Environmental Engineering Reference
In-Depth Information
required in different geographical areas to determine important parameters that
potentially affect metal (and other constituents) exposures; such parameters include
infi ltration factors for house construction and insulation, air conditioning and occu-
pant behaviors.
3.2
Epidemiology
It has been reported in a large number of studies that incremental increases in ambi-
ent PM concentrations are followed 1-3 days later by increases in respiratory and
cardiovascular morbidity and mortality. Fewer studies have investigated the role of
specifi c components of the total mass of ambient PM, including the transition met-
als of interest to this review. Table
4
summarizes the concentrations of metals (when
reported), population of interest, and health effects evaluated in each of the studies
discussed in this section.
3.2.1
Aging Population
Four studies that focused specifi cally on associations between metals in ambient
PM
2.5
and hospital admissions or mortality in the aging population were identifi ed
for this review (Bell et al.
2009
; Lipfert et al.
2006
; Ostro et al.
2007
; and Suh et al.
2011
). All of the studies reported statistically signifi cant effects (either p <0.10 or p
<0.05) for one or more transition metals and increases in respiratory and/or cardio-
vascular outcomes. The studies are briefl y discussed below.
Bell et al. (
2009
) examined respiratory and cardiovascular hospitalizations for
persons 65 years or older from exposure to county-specifi c levels of PM
2.5
As, Cu,
Fe, Ni, Ti, Zn, and V, in 106 U.S. counties. Bayesian hierarchical regression model-
ing showed a statistically signifi cant relationship between short-term changes in V
(average conc. 3 ng/m
3
) and Ni (average conc. 2 ng/m
3
) concentrations and a higher
risk of cardiovascular and respiratory hospitalization. Concentrations of the other
metals were not signifi cantly associated with hospitalizations.
Ostro et al. (
2007
) examined associations between 12 metals in PM
2.5
and daily
mortality in a time-trend study of residents 65 years and older in six California
counties. Increases in mortality were signifi cantly associated with Zn for 1 and
3-day lags. There were signifi cant associations for Cu, Fe, Mn, Ti, V, and Zn (but
not for Ni), and daily mortality deaths during the cooler months. The average con-
centration for Fe was 124 ng/m
3
, with averages for the other metals ranging from 2
to 12 ng/m
3
, (similar to the nationwide means from the STN shown on Table
1
).
Lipfert et al. (
2006
) investigated the effects of 15 PM
2.5
-associated metals on
long-term mortality for U.S. military veterans, aged 60 years or older. In a propor-
tional hazards model, Ni and V, but not As, Cu, Fe, Mn, Se or Zn, had signifi cant
effects on mortality. The average concentrations of Ni and V were 1.73 ng/m
3
and
1.90 ng/m
3
, respectively.
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