Document dndzbGVwZ1GK6awygX09Jv3w5

workshop on Indoor Air Quality hlajor Sources of Exposure to Benzene and Other Volatile Organic Chemicals192 once Wallad Received March 7, 1989 The major sources of human exposure to about a dozen volatile organic chemicals (VOCs) have recently been identified.' For nearly every chemical, the major sources of exposure are completely different from the major sources of emissions. This finding implies that current environmental regulations and control strategies are misdirected. Important sources of exposure are typically not regulated in any way, whereas unimportant sources are heavily regulated. Vast sums of money are spent on problems involving little risk (e.g., h a w d o u s waste sites), whereas few resources are expended on problems involving higher risk (e.g., indoor air pollution). The following paper summarizes recent fmdings regarding major sources of exposure to several VOCs. Benzene is selected as a case study. Brief discussionsof tetrachloroethylene and paradichlorobenzene are also included. KFY WORDS:&ntene; exposure; organic chemicals; tetrachloroethylene. 1. INTRODUCTION roform and the three other trihalomethanes, which have important routes through drinking water and beverages, About 800 people have now had their exposure to VOCs measured Since they were selected to represent a larger population of about a million resi- dents of eight US. cities, their exposures probably rep- resent the nationwide experience fairly. We review these findings, and consider their implications on the nation's environmental policies. EPA's TEAM Studies targeted about 25-30 chem- icals, of which about 15 'were found to be prevalent (measurable in more than 20% of samples). Simulta- neous sampling of personal air, outdoor air, and drinking water showed that, for most of the chemicals, inhalation provided 99% of the exposure. (Exceptions were chlo- ' Paper presented at the Workshop on Exposure and Risk, Harvard 'University, Cambridge. Massachusetts. December 68, 1988. This paper has not been reviewed for policy implications by the U.S. Environmental Protection Agency and dou not necessarily reflect EPA policy. ' U.S. Environmental Protection Agency. 401 M Street. SW, RD-680. Washington, D.C. 20460. and limonene, a food and beverage additive. Even for these exceptions, inhalation was an important if not dominant route of exposure.) Therefore, we shall concentrate on inhalation exposure in what follows. We shall consider three chemicals of interest: benzene, tetrachloroethylene, and paradichlorobenzene. 2. BENZENE Exposures to benezene were measured for about 630 people in five locations. Outdoor air levels were measured near the homes of about 220 participants. The personal exposures averaged 16 ~ g / r nt~he; outdoor air levels averaged 6 pg/m3 (Table I). If we assume that outdoor air infiltrates homes and workplaces with no losses as it crosses the building envelopes, then we can attribute no more than 6 &m3 to outdoor sources: the remaining 10 &n3 is due to some combination of personal activities and indoor sources. 59 NJ MD LA. A-P NC Totrl 340 86 70 70 232 132 68 10 24 6 734 304 28 19 14 8 9 16 9 8 8 2 3 6 Population-weighted 2Chour arithmetic mean (Fglm'): NJ = Bayonne-Elizabeth. New Jersey (Fall 1981); MD = Baltimore, Maryland (Spring 1987); L.k = Los Aageles. cdifornia (two seasons. 1984 and 1987); A-P = Antioch-Pittsburgh, California (June 1984); NC = Greensboro, North Carolina ( M a y 1982). 2.1. Active Smoking Before discussing what these sources a n , however, we need to take account of a source that is not reflected in the average measured exposure of 16 &m3: mainstream cigarette smoke. Based on measurements of benzene in mainstream cigarette smokem Wallace('**)has estimated that mainstream smoke contributes about 1.8 mg/day to the average smoker's intake of benzene. This corresponds to an average ada'itbnal exposure for smokers of about 90 p&lm3(assuming 20 m3/day respiration rate). Since there are about 50 million smokers in the U.S., the total benzene exposure for them is roughly equal to the total benzene exposure from all other sources for the remainder of the population. 2.2. Passive Smoking Studies of 500 homes in both the U.S.m and in West Germany(1o)have indicated that homes with smokers have median indoor air benzene concentrationsabout 4 pg/m3 higher than in homes without smokers. Since at least half of U.S. homes contain smokers, we can calculate that about 2 &m3 is contributed, on average, by passive smoking. 2.3. Automobile Travel A recent study in California (D. Shikiya, unpublished data) indicates that automobile interior concentra- tions of benzene during commutes in La Angeles average about 13 ppb (40kglm'). The same concentration had been estimated by Wallace,Cm based on the TEAM Stud- .-. to the rest of the country, and assuming about 1 born per day in the automobile, this exposure would c o n m i Ute roughly another 2 @m3 to average exposure. Besides traveling in autos, filling gas tanks could contribute a portion of benzene exposure, although the total estimated contribution is only 0.2 pg/m3 (about 10%of the effect of automobile travel). 2.4 Attached Garages Gammage(") and McClenny('*) reported finding gasoline vapor in homes with attached garages. This could arise from evaporative emissions following parking, or from storage of gasoline in the garage. No estimates of the extent of exposure from these sources have yet been - made. 2.5 Products and Materials ~ _. More than 200 products and materials were found to emit benzene in studies carried out by NASA.(") Sheldon et al.,(*4J5fo)und benzene being emitted from several paints and adhesives, although indoor concentrations in two buildings constructed from these materials were not elevated. Thus these sources may contribute to exposure, although no estimates have been made of the contribution of products and materials to personal ex- posure. , 1 1 , 2.6. Occupational Workers in the chemical, manufacturing, and transportation industries may be exposed to elevated levels of benzene. However, the contribution of occupational exposure to the average exposure measured in the TEAM Studies appears to be relatively small. J I 3 2.7. Outdoor Air A study of morning rush-hour (6-9AM) concentrations of benzene in 39 cities gave a median concentration of 6 pg/m3,(I6)agreeing well with the mean value of 6 &m3 observed Over 24-hr periods in residential areas in the TEAM Study. The major sources of benzene in the atmosphere are mobile sources (auto exhaust and evaporative emissions) and industrial (petroleum refineries, petrochemical manufacturing. coke wens) sources. Mobile sources appear to be more important than sta- 1 I i 1 ,Benzene and Other Volatile Organic Chemicals tioflaw sources in contributing to outdoor benzene Iwels. For example, in the 394ty study, cities with heavy trochemid industries such as Houston, Texas (ranked $,); Beaumont, Texas (17th); Lake Charles, Louisiana (19th); and Orange, Texas (31st)were not particularly in benzene concentrations. Recent estimates of attribute about 85% of emissions to mobile WUrCeS, 15% to stationary sources. 2.8 Residence Near Industry AciMV Smoking Unknown personal Ambient Passive smoking OccuDational Filling gas tank (PdW 1800 150 120 50 loo00 10 ( X lo? 53 240 240 190 0.25 100 (W 50 m m 5 1 <1 The first TEAM Study c5) found no difference in benzene exposures of 150 subjects living within 1 km of chemical and petroleum refineries in Bayonne and Elizabeth, New Jersey, compared to 150subjects living I more than 1 km distant. Since such facilities are con- I centrated in only a few places in the U.S., even a positive finding would have little effect on the nationwide , average exposure to benzene. 2.9. Food Although a number of publications have referred to benzene in vegetables, meat, and eggs, the TEAM Study found little evidence that diet made any difference in benzene levels in breath. Since the same breath measurements were conclusive in identifying smoking as an important source, it is felt that food cannot be an important source of exposure to benzene. 2.10. Wood Smoke Few measurements are available to allow an estimate of the importance of wood smoke on benzene exposure. Since only a few localities use wood burning to an appreciable extent, and then for only a few months of the year, wood smoke should not make an appreciable contribution to nationwide average exposure to benzene. 2.11. Summary: Sources of Benzene Exposure From the above considerations, we can construct a nationwide benzene exposure budget (Table 11) apportioning the &sewed benzene exposures to the most important sources. The results indicate that smoking accounts for roughly half of the exposure, with the remaining half split fairly evenly between personal activities (=30%) and the traditional outdoor sources (-20%). On the other hand, emissions pnsent a very differ- 3% EMISSIONS PWWMl ms ' EXPOSURES Fig. 1. Benzene: Emissions vs. exposures (TEAM study, Los Angeles, 1987). ent picture. The traditional sources-motorvehicles and industry-account for 97% of the total emissions, compared to 3% from cigarettes and materials. The relative importance of these different sources are compared for emissions and exposures in Fig. 1. These findings have important effects on our r e g ulatory and control strategies. For example, if emissions from all stationary sources were reduced by a Draconian 50%, the total reduction in population exposure would be an unnoticeable 2% (50% x 15% X 20%). The same effect could be achieved by reducing the average benzene content of cigarettes by 4% (from 57to 55 pg/m3). This raises the interesting question of whether a steel company might trade "exposure credits" with a tobacco company-the latter reducing the tar and nicotine content of its cigarette slightly (in return for appropriate remuneration) to allow a below-standard coke Oven to continue in operation. The idea of trading in exposure rather than emissions is described in Smith.(*n 3. TETRACHLOROETHYLENE Exposures to tetrachloroethylene are compared to outdoor levels in Table 111. The difference between per- 62 Tabk UX. P e d Exporures to Tetnchlomthylenc C o m p e d to Ambient Levclr in S k TEAM Study Locations hation NJ h4D LA A-P ND NC No. of Samples Pcn~nrl Ouidool 539 1ss 70 70 232 131 76 10 23' 6 24 6 Concentration` Penonal Outdoor 2s 5 72 14 4.5 6 0.6 91 7 0.9 Total 964 378 12 2.3 Population-weighted24-hr arithmetic mean (pglm'). NJ = BayonoeEliibcth. New Jer~ey(three seasons, 1981-83); MD = Baltimore, -Maryland (Spriag 1987), L.A. = Los Angeles, California (two sea- sons, 1984 and 1987); A-P = Antioch-Piitsburg, California (June 1984); ND Devils Lake, North Dakota (October 1982); NC = Greensboro, North CMlina (May1982). * One outlier (800&n3) removed. sonal exposures and outdoor concentrationsis even more striking than for benzene, with outdoor air providing only about 20% of total exposure. Unlike benzene, however, tetrachloroethylene has few sources of exposure. The main source of exposure for most people is probably dry-cleaned clothes. office,the dry-cleaning shop, and the outdoors) arc a+ s e w d in Table IV. 3.2. Outdoor Air The main use of tetrachloroethylene is as a dry- cleaning solvent-a majority of U.S.dry-cleaning shops employ tetrachloroethylene as the primary solvent. Thus the dry-cleaning shop is considered the major source of outdoor tetrachloroethylene. However, these emission, account for no more than 20% of total exposure. Thus, reducing emissions from dry cleaning shops by our un- realistic factor of 50% would result in a barely noticeable 10% reduction in exposure. The same reduction might be achievable if people hung their dry cleaning outside for an 8-hr period before taking it into the house. Tbc major sources of exposure are compared to the major emission sources in Fig. 2. 4. PARADICHLOROBENZENE Results from six TEAM Study cities showed that paradichlorobenzene was almost exclusively an indoor air pollutant, outweighing outdoor air by more than 20 3.1 Dry-Cleaned Clothes Early TEAM studies showed that tetrachloroethylene levels were higher among employed people, suggesting that exposure to one's own or to coworkers' drycleaned clothes could be important. A recent TEAM study(*s) has indicated that tetrachloroethylene levels in homes increase by factors of 100-fold (to levels exceed- ing 100 &m3) following the introduction of dry-cleaned clothes into the home. (The study also indicated that indoor air levels decrease when the clothes are removed from the home and increase when they are put back, thus supporting the notion that "airing out" the clothes on a balcony or patio before introducing them into the home can be effective in reducing exposure.) The same study showed that wearing the clothes also increased personal exposure. Finally, a small but noticeable source of exposure occurs during the few minutes the clothes are being picked up at the dry cleaning shop; earlier TEAM Studies(19)indicated that levels in dry-cleaning shops varied between 10,OOO and 20,000 pg/m3. Thus a 5-min exposure would provide as much teqachlonxthylene as 5 days of normal exposure. The contributions to total exposure of these four sources (the home, the Table IV. National Exposure Budget for Tetnchlorocthyknc source -tegory Population Mean Percent Gmtniuliaa exposed exposure oftime tototllapsum 1-( (Irghd) uposed (P*? Offife Home Outdoon Dry-clcaningshop Other uses im 238 238 85 ? 18 z 683 3 100 10,OOO 0.01 ?? 2 5 3 <1 -1 Total 238 12 100 12 41.81 EMISSIONS 121 EXPOSURES Q. 2. Tetnchlomcthylene: Emissions vs. exposures (TEAM study. Los Angela, 1987). \ I Benzene and Other Volatile Organic Chemicals 63 to 1(Table V).Assuming that one third of homes contain pa,we may calculate that users of these products are increasing their exposures by factors of roughly 60 to nonusers. 4.1. Sources of Exposure This chemical has two major uses: to mask odors and to kill moths. Both uses require that the chemical maintain a high concentration in the home for periods of months or even years. A large number of American homes may contain high levels of pDCB. Many schools, offices, hotels and other places with public restrooms also use p-DCB to mask odors. About 12 million pounds annually is used to kill moths. An estimated 25% of American households contain mothballs, moth crystals, or moth cakes formed from nearly pure p-DCB, although only 12% of TEAM Study homes in Baltimore and Los Angeles reported having moth repellents in their homes. About 70% of TEAM Study homes in Baltimore and Los Angeles reported using air fresheners or bathroom deodorants. Paradichlorobenzene accounts for a fraction of the air freshener market (perhaps 10%). Assuming 25% of homes have p D C B moth repellents and an additional 7% have pDCB air fresheners, we may calculate that about a third of the 85 million homes in the U.S. contain pDCB. In 1986, following a two-year test of male and female rats and mice, the National Toxicology Program announced that p-DCB caused several different types of Table V. Personal Exposures to Para-dichlorobenzeneCompared to Ambient Lcvels in Six TEAM Study Locatioas Location No. of Samples Personal Outdoor Concentratiod Personal Outdoor NJ 539 155 55 1.3 MD 70 70 33 -b LA. 232 131 1s 1.6 A-P 76 10 6 0.3 ND 24 6 16 0.7 NC 24 6 11 0.7 Total %5 378 23 1 -Population-weighted 24-hour arithmetic mean (&m'). NJ Bay- -onne-Elizabeth, New Jemy (three WON. 198143). MD Balti- more, Maryland (Spring 1987); LA. = Los Angeles. California (rwo seasons, 1984 and 1987); A-P = Andoch-Pinsburg, Cdifornir (June -1984); ND = Devils Lake, N o h Dakota (October 1982b NC Greensboro, Nortb Carolina (May1982). Not measured using Tenax. malignant tumors in both sexes of the mice and in male rafi`m). Traditionally, when a chemical causes cancer in two different species of mammals, it is considered a probable human carcinogen. In this cas, because the tumors occurred in the male rat kidney and the mouse liver, both of which have been questioned for their relevance to human cancer, p-DCB has been provisionally classified as a possible human carcinogen. 5. DISCUSSION For each of the three chemicals discussed above, the "traditional" sources of emissions (mobile sources, industry) have accounted for only 2-20% of total human exposure. This same conclusion has been documented for a number of other volatile organic chemicals: styrene, xylenes, ethylbenzene, trimethylbentenes, chloroform, trichloroethylene, a-pinene, limonene, decane, undecane, etc.(lSs) For most of these chemicals, the major sources of exposure have been identified (personal activities, consumer products, building materials), but cannot be regulated under existing environmental authorities. This situation has led to a peculiar split in the perception of risk. The public perceives indoor air pollution as considerably 1- risky than, say, hazardous waste sites (Environment, August 1988)whereas experts at PA put indoor air and consumer product exposure at the top of the list of health risks, with hazardous waste sites near the bottom.(21) Nonetheless, the amount of resources devoted to these two problems reflect the public perception, not that of the experts. How can this situation be rectified? A continuing process of consumer information and media attention may ultimately result in greater public awareness of the problem. Some steps to reduce exposure can be taken by the public without waiting for cumbersome govemment attempts at regulation. Other actions, such as setting up consensus guidelines, can be taken by professional organizations: e.g., ASHRAE (ventilation requirements), ASTM (standardized testing for organic emissions from building materials). Information on the economic impacts of indoor air pollution may ultimately convince employers to improve their employees' working conditions. Market forces may also play a rolemanufacturers may find substitute chemicals or processes leaving less residue in their products, if the public demands it. ( n e bellwether chemical here may be formaldehyde-panicleboard with up to ten times less formaldehyde emission potential is now available, at a price). Wall66 6. CONCLUSIONS We have shown that the major Sources of emissions of three chemicals account for only a small proponion (2-20%) of total exposure. For all three chemicals (and for a number of other VOCs), the main sources of atp u r e are personal activities (such as smoking or wearing dry-cleaned clothes) or consumer products (such as morn air fresheners). These sources of exposure are intrinsically more difficult to regulate than the traditional mobile and industrial sources; moreover, authority to regulate them appears to be lacking in many instances. A combination of public information, voluntary consensus guidelines, and market forces are needed to deal with this problem. REFERENCES 1. L. A. Wallace (1937). Tor01Erposuk Ass~nuruMethoddogv SO&.- SummatyandAna&sk V d I (Washington, D.C, United States Emrironwntal Protection Agency). 2 R. W. Handy, et aL (1987). Total Exposum Assessment Me&- oddogy fI`Uh4) study: SIOndoni Opcmting k e h s , Vd N (Washington. D.C., United States Environmental Protection --Alency). 3. E. D. Pelkzari, K. Penitt, T. D. Hutwell, L. C. Michael, R. Whitwm. R W. Handy. D. Smith. and H.Zelon (1987).Toad Eqmm &ament -eM (TUMj study: E b b a h and Bouonru. New Jmy;Drvik lake, N o d Dakm; and Grrcnr- bora. N o d Ckdina. V d I1 (Wasbinptoa, D.C United States 4. E. D. PrILimri K. MUAgT,.ewD.).HmweU, L. C. Miduel, R Whitmore, R W.Handy, D.Smith, and H.&loa (1987). T d W o s mAwusmau Mehniobgy I W SW:ScLCrcd Canmunitksin Narthrm and soulhun Cali/onia V d Ill (Washing- ton, D.C. United States Environmcntrl Rotedion A g e q ) . 5. L.A. W W ,E. D. PeUirUri, T. D. Hutwell, C. Spamino, R whitmore, L. Sheldoa, H.Zebu, and R. Pcrritt (1987). "The TEAM study: P~fmr~Edxposm to Toxic Substances in Air. Drinlting Water. and Bru Nortb Carolina. and North tDbakoofta4."00ER~esiid~ennhtts..ofaN;enw uJernsey., 6. L. A. Wallace, E. D. PeUizzari, T. D. Hutwell, R. Whitmon. H. Zelon, R. Pcrritt. and L. Sheldon (1988). "The California TEAM Study. Breath Coaccntrations and Pmonal Exposuns to 26 Volatik Compounds in Air and DrinlringWater of 188 Resc dents Of h hgck.htioch. and Pinsburg, C&" Amos. En- Vtwr 22. 2141-2163. 7. c. Higgins et at. (1983).``&Pli~tions Of TraPPk b Smoking," J. ASSOC. W U ~ A M Wchm~ Y 1074- 1083. 8. L. A. Wallace (1989)."Major Sources of Benzene -," fiv.Healih Perspectives 82. 165-169- 9. L. Wallace, E. pellizzari. T. Hartwell, K. Pemltt. a d R. Z b genhs, (1987)."Exposures to Benzene and Other Vohtik COQ. pounQ frnn A&T and Pass+ SmOking." Arch. fiwHcolbh 42,272-279. 10. C. Kraux, W. Mailahn, R. Nagel, C. %huh. B. Seif~rt.ud D. mrich (1987)." h u n e n c e of volatile organic compoundsin tbe air of 500 Homes in the Federal Republic of Gcrmay," in I'm ceedingsof The 4th International cmfemncr on IndoorA i Quclr- ity a d Cfimate,Vol. 1. (Institute for Sod, Water, and Air Hy-, Berlin ), pp. 102-106. 11. R. 8. Gammage, D. A. White. and K. C. Gupta, (1984)."Ro. idential Measurements of High Volatility Organics and Them Sources." in Indoor Air, v. 4. (Swedish Council for B u i l d q Research, Stockholm, Sweden). pp. 157-162. 12. W. A. McClenny, T. A. Lumpkin, J. D. Pkil, K. D. O l i , D. K. Bubaa, J. W. Faircloth, and W. H. Daniels, (1986)."Can- ister-based VOC Samplers," in Pmzediqs of the EpAupcA S m r i W n on Measumment qfTmic Air Pollutants (AirM. h t . Assoc. Pinsburgh. Pennsylvania). 13. National Aeronautia and Space Industry, Houston, Texas, k tcrials Testing Data Base. 14. L. Sheldon, R. Handy, T. D. Hartwell. R. W. Whiunon, H. S.-- Zelon. and E. D. Pellizzari (1988).Indoor Air QuuUy in pLblic Bildings, Volume I (US. Environmental Protection Agency, Washington, D.C., EPA/aOola8&@09a). 15. L. Sheldon, H. Zelon. J. Sickles, C. Eaton, and T. Hamven (1988). IndoorAir Quality m WUBuildings, V o h II (US. Environmental Protection Agency. Washington D.C.. EpAMo(v 6-88/W). 16. R.L. Seila (1987). "JuneSeptember. 6 9AM, Ambient Air Ben- zene Concentrations in 39 U.S. Cities, 1984-1986." in heed in@ of the 1987 U.S. EPA-Apc1 Symposiwn on Measmment of Taxic and Related Air Pollutants. Air Pollution Control Assod- ation, Pittsburgh. Pennsylvania. 17. K. Smith (1988)."Air Pollution: Assessing Total Exposure in thc United States," Environment 38. 10-38. 18. E. D. Pcllizzari, K. W. Thomas, D. J. Smith, R. Pemn. and M. Morgan, (1987).Total Arccsrmmr Me- cIEIM)r 1987 Study in New Jersey Final Draft (Contract I 68-02-4544. U.S. Environmental Protection Agency. Washington D.C.). 19. E. D. Pellizzari et al. (1984). Total Exposure Assessment Me&- odology (TUM): Dry Cleanem SnUry (EPA contract no. 68-02. 3626. U.S. EPA. Office of Research and Development. Wash- ington, D.C.). 20. National Toxicology Program (NTP)(1986). Technical Report on the Toxicity and Carcinogenesis of 1,4-Dichlorobcnzene (CAS +106-46-7)in F344h Rats and B6C3F1 Mice (Gavage Study). NTP Technical Repon NO. 319, Board Draft, March 1986. 21. U.S. Environmental Proteaion Agency (1988). Tlu Imide Story: A Conrumrr's Guide to IndwrAir Pollution (Washington. D.C.).