Environ. Sci. Techno/. 1995, 29, 494-500
Introduction
in k s e Dust and T d - i n Sail J A N E C . CHUANG,' PATRICK J. CALLAHAN, RONALD G. M E N T O N , A N D SYDNEY M . GORDON Battelle, 505 King Avenue, Columbus, Ohio 43201 -2693
R O B E R T G . LEWIS A N D N A N C Y K . WILSON Atmospheric Research a n d Exposure Assessment Laboratory, US.Environmental Protection Agency, Research Triangle Park, North Carolina 2771 1
An analytical method was developed and employed to determine polycyclic aromatic hydrocarbons (PAH) in house dust and soil. The method was applied to the analysis of samples collected in an eighthome pilot study that was conducted in Columbus, OH, before and after the 1992/1993 heating season. The purpose of the study was to obtain concentration profiles of PAH in house dust and track-in soil, and to determine whether the track-in of outdoor soil contributes to PAH in house dust. A total of 19 PAH, ranging from naphthalene (2-ring) to coronene (7ring), were monitored. The sums of concentrations of the 19 PAH ranged from 16 to 580 ppm (w/w) in house dust, from 58 to 5500 ppm in entryway soil, from 0.58 to 1200 ppm in pathway soil, and from 0.63 to 63 ppm in foundation soil. In general, the concentration trend was as follows: entryway soil > house dust > pathway soil > foundation soil. PAH levels in house dust and track-in soil were of the same order of magnitude before and after the heating season. In house dust samples, levels of most 4- to 6-ring PAH, the sums of the 19 PAH, and the sums of the PAH that are probable carcinogens correlated well ( r > 0.90 a t p < 0.001) with the corresponding levels in the entryway soil samples.
Recent studies to develop suitable sampling and analysis methods for establishing human exposureto pesticides have shown that relatively high levels of pesticide residues can occur in house dust (1). Residues tracked into the home may remain in carpets for prolonged periods due to the absence of environmental weathering effects. These residues may be picked up by the skin on contact. Once on the skin, pesticides as well as other pollutants may be absorbed directlyor transferred to the mouth and ingested. Because young children spend a great deal of time on the floor, they are particularlysusceptible to exposure to these chemicals as a result of dermal contact with house dust and the frequent hand-to-mouth contact that accompanies their normal play activities. An estimate of average daily soil and dust ingestion by young children ranges from 0.02 to 0.2 g, with a potential for up to 5 glday for children exhibitingpica behavior who live in a dusty home or have access to exposed soil (2, 3). Polycyclic aromatic hydrocarbons (PAH) have been found in indoor and ambient air (4, 5). Many PAH are known animal carcinogensor mutagens, and adverse health effects have been linked to exposure to PAH (6, 7). Environmental tobacco smoke has been shown to be the most important source of PAH in indoor air (4). Other indoor activities that may contribute to PAH concentrations in indoor air are the use of unvented kerosene space heaters (81, the use of gas cooking and heating appliances (41, and the use of wood-burning fireplaces (9). Outdoor air can also intrude and raise indoor PAH levels (4). Relatively high PAH levels have been found in dust or soil samples taken near heavy automobile traffic (10, 11). Therefore, homes located downwind of the heavy traffic may have higher PAH levels in the house dust than those in lighter traffic areas. Very little information is available, however, about the occurrence and distribution of PAH in house dust resulting from indoor sources or from track-in of outdoor dislodgeablesoil residues. Some data from lead studies also suggest a possible magnification of lead in soil near foundations (12).If such magnification occurs, it may be due to the deposition of atmospheric Pb on the roof and the outside surfacesof the house, which then falls or washes down to the soil near the drip line of the roof. It is not clear whether such magnification also occurs with PAH. There are no established monitoring methods for PAH in house dust and track-in soil. A small-scale pilot study was therefore undertaken to evaluate monitoring methods for PAH in dust and soil samples. The specific objectives of this small-scale study were to develop and evaluate methods for PAH that can be used in a larger study; to collect preliminary information about the levels and distributionof PAH in house dust and track-in soil; to obtain preliminary information about the potential track-in of outdoor soil residues and its contribution to PAH in house dust: and to collect information about the potential for magnification of PAH levels in foundation soil. It is important to note that the primary purpose of this smallscale pilot study was to evaluate methods and obtain information necessary for designing a larger study. The * Author to whom correspondence should be addressed.
494. ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29, NO. 2,1995
0013-936x/95/0929-0494$09,00/0
0 1995 American Chemical Society
data gathered are therefore representative only of the locations and periods sampled and do not necessarilyapply to the larger population.
Experimental Section Analytical Method Evaluation. Soxhlet and sonication
extraction methods were evaluated for removing PAH from the dust and soil sample matrices. For the Soxhlet evaluation, known amounts of perdeuterated PAH were spiked into each aliquot of the house dust and extracted with dichloromethane (DCM) for 12 h. The DCM extract was fractionated using a silica gel column. Three elution solvents, hexane, hexaneIDCM (l:l), and methanol, were applied to the silica gel column. The target hexaneIDCM fraction was concentrated to 1 mL for subsequent gas chromatographyImass spectrometry (GCIMS)analysis. In a second experiment, both the dust and soil samples were spiked with known amounts of perdeuterated PAH and Soxhlet-extractedwithhexane for 12 h. The hexane extract did not need additional cleanup prior to GCIMS analysis. Different sonication conditions were evaluated for the dust and soil samples. Each 200-mg aliquot of dust or soil was spiked with a known amount of perdeuterated PAH and extracted with 10 mL of hexane in a sonication bath for 60 min. The hexane extract was removed, and an extra 10 mL of hexane was added to the sample, which was sonicated for another 60 min. The experiments were repeated for two 30-minextractions, one 25-min extraction, and two 15-minextractions. The resulting hexane extracts were filtered and concentrated to 2 mL for GUMS analysis. The extracts and target fractions were analyzed by GC/ MS using 70-eV electron ionization (EI). A Finnigan TSQ45 GClMSIMS instrument, operated in the GUMS mode, was used. Data acquisitionand processingwere performed with an INCOS 2300 data system. The GC column was a DB-5 fused silica capillary column (30 m x 0.25 mm, 0.25 pm film thickness, Supelco), and the column outlet was located in the MS ion source. Helium was used as the GC carrier gas. Following injection, the GC column was held at 70 "C for 2 min and temperature-programmed to 290 "C at 8 "C Imin. The MS was operated in the selected ion monitoring (SIM) mode. Masses monitored were the molecular ions and their associated characteristicfragment ions. Identification of the target compounds was based on their GC retention times relative to those of the internal standards [2Hlolphenanthrene,9-phenylanthracene, and [2H12]benzo[elpyrene. Quantification of target compounds was based on comparisons of the respective integrated ion current responses of the target ions to those of the corresponding internal standards using average response factors of the target compounds generated from standard calibrations ( 4 ) . Pilot Field Study. A small-scale pilot field study was conductedprior to and subsequent to the 1992/1993heating season by collecting and analyzing house dust and soil samples from eight homes located in Columbus, OH. Questionnaires were administered to obtain information about relevant household characteristics. None of the householdsused unvented space heaters. Four households were inhabited by nonsmokers and four by smokers. Of the eight homes initially selected for the first sampling session (I)conducted in June 1992,one residence (no.H05a) was an apartment, not a single familyhome. It was replaced with a house (no. H05)in the second (11) and third (111)
sampling sessions conducted in October 1992 and April 1993, respectively. Only house dust samples were taken during sampling session I. House dust, entryway soil, and pathway soil samples were taken during sampling sessions I1and 111,and foundation soil sampleswere collected during sampling session 111. The high-volumesmall surface sampler (13,141 (HVS3) was used to collect samples of carpet-embedded dust from designated areas in the carpet in either the living room (homes H01, -3, -4, -5, -6) or the family room (homes H02, -7, -8). The HVS3 consists of a high-powered vacuum cleaner equipped with a sampling nozzle that can be adjusted to a specific static pressure within the nozzle, a cyclone to separate particles 5pm mean diameter and larger at a flow rate of 9.5 LIS (20 cfm), and a Teflon bottle to collect the sample. Prior to sampling each home, the HVS3 was disassembled and cleaned. The HVS3 was operated according to the manufacturer's instructions (15) and an ASTM standard guide (16'). The sampling procedure for house dust involved selecting an area of each carpet in the main traffic path through the carpet and at least 1 m from any outside door. A 76 x 100 cm rectangle was marked out with masking tape and the width was subdivided into 10 7.6-cm wide segments. The HVS3 was run slowly forward and backward across the 100-cmlength of the rectangle a total of eight times along each 7.6-cm width. After the eighth pass, the unit was gradually moved over to the next segment, and the procedure was repeated until all 10 segments had been sampled, for a total area of 0.76 m2. A sample of entrywaysoilwas collected from the doormat originallyplaced at the primary entrance to each home. If the amount of sample collected at the main entrance was insufficient, an extra sample was also collected at a secondary entrance to the home. In all the households, the doormats were placed either inside the houses or inside the attached garages. The sample was obtained by turning over the doormat and placing it on a clean sheet of aluminum foil. Then, the back of the mat was beaten for several minutes before it was removed from the foil. The loose particles on the foil were poured into a clean, prelabeled glass jar. The same procedure was followed during the first two sampling sessions. A month prior to sampling session 111,a new doormat was delivered to each home and placed indoors in the main entrance area. Entryway samples were again collected using the same procedure. Pathway soil samples were collected from at least three locations along the primary pathway to the home. At each sampling location, soil was scraped with a trowel from the top 0.5-cm surface of the soil over an area of at least 0.1 m2 and placed in a clean prelabeled glass jar. Foundation soil samples were collected within 0.6 m of the foundation on each side of the house and placed in a clean jar. At each sampling location, soil was scraped from the top 2.0-cm surface of the soil. If samples could not be obtained from one side of the house, extra samples were collected from one of the other sides of the house. An aliquot of each dust and soil sample was spiked with known amounts of perdeuterated PAH, and each sample was extracted twice with 10 mL of hexane in a sonication bath for 30 min. The hexane extracts were combined, filtered, and concentrated to 2 mLfor subsequent analysis. The GUMS method used was described earlier in the Analytical Method Evaluation section. VOL. 29, NO. 2,1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1
Recoveries of Perdeuterated PAH fnm Spiked House Dust and Soil Sample recovtm I%)
compound
Sox-DCW
Sox-hexane*
son4
son-bd
son-co
son-df
Sox-hexanes
son-bh
8 8 f 13 91f11 93f8.4 [2H1~lchrysene [2H~~lbenzo[kl-fluoranthene 94 f 2.8 93 f 7.7 [2H1~l~erylene
91 f 13 93f13 100f5.8 100 f 6.4 97 f 4.6
7 4 f 4.0 80 f 2.5 8 3 f 1.2 100 f 0.7 95 f 4.4
91 f 5.6 100 f 0.6 95f5.0 98 f 2.1 97 f 4.2
79 f 12 87 f 12 80f 12 79 f 12 71 f 15
80 f 9.1 89 f 9.3 8 0 f 12 100 f 5.8 100 f 5.0
77 f 5.7 94 f 6.4 9Of 11 90 f 14 9 4 f 9.2
91 f 5.0 97 f 3.5 93f3.5 98 f 1.5 97 f 5.8
lZHl~lfluorene [ZHl~lpyrene
a Four replicate spiked dust samples were Soxhlet-extracted with DCM, fractionated on a silica gel column, and analyzed by GCIMS. Triplicate spiked dust samples were Soxhlet-extracted with hexane and analyzed by GUMS. Triplicate spiked dust sampleswere extracted twice with hexane in a sonication bath for 60 min and analyzed by GC/MS. dTriplicate spiked dust samples were extracted twice with hexane in a sonication bath for 30 rnin and analyzed by GCWS. 'Triplicate spiked dust samples were extracted once with hexane in a sonication bath for 25 rnin and analyzed by GUMS. 'Triplicate spiked dust samples were extractedtwice with hexane in a sonication bath for 15 min and analyzed by GC/MS. Duplicate spiked soil samples were Soxhlet-extracted with hexane and analyzed by GUMS. Triplicate spiked soil samples were extracted with hexane in a sonication bath for 30 min and analyzed by GUMS.
Results and Discussion
TABLE 2
Evaluation of Analytical Methods. Extraction efficiencies for PAH from spiked dust and soil samples under various experimental conditions are presented in Table 1. Quantitative recovery ('80%) of the spiked perdeuterated PAH was achieved when either DCM or hexane was used as the extraction solvent with the Soxhlet technique. Both DCM and hexane effectivelyremove PAH from the dust, but DCM requires the extra silicagel cleanup step. Therefore,hexane was used as the extraction solvent in the experiments to evaluate various sonication conditions. Quantitative recoverieswere obtainedunder allsonication conditions used. Slightly better recoveries were achieved when the dust sample was sonicated twice with hexane for 30 min. The recoveries in this experiment ranged from 91 f 5.6% for [2Hlolfluoreneto 100 f 0.6% for [2Hlo]pyrene.This sonication condition was used with the spiked soil samples, and recoveries ranged from 91 f 5.0% ([2Hl&luorene)to 98 f 1.5% ([2H12]benzo[k]fluoranthene). Quantitative recovery of the perdeuterated PAH was obtained with both extraction methods. The native PAH concentrations were also determined using these two extraction methods. The results for the native PAH are summarized in Table 2. The PAH concentrations were calculated based on the weight of the samples corrected for moisture and expressed in units of microgramsper gram (ppm w/w). Similar concentrations of native PAH were obtained from samples prepared by both extraction methods. The PAH were measured in the triplicate samples with a precision of 15%relative standard deviation (RSD) with the sonication method and 19%RSD with the Soxhlet extraction method. Because the sonication method requiresless solvent and a shorter extractiontime,the samples collected in the field study were extracted by sonication in two 30-min extractions using hexane. House Dust Loading. The collectedhouse dust samples were sieved into course and fine ( < 150 ,urn) fractions. The fine fractions were used for PAH analysis. The ratio of the dust loading (g/m2)in the fine fraction to the total dust loading in sampling sessions I, 11, and I11 ranged from 0.69 to 0.85, from 0.48to 0.83, and from 0.63 to 0.87,respectively. Dust loadings obtained from each house were within the same order of magnitude before (sessions I and 11) and after (session111)the heating season. Figure 1is ahistogram showing the fine dust loadings for the sampled households as a function of the sampling session. The carpet in house no. H03 (nonsmoker's house) showed the highest loading in all three sampling sessions. The total and the fine dust
PAH Concentrations in House Bust Samples Extracted by Soxhlet and Sonication Methods
496 1 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29, NO. 2, 1995
concentration(ppm) compound
r!ng size
naphthalene acenaphthylene acenaphthene fluorene phenanthrene anthracene retene fluoranthene pyrene benz[slanthraceneC chrysenec cyclopenta[c,dlpyrene benzofluoranthenesC benzo[elpyrene benzo[alpyrenec indenoIl,2,3-c,dlpyreneC di benz[e,h]anthraceneb benzo[g,h,ilperylene coronene
2 3 3 3 3 3 3 4 4 4 4 5 5
5 5 6 6 6 7
Soxhl.et extractma
sonication axtraction*
0.53 f 0.10(19) 0.35f 0.04 (11) 0.58f 0.11 (19) 0.52f 0.05 (9.6) 1.31 f 0.14(11) 1.06f 0.05 (4.7) 2.57 f 0.24(9.3) 2.07 f 0.1 1 (5.3) 46.8f 4.4 (9.4) 41.0f 1.8(4.4) 4.23 f 0.40(9.4) 3.91 f 0.43 (11) 0.48 f 0.09 (19) 0.36f 0.04 (10) 90.0 f 14.1 (16) 90.1 f 5.5 (6.1) 70.2f 8.5(12) 68.2f 2.2 (3.3) 34.8 1.8(5.2) 24.4f 2.5 (10) 45.9f 2.8(6.1) 34.4f 4.2 (12) 0.38f 0.04 (10) 0.36f 0.03 (8.3) 47.2f 3.9 (8.3) 50.2i 2.8 (5.6) 41.9 f 4.4(10) 40.7f 3.0 (7.5) 46.2f 6.4(14) 53.8f 6.0(11) 34.3 f 4.3 (12) 40.8f 3.1 (7.6) 31.8f 5.0 (16) 34.9f 2.5 (7.2) 6.89f 0.83 (12) 7.49 f 0.17 (2.3) 6.41 f 0.49 (7.6)7.22f 1.09 (15)
a Triplicate spiked dust samples were Soxhlet-extracted with hexane for 12 h; the reported values are av f SD (%). *Triplicate spiked dust samples were extracted twice with hexane in a sonication bath for 30 min; the reported values are av f SD (%I. These PAH compounds are in the U S . EPA's Integrated ranked as probable human carcinogens (8-2) Risk Information System.
loadings in this house in the three samplingsessions ranged from 7.43 to 8.48 and from 6.49 to 7.20 g/m2,respectively. In general, higher dust loadings were found in nonsmokers' houses (H02,H03, H07, and H08) compared to those in the smokers' houses (H01, H04, H05, and H06). As discussed below, one of the houses with high dust loadings (H08) consistentlyyielded the highest PAH concentrations in dust in allthe houses sampledand for allthree samplingsessions. PAH ConcentrationProfiles. The target PAH measured in the dust and soil samples are the same as those described in Table 2. A total of 19 PAH, consistingof one 2-ring PAH, six 3-ring PAH, four $-ring PAH, four 5-ring PAH, three 6-ringPAH, and one 7-ringPAH, were measured. Of these, seven are ranked as probable human carcinogens (B-2) in the U.S.EPA's Integrated Risk Information System (IRIS). Figure 2 shows the PAH concentration profiles by ring size in the dust samples collected in sampling session I. As shown in Figure 2, the concentrations of each target PAH were summed by ring size, and the ratios to the PAH groups with the highest concentrations (Le., the most abundant
Session I Session I I f~~ ’~.]Session 111 E..’.’.
I
~
FIGURE 1. Fine house dust (
