i UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
' WASHINGTON D.C. 20460
OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY BOARD
June 05, 2006
EPA-CASAC-06-007
Honorable Stephen L. Johnson
Administrator
U.S. Environmental Protection Agency
1200 Pennsylvania Avenue, NW
Washington, DC 20460
Subject: Clean Air Scientific Advisory Committee's (CASAC) Teleconference Meeting
to Provide Additional Advice to the Agency Concerning Chapter 8 (Integrative
Synthesis) of the Final Ozone Air Quality Criteria Document (AQCD)
Dear Administrator Johnson:
EPA's Clean Air Scientific Advisory Committee (CASAC or Committee), supplemented
by subject-matter-expert Panelists — collectively referred to as the CASAC Ozone Review Panel
(Ozone Panel) — met via a public teleconference on May 12, 2006, to provide additional advice
to the Agency concerning Chapter 8 (Integrative Synthesis) of EPA's Final Air Quality Criteria
for Ozone and Related Photochemical Oxidants (Second External Review Draft)., Volumes I, II,
and III, (EPA/600/R-05/004aF-cF, February 2006), also known as the Final Ozone Air Quality
Criteria Document (AQCD). The current Clean Air Scientific Advisory Committee roster is
found in Appendix A of this report, and the CASAC Ozone Review Panel roster is attached as
Appendix B. Panel members' individual review comments are provided in Appendix C.
The members of the Ozone Panel are in general agreement that, in its development of the
Integrative Synthesis chapter in the Final Ozone AQCD, the Agency has been reasonably
successful in assembling the relevant information and incorporating findings from atmospheric
sciences, toxicology, human clinical studies and epidemiology. Nevertheless, in view of the
acknowledged role of the Ozone AQCD in informing the 2nd draft Ozone Staff Paper and,
ultimately, potential revisions to the national ambient air quality standards (NAAQS) for ozone,
the CASAC is of the opinion that there are some important issues that are not presented well, or
at all, in this chapter. These include: the utility of time-series studies in assessing the risks from
ozone exposure; the problem of exposure measurement error in ozone mortality time-series
studies; use of ozone as a surrogate marker for other toxic photochemical pollutants; a general
downplaying of animal-to-human extrapolation studies; and the need for inclusion of welfare
issues (i.e., leading to the establishment of secondary standards for criteria air pollutants) in an
integrative synthesis chapter. Each of these issues is discussed in greater detail below.
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1. Background
The CASAC, comprising seven members appointed by the EPA Administrator, was
established under section 109(d)(2) of the Clean Air Act (CAA or "Act") (42 U.S.C. § 7409) as
an independent scientific advisory committee, in part to provide advice, information and
recommendations on the scientific and technical aspects of issues related to air quality criteria
and NAAQS under sections 108 and 109 of the Act. Section 109(d)(l) of the CAA requires that
EPA carry out a periodic review and revision, where appropriate, of the air quality criteria and
the NAAQS for "criteria" air pollutants such as ozone. The CASAC, which is administratively
located under EPA's Science Advisory Board (SAB) Staff Office, is a Federal advisory
committee chartered under the Federal Advisory Committee Act (FACA), as amended, 5 U.S.C.,
App. The Ozone Panel consists of the seven members of the chartered (statutory) CASAC,
supplemented by sixteen technical experts.
EPA is in the process of updating, and revising where appropriate, the AQCD for ozone
and related photochemical oxidants published in 1996. This teleconference was a continuation
of the Ozone Panel's peer review of the revised Ozone AQCD in this present NAAQS review
cycle for ozone. In the CASAC's final letter/report to you from the Ozone Panel's December 6-
7, 2005 meeting (EPA-CASAC-06-003, dated February 10, 2006, posted at the following URL:
http;//www_.ega^ we advised you that:
"... given the critical importance of the exposure and human health effects integrative
synthesis chapter in the development of the 2nd draft Ozone Staff Paper, after EPA issues the
final Ozone AQCD on February 28, 2006, the CASAC will determine whether there is a need to
convene a public meeting to conduct any additional review of Chapter 8."
On March 21, 2006, the Agency's National Center for Environmental Assessment
(NCEA-RTP) published the Final Ozone AQCD. After canvassing the members of the Ozone
Panel, we decided that, despite the fact that the AQCD has already been finalized, it would be
beneficial to hold a public teleconference meeting to provide additional advice to the Agency
concerning the integrative synthesis chapter of the Final Ozone AQCD in order to inform EPA's
preparation of the 2nd draft Ozone Staff Paper and, ultimately, the proposed NAAQS for ozone.
2. CASAC's Additional Advice Concerning Chapter 8 of the Final Ozone AQCD
It is the assessment of the CASAC that, in its development of the Integrative Synthesis
chapter in the Final Ozone AQCD, EPA has taken a fairly standard approach to putting together
the relevant information, and incorporating findings from atmospheric sciences, toxicology,
human clinical studies and epidemiology. In general, this is done reasonably successfully.
Unfortunately, there are some issues that are important when considering revisions to the
NAAQS that are not presented well, or at all, and that have substantial implications for the
Ozone Staff Paper. A discussion of the major issues is presented below and, as previously noted,
individual comments of Ozone Panel members are attached.
Utility of Time-Series Studies
The first area of concern is how time-series studies are used in assessing the risks from
ozone exposure. While the epidemiological evidence on the health effects of ozone constitute
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only a fraction of the totality of the scientific knowledge based on ozone health effects, this
evidence plays a disproportionately large role in the policymaking process. The ozone time-
series studies, particularly the mortality time-series studies, could potentially play an especially
important role in this process, as they did for particulate matter (PM), and therefore deserve
special attention. An issue that needs to be confronted relates to the utility of these time-series
studies in the NAAQS-setting process. Motivation for this concern is partly based on the
observation that time-series findings indicate associations of mortality with not only PM and
ozone, but with all of the criteria pollutants (see Stieb etal., J. Air Waste Manage. Assoc. 2002,
2003; the complete references are below).
Since it is unlikely that each of these pollutants will have similar short-term effects on
mortality, these findings suggest that while the time-series study design is a powerful tool, being
able to detect very small effects that could not be detected using other designs, it is also a blunt
tool. The Clean Air Act requires that NAAQS be set for individual criteria air pollutants using
the best available science. Because results of time-series studies implicate all of the criteria
pollutants, findings of mortality time-series studies do not seem to allow us to confidently
attribute observed effects specifically to individual pollutants. This raises concern about the
utility of these types of studies in the current NAAQS-setting process and could serve to
motivate interest in taking a broader perspective on regulating air pollution that incorporates the
entire mixture of community air pollutants.
Time-series studies typically make use of data from available air pollution monitoring
network sites in which concentrations of various subsets of the criteria pollutants are measured.
Study findings focus on identification of associations between day-to-day variation in these
concentrations and daily mortality. Not only is the interpretation of these associations
complicated by the fact that the day-to-day variation in concentrations of these pollutants is, to a
varying degree, determined largely by meteorology, the pollutants are often part of a large and
highly-correlated mix of pollutants, only a very few of which are measured. For the ozone and
other photochemical oxidant NAAQS, this pollutant mix includes a large number of both gas-
and particle-phase photochemical oxidant pollutants. Unfortunately, we have only limited
information on the specific chemical composition, toxicity and, equally importantly, the
population exposure of oxidant pollutants other than ozone.
Error in Estimating Exposure to Ozone
The Ozone Staff Paper should consider the problem of exposure measurement error in
ozone mortality time-series studies. It is known that personal exposure to ozone is not reflected
adequately, and sometimes not at all, by ozone concentrations measured at central outdoor
monitoring sites. Typically, personal exposures are much lower than the ambient concentrations,
and can be dramatically lower depending on time-activity patterns, housing characteristics and
season. In addition, and of particular importance for the ozone time-series studies, there can be
no correlation between personal concentrations of ozone measured over time and concentrations
measured at central outdoor sites. The population that would be expected to be potentially
susceptible to dying from exposure to ozone is likely to have ozone exposures that are at the
lower end of the ozone population exposure distribution, in which case this population would be
exposed to very low concentrations of ozone indeed, and especially so in winter. Therefore it
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seems unlikely that the observed associations between short-term ozone concentrations and daily
mortality are due solely to ozone itself.
Another implication of ozone measurement error that is relevant to the NAAQS-setting
process is that this degree of measurement error would be expected to have a substantial impact
on the ability to detect a threshold of the concentration-response relationship below which no
ozone effects are discernible. Pollutant exposure measurement error obscures true thresholds in
the concentration-response relationship, and this effect worsens with increasing degrees of
measurement error. Since threshold assumptions are incorporated in the Agency's risk
assessment and risk analyses, this issue will need to be addressed.
Ozone as a Surrogate for Other Toxic Agents
At least two questions arise from these observations that are relevant to the ozone
NAAQS-setting process: (1) What chemical agent or agents are at least partly responsible for
the observed associations between ozone and mortality in the time-series studies?; and (2) Do we
require an immediate answer to this question of whether ambient ozone adequately serves as a
surrogate marker that, when controlled, effectively mitigates health impacts of this entire mix of
pollutants? One possible explanation for the observed associations of ozone with mortality is
that ozone itself may be serving as a marker for other agents that are contributing to the short-
term exposure effects on mortality. This would require that outdoor concentrations of these
agents are correlated over time with outdoor ozone concentrations, which is to be expected if
they are products of the same atmospheric processes that lead to ozone formation, and that these
outdoor pollutant concentrations are better correlated with personal exposures than is the case for
ozone itself.
We have very little information on these last two issues at this time to make a strong
argument for this, although it is a plausible argument. It should be noted that the observed
associations pertain to total mortality, which implies that ozone is causing acute effects on the
cardiovascular system, and not merely on the respiratory system. As indicated in Chapter 8 of
the air quality criteria document, our understanding of cardiovascular effects of ozone is
currently very limited compared to our understanding of ozone's effects on the lung.
Animal-to-Human Extrapolation
The Integrative Synthesis chapter touches upon animal-to-human extrapolation issues in a
number of places, with the general theme being one of concern that such extrapolations cannot
be accomplished for ozone. The Ozone Panel did not agree with the extent to which these
extrapolations are downplayed, and offers the following comments, primarily for the benefit of
Agency staff who are involved in the development of the 2nd draft Ozone Staff Paper. The
experiments by Hatch discussed on page 8-31 of the Final Ozone AQCD give the reader the
impression that rats are more sensitive to ozone than are humans. However, if one adjusts for
ventilation differences between exercising humans and resting rats and body mass differences,
the relationships between inhaled dose and biological responses in these studies are in reasonably
good agreement.
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In addition, the statement found on page 8-16 that "some" subjects are reproducible over
time in their response to ozone is deceptive. The work of McDonnell and his EPA colleagues
clearly shows that the vast majority of subjects are reproducible over time in their response to
ozone exposure. Moreover, the 1996 publication by Overton et al. shows that anatomical dead
space accounts for the major part of heterogeneity among subjects seen in acute pulmonary
function responses in human clinical studies.
The chapter inconsistently presents the case for and against animal-to-human
extrapolation by first contending that physiological differences lead to large uncertainties in such
extrapolations, and subsequently stating the agreement between the species is sufficient to
support a common mode of action for ozone in producing biological effects. The latter is, in fact,
the more appropriate interpretation in view of the commonality of pulmonary function changes,
protein in lavage fluid, and a number of other biological endpoints between animals and humans.
In the preparation of the 2nd draft Ozone Staff Paper, EPA staff should pay particular attention to
the book chapter published by Ozone Panel member Dr. Charles Plopper ("Time-response
profiles: Implications for injury, repair and adaptation to ozone"; complete reference below)
concerning the importance of the relationship between ozone exposure in different scenarios and
the resulting biological responses (found in Appendix D). This gives rise to exposure/dosimetry
issues in terms of the pattern of biological response, and most likely requires a translation of the
animal exposures via a dosimetry model for full application to assessing human equivalent
exposure scenarios.
Inclusion of Welfare Issues in Integrative Chapters
The members of CASAC understand that the exposures and adverse effects of criteria
pollutants on public health have been the principal focus of the Agency's traditional sense of
responsibility to the people of the United States. But the U.S. Congress, in passing the Clean Air
Act Amendments of 1970, established that both public-health-based primary standards and
public-welfare-based secondary standards for criteria air pollutants should be set as part of the
NAAQS. Thus, the integrative chapters for criteria pollutants need to include discussion of
issues related to the setting of the both the primary and secondary standards.
The issues addressed above have direct implications for the Ozone Staff Paper, and
should be given thoughtful consideration in drafting the next version. They are particularly
relevant to the ozone risk assessment and risk analyses in which mortality time-series studies
have previously played a central role. The CASAC plans to have a general discussion of the
utility of time-series epidemiology studies for risk assessment purposes in a meeting at a later
date. We look forward to providing additional advice on this important issue in the future. As
always, we wish the Agency staff well in this important endeavor.
Sincerely,
/Signed/
Dr. Rogene Henderson, Chair
Clean Air Scientific Advisory Committee
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References:
Stieb, DM; Judek, S; Burnett, RT. Meta-analysis of time-series of air pollution and
mortality: Effects of gases and particles the influence of cause of death,
Journal of the Air & Waste Management Association., 52 (4): 470-484, 2002
Stieb, DM; Judek, S; Burnett, RT. Meta-analysis of time-series of air pollution and
mortality: Update in to the use of generalized additive models
Journal of the Air & Waste Management Association., 53 (3): 258-261, 2003
Plopper, C.G., R. Paige, E. Schelegle, A. Buckpitt, V. Wong, B. Tarkington, L. Putney and D.
Hyde. (2000) Time-response profiles: Implications for injury, repair and adaptation to ozone,
pp. 23-37. In U. Heinrich and U. Mohr, (Eds.), Relationships Between Acute and Chronic
Effects of Air Pollution. ILSI Press: Washington, DC.
Appendix A - Roster of the Clean Air Scientific Advisory Committee
Appendix B - Roster of the CAS AC Ozone Review Panel
Appendix C - Review Comments from Individual CASAC Ozone Review Panel Members
Appendix D - "Time-response Profiles: Implications for Injury, Repair, and Adaptation to
Ozone" (Hopper et a/.)
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Appendix A - Roster of the Clean Air Scientific Advisory Committee
U.S. Environmental Protection Agency
Science Advisory Board (SAB) Staff Office
Clean Air Scientific Advisory Committee (CASAC)
CHAIR
Dr. Rogene Henderson, Scientist Emeritus, Lovelace Respiratory Research Institute,
Albuquerque, NM
MEMBERS
Dr. Ellis Cowling, University Distinguished Professor-at-Large, North Carolina State
University, Colleges of Natural Resources and Agriculture and Life Sciences, North Carolina
State University, Raleigh, NC
Dr. James D. Crapo, Professor, Department of Medicine, National Jewish Medical and
Research Center, Denver, CO
Dr. Frederick J. Miller, Consultant, Cary, NC
Mr. Richard L. Poirot, Environmental Analyst, Air Pollution Control Division, Department of
Environmental Conservation, Vermont Agency of Natural Resources, Waterbury, VT
Dr. Frank Speizer, Edward Kass Professor of Medicine, Channing Laboratory, Harvard
Medical School, Boston, MA
Dr. Barbara Zielinska, Research Professor, Division of Atmospheric Science, Desert Research
Institute, Reno, NV
SCIENCE ADVISORY BOARD STAFF
Mr. Fred Butterfield, CASAC Designated Federal Officer, 1200 Pennsylvania Avenue, N.W.,
Washington, DC, 20460, Phone: 202-343-9994, Fax: 202-233-0643 (butterfield.fred@epa.gov)
(Physical/Courier/FedEx Address: Fred A. Butterfield, III, EPA Science Advisory Board Staff
Office (Mail Code 1400F), Woodies Building, 1025 F Street, N.W., Room 3604, Washington,
DC 20004, Telephone: 202-343-9994)
A-l
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Appendix B - Roster of the CASAC Ozone Review Panel
U.S. Environmental Protection Agency
Science Advisory Board (SAB) Staff Office
Clean Air Scientific Advisory Committee (CASAC)
CASAC Ozone Review Panel
CHAIR
Dr. Rogene Henderson*, Scientist Emeritus, Lovelace Respiratory Research Institute,
Albuquerque, NM
MEMBERS
Dr. John Balmes, Professor, Department of Medicine, University of California San Francisco,
University of California - San Francisco, San Francisco, California
Dr. Ellis Cowling*, University Distinguished Professor-at-Large, North Carolina State
University, Colleges of Natural Resources and Agriculture and Life Sciences, North Carolina
State University, Raleigh, NC
Dr. James D. Crapo*, Professor, Department of Medicine, National Jewish Medical and
Research Center, Denver, CO
Dr. William (Jim) Gauderman, Associate Professor, Preventive Medicine, Medicine,
University of Southern California, Los Angeles, CA
Dr. Henry Gong, Professor of Medicine and Preventive Medicine, Medicine and Preventive
Medicine, Keck School of Medicine, University of Southern California, Downey, CA
Dr. Paul J. Hanson, Senior Research and Development Scientist, Environmental Sciences
Division, Oak Ridge National Laboratory (ORNL), Oak Ridge, TN
Dr. Jack Harkema, Professor, Department of Pathobiology, College of Veterinary Medicine,
Michigan State University, East Lansing, MI
Dr. Philip Hopke, Bayard D. Clarkson Distinguished Professor, Department of Chemical
Engineering, Clarkson University, Potsdam, NY
Dr. Michael T. Kleinman, Professor, Department of Community & Environmental Medicine,
University of California - Irvine, Irvine, CA
Dr. Allan Legge, President, Biosphere Solutions, Calgary, Alberta, Canada
B-l
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Dr. Morton Lippmann, Professor, Nelson Institute of Environmental Medicine, New York
University School of Medicine, Tuxedo, NY
Dr. Frederick J. Miller*, Consultant, Cary, NC
Dr. Maria Morandi, Assistant Professor of Environmental Science & Occupational Health,
Department of Environmental Sciences, School of Public Health, University of Texas - Houston
Health Science Center, Houston, TX
Dr. Charles Plopper, Professor, Department of Anatomy, Physiology and Cell Biology, School
of Veterinary Medicine, University of California - Davis, Davis, California
Mr. Richard L. Poirot*, Environmental Analyst, Air Pollution Control Division, Department of
Environmental Conservation, Vermont Agency of Natural Resources, Waterbury, VT
Dr. Armistead (Ted) Russell, Georgia Power Distinguished Professor of Environmental
Engineering, Environmental Engineering Group, School of Civil and Environmental
Engineering, Georgia Institute of Technology, Atlanta, GA
Dr. Elizabeth A. (Lianne) Sheppard, Research Associate Professor, Biostatistics and
Environmental & Occupational Health Sciences, Public Health and Community Medicine,
University of Washington, Seattle, WA
Dr. Frank Speizer*, Edward Kass Professor of Medicine, Channing Laboratory, Harvard
Medical School, Boston, MA
Dr. James Ultman, Professor, Chemical Engineering, Bioengineering Program, Pennsylvania
State University, University Park, PA
Dr. Sverre Vedal, Professor of Medicine, Department of Environmental and Occupational
Health Sciences, School of Public Health and Community Medicine, University of Washington,
Seattle, WA
Dr. James (Jim) Zidek, Professor, Statistics, Science, University of British Columbia,
Vancouver, BC, Canada
Dr. Barbara Zielinska*, Research Professor, Division of Atmospheric Science, Desert Research
Institute, Reno, NV
SCIENCE ADVISORY BOARD STAFF
Mr. Fred Butterfield, CASAC Designated Federal Officer, 1200 Pennsylvania Avenue, N.W.,
Washington, DC, 20460, Phone: 202-343-9994, Fax: 202-233-0643 gov)
* Members of the statutory Clean Air Scientific Advisory Committee (CASAC) appointed by the EPA
Administrator
B-2
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Appendix C - Review Comments from
Individual CASAC Ozone Review Panel Members
This appendix contains the preliminary and/or final written review comments of
the individual members of the Clean Air Scientific Advisory Committee (CASAC)
Ozone Review Panel who submitted such comments electronically. The comments are
included here to provide both a full perspective and a range of individual views
expressed by Panel members during the review process. These comments do not
represent the views of the CASAC Ozone Review Panel, the CASAC, the EPA Science
Advisory Board, or the EPA itself. The views of the CASAC Ozone Review Panel and
the CASAC as a whole are contained in the text of the report to which this appendix is
attached. Panelists providing review comments are listed on the next page, and their
individual comments follow.
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Panelist Page#
Dr. Ellis Cowling C-3
Dr. William (Jim) Gauderman C-4
Dr. Henry Gong C-6
Dr. Rogene Henderson C-7
Dr. Michael T. Kleinman C-8
Dr. Morton Lippmann C-l 1
Dr. Frederick J. Miller C-13
Dr. Maria Morandi C-15
Dr. Charles Plopper C-17
Dr. Frank Speizer C-19
Dr. James Ultman C-21
Dr. Sverre Vedal C-22
Dr. James (Jim) Zidek C-23
Dr. Barbara Zielinska C-24
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Dr. Ellis Cowling
Dr. Ellis Cowling
North Carolina State University
May 1, 2006
Review of the Integrated Synthesis Chapter (Chapter 8) in the Final (2006) Criteria Document
for Ozone and Related Photochemical Oxidants
My major concern about the Integrative Synthesis Chapter (Chpater 8) for the Final Air
Quality Criteria Document for Ozone and Related Photochemical Oxidants (EPA/600/R-
05/004aF) is its exclusive focus on "Ozone Exposure and [Public] Health Effects." Integrative
Synthesis is at least as much needed with regard to "Ozone Exposure and Public Welfare
Effects" as it is on "Ozone Exposure and Public Health Effects."
All of us on CASAC understand that the exposures and adverse effects of criteria pollutants
on public health have been the principal focus of EPA's traditional sense of the Agency's sense
of responsibility to the people of the United States. But many of us also believe that the intent of
the US Congress in passing the Clean Air Act Amendments of 1970 was to establish both:
• public-health based Primary Standards, and also
• public-welfare based Secondary Standards
for Criteria Pollutants as part and parcel of the National Ambient Air Quality Standards.
The language of the Clean Air Act is quite explicit with regard to both the public-health
effects and public welfare effects of criteria pollutants - the Congress directed that the
Administrator of EPA shall: 1) identify air pollutants that "in his judgment, may reasonably be
anticipated to endanger public health and welfare," and 2) define National Ambient Air Quality
Standards that are "requisite to protect the public welfare from any known or anticipated adverse
effects associated with the presence of [the] pollutant in the ambient air."
The phrase "known or anticipated" provides both a significant degree of discretion, and a
substantial responsibility for the Administrator to use prudent professional judgment in dealing
with uncertainties and deficiencies in available scientific evidence regarding the exposure and
effects of ozone and other photochemical oxidants on crops, forests, and natural ecosystems and
their relationship to values held dear by the people of our country.
Thus, we hope that the Integrative Synthesis Chapters of all future Criteria Documents, (and
Staff Papers based on these Criteria Documents), will include Integrative Synthesis Chapters that
are indeed inclusive - chapters that describe the science that undergirds wise public policy
decisions aimed at protecting both the public-health concerns and interests of our people — as
well as the public-welfare concerns and interests of our people.
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Dr. William (Jim) Gauderman
Chapter 8, Integrative Synthesis
Jim Gauderman
5/12/05
Throughout the document, the term 'inconclusive' is used to denote non-significant. A large,
well-conducted study that finds no significant association should not be characterized as
inconclusive. Smaller studies that do not find a significant association should also be
characterized as such, perhaps with a caveat about low power.
Consistent units (ppm or ppb) should be used throughout
8-9, line 13: replace 'an optimal' with 'the'
8-12, line -9: eliminate 'sham' and remove parentheses from 'clean air'. Two lines down,
replace 'versus more closely mimicking' with 'rather than'
8-14: The last sentence that carries over onto 8-15 does not make sense.
8-15: I found the paragraph beginning with 'New uptake...' unsatisfying in that it did not
provide a clear summary of the directions of differences. For example, rather than saying there
were gender differences, the paragraph should indicate whether effects were higher for males or
females. This would not take much space and would improve the value of this summary
paragraph.
8-29, Table 8-1: 'Interindividual variability' is not a susceptibility factor. Eliminate 'being
recognized'.
8-33, line 13: Why focus only on studies from U.S. and Canada? Despite this caveat, the
document goes on to reference studies from Europe, for example on 8-38 and 8-58.
8-40, line -4: define 'per standardized Os increment'
8-41, line -10: replace 'quantitative results' with 'quantitatively equivalent results'
8-43, line -5: 'analyses' should be 'analysis'
8-44, line 5: This sentence seems like a copout. If this is the case, how can we move forward to
consider a revised standard? If the difficulty of finding a threshold below 0.08 is what is meant,
this should be stated more explicitly
8-47, line -9: replace 'pulmonary function' with 'response'
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8-50, line 7: replace 'cross-section' with 'longitudinal'. In the last paragraph, caveats should be
included to point out the high exposure levels to which the monkeys were exposed and the
limited relevance of these levels to current ambient Os levels.
8-53, lines 6, 7: replace 'fine' with 'ultrafme'
8-54, line -3: replace 'of with 'to'
8-60, line 11: replace 'smaller increases' with 'growth deficits'.
8-61, line 9: replace 'diminished' with 'smaller' here and 13 lines below.
8-79, line 10: insert 'exposure to current ambient levels of between 'long-term' and '(V
C-5
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Dr. Henry Gong
COMMENTS ON CHAPTER 8 (INTEGRATIVE SYNTHESIS)
Draft AQCD, February 2006.
Henry Gong, Jr., M.D., 4/30/06 (revised 5/1/06)
I have reviewed the revised chapter 8. I also concur with the comments by several CASAC
colleagues (Drs. Vedal, Zidek, and Lippmann).
The Staff has generally produced an improved chapter (integration) with sharper focus and
exposition on key issues such as those posed by the review in December 2005. The "integration"
will always remain a challenging task but I am comfortable with the current version, in
particular, in the area of the clinical studies.
Specific Comments:
1. I am pleased that Dr. Adams' recently published study was reviewed accordingly since
we lack many clinical studies using such low ozone exposure concentrations. The
inclusion of Fig 8-1B is an excellent example of the pitfalls of relying on group means
and the concept of adjusting for filtered-air responses ("ozone-induced"). The total
number of subjects in Adams' studies remains much smaller than in McDonnell's study.
I wonder if one can calculate post hoc the expected real effect size versus the probability
of finding a statistically significant effect for Dr. Adams' studies with ozone levels at
0.04 and 0.06 ppm, given the small number of subjects and inherent variability of FEV1
responses. This calculation might provide some measure of confidence about a "true
negative."
2. Page 8-50/lst para: "There are no data available from controlled human chamber studies
that evaluated chronic exposure regimens." This sentence is unnecessary and should
probably be deleted. The statement is misleading since its interpretation relies on your
perspective. One reaction is that it is obviously impractical and unethical to study
subjects inside an environmental chamber for 5 or 10 years! Some investigators have
reported intrasubject reproducibilty of ozone responsiveness over months (McDonnell
and Bedi, I believe) but not over years. However, aging is an unavoidable factor since
people apparently develop less ozone responsiveness with aging.
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Dr. Rogene Henderson
Comments on Chapter 8
Rogene Henderson
My major comment is on the content of the chapter. If it is too late to consider my
suggested changes, I would hope they might be taken into account for subsequent integrative
chapters in CDs.
I think the purpose of this integrative chapter is to facilitate the development of the Staff
Paper. The main concerns are whether ozone causes specific health effects and, if so, AT
WHAT LEVEL OF EXPOSURE. Based on these findings, the Staff Paper will attempt to
discern whether the current regulatory levels for ozone need to be altered.
I found Chapter 8 placed much emphasis on what health effects are induced, but did not
focus enough on the level of exposure required to induce the effects. For example, the first 27
pages of the chapter are a summary (repeat) of what was said in earlier chapters. I did not think it
needed, or at least not in such a lengthy form. There is a shortened version of this summary
starting on page 8-73 (sort of a summary of a summary) and it might serve as a better starting
point than the detailed repeated report in the initial part of the chapter. Another approach might
be to develop a summary table with references to the place in earlier chapters where the study is
described in detail.
The lack of focus on the level causing the effects can be seen in the tables. In Table 8-1,
8-2, and 8-3, we need a column(s) indicating the level of ozone exposure associated with the
effects. The exposure level is key to setting the regulations.
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Dr. Michael Kleinman
Dr. Michael Kleinman
Chapter 8 Comments
General Comments
This chapter is very comprehensive but loses focus. It could be significantly shortened. It might
be useful to focus on the integrated findings that directly support the recommendations for
revisions to the NAAQS that are presented in the Staff Paper. It is important to clearly establish
that the data used to support the recommendations are coherent, consistent and rational.
Specific Comments
Pg 8-31 L9-11 The Hatch findings need to be placed in context with the dosimetry information,
i.e. after adjustment for ventilation differences between exercising humans and resting
rats and body mass differences, the relationships between inhaled dose (|ig/kg bw) and
biological response for humans and rats are in agreement. The way this is presented
suggests that the rat is 5 times less sensitive than the humans, which is not true!
Pg 8-32 L 8-10 I assume that this information relates to ambient as opposed to laboratory
exposures. If so one needs to acknowledge that there might be some efforts to self-
medicate before seeing a physician. In addition, this discussion needs to be integrated
with observations of duration of O3 episodes. O3 episodes are rarely a 1 day event. The
controlled study data clearly show that effects of O3 are worse on the second day of an
intermittent exposure. By the third day there may be some attenuation of responses. To
further complicate things, there may be cumulative effects as well as progressive effects
that relate to lags. The paragraph should be expanded to take these factors into account.
Pg 8-36 L5 It should be noted that observation of attenuation of 03-induced inflammatory
response (Kopp et al. 1999) was consistent with earlier pulmonary function studies (Linn
et al. 1988) which showed that individuals in Los Angeles were responsive to controlled
O3 exposure in the spring but that the response was attenuated when measured in the fall
after a summer of relatively high ambient O3 exposures. Sensitivity to O3 was recovered
by the following spring indicating that response attenuation is transient.
Pg 8-36 LI 1 The basis for stating why "these findings must... be considered inconclusive"
should be presented. For example, ... due to possible confounding by PM2.5, elemental
carbon and NO2 (Chan et al. 2005; Holguin et al. 2003; Liao et al. 2004; Park et al.
2005).
Pg 8-37 L5-6 Several studies showed an association between ambient ozone exposures and
emergency room visits for respiratory disease (Bates et al. 1990; Castellsague et al. 1995;
Cody et al. 1992; Ponce de Leon et al. 1996; Stieb et al. 1996). The statement could lead
one to presume that the association is due to lack of control for confounding by
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temperature. There should some more detailed explanation or interpretation offered. For
example, could it be noted that reasons for finding relationships with warm weather
ozone exposure but not for year-round exposure might be that during winter there is less
photochemical production of O3 and that the O3 effects might be masked by other
pollutants whereas this is less of a problem during the high O3 season?
Pg 8-38 L28-30 Should some statement be made that given the significant associations between
mortality and exposures at or below 98th percentile 8-h max O3 levels of 80-85 ppb there
is little or no margin of safety offered by the current NAAQS?
Pg 8-42 L 20-21 In terms of public health it is important to note that the percent of individuals
showing decreased pulmonary function showed a dose-related response with respect to
O3 at levels of 0.06 ppm. The group mean differences rely on only part of the entire data
set. It might be more useful in the establishment of health protective standards to use all
the data in a regression format to better estimate the region for which significant numbers
of individuals might experience adverse effects.
Pg 8-43 L 9-10 Again, relating to margin of safety, these findings suggest that the current
standard is less protective than it should be. Shouldn't this be one of the conclusions in
the Staff Paper??
Pg 8-43 L 27 Change to "A more formal threshold analysis..."
Pg 8-44 L 5 Perhaps it would be more accurate to state that there is insufficient evidence to
support a threshold for adverse effects of O3. Furthermore, if there is a threshold, the
data seem to indicate that it would be lower than the current 8-h standard of 80 ppb.
Bates DV, Baker-Anderson M, Sizto R. 1990. Asthma attack periodicity: a study of hospital
emergency visits in Vancouver. Environ Res 51(1):51-70.
Castellsague J, Sunyer J, Saez M, Anto JM. 1995. Short-term association between air pollution
and emergency room visits for asthma in Barcelona. Thorax 50(10): 1051-1056.
Chan CC, Chuang KJ, Su TC, Lin LY. 2005. Association between nitrogen dioxide and heart
rate variability in a susceptible population. Eur J Cardiovasc Prev Rehabil 12(6):580-586.
Cody RP, Weisel CP, Birnbaum G, Lioy PJ. 1992. The effect of ozone associated with
summertime photochemical smog on the frequency of asthma visits to hospital
emergency departments. Environ Res 58(2): 184-194.
Holguin F, Tellez-Rojo MM, Hernandez M, Cortez M, Chow JC, Watson JG, et al. 2003. Air
pollution and heart rate variability among the elderly in Mexico City. Epidemiology
14(5):521-527.
Kopp MV, Ulmer C, Ihorst G, Seydewitz HH, Frischer T, Forster J, et al. 1999. Upper airway
inflammation in children exposed to ambient ozone and potential signs of adaptation. Eur
RespirJ14(4):854-861.
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Liao D, Duan Y, Whitsel EA, Zheng ZJ, Heiss G, Chinchilli VM, et al. 2004. Association of
higher levels of ambient criteria pollutants with impaired cardiac autonomic control: a
population-based study. Am JEpidemiol 159(8):768-777.
Linn WS, Avol EL, Shamoo DA, Peng RC, Valencia LM, Little DE, et al. 1988. Repeated
laboratory ozone exposures of volunteer Los Angeles residents: an apparent seasonal
variation in response. Toxicol Ind Health 4(4):505-520.
Park SK, O'Neill MS, Vokonas PS, Sparrow D, Schwartz J. 2005. Effects of air pollution on
heart rate variability: the VA normative aging study. Environ Health Perspect
113(3):304-309.
Ponce de Leon A, Anderson HR, Bland JM, Strachan DP, Bower J. 1996. Effects of air pollution
on daily hospital admissions for respiratory disease in London between 1987-88 and
1991-92. JEpidemiol Community Health 50 Suppl I:s63-70.
Stieb DM, Burnett RT, Beveridge RC, Brook JR. 1996. Association between ozone and asthma
emergency department visits in Saint John, New Brunswick, Canada. Environ Health
Perspect 104(12): 1354-1360.
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Dr. Morton Lippmann
Comments of Dr. Morton Lippmann
NYU School of Medicine
April 17, 2006
Chapter 8 (Integrative Synthesis) of Final Ozone AQCD
I've read through Chapter 8 of the Feb. 2006 draft of the Ozone CD, and find it to be generally
satisfactory. It could be condensed somewhat if time and resources permitted tighter editing.
Also, it should be more consistent in its use of ozone concentrations. There are many places
where they are in ppm, others where they are in ppb, and still others where they are in ppm, with
ppb in parentheses. Also, "in vivo" and "in vitro" should be italicized.
My major criticism is that there is not nearly enough emphasis in the discussion of the
epidemiological studies of the fact that O3 needs to be considered as a surrogate index for the
photochemical mixture containing O3.1 point this out first in my note for page 8-2 below. There
needs to be a new introduction to the discussion of the epidemiology that explains why this
distinction is needed in the integrative discussion of the laboratory-based studies and the field
and larger population epidemiology. This was an issue discussed by the CASAC ozone Panel at
our last meeting, and I sensed that we felt it was important for NCEA to implement it when
revising Chapter 8.
The following are some specific corrections and suggested edits:
p. 8-1, para. 2,1. 3: change "nitrogen oxides (NOx)" to "nitrogen dioxide (NO2)."
p. 8-2, para. 1,1. 5-7: change "whereas less attention is accorded to the distinctly much more
limited available information on other photochemical oxidants, e.g., PAN or H2O2." to "and on
O3 as an index of the mixture of photochemical oxidants, including PAN, H2O2, and oxygen
containing radicals, for which much more limited information is available."
p. 8-3, para. 2,1. 5: change "clean" to "cleaner."
p. 8-3, para. 3,1. 2: insert "finer scale" before "spatial."
p. 8-4, para. 2,1. 8: insert "due to springtime intrusions of stratospheric O3" after "Hemisphere."
p. 8-8, para. 2,1. 14: change "O3" to "photochemical oxidant."
p. 8-8, para. 3,1. 4: delete "somewhat."
p. 8-15, para. 2,1. 4: insert "generally" before "having."
p. 8-25, para. 2,1. 7-12: A reference should be provided to support this statement.
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p. 8-63, para. 1,1. 8, 10, and 14: insert "onset" before "risk."
p. 8-69, para. 2,1. 12: insert "Thurston et al. (1997) showed that asthmatic children did receive a
physician-ordered increase in medication in proportion to the ambient O3 concentration." before
"Such."
p. 8-74, para. 2,1. 12: add "below O.OSppm, and even below 0.06ppm" after "levels" (Spektor et
al. 1988).
p. 8-75, para. 2,1. 2: change "0.08" to "0.06" (based on Adams 2006)
p. 8-75, para. 2,1. 12: delete "likely."
p. 8-75, para. 2,1. 13: insert (Thurston et al. 1997)" after "children."
p. 8-80, para. 1,1. 3: change "increased risk of mortality" to "reduced longevity." (This is to
distinguish between the evidence from the time-series studies of daily mortality, and the lack of
evidence for increased annual mortality.)
p. 8-80, para. 2,1. 8: insert "short-term" before "responsiveness."
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Dr. Frederick J. Miller
Dr. Fred J. Miller
May 18, 2005
Integrative Synthesis: Ozone Exposure and Health Effects
Chapter 8
General Comments
This second version of the integrative synthesis chapter is greatly improved over the first. The
collective evidence for ozone health effects based upon dosimetry, animal lexicological, human
clinical, and epidemiological data is well presented and laid out in a logical manner. The sections
of the chapter are inconsistent in their use of references, a situation that a final edit could correct.
Despite the improvements, there are a number of points made in the chapter that are either
incorrect or that would benefit from expansion or rewording if it were not for the fact that the
Ozone Criteria Document has already been finalized. Nonetheless, the following comments are
offered so that EPA staff charged with development of the Ozone Staff Paper can benefit from
them.
• The discussion of Policy Relevant Backgrounds does not bring out that these values are
dependent on the time of the year. In addition, I would echo the comments of Dr. Zidek
concerning the influence of measurement error on PRB values and their usefulness in
assessing risk.
• The section on dosimetry still does not discuss one of the most important findings since
the last CD, namely that anatomical dead space is a major driver of the delivered dose of
ozone and probably accounts for a major part of the heterogeneity seen in responses in
human clinical studies. I noted this in my comments on the first draft of this chapter.
• The statement is made on page 8-8 that ambient and personal exposures are well
correlated. As Dr. Zidek noted in his comments, the available studies do not support a
strong conclusion on this point.
• At the start of Section 8.3.1, the statement is made that "Children tend to be more active
outside and, therefore, often manifest a higher breathing rate than most adults". The fact
is that children have a higher basal rate period. So the sentence is somewhat misleading.
• On page 8-12, the statement is made that "Earlier animal toxicology studies were carried
out using relatively high 03 exposure concentrations/doses that do not reflect "real
world" exposure scenarios". This was in reference to studies available for the 1996
AQCD. This statement is incorrect. The EPA chronic O3 study conducted in the 1980s
mimicked real world patterns and started with a background exposure of only 0.06 ppm.
• There are discrepancies on pages 8-13 and 8-14 concerning animal to human
extrapolations. First it is contended that molecular differences between animals and
humans lead to large uncertainties in animal to human extrapolations. Yet on the next
page, there is discussion purporting a common mode of action for O3 between animals
and humans. In the opinion of this reviewer, extrapolation for various endpoints is quite
possible, has been done successfully in the past, and is done a disservice by the
statements of the author(s) of this section. Some of the examples and discussion in
Chapter 4 support the practicality of animal to human extrapolation for ozone effects.
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In the last paragraph on page 8-14, the statement is made that newer studies show that
uptake decreases as airflow rate increases. This observation has been known since the
1970s based upon the work of Aharonson and also by Frank and colleagues.
On page 8-16, the statement is made that some subjects are reproducible over time in
their response to ozone. I would submit that the work of McDonnell and colleagues
shows that the vast majority of subjects are reproducible over time in their response to
ozone exposures. Thus, the use of "some subjects" is misleading.
Triangle exposures (p. 8-19) are said to reflect ambient patterns better than square wave
exposures, which is correct. However, has the length of time to the peak of the triangle in
the exposure studies been truly reflective of "real world" patterns? The reasonableness of
triangle versus square wave exposure scenarios most likely varies depending upon
geographic location, particularly across the United States.
In Figure 8-3, the authors should have made clear in the legend that these resolution times
relate to brief exposures to ozone.
On page 8-31, some aspects of animal to human extrapolation are discussed. Here would
have been a good place to make reference to studies on protein in lavage fluid and how
dosimetry models have been used to integrate the experimental findings across species.
This presumes that this material was reworded in Chapter 4 in response to my comments
on the August 2005 version of Chapter 4.
"Tolerance" is used incorrectly in multiple places in this integrative synthesis chapter.
Tolerance has a very specific definition arising from animal toxicological studies wherein
exposure to a lower level of a chemical imparted protection from effects when animals
were subsequently exposed to higher concentrations of the chemical. The authors should
have stuck with "attenuation" in describing the diminishing or lack of occurrence of
changes with repeated ozone exposures.
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Dr. Maria Morandi
Comments on Chapter 8 - Maria T. Morandi
Chapter 8 appears to give more weight to the cardiovascular and mortality effects (Sections 8-3
on page 8-27 to 8-32; pages 8-36 to 8-39 and section on cardiovascular effects, and section
8.6.3) studies than the Panel considered scientifically appropriate given the available evidence
and uncertainties, the latter being especially important with regards to exposure estimate error.
The other consideration, as discussed by the Panel, is the discrepancy between the levels of
ozone at which exposure-effects are observed in chamber studies of acute lung function, and the
significantly lower measurements (compared to the chamber exposures and outdoor
concentrations) reported by studies that have conducted personal exposure measurements of
ozone, and the results of epidemiology studies of acute effects that use the ambient
measurements as the surrogate for exposures. These differences suggest that ozone may be acting
at least in part as a surrogate for other oxidants that are formed via chemical reactions leading to
ozone formation and accumulation.
Page 8-3
Quote: "Median values of daily 1-h max Ch were typically much higher in large urban areas or in
areas downwind of them. For example, in Houston, TX they approached 0.20 ppm during the
same 2000-2004 period."
The text appears to imply that the median values of daily-1-h max of ozone for Houston in the
2000-2004 period approached 0.20 ppm, which cannot not be correct. 0.20 ppm is reasonable
as the maximum 1-hr concentration over the period, not the median of the 1-hour max. On pages
8-4 and 8-5 the text says that 1-hour maximum values approach 0.20 ppm in the Eastern US and
California, the latter been similar to maxima in Houston.
Page 8-8
Quote: "Thus, activity level is an important consideration in determining potential Ch exposure
and- dose received"
Exposure is concentration X time only. Potential dose is concentration X time X inhalation rate
(such as minute volume); inhalation rate varies with activity level.
Section 8.3
1st two paragraphs: This section needs to be tempered regarding the assumption that ambient
measurements are a good estimate of personal exposures in a population. This is a reasonable
assumption in many, but not all, cases. Thus, there could be significant exposure estimate errors
when comparing exposure-response across different subgroups in a population, or across
different populations, because correlations between outdoor and indoor concentrations may not
be necessarily high everywhere. For example, in Houston, which has a very high utilization of
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conventional air conditioning (and, consequently, very low indoor ozone concentrations in a
large fraction of homes during the ozone season), the ambient concentrations may not be good
indicators of personal exposures for a large proportion of the population because the indoor
residential concentrations remain essentially unchanged - frequently at or below the detection
limit of the ozone monitor- while the outdoor concentration varies significantly increasing,
peaking, and declining during the day (see prior versions of the AQD for citations to the 1980
Houston Asthma Study). In other cities where natural ventilation or evaporative AC
predominates, outdoor concentrations are indeed a better surrogate of personal exposures
because they correlate with the indoor concentrations. Perhaps the text should be modified to
indicate that the outdoor concentrations are the only available index (rather than "most useful")
of exposure distributions at this time.
Section 8.3.2:
This section does not mention at all the impact of HVAC systems on indoor ozone
concentrations, which is more than just due to low AER. In residences or commercial buildings
with HVAC systems, a large fraction of the indoor air re-circulates in the ductwork which
provides additional surfaces for ozone decay and reactions with materials deposited in the filter.
Some additional editorial suggestions:
Page 8-12:
"...to help identify potential mechanisms(s) of action..."
"Since then a few newer, more recent human clinical and... air pollutant mixtures; and . tThe
results..."
Page 8-21
Quote: "..most important biological markers of Ch-induced injury response mechanisms in both
humans..."
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Dr. Charles Plopper
CASAC-Chapter 8
Integrative Synthesis: Ozone Exposure and Health Effects
Comments by C.G. Plopper
One of the fundamental issues missing in the overview of the section (8.4.1) dealing with
Integration of Experimental and Epidemiologic Evidence is a discussion of the patterns of
biologically relevant exposure conditions. The issues which are involved include establishing the
biological impact when:
1) The peak exposure concentration exceeds the threshold necessary to produce a response
an acute biological response;
2) the duration of the exposure period where the peak exceeds the threshold for acute
biological response;
3) The number peak days that reach biologically relevant concentrations with less than 24
hour intervals of non-biologically responsive concentrations;
4) The extent of this interpeak interval.
When peaks are separated by 24 hours or less (usually approximately 18 hours) the biological
response is less as exposure progresses than if the interexposure interval extends beyond seven
days. Short interexposure periods (less than 24 hours) during multiple repeated exposure results
in the production of a phenomenon called tolerance. In other words, a repeated history of
exposures above the threshold on successive days results in a depression of the acute response
and decreased sensitivity. An additional aspect of this response is that once a series of these
exposure regimens have occurred in which repeated peak days last over a significant period of
time, generally 4-7 days, the biological response will be altered when additional exposures occur
in the future.
It is difficult to address the cross cutting issues relevant to assessment/interpret of ozone health
effects without including the relationship between exposure scenarios and the biological
response. The chapter as written does not clearly separate acute responses, versus chronic
responses, versus the development of tolerance and how exposure history influences both acute
and chronic responses. While this section summarizes earlier animal studies, it does not really
address the exposure/dosimetry issue in terms of the pattern of biological response.
There are discussions throughout section 8.4.1 and .2 which refer to doses and assessments, but
do not clearly differentiate how the pattern of exposure can influence the measurements. This is
especially critical for the section on lung inflammation. The paragraph ending at the top of page
8-36 is a good example of how the exposure scenario impacts the biological response and how
this alters the endpoints that are measured physiologically.
It would be helpful for the discussion to break out the differences between long term exposure
and chronic effects, because the effects depend on the population exposed, the history, and the
pattern of exposure during the acute phases of response. In section 8.6.2 no mention is made of
the fact that exposure history for subjects in the human studies were not addressed. The same
situation was true when the bottom of page 8-50 which discusses long term infant studies, but
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does not include the studies of young adult rhesus monkeys which found essentially the same
time of response.
In the beginning of section 8.7 there is a discussion of the susceptible and vulnerable populations
and issues which may alter susceptibility. The issue of exposure history is ignored in this section.
Some discussion somewhere needs to be included, because this is a critical factor in judging the
level of sensitivity of populations and dictates whether individuals will appear more or less
susceptible to chronic injury.
The same is true for the discussion on page 8-58 and on pages 8-60 and 8-61, especially the last
paragraph in section 8.7.2.
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Dr. Frank Speizer
Comments on Chapter 8, Feb. 2006 Final Ozone AQCD
Submitted by Frank E. Speizer, MD
General Comment:
The organization of the chapter works well. I particularly like the way the added new
data are presented as an extension of the 1996 document. Notably, no negative or inconsistent
findings are mentioned until the epidemiology section. Does this mean that there are no tox or
human exposure studies that are null, or is the publication bias stronger than in the epi field?
Some discussion of this is warranted.
The integrated discussion of the possible mechanisms from tox and human studies as
related to the epidemiological finding is a useful addition in pulling the data together. The
summary of the finding is complete. What are missing are staff recommendations for a standard.
I would have thought that the concluding section of this chapter should contain this discussion.
Is it still to come? When will we have a chance to see it?
Specific Comments:
Page 8.2, first full para, line 8: Take out word "various"
Page 8.2, last paragraph. Whole paragraph is totally redundant with last sentence of previous
paragraph and can be left out.
Page 8.3, section 8.2.1, lines 8-9. I think this should be qualified with something like "except for
Los Angeles and Houston as well as other sites in California".
Page 8.12, first full paragraph. It doesn't make sense to leave out Chapter 7 in this intro
paragraph, particularly since the title of the section includes Epidemiology and 2 paragraphs later
on page 8.13, the Epidemiology studies are introduced.
Page 8.17,text lines 5-6: suggest take out "and seem physiologically insignificant". This is
simply catering to the lack of understanding of group mean differences and the rest of the
sentence adequately addresses the issue.
Page 8.18, last para, line 1: "triangular exposure profile" is jargon. Needs to be defined up front
rather than at end of paragraph on page 8.19.
Page 8.20, last para, line 8: Change "common" to "Spirometric"
Page 8.21, last para, line 1: Take out word "most"
Page 8.34, second full para, lines 8-9: Take out sentence, already said above.
Page 8.34, last para, line 2: Change 40.3ppb (SD 15.2) to .04ppm (SD .015)
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Page 8.38, para 1, line 6: This is a bit of overstatement. Most of the studies presented were not
really "designed specifically to examine the effects of O3"... I think the word "specifically"
might be removed without changing the meaning of the sentence and would be more accurate.
Page 8.39, para 1, lines 14-18: These two sentences may lead to confusion. I think I know what
the author is trying to say, but there is a whole science about omission and commission in using
underlying and contributory cause of death. None of it has to do with causality as expressed
here. The fact that a contributory cause of death may be the underlying cause and is
misclassified has little to due with causality as related to air pollution. (It is for this reason that
many authors use cardiopulmonary when doing analysis of air pollution health effects, and can
use cardiovascular since it represents more than 60% of the total.) The last sentence presumes
the coding rules are being ignored. Suggest simply leave off the last two sentences.
Page 8.55, second full para, last line: Agree with statement but I did not see many O3 epi
studies quoting exposures below .OSppm.
Page 8.67, 8.68, Tables 8.2 and 8.3: Not clear that the definitions of small, moderate and large
are correct for change in bronchoresponsiveness. Footnote says a 100% change equivalent to a
50% decrease in PD20. (I recognize that this table is reproduced from 1996, but that doesn't
mean it should be accepted without comment). I would have thought a 20% decrease in PD20
was significant, and adjusting up from there would change cut off points. Similarly for changes
with airways resistance, the cuts offs are too high.
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Dr. James Ultman
Comments on Revised Chapter 8
James Ultman
May 20, 2006
It is apparent that considerable effort has gone into the development and refinement of this
chapter, and it does provide a useful (but unnecessarily lengthy) summary of the previous
chapters and their annexes.
The authors of the chapter successfully demonstrate that there is a strong homology of ozone-
induced responses between animals and people, implying that the underlying biological
mechanisms are similar among the different species. On the other hand, the authors point out
that there are differences in gene transcription between animals and man, implying that ozone-
induced responses may not occur by the same mechanisms. In addition, the chapter says very
little concerning the application of dosimetry to bridge the gap between exposure, dose and
response. Overall, this chapter should have sent a much clearer message that we have the tools
to perform quantitative interspecies or intraspecies extrapolations using quantitative dosimetric
analyses.
I would hope that the staff document would, in fact, not hesitate to use such analyses, where
appropriate. A particular situation that comes to mind is the extrapolation of health effects
observed in adults to the comparable effects in children by taking into account differences in
lung sizes and ventilation rates.
Also, I strongly agree with Rogene Henderson's comment that there are no definitive statements
in the chapter regarding specific exposure levels at which ozone-induced health effects of
various types are likely occur. Thus, very little explicit guidance is provided to those developing
the Staff Document.
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Dr. Sverre Vedal
Comments on Feb 2006 draft Ozone Criteria Document, chapter 8 (Integrative Synthesis)
This version of chapter 8 has improved its focus on observational study effects at or below the
current NAAQS, and it continues to do a good job in integrating findings from different
disciplines. But, in my opinion, some major issues that would seem to be critical for moving
ahead with the Staff Paper are not handled well.
1. The issue of exposure (or the lack of it) in the new mortality time series studies, studies that
will likely play a central role in discussions on revising the standard, is not really touched on, as
it was to some extent in Ch.7.1 previously made extensive comments in this regard on Ch.7 and
Ch.8 of the last draft, and will not repeat them now. The points remain relevant. I agree with
Jim Zidek's points on measurement error as well, and refer you to his comments. I would not
relish the prospect of a risk analysis carried out by OAQPS on the basis of the time series
mortality studies until the issue of exposure has been thoroughly aired.
2. Exposure measurement error in the case of ozone will have a much more substantial effect on
obscuring a concentration-response threshold than in the case of PM. This would seem to be an
important issue when planning an ozone risk analysis, but is not mentioned.
3. If we think, on the other hand, that ambient ozone concentration in observational studies is
important more as a measure of photochemical pollutants in general, rather than as a measure of
ozone exposure specifically, then this should be stated. Then an issue will become one of
evaluating what evidence we have for exposure to, and effects of, these pollutants, about which I
suspect we know relatively little.
4. The bottom line on chronic effects puts more emphasis on the studies of seasonal lung
function effects in children than those of longer-term effects -1 think this is a misplaced
emphasis.
5. There are also some factual errors (e.g., the Gong study did in fact show increased heart rate
due to ozone).
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Dr. James (Jim) Zidek
COMMENTS ON CHAPTER 8 OF THE AQCD FOR OZONE
Prepared by Jim Zidek, April 17, 2006
The synthesis chapter seems quite well written. I have just a few comments limited to topics
connected with comments I submitted during the Draft AQCD reviews.
Page 8-7: In the revised AQCD, I was pleased to see some discussion of CTM estimation errors
on page 2-21 and 2-22 and the need to evaluate them "by comparison with field data".
Moreover, interesting discussion of such errors for GEOS-CHEM has been included in Chapter 3
(eg page 3.52) and even in the Executive Summary. Yet Chap 8 ignores them. This omission
highlights the need to address them in the Staff paper and how they are to be accommodated in
calculating the ozone standard. In particular, should the standard be raised, lowered of left
unadjusted in view of that error in estimating the PRB? Would a big error lead to the adoption of
a different PRB level than a small one?
Page 8-8: Here we find the following statement: "Nevertheless, although substantial variability
may exist among personal measurements, human exposure studies have observed that daily
average personal Ch exposures for the general population tend to be reasonably well correlated
with monitored ambient Ch concentrations." This seems to be an example of the ecologic effect,
making its relevance for the Staff paper doubtful. Moreover, it seems at odds with the preceding,
"However" sentence. Finally, I would note that pages 3-72 & 3-73 give a mixed picture of this
association. One study produced an insignificant or barely significant association, the other a
significant association. Moreover the second found that "ambient Os levels overestimated
personal exposures 3- to 4-fold in the summer and 25-fold in the winter" hardly giving one
confidence that the population average exposure is reasonably "well correlated" with ambient
levels.
Page 8-8: The next sentence to that above concludes: "Therefore, ambient Os monitoring data
appear to provide the most useful index of human Os exposure currently available to help
characterize health outcomes associated with Os exposures of large population groups." This
sentence suggests indices other than ambient levels were considered and rejected but I cannot
find such alternatives in the AQCD. Instead many indices (i.e., "metrics") based on ambient
monitoring measurements are discussed.
The real aim of these two sentences seems to be support for ambient monitoring based criteria.
Even more support appears in the "Thus" sentence in the middle of Page 8-10. However, based
on the evidence offered in the AQCD, that support seems more tenuous than Chap 8 lets on. If
additional evidence can be found, the Staff paper should cite it, as this is a contentious issue. It
is one reason why APEX and other such methods have to be used in contexts like this to try to
forecast the actual effect a change in the AQS might have on human exposure.
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Dr. Barbara Zielinska
Comments on Chapter 8 (Integrative Synthesis) of the Ozone AQCD
By Barbara Zielinska, April 30, 2006
In general, I found Chapter 8 well written and informative. However, there are still some issues
that are not represented adequately in this integrative synthesis. I agree with Jim Zidek that the
uncertainties of the GEOS-CHEM global model estimates of Policy Relevant Background (PRB)
should be mentioned in the integrative synthesis - this is important for the future ozone standard
determination. I also think that the Section 8.3 on human exposures to ambient ozone has some
problems. Although the Section mentions briefly the problems with estimating human exposure
on the basis of central monitoring data, it still maintains that the ambient O3 concentrations
measured outdoors at community monitoring sites provide the most useful index of human O3
exposure (page 8-8 and 8-10). I don't think that the AQCD provides strong evidences for such a
statement. I'm also not sure if ambient O3 concentrations and/or (?) personal O3 exposure
monitor measurements may serve as "surrogate indices of exposures to broader O3 -containing
ambient mixtures of photochemical oxidants and/or other pollutants" (page 8-10). Which "other
pollutants"? I don't think that there are sufficient evidences provided in the Ozone AQCD
supporting such a statement.
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Appendix D - "Time-response Profiles: Implications for Injury,
Repair, and Adaptation to Ozone" (Hopper et al.}
Time-response Profiles: Implications for Injury, Repair, and Adaptation to
Ozone
C. PLOPPER, R. PAIGE, E. SCHELEGLE, A. BUCK-PITT, V WONG, B. TARKINGTON, L. PUTNEY, AND D. HYDE
School of Veterinary Medicine and California Regional Primate Research Center, University of California,
Davis, CA, USA
Correspondence: Dr. Charles G. Plopper, School of Veterinary Medicine, Department of Anatomy,
Physiology and Cell Biology, One Shields Avenue, UC Davis, Davis, CA 95616, USA
Introduction
The biological response of the respiratory system to exposure to oxidant air pollutants such as
ozone follows a well-characterized pattern of cellular injury, inflammatory and repair events which is highly
dependent upon the inhaled concentration and the length of the exposure. There is clear dose-response
curve of acute injury for the initial exposure of naive animals and humans under experimental conditions.
The initial cellular injury sets in motion a series of inflammatory and repair processes which follow a
relatively uniform time course regardless of the extent of the acute injury, unless it is so massive as to be
fatal. Under experimental conditions, these repair processes lead to the reestablishment of the pre-exposure
steady-state within a finite period of time. Imposition of additional periods of exposure to injurious
concentrations during the repair process alters the cellular events and leads to the establishment of a new
steady-state where inflammation is markedly reduced and the cells which repopulate the injury site are
resistant to further acute injury by oxidant gases. This is true regardless of how long the exposures are
continued. Despite the very large number of long-term exposure studies, the utility of experimental animal
studies for estimating the long-term risk to human populations of ambient exposure conditions appears
limited. One of the limitations is that concentration multiplied by time does not equal effect (Gelzleichter
et al., 1992). Depending on the measures used to assess effects, the response may actually appear to
diminish over time. A second limitation is that ambient conditions are such that the periods when oxidant
gas concentrations are elevated to levels which can produce injury are highly variable. The period below
threshold concentrations can vary from as little as 18 hours to as long as many months.
Additionally, these periods generally cycle annually. The intent of this review is to examine the issue
of time in terms of the temporal characteristics of exposure conditions and the pattern of biological responses
on which exposures are imposed.
Exposure Pattern
For the purposes of this discussion, exposure patterns will be characterized by three key parameters:
concentration, duration of exposure (or exposure period), and the length of time between exposures when the
concentration is below the biological response threshold (the interexposure interval (Figure 1 a). Ambient
exposures are variable in nature, with daily and seasonal variations in concentration (Figure 1 b-d) (USEPA,
1996). As the examples in Figure 1 illustrate, under ambient conditions the duration of exposure to
elevated ozone concentrations on a daily basis is approximately 6 hours. The peak concentrations during
this 6-hour period are highly variable by season. And there are many days, even during seasons
associated with high average ambient levels, when the ambient concentration is very low or near
background.
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Biologic Response
The response of the respiratory system to ozone exposure can be characterized in terms of the
initial injury and inflammatory responses, followed by proliferation and repair of the epithelium at the
site of injury. While there are a variety of biologic responses following ozone exposure, for the sake of
comparison we will consider only the epithelial and inflammatory responses summarized in Figure 2.
Initial responses include injury and death of ciliated cells in conducting airways and squamous
epithelial cells in the centriacinar region of the parenchyma. This phase, which appears to occur within
the first 8-12 hours of exposure, is associated with marked increases in intraluminal exudate that initially
contains primarily epithelial cells and serum proteins, with minimal or no changes in the interstitium.
This phase also includes degranulation of secretory cells. Subsequently, injured epithelium exfoliates and
there is an increase in exudate containing inflammatory cells, primarily neutrophils and eosinophils. (See
Paige and Plopper, 1999, for detailed review.)
Proliferation of the epithelium, concurrent with downregulation of intraluminal exudates, marks
the next stage of response. Significant numbers of inflammatory cells may still be found migrating
through the epithelium at this stage, but within 7 days the acute inflammatory response is almost
completely resolved. At this time, epithelial proliferation has greatly diminished, the epithelium is often
hyperplastic, and proliferation of matrix components is in progress. After completion of this series of
events, subsequent responses are dependent upon whether or not exposure to injurious concentrations
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continues. If exposure ceases,
s, the affected compartments will revert to pre-exposure steady-state within
7-10 days.
Effects of continued long-term exposure include persistent hyperplasia, low-grade chronic
inflammation with few exudative cells (primarily macrophages), and increased synthesis of collagen.
Short-term Exposures
Very short exposures (as little as 2 hours) initiate the acute response to ozone (Figure 3) (Plopper
et al., 1998). After 2 hours exposure to 1 ppm ozone there was a significant increase in abundance of
necrotic cells corresponding with a significant decrease in abundance of intact epithelial cells. While
polymorphonuclear leukocytes and eosinophils were significantly increased in number following a 2
hour exposure to 1 ppm ozone, macrophages exhibited a significant decrease.
When the exposure duration is increased (50-hour exposure of Rhesus monkeys to 0.8 ppm ozone)
necrosis occurs immediately after the onset of exposure, peaks after about 12 hours of exposure and is
completely resolved by 24 hours (Figure 4) (Castleman et al., 1980). Proliferation increases to maximum
over the 2 days of exposure. After 50 hours of exposure, the acute necrotic phase is complete and repair
has begun.
As the length of time for the exposure episode is increased, the pattern of response changes.
Schwartz et al., 1976 contrasted the biologic response in a continuous versus intermittent exposure.
Rats were exposed to ozone for 7 days for either 8 hours per day (interexposure interval of 16 hours) or
continuously (no interexposure interval). As the biologic response graphs illustrate (Figure 5), the early
neutrophil infiltration is indistinguishable between the two exposure regimes. Epithelial hyperplasia is
also equivalent in both exposure regimes, reaching maximum after 4 days of exposure and remaining
elevated for the remainder of the 7 days. The key difference observed in this study was in the response of
macrophages. An 8-hour per day exposure resulted in an increase in the number of alveolar macrophages,
reaching maximum after about 3 days of exposure. In animals exposed for 24 hours per day, the same
temporal relationship is observed with the maximum increase observed after about 3 days, but the number
of macrophages is considerably greater than that observed in the 8 hour per day rats. Histopathology in
the two different exposure groups is indistinguishable after the first 2 days.
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I BIOLOGIC RE SPONSe
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Long-term Exposure
If the exposure period is extended beyond one week, and the interexposure interval is kept short enough
(less than 3 days) to prevent later phases of the repair cycle to occur, chronic lesions develop. Bronchiolar
hyperplasia in response to a relatively standard long-term exposure protocol is illustrated by Harkema et
al.,1993 (Figure 6). Macaque monkeys were exposed to 0.30 ppm ozone for 8 hours per day for 90 days,
resulting in bronchiolar hyperplasia and interstitial fibrosis.
When the total exposure period is increased further hyperplastic lesions develop which are very similar to
those observed in primates exposed everyday. Figure 7 illustrates the response of the rat terminal bronchiolar
epithelium to a 20-month exposure 1 ppm ozone (6 hours per day, five days per week) (Plopper et al., 1994),
including bronchiolarization of the alveolar duct (Figure 7).
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In a modification of the above exposure regimen, rats were exposed for 78 weeks to a peak
concentration of 0.25 ppm ozone over the course of 8 hours for 5 days per week, with a continuous
baseline subthreshold concentration of 0.06 ppm ozone for 15 hours per day 7 days per week (Chang et
al., 1992). Inflammation peaked early and resolved within the first few days of exposure (Figure 8).
Fibroblast proliferation initiated shortly after the resolution of inflammation, peaked after about 1 week
of exposure, and continued at a lower level for the remainder of exposure. Type I cell hyperplasia peaked
after 1 week of exposure, resolved by 3 weeks, and started a gradual increase at about 6 weeks of
exposure, reaching maximum severity over the course of 78 weeks. The latter underscores that with
continued exposure, events that appear to resolve early recur.
Extension of Interexposure Interval
The next issue is what happens when the interval between exposures is increased to a sufficient
length of time for repair to be complete (over 7 days). Plopper et al., 1978 (Figure 9) compared the
response of rats exposed either 6 or 27 days after an initial 3 day exposure to ozone. Early responses to
ozone included an influx of neutrophils followed by necrosis. The neutrophils resolved by the end of the
3 day exposure. Necrosis reached maximum after day 3 and resolved by day 6 (3 days after cessation of
exposure). Re-exposure on day 30 (27 days after cessation of exposure) results in the same pattern of
neutrophil influx and necrosis. This is not necessarily surprising since the normal course of repair should
result in an epithelium that is completely repaired more than three weeks after cessation of exposure. Re-
exposure on day 9 (6 days after cessation of exposure) yields a response similar to that observed in naive
animals and in rats re-exposed 27 days after the initial exposure. For two exposure cycles, the acute
inflammatory response and subsequent necrosis are the same as the initial exposure.
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EXPOMRE
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In an exposure regimen with a longer interexposure interval, Barr et al., 1990 (Figure 10) used an
episodic exposure pattern of five 8-hour days of exposure to 0.95 ppm ozone followed by a 9-day
recovery period. This pattern was repeated for a total of 90 days. Alternately, rats were exposed daily.
While epithelial hypertrophy was not significantly different between daily and episodically exposed rats, the
interstitial components were markedly different with a significant increase in interstitial thickness in
episodically-exposed compared to daily-exposed rats.
Additional increases in the length of time between exposures appears to further alter the biologic
response. Hyde et al., 1989 (Figure 11) assessed total lung collagen and bronchiolar hyperplasia in Rhesus
monkeys exposed to 0.25 ppm ozone. Monkeys were exposed 8 hours per day for either 18 continuous
months or for alternating one-month periods. There was no discernable difference in the degree of
bronchiolar hyperplasia in either exposure group, yet monkeys exposed on alternate months had
considerably greater total lung collagen compared to monkeys exposed for 18 continuous months. This
suggests that while the acute response (e.g., necrosis, inflammation) appears to be equivalent for
subsequent exposures, the late responses involving repair may be altered.
Given the previous data, it was apparent that an episodic exposure with an extended interexposure
interval and multiple sampling points would provide a better understanding of the impact of variable
exposure conditions on pathogenesis. Recently, we employed an exposure scenario similar to that of Barr
et al., 1990, but with more frequent sampling. Rats were sampled at the beginning and end of each 5-day
exposure period and at the end of each 9-day recovery period through day 29 (Figure 12). On the 5th day
of the first exposure period, the epithelium appears hyperplastic (Figure 13c), yet the epithelium appears
similar to control by 9 days after the first exposure period (Figure 14a). At the onset of the second set of 5-
day exposures, inflammation, necrosis and hyperplasia were attenuated compared to that observed in the first
exposure (Figure 14b). Nine days after the second 5-day exposure period, bronchiolarization of the central
acinus persists (Figure 15).
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EXPOSURE BS6IMEN
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Summary and Conclusions
The response of the respiratory system to oxidant air pollutants such as ozone is highly dependent on
inhaled concentration and time. In ambient conditions, the synthesis of tropospheric ozone is cyclic in nature,
with ozone concentrations rising highest in mid-afternoon and dropping lowest in the pre-dawn hours.
Additionally, tropospheric ozone concentrations exhibit daily and even seasonal variations. However, most
experimental studies employ exposure protocols with near-continuous exposures. The episodic nature of
ambient exposure conditions in humans suggests that reliable assessments of risk must include a clear
understanding of the impact of cyclic exposure conditions on biological time response profiles. The biological
response of the respiratory system in naive animals to the initial ozone exposure follows a stereotypic cellular
injury and inflammatory cycle. The imposition of additional oxidant stress by repeated exposure impacts
the response variably, depending on the time during injury or repair when re-exposure occurs. The length
of the interval between exposures appears to be more critical in determining the long-term impact of
repeated exposures than the total duration of the exposure episode. Near-continuous exposure for a
significant period of time (measured in months) fundamentally alters both the pattern of toxic cellular
injury and the nature of the inflammatory response. Not only is the periodicity of the exposure important,
but the duration of interexposure intervals also appears to effect biological response. The episodic nature
of ambient exposure conditions appears to represent a greater health risk than would be expected based on
extrapolation from experimental conditions relying on near-continuous exposure scenarios.
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Acknowledgements
This work is funded by NIEHS ES 00628, 09681, RR00169, and T32 ES 7059 (Paige)
References
Barr BC, Hyde DM, Plopper CQ Dungworth DL (1990) A comparison of Terminal airway remodeling in
chronic daily versus episodic ozone exposure. Toxicology and Applied Pharmacology 106:384-407.
Casdeman WL, Dungworth DL, Schwartz LW, Tyler WS (1980) Acute respiratory bronchiolitis: An
ultrastructural and autoradiographic study of epithelial cell injury and renewal in Rhesus monkeys
exposed to ozone. American Journal of Pathology 98:811-840.
Chang LY, Huang Y, Stockstill BL, Graham JA, Grose EC, Menache MQ Miller FJ, Costa DL, Crapo JD
(1992) Epithelial injury and interstitial fibrosis in the proximal alveolar regions of rats chronically
exposed to a simulated pattern of urban ambient ozone. Toxicology and Applied Pharmacology
115:241-252.
Gelzleichter TR, Witschi H, Last JA (1992) Concentration-response relationships of rat lungs to exposure
to oxidant air pollutants: A critical test of Haber's law for ozone and nitrogen dioxide. Toxicology and
Applied Pharmacology 112:73-80.
Harkema JR, Plopper CQ Hyde DM, St. George JA, Wilson DW, Dungworth DL (1993) Response of
Macaque bronchiolar epithelium to ambient concentrations of ozone. American Journal of Pathology
143(3)857-866.
Hyde DM, Plopper CQ Harkema JR, St. George JA, Tyler WS, Dungworth DL (1989) Ozone-induced
structural changes in the monkey respiratory system. In: Schneider T, Lee SD, Wolters GJR, Grant LD
(Editors), Atmospheric Ozone Research and its Policy Implications, Elsevier Science Publishers B.V,
Amsterdam, pp. 523-532.
Paige RC, and Plopper CG (1999) Acute and Chronic Effects of Ozone in Animal Models. In: S Holgate,
H Koren, J Samet, and R Maynard (Editors), Air Pollutants and Effects on Human Health. Academic
Press Ltd, London. In Press.
Plopper CQ Chow CK, Dungworth DL, Brummer M, Nemeth TJ (1978) Effect of low level of ozone on
rat lungs: II. Morphological responses during recovery and re-exposure. Experimental and Molecular
Pathology 29:400-411.
Plopper CQ Chu FP, Haselton CJ, Peake J, Wu J, Pinkerton KE (1994) Dose-dependent tolerance to
ozone: 1. Tracheobronchial epithelial reorganization in rats after 20 months' exposure. American
Journal of Pathology 144(2) :404-421.
PlopperCQ Hatch GE, Wong V, Duan X, WeirAJ, Tarkmgton BK, Devlin RB, Becker S, Buckpitt AR
(1998) Relationship of inhaled ozone concentration to acute tracheobronchial epithelial injury, site-
specific ozone dose, and glutathione depletion in Rhesus monkeys. American Journal of Respiratory
Cell and Molecular Biology 19:387-399.
Schwartz LW Dungworth DL, Mustafa MG, Tarkington BK, Tyler WS (1976) Pulmonary responses to rats
to ambient levels of ozone. Laboratory Investigation 34(6):565-578.
USEPA (U.S. Environmental Protection Agency) (1996) Air Quality Criteria for Ozone and Other
Photochemical Oxidants. Research Triangle Park, NC: Office of Health and Environmental
Assessment, Environmental Criteria and Assessment Office; report no. EPA/600/P-93/004cF. 3v.
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NOTICE
This report has been written as part of the activities of the U.S. Environmental
Protection Agency's (EPA) Clean Air Scientific Advisory Committee (CASAC), a
Federal advisory committee administratively located under the EPA Science Advisory
Board (SAB) Staff Office that is chartered to provide extramural scientific information
and advice to the Administrator and other officials of the EPA. The CAS AC is
structured to provide balanced, expert assessment of scientific matters related to issue
and problems facing the Agency. This report has not been reviewed for approval by the
Agency and, hence, the contents of this report do not necessarily represent the views and
policies of the EPA, nor of other agencies in the Executive Branch of the Federal
government, nor does mention of trade names or commercial products constitute a
recommendation for use. CASAC reports are posted on the SAB Web site at:
http ://www. epa.gov/sab.
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