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(19) Jaffrezic-Renault,N.; Pichat, P.; Foissy, A.; Mercier, R. J . Phys. Chem. 1986, 90,2733-2738. (20) Egerton, T. A,; King, C. J. J. Oil Colour Chem. Assoc. 1979, 62, 386-391. (21) Bockris, J. OM.; Uosaki, K. Znt. J. Hydrogen Energy 1977, 2, 123-138. (22) Bonhomme, G.; Lemaire, J. C. R. Acad. Sci., Ser. 2 1986, 302, 169-774. (23) Boule, P.; Guyon, C.; Lemaire, J. Toxicol. Enuiron. Chem. 1984, 7, 97-110. (24) Pichat, P. In Photochemistry, Photocatalysis and Photo-
reactors; Schiavello, M., Ed.; Reidel: Dordrecht, The
Netherlands, 1985; pp 425-455. (25) Pichat, P.; Disdier, J.; Herrmann, J. M.; Vaudano, P. NOUIJ. J . Chim. 1986,10, 545-551. (26) Herrmann, J. M.; Mozzanega, M.-N.; Pichat, P. J. Photochem. 1983,22, 333-343. (27) Hashimoto, K.; Kawai, T.; Sakata, T. J. Phys. Chem. 1984, 88, 4083-4088. (28) Ho, P. C. Enuiron. Sci. Technol. 1986,20, 260-267. Received for review August 1, 1989. Accepted February 2,1990. This study was supported by the Commission of the European Communities [Contract EV4E-0068-C(CD)].
Comparison of Indoor, Backyard, and Centralized Air Monitoring Strategies for Assessing Personal Exposure to Volatile Organic Compounds Larry C. Michael," Edo D. Pelllzzarl, Rebecca L. Perrltt, and Tyler D. Hartwell
Research Triangle Institute, P.O. Box 12194, Research Triangle Park, North Carolina 27709 Dane Westerdahl
California Air Resources Board, Sacramento, California Wllllam C. Nelson
Atmospheric Research and Exposure Assessment Laboratory, US. Environmental Protection Agency, Research Triangle Park, North Carolina 277 11 Air concentrations of toxic vapor-phase organic compounds are compared for residential indoor, residential outdoor, and centralized locations by using two sampling strategies, Tenax GC sorbent cartridge sampling and Summa-polished canister sampling, both with gas chromatography/mass spectrometry analysis. All sample collection was performed in Los Angeles County, CA, during July 1987, as part of the Total Exposure Assessment Methodology (TEAM) study. Graphical and statistical analysis of the data from both sampling techniques revealed a lack of agreement between levels of target compounds measured at the three location types (indoor, outdoor, central). Correlations of measured concentrations between pairs of locations also showed very little relationship for any of the target compounds. The conclusion of the study is that a centrally located sampling site cannot be used to predict outdoor residential (i.e., backyard) levels, which in turn cannot be used to predict indoor levels at the proximate residence. Introduction The Total Exposure Assessment Methodology (TEAM) study was designed to develop methods for measuring an individual's total exposure to pollutants occurring in indoor and outdoor residential environments, and the resulting body burden of toxic and carcinogenic chemicals. Specific methods were developed for assessing human exposure through air, water, and food in several U S . cities ( I , 2), including a 1984 study of Los Angeles County residents. In July 1987, a follow-up TEAM study was conducted in Los Angeles County, CA, on 43 households (many repeated from 1984) with an objective to compare levels of vaporphase organics inside and outside each home with the levels occurring at a centrally located outdoor monitoring station. In this effort, two complementary sampling and analysis techniques, employing Tenax GC sorbent cartridges and Summa-polished canisters, were applied at both the central monitoring station and the individual 996
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residences. Assessment of human exposure to hazardous chemicals, and the projected body burden resulting from exposure, requires that levels of the target chemicals in the individuals' immediate environment be accurately measured. This paper examines whether using a centrally located air monitoring station to predict backyard volatile organics levels is appropriate and, further, whether outdoor monitoring reflects the proximate indoor chemical environment. The results of the entire study and the associated data are presented elsewhere (3). Materials and Methods The target population for the data discussed in this paper included individuals who participated in the TEAM study conducted in 1987 (2). These study participants were solicited from the communities of Torrance, Carson, Hermosa Beach, Redondo Beach, Manhattan Beach, Lomita, Harbor City, and Hollywood Riviera, CA. Although personal and fixed-site air (indoor and outdoor), breath, canister air (indoor and outdoor), and drinking water samples were collected from each participant, only air samples will be discussed here. Volatile organic compounds (Table I) were collected on Tenax GC (Enka Research Institute, Arhem, The Netherlands) by pulling air through a 6.0 X 1.3 cm i.d. sorbent bed contained in a glass tube with a Du Pont Model P125A constant flow pump (E.I. du Pont de Nemours, Inc., Kennett Square, PA). Preparation of these cartridges followed a rigorous procedure ( 4 ) to ensure minimal background from the sampling device. Sample collection periods were approximately 12 h, beginning at 0800 and 2000 h. Pump flows were adjusted to provide for sampling approximately 18 L of air. Glass fiber filters (Gelman, 25 mm) were attached to the inlet end of the Tenax cartridge to remove particulates from the sampled air. Indoor Tenax samplers were located in the kitchen or dining area of the home at a height of 3-6 f t above the floor. Outdoor Tenax air samplers were contained inside a metal box for pro-
0013-936X/90/0924-0996$02.50/0
@ 1990 American Chemical Society
Flgurs 1. Residential communities of participants in the Los Angeles County TEAM study; location of central fixed site indicated.
tection from the weather elements, with only the inlet end of the cartridge protruding. Outdoor samples were typically collected in the backyard of the residence at a height of 3-6 f t above the ground and, if possible, away from structures. Overnight and daytime Tenax samples were collected indoors and outdoors (four total) at each of the 43 residences. Tenax cartridges were stored in a heliumisolation environment at all times, except during actual sample collection. Evacuated Summa-polished (Nolectrics Corp., Cleveland, OH) stainless steel canisters (6-L nominal volume) were meticulously cleaned prior to sampling by sequential evacuation (0.1 Torr) and pressurizing with nitrogen while maintaining the canister temperature at 150 "C. Background checks were performed on 25% of the cleaned, evacuated devices to verify that all of the measurable contaminants had been removed. Samples (4-L nominal volume) were collected by using Tylan Model FC-260 mass flow controllers (Tylan Corp., Torrance, CA) to provide a fixed volume over the collection period. Canister samples, both indoor and outdoor, were collected adjacent to Tenax samples and, unlike Tenax samples, were collected a t only 8 of the 43 homes. The centrally located fixed-site collection station was operated for a continuous 10-day period during July 1987, concurrent with air monitoring outside the study participants' homes. Overnight and daytime Tenax GC samples were collected at the central station on each of these days. A book storage room of the Madrona Middle School in Torrance, CA (Figure 1)was outfitted with the monitoring
Table I. Method Limits of Detection for Tenax and Canister Target Compounds no.
compound
1 2 3 4 5 6 7 8 9
dichloromethane chloroform l,l,l-trichloroethane carbon tetrachloride benzene trichloroethylene toluene n-octane tetrachloroethylene ethylbenzene p-xylene o-xylene styrene n-nonane a-pinene n-decane p-dichlorobenzene limonene n-undecane dodecane
10
11 12 13 14 15 16 17 18 19 20
method LOD, rg/m3 TenaxO canisterb C
0.22 0.16 0.17 0.09 0.12 c
0.16 0.05 0.02 0.06 0.09
0.45 0.45 1.50 0.75 0.35 c 0.75 1.15 0.70 0.50 0.80 0.60
0.09
C
0.09 0.14 0.03 0.12 0.12 0.03 0.14
C
C
2.55 0.50 C
c c
Assuming an 18-L sample volume. Instrumental limits of detection. Not a target compound for this technique. a
equipment (Figure 2). This site was near participant residences and was not in an exceptionally high traffic area. Outside air was drawn through a 1/4-in.Teflon tube extended through the wall of the room to the roof of the Environ. Sci. Technol., Voi. 24, No. 7, 1990
887
Figure 2. Apparatus for concurrent collection of canister and Tenax samples at the central fixed site. Key: (1) stainless steel bellows pump, operated at ca. 10 L/min; (2) glass manifold; (3) support pole; (4) Tenax GC cartridge (10 cm X 1.3 cm i.d.); (5) Du Pont P125A personal sampling pump, operated at 25 mL/min; (6) canister sampling system; (7) air outlet; (8) air inlet; (9) capped manifold inlets, used alternately for collection of duplicate samples; (10) Swagelok stainless steel union; (1 1) Teflon (PTFE) tubing.
building (approximately 12 f t above ground level). A continuous flow of air was passed through the glass manifold by means of either a single rubber diaphragm pump or a stainless steel bellows pump, both operated at approximately 3 L/min. Time-integrated Tenax GC and canister samples were collected from the manifold over 12-h periods beginning each day at approximately0800 and 2000 h. These times corresponded to the approximate sampling periods at the participants' homes. Canister air samplers were deployed at the central monitoring station for only 5 of the 10 sampling days the station was operated. Data quality for all samples was evaluated by analyzing blank and control samples (both canisters and Tenax cartridges) interspersed with field samples. Controls were Tenax GC cartridges and canisters fortified with approximately 200 ng of each compound prior to sampling. Blank and control samples were transported, unopened, with the field samples to monitor contamination or losses during sample collection, storage and transport. Mean background and recovery values were calculated from blanks and controls, respectively, and were mathematically applied in the processing of Tenax sample data according to the equation [ng (t) - ng (bkgd)] X 100 conc, = ( % recovery,) (sample volume) where conc, is the concentration of the target analyte in ng/L; ng (t) is the mass (ng) of target analyte found on the Tenax cartridge; ng (bkgd) is the mean mass (ng) of target compound found in Tenax blanks; % recovery is the mean percent recovery calculated from Tenax controls; and sample volume is the volume (L) of air collected on the 998
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Tenax cartridge. Similarly, canister data were processed according to the equation (concinit- concbkgd)x 100 conc = (% recovery,) where conc, is the concentration of the target analyte (ng/L); concinitis the uncorrected target analyte concentration; concbkd is the mean target analyte concentration in canister blanks; and % recovery is the mean percent recovery calculated from canister controls. Exposed Tenax GC cartridges were analyzed by thermal desorption-injection capillary gas chromatography/mass spectrometryon a Finnigan Model 4500 mass spectrometer interfaced to an INCOS data system. In brief, volatile organics were thermally desorbed from the Tenax GC, at 260 "C with a nominal helium flow, into a liquid nitrogen cooled, nickel capillary trap (5-7). The condensed vapors were then introduced into a high-resolution fused-silica capillary chromatography column by ballistic heating of the trap to 250 "C (6, 8). Sample constituents were characterized and quantitated by electron impact (70 eV) mass spectrometry by measuring the area of the extracted full-scan ion current profile (6,9,IO). Canister samples were analyzed by cryogenic trapping of approximately 100-mL aliquots followed by gas chromatography/mass spectrometry/computer (GC/MS/COMP) analysis. Method limits of detection for canister and Tenax samples are shown in Table I. Target compounds were slightly different for the two sampling/analysis procedures. Statistical procedures were run on the entire data set of all sampling locations (43 households plus the central fixed site) using SAS Version 6.0 (SAS Institute, Cary, NC)
h
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'i
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coi
n
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Figure 3. Summary statistics for overnight Tenax samples. Compound numbers are identified in Table I; c, central fixed site; 0 , outdoor residential; i, indoor residential. 13
n
n
I
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4
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Figure 4. Summary statistics for daytime Tenax samples. Compound numbers are identlfled in Table I; c, central fixed site; 0 , outdoor residential; i, indoor residential.
on an IBM Model 3081 computer. However, because data were grouped with respect to concurrent sampling (Le., indoor, outdoor, and central fixed-site samples collected at the same time) actual data set sizes were considerably smaller. Only complete sample sets, those having all three pieces of data (either a value or the limit of detection), were included in the analyses. Differences in median values between central, outdoor, and indoor sites were tested for significance by using the Wilcoxon signed rank test (11) in SAS. Graphical data output was obtained by using SYMPHONY (Lotus Development Corp., Cambridge, MA)
on an IBM PC-AT computer.
Results and Discussion Tenax Samples. Summary statistics generated for overnight and daytime Tenax samples are shown in Figures 3 and 4, respectively. Median, 25th quartile, and 75th quartile values are illustrated for each target compound at each of the three concurrent sampling locations: central fixed site (c), residential outdoor (o),and residential indoor (i). Compounds are ordered from left to right in decreasing volatility and are identified by the compound numbers Environ. Sci. Technoi., Vol. 24, No. 7, 1990
999
Table 11. Wilcoxon Signed Rank Test for Significant Differences between Medians in Tenax Samples
no. 2 3 4 5 6 8
9 10 11
12 13 14 15 16 17
18 19
20
compound
overnightavb daytimearb in in out in in out vs vs vs vs vs vs out cent cent out cent cent
chloroform 1,1,1-trichloroethane t carbon tetrachloride t benzene t trichloroethylene t n-octane t tetrachloroethylene t ethylbenzene t p-xylene t o-xylene t styrene t n-nonane t a-pinene t n-decane t p-dichlorobenzene t limonene t n-undecane t n-dodecane
t t t t t t + t t t t + + t t t
-
-
-
t
t t t t t t t t + t t t + + t t + t + t t t + + t t t t t t t t t t t t t t t t t t t c + t t t t t + t + t t + t
(-) not significantly different a t the 0.05 level; (t)significantly different at the 0.05 level. *In, indoor; out, outdoor; cent, central. CInsufficientdata (
