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THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 25 2 The Physicochemical Nature of Sidestream Smoke and Environmental Tobacco Smoke INTRODUCTION Mainstream smoke (MS) is the aerosol drawn into the mouth of a smoker from a cigarette, cigar, or pipe. Sidestream smoke (SS) is the aerosol emitted in the surrounding air from a smoldering tobacco product between puff-drawing. SS is a major source of environmental tobacco smoke (ETS), i.e., air pollution caused by the burning of tobacco products. Other contributors to ETS are the exhaled portion of MS and the smoke that escapes from the burning part of a tobacco product during puff-drawing. In addition, some volatile components (e.g., carbon monoxide) diffuse through cigarette paper and contribute to ETS. Tobacco smoke aerosols are diluted with air by the time they are inhaled as ETS air pollutants. Furthermore, the physical characteristics and chemical composition of ETS change as the pollutants âageâ: nicotine is volatilized; particle sizes decrease; nitrogen oxide gradually oxidizes to nitrogen dioxide; various components of the ambient air (e.g., radon daughters) can be adsorbed on the particles; and other physicochemical changes can occur. In the scientific literature, the terms âpassive smoke,â âpassive smoking,â and âinvoluntary smokingâ are used often. These terms do not adequately describe ETS and its inhalation, but they are used interchangeably with âETSâ in this report. Most of the reported data on MS, SS, and ETS pertain to cigarette smoking. Few comparative data on smoke pollutants from other tobacco products are available.
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 26 In the laboratory, cigarettes, cigars, and pipes are smoked by machines under standardized conditions (Wynder and Hoffmann, 1967) to obtain reproducible data for the determination of various individual constituents of undiluted MS and SS. Such data provide a scientific basis for comparing tobacco products and brands. The standardized machine-smoking conditions were developed 3 decades ago to simulate human smoking behavior (Wartman et al., 1959). However, these can differ substantially from those of today's cigarette smokers, especially in the case of filter-tipped products that are designed to deliver low yields of tar and nicotine (Herning et al., 1981). For cigarettes and cigarette-like cigars weighing up to 1.5 g, the most widely used machine-smoking conditions in the test laboratory are as follows: one 35-ml puff lasting 2 seconds taken once a minute. The butt length for nonfilter cigarettes is 23 mm. For filter-tipped cigarettes, the total length is increased 3 mm for filter tip plus overwrap (Pillsbury et al., 1969; Brunnemann et al., 1976). For cigars, the conditions are as follows: a 30-ml puff taken once every 40 seconds and a butt length of 33 mm (International Committee for Cigar Smoke Study, 1974). For pipe smoking the test calls for a bowl filled with 1 g of tobacco and for a 50-ml puff lasting 2 seconds to be taken every 12 seconds (Miller, 1964). Several devices have been used for generating SS from cigarettes and cigars (Dube and Greene, 1982). Among them, the Neurath and Ehmke chamber or modification thereof have been used for chemical analytic work on SS (Neurath and Ehmke, 1964; Brunnemann and Hoffmann, 1974). When SS is generated, a stream of air is sent through a chamber at 25 ml/second. At this rate, the tar and nicotine yields in the MS of cigarettes and cigars smoked in the chamber are similar to those obtained by smoking cigarettes or cigars in the open air. However, the velocity of the airstream through the chamber has considerable influence on the yields of individual compounds in SS (RÃ¼hl et al., 1980; Klus and Kuhn, 1982). In order to collect the particulate matter of MS and SS, the aerosols are directed through a glass-fiber filter that traps more than 99% of all the particles with diameters of 0.1 Âµm or more (Wartman et al., 1959). The portion of the smoke that passes through the filter is designated as the vapor phase. This arbitrary separation into particulate phase and vapor phase does not necessarily reflect the physicochemical conditions prevailing in MS and
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 27 SS. However, it does reflect specific trapping systems and analytic methods that have been developed for the standardized determination of individual components or groups of components in MS or SS (Brunnemann and Hoffmann, 1982; Dube and Greene, 1982). Standardized machine-smoking conditions do not exactly duplicate the smoking patterns of an individual, which depend on many factors. For example, low nicotine delivery in cigarette smoke generally induces a smoker to puff more frequently (up to 5 puffs/minute), to draw larger volumes (up to 55 ml/puff), and to inhale more deeply. Puffing more frequently increases the amount of tobacco consumed during generation of MS and thus diminishes the amount of tobacco burned between puffs. This, in turn, affects the release of combustion products in SS, so an increase in puff frequency diminishes the production of SS and ETS. Also, smoking behavior appears to depend strongly on the blood concentration of nicotine that the smoker desires to reach (Krasnegor, 1979; Grabowski and Bell, 1983). The smoker, because of proximity to the source, usually inhales more of the SS and ETS originating from the burning of the tobacco product than a nonsmoker; however, we do not know the exact amount and we do not know the degree to which inhaled SS and ETS aerosols are retained in the smoker's respiratory tract. Model studies with MS have shown that more than 90% of some hydrophilic volatile components (e.g., acetaldehyde) is retained after inhalation by the smoker (Dalham et al., 1968a). Therefore, one may assume that a large proportion of the hydrophilic agents in the vapor phase of SS and ETS is also retained when smoke-polluted ambient air is inhaled. In the case of hydrophobic components of the vapor phase of MS (e.g., carbon monoxide), the retained fraction depends on the depth of inhalation, but it hardly ever exceeds 50% (Dalham et al., 1968b). An active smoker generally retains 90% or more of MS particles (Dalham et al., 1968b; Hiller, 1984), whereas a nonsmoker exposed to ETS appears to retain a smaller percentage of ETS particles. It has been calculated that, depending on the degree of SS pollution, a nonsmoker exposed to ETS can retain 0.014 to 1.6 mg of particles per day from ETS (Hiller, 1984).
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 28 SIDESTREAM SMOKE The SS generated between puffs originates from a strongly reducing atmosphere. Therefore, undiluted SS contains more combustion products that result from oxygen deficiency and thermal cracking of molecules than does MS. In addition, SS formation involves generation of higher amounts of compounds from nitrosation reactions. Consequently, SS differs substantially from MS. Table 2â1 compares MS and SS from nonfilter cigarettes. During the consumption of one whole cigarette under standard smoking conditions, the formation of cigarette MS generated during 10 puffs (each 2 seconds) of a blended nonfilter cigarette requires 20 s and consumes 347 mg of tobacco. The formation of SS from the same cigarette smoldering requires 550 seconds and consumes 411 mg of tobacco. However, as shown with experimental cigarettes, the amounts of tobacco consumed during and between puffs depend greatly on the type of tobacco (Johnson et al., 1973a). In addition, MS and SS are generated at different temperatures. For example, under laminar atmospheric conditions, the SS of a smoldering cigarette enters the surrounding atmosphere about 3 mm in front of the paper burn line, at about 350Â°C (Baker, 1984). The pH of the MS of a blended American cigarette ranges from 6.0 to 6.5, whereas the pH of SS is 6.7 to 7.5. Above a pH of 6.0, the proportion of unprotonated nicotine in undiluted smoke increases; therefore, SS contains more free nicotine in the gas phase than MS. The pH of SS of cigars is 7.5 to 8.7; pH values for pipe smoke have not been reported (Brunnemann and Hoffmann, 1974). Under conditions prevailing in MS, SS, and ETS, unprotonated nicotine is primarily present in the vapor phase; its absorption through the mucous membranes is faster; thus, its pharmacologic effect is different from that of unprotonated nicotine in the particulate matter (Armitage and Turner, 1970). About 300â400 of the more than 3,800 compounds identified in tobacco smoke have been measured in MS and SS. Table 2â2 lists the amounts of selected substances reported to occur in the MS and in SS from the burning of a whole nonfilter cigarette and the range of the ratio of their amounts in SS/MS. A ratio greater than unity means that more of a substance is released in SS than in MS. The separation of the compounds in Table 2â2 into vapor phase and particulate phase constituents reflects the conditions
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 29 prevailing in MS and does not apply to the distribution of these compounds in the vapor phase and particulate phase of SS. TABLE 2â1 Some Physiocochemical Characteristics of Fresh, Undiluted Mainstream and Sidestream Smoke from a Nonfilter Cigarettea Characteristics MS SS Reference Duration of smoke production, s 20 550 Neurath and Horstmann, 1973 Tobacco burned, mg 347 411 Neurath and Horstmann, 1973 Peak temperature during formation, Â°C 900 600 Wynder and Hoffmann, 1967 pH 6.0â6.2 6.4â6.6 Brunnemann and Hoffmann, 1974 Number of particles per cigarette 10.5Ã1012 3.5Ã1012 Scassellatti-Sforzoline and Savino, 1968 Particle size, Âµ m 0.1â1.0 0.01â0.8 Carter and Hasegawa, 1975; Hiller et al., 1982 Particle mean diameter, Âµm 0.4 0.32 Carter and Hasegawa, 1975; Hiller et al., 1982 Gas concentration, vol.% Carbon monoxide 3â5 2â3 Keith and Derrick, 1960 Carbon dioxide 8â11 4â6 Wynder and Hoffmann, 1967 Oxygen 12â16 1.5â2 Baker, 1984 Hydrogen 3â15 0.8â1.0 Hoffmann et al., 1984a,b aDatawere obtained under standard laboratory smoking conditions of one puff per minute, lasting 2 s, and having volume of 35 ml. Mainstream smoke collected directly from end of cigarette. Sidestream smoke was measured 4 mm from burning cone (gas temperature, 350Â°C). The ratio of the amount of tobacco burned during SS generation to that burned during MS generation is 1.2:1 to 1.5:1 (see Table 2â1 for data on nonfilter cigarettes). Therefore, if one assumed that the combustion process is the same during the generation of the two kinds of smoke, the ratios of their various constituents would also be between 1.2:1 and 1.5:1. That is not the case, as indicated by the higher SS/MS values in Table 2â2. For instance, in the first part of Table 2â2, which lists volatile compounds, the ratios for carbon monoxide range from 2.5 to 4.7, for carbon dioxide from 8 to 11, for acrolein from 8 to 15, and for benzene about 10.
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 30 TABLE 2â2 Distribution of Constituents in Fresh, Undiluted Mainstream Smoke and Diluted Sidestream Smoke from Nonfilter Cigarettesa Constituent Amount in MS Range in SS/MS Vapor phaseb Carbon monoxide 10â23 mg 2.5â4.7 Carbon dioxide 20â40 mg 8â11 Carbonyl sulfide 18â42 Âµg 0.03â0.13 Benzenec 12â48 Âµg 5â10 Toluene 100â200 Âµg 5.6â8.3 Formaldehyde 70â100 Âµg Acrolein 60â100 Âµg 8â15 Acetone 100â250 Âµg 2â5 Pyridine 16â40 Âµg 6.5â20 3-Methylpyridine 12â36 Âµg 3â13 3-Vinylpyridine 11â30 Âµg 20â40 Hydrogen cyanide 400â500 Âµg 0.1â0.25 Hydrazined 32 ng 3 Ammonia 50â130 Âµg 40â170 Methylamine 11.5â28.7 Âµg 4.2â6.4 Dimethylamine 7.8â10 Âµg 3.7â5.1 Nitrogen oxides 100â600 Âµg 4â10 N-Nitrosodimethylaminee 10â40 ng 20â100 N-Nitrosodiethylaminee ND-25 ng <40 N-Nitrosopyrrolidinee 6â30 ng 6â30 Formic acid 210â490 Âµg 1.4â1.6 Acetic acid 330â810 Âµg 1.9â3.6 Methyl chloride 150â600 Âµg 1.7â3.3 Particulate phaseb Particulate matterc 15â40 mg 1.3â1.9 Nicotine 1â2.5 mg 2.6â3.3 Anatabine 2â20 Âµg <0.1â0.5 Phenol 60â140 Âµg 1.6â3.0 Catechol 100â360 Âµg 0.6â0.9 Hydroquinone 110â300 Âµg 0.7â0.9 Aniline 360 ng 30 2-Toluidine 160 ng 19 2-Naphthylaminec 1.7 ng 30 4-Aminobiphenylc 4.6 ng 31 Benz[a]anthracenee 20â70 ng 2â4 Benzo[a]pyrened 20â40 ng 2.5â3.5 Cholesterol 22 Âµg 0.9 Î³-Butyrolactonee 10â22 Âµg 3.6â5.0 Quinoline 0.5â2 Âµg 8â11 Harmanf 1.7â3.1 Âµg 0.7â1.7 Nâ²-Nitrosonornicotinee 200â3,000 ng 0.5â3 NNKg 100â1,000 ng 1â4 N-Nitrosodiethanolaminee 20â70 ng 1.2
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 31 Constituent Amount in MS Range of SS/MS Cadmium 100 ng 7.2 Nickeld 20â80 ng 13â30 Zinc 60 ng 6.7 Polonium-210c 0.04â0.1 pCi 1.0â4.0 Benzoic acid 14â28 Âµg 0.67â0.95 Lactic acid 63â174 Âµg 0.5â0.7 Glycolic acid 37â126 Âµg 0.6â0.95 Succinic acid 1 10â140 Âµ g 0.43â0.62 aData from Elliot and Rowe (1975); Schmeltz et al. (1979); Hoffmann et al. (1983); Klus and Kuhn (1982); Sakuma et al. (1983, 1984a,b); Hiller et al. (1982). Diluted SS is collected with airflow of 25 ml/s, which is passed over the burning cone. b Separation into vapor and paniculate phases reflects conditions prevailing in MS and does not necessarily imply same separation in SS. cHuman carcinogen (U.S. Department of Health and Human Services, 1983). d Suspected human carcinogen (U.S. Department of Health and Human Services, 1983). eAnimal carcinogen (Vainio et al., 1985). fl-methyl-9H-pyrido[3,4-b]-indole. g NNK=4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone. The high SS/MS values of carbon monoxide and carbon dioxide show that more of each of these constituents is generated in the oxygen-deficient cone during smoldering than during puff-drawing. After passing briefly through the hot cone, most of the carbon monoxide is oxidized to carbon dioxide, probably because of the high temperature gradient and sudden exposure to air. The high SS/MS values of volatile pyridines are thought to be due to the fact that these compounds are formed from the alkaloids during smoldering (Schmeltz et al., 1979). Hydrogen cyanide is formed primarily from protein at temperatures above 700Â°C (Johnson and Karg, 1971). Thus, smoldering of tobacco at 600Â°C does not favor the pyrosynthesis of hydrogen cyanide to the extent that it occurs during MS generation. With regard to the carcinogenic potential of SS, it is important to consider the SS/MS ratio of NOxâ4 to 10. More than 95% of the NOx inhaled by the smoker is in the form of nitric oxide, and only a small portion is oxidized to the powerful nitrosating agent, nitrogen dioxide. Only a small fraction of nitric oxide is expected to be retained in the respiratory system by being bound to hemoglobin. NOx released into the environment in SS
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 32 is partially oxidized to nitrogen dioxide (Vilicins and Lephardt, 1975). Thus, environments polluted with SS are expected to contain increased concentrations of the hydrophilic nitrosating agent, nitrogen dioxide. Perhaps the most remarkable data in this portion of Table 2â2 are the very high SS/MS values of ammonia, nitrogen oxide, and the volatile N-nitrosamines. Studies with [15N]nitrate have shown that, during burning of tobacco, nitrate is reduced to ammonia, which is released to a greater extent in SS than in MS during puff-drawing (Just et al., 1972). An extreme example is the case of a cigarette made exclusively from burley tobacco, a variety generally rich in nitrate (2.0â5.0% in U.S. survey); ammonia is released in SS at 8,500 Âµg/cigarette (SS/MS 170, according to Johnson et al., 1973b). (In the case of a blended cigarette, the greater generation of ammonia in SS causes an increased pH, which can be above 7, whereas the pH of MS is about 6.) The ranges of high SS/MS ratios of the highly carcinogenic volatile N-nitrosamines (such as N- nitrosodimethylamineâ20 to 100) have been well established (Brunnemann et al., 1977, 1980; RÃ¼hl et al., 1980). The second part of Table 2â2 lists some constituents of particulate matter, their amounts reported to occur in MS during the burning of one cigarette, and ranges of the relative amounts in SS/MS. The increases in SS of tobacco-specific N-nitrosamines, such as 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), N- nitrosodiethanolamine, and Nâ²-nitrosonornicotine, are up to fourfold. Presently we do not know whether the tobacco-specific N-nitrosamines are present in the particulate phase or in the vapor phase of ETS (Hoffmann and Hecht, 1985). Constituents of the vapor phase would be less likely to settle with the smoke particles, but would remain in the ambient air for longer spans of time. Research is needed to evaluate this distribution, which is important with respect to the carcinogenic potential of SS. The meaning of the abundant release of amines in SS (SS/MS, to 30- fold)âas indicated by the data in aniline, 2-toluidine, and the alkaloidsâshould also be examined. Some amines are readily nitrosated to N-nitrosamines, but analytic data on secondary reactions of amines in polluted environments are lacking.
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 33 TABLE 2â3 Relative Concentrations (SS/MS) of Selected Components in Fresh, Undiluted Smoke of Four 85-mm Commercial American Cigarettesa Constituentc Constituent Concentrations in Smokeb Cigarette A, NF Cigarette B, F Cigarette C, F Cigarette D, PF SS SS/MS SS SS/MS SS SS/MS SS SS/MS Tar, mg/g 22.6 1.1 24.4 1.6 20.0 2.9 14.1 15.6 Nicotine, mg/g 4.6 2.2 4.0 2.7 3.4 4.2 3.0 20.0 CO, mg/g 28.3 2.1 36.6 2.7 33.2 3.5 26.8 14.9 NH3, mg/g 524 7.0 893 46 213.1 6.3 236 5.8 Catechol, Âµg/g 58.2 1.4 89.8 1.3 69.5 2.6 117 12.9 BaP, ng/g 67 2.6 45.7 2.6 51.7 4.2 448 20.4 NDMA, ng/g 735 23.6 597 139 611 50.4 685 167 NPYR, ng/g 177 2.7 139 13.6 233 7.1 234 17.7 NNN, ng/g 857 0.85 307 0.63 185 0.68 338 5.1 aData from Adams et al. (1985). Tar values for MS: cigarette A, 20.1 mg; cigarette B, 15.6 mg; cigarette C, 6.8 mg; cigarette D, 0.9 mg. b NF=nonfilter cigarette; F=filter cigarette; PF=cigarette with perforated filter tip; BaP=benzo[a]pyrene. cNDMA=N-nitrosodimethylamine; NPYR=N-nitrosopyrrolidine; NNN=Nâ²-nitrosonornicotine. To comprehend the data in Table 2â2 fully, some aspects should be emphasized. First, the data are based on analyses of nonfilter cigarettes that were smoked under standard laboratory conditions. Second, those conditions, established according to smoking patterns observed 3 decades ago, have been shown not to reflect today's smoking behavior. The difference is especially evident in the case of filter cigarettes designed for low smoke yields. Most consumers inhale the smoke of such cigarettes more intensely than the smoke of nonfilter cigarettes (Hill and Marquardt, 1980; Herning et al., 1981). This difference affects the yield of SS. Conventional cigarette filter tips primarily influence the yield of MS, but have little impact on SS yield. However, highly active filter tips, especially those with perforations, also affect the yield of SS (Adams et al., 1985). It is apparent in Table 2â3 that for all cigarettes studied the SS/MS values are greater than 1 for many toxic and carcinogenic constituents.
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 34 TABLE 2â4 Measured Concentrations of Carbon Monoxide in ETSa Location Tobacco Ventilation Carbon Monoxide Concentrations, ppm References Burned Nonsmoke Controls Mean Range Mean Range Rooms â â â 4.3â9 2.2Â±0.98 0.4â4.5 Coburn et al., 1965 Train 1â18 Natural â 0â40 â â Harmsen and smokers Effenberger, 1957 Submarines 157 Yes Yes <40 â â â Cano et al., 1970 (66 m3) cigarettes/ <40 â â â day 94â103 cigarettes/ day 18 military â Yes <2â5 â â â U.S. Department aircraft of Transportation, 1971 8 commercial â Yes <2 â â â U.S. Department aircraft of Transportation, 1971 Rooms â â â 5â25 â â Porthein, 1971 14 public â â <10 â â â Perry, 1973 places Ferry boat â â 18.4 â 3.0Â±2.4 â Godin et al., 1972 Â±8.7 Theater foyer â â 3.4Â±0.8 â 1.4Â±0.8 â Godin et al., 1972 Intercity bus 23 cigarettes 15 changes/h 32 â â â Seiff, 1973 3 cigarettes 15 changes/h 18 â â â 2 conference â 8 changes/h â 8 (peak) 1â2 â Slavin and Hertz, rooms 1975 Office â 236 m3/h â <2.5â â â Harke, 1974 â Natural â 4.6 â â â < 2.9â 9.0 Automobile 2 smokers (4 Natural â 42 â 13.5 Harke and Peters, cigarettes) Mechanical â (peak) â (peak) 1974 32 15.0 (peak) (peak) 9 night clubs â Varied 13.4 6.5â41.9 â â Sebben et al., 1977 14 restaurants â â 9.9Â±5.5 â 9.2 3.0â35 Sebben et al., (outdoor) 1977 45 restaurants â â 8.2Â±2.2 7.1Â±1.7 â â Sebben et al., 1977
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 35 33 stores â â 10.0 11.5Â±6.5 11.5Â±6.5 â Sebben et al., Â±4.2 1977 3 hospital â â â 4.8 â â Sebben et al., lobbies 1977 6 coffee houses Varied â 2â23 â â â Badre et al., 1978 Room 18 â 50 â â â Badre et al., smokers 1978 Hospital lobby 12â30 â 5 â â â Badre et al., smokers 1978 2 train 2â3 â â 4â5 â â Badre et al., compartments smokers 1978 Automobile 3 smokers Natural, open 14 â â â Badre et al., 2 smokers Natural, 20 â â â 1978 closed 10 offices â â 2.5Â±10 1.5â1.0 2.5Â±1.0 1.5 Chappell and Â±4.5 Parker, 1977 15 restaurants â â 4.0Â±2.5 1.0â9.5 2.5Â±1.5 1.0â Chappell and 5.0 Parker, 1977 14 night clubs â â 13.0 3.0â29.0 3.0Â±2.0 1.0â Chappell and and taverns Â±7.0 5.0 Parker, 1977 Tavern â Artificial 8.5 â â â Chappell and â None â 35 â â Parker, 1977 (peak) Office â Natural, open 1.0 10.0 â â Chappell and (peak) Parker, 1977 Restaurant â Mechanical 5.1 2.1â9.9 4.8 â Fischer et al., (outdoors) 1978 Restaurant â Natural 2.6 1.4â3.4 1.5 â Fischer et al., (outdoors) 1978 Bar â Natural, open 4.8 2.4â9.6 1.7 â Weber et al., (outdoors) 1976 Cafeteria â 11 changes/h 1.2 0.7â1.7 0.4 â Weber et al., (outdoors) 1976 44 offices â â 1.1 6.5 â â Weber, 1984 (max) 25 offices â â 2.78 â 2.59Â±2.33 â Szadkowski et Â±1.42 al., 1976 Tavern â 6 changes/h 11.5 10â12 2 (outdoors) â Cuddeback et al., 1976 Tavern â 1â2 changes/h 12.0 3â22 â â Cuddeback et al., 1976 aTime-weighted average (TWA) of carbon monoxide, 50 ppm (55 mg/m3 ). TWA=average concentration to which worker may be exposed continuously for 8 h without damage to health (National Institute for Occupational Safety and Health, 1971).
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 36 PRINCIPAL CHEMICAL CONSTITUENTS OF ENVIRONMENTAL TOBACCO SMOKE Air dilution physicochemically changes SS and other contributors to ETS. Depending on the degree of air dilution of SS, the concentration of particles in ETS can range from a few micrograms to 300â500 mg/m3. A high degree of air dilution can reduce this yield to a few micrograms per cubic meter. At the same time, the median diameter of the particles will decrease from 0.32 Âµm to 0.14 or 0.098 Âµm (Keith and Derrick, 1960; Wynder and Hoffmann, 1967; Ingebrethsen and Sears, 1985). Another change caused by air dilution of SS is the volatilization of nicotine. In ETS, nicotine is present almost exclusively in the vapor phase (Eudy et al., 1985). In addition, redistributions of other constituents in SS due to air dilution might account for the presence of other semivolatile chemicals in the vapor phase of ETS, but we lack data on such effects. The scientific literature contains an abundance of data on indoor air pollution by ETS (U.S. Public Health Service, 1979; National Research Council, 1981). We limit our review here to measurements made under field conditions and have excluded data from experimental studies. Most of the published data, summarized in Tables 2â4 through 2â9, do not exclude the possibility that, even though the respiratory environments analyzed were polluted largely by ETS, some other sources of pollution contributed to the reported concentrations of individual agents. (Many studies have dealt with the measurement of particulate matter in environments polluted by tobacco smoke. Chapter 5 discusses the measurement of particulate matter, and the results of the studies are summarized in Table 5â1.) Table 2â4 shows concentrations of carbon monoxide measured in a variety of indoor spaces with and without occupancy by smokers. Carbon monoxide concentrations were generally higher in spaces where smoke was present. They were highly variable, however, and collected data on each space were insufficient (e.g., number of cigarettes smoked and volume of space) to show a consistent relationship. Tobacco is the only known source of nicotine, so the Nicotiana alkaloid is a specific indicator for tobacco smoke pollution. Nicotine concentrations in smoke-polluted rooms were generally found to be 5â50 Âµg/m 3 and much higher (up to 500 Âµg/m3) in
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 37 heavily polluted environments (Table 2â5). In small interior compartments, such as automobiles, occupants who smoke tobacco have generated nicotine concentrations of 1,010 Âµg/m3 (Badre et al., 1978). Freshly generated tobacco smoke contains nitric oxide, but not nitrogen dioxide. On release into the environment, nitric oxide is gradually oxidized to nitrogen dioxide. The estimated half-life of nitric oxide is 10â20 minutes, depending on the degree of air dilution. Table 2â6 shows concentrations of nitric oxide and nitrogen dioxide in smoke-polluted environments and indicates means ranging from 9 to 195 ppb for nitric oxide and 21 to 76 ppb for nitrogen dioxide. Generally, the nitrogen oxide values reported in Table 2â6 are significantly in excess of those observed for outdoor atmospheres. However, some severe air pollution episodes in industrial areas have reportedly caused levels of 100 ppb, which persisted over several hours or even for several days (Goldsmith and Friberg, 1977). As a constituent of the respiratory environment, nitrogen dioxide conceivably contributes to endogenous nitrosation, which leads to the presence of nitrosamines in exposed subjects. Whereas it has been clearly demonstrated that inhaled cigarette smoke increases the endogenous formation of N-nitrosamines (Hoffmann and Brunnemann, 1983; Ladd et al., 1984; Lu et al., 1986; Tsuda et al., 1986), the endogenous formation of N-nitrosamines in nonsmokers exposed to ETS has so far not been demonstrated (Brunnemann et al., 1984). Tables 2â7 and 2â8 show concentrations of acrolein and acetone in ETS. These volatile carbonyl compounds are known to affect mucociliary function and thus inhibit the clearance of smoke particles from the lung (Wynder and Hoffmann, 1967). Table 2â9 shows concentrations of some additional toxic agents in ETS. Benzene, N-nitrosodimethylamine, N-nitrosodiethylamine, and the polynuclear aromatic hydrocarbons, represented by benzo[a]pyrene, are of concern, because they are known carcinogens (Vainio et al., 1985). RADIOACTIVITY OF ENVIRONMENTAL TOBACCO SMOKE The radioactive isotopes of lead (Pb-210), bismuth (Bi-210), and polonium (Po-210), known as long-lived radon daughters in the decay chain of uranium via radium and radon (Radford and
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 38 TABLE 2â5 Measured Concentrations of Nicotine in ETSa Location Tobacco Burned Ventilation Nicotine Concentrations, Âµg/ References m3 Mean Range Train â Natural, closed â 0.7â3.1 Harmsen and Effenberger, 1957 6 coffee houses Smokers varied â â 25â52 Badre et al., 1978 Room 18 smokers â 500 â Badre et al., 1978 Hospital lobby 12â30 smokers â 37 â Badre et al., 1978 2 train compartments 2â3 smokers â â 36â50 Badre et al., 1978 Automobile 3 smokers Natural, open 65 â Badre et al., 1978 Natural, closed 1,010 â Submarines (66 m3) 157 cigarettes/day Yes 32 â Cano et al., 1970 94â103 cigarettes/ Yes 15â35 â day Train â â 4.9 â Hinds and First, 1975 Bus â â 6.7 â Hinds and First, 1975 Bus waiting room â â 1.0 â Hinds and First, 1975 Airline waiting room â â 3.1 â Hinds and First, 1975 Restaurant â â 5.2 â Hinds and First, 1975 Cocktail lounge â â 10.3 â Hinds and First, 1975 Student lounge â â 2.8 â Hinds and First, 1975 44 offices â â 0.9Â±1.9 13.8 (peak) Weber and Fischer, 1980 aTime-weighted average (TWA) of nicotine, 500 Âµg/m3. TWA=average concentration to which worker may be exposed continuously for 8 h without damage to health (National Institute for Occupational Safety and Health, 1971).
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 39 TABLE 2â6 Measured Concentrations of Nitrogen Oxides in ETSa Location Tobacco Ventilation Nitrogen Oxides Concentrations, ppb References Burned Mean Range Nonsmoke Control, Mean Restaurant â Mechanical NO2 76 59â105 63 (outdoors) Fischer et al., 1978 NO 120 36â218 115 (outdoors) Restaurant â Natural NO2 63 24â99 50 (outdoors) Weber, 1984 NO 80 14â121 11 (outdoors) Bar â Natural, open NO2 21 1â61 48 (outdoors) Weber et al., 1979 NO 195 66â414 44 (outdoors) Cafeteria â 11 changes/h NO2 58 35â103 27 Weber et al., 1979 NO 9 2â38 5 44 offices Varied Varied NO2 24Â±22 115 (peak) â Weber and NO 32Â±60 200 (peak) â Fischer, 1980 aTime-weighted averages (TWAs): nitric oxide, 25 ppm; nitrogen dioxide, 1 ppm. TWA=average concentration to which worker may be exposed continuously for 8 h without damage to health (National Institute for Occupational Safety and Health, 1971).
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 40 TABLE 2â7 Measured Concentrations of Acrolein in ETSa Location Tobacco Burned Ventilation Acrolein Concentrations References Mean Range Coffee houses Varied â â 0.03â0.10 mg/m3 Badre et al., 1978 Room 18 smokers â 0.185 mg/m3 â Badre et al., 1978 Hospital lobby 12â30 smokers â 0.02 mg/m3 â Badre et al., 1978 2 train compartments 2â3 smokers â â 0.02â0.12 mg/m3 Badre et al., 1978 Automobile 3 smokers Natural, open 0.03 mg/m3 â Badre et al., 1978 2 smokers Natural, closed 0.3 mg/m3 â Restaurant â Mechanical 7 ppb â Fischer et al., 1978 â Natural 8 ppb â Bar â Natural, open 10 ppb â Weber et al., 1976 Cafeteria â 11 changes/h 6 ppb â Weber et al., 1976 aTime-weighted average (TWA) of acrolein, 0.1 ppm. TWA=average concentration to which worker may be exposed continuously for 8 h without damage to health (National Institute for Occupational Safety and Health, 1971).
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 41 TABLE 2â8 Measured Concentrations of Acetone in ETSa Location Tobacco Burned Ventilation Acetone Concentrations, mg/m3 References Mean Range 6 coffee houses Varied â â 0.91â5.88 Badre et al., 1978 Room 18 smokers â 0.51 â Badre et al., 1978 Hospital lobby 12â30 smokers â 1.16 â Badre et al., 1978 2 train compartments 2â3 smokers â â 0.36â0.75 Badre et al., 1978 Automobile 3 smokers Natural, open 0.32 â Badre et al., 1978 2 smokers Natural, closed 1.20 â aTime-weighted average (TWA) of acetone, 250 ppm. TWA=average concentration to which worker may be exposed continuously for 8 h without damage to health (National Institute for Occupational Safety and Health, 1971).
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 42 TABLE 2â9 Measured Concentrations of Various Toxic Agents in Rooms Polluted with ETS Pollutant Location Concentration Nonsmoke Control References Concentration Benzene Public places 20â317 Âµg/m3 â Badre et al., 1978 N-Nitrosodimethylamine Restaurant, public 0.01â0.24 Âµg/m3 0.005 Âµ g/m3 (inside) Brunnemann et al., places 1977; Stehlik et al., 1982 N-Nitrosodiethylamine Restaurant, public <0.01â0.2 Âµg/m3 â Stehlik et al., 1982 places Anthanthrene Coffee houses 4.1â9.4 ng/m3 2.8â7.0 ng/m3 Just et al., 1972 (outdoors) Benzo[a]fluorene Indoors 39 ng/m3 â Grimmer et al., 1977 Benzo[a]pyrene Restaurant, public 2.8â760 ng/m3 4.0â9.3 ng/m3 Galuskinova, 1964; (outdoors) Just et al., 1972; Perry, 1973; Grimmer et al., 1977 Benzo[-]pyrene Coffee houses 3.3â23.4 ng/m3 3.0â5.1 ng/m3 Just et al., 1972 (outdoors) Coronene Coffee houses 0.5â1.2 ng/m3 1.0â2.8 ng/m3 Just et al., 1972 (outdoors) Perylene Coffee houses 0.7â1.3 ng/m3 0.1â1.7 ng/m3 Just et al., 1972 (outdoors) Pyrene Coffee houses 4.1â9.4 ng/m3 0.1â1.7 ng/m3 Just et al., 1972 (outdoors) Phenols (volatile) Coffee houses 7.4â11.5 ng/m3 â Just et al., 1972
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 43 Hunt, 1964; Martell, 1975; Hill, 1982), are present in tobacco and therefore appear in tobacco smoke. Furthermore, when radon is present in the air, aerosol particles, including those of tobacco smoke, tend to adsorb the earlier decay products of radon, namely the so-called short-lived daughters (Po-218, Pb-214, Bi-214, and Po-214), i.e, those preceding the long-lived daughters in the decay chain (Raabe, 1969; Kruger and Nothing, 1979; Bergman and Axelson, 1983). The presence of Pb-210 and subsequent decay products in tobacco might derive from uptake of Pb-210 from the soil, especially if radium-rich phosphate fertilizers have been used (Tso et al., 1966). It may also result from adsorption of short-lived radon daughters on the leaves of the tobacco plant when phosphate fertilizers are used and the leakage of radon from the ground is therefore increased. This adsorption applies to short-lived daughters, which then decay to the long-lived Pb-210, and subsequent nuclides found in the tobacco when phosphate fertilizers, containing radium-226, are used (Fleischer and Parungo, 1974; Martell, 1975). The origin of these decay products could also be due to the general occurrence of radon in the atmosphere (Hill, 1982). In recent years, relatively high concentrations of radon and short-lived radon daughters have been found in indoor air in homes in several countries (Nero et al., 1985). In clean air, the short-lived radon daughters tend to be more unattached to aerosol particles and therefore are more easily deposited on walls, furniture, etc., especially through electrostatic forces. In the presence of an aerosol like tobacco smoke, some of the short-lived radon daughters are attached to particles, and therefore remain available for inhalation to a much greater extent than would otherwise be the case. Indoor radon-daughter concentration can more than double in the presence of tobacco smoke (Bergman and Axelson, 1983). Since radon daughter exposure is a well-known cause of lung cancer in miners, the described attachment of radon daughters to cigarette smoke would contribute to the carcinogenic potential of ETS (Little et al., 1965; Rajewsky and Stahlhofen, 1966; Radford and Martell, 1978). Given the presence of appreciable amounts of radon in indoor air, irradiation of the bronchial tract from radon daughters attached to smoke aerosol could be more important than the irradiation from the long-lived daughters in the tobacco itself. This subject needs further research, especially in light of recent reports on the widespread prevalence of indoor radon throughout the world.
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 44 TOXIC AND CARCINOGENIC AGENTS IN TOBACCO SMOKE Combustion products of cigarettes are the main contributors of ETS. Therefore, comparisons of concentrations of specific toxins and carcinogens in ETS (Tables 2â4 through 2â9) with corresponding concentrations in MS are relevant. However, comparisons of MS and ETS can be appropriate only if one considers the important differences in chemical composition (including pH) and physicochemical nature (e.g., particle size, air dilution factors, and distribution of agents between vapor and particulate phases) between the two aerosols. Furthermore, ETS in indoor environments is often accompanied by pollutants in the work environment or derived from other sources, such as cooking stoves and space heaters. There are also important differences between inhaling ambient air and inhaling a concentrated smoke aerosol during puff-drawing. Finally, chemical and physicochemical characteristics based on analysis of smoke generated by machine smoking are not fully comparable with those of compounds generated when a smoker inhales cigarette smoke. Especially in the case of low-yield cigarettes, the yields of constituents appear to be different between machine smoking and human smoking (Herning et al., 1981). Table 2â10 compares concentrations of some smoke constituents in the MS generated in the laboratory from one cigarette to those inhaled by a nonsmoker exposed to ETS for 1 hour.* The physical and chemical changes that occur in reactive smoke constituents during aging of the compounds after their emission into the environment must also be considered. For example, nitric oxide is generated in a cigarette during smoking and is chemically * The computations for exposures to nonsmokers for 1 hour in Table 2â10 are made using the equation: assuming an average respiratory rate of 10 L/minute. To convert from ppm (or ppb) to mg/m3, the following equation is used: where RT at 20Â°C is 24.45.
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 45 intact when it leaves the cigarette in MS about 2 seconds later. However, once emitted into SS and diluted to become an ETS component, nitric oxide is partially oxidized to nitrogen dioxide and progressively more oxidized as more time elapses, producing a potent hydrophilic nitrosating agent. SUMMARY AND RECOMMENDATIONS The smoldering of tobacco between puffs generates SS. Undiluted SS contains some toxic compounds in much higher concentrations than MS, especially ammonia, volatile amines, volatile nitrosamines, some nicotine decomposition products, and aromatic amines. Furthermore, decay products of radon from the tobacco and from other sources adsorbed on some particles in indoor air might contribute to the carcinogenic potential of ETS. SS is a major contributor to ETS. Respiratory environments that are polluted with SS contain measurable amounts of nicotine and other toxic agents, including carcinogens. We lack data on the presence and concentrations of many of the known SS components in polluted, enclosed environments. The concentrations of toxic agents of ETS are governed primarily by the amount of tobacco smoked, the degree of ventilation, and the volatility of the agents. Future studies should concentrate on the analysis of toxic and carcinogenic agents in smoke-polluted environments. What Is Known 1. SS is the aerosol that is freely emitted into the air from the smoldering tobacco products between puffs. 2. ETS consists of diluted SS, exhaled MS, smoke that escapes from the burning cone during puff- drawing, and vapor-phase components (such as carbon monoxide) that diffuse through cigarette paper into the environment. However, secondary reactions can occur before a nonsmoker inhales ETS, such as aging, volatilization of nicotine, and adsorption of radon daughters on particles. 3. Undiluted SS contains higher concentrations of some toxic compounds than undiluted MS, including ammonia, volatile amines, volatile nitrosamines, nicotine decomposition products, and aromatic amines. 4. Conventional cigarette filter tips primarily influence the yield of MS, but have little impact on the yield of SS. Highly active filter tips, especially perforated ones, also affect the yield of components in SS.
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 46 TABLE 2â10 Concentrations of Toxic and Carcinogenic Agents in Cigarette Mainstream Smoke and ETS in Indoor Environmentsa Agentc Mainstream Smoke from Nonfilter Inhaled as ETS Constituent During 1 Exceptionally High Valuesb Cigarette Hour: Range Weight Concentration Weight Concentration Weight Concentration CO 10â23 mg 24,900â57,400 ppm 0.6â13 mg 1â18.5 ppm 22 mg 32 ppm NO 100â600 Âµg 230,000â1,380,000 7â88 Âµg 9â120 ppb 144 Âµ g 195 ppb ppb NO2 <5 Âµg <7,600 ppb 24â86 Âµg 21â76 ppb 119 Âµ g 105 ppb Acrolein 60â100 Âµg 750,000â125,000 80â69 Âµg 6â50 ppb 110 Âµg 80 ppb ppb Acetone 100â250 Âµg 120,000â300,000 210â710 Âµg 150â500 ppb 3,400 Âµg 2,400 ppb ppb Benzened 12â48 Âµg 11,000â43,000 ppb 12â190 Âµg 6â98 ppb 190 Âµg 98 ppb NDMAe 10â40 ng 9â38 ppb 6â140 ng 0.003â0.077 ppb 140 ng 0.072 ppb NDEAe 4â25 ng 3â17 ppb <6â120 ng <0.002â0.05 ppb 120 ng 0.05 ppb Nicotine 1,000â2,500 430,000â1,080,000 0.6â30 Âµg 0.15â7.5 ppb 300 Âµ g 75 ppb Âµg ppb BaPf 20â40 ng 5â11 ppb 1.7â460 ng 0.00027â0.074 ppb 460 ng 0.074 ppb aValues for inhaled ETS components calculated from values in Tables 2â4 through 2â9 and respiratory rate of 10 L/min. Data from unventilated interiors of automobiles excluded (Badre et al., 1978). Concentrations for MS are calculated by diluting weights given in volume of 350 ml, that is 10 puffs at 35 ml/puff. b Chosen to classify reported data that require confirmation. cNDMA=N-nitrosodimethylamine; NDEA=N-nitrosodiethylamine; BaP=benzo[a]pyrene. d Human carcinogen, according to International Agency for Research on Cancer (Vainio et al., 1985); suspected carcinogen, according to American Conference of Governmental Industrial Hygienists (1985). eAnimal carcinogen according to the International Agency for Research on Cancer (Vainio et al., 1985). fSuspected human carcinogen according to the International Agency for Research on Cancer (Vainio et al., 1985) and according to the American Conference of Governmental Industrial Hygienists (1985).
THE PHYSICOCHEMICAL NATURE OF SIDESTREAM SMOKE AND ENVIRONMENTAL TOBACCO SMOKE 47 5. Radioactive decay products in tobacco itself, for instance, Pb-210 and Po-210, and short-lived radon daughters adsorbed on smoke particles in indoor air can contribute to the carcinogenic potential of ETS. 6. ETS in indoor environments is accompanied by pollutants, such as nitrogen oxides and carbon monoxide, derived from other sources, including cooking stoves and space heaters. ETS contains measurable amounts of nicotine and other toxic agents, including carcinogens. The concentrations of toxic agents of ETS are governed primarily by the amount of tobacco smoked, the degree of ventilation, and the volatility of the agents. 7. Nicotine, found in MS primarily in the particulate phase, occurs in ETS primarily in the vapor phase. Therefore, filters designed to reduce particles in the air will not substantially alter the nicotine concentration. What Scientific Information Is Missing 1. We lack data on the presence and concentrations of toxic and carcinogenic components in tobacco- smoke-polluted enclosed environments. 2. The distributions of various agents in vapor and particulate phases of ETS are not well characterized. Further, the effect of air-cleaning systems on these distributions has not been studied. Distributions are important with respect to the carcinogenic potential of ETS. 3. We need to examine the importance of the abundant release of amines into ETS. We lack analytic data on secondary reactions of amines in polluted air, such as N-nitrosation and condensation with other ETS components. 4. The transfer of constituents other than nicotine from the particulate phase of SS to the vapor phase of ETS could be important with respect to the retention of ETS in the respiratory tract of nonsmokers. 5. We do not know the extent to which nitrogen dioxide can contribute to endogenous nitrosation in nonsmokers as a constituent of the respiratory environment. Endogenous nitrosation leads to nitrosamines in exposed subjects.
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