Environmental Engineering Reference
In-Depth Information
3.1.2
Summary of Indoor and Personal Concentrations of Target Metals
Outdoor concentrations are not necessarily good guides to actual exposures. Most
people spend most of their time indoors. Homes and buildings can act as a partial
barrier to outdoor particles. However, indoor sources of particles also exist. Certain
elements, such as sulfur, tend to have lower concentrations indoors, because few
indoor sources exist, whereas levels of other elements tend to be higher indoors
from sources such as cigarette smoke, cooking, and resuspension from clothes and
fl oors because of particle mobility or cleaning processes (Wallace et al.
2008
). Two
valuable sources of particulate exposures levels are available and are the Toxicity
and Exposure Assessment for Children's Health (TEACH) (Kinney et al.
2005
,
2008
) studies, and the Relationships of Indoor, Outdoor, and Personal Air (RIOPA):
part II. analyses of concentrations of particulate matter species (Turpin et al.
2007
),
in which indoor and outdoor PM
2.5
and elemental concentrations at 60-100 homes
were measured in each of fi ve cities or larger regions. The indoor and outdoor results
for the target elements found in PM
2.5
are summarized in Table
3
. The indoor/out-
door (I/O) ratios, based on these results, are also shown. Metals such as V and Mn
have I/O ratios <1 in all fi ve areas, indicating few indoor sources. Metals with I/O
ratios that often exceed one include Zn and Cu, indicating the presence of indoor
sources (Adgate et al.
2007
). Therefore, we expect human exposure for these two
metals to be several times higher than their reported ambient levels. The RIOPA and
TEACH studies did not include smokers. In a separate study, the target metals asso-
ciated with tobacco smoke (viz., Cr, Ni, Zn, and As) were increased by factors of
8-22, compared to reference indoor atmospheres (Slezakova et al.
2009
).
Personal daytime exposures to 14 elements in the PM
10
fraction were shown to
be elevated by more than 50% compared to concurrent indoor concentrations in the
Particle TEAM study performed in Riverside, CA (Ozkaynak et al.
1996
). The
source of this “personal cloud” has not been unambiguously identifi ed, but may
arise from resuspension of particles from clothes or fl oors, or it may be due to a
proximity effect, in that personal activities such as cooking or vacuuming involve
closer distances to the source than the fi xed location of the indoor monitor. The
PM
10
personal cloud was shown to be about 35
g/m
3
in the Personal Total Exposure
Assessment Methodology (PTEAM) (Clayton et al.
1993
; Ozkaynak et al.
1996
;
Thomas et al.
1993
) and other studies (Pellizzari et al.
1999
). However, multiple
studies of the PM
2.5
fraction have shown a much smaller personal cloud, on the
order of 2-3
ʼ
g/m
3
, suggesting that the PM
10
personal cloud consists mostly of
coarse particles (Wallace
2000
). Coarse particles are more easily resuspended than
fi ne particles due to Van der Waals forces attracting the fi ne particles to surfaces.
Although a small personal cloud has been reported in most PM
2.5
studies, a very
large personal cloud ranging from 13 to 25
ʼ
g/m
3
was reported in the RIOPA study,
in which the concurrent indoor concentrations were about a factor of 2 higher. In
contrast to the other studies, no personal cloud was reported in the TEACH study.
Even larger personal/indoor factors, ranging up to 6.9, were found in the RIOPA
study for metals such as Cr, Cu, Fe, Mn, Ni, Ti, and Zn. Increased personal expo-
sures for these metals were reported in the TEACH study, but at more modest ratios
<1.5, except for Ni in Los Angeles (2.6) and Cr, Fe, and Mn in New York City (5.4,
3.0, and 2.6, respectively).
ʼ
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