Similar to vegetation experiments performed
in the 1980s (e.g., Musselman et al., 1983; Hogsett et
al., 1985), controlled human health laboratory study results
have shown a difference in response to square-wave (i.e., constant
concentration) O3 exposures and triangular (i.e., variable) exposures.
For example, triangular exposures used by Hazucha et al.
(1992) and Adams (2003a; 2006), suggest that variable exposures
can potentially lead to higher FEV1 responses than square-wave
exposures at overall equivalent O3 doses. An important observation
from these three experiments is that the higher hourly average
concentrations elicit a greater effect than the lower hourly
average values in a non-linear manner (Hazucha and Lefohn, 2007).
It has become apparent that controlled human health laboratory
simulations of air-pollution risk-assessment need to employ O3
concentration profiles that more accurately mimic those encountered
during summer daylight ambient air pollution episodes (Adams
and Ollison, 1997; Lefohn and Foley, 1993; Rombout et al.,
1986). For many years, vegetation and some human health researchers
have designed exposure regimes that has resulted in the application
of triangular-type exposure regimes. Based on the published literature
combined with the most recent findings from the EPA (2006), summarized
ambient air quality data provide important evidence for those
vegetation and human health clinical researchers who are applying
varying hour-by-hour O3 concentrations (i.e., triangular exposure
regimes) in their experiments. Recent findings from Lefohn (2006)
indicated that square-wave O3 patterns of exposure occur fairly
rarely under ambient conditions. The investigator found that
if one defined a "square wave" profile as experiencing
a variable range of 4 ppb or less over an 8-hour period, only
1.51% of all sequences (28,148) would be classified as representing
a "square wave".
Over a six-year period, A.S.L. & Associates has collaborated
with clinical health researchers in designing realistic ambient-type
regimes used in experiments involving controlled laboratory exposures
of human volunteers. These realistic ambient-type O3 exposures
are applied to assess the influence of the exposure patterns
of hourly average concentrations on specific biological endpoints.
Using hourly average O3 values, A.S.L. & Associates has developed
a statistical methodology for identifying "typical"
sequences of 8 hourly values that are associated with actual
8-hour patterns. As part of its ongoing research to identify
viable alternative forms of air pollution standards to protect
human health, A.S.L. & Associates continues its collaborative
research program with clinical health researchers in assessing
the effects of realistic patterns of O3 exposure on human health
endpoints.
References
Adams, W. C. (2003a) Comparison of chamber
and face mask 6.6-hour exposure to 0.08 ppm ozone via square-wave
and triangular profiles on pulmonary responses. Inhalation Toxicology
15: 265-281.
Adams, W. C. (2006). Comparison of Chamber
6.6-h Exposures to 0.04 - 0.08 ppm Ozone Via Square-Wave and
Triangular Profiles on Pulmonary Responses. Inhal Toxicol. Inhalation
Toxicology 18, 127-136.
Adams, W. C.; Ollison, W. M. (1997) Effects
of prolonged simulated ambient ozone dosing patterns on human
pulmonary function and symptomatology. Presented at: 90th annual
meeting of the Air & Waste Management Association; June;
Toronto, Ontario, Canada. Pittsburgh, PA: Air & Waste Management
Association; paper no. 97-MP9.02.
Hazucha, M. J.; Folinsbee, L. J.; Seal,
E., Jr. (1992) Effects of steady-state and variable ozone concentration
profiles on pulmonary function. Am. Rev. Respir. Dis. 146: 1487-1493.
Hazucha, M. J.; Lefohn, A. S. (2007) Nonlinearity
in Human Health Response to Ozone: Experimental Laboratory Considerations.
Atmospheric Environment. 41:4559-4570.
Hogsett, W. E.; Tingey, D. T.; Holman,
S. R. (1985) A programmable exposure control system for determination
of the effects of pollutant exposure regimes on plant growth.
Atmospheric Environment 19: 1135-1145.
Lefohn, A. S.; Foley, J. K. (1993). Establishing
Ozone Standards to Protect Human Health and Vegetation: Exposure/Dose-Response
Considerations. J. Air Waste Manag. Assoc. 43(2):106-112.
Lefohn, A.S. (2006). Personal Communication.
A.S.L. & Associates, Helena, Montana.
Musselman, R. C.; Oshima, R. J.; Gallavan,
R. E. (1983) Significance of pollutant concentration distribution
in the response of `red kidney' beans to ozone. J. Am. Soc. Hortic.
Sci. 108: 347-351.
Rombout, P. J. A., Lioy, P. J.; Goldstein,
B. D. (1986). Rationale for an eight-hour ozone standard. J.
Air Pollut. Control Assoc. Vol. 36, no. 8, pp. 913-917.
U.S. Environmental
Protection Agency (2006) Air Quality Criteria for Ozone and Related
Photochemical Oxidants. Research Triangle Park, NC: Office of
Research and Development; report no. EPA/600/R-05/004af.
