Rb. Schlesinger et Lc. Chen, COMPARATIVE BIOLOGICAL POTENCY OF ACIDIC SULFATE AEROSOLS - IMPLICATIONS FOR THE INTERPRETATION OF LABORATORY AND FIELD STUDIES, Environmental research, 65(1), 1994, pp. 69-85
Biological responses to inhaled acid sulfates result from the depositi
on of hydrogen ion (H+) on airway surfaces. Thus, effects from sulfuri
c acid and ammonium bisulfate, the two major ambient species, have bee
n assumed to be the same for a given H+ concentration within the expos
ure atmosphere, assuming similar respiratory tract deposition patterns
. However, recent inhalation studies have indicated that sulfuric acid
is disproportionately potent compared to ammonium bisulfate when the
H+ content of the exposure atmosphere is considered, suggesting that s
ome factors following inhalation affect the amount of H+ contacting ai
rway surfaces. This study assessed a mechanism potentially underlying
this phenomenon, namely, the extent of neutralization by respiratory t
ract ammonia. This was evaluated using a physical model system designe
d to mimic transit of these aerosols in the upper respiratory tract of
the animal model used in this laboratory, the rabbit. The results sug
gest that for equal exposure quantities of H+, more acid would be depo
sited when sulfuric acid is inhaled than when ammonium bisulfate is in
haled. Furthermore, results from a series of in vitro exposures of tra
cheal epithelial cells to sulfuric acid and ammonium bisulfate aerosol
s indicated that the biological response is a function of the total ma
ss (ionic) concentration of Ht deliverable to the cells or the total e
xtractable Ht per particle. The results of this study have possible im
plications for ambient monitoring of particulate associated strong aci
dity, suggesting that it may be necessary to speciate such measures in
to the relative amounts of H+ as sulfuric acid or ammonium bisulfate i
n order to most accurately relate atmospheric acid levels to observed
health effects. In addition, since much of the ambient particulate-ass
ociated Ht exists as sulfuric acid/ammonium bisulfate mixtures rather
than pure compounds, H+-associated health effects from controlled expo
sure studies of sulfuric acid may not be transferable to ambient popul
ation situations on a 1:1 basis. Since any such errors in exposure ass
essment will necessarily bias downward the strength of Ht-related heal
th effects associations found via epidemiological studies, failure to
address the speciation of H+ may cause such studies to underestimate t
he human health effects of strong acids. (C) 1994 Academic Press, Inc.