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Principal Investigator: L Sheldon
Research Triangle Park, North Carolina
December 1992
ARB Contract No. A933-144 (Full Report)
ABSTRACT
The primary purpose of this study was to obtain indoor and outdoor air concentration data for benzo[a]pyrene,
other polycyclic aromatic hydrocarbons (PAHs), and phthalates in California residences to be used in making exposure
predictions. To meet these objectives, a field monitoring study was performed in 125 homes in Riverside, California
in the fall of 1990. In each home, two 12-hour indoor air samples were collected during daytime and overnight periods.
In a subset of 65 homes, outdoor air samples were also collected. PAH and phthalate concentrations were measured
in collected air samples using gas chromatography /mass spectrometry techniques. Along with field monitoring, information
on potential source usage in the home was collected using questionnaires. This study was performed in conjunction
with an indoor air/personal exposure monitoring study for particulates sponsored by the U. S. Environmental Protection
Agency.
Prior to statistical analysis, sampling weights were developed. When the sample size was sufficiently large, these
weights were applied to the field monitoring results which allowed statistical estimates to be made that represented
61,520 households in Riverside (excluding the area around March Air Force Base) with at least one nonsmoking resident
over the age of 10. Mean air concentrations and concentration distributions were calculated for the target PAHs
and phthalates in four sample types (indoor/daytime, indoor/nighttime, outdoor/daytime, and outdoor/nighttime).
It should be emphasized that results from this study are for one city during a single season and that PAH and phthalate
air concentrations and relationships may be different in different seasons and in different parts of the state.
Results showed several interesting trends for the PAHs. First, relative air concentrations for the individual
PAH species in all four sample types show highest concentrations for the more volatile, 3- and 4-ringed species
and lowest concentrations for the particulate phase 5-, 6-, and 7-ringed species. Highest median air concentrations
were found for phenanthrene (8.8 to 16 ng/m3) followed by acenaphthylene (1.8 to 6.9 ng/m3),
fluoranthene (1.6 to 23 ng/m3), and pyrene (1.6 to 20 ng/m3). Median concentrations for the
particulate phase 5- to 7-ringed species were an order of magnitude lower with lowest median air concentrations
reported for benzo[a]pyrene (0.09 to 0.20 ng/m3) and benzo[e]pyrene (0.13 to 0.22 ng/m3).
Second, indoor air samples showed little or no increase in median or mean air concentrations compared to outdoor
concentrations, although several homes did show very high PAH concentrations. Third, indoor air concentrations
for most PAHs, including benzo[a]pyrene (BaP) were higher in homes where smoking took place compared to homes where
there was no smoking. The maximum indoor concentration for BaP was 56 ng/m3 compared to the maximum
outdoor concentration at 29 ng/m3. Finally, considerably higher nighttime concentrations were reported
for outdoor samples compared to the daytime samples. For example, the median nighttime/outdoor air concentration
for BaP was 0.19 ng/m3 while the corresponding daytime concentration was less than half that value at
0.09 ng/m3. This trend was seen for alI of the particulate phase 5- to 7-ringed PAHs as well as the
more volatile 3-ringed species. This effect probably resulted from photodegradation of PAHs during the day. All
of the phthalates (except di-n-octylphthalate) showed high indoor air concenttations compared to the PAHs.
Diethylphthalate and di-n-butylphthalate showed the highest indoor air concentrations with median daytime concentrations
of 340 and 420 ng/m3, respectively. Median outdoor air levels for the phthalates were at least an order
of magnitude lower than the corresponding indoor levels. Di-n-octylphthalate had median concentrations below the
quantifiable limit (3.2 ng/m3) for all four sample types. These data suggest that indoor phthalate concentrations
arise primarily from indoor sources and that most of the exposure to airborne phthalates will occur indoors.
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