plastic box over a saturated solution of calcium nitrate for a week. At the laboratory temperature, an excess of calcium nitrate in contact with a saturated aqueous solution provides a constant 55% RH in the enclosure because the hydration constant of the salt is dependent only on temperature (CRC 1986-87). Ten cigarettes were smoked by a smoking machine (35 mL puff volume over 2 seconds every minute until a butt length of 23 mm), and only SS was discharged into a tight 10 m 3 experimental chamber (227 x 219 x 219 cm) made of glass and stainless steel (Guillemin 1975). It was necessary to use four fans at the corners to homogenize the indoor air for 20 min after the initial lighting of the cigarettes, although previous experiences have shown that keeping the fans in operation results in substantial impaction of particles. The fans were switched off during the sampling phase. SS was left to age over an eight-hour period per day under static conditions. The experiments were repeated over five days. Carbon monoxide was used to monitor for leakage in the chamber prior to the generation of SS.

Sampling and analyses Due to the decay of smoke in the chamber, the sampling time for the first four points was 30 min, then 1 hour, and, finally, 2 hours for the last two samples. A Millipore filter holder cassette equipped with a 47 mm diameter Cambridge filter was connected to a cartridge of Cls cross-linked with silica. This allows the sampling of total smoke particulate matter (TPM) and vapor phase PAH at a flow rate of 10 L/min. The weight of TPM was determined on a microbalance after reconditioning the filters at a constant 55% RH at laboratory temperature. Tar was determined as the weight of the dry residue of the methanol extract of the TPM filters after evaporation of the solvent. CO was monitored with an electrochemical dosimeter calibrated against a known concentration of standard gas. A ceramic tube containing Carbotrap (Supelco Inc.) as an adsorbent was used to trap the gas and particu l a t e n i c o t i n e s a m p l e d with a p e r s o n a l p u m p at 0.1 L/min. Chemical analysis was made by mic r o w a v e t h e r m a l d e s o r p t i o n and c a p i l l a r y gas chromatography. The total nicotine concentration was calculated relative to a standard curve obtained from the dynamic generation of a known quantity of nicotine

Tobacco smoke constituents

59

in air. Total PAH were determined in the combined cyclohexane extract of the Cls and the dry residue of methanol extract. Deuterated phenanthrene dl0 and benzoin]anthracene d12 were added as internal standards. Following enrichment by partitioning the cyclohexane phase in dimethylformamide according to the schema of Grimmer (1972), the PAH extract was fractionated by reverse-phase, high-performance liquid chromatography with the collection of the corresponding elution volume. Reduction of volume was first made to 1 mL by a Rotavapor, then to 50 gL under a flow of nitrogen at 45°C to avoid the loss of volatile PAH. PAH were separated by capillary gas chromatography and detected by mass spectrometry. The identity of the PAH was based on both comparison of the retention time of the peak to that of a reference compound and on the molecular ion fragment. Calculations of initial concentrations, Co, and halflives of residence To.s

Eight data points were obtained per experiment corresponding to the integrated samples taken along the time course. Calculations of T0. 5 of the SS constituents in the air were made using a semilog plot of the concentration as a function of time. Data from all the experiments are computed either separately or are combined. From the linear relationship of the plot, it can be assumed that the kinetics of decay is a firstorder process. The kinetic equation can be rearranged as: Log C = -(0.693/2.303 x T0.5)t + Log C o which is the equation of a line Y = aX + b. In the rearranged equation, the true zero point C O (at time t=O) of the curve is calculated as Co--lOb, b being the ordinate at the origin. C is the concentration at the corresponding time t, and C O is the unknown initial concentration in this experimental design. The halflife of residence T0.s is calculated as the negative reciprocal value of the slope a of the equation. The validity of the above assumption is estimated from the correlation coefficient R of the regression line.

RESULTS Preliminary tests have shown that the half-lives for the natural dissipation of some constituents in SS under static conditions in the chamber are about 2 to 3 hours. In the hypothesis that the decay of smoke constituents is a first-order kinetics, the experimental design should ensure that data collection be run at least over twice or more the duration of the phenomenon. On the other hand, an exponential decay implies that the sampling strategy takes into account the rapid decline of the first part of the curve. Thus, more smoke samples are collected at the beginning over shorter sampling times, while this sampling time can be longer at the end since the relative difference between two adjacent samples is small. Another reason for the eight-hour aging of SS is that the timeweighted average concentration is usually taken over that time interval when exposure is considered, especially in the work environment. With the design used, for an integrated value of the concentration over this period, the derived data are thus obtained from measurements and are not extrapolated. Considering the number of smoked cigarettes and the chamber volume, the contribution of CO that evolves from the SS into a close environment is 91 mg per cigarette per m 3. The CO concentration appeared to be directly proportional to the number of cigarettes smoked, as also has been reported previously (Hoegg 1972). In a tight experimental chamber, the nonreactive CO can only be evacuated by ventilation. During the SS generation and throughout the sampling periods, the relative humidity measured in the chamber is typically 46% and the temperature 21 to 22°C. Figs. 1 through 3 illustrate the kinetics of dissipation of TPM, tar, and nicotine; the decays of a few PAH from 2 to 6 rings are reported in Fig. 4. The dispersion of data in day-to-day experiments is shown. Each data point is centered on the middle of the sampling period. The regression line is computed from the 40 or so data points available, and the overall R expresses the validity of the assumption relative to the best-fit line. In Table I, the calculated initial concentrations, C o, are expressed as the amount of TPM, tar and

Table I. Half-lives of residence in the air and initial concentrations. Constituents TPM Tar Nicotine

[mg/m8] [rag/ma] [gg/m s]

R

Co

T=

0.977 0.972 0.932

13.8!-0.7 2.6_+0.4 12.9-I__-1.0 2.8x~0.8 92 +15 2.1_+0.3

60

T. Vu-Duc and C. K. Huynh

TOTAL PARTICULATE MATTER LoglO(Conc.) [mg/m3]

1.4

1.2

.

Y - - 0 . 1 1 8 X ÷ 1.14 [ R - 0 , 9 7 7 1

1 0.8 0.6 .

0.4 0.2 0 0

I

I

I

I

I

I

I

1

2

3

4

5

6

7

HOURS n

Day 1

+

Day 2

Day 4

x

Day §

• ~

Dey 3 Calculated

Fig. 1. Kinetics of dissipation and day-to-day experimental variations (TPM).

TAR LoglO (Conc.) [mg/m3]

1.4 1.2

+ Y " - 0 . 1 0 9 X + 1.111 [ R ' 0 . 9 7 2 1

1 0.8 0.6 0.4 0.2 0

0

I

I

I

I

I

t

I

1

2

3

4

,5

8

7

8

Hours n

Day 1

+

Day 2

Day 4

x

Day 6

• ~

Day3 Calculated

Fig. 2. Kinetics of dissipation and day-to-day experimental variations (Tar).

nicotine per cigarette per m 3, with their relative standard deviations. In this experimental design, the initial concentration of each smoke constituent is not that determined in the initial sample. C o is an extrapolated value from the set of data points and corresponds to the "true" initial concentration. The emission rate of SS in the chamber shows that a single cigarette accounts for 13.8 mg of TPM, 92 gg of nicotine, and 13 mg of tar per a unit volume of one cubic meter. The half-life of residence describes the rate of dissipation of a smoke pollutant. In a nonventilated environment, it takes 2.6 hours for the TPM to decay by half of its initial concentration. This

value is to be compared with the 2.8 hours of tar from each of the same samples. The depletion of nicotine is a little faster, 2.1 hours, and is probably due to facile adsorption on the wall of the chamber. Considering all the factors involved in obtaining these data, such as the reproducibility of day-to-day generation of smoke, collection, and laboratory analyses, the consistency of the values appears quite satisfactory. About 65 PAH and their methylated derivatives can be separated and identified by mass spectrometry; a few PAH are not detectable or are absent in SS. The list of PAH is presented in Table 2, with the respective half-lives, C o, the correlation coefficient

Tobacco smoke constituents

61

NICOTINE LoglO ( C o n c ) {ug/m3] 3 2.5

v

2

Y - - 0.142X + 1.964 [R"0.932]

•

E]

Q

1.5 1

0.5 0 0

I

I

I

I

I

I

I

1

2

3

4

5

6

7

Hours Day 1

+

Day 2

"~ D a y 3

[3

Day 4

--Calculated

Fig. 3. Kinetics of dissipation and day-to-day experimental variations (Nicotine).

PAH LoglO(Conc.) [ng/m3] 4

o

o

+ "x

-1 0

t

I

I

I

I

I

t

1

2

3

4

5

6

7

Hours --

Naphthalene

-'~

Anthracene

Benzo[a]pyrene

~

Dlbenzola,hlenthrac.

~

Pyrene

Fig. 4. Kinetics of dissipation of some PAH.

R, and N, the number of data points used to compute the curves. At maximum, only eight data points are available, since the determinations are made on combined samples of the same sampling time because of the detection limit of the analytical method. Despite some irregularities, there is a clear decline of T0.5 for low-molecular-weight PAH from 128 to 156. Compared to the 2.6 hours half-life of TPM, the higher To.5 of the light PAH (up to 20 hours for naphthalene) suggests that they coexist in the vapor and particulate phases. As the analytical procedure determines the global PAH concentrations in both phases, the results

suggest that the 2-ring PAH are found predominantly in the gas phase, and this contributes to the longer residence time. For PAH from 3 to 7 rings, an overall half-life would be 2 hours. A general explanation for the difference of half-lives between the 2-ring PAH and the 3- to 7-ring members is the relative difference of their vapor pressures governed by the gasparticle equilibria at laboratory temperature. Thus, the lower vapor pressure of methylbenzo[a]anthracone relative to that of naphthalene results in a longer T0.s for this latter compound. A precise interpretation of the observed trend on the slight increase with

62

T. Vu-Duc and C. K. Huynh

Table 2. Half-lives of residence in the air and initial concentrations of PAH.

MW 128 142 142 152 154 156 156 156 156 156 156 166 170 170 170 178 178 192 192 192 202 202 206 206 206 206 216 216 216 226 226 228 228 228 230 242 242 242 242 242 242 242 252 252 252 252 252 256 276 276 276 278 278 278 278 300

PAH Naphthalene 2-Methylnnphthalene 1-Methylnaphthalene Acenaphthylene Acenaphthene 1-Ethylnaphthalene 2,6-Dimethylnaphthalene 1,3-Dimethylnaphthalene 1,4+ 1,5-Dimethylnaphthale ne * 1,2-Dimethylnaphthalene 1,8-Dimethylnaphthalene Fluorene 1,6,7-Trimethylnaphthalene 2,3,6-Trimethylnaphthalene 2,3,5-Trimethylna phthalene Phenanthrene Anthracene 1-Methylnhenanthrene 1-Methylanthracene 9-Methylanthracene Fluoranthene Pyrene 3,6-Dimethyl phenanthrene 2,7-Dimethylphenanthrene 1,8-Dimethylphenanthrene 9,10-Dimethylanthracene Benzo[a]fluorene Benzo[b]fluorene 1-Methylpyrene Benzo[ghi]fluorauthene Cyclopents[cd]pyrene Benzo[a]anthracene Chrysene+Triphenylene* Naphthacene 1,3-Dimethylpyrene 1-Methylbenzo[a]anthracene 12-Methylbenzo[a]anthracene 3-Methylchrysene 2-Methylchrysene 5-Methylchrysene 6+4-Methylchrysene* 1-Methylchrysene Benzo[b+j+k]fluoranthene* Benzo[a]fluoranthene Benzo[e]pyrene Benzo[a]pyrene Perylene 7,12-Dimethylbenzo[a]anthracene Anthanthrene Indeno[ 1,2,3-cd]pyrene Benzo[ghi]perylene Dibenzo[aj]anthracene Dibenzo[a,e+a,h]anthracene* Benzo[b]chrysene Picene Coronene

Tm

Co

[hours]

[ng/m 3]

20.6 11.9 12.1 4.2 1,4 6.7 4.2 4.3 3.8 3.8 1.2 3.4 3.0 2.9 2.8 2.0 1.4 1.6 1.7 1.3 1.6 1.4 1.6 1.5 1.6 1.3 1.1 1.2 1.2 1.7 1.9 1.6 1.6 1.3 1.1 1.5 1.8 2.4 1.7 1.7 1.9 1.5 2.4 2.1 2.2 2.0 2.1 1.6 2.8 2.5 2.5 2.8 2.0 2.6 2.0 2.0

729.8 183.3 123.4 17.0 362.1 23.7 58.6 80.7 23.0 25.9 152.0 43.3 98.8 63.7 59.8 111.9 13.1 136.1 100.8 16.4 214.4 194.1 33.9 80.4 152.0 96.0 31.9 98.0 94.0 72.2 14.6 101.4 119.7 150.8 22.0 50.0 37.0 46.9 58.1 35.5 25.2 16.0 42.0 54.4 42.6 58.4 14.6 40.9 11.4 16.5 12.1 5.3 4.4 6.8 7.1 4.7

R

N

0.775 0.772 0.788 0.948 0.930 0.884 0.961 0.983 0.986 0.987 0.915 0.980 0.959 0.957 0.938 0.946 0.977 0.972 0.952 0.958 0.976 0.988 0.984 0.985 0.984 0.981 0.978 0.990 0.984 0.979 0.896 0.991 0.986 0.982 0.987 0.950 0.962 0.861 0.962 0.936 0.965 0.816 0.961 0.965 0.942 0.966 0.889 0.918 0.872 0.709 0.746 0.705 0.818 0.636 0.742 0.866

* Not separated by GC-MS PAH n o t detected: 2-Methylphenanthrene, 2-Methylanthracene, Benzo[c]phenanthrene, Benzo[c]chrysene, Dibenzo[a,1]pyrene, Dibenzo[a,e]pyrene, Dibenzo[a,i]pyrene, Dibenzo[a,h]pyrene.

Tobacco smoke constituents

high-molecular-weight PAH (5-7 rings) is difficult. The numerous experimental manipulations used to come to a PAH value have a direct consequence on the reliability of To.5, which is only influenced by the slope of the regression line, i.e., the rate of decay. For an identical slope, the amplitude of the ordinate at origin influences C o.

DISCUSSION The concentration of SS emitted by one cigarette in a 1 m 3 volume is hardly tolerable as has been experienced. When 20 cigarettes are smoked in the chamber, it is observed that the smoky atmosphere is so dense that measurements under these circumstances are not realistic in comparison with real situations. In studies with exposures to volunteers, smoke concentrations fivefold less have been used (Curvall et al., 1987). This experimental model is still far from ETS in common situations. However, it has helped to issue emission rates and some dissipation constants for a few constituents in SS. Within one set of experiments, the dispersion in day-to-day generation of SS can be reasonably controlled. But other factors could influence the comparability of one work to another. These include the variations in the composition of tobacco mixture, the conditioning of cigarettes, the combustion characteristics, and the nature of the smoke parameter of interest. For instance, the transformation and growth of particles influence the measurements of TPM (Vu-Duc and Huynh 1987). It can be suspected that the composition of smoke particles has changed with time and that the weight of TPM in the last sample is not made of the contribution of the particles in the first sample. Further experiments are needed to examine the fluctuations of T0. 5 in a more dilute atmosphere. On the other hand, the production of CO and nicotine appears quite reproducible. A report by the Laboratory of the Government Chemist (1982) and Rickert etal. (1984) have shown that tar and nicotine levels in S S are comparable regardless of whether they come from medium-, low-, or ultra-low-tar cigarettes. Nicotine and tar are presently the common parameters used to ascribe the strength of a cigarette brand; for this reason, it was attempted to examine the measurement of tar in the diluted sidestream smoke of the test chamber. Moreover, most of the toxic organic compounds are found in tar. But it is unlikely that tar could be used as an index of cigarette pollution in real, everyday situations. The classical smoke markers like TPM, nicotine, or CO have been determined in view of any possible relation-

63

ships with PAH and in connection with published data in the literature. An objective characterization of the exposure to ETS requires a specific air marker of the smoke. Regarding the carcinogenic effect on the lungs from passive smoking, an indice of the PAH family would be helpful, since PAH are widely known to develop this biologic activity. Prior to the search for any new marker of the category, the residence time of PAH in the air has to be studied. From the analytical profile of PAH, even a careful observation does not enable the pinpointing of one PAH that can be representative of the category and specific to tobacco smoke. Finally, this marker is not necessarily a single compound, but possibly is a combination of several constituents. Further examination of the results is under progress. Data on the emission rate of SS, i.e, the amount of pollutants in the SS generated by a cigarette, and data on the half-life of residence in the air of a constituent are useful to mathematical modelization studies on ventilation rate regarding tobacco smoke as a source (Repace and Lowrey 1983) or on exposure estimations (Crawford 1987; Rickert 1988). Provided the number of smoked cigarettes and the volume of premises are known, the ventilation rate needed to attain a less toxic level or a comfort level (Cain etal. 1983) can be calculated. In fact, in real situations, the dissipation of the SS pollutants, with exception of the odor, is expected to be faster as a result of air motion or absorption by the materials.

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T. Vu-Duc and C. K. Huynh

Council, National Academy Press, Washington, D.C., p. 14.; 1986. Neurath, G. and Ehmke, H. Apparatur zur Untersuchung des Nebenstromrauches, Beltr. Tabakforsch. 2, 117-121; 1964. Repace, J.L. and Lowrey, A.H. Modeling exposure of nonsmokers to ambient tobacco smoke, Air Poll. Control Assoc. 76th annual meeting, 83-64.20 l - l l . Rickert, W.S. Some considerations when estimating exposure to environmental tobacco smoke (ETS) with particular reference to the home environment, Can. J. Public Hhh. 79, 33-39; 1988. Rickert, W.S., Robinson, J.C. and Collishaw, N. Yields of tar, nicotine, and carbon monoxide in the sidestream smoke from 15 brands of Canadian cigarettes, Am. J. Public Health 74, 228-231; 1984. Sakuma, H., Kusuma, M., Yamaguchi, K. and Sugawara, S. The distribution of cigarette smoke components between mainstream and sidestream smoke, HI. Middle and high boiling components. Beitr. Tabakforsch. 12, 251-258; 1984. Spengler, J.D. and Cohen, M.A. (1985) Emissions from indoor combustion sources. In Indoor Air and Human Health, Gammage, R.B. and Kaye, S.V., eds, Lewis Publishers, Inc., Chelsea, MI, pp. 261-278; 1985. Sterling, T.D., Dimich, H. and Kobayashi, D. Indoor byproducts levels of tobacco smoke: A critical review of the literature, J. Air Pollut. Control Ass. 32, 250-259; 1982. Tang, H., Richards, G., Gunther, K., Crawford, J., Lee, M.L., Lewis, E.A. and Eatough, D.J. Determination of gas phase nicotine and 3-ethenylpyridine, and particulate phase nicotine in environmental tobacco smoke with a collection bedcapillary gas chromatography. J. High Resol. Chromatog. & Chromatog. Comm. 110 775-782; 1988. Vu-Duc, T. and Huynh, C.K. Deposition rates of sidestream tobacco smoke in an experimental chamber, Toxicol. Letters 35,59-65; 1987.