&EPA
United States
Environmental Protection
Agency
Environmental Research
Laboratory
CorvallisOR 97333
EPA-600/3-34-037
February 1984
Research and Development
A Review and
Assessment of the
Effects of Pollutant
Mixtures on
Vegetation—
Research
Recommendations
-------
EPA-600/3-84-037
February 1984
A REVIEW AND ASSESSMENT OF THE EFFECTS OF POLLUTANT MIXTURES ON VEGETATION
-RESEARCH RECOMMENDATIONS-
Vegetation Effects Workshop
April 21-22, 1983
Raleigh, North Carolina
Prepared by
Allen S. Lefohn
Douglas P. Ormrod
January 30, 1984
Project Officers
Eric M. Preston
David T. Tingey
Air Pollution Effects Branch
Corvallis Environmental Research Laboratory
United States Environmental Protection Agency
Corvallis, Oregon, 97333
CORVALLIS ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
CORVALLIS, OREGON, 97333
-------
NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
-------
CONTENTS
Acknowledgement vi
Preface vi i
List of Participants ix
Executive Summary S-l
Introduction S-l
Characterizing Ambient Air Quality Exposures S-l
Vegetation Effects S-3
Exposure Regimes S-4
Development of Minimum Guidelines for Research Protocols S-4
Predictive Investigations S-4
Conclusion S-5
1. Role of Pollutant Mixture Studies in Establishing National
Ambient Air Quality Standards 1
Introduction 1
The Standard Review and Development Process 2
Overview of Recent Vegetation Standard Reviews 5
Use of Mixture Studies in Ongoing Standard Reviews 8
Identification and Treatment of Uncertainties 8
Genetics and Environment 9
Exposure Situations 9
Experimental Exposure Regimes 11
Mechanisms of Action 13
Biological Endpoint 13
Summary 14
2. The Co-Occurrenc of S0?/N0?, CK/SO?, and CU/NO? Mixtures in
Ambient Air 16
Introduction 16
The Pollutants 17
The Data Bases 18
Results 20
S0?/N0? 21
037S02 29
Discussion 38
Conclusion 45
3. Effects of Pollutant Mixtures on Vegetation 4o
Introduction 46
Experimental Methods and Interpretation of Data 47
Characteristics of Plant Response 56
Foliar Symptoms 56
S0? + 0-, 58
SOp + NtL 61
Growth and Yi&ld 61
S00 + 00 63
-------
S0? + N0? 63
NO + O/ 6634
+ N0 + 0, 65
er Mixtures 66
Physiological and Metabolic Responses 66
Accumulation and Uptake 73
Modifiers of Plant Response 75
Genetic Factors 75
Phenological Factors 78
Environmental Factors 79
Summary 81
4. Research Needs 83
Ambient Air Quality Exposure 83
Vegetation Effects 83
5. Recommendations 86
Introduction 86
Air Quality 86
Biological Effects 88
Introduction 88
Realistic Exposure Regimes 88
Development of Minimum Recommendations for
Research Protocols 89
Predictive Capabilities 90
Conclusion 91
References 93
I V
-------
TABLES
Table 1-1 Plant Exposure to Criteria Pollutants 7
Table 2-1 Summary of Site Years Analyzed (EPA, EPRI SURE,
and TVA Data) 44
Table 3-1 Visible Foliar Injury on Various Plant Species in Response
to the Joint Action of SO- + (k 59
Table 3-2 Growth and Yield of Various Plant Species in Response to
the Joint Action of SO- + 0, 60
Table 3-3 Direct Comparisons of Species Sensitivity to SCL + (U
SO- + N02, and 03 + N02, and HF + S0? 76
Table 3-4 Direct Comparisons of Cultivar Sensitivity Within Species
to S02 + 03 77
-------
FIGURES
Figure 1-1
Figure 1-2
Figure 1-3
Figure 2-1
Figure 2-2
Figure 2-3
Figure 2-4
Figure 2-5
Figure 2-6
Figure 2-7
Figure 2-8
Figure 2-9
Figure 2-10
Figure 2-11
Figure 2-12
Figure 2-13
Figure 2-14
Figure 2-15
Figure 2-16
Figure 2-17
Figure 2-18
Figure 2-19
Figure 2-20
The StandarcLReview and Development Process
Seasonal S04 wet deposition
(mg/m ) for North America, "Summer" April
through October 1979 and "Winter" November 1979
through March 1980
Temporal changes in ground level concentrations of
SOo, N02, and 03 during a fumigation
event near a coal-fired power plant (modified
with permission from Noggle and Jones 1981)
SOp/NOo Co-Occurrence, Frequency Site
Distribution
Indian River, Delaware, S02/NOX
Co-Occurrence
S02/N02
S02/N02
S02/N02
Paradise, Kentucky
Co-Occurrence
Allen Steam Plant, Tennessee
Concentration Over Time
Allen Steam Plant, Tennessee
Co-Occurrence
Fontana, California S02/N02
Co-Occurrence
Kansas City, Kansas S02/N02
Co-Occurrence
O^/SOo Co-Occurrence, Frequency Site
Distribution
Fontana, California 03/SO?
Co-Occurrence
Madison County, Illinois 03/SOp
Co-Occurrence
Scranton, Pennsylvania 0.,/SOp
Co-Occurrence
Rockport, Indiana 0.,/SOo
Co-Occurrence
Paradise, Kentucky 03/S02 Concentrations
Over Time
Paradise, Kentucky 03/S02
Co-Occurrence
0-,/NOp Co-Occurrence, Frequency Site
Distribution
Rubidoux, California O^/NOo
Co-Occurrence
Indian River, Delaware 03/NO
Co-Occurrence
Paradise, Kentucky 03/N02
Co-Occurrence
Allen Steam Plant, Tennessee 03/N02
Co-Occurrence
Allen Steam Plant, Tennessee 03/N02
Concentrations Over Time
10
12
22
24
24
25
27
27
28
30
31
31
33
33
34
36
37
39
39
40
40
41
v i
-------
Figure 3-1 Examples of Contour Plots Illustrating the Response of
Lettuce, Radish, and Pea to 6-hour Exposures to
Combinations of Cu and SCu 51
Figure 3-2 Graphical Representation of the Four Response Regions of
Practical Interest When Two Pollutants are Combined 54
-------
ACKNOWLEDGEMENT
Bruce Jordan and Larry Zaragoza would like to provide acknowledgement to
John Bachmann, Kent Berry, John Haines, Pam Johnson, David McKee, and Harvey
Richmond for their comments during the preparation of the material that
appears in Chapter 1.
Allen S. Lefohn would like to acknowledge the assistance of the
following individuals and organizations for providing information that was
used in the data analysis described in Chapter 2:
1. Ms. Cel Allard, Center for Data Systems and Analysis,
Montana State University, Bozeman, Montana for
developing the software programs necessary to access
A.S.L. & ASSOCIATES' copy of the SAROAD data base.
2. Dr. Tom Curran and Mr. Jim Reagan of the EPA, Research
Triangle Park, North Carolina, for providing insight
into the EPA SAROAD and EPRI SURE data bases.
3. The Tennessee Valley Authority for providing its air
quality monitoring data on a timely basis, in a
readable format.
EPA wishes to acknowledge A.S.L. & Associates for assisting in the
integration, and editing of this report.
VI I I
-------
PREFACE
On April 21-22, 1983, a workshop sponsored by the U.S. Environmental
Protection Agency Corvallis Environmental Research Laboratory, was hosted in
Raleigh, North Carolina to develop research recommendations concerning the
effects of pollutant mixtures on vegetation. Prior to the meeting, EPA asked
several individuals to develop position papers to a) describe the use of
information on plant response to pollutant mixtures in setting ambient air
quality standards; b) characterize the spatial and temporal characteristics of
air pollutant mixtures in the ambient air; and c) summarize the vegetation
effects literature associated with pollutant mixtures. The material was
integrated into the first three chapters of this report. The following
individuals are acknowledged for the writing of the position papers:
Studies of Combined Exposure Effects on Vegetation:
Role in Establishing National Ambient Air Quality Standards
Bruce Jordan and Lawrence J. Zaragoza
EPA Office of Air Quality Planning and Standards
Research Triangle Park, NC
The Co-Occurrence of Sulfur Dioxide/Nitrogen Dioxide,
Ozone/Sulfur Dioxide, and Ozone/Nitrogen Dioxide
Mixtures in Ambient Air
Allen S. Lefohn
A.S.L. & Associates
Helena, MT
Effects of Pollutant Mixtures on Vegetation
Delbert C. McCune
Boyce Thompson Institute
Ithaca, New York
Douglas P. Ormrod
University of Guelph
Guelph, Ontario, Canada
Richard A. Reinert
North Carolina State University
Raleigh, NC
At the invitation of EPA, eighteen individuals participated in the
two-day workshop. Participants were asked to critically review the position
papers and 1) summarize the information gaps and assess the significance of
the problems associated with those pollutant mixtures exposures that affect
vegetation; and 2) identify and recommend activities that would assist the
Agency in filling these research gaps.
From these activities (position papers and panel deliberations), EPA's
Corvallis Laboratory has produced this document to summarize
-------
o the processes involved in developing ambient air quality
standards;
o the spatial and temporal distribution of gaseous
pollutant mixture concentrations;
o the effects of gaseous pollutant mixtures on vegetation;
o information gaps; and
o recommendations on research that is required to fill the information
gaps.
While the subject was addressed, no attempt was made to prioritize the
general research categories because panel members believed pollutant ambient
monitoring characterization and vegetation effects research efforts were
complementary.
-------
LIST OF PARTICIPANTS
Air Pollutant Mixtures Vegetation Effects Workshop Participants
Thomas C. Curran
U.S. Environmental Protection Agency
Monitoring and Data Analysis Division
Research Triangle Park, North Carolina
J.H.B. Garner
U.S. Environmental Protection Agency
Environmental Criteria and Assessment Office
Research Triangle Park, North Carolina
Walter W. Heck
North Carolina State University
P.O. Box 518
Raleigh, North Carolina
Pam M. Johnson
U.S. Environmental Protection Agency
Strategies and Air Standards Division
Research Triangle Park, North Carolina
Bruce C. Jordan
U.S. Environmental Protection Agency
Strategies and Air Standards Division
Research Triangle Park, North Carolina
Allen S. Lefohn
A.S.L. & Associates
Helena, Montana
Delbert McCune
Boyce Thompson Institute
Cornell University
Ithaca, New York
David Olszyk
Statewide Air Pollution Research Center
University of California
Riverside, California
Douglas P. Ormrod
University of Guelph
Department of Horticultural Science
Guelph, Ontario CANADA
Ronald Oshima
California Department of Food and Agriculture
Environmental Monitoring
Sacramento, California
X I
-------
Eric M. Preston
U.S. Environmental Protection Agency
Environmental Research Laboratory-Corvallis
Corvallis, Oregon
Richard A. Reinert
U.S. Department of Agriculture
Plant Pathology Department
North Carolina State University
Raleigh, North Carolina
George E. Taylor, Jr.
Environmental Sciences Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee
Ted W. Tibbitts
Horticulture Department
University of Wisconsin-Madison
Madison, Wisconsin
David T. Tingey
U.S. Environmental Protection Agency
Environmental Research Laboratory-Corval1 is
Corvallis, Oregon
Michael Treshow
Department of Biological Sciences
University of Utah
Salt Lake City, Utah
David E. Weber
U.S. Environmental Protection Agency
Office of Research and Development
Washington, D.C.
Larry Zaragoza
U.S. Environmental Protection Agency
Strategies and Air Standards Division
Research Triangle Park, North Carolina
X I I
-------
EXECUTIVE SUMMARY
INTRODUCTION
The Environmental Protection Agency (EPA) is responsible for
periodically reviewing and revising all national ambient air quality standards
(NAAQS). The Clean Air Act (CAA) requires EPA to establish national ambient
air quality standards for ambient air pollutants which may endanger human
health and welfare. Secondary ambient air quality standards must be adequate
to protect the public welfare from any known or anticipated adverse effects
associated with the presence of a criteria air pollutant. To help the Agency
develop data that assess the effects of pollutant mixtures on vegetation, the
EPA Corvallis Environmental Research Laboratory sponsored a workshop in
Raleigh, North Carolina on April 21-22, 1983. Participants reviewed position
papers to 1) summarize the information gaps and assess the significance of the
problems associated with pollutant mixture exposures that affect vegetation
and 2) identify and recommend activities that would help the Agency fill these
research needs. This report includes both the position papers and the workshop
deliberati ons.
The ranking of research needs was addressed by the workshop
participants. Members believed that no research areas are independent from
another and should be treated collectively. For example, the biological
research efforts are dependent upon a knowledge of the pollutant
concentrations occurring in the field under ambient conditions. Thus,
environmental, genetic, and phenological variables should be considered when a
study is initiated.
CHARACTERIZING AMBIENT AIR QUALITY EXPOSURES
Different air quality exposure regimes exist for sulfur dioxide (S0~),
ozone (Oq), and nitrogen dioxide (NO-). These regimes affect the frequency of
co-occurrence and sequential exposures that vegetation may experience. An
analysis of the 1981 EPA air quality data base (SAROAD), Electric Power
S-l
-------
Research Institute (EPRI) 1978 SURE, and Tennessee Valley Authority (TVA) data
bases indicates that SO-, NCL, and 03 may co-occur in various concentrations
in rural, suburban, and urban areas. Analyses of the data bases show that the
frequency of co-occurrence (using 0.05 ppm as the definition of an event) is
small for many rural sites. For most of the cases analyzed, events lasted only
a few hours and were separated by intervals of weeks or months.
The panel recommends that air quality data be evaluated further to study
patterns of occurrence of the combined pollutants to establish guidelines for
designing plant interaction research investigations. The three pollutants of
primary interest are SO-, 0.,, and NO^. The effects of these pollutants on
vegetation can be evaluated using the available air quality data and the
research information dealing with individual effects. In addition, the panel
recommends that acidic deposition be considered as a pollutant with the
potential for interaction with the above three air pollutants.
The recommendation is to analyze existing air quality data bases
(starting with SAROAD) to derive the joint probability distributions of
pollutants and,the diurnal patterns of exposure for plant exposure
experiments. Additional sources of rural air quality data could include the
USDA Forest Service, EPRI (SURE), EPA (NCLAN), and permits monitoring programs
(e.g., PSD applications). This analysis is to include the following:
1) A search of the data base for locations where either
co-occurrence or sequential exposures (starting with a
24-hour time step) occur. This search would include
separate listings at several threshold concentrations
(e.g., 0.05, 0.04, 0.03, and 0.02 ppm).
2) Once locations are identified, the monitoring data bases
at the- locations should be presented as joint frequency
distributions and as diurnal time series. It is
suggested that the utility of spectral analysis
(Fourier series) and the Box Jenkins model should be
explored.
3) The results of this process should be disseminated to
research groups to guide experimental exposures used in
interaction experiments.
S-2
-------
The panel recommends that potential data displays for individual
pollutants include: 1) three-dimensional plots of concentration, duration, and
frequency; 2) diurnal plots for individual pollutants in terms of mean
concentraiton and frequency greater than particular concentrations. These
analyses should be summarized for the growing season (or some relevant time
period) and should also serve to identify potential anomalies.
The air quality analyses would provide information that could be used to
identify general patterns of exposure that relate to geographic regions or
source configurations. It may be necessary to supplement the air quality data
around point sources by considering the use of dispersion models to provide
information on levels, diurnal patterns, and time between episodic events.
VEGETATION EFFECTS
Pollutant mixtures may induce plants to exhibit different types of
responses which are influenced by several variables that are often difficult
to predict. The three general categories of responses that may follow plant
exposures to mixtures of ambient air pollutants are additive, greater than
additive, and less than additive. All three responses are found to some degree
in the experimental results using SCL, CL, and N0?. Taken as a whole, the
current information on both long- and short-term combined exposure studies
provides conflicting results that are difficult to interpret.
The workshop members agree that research efforts should be directed
toward important plants (including agronomic, horticultural, and native
plants, and tree species). The panel believes that the gaps in knowledge can
only be filled by an integrated effort involving growth chambers, greenhouses,
and field plots.
S-3
-------
Exposure Regimes
The panel is aware that the understanding of the response of plants to
various exposure regimes is crucial. Plant effects must be associated with air
pollutant peaks, means, length of exposure, and time between exposures that
mimic realistic ambient pollutant exposures. Research should evaluate the
vegetation effects associated with sequential exposures of pollutant mixtures
which duplicate ambient conditions.
Development of Minimum Guidelines for Research Protocols
The panel recommends that a minimum set of standardized procedures be
developed to ensure the quality assurance of plant response studies.
Generalized guidelines should be proposed for 1) plant growth conditions, 2)
environmental and plant monitoring, 3) pollutant exposures, and 4) uniform
terminology (describing plant response characteristics). The most efficient
experimental designs and analysis procedures available (relevant to a specific
experimental goal) should be implemented (e.g., covariate analysis, analysis
of variance, and rotatable design). It is proposed that the minimum guidelines
be developed through two or three workshops.
Predictive Investigations
One purpose of pollutant interaction research is to develop predictive
capabilities for assessing vegetation effects. Predictive models can provide
estimates of vegetation effects under a variety of conditions not feasible
with direct experimentation. In order to properly generate the information
necessary to develop such predictive models, data are needed from research
programs involving studies that define 1) the modes of action and 2) the
sources of biological variation.
The following research activities are recommended and considered
instrumental in the development of this predictive capability:
S-4
-------
1) Modes of Action: The objective of this research activity
is to understand how air contaminants influence biological
processes and in doing so, determine whether their actions
may cause significant ecological alterations. It is
necessary that studies address modes of action for
pollutants singly and in combination. The research effort
should include both sequential and co-occurrence exposures
and should be conducted with an appreciation of realistic
exposure regimes. The biological level of organization to be
investigated should focus on processes at all levels of
plant organization (i.e., the cell, whole-plant, population,
and ecosystem). The panel believes that there should be two
major areas of interest
a) The relationships between different mechanisms of
pollutant response.
b) The varying biological responses attributed to
different levels and combinations of air pollutant
exposure.
2) Sources of Variation: The plant response to a given
exposure regime varies significantly with specific
environments, environmental changes, and the stage of plant
development. The panel recommends research that focuses on
each of the following:
a) environmental factors-the significance of edaphic
(e.g., soil water availability, soil nutrients),
climatic (e.g., temperature, light, relative
humidity, elevated carbon dioxide, etc.) and biotic
factors (e.g., pathogens, symbionts, competition,
etc.).
b) genotype factors-the significance of intra- (e.g.,
cultivar, population) and interspecific genotypes.
This includes phenology as a source of variation.
3) Modeling-The development of data that describe the
process and mechanistic activities associated with air
pollutant mixture vegetation effects should allow for the
development of conceptual and quantitative models that
describe observed biological response.
CONCLUSION
It is the opinion of the workshop participants that the position paper
focusing on ambient exposures was an initial attempt to identify realistic
S-5
-------
exposure regimes that exist in the ambient air. The panel believes that
additional efforts should be made to supplement the existing analysis and that
they should simultaneously proceed as the biological vegetation effects
research is implemented. It was recommended that the results of the air
quality characterization should feed directly into the design of the pollutant
mixture experimental protocols.
The process and mechanistic research activities should involve two
stages: 1) a biological effects screening exercise to prioritize which air
pollutant mixture exposures are most likely to be significant, 2) a more
detailed investigation that is performed under field and laboratory situations
for the purpose of quantifying the significance of the major factors affecting
plant response.
It was the conclusion of the panel members that the conceptual models
should combine existing models of joint action with the data that describe the
modes of biological action. The quantitative models should be capable of
providing accurate and precise estimates of plant response. In addition, the
models should be able to complement the physical and/or biological processes
that are responsible for producing the observation.
S-6
-------
1. ROLE OF POLLUTANT MIXTURE STUDIES IN ESTABLISHING
NATIONAL AMBIENT AIR QUALITY STANDARDS
INTRODUCTION
The Clean Air Act (P.L. 95-95) requires that the Environmental
Protection Agency establish national ambient air quality standards (NAAQS) for
certain air pollutants that, if present in the ambient air, may endanger human
health and welfare. Primary NAAQS are established to protect human health
while secondary NAAQS are established to protect public welfare. Section
302(h) of the Act specifies that the effects of air pollution on crops and
other vegetation are among the effects that must be considered in establishing
secondary NAAQS.
The original NAAQS were established in 1971 and included secondary
standards set at levels designed to protect public welfare including effects
on crops and other vegetation. No detailed discussion of the rationale for the
secondary standards was provided in the original proposal and promulgation
notices (36 FR 1502, 36 FR 5867, 36 FR 8186). The secondary standard for ozone
(Oo), which the original criteria document associated with damage to
vegetation, was set equal to the primary standard. Based on comparison of the
original sulfur dioxide ($02) standards and supporting documents, it appears
that support for the SO- standard levels was based upon a limited number of
studies and that the issue of the importance of pollutant mixtures was not
raised (DHEW 1970). Available information does not suggest that the effects of
nitrogen dioxide (NO,,) on vegetation played a role in setting the original N0?
standard.
The potential for increasing plant sensitivity by the presence of
multiple pollutants is significant because emission sources often release
different pollutants within an area. However, there is often considerable
controversy over the characterization of plant response in the presence of
even a single pollutant. The assessment of plant response to pollutant
mixtures is a more difficult task.
-------
This chapter describes how information on pollutant mixtures is being
considered and provides suggestions that should increase the utility of
studies on plant response to pollutant mixtures in the standard review process
for NAAQS. Focus is placed on evaluations developed during ongoing standard
reviews, with discussion of past review practices included.
The Standard Review and Development Process
The complex standard review and development process is designed to
solicit the best available scientific information and public comment. The use
of welfare information and those factors that have appeared to be most
influential in the ultimate decision-making process are described by Bachmann
and Zaragoza (1983). More general discussions of the process are provided
elsewhere (O'Connor 1980, Padgett and Richmond 1983, Zaragoza 1982). In order
to better understand the role of scientific information in this process, this
section highlights those activities that most pertinent to the present subject
area.
The standard review and development process combines scientific review
and assessment with the judgment of EPA's Administrator. As Figure 1-1 shows,
the first part of this process involves an in-depth scientific review,
including the collection of relevant information and review by specialists
within each scientific area. When available scientific information can resolve
questions so that uncertainty is small, the degree of judgment required of the
Administrator for a given degree of protection is reduced.
The criteria document development process is the Agency's means of
conducting an unbiased and public review of all literature used in support of
a particular standard. Once a study is included in the criteria document, the
characterization of that study will play a major role in determining its
potential utility in the standard-setting process. Those investigators who
employ reliable methodologies and who design experiments so that their results
-------
SCIENTIFIC
RESEARCH
'
'
1
/DRAF
PAF
l
REVIEW AND
REVISE/REAFFIRM
WITHIN 5 YF.ARS
4
CHIItHIA /" ' "/
* DOCUMENT J W°RK'NG I
INITIATION1 7 °RAFTl /
YES .XX">X\ / EXTERNAL /
\Tx^ / DRAFT^ /
TNO A
COMMENT I
ANALYSIS "
AND REWRITE1
f
T STAFF / CASAC REVIEW
gp2,3 /' ' " ^* AND HUBLIC .-.^^
, .7 MFFJING3
fl
I • IMPI ruiruTATinu
WORKSHOP1 F|RST EXTERNAL
- • CONSULTANTS ^ Dci/lcuu
• SCIEN
"EXPE
TIFIC " ORAFT1,2
RTC"
\ '
COMMENT CASAC REVIEW
AND REWRITE1 MEETING
n fKiiRF j*-
| NO
COMMENT
ANALYSIS
NO REWRITE3
YES PREPARATION
PACKAGE3
- / STANDARD /^ COMMENT .
/PROMULGATION3/^ ANALYSIS4
ADMINISTRATOR
* DECISION
' '
/ STANDARD /
7 PROPOSAL2-3 /
Fiqure 1-1. The Standard Review and Development
Zaragoza 1982)
Process (reproduced with permission from
^Office of Research and Development assumes primary responsibility for these activities. The Environ-
mental Criteria and Assessment Office (ECAO) plays a major role in preparation of the criteria document.
^Public comment is requested at this stage.
-^Managed by the Office of Air, Noise, and Radiation.
^This phase of the process includes one or more public meetings, receipt and formal review of public com-
ments, the preparation of a revised regulatory decision package, formal Agency review, and a final deci-
sion by the Administrator.
-------
will be relevant to ambient situations usually produce studies that prove to
be of greatest relevance in standard-setting.
As Figure 1-1, illustrates, the next step in the standard review process
is the development of a "staff paper." The staff paper evaluates and
interprets available scientific and technical information most relevant to the
standard review, and presents recommendations on alternative approaches to
revising or maintaining standards.
Both the criteria document and staff paper are reviewed by the Clean Air
Scientific Advisory Committee (CASAC). The CASAC is an independent scientific
review committee established by the Clean Air Act to provide the Administrator
with advice on the scientific issues related to NAAQS. The Clean Air Act
specifies that CASAC be composed of seven members, including at least one
member of the National Academy of Science, one physician, and one person
representing State Air Pollution control agencies. Formal review on each
document is complete when a "closure" memorandum, which indicates committee
endorsement of the document, is sent from the CASAC chairman to the
Administrator.
The effects of pollutant mixtures are currently assessed as modifying
influences on plant sensitivity for a pollutant under review. This is
consistent with section 108 of the Clean Air Act, which specifies that the
criteria for a pollutant shall include information on "the types of air
pollutants which, when p'resent in the atmosphere, may interact with such
pollutant to produce an adverse effect on public health or welfare." In
ongoing reviews, the concern for pollutant mixtures arises when exposure to
pollutant mixtures appears to be greater than the effects that would be
expected from exposure to the individual pollutants. If it is determined that
a combination exposure could produce effects that are greater than the effects
of exposure to an individual pollutant, then adjustments in the level of the
standards for the individual pollutant may be the appropriate response. While
consideration could be given to establishing a combined standard, the details
-------
of specifying and complications associated with implementing such a standard
would have to be carefully evaluated.
Secondary ambient air quality standards must be adequate to protect the
public welfare from any known or anticipated adverse effects associated with
the presence of a criteria air pollutant. Given the mandate in the Clean Air
Act to protect public welfare from any known or anticipated adverse effect, it
is incumbent upon the Agency to consider the effects of pollutant mixtures on
vegetation. The task of deciding which or at what point welfare effects become
adverse is a difficult one. Because there is usually no sharp demarcation
between a level where effects of uncertain significance are reported and a
level where clearly adverse effects occur, the Act explicitly requires the
Administrator to exercise judgment in setting a standard. Though relying
heavily on scientific advisors for technical evaluation of data and for those
judgments that are scientific in nature, the Administrator alone is
responsible for considering risks and determining at which point effects
should be regarded as adverse.
RECENT VEGETATION STANDARD REVIEWS
Pollutant mixture studies become most important for standard review
exercises when the presence of additional pollutants causes effects that are
greater than the effects of exposure to the pollutant alone. Although Tingey
et al. (1971 a, 1973a) have reported such results, these studies have not
provided compelling support for either a combination standard or a more
stringent standard based on pollutant mixture effects (EPA 1982a, 1982b).
Plants exposed to pollutant mixtures may exhibit different types of
responses that are influenced by several variables that are often difficult to
predict. The general kinds of responses that may follow plant exposures to
mixtures of ambient pollutants are described in Chapter 3. All these kinds of
responses are found to some degree in the experiments using S0?, CU, and N0?.
-------
Available information, taken primarily from laboratory studies of foliar
injury, report the following responses to pollutant mixtures (EPA 1982a,
1982b):
a. At lower concentrations (e.g., 0.10 ppm NOp and 0.05 ppm SO- for a
few hours), little, if any, foliar injury is observed from either
mixtures or single pollutants alone.
b. At higher concentrations (e.g., 0.10 ppm 0., and 0.50 ppm of S0? for
a few hours), foliar injury may be greater than the amount of foliar
injury that could be predicted by adding the amount of foliar injury
produced by either pollutant alone.
c. At still higher concentrations, usually not observed in the ambient
air, the amount of foliar injury produced may be equal to or less
than that predicted by adding the amount of foliar injury produced
by each pollutant alone.
If these generalizations are correct, greater than additive responses should
have a greater potential for occurring in the ambient air than additive or
less than additive responses.
The interpretation of the results of pollutant mixture studies is also
complicated by the exposure regimes used. Although studies employing
unrealistic exposure 'regimes may contribute to our understanding of plant
response, they are very difficult to use in assessing impacts of air pollution
on vegetation. For example, it is reasonable to expect concurrent S0? and N0?
exposures for peak exposures hear a coal-fired boiler (Table 1-1). However, it
is unlikely that high 0^ concentrations would co-exist with peak S02 and N02
levels because nitric oxide (NO) would titrate the 0^, increasing NOo and
reducing 0., concentrations. Such information suggests that experimental
designs employing sequential exposure to pollutants would be a more realistic
approach for simulating exposure regimes.
-------
Table 1-1. Plant Exposure to Criteria Pollutants
Pollutant(s)
Sources
Exposure Pattern
Character!sties
Comments
03*
N02**
SO,
Not a primary emi ssion;
results from photo-
chemical reactions
involving reactive
hydrocarbons, nitrogen
oxides and oxygen.
Results from combustion
processes from mobile and
industrial and domestic
(e.g. , oi 1 furnace)
sources.
Emitted primarily from
combustion or processing
of sulfur containing
fossil fuels and ores.
- Peak 63 concentrations
at some sites can exceed
0.2 ppm over an hour.
- Average (yearly) 03
concentrations can range
between 0.025 and 0.07
ppm.
Concentrations tend to
reach short-term peaks
near sources (0.06 to
about 0.5 ppm for peak
hourly averages).
Long-term yearly averages
range between 0.01 and 0.08
ppm in urban areas and are
about 0.001 in rural areas.
Modeling results indicate
that the current 24-hour
standard would not prevent
1-hour peaks in the range
of 0.5 to 0.75. Seasonal
averages occurring over
large regions tend to be
higher in the northeastern
U.S. (-0.01 to 0.02 ppm)
than in other parts of the
U.S.
*Source: EPA 1978.
**Source: EPA 1982a.
"^Source: EPA 1982b.
^Source: Personal communication from H. Cole to L. Zaragoza.
Peak 03 levels may occur in
the same region as elevated
S02 concentrations, but peak
levels of each pollutant
would be expected to occur at
different times.
If nitric oxi de i s
released in the
presence of 03, then
the 03 will be
titrated increasing
N02 and decreasing 03
concentrati ons.
Peak S02 level s near
sources (e.g., coal-fired
power plants) are strongly
affected by meteorology.
It is likely that short-
term peak concentrations of
S02 and N02 would have
considerable overlap (some
displacement of the peak
N02 level relative to the
peak S02 level is expected
due to possible conversion of
NO to N02).tt
-------
Use of Mixture Studies in Ongoing Standard Reviews
Taken as a whole, the cumulative information on both long- and
short-term combined exposure studies provides conflicting results that are
difficult to interpret. Biological responses to pollutant mixtures do not show
consistent patterns. The situation is further complicated by the use of
exposures in both acute and chronic exposure studies that are not
representative of exposure patterns, distributions, and levels of pollutants
observed in ambient air.
The criteria documents and staff papers recently have been completed for
both SO and NOV. Based on its review of the criteria documents, EPA staff
A A
concluded that the available data on combination exposures indicate that plant
responses to NOp and SOp, either together or in various combinations with Oo,
are highly variable. For example, one study reported that exposure of a
commercial crop species to equal concentrations (0.20 ppm) of NOp and SOp
caused less injury in five of six species tested (Tingey et al. 1971a). In the
review of the SOp standard, studies examining effects of SOp near point
sources included some NOp and higher 0^ before and after the SOp fumigation
events. Injury attributed to SOp under these conditions resembled typical SOp
foliar injury; it is not possible to determine whether plants in this study
responded to different levels of SOp from those reported in studies of SOp
alone.
IDENTIFICATION AND TREATMENT OF UNCERTAINTIES
Additional research is necessary to reduce uncertainties associated with
assessing regulatory alternatives. This section presents major areas of
uncertainty that are identified in recent EPA staff assessments of information
for recent NAAQS reviews (EPA 1982a, 1982b). A more explicit treatment is
being developed for handling uncertainties in the biological information that
is used to support regulatory alternatives. The relative prioritization of
these research needs from a regulatory perspective is not directly addressed.
As the discussion of plant response to pollutant mixtures in earlier sections
8
-------
indicates, response can vary greatly. Interpretation and comparison of results
from different studies is complicated by variability in plant response, which
is influenced by a number of factors, including: experimental exposure regime,
exposure situation, biological endpoint, fundamental response triggering
mechanisms, genetics, and environment.
Perhaps the greatest impact of pollutant mixtures lies in the potential
effects of the complex mix of pollutants that is associated with acidic
deposition. Here SCL, acid aerosols, CU, and other pollutants may cause or
promote ecosystem effects. Figure 1-2 shows regional wet deposition of
sulfates for "summer" and "winter" seasons, with wet sulfate deposition
occurring over relatively large areas. If available data from the Electric
Power Research Institute's Sulfate Regional Experiment (SURE) are
representative of regional S0? and sulfate levels, then SC^ levels may be
expected to be substantially higher than sulfate levels (Mueller et al. 1980).
Moreover, ozone and other photochemical oxidants and other acidic aerosols
(e.g., nitrates, organics) also occur, in these same regions.
Genetics and Environment
Both genetics and environment can affect plant sensitivity to pollutants
(EPA 1982a, 1982b). Different species vary in their sensitivity to pollutant
exposure, even when environmental conditions are identical. Moreover, the
influence of environment, especially light and water stress, have been shown
to produce profound effects on plant sensitivity to air pollutants.
Exposure Situations
The air quality information used to supplement the standard review and
development process focuses on defining and characterizing exposure to
populations that might be impacted. In the case of vegetation, air quality
information is usually separated into one of three exposure situations: point,
area, and regional exposures. The conditions of plant exposure for each of
these situations differ, as do the concentrations associated with different
-------
Unit Co
tng/mi
250
500
750
1000
1500
ZOOO
3000
4OOO
rw«r*ons:
Kg/ha
2.5
5.0
7.5
10
15
20
30
40
SO.' 71
•q/ha 4-
52 )
104 y
I5« \
210 \
315 ~
420
630
HO
SO. W«f [
Apr-Oct
^oc
— ^
2SC
1
/
/ /
< /
^c
\
)«poi,t
1979
ISO
SO*
Nov 1979-Mar I960
Figure 1-2. Seasonal S042' wet deposition (mg/m2) for North America,
"Summer" April through October 1979 and "Winter" November 1979
through March 1980. Sites (A) reporting data are from the NADP
and CANSAP precipitation monitoring networks (reproduced with permission
from Glass and Brydges 1981).
-------
averaging periods, the distribution of concentrations within an averaging
period, and the spatial distribution of concentrations. Table 1-1 summarizes
information related to plant exposure including: emission sources,
characteristics of plant exposure patterns (e.g., peak and mean
concentrations), and potential for combined exposures.
Experimental Exposure Regimes
Studies of plant exposure are separated into two basic categories: plant
responses to controlled exposure and plant response to uncontrolled exposures
in the field. In general, controlled exposure studies have not used exposure
regimes representative of those expected to occur in the ambient air.
Interpretation of some earlier controlled exposure studies is not only
complicated by unrealistic exposure regimes but also by growing conditions
that were unusually favorable for plant growth, which probably increased the
sensitivity of plants (EPA 1982b).
The differences in the distribution of pollutants in time, space, and
concentration can be shown by comparison of regional and point source
situations. Figure 1-2, illustrated regional concentrations over seasonal
averaging periods. Although pollutant concentrations may be elevated to some
extent, over relatively large regional levels, the changes in pollutant
concentration are typically gradual and extend over large distances. The
situation is markedly different in the case of point sources. Figure 1-3 shows
a fumigation event near a coal-fired power plant; changes in pollutant
concentration are most strongly influenced by wind direction, windspeed,
emissions, anci mixing Ipvel. Fumigation events in this situation tend to last
only a short time. During these fumigations, plants are typically exposed to
both SCL and NCL in SCL/NCL ratios ranging from 3 to 15. As concentrations of
these pollutants decrease, the concentrations of SCL and N0? may show
convergence (Noggle and Jones 1981). Although SCL and NCL may be present
simultaneously, it is unlikely that peak CL concentrations would occur
simultaneously. This situation tends to occur because nitric oxide (NO)
titrates CL, elevating NCL concentrations and reducing CL concentrations. Such
-------
0.06
0.04
0.02
O
NO
IX)
0.06 -
o
8 0.50
0.40
0.30
0.20
0.10
1000
1100
1200
TIME OF DAY
1400
Figure 1-3. Temporal changes in ground level concentrations of SCL, NCL,
and 0 during a fumigation event near a coal-fired power plant (moaifiea
with permission from Noggle and Jones 1981).
-------
information suggests that experimental designs employing sequential exposure
to pollutants could be a more realistic approach for simulating exposure
regimes (see Chapter 2 for further discussion).
Observations of plant response in the field are needed to confirm
observations in controlled exposure studies. However, the lack of control of
environmental variables affecting plant sensitivity, including the presence of
other pollutants, reinforces the need for these studies to be complemented by
controlled exposure studies.
Mechanisms of Action
The weaknesses in our understanding of the mechanisms of damage preclude
the use of mechanistic models as a predictive tool. Available studies on the
mechanisms by which pollutants cause effects have focused on single
pollutants. Basic information on the physiology, growth, and development of
plants eventually should be useful in the development of mechanistic models.
Even studies that have used reasonable concentrations for the averaging
periods selected, they have not generally reflected the distribution of air
pollutants within the averaging period that might be expected for the
situation. Studies by Mclaughlin et al. (1979) demonstrate that the relative
distribution of air pollutants within an averaging period can be an important
determinant of plant response to SCL.
Biological Endpoint
The evaluation of plant response for purposes of setting NAAQS is
complicated by consideration of different biological endpoints. Depending on
the objective of the study, researchers have employed a variety of endpoints
in examining the effects of air pollutants on vegetation. However, those
endpoints that can be used as a measure of the intended use of the plant are
most useful.
13
-------
As the standard-setting process has evolved, the use of information in
the process has changed. Available information suggests that foliar injury
played a prominent role in the setting of the original NAAQS. However, in
1979, one of the primary reasons for the relaxation of ozone secondary
standard was the lack of data showing reductions in growth and yield in
agricultural crops or native vegetation at exposures below the level at which
the primary standard was set. Currently, major emphasis is placed upon the
characterizing impacts on intended use of the plant. Using this approach,
foliar injury is of greater importance in ornamentals, native vegetation, and
crops whose leaf appearance can be an important consideration in marketability
(e.g., spinach).
Because a number of studies have employed foliar injury as the endpoint,
the associations between foliar injury and yield have been sought by some
researchers as a means of estimating possible effects on yield from foliar
injury data. Although increases in foliar injury and decreases in growth and
yield tend to occur simultaneously when pollutant exposures are sufficiently
high, foliar injury is an imprecise measure of the effect of pollutants on
growth and yield parameters. Growth and yield reductions may occur with
minimal or no accompanying foliar injury (Reinert and Weber 1980) and it is
possible to have foliar injury with no apparent effect on crop yield (Heagle
et al. 1974). It is possible that effects on growth and yield are most
consistently related to increases in foliar injury when development is limited
by photosynthetically active surface area or leaf area.
SUMMARY
Conflicting results from both short- and long-term mixture studies are
difficult to interpret. Although these studies indicate that pollutant
mixtures can produce effects that are greater than additive, especially at low
exposure levels, additional research is needed to resolve reported differences
in biological responses. In addition to resolving these differences,
information in the following areas would be useful for improving the
scientific basis of regulatory activities designed to protect vegetation:
14
-------
a. Differences in peak pollutant concentrations associated with the
temporal and spatial patterns should be reflected in the design of
exposures employed for pollutant mixture studies.
b. Exposures should be representative of peak and mean concentrations
occurring in the ambient air.
c. The mechanisms by which plants respond to pollutant stress should be
elucidated.
Current studies involving pollutant mixtures are still characterizing
the types of biological responses to pollutant exposure. Methodologies have
evolved sufficiently to develop reasonable models of plant response to
pollutant mixtures in the field.
15
-------
2. THE CO-OCCURRENCE OF S02/N02, 03/S02, AND 03/N02
MIXTURES IN AMBIENT AIR
INTRODUCTION
A great deal of the air pollution vegetation effects literature deals
with the direct impacts associated with 0,, S02, and N02 air pollutants acting
as independent phytotoxic agents; there is. a dearth of information that
describes the effects associated with their mixtures. Critical to the
development of relevant dose-response data is the identification of N02, S02,
and Oo exposure regimes that adequately describe the concentration, frequency
O ' ; ' s
of events, length of occurrence, and time between events. A review of the U.S.
EPA's air quality data information base, SAROAD, the Electric Power Research
Institute's Sulfate Regional Experiment (SURE) data, and the Tennessee Valley
Authority's (TVA) air quality monitoring data was undertaken to characterize
the exposure of pollutant mixtures at specific sites across the United States.
Air quality information reported by EPA for 1981, EPRI SURE data for May
through September 1978, and TVA data for May through September 1978, 1979,
1980, and 1981 were reviewed.
In developing estimates of plant exposure to pollutants, consideration
should be given to characterizing exposures that are similar to ambient
conditions. For the purposes of this analysis, we have utilized hourly
averaged air quality data because the short averaging time provides important
information to those scientists interested in developing pollutant exposure
regimes for vegetation effects research.
Co-occurrence is defined as the simultaneous occurrence of hourly
averaged concentrations at 0.05 ppm or greater for pollutant pairs (S0?/N0~,
03/S02, or 03/N02). A 0.05 ppm concentration was selected because minimum
biological responses have been shown to exist at these levels. Tingey et al.
(1971a) reported that a 4-hour exposure of several crops to levels up to 2 ppm
N02 and 0.5 ppm S02, caused no injury when administered singly. Slight foliar
16
-------
injury was observed at 0.05 ppm N02 and 0.05 ppm S02- Ashenden (1978, 1979a)
and Ashenden and Williams (1980) reported growth and yield suppression from
combined exposures of 0.1 ppm NO^ and 0.1 ppm SO-, using a constant fumigation
exposure for 103.5 hours per week for 20 weeks. These exposures caused
significant reductions in the growth parameters of all four grass species
tested. Because these exposures were based on a constant fumigation regime
greater than one hour, it was believed that a one time hourly co-occurrence of
0.05 ppm represented a conservative definition for an event.
Based on a review of available data, EPA has previously concluded that
there is inadequate evidence to determine a yield reduction relationship
associated with vegetation effects for various ambient exposure combinations
of pollutant gases (EPA 1981a, I982b). This chapter explores the
characteristics of co-occurring air pollutant mixtures and identifies
exposures that may be considered typical of several rural monitoring sites
across the United States.
THE POLLUTANTS
Sulfur dioxide is one of a number of sulfur-containing compounds found
in the atmosphere. Although SO,, enters the air primarily from the burning of
coal and oil, it is also produced by other industrial and natural processes.
EPA reports (EPA 1981b) that nationally, the urban SO- problems have
diminished so that only a few urban areas now exceed the air quality standard.
Pollutant peaks appear to be controlled by emissions and the topographical and
meteorological conditions associated with air monitoring sites (EPA 1981b).
Nitrogen dioxide is one of a family of nitrogen oxides. Nitrogen dioxide
plays a major role in the atmospheric reactions which produce photochemical
oxidants (EPA 1981b). Two major factors that affect NO- concentrations are
mobile source emissions and photochemical oxidation; both contribute to the
observed diurnal variation in NO concentrations. EPA (1981c) reports that
A
such a variation is described by a rapid increase in N0? in the morning as the
result of NO emissions and photochemical conversion to NO,,. This is followed
17
-------
by a decrease of NCL in the midmorning due to advection and increasing
vertical dispersion and loss of NC^ in various atmospheric chemical
transformation reactions. Peaks in the N02 concentration are often observed
during other times (EPA 1981c); elevated N02 levels usually occur between 7 PM
and 6 AM.
Unlike other gaseous criteria pollutants, 03 is not emitted directly by
specific sources. It is a secondary pollutant, formed in the air by
photochemical chemical reactions between nitrogen oxides and volatile organic
compounds, such as gasoline vapors, chemical solvents, and the combustion
products of various fuels. Because the chemical reactions necessary to produce
0., are principally controlled by sunlight, in most parts of the country 03
reaches peak levels during the late spring and summer months between 11 AM and
4 PM. Year-to-year variations are associated with factors such as meteorology,
measurement and calibration techniques, and quality control procedures (EPA
1981b).
THE DATA BASES
In accordance with the requirements of the Clean Air Act and the
Environmental Protection Agency's regulations for State Implementation Plans
(SIPs), ambient air quality data resulting from air monitoring operations of
state, local, and Federal networks must be reported to EPA each calendar year.
The SAROAD base is the established medium for the information distribution.
Ambient observations reported to EPA must satisfy minimum summary
criteria—sampling interval (e.g., continuous, noncontinuous) and period of
coverage (e.g., quarterly, annually). The criteria (EPA 1982c) for continuous
observations, with sampling intervals of less than 24 hours, are
1. Data representing quarterly periods must reflect a
minimum of 75 percent of the total number of possible
observations for the applicable quarter.
2. Data representing annual periods must reflect a minimum
of 75 percent of the total number of possible
observations for the applicable year.
18
-------
The SURE program is an EPRI-sponsored investigation of air quality in
the northeastern United States. The program is directed primarily at regional
definition of the relationships between emissions of SCL and the distribution
and concentrations of its reaction product, sulfate. The ultimate objective is
to develop a regional-scale air quality model capable of predicting sulfate
levels as a function of sulfur dioxide emissions. Investigator-s have collected
S02, NO, NOX, 03, and total suspended particulate matter (TSP) air quality
data for nine sites that EPRI identified as removed from major local emissions
of the above pollutants and their precursors (EPRI 1982). The EPRI remote
sites provide a valuable data base from which the frequency of co-occurrence
of pollutant mixtures can be evaluated. In 1978, the nine SURE sites were
located at
Montague, Massachusetts
Scranton, Pennsylvania
Indian River, Delaware
Duncan Falls, Ohio
Rockport, Indiana
Giles County, Tennessee
Ft. Wayne, Indiana
Research Triangle Park, North Carolina
Lewisburg, West Virginia
Eight sites were included in the analysis because they were considered
rural. For the purpose of this study, sites located near agricultural land and
containing a point source were identified as rural. Thus, Scranton,
Pennsylvania and Indian River, Delaware, with SO^ point sources nearby, were
considered rural and included in the analysis. Similarly, sites influenced by
automobile emissions (diurnal N0x fluctuations) such as Rockport, Indiana and
Ft. Wayne, Indiana, were categorized rural because they were surrounded by
agricultural land.
The TVA provided printouts of hourly averaged ambient air quality data
for those sites where simultaneous monitoring occurred for 0.,, S0?, and N0?.
For this analysis, data from seven sites were used:
19
-------
Allen 7 (Shelby County, Tennessee) 1978 T 1980
Paradise 21 (Muhlenberg County, Kentucky) 1978-1982
Paradise 23 (Muhlenberg County, Kentucky) 1980
Giles County (Tennessee) 1980 - 1982
Land Between the Lakes (Trigg County, Tennessee) 1982
Murphy Hill (Marshall County, Alabama) 1980
Saltillo (Harden County, Tennessee) 1979 - 1980
The Allen 7 site is in an urban location near downtown Memphis and is a
point source monitor for the Allen Steam Plant (6.6 km away). TVA reports that
there are various types of heavy industry located 0.8 km to the northwest, an
oil refinery 0.8 km to the south, and an interstate highway 400 m to the east.
Paradise 21 and 23 are rural sites used to monitor the Paradise Steam Plant.
Paradise 21 and 23 are 7.0 km and 6.0 km from the point source. There are no
other major pollutant sources nearby. Most of the surrounding area is
cultivated or in pasture. The Giles County site is rural, serving as a
regional air quality background monitor, remote from any major sources of air
pollutants. The Land Between the Lakes site is also a background monitor;
virtually all the surrounding area is forested. The Murphy Hill and the
Saltillo monitoring locations are PSD background sites. Thus, except for Allen
7, all TVA sites used in this analysis are located in remote areas.
RESULTS
To identify and characterize pollutant distribution at specific sites,
the 1981 hourly averaged SAROAD air quality data were reviewed to identify all
sites with a maximum NO^, SO^, or 03 concentration equal to or greater than
0.05 ppm. Each site was then evaluated by determining whether one of the other
two pollutants was co-monitored and also experienced an hourly averaged
concentration equal to or greater than 0.05 ppm. After identifying those
co-monitoring sites, the data base was evaluated with the following criteria:
1. Identify those sites where co-monitoring of S0? and N09
occurred and where 0.05 ppm was measured for each 2
pollutant at least once during the 1981 sampling period.
20
-------
2. Identify those sites where co-monitoring of 0, and S02
occurred and where 0.05 ppm was measured for each
pollutant at least once during the 1981 sampling season.
3. Identify those sites where co-monitoring of 0., and N02
occurred and where 0.05 ppm was measured for each
pollutant at least once during the 1981 sampling season.
Using the site identification code and the above criteria, a computer
listing of the hourly averaged concentrations, by day and by month, was
obtained for each of the 1981 SAROAD ozone, nitrogen dioxide, and sulfur
dioxide monitoring sites for the months May through September 1981. Data from
each identified site were reviewed for the possibility of the co-occurrence of
0.05 ppm S02/N02, 03/S02, or 03/N02 at least once during the months May
through September. At least three months of data during the five-month period
had to be available. Using the SAROAD site identification coding (EPA 1976),
the selected monitoring locations were segregated into "rural" and "non-rural"
categories. Rural sites are considered by EPA to be those monitoring locations
that have not been designated as center city, suburban, or remote (far enough
from any activity to measure geophysical background levels).
SO /NO
Most sites experienced fewer than 10 co-occurrences of S0?/N0? during
May through September. Usually there were weeks, sometimes months, between
co-occurrences. Figure 2-1 illustrates the frequency site distribution for the
S02/N02 co-occurrences. All of the rural sites sampled experienced less than
50 co-occurrences during the five-month season. This amounts to less than 1.5%
of the total hours available (3,672) during the period. Only 6 of the 32 rural
site years had more than 10 co-occurrence events; most non-rural sites
experienced more than 10 events. Philadelphia experienced 123 co-occurrences
during 1981.
The Indian River, Delaware rural site (located near the Indian River
Power Plant) experienced a series of co-occurrence events (each lasting
several hours) on May 26 and 27, and September 13, 19, and 23, 1978. Figure
2-2 shows the distribution of sulfur dioxide and nitrogen dioxide during the
21
-------
120"*
100**
* ******
* ******
80** ******
*
*
0 *
F
*
60**
S *
-> *
*
*
I
T 40'
E
S
*
20**
* ****** ******
* ****** ******
* ****** *xx*** ****** ****** ******
) *>AMA*AA*A>M^oa********»*UA*J^A****UA*****^
<10 20 30 40 50 60 70 80 90 >90
NO. OF CO-OCCURRENCES
Figure 2-1. S02/N02 Co-Occurrence, Frequency Site Distribution
22
-------
24-hour period of September 13, 1978. The numbers of events during the day
began in early morning and lasted for several hours during the daylight. The
episode disappeared the following day.
During 1979, the Paradise #21 TVA rural site experienced six
co-occurrence episodes. The May 15 episode is presented in Figure 2-3. The one
co-occurrence during that day was a typical pattern of episodes monitored
during the season.
During 1980, the Allen Steam Plant No. 7 TVA site had 29 episodes.
Figure 2-4 illustrates the concentration of S0? and N0? over the period May
through September. The number of co-occurrences during the day was small and
the time period between episodes was large. Figure 2-5 shows the episode for
July 30.
Figure 2-6 illustrates the June 27, 1981 episode for Fontana,
California. The site has been designated by EPA as rural industrial. During
the five months monitored in 1981, the site experienced a large number of
occurrences of nitrogen dioxide concentrations equal to or above 0.05 ppm. The
frequency of occurrence was so great that when an S0~ concentration above 0.05
ppm occurred, there was a high probability of the simultaneous occurrence of
SO,, and NOo concentrations above 0.05 ppm. Figure 2-6 shows the presence of
the large number of nitrogen dioxide concentrations above 0.05 ppm.
In contrast, the Kansas City, Kansas monitoring site experienced a small
number of NO- occurrences above 0.05 ppm (94 ug m ) during the five-month
period. The frequency of S02 concentrations equal to or greater than 0.05 ppm
(131 ug m~3) during the period was typical of the data produced for many of
the rural sites analyzed. Figure 2-7 shows the exposure regime of S0? and NO?
on September 4, 1981. On that date, at 9 PM, the sulfur dioxide concentration
was 0.06 ppm (134 ug m ) and the nitrogen dioxide concentration was 0.05 ppm
(102 ug m ). The simultaneous readings equal to or above 0.05 ppm lasted for
only two hours.
23
-------
IV)
C
0
/
N
C
E
N
T
R
fl
T
I
0
.24-,
.20-
. 16-
. 12-
NOX --
SO,
.08-
.04-
T
10
i i i 1 1 r
12 14 16 18 20 22
24
- TIME OF DflT
Indian River, Delaware
September 13, 1978
Figure 2-2. Indian River, Delaware, SO-/NO Co-Occurrence.
C
0
N
C
E
N
T
R
q
T
I
0
N
.GO-i
.50-
.40-
.30-
.20-
. 10-
.00-
~ i i i i i i n i i i i
2 4 G 8 10 12 14 16 18 20 22 24
S02 TIME OF DRY
Paradise, Kentucky
May 15, 1979
Figure 2-3. Paradise, Kentucky, S02/N02 Co-Occurrence.
-------
c_n
Q_
Q.
LU
O
O
C_3
Allen #7
(1980)
HAY JUN
Figure 2-4. Allen Steam Plant, Tennessee, S02/N02 Concentration Over Time.
JUL
-------
en
o_
Q_
o
LoJ
O
O
O
M
.52-
.28-
.24-
.ie-
.12-
.B8-
.32
.28-
.24-
.29-
.18-
.12-
.04-
I
SEP
JUL AUC
Figure 2-4. Allen Steam Plant, Tennessee, SC^/NCL Concentration Over Time (Cont.)
-------
C
0
N
C
E
N
T
R
q
T
I
0
N
P
P
M
.24-1
10 12 14 16 18 20 22 24
.OO-1
SO-
TIME OF DRY
Allen Steam Plant, Tennessee
July 30, 1980
0
N
C
E
N
T
.24-1
.20-
'2
.08
.04
.00
N02
S00
< I I I I I I i 1 I I 1
2 4 6 8 10 12 14 16 18 20 22 24
TIME OF DPT
Fontana, California
June 27, 1981
Figure 2-5. Allen Steam Plant, Tennessee, S02/N02 Co-Occurrence. Figure 2-6. Fontana, California, S02/N02 Co-Occurrence.
-------
c
0
N
C
E
N
T
R
fl
T
I
0
N
U
G
/
M
3
180-i
150-
120-
90-
60-
30
0
1 1 1 1 1 1 1 1 1 1 1 1
2 4 6 8 10 12 14 16 18 20 22 24
N02
2 TIME OF DflT
Kansas City, Kansas
September 4, 1981
1ppm = 1960 u9/m3 at 25°C and 1 ATM pressure.
Figure 2-7. Kansas City, Kansas, SC^/NC^ Co-Occurrence.
28
-------
Figure 2-8 shows the frequency site distribution for the number of
occurrences of CL and SCU for the monitoring locations analyzed. The majority
of sites (135) experienced less than 10 co-occurrences during the season. Only
the Rockport, Indiana and Paradise No. 21 sites had more than 40
co-occurrences during the season (48 and 45, respectively), a small number
when compared with the total number of sites that measured SOp/NC^ and Oo/NOo.
The Fontana, California site experienced numerous occurrences of ozone
episodes above 0.05 ppm. Therefore, there was a high probability that when the
sulfur dioxide hourly averaged concentration rose above 0.05 ppm, both
pollutants would be present at levels equal to or greater than 0.05 ppm.
Events of co-occurrence, lasting a few hours each, were present in June, July,
August, and September 1981. Figure 2-9 presents the July 23 data for the site.
A large number of ozone episodes above 0.05 ppm is evident. However, only a
few SOp hourly values above 0.05 ppm were present.
The Madison County, Illinois site has been coded as rural. Events of
co-occurrence were present in May, June, and September 1981. The controlling
variable for determining co-occurrence was sulfur dioxide with ozone events
above 0.05 ppm present in sufficient amounts so as not to be the limiting
factor. As in previous examples, the number of events during the entire period
was small. Figure 2-10 shows the exposure pattern for a co-occurrence episode
for May 27, 1981. The number of SO,, concentrations above 0.05 ppm is small.
The ozone hourly data for Scranton, Pennsylvania were missing for the
Pennsylvania site (May, June and July 1978). Available data did show
sufficient amounts of ozone concentrations above 0.05 ppm to indicate that the
co-occurrences were controlled by SO- events. Co-occurrences were present in
29
-------
ibbbbbbbyobobk-
20
30
40
50
NO. OF CO-OCCURRENCES
Figure 2-8. (L/SOp Co-Occurrence, Frequency Site Distribution
30
-------
c
0
N
.21-
C
E
N
. 17-
T
R
fl
. 13-
T
r
i
0
.08-
N
P
.04-
P
M
S09
r
0
' N
.21-
• • r
f E
m - m- - m
N
.]/-
T '
P
fl
.13-.
f
V ' -08-
\ ' N
r \
A \ p
f \ p
' 1 \ *
' / \ M
- ••- - a - -.r - • -4 -* ^ , •
'
•f\ '
- -• • -»-»-* , — -* \ , . • -r - i
11 I I I I 1"1T"T1 .00, ,T , | | •[ i - •; | " • 1
2 4 6 8 10 12 14 16 18 20 22 24 2 4 G 8 10 12 14 16 18 20 22 2'
°3 — -
Fontana, California
July 23, 1981
Figure 2-9. Fontana, California, O^/SO- Co-Occurrence.
Madison County, 111inois
May 27. 1981
Figure 2-10. Madison County, Illinois, 0,/SOp Co-Occurrence.
-------
July, August, and September. Figure 2-11 presents data for August 1, 1978.
Ozone levels were above 0.05 ppm during mid-day when sulfur dioxide exposures
were high. The sulfur dioxide concentrations above 0.05 ppm decreased in the
early afternoon and the co-occurrences disappeared.
The Rockport, Indiana, site experienced co-occurrences in June, July,
August, and September. An event would last for a few hours, then be followed
by several days or weeks of no co-occurrence before another event. The number
of ozone events was great and therefore, co-occurrence was controlled by the
S02 events. Figure 2-12 describes the co-occurrence episode for August 25,
1978. The ozone remained above 0.05 ppm between 9 AM and 4 PM and the sulfur
dioxide concentrations above 0.05 ppm defined the number of co-occurrences.
In 1978, the Paradise #21 TVA rural site experienced a large number of
co-occurrences. Figure 2-13 shows the concentration of hourly averaged 03 and
S0? concentrations from May through September. Figure 2-14 illustrates the
exposure regime during an episode on September 21, 1978. The ozone levels
remained fairly constant during daylight, and the sulfur dioxide
concentrations defined the number of co-occurrences.
Figure 2-15 presents the summary of the frequency distribution for those
sites that were analyzed for O.,/^ co-occurrences. For the three pairs of air
pollutants, the ozone.-nitrogen dioxide combination showed, by far, the
greatest number of co-occurrences. Several sites in the South Coast Air Basin
of Southern California experienced more than 450 co-occurrences. The rural
sites of Riverside, Fontana, and Rubidoux, California had more than 100
co-occurrences. However, most of the analyzed sites (143) experienced fewer
than 10 co-occurrences. Denver, Colorado and San Jose, California did
experience more than 100 co-occurrences.
Rubidoux, California, located in the South Coast Air Basin, is
designated as a rural commercial site. There were ozone and nitrogen dioxide
co-occurrences in May, June, July, August, and September 1981. Because
nitrogen dioxide concentration maxima tended to peak in the evening or early
32
-------
CO
CO
C
0
N
C
E
N
T
R
H
T
I
0
17-'
. 10-'
.07H
.03-1
.00
.20-,
SO,
20 22 24
TIME OF DRY
Scranton, Pennsylvania
August 1. 1978
0 12 14 16 18 20 22 24
.Q7H
.00
so.
TIME OF DflT
Rockport, Indiana
August 25, 1978
Figure 2-11. Scranton, Pennsylvania, 0,/S02 Co-Occurrence.
Figure 2-12. Rockport, Indiana, 03/S02 Co-Occurrence.
-------
Q_
Q_
O
-------
OJ
en
Q_
CL
o
UJ
CJ
CD
.58-
.49-
.55-
.29-
° .21-
.11-
.07-
:r.:.-ilbu
L
i
I
Am It L L ti i
uumt^i i- ki^Ml n4*nMl «r-^^i A^^^kMPi« ft • Wl m
{-
lAAnmvIL>
^UjJI^L^
jjl
:it,
.35-
2
O
S .2.
.14-
JUL
AUC SEP
Figure 2-13. Paradise, Kentucky, 03/S02 Concentration Over Time (Cont.)
-------
C
0
N
C
E
N
T
R
q
T
I
0
N
37-J
22-J
• *--* *--»----—
I I I I I I I I I I I I
2 4 6 8 10 12 14 16 18 20 22 24
°3 --
SCL
' TIME Or DRY
Paradise, Kentucky
September 21, 1978
Figure 2-14. Paradise, Kentucky, 03/S02 Co-Occurrence.
36
-------
150*
*
*•
*
*
*
*
*•
*
*
1 ?S**
*
*•
*r
*
*•
*
*
*
*
*•
100*
*
*
*
*•
*
*******
******
******
******-
******
*******
******
*i***X-
***x**
•****x*
*******
******
******
****x*
***x**
•)bt;feJoi^-
***3t**
*******
***xx*-
***wk*-
******
*******
******
7 c:**-
' J
******
**x*x*-
•****>*
*A***X
*******
*******
******
*Wc*x*-
**fcdot
50**
25**
****>*•
****xJr
*******
•*****x
*fcyodr
******
*3t*-toc*
******
******
****X*
**K**A-
******
******
******
*****x
****** ^^^
•*/obtb
*fct^**
•***••.-bi.
<10 20 30 40
50 60 70 80
90 >90
NO. OF CO-OCCURRENCES
Figure 2-15. CL/NCL Co-Occurrence, Frequency Site Distribution
37
-------
morning, the co-occurrences were present at these times. Figure 2-16
illustrates the monitoring data for June 26, 1981. Because ozone
concentrations were mostly above 0.05 ppm, the number of co-occurrences was
large.
The Indian River, Delaware site experienced its only two co-occurrences
on June 3, 1978. There were NO events on May 26 and September 13, but they
A
did not match the dates of the many ozone events. Figure 2-17 shows that the
co-occurrences appeared in the late afternoon and early evening.
During 1979, the Paradise No. 21 site experienced the only
co-occurrence that was measured from 1978 through 1982. Figure 2-18 shows the
exposure regime on July 17, 1979. The co-occurrence was measured at 11 AM in
the morning.
The Allen Steam Plant No. 7 TVA site experienced nine
co-occurrences during the 1978 season. Figure 2-19 describes the episode that
took place on July 6. Ozone concentrations were fairly high during the
daylight hours. In the early evening, the nitrogen dioxide concentrations rose
above 0.05 ppm, resulting in the co-occurrence events. Figure 2-20 shows the
hourly averaged concentrations for 0, and N0? for May through September.
DISCUSSION
The seasonal variation in specific pollutants was evident. For all 1981
SAROAD sites that measured ozone above 0.05 ppm, 92% of the maximum hourly
readings were observed during the May through September period. Less than 20%
of the N0? hourly maxima were recorded during the same period. While the daily
ozone hourly peak concentration usually occurred in the late morning and early
afternoon, the daily nitrogen dioxide peak usual ly occurred in the early
morning or late evening. Many of the sulfur dioxide peaks occurred during the
daylight hours.
38
-------
OJ
UD
C
0
N
C
E
N
T
R
R
T
I
0
N
.24-1
,20-
16-
12-
.08-
.04-
°3 —-
NO-
. 00 i , . T . T .' ,
2468
i r T i i i ^ i
12 14 16 18 213 22 24
TIME OF DflT
Rubidoux, California
June 26, 1981
C
0
N
C
E
N
T
R
fl
T
I
0
.24-,
.20-
16-
.08-
,04-
.00
°3 ™-
-••-•• »%
jr-.-^
T ~ "1 1 —'—I 1 1 1~
10 12 14 16 18 20 22 24
TIME OF DflT
Indian River, Delaware
June 3, 1978
Figure 2-16. Rubidoux, California, 03/N02 Co-Occurrence.
Figure 2-17. Indian River, Delaware, Cu/NO Co-Occurrence.
«j X
-------
o
c
0
N
. 17-
C
E
N
.13-
T
R
fl
. 10-
T
I
0
.07-
N
P
.03-
P
M
.00-
r • ",
y
j * *•-
A -•• '•' >k-
W '> •' • • •«.
/;' \ V '»
/,' \
/;' 1
// \/ \
'
, " i i i * i i i i i i
2 4 6 8 10 12 14 16 18 20 22 2
NO,
X ——— -t- r tit— r»r- n/-iv
.20-1
Paradise, Kentucky
July 17, 1979
Figure 2-18. Paradise, Kentucky, 03/N02 Co-Occurrence.
8 10 12 14 16 18 20 22 24
TIME OP DQY
Allen Steam Plant, Tennessee
July 6, 1978
Figure 2-19. Allen Steam Plant, Tennessee, 03/NO- Co-Occurrence.
-------
.32-
.28-
.24-
.29-
.16-
fM
i .121
D-
CX
O
O
Allen # 7
(1978)
JUM
JUL
Figure 2-20. Allen Steam Plant, Tennessee 03/N02 Concentration Over Time.
-------
.at-
o
-------
Using rural and non-rural 1981 SAROAD data and the criteria previously
mentioned, 66 percent of the sites that co-monitored S09 and NCL experienced a
co-occurrence at least once during the five-month period. Of the CL/SO^ sites,
63 percent experienced a co-occurrence at least once; 71 percent of those
sites that co-monitored CL and N02 experienced at least one co-occurrence
during the period.
The EPRI SURE hourly averaged air quality data for S09, (L, and NO were
C. u X
analyzed for co-occurrence events. Because the EPRI data were reported in N0x,
S09, and 0, concentrations, it was assumed for this study that the NO could
L. -J X
serve as a surrogate for N09 concentrations; using NO as a surrogate results
C. A
in an overestimate of the co-occurrences of N02 with either S02 or On- Eight
EPRI sites were reviewed for the co-occurrence of pollutant mixtures where the
concentrations were equal to or greater than 0.05 ppm. Only one site (Indian
River, Delaware) experienced at least one co-occurrence of S09/N0 . Four EPRI
c. X
sites experienced at least one co-occurrence of 0.,/S09 (Scranton,
Pennsylvania; Duncan Falls, Ohio; Rockport, Indiana; and Giles County,
Tennessee). The Indian River site was the only one that experienced at least
one co-occurrence of Oo/NO during the period May through September.
The TVA provided hourly averaged air quality data for seven sites that
had monitored the three pollutants since 1978. Of the 14 site years reported
for S02/N02 co-monitoring, eight reported co-occurrence at least once. Of the
14 site years reported for 03/S02, 11 showed co-occurrence. For the 12 site
years recorded for 03/N02, only 4 showed co-occurrence.
Table 2-1 summarizes the results of the SAROAD, SURE, and TVA data
analysis. For ozone, sulfur dioxide, and nitrogen dioxide, there were 752,
921, and 345 total site years monitored, respectively. Of the total monitored,
370 (03), 321 (S02), and 291 (N02) site years were identified for those
locations where co-monitoring occurred. Using the monitoring data produced
from EPA, EPRI, and TVA, 32, 36, and 34 rural monitoring site years were
evaluated for S02/N02, O-i/SOo, and Oo/N02 co-occurrences, respectively.
43
-------
Table 2-1 Summary of Site Years Analyzed
(EPA SAROAD, EPRI SURE, and TVA Data)
Pollutant Total # Site Years # Sites Yrs. Where # Rural Site Yrs. > Thresh.
Monitored Pollutant > Threshold & Co-Monitoring Occurred
and Co-Monitoring Occurred
°3 752
S02 921
N02* 345
S02/N02*
o3/so2
03/N02*
370
321
291
91
124
146
40
37
37
32
36
34
* EPA provided the EPRI SURE monitoring data in the form of N0x, S02, and
concentrations. EPA and TVA reported N02, S02, and 03 concentrations.
44
-------
CONCLUSION
Analysis of selected ambient air quality data collected by EPA, EPRI,
and TVA shows that, for most cases, the constant artificial fumigation
exposures do not mimic actual exposures. Since co-occurrence may be
infrequent, researchers may want to focus on the sequential pollutant
exposures characteristic of the rural sites analyzed. For example, while the
daily ozone hourly peak concentration usually occurred in late morning and
early afternoon, nitrogen dioxide typically peaked in the early morning or
late evening. Similarly, sulfur dioxide episodes mostly appeared during the
same daylight hours that ozone concentrations reached their maximum.
The monitoring data used in this analysis support the conclusion that 1)
co-occurrence of pollutant mixtures lasts only a few hours per episode and 2)
the time between episodes is great (weeks, sometimes months). The analysis of
rural air monitoring data, generated by three different organizations,
represented a first-step effort in characterizing rural sampling sites. Air
quality data from a subset of the data bases were used to identify the
distributions for S02/N02, 03/S02, and 03/N02 co-occurrences, respectively.
Many of the sites were located in rural agricultural areas.
The lack of a comprehensive rural air monitoring data base has made it
difficult to judge the representativeness of those sites used in the analysis.
However, by 1) defining hourly averaged concentrations of 0.05 ppm and above
as an event, and 2) combining air quality data bases (SAROAD, SURE, and TVA),
the analysis shows a consistent exposure pattern, suggesting that the use of
sequential exposure regimes should receive more attention and that researchers
may want to reconsider their importance relative to co-occurrence exposure
regimes.
45
-------
3. EFFECTS OF POLLUTANT MIXTURES ON VEGETATION
INTRODUCTION
The first comprehensive reviews of literature on mixture effects were
published eight years ago (Reinert et al. 1975, Williams and Ricks 1975). Much
of the research concerning air pollutants and pollutant mixtures has since
been summarized in several books (Heck et al. 1982, Ormrod 1978, Unsworth and
Ormrod 1982), recent review articles (Ormrod 1982, Wellburn 1982), and
research reports (Fujiwara 1973, Fujiwara and Ishikawa 1976, Ishikawa 1976,
Reinert and Heck 1982, Yamazoe and Mayumi 1977). These reviews and summaries
reveal that only a few combinations of pollutants have been studied and that
little attention has been given to environmental and biological factors that
influence vegetation responses. Few studies have dealt with any aspects of the
responses of major plant species to mixtures of air pollutants at ambient
concentrations administered under typical ambient environmental
condi tions.
When two pollutants occur in combination, there is the possibility of
visible injury totaling more than the sum of visible injury caused by each
pollutant alone. This concept, which has encouraged research, has been
extended to changes in growth and yield as well as to biochemical and
physiological changes in plants following exposure to pollutant mixtures. The
concept is only one of the possible categories of plant response to pollutant
mixture but it is the one which may be of greatest concern in vegetation
effects assessment. When one pollutant has no effect on the plant response to
the other pollutant, the category is termed no joint action. The category
joint action implies that both pollutants have some effect on the plant
response. This latter category is frequently divided into the subcategories
additive response, when effect^ equals effect^ plus effect^, and interaction,
when effect^ is not equal to effect^ plus effect,,. There are two possible
types of interaction: synergism (greater than additive action) when effect,,,
is greater than effect^ plus effect2, and antagonism (less than additive
action) when effect^ is less than effect-^ plus effect,,. It is the concept of
synergism that has been of greatest interest and concern. It would be
difficult, using the present experimental knowledge, to fully characterize the
46
-------
nature of the joint action of two or more pollutants on major species in
environments typical of ambient conditions.
Joint action of major gaseous pollutants has been by far the most
studied kind of mixture response. This is because the more phytotoxic air
pollutants are gaseous (e.g., CL, SCL, NOo and HF); there is a greater
knowledge of their atmospheric chemistry and occurrence; and they are easily
generated and monitored in experiments. However, there has been little or no
research on mixtures involving minor gaseous pollutants (e.g., H~S, HC1, C^j
NhL, and (^H*). Air pollutants occur also as aerosols or as dissolved or
suspended material in precipitation. Some information is available on
gas-aerosol joint action (Krause and Kaiser 1977, Singh 1980). Aside from
problems created by the physical and chemical heterogeneity of aerosols,
deposited material remains on plant foliage after joint exposure has ceased
and thus constitutes a virtually continuous source of exposure. For this
reason, the interaction of gases with ions of trace elements or heavy metals
(e.g., Cd, Ni, Cu, and Zn) on or in plants may be important (Czuba and Ormrod
1974, Krause and Kaiser 1977, Lamoreaux and Chaney 1978, Ormrod 1977, Toivonen
and Hofstra 1979).
The intent of this chapter is to summarize and interpret existing data
concerning plant responses to pollutant mixtures. Since 0.,, S0?, and N0? have
had most attention to date in mixtures research, much of the discussion will
focus on paired combination mixtures (0, + S0?, 0-^ + N0?, S0? + N0?) and on
combinations of 0., + SO- + NO^. Even though most research has focused on the
above noted mixtures, studies of mixtures of S0? + HF (Mandl et al. 1975,
Mandl et al. 1980, Matsushima and Brewer 1972, McCune 1983) and N02 + HF
(Amundsen et al. 1982) have also been reported. Also there have been recent
reports concerning interactions between acid rain and S0? (Irving and Miller
1981) and acid rain and 03 (Troiano et al. 1981).
EXPERIMENTAL METHODS AND INTERPRETATION OF DATA
The species of concern, stage of growth, and other plant factors,
together with the need for control, separate and combined treatments, and
considerable statistical precision, have dictated certain requirements for
47
-------
methodology in mixture studies. Experimental protocol appropriate for mixture
studies has been developed to increase the validity and comparability of air
pollutant research (Heck et al. 1979). Studies of mixture effects have taken
place in controlled environment chambers, in greenhouses, and in field
facilities. Each system has its particular merits. Fully controlled
environments provide relatively high precision and repeatability but response
patterns may not correspond well with field responses. Field facilities
provide the most direct comparison with open field conditions but
results may not be replicable because of changing weather patterns outdoors.
Most studies to date of mixture effects have been conducted in
controlled environments or greenhouses. The utilization of continuous stirred
tank reactor chambers by Heagle and Johnston (1979), Le Sueur-Brymer and
Ormrod (1983), Reinert and Nelson (1980), and others has been a recent
innovation in mixtures research. A few mixture studies have been conducted
entirely in field facilities and a few have included both field evaluations
and controlled exposures in an attempt to allow direct comparisons. Menser and
Hodges (1970) compared tobacco cultivar sensitivity to 07 + S09 in the field
O L-
with that determined with controlled exposures in the greenhouse. There was a
major shift of sensitivity of one cultivar. Hodges et al. (1971) also reported
comparisons of chamber responses of tobacco to 03 + S0? with field responses.
Beckerson et al. (1979) compared bean cultivar sensitivity to 0^ + SOp in
controlled environments with injury development following ambient outdoor
exposure. Outdoor responses correlated more strongly with sensitivity to 0-
than with sensitivity to mixtures.
Outdoor exposure chambers, with environmental conditions more
characteristic of ambient conditions, have been used by some researchers.
Heagle et al. (1974, 1983) used open-top outdoor chambers for long-term 0^ +
O
S02 treatment of soybean. Mandl et al. (1980) used similar chambers to study
S02 + HF responses of sweet corn and Heggestad and Bennett (1981) used such
chambers to observe SO^ enhancement of 0^ injury to snap beans. Hill et al.
(1974) used a portable field chamber to expose desert plants to S02 + N0? at
concentrations measured downwind of a large coal-fired power plant, while
Thompson et al. (1980) used open-top chambers for their studies of desert
plant responses to S02 + N02- Other field chambers have been utilized by
48
-------
Foster et al. (1983) and Oshima (1978). Bennett et al. (1980) grew snap beans
in the field and exposed them to CL + H?S through a plastic duct assembly. A
linear gradient exposure technique was used by Reich et al. (1982). Ashenden
et al. (1982) have described a system for exposing plants to SCL + N02, using
hemispherical greenhouses having good air circulation and near-ambient
temperatures.
Numerous studies exist which allow only individual comparison of
treatments because there were not sufficient experimental units available to
permit a full concurrent examination of mixture effects. In all these studies,
the interaction or dependency of the effect of one pollutant on the level of
another could not be fully evaluated due to missing treatments. An important
consideration was whether or not there were enough exposure chambers to run
all treatments at the same time. If not, considerable confounding may have
developed when treatments could not be evaluated under similar conditions.
This might have resulted in apparent pollutant interactions which did not
reflect the true plant response.
Most researchers have used factorial experiments and analysis of
variance for interpretation of combined effects of pollutants, A statistically
significant interaction of two pollutants has been regarded as evidence for
synergistic or antagonistic effects. Such techniques were used by Ashenden
(1979a, 1979b), Bull and Mansfield (1974), Gardner and Ormrod (1977), Heagle
and Johnston (1979), Tingey and Reinert (1975), Tingey et al. (1973b),
Wellburn et al. (1976), and others.
More information may be obtained concerning the ability of each
pollutant to produce a biological response by averaging effects over the
presence and absence of other pollutants. One type of factorial design
involves using one concentration of each of three pollutants, alone and in all
two- and three-way mixtures, plus a charcoal-filtered air control treatment.
Thus, eight treatments are involved and the main and interaction effects of
each pollutant factor can be assessed through treatment component contrasts
(Heck et al. 1979). Experiments using this design have been reported in which
pollutant concentrations were either high (Reinert and Gray 1981, Reinert and
Heck 1982) or low (Reinert and Heck 1982). The exposure durations varied from
49
-------
3-6 hours and the number of exposures from one (Reinert and Gray 1981) to many
(Reinert and Sanders 1982, Sanders and Reinert 1982a, 1982b). Plant species
(Reinert and Sanders 1982, Sanders and'Reinert 1982b), as well as cultivars
within species (Sanders and Reinert 1982a),' have been compared using this
design.
Additional information on the nature of interactions can be obtained by
determining the effect of increasing concentrations of one pollutant on plant
growth and other responses in the presence of more than one concentration of a
second pollutant. When three or more concentrations of one or both pollutants
are used in the experimental design, the dose-response relationships may be
v,
evaluated. The responses may be described as linear or curvilinear and further
serve to interpret some of the complexities of additivity, synergism, and
antagonism found when only one concentration of each pollutant is used. Such a
mathematical/statistical approach to CL + SCL + NOp interactions has been used
by Reinert et al. (1982) to study the influence of sub-injury threshold
concentrations of SO,, + NCL on plant responses to 0,. A numerical evaluation
of dose-response surfaces in terms of linear and curvilinear components was
also presented.
Ormrod et al. (1983a) utilized quadratic polynomial equations,
three-dimensional response surfaces, and contour plots to evaluate the effects
of (L and SOp on one cultivar each of lettuce, radish, and pea, using a
rotatable experimental design. The use of the rotatable design decreased the
number of required treatments, compared with a full factorial design. For this
study, plants were grown in a controlled environment chamber and exposed to
seven combinations of CL and SOp. Injury was evaluated on the basis of visible
chlorosis and necrosis and growth was evaluated as leaf area and dry weight.
The contour graphs in Figure 3-1 are two-dimensional representations of
three-dimensional surfaces. The concentrations of SOp and (K form the abscissa
and the ordinate, respectively, and the response is shown as a series of
isoeffect or contour lines. The shapes of the isoeffect lines illustrate
cross-sections of the surface, while their'spacing shows the rate of change or
curvature of the surface. These contour plots indicated the diversity of
response patterns and particularly that,some response "variables demonstrated
50
-------
/\/\yX/\/s
\/\'\/^'
Figure 3-2. Graphical representation of the four response regions of
practical interest when two pollutants are combined. For
explanation of I, II, III, and IV, see text. The blank portion in
the area in which no effects occur, E3 designates the area with
pollutant A effects, S3 designates the area with pollutant B
effects, and S3 designates the area with combined effects of A
and B. The number of circles indicate numbers of results with
each kind of outcome in the research on effects of SO- + N0? on
native desert plants reported by Thompson et al. (198u).
51
-------
additive effects at low concentrations of 03 + S02 and antagonistic responses
with increasing concentration of both gases in combined treatments.
Other statistical methods have also been used. White et al. (1974) used
tests of non-additivity of pollutant effects. A statistical test of synergism
has been made with models derived by polynomial analysis of injury index data
(Macdowall and Cole 1971). Chi-squared analysis was used by Jacobson and
Colavito (1976). Probit analysis has been used to interpret antagonism and
synergism, by determining median effective doses (Macdowall and Cole 1971,
Jacobson and Colavito 1976). To increase precision, Ormrod et al. (1983b) used
covariate measurements to account for significant within-treatment variation
in plant growth. Some differences that were not significant in conventional
analysis of variance were significant when tested by analysis of covariance.
Most reports of studies involving mixtures have included, or implied, an
assessment of the joint action of the pollutants in terms of additive effects,
greater than additive (synergistic) effects, or less than additive
(antagonistic) effects, using the terminology of Tingey and Reinert (1975).
Responses have been expressed in terms of amount of injury or changes in
threshold concentrations causing injury. Additivity has been suggested for a
number of diverse plant responses (Ormrod 1982), but many reports have
suggested synergistic responses. Reports of antagonistic responses have been
more limited. Many of the reports on additivity, synergism, and antagonism
indicated that the nature of the interaction was dependent on factors such as
pollutant concentration and exposure duration, as well as on the species and
gases studied.
The threshold phenomenon may be an important component of response
patterns to mixtures. In general, when pollutant concentrations are below or
at the threshold for individual visible injury responses, synergism (in terms
of reduced growth and plant yield) is more frequently observed. As the
concentrations of both pollutants increase in mixture above their individual
injury thresholds, weight loss may only be additive. When the concentrations
of the pollutants are relatively high, antagonism often develops and further
weight loss may be minimal. This threshold phenomenon resulting in apparent
synergism wi11 be particularly important in 2 X 2 factorial experiments for
52
-------
the case when neither pollutant alone produces a response, but their
combination does. When a threshold exists, it is possible that an apparent
interaction results because no injury occurs until the weighted sum of the two
components exceeds a certain value. The weighting would give a measure of the
relative effectiveness of each component. The sum of individual effects, near
the threshold, may not be the appropriate term for comparison with joint
effects to determine interaction.
For a particular set of combinations of two pollutants, the responses
can be graphically presented to illustrate the four regimes of practical
interest: (I) where neither an effect of pollutant A, pollutant B, nor
combined effects of A and B occur; (II) where combined effects occur but an
effect of neither A nor B occurs; (III) where two or more of the three effects
occur; and (IV) where effects of A or B occur but combined effects of A and B
do not. These four possible outcomes for a single and mixed two pollutant
study are diagrammed in Figure 3-2. The frequencies of such outcomes are
illustrated for the data of Thompson et al. (1980) who exposed several desert
species to a wide concentration of single and mixed SCL and NOo for several
weeks. An effect was considered to be a decrease in some measure of weight,
linear growth, or reproduction to less than or equal to 90% of the unexposed
controls. The effects were grouped into the four possible outcomes as
indicated by the Roman numerals in Figure 3-2. This illustrates that all types
of outcomes were found with these exposure regimes used in this research
project, but that the most frequent responses were either no effects or
effects of both combined and single gases.
Most research with mixtures has been conducted in controlled exposure
facilities using certain concentrations of gases for a specified duration.
While the need for systematic testing of a range of mixture concentrations has
been recognized (Heagle and Johnston 1979, Mandl et al. 1975), few
investigators have described the exposure in terms of dose (the combination of
pollutant concentration and duration), or have manipulated the components of
dose. The concept of pollutant flux or uptake rate has barely appeared in the
literature on effects of air pollutant mixtures even though the amount of
pollutant sorbed may be much more closely related than concentration to the
response.
53
-------
Figure 3-2. Graphical representation of the four response regions of
practical interest when two pollutants are combined. For
explanation of I, II, III, and IV, see text. The blank portion in
the area in which no effects occur, E3 designates the area with
pollutant A effects, G3 designates the area with pollutant B
effects, and EB designates the area with combined effects of A
and B. The number of circles indicate numbers of results with
each kind of outcome in the research on effects of S00 + N00 on
native desert plants reported by Thompson et al. (1980).
2
54
-------
Most investigators to date have used simultaneous exposures to
nonvarying concentrations. In the natural environment, peak concentrations of
pollutants may occur at different times for different pollutants. Such
patterns may have considerable impact, with the preconditioning of plants by
one pollutant affecting their response to another pollutant. Matsushima and
Brewer (1972) investigated sequential reciprocal exposures of orange to SO- +
HF to determine whether one gas influenced the subsequent response of the
plants to the other gas, but found little effect. Costonis (1973) found a
sequence of CU followed by SCL to be more toxic to eastern white pine than
exposure to both gases simultaneously. White et al. (1974) found that neither
SOp nor NOp pretreatment of alfalfa affected response to a subsequent exposure
to SCL + NO-. Exposure to SO- before exposure to 0, + SO- markedly influenced
bean, cucumber and tomato sensitivity (Hofstra and Beckerson 1981). Many
investigators have subjected plants to intermittent treatments within overall
long-term exposures. Tingey et al. (1971b, 1973b) noted that this might allow
plants to repair injury and regain normal metabolic functions during the
non-exposure period.
In some cases where many processes are involved, such as in components
of yield, there may be a multiplicative, rather than additive, effect. Each
process may have a different dose-response function. For example, Reich et al.
(1982) showed different dose-response relationships for three components of
soybean yield. In such a case the dose-response relationship may be
approximated by a third- or higher-degree polynomial or at least a four
component function. Sometimes a multivariate approach may help to elucidate
the nature of the effects or at least serve to simplify the nature of the
responses. For example, in chronic exposures to CL and/or SO- of alfalfa,
treatment-induced changes in foliage and root dry weight were so closely
associated that a weighted sum of the two could serve as a single measure of
response (Tingey and Reinert 1975). On the other hand, with acute exposures of
radish, 0, and S0? appeared to have opposite effects on a weighted sum of root
and leaf dry weight, but no interaction. However, with reference to a weighted
contrast between roots and leaves, their effects alone were similar
(decreasing the difference between root and shoot), but opposite (increasing
differences) when both were present.
55
-------
Whether the concern is about visible injury on foliage or growth
effects, one should not expect response to be linear with dose nor should one
expect a single mode-of-action as pollutants may induce increases, as well as
decreases, in growth (Bennett et al. 1974) or other responses. It may well be
that linearity is adequate over narrow ranges, but not over the entire range
of interest. When a linear dose-response function is found, as with the total
dry weight of radish plants (Tingey et al. 1971b), the dose can be expressed
as a weighted sum of SOp and Oo concentrations. Other responses also appear to
approximate what would be expected from a linear relationship to a weighted
sum (e.g., K-efflux from 'White Cascade' petunia leaf discs [Elkiey and Ormrod
1979a]). When a quadratic function is found (Tingey et al. 1973b), a weighted
sum of SOp and CU concentrations, which implies a constant relative
effectiveness, may also be used as a dose-variable.
CHARACTERISTICS OF PLANT RESPONSE
Responses to pollutants and pollutant mixtures have been detected in
several ways: visible symptoms of injury; altered growth and development;
physiological and metabolic imbalances; and accumulations of certain elements.
Growth and yield are often the most important response variables and it is
probably this concept that effects may be greater than additive (synergistic)
that has been the predominant concern of combined pollutant studies.
Foliar Symptoms
The practical significance of visible foliar response has been mainly
in the diagnosis of effects. Kinds of symptoms, and their distribution on a
plant or between species, have provided the investigator with inferences as to
the kinds of air pollutants (qualitative factors). The degree of symptom
development has allowed inferences as to amount of pollutant or exposure
(quantitative factors). Degrees of symptom development has also served as a
measure of the likelihood of effects on growth and reproduction.
Exposure-effect relationships derived from visible injury data have allowed
inferences to be made as to the nature of the dose-response relationship, the
effects of biologic and environmental factors upon it, and the mode of action
of air pollutants in the plant. However, if the combined effect of pollutants
56
-------
of air pollutants in the plant. However, if the combined effect of pollutants
alters the qualitative or quantitative foliar symptom characteristics, errors
in diagnosis could have occurred.
Many investigators have devised a leaf injury rating system and have
used the data obtained for interpretation of mixture effects. Few have
assessed differences in appearance by providing descriptions of the injury. In
some cases, experiments did not last long enough to permit the development of
stable injury symptoms. In general, ozone injury symptoms have dominated in
studies of mixtures of 03 + S02 (Menser and Heggestad 1966, Menser and Hodges
1970, Hodges et al. 1971, Tingey et al. 1971a, 1973b, Heagle et al. 1974,
Elkiey and Ormrod 1979b). There were exceptions and, in some cases, different
symptoms developed in response to the combination. Grosso et al. (1971) found
different symptoms of 0^ + S02 on tobacco leaves than when CL alone was the
pollutant. Combined CL + SO- injury to apple leaves differed from either CL or
SO- injury (Kender and Spierings 1975, Shertz et al. 1980a). Undersurface
glazing, a symptom usually attributed to PAN, was found on petunia leaves
exposed to CL + SO- (Lewis and Brennan 1978). Cucumber exposed to 0- + SO- had
an additional symptom of interveinal chlorosis, compared with CL alone
(Beckerson and Hofstra 1979a). Visible injury to three woody species, caused
by exposure to 0- + SCL, included symptoms of each pollutant alone (Carlson
1979). Acute responses of eastern white pine to CL + SCL had different
symptoms from responses to either CL or SCL alone (Costonis 1973), but
Dochinger et al. (1970) reported that (L and SO- separately or in combination
produced the same initial symptoms on eastern white pine.
Duration of exposure is important. Jacobson and Colavito (1976)
indicated antagonism of CL + SO- in navy bean and attenuation of visible
injury with short term exposure. This contrasted with Hofstra and Ormrod
(1977) who found unique and severe injury symptoms on navy bean leaves by 0- +
SO- after several days' exposure. Symptoms of injury from mixtures of SO- +
NO- differed greatly, in several species, from those caused by single gases
(Tingey et al. 1971b). In contrast, Hill et al. (1974) found the symptoms of
SO- + NO- on many species to be the same as those for SCL, and Matsushima and
Brewer (1972) found SO- + HF -induced chlorotic patterns to be the same as for
individual gases. Kohut and Davis (1978) found an interaction of 0^ + PAN
57
-------
which affected lower and upper leaf surfaces. On. the lower surface, the two
gases were antagonistic in causing injury; on the upper surface, they were
additive or synergistic.
so2 + o3
The synergistic action of SOp + 03 first noted on tobacco in 1966
(Menser and Heggestad 1966) encouraged all subsequent research on pollutant
mixtures. During the first few years that followed, the concept of
greater than additive or synergistic amounts of foliar injury, following
exposure to pollutant mixtures, became accepted as a frequent occurrence.
However, Tingey et al. (1973a) reported that not all visible-injury response
to mixtures of SCL + 0, was synergistic. They concluded that foliar injury
responses for six plant species could be additive, greater than additive, or
less than additive depending on the species, and on the concentration and
exposure duration of both pollutants. Visible foliar injury has been widely
used to evaluate variable species responses to S0? + (k. Examples of research
reports illustrating the nature of joint effects on visible injury are
presented in Table 3-1. The diversity of effects obtained in such research
serves to illustrate the importance of subtle or controlled factors in
addition to the more obvious species and dose differences.
The experimental concentrations, durations, and frequencies of gaseous
pollutant exposure have varied widely (see Tables 3-1 and 3-2). The longest
concentrations studied could occur in the ambient environment (see Chapter 2)
but no other features of the exposure doses reflected the ambient polluted
environment. Thus, it is not possible, at this stage, to estimate the
probability of occurrence in the ambient environment of such experimental
conditions. The experimental durations, frequencies, and constant
concentrations used in the artificial fumigations do not represent the real
temporal patterns in ambient polluted environments. Also most mixture
experiments to date have not been designed to study effects of sequential
exposures.
58
-------
Table 3-1
Visible foliar injury on various plant species
in response to the joint action of S0? + 0,
Species
°:
Apple
Grape
Navy bean,
tobacco
Navy bean,
soybean
Soybean
Radish,
cucumber
Soybean
Pinto bean
Begonia
Pea
Poplar
Tobacco
Tobacco,
alfalfa
2 cone
0.8
0.8
0.8
0.15
1.0
0.15
0.15
0.25
0.3
0.13
0.05
0.03
0.1
Dose
S02 conca
0.8
0.8
1.6
0.6
1.5
0.15
0.15
0.8
1.8
1.23
0.2
0.28
1.0
L.
Duration
4 h
4 h
6 h/5 d
6 h/5 d
0.75-3 h
6 h/5 d
6 h/5 d
3 h
4 h/5d
4 h
3 h
4 h
4 h
Effect(s) obtained
antagonism
synergism, antagonism
antagonism, no effect
antagonism
synergism, antagonism,
additive
synergi sm
antagoni sm
synergism, antagonism
synergi sm
synergi sm
synergi sm
synergi sm
synergism, no effect
Reference
Shertz et al . 1980a
Shertz et al . 1980b
Jacobson and Colavito 1976
Hofstra and Ormrod 1977
Heagle and Johnston 1979
Beckerson and Hofstra 1979a
Beckerson and Hofstra 1979a
Miller and Davis 1981a
Gardner and Ormrod 1977
Olszyk and Tibbitts 1981
Karnosky 1976
Menser and Heggestad 1966
Tingey et al . 1973a
Broccol i , cabbage,
radi sh
Tomato
Eastern white
pine
Eastern white
pine
Eastern white
pine
0.1
0.03
0.1
0.05
0.025
1.0
0.28
0.1
0.05
0.05
4 h
4 h
8 h/8 w
2 h
6 h
synergism, additivity
no effect
antagonism, additivity
no effect
synergi sm
antagoni sm
synergi sm
Tingey et al . 1973a
Tingey et al . 1973a
Dochinger et al . 1970
Costonis 1973
Houston 1974
Maximum concentrations (ppm) used -"n the research. A range of concentration was used by some
investigators.
h=hours, d=days, w=weeks, 6h/5d=6 hours per day for 5 days, 8h/8w=8 hours per day for 8 weeks
compared with effects of single gases, as presented by the authors. Different methods may have been
used to arrive at the effects statements.
59
-------
Table 3-2
Growth and y.ield of various plant species in response
to the joint action of SC^ + 0,
Species
C
Radish
Radish
Tobacco
Alfalfa
Eastern
white pine
Navy bean
Snap bean
Soybean
Soybean
Soybean
Soybean
Begoni a
Popl ar
Apple
Turf grasses
)j cone.3
0.45
0.05
0.05
0.05
0.025
0.15
ambi ent
0.1
1.0
0.05
0.25
0.3
0.25
0.4
0.15
Dose
0.45
0.05
0.25
0.05
0.5
0.6
0.3
0.1
1.5
0.05
0.25
1.2
0.5
0.4
0.15
S02 conc.a
4h
8h/5d/5w
8h/5d/4w
8h/5d/12w
6h
6h/5d
6h/5d/4w
6h/133d
0.75-3h
8h/5d/3w
4h/3d/llw
4h
12h/24d
4h
6h/10d
Effect(sJ obtained1-
Duration
additive,
root most responsive
additive
root most responsive
synergistic root,
additive shoot
antagonistic on plant wt.
antagonistic on needle
length
antagonistic on plant wt.
synergistic on fruit yld.
additive on seed yield
synergistic, antagonistic
ad d i t i v e
synergistic on plant wt.
additive on pi ant wt.
synergistic on shoot wt.
antagonistic on plant wt.
synergistic on shoot gr.
synergistic or additive
Reference
Tingey and Reinert 1975
Tingey et al. 1971b
Tingey and Reinert 1975
Tingey and Reinert 1975
Houston 1974
Hofstra and Ormrod 1977
Heggestad and Bennett 1981
Heagle et al. 1974
Heagle and Johnston 1979
Tingey et al . 1973b
Reinert and Weber 1980
Gardner and Ormrod 1977
Noble and Jensen 1980
Shertz et al. 1980a
Elkiey and Ormrod 1980
Maximum concentrations (ppm) used in the research
h=hours, d=days, w=weeks, 8h/5d/5w=8 hours per day for 5 days per week for 5 weeks.
Compared with the effects of single gases, as presented by the authors.
60
-------
Studies concerning mixtures of NCL and SO,-, have been few. Tingey et al.
(1971a) found that mixtures of NO,, and SO^ at concentrations _< 0.25 ppm
following one 4-hour exposure, caused visible injury in six plant species,
whereas there was no visible injury to plants exposed to N0? (2.0 ppm) or S0?
(0.5 ppm) alone for the same exposure duration. Decormis and Luttringer (1977)
also have reported synergistic injury responses in tomato, geranium, and
petunia from exposure to a mixture of S02 (0.3 ppm) and NO- (0.5 ppm). The
resulting injury symptoms differed from those caused by N0? or S0? alone.
Nearly all of the published visible injury responses to mixtures of N0? + S0?
have occurred at concentrations at which N0~ or SO^ alone did not injure
plants, using the same exposure duration.
Growth and Yield
The quantitative characteristics of plant response, unlike the visible
injury responses, are measured on a continuous scale and no qualitative
distinction may be available with respect to which response is characteristic
of one pollutant or another. Measures of growth or yield that can be
translated into economic terms are generally of primary significance. Other
measures of growth response may be viewed as useful in explaining or
predicting characteristics of plant response that can be extrapolated to
yield. Several studies of yield responses to mixtures have been reported. Such
studies have usually involved long-term exposures.
While visible injury may be a useful variable in determining how plants
might be expected to respond to mixtures, the magnitude of visible injury does
not always correlate well with other responses such as plant weight and yield
changes. For example, if the visible injury response is greater than additive,
the changes in foliage weight compared with the control and the pollutants
alone may be only additive or not different at all. This is especially true
when the magnitude of injury is extremely small or large. Also, close
relationships between plant growth and foliar injury are not necessarily to be
expected, because plant growth is a composite of many reactions, any of which
may be limiting (Tingey et al. 1973b). Substantial growth reductions, with or
-------
without visible leaf injury, may be the result of more than reduction of leaf
area; they may also be attributable to decreases in the formation of plant
parts (Ashenden 1979b). There are published examples of plant growth reduction
without foliar injury (Kress et al. 1982a, 1982b) and foliar injury without
substantial growth reductions (Mandl et al. 1975). Also photosynthesis rates
can be reduced without vi'sible symptoms (Carlson 1979).
Root growth has seldom been measured in gas mixture studies. Although it
is unlikely that the pollutants penetrate rooting media and exert a direct
effect on roots (Tingey et al. 1971b), root growth may be a sensitive
indicator of the physiological status of plant shoots because reductions in
root growth may indicate diminished photosynthesis or interference with
translocation. Also, reductions in root growth in response to gas mixtures may
have a secondary effect on the whole plant as a result of decreases in the
absorption of water and nutrients. Root growth was reduced more than top
growth in soybeans by (L + SO- mixtures, probably as a result of reduced
translocation of photosynthate to the roots (Tingey et al. 1973b). Greater
reduction in root growth than in top growth of soybean indicated that root
growth was more sensitive than top growth (Tingey and Reinert 1975). Radish
root (technically part hypocotyl) growth has been used to probe leaf/root
relationships. Fresh weight of radish leaves was reduced by a smaller
percentage than was root fresh weight after the same Ck + SOp treatment,
indicating either that available photosynthate was sufficient for normal leaf
growth but insufficient for normal root growth, or that there had been a
change in partitioning (Tingey et al. 1971b). Reinert and Gray (1981) found
the root weight of radish to be decreased by NCL, S0? and CU combinations,
even though foliage was the direct receptor of the pollutant stress.
Reproductive ability may be changed by mixtures as a result of direct
action on generative tissues or some indirect effects. Deleterious effects of
combined S0? + F on reproduction in Scots pine have been reported by Rogues et
al. (1980). Mixtures also interfered with reproduction in lily; SOp + N0?, (L
+ NOp and N0? + formaldehyde markedly inhibited pollen-tube elongation (Masaru
et al. 1976).
62
-------
so2 + o3
Researchers realized some of the limitations of studies based solely on
visible foliar injury in the early 1970s and initiated studies to evaluate the
effects of S0? + CL mixtures on growth and yield of numerous plant species.
Examples of these studies are presented in Table 3-2. Two additional reports
have presented effects of SCL and 0, alone and in mixture on the parasitism of
nematodes on soybean (Weber et al. 1979) and tomato (Shew et al. 1982). These
reports have resulted in a more meaningful understanding of how SCL + Oo
influences plant growth and development. There are some limitations to the use
of the data. There is little information concerning the effects of SCL and CU
mixtures at various stages of development, since usually plant growth or yield
at final harvest have been the only response variables measured. Another
limitation is that species sensitivity determinations generally involved only
one cultivar. There is a wide genetic variation in response to CL among
cultivars within a species. Sensitivities of various cultivars to SCL and CK
alone and in combination have shown differential responses which suggest that
antagonism or synergism may result from differential sensitivity to each of
the pollutants alone (see Modifiers of Plant Response-Genetic Factors).
There have been several recent reports on SCL + NCL interactions leading
to greater-than-addi ti ve growth reductions. Two grass species were exposed to
weekly means of 0.06-0.08 ppm of N0? and S02 alone and in combination
(Ashenden 1979a). The mixture of N02 + S02 and S02 applied alone caused
significant reduction in leaf area and plant dry weight of Dactylis glomerata
L. and Poa pratensi s L. There were also reductions in the number of tillers
and leaves of both species exposed to NO- + SCL but senescence was not
enhanced (Ashenden 1979b;. Similar effects were found on Lol i urn mul ti f 1 orum
Lam. and Phleum pratense L. (Ashen.!--, and Mansfield 1978; Ashenden and
Williams 1980; Mansfield and Ashenden 1978). It was concluded that N02 and S02
in combination were more toxic to the grass species than was predicted by
summing their individual effects on growth.
63
-------
Irving et al. (1982) dispensed SOp and NCL through a system of aluminum
pipes suspended over a canopy of field-grown soybeans. The soybeans were
fumigated on ten occasions, with mean concentrations of S0? during fumigation
ranging from 0.13-0.42 ppm, while N02 ranged from 0.06-0.40 ppm. Results from
the 2-year study showed that exposures to N02 alone had no effect on soybean
seed yields. Exposure to S02 alone decreased yield by 6% the second year.
Mixtures of SOp and N02 in both years of the study resulted in yield decreases
ranging from 9-25%. These losses, however, were obtained in the presence of
7-hour average ambient 0, levels ranging from 0.006-0.095 ppm. Thus, 03 may
have caused some of the NOp x S02 interaction on soybean yield. Amundson and
Weinstein (1980) exposed soybean to S02 (0.0, 0.1, and 0.3 ppm) and N02 (0.1
ppm), singly, and in combination for 4 hours daily for a period of 14 days
during pod fill in open top field chambers. Sulfur dioxide (0.3 ppm) + N02
(0.1 ppm) caused early senesence and reduced yield, compared with plants
exposed to S02 (0.3 ppm) alone. Nitrogen dioxide (0.1 ppm) in the presence of
SOp (0.1 ppm) had no effect on soybean yield. Klarer (1982) exposed soybean in
the vegetative growth stage to single and mixed N02 (0.0, 0.1. and 0.2 ppm)
and S02 (0.0, 0.2 and 0.3 ppm) 15 times, every other day for three hours per
day. Leaf, stem, and root dry weights were'significantly less (18, 12, and
32%, respectively) when the four mixture treatments were averaged together and
compared with the mean of the four treatments of N02 and S02 alone. The
response of soybean to N02 and S02 was nearly linear.
Nitrogen dioxide and SOp mixture studies have not been limited to
herbaceous plants. A 37% reduction in the growth of poplar was reported
following continuous 8-week exposure to 0.06 ppm SOp + 0.06 ppm NOpj no growth
reductions were observed following exposure to S02 or NOp alone (Whitmore et
al. 1982).
N02 + 03
The effects of N02 + 03 generally have not been studied. However, in
recent reports of two- and three- pollutant mixture treatment comparisons, the
N02 + 03 treatment has been included. Kress and Skelly (1982) have studied the
response of seven tree species to N02 (0.1 ppm) and 03 (0.1 ppm) alone and in
mixture for six hours per day, for 28 consecutive days. Virginia pine and
64
-------
loblolly pine height were significantly suppressed by NCL + CL treatment.
There were significantly less than additive suppressions of sweetgum root and
total dry weight and white ash root weight.
Only a few studies of three-gas interactions have been conducted to date
and response patterns are complex. In some cases the experimental design has
limited the interpretation of the research. For example, Elkiey and Ormrod
(1980) exposed 18 turfgrass cultivars, representing six species, to N0?, S0?,
and CL singly at 0.15 ppm of each pollutant and to a mixture of all three
pollutants (0.15 ppm of each gas). The three-pollutant mixture treatment
caused more leaf injury and greater reduction in leaf area in most cultivars
when compared with the additive effects of the pollutants singly. The lack of
two-pollutant mixture treatments was a limitation to the full interpretation
of this research. Similarly, Yamazoe and Mayumi (1977) exposed sweet corn and
rice for one 24 hour period to N0? (0.5 ppm) + 0^ (0.15 ppm), alone and in
mixture, and to a mixture of N02 (0.5 ppm) + S0? (0.15 ppm) + CL (O.lSppm).
The mixture of N02 + CL caused additive injury in rice but not in sweet corn,
while injury in both sweet corn and rice from the N02 + S02 + 0^ suggested an
antagonism by SO^. The lack of certain treatment combinations prevented full
interpretation of this research.
The N0? + S0? dose/response relationship was studied with snap bean
exposed to N02 (0.0, 0.05, and 0.1 ppm) + S02 (0.0, 0.1 and 0.15 ppm), in the
presence of 0.05 ppm 0-, under greenhouse exposure conditions (Reinert and Heck
1982). Nitrogen dioxide at 0.1 ppm in the presence of 0.05 ppm CL and the
absence of SCL, caused a 10% loss of snap bean fruit fresh weight. When S02
was held constant at 0.1 ppm, there was a 15% and 11% weight loss in bean
fruit as N0? was increased to 0.05 or to 0.1 ppm, respectively. These data
suggest a significant effect of N0? in the presence of S0? and CL at ambient
air concentrations of all three pollutants.
Kress et al. (1982a) found substantial growth suppression in loblolly
pine by using mixtures of CL, N0~, and S02 at concentrations below the
national ambient air quality standards for each pollutant singly. They also
65
-------
found greater growth suppression of American sycamore with (L + S02 + N02 than
with two-gas mixtures, without foliar injury (Kress et a "I. 1982b).
The use of full factorial designs to evaluate 3-way mixtures by Reinert
and colleagues (Reinert and Gray 1981, Reinert and Sanders 1982, Sanders and
Reinert 1982a, 1982b) has led to the emergence of several concepts. Nitrogen
dioxide in mixture with SO- and/or CU has significantly reduced growth and
yield in crop plants. In nearly every instance, the three-pollutant mixture,
N09 + S0? + Oo, caused more loss in weight and yield than the single gases or
IL L. O
two-pollutant mixtures. If the plant is capable of developing repair
mechanisms against stress by 0,, it appears that under the simultaneous stress
of NCL, S0?, and 03, repair mechanisms may not be able to function, and plant
productivity is reduced.
Other Mixtures
Mixtures of 0.8 ppm SO- + 2.5 to 13 ppb HF for 23 days decreased linear
growth and leaf area of orange in the research of Matsushima and Brewer
(1972). Mandl et a). (1975) found no significant effects of 0.15 or 0.3 ppm
S0? + 0.6 to 0.9 ppb HF for 7 days on growth of several species even though
there were visible symptoms of injury. Gas-precipitation interactions have
been studied concerning acidity of rain and the occurrence of SO- or
photochemical oxidants. In soybeans, Irving and Miller (1981) found 0.19 or
0.79 ppm SO- in 17 or 24 4-hour exposures to have deleterious effects that
were not affected by simulated acid precipitation of pH 3.1 every 5 days.
Troiano et al. (1962) used open-top chambers to study the interaction of
ambient 0^ and simulated acid rain of pH 4.0, 3.4, or 2.8 on soybean seed
quality.
Physiological and Metabolic Responses
Exposure to pollutant mixtures may result in physiological and metabolic
responses which in turn result in growth and yield reduction. The means by
which these responses occur are not well known. One predominant mechanism is
the physiological or metabolic alteration induced by one pollutant which then
increases or decreases the susceptibility of the plant to another pollutant.
66
-------
This would appear to be a most likely means of explaining the effects of two
successive exposures to different pollutants (Hofstra and Beckerson 1981,
Masaru et al. 1976). A change in sensitivity would be the most likely
explanation for some observations of the joint action of pollutants on foliage
(Miller and Davis 1981a) where the effects on uptake were not similar or where
new kinds of symptoms occurred (Mandl et al. 1980, Lewis and Brennan 1978).
Little is understood concerning the metabolic and physiological action
of pollutants in mixture. Many experiments have established dependent or
independent relationships among pollutants through statistical
interpretations. However, further physiological and/or biochemical mechanisms
associated with photosynthate production, growth regulation, water relations,
changes in metabolic pathways, metabolite and nutrient allocation, enzyme
function, and those processes associated with energy production and
utilization at the cellular level have not been studied thoroughly.
Studies of enzyme activity have indicated that, in some cases, the
threshold concentration of a pollutant required to produce a change in enzyme
activity was lowered when combinations of pollutants were used (Horsman and
Wellburn 1975). For combinations of 0.1 or 1.0 ppm N02 and 0.2, 1.0, 1.5, or
2.0 ppm S0? synergistic interactions were found in pea seedlings in terms of
increased activities of peroxidase, glutamate-pyruvate transaminase (GPT), and
glutamate oxaloacetate transaminase (GOT), and decreases in chlorophyll
content and ribulose 1,5-diphosphate carboxylase (RuDPC) activity. These
changes occurred in the absence of visible injury. The inhibition of RuDPC may
be due to an accumulation of sulfite ions in the chloroplasts. The increases
of GPT and GOT activity indicate a disturbance in amino acid metabolism. If
these types of metabolic activities continued, the plant will eventually
develop some visible evidence of injury. However, these observations do not
necessarily explain additive or synergistic effects of mixtures. Examination
of numerous other enzyme responses also indicated different responses to the
combination gas than to single gas exposures (Wellburn et al. 1976).
67
-------
Nitrite reductase (NiR) activity due to N02, S02, or N02 + S02 has been
investigated (Wellburn 1982, Wellburn et al. 1981). Sulfur dioxide had little
effect on NiR, but NCL increased its activity. The mixture of S02 and N02
reduced NiR activity. Thus, Wellburn (1982) proposed that the presence of S02
prevents the induction of additional NiR by N02 which would normally lead to
ammonia and amino acid synthesis.
Studies of metabolic function and biochemical changes in plants do not
presently provide any definite evidence of a specific site of action for SCL +
N0? + CU synergism. It is possible that (as shown by changes in permeability,
Elkiey and Ormrod 1979b, Beckerson and Hofstra 1980), 03 or S02 could alter
the permeability of cellular membranes to other dissolved pollutants or their
reaction products in the aqueous phase. The findings of Wellburn and others
(Horsman and Wellburn 1975, 1976, Wellburn 1982, Wellburn et al. 1976, 1981)
concerning the interactions of N0? and SO^ may support the concept that
membrane integrity is damaged rapidly by the inability of the plant to
detoxify N0? in the presence of S0?. With increasing S0?, sulfite accumulates
(Malhotra and Hocking 1976) and the dual impact of sulfite and nitrite on
membrane integrity in the presence of 0-, may allow CU to enter the cell freely
O -J
on a continuing basis. Ozone could then cause injury while S0~ and NO- were
impairing specific enzyme functions leading to energy utilization, as well as
impairing transport and allocation of needed cell repair components to
counteract the stress from further exposure to all three pollutants.
Studies of the influence of mixtures on the chemical composition of
plants have been largely concerned with chlorophyll concentration. Horsman and
Wellburn (1975) found decreased chlorophyll with S02 + NO- even though N0?
alone increased chlorophyll. Olszyk and Tibbitts (1981) established that
near-threshold injury by 0^ + SO- on peas could be evaluated by chlorophyll
concentrations of expanded leaves, as well as by surface area of expanding
leaves.
Research concerning mixtures has also involved an examination of gas
exchange between plants and polluted atmospheres. Black (1982) suggested that
-------
a pollutant-induced change in stomatal aperture and function would result in
important consequences by altering a) photosynthetic CCL uptake and
transpirational water loss, b) the rate at which the pollutant enters the
plant and arrives at the metabolic sites, and c) metabolism, resulting in
growth and yield change. Stomata may be induced to either open or close in
response to SCL depending on the species, SO- concentration, duration of
exposure, and environmental conditions at the time of exposure (Black 1982).
There are reported instances of S0? enhanced stomatal opening in 16 plant
species and S0? enhanced closure or depressed transpiration in 24 plant
species. In fact, enhanced opening and closure have been reported to occur
within the same species (Black 1982).
This realization that SCL-induced effects on physiological processes in
plants are exceedingly variable may offer an explanation for many reported
incidences of synergistic and antagonistic responses of plants to pollutant
mixtures. When more visible injury develops from a mixture of SO- + 0, than
from either pollutant alone, some investigators have reasoned that SCL in
mixture decreases stomatal resistance, allowing more CU to enter. Beckerson
and Hofstra (1979a, 1979b) have tried to develop an experimental basis for
understanding antagonism and synergism of visible injury response and stomatal
resistance by using species such as navy bean and soybean, which respond
antagonistically, and cucumber and radish, which respond synergistically to
SCL + CL. White beans were exposed to 0.15 ppm SO- and 0.15 0- singly and in
combination six hours per day for five days (Beckerson and Hofstra 1979a). The
SO- + 0- mixture increased stomatal resistance (depressed stomatal opening)
about 30% more than 0- alone during the first th^ee days of exposure and the
amount of injury was 50 times less than for 0, alone (Beckersor and Hofstra
1979a). Sulfur dioxide alone decreased stomatal resistance (enhanced stomatal
opening). Thus, it was concluded that any protective action of SO- against 0-
injury (antagonism) was not completely explained on the basis of stomatal
response of white bean.
Investigations were continued using radish, cucumber, and soybean. In
all three species, SO,, decreased stomatal resistance, 0- increased resistance,
69
-------
and the S00 + 0, mixture increased resistance much more than Oo alone
(Beckerson and Hofstra 1979b). Hofstra and Beckerson (1981) also found that
SCL pre-treatment of white bean and cucumber did not prevent increased
stomatal resistance following exposure to SO,, + 0^ and 03 alone, at
concentrations used in previous studies (Beckerson and Hofstra 1979a). They
also reported that the presence of SO,, in mixture with 03 reduced the
CU-induced increase in membrane permeability in white bean and soybean, but
not in radish and cucumber (Beckerson and Hofstra 1980). This suggested
differential modes of action of S0? + Oo alone or in mixture, acting at
(_ O
membrane sites within the plant. In summary, Beckerson and Hofstra concluded
that stomatal function can be disregarded as having any major influence on S0?
+ Oo interactions and as a mechanism for understanding synergistic, additive,
or antagonistic plant responses to SO.-, + On, at least for the species studied.
They further proposed that in the case of synergism in radish and cucumber,
S0? may have altered the nutritional or enzymatic status of the plant, thus
increasing sensitivity to 0., (Hofstra and Beckerson 1981). Nevertheless,
further research is warranted on stomatal responses to SO,, + 0,, utilizing
techniques having greater resolution and more statistical strength. In
addition, stomatal responses need to be related to visible injury and to air
pollutant flux into leaves.
Stomate function also has been studied in attempts to explain the
additive and frequently greater than additive response of plants to N0? + S0?.
Arnundson and Weinstein (1981) found high leaf resistance in soybean plants
exposed to SO,, (2.0 ppm) + NO,, (0.5 ppm), partially accounting for
antagonistic effects of the two gases. Ashenden (1979a) found that N0? (0.1
ppm) and SO,-, (0.1 ppm) alone caused short-term increases in bean leaf
transpiration rates, while N0n + SO,, in mixture decreased transpiration.
Stomate function was apparently not involved in the synergistic foliar injury
response resulting from mixtures of NO- + SOp. However, Ashenden gave a
possible explanation for the synergistic foliar injury response to mixtures of
N02 + SO,, by proposing that the stomata were closing in response to
physiological injury within the leaf. Since N00 and S02 interfere with
respiration, there is a possibility that increased C02 concentrations could
70
-------
arise within the leaf and subsequently decrease stomatal opening (Ashenden
1979a). Amundson et al. (1982) found a HF (0.6 and 1.9 ppb) and N02 (0.6 and
1.2 ppm) interaction, with less HF injury on sweet corn in the presence of the
higher of the two N0? concentrations. Leaf resistance was higher in the
combined treatments. There was greater stomatal closure of snap beans with H?S
+ 03 than with H2S alone (Coyne and Bingham 1978). Williams et al. (1971), in
evaluating the interaction between SO^ and particulates at naturally polluted
sites, noted that particles accumulated in stomatal pores, probably keeping
them open, increasing permeability, and admitting more S0?. When pollutants
are sorbed or deposited on foliar surfaces and then penetrate through the
cuticle, reciprocal effects on uptake are unknown. Thus, interactions of
pollutants might be explained readily, in some cases but not others, on the
basis of direct effects on stomatal opening. However, there is considerable
evidence that other factors in the plant, in addition to stomata, have an
important role in determining responses to pollutants.
Impairment of photosynthesis by mixtures has been studied by several
investigators. Carlson (1979) found that photosynthesis rates of sugar maple
and white ash leaves exposed to CL (0.5 ppm) + SO- (0.5 ppm) decreased more
than additively. The reduction in photosynthesis was least when irradiance was
optimal. Ormrod et al . (1981) found joint action of concentrations of 0~
(0-0.25 ppm) + SO,, (0.04 ppm) in suppressing net photosynthesis in broad bean,
but there was recovery if visible leaf injury did not occur (Black et al.
1982). Similarly, Le Sueur-Brymer and Ormrod (1983) found mixtures of 0., (.067
pprn) + SOp (0.3 ppm) suppressed net photosynthesis of fruiting soybeans when
single gases did not. However, the photosynthesis apparatus apparently adapted
readily to the stress because net photosynthesis was no longer decreased by
the mixture after two successive six-hour daily exposures. Substantial
reduction in photosynthesis of peas by S0? (0.0 to 0.25 ppm) + NO- (0.0 to
0.25 ppm) was noted by Bull and Mansfield (1974). White et al. (1974) found
greater than additive effects of S0? (0.15-0.35 ppm) + NO- (0.1-0.2 ppm) on
net photosynthesis of alfalfa. Net photosynthesis rates of sunflower leaves
were depressed by all combinations of 0,, (0.2 ppm), SO- (0.2 ppm), and NO-
(1.0 ppm) (Furukawa and Totsuka 1979). At a higher than ambient CO-
71
-------
concentration (645 ppm), the inhibition of net photosynthesis by S02 ("0.8
ppm) + N0? ("0.3 ppm) was less than half that at an ambient concentration (315
ppm) (Hou et al. 1977). Addition of 0.072 ppm 03 to 0.74, 3.25, or 5.03 ppm
H9S resulted in greater reductions in net photosynthesis rates of snap beans
L-
than those caused by H^S alone (Coyne and Bingham 1978).
While many anatomical studies of tissue and cell injury have been
conducted with single pollutant gases, very little has been done with
mixtures. Solberg and Adams (1956) found no differences in microscopic injury
of apple leaves between single and mixed S02 (0.5 ppm) + HF (5 ppb) for 4
hours per day for 2 days. However, Evans and Miller (1975) found different
sites of injury for single or mixed 0., (0.45 ppm) + SO- (0,45 ppm) for 9 hours
in pine needles. Krause and Jensen (1978) found inclusions in poplar leaf
cells exposed to 03 (0.15 ppm) + SO^ (0.25 ppm) for 12 hours per day for 21
days that were not in leaves exposed to single gases. Leaf surfaces were
injured by the mixture but single gases had no effect (Krause and Jensen
1979).
Recovery from mixture-induced injury to plant processes to normal levels
of functional activity has been reported. Net photosynthesis, impaired by 0.,
(0.05-0.30 ppm) + SO- (0.04 ppm) for 4 hours recovered if there was no visible
injury to broad bean leaves (Black et al. 1982). Bennett et al. (1980) found
recovery of bean growth and yield following 0~ (0.046 to 0.127 ppm) + HLS (0,3
to 7 ppm) exposure. Kress et al. (1982b) reported recovery in growth of
American sycamore after injury by 0^ (0.05 ppm) + SO- (0.14 ppm) + N0? (0.10
ppm) for 6 hours per day for 28 days. The mechanisms of recovery from
pollutant injury have been described by Tingey and Taylor (1982). The extent
and speed of re-establishment of a normal metabolic state following pollutant
mixture injury will be an important determinant of economic loss from exposure
to mixtures, but economic losses have not been estimated on these bases.
A possible explanation of apparently diminished injury from 0. + S0?
mixtures was the chemical combination of these gases in exposure chambers
(Costonis 1973). However, no evidence was obtained for reactions that would
72
-------
lower the concentration of either gas (Jacobson and Colavito 1976). A direct
reaction between CL and S0? may occur in plant tissue and the direct aqueous
oxidation of SCL by 03 has been described (Heagle and Johnston 1979).
Accumulation and Uptake
Accumulation may be considered a major concern for several reasons.
First, with reference to HF and certain airborne particulate compounds,
accumulation of a toxicant by the plant constitutes a potential hazard to
consumers of the plant. Second, uptake and accumulation of a pollutant can be
viewed as the first links in a chain of events leading to some altered state
or process that may be detrimental. Third, tissue levels of pollutants are
often used as diagnostic measures to assess exposures. As discussed by McCune
(1983), many factors influence the effect of S0?, NCL, or 0, on the
accumulation of fluoride from HF. One of the major difficulties in the
interpretation of effects arises when the levels of exposure are too few to
determine whether accumulation of F is linear with exposure. If the plant is
exposed successively while it is growing, exposures during the latter periods
should be weighted more heavily than those during the earlier periods to
compensate for growth dilution. If one pollutant affected growth during a
series of exposures to HF, wherein the concentration of HF varied, the result
would be an apparent effect on F-uptake itself. Another aspect of this problem
appears when pollutant mixtures affect the uptake of minerals from the rooting
medium and their distribution within the plant. Increased cadmium
concentration in young leaves of cress during 0, exposure was noted by Czuba
and Ormrod (1981). Immediately after ozone exposure, there was stimulated
uptake of cadmium and redistribution of cadmium between the leaves and stem.
The actual uptake of pollutant gases, rather than the concentration or
dose, would be expected to relate most closely to biological responses. There
is little information available on pollutant uptake rates from gaseous
mixtures. The amount of pollutant sorbed by plants is the product of the
uptake rate or flux and the duration of exposure. Also, sorption includes both
absorption through stomata or cuticle into the mesophyll tissue of leaves,
73
-------
while it may be metabolically active, and adsorption on surfaces which may
injure the surface materials, but not penetrate into areas of metabolic and
physiological significance. Elkiey et al. (1982) exposed shoots of ten shade
tree species to 0^ (0.25 ppm) + S02 (0.4 ppm) + N09 (0.4 ppm) for 6 hours and
measured individual uptake rates. Sorption from the mixture was consistently
less than from single gases in species that did not close stomata at night,
while single and mixed gases had similar sorption if stomata closed at night.
There was less absorption of each gas from the 3-gas mixture than from single
gases by Kentucky bluegrass plants (Elkiey and Ormrod 1981a).
In this study, plants of nine Kentucky bluegrass cultivars were exposed
to 00, SOp, NOp, or a mixture of the three gases for three days to determine
absorption and adsorption rates of each gas. Absorption rates into stomata
differed among cultivars and generally decreased with longer exposure. Leaves
of insensitive cultivars generally absorbed less of the single gases than the
leaves of sensitive cultivars. Adsorption rates on leaf surfaces, determined
with stomata closed, were substantial and varied with pollutant gas and
cultivar. Absorption of 03 (0.25 ppm), S02 (0.4 ppm) and N02 (0.4 ppm) by
petunia plants from single gases was generally greater than from the mixed
gases (Elkiey and Ormrod 1981b). Absorption rates tended to decrease gradually
throughout the day and from day to day with continuous exposure. Accumulation
of tissue sulfur and nitrogen in petunia plants did not agree well with uptake
rates. Tissue analysis of petunia plants exposed to 0., + SOp + NOp mixtures
indicated less accumulation of sulfur from mixed than single SOp, and less
total nitrogen in plants exposed to any N0? compared with those not exposed
(Elkiey and Ormrod 1981c). This suggests that sulfur- and nitrogen-containing
volatiles may be released by exposed plants or that nutrient uptake and
distribution or re-distribution may be affected by the pollutant treatments.
There is considerable information available on pollution uptake, based
upon studies of single pollutants. Those studies provide conceptual models
which should be useful in considering the uptake of pollutant mixtures by
plants. The collection and interpretation of uptake data should help resolve
74
-------
the conflicting results of experiments conducted in different environments
with differing exposure regimes.
MODIFIERS OF PLANT RESPONSE
Genetic Factors
Resistances to pollutant mixtures have genetic and environmental
components. The most useful comparisons of species sensitivities to mixtures
are those based on studies in which more than one species was exposed at the
same time in the same facilities under the same environmental conditions.
There have been several reports of research of this kind (Table 3-3)
indicating large differences in species sensitivity to various mixtures.
Most investigators have used one cultivar or line to represent a
species, even though there is ample evidence, from single-gas and mixed-gas
studies, that there can be wide variation in cultivar response within species
(Ormrod 1978). There have been several studies reported in which cultivar
responses to mixtures of SOp + 0-, were directly compared at the same time
(Table 3-4). In forest species, Kress et al. (1982a) found differential
sensitivity to 0, + N0? + SO- among lines of loblolly pine.
The degree of association of sensitivity to S0? and 0^ among cultivars
within species has been examined by means of a distribution-free measure of
association, Kendall's Tau statistic. Its value was 0.455 for 17 cultivars of
Kentucky bluegrass (Murray et al. 1979); 0.2018 for 19 cultivars of soybean
(Miller et al. 1974); and 0.1346 for 33 cultivars of bean (Beckerson et al.
1979). However, sensitivities to a mixture of S0? (0.15 ppm) + 0^ (0.15 ppm)
for 6 hours per day for 5 days in the bean cultivar study were associated with
both S0? and 0- sensitivity (tau - 0.3570 and 0.4227, respectively). Karnosky
(1976) found some association of S0? and 0~ sensitivity in five lines of
trembling aspen. In Picea abies, resistance to HF and to SO,-, appeared to be
positively correlated (Halbwachs and Kronberger 1979). When the joint
distribution of sensitivities has a positive correlation, a population of
75
-------
Table 3-3
Direct comparisons of species sensitivity to SCL + 0
SO, + NO,, 0-, + NO,, and HF + SO,
J3
M-xture
Species compared
Reference
so2 + o3
S0
J3
HF
SO,
Tobacco, radish, alfalfa, cabbage, broccoli,
tomato, onion, bromegrass, spinach
Tobacco, alfalfa, radish
Navy bean, tobacco
Radish, cucumber, soybean
Navy bean, soybean, cucumber, radish
Sugar maple, black oak, and white ash
Ginseng, radish, tobacco
Lettuce, radish, pea
Tomato, radish, oats, tobacco, pinto bean,
soybean
Several native desert species
Radish, swiss chard, oats, peas, orchard gras:
annual ryegrass, timothy, perennial ryegrass,
Orchard grass, perennial ryegrass
Forest tree species
Sweet orange, mandarin
Bean, barley, sweet corn
Tingey et al. 1973a
Tingey and Reinert 1975
Jacobson and Colavito 1976
Beckerson and Hofstra 1979a
Beckerson and Hofstra 1980
Carlson 1979
Proctor and Ormrod 1981
Ormrod et al. 1983b
Tingey et al. 1971a
Hi 11 et al. 1974
Thompson et al. 1980
Ashenden and Mansfield 1978
Ashenden 1979b
Kress and Skelly 1982
Matsushima and Brewer 1972
Mandl et al. 1975
76
-------
Table 3-4
Direct comparisons of cultivar sensitivity within species to S0? + CU
Species
Number of cultivars compared
Reference
Tobacco
Tobacco
Tobacco
Soybean
Navy bean
Strawberry
Petuni a
Bean
Soybean
Begoni a
3
9
3
2
2
6
3
33
2
5
Menser and Heggestad 1966
Menser and Hodges 1970
Tingey et al. 1973a
Tingey et al. 1973b
Jacobson and Colavito 1976
Rajput et al. 1977
Elkiey and Ormrod 1979c
Beckerson et al. 1979
Heagle and Johnston 1979
Reinert and Nelson 1980
77
-------
plants should be less affected by a mixture than would be expected should the
distribution of sensitivities to each pollutant suggest an assumption of an
independent distribution.
While most investigators have not reported the extent of plant-to-plant
variation in sensitivity to mixtures, Skelly et al. (1972) reported high
variability among eastern white pine trees in response to ambient SCL + NCL.
Although it might be expected that an exposure to SO- would affect the mean
tolerance of plants to (L (Jacobson and Colavito 1976, Macdowall and Cole
1971), the latter investigation showed an effect of SCL on dispersion of
tolerance as indicated by changes in slopes of probit regressions.
The use of highly sensitive species or cultivars as test plants to
indicate the presence of single pollutants is widely practiced, but only two
recommendations of plant indicators of mixtures have been made. Menser and
Hodges (1970) suggested 'Burley 49' tobacco and Grosso et al. (1971) suggested
Nicoti ana glutinosa for detection of CL + S0? effects.
Phenological Factors
Plant development stage may also be an important determinant of
sensitivity to pollutant mixtures. Few studies of mixture effects have
considered the impact of leaf age or growth stage on sensitivity to
pollutants, since usually plant yield and biomass at final harvest have been
the only response variables measured. Menser and Heggestad (1966) noted that
older tobacco leaves were more sensitive to CL ("0.03 ppm) + SCL ("0.26 ppm)
for 2 or 4 hours than younger leaves. The midshoot leaves of grape and apple
were most sensitive to 03 (0.4 ppm) + S02 (0.8 ppm) for 4 hours (Shertz et al.
1980a, 1980b). Alteration of the susceptibility of leaves by the stage of
development is another area in which distributional aspects of the combined
effects of pollutants have not been considered. One obvious example is where
younger leaves tend to be susceptible to one pollutant and older leaves to
another. If the exposures are consecutive or separated in time for plants with
determinate growth, the sequence of exposures will determine the effects.
78
-------
Environmental Factors
There may be a strong environmental component in determining plant
sensitivity to mixtures, as well as in modifying genetically determined
sensitivity. Irradiance, temperature, water supply, and other environmental
factors are known to affect plant responses to air pollutants and have been
studied extensively for single gases (Ormrod 1978). However, studies of
environmental effects on mixture responses have been more limited. Carlson
(1979) found much more visible injury and growth suppression of sugar maple
and white ash by 0^ + S02 at high than at low irradiance. Miller and Davis
(1981b) found that exposure temperatures affected the type of CL + S0? visible
injury symptoms in beans, as well as the amount and location of injury.
The water status in each component of the soil-plant-atmosphere
continuum may alter response to mixtures as there may be an interaction with
CO- concentration. More injury was noted after exposure of eastern white pine
to 0, + S02 during periods of high humidity compared with low humidity (Jaeger
and Banfield 1970). Humidity was found to have a marked effect on the
diffusive resistance response of petunia leaves to CL + SCL. Exposure of
petunia to SCL (0.8 ppm) + 0^ (0.4 ppm), for 4 hours at 50% relative humidity,
caused an increase in stomatal resistance, regardless of cultivar sensitivity
to (L. However, at 90% relative humidity, there was an increase in stomatal
resistance only in the 0, sensitive cultivar, 'White Cascade' (Elkiey and
Ormrod 1979a). Although changes in relative humidity, leaf water potential
(Elkiey and Ormrod 1979a), and membrane permeability (Elkiey and Ormrod 1979b)
may be demonstrated among cultivars of differing 0, sensitivity, these
phenomena did not completely explain differences in petunia cultivar
sensitivity to SCL and CL alone and in mixture.
Plant water status not only affects the responses to mixtures but also
is affected by plant exposure to mixtures. Plant water potential decreased
quickly on exposure of petunia to CL + SO- (Elkiey and Ormrod 1979c). Leaf
diffusive resistance changes are an indication of altered stomatal action.
79
-------
Adequate soil water, optimal mineral nutrition, high relative humidity, and
sufficient irradiance will lead to full stomatal opening, subjecting the leaf
tissue to maximal pollutant entry initially (Carlson 1979).
The C0? research of Hou et al. (1977) was based on the recognition that
C0?, as well as S02 and NOX, is included in the exhaust gases of many
industries. The ratio of SCLrNC^rCOo concentrations occurring downwind from a
power plant burning coal (1:0.33:326) was used in controlled exposure studies.
Doubling the CCL concentration increased net photosynthesis of alfalfa in S02
+ N0?, even though this mixture decreased net photosynthesis in ambient CCL.
Another factor that could vary and exert an effect in the field is
mineral nutrition. Elkiey and Ormrod (1981a) exposed turfgrass plants growing
at different nitrogen and sulfur nutrition levels to (L (0.1 ppm, 6 hours per
day) + S0? (0.15 ppm continuously) + NOo (0.15 ppm continuously) for 10 days.
Low sulfur or low nitrogen usually enhanced the effect of S0? or N0?,
respectively. Misting with deionized water increased severity of visible
injury. In the compilation of effects of mineral nutrition and responses of
plants to pollutants by Cowling and Koziol (1982), one can see that the
nutrient-determined tolerances of plants are positively or negatively
correlated, depending upon the crop, nutrient element, and set of pollutants.
For example, in tomato, tolerance to HF decreased but tolerance to 0,
increased with P-deficiency; in tobacco, tolerance to 03 or to S02 increased
and then decreased as the supply of N increased; in barley, tolerance to HF
decreased with deficiencies of P, K, or Ca and tolerance to S02 decreased with
Ca- or K-deficiency, but increased with P-deficiency. An important part of
this review was the attempt mechanistically to reconcile and explain the
effects of nutrients. Some could be attributed to increased or decreased
uptake of pollutants and others to effects on the inherent, metabolic
susceptibility. Whether the presence of one pollutant alters the
nutrient-determined response of a plant to another pollutant is unknown. To
the extent that the effects of other environmental factors can be similarly
partitioned, one could also predict their likely effects on the joint action
80
-------
of pollutants. For example, the effects of temperature were not concordant
with effects on gaseous exchange (Miller and Davis 1981b).
The only report of chemical protection against mixture injury indicated
that benomyl protected pinto beans from the two oxidants, CL + PAN (Pell
1976).
SUMMARY
The available literature indicates that most pollutant mixture research
has been confined to the use of various combinations of (L, S0?, and N0? on
major species. Other combinations of gases have had much less attention and
almost no research on interactions of gaseous, aerosol, and precipitation
pollution has been reported. Many species of considerable economic or
ecological importance have had little or no attention. Visible injury has been
the most frequently reported response variable but concern for growth and
yield effects has increased in recent years. The visible injury may not
adequately reflect growth and yield responses. Discovery of additive and
synergistic responses to two and three pollutant mixtures has provided the
impetus for further study and for concern about impacts of mixtures.
Suitable experimental methods and statistical analyses are available for
effective studies of mixtures but some of the most appropriate experimental
designs and analyses are not widely used. Experiments have been conducted in
controlled environments, chambers, greenhouses, and field facilities; each of
these approaches has strong and weak points, and the effectiveness will depend
on the purpose of each experiment. Some disparities in results between
experimental approaches have been reported. Diversity and ambiguity of
terminology have created some difficulty in interpretation, but clear
definitions of joint action, additivity, synergism, and antagonism are
avai1ab1e.
Exposure of plants to pollutant mixtures affects visible injury
development, growth, yield, physiological processes, biochemical activities,
81
-------
and plant anatomy with responses often differing from those due to the single
components of the mixture. Photosynthesis, transpiration, pollutant uptake
rates, enzyme activities, stomatal function, tissue elemental concentration,
and other response variables may be differentially affected by mixtures
compared with single gases. Much of the information on physiology and
biochemistry is fragmentary and, while stomate function and pollutant uptake
have been most extensively studied, the data are difficult to interpret as
these responses are extremely sensitive to environmental changes.
Species differ widely in sensitivity to pollutant mixtures and there may
be large cultivar differences within species, as well as plant-to-plant
variation in response. Plant and leaf development stages may be important
determinants of sensitivity to mixtures but there have been few studies of
this concept. Environmental factors, including irradiance, CCL concentration,
temperature, water status, and nutrition may affect mixture responses. Little
is known of the effects of pollutant mixtures on plant hardiness, reproductive
processes, competitive ability and interactions in ecosystems. It is clear,
from the few studies conducted in which appropriate follow-up measurements
were made, that plants can recover from mixture stresses and even adapt to
them. The relationship of concentration and duration in determining doses of
mixtures has had little attention nor have the flux rates of pollutants from
mixtures to plants, even though actual uptake is likely to be an important
determinant of injurious effects. There has been little study of the effects
on plants as a result of changing pollutant mixture composition and
concentration patterns that may occur in nature.
82
-------
4. RESEARCH NEEDS
AMBIENT AIR QUALITY EXPOSURE
Based upon a review of the scientific presentations and their knowledge
of the scientific literature, the panel members determined that a series of
technical gaps exists in defining the effects of air pollutant mixtures on
vegetation.
The panel concluded that the ambient air quality air pollution review
described in Chapter 2 represented a first step in understanding the
characterization of co-occurrence and sequential exposure regimes present
under ambient conditions.
o Additional evaluation is required to determine the
important exposure sequences of air pollution.
VEGETATION EFFECTS
The identification of regimes of pollutant mixtures representative of
ambient exposures is important because these regimes define concentration
peaks, means, varying times of exposures, and time between events to be used
in vegetation experiments. Access to the existing data bases facilitates the
design of experiments that mimic the exposures representative of ambient
condi ti ons.
o fit present, there are extensive knowledge gaps on
effects on major crop species, garden and amenity
plants, and native herbaceous and tree species. Current
data are based on experiments conducted with different
methodologies, environments, experimental designs, and
interpretation.
83
-------
o The panel believed that the effects on vegetation
resulting from the interaction of pollutant gases and
acid deposition, aerosols and heavy metals on soils need
further study.
o Added information is required to describe the
mechanistic and plant processes at realistic exposure
regimes for pollutant mixtures.
o Little data exist to explain the assimilative
allocation, physiological, and biological responses that
relate to vegetation dose-response studies. Little data
are available on relating uptake rates to pollutant
mixtures.
o The current data base does not provide sufficient
information to understand the genetics of vegetation
response to mixtures. Species, cultivar, and individual
plant variability have not been well-characterized. The
heritability of mixture sensitivity and its relationship
to single pollutant sensitivity have not been
characterized adequately.
o For vegetation effects research involving air pollutant
mixtures, as well as for singular pollutant exposures,
there exist a paucity of data describing environmental
effects (e.g., temperature, soil moisture, humidity,
wind velocity, nutrition, and age).
The panel strongly urged the selection of specific research
investigations that were applicable to address high priority research
questi ons.
84
-------
o The panel believed that additional information was
needed to develop modeling and predictive capabilities.
Sources of information about phenology, environmental,
and genetic (intra- and interspecific) variation need to
be quantified to describe interdependent effects.
o The changes in plant sensitivity to gas mixtures with
changing leaf age and development stage have had little
study. Information is especially lacking on sensitivity
during the fruiting period.
o There is little or no information on effects of mixtures
on plant hardiness, reproduction, nutritional value, and
other characteristics affecting adaptation and
utilization of plants. While there is now some evidence
for the existence of plant recovery and adaptation
processes, little is known of the nature of such
homeostatic processes and mechanisms.
o The panel believed that there have been few attempts to
fully utilize alternative statistical designs and
analyses. Such methods could include covariate
measurements, rotatable designs, and response surface
presentations.
Following the identification of research requirements, the panel focused
on recommending the specific direction in which air pollution mixture
vegetation research should follow. Chapter 5 presents the panel's findings.
85
-------
5. RECOMMENDATIONS
INTRODUCTION
The potential value of prioritizing research needs was addressed by the
panel. The members believed that research areas were not independent of each
other. For example, the biological research efforts described later in this
chapter are dependent upon a knowledge of the pollutant concentrations
occurring in the field under ambient conditions. The panel has concluded that
environmental, genetic, and phenological variables should be considered when
research studies are initiated.
AIR QUALITY
An analysis of the EPA SAROAD, EPRI SURE, and TVA data bases indicates
that S0?, NO-, and 0, may co-occur in various concentrations in rural,
suburban, and urban areas. For many rural sites, co-occurrence (using 0.05 ppm
as the definition of an event) is infrequent. For most cases analyzed, events
lasted for only a few hours and were separated by weeks or months.
The panel recommends that
o air quality data be further evaluated using patterns of
occurrence of the combined pollutants to establish
guidelines for designing plant interaction research
investigations. The primary pollutants of interest are
SO.,, Oy and NO-,; they can be evaluated using the
available air quality data and research information
dealing with the individual effects on vegetation.
o acidic deposition be considered as a pollutant with
potential for interaction with SO 0 and NO.-,.
86
-------
o an analysis of existing air quality data bases (starting
with SAROAD) be instituted to derive the joint
probability distributions of pollutants and the diurnal
patterns of exposure for plant exposure experiments.
Additional sources of rural air quality data could
include the USDA Forest Service, EPRI (SURE), EPfl
(NCLAN), as well as permit monitoring programs (e.g.,
PSD applications). This analysis is to include:
1) Search the data base for locations where either
co-occurrence or sequential exposures occur. This
search would include separate listings at several
threshold concentrations (e.g., 0.05, 0.04, 0.03,
and 0.02 ppm).
2) Once locations are identified, the monitoring data
bases at the locations should be presented as joint
frequency distributions and as diurnal time series.
The utility of spectral analysis (Fourier series)
and the Box Jenkins model should be explored.
Jj The results of this process should be disseminated
to research groups to guide experimental exposures
used in interaction experiments.
o potential data displays for individual pollutants could
include: 1) three-dimensional plots of concentration,
duration, and frequency; 2) diurnal plots for individual
pollutants in terms of mean levels and frequency above
particular levels. These analyses would utilize data
from the growing season for some relevant time period)
and could also serve to identify potential anomalies (in
terms of data values or sites).
The air quality analyses would provide information that could be used to
identify general patterns in terms of geographic region or source
configuration. It may be necessary to supplement the air quality data for
point source pollutants by considering the use of dispersion models to provide
information on levels, diurnal patterns, and time between episodic events.
87
-------
As a result of the analysis, it is anticipated that the information
would provide researchers with relevant exposure patterns that have a known
probability of occurrence. In addition, the information that describes the
rural site exposures might also be compared to urban results so that
researchers can establish possible exposure relationships.
BIOLOGICAL EFFECTS
Introduction
The identified research needs are divided into two areas which have not
been assigned a specific funding. The panel believes the activities are
complementary and fill gaps in the information base that describe the effects
of pollutant mixtures on vegetation. The work group members stated that
o research efforts should be directed toward major crop
species, cultivated plants (including commercial crops
and plants utilized for garden and home use), and native
herbaceous and tree species.
o to assist in the design of future research on the
effects of pollutant mixtures on vegetation, available
air quality data should be re-evaluated to help identify
appropriate response data needed from plant experiments.
The panel feels that knowledge gaps can only be filled by an
integrated research effort with growth chambers, greenhouses, and
field plots.
Realistic Exposure Regimes
The panel believes it essential to understand the response of plants to
various exposure regimes.
88
-------
o Effects must be associated with air pollutant peaks,
means, length of exposure, and time between exposures.
Research using realistic ambient pollutant exposures
should evaluate the vegetation effects associated with
sequential exposures of pollutant mixtures that mimic
ambient conditions.
Development of Minimum Recommendations for Research Protocols
The panel recommends that
o a minimum set of standardized procedures, to ensure the
quality assurance of plant response studies, should be
established. Generalized guidelines should be proposed
for 1) plant growth conditions, 2) environmental and
plant monitoring, Jj pollutant exposures, and 4) uniform
terminology (describing plant response characteristics).
The most efficient experimental designs and analysis
(relevant to a specific experimental goal) should be
implemented (e.g., covariant analysis, analysis of
variance, and rotatable design). It is proposed that
these minimum guidelines be developed through a series
of workshops involving scientists experienced in
designing and implementing research on the impacts of
air pollution on vegetation.
o as part of a generalized protocol that researchers
should clearly define the meaning of agreed upon
concepts (e.g., less than additive, synergism, and
antagonism).
89
-------
Predictive Capabilities
The purpose of the pollutant Interaction research is to develop
predictive capabilities for assessing vegetation effects when experimental
data are insufficient. Predictive capabilities allow for the extrapolation of
results to ambient exposure conditions that have previously not been tested.
To properly develop the information necessary to predict vegetation effects
associated with pollutant mixtures, it is necessary to implement a research
program involving studies that elucidate 1) the modes of action and 2) the
sources of biological variation. From these experimental results will come the
modeling required to develop the predictive capabilities that are necessary to
quantify possible effects on vegetation.
As part of the development of predictive capabilites, the panel
recommends that the following research activities be implemented:
o Afoc/es of fiction: The objectives of this research
activity is to understand how air contaminants influence
biological processes. Studies need to address modes of
action of pollutants singly and in combination. The
research effort should include both sequential and
co-occurrence exposures and should be conducted with an
appreciation of realistic exposure regimes. The
biological level of organization should focus on
processes at all levels of plant organization (i.e., the
cell, whole-plant, population, and ecosystem). The panel
believes that there should be two major areas of
interest
a) The relationship between the different mechanisms
of pollutant response.
b) Ihe varying biological responses attributed to
different levels of air pollutant exposure.
90
-------
o Sources of Variation: The plant response to a given
exposure regime varies significantly with specific
environments, and stage of plant development. The panel
recommends research that focuses on each of the
following:
a) genotype-the significance of intra- (e.g.,
cultivar, population) and interspecific genotypes.
This includes phenology as a source of variation.
b) environment-the significance of edaphic (e.g., soil
water availability, soil nutrients), climatic
(e.g., temperature, light, relative humidity,
elevated carbon dioxide, etc. ) and biotic factors
(e.g., pathogens, syrrtionts, competition, etc.).
o f^bdeling-The development of data that describe the
process and mechanistic activities associated with air
pollutant mixture vegetation effects should allow for
the development of conceptual and quantitative models of
biological response.
CONCLUSION
It is the opinion of the workshop participants that the position paper
(which is presented in Chapter 2) focused on ambient exposures and represented
an initial attempt to identify realistic exposure regimes that exist in the
ambient air. The panel believes that
o additional efforts should be made to supplement the
existing analysis.
o the efforts should proceed simultaneously as the
biological vegetation effects research is
implemented.
-------
o the results of the air quality characterization should
be used in developing the design of the pollutant
mixture experimental protocols.
The first two stages of the process and mechanistic research should
include
o a biological effects screening exercise to prioritize
which air pollutant mixture exposures are most likely to
be significant. This effort is suitable in controlled
exposure facilities, and
o a more detailed investigation performed under field and
laboratory situations for the purpose of quantifying the
significance of the major factors affecting plant
response.
In regard to conceptual models, it was the conclusion of the panel
members that
o they should combine existing models of joint action with
the data that describe the modes of biological action.
The quantitative models should be capable of providing
accurate and precise estimates of plant response. In
addition, the models should be compatible with the
conceptual interpretation of the modes of action.
92
-------
REFERENCES
Amundson, R.6., and L.H. Weinstein. 1980. The effects of S0? and NO- alone and
in combination on the yield of soybean. Plant Physiol. 65:152
supplement.
Amundson, R.G., and L.H. Weinstein. 1981. Joint action of sulfur dioxide and
nitrogen dioxide on foliar injury and stomatal behaviour in soybean. J.
Environ. Quality 10:204-206.
Amundson, R.6., L.H. Weinstein, P. Van Leuken, and L.J. Colavito. 1982. Joint
action of HF and NO,, on growth, fluorine accumulation, and leaf
resistance in Marcross sweet corn. Environ. Exp. Bot. 22:49-55.
Ashenden, T.W. 1978. Extreme pollution sensitivity of grasses when S0? and
N09 are present in the atmosphere together. Nature, 273:142-143.
Ashenden, T.W. 1979a. The effects of long-term exposures to S0? and N0?
pollution on the growth of Dactylis glomerata L. and Poa pratensis L.
Environ. Pollut. 18:249-258.
Ashenden, T.W. 1979b. Effects of SO,, and NO- pollution on transpiration in
Phaseolus vulgaris L. Environ. Pollut. 18:45-50.
Ashenden, T.W., and T.A. Mansfield. 1978. Extreme pollution sensitivity of
grasses when S09 and N09 are present in the atmosphere together. Nature
273:142-143. ^ ^
Ashenden, T.W., and I.A.D. Williams. 1980. Growth reductions in Lolium
multiforum and Phleum Pratense as a result of S0? and N0? pollution.
Environ. Pollut. 21:131-139.^
Ashenden, T.W., P.W. Tabner, P. Williams, M.E. Whitmore, and T.A. Mansfield.
1982. A large scale system for fumigating plants with S0? and N0?.
Environ. Pollut. (Ser. B.) 3:21-26. *
Bachmann, J., and L.J. Zaragoza. 1983. Protecting public welfare: the role of
environmental effects information in air standards development.
Presented at the 76th Air Pollution Control Association National
Meeting, Atlanta, GA. June 19-24, 1983. 83-3.1.
Beckerson, D.W., and G. Hofstra. 1979a. Response of leaf diffusive resistance
of radish, cucumber and soybean to 0, and SO,, singly or in combination.
Atmos. Environ. 13:1263-1268.
Beckerson, D.W., and G. Hofstra. 1979b, Stomatal responses of white bean to 0-,
and S0? singly or in combination. Atmos. Environ. 13:533-535.
Beckerson, D.W., and G. Hofstra. 1980. Effects of sulphur dioxide and ozone,
singly or in combination, on membrane permeability. Can. J. Bot.
58:451-457.
93
-------
Beckerson, D.W., G. Hofstra, and R. Wukasch. 1979. The relative sensitivities
of 33 bean cultivars to ozone and sulfur dioxide singly or in
combination in controlled exposures and to oxidants in the field. Plant
Dis. Rep. 63:478:482.
Bennett, J.P., H.M. Resh, and V.C. Runneckles. 1974. Apparent stimulation of
plant growth by air pollutants. Can. J. Bot. 52:35-41.
Bennett, J.P., K. Barnes, and J.H. Shinn. 1980. Interactive effects of hLS and
6.5 on the yield of snap beans (Phaseolus vulgaris L.) Environ. Exp.
BOt. 20:107-114.
Black, V.J., D.P. Ormrod, and M.H. Unsworth. 1982. Effects of low
concentrations of ozone, singly and in combination with sulphur dioxide
on net photosynthesis rates of Vicia faba L. J. Exp. Bot. 33:1302-1311.
Black, V.J. 1982. Effects of sulfur dioxide on physiological processes in
plants. In: M.H. Unsworth and D.P. Ormrod (eds.) Effects of Gaseous Air
Pollution in Agriculture and Horticulture. 11:225-246. London/Boston:
Butterworth Scientific. 532 pp.
Bull, J.N., and T.A. Mansfield. 1974.
and N00. Nature 250:433-444.
Photosynthesis in leaves exposed to SO.
Carlson, R.W. 1979. Reduction in the photosynthetic rate of Acer, Quercus and
Fraxinus species caused by sulphur dioxide and ozone. Environ. Pollut.
18:159-170.
Costonis, A.C. 1973. Injury to eastern white pine by sulfur dioxide and ozone
alone and in mixtures. Eur. J. Forest Pathol. 3:50-55.
Cowling, D.W., and M.J. Koziol. 1982. Mineral nutrition and plant responses to
air pol lutants.pp. 349-375. lr\_: M.H. Unsworth and D.P. Ormrod (eds.)
Effects of Gaseous Air Pollution in Agriculture and Horticulture.
London/Boston: Butterworth Scientific. 532 pp.
J. Air
Coyne, P. I., and G.E. Bingham. 1978. Photosynthesis and stomatal light
responses in snap beans exposed to hydrogen sulfide and ozone.
Pollut. Control Assoc. 28:1119-1128.
Czuba, M., and D.P. Ormrod. 1974. Effects of cadmium and zinc on ozone-induced
phytotoxicHy in cress and lettuce. Can. J. Bot. 52:645-649.
Czuba, M., and D.P. Ormrod. 1981. Cadmium concentrations in cress shoots in
relation to cadmium-enhanced ozone phytotoxicity. Environ. Pollut.
(Ser. A) 25:67-76.
Decormis, !_„, and M. Luttringer. 1977. Influence of sulfur dioxide and
nitrogen dioxide synergism. (Effects sur les vegetaux de la synerqie
dioxxyde de soufre-oxides d. azote). Pollut. Atmos. 75:245-247.
94
-------
Department of Health, Education, and Welfare (DHEW). 1970. Air quality
criteria for sulfur oxides. National Air Pollution Control
Administration, Washington, DC. pp. 61-66, 160-161.
Dochinger, L.S., F.W. Bender, P.O. Box, and W.W. Heck. 1970. Chlorotic dwarf
of eastern white pine caused by an ozone and sulphur dioxide
interaction. Nature 255:476.
Electric Power Research Institute. 1982. Eastern Regional Air Quality
Measurements. Vol. 1. Prepared by Environmental Research & Technology,
Inc. EPRI EA-1914, Palo Alto, CA.
Elkiey, T., and D.P. Ormrod. 1979a. Leaf diffusion resistance responses of
three petunia cultivars to ozone and/or sulfur dioxide. J. Air Pollut.
Control Assoc. 29:622-625.
Elkiey, T., and D.P- Ormrod. 1979b. Ozone and/or sulphur dioxide effects on
tissue permeability in petunia leaves. Atmos. Environ. 13:1165-1168.
Elkiey, T., and D.P. Ormrod. 1979c. Ozone and sulphur dioxide effects on leaf
water potential of Petunia. Z. Pfansenphysiologie 91:177-181.
Elkiey, T., and D.P. Ormrod. 1980. Response of turfgrass cultivars to ozone,
sulfur dioxide, nitrogen dioxide, and their mixture. J. Amer. Soc.
Hort. Sci. 105:664-668.
Elkiey T., and D.P. Ormrod. 1981a. Sulphite, total sulphur and total nitrogen
accumulation by petunia leaves exposed to ozone, sulphur dioxide and
nitrogen dioxide. Environ. Pollut. (Ser. A). 24:233-241.
Elkiey, T., and D.P. Ormrod. 1981b. Sorption of 0,, SOj, NOp or their mixtures
by nine Poa pratensis cultivars of differing pollutant sensitivity.
Atmos. Environ. 15:1739-1743.
Elkiey, T., and D.P. Ormrod. 1981c. Absorption of ozone, sulfur-dioxide, and
nitrogen dioxide by petunia plants. Environ. Exp. Bot. 21:63-70.
Elkiey, T., D.P. Ormrod, and B. Marie. 1982. Foliar sorption of sulfur
dioxide, nitrogen dioxide, and ozone by ornamental woody plants.
HortScience 17:358-360.
Environmental Protection Agency. 1976. AEROS Manual Series Volume V: AEROS
Manual of Codes. Office of Air and Waste Management, Office of Air
Quality Planning and Standards, Research Triangle Park, NC.
EPA-450/2-76-005.
Environmental Protection Agency. 1978. Air Quality Criteria for Ozone and
Other Photochemical Oxidants. Environmental Criteria and Assessment
Office, Research Triangle Park, NC. EPA-600/8-78-004.
95
-------
Environmental Protection Agency. 1981a. Preliminary assessment of health
and welfare effects associated with nitrogen oxides for
standard-setting purposes. Prepared by the Division of Strategies and
Air Standards. United States Environmental Protection Agency, Research
Triangle Park, North Carolina.
Environmental Protection Agency. 1981b. 1980 ambient assessment—air
portion. Office of Air Quality Planning and Standards, Research
Triangle Park, North Carolina.
Environmental Protection Agency. 1981c. Air Quality Criteria for Oxides of
Nitrogen. Prepared by the Environmental Criteria and Assessment
Office, Research Triangle Park, North Carolina. EPA-600/8-82-026.
Environmental Protection Agency. 1982a. Review of the National Ambient Air
Quality Standards for Nitrogen Oxides: Assessment of Scientific and
Technical Information: OAQPS Staff Paper. Prepared by the Office of Air
Quality Planning and Standards, EPA, Research Triangle Park, NC.
EPA-450/5-82-002.
Environmental Protection Agency. 1982b. Review of the National Ambient Air
Quality Standards for Sulfur Oxides; Assessment of Scientific and
Technical Information. Prepared by the Division of Strategies and Air
Standards. United States Environmental Protection Agency, Research
Triangle Park, North Carolina.
Environmental Protection Agency. 1982c. Air Quality Data - 1981 Annual
Statistics Including Summaries with Reference to Standards. Office of
Air Planning and Standards, Research Triangle Park, North Carolina.
EPA-450/4-82-007.
Evans, L.S., and P.R. Miller. 1975. Histological comparison of single and
additive 0^ and S0? injuries to elongating Ponderosa pine needles.
Amer. J. BOt. 62:416-421.
Foster, K.W., H. Timm, C.K. Labanauskas and R.J. Oshima. 1983. Effects of
ozone and sulfur dioxide on tuber yield and quality of potatoes. J.
Environ. Qual. 12: In press.
Fujiwara, T. 1973. Damage to plants caused by complex pollution of atmosphere.
Snokubutsu Boeki. (Plant Protection) 27:233-236.
Fujiwara, T., and H. Ishikawa. 1976. Actual effects of combination of sulfur
dioxide, nitrogen dioxide and ozone on some plants (in Japanese with
English summary). Bull. Bio-Environ. Lab,, No. 476001. 1019 pp.
Furukawa, A., and T. Totsuka. 1979. Effects of N0?, S0? and 0? alone and in
combination on net photosynthesis in sunflower. Environ. Control Biol.
17:161-166.
96
-------
Gardner, J.O., and D.P. Ormrod. 1977. Response of Reiger begonia to ozone and
sulphur dioxide. Sci. Hort. 5:171-181.
Glass, G.E., and T.G. Brydges. 1981. Problem complexity in predicting impacts
from altered precipitation chemistry. Presented at Int. Conf. on Acid
Precipitation Impacts, Cornell University, Ithaca, NY. August 1981.
Grosso, J.J., H.A. Menser, G.H. Hodges, and H.H. McKinney. 1971. Effects of
air pollutants on Nicotiana cultivars and species used for virus
studies. Phytopathology 61:945-950.
Halbwachs, G., and W. Kronberger. 1979. Das Verhalten F- and S0?- resistenter
fichtenklone verschledener herkunft in pinem rauchschaden? gebiet. Zb.
Inst. Gozdno. Lesn. Gospos. Ljubljana, pp. 259-268.
Heagle, A.S., and J.W. Johnston. 1979. Variable responses of soybeans to
mixtures of ozone and sulfur dioxide. J. Air Pollut. Control Assoc.
29:729-732.
of
Heagle, A.S., D.E. Body, and G.E. Neely. 1974. Injury and yield responses
soybean to chronic doses of ozone and sulfur dioxide in the field.
Phytopathology 64:132-136.
Heagle, A.S., W.W. Heck, J.O. Rawlings, and R.B. Philbeck. 1983. Effects of
chronic doses of ozone and sulfur dioxide on injury and yield of
soybeans in open-top chambers. Crop Sci. In press.
Heck, W.W., S.V. Krupa, and S.N. Linzon. 1979. Methodology for the Assessment
of Air Pollution Effects on Vegetation. Air Pollution Control
Association, Pittsburgh.
Heck, W.W., W.W. Cure, D.S. Shriner, R.J. Olson, and A.S. Heagle. 1982. Ozone
impacts on the productivity of selected crops. In : J.S. Jacobson and
A. A. Millen (eds.) Symposium on the Effects of Air Pollution on Farm
Commodities. Isaak Walton League of America, Arlington, VA.
Heggestad, H.E., and J.H. Bennett. 1981. Photochemical oxidants potentiate
yield losses in snap beans attributable to sulfur dioxide. Science
213:1008-1010.
Hill, A.C., S. Hill, C. Lamb, and T.W. Barrett. 1974. Sensitivity of native
desert vegetation to S02 and to S0? and N0? combined. J. Air Pollut.
Control Assoc. 24:153-157.
Hodges, G.H., H.A. Menser, and W.B. Ogden. 1971. Susceptibility of Wisconsin
Havanna tobacco cultivars to air pollutants. Argon. J. 63:107-111.
Hofstra, G., and D.W. Beckerson, 1981. Foliar responses of five plant species
to ozone and a sulphur dioxide/ozone mixture after a sulphur dioxide
pre-exposure. Atmos. Environ. 15:383-389.
97
-------
Hofstra, G., and D.P. Ormrod. 1977. Ozone and sulphur dioxide interaction in
white bean and soybean. Can. J. Plant Sci. 57:1193-1198.
Horsman, D.C., and A.R. Wellburn. 1975. Synergistic effect of SO- and NO-
polluted air upon enzyme activity in pea seedlings. Environ. Polmt,
8:123-133.
Horsman, D.C., and A.R. Wellburn. 1976. Guide to the metabolic and biochemcial
effects of air pollutants on higher plants. In: T. A. Mansfield (ed.)
Effects of Air Pollutants on Plants, pp. 1857T89.
Hou, L.Y., A.C. Hill, and A. Soleimani. 1977. Influence of CO,, on the effects
of S02 and NO- on alfalfa. Environ. Pollut. 12:7-16.
Houston, D.B. 1974. Response of selected Pinus strobus L. clones to fumigation
with sulfur dioxide and ozone. Can. J. For. Res. 4:65:68.
Irving, P.M., and J.E. Miller, 1981. Productivity of field-grown soybeans
exposed to acid rain and sulfur dioxide alone and in combination J.
Environ. Quality 10:473-478.
Irving, P., J.E. Miller, and P.B. Xerikos. 1982. The effect of N02 and S02
alone and in combination on the productivity of field-grown soybeans.
JJK T. Schneider and L. Grand (eds.) Air Pollution by Nitrogen Oxides.
pp. 521-531. Amsterdam, The Netherlands: Elsevier Scientific.
Ishikawa, H. 1976. Sensitivity of cultivated plants to air pollutants. Report
from Bio Enviroment Laboratory, Central Research Institute of Electric
Power Industry, 1646 Abiko Chiba, Japan.
Jacobson, J.S., and L.J. Colavito. 1976. The combined effect of sulfur dioxide
and ozone on bean and tobacco plants. Environ, Exp. Bot. 16:277-285.
Jaeger, J., and W. Banfield. 1970. Response of eastern white pine to prolonged
exposure to atmospheric levels of ozone, sulfur dioxide, or mixtures of
these pollutants. Phytopathology 60:577.
Karnosky, D.F. 1976. Threshold levels for foliar injury to Populus tremuloides
by sulfur dioxide and ozone. Can. J. For. Res. 6:166-169~
Kender, W.J., and F.H.F.G. Spierings. 1975. Effects of sulfur dioxide, ozone,
and their interactions on 'Golden Delicious' apple trees. Neth. J.
Plant Pathol. 81:149-151.
Klarer, C.I. 1982. Effects of sulfur dioxide and nitrogen dioxide, singly and
in combination over time on ribulose bisphosphate carboxylase activity
and vegetative growth of soybean. M.S. Thesis, North Carolina State
Univ., Raleigh, NC. 76 pp.
Kohut, R.J., and D.D. Davis. 1978. Response of pinto bean to simultaneous
exposure to ozone and PAN. Phytopathology 68:567-569.
-------
Krause, C.R., and K.F. Jensen. 1978. Microtopographical changes in hybrid
poplar leaves associated with air pollution exposure. Scan. Elec.
Micros. 2:755-758.
Krause, C.R., and K.F. Jensen. 1979. Surface changes on hybrid poplar leaves
exposed to ozone and sulfur dioxide. Scan. Elec. Micros. 3:77-80.
Krause, G.H.M., and Kaiser, H. 1977. Plant response to heavy metal and sulphur
dioxide. Environ. Pollut. 12:63-71.
Kress, L.W., and J.M. Skelly. 1982. Response of several eastern forest tree
species to chronic doses of ozone and nitrogen dioxide. Plant Dis.
66:1149-1152.
Kress, L.W., J.M. Skelly, and K.H. Hinkelmann. 1982a. Growth impact of CU, N02
and/or SO^ on Pinus taeda. Environ. Monit. Assess. 1:229-239.
Kress, L.W., J.M. Skelly, and K.H. Hinkelmann. 1982b. Growth impact of CU, NOn
and/or SO^ on Plantanus occidental is. Agric. Environ. 7:265-274.
Lamoreaux, R.J., and W.R. Chaney. 1978. Photosynthesis and transpiration of
excised silver maple leaves exposed to cadmium and sulphur dioxide.
Environ. Pollut. 17:259-268.
Le Sueur-Brymer, N.M., and D.P. Ormrod. 1983. Net photosynthesis rates of
fruiting soybean plants exposed to ozone and sulphur dioxide singly or
in combination. Can. J. Plant Sci. (submitted for publication).
Lewis, E., and E. Brennan. 1978. Ozone and sulfur dioxide mixtures cause a
PAN-type injury to petunia. Phytopathology 68:1011-1014.
Macdowall, F.D.H., and A.F.W. Cole. 1971. Threshold and synergistic damage to
tobacco by ozone and sulfur dioxide. Atmos. Environ. 5:553-559.
Malhotra, S.S., and D. Hocking. 1976. Biochemical and cytological effects of
sulphur dioxide on plant metabolism. New. Phytol. 76:227-237.
Mandl, R.H., L.H. Weinstein, and M. Keveny. 1975. Effects of hydrogen fluoride
and sulphur dioxide alone and in combination on several species of
plants. Environ. Pollut. 9:133-143.
Mandl, R.H., L.H. Weinstein, M. Dean, and M. Wheeler. 1980. The response of
sweet corn to HF and S0? under field conditions. Environ. Exp. Bot.
20:359-365.
Mansfield, T.A., and T.W. Ashenden. 1978. Extreme pollution sensitivity of
grasses when S0? and N0? are present in the atmosphere together. Nature
273:142-143. i
99
-------
Masaru, N., F. Syozo, and K. Saburo. 1976. Effects of exposure to various
injurious gases on germination of lily pollen. Environ. Pollut.
11:181-187.
Matsushima, J., and R.F. Brewer. 1972. Influence of sulfur dioxide and
hydrogen fluoride as a mix or reciprocal exposure on citrus growth and
development. J. Air Pollut. Control Assoc. 22:710-713.
McCune, D.C. 1983. Interaction of fluorides with air pollutants. Intern.
Fluoride Symp. Utah State Univ., Logan, UT, May 24-27, 1982.
Mclaughlin, S.B., D.S. Shriner, R.K. M'Conathy, and L.K. Mann. 1979. The
effects of S0? dosage kinetics and exposure frequency on photosynthesis
and transpiration of kidney beans (Phaseolus vulgaris, L.). Environ.
Exp. Bot. 19:179-191.
Menser, H.A., and H.E. Heggestad. 1966. Ozone and sulfur dioxide synergism:
injury to tobacco plants. Science 153:424-425.
Menser, H.A., and G.H. Hodges. 1970. Effects of air pollutants on burley
tobacco cultivars. Agronomy J. 63:265-269.
Miller, C.A., and D.D. Davis. 1981a. Response of pinto bean plants exposed
to Ov S0?, or mixtures at varying temperatures. HortScience
16:548-556.
Miller, C.A., and D.D. Davis. 1981b. Effect of temperature on stomatal
conductance and ozone injury of pinto bean leaves. Plant Dis.
65:750:751.
Miller, V.C., R.K. Howell, and B.E. Caldwell. 1974. Relative sensitivity of
soybean genotypes to ozone and sulfur dioxide. J. Environ. Qual.
3:35-37.
Mueller, P.K., G. M. Hidy, K. Warren, T.F. Lavery, and R.L. Baskett. 1980. The
occurrence of atmospheric aerosols in the northeastern United States.
In: Aerosols: Anthropogenic and Natural, Sources and Transport. New
York Academy of Sciences, New York, N.Y., pp. 463-482.
Murray, J.J., R.K. Howell, and A.C. Wilton. 1979. Differential response of
seventeen Poa protansis cultivars to ozone and sulfur dioxide. Plant
Dis. Rep. 59:852-854.
Noble, R.D., and K.F. Jensen. 1980. Effects of sulfur dioxide and ozone on
growth of hybrid poplar leaves. Amer. J. Bot. 67:1005-1009.
Noggle, J.C., and H.C. Jones. 1981. Regional effects of multiple air
pollutants on plants. Presented at the 1981 Annual Meeting of the Air
Pollution Control Association, Philadelphia, PA. Paper #42.5.
100
-------
O'Connor, J.R. 1980. Overview of the criteria review and standard setting
process. Presented at the 1980 Air Pollution Control Association
Specialty Conference on the Technical Basis for a Size Specific
Participate Standard. Danvers, Massachusetts, pp. 15-25.
Olszyk, D.M., and T.W. Tibbitts. 1981. Stomatal response and leaf injury of
Pisum sativum L. with SO- and 03 exposures. Plant Physiol. 67:539-544.
Ormrod, D.P. 1977. Cadmium and nickel effects on growth and ozone sensitivity
of pea. Water, Air, Soil Pollut. 8:263-270.
Ormrod, D.P. 1978. Pollution in Horticulture. Elsevier, Amsterdam.
Ormrod, D.P. 1982. Air pollutant interactions in mixtures. Pages 307-331. In:
M.H. Unsworth and D.P. Ormrod (eds.). Effects of Air Pollution in
Agriculture and Horticulture. Butterworths, London.
Ormrod, D.P., V.J. Black, and M.H. Unsworth. 1981. Depression of net
photosynthesis in Vicia faba L. exposed to sulphur dioxide and ozone.
Nature 291:585-586.
Ormrod, D.P., D.T. Tingey, and M.L. Gumpertz, and D.M. Olszyk. 1983a.
Utilization of a response surface technique in the study of
physiological responses to ozone and sulfur dioxide mixtures. Ms. in
preparation.
Ormrod, D.P-, D.T. Tingey, and M.L. Gumpertz. 1983b. Covariate measurements
for increasing the precision of plant response to 0, and S0?.
HortScience (submitted for publication).
Oshima, R.J. 1978. The impact of sulfur dioxide on vegetation: A sulfur
dioxide-ozone response model. California Air Resources Board, Agreement
No. A6-162-30.
Padgett, J., and H. Richmond. 1983. The process of establishing and revising
National Ambient Air Quality Standards. J. of Air Pollut. Control
Assoc. 33:13-16.
Pell, E.J. 1976. Influence of benomyl soil treatment on pinto bean plants
exposed to peroxyacetyl nitrate and ozone. Phytopathology, 66:731-733.
Proctor, J.T.A., and D.P. Ormrod. 1981. Sensitivity of ginseng to ozone and
sulfur dioxide. HortScience 16:647:648.
Rajput, C.B.S., D.P. Ormrod, and W.D. Evans. 1977. The resistance of
strawberry to ozone and sulfur dioxide. Plant Dis. Rep. 61:222-225.
Reich, P.B., R.G. Amundson, and J.P. Lassoie. 1982. Reduction i soybean yield
often exposure to ozone and sulfur dioxide using a Linear Gradient
Exposure Technique. Water, Air, Soil Pollut. 17:29-36.
10'
-------
Reinert, R.A., and T.N. Gray. 1981. The response of radish to nitrogen
dioxide, sulfur dioxide, and ozone, alone and in combination. J.
Environ. Quality 10:240-243.
Reinert, R.A., and W.W. Heck. 1982. Effects of nitrogen dioxide in combination
with sulfur dioxide and ozone on selected crops. In: (T. Schneider and
L. Grant (eds.) Air Pollution by Nitrogen Oxides, pp. 533-546.
Amsterdam, The Netherlands: Elsevier Scientific.
Reinert, R.A., and P-V. Nelson. 1980. Sensitivity and growth of five Elatior
Begonia cultivars to SOP and 0^ alone and in combination. J. Amer. Soc.
Hort. Sci. 105:721-723.
Reinert, R.A., and J.S. Sanders. 1982. Growth of radish and marigold
following repeated exposure to nitrogen dioxide, sulfur dioxide, and
ozone. Plant. Dis. 66:122-124.
Reinert, R.A., and D.E. Weber. 1980. Ozone and sulfur dioxide-induced changes
in soybean growth. Phytopathology 70:914-916.
Reinert, R.A., A.S. Heagle, and W.W. Heck. 1975. Plant response to pollutant
combinations. In: J.B. Mudd, and T.T. Koslowski (eds.) Responses of
Plants to Air Pollution, pp. 159-177. Academic Press, New York.
Reinert, R.A., D.S. Shriner, and J.O. Rawlings. 1982. Responses of radish
to all combinations of three concentrations of nitrogen dioxide, sulfur
dioxide, and ozone. J. Environ. Quality. 11:52-57.
Roques, A., M. Kerjean, and D. Auclair. 1980. Effets de la pollution
atmospherique par le fluor et le dioxide de soufre sur 1'appareil
reproducteur fermelle de Pinus sylverstris en foret de roumare (Seine
Maritime, France). Environ. Pollut. (Ser. A). 21:191-201.
Sanders, J.A., and R.A. Reinert. 1982a. Screening azalea cultivars for
sensitivity to nitrogen dioxide, sulfur dioxide and ozone alone and in
mixtures. J. Amer. Soc. Hort. Sci. 107:87-90.
Sanders, J.S., and R.A. Reinert. 1982b. Weight changes of radish and marigold
exposed at three ages to N09, S09 and 07 alone and in mixture. J. Amer.
Soc. Hort. Sci. 107:726-730: ^ J
Shertz, R.D., W.J. Kender, and R.C. Musselman. 1980a. Foliar response and
growth of apple trees following exposure to ozone and sulfur dioxide.
J. Amer. Soc. Hort. Sci. 105:594-598.
Shertz, R.D., W.J. Kender, and R.C. Musselman. 1980b. Effects of ozone and
sulfur dioxide on grapevines. Sci. Hort. 13:37-45.
Shew, B.B., R.A. Reinert and R.R. Barker. 1982. Response of tomatoes to
ozone, sulfur dioxide, and infection by Pratylenchus penetrans.
Phytopathology 72:822-826.
102
-------
Singh, S.N. 1980. Synergistic action of particulate and gaseous pollutants on
the growth of Triticum aestivum L. J. Exp. Bot. 31:1701-1705.
Skelly, J.M., L.D. Moore, and L.L. Stone. 1972. Symptom expression of eastern
white pine located near a source of oxide-nitrogen and sulfur dioxide.
Plant Dis. Rep. 56:3-6.
Solberg, R.A., and R.F. Adams. 1956. Histological responses of some plant
leaves to hydrogen fluoride and sulfur dioxide. Amer. J. Bot.
43-755-760.
Thompson, C.R., G. Kats, and R.W. Lennox. 1980. Effects of SO- and/or NO- on
native plants of the Mohave Desert and eastern Mohave-Colorado Desert.
J. Air Pollut. Contr. Assoc. 30:1304-1309.
Tingey, D.T., and R.A. Reinert. 1975. The effects of ozone and sulphur dioxide
singly and in combination on plant growth. Environ. Pollut. 9:117-125.
Tingey, D.T., and G.E. Taylor, Jr. 1982. Variation in plant response to ozone:
a conceptual model of physiological events. Pages 113-138. In: M.H.
Unsworth and D.P. Ormrod (eds.). Effects of Gaseous Air Pollution in
Agriculture and Horticulture. Butterworths, London.
Tingey, D.T., R.A. Reinert, J.A. Dunning, and W.W. Heck. 1971a. Vegetation
injury from the interaction of nitrogen dioxide and sulfur dioxide.
Phytopathology 61:1506-1511.
Tingey, D.T., W.W. Heck, and R.A. Reinert. 1971b. Effect of low concentrations
of ozone and sulfur dioxide of foliage, growth and yield of radish. J.
Amer. Soc. Hort. Sci. 96:369-371.
Tingey, D.T., R.A. Reinert, J.A. Dunning, and W.W. Heck. 1973a. Foliar injury
responses of eleven plant species to ozone/sulfur dioxide mixtures.
Atmos. Environ. 7:201-208.
Tingey, D.T., R.A. Reinert, C. Wickliff, and W.W. Heck. I973b. Chronic ozone
or sulfur dioxide exposures, or both, affect the early vegetative
growth of soybean. Can. J. Plant Sci. 53:875-879.
Toivonen, P.M.A., and G. Hofstra. 1979. The interaction of copper and sulphur
dioxide in plant injury. Can. J. Plant Sci. 59:475-479.
Troiano, J., L. Colavito, T. Heller, and D.C. McCune. 1981. Effect of
simulated acid rain and photochemical oxidant on seed development in
soybean. Phytopathology 71:565 (abst.).
Troiano, J., L. Colavito, T. Heller, and D.C. McCune. 1982. Viability, vigor,
and maturity of seed harvested from two soybean cultivars exposed to
simulated acidic rain and photochemical oxidants. Agric. Environ.
7:275-283.
103
-------
Unsworth, M.H., and D.P. Ormrod. 1982. Effects of Gaseous Air Pollution in
Agriculture and Horticulture. London/Boston: Butterworth Scientific.
532 pp.
Weber, D.E., R.A. Reinert, and K.R. Barker. 1979. Ozone and sulfur dioxide
effects on reproduction and host-parasite relationships of nematodes.
Phytopathology 69:624-628.
Wellburn, A.R. 1982. Effects of SO- and N0? on metabolic function. _!TK M-H-
Unsworth and D.P- Ormord (eds.) Effects of Gaseous Air Pollution in
Agriculture and Horticulture. 8:169-188. London/Boston: Butterworth
Scientific. 532 pp.
Wellburn, A.R., T.M. Capron, H.S. Chan, and D.C. Horsman. 1976. Biochemical
effects of atmospheric pollutants on plants. Pp. 105-114. In: T.A.
Mansfield (ed.). Effects of Air Pollution on Plants. Cambridge
University Press, Cambridge.
Wellburn, A.R., C. Higginson, D. Robinson, and C. Walmsley. 1981. Biochemical
explanations of more than additive inhibitory effects of low
atmospheric levels of sulfur dioxide plus nitrogen dioxide upon plants.
New Phytologist 88:223-237.
White, K.L., A.C. Hill, and J.H. Bennett. 1974. Synergistic inhibition of
apparent photosynthesis rate of alfalfa by combinations of sulfur
dioxide and nitrogen dioxide. Environ. Sci. Technol. 8:574-576.
Whitmore, M.E., P.H. Freer-Smith, and T. Davis. 1982. Some effects of low
concentrations of S0~ and/or N0? on the growth of grasses and poplar.
pp. 483-485. In: M.R. Unsworth and D.P. Ormrod (eds.) Effects of
Gaseous Air PoTTution in Agriculture and Horticulture. London/Boston:
Butterworth Scientific. 532 pp.
Williams, R.J.H., and G.R. Ricks. 1975. Effects of combinations of atmospheric
pollutants upon vegetation. In: M.J. Chadwick and G.T. Goodman (eds.)
15th Symposium of the British Ecological Society. London: Blackwells
Science Publication, pp. 127-137.
Williams, R.J.H., M.M. Lloyd, and G.R. Ricks. 1971. Effects of atmospheric
pollution on deciduous woodland. I. Some effects on leaves of Quercus
petraea (Mattuschka)- Leibl. Environ. Pollut. 2:57-68.
Yamazoe, F., and H. Mayumi. 1977. Vegetation injury from interaction of mixed
air pollutants. Proc. Inter. Clean Air. Congr. Tokyo, Japan.
Zaragoza, L.J. 1982. The Use of Biological Information in the Development of
National Ambient Air Quality Standards. Available through University
Microfilms International. Ann Arbor, MI.
104
-'USGPO: 1984 — 759-102/0875
------- |