Document 38mDYLLOox4XJ5dkq016VdYx

Environmental Health Perspectives Vol. 82, pp. 165-169, 1989 Major Sources of Benzene Exposure by Lance A. Wallace* Data from EPA's TEAM Study allow us to identify the major sources of exposure to benzene for much of the U.S. population. These sources turn out to be quite different from what had previously been considered the important sources. The most important source of exposure for 50 million smokers is the mainstream smoke from their cigarettes, which accounts for about half of the total population burden of exposure to benzene. Another 20% of nationwide exposure is contributed by various personal activities, such as driving and using attached garages. (Emissions from consumer products, building materials, paints, and adhesives may also be important, although data are largely lacking.) The traditional sources of atmospheric emissions (auto exhaust and industrial emissions) account for only about 20% of total exposure. Environmental tobacco smoke is an important source, accounting for about 5% of total nationwide exposure. A number of sources sometimes considered important, such as petroleum refining operations, petrochemical manufacturing, oil storage tanks, urban-industrial areas, service stations, certain foods, groundwater contamination, and underground gasoline leaks, appear to be unimportant on a nationwide basis. Introduction Benzene is recognized as a human leukemogen (1). It is regulated in the workplace in most countries. In the U.S., it is one of only a few chemicals that are regulated under Section 112 of the Clean Air Act as a Hazardous Air Pollutant. Nonetheless, until recently the main sources of exposure to the general population have remained obscure. Chemical plants, petroleum refining operations, oil storage tanks, major urban-industrial areas, and gasoline service stations have been suspected major sources of exposure. Food, water supplies, and landfills have also been mentioned as possible major sources. Now, a large study of human exposure to benzene (EPA's TEAM Study) has been completed, with the surprising result that the main sources of human exposure are associated with personal activities, not with the socalled "major point sources" mentioned above. This paper will attempt to create a nationwide exposure budget, identifying the main sources of benzene exposure for the U.S. population, by drawing on the TEAM Study find- ings. Review of TEAM Study Findings The TEAM Study is described in detail in a four-volume EPA publication (2-5) and in several journal articles (6-10). Following is a brief summary of the study and its findings with respect to benzene. The study measured *U.S. Environmental Protection Agency, 401 M St. SW, Washington, DC 20460. 24-hr personal exposures in air and drinking water to 20 to 25 target volatile organic compounds for a probabilistically selected group of subjects in Elizabeth-Bayonne, NJ; Los Angeles, CA; Antioch-Pittsburg, CA; Greensboro, NC; and Devils Lake, ND. (In 1987, another city, Baltimore, MD, was sampled. Preliminary results are in- cluded in this paper.) Subjects were selected according to a three-stage stratified survey design. In each city, a target population was selected using census information. Blocks of homes were stratified according to socioeconomic factors and proximity to potential industrial and mobile sources. In the second stage, a large number of homes (about 5500 in New Jersey and 2000 in California) were visited, and trained interviewers collected information on age, sex, occupation, smoking status, and other factors for each person in the household. This information was used to deter- mine the prevalence of potential exposure factors in the target population and to allow selection of those persons more likely to be exposed. Since the probability of selection was known for the entire target population, the measured concentrations, when weighted by the inverse of the probability of selection, apply to the entire population. A total of about 700 subjects representing more than 800,000 residents of the various cities collected two 12-hr air samples and 1 to 2 tap water samples during a 24-hr period. Concurrent outdoor air samples were collected from the backyards of a subset (about 200) of the subjects' homes. At the end of 24 hr, each subject provided a sample of exhaled breath to a van-mounted spirometer. Both air and breath samples were collected on Tenax cartridges and analyzed by GC/MS. 166 L. A. WALLACE Results Population-weighted personal exposures to benzene (Table 1) exceed the outdoor air concentrations (Table 2) in every city. The overall mean personal exposure is about 15 Mg/m3, compared to an overall mean outdoor con- centration of only 6 ,ug/m3. When maximum exposures are compared to maximum outdoor concentrations, the difference is even more striking: 500 ,Ag/m3 for the personal exposure maximum compared to 90 ,g/m3 for the outdoor maximum. These results imply that personal activities or sources in the home far outweigh the contribution of outdoor air to human exposure to benzene. Since most of the traditional sources exert their effect through outdoor air, we must find new sources to explain the increased per- sonal exposures observed. Smoking Examination of exhaled breath concentrations against personal activities identified one activity as paramount: smoking tobacco. Smokers typically have breath concentrations of benzene around 14 Hg/m3, while nonsmokers range around 2 ,ug/m3 (Fig. 1). From measurements of benzene content in mainstream smoke [57 ,.g benzene in the average sales-weighted tar and nicotine cigarette (11)] we can calculate that the average smoker (32 cigarettes/day) takes in about 1.8 mg of benzene per day. This is nearly 10 times the average daily intake of nonsmokers (12,13). Passive Smoking Passive smoking was also an important source of benzene exposure. Median levels of benzene in 200 homes without smokers were 7,g/m3; in 300 homes with one or more smokers, median levels were 10.5 pg/m3. This rep- resents a 50% increase in benzene exposures of spouses and children in homes of smokers. A recent study of 500 homes in West Germany (14) replicated this result, with median values of 6.5 ,g/m3 in nonsmoking homes and 11 ,g/m3 in smoking homes (Fig. 2). Work exposures were also increased; nonsmokers not exposed at home who stated they were exposed to tobacco smoke more than 50% of the time they were at work showed significantly higher breath concentrations (Mann-Whitney nonparametric test) than those exposed to tobacco smoke at work less than 50% of the time. Table 1. Population-weighted personal exposures to benzene in five U.S. cities. Arithmetic Arithmetic Geometric Geometric Percentile TEAM sitea n mean SE mean SD Median 75 90 95 Maximum NJ night 347 29.7 NJ day 340 26.2 5.22 12.5 1.68 11.2 2.6 15 32 54 73 510 2.6 17 32 65 81 270 NC night 24 10.2 1.87 2.23 1.9 12 16 30 41 43 NC day 24 7.93 1.55 1.55 2.1 7.6 13 20 32 36 LA1 night LA1 day 112 112 16.5 19.1 1.30 13.6 1.53 15.1 2.6 15 21 30 34 43 2.1 15 23 35 51 86 LA2 night 50 7.78 1.31 4.69 2.9 4.4 9 25 29 35 LA2 day 50 10.5 1.62 6.88 2.4 7.2 12 25 34 54 AP night 69 6.47 1.13 4.63 2.5 4.4 7.5 16 18 32 AP day 67 8.47 0.87 6.83 2.1 6.3 11 17 21 25 MD night 70 20.7 1.42 12.3 2.5 13 26 42 66 104 MD day 70 16.4 1.24 8.38 2.3 11 22 32 45 129 aNJ: Bayonne-Elizabeth, NJ; fall 1981; population, 130,000. NC: Greensboro, NC; May 1982; population, 130,000. LAl: Los Angeles, CA; February 1984; population, 360,000. LA2: Los Angeles, CA; May 1984; population, 330,000. AP: Antioch-Pittsburg, CA; June 1984; population, 90,000. MD: Baltimore, MD; March 1987; population, Not yet weighted. Table 2. Outdoor concentrations of benzene in three U.S. cities. Arithmetic Arithmetic Geometric Geometric Percentile TEAM sitea n mean SE mean SD Median 75 90 95 Maximum NJ night 84 8.6 NJ day 88 9.5 1.04 0.95 4.1 2.0 6.7 11 15 24 91 3.8 2.1 7.8 16 20 27 44 LA1 night 24 18.9 1.86 16.5 1.4 19 25 32 33 33 LA1 day 24 13.2 1.34 11.2 1.3 14 18 21 22 35 LA2 night LA2 day 23 24 3.1 4.2 0.45 0.82 2.6 2.0 2.5 4.4 5.8 6.7 8.5 3.2 2.2 3.1 4.8 8.7 12 15 AP night 10 1.8 0.32 1.6 1.7 1.7 1.9 3.2 - 3.6 AP day 10 2.0 0.63 1.5 2.5 1.3 1.6 6.3 - 6.3 aNJ: Bayonne-Elizabeth, NJ; fall 1981; population, 130,000. LAl: Los Angeles, CA; February 1984; population, 360,000. LA2: Los Angeles, CA; May 1984; population, 330,000. AP: Antioch-Pittsburg, CA; June 1984; population, 90,000. BENZENE EXPOSURE 167 ug/m3 25 20 15 10 5- 0 NJ lt L.A.1 L.A.2 MD TEAM Study Locations SMOKERS 1 NONSMOKERS A-P FIGURE 1. Geometric mean benzene concentrations in the breath of smokers exceeded breath concentrations of nonsmokers at all TEAM Study sites: Bayonne-Elizabeth, NJ (smokers, n = 150; nonsmokers, n = 188); Los Angeles, CA in February 1984 (smokers, n = 29; nonsmokers, n = 85); Los Angeles, CA, in May 1984 (smokers, n = 11; nonsmokers n = 40); Baltimore, MD (smokers, n = 30; nonsmokers, n = 45); and Antioch-Pittsburg, CA (smokers, n = 19; nonsmokers, n = 49). Auto-Related Activities Stepwise regressions of breath concentrations and personal air exposures identified several auto-related activities as sources of benzene exposure. Exposure to auto exhaust, time spent in an auto, or pumping gas all resulted in increased personal exposure to benzene. Since benzene forms 1 to 2% of most gasoline blends, it is given UG/M3 12 10 USA FRG USA FRG HOMES WITH SMOKERS HOMES W/O SMOKERS FIGURE 2. Benzene concentrations in the homes of smokers were about 50% higher than in the homes of nonsmokers, both in the U.S. and in West Germany. U.S. values are geometric means based on 528 homes (343 with smokers, 185 without) in New Jersey and California; West German values are medians based on 488 homes. off as a vapor by hot engines and by fuel tanks and is also a constituent of auto exhaust. Therefore we may identify three potential major sources of auto-related exposure to benzene: auto travel, filling gas tanks, and parking hot cars in attached garages. Auto Travel. All four studies in New Jersey and California showed increases in the amount of benzene exposure in proportion to time spent in the car. Benzene concentrations in the car could not be reliably determined because exposures were averaged over 12 hr; however, concentrations of 3 to 4 times normal exposures (i.e., 40 to 60 pg/m3) were calculated. Pumping Gasoline. Several stepwise regressions identified pumping gasoline as a significant source of benzene exposure. Concentrations were estimated to be on the order of 1 ppm (3000 ,g/m3). Since that calculation, a study found about 1 ppm exposure at breathing level while pumping gasoline (15). Attached Garages. Gasoline vapors from attached garages have been observed in homes in several studies (16,1?). No quantitative estimates of benzene concentra- tions due to these emissions have yet been made. Occupational Exposures According to the N4tional Institute of Occupational Safety and Health, about 240,000 workers are exposed to benzene (18). The occupational limit is presently 1 ppm. Thus, a realistic estimate of exposure might be 100 ppb/worker, or 2.4 x 104 person-ppm. Consumer Products About 400 of 5000 materials and products tested by the National Air and Space Administration emitted benzene vapors, in amounts ranging from 0.01 lAg/g up to 140 pg/g (19). Paints, adhesives, marking pens, rubber products, tapes, and other common categories of materials emitted benzene. Other studies have also shown that latex paints emit benzene (20,21). Insufficient data exist to estimate exposures from any one category, but it seems likely that a substantial portion of the indoor excess of benzene (once contributions from tobacco smoke and auto emissions in attached garages are subtracted) can be attributed to the category of emissions from materials, surface coatings, or consumer products. Other Sources of Benzene Exposure We have mentioned other possible sources of benzene exposure. Several of these sources have been investigated in the TEAM Study and have been found to be relatively unimportant. For example, persons living close to the heavy petrochemical and refining operations at New Jersey and Los Angeles had no greater exposures than those living farther away. Although outdoor levels were higher in New Jersey and Los Angeles than in Greensboro, NC, this seems to be due to a higher intensity of automobile traffic, since the petrochemical manufacturing areas of Antioch-Pittsburg, CA, also had low outdoor levels of benzene. 168 L. A. WALLACE Since the TEAM Study measured breath levels of benzene, exposure to any important unmeasured sources (such as food and beverages) should have resulted in increased breath concentrations. In fact, this was the case for cigarette smokers, whose breath levels exceeded their apparent exposures through air as measured by the personal monitors. However, no other noticeable discrepancies between apparent exposure and measured breath concentrations have been found. Therefore, exposure through food, beverages, and drinking water is believed to be unimportant for most persons. As the TEAM subjects were drawn from areas where little use of wood stoves or kerosene heaters was made, it remains possible that these combustion sources will prove to be important sources of exposure to benzene. Calculation of Exposure Budget Having identified the main sources of benzene exposure and the concentrations associated with each, it remains to estimate the number of people exposed to each source. About 50 million persons smoke cigarettes in the U.S.(22); Perhaps 100 million persons pump gasoline 70 min per year, and the entire population (240 million) is exposed to indoor air, outdoor air, and air in autos. We can assume that two-thirds are passive smokers at home and at work (23) with workplace exposures to benzene from tobacco smoke equaling home exposures (3 ,ug/m3). These assumptions lead to the conclusion that more than half of the entire nationwide exposure to benzene results from smoking tobacco or being exposed to tobacco smoke. The remainder is split nearly evenly between personal and outdoor sources. The main personal sources are driving or riding in automobiles and using products that emit benzene. The main outdoor source is likely to be automobile exhaust, based on the lack of evidence for increased exposure in areas near petroleum refining and petrochemical operations. Based on the TEAM Study findings, it appears that the following are not important sources of exposure to ben- zene on a nationwide basis: chemical plants, petroleum refining operations, oil storage tanks, drinking water, food, and beverages. Risk An adequate calculation of benzene-related risk may be impossible with present knowledge. However, if risk is proportional to exposure, then the relative risks associated with major sources of exposure will be in the same proportion as the exposures themselves. The excess risk of leukemia associated with 70 years of exposure to 1 j,m/m3 benzene has been estimated by EPA to be 8 x 1l - 6(24) and by a group at Harvard University to be 4 X 10 -6 (25). Using the EPA potency estimate and the measured TEAM Study mean exposure of 15 ,ug/m3 extrapolated to the U.S. population, one can calculate roughly 400 benzene-related leukemia cases/year due to the major indoor and outdoor sources: auto exhaust, driv- ing, passive smoking and consumer product emissions (Table 3). An additional 500 cases can be calculated to occur among cigarette smokers inhaling benzene in mainstream smoke. Cigarette smokers have in fact been observed to be at about 50% higher risk of leukemia mortality (27), which would result in about 1000 excess cases of leukemia in smokers annually. Thus, benzene in cigarette smoke may account for a significant portion of the observed excess leukemia mortality among smokers. Conclusion On a nationwide basis, the most important single source of benzene exposure is active smoking of tobacco. Smoking accounts for about half of the total population exposure to benzene. Personal exposures due to riding in automobiles, passive smoking, and exposure to consumer products account for roughly one-quarter of the total exposure, with outdoor concentrations of benzene, due mainly to vehicle exhaust, accounting for the remaining Table 3. Benzene exposures and risks. Activity Intake, pAg/day Population at risk Cases/yeara Smoking 18 53 x 106 500 Passive smoking 50c 200 x 106d 50 Outdoor levels 120e 240 x 106 150 Driving/riding auto 40 200 x 106 40 Filling gas tank 109 100 x 106 5 Occupational l0000h 240 x 10 10 Other personal 150 240 x 106 200' Total 960 'b5U7sijngg/caiguanrietttreis(kHiogfg8inxs) 10- 6 (jAg/m3) . x 32 cigarettes/day. C3 ,ug/m3 x 17 hr/day indoors x 1 m3/hr respiration. dApproximately 80% of persons exposed to environmental tobacco smoke. 'TEAM outdoor average in eight locations = 6 pg/m3 x 20 m3/day. 6'1Fepwpmdatxa available, assumed 70 min/year. 40 pig/m3 in vehicle x 1 hr/day. hAssumed 1000 ,ug/m3 x 10 m3/8 hr workday. 'NIOSH estimate of number of workers exposed to benzene. 'Obtained by subtraction from published estimate of 460 nonsmoking cases/year (26). Includes emissions from surface coatings, consumer products, evaporative emissions from autos in attached garages, etc. BENZENE EXPOSURE 169 portion. Occupational exposures, pumping gasoline, living near chemical plants or petroleum refining operations, food, water, and beverages appear to account for no more than a few percent of total nationwide exposure to benzene. Although the research described in this article has been funded by the United States Environmental Protection Agency, it has not been subjected to Agency review and therefore does not necessarily reflect the views of the Agency. REFERENCES 1. IARC. Evaluation of the carcinogenic risk of chemicals to humans. IARC Monograph No. 219. International Agency for Research on Cancer, Lyon, France, 1982. 2. Wallace, L. A. The TEAM Study: Summary and Analysis, Vol. I. EPA 600/6-87/002a, NTIS PB 88-100060, U.S. EPA, Washington, DC 1987. 3. Pellizzari, E. D., Perritt, R., Hartwell, T. D., Michael, L. C., Sheldon, L S., Sparacino, C. M., Whitmore, R., Leninger, C., Zelon, H., Handy, R. W., Smith, D., and Wallace, L. A. Total Exposure Assessment Methodology (TEAM) Study: Elizabeth and Bayonne, New Jersey; Devils Lake, North Dakota, and Greensboro, North Carolina, Vol. II. EPA 600/6-87/002b, NTIS PB 88-100078, U.S. EPA, Washington, DC 1987. 4. Pellizzari, E. D., Perritt, R., Hartwell, T. D., Michael, L. C., Whitmore, R., Handy, R. W., Smith, D., Zelon, H., and Wallace, L. A. Total Exposure Assessment Methodology (TEAM) Study: Selected Communities in Northern and Southern California, Vol. III. EPA 600/6-87/002c, NTIS PB 88-100086, U.S. EPA, Washington, DC, 1987. 5. Handy, R. W., Smith, D. J., Castillo, N. P., Sparacino, C. M., Thomas, K., Whitaker, D., Keever, J., Blau, P. A., Sheldon, L. S., Brady, K. A., Porch, R. L., Bursey, J. T., and Pellizzari, E. D. Standard Operating Procedures Employed in Support of an Exposure Assessment Study. EPA 600/6-87/002d, NTIS PB 88-100098, U.S. EPA, Washington, DC, 1987. 6. Wallace, L. A., Zweidinger, R., Erickson, M., Cooper, S., Whitaker, D., and Pellizzari, E. Monitoring individual exposure: measurement of volatile organic compounds in breathing-zone air, drinking water, and exhaled breath. Environ. Int. 8:269-282 (1982). 7. Wallace, L. A., Pellizzari, E., Hartwell, T., Rosenzweig, R., Erickson, M., Sparacino, C., and Zelon, H. Personal exposure to volatile organic compounds: I. Direct measurement in breathing-zone air, drinking water, food, and exhaled breath. Environ. Res. 35: 293-319 (1984). 8. Wallace, L. A., Pellizzari, E., Hartwell, T., Sparacino, C., Sheldon, L., and Zelon, H. Personal exposures, indoor-outdoor relationships and breath levels of toxic air pollutants measured for 355 persons in New Jersey. Atmos. Environ. 19: 1651-1661 (1984). 9. Wallace, L. A., Pellizzari, E. D., Hartwell, T. D., Sparacino, C., Whitmore, R., Sheldon, L., Zelon, H., and Perritt, R. The TEAM study: personal exposures to toxic substances in air, drinking water, and breath of 400 residents of New Jersey, North Carolina, and North Dakota. Environ. Res. 43: 290-307 (1987). 10. Wallace, L. A. Personal exposures, indoor and outdoor concentrations and exhaled breath concentrations of selected volatile organic compounds measured for 550 residents of New Jersey, North Dakota, North Carolina and California. Toxicol. Environ. Chem. 12: 215-236 (1986). 11. Higgins, C., Griest, W. H., and Olerich, G. Applications of Tenax trapping to analysis of gas phase organic compounds in ultra-low tar cigarette smoke. J. 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Air Pollution Control Association, Pittsburgh, PA, 1986, pp. 458-466. 16. Gammage, R. B., White, D. A., and Gupta, K. C. Residential meas- urements of high volatility organics and their sources. In: Indoor Air: Chemical Characterization and Personal Exposure, Vol. 4 (B. Berglund, T. Lindvall, and J. Sundell, Eds.) Swedish Council for Building Research, Stockholm, Sweden, 1984. 17. McClenny, W. A., Lumpkin, T. A., Pleil, J. D., Oliver, K. D., Bubacz, D. K., Faircloth, J. W., and Daniels, W. H. Canister-based VOC samplers. In: Proceedings of the 1986 EPA/APCA Sympo- sium on Measurement of Toxic Air Pollutants. Air Pollution Control Association, Pittsburgh, PA, 1986, pp. 402-407. 18. NIOSH, Criteria for a Recommended Standard for Occupational Exposure to Benzene. National Institute for Occupational Safety and Health, U.S. Dept. of Health, Education and Welfare, Washington, DC, NIOSH 74-137, 1984. 19. Ozkaynak, H., Ryan, P. B., Wallace, L. A., Nelson, W. C., and Behar, J. V. Source and emission rates of organic chemical vapors in homes and buildings. In: Indoor Air '87: Proceedings of the Fourth International Conference on Indoor Air Quality and Climate, August 17-21, 1987. Institute for Water, Soil, and Air Hygiene, W. Berlin, 1987, pp. 17-21. 20. Wallace, A., Pellizzari, E., Leaderer, B., Hartwell, T., Perritt, R., Zelon, H., and Sheldon, L. Emissions of volatile organic compounds from building materials and consumer products. Atmos. Environ. 21: 385-393 (1987). 21. Sheldon, L. S., Zelon, H., Hartwell, T. D., Perritt, R., Michael, L., and Pellizzari, E. D. Indoor Air Quality in Public Buildings, Vol. II. U.S. Environmental Protection Agency, Research Triangle Park, NC. EPA 600/6-88/009b, 1988, in press. 22. NCHS. Changes in Cigarette Smoking and Current Smoking Practices among Adults: United States, 1987. Advance data No. 52. National Center for Health Statistics, Dept. of Health, Education and Welfare, Hyattsville, MD, 1979. 23. 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