chapter four Organic contaminants A large variety of natural and synthetic organic compounds can be found in indoor environments. These include very volatile organic compounds (VVOCs) which have boiling points ranging from <0°C to 50–100°C, volatile organic compounds (VOCs) with boiling points ranging from 50–100°C to 240–260°C, semivolatile organic compounds (SVOCs) with boiling points ranging from 240–260°C to 380–400°C, and solid organic compounds (POMs) with boiling points in excess of 380°C. In the last case, POMs may be com- ponents of airborne or surface dusts. Organic compounds reported to contaminate indoor environments include a large variety of aliphatic hydrocarbons, which may be straight, branch-chained, or cyclic (contain single bonds [alkanes] or one or more double bonds [alkenes]); aromatic hydrocarbons (contain one or more ben- zene rings); oxygenated hydrocarbons, such as aldehydes, alcohols, ethers, ketones, esters, and acids; and halogenated hydrocarbons (primarily chlorine and fluorine containing). These may be emitted from a number of sources including building materials and furnishings, consumer products, building cleaning and maintenance materials, pest control and disinfection products, humans, office equipment, tobacco smoking, and other combustion sources. Organic compounds which are seen as relatively distinct indoor contam- ination problems include the aldehydes, VOCs/SVOCs which include a large number of volatile as well as less volatile compounds, and pesticides and biocides which are, for the most part, SVOCs. I. Aldehydes Aldehydes belong to a class of compounds called carbonyls. Carbonyls, which include aldehydes and ketones, have the functional group © 2001 by CRC Press LLC in their chemical structure. The carbonyl is in a terminal position in alde- hydes. A compound is described as an aldehyde if it has one terminal car- bonyl, a dialdehyde if it has two, and a trialdehyde if it has three carbonyls. Aldehydes include saturated (single bonds) aliphatic, unsaturated (one or more double bonds) aliphatic, and aromatic or cyclic compounds. Satu- rated aliphatic aldehydes include formaldehyde (one carbon), acetalalde- hyde (two carbons), propionaldehyde (three carbons), butryaldehyde (four carbons), valeraldehyde, glutaraldehyde, etc. As can be seen in Table 4.1, glutaraldehyde is a dialdehyde with carbonyls on both ends of the molecule. Unsaturated aliphatic aldehydes contain a carbon–carbon double bond (Table 4.1). They include acrolein (acryaldehyde), methacrolein, and cro- tonaldehyde. Methacrolein is commonly used to produce methyl methacry- late, an eye-irritating ester used as an adhesive in many industrial applica- tions. Aromatic aldehydes include compounds such as benzaldehyde and cinnamaldehyde. Table 4.1 Chemical Structures and Properties of Common Aldehydes Compound Structure M. W. Solubility (g/L) Formaldehyde 30.03 560 Acetaldehyde 44.05 200 Glutaraldehyde 100.12 Miscible Acrolein 56.06 210 Crotonaldehyde 76.09 181 Benzaldehyde 106.11 3 Source: From Leikauf, G.D., in Environmental Toxicants: Human Exposures and their Health Effects , Lippman, M., Ed. , Van Nostrand Reinhold (John Wiley & Sons), New York, 1992, chap. 2. With permission. H –C=O | H C H O O CH 3 HC O H CCHCH 2 O H C CHCHCH 3 © 2001 by CRC Press LLC Individual aldehydes differ in their molecular structure, solubility, chem- ical reactivity, and toxicity. Only a relative few have industrial and commer- cial applications which may result in significant indoor exposures, are by- products of other processes, or have biological activities that have the poten- tial for posing major public health concerns. Those which, at present, are known to cause either significant indoor air contamination and/or adverse health effects include formaldehyde (HCHO), acetaldehyde, acrolein, and glutaraldehyde. Many aldehydes are potent sensory (mucous membrane) irritants; some are skin sensitizers; and there is limited evidence that several aldehydes may be human carcinogens. A. Sensory irritation Because of their solubility in aqueous media and their high chemical activity, aldehydes as a group are potent mucous membrane irritants (affecting eyes and mucous membranes of the upper respiratory tract). This irritation is associated with maxillary and ophthalmic divisions of trigeminal nerves in nasal and other mucosa which respond to chemical/physical stimuli. These serve as respiratory defense mechanisms through the perception of pain or irritation and reduced contaminant inhalation. Measured decreases in respiratory rates in rats and mice on exposure to irritant chemicals have been used to evaluate the irritation potential of alde- hydes and other substances using a standard mouse bioassay. Doses required to cause a reduction of breathing rates by 50% (RD 50 ) for selected aldehydes are summarized for mouse bioassays in Table 4.2. As can be seen, RD 50 values range by more than three orders of magnitude. Formaldehyde and the unsat- Table 4.2 RD 50 Values for Swiss-Webster Mice Exposed to Aldehydes Chemical RD 50 value (ppmv) Formaldehyde 3.2 Acetaldehyde 2845 Propionaldehyde 2052 Acrolein 1.03 Butryaldehyde 1015 Isobutryaldehyde 4167 Crotonaldehyde 3.53 Valeraldehyde 1121 Isovaleraldehyde 1008 Caproaldehyde 1029 2-Ethybutryaldehyde 843 2-Furaldehyde 287 Cyclohexane carboxaldehyde 186 3-Cyclohexane-1-carboxaldehyde 95 Benzaldehyde 333 Source: From Steinhagen, W.H. and Barrow, C., Toxicol. Appl. Pharmacol ., 72, 495, 1982. With permission. © 2001 by CRC Press LLC urated aldehydes, acrolein and crotonaldehyde, were the most potent sen- sory irritants; the saturated aldehydes, acetaldehyde and propionaldehyde, were least potent. These data, which do not include glutaraldehyde (a potent irritant in rats), indicate that only a few aldehydes have the potential to be significant mucous membrane irritants at the relatively low concentrations that occur in indoor environments, such as residences and nonresidential, nonindustrial buildings. Of these HCHO, acrolein, and glutaraldehyde are the most notable. Though a relatively weak sensory irritant, acetaldehyde is a common contaminant of both indoor and ambient (outdoor) air. B. Formaldehyde Formaldehyde is molecularly the smallest and simplest aldehyde. It is unique because the carbonyl is attached directly to two hydrogen atoms (Table 4.1). Due to its molecular structure, HCHO is highly reactive chemi- cally and photochemically. It has good thermal stability relative to other carbonyls and has the ability to undergo a variety of chemical reactions, which makes it useful in industrial and commercial processes. As a conse- quence it is among the top 10 organic chemical feedstocks used in the U.S. Formaldehyde is a colorless, gaseous substance with a strong, pungent odor. On condensing, it forms a liquid with a high vapor pressure (boiling at –19°C). Because of its high reactivity, it rapidly polymerizes with itself to form paraformaldehyde. As a consequence, liquid HCHO must be held at low temperature or mixed with a stabilizer (such as methanol) to pre- vent/minimize polymerization. 1. Uses/sources Formaldehyde is commercially available as paraformaldehyde, which con- tains varying lengths of polymerized HCHO molecules. It is a colorless solid that slowly decomposes and vaporizes as monomeric HCHO at room tem- perature. It has been used in a variety of deodorizing commercial products, such as lavatory and carpet preparations. Formaldehyde is also commercially available as formalin, an aqueous solution that typically contains 37 to 38% HCHO by weight and 6 to 15% methanol. Because of HCHO’s volatility, formalin also has a strong, pungent odor. In solution it is present as methylene glycol (CH 2 (OH) 2 ); in concen- trated solutions it is in the form of polyoxymethylene glycol (HO-CH 2 O) n -H. As a chemical feedstock, HCHO is used in many different chemical processes. Of particular significance to indoor environments is its use to produce urea and phenol–formaldehyde resins (50% of HCHO consumed annually). Urea–formaldehyde (UF) copolymeric resins are used as wood adhe- sives in the manufacture of pressed-wood products such as particle board, medium-density fiber board (MDF) and hardwood plywood, finish coatings (acid-cured), textile treatments (permanent-press finishes), and in the pro- duction of urea–formaldehyde foam insulation (UFFI). Urea–formaldehyde © 2001 by CRC Press LLC wood adhesives are colorless and provide excellent bonding performance. They are, however, somewhat chemically unstable, releasing monomeric HCHO on hydrolysis of methylol end groups and, less commonly, methyl- ene bridges. Their decomposition is sensitive to product moisture levels as well as relative humidity. Because of resin sensitivity to moisture, UF- bonded wood products are intended only for indoor use. Historically UF- based adhesives were formulated with relatively high HCHO to urea ratios (F:U 1.5:1) to enhance performance by ensuring that there was sufficient HCHO present to achieve cross-linking of all primary and secondary amino groups. Because of this excess HCHO associated with the resin, UF-based wood adhesives emitted significant levels of free HCHO into indoor envi- ronments, particularly in the first months or so in the life of a product. Because of high HCHO emissions, indoor concentrations, and health com- plaints, UF-bonded wood products are presently manufactured with low F:U ratios (e.g., 1.05:1) and thus emit much less HCHO. Though HCHO emissions from UF-bonded wood products are substantially lower than those of two decades ago (<10%), they continue to be a significant source of indoor HCHO concentrations. Most emissions are associated with the hydrolytic decomposition of the resin copolymer. Phenol–formaldehyde resins receive significant use as exterior-grade adhesives in the manufacture of softwood plywood and oriented-strand board (OSB) products that are widely used in new home construction. Phe- nol–formaldehyde (PF)-bonded wood products have historically had low HCHO emissions compared to UF-bonded wood products. Emissions from the latter were once 1000 times greater than from PF-bonded products. Formaldehyde is produced in the thermal oxidation of a variety of organic materials. As a consequence, it is found in the emissions of motor vehicles, combustion appliances, wood fires, and tobacco smoke. It is also produced in the atmosphere as a consequence of photochemical reactions and hydrocarbon scavenging processes, and in indoor air as a result of chemical reactions. 2. Exposures Formaldehyde is omnipresent in both ambient and indoor environments. Ambient concentrations are usually <10 ppbv in urban/suburban loca- tions but may reach peak levels of 50 ppbv or more in urban areas subject to significant atmospheric photochemistry (e.g., south coast of California). Formaldehyde levels in indoor environments are on average significantly higher (order of magnitude or more) in residential, institutional, and commercial buildings than background ambient levels. Concentrations vary from structure to structure, depending on the nature of sources present and environmental factors which may affect emissions and indoor concentrations. Historically, the major sources of HCHO emissions have been wood products bonded with UF resins, UF-based acid-cured finishes, and in houses retrofit insulated (in the 1970s and early 1980s) with UFFI. Formaldehyde © 2001 by CRC Press LLC emission rates from a variety of construction materials and consumer prod- ucts available in the early 1980s marketplace are summarized in Table 4.3. Pressed wood products have been the major source of HCHO contam- ination in indoor environments. Particle board has been used as underlay- ment in conventional homes; floor decking in manufactured homes; compo- nents of cabinetry, furniture, and a variety of consumer products; and as a decorative wall paneling. Because of marketplace changes, it is now little used as underlayment in conventional houses, and fewer than 50% of new manufactured homes are constructed with particle board floor decking. Hardwood plywood has been used as a decorative wall covering and as a component in cabinets, furniture, and wood doors. Medium-density fiber board has been used in cabinet, furniture, and wood door manufacture. Acid- cured finishes, which often contain a mixture of urea and melamine–form- aldehyde resins, are used as finish coatings on exterior wood cabinet com- ponents, fine wood furniture, and hardwood flooring. Urea–formaldehyde foam insulation or similar products are occasionally used to retrofit insulate houses in North America and are commonly used in the United Kingdom. Prior to a ban by the Consumer Product Safety Commission (CPSC) in the U.S. (subsequently voided in a federal appeals court) and a ban by the Canadian government in the early 1980s, UFFI was applied in over 500,000 U.S. residences and 80,000 in Canada. Formaldehyde concentrations in U.S. residences based on data collected in the late ‘70s to mid ‘80s are summarized in Table 4.4. As indicated previ- ously, significant improvements (reduced emission rates) in UF-bonded wood products have occurred since the mid ‘80s, and there have been changes in products used in construction. As a consequence, HCHO levels in building environments (particularly residences) are significantly lower in houses built since 1990 than in those constructed previously. Formaldehyde levels in new mobile homes are rarely >0.20 ppmv, and are more likely to be in the range of 0.05 to 0.15 ppmv. In other new residential buildings Table 4.3 Formaldehyde Emissions from Construction Materials, Furnishings, and Consumer Products Product Emission rate range ( µ g/m 2 /day) Medium-density fiberboard 17,600–55,000 Hardwood plywood paneling 1500–34,000 Particle board 2000–25,000 UFFI 1200–19,200 Softwood plywood 240–720 Paper products 260–280 Fiberglass products 400–470 Clothing 35–570 Source: Data extracted from Pickrell, J.A. et al., Environ. Sci. Tech ., 17, 753, 1983; Matthews, T.G., CPSC-IAG-84-1103 , Consumer Product Safety Commission, Washington, D.C., 1984; and Grot, R.A. et al. , NBSIR 85-3225 , National Bureau of Standards, Washington, D.C., 1985. © 2001 by CRC Press LLC constructed in the U.S. and Canada, concentrations are unlikely to exceed 0.10 ppmv, with concentrations <0.05 ppmv the norm. In office buildings, HCHO levels are rarely >0.05 ppmv, with concentrations in the range of 0.02 to 0.03 more common. 3. Factors affecting formaldehyde levels Formaldehyde levels in building environments are affected by a number of factors. These include the potency of formaldehyde-emitting products present, the loading factor (m 2 /m 3 ), which is described by the surface area (m 2 ) of formaldehyde-emitting materials relative to the volume (m 3 ) of inte- rior spaces, environmental factors, materials/product age, interaction effects, and ventilation conditions. As indicated in Table 4.3, formaldehyde-emitting materials have histor- ically differed in their emission potential. These differences have decreased with product improvements. Medium-density fiber board and acid-cured finishes have been among the most potent formaldehyde-emitting materials. a. Loading factor. Mobile homes have had the highest reported con- centrations of HCHO. This has been the case in good measure because of the high loading rate of formaldehyde-emitting wood products. In the past, mobile homes were constructed using particle board floor decking, Luan plywood wall covering, and wood cabinets (made from various combina- Table 4.4 Formaldehyde Concentrations in U.S. Houses Measured in the Period 1978–1989 Concentration (ppmv) Study N Range Mean Median Urea-Formaldehyde Foam Insulated Houses New Hampshire 71 0.01–0.17 — 0.05 Consumer Product Safety Commission 636 0.01–3.4 0.12 — Manufactured Houses Washington 74 0.03–2.54 — 0.35 Wisconsin 137 <0.10–2.84 — 0.39 California 663 — 0.09 0.07 Indiana 54 0.02–0.75 0.18 0.15 Conventional Houses Texas 45 0.0–0.14 0.05 — Minnesota 489 0.01–5.52 0.14 — Indiana (particle board underlayment) 30 0.01–0.46 0.11 0.09 California 51 0.01–0.04 0.04 — Source: From Godish, T.J., Indoor Air Pollution Control , 1st ed., Lewis Publishers, Chelsea, MI, 1989. With permission. © 2001 by CRC Press LLC tions of particle board, MDF, Luan plywood, and hardwood). As a conse- quence, they had relatively high surface/volume ratios (expressed as m 2 /m 3 ) of formaldehyde-emitting wood products. b. Temperature and relative humidity. Environmental factors such as temperature and humidity have significant effects on HCHO levels in build- ings where UF-bonded wood products are major HCHO sources. The effects of temperature on indoor HCHO concentrations is exponential, whereas the effect of relative humidity is linear. Combined effects of various temperature and humidity regimes on HCHO levels in a mobile home can be seen in Table 4.5. Note that the highest combination of temperature and humidity (30°C, 70% RH) resulted in indoor concentrations that were 5 times greater than the lowest combination (20°C, 30% RH). Experimentally derived relationships between HCHO levels and tem- perature and HCHO levels and relative humidity have been used to develop equations to “correct” (or more appropriately, standardize) HCHO levels determined under different environmental conditions to temperature and humidity conditions such as 25°C and 50% RH. The Berge equation is widely used to standardize HCHO concentrations. It has the following form: (4.1) where C X = standardized concentration (ppmv) C = measured concentration (ppmv) e = natural log base 2.7818 R = coefficient of temperature (9799) T = temperature at test (°K) T O = standardized temperature (°K) A = coefficient of humidity (0.0175) H = relative humidity at test (%) H O = standardized relative humidity (%) Table 4.5 Effect of Temperature and Relative Humidity on Formaldehyde Levels in a Mobile Home Under Controlled Environmental Conditions Temperature (°C) Relative humidity (%) Concentration (ppmv) % maximum value 30 70 0.36 100 25 70 0.29 81 30 50 0.28 78 30 30 0.23 64 25 50 0.17 47 25 30 0.14 39 20 70 0.12 33 20 50 0.09 25 20 30 0.07 19 C X C 1 A(H–H O )e –R(1/T–1/T O ) +[] = © 2001 by CRC Press LLC The Berge equation is a relatively good predictor of HCHO concentration at standard conditions when measured under a variety of environmental conditions. It has been reported to have a standard error of ±12% within a 95% confidence level. c. Decrease in formaldehyde levels with time. Formaldehyde levels decrease significantly with time. A generalized relationship between HCHO levels and product or home age with time can be seen in Figure 4.1. Rapid reductions of HCHO levels can be seen to occur in the early life of formal- dehyde-contaminated residences or emitting products. After an initial rapid decline, HCHO levels decrease at a much slower rate, with relatively ele- vated levels continuing for years. Several investigators have attempted to model changes in HCHO levels with time, using exponential model equations as well as statistical analyses. Exponential models that describe the decay of radioactive isotopes as well as first-order chemical reactions predict a constant half-life. Studies of field data indicate that HCHO decreases with time are exponential only in part, with half-lives that increase in time. Statistical and graphical evaluations of Wisconsin mobile homes tested for HCHO in the early 1980s indicated half- life values of 3, 5, 12, and 72 months. Because HCHO levels depend on a variety of source and environmental variables, it is unlikely that a model equation could be developed that would reliably predict the decay of HCHO levels under the many source and envi- ronmental conditions that have and continue to exist in North American residences. However, double exponential models have been shown to be relatively good predictors of changing HCHO levels with time (see Chapter 9). The decay rate is dependent on emission rates that are affected by tem- perature, relative humidity, and interaction effects between formaldehyde- emitting materials, as well as ventilation rates (increasing temperature, humidity, and ventilation rates increase emission rates and, as a conse- quence, decay rate). Therefore, half-lives would be expected to be shortened Figure 4.1 Generalized decrease of formaldehyde with time. © 2001 by CRC Press LLC (HCHO levels would decline more rapidly) with increasing temperature, relative humidity, and ventilation. Interaction effects described below would, if all other factors were standardized, likely increase the time period required for a 50% reduction in HCHO levels. d. Interaction effects. In building environments that contain multiple UF-based emission sources, measured concentrations are typically similar or are slightly above sources with the highest emission potential present (most potent source) rather than the sum of emissions/emission potentials of all formaldehyde-emitting sources. Such interaction effects are due to a vapor pressure phenomenon. High vapor concentrations associated with emissions from potent sources suppress emissions from less potent sources. e. Ventilation. Ventilation associated with infiltration, opening win- dows, and mechanical induction can affect indoor concentrations of HCHO as well as emission rates. Formaldehyde levels decrease with increasing ventilation rates. The relationship is not linear because a doubling in the ventilation rate is associated with only a 30 to 35% decline in HCHO levels (due to increased emission rates). Natural ventilation associated with infil- tration appears to have a significant effect on HCHO levels. Under controlled conditions, HCHO levels reach their maximum values when indoor/outdoor temperature differences are small. Lowest HCHO levels in northern climates are observed during the cold season, especially on cold winter days (Figure 4.2) when indoor/outdoor temperature differences are large. f. Tobacco smoke. Since HCHO is a by-product of combustion pro- cesses, smokers, as can be expected, are exposed to high HCHO levels (on the order of 40 to 250 ppmv in a single puff). Formaldehyde emissions from burning cigarettes are indicated in Table 4.6. Nonsmokers are exposed to significantly lower levels from environmental tobacco smoke (ETS) because of the significant dilution effects that occur. Because of interaction effects Figure 4.2 Relationship between indoor formaldehyde levels and outdoor temperatures. © 2001 by CRC Press LLC [...]... (ng/m3) Day care School Office 1 Office 2 Office 3 Office 4 center classroom 1128 2055 1273 1003 1 144 957 9 34 993 862 1393 789 201 890 43 78 1239 863 987 710 746 718 3 64 977 710 278 1070 1910 140 9 1173 21 74 658 1 146 1039 47 8 891 1078 241 980 3871 1301 1226 2 146 1282 1178 965 47 5 578 840 40 4 1 144 549 2 1515 1306 3 040 8 341 1308 952 49 1 1 240 1 346 1053 45 99 145 1 3192 148 8 1987 7803 1223 692 502 1279 1195 111 Source:... DanTable 4. 13 VOC Mixture Used in Danish Human Exposure Studies Compound n-Hexane n-Nonane n-Decane n-Undecane 1-Octene 1-Decene Cyclohexane 3-Xylene Ethylbenzene 1,2 , 4- Trimethylbenzene n-Propylbenzene α-Pinene n-Pentanal n-Hexanal Isopropanol 2-Butanol 2-Butanone 3-Methyl-3-butanone 4- Methyl-2-pentanone n-Butylacetate Ethoxyethylacetate 1,2-Dichloroethane Weight ratio 1.0 1.0 1.0 0.1 0.01 1.0 0.1 10.0 1.0... α-Limonene n-Hexane Hexanal α-Pinene Tetrachloroethane Naphthalene Toluene TXIB n-Dodecane 2-Ethyl-1-hexanol o-Xylene Butyl acetate 1,1,1-Trichloroethane 1,3,5-Trimethylbenzene 1,2 , 4- Trimethylbenzene 4- Methyl-2-pentanone Frequency = 61 to 80% 1 , 4- Dichlorobenzene 3-Methyl pentane Frequency = 41 to 60% Trichloroethane Methylene chloride Frequency = 21 to 40 % Trichlorofluoromethane Trichloro-trifluoroester 4- Phenycyclohexene... Proc Indoor Air ‘99, Edinburgh, 2, 43 4, 1999 © 2001 by CRC Press LLC Table 4. 12 Concentrations of Phthalate Compounds Measured in 125 California Residences Compound Diethylphthalate Di-n-butylphthalate Butylbenzyl phthalate Di-2-ethylhexyl phthalate Di-n-octyl phthalate Concentration (ng/m3) Median 90th percentile 340 42 0 34 110 BLD 840 1300 240 240 9.7 Indoor/ outdoor ratio 4. 3 14. 0 4. 3 1.7 1 .4 Source:... concentration (ng/m3) o-Phenylphenol Chlordane Heptachlor Propoxur Chlorpyrifos Diazinon Dieldrin Lindane (γ-HCH) Dichlorvos Malathion 90 50 50 49 29 16 12 10 2 2 44 .5 199.0 31.3 26.7 9.8 48 .4 1.0 0.5 4. 3 5.0 72 83 70 38 30 10 34 21 1 0 22.8 34. 8 3.6 17.0 5.1 2.5 4. 2 9.5 1.5 0.0 Source: From Whitmore, R.W et al., Arch Environ Contam Toxicol., 26, 47 , 19 94 With permission Ortho-phenylphenol was detected... low concentrations (circa 20 ppbv) Aldehydes produced as a result of indoor chemical reactions have lower odor thresholds and may cause more sensory irritation than their precursors Odor thresholds are reported as 1.9 pptv for cis-2-nonenal and trans-6-nonenal, 17 pptv for 8-nonenal, and 24 pptv for trans-3-nonenal and cis-3-nonenal Indoor chemistry involving production of aldehydes, and aldehydes as... 1,1,1-trichloroethane, and trichloroethylene, were also commonly measured © 2001 by CRC Press LLC Table 4. 7 Frequency of Detected VOCs/SVOCs in the USEPA BASE Study of 56 Randomly Selected Office Buildings VOCs Acetone Styrene n-Undecane 2-Butoxyethanol n-Decane Octane Benzene Pentanal Ethylbenzene Texanol 1 and 3 Phenol Frequency = 81 to 100% 2-Butanone m- and p-Xylene 4- Ethyltoluene Nononal Nonane α-Limonene... Lindane (γ-HCH) Dichlorvos Malathion α-Hexachlorocyclohexane Aldrin Bendiocarb Carbaryl Winter Mean Mean % concentration % concentration households (ng/m3) households (ng/m3) 100 85 85 83 79 61 58 34 33 27 25 21 23 17 370.0 528.0 96.0 42 1.0 147 0 3 24. 0 163.0 20.2 1 34. 0 20.8 1.2 31.3 85.7 68.1 29 95 79 83 62 94 92 68 10 17 22 31 20 0 120.0 162.0 59.0 85.7 7.2 220.0 72.2 6.0 24. 5 20 .4 1.1 6.9 3 .4 0.0 Source:... © 2001 by CRC Press LLC Table 4. 8 Median and Maximum Concentrations of 12 VOCs Observed at the Highest Concentrations in the USEPA BASE Study of 56 Randomly Selected Office Buildings VOC Acetone Toluene d-Limonene m- and p-Xylene 2-Butoxyethanol n-Undecane Benzene 1,1,1-Trichloromethane n-Dodecane Hexanal Nonanal n-Hexane Median concentration (µg/m3) 29.0 9.0 >0.1 5.2 4. 5 3.7 3.7 3.6 3.5 3.2 3.1 2.9... monobutyl ether acetate 1,2-propylene glycol 1,2-propylene glycol monomethyl ether 1,2-propylene glycol monobutyl ether 1,2-propylene glycol monophenyl ether Mean concentration (µg/m3) Maximum concentration (µg/m3) 0.8 8.1 2.3 0.1 20.1 259.7 108 6.5 0.6 1 64 1 .4 3.0 1.7 108 158 302 8 .4 9.9 98 835 6.3 41 9 0.7 110 Source: From Pheninger, P and Marchl, D., Proc Indoor Air ‘99, Edinburgh, 4, 171, 1999 Ethylene . -Xylene TXIB n -Undecane 4- Ethyltoluene n -Dodecane 2-Butoxyethanol Nononal 2-Ethyl-1-hexanol n -Decane Nonane o -Xylene Octane α -Limonene Butyl acetate Benzene n -Hexane. 220.0 Toluene 9.0 360.0 d-Limonene >0.1 140 .0 m- and p-Xylene 5.2 96.0 2-Butoxyethanol 4. 5 78.0 n-Undecane 3.7 58.0 Benzene 3.7 17.0 1,1,1-Trichloromethane 3.6 45 0.0 n-Dodecane 3.5 72.0 Hexanal. acetate Benzene n -Hexane 1,1,1-Trichloroethane Pentanal Hexanal 1,3,5-Trimethylbenzene Ethylbenzene α -Pinene 1,2 , 4- Trimethylbenzene Texanol 1 and 3 Tetrachloroethane 4- Methyl-2-pentanone Phenol Naphthalene