### United States Office of Research and EPA/600/8-88/105F 

# Environmental Protection Development January 1992 Agency Washington DC 20460



### N,

# EPA/600/8-88/ 105F JANUARY 1992



# SLTMIVIARY OF SELECTED NEW INFORMATION

ON EFFECTS OF OZONE ON HEALTH AND VEGETATION

Supplement to Air Quality Criteria for Ozone and Other Photochemical Oxidants

Environmental Criteria and Assessment Office Office of Health and Environinental Assessment U. S. Environmental Protection Agency Office of Research and Development Research Triangle Park, NC 27711

K* Printed on Recycled Paper

# DISCLAIMER

This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. Mention of trade narnes or commercial products does not constitute endorsement or recommendation for use.

ii

# CONTENTS 

# Page

LIST OF TABLES

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv ABSTRACT

....................................... v AUTHORS ........................................ vn CONTRIBUTORS AND REVIEWERS . . . . . . . . . . . . . . . . . . . . . . . vii
1. SUMMARY OF SELECTED NEW INFORMATION ON EFFECTS OF OZONE ON HEALTH AND VEGETATION . . . . . . . . . . . . . . . . 1-1 1.1 INTRODUCTION ............................ 1-1 REFERENCES ................................... 1-2
2. EFFECTS OF OZONE ON VEGETATION . . . . . . . . . . . . . . . . . 2-1 2.1 STUDIES RELEVANT TO SELECTION OF THE AVERAGING TIME FOR THE SECONDARY NAAQS FOR OZONE ............................... 2-1 2.2 SUMMARY AND CONCLUSIONS: VEGETATION EFFECTS

............ ............... ... 2-9 2.2.1 Exposure Duration . . . . . . . . . . . . . . . . . . . . . . . 2-9 2.2.2 Peak Concentrations . . . . . . . . . . . . . . . . . . . . . . 2-10 2.2.3 Comparison of Exposure Indices . . . . . . . . . . . . . . 2-11 2.2.4Evaluation of the 7-Hour (or 12-Hour) Seasonal Mean . . . . . . . . . . . . . . . . . . . . . . . . . 2-11 REFERENCES ................................... 2-13
3. EFFECTS OF OZONE ON HEALTH

. . . . . . . . . . . . . . . . . . . . . 

# 3-1 3.1 HEALTH STUDIES RELEVANT TO SELECTION OF THE PRIMARY NAAQS FOR OZONE

. . . . . . . . . . . . . . . 

# 3-1 3.1.1 Human Clinical Studies

. . . . . . . . . . . . . . . . . . . . 

# 3-1 3.1.2 Field and Epidemiological Studies

. . . . . . . . . . . . . 

# 3-27 3.1.3 Laboratory Animal Studies

. . . . . . . . . . . . . . . . . . 

# 3-43 3.1.3.1 Effects of Multihour Exposures

. . . . . . . . 

# 3-43 3.1.3.2 Effects of Multiday Exposures

. . . . . . . . . 

# 3-45 3.1.3.3 Effects of Chronic Exposure to Ozone .... 3-46 3.1.3.4 Animal-to-Human Extrapolation

. . . . . . . . 

# 3-52 3.2 SUMMARY AND CONCLUSIONS: HEALTH EFFECTS DATA.................................... 3-56 3.2.1 Exposure Dynamics for Short-Term Ozone Exposure Effects

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

# 3-57 3.2.2 Evaluation of Differential Susceptability of Potential Special Risk Groups

. . . . . . . . . . . . . . . . 

# 3-61 3.2.3 Ozone Impacts on Lung Structure/Chronic Disease Processes

............................ 3-62 3.2.4 Ozone Dosimetry Aspects

. . . . . . . . . . . . . . 

# 3-64 REFERENCES

................................... 3-65

iii

# LIST OF TABLES

u _ _ er 

# Pa

~ 

# e

3-1 Controlled Human Exposure Laboratory Studies Relevant to

Review of the 1-Hour NAAQS for Ozone

. . . . . . . . . . . . . . 3-3 3-2 Key Human Studies Demonstrating Lung Function

Decrements Near the Current 1 Hour NAAQS for Ozone ..... 3-10 3-3 Field and Epidemiologic Studies on Effects of Ozone

....... 3-28 3-4 Experimental Animal Studies on the Relative Influence

of Ozone Concentration and Duration of Exposure ......... 3-44 3 5 Chronic Ozone Effects in Experimental Animals

.......... 3-47 3-6 Studies Relevant to Potential Animal-to-Human

Extrapolations

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-53

1V

# ABSTRACT

Since completion of the 1986 air quality criteria document for ozone, additional information has become available that warrants consideration by the U.S. Environmental Protection Agency (U.S. EPA) in its review of the National Ambient Air Quality Standards (NAAQS) for ozone. This summary reviews and evaluates selected literature published from 1986 through early 1989 on the vegetation and health effects resulting from exposure to ozone. Emphasis has been placed on evaluation of key human health effects literature and other data most pertinent to determination by U.S. EPA of the appropriate level and form of the primary NAAQS and the appropriate form of the secondary NAAQS.

v

# AUTHORS

Dr. Daniel L. Costa, Health Effects Research Laboratory, OHR, ORD, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711. Dr. Lawrence J. Folinsbee, C. E. Environmental, Inc., Suite 200, 800 Eastowne Drive, Chapel Hill, North Carolina 27514. Mr. James A. Raub, Environmental Criteria and Assessment Office, MD-52, OHEA, ORD, U.S. Environrnental Protection Agency, Research Triangle Park, North Carolina 27711. Ms. Beverly Tiiton, Environmental Criteria and Assessment Office, MD-52, OHEA, ORD, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711. Dr. David T. Tingey, Environmental Research Laboratory, OEPER, ORD, U.S. Environmental Protection Agency, 200 S.W. 35th Street, Corvallis, Oregon 97333.

.



# CONTRIBUTORS AND REVIEWERS
Dr. Robert S. Chapman, Dr. Timothy R. Gerrity, Dr. Carl G. Hayes, Dr. Donald H. Horstman, Dr. Hillel S. Koren, Dr. William F. McDonnell, Dr. Frederick J. Miller, and Dr. John H. Overton, Health Effects Research Laboratory, OHR, ORD, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711. Dr. Lester D. Gra.nt and Dr. Judith A. Graham, Environmental Criteria and Assessment Office, OHEA, ORD, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711. Dr. Milan J. Hazucha, Center for Environmental Medicine and Lung Biology, The University of North Carolina, Chapel Hill, North Carolina 27514. Dr. William Hogsett, Environmental Research Laboratory, OEPER, ORD, U.S. Environmental Protection Agency, 200 S.W. 35th Street, Corvallis, Oregon 97333. Dr. Allan Marcus, Battelle-Applied Statistics, 200 Park Drive, P.O. Box 12056, Research Triangle Park, North Carolina 27709. Dr. James H. Ware, Harvard University, School of Public Health, Department of Biostatistics, 677 Huntington Avenue, Boston, Massachusetts 02115.

vil

# 1. SLTMIVIARY OF SELECTED NEW INFORMATION

ON EFFECTS OF OZONE ON HEALTI-I

AND VEGETATION

1.1 INTRODLTCTION The U.S. Environmental Protection Agency (U.S. EPA) document, 

# Air Quality Criteria

, 

# for Ozone and Other Photochemical Oxidants, completed in August 1986 providedcomprehensive evaluation of the relevant scientific literature on ozone published through mid1986 (U.S. Environmental Protection Agency, 1986). The criteria document was prepared by the Office of Research and Development for use as the scientific basis for decision making by the Agency regarding retention or revision of primary and secondary National Ambient Air Quality Standards (NAAQS) for ozone. Since coinpletion of the 1986 document, additional information has become available that warrants consideration by the Agency in its review of the NAAQS for ozone. As a supplement to the 1986 document, this summary reviews and evaluates published literature concerning exposure- and concentration-response relationships observed for vegetation effects and for health effects in humans and experimental animals. Emphasis has been placed on evahiation of new human health effects literature and other data most directly pertinent or useful for determining the appropriate level and form of the primary standard and the . appropriate form of the secondary standard. Selected important data on dosimetry and on experimental animal studies that elucidate concentration x tilne (duration) exposure-response relationships have also been included. As required by the Clean Air Act, an earlier external review draft of this Supplement (U.S. Environmental Protection Agency, 1988) was publicly peer-reviewed by the Clean Air Scientific Advisory Committee (CASAC) of U.S. EPA's Science Advisory Board (McClellan, 1989). The publications reviewed and evaluated in this supplement were selected from approximately 500 new articles and abstracts on the health effects of ozone and from about300 new articles and abstracts on the vegetation effects of ozone that appeared as peerreviewed journal publications Qr as proceedings papers from 1986 through early 1989. Since

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# the time of review by CASAC, several of the abstracts and articles previously cited in the

draft supplement as "in press" or "submitted for publication" have been publisl'aed. In such cases, the citation has been updated in this final version of the supplement, including several revised citations of 1989 (a.nd a few later) publications.



# R.EF'ERENCES IVIcClellan, R. O. (1989) [Letter of CASAC closure on the 1988 ozone criteria document supp:lement to William K. Reilly, Administrator, U.S. Environmental Protection Agency]. Washington, DC: U.S. Environmental Protection Agency, Clean Air Scientific Advisory Conunittee; May 1. U.S. Environmental Protection Agency. (1986) Air quality criteria for ozone and other photoclhemical oxidants. Research Triangle Park, NC: Office of Health and Environmental Assessment, Environmental Criteria and Assessnient Office; EPA report nos. EPA-600/8-84-0200-ef. Available from: N'7CIS, Springfield, VA; PB87-142949. U.S. Environmental Protection Agency. (1988) Summary of selected new information on effeci:s of ozone in health and vegetation: draft supplement to air quality criteria for ozone and other photochemical oxidants. Research Triangle Park, NC: Office of Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no. EPA-600/8-88/105A. Available from: NTIS, Springfield, VA; PB89-135123.

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# 2. EFFECTS OF OZONE ON VEGETATIOIlT

2.1 STUDIES RELEVANT TO SELECTION OE THE AVERAGIIiTG TINIE F012 THE SECONDARY NAAQS EOla OZONE A review by Hogsett et al. (1988) discusses the biological, environmental, and exposure-dynamic factors (e.g., concentration, duration, frequency, threshold, respite time) that influence the magnitude of the biological responses of plants. These factors contribute to observed variability in responses, and thus become considerations in measures of exposure that best describe plant response to poliutant exposure. The various types of exposure indices that have been used historically to describe pollutant exposure were also evaluated. The ultimate goal of investigations of factors influencing plant response is to develop exposure indices that account for all of the variation in the exposure-response relationship. However, a second and more practical goal is that of developing or specifying indices useful for standard setting. An index for a standard should be simple, not site-specific, and as generic as possible. Musselman et al. (1986) examined the influence of two different patterns of ozone (0 3 ) 

# exposure on beans. The studies were conducted in a greenhouse and the plants were exposed to either a simulated ambient or a.uniform 0 3 concentration. The simulated ambient exposures followed the ambient exposure patterns of Riverside, CA (03 concentration range: 0.058 to 0.40 ppm; peak exposure duration: 0.5 to 1.5 h; and total exposure duration: 6 h). The uniform distribution was selected to match the total dose and peak concentration of the simulated arnbient exposure (0 3 concentration: 0.30 or 0.40 ppm; exposure duration: 2.3 h). Exposures occurred weekly, and the plants received one, two, or three exposures before being harvested 6 days after their last exposure. Both 0 3 exposures induced foliar injury and reduced plant growth; and the effects of the two distributions were not statistically different. Consequently, if the maximum concentrations and "total doses" are equal; peak shape appears not to be an important variable. Kohut et al. (1988) examined the effect of peak concentration and exposure frequency on the responses of kidney beans to 0 3 . The plants were exposed to one of four 0 3 exposure regimes: (1) constant exposure to 0.05 ppm daily; (2) fluctuating exposure to 0:08 ppm on

2-1

# alternate days (Monday, Wednesday, and' Friday); (3) cluster exposure to 0.08 ppm on three

consecutive days (Wednesday, Thursday, and Friday); and (4) exposure to 0.12 ppm on two consecutive days (Thursday and Fri.day) or charcoal-filtered air. The exposure duration was 4 h and yielded weekly mean concentrations between 0.05 and 0.06 ppm. The test plants were grown in pots and exposed to 0 3 in open-top chambers under field conditions. Plants were harvested weekly throughout the study. Although there were two replicates of each 0 3 treatment, the experiment was not replicated in time. In the early harvests„ the plants receiving the peak exposures were significantly impaired. By the final harvest (12 weeks), however, there were no significant effects of 0 3 on any of the plant growth or yield parameters. The authors concluded that the plants integrated the impacts, and, consequently, that "...the response of the plants was related to the mean rather than the peak concentration of exposure." This conclusion is difficult to substantiate with the data, as none of the 0 3 exposures produced a significant effect at the final harvest. It is therefore iiot possible to determine whether the various treatments differentially affected plant response. Heagle et al. (1986) studied the responses of soybeans to chronic doses oiF ozone applied in two different ways. Plants were grown in the field using standard National Crop Loss Assessment Network (NCLAN) methodology except for the way in whiclz the 0 3 was dispensed. In one set, various constant amounts of 0 3 were added to the ambient air for 7 h/day; for the second set, the 0 3 was increased above the ambient air by proportional amounts. Although there was a constant addition of 0 3 to the ambient air, in the constantaddition treatments, the resultant exposure regime was not "square wave" because the 0 3 concentxation in the ambient air varied throughout the exposure. The principle effect of the constant addition or proportional addition treatments was to create various levels of exposures. The 0 3 concentrations were expressed as the 7-h seasonal means. The authors concluded that the two different types of exposure regirnes produced identical responses. Several trends in the data, however, cast doubt on the validity of this conclusion. The authors clearly state that the proportional additions caused the more frequent occurrence of elevated concentrations, but their exposure index (the 7-h seasonal mean) failed to characterize or reflect this elevated exposure. In fact, the 7-h means for the proportional additions were lower than those for the comparable constant-addition treatments. The authors also reported that the slope of the "dose-re'sponse curve" for the proportional additions was

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# greater than for the constant additions. The authors speculated that an extension of the dose range might have shown significant results. The failure of the 7-h seasonal mean to adequately characterize the higher concentrations is not surprising beca.use a previous paper (Cure - et al. , 1986) from the same group states that the 7-h seasonal mean was selected specifically because it was less sensitive to variations in 0 3 patterns. Consequently, the conclusions of the authors must be viewed with skepticism. Heagle et al. (1987) also evaluated the influence on tobacco yield of daily 0 3 exposure duration and fluctuations in concentrations. Plants were grown in the field using standard NCLAN methodology except for the 0 3 -dispensing protocol. In one set of studies, various constant amounts of 0 3 were added to the ambient air for 7 h/day; to the second set, the 0 3 was increased above the ambient air by proportional amounts. In addition, the study compared the effects of 7- and 12-h exposures on tobacco yield. The 0 3 concentrations were expressed as the 7- and 12-h seasonal means. Yield was reduced to a greater extent by 12-h than by 7-h exposures. The authors concluded that the two different types of 7-h exposure regimes (7-h consta.nt and 7-h proportional) produced identical responses. Additional analyses of the soybean (Heagle et al., 1986) and tobacco (Heagle et al., 1987) data sets were carried out by Rawlings et al. (1988) to evaluate various exposure indices and the influence of exposure duration on plant response. The results from the soybean data and the 12-h studies with tobacco suggested that the peaks should be given greater weight. In contrast; the 7-h studies with tobacco suggested that the arithmetic mean was sufficient and that the peaks did not require additional weighting. Rawlings et al. acknowledged that these results must be viewed with caution, because the differences in exposure profiles between the constant and proportional 0 3 additions were relatively small, thus limiting the power of the experiment for determining the "best" exposure index. This same caveat also applies to the conclusions reached by the authors of the soybean (Heagle et a1., 1986) and tobacco (Heagle et al., 1987) studies. The analysis of exposure duration found that 12-h exposures caused greater effects than 7-h exposures (Rawlings et al., 1988). The negative impact of the exposures did not increase linearly with exposure duration (i.e., the decrease in yield loss was not directly proportional to the increased length of exposure). In a study by Adomait et al. (1987), white beans (Phaseolus vulgaris) were grown in field plots throughout southern Onta.rio, Canada. Piants at each location were treated with a

2-3

# chemical protectant, ethylenediurea. (EDU), to reduce or eliminate the impact of 0 3 on yield,

which was determined as the difference between the yields of EDU and non-EDU treated plots at each location. Ozone exposure was expressed as the cumulative 0 3 conicentrations above a threshold of 0.08 ppm for the month of August. Yield decreased as the cumulative 0 3 concentration increased. The addition of temperature and rainfall to the regression equation, in an attempt to approximate 0 3 flux into the plant, significantly improved the fit of the regression equation to the data. To express the experimental results, the authors assumed that the elevated 0 3 concentrations (peaks) were irnportant and that the. irnpact was the cumulative result of multiple exposures. Data used in a study by Cure et al. (1986) were generated using sta.ndard open-top chamber NCLAN protocols. The study did a three-way comparison of relationships among the 7-h seasonal mean, the 1-h seasonal rnean, and the 1-h maximum for the seELson. For two of the three comparisons, the 7-h/1-h ratio was essentially consta.nt, suggesting i:hat these two variables differed by a consta.nt. For the other comparison, the ratio was less stable. The authors concluded, however, that the 7-h and 1=h seasonal means were surrogate,s for each other. The ratio of the 1-h maximum to the 7-h seasonal mean was highly unstable, which suggests that the maximum was poorly related to the long-term mea.n. The authors selected a seasonal mean for two reasons: (1) They assumed that crop yield reductions resulted from an accumulation of daily 0 3 effects over the growing season; a.nd (2) the seasonal ineans were much less sensitive to peak variations in yearly 0 3 patterns, especially at concentrations near the current ambient levels. In a study by McCool et al. (1986), plants grown in a standard soil were exposed to a range of 0 3 levels in closed-top exposure chambers and the yields were determined. The authors developed yield-loss functions that related decreased crop yield to a curnulative exposure index for 12 crops. Ozone exposure was characterized as the cumulative concentrations greater than 0.10 ppm. The concentration threshold (0.10 ppm) was chosen because it was the California state 0 3 standard. A threshold concentration for 0 3 was used 

# to avoid giving equal mathematical weight to the numerous low concentrations a l rid to ignore the low nighttime background in calculating the exposure. In a field study using closed-top exposure chambers, McCool et al. (1987) assessed the impact of O g on four vegetables (turnip, beet, onion, lettuce). The exposure-response

2-4

# functions were best described as a linear function with increasing exp.osure. Both the sum of

the concentrations > 0.10 ppm and the 12-h seasonal mean concentration 

# were used in developing the exposure-response functions. Neither exposure index was uniformly best. A 3-year field study was conducted by Smith et al. (1987) in which the effects of 0 3 on foliar injury and yield were assessed using the chemical protecta.nt EDU. 

# Ozone exposure was characterized as the 7-h seasonal mean and as the cumulative exposure (using various concentration thresholds). The EDU treatment did not significantly enhance crop yieid. Yield and foliar injury, respectively, were similar among cultivars and over years. Although the ambient 0 3 exposures between 1983 and 1984 were substantiaily different, as indicated by the various cumulative statistics, this difference was not reflected in the 7-h seasonal mean. These data are a.nother example of the lack of sensitivity of the mean to temporal variations in 0 3 exposures: Open-top chambers were used by Wang et al. (1986a) in a field study to exarnine the effects of ambient 0 3 on the growth and foliar injury of three tree species. Ozone was characterized as the number of daily occurrences above 0.08 and 0.12 ppm. The authors concluded that 0 3 significantly impaired the growth of hybrid poplar in the absence of visible foliar injury. There were 20 days when 0 3 exceeded 0.08 ppm and 1 day when the concentration exceeded 0.12 ppm. In a 3-year study with quaking aspen, Wang et al. (1986b) found that plant growth was reduced 12 to 24 %. In only one of the years was the current National Ambient Air Quality Sta.ndard for 0 3 exceeded. The observations that growth reductions can occur in the absence of the ambient 0 3 concentration exceeding the level of the current standard are consistent with the recent analysis of Lee et al. (1989), which forecast significant effects oir crop yield when the standard was not exceeded. Only a limited number of studies have been conducted with the specific objective of developing or evaluating various exposure indices; several studies have reanalyzed existing exposure-response data to evaluate a range of exposure indices. The results of these retrospective analyses have provided useful concepts and their conclusions are in general agreement. Because the experiments analyzed were not specifically designed to evaluate various indices; the differences among the actual exposure treatments (frequency of 0 3 occurrences) may be relatively small. Consequently, the power of these studies is less than desirable.

2-5

# Reanalysis of several NCLAN data sets (soybean a.nd wheat from Argonne, IL; cotton

from Shafter, CA; and alfalfa from Corvallis, OR) was performed by Lee et al. (1987) using various mean and cumulative peak-weighted exposure indices (e.g., concentrati<in threshold and funetional pealc weighting). Exposure indices that included all the data (24 h) performed better than those that used only 7 h of data. The 7-h seasonal mean was never "best" and was near optimal in only 5 of 14 cases. From a modeling standpoint, the exposure indices that emphasized peaks performed better than those that gave equal weighting to al1 eoncentrations; indices that accumulated the exposures performed better than those that averaged the exposures. In a more extensive retrospective a.nalysis of NCLAN data, Lee et al. (1988) fit 24 common and 589 general phenologically weighted, cumulative-impact (GPW(CI) exposure inclices to the response data from seven crop studies (2 years of data for each). The "best" exposure indices were those that displayed the smallest residual sums of square error when the yield response data were regressed on the various 0 3 exposure indices using the BoxTidwell model. The "best" exposure index was a GPWCI with sigmoid weighting on eoncentration and a gamma weighting function as a surrogate for changes in plaait sensitivity over time. Cumulative indices (with concentration thresholds) performed as well as the GPWCIs, whereas mean indices did not perform as well. The general conclusions of the autliors were, "While no single index was deemed "best" in relating ozone exposure to plant response, the top-performing indices were those indices that (1) cumulated the hourly ozone concentrataons over time, (2) used a sigmoid weighting scheme which emphasizes concentrations of 0.06 ppm and higher, and (3) phenologically weighted the exposure such that the greatest weight occurs during the plant growth stage. These findings illustrate the importance of the duration of exposure, the importa.nce of repeated peaks, and tYte time of increased sensitivity in assessing the impact of ozone on plant growth. " Although peak concentrations should be given greater weight, the authors suggested that lower concentrations sltould also be included but given lesser weight in the calculation of a.n exposure index. The paper by Tingey et al. (1989) is essentially a condensation of the paper by Lee et al. (1988) and therefore the conclusions are basically the same. However, the: paper does show the iinportance of exposure duration in influencing the magnitude of plant response and the limitation of the seasonal mean to specifically incorporate varying exposure d:urations.

2-6

# For example, the mean cannot distinguish among exposures to the same average concentrations over different durations (e.g., for 

# 10, 50, or 100 days). Wheat and soybea.n data sets (Kohut et al., 1987, 1986) collected using standard NCLAN protocols at Ithaca, NY, were reanalyzed by Lefohn et al. (1988a) to compare exposure indices. The authors used the 7-h mean a.nd cumulative statistics with thresholds, or peak weighting. The data were fit with both linear and Weibull response models. No one exposure statistic was best for all data sets or response models. The linear model showed no strong tendency to fit any exposure index; however, a peak-weighted statistic and the number of occurrences > 0.08 ppm or the sum of the concentrations > 0.08 ppm had a higher R 2than the 7-h seasonal statistic. When the Weibull model was used, the cumulative statistics performed better than the seasonal means. The authors also concluded that a sigmoid peak-weighted scheme was better than a threshold approach because it included the effects from the concentrations below the selected threshold concentration but gave thern less weight. The paper by Lefohn et al. (1988a) has engendered discussion in the literature about the interpretation of the data (Runeckles, 1988; Parry and Day, 1988). Both groups of respondents thought that the paper contained insufficient data and evidence to support the conclusion that peak-weight exposure indices should be used in developing exposure-responsefunctions. However, Runeckles tempered his criticism with the observation that peakweighted 'indices perforined at least as well as inean indices. Also, the respondents criticized the cornpilation of the 2 years of wheat data into a single model when the exposure durations were markedly different. In response, Lefohn et al. (1988b) stated that the wheat data support the need to include a cumulative component in an exposure index. They concluded that, "The cumulative index is more relevant to use in the standard-setting process than seasonal means, which ignore the length of the exposure period." Musselman et al. (1988) conducted a retrospective analysis of crop loss data originally collected by Oshima et al. (1976) (see U.S. Envirorimental Protection Agency, 1986). The analysis was based on data for five crops, but those data were not replicated in time. The plants were grown in pots in standardized soil and were provided with adequate water and nutrients. The plants were placed at 9 to 12 sites along an ainbient 0 3 concentration gradient in the Los Angeles Basin. The crop loss data were originally summarized by Oshima et al.

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# (1976) on the basis of the cumulated concentration above 0.10 ppm for the growing season.

In this study, the authors tested (1) various peak indices, (2) daily mean indices, and (3) indices based on subsets of a 24-h day: No single exposure index was "best" for the five crops. Ozone indices utilizing a concentration threshold level performed well for most crops, but the optimum threshold level varied with the particular index calculated. Some of the "better" indices were (1) seasonal mean of concentrations above 0.09, 0.12, or 0.14 ppm; (2) mean of all daily peak concentrations; (3) sum of the daily peaks squared above a concentration of 0.15 ppm; and (4) total number of seasonal peaks above 0.12 pprn. The 7- or 12-h seasonal means were not among the better-performing indices. Lazsen et al. (1988) evaluated 14 0 3 exposure indices for their ability to predict crop yield loss. The second highest daily maximum concentration and 13 other indices, including the effective mean 0 3 concentration and the summer daytime average (M7), we:re calculated for 80 "agricultural" National Aerometric Data Bank sites and for multiple years, for a total of 320 site-years. In contrast to other retrospective analyses, separate exposure.-response functions were not derived from biological data for each exposure index. Larsen et al.. (1988) used ambient air monitoring data to derive correlations between the effective mean and other air quality indices. These correlations (based only on ambient air monitoring data) were used to express the plant response data in terms of the different indices (i. e. , the lognorinal model that expressed crop reduction as a function of the effective mean concentration [Larsen and Heck, 1984] was used to generate crop loss estimates for the 320 site-years of ambient data). Because there was no ,biological variation in the data, correlations between the exposure indices and estimated crop reductions were, in fact, measures of association between the (transformed) effective mean and the other indices. Consequently, no evidence that the mean indices were better correlated with plant response than other indices can be inferred from the analysis of Larsen et al. (1988). Larsen et al. (1983) developed an exposure-response model that relates 0 3 impact on plants to a cumulative index that they denoted as the total impact. A 75-day exposure for 7 h/day was originally assumed for calculating the estimated crop reduction for soybean (this may not be representative of the phenological life span of soybean). In the original analysis, the effective mean was not calculated from the hourly 0 3 concentrations for the NCLAN studies but was estimated by multiplying M7 by 1.15 for charcoal-filtered and nonfiltered

:

# exposures (and supplementing the nonfiltered exposures with the constant additions for other exposures). Further, treatment means rather than chamber means were used 

# in estimating the lognormal rnodel. Consequently, this lognormal model is inaccurate and needs to be estimated more precisely for use in the selection of exposure indices for use as 

# a 0 3 standard. The adequacy of the lognormal model using other exposure indices must also be determined. Reich and Amundson (1985) have reviewed a series of field and controlled-environment studies to assess the impact of 0 3 on photosynthesis. The authors stated, "...it may be inappropriate as well as difficult to compare directly the response of the species on the basis of a mean 0 3 exposure concentration. However, when the responses are compared on the basis of a unit dose of 0 3 , the results are more easily interpreted. " A unit dose of 0 3 as defined by the authors means cumulative exposure (i.e., total parts per million). The 0 3 -induced decrease in growth was directly related to reduced photosynthesis, which was decreased by the cumulative 0 3exposure.



# 2.2 SUMMARY AND CONCLUSIONS: VEGETATION EFFECTS Recent literature concerning the appropriate averaging time for an exposure index for 0 3 effects on vegetation was evaluated in relation to (1) the role of dxposure duration, (2) the role of peak 0 3 concentrations, (3) comparison of exposure indices, and (4) evaluation of the 7=h seasonal mean. 

# 2.2.1 Exposure Duration Increasing the duration in the exposure index from a 7-h seasonal mean to a 12-h seasonal mean caused a greater decrease in yield. A comparison of 7- and 24-h exposureindices showed that 24-h indices provided an even better statistical fit to the exposureresponse data. Although plant effects increased with exposure duration, the study of Rawlings et al. (1988) showed that the increase in plant response was not proportional to the increase in exposure duration. All the recent studies that used impaired plant growth or yield as an adverse effect specifically selected exposure indices that might reflect the cumulative impact of effects throughout the growing season. For example, Cure et al. (1986) stated that crop yield

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# reductions result from an accumulation of daily 0 3 effects over the growing se:ason. Reich

and Amundson (1985) stated that the 0 3 -induced decrease in growth was directly related to reduced photosynthesis, which was impaired by the cumulative 0 3 dose. These data can be interpreted to mean that growth and yield are reduced by repeated 0 3 episodes, because that is how 0 3 occurred in the.studies and how it occurs in nature. These studies support the conclusion that a cumulative 0 3 exposure index is needed that reflects the total exposure that the plant experiences. This conclusion is consistent with the 1986 U.S. EPA criteria document (U.S. Environmental Protection Agency, 1986), which states, "When plant yield is considered, the ultirnate impact of an air pollutant on yield depends on the integrated irripact of the pollutant exposures during the growth

~ 

# of the plant. " By inference or deduction, then, a mean of unspecified time (days or months) is iziappropriate because the lack of specification of "time" results in a variable duration of

, 

# 0 3 accumulation.


# 2.2.2 Peak Concentrations IVlost of the recent studies, except for papers reporting results of the NCLAN program, selected exposure indices that cumulated the exposure and preferentially weighted the peaks. Three main peak-weighting approaches have been used: (1) a concentration threshold approach, in which the concentrations above the selected threshold are sumrneci or in which the number of days or hours above the concentration threshold are summed; (2) an allometric or exponential weighting, in which all concentrations are raised to a specific exponential power; and (3) a sigmoid weighting, in which all concentrations are weighted with a multiplicative weighting factor (which depends on concentration). The threshold weighting approach assumes that only the concentrations above the selected concentration threshold are biologically active. Recent studies have sh.own that the concentrations below the selected concentration threshold or cutoff may also ha.ve biological iniportanee. It is also likely that the appropriate concentration threshold differs between species, with environmental conditions, and with endpoint measured. Functional weighting approaches using either an allometric or sigmoid we.ighting are preferred to the concentration threshold approach. These approaches do not censor concentrations, but rather give weight, although not equal, to all concentrations in eliciting a



# 2-10

# biological response. Specific comparisons of the functional weighting to the threshold

approaches showed that they yielded better statistical fits to the data. Also, the sigmoid weighting functions appeared to perform better than the allometric weighting approach. The conclusions found in recent literature regarding the importance of cumulative peak concentrations in causing vegetation responses are consistent with the data and conclusions presented in the 1986 criteri.a document (U.S. Environmental Protection Agency, 1986). 

# 2.2.3 Comparison of Exposure Indices There have been several studies (Lee et al., 1987, 1988, 1989; Lefohn et al., 1988a; 1VIusselman et al., 1988) conducted that were retrospective analyses of existing plant-response data sets. These authors evaluated the relative efficacy of existing and proposed exposure indices, using a large number of crop data sets. The exposure indices included various means and cumulative statistics using both threshold and functional concentration weighting. The authors concluded that there was no single exposure index that was best for all crop species or for all data sets. These studies are all in agreemeint, however, that (1) mean indices are not among the best indices and (2) the preferred (yielded best statistical fit to the data) exposure indices curnulated the exposure impact over the growing season and preferentially weighted the peak concentrations. 

# 2.2.4 Evaluation of the 7-Hour (or 12-Hour) Seasonal Mean The 7-h seasonal mean is the most commonly used exposure index in the literature reviewed in the 1986 U.S. EPA criteria document (U.S. Environmental Protection Agency, 1986), and it continues to be used by investigators. Mathematically, the mean contains all hourly concentrations making up the exposure period and treats all concentrations equally, thus implying that (1) all concentrations of 0 3 (across the range of concentrations to which plants are exposed in a growing season) are equally effective in causing a response, and (2) the contributions of the peak concentrations to the response are minimal. The mean treats low-level, long-term exposures the same as high-concentration, short-term exposures; a scenario that the literature does not support (e.g., the 1986 U.S. EPA criteria document). An infinite number of hourly distributions, from those containing many peaks to those containing none, can yield the same 7-h seasonal mean. Cure et al. (1986) reported that mean

2-11

# characteriza.tions of 0 3 exposure were much less sensitive than the daily 1-h maximum to

variations in yearly 0 3 patterns. Also, Reich and Amundson (1985) stated, "...it may be inappropriate as well as difficult to compare directly the response of species on the basis of a mean 0 3 exposure concentration. However, when the responses are compared on the basis of a unit dose of 0 3 , the results are more easily interpreted. " The use of a mean exposure index for characterizing exposures implies cex

- tain assumptions.

1. A. seasonal mean assumes that crop yield reductions result from the accumulation of daily 0 3 effects over the growing season (Cure et al. , 1986). 2. A mean assumes that the distribution of hourly 0 3 concentrations (over the averaging time) are not highly skewed and that the distribution 

# is uniinodal. In the ambient, the 0 3 concentration distributions are frequently skewed toward the higher concentrations. 3. The mean weights all concentrations within the selected averaging tirne equally. 4. The mean does not specifically include an exposure duration compone:nt; it camiot distinguish between two exposures to the same concentration but of different durations (e.g., 50 or 100 days). 5. The mean assumes that the selected time interval, over which the concentrations are averaged, is the period of highest hourly occurrences of 0 3 or any other pollutant being examined. 6. The mean index assumes that peak events do not need to be given spe.cial consideration. This is not consistent with results showing that short-terin peak concentrations are important in determining vegetation response (see, e.g., the 1986 U.S EPA criteria document).
The correlation between the 7-h seasonal mean (M7) and the second-highest daily maximum 1-h concentrations (i. e. , HDM2, the current 0 3 standard) was low (r = 0.54) due to the insensitivity of peak concentrations in the M7 calculation (Lee et al., 1989). A wide range of temporal distributions with HDM2 between 0.06 and 0.24 ppm was found at sites with M7 values between 0.036 and 0.048 pprn. Temporal distributions of ambient 0 3 data at 83 nonurban sites showed large spatiai differences across these sites, with the HDM2 ranging

2-12

# from 0.06 to 0.24 ppm. In contrast, the 7-h seasonal mean (M7 calculated from May to

September) across the 83 sites showed small differences (i.e., 90% of the sites had M7 values between 0.03 a.nd 0.06 ppm).



# REFERENCES Adomait, E. J.; Ensing, J.; Hofstra, G. (1987) A dose-response function for the impact of 0 3 on Ontario-grown white bean and an estimate of economic loss. Can. J. Plant Sci. 67: 131-136. Cure, W. W.; Sanders, J. S.; Heagle, A. S. (1986) Crop yield response predicted with different characterizations of the same ozone treatments. J. Environ. Qual. 15: .251-254: Heagle, A. S.; Lesser, V. M.; Rawlings, J. O.; Heck, W. W.; Philbeck, R. B. (1986) Response of soybeans to chronic doses of ozone applied as constant or proportional additions to ambient air. Phytopathology 76: 51-56. ` Heagle, A. S.; Heck, W. W.; Lesser, V. M.; Rawlings, J. O. (1987) Effects°of daily ozone exposure duration and concentration fluctuation on yield of tobacco. Phytopathology 77: 856-862. Hogsett, W. E.; Tingey, D. T.; Lee, E. H. (1988) Ozone exposure indices: concepts for development and evaluation of their use. In: Heck, W. W.; Taylor, O. C.; Tingey, D. T., eds. Assessmeiit of crop loss from air pollutants: proceedings of an international conference; October 1987; Raleigh, NC. New York, NY: Elsevier Applied Science; pp. 107-138. Kohut, R. J.; Amundson, R. G.; Laurence, J. A. (1986) Evaluation of growth and yield of soybean exposed to ozone in the field. Envi'ron. Pollut. Ser. A 41: 219-234. Kohut, R. J.; Amundson, R. G.; Laurence, J. A.; Colavito, L.; Van Leuken, P.; King, P. (1987) Effects of ozone and sulfur dioxide on yield of winter wheat. Phytopathology 77: 71-74. Kohut, R. J.; Laurence, J. A.; Colavito, L. J. (1988) The influence of ozone exposure dynamics on the growth and yield of kidney bean. Environ. Pollut. 53: 79-88. Larsen, R. I.; Heck, W. W. (1984) An air quality data analysis system for interrelating effects, standards, and needed source reductions: part S. an effective mean 0 3 crop reduction mathematical model. J. Air Pollut. Control. Assoc. 34: 1023-1034. Larsen, R. I.; Heagle, A. S.; Heck, W. W. (1983) An air quality data analysis system for interrelating effects, standards, and needed source reductions: part 7. an 0 3 SO z leaf injury mathematical model. J. Air Pollut. Control Assoc. 33: 198-207. Larsen, R. I.; McCurdy, T. R.; Johnson, P. M.; Heck, W. W. (1988) An air quality data analysis system for interrelating effects, standards, and needed source reductions: part 10. potential ambient 0 3 standards to limit soybean crop reduction. JAPCA 38: 1497-1503. Lee, E. H.; Tingey, D. T.; Hogsett, W. E. (1987) Selection of the best exposure-response model using various 7-hour ozone exposure statistics. Research Triangle Park, NC: U.S. Environmental Protection Agency, Office of Air Quality Pianning and Standards.



# 2-13

## Lee, E. H.; Tingey, D. T.; Hogsett, W. E. (1988) 'Evaluation of ozone exposure indices in exposure-response modeling. Environ. Pollut. 53: 43-62. Lee, E. H.; Tingey, D. T.; Hogsett, W. E. (1989) Interrelation of experimental exposure and a:mbient air quality data for comparison of ozone exposure indices and estimating agricultural losses. Corvallis, OR: U.S. Environmental Protection Agency, Environmental Research Laboratoiy; EPYL report no. EPA-600/3-89-047. Available from: NTIS, Springfield, VA; PB89-195036. Lefohn, A. S.; Laurence, J. A.; Kohut, R. J. (1988a) A comparison of indices that describe the relationship between exposure to ozone and reduction in the yield of agricultural crops. Atmos. Environ. 22: 1229-1240. Lefohn, A. S.; Laurence, J. A.; Kohut, R. J. (1988b) Authors' reply [A response to comments by Runeckles, 1988b]. Atmos. Bnviron. 22: 1242-1243. IvIcC'ool, P. M.; Musselman, R. C.; Teso, R. R.; Oshima, R. J. (1986) Dete rminin 

## g crop yield losses from air pollutants. Calif. Agric. 40(July-August): 9-10. McCool, P. M.; Musselman, R. C.; Teso, R. R. (1987) Air pollutant yield-loss assessment for :Four vegetable crops. Agric. Ecosyst. Environ. 20: 11-21. Musselman, R. C.; Huerta, A. J.; McCool, P. M.; Oshima, R. J. (1986) Response of beans to simulated ambient and uniform ozone distributions with equal peak concentration. J. Am. Soc. Hortic. Sci. 111: 470-473. Musselman, R. C.; McCool, P. M.; Younglove, T. (1988) Selecting ozone exposure statistics for determining crop yield loss from air pollutants. Environ. Pollut. 53: 63-78. 

## Oshima, R. J.; Poe, M. P.; Braegelmann, P. K.; Baldwin, D. W.; Van Way, V. (1976) Ozone dosage-crop loss function for alfalfa: a standardized niethod for assessing crop losses from air pollutants. J. Air Pollut. Control Assoc. 26: 861-865. Parry, M. A. J.; Day, W. (1988) A comparison of indices that describe the relationship between exposure to ozone and the reduction in the yield of agricultural crops [Conunents on article by Lefohn et al., 1988]. Atmos. Environ. 22: 2057-2058. Rawlings, J. O.; Lesser, V. M.; Heagle, A. S.; Heck, W. W. (1988) Alternative ozone dose metrics to characterize ozone impact on crop yield loss. J. Environ. Qual. 17: 285-291. Reich, P. B.; Amundson, R. G. (1985) Ambient levels of ozone reduce net photosynthesis in tree and crop species. Science (Washington, DC) 230: 566-570. Runeckles, V. C. (1988) A comparison of indices that describe the relationship between exposure to ozone and reduction in the yield of agricultural crops [Comments on article by Lefohn et al., 1988]. Atmos. Environ. 22: 1241-1242. Snuth, G.; Greenhalgh, B.; Brennan, E.; Justin, J. (1987) Soybean yield in New Jersey relative ito ozone pollution and antioxidant application. Plant Dis. 71: 121-125.

2-14

## Tingey, D. T.; Hogsett, W. E.; Lee, E. H. (1989) Analysis of crop loss for alternative ozone exposure indices.

In: Schneider, T.; Lee, S. D.; Wolters, G. J. R.; Grant, L. D., eds. Atmospheric ozone research and its policy implications: proceedings of the 3rd US-Dutch international symposium; May 1988; Nijmegen, The Netherlands. Amsterdam, The Netherlands: Elsevier Science Publishers; pp. 219-227. (Studies in environmental science 35). U.S. Environmental Protection Agency. (1986) Air quality criteria for ozone and other photochemical oxidants. Research Triangle Park, NC: Office of Health and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report nos. EPA-600/8=84-0200-ef. Available from: NTIS, Springfield, VA; PB87-142949. Wang, D.; Bo +
- mann 

## , F. H.; Karnosky, D. F. (1986a) Regional tree

~ 

## rowth reductions due to ambient ozone: evidence from field experiments. Environ. Sci. Technol. 20: 1122-1125: Wang, D.; Karnosky, D. F.; Bormann, F. H. (1986b) Effects of atnbient ozone on the productivity of 

## Populus tremuloides Michx. grown under field conditions. Can. J. Ror. Res. 16: 47-55.



# 2-15

# 3. EFFECTS OF OZONE ON HEALTH

3.1 HEALTH STUDIES RELEYANT TO SELECTION OF THE PRIMARY NAAQS FOR OZONE 3.1.1 Human Clinical Studies The strongest and most quantifiable concentration-response data on the acute health effects of ozone (0 3 ) are provided by the controlled human exposure studies, in which significant decrements in pulmonary function have been reported (U. S. Environmental Protection Agency, 1986). In most of these studies, the greatest atterition has been focused on decrements in forced expiratory volume in 1 s(FEV 1 ) because this measure of lung function represents a summation of changes in both lung volume and resistance. At the lower 0 3 concentrations of interest for standard-setting (<0.12 pprn), however, the observed decrements in FEV 1 primarily reflect decrements in forced vital capacity (FVC), with little or no contribution from changes in airway resistance. These changes in FEV 1 are caused by a reduced inspiratory capacity that most likely results froin sensitization or stimulation of airway irritant receptors. Scientific evidence presented in the 1986 U.S. EPA criteria document (U.S. Environmental Protection Agency, 1986) established that pulmonary function decrements are generally observed in healthy adults after 1 to 3 h of exposure as a function of the level of exercise performed and the 0 3 concentration inhaled during the exposure. Decrements in lung function have been reported to occur in some groups of healthy adults at the current level of the standard (0.12 ppm) or somewhat higher. Also, pulmonary function decrements have been observed in children and adolescents at concentrations of 0.12 ppm and 0.14 ppm, respectively, with heavy exercise. At the lower 0 3concentrations in the range 0.12 to 0.16 ppm, the average group mean changes in lung function are generally small (<_6%), and the medical significance of these changes is a matter of controversy. Some individua.ls, however, are intrinsically more responsive to 0 3 than others and exhibit noticeably largerthan-average pulinonary function decrements than the rest of the group. Such larger (> 10%) decrements in lung function may be of some medical significance to the affected individuals.
3-1

# More recent controlled hu.man exposure studies appearing after the completion of the

1986 criteria document have further confirmed and extended the above types of fmdings, as well as denionstrating some additional new types of effects. The most pertinenr of these newer studies are summarized in Table 3-1. The newer studies noted in Table 3-1 add most extensively to our knowledge concerni.ng pulrnonary function decrements associated with acute 0 3 exposures near the current 1-h NAAQS for 0 3 . The newer pulmonary function decrement findings are summarized in Table 3-2 in relation to the earlier such findings previously discussed in the 1986 criteria document. Two of the more recent studies, by Linn et al. (1986) and Avol et al. (1987), add to the information reviewed in the 1986 U.S. EPA criteria document (U.S. Environmental Protection Agency, 1986) on lung function changes occurring in healthy childreh and young adults exposed to low concentrations of 0 3 while exercising at rnoderate to heavy loads. Datn presented by Linn et al. (1986) in a controlled huinan study of healthy young adultsexercising intermittently at heavy work loads have added more detailed concentrationresponse information at low 0 3 concentrations ranging from 0.08 to 0.16 ppm. The 0 3 responsiveness of subjects in this study falls somewhere between that of subj.ects studied by McDonnell et al. (1983) and of those studied by Kulle et al. (1985) under similar exposure conditions (see Table 3-2). These subjects were also less responsive than the group , previously studied by Avol et a1. (1984), who were exposed to similar concentra.tions of 0 3 but with continuous exercise for 1 h. Although the authors of this report could not offer a definitive explanation for differences among these studies, they pointed out that individual biological factors such as the presence of asthma or clinical respiratory allergies and bronchial reactivity in individual subjects, as well as external factors such as ambient exposure history or differeiices in controlled exposure conditions during the study, might contribute to differences in cohort responsiveness to 0 3 . It is obvious that more research is needed to better define the possible reasons for the large variations in responsiveness to 0 3 in individuals and the variations in group mean responsiveness across studies. Avol et al. (1987) presented data from a laboratory field study of healthy children (8 to 11 years old) exercising continuously for 1 h in ambient air containing a mean O g concentration of 0.11 ppm. The same authors (Avol et a1., 1985a,b) previously studied adolescent subjects (12 to 15 years old) under a similar protocol, although the

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## 3-14

# 0 3 concentration and exercise level were lower in the more recent study. No significant changes in respiratory function or symptoms were found in the group, probably because of the lower doses of 0 3 . Regression a.nalyses of individual data, however, suggested that individuals receiving high doses 

# of 0 3 had effects that were comparable to those found in adolescents and young adults, although no definitive comparisons could be made because of differing ambient exposure levels and large intersubject variability in responsiveness to 0 3

. 

# This finding is also consistent with the controlled exposure study by McDonnell et al. (1985a,b) indicating that the effects of 0 3 on lung spirometry in children were very similar' to those found in adults exposed under similar conditions, except that no significa.nt increases in symptoms were found in children. Therefore, based on the available pulmonary function data, young children and adolescents do not appear to respond differently to 0 3 than do adults. A series of`papers describing the effects of 0 3 on subjects greater than 50 years of ageappeared between 1986 and 1989 (Bedi et al., 1988; Bedi and Horvath, 1987; DrechslerParks et al., 1987, 1989; Reisenauer et al., 1988) (see Table 3-1). Bedi and Horvath (1987) described the decrease in pulmonary function response in a single subject studied at age 32 and again at age 40. The major iinportance of this study is that it dernonstrated a decline in response of considerable magnitude (AFEV 1 of —25 % decreased to —5 % over 8 years) that was observed longitudinally. This lends credence to the results of the cross-sectional studies indicating a decreased response in older subjects. Drechsler-Parks et al. (1987) compared a group of older (age 51 to 76) subjects exposed to 0.45 ppm 0 3 with a group of young adults studied under the same protocol (2-h intermittent exercise at 25 Llmin). The older subjects had substantially smaller changes in function than the younger subjects, both male and female. Changes in FVC in the older subjects averaged —5.3 % and in the young adults, —14.1 %. Similar differences were observed for other functional measurements. Similar data for 0 3 exposure are reported in a second paper by Drechsler-Parks et al. (1989). Bedi et al. (1988) reported the results of a study in which older subjects were exposed to this same 0 3 concentration (0.45 ppm) on three separate occasions. The responses were not reproducible from one exposure to the next. The group average did not change

3-15

# appreciably between exposure series, indicating that even though the older subjects have more

variable responses, they are less responsive to 0 3 , as a group, than younger subjects. Reisenauer et al. (1988) also studied a group of older subjects, age 55 to 74 years. These 0 3 exposures were conducted at 0.2 and 0.3 ppm 0 3 using a light intermittent exercise regime. There were no significant changes in FEV 1 0 . For the 0.3 ppm exposures, however, the female subjects (n = 10) had a slight rise (13 %) in total respiratory resistance that was statistically significant. The implication of these differences in responsiveness to 0 3 in older subjects is unclear. Only standard spirometry tests have been used to evaluate responses. It is not known if changes in airway resistance or airway responsiveness to methacholine or histamine are similarly attenuated in older subjects. The possibility of inflammatory responses has not been studied in these older subjects. Four additional publications (Eschenbacher et al., 1989; Kreit et al., 1989; Koenig et al., 1988; Koenig et al., 1987) report the results of controlled human exposure studies on the effects of 0 3 on asthmatics (see Tab1e 3-1). Also of interest is a new study of subjects with allergic rhinitis (McDonnell et al., 1987). Kreit et al. (1989) studied nine asthmatics exposed to 0.4 ppm 0 3 for 2 h while perforniing intermittent exercise with a ventilation of about 53 L/min. A11 subjects had a history of physician-diagnosed asthma and were sensitive to methacholine. Medications were withheld for at least 12 h prior to exposure. Nine nonasthmatic subjects were also studied under the same protocol. Both groups of subjects had significant decreases in FVC, FEV1, FEV 1 /FVC, forced expiratory flow at 25 to 75% of FVC (FEF25-75), and inspiratory capacity after 0 3 exposure. The changes in FEV i , FEV 1 /FVC, and FEF

~ 5 

# - 75 were more negative in the asthmatics than in the normals (e. g. , A% FEV 1 was —13.4 % in normals and —23.1 % in asthmatics). Specific airway resistance (SR aW ) was not significantly increased in normals but was in asthmatics after 0 3 exposure. A significant increase in SR aW also occurred after air exposure in the asthmatics. The change in SR aW after 0 3 was more than twice that after exercise in air (ASR aw air =+3.82, ASR aw ozone =+8:02 cm H 2 0/L/s). Both groups experienced a similar relative increase in methacholine responsiveness after 0 3 exposure, expressed as a decrease in the provocative rnethacholine concentration that

3-16

# causes a 100% increase in baseline SR a

,. 

# It is important to, note that these subjects underwent methacholine challenge both 90 min before and 90, min after exposure. It is not clear to what extent the preexposure challenge may have confounded the results, particularly because the nonasthmatics received a substantially larger dose of methacholine than the asthrnatics. Normal subjects appeared to have a depressed FEF25-7$ prior to exposure (=12% decrease after methachoiine challenge). There were no differences in 0 3 -induced symptom responses between normals and asthmatics. A second report of this study (Eschenbacher et al. , 1989) additionally included a description of the effects of indomethacin pretreatment in 0 3 -exposed normal subjects. The data for adult asthmatics were those reported by -Kreit et al. (1989). Indomethacin pretreatment in normals caused a marked decrease in 0 3 -induced spirometry changes (OFEV 1 — 0 3 

# = — 21. 5 % ; DFEV i — 0 3 

# + indomethacin = —10. 6 %) . However, there was also a surprising, but substantial, placebo effect, suggesting a possible behavioral component in 0 3 response. Indomethacin, an inhibitor of cyclooxygenase pathways of arachidonic acid metabolism, had no effect on the increase in airway responsiveness caused by 0 3 . Indomethacin appears to primarily block the "restrictive" (i.e., decreased FVC) effect of 0 3 and does not alter the bronchoconstrictive or airway reactivity responses. Of additional interest was the observation that "normal" subjects in the indomethacin study had an FEVi decrease, after an identical protocol, which was not unlike the response of the asthmatics, thus raising the question of the normality of the subjects or the possible confounding effect of a preexposure methacholine challenge. Further research is, therefore, needed to fully understand any potential differences in 0 3 responsiveness between asthmatic and healthy adult subjects. The responses of adolescent asthmatics to 0.12 ppm and 0.18 ppm 0 3 were tested by Koenig et al. (1987). The mouthpiece exposure sequence consisted of 30 min rest followed by 10 min exercise (minute ventilation 

# [ V E ] = 33 L/min). In addition to the 10 asthmatics, 10 healthy adolescents were also studied. There was a significant increase in total respiratory resistance (forced oscillation method) in both normals and asthmatics exposed to 0.18 ppin 0 3 . There were no significant changes in FEV l in either subject group. At 0.12 ppm 0 3 

# , there were no significant differences that could be attributed to 0 3 in either asthinatics or normals.

3-17

# Koenig et al. (1988) have also studied adolescent asthmatics (n = 10) and healthy



# adolescents (n = 10) exposed to either air, 0.12 ppm 0 3 , 0.3 ppm nitrogen dioxide (NO 2 ), 

# or the combination of 0 3 

# plus NO 2 . The mouthpiece exposures lasted 60 min and included two 15-min exercise periods during which ventilation averaged about 35 L/min. Medications were discontinued at least 4 h prior to exposure. In the asthmatics, an 11 % decrease in FEF50% was observed after 0.12 ppm 0 3 exposure. One of the subjects had an exceptionally large decrease in FEF 50% of —60%, which occurred approximately 20 min after the end of exposure. This same subject did not have a large change in FEF 50% when exposed to 03 plus NO 2 , suggesting that the response of this individual to 0 3 may have been anomalous. There were no other responses attributed to 0 3 in this study, either in normal or asthmatic subjects. The authors tentatively suggested that adolescent asthrnatics may be slightly more responsive to these low levels of 0 3 . However, replication of these observations will be required before this suggestion can be substantiated. McDonnell et al. (1987) studied 26 subjects with allergic rhinitis to determine if the presence of allergies was a predisposing factor for 0 3 sensitivity. These allergic subjects had airway responses to histamine that were similar to a comparable group of nonallergic subjects. Exposure to 0.18 ppm 0 3 for 2 h with heavy intermittent exercise caused increased responsiveness to histamine and a decrease in several spirometric variables. The only apparent difference between the allergic subjects and previously exposed nonallergic subjects was a significant increase in airway resistance in the allergic subjects. These data on allergic and asthmatic subjects suggest that both of these groups have a greater rise in airway resistance after 0 3 exposure than do normal subjects. The relative order of airway responsiveness to 0 3 is normal < allergic < asthmatic. Between 1987 and 1989, a series of reports were presented or published concerning a sttidy of apparent seasonal variation in 0 3 responsiveness in residents of Los Angeles (Avol et al., 1988; Hacl:ney and Linn, 1989; Hackney et al., 1989; Linn et al., 1988) (see Table 3-1). The definitive report of this study is the journal publication by Linn et al. (1988). From a large number of subjects tested for 0 3 responsiveness, 12 responsive and 13 nonresponsive subjects were selected to participate in further testing. Cbaracteristics of the subjects are presented below:

W-1

# Gender Age Health Status Mean •AFEV i

Nonresponders 8M/5F 5> 30 All Normal + 1% Responders 5M/7F 2> 30 4 Normal —12.4 % 6 Atopic 2 Asthmatic
In all tests, subjects were exposed to 0.18 ppm 0 3 during 2 h of intermittent heavy exercise (ventilation = 35 L/min/m 2body surface area [BSA]) at 35 °C and 35% relative humidity (RH). These 25 subjects participated in two more pairs of exposure to 0 3 and clean air. The initial tests were conducted in late spring (1986) and the followup tests occurred in late summer/early fall (1986) and again in winter (early 1987). A subsequent follow-up test with a smaller number of subjects (17 of the 25) occurred in spring (1987). The differences between responsive and nonresponsive subjects, which were of course significant at the time of the first test, were no longer significant at the first two follow-up studies in late summer and winter. This suggested the possibility that ambient oxidant exposure during the summer months produced an "adaptation" response that persisted for several months. This suggestion was further strengthened when a reduced number of subjects were exposed to 0 3 again, one year later. At this time, the responsive subjects appeared to regain their sensitivity to 0 3 exposure. The mean absolute changes in FEV 1 for the four exposures in the responsive subjects were —385, —17, +16, —347 mL respectively for the spring, fall, winter, and spring tests respectively. Corresponding changes for the iionresponders were +28, +90, +34, +81 mL. Because the experimental design was not optimal, these results need to viewed with caution and, as the authors state, "It is not clear that these results can be generalized." Nevertheless, these findings clearly suggest that results of experimental 0 3 exposures of residents of high oxidant areas must be viewed with caution if frequent ambient exposure was a possibility during the period of experimental exposure. Additional information presented by Hackney et al. (1989) indicated that 8 of the 12 responders were reactive to methacholine and had a history of respiratory. allergies. In addition, 10 of the 12 responders had a history of some syrnptomatic coinplaints when exposed to "smog". The authors suggested that allergy or atopy may be a risk factor for excess response to 0 3 although other studies have indicated that increased airway reactivity is not predictive of 0 3 responsiveness. They further speculated that nonresponders could be at gmLtm

# increased risk for chronic health effects of cumulative ambient 0 3 exposure because they

would be less likely to avoid such exposures because of their lack of symptomatic complaints. Controlled human exposure studies reviewed earlier in the 1986 U.S. EPA criteria clocument have suggested that some impairment of exercise performance may be associated with 0 3 exposure. Subjective statements made by individuals engaged in these controlled studies indicate that the perception of pain occurring with deep breathing may be an important factor that limits performance of continuous heavy exercise at 0 3 concentrations > 0.18 ppm. Studies by Gong et al. (1986) and by Schelegle and Adams (1986) substantiate these earlier findings, whereas a third study by Linder et al. (1988) suggests that small decrements in maximal exercise performance may occur at O, concentrations <0.18 ppm (see Table 3-1). Gong et al. (1986) found that maximal performance tested after exposure of endurance athletes continuously exercising at heavy work loads 

# ( V E = 89 L/min) for 1 h in a hot environment was impaired in 0.20 ppm 0 3 . This level of 0 3 exposure also reduced pulmonary function and enhanced respiratory symptoms and airway responsiveness to histamine. Maximal performance was not impaired after exposure in 0.12 ppm 0 3 , despite sma11 but significant group mean decrements (5.6 %) in FEV 1 . Sirnilarly, Schelegle and Adams (1986) found that exercise perforrriance, as determined by completion of the exposure protocol, was impaired following exposure of endurance athletes who were continuously exercising at heavy work loads 

# (V E = 87 L/min) for 1 h at 0 3 concentrations >0.18 ppm, but not at 0.12 ppm. Significant decrements in pulmonary function and increased respiratory symptoms also occurred at >0.18 ppm 0 3

. 

# The effect of 0 3 inhalation on performa.nce of maximum exercise tests was also studied by a group of Swiss investigators (Linder et al., 1988). Twenty-four subjects (12M, 12F) were studied while performing maximal incremental exercise tests. The maximum exposure duration was 28 min and the minimum was 16 min. The tests were performed 

# in clean air, 0.07 ppm 0 3 , and 0.13 pprn 0 3 in an environmental chamber (24 °C; 50% RH). Small, but significant (t-test), increases (2%) in FEV 1 o were observed after clean air exposure. Except for women exposed to 0.13 ppm (-1.4%), no changes in FEV 1 were observed with 0 3 exposure. Performance on the maximum exercise test was decreased 11 % in women and 7% in men at 0.13 ppm and 5% and 4%, respectively, at 0.07 pprn (p < 0.05, t-test). During the tests conducted at 0.13 ppm, there was also a small decrease (2.5 to 5%) in

3-20

# anaerobic threshold, defined as the workload at which the venous lactate concentration exceeded 4 mM. It is not clear to what extent the exercise performance test results may reflect behavioral responses to the odor of 0 3

. 

# There are a number of questions that may be raised about the paper by Linder et al. (1988). From the graphical presentation of the data on FEV i , it appears that no significant changes would be detected by an appropriate statistical a.nalysis (i.e., an analysis of variance appropriate for repeated measures, rather than multiple t-tests). The authors did not indicate whether appropriate precautions were taken to randomize or '°blind" the exposures. Furthermore, no information is provided about the selection criteria for subjects. Because the effects were reported for very low exposure concentrations and brief exposure durations (maximum 28 min) and because they appear to be out of line with previous studies of exercise performance during 0 3 exposure, it is important to determine if these qbservations can be verified. The data currently available indicate that reduction in exercise performance may occur in many well-conditioned athletes after performing continuous heavy exercise for 1 h at 0 3 concentrations >_0.18 ppm. These athletes are capable of sustaining very high exercise V E (i.e., > 80 L/min) for 1 h. Any performance decrements occurring at 0 3 concentrations <0.18 ppm are less certain and need to be verified. It must be noted, however, that other environmental conditions, such as increased ambient temperature and/or relative humidity, may independently affect subjective symptoms and may independently impair exercise performance. Therefore, it may be difficult to differentiate work performance effects caused by 0 3 from physiological or behavioral effects caused by other conditions in the environment. Studies utilizing longer exposure durations, particularly at lower levels of exercise, were not previously reviewed in the 1986 U.S. EPA criteria document. Among the newer studies, two (Folinsbee et al., 1988; Horstman et al., 1989, 1988) address the effects of 0 3 exposures for durations > 2 h(see Table 3-1). The first of these was designed to determine the effects of prolonged exposure to the present level of the 1-h NAAQS for 0 3 (0.12 ppm) on 10 young adult subjects that are representative of individuals who spend most of the day outdoors exercising at moderate intensities (e.g., adults performing heavy labor). Subjects were exposed to either 0.0 or 0.12 ppm 0 3 for a total of 6.6 h. During the exposure, the subjects exercised for six periods of 50 min each; each exercise period was followed by

3-21

# 10 min of spirometry testing and rest. An additiona135 min for lunch was interposed

between the third and fourth exercise period. The ventilation during the exercise averaged about 41.5 L/min and heart rate ranged from 108 to 124 beats/min. Prolonged exposure to 0.12 ppm 0 3 resulted in progressively larger changes in respiratory function and symptoms with time. By the end of 6.6 h of exposure, group mean. changes were as follows: FEV i had decreased 13.0%, FVC had decreased 8.3%, and FEF25 75% had decreased 17.4%. On forced inspiratory tests, forced inspiratory v,ital capacity and forced inspiratory volume in 0.5s were decreased 12.6 and 20.7%, respectively. Respiratory symptoms of cough and pain on deep inspiration increased with the increasing duration of 0 3 exposure. There was also -a marked increase (about twofold) in airway responsiveness to methacholine following 0 3 exposure. No changes were observed with clean air exposure. The changes in lung function reported at the end of exposure were similar in magnitude to those previously observed in healthy subjects performing at heavy levels of exercise ( V E

~ 

# : 60 L/min) in much higher 0 3 concentrations (> 0.2 ppm) for shorter durations (i.e., <2 h). The need for additional concentration-response information led to a subsequent study using the same 0 3 exposure protocol. Twenty subjects were exposed for 6.6 h to four 0 3 concentrations (0.0, 0.08, 0.10, a.nd 0.12 ppm) in random order. The results of this study were reported, in part, at the 1988 U.S.-Dutch symposium (Horstman et al., 1989) and at the 1988 Annual Air Pollution Control Association Meeting (Horstman et al., 1988). The ventilation in this study was slightly lower than in the first study, averaging .38.9 L/min. The FEV I.O decreased by 7, 7, and 12.3% at 0.08, 0.10, and 0.12 ppm, respectively. The airway resistance response to methacholine was increased by factors of 1.56, 1.89, and 2.21, respectively. There was also a significant increase in the symptom of pain u.pon deep breath, a typical symptom of acute 0 3 exposure. The study by Folinsbee et al. (1988) is the first clinical study to demonstrate increased airway reactivity to inhaled bronchoconstrictors in subjects exposed to low 0 3 concentrations for prolonged periods of time. Other studies reported in the recent literature have identified these effects in humans exposed to 0 3 for shorter durations (see Table 3-1). The study by McDonnell et al. (1987) described an increase in airway reactivity to histamine in 26 healthy subjects with allergic rhinitis who were exposed to 0.18 ppm 0 3 for 2 h while undergoing

3-22

# heavy 

# (V E = 64 L/min) intermittent exercise. Seltzer et a1. (1986), in a study of 10 healthy individuals exposed for 2 h to air and to either 0.4 or 0.6 ppm 0 3 while undergoing moderate intermittent exercise, observed an increase in the number of neutrophils in bronchoalveolar lavage (BAL) fluid 3 h after 0 3 exposure. Furthermore, they observed an increase in airway reactivity to methacholine following 0 3 exposure and their data were suggestive , of an association between the degree of inflammation and the increase in airway reactivity. A series of reports by Koren et al. (1989a,b; 1988a,b) described the inflammatory and biochemical changes in the airways consequent to 0 3 exposure (see Table 3-1). In these studies, subjects were exposed to 0.40 pprn for 2 h while performing intermittent exercise (15 min exercise, 15 min rest) at a ventilation of 70 L/min (35 L/min/m 2 BSA) (i.e., the same protocol as used by McDonnell et al., 1983). The main purpose, of these studies was to examine cellular and biochemical responses in the airways of ozone exposed subjects. To accomplish this, BAL was performed about 18 h after the 0 3 exposure. Standard lung function tests were also performed before a.nd after exposure. A mean decrease in FEV 1 of 960 mL after 0 3 exposure was reported. An eightfold increase in polymorphonuclear leukocytes (PMNs) was observed after 0 3 exposure, confirming the observations of Seltzer et al. (1986). 

# A twofold increase in protein, albumin, a.nd immunoglobulin G were indicative 

# of increased epithelial permeability as previously suggested by the technetium-labeled diethylene triamine pentacetic acid (DTPA) clearance studies of Kehrl et al. (1987) . In addition to confirmation of these previous findings, Koren et al. (1989b) provided evidence of stimuiation of fibrogenic processes including increases in fibronectin (6.4 x), tissue factor (2.1 x), Factor VII (1.8 x), and urokinase plasminogen activator (3.6x). There was a twofold increase in the level of prostaglandin E 2 and a similar elevation of the complement component C3a. Levels of the leukotrienes LTC 4 and LTB 4 were not affected. Koren et al. (1989a) reported that an inflammatory response, as indicated by increased levels of PMNs, was also observed in BAL fluid from subjects exposed to 0.1 ppm 0 3 for 6.6 h(same protocol as Folinsbee et al., 1988). Further evidence supporting the hypothesis that cyclooxygenase products of arachidonic acid metabolism (prostaglandins, thromboxane) may piay a role in 0 3 -induced spirometry cha.nges comes from a study by Schelegie et al. (1987). These investigators demonstrated a significant attenuation of decrements in FVC and FEV 1 o when subjects were treated with the

3-23

# cyclooxygenase inhibitor indomethacin prior to 0 3 exposure. Subjects were exposed to

0.35 ppm for 1 h of continuous exercise (60 L/min); FEV 1.0decreased 26.3% on the no-drug day, but only 10.6 % after indomethacin pretreatment. The above studies indicate that the inflammatory process caused by 0 3 exposure is promptly initiated (Seltzer et al., 1986) and persists for at least 18 h(Koren et al., 1989b). The time course of this inflammatory response and the 0 3 exposures necessary to initiate it, however, have not yet been fully elucidated. Furthermore, these studies deinonstrate that cells and enzymes ca.pable of causing damage to pulmonary tissues were increased and the ' proteins that play a role in the fibrotic a.nd fibrinolytic processes were elevated as a result of 0 3 exposure. Graham et al. (1988) showed an increase in PMNs in nasal lavage fluid collected from subjects exposed to 0.50 ppm for 4 h at rest. There was a 3.5-fold increase in nasal PMNs immediately after exposure and this increased further (6.5-fold) by the following day (i.e., 20 h later). This study suggests that a nasal inflammatory response may serve as a qualitative indicator of an inflammatory response in the lung. Kehrl et al. (1987) observed an increased rate at which inhaled technetium-labeled DTPA diffused from the airway and alveoli into the bloodstream in eight healthy subjects who endured heavy exercise for 2 h in 0.4 ppm 0 3 . Kehrl et al. (1989) reported results from an additional 16 subjects studied in the same manner. For the combined group of 24 subjects exposed for 2 h to 0.40 ppm 0 3 , the average rate of clearance of technetium-labeled DTPA was 1.08 %/min. This clearance rate was some 60 % faster than that observed after air exposure. The average 0 3 -induced decrement in FVC in these subjects was —10%. This study confirms that clearance of technetium-labeled DTPA is accelerated after 0 3 exposure and, in conjunction with the Koren et al. (1988a,b; 1989a,b) observations, strongly suggests that this accelerated clearance is due, in part, to an increased epithelial permeability within the lung. These changes in permeability are most likely associated with acute inflammation and could potentially allow better access of inhaled antigens and other substances to the submucosa. Results from studies of these endpoints at lower 0 3 levels have not been reported. These observations by Koren, Kehrl, and co-workers have raised the question of whether acute inflammation occurs following exposure to low levels of 0 3 for prolonged

3-24

# periods of time (> 2 h). Results from studies determining if these newly identified 0 3 effects are occurring at low 0 3 concentrations (i.e., <0.12 ppm) remain to be more fully reported and evaluated. This information will improve our understanding of the nature of inflammatory responses, including the biochemical and molecular changes in the lung, that occur in 0 3 -exposed subjects. Another series of papers by Gerrity and co-workers (Gerrity, 1987; Gerrity et al., 1988; Gerrity a.nd McDonnell, 1989) examining 0 3 uptake in _the respiratory tract have important implications for modeling the health effects of. 0 3 exposure in humans and for extrapolating data from animals to humans (see Table 3-1). Gerrity et al. (1988) studied 18 healthy young males to determine the fractional uptake of 0 3 by the upper respiratory tract (URT), excluding the larynx, and by the lower respiratory tract (I.,RT), including the larynx. In order to measure 0 3 concentrations during the breathing cycle, a. chemiluminescent 0 3 analyzer was modified to increase its response time. Gas was sampled at the level of the posterior larynx from a tube inserted through the nose. Mean inspired and mean expired (alveolar) values of pharyngeal 0 3 concentration were used to compute the fractional uptake of 0 3 in the URT and LRT. The investigators studied the effects of cha.nges in 0 3 concentration (0.1, 0.2, 0.4 ppm), 

# breathing frequency (12 and, 24 breaths per minute) and mode of breathing (nasal, oral, oronasal). The differences between the various treatment conditions were small; the average URT uptake was about 40 % and average LRT uptake was about 91 %(of the 0 3 that reached the larynx), resulting in an average total respiratory tract uptake of approximately 95 %.. (In other words, of the 0 3 entering the URT, about 40 % was removed. Of the remaining 60 % that reached the trachea, 91 % was removed. Total uptake is therefore 40 %+(0.91 x 60 %) = 95 %.) Increased frequency of breathing caused a decreased fractional removal of 0 3 in both URT and LRT, presumably because of decreased residence time in the airway and increased flow rate. The lowest fractional removal of 0 3 in the URT occurred during nasal breathing. The differences between nasal and oral or oronasal breathing, however, were very small. The lack of significa.nt differences between nasal and oral breathing on 0 3 -induced changes in lung function and respiratory symptoms was recently reported by Hynes et al. (1988), also suggesting that the mode of inhalation may not affect 0 3 uptake as much as previously expected.

3-25

# In a second paper, Gerrity a.nd McDonnell (1989) reported the influence of the

0 3 -induced change in breathing pattern on the 0 3 uptake efficiency. Subjects were exposed to 0.4 ppm 0 3 during continuous 60 min exercise at a ventilation of about 40 L/min. At the end of the exposure, there was a 25 % reduction in spontaneous tidal volume and a 45 % increase in breathing frequency. Associated lung function changes included a 13 % reduction in FVC and an 18% reduction in FEV l . The change in breathing pattern was accompanied by a 9% reduction in the LRT 0 3 uptake efficiency (fractional LRT uptake decreased from 68 % to 62 %). Total 0 3 uptake (about 80 %) was only reduced about 4% because there was a slight increase in 0 3 uptake in the URT. The reduction in LRT 0 3 uptake was correlated with the decrease in tidal volume, suggesting that an increased depth of inspiration increases the dose delivered to the LRT. The 0 3 uptake "efficiencies" reported in these two papers are not strietly comparable because the methods used to make the calculations of 0 3 uptake were different in each paper. The authors suggested that the reduction in tidal volume may act as a protective mechanism for the lower airways, but that the loss of this response with repeated exposures may permit increased 0 3 delivery to the lower respiratory tract. Gerrity (1987) described a model of nasopharyngeal uptake of 0 3 using data from various animal species, including humans. The conclusion reached in this analysis was that nasopharyngeal 0 3 uptake decreases with increasing flow but that there was also a considerable species variation in uptake (see Section 3.1.3.3 and Table 3-6). The above observations of Gerrity and co-workers have important implications for interpretation of heavy exercise studies: Increased tidal volume increased LRT 0 3 delivery, but there may be a limit beyond which inereases in tidal volume will not cause increased LRT O g delivery. Further modeling studies will hopefully address whether such a limit exists in the physiological range of human ventilation. Available data on respiratory tract uptake efficiency in humans appears to fit the predieted model, making it possible to develop dose-response information from the wealth of controlled human exposure studies that have already been published. The current likelihood of making animal-to-human extrapolations based on this information and on the comparison of respiratory tract uptake of 0 3 across different mammalian species is discussed later in Section 3.1.3.3.

3-26

# 3.1.2 I+ield and Epidemiological Studies

Field and epidemiological studies reviewed earlier in the 1986 Criteria Document (U.S. Environmental Protection Agency, 1986) reported 

# a variety of results concerning associations between exposures to ambient 0 3 and various measures of respiratory effects. The results of many of these studies were found to be directionally consistent with the findings of controlled human exposure studies, especially those providing reasonably good evidence for associations between ambient 0 3 exposures and acute pulmonary function decrements. Results of other epidemiology studies evaluating other health endpoints, e.g. exacerbation of asthma or other chronic lung diseases, were found to be more difficult to interpret due to methodological limitations, but some of these latter studies tended to point toward possibie increases in symptom aggravation or changes in lung function of asthmatic sub_jects being associated with increased total oxidant levels, ambient 0 3 concentrations, or interactions between ambient 0 3 levels and temperature. However, no consistent pattern of findings for aggravation of symptoms or iung function changes emerged for patients with other types of chronic lung disease. Newer field and epidemiology studies (summarized in Table 3-3), as with the older literature, continue to provide sornewhat mixed results across various health endpoints measured—with most progress having been made with regard to provision of further information concerni.ng exposure dynamics related to the induction of pulmonary function decrements by short-term ambient 0 3 exposures. Included among the newer studies published since 1986 are reports by Raizenne and coworkers on several aspects of field studies of children in two summer camps in Ontario (Raizenne et al., 1987; 1989), one at Lake Couchiching (LC) about 100 km north of Toronto, Ontario, and one at, a Girl Guide camp on the north shore of Lake Erie. In the LC study (Raizenne et al., 1987), the strongest association between iung function and environmental variables was found in nonasthmatics, with FVC decrements correlated (p < 0.01) with 24-h lag functions for average SO 4

—
, 

# partilces <2.5 μm (PM 2 5 ), and temperature. The association of peak expiratory flow rate (PEFR) with unlagged 1-h 0 3 was statistically significant and the average slope of the regression line was —2.7 (mL/s/ppb). Temperature was significantly associated with all lung indices in nonasthmatics but not in asthmatics. The average slope of PEFR for teinperature in nonasthmatics was —21.7, a much stronger association of PEFR with temperat'ure than with 0 3 . Coefficients of variation

3-27

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# (CV %) were stable across the daily morning and evening tests of pulmonary function.

Although asthmatics had somewhat larger CV %, no statistical differences 

# in CV % for a. m. versus p.m. tests were seen in either group. Activity or exercise levels were not estimated, nor was amount of iindoor (as on rainy days) versus outdoor activity estimated (i.e., actual exposure as well as proportion of higher versus lower exercise 1evels). Raizenne et al. (1989) also presented preliminary data from a study of the effects of air pollution on girls aged 8 to 14 who attended one of three consecutive 2-weelc sessions of the Girl Guide camp on Lake Erie (June 29 through August 9, 1986). The health status of each camper participati.ng in the study (112 of 145) was characterized by questionnaires completed by parents, by bronchial challenge with methacholine (positive responses were classified as Mch+ and negative responses were classified as Mch—), and by skin-prick tests for atopy. The influence of air pollution episodes on lung function was examined by comparing lung function responses for each girl on episode days with mea.n responses on "control" days (the latter defined as days with a 1-h 0 3 maximum of <90 ppb; SO 4 —< 15 ,ug/m 3 ; and sulfuric acid, H 2 SO 4 , <10 μg/m 3 ). Also, lung function on the morning following an 0 3 episode versus the average function on controf days was examined. Maximum decrements of 3.5 % and 7% for FEV 1 o and PEFR, respectively, were reported to be associated with four distinct air pollution episodes in which 0 3 , H + , and SO 4 —were all elevated. Only FEV 1 o changes were statistically significant and only on 2 episode days (one each in Camp Sessions 1 and 2). For each camp session, the mean values for FVC, FEV 1 0 , and maximum mid-expiratory flow rate (MMEF) exhibited a U-shaped pattern over time; larger first-day decrements were followed by a subsequent, more gradual return to baseline. This pattern was not observed for PEFR. The largest FEV t o and PEFR decrements were observed in methacholine responsive (Mch+) children the morning after (July 26) the highest 0 3 level measured (July 25) during the study. In Mch — children, however, the FEV 1 o change was positive and the PEFR change was negative, both on July 25 and July 26. In Camp Session 3, improvement in both FEV 1 o and PEFR were noted. The authors postulated the exposure of campers in Session 3 to a regional episode prior to their arrival in camp, with recovery occurring while at cainp. No hypothesis was put forward to explain the positive FEV l o change in Mch— children on the day of the highest peak 0 3 level and on the day following. The lack of an aggregate analysis and the presence

3-33

# of largely unexplained temporal trends in pulmonary function make interpretation of these

study results difficult. This report of the study does not provide strong evidence for the effects of 0 3 or of air pollution episodes on pulmonary function. On Ju1y 25, when the 1-h 0 3 1eve1 was elevated (143 ppb), 12 subjects performed pre- and postexercise spirometry (exercise level and resulting 

# V E not estimated). For this subset of subjects, postexercise FVC and FEV i o were observed to increase on control day tests and to decrease on the episode day (results on the episode day were compared with the mean pulmonary function test results for all control days). The function changes did not attain statistical significance, however (Raizenne et al., 1989). During the study of girls attending the Lalce Erie residential camp, investigators (Raizenne and Spengler, 1989) examined the use of heart rate as a surrogate for pulmonary ventilation during daily activities. A dosimetric model was developed using heart-rate data from a standardized exercise test and from portable heart-rate recording devices. Individual exposure estimates were developed, based on time-activity data, and were related to changes in lung function observed in the children. For both 0 3 and H 2 SO 4 , the slopes of function (i.e., peak expiratory flow rate, PEFR) versus pollutant did not differ from zero when the data were adjusted for dosimetry. Adjusted data for FEV 1 owere not reported. From a field study they conducted in 1984 at a YMCA summer camp (Fairview Lake) in northwestern New Jersey, Spektor et al. (1988a) have reported associations between 0 3 and variations in respiratory functions for 91 children attending camp for at least 2 weeks. Average slopes for the regressions between 0 3 concentrations and functions were significantly negative (p < 0.05) for FVC, FEV l o , MMEF, and PEFR for all children and for boys and girls separately. Comparable data were obtained for cohort subsets (2-week campers). When data were truncated at a heat stress index (temperature-humidity index, THI) of 78 °F, the average slopes for girls were reduced by half for the data sets restricted to THI <78 °F, eliminating significant differences in FEV t o changes between girls and boys. Little or no eomparable effect of a heat stress component was seen in boys. Activity levels were not estimated, so that the V E component of the responses was not estimated for individual children or for cohort subsets. As reported by the authors, multiple regression analyses indicated that the O g concentration in the hour preceding spirometry, the curnulative daily 0 3 exposure during

3-34

# the hours between 9:00 a. m. and the function measurement, ambient temperature, and

humidity were the most explanatory environmental variables for daily variations in pulmonary function, with the 1-h 0 3 concentration having the strongest influence. The authors calculated predicted average functional decrements from the average slopes of the base data set (Table 3-1, Spektor et al., 1988a), assuming the exposure-response curve to be linear, of FVC, 4.9%; FEV, 7.7%; PEFR, 17%; and MMEF, 11% for 0 3 at the current standard of 120 ppb. Of the 91 children studied, 33 (36%) had individually statistically significant FEV 1 o responses, with a.n average coefficient in that subset of —2.97 mL/ppb, or about a 16% decrement—again assuming linearity—at 120 ppb 0 3 . The values for the 2-week subsets are generally consistent directionally with 0 3 concentrations in the respective 2-week periods and the total period. Likewise, slopes for data truncated at < 60 ppb and < 80 ppb 0 3 show general directional consistency with the 0 3 concentration data, except for FEF25-75• 

# Several considerations should be noted. Ozone and temperature are statistically correlated in this study (r = 0.37), with evidence of effects of heat stress on 0 3 -associated decrements in function. If the respiratory effects depend nonlinearly on interactions between temperature (or THI) and 0 3 , this may confound interpretation of the effects of 0 3 . Data were truncated at 60 and 80 ppb a.nd the conclusion was drawn that 0 3 -associated effects occurred at < 60 ppb. A formal test for threshold would seem to be in order. The differing number of pulmonary function test days does not appear to have been adequately accounted for in the pooled analysis. The results of this well-conducted study would be strengthened, however, by additional analyses. As reported, calculated decreinents at the level of the current standard should be interpreted cautiously. Spektor et al. (1988b) conducted a field study of the effects of 0 3 in ambient air on pulmonary function in 30 healthy adult nonsmokers (20 males, all Caucasian; 10 females, 2 non-Caucasian) exercising outdoors each work day (between 11:30 a.m. a.nd 6:30 p.m., June 27-August 2, 1985, except for July 4 and 5) in Sterling Forest research park in Tuxedo, New York. A respiratory questionnaire was administered before exercise and spirometry was performed before and after exercise. The outdoor exercise regimen was selected by the subject. Following each exercise stint, the subject measured his own pulse rate. Ventilation 

# ( V E ) for each exercise period was estiinated from the subject-reported heart-rate data,

3-35

# calibrated from heart-rate data recorded from indoor treadmill exercise at a pace similar to

the outdoor exercise level. For each subject, on each exercise day, pre- and postexercise function rneasurements were taken, and changes in function were determined for FVC, FEV i o , (FEV 1 o /FVC), PEFR, and FEF 2 ,

5

_ 75 . Subject-specifc exposures were estimated from duration of exercise, mean 0 3 concentration during the exercise period, 

# V E , and the tidal 0 3 inhaled during exercise. Pollutants and environmental variables measured were 0 3 , S0 2 , nitrogen oxides, ambient aerosols (PM 15 and PM 2 5 ), aerosol acidity and other fine-particle ions, temperature, humidity, and wind speed and direction. Pulmonary function variables were regressed 

# on mean O g concentration during exercise for each subject, as well as against the 0 3 concentration during exercise on the preceding day. Interactions of other environmental variables with 0 3 were tested. All pulmonary function indices showed significant (p < 0.01) 0 3 -associated decrements. No clear effects from other variables on the effects of 0 3 were seen. Mean decrements were reported as smaller in 10 subjects with 

# V E > 100 L/min than those in 10 subjects with 

# cV F of 60 to 100 L/min or those in 10 subjects with 

# V E < 60 L/min. The decrements were reported to be about twice as large as those seen in 1- to 2-h chamber studies in which 

# V E levels were comparable. No association was found between preexercise lung function and mean 0 3 concentration during exercise on the preceding day (no evidence of persistence of 0 3 effects). No symptomatic responses were reported. A.nalysis of lung function changes for ventilations of 50 to 80 L/min was reported by the authors to indicate that the influence of 

# V E on lung function decrements peaks at about 80 L/min: This study substantiates the effects of 0 3 on pulmonary function in populations engaging in continuous exercise outdoors for short periods of time (15 to ca. 60 min; average duration of ca. 30 min). The study further suggests that pulmonary function decrements observed with ambient exposures to 0 3 at 0.12 ppm or somewhat lower may be larger than those seen 'With comparable 0 3 exposure concentrations and exercise conditions in controlled human exposure chamber studies, possibly due to potentiation of 0 3 effects by other ambient cofactors. In a study by Kinney, the effects of air pollutants on lung function were measured by spirometry in children (ages 10-12, 90 male and 64 female) in Kingston and Harriman, TN,

3-36

# with spirometry done at least six times, > 1 week apart, from February through April 1981

(Kinney, 1986; cited in Kinney et al., 1988). Ozone and other pollutants were monitored at a single site in central Harriman. Temperature and aeroallergens were not measured. Values for FVC, FEVo 7$ , MMEF, and 

# V 75% were regressed (ordinary least squares model) on the 1-h maximum 0 3 concentrations and on the 24-h-average fine particles (FP) and FP-SO 4 — concentrations. Ozone concentrations ra.nged from 3 to 63 ppb during the study. Concentrations of other pollutants (S0 2 , NO 2 , total suspended particulate (TSP), inhalable particles (IP), respirable suspended particles (RSP), and FP) were not reported. Slopes of all four lung function-0 3 regressions were significantly negative. A positive mean slope of MMEF on fine particle concentrations was reported. As noted in Kinney et al. (1988), outdoor-only monitoring and lack of time-activity data compromise the specification of true exposures; and the low 0 3 concentrations present during the study detract from plausibility. Kinney et al. (1988) later published an interpretive evaluation of five epidemiological studies of the effects on lung function of acute exposures to 0 3 . In that review, they compared the coefficients of 0 3 -associated lung function declines reported in those epidemiology studies with modeled exposure-response relationships for such effects derived from a synthesis by Hazucha (1987) of results from controlled huinan exposure studies. Hazucha (1987) modeled the effects of exercise-related ventilation rates 

# ( V E ) in potentiating the effects of 0 3 on pulmonary function, using pooled data from 2-h chamber studies of healthy young adults exercising intermittently. Kinney' et al. (1988) reexpressed the data of Hazucha (1987) in units consistent with the epidemiologic study results (assuming a linear relationship between lung function decline and concentrations up to 100 ppb and using baseline functions obtained in Kinney, 1986). The resulting coefficients were reported as being larger than those from controlled studies, especially for FVC (which was about five times the mean FVC coefficients from the controlled studies). Kinney et al. (1988) concluded that the "effective" exposures in the epidemiologic studies were cumulative over longer periods (from 8 to 12 h versus the 2-h exposures used to generate the controlled exposure data analyzed by Hazucha). The Kinney et al. (1988) analysis provides further results suggesting that possibly larger lung function decrements occur with ambient 0 3 exposures than those seen in controlled human exposure studies. However, caution is warranted given several considerations. For

3-37

# one, no justification was given for the use of the linear model and the transforrnation of data

from Hazucha (1987), who had used a quadratic model. At concentrations :5100 ppb, a linear model would tend to overestimate lung fiinction decrements if the quadratic rnodel is actually more appropriate, whereas at higher 0 3 concentration's the linear model would underestimate lung functiion deeline in comparison to a quadratic niodel. Unfortunately, although the upper eiid of the range of 0 3 concentrations measured in the epidemiologic studies reviewed partially overlaps the lower end of the range used in the controlled studies modeled by Hazucha, the mean concentrations in the respective epidemiologic studies from which data were used were < 100 ppb—thereby not allowing for a direct comparison of the magnitudes of the effects seen with ambient versus controlled •exposures across a fuller range of exposures of interest (e.g., 0.05 to 0.15 ppm 0 3 ). Also complicating the comparison are possible differences in exposure durations—leading, in fact, to the postulation by Kinney et al. that the effective 0 3 exposures

~ 

# (including lower ambient 0 3 levels) were likely to have been more prolonged (8 to 12 h) in the epidemiology studies than the exposure duration (2-h) used in the controlled exposure studies. Lioy and Dyba (1989) also reported a new analysis of previous data suggestive of prolonged 0 3 exposures being the effective exposures in an earlier field study conducted in Mendham, NJ, as reported on by Bock et al. (1985) and Lioy et al. (1985). In this case, Lioy and Zyba used a time-activity pattern analysis for a hypothetical typical camper that would liave experienced a usual daily activity schedule analogous to children participating in the Mendham summer camp study. They found that the time-activity analysis indicated a likelihood that periods of increased exercise for the cainper would have likely occurred over prolonged periods of time (several hours) during which ambient ozone levels were elevated (i.e., above 0.10 to 0.12 ppm). Evaluation of the total estimated 0 3 dosages likely experienced on successive days of a 4-day 0 3 episode further led them to hypothesize that the accumulated, multihour doses from prolonged daily exposures to ambient 0 3 may have been niost importaiit in producing the pulmonary function decrements earlier reported for the Mendham study, rather than next day residual effects being due to peak 0 3 concentrations. Vedal et al. (1987) reported data from an 8-ino panel study of symptoms and concurrent but successive 9-week PEFR studies in asthmatic and nonasthmatic school children living in the Chestnut Ridge area of western Pennsylvania. Neither respiratory symptoms nor PEFR



# cm

# was strongly associated with any of the environmental variables, which. included peak 1-h 0 3 , .

NO 2 , S0 2 , and CoH, and daily temperature. Level of PEFR on the previous day was the strongest predictor of daily PEFR. True exposures to 0 3 and other pollutants may have been misspecified, because data were obtained from only one monitor for the whole area, except for S0 2 , for which an average of values from 17 monitors was used; and individual exposures and activity levels were not estimated. Further., levels of 0 3 during this schoolyear study were very low, with the daily maximum 1-h levels ranging from 0 to 129 ppb, with a mean of 32.4 ppb. Results for the 1980-1981 school year have been recently reported by Dockery et al. (1989) from an ongoing study of the effects of ambient air pollution on respiratory health in children living in six cities in the United States: Watertown, MA; Kingston-Harriman, TN; Steubenville, OH; Portage, WI; a geographically defined portion of St. Louis, MO; and Topeka., KS. Previous results showed that the reported prevalence of chronic cough, bronchitis, and chest illness increased by about a factor of two across the range of TSP and S0 2 concentrations measured in the six cities. Lung function was determined at school by spirometry, and a respiratory illness and symptom questionnaire was completed by each child's parents. Pollutants measured included TSP and particles <15 μm (PM 1$ ) and PM 2 5 , 03, NO 2 , and S0 2 . Continous measurements (hourly values) of S0 2 , NO 2 , 0 3 , and meteorological variables, as well as daily values for varrious particle measures (e.g., TSP, PM 15 , PM 2 5 , etc.), were taken. Monthly means for each pollutant were calculated from daily means, and an estimate of air pollution exposure during the previous year was obtained for each child by averaging the monthly means for a given city for the 12 mo preceeding the child's spirometry test. All pollutant concentrations were highly positively correlated with each other in all cities, except for, 0 3 , which was highest in those, cities with low levels of the other pollutants. The pulmonary function parameters measured were. FVC,, FEVi.o

~ 

# FEV o 75 , and MMEF. Five respiratory iilness or symptom categories were also considered: bronchitis, cough; chest illness, wheeze, and asthma. As in previously reported results from earlier years of this. study, chronic cough, bronchitis, and chest illness were positively associated with all three measures of particulate poilution—TSP, PM 15 , and PM 2 5 —but only associations with PM is were statistically significant. Sulfur dioxide, which showed correlation with the particulate measures, was

3-39

# much more weakly associated than particles with the respiratory symptoms. The association

of NO2 with respiratory symptoms was also weak. There were negative associations of 0 3 with cough and chest illness, but annual 0 3 showed a strong positive association with asthma and hay fever (in contrast to negative associations of these symptoms with-all other measured air pollutants). No association was found between air pollutant levels and the pulmonary function measures, including FEV 0.75 and MMEF, which are more sensitive measures of small airway impairment than FEV i o and FVC. This led the authors to conclude that the increased rates of illness observed for some pollutants were not likely associated with permanent loss of pulmonary function—at least in preadolescent years. Bates and Sizto (1987) have reanalyzed earlier data (Bates and Sizto, 1983; Bates, 1985) and extended their analyses to more recent data (now covering 1974 and 1976-1983) for examining correlations between environmental varriables and hospital admissions for 79 acute-care hospitals in southern Ontario, Canada. Pollutant concentration data for 0 3 , NO 2 , sulfur dioxide (S0 2 ), coefficient of haze (CoH), and sulfate (SO 4 !) 

# were collected at 17 sampling stations located across a 280-mile corridor between the Windsor and Peterborough areas of Southern Ontario. Correlations were exarnined for relationships among environmental variables and between environmental variables and three categories of hospital admissions for winter (January-February) and summer (July-August), i.e. for total respiratory admissions (TRA), TRA minus asthma (TRA—A), and nonrespiratory admissions, separately. The authors concluded that an association exists in southern Ontario between 0 3 and TRA and TRA—A in summer, but they note that these results are not in agreement with those of Richards et al. (1981), who found no associations between 0 3 and adrnissions to children's hospitals or emergency room visits in Los Angeles, where 0 3 levels are higher than those in southern Ontario. They concluded, as well, that aerosol SO 4 –levels explain the highest percentage variance in TRA from pollution in summer, but are not correlated with TRA 

# in winter. They also concluded that 0 3 and SO 4 –may be surrogates for one or more other species that travel with them in summer but not in winter, such as hydrogen ions (H + ) in the fne-particle range. Lastly, it should be noted that Bates and Sizto (1987) specifically tested the maxirnal 8-h 0 3 average for correlation' with TRA. The Pearson correlation coefficient was not affected by substitution of the 8-h value in place of the mean of the hourly

3-40

# 0 3 maxima previously used. The correlation between the 1-h and 8-h 0 3 maxima across all

monitoring stations was 0.986. Using the same methodology, Bates and Sizto (1989) examined aerometric and hospital admissions data for June, July, and August 1983 and for June in the years 1979 through 1985 because June 1983 was observed to have 0 3 levels higher than those in any July or August previously examined. Analyses showed no excess respiratory admissions in June 1983. Furthermore, in years for which excess hospital admissions were observed in June (1982 and 1985), increased admissions were in the categories of "acute bronchitis" and "asthma," but not in other respiratory categories, a finding inconsistent w.ith 0 3 -associated excess admissions reported earlier. The authors concluded that these findings cast doubt "on the primacy of 0 3

as the cause" of increased admissions, and that there are reasons against attributing excess admissions either to 0 3 or SO 4

— . 

# Although asthmatics are not unequivocally more sensitive to 0 3 than nonasthmatics, neither have they been shown to be less sensitive (U.S. Environmental Protection Agency, 1986). Therefore, the findings of an epidemiologic study of asthmatics reported by Gong (1987) are of particular interest. Gong (1.987) studied the relationship between air quality and the respiratory status of 83 asthmatics living in a high-oxidant area of Los Angeles County. The study covered February to December 1983, but data analyses were limited to a 230-day period (April 15-November 30) because of staggered entry of subjects into the study and the high frequency of missing or incomplete data encountered in the earlier part of the study period. Regression and correlation analyses between 0 3 and average symptom scores, asthma medication index (AMI), and day and night PEFR across subjects showed weak, nonsignificant relationships. These daily outcome variables were compared for days with maximum 1-h-average 0 3 in three ranges: G 

# 0.12 ppm, 0.12-0.19 ppm, and > 0.20 ppm; "no statistical or clinical significance was detected." Individual exposures and activity patterns were not estimated in these two analyses. Multiple regression analyses also indicated the lack of a significant overall relationship between 0 3 (and other independent variables) and respiratory status, despite the use of lagged variables and the inclusion of other pollutants, meteorological variables, aeroallergens, and AMI. Total suspended particulates directly . affected PEFR, but the relationship was not consistent in the analysis. Aeroallergens showed

3-41

# significantly negative relationships to respiratory variables, but only the effect of trees was

considered clinically relevant. Temperature and humidity showed no significant effect on the respiratory variables in this study. Although there was no significant overall effect of 0 3 on respiratory variables in the 83 asthmatic subjects, multiple regressioii analysis of subjects whose 0 3 coefficients on various days were in the top quartile for dependent variables (respiratory measures) showed significant and consistent effects of 0 3 on day t and the previous day (t-1). 1'vlultiple regression testing of subsets for associations of symptom score or day or night PEFR on the same day's 0 3 and the previous day's value of the same responses showed highly significant 0 3 coefficients for•all three respiratory nieasures. The clinical significance of responses in symptom scores and day and ni,ght PEFR was evaluated for all subjects by individual regression analyses. No subject had evidence of significant worsening of symptoms attributable to 0 3 during the study. Adult subjects with high scores in fatigue, hyperventilation, dyspnea, congestion, and rapid breathing in the Asthma Symptom Checklist had more negative slope coefficients for 0 3 than subjects with low-to-moderate scores on the checklist. "Responders" (statistically identified by multiple regression analysis) scored consistently higher in the the factors representing fatigue, hyperventilation, and rapid breathing. The higher scores of these responders, however, "were apparently not associated with differences in ambient ozone concentrations since the test scores were similar during relatively low (first test) a.nd high (second test) ozone days. The significance of the psychological results is unclear at this time and will be the subject of further analyses" (Gong, 1987). Lastly, it should be noted that a reanalysis by Schwartz et al. (1988) of the Los Angeles epidemiology study of student nurses earlier reported by Hammer et al. (1974) confirmed the Hammer et al. results showing oxidants to be significantly associated with eye discomfort and cough. However, earlier reported associations between oxidants and headache or chest discomfort were not confirmed. The relationship of oxidants to eye irritation has been previously reported by others and appears to be related to peroxyacetal nitrate (PAN) rather than 0 3 . Cough has been shown, however, to be a respiratory symptom related to 0 3 , and the present reanalysis (using logistic regression models and time-series analyses controlling for autocorrelation effects) conf rmed the presence of an apparent threshold for "cough"

3-42

# earlier found by the "hockey-stick" function analysis done by Hammer et al. (1974). The

upward flexure point in the dose-response curve occiirs near the value reported by Hammer et al. (ca. 20 pphm total oxidants)—a value likely including 0 3 levels well above the current 1-h 0 3 NAAQS of 0.12 ppm. 

# 3.1.3 Laboratory Animal Studies The more recently published reports on the animal toxicology of 0 3 were evaluated according to their overall relevance to the issues of 0 3 toxicology described below. A report not clearly applicable or unique in its contribution was not considered. Hence, studies that added little or no data or insight to the issues being addressed, or that corroborated or tended to duplicate the content of other studies contained in the Ozone Criteria Document (U.S. Environmental Protection Agency, 1986) were eliminated in order to summarize the newer pertinent data as briefly as possible. Additional literature has been selected for review here that contained information on (1) the effects of multihour and multiday exposures to 0 3

, 

# (2) the potential health effects of chronic 03 exposure, and (3) the conceptual and empirical linkages between animal and human 0 3 toxicology (i.e., extrapolation). Information on a less-specific, but nevertheless important, aspect of 0 3 toxicity (e.g., "adaptation") is given here as well.
3.1.3.1 Effects of Multihour Exposures Three studies on the effects in animals of multihour exposures to 0 3 (Table 3-4) have been reported (Van Bree et al., 1989; Rombout et al., 1989; Costa et al., 1989). Results of these studies point to the fact that concentration (C) dominates duration of exposure (T) in eliciting a toxic response to the lung as determined by lavagable plasma protein on the lung surface. All three studies suggest that exposure C and T can be modeled mathematically and clearly demonstrate the dominance of C in eliciting effects. Although the effect of T on response is clearly C dependent, the influence of T 

# is apparent at all levels, with some indication that C and T interact in a synergistic manner in the low C-long T exposures. Although further work on this last point is needed, it appears that the C x T approach only holds for a given C and cannot be applied in a general fashion.

3-43.-, 

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# Costa et al. (1989) have attempted to address whether the apparent cumulative loss of

lung function seen with 0 3 exposure in human subjects also occurs in experimental laboratory animals. As reported in humans by Folinsbee et al. (1988), FVC fell in

~ 

# a linear fashion with estimated cumulative exposure, which incorporated ventilation, but only at lower concentrations (<0.5 ppm for up to 7 h). At 0.8 ppm, the effect of T on the C'response dramatically increased, as was seen in, their matrix studies of C x T relationships a.nd in similar studies by Van Bree et al. (1989). Hence, the impact of T is C dependent. It should be noted, however, that the apparent cumulative toxicity of 0 3 may be endpoint dependent as well and that the simpie loss of lung volume, FVC or FEV l , may demonstrate such a relationship (linearity) more clearly than more interdependent measures such as DL Co and N 2 washout.
3.1.3.2 Effects of Multiday Exposures An animal model has been developed (Costa et al., 1988) that exhibits the same pattern of attenuated response to intermittent short-term 0 3 (a phenomenon known as "adaptation") as has been described in humans. More specifically, repeated 2-h exposures of rats for up to 5 days resulted in adaptation or attenuation of the 0 3 -induced functional deficits, with sustained but not worsening protein accumulation occurring in the lavage. Howeve.r, the histopathology of these animals appeared to worsen and evolve from an acute to a more chronic inflammatory pattern. Recovery or exposure points beyond 5 days were not conducted. Antioxidant levels of the lung tissues showed a slight upward trend during this period, but their role in the pattern of response is unclear. This model demonstrates that morphological and biochemical changes continue even whiie lung dysfunction attenuates with repeated 0 3 exposure, suggesting that the use of lung function tests alone to assess injury can result in misinterpretation of risk to health with repeated exposures to 0 3 . Whatever the precise mechanisms and attenuation events, however, animal studies have demonstrated that chronic exposures cause effects, some of which are irreverisible. The protein and PMN response to repeated 12 h nocturnal exposures for up to 3 days as an analogue of an 0 3 "episode" appeared to be governed by the initial exposure only (Van Bree et al., 1989). In other words, the degree of response and recovery time were unaltered by additional exposures during the 2- or 3-day period.

3-45

# 3.1.3.3 Effects of Chronic Exposure to Ozone

Several recent reports on 0 3 effects in laboratory animals have focused on the structural alterations of the distal lung associated with prolonged, repeat.ed exposures (see Table 3-5). Tn botli the adult and neonate rat (Barry et al. , 1988; Grose et al. , 1989; Huang et al. , 1988; Gross and White, 1987) and the monkey (Tyler et al., 1988; Hyde et al., 1989), high (;-

~ 

# 0.25 ppm) ambient levels of 0 3 appear to similarly affect the junctional airways of the distal bronchioles and the proximal alveoli. Shifts in cell population occur that result in more cuboidal cells interfacing the airway lumen, effectively presenting less cell surface to the air, and presumably reducing individual cell dose (Crapo et al., 1985; Barry et al., 1985, 1988; Sherwin and Richters, 1985). Interstitial inflammation predominates over time, resulting in thickened septal areas that do not completely recover during several weeks of postexposure clean air (Huang et al., 1988; Barr et al., 1988; Moffatt et al., 1987). These findings are largely consistent with the reports of enhanced collagen deposition and reduced turnover with very high ambient levels of 0 3 (0.57 to 0.8 ppm) in monkeys (Reiser et al., 1987) and rats (Hacker et al., 1986; Pickrell et al., 1987), but appear discrepant with collagen analyses in chronically exposed rats at very low 0 3 concentrations (Filipowicz and McCauley, 1986; Wright et al., 1988), unless exposure is intermittent (Tyler et al., 1988). A preliminary report from the U. S. EPA's chronic 0 3 study (Grose et al. , 1989) showed that repeated daily exposure of rats to a daily episodic profile of 0 3 (22 h, 0.06-ppm background with a 0.25-ppm peak; equivalent to a square wave that averaged 0.19 ppm over 9 h) for 12 mo resulted in small, but significant, decrements in lung function that were consistent with early signs of focal fibrogenesis in the proximal bronchoalveolar junction (see Chang et al., 1991). Augmentation of lavagable protein levels and tissue fractions of. ascorbate- and glutathione-related enzymes after 12 mo of 0 3 exposure were indicative of the continued oxidant challenge. Further results of these studies through to 18 mo of exposure and with recovery periods will be published. The functional implications of these alterations in distal airway architecture have been explored in one higher level 0 3 study (0.5 ppm) in which airflow mechanics were reversibly altered (Gross and White, 1987). Changes in lavagable enzymes in rats (Grose et al., 1989) and lipids in monkeys (Rao et al., 1985a,b) after prolonged exposures are consistent with shifting cell populations and/or inflammation,

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# 3-51

# but remain nonspecific effects that still need to be linked with progressive injury or defensive

adjustments to the 0 3 challenge. Ozone also has a significant impact on nasal epithelium and mucosal lining (Harkema et al., 1987a,b). The health significance of this finding is uncertain, but is consistent with the deposition data on 0 3 from both animal and human studies. Hence, though 0 3 is relatively insoluble in water, the nose appears to provide some degree of scrubbing, and thus, provides protection to the deeper lung. 5pecies differences in this capability are an importa.nt extrapolation question (see below).
3.1.3.4 Animal-to-Huwman Extrapolation The more recently published studies cover two aspects of extrapolation: (1) models and their validation and (2) species comparisons. The Miller model (Miller et al., 1987a,b; Overton et al., 1987; Miller and Overton, 1989) of lower respiratory tract deposition of 0 3 has been enhanced with the incorporation of both ventilatory parameters and empirically derived anatomical data (see Table 3-6). Use of the model with input parameters from several rodents and humans indicates preferential deposition, and presumably associated injury, in the bronchoalveolar junction, which is consistent with empirical findings in laboratory. ainimals. The model agrees well with the total and partitioned uptake values determined in human studies (Gerrity et al., 1988), though it fits less well with the rodent uptake data (Wiester et al., 1988). Although the reasons for this are not as yet clear, the overall consistency of the predicted deposition distribution within the lung and the approximate equality of dose rate/surface area increase confidence in the model (Gerrity and Wiester, 1987). Both human and animal uptake studies of 0 3 have been conducted (see Tables 3-1 and 3-6). Although humans (Gerrity et al., 1988) appear to retain a somewhat greater fraction of the inhaled 0 3 than do rodents (Wiester et al., 1988), the biological significa.nce of this difference is uncertain at this time, especially considering the slight differences in technique. Santrock et al. (1989) have shown that with continued exposure, products of 0 3 , as indicated by an oxygen-18 ( 18 

# 0) label, accumulate in - the lungs of mice with continued exposure. The difference in total uptake between humans and laboratory rodents may result in part from differences in nasopharyngeal removal of 0 3 (40 % in humans, 17 % in rats; as reported by ,

3-52

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# Hatch et al., 1989), resulting in shifts in regional doses in the two species (surface area

differences and other factors are incorporated). Significant biological variations in lung tissue concentrations of several antioxidants have also been reported (Bryan and Jenkinson, 1987; Slade et al., 1985). How these antioxidants act individually or collectively as a defense against exogenous oxidants is not clear, especially considering that five anim.al species tested for 0 3 toxicity in concentration-response studies using BAL protein did not show corresponding variations in their susceptibilities (Hatch et al., 1986). Thus, target tissue dosimetry data, such as that being pursued with i8 0 are needed, along with additional species sensitivity data to refine this issue. Nevertheless, the ability of the mathematical model to discern relative species sensitivities is encouraging, despite its evolutionary state (Miller and Overton, 1989). Further work is still n..eded,• however, to clarify various input components of the model, such as the roles of reactive surface fluid components and regional ventilation, for example, thereby ensuring its continued refinement and applicability to the extrapolation issue (Hanna et al., 1989).



# 3.2 SUMMARY AND CONCLUSIONS: HEALTH EFFECTS I1ATA Concisely summarized below are the key findings and conclusions that emerge from the above review of the most pertinent, key 0 3 health effects studies published in the 1986 to early 1989 period after completion of the 1986 U.S. EPA Ozone Criteria Document. The newer studies reviewed from the 1986-1989 period provide further inforrnation related to evaluation of several key issues pertinent to decision making regarding potential revision of the primary 0 3 NAAQS. Such issues include: (1) clarification of exposure dynamics (i.e., characterization of effective exposure patterns-concentrations, durations, etc.) determining the induction of acute effects (pulmonary function decrements, respiratory symptoms, lung inflammation, etc.) associated with short-term 0 3 exposures; (2) evaluation of potential increased (or decreased) susceptibility of various population groups earlier hypothesized as possibly being at differential risk for 0 3 -induced health effects; (3) evaluation of the potential for induction of chronic lung damage/disease by repeated short-term and/or ` more chronic 0 3 exposures; and (4) additional clarification of 0 3 dosimetry aspects of

3-56

# importance in better understanding observed human exposure effects and to enhance

capabilities to carry out both qualitative and quantitative animal-to-human extr.apolations. 

# 3.2.1 Exposure Dynamics for Short-Term Ozone Exposure Effects Newer data from 1- and 2-h controlled human exposure studies (Avol et al., 1987; Linn et al., 1986) add to earlier existing concentration-response data indicating that lung function decrements occur in children and young' adults exposed for 1 to 2 h to low 0 3 concentrations ranging from 0.12 to 0.16 ppm while performing moderate to heavy exercise. Explanations for variations across studies in reported lowest-observed-effects-levels among individuals and among cohorts include: subject characteristics, exposure histories of subjects, exercise levels, and possible but presently unidentified differeinces in actual controlled exposure conditions. Data from two other newer studies (Gong et al., 1986; Schelegle and Adams, 1986) also substantiate earlier findings that statistically significant reductions in maximal exercise performance may occur in well-conditioned athletes after performing conxinuous heavy exercise 

# (V E > 80 L/min) for 1 h at 0 3 concentrations >_0.18 ppm, but not at 0.12 ppm. Data from a third study (Linder et al. , 1988) suggest that small decrements in maximai exercise performance may occur at 0 3 concentrations < 0.18 ppm, but liinitations and questions concerning this study require further verification of the results. Environmental conditions such as high ambient temperature and/or relative humidity may affect subjective symptoms and may independently impair exercise performance such that differentiation between 0 3 -induced effects and effects of other environmental conditions may be difficult. In addition, newly emerging controlled human exposure studies of prolonged exposure (for up to 6.6 h) to low 0 3 concentrations, ranging from 0.08 to 0.12 ppm report progressively larger pulmonary function decrements and increased respiratory symptoms with increasing duration of exposure at moderate exercise levels 

# ( V E = 40 L/min) (Folinsbee et al., 1988; Horstman et al., 1988, 1989). The effects are similar in magnitude to those previousiy reported for healthy subjects performing heavy exercise 

# (V E > 60 L/min) in high ozone concentrations (>0.2 ppm) for shorter durations, (:Z-2 h). In addition to the above, new data also demonstrate increased lung inflammatory and biochemical changes from exposures to moderately high levels (0.40 ppm) of 0 3 for 2 h with intermittent exercise (V E = 70 L/min), as determined from BAL 18-h post-0 3 -exposure

3-57

# (Koren et al., 1989a,b; 1988a,b). Cells and enzymes capable of causing damage to

pulmonary tissues, along with proteins involved in fibrotic and fibrinolytic processes, were increased at 18-h postexposure. Also, evidence of increased epithelial permeability from the air to blood compartments (as determine,d by clearance of technetium-labeled DPTA) was observed (Kehri et al., 1987). Koren et al. (1989a) further reported elevated PMNs, also as determined by BAL, in subjects exposed for 6.6 h to 0.1 ppm 0 3

. 

# Three newer studies on the effects in laboratory animals of multihour 0 3 exposures provide information on relationships between concentration (C) and duration (T, time) of exposure. Rombout et al. (1989), Van Bree et al. (1989), and Costa et al. (1988) report that C dominates T in eliciting 0 3 -induced changes in lavagable protein and antioxidant enzyme levels. Preliminary modeling efforts describing these data suggest that C x T interaction (synergism) occurs at decreased C and increased T; however, C x T relationships can only be applied at a given C and cannot be applied in general. The time of day of exposure is also an important determinant of oxida.nt toxicity because nocturnal exposures cause greater responses than do diurnal exposures, possibly due to dosimetric differences because rats exercise more at night. These results suggest that the primary determinants of acute 0 3 lung toxicity may, therefore, be exposure concentration and time of day of exposure, followed by the duration of exposure. Also, certain other newer information suggests that interpretation of the results of controlled human 0 3 exposures should take into account whether frequent ambient exposure was a possibility during the period of study (Avol et al., 1988; Hackney and Linn, 1989;

. 1`Iackney et al., 1989; Linn et al., 1988). This information also suggests that further work is still needed to resolve the implications of attenuation of pulmonary function responses to 0 3 . Subjects grouped according to their responses in the early spring to 0.18 ppm 0 3 for 2 h with intermittent exercise were tested the following fall, winter, and again the next spring. Although "nonresponders" showed little seasonal variation in their response to 0 3 , " 

# responders" showed attenuated responses in the fall, persistence of attenuation into the winter, and a return to their initial lung function responses to 03 by the following spring. Many of the responders were reactive to methacholine and had histories of respiratory allergies and/or symptomatic complaints when previously exposed to smog.

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# Newer field a.nd epidemiological studies have employed numerous refinements over

some of the older studies, in the form of (a) better estimates of exposure, not just to 0 3 but also to other pollutants and other environmental variables that can confound or otherwise influence the outcome (e.g., Bates and Sizto, 1987; Spektor et al., 1988a;b; Raizenne et al., 1987); (b) use of serial measurements of pulmonary function for determining correlations with pollutants and other environmental variables (e.g., Raizenne et al., 1987, 1989; Spektor et al., 1988a,b); and (c) better biomedical characterization of cohorts (e.g., Raizenne et al., 1987, 1989; Gong, 1987). Despite their refinements, however, newer field a.nd epidemiologic studies have produced mixed results regarding the possible role of 0 3 versus the roles of other agents or factors in eliciting the functional decrements and/or rates of respiratory symptoms or respiratory disease observed. Although functional decrements and respiratory symptoms have been shown in a number of studies to be statistically associated with 0 3 , other studies have shown them to be wholly attributable to particles (e.g., Dockery et al., 1989), partially attributable to particles (e.g., Kinney, 1986), or partially attributable to other environmental factors such as ambient temperature or humidity (e.g., Spektor et al., 1988a) or even aeroallergens (e.g., Dockery et al., 1989; Gong, 1987). Data reported from some of the newer field and epidemiologic studies (e. g. , Raizenne et al., 1987, 1989; Spektor et al., 1988a,b; Kinney et al., 1988) show pulmonary function decrements that are as large or larger than those observed in human controlled (chamber) studies. Investigators have variously interpreted these larger decrements as likely being due to: (a) cumulative effects of 0 3 occurring as the result of multihour exposures; (b) interactive effects with other pollutants (additive or synergistic effects); (c) interactive or possibly independent effects of other environmental factors (e.g., temperature); (d) possible misspecification of true exposures, either because of inadequate knowledge of dosimetry or other types.of inadequacies in exposure characterization; and/or (e) possible persistence of effects from one day to the next. Although permitting easier comparison of epidemiologic findings with chamber-study data, the method of reporting raises several questions that need to be further evaluated. For example, data on functional decrernents have been reported as —mL/ppb 0 3 for measures such as FEV 1 oand FVC and as —mL/sec/ppb for measures such as PEFR and MMEF. Expression of data in this form assumes that (a) 0 3 -induced changes in respiratory function

3-59

# are linear across all concentrations encountered in these studies (from zero up through

episodic levels); and (b) the relationships among C, T, and 

# V E do not change with variations in these respective components of exposure. These assumptions are open to question, especially considering results from newer animal C 

# x T studies. For example, the relationships between respiratory function changes and the respective -components of exposure —C, T, and 

# V E —have not been tested at concentrations <0.08 ppm in char.nber studies; and data obtained in chamber studies at the lowest concentration used (0.08 pprn) have not been modeled to determine whether changes in the influence of respective components are monotonic across ranges of C, T, or V E . Furthermore, questions of nonlinearities in the respective effects of C, T, and 

# VE on 0 3 -induced pulmonary function changes are far from resolved. Also, Kinney et al. (1988), transformed data from controlled (chamber) studies modeled by Hazucha• (Hazucha, 1987; U.S. Environmental Protection Agency, 1986) and compared them with data from five epidemiologic studies. The transformation assumed the applicability of a linear model even though Hazucha had fit data from controlled (chamber) studies to a quadratic model in describing changes in pulmonary function as a function of 

# V E . Mean concentrations in the five epidemiologic studies were lower than the lowest concentration used in the controlled studies modeled. As for respiratory symptoms, the newer field and epidemiologic studies have reported lack of association of various respiratoiy symptoms with 0 3 more often than they have reported demonstration of such an association with the typically low 0 3 levels studied. Studies reporting no significant increases in symptoms following short (1-h to multihour) daily exposures (over multiple days to multiple months) to ambient air containing 0 3 include: (a) studies of children attending day or residential camps (Raizenne et al. , 1987, 1989; Spektor et al., 1988a), (b) at least two panel studies (Dockery et al., 1989; Vedal et al., 1987), and (c) a study of adults exercising outdoors nearly every day (Spektor et al., 1988b). Another study (Schwartz et al., 1988), reanalyzing data from the Hammer et al. (1974) panel study of nurses in Los Angeles and using currently more widely accepted statistical approaches, did show that cough was associated with total oxidants, but only at relatively high levels (where 0 3 concentrations were likely well above 0.12 ppm).

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# 3.2.2 Evaluation of Differential Susceptability of Potential Special Risk

Groups Newer data published in the 1986-1989 period provides further data usefui in evaluating possible differential sensitivity in two of several subpopulation groups of interest: (1) the 

# elderly and (2) asthmatics. With regard to the first group, in controll.ed human exposure studies, older subjects (>_50 years old) appear to have smaller changes in lung function than younger subjects when exposed to similar 0 3 concentrations (Bedi et al., 1988; Bedi and Horvath, 1987; Drechsler-Parks et al., 1987, 1989; Reisenauer et al., 1988). There were no significant differences between the responses of inen and women to 0 3 exposure for FEV 1 and FVC, although women had a significant increase in total respiratory resistance (Reisenauer et al., 1988). Because women had slightly lower mean exercise 

# V E during the studies, the data suggest that women may be somewhat more responsive to 0 3 than men (Drechsler-Parks et al., 1987; Reisenauer et al., 1988). The responses to 0 3 may be less reproducible, however, in older than in younger adults (Bedi et al., 1988). These results suggest a possible dropoff in responsiveness to 0 3 -induced pulmonary function changes sometime in late middle-age. As for asthmatics, in other new studies of adults with and without asthma (Kreit et al., 1989; Eschenbacher et al., 1989), both groups experienced similar responses to 0.4-ppm 0 3 exposure, as indicated by decrements in standard spirometric pulmonary function tests and airway responsiveness to methacholine. Specific airway resistance was not increased in nonasthmatics, but in asthmatics nearly twice the increase in SR aW was seen after exercise in 0 3 versus air exposures. No symptom differences were observed between adult asthmatics and nonasthmatics. Preexposure challenge with methacholine may have confounded the resuits, however. Responses were also similar for adolescent asthmatics and nonasthmatics exposed to 0.12 and 0.18 ppm 0 3 (Koenig et al., 1987, 1988), although a small but significant increase in FEF 50% was observed in asthmatics after 0.12 ppm 0 3 exposure. In the adult nonasthmatics studied by Eschenbacher et al. (1989), indomethacin pretreatment blocked the restrictive but not the airway reactivity component of the effects of 0 3 ; a placebo effect was also observed in these nonasthmatics. A study by McDonnell et al. .(1987) indicates that adults with allergic rhinitis show similar airway responsiveness to histamine after exposure to 0.18 ppm 0 3 as a comparable group of nonallergic subjects. The only

'il

# difference was a significant increase in airway resistance in the allergic subjects. The newer

data on allergic and asthmatic subjects suggest that both of these groups have a greater increase in airway resistance after 0 3 exposure than do healthy subjects. The apparent order of airway responsiveness to 0 3 from these studies is normal < allergic < asthmatic subjects. Further research will be required, however, before this hypothesis can be substantiated. Results from a few of the newer epidemiology studies are also suggestive of possible increases in asthma or allergic responses among some individuals. For exainple, Dockery et al. reported a positive association of annual 0 3 exposures to increases in asthma and hay fever symptoms in schoolchildren, but not with other respiratory symptoms or pulmonary function decrements. Also, in a panel study more specifically on asthmatics, Gong (1987) reported that, although respiratory symptoms occurred during the study, they did not correlate signifiicantly with 0 3 ; and no worsening of syinptoms attributable to 03 occurred in overall group statistical analyses. However, other multiple regression analyses of responses of those asthmatics in the top quartile for respiratory measures did show relationships between the respiratory measures and 0 3 , but these associations showed no clear concentration-response pattern (Gong, 1987). 

# 3.2.3 Ozone Impacts on Lung Structure/Chronic Disease Processes Several studies, by Koren et al. (1988a,b; 1989a,b) and Kehrl et al. (1987), were noted earlier as showing increased lung inflammatory responses and other biochernical changes capable of causing damage to pulmonary tissue, as well as increased lung epithelial permeability, with 2-h exposures of humans to 0.4 ppm 0 3 and elevated PMI'1s in BAL fluids following 6.6-h exposure to low 0 3 levels (0.1 ppm). These results increase concern regarding possible induction of chronic lung damage by 0 3 exposures and lead to questions about effective exposure dynamics possibly related to such effects. Costa et al. (1988) have demonstrated that laboratory animals exhibit a similar pattern of attenuated pulmonary function changes in response to repeated short-term 0 3 exposure as previously described in humans. Both morphological and biochemical changes, however, occur wliile lung dysfunction attenuates with repeated 0 3 exposure. These results add to coneern that the attenuation phenoinenon for short-term pulmonary functioii changes may not be benefieial, but rather may increase the potential for more serious chronic lung damage.

3-62

# They also suggest that the use of lung function tests alone to assess 03-induced lung injury

may result in misinterpretation of data concerning health risks associated with multiday 0 3 exposures. More research is needed, therefore, to improve our knowledge of relationships between acute and chronic lung injury. Other new studies in monkeys and rodents provide further support for earlier findings that prolonged, repeated exposure to high concentrations of 0 3 (>0.4 ppm) lead to the development of peribronchiolar inflammation (Barr et al., 1988; Moffatt et al., 1987), increased lung collagen content (Reiser et al. , 1987; Pickrell et al. , 1987; Hacker et al. , 1986), and lung function changes (Gross and White, 1986, 1987). Even at lower 0 3 concentrations (0.12 to 0.30 pnm), a lesion is still evident at the junction of the conducting airways and the gas exchange regions of the lung, characterized by cell population shifts along with interstitial inflammation and thickening (Huang et al., 1988; Crapo et al., 1985; Barry et al., 1985, 1988; Sherwin and Richters, 1985), but without increased lung collagen content in rats (Wright et al., 1988; Filipowicz and McCauley, 1986). In a chronic exposure study (0.25 ppm, 8 h/day, 18 mo), one group of monkeys was exposed to 0 3 for each day of the 18 mo, whereas another group was exposed to 0 3 every other month, with the intervening month being an air exposure (Tyler et al., 1988). Thus, on a C x T basis, the intermittent group received half the amount of 03 exposure. Both groups of monkeys had morphometric changes, such as respiratory bronchiolitis, but only the intermittent groups had an increase in total lung collagen and pulmonary function changes. This suggests that under these experimental conditions, intermittent exposure could enhance the potential for the development of fibrogenic processes and indicates that to understand the health effects of 0 3

, 

# it is critical to better understand the effects ambient exposure patterns. Preliminary information (Grose et al., 1989) from an exposure that mimics an urban 0 3 pattern (0.19 ppm average concentration of 0 3 over 9 h) of rats for 12 mo indicates that significant decrements in lung function also occur at these iower 0 3 concentrations that are consistent with early signs of focal fibrogenesis in the centriacinar region of the lung. Increased lavagable lipids in monkeys (Rao et al., 1985a,b) found after prolonged exposure to ambient levels of 0 3 (0.15 to 0.30 ppm) are also consistent with the shifting cell populations and/or inflammation reported at these concentrations. Multiple exposures to ambient levels of 0 3 (0.15 and 0.30 ppm, 8 h/day for 6 or 90 days) also cause injury and cellular changes in

3-63

# transitional and respiratory epithelium of the nose of nonhuman primates (Harkema et al.,

1987a,b; Hyde et al., 1989). 

# 3.2.4 Ozone Dosimetry Aspects Newer studies related to the dosimetry of 0 3 show that differences in mode of breathing do not produce appreciable differences in fractional uptake of 0 3 in the respective regions of the human respiratory tract. Increased frequency of breathing results in a decreased fractional removal of 0 3 in both the URT and the LRT, possibly as the result of decreased residence time in the airways and increased flow rate. The lowest fractional removal of 0 3 in the URT occurred during nasal breathing, so that shifts from nasal to oronasal breathing resulting from exercise would somewhat offset increases in delivered dose caused by increased ' breathing frequency (Gerrity et al., 1988). Ozone-induced changes in tidal volume during 60-min, continuous-exercise 

# (V E

= 40 L/min) exposures to 0.4 ppm resulted in a slight reduction in total 0 3 uptake (4 %) and a larger reduction in LRT 0 3 uptake (9 %). Thus, the typical 0 3 -induced reduction in tidal volume may partially protect the lower airways, with possible loss of that protection with recovery of normal tidal volume that occurs during multiday exposure (Gerrity and McDonnell, 1989). Increased flow rates appear to reduce nasopharyngeal uptake (Gerrity, 1987). Additional modeling is need, howe•ver, to determine the effects of heavy exercise on regional dosimetry, especially on 0 3 uptake in the LRT. Additional data are still needed in other areas important to animal-to-human extrapolation, namely, relative species sensitivities. Iviathematical dosimetry models indicate preferential deposition of 0 3 in the bronchoalveolar junction of several species of laboratory animals and in humans that is consistent with laboratory animal data on the site of the 0 3 morphological lesion (Miller and Overton, 1989; Miller et al., 1987a,b; Overton et al., 1987). Humans appear to retain a greater fraction (95%) of inhaled 0 3 than do rats (50%), but tissue dose rates/surface area in each species may not be that different if nasopharyngeal partitioning is considered (Wiester et al., 1987, 1988; Gerrity and Wiester, 1987; Gerrity, 1987). Target dosimetry data, such as that being conducted with [18]0 3 (Hatch et al., 1989; Santrock et al., 1989; Aissa and Hatch, 1988; Hatch and Aissa, 1987) ai

- e needed, along with species sensitivity data (Bryan and Jenlcinson, 1987; Hatch et al., 1986; Slade et al., 1985) to better refine this issue.

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