EPA-R3-73-030
EFFECTS OF SULFUR OXIDES
IN THE
ATMOSPHERE
ON VEGETATION;
Revised Chapter 5 for Air Quality Criteria for Sulfur Oxides
Task 16
ROAP No. 26AAA
Program Element 1A1001
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
September 1973
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development,
Environmental Protection Agency, have been grouped into five
series. These five broad categories were established to facili-
tate further development and application of environmental tech-
nology . Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface
in related fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ECOLOGICAL RESEARCH
series. This series describes research on the effects of pollution
on humans, plant and animal species, and materials. Problems
are assessed for their long- and short-term influences. Investi-
gations include formation, transport, and pathway studies to
determine the fate of pollutants ai~A their effects. This work
provides the technical basis for setting standards to minimize
undesirable changes in living organisms Li the aquatic, terres-
trial, and atmospheric environments.
11
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PREFACE
Air quality criteria state what science has thus far been able to measure of
the obvious as well as the insidious effects of air pollution on man and his
environment. Criteria provide the most useful basis presently available for
determining the levels of air pollutants that will protect the public health
and welfare. The Clean Air Act states: "Air quality criteria for an air
pollutant shall accurately reflect the latest scientific knowledge useful in
indicating the kind and extent of all identifiable effects on public health or
welfare which may be expected from the presence of such pollutant in the
ambient air, in varying quantities."
Air Quality Criteria for Sulfur Oxides* was issued under the 1967
amendments to the Clean Air Act. National ambient air quality standards
were proposed, based on these criteria, and were promulgated under the
1970 amendments to the Clean Air Act.
The Clean Air Act states that the Administrator of the Environmental
Protection Agency (EPA) "shall from time to time review, and, as
appropriate, modify, and reissue any criteria . . ." Limitations in the criteria
for secondary standards in Air Quality Criteria for Sulfur Oxides,* which
became ^apparent since the adoption of Air Quality Standards, prompted
review and revision of Chapter 5, "Effects of Sulfur Oxides in the
Atmosphere on Vegetation." This document presents the revision to Chapter
5, and also includes revised portions of Chapter 10, "Summary and
Conclusions," that relate to effects on vegetation.
This revision includes a number of studies completed since initial
publication in 1969. All data expressed in micrograms per cubic meter are
referenced to 25° C and a pressure of 1013.2 mb (760 mm Hg) unless stated
otherwise.
Following the initial revision by EPA personnel, there was a sequence of
review and revision by (1) the National Air Quality Criteria Advisory
Committee, which has a membership broadly representative of industry,
universities, conservation interests, and all levels of government, and by (2)
individuals specially selected for their competence, expertise, or special
interest in the effects of air pollutants on vegetation. The efforts of these
reviewers, without which this document could not have been completed
successfully, are acknowledged individually on the following pages.
As required by the Clean Air Act, appropriate Federal departments and
agencies were consulted prior to issuing this criteria document. A Federal
consultation committee, comprised of members designated by the heads of
departments and agencies, reviewed the document and met with EPA staff
members to discuss -their comments. These representatives are also listed
following this discussion.
*Air Quality Criteria for Sulfur Oxides. U.S. Department of Health Education and
Welfare, National Air Pollution Control Administration. Washington, D.C. Publication
No. AP-50. January 1969. 178 p.
ill
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The EPA is pleased to acknowledge the efforts of each of the persons
specifically named, as well as the many not named, who contributed to
producing this document. Their participation does not necessarily imply
complete endorsement of all the conclusions presented herein; in the last
analysis, the Environmental Protection Agency alone retains full respon-
sibility for its contents.
Russell E. Train
Administrator
Environmental Protection Agency
IV
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NATIONAL AIR QUALITY CRITERIA ADVISORY
COMMITTEE
CHAIRMAN
Dr. John F. Finklea, Director
National Environmental Research Center
Research Triangle Park, North Carolina
Dr. Mary O. Amdur
Associate Professor of Toxicology
School of Public Health
Harvard University
Boston, Massachusetts
Dr. David M. Anderson
Manager of Environmental Quality Control
Bethlehem Steel Corporation
Bethlehem, Pennsylvania
Dr. Anna M. Baetjer
Professor Emeritus of Environmental
Medicine
Department of Environmental Medicine
School of Hygiene and Public Health
The Johns Hopkins University
Baltimore, Maryland
Dr. Samuel S. Epstein
Swetland Professor of Environmental
Health and Human Ecology
School of Medicine
Case Western Reserve University
Cleveland, Ohio
Dr. Arie J. Haagen-Smit
Professor and Director
Plant Environment Laboratory
California Institute of Technology
Pasadena, California
Dr. John V. Krutilla
Director
Natural Environment Program
Resources for the Future, Inc.
Washington, D.C.
Dr. Frank J. Massey, Jr.
Professor, School of Public Health
University of California
Los Angeles, California
Dr. James McCarroll
Professor and Chairman
School of Public Health
and Community Medicine
Department of Environmental Medicine
Department of Environmental Health
University of Washington
Seattle, Washington
Dr. Eugene P. Odum
Director, Institute of Ecology
University of Georgia
Athens, Georgia
Mr. Morton Sterling
Director, Wayne County Air Pollution
Control Division
Wayne County Department of Health
Detroit, Michigan
Mr. Arthur C. Stern
Professor of Air Hygiene
University of North Carolina
Chapel Hill, North Carolina
Dr. Raymond R. Suskind
Director, Kettering Laboratory
College of Medicine
University of Cincinnati
Cincinnati, Ohio
Mr. Elmer P. Wheeler
Manager, Environmental Health
Medical Department
Monsanto Company
St. Louis, Missouri
Dr. John T. Wilson, Jr.
Professor and Chairman
Department of Community Health
Practice
College of Medicine
Howard University
Washington, D.C.
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CONTRIBUTORS AND REVIEWERS
Dr. Thomas W. Barrett
Professor of Agronomy
Arizona State University
Division of Agriculture
Tempe, Arizona
Dr. C. Stafford Brandt
Bureau of Air Quality Control
Department of Health and Mental
Hygiene
Environmental Health Administration
Baltimore, Maryland
Dr. Harris M. Benedict
Staff Scientist
Stanford Research Institute
Menlo Park, California
Dr. Leon S. Dochinger
Principal Plant Pathologist
United States Department of
Agriculture
Forest Service
Delaware, Ohio
Dr. William A, Feder
Professor
University of Massachusetts
Suburban Experiment Station
Waltham, Massachusetts
Dr. Jay Jacobson
Boyce Thompson Institute for
Plant Research, Inc.
Yonkers, New York
Dr. Wilhelm Knabe
Landesanstalt fuer Immissions und
Bodennutzungsschutz
Des Landes Nordrhein-Westfalen
Essen, West Germany
Dr. Emanuel Landau
Chief, Epidemiologic Studies Branch
Division of Biological Effects
Bureau of Radiological Health
Department of Health, Education, and
Welfare
Public Health Service
Food and Drug Administration
Rockville, Maryland
Dr. S. N. Linzon
Chief, Phytotoxicology Section
Ministry of the Environment
Air Management Branch
Toronto, Ontario, Canada
Dr. O. Clifton Taylor
Associate Director
University of California, Riverside
Statewide Air Pollution Research Center
Riverside, California
Dr. Leonard H. Weinstein
Program Director
Environmental Biology
Boyce Thompson Institute for Plant
Research, Inc.
Yonkers, New York
VI
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FEDERAL AGENCY LIAISON REPRESENTATIVES
Department of Agriculture
Dr. Theodore C. Byerly
Assistant Director of Science
and Education
Office of the Secretary
Department of Commerce
Dr. James R. McNesby
Manager, Measures for Air Quality
Institute for Materials Research
National Bureau of Standards
Department of Defense
Commander Harvey A. Falk, Jr.
Director for Environmental Media
Office of the Assistant Secretary of
Defense
Department of Health, Education, and
Welfare
Dr. Charles H. Powell
Director, Office of Research and
Standards Development
National Institut of Occupational
Safety and Health
Department of Housing and Urban
Development
Mr. Richard H. Broun, Deputy Director
Office of Community and Environmental
Standards
Community Planning and Management
Department of the Interior
Mr. Harry Moffet
Deputy Assistant Director - Minerals
and Energy Policy
U.S. Bureau of Mines
Department of Justice
Mr. Walter Kiechel, Jr.
Deputy Assistant Attorney General
Land and Natural Resources Division
Department of Labor
Mr. F.A. Van Atta
Office of Compliance
Occupational Safety and Health
Administration
Department of Transportation
Dr. Richard L. Strombotne
Office of the Assistant Secretary
for Systems Development and
Technology
Department of the Treasury
Mr. Gerald M. Brannon
Director, Office of Tax Analysis
U.S. Atomic Energy Commission
Dr. Martin B. Biles
Director, Division of
Operational Safety
Federal Power Commission
Mr. T.A. Phillips
Chief, Bureau of Power
General Services Administration
Mr. Harold J. Pavel
Director, Repair and Improve-
ment Division
National Aeronautics and Space
Administration
Mr. Ralph E. Cushman
Special Assistant
Office of Administration (Code B)
National Science Foundation
Dr. O.W. Adams
Program Director for
Structural Chemistry
Tennessee Valley Authority
Dr. F.E. Gartrell
Director of Environmental
Research and Development
U.S. Postal Service
Mr. Robert Powell
Assistant Program Manager
Veterans Administration
Mr. Gerald M. Hollander
Director of Architecture and
Engineering
Office of Construction
VII
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INTRODUCTION
Pursuant to authority delegated to the Administrator of the Environ-
mental Protection Agency, Revised Chapter 5 of Air Quality Criteria for
Sulfur Oxides, Effects of Sulfur Oxides in the Atmosphere on Vegetation,
including revisions to related parts of Chapter 10, "Summary and Con-
clusions," is issued in accordance with Section 108 of the Clean Air Act (42
U.S.C. \857etseqJ.
Air quality criteria are an expression of the scientific knowledge of the
relationship between various concentrations of pollutants in the air and their
adverse effects on man and his environment. Air quality criteria are
descriptive; that is, they describe the effects that have been observed to
occur when the ambient air level of a pollutant has reached or exceeded a
specific figure for a specific time period. In developing and using criteria,
many factors have to be considered. The chemical and physical charac-
teristics of the pollutants and the techniques available for measuring these
characteristics must be considered, along with exposure time, relative
humidity, and other conditions of the environment. The criteria must
consider the contribution of all such variables to the effects of air pollution.
Further, the individual characteristics of the receptor must be taken into
account.
The criteria in this document serve as the bases for National Secondary
Ambient Air Quality Standards. National Secondary Ambient Air Quality
Standards specify a level of air quality, the attainment and maintenance of
which in the judgment of the Administrator, based on criteria, are requisite
to protect the public welfare from any known or anticipated adverse effects
associated with the presence of such air pollutant in the ambient air.
Upon promulgation of the standards, each State must prepare im-
plementation plans that describe how these standards will be met. The Clean
Air Act has provisions ensuring that a plan is prepared and carried out by
each State or by EPA where States default or otherwise are judged incapable
of meeting the standards.
vin
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CONTENTS
Page
A. GENERAL 1
B. SYMPTOMS OF THE EFFECTS OF SULFUR DIOXIDE ON
VEGETATION 1
1. Visible Effects 1
a. Acute Injury 2
b. Chronic Injury 2
2. Subtle Effects 2
3. Physiological Effects 3
a. Photosynthesis 3
b. Stomatal Relationships 3
c. Changes in Chemical Composition 3
d. Growth and Yield Reductions 4
C. MECHANISM OF ACTION 4
D. FACTORS AFFECTING RESPONSE OF VEGETATION TO
SULFUR DIOXIDE 4
1. Environmental Factors 4
a. Temperature 4
b. Humidity 5
c. Light 5
d. Edaphic Factors 5
e. Diurnal Changes 6
f. Interaction with Other Pollutants 6
2. Genetic Factors 6
3. Stage of Development 6
E. PROBLEMS IN DIAGNOSIS AND ASSESSMENT OF THE
ECONOMIC IMPACT OF SULFUR DIOXIDE 7
F. EFFECTS ON LOWER ORGANISMS 8
G. ACID PRECIPITATION 9
H. MISCELLANEOUS ASPECTS OF SULFUR DIOXIDE EFFECTS
ON VEGETATION 10
1. Vegetation as a Sulfur Dioxide Sink 10
2. Effects of Sulfuric Acid Mist on Vegetation 10
I. EFFECTS ON BIOMASS AND YIELD 10
J. DOSE-INJURY RELATIONSHIPS OF SULFUR DIOXIDE TO
VEGETATION RESPONSE 12
ix
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Page
1. Mathematical Equations 14
2. Dose-Injury Data 16
K. SUMMARY 32
L. CONCLUSION 34
M. REFERENCES 35
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LIST OF TABLES
Table Page
5-1 Sulfur Dioxide Concentrations and Associated Vegetational
Effects in Research Areas at Biersdorf, Germany 13
5-2 Changes in Net Tree Volume of Eastern White Pine Associated
with Sulfur Dioxide Concentrations near a Smelter Complex in
Sudbury, Canada 14
5-3 Growth Reduction in Vegetation Exposed to Sulfur Dioxide for
Long and Short Time Periods 15
5-4 Seasonal Average Sulfur Dioxide Concentrations Associated
with Foliar Injury to Spruce in Two Locations in Czechoslo-
vakia 17
5-5 Concentrations of Sulfur Dioxide Causing Injury to Sensitive
Vegetation 18
5-6 Sulfur Dioxide Concentrations Causing Injury to Agricultural
and Forest Species 19
5-7 Vegetational Response to Sulfur Dioxide in Combinations with
either Ozone or Nitrogen Dioxide 21
5-8 Projected Sulfur Dioxide Concentrations that Will Produce
Threshold Injury to Vegetation for Short-Term Exposures ... 24
5-9 Lists of Plants in Three Susceptibility Groups by Sensitivity to
Sulfur Dioxide 25
XI
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EFFECTS OF SULFUR OXIDES IN THE ATMOSPHERE
ON VEGETATION;
Revised Chapter 5 for Air Quality Criteria for Sulfur Oxides
A. GENERAL
The sulfur oxides represent one category of
pollutants that affect plant life. Within this
category of pollutants, sulfur dioxide (SO2)
appears to be the major causal agent of plant
injury, although plants may respond to other
compounds of sulfur such as sulfuric acid
aerosols. In one of the earliest reports
concerning SO2 injury to plants, Stoeck-
hardt,1 in 1871, discussed smoke damage to
forest trees in Germany. Since this early
report, extensive experiments and observa-
tions of the effects of SO2 on vegetation have
been made by investigators in all parts of the
world. Thomas,2 >3 Brandt and Heck,4 Katz
and McCallum,5 and Daines,6 have written
reviews of these studies. Studies of the effects
of sulfur oxides upon vegetation need to be
continued if the manner in which sulfur
oxides cause plant injury is to be understood.
Plants vary greatly in their response to
SO2. This variation in response by plants is
due to their genetic composition, to their
response to environmental factors, individual-
ly and in combination, and to the time-
concentration relationship of SO2 by itself
and in combination with other atmospheric
pollutants. Variation in any one of the
complex of interacting factors will result in a
variation in plant response.
This document is not intended as a com-
plete, detailed literature review, and it does
not cite every published article relating to
effects of sulfur oxides in the ambient atmos-
phere upon vegetation. However, the litera-
ture, comprising more than 700 articles, has
been reviewed thoroughly for information
related to the development of criteria. The
document, based on both professional and
scientific judgment, not only summarizes the
current scientific knowledge of air pollution
effects by sulfur oxides upon vegetation, but
also points up the major deficiencies in that
knowledge.
B. SYMPTOMS OF THE EFFECTS OF
SULFUR DIOXIDE ON VEGETATION
The effects of SO2 upon plants can be
classified into two general categories: visible
effects and subtle effects. Visible effects are
identifiable pigmented or necrotic foliar
patterns that result from major physiological
disturbances to plant cells. Subtle effects are
those that are not visibly identifiable but
result in measurable growth or physiological
changes in the plant. Subtle effects are not
visibly identifiable and can be identified only
when measurable growth or physiological
changes occur in the plant. Both visible and
subtle effects are physiological effects and
result from the disturbance of biochemical
processes at the molecular level. Whether or
not the biochemical disturbances give rise to
visible symptoms determines the category to
which they are assigned.
1. Visible Effects
Visible effects to plants can be further
classified into acute and chronic injury. Acute
injury is severe injury that occurs within a few
hours after exposure and is characterized by
the collap»? of cells with the subsequent
development of necrotic patterns. It is as-
sociated with high, short-term SO2 concentra-
tions, although severe injury, similar to acute
injury, may develop from chronic exposures.
Chronic injury is light to severe injury that
developes from exposure over an extended
time period. It is associated with long-term
exposures where the pollutant concentration
is sufficiently high to produce some cell
destruction or disruption. It is identifiable by
chlorotic or other pigmented patterns and in
some instances is associated with necrotic
markings. Acute injury symptoms are general-
ly more characteristic of a specific pollutant
than those of chronic injury, which are not
necessarily specific for a particular toxic
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agent. Insects, nutrition, microbiotic diseases,
and other factors can produce leaf injury
patterns similar to those induced by SO2.
Foliar symptoms in plants have often
provided the first indication of a pollution
problem; however, since SO2 type symptoms
may result from other abiotic and/or biotic
influences, related evidence must be con-
sidered before attributing injury to SO2. The
related evidence should include a knowledge
of SO2 sources and observations showing
decreased injury levels with increasing distance
from the source. Monitoring of pollution
concentrations, consideration of meteoro-
logical conditions, and observation of several
plant species, especially when symptoms are
not characteristic, can also aid in the diagnosis
of injury. The use of field chambers from
which pollution has been removed may also
contribute to identifying the cause of injury.
Descriptions of SO2 injury are found in
numerous publications.2'3'6"9 These reports
also consider symptoms caused by other
pollutants and various biotic and environ-
mental stresses that may produce symptoms
resembling those caused by SO2. Summaries
of effects on a large number of plant species
susceptible to SO2 are given by Wood10 and
by Middleton and Taylor.11 Three pictorial
atlases document visual SO2 symptoms12"14
and include detailed descriptions of injury
with a listing of SO2 susceptible species.
a. Acute Injury
12.13
Acute symptoms of SO2 injury result from
the rapid absorption of toxic concentrations
of the gas. In broad-leaved plants, tissues in
sharply defined marginal and interveinal areas
take on a dull water-soaked appearance im-
mediately after exposure. These areas subse-
quently dry and may bleach to ivory or
become brown to reddish-brown in color. The
separation of injured areas from surrounding,
apparently healthy, tissue is usually distinct.
Injury seldom extends across leaf veins unless
the injury is severe.
The basic bleached and collapsed blotches
described on broad-leaved plants are, how-
ever, also typical of grass foliage. The final
bleached pattern between the parallel veins of
grass leaves gives a streaked effect.
Acute injury of conifers usually occurs in
bands on needle tips, with injured areas taking
on a red-brown color. Injured- areas change
from the usual dark green color to a lighter
green, and lesions develop yellow-brown and
finally red-brown coloration. In severe cases,
discoloration may involve the whole needle.
The affected trees usually cast their needles
prematurely.
b. Chronic Injury12 >13
Low concentrations of sulfur dioxide
require several days or weeks to cause the
development of the yellowing or chlorotic
symptoms of chronic injury. The chlorotic
effect, with varied color patterns, often
resembles premature senescence. Necrosis
may develop in some plants, resulting in white
bleached areas or red to brown coloration,
which may resemble acute injury. Chronic
injury may be followed by leaf abscission. A
large amount of sulfate is found in leaves with
chronic symptoms, whereas leaves that are
acutely injured show only a small increase in
sulfate content. However, large quantities of
sulfate may accumulate in leaf tissue without
visible leaf symptoms.15'16 Both acute and
chronic injury symptoms may develop upon
the same plant. The period of development
and the sensitivity of the plant to particular
sulfur dioxide concentrations are important in
differentiating the type of injury.
Chronic injury, when exhibited on plants
exposed to SO2, is due to either short-term
peaks or long-term average concentrations.
The general consensus of most investigators is
that short-term peaks are more important
than long-term averages.
2. Subtle Effects
Subtle effects, as a concept, implies that
SO2 can interfere with physiological and
biochemical processes and with plant growth
and yield without attendant development of
visible symptoms. The processes are mi-
croscopic or molecular in nature. Therefore,
in order to determine their existence, studies
have to be conducted that can detect whether
measureable changes in the rate of photo-
synthesis, in stomatal behavior, and in growth
or yield have occurred.
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3. Physiological Effects
Physiological effects include both visible
and subtle effects. Both types of effects result
from the disturbance of physiological
processes at the molecular level. Whether or
not the physiological changes give rise to
visible symptoms determines to which cate-
gory they are assigned.
a. Photosynthesis
Wislicenus17 indirectly related SO2 to
photosynthesis in demonstrating that the
sensitivity of spruce to SO2 was proportional
to light intensity. Thomas and Hill18 and
Katz9 reported that exposures of alfalfa to
high concentrations of SO2 for short time
periods resulted in a transitory reduction in
carbon dioxide (CO2) assimilation; recovery
began within an hour after treatment. In the
latter experiments,9 the CO2 suppression
response was recorded for about 2 days. Katz
and Lathe8 and Katz9 reported that SO2
concentrations of 262 to 524 jug/m3 (0.1 to
0.2 ppm) did not affect photosynthesis,
respiration, stomatal behavior, or growth but
that concentrations above 1048 jug/m3 (0.4
ppm) did affect sensitive plants, if the
stomata were open.
These results and the research of
others1 9 >2 ° indicate that the rate of photo-
synthesis is reduced soon after sensitive plants
are exposed to SO2. If visible injury does not
occur, the photosynthetic rate returns to
normal after exposure terminates, but if
injury results, complete recovery is not
attained. The magnitude of the photo-
synthetic response varies with respect to
pollutant concentrations, environmental
influences, and plant sensitivity.21"24
Recent information indicated that SO2 was
reduced to hydrogen sulfide (H2 S) by several
plant species during and after fumiga-
tion.25"27 This reaction may be associated
with photosynthesis, since the response was
obtained only in the presence of light.2 7
b. Stomatal Relationships
Stomata are the principal avenue of SO2
entrance into plant leaves. Conditions that
favor open stomata result in increased SO2
assimilation and increased plant sensi-
tivity.3'9'28 Majernik and Mansfield29'30
demonstrated a stimulation of stomatal open-
ing in bean plants when they were exposed to
SO2 at relative humidities above 40 percent
but a suppression of stomatal opening at a
relative humidity of 32 percent.
Katz9 found a slight reduction in the
number of open stomata after exposing alfalfa
to 2358 /ug/m3 (0.9 ppm) of SO2 and a
significant reduction after exposure to 2620
jug/m3 (1 ppm). Continuous fumigation at an
average concentration of 1050 /xg/m3 (0.4
ppm) did not influence stomatal opening until
acute injury symptoms developed. Vogl19
reported that stomata of pine remained open
after plants were injured. Neither of these
reports included humidity conditions.
Spedding31 presented information that
suggested that humidity influenced the as-
similation of SO2 when stomata were closed
and that SO2 also entered plant tissues
through the cuticle.
c. Changes in Chemical Composition
Sulfur dioxide exposures may result in
changes in the chemical composition of
plants. Materna3 2 found increases in sulfur
and potassium levels when spruce needles
were exposed in spring, but calcium and
magnesium levels were not affected. For
citrus leaves, calcium and potassium levels
decreased during winter exposures; however,
in the summer, calcium levels were not
affected and potassium content increased.33
Materna34 reported increases in the silicic
acid content of spruce needles injured by
SO2.
Arndt3 5 demonstrated increases in amino
acid concentrations of herbaceous plants after
exposure to 660 jug/m3 (0.25 ppm) SO2. The
amount of increase depended on specific
amino acids and plant species. In exposures
producing chronic injury, Boertitz2! reported
no significant change in pH, carbohydrate, or
amino acid content of extracts from spruce
needles; however, in more recent field studies
of the Ore Mountain area, he found increases
in the carbohydrate levels and pH values of
needle extracts.36
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Injury resulting from chronic SO2 exposure
can usually be confirmed by the presence of
high sulfur content in leaves, although varia-
tion in normal sulfur content must be
considered.7'37 In Japan,38 sulfur content of
citrus leaves correlated with atmospheric SO2
concentrations. Katz9 demonstrated that
sulfur content increased with time of
exposure. Under natural conditions, analysis
can reflect the degree of pollution to which
vegetation has been exposed. In some
industrial areas, McCool and Johnson39
found a decrease in sulfur content of vegeta-
tion with an increase in distance from the
SO2 source.
d. Growth and Yield Reductions
Growth and yield reductions may result in
the absence of visible injury. Tingey et a/.40
demonstrated reduced root weights of radish
when exposed to SO2 concentrations of 131
to 160 jug/rrf (0.05 to 0.06 ppm) for
40 hr/week for 5 weeks in greenhouse
exposure chambers; however, the second run
of the experiment did not produce the same
plant response. Other studies by Reinert et
al.41 showed reductions in several growth
parameters for Bel W3 tobacco when exposed
to 262 jug/m3 (0.1 ppm) SO2,8 hr/day, 5
days/week, for 4 weeks in greenhouse
exposure chambers. Bel W3 is a variety of
tobacco extremely sensitive to injury by SO2
and has been used as a plant monitor. Both of
the above studies were conducted under
conditions which would seldom, if ever, be
found in the ambient air. More studies are
needed to verify the results.
In ambient air studies, Bleasdale42
reported that growth of rye grass was reduced
when the maximum average SO2 concentra-
tions for 24 hours were between 262 and 524
jug/m3 (0.1 and 0.2 ppm) for 2 and 3 days
during experiments of 63 and 73 days. In this
study, interactions with pollutants other than
SO2 were not considered and may have
contributed to the observed growth response.
C. MECHANISM OF ACTION
The mechanism by which plants are injured
by SO2 is not understood. Transient physio-
logical effects, subtle growth reductions, and
acute injury symptoms may result from the
formation of sulfite ions and their effect on
membrane integrity. Acute injury does not
occur if the rate of SO2 absorption does not
exceed the capacity of the plant to oxidize
the sulfite to sulfate ions. Under long-term
SO2 stress, sulfates thus formed may ac-
cumulate with the subsequent development of
chronic injury symptoms.33
D. FACTORS AFFECTING RESPONSE OF
VEGETATION TO SULFUR DIOXIDE
The response of a given variety or species
of plants to a specific air pollutant cannot be
predetermined on the basis of the known
response of related plants to the same pol-
lutant. Neither can the response be pre-
determined by a given response of a plant to
similar doses of different pollutants. The
interplay of genetic susceptibility, growth
stage, and environmental influences must be
considered for each plant and pollutant. No
one factor may be considered independently
of the other factors.
1. Environmental Factors
a. Temperature
Plants are more resistant 1o SO2 at
temperatures below 40° F.43'47 Setterstrom
and Zimmerman43 reported that buckwheat
was equally susceptible to injury at 65° and
105°F. Several investigators9'48 have
reported greater resistance in conifers during
the winter and have related this to lower
physiological activity of plants. Resistance
may increase during winter dormancy with
low gas exchange rates; however, even at low
levels of physiological activity, conifers may
be injured, especially in areas with higher SO2
concentration during winter months. In ad-
dition, temperatures are often near 40° F
during winter seasons in many areas. Van
Haut and Stratmann13 indicated that conifers
remain sensitive during the winter when water
is available to them. In the spring, with
increases in physiological activity, sensitivity
to SO2 also increases. On the basis of studies
with Douglas fir and yellow pine, Katz9
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reported that in the spring, with increases in
physiological activity, sensitivity to SO2 also
increases. Exposures to SO2 at concentrations
of 1965 Mg/m3 (0.75 ppm) for 147 hours
near the end of the winter dormancy period
resulted in foliar injury of 55 percent; how-
ever, in early autumn this concentration was
applied for 334 hours without the develop-
ment of injury. For spruce, experiments have
demonstrated increased sensitivity in the
spring and autumn when compared with
summer and winter seasons.49
b. Humidity
Sensitivity to SO2 tends to increase with
increasing humidity.43^*5 Wells45 noted that
in the Salt Lake Valley 70 percent appeared
to be the critical humidity level. Above 70
percent, plants were much more susceptible
to injury by sulfur dioxide than below.
Swain44 concurred but stated that increases
in relative humidity (RH) from 70 to 100
percent did not result in much increase in
sensitivity. In 1-hour exposures at an average
concentration of 3537 jug/m3 (1.35 ppm)
SO2, Zimmerman and Crocker5 ° found that
variations between 50 and 75 percent RH had
little effect on plant sensitivity. Setterstrom
and Zimmerman43 concluded that for RH
values above 40 percent, differences of 20
percent RH are required to produce detect-
able differences in sensitivity; however, they
mention that O'Gara in an address before the
American Institute of Chemical Engineers
stated that plants were three times as sensitive
at an RH of 100 percent as at 30 percent.
Thomas and Hendricks28 reported a 90
percent loss in sensitivity when RH was
reduced from 100 to 0 percent. Generally,
resistance to injury by sulfur dioxide seems to
be associated with decreasing relative
humidity; however, variations associated with
a particular plant species or with environ-
mental conditions do exist.
Under conditions of high humidity, a
sulfuric acid mist may form. In fog,5 * >5 2 this
acid mist may cause leaf spotting on several
plant species.
c. Light
Setterstrom and Zimmerman43 reported
that buckwheat was more susceptible to
injury from SO2 when grown under condi-
tions of reduced light intensity. A 65 percent
reduction in light intensity (to approximately
3000 foot-candles) resulted in greater suscep-
tibility than that for plants grown in full
sunlight (approximately 10,000 to 12,000
foot-candles) or under conditions of 25 and
35 percent reduction in light intensity. Light
received prior to treatment affected sensitivity,
since plants kept in the dark for 2 hours
preceding SO2 exposure were more resistant
than comparable plants kept in the light.50
Plants are 5 to 6 times as resistant to SO2 in
the dark as in the light.13'45 Since stomata
of most plants are closed during darkness,
plants are more tolerant of SO2 in the
absence of light. In studies conducted at night
with exposure to 2227 jug/m3 (0.85 ppm) for
4 hours, foliar injury of alfalfa, tomato,
buckwheat, sweet clover, oats, rye, and barley
was not observed; however, injury resulted
during daylight exposures of 2096 Mg/m3
(0.8 ppm) of SO2 for periods of 1 or 2
hours.50 In experiments with bush beans,
SO2 exposures that produced moderate injury
during the day had no effect at night.13-53
However, when plants were exposed during
the day following a night exposure, injury was
greater than the single day exposure. The
reverse order also resulted in increased injury,
as did exposure under continuous light for 24
hours.
d. Edaphic Factors
Plants are more sensitive to SO2 when
adequate soil moisture is available for normal
plant growth. Minor variations in soil
moisture have no detectable effect on sensi-
tivity; however, when moisture content ap-
proaches the wilting point or if wilting occurs,
plant resistance increases.9 >4 3 >5 ° >5 4 Brandt
and Heck4 recommended withholding water
from greenhouse and irrigated crops during
periods of high pollution potential :>s a
preventative measure for reducing damage.
Investigations of the effect of soil nutrient
levels in relation to plant sensitivity have
involved comparisons of plants growing under
various nutritional or fertilization levels. Such
studies indicate an increased resistance with
increased fertilization in rape, spinach, and
radish.54 Varied results have been recorded
-------
for pine.55"57 In the Ore Mountains of
Czechoslovakia,34 nutrient applications
resulted in an increase in resistance to SO2 for
several tree species. In field and laboratory
experiments, Cotrufo and Berry58 found a
reduction in SO2 induced needle necrosis of
several white pine clones after fertilizer ap-
plications. In contrast, deficiencies of
nitrogen and sulfur were correlated with
increased resistance for tobacco and
tomato.59 With alfalfa,43 nutrient deficient
conditions increased sensitivity, but with oats,
increases in nitrogen and other nutrients v/ere
associated with increased sensitivity.54
Few studies have considered the influence
of soil structure, soil temperature, aeration,
and the biotic complex on plant sensitivity.
Brandt and Heck4 state that sensitivity is
reduced when plants are grown in heavy soils.
This may be the result of lower oxygen
tensions. In studies involving three plant
species and four soil types, Guderian60 found
that plant injury varied in respect to soil type,
•iitrogen application, and species of plant.
e. Diurnal Changes
The sensitivity of plants to SO2 may vary
during the day. Factors that favor open
stomata and photosynthesis also favor SO2
assimilation. Under these conditions, plants
are more sensitive during the morning than
during the afternoon. Thomas and
Hendricks28 concluded that on a cloudless
day exposure of alfalfa early in the morning
resulted in only slight injury, while exposure
later in the morning resulted in increased
injury; plants exposed between late morning
and mid-afternoon had decreased injury, with
the most rapid decrease later in the day.
Although climatic conditions and stomatal
movements are important factors in diurnal
injury patterns, decreases in sensitivity during
afternoon periods may be related to the
accumulation of carbohydrates in leaves13 '2 8
or to an increase in buffering capacity of
plant tissues.54
/ Interactions with OtherPollutants
Ambient air is composed of many different
pollutants. A few studies have considered this
fact, but most studies deal -with single pol-
lutant effects. The interaction of ozone (03)
with SO2 was first reported on Bel W3
tobacco by Menser and Heggestad.6* The
interaction of these air pollutants affecting
injury and growth in several other species has
been reported.62"64 Injury to six plant
species from the interaction of nitrogen
dioxide (NO2) and SO2 has recently been
reported.6 s Growth and injury results are
further discussed in Section J.2. The inter-
actions shown between SO2 and other pol-
lutants offers a partial explanation for oc-
casional inconsistencies between results
obtained in laboratory studies in which only
single pollutants were used and the results
obtained in the natural environment. For
example, growth reductions of radish oc-
curring after exposures to mixtures of
SO2/O3 were greater than reductions from
SO2 alone.
2. Genetic Factors
Plant sensitivity to SO2 can be considered
as a function of morphological and bio-
chemical characteristics controlled by the
genetic plasticity of the plants within a
population. Thus, some plants are more sensi-
tive than others to pollution stress. Both
inter- and intraspecific differences in sensi-
tivity occur. For example, sensitivity varia-
tions within species have been demonstrated
with spruce66 and white pine.6'7 In this
regard, SO2 acts as a selection pressure
mechanism. The more resistant variants
within a species continue normal growth and
existence, but under this SO2 pressure, the
more sensitive types weaken and may not
survive within the polluted area.
Shapiro, Servis, and Welcher,68 based on
experiments conducted with isolated DNA
and bacteria, using sodium bisulfite, have
suggested that SO2 in the atmosphere may
constitute a genetic hazard. At present, how-
ever, there is no basis for extrapolating from
such experiments to living organisms that are
structurally and functionally more complex.
3. Stage of Development
The growth stage or phase of development
at which plants are exposed to SO2 affects
-------
their susceptibility and the yield losses asso-
ciated with injury. Wells69 reported that
barley yields were slightly reduced by SO2
exposures when plants were from 10 to 60 cm
high, but that yields were reduced by 20 to
30 percent if plants were exposed during early
grain development. For wheat, Brisley and
Jones7 ° demonstrated greater yield reduc-
tions with exposure in the early stages of
growth than in later stages. Thomas71 demon-
strated that injury to cereals at tillering could
be sustained with little loss in yield, but that
yield was reduced much more by injury after
culms had formed. In several plant species,
van Haut5 3 reported a "critical development
stage" in which there was a high probability
that leaf injury would result in reduced yield.
This critical stage occurred with bean shortly
before flowering and during pod growth; with
radish, at'the young seedling stage and again
as the roots began to increase in size; and with
oats just before panicle emergence, at flower-
ing, and during flower opening.
The leaves of most plants are more sensitive
to SO2 just after maximum expansion has
occurred. Developing and older leaves tend to
be more resistant.7 >4 3 >5 3 Variation in suscep-
tibility between species has been observed.
Van Haut5 3 found that needles of pine and
larch are very sensitive to SO2 before growth
has been completed.
E. PROBLEMS OF DIAGNOSIS AND
ASSESSMENT OF THE ECONOMIC
IMPACT OF SULFUR DIOXIDE
The plant is a product of its environment.
Every environmental factor, favorable or un-
favorable, produces a response in the .plant.
Sulfur dioxide interacts with other environ-
mental factors such as the climate, soil, biota
(insects, man, and microorganisms), and the
genetic constitution of the plant to produce
responses within the plant. Injury produced
by SO2 may not only be modified or ob-
scured by these other environmental factors,
but the plant may develop injuries from these
other factors that are difficult or impossible
to distinguish from those caused by SO2.
Ornamental and agronomic crops grown
under special management practices must be
carefully examined before attributing poor
growth to SO2. Many bacterial, viral, and
fungal diseases, as well as insect infestation,
can produce symptoms in plants that are
quite similar to those produced by SO2. To
aid in making definitive diagnoses of SO2
effects upon vegetation, injuries must be
observed in the field and supported by labora-
tory studies using different levels of the
pollutant. Laboratory and field chamber
studies are essential if qualitative and quanti-
tative models of pollutant effects upon
vegetation are to be developed. Since it is
impossible to include all parameters, labora-
tory and field chamber studies do not
simulate ambient field conditions.
The question that must be answered in the
assessment of SO2 damage to plants is
whether or not the plant has been so altered
by the pollutant as to significantly influence
its growth, survival, yield, or use. In cases
where leaf injury impairs the use of the plant
for food, as in the case of cabbage or lettuce,
or for ornamental purposes, assessment is
relatively straightforward. However, where
the marketable product is not influenced by
appearance, assessment of economic damage
is more difficult. Hill and Thomas72 showed
that the yield of alfalfa was reduced in
proportion to the area of the leaf destroyed.
The economic impact of leaf injury to fruit
trees is extremely difficult to assess because
the effect upon the fruit is not known.
In discussing the effect of air pollution on
vegetation, Guderian, van Haut, and Strat-
mann7 3 have suggested a method of making
the distinction between the terms injury and
damage in cases where the effects of air
pollution on vegetation is concerned. Ac-
cordingly, injury is defined as any identifiable
and measurable response of a plant to air
pollution. Damage resulting from air pollution
injury is defined as any identifiable and
measureable adverse effect upon the desired
or intended use of a plant or of a product
derived from the plant. Thus, in using these
terms, leaf necrosis of alfalfa is a symptom of
injury; however, any assessment of damage
requires a judgment that the injury affects the
yield or use of the plant.
There are instances, also, where the esthetic
or sentimental value of the plants is impaired
-------
by SO2. Examples of these are the vegetation
growing on a hillside and a tree planted by a
particular college or university class as a
memoir of their college days. In the first
instance, leaf damage or the death of the
plants detracts from the view. In the second,
the tree is largely of sentimental value, and its
demise is extremely difficult to assess in
dollars and cents.
F. EFFECTS OF LOWER ORGANISMS
The effects of SO2 on nonvascular plants
and on plant pathogens have been studied by
many investigators. The majority of these
studies have considered the incidence of
specific organisms within areas influenced by
SO2 emissions. The absence of species of
lichens and bryophytes has been correlated
with the presence of low concentrations of
SO2-74"79 Lichens have been used in the
recognition and monitoring of SO2,80"82 and
qualitative scales for estimating SO2 con-
centrations have been developed on the basis
of sensitivity differences among species.
Skye83 found that the diversity of species
was reduced in areas with an annual SO2
concentration of approximately 39.3 jug/m3
(0.015 ppm) (determinations were averaged
over 4-week periods). Gilbert74 found that
several species of bryophytes and lichens
disappeared when winter averages (October-
April) exceeded 52 ng/m3 (0.02 ppm). In a
lichen transplant study, death of the test
species occurred within 29 days at locations
with the highest average SO2 concentrations.
The SO2 concentration, determined inter-
mittently, averaged 230 Mg/m3 (0.087
ppm).84
The extreme sensitivity of lichens to SO2
appears to be due to the breakdown of the
algal component. Rao and LeBlanc85 have
shown that SO2 absorption by lichens causes
the decomposition of chlorophyll a to
phaeophytin a. Experimentally, chlorophyll
breakdown occurred when the lichens were
exposed to concentrations of 13,100 Mg/m3
(5 ppm) for 24 hours.
The importance of long-term average con-
centrations versus many shorter terms of
higher concentrations on the reaction in
lichen populations awaits critical study.
The effects of SO2 have also been inves-
tigated in relation to the occurrence of
various biotic plant diseases. Koeck86
observed the absence of mildew on oak in
areas near SO2 sources, while the disease was
widespread in areas distant from these
sources. Scheffer and Hedgcock87 observed
that the incidence of several rust and other
fungal diseases was low in areas influenced by
SO2, but root rot caused by Armillaria mellea
and bark beetle infestations were more
prevalent on declining trees affected by SO2.
This relationship is characteristic of these
secondary pathogens. For soil pathogens,
population increases may be related to in-
creases in soil acidity in addition to the
presence of more susceptible hosts.88
Saunders8 9 demonstrated that SO2 reduced
the incidence and severity of the fungus
Diplocarpon rosae, causing blackspot of roses.
Results from field studies suggested that
average daily concentrations above 105 Mg/m3
(0.04 ppm) SO2 nearly eliminated the black-
spot disease.
In sample areas near a Sudbury, Ontario,
smelter complex, Linzon90 noted that fewer
white pine trees were affected by blister rust,
heart rot, and insect infestation. In contrast,
the occurrence of bark abnormalities was
higher on white pine near the smelter
complex than in other research areas. These
abnormalities consisted of a rough bark or
canker condition and a purple bark condition
that appeared as an unnaturally purplish
color.
In southern Poland,91 acidification of tree
bark was correlated with air pollution by
SO2. The relationship of this phenomenon to
the growth and development of bark
organisms has not been studied.
In severely injured conifer stands,
Boesener9 2 found higher populations of bark
breeding insects than in stands that exhibited
lower amounts of injury. Boesener indicated
that the high insect populations accelerated
tree decline. In another insect population
study, Przybylski93 observed increases in
aphid populations in areas near an SO2
source. He concluded that this increase may
be related to reductions in aphid predators.
8
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G. ACID PRECIPITATION
The oxidation and the solution of SO2 in
water has increased the acidity of precipita-
tion in several areas of the world. Based on
pH values dating from 1955, Oden94 reported
an increase in acidity of precipitation over a
12-year period in Sweden. The lowest single
value, a pH of 2.8, was recorded in 1967. A
similar trend has been reported in the north-
eastern United States. Within this region, the
lowest annual average pH of 4.03 was
recorded at the Hubbard Brook Experimental
Forest, New Hampshire.95 At Hubbard
Brook, the lowest single pH was 3.0. Such
trends have been related to SO2 and to some
extent to oxides of nitrogen (NOX) emissions
from industrial complexes within these areas.
In addition, particulate matter emitted from
combustion processes also contributes to in-
creased acidity.96'97
Values associated with nonindustrialized
areas are also lower than the neutral pH of
7.0, but these values are related to the
conversion of normal atmospheric CO2 to
carbonic acid rather than to the stronger acids
resulting from reactions with SO2. In these
nonindustrial areas, pH values between 4.9
and6.898'101 have been recorded.
The acidic precipitation has resulted in
increased acidity of soils, rivers, and
lakes.7 ,7! ,94,! °2 Several researchers have
related increased soil and water acidification
to ground level concentrations of
SO2.7'102'103 Increases in soil acidity can
affect the availability of plant nutrients and
change the species composition of soil micro-
organisms, with possible concomitant reduc-
tions in the rates of mineralization and
decomposition processes.94'104'105 Changes
in these processes can affect the growth and
development of higher plants. Although soil
acidification did not appear to affect de-
composition processes in an arid indus-
trialized region of Czechoslovakia, the
number of aerobic bacteria and actinomycetes
was reduced in research plots near the pol-
lutant source, while increases in fungal
populations were recorded.79 Fungi are more
tolerant of acidic conditions.
Oden94 indicated that effects on plant
growth are related to the content of basic
compounds in the soil. In this regard, soils of
basic composition, such as arable soils, are
more resistant to pH change. Calculations
have revealed that acidification of these soils
will require a time period of 125 to 1000
years. This period could increase with
weathering and application of lime to soils.
For forest soils, which tend to be more acidic,
this time period is only 30 to 50 years. Sandy
soils are affected most by the acidification
reaction; whereas, soils of limestone and
basalts are affected least because weathering
of these materials effectively neutralizes the
acidic effect.
Conclusive evidence involving the effect of
soil acidification on forest productivity has
not been presented; however, several reports
have described possible influences.105 In
Norway and Sweden, the amount of calcium
in upper soil zones was related to forest
productivity. This relation was based on the
conversion of calcium carbonate (CaCO3) to a
more soluble calcium sulfate (CaSO^) com-
pound by the action of sulfuric acid (.I2SO4)
from precipitation. Compounds of calcium
were then removed from the soil by leaching
and run-off. Growth effects were estimated
from the relationships of acid deposition to
calcium removal and the effect of reduced
quantities of calcium on forest growth. Based
on this information, an annual decrease in
growth of about 1 percent per year was
determined.
Other investigations in Sweden have
compared tree growth in areas affected by
acidification with relatively unaffected
regions. Comparisons of the two areas
indicated that tree growth was reduced in
affected areas. In this case, the annual growth
reduction amounted to approximately 0.3
percent per year. If the 1965 to 1970 levels of
sulfur emissions remain constant, a reduction
in forest growth of between 10 and 15 percent
has been estimated for the year 2000. * °5
The effect of acidic precipitation on
herbaceous plants has also been studied.
Cohen and Ruston106 demonstrated reduc-
tions in the growth of timothy grown in pots
when plants were irrigated with acid rain and
H2SO4 solutions at concentrations between
10 and 320 ppm. This was within the range of
normal acidity levels of 5 to 100 ppm H2SO4 .
-------
Leaching of nutrients from plant foliage
has also been associated with the increased
acidity of precipitation. In the Ore
Mountains, Materna107 found that sulfur in
precipitation contributed 39 kg sulfur per
hectare (ha) per year to soil of an open area,
whereas soil under a forest canopy received
133 kg/ha-yr. With leaf fall, an additional 10
to 20 kg/ha-yr was supplied. In addition to
increases in soil acidity, leaching from plant
foilage may contribute to reductions in plant
nutrients, decreases in growth, and changes in
foliar microflora.
The effect of increasing acidic precipitation
in the northeastern United States on vegeta-
tion, streams, and the soil has not been
adequately studied.
H. MISCELLANEOUS ASPECTS OF
SULFUR DIOXIDE EFFECTS ON
VEGETATION
Although the aspects discussed in this
section do not impinge directly on air quality
standards, they should be considered in any
control activity. These include possible usage
of vegetation as a sink for SO2 and the effects
of sulfuric acid aerosols.
1. Vegetation as a Sulfur Dioxide Sink
The maintenance of protective vegetational
areas, or green belts, near industrial
complexes has been a recent topic in urban
and regional planning.1 ° 8 >* ° 9 The concept of
SO2 removal by vegetation results from as-
similation of SO2 by plant foliage and the
deflection of polluted air masses above vegeta-
tional areas.108'110 Martin and Barber's110
studies demonstrated a maximum SO2 reduc-
tion of 157 jug/m3-hr (0.06 ppm/hr) by
hawthorne hedge. Variations in uptake were
associated with the physiological activity of
the plants and the environmental conditions
affecting the plants. In areas containing a
large number of emission sources, Wentzel1 ° 9
indicated that vegetation belts offered only
limited protection. Lampadius111 found only
slight differences in SO2 concentrations
within forest stands, forest edges, and clear-
ings. He concluded that removal of SO2 by
forest vegetation was of minor importance.
Although vegetation may reduce the level of
SO2 in some instances, there is no evidence
that it will have a major impact on ambient
SO2 concentrations.
2. Effects of Sulfuric Acid Mist
on Vegetation
Thomas, Hendricks, and Hill5 2 discussed
experiments in which plants were treated with
sulfuric acid aerosols at concentrations of
78,600 to 170,300 Mg/m3 (30 to 65 ppm).
Sulfuric acid droplets settled' on dry leaves
without causing injury, but when the leaf
surface was wet, a spotted type of injury
developed. Middleton, Darley, and Brewer51
and Thomas, Hendricks, and Hill5 2 reported
that this type of injury occurred in the Los
Angeles area during periods of heavy air
pollution accompanied by fog when the
surface of the leaf may be wet. Injury may
also occur in the absence of fog near combus-
tion effluents containing sulfur oxides when
the dew point of the gas effluent results in
acid droplet formation.
The sequence of symptom development is
one in which the exposed surface, usually the
upper surface, shows the initial necrosis. The
pH of moisture on the leaf surface may be less
than 3.0. Cellular collapse and many small
spots develop progressively through the upper
epidermis, mesophyll, and lower epidermis of
the leaf, leaving scorched areas. No glazing or
bleaching accompanies this injury, and leaf
areas covered by exposed leaves show no
marking. In the Los Angeles area, injury of
Swiss chard and beets was more nearly
typical of all plant species examined. Alfalfa
also developed a spotted injury pattern.
Spinach, being more uniformly wetted by fog,
developed a more diffuse type' of injury.
1. EFFECTS ON BIOMASS AND YIELD
Although evidence has been presented (Sec-
tion B.3.d) that shows a growth reduction in
the absence of visible injury, the early litera-
ture supports the view that visible injury is
closely correlated with yield and/or growth
reductions. Thomas3 and Katz9 concluded
that growth effects do not occur until at least
10
-------
5 percent of the foliage is visibly injured.
Yield reduction from acute SO2 injury was
found to be equivalent to the removal of the
same amount of leaf tissue. Light to moderate
defoliation of cotton from SO2 exposure had
no detrimental effect on fiber grade, staple
length, or ginning percentage.112
Guderian113 found that the order of sensi-
tivity, as determined by leaf necrosis and
yield, was often different when comparing
several grass and forage species and native
plants common to open fields. For example,
based on leaf necrosis, alfalfa ranked high
with regard to sensitivity; however, when
yield was considered, this plant ranked in the
resistant category. Guderian and Strat-
mann114 J11 s found that growth and yield of
potato were progressively reduced with in-
creased pollution intensity. In addition, seed
tubers "obtained from heavily polluted areas
gave significantly lower yields in the following
year than tubers of the same weight obtained
from crops grown in control areas.
Guderian113 reported changes in the com-
position of plant societies after exposure to
SO2.
Many studies have shown that the reduc-
tion in crop yield from exposure to S02 is
proportional to the percentage of leaf area
destroyed.8>6 9,70,72,116 "j^is relationship is
adequately expressed in the equation:
y - a - bx
(5-1)
where: y = yield expressed as percentage
of control
a - a constant, approximately 100
percent
b = slope of yield/leaf-destruction
curve
x = percentage of leaf area de-
stroyed
Hill and Thomas7 2 exposed field alfalfa plots
to 2620 to 13,100 Mg/m3 (1 to 5 ppm) of
SO2 for a single exposure or multiple
exposures of 1 to 2 hours during the growth
of the crop. The equations developed show:
1. Single fumigation at early, medium, or
late stage, representing either 25, 50,
or 80 percent of the growth period of
crop:
>> = 99.5 -0.30.x
n =96
r = 0.64 ±0.06
Sy = 7.4 percent
(5-2)
2. Double fumigation at early and
medium, early and late, or medium
and late stages in the growth of the
crop:
y = 95.5-0.49.x
n = 34
r = 0.79 ±0.07
= 8.2 percent
(5-3)
3. Triple fumigation at early, medium,
and late stages in the growth of the
crop:
y =96.6-0.75*
n =12 (5-4)
r = 0.98 ±0.014
Sy- 4.1 percent
where: n = number of plots fumigated
r = correlation coefficient
Sy = standard deviation of individ-
ual yields from the regression
line
Similar results were obtained by clipping a
percentage of leaf tissue equal to that
damaged by SO2 from a group of test
plants.72 An equation similar to that above
was developed for alfalfa using exposures of 1
to 600 hours and from 262 to 7860
(0.1 to 3 ppm) of SO,-28
y = 99 - 0.37*
n = 103
r = 0.48
= 8.8 percent
(5-5)
Results from barley,69 wheat,70 and cot-
ton1 16 studies differ from alfalfa in that the
production of grain and cotton is a measure
of the yield and not of the vegetative growth.
The stage of development of the plant when
leaf destruction occurs is very important, with
the most important stage of growth being
near the time of blossom and fruit develop-
ment. Examples for barley,6 9 using Equation
5-1, show:
11
-------
1. Early stage, less than 25 cm in height:
y = 98 - 0.06*
n = 18 (5-
r=0.13
Sy = l2.2 percent
2. Heading out stage:
y = 98 - 0.40*
« = 60
A-= 0.74
•S = 10.2 percent
(5-7)
Data from experiments dealing with other
crops were used in the same basic equation
(5-1). Controlled additions of SO2 in these
field experiments have shown correlations
between visible leaf injury and the ultimate
crop yield.
The most comprehensive growth-yield
experiments conducted in the vicinity of an
SO2 source were carried out in Biersdorf,
Germany.114*115,117,118 A wide variety of
plants, including cereals, vegetables, trees,
forage and fruit crops, were studied at five
locations at differing distances from a single
pollution source (Table 5-1).! 14 >'15 >l 18 The
tests were run over the 7-month growing
seasons of 1959 to 1960. Foliar symptoms
were observed at all locations, and growth and
yield reductions were determined by compar-
ison with a control site free of SO2. A review
of maximum SO2 concentrations and the
percent of time that measureable SO2 levels
existed suggests that many short-term high-
concentration episodes were responsible for
the injury and growth reductions that oc-
curred. The 30-minute averages are indicative
of the highest values that might produce an
effect in the time period used.
Growth suppression and injury develop-
ment of white pines were reported by
Linzon90,119 based on data from field plots
that were located up to a distance of 25 miles
from a smelter complex near Sudbury,
Ontario, Canada. Results from this forest
ecosystem study are shown in Table
5-2.''9 >' 20 Average SO2 concentrations over
a 10-year period for 6-month growing seasons
are shown for each of three experimental
locations. The frequency of 30-minute
average concentrations above three values are
shown to provide an indication of the
maximum concentrations that might produce
injury and growth effects. The net change in
tree volume is used as the measure of growth.
Linzon90 noted that persistent high con-
centrations of SO2 produced certain well
defined growth effects on white pine. How-
ever, there was a sharp improvement in the
growth of white pine when SO2 levels
dropped below 655 Mg/m3 (0.25 ppm).
In a comprehensive study of the smelter at
Trail, British Columbia, the growth of
Douglas fir, yellow pine, and lodgepole pine
was adversely affected for a distance of 12 to
18 miles from the smelter.9 Daessler,
Kaestner, and Ranft121 have presented
evidence showing growth reductions for
several conifer and deciduous tree species
growing near a zinc smelter. Chlorotic dwarf
of white pine has been studied in the United
States,122 but few investigators have con-
sidered growth effect on other tree species. In
Germany, the growth of European beech and
larch was reduced in areas influenced by SO2
emissions.13
Growth suppression in the absence of foliar
injury (Section B.3.d) for ambient air
exposures42 and for controlled greenhouse
exposures
4 0 ,4 1
are presented in Table 5-3.
Reduced growth of several plants exposed in
field chambers to know^1 concentrations of
SO2 over specific time pe/iods are also shown
in Table 5-3.113
The results from tobacco at 262 Mg/m3
(0.1 ppm)SO2 and radish at 131 Mg/m3 (0.05
ppm) SO2 showed a reduction in certain
growth parameters for these two species when
grown under conditions of maximum sensi-
tivity to SO2. The conditions under which
these results were obtained would probably
never be duplicated under ambient condi-
tions. These controlled studies were well
conceived and reflect the best growth data
available from more recent studies.
]. DOSE-INJURY RELATIONSHIP OF
SULFUR DIOXIDE TO VEGETATION
RESPONSE
The interrelations of time and concentra-
tion (dose) as they affect injury to plants are
12
-------
Table 5-1. SULFUR DIOXIDE CONCENTRATIONS AND ASSOCIATED
VEGETATIONAL EFFECTS IN RESEARCH AREAS AT BIERSDORF,
GERMANY
Average
concentration,3
Mg/m3 (ppm)
7959 7960
338(0.129) 388(0.145)
183(0.070) 272(0.104)
Maximum
concentration,''
Jjg/m3 (ppm)
7959 7960
14,148(5.4) 17,292(6.6)
9432(3.6) 17,030(6.5)
Species
Wheat, rye, oats
Rape, alfalfa,
red clover
Potato, beet,
spinach
Tomato, carrot
Wheat, rye, oats
Rape
Alfalfa, red clover
Effects0
1
1,2
1,2
1
1
2
1,2
Potato, beets,
spinach
Carrot
Apple, sweet cherry,
plum, current,
1,2
123(0.047) 134(0.051)
45(0.017) 66(0.025)
37(0.014) 26(0.010)
gooseberry
Pedunculate oak, red
beech, larch
6288(2.4) 5764(2.2) Wheat, rye, oats
Rape
Potato, beet
Alfalfa, red clover
Spinach
Apple, current,
gooseberry
Sweet cherry, plum
Current
Pedunculate oak, red
beech, spruce, larch
3406(1.3) 4978(1.9) Winter wheat
Potato
Spinach
Apple
Current
Gooseberry
Pedunculate oak, red
beech, spruce, larch
2096 (0.8) 4454 ( 1 .7) Spinach
Gooseberry
1,2
3
1
2
1
1,2
2
1,2
3
1,3
3
1
1
2
2
1,3
1,2;
3
2
1,3
,3
,3
,3
"Average concentrations for 7-month growing season (4/1-10/31) determined by multiplying the percent of time
that measurable concentrations were found by average concentrations during this tune period Values reflect re-
sults from five stations radiating from a single source.
''Maximum concentrations bated on 30-mmute averages
'Plant responses based on 1959 and 1960 growing season
I * Reduction in yield
2 * Reduction in quality
3 • Reduction in growth (shoot height, diameter of stem, and/or foliage dry weight).
13
-------
Table 5-2. CHANGES IN NET TREE VOLUME OF EASTERN WHITE PINE
ASSOCIATED WITH SULFUR DIOXIDE CONCENTRATIONS
NEAR A SMELTER COMPLEX IN SUDBURY, CANADA
Average
concentration,3
Mg/m3 (ppm)
Concentration
frequencies, percent'3
655Mg/m3 1310/xg/m3 2620
(0.25 ppm) (0.50 ppm) (1.0 ppm)
Net average annual gain or
loss in total tree volume0
118(0.045)
45(0.017)
21 (0.008)
5.92
0.98
0.33
2.36
0.11
0.01
0.38
0.01
0.00
Tree volume reduced 1 .3% over
10-yr period.
Tree volume reduced 0.6%
over 10-yr period.
Tree volume increased 1 .6%
over 10-yr period^
aAverage concentrations for 6-month growing season (5/1-10/31) over a 10-year period (1954-1963). Values are
from three stations radiating from a group of three major S02 sources.
^Concentration frequencies based on the percentage of 1 /2-hour average concentrations above the respective SC>2
values over the 10-year period.
cWhite pine sampling areas were located several miles from the air monitoring sites, but were within the same con-
centration isopleths.
^Increases in tree volume were measured at white pine sampling areas located near the SC>2 monitoring station far-
thest from the three sources.
essential elements of air quality criteria. There
are insufficient data in the literature to
develop equations capable of defining effects
of chronic injury, or the reduction of growth,
yield, or quality of plant material. There have
been several attempts to develop rational
models to express time-concentration-
response results of plants to acute exposures
from SO2 • Several empirical relationships
have been proposed that give some insight as
to what may happen under a given set of
circumstances.
1. Mathematical Equations
The first dose-response relationship for
SO2 was developed by O'Gara123 under
growth conditions that produced maximum
sensitivity in the plant studied. The equation
was developed from exposures of alfalfa over
a relatively short period of time with the
production of acute injury. Thomas and
Hill124 modified the O'Gara equation for
alfalfa, but the generalized equation can be
shown as:
t(c - a) = ,
(5-8)
where: t -
c =
a =
time, hours
concentration of pollutant
when it is above the threshold,
ppm
threshold concentration below
which no injury occurs regard-
less of length of exposures,
ppm
b - constant
The parameters a and b are dependent on the
species and variety of plant and the degree of
injury. The equation can be rearranged to:
c =-r
(5-9)
The plot of c versus \jt is a straight line. The
parameter a is the intercept for \/t = 0, or
14
-------
Species
Table 53. GROWTH REDUCTION IN VEGETATION EXPOSED TO SULFUR
DIOXIDE FOR LONG AND SHORT TIME PERIODS
Concentration3 Exposure Refer-
3 (ppm) time Effect Conditions ence
Tobacco
(Nicotiana tabacum L.
"BelW3")
Radish
(Raphanus sativus L.
"Cherry Bell")
Ryegrass
(Lolium perenne L.
"Aberystwyth S23")
Timothy
(Phleum pratense L.)
262 (0.1) 8hr/day,
5 days/wk,
(4 wks)
131 (0.05) 8hr/day,
5 days/wk,
(5 wks)
<262 «0.1)b 63 days
<262 (<0.1)c 77 days
2489 (0.95) 8 hr
Alsike clover
(Trifolium hybridum L.) 2489 (0.95) 8 hr
Crimson clover
(Trifolium incarnatum L.) 2489 (0.95) 8 hr
Red clover
(Trifolium pratense L.)
2489 (0.95) 12hr
Italian rye
(Lolium multiflorum Lmk.) 2489
(0.95) 12hr
Mixtures of:
T. pratense
and
L. multiflorum
Vetch (Vicia saliva L. and
V.faba L.), pea (Pisum
arvense L.) and lupine
(Lupinus lentens L.)
2489 (0.95) 12hr
996 (0.38) 48 hr
Reduced Greenhouse 41
growth exposure
chambers
Reduced Greenhouse 40
growth exposure
chambers
Reduced Ambient 42
growth air
greenhouse
Reduced 42
growth
Reduced Field 113
growth exposure
chambers
Reduced Field 113
growth exposure
chambers
Reduced Field 113
growth exposure
chambers
Reduced Field 113
growth exposure
chambers
Reduced Field 113
growth exposure
chambers
Reduced Field 113
growth exposure
Growth chambers
not
affected
Reduced Field 113
growth exposure
for all chambers
species
a Average concentrations over the reported time periods. Inaccuracies associated with instrumentation result in
deviations as great as ± 10 percent.
b Except 2 days at concentrations of 262 to 524 M8/m^ (0-1 to 0.2 ppm).
c Except 3 days at concentrations of 262 to 524/ug/m3 (0.1 to 0.2 ppm).
15
-------
when t is infinitely large. Thus a could be
considered the threshold concentration for
injury.
The O'Gara equation (5-8) could also be
written:
t = b
\
c - a
(5-10)
Zahn125 proposed a function that he sug-
gested would fit experimental data over
longer time periods better than the O'Gara
equation. The equation expressed in the same
form as Equation 5-10 above is:
Q.SC
c (c - a}
(5-11)
The threshold value a was given as 0.1 for
alfalfa; b was called a dimensional resistance
factor that incorporates the influence of
environmental conditions. Comparing the
three equations (5-8, 5-10, 5-11), the time
required for threshold injury for alfalfa at an
SO2 concentration of 1048 Mg/m3 (0.4 ppm)
would be 13, 6, or 10 hours. At higher
concentrations of SO2, there are only minor
differences of time.
Guderian, van Haut, and Stratmann73
recognized that the O'Gara equation did not
give the best fit to their observations for
either short- or long-term exposures. This led
to the development of an exponential equa-
tion of the form:
= Ke
-b(c-a)
(5-12)
where: t
K
e
b
c -
a =
time, hours
vegetation lifetime, hours
base of the natural logarithm
biological complex factor
(which includes the influences
of environmental factors)
concentration of pollutant
when it is above the threshold,
ppm
injury threshold, ppm
These parameters vary with species, environ-
mental conditions, and degree of injury.
In the midtime ranges of 0.5 to 12 hours,
all of the equations fit the available data
reasonably well; however, the exponential
form (Equation 5-12) fits over a wider range
of time. These equations relate a given time
and concentration to a specific percentage of
injury. They have been developed using
experimental data from a limited number of
plant species.
These two-dimensional models are limited
in their application since they do not in-
corporate the relationships of the many
factors that affect plant response to SO2. A
multivariate model is needed if these relation-
ships are to be considered. Wolozin and
Landau126 proposed a nonlinear function
incorporating all relevant factors that affect a
plant's response. They suggest that in any
multivariate analysis the following factors be
considered: differing SO2 levels, duration and
frequency of such levels, relative humidity,
temperature, diurnal pattern of SO2 con-
centrations, species of plant, and stage of
plant growth.
2. Dose-Injury Data
Since useful mathematical models are not
available, an extensive summary of time-
concentration-response data found in the
literature is necessary. A discussion of growth
effects was presented in Section I, and the
data were summarized in Tables 5-1, 5-2, and
5-3. This section will be limited to a
discussion of acute effects that occur over a
relatively short time span, results of field
exposures where identifiable injury is present,
and results of experiments utilizing mixtures
of pollutants. In most cases (except Table 5-7,
which shows the response of white pine and
radish to low mixture concentrations over a
period of several weeks), the responses noted
are the result of acute exposures to the
toxicant in question.
A study comparing spruce forests in a high
and in a medium pollution area was
conducted in Czechoslovakia.4 6 Results are in
terms of a relative determination of foliar
injury to spruce. Four-month growing season
averages and 30-minute maximum concentra-
tions of SO2 are reported. Although the
injury results, presented in Table 5-4, are not
easily quantified, the injury observed was of
the acute type. Materna, Jirgle, and Kucera46
16
-------
Table 54. SEASONAL AVERAGE SULFUR DIOXIDE CONCENTRATIONS
ASSOCIATED WITH FOLIAR INJURY TO SPRUCE
IN TWO LOCATIONS IN CZECHOSLOVAKIA
Average
concentrations,3 >
Mg/m3 (ppm)
Maximum
concentrations,'3 >c
3 (ppm)
Foliar injury
68 (0.026)
943 (0.36)
Severe
47(0.018)
812(0.31)
Moderate
a Average concentrations for 4 months of the growing season (6/1/66 - 9/30/66) determined from day and night
monthly averages.
bMonitoring instruments functioned with an error less than 10 percent only when concentrations were above
150Mg/m3.
c Maximum concentrations based on highest 30-minute average.
state that their monitoring instruments
functioned with an error less than 10 percent
only when concentrations were above 150
Mg/rn3.
Many experiments have related time and
concentration to a response in plants sensitive
to SO2. It is reasonable that experiments and
field observations relating to short-time acute
threshold responses be reviewed for inclusion
in a table of plant responses. Results from
three investigations are shown in Table
5.5 70,127,128 The resuits Of tne white pine
study127 are included because they report
effects at much lower concentrations than
noted before. It should be noted that the
procedures followed in making the plant
grafts and the measurement techniques used
make the results in the reference of question-
able value.12 7
Table 5-6 lists agricultural and forest
species growing in the area of Sudbury,
Ontario, Canada.129 Shown are the minimal
average concentrations for which injury was
observed after exposures of 1, 2, 4, and 8
hours. These field observations relate to the
total pollution load over the 8-hour averaging
period. The average injury was 10 percent on
the leaves affected.12 9
The interaction of SO2 with other pol-
lutants was briefly discussed in Section D. 1 .f.
Only interactions between SO2 and 03 and
SO2 and NO2 have been studied. These
results, presented in Table 5-7,40'6 1"6S are
not based on extensive studies but are
preliminary. They point out some conflicting
reports, which need in-depth study. It is
apparent that, under certain conditions and
with given levels of gases in the gas mixtures,
some plants can be more severely affected
than by individual pollutants. However, there
are cases where plants are apparently
protected by pollutant mixtures. Neverthe-
less, the potential for damage at low concen-
trations of pollutant mixtures exists.
Using the threshold concentrations from
Tables 5-5, 5-6, and 5-7 and information
involving effects that relate time and
concentration over short time periods,
projected SO2 concentrations causing injury
to three susceptible groupings of plants were
developed (Table 5-8). This table was taken
with minor changes from Heggestad and
Heck.130 Table 5-9 gives a complete list of
plants that have been studied in relation to
SO2. The plants in Table 5-9 are categorized
using the sensitivity scale used in Table 5-8.
Within each susceptibility grouping, the plants
are listed alphabetically by family.
17
-------
Table 5-5. CONCENTRATIONS OF SULFUR DIOXIDE CAUSING INJURY
TO SENSITIVE VEGETATION3
Concentration'1
Species jug/m3 (ppm)
White pine
(Pinus strobus L.)
Alfalfa
(Medicago saliva L.)
Broccoli
(Brassica oleracea var.
botrytis L.)
Apple
(Malus sp. "Manks
Codlin")
Pear
Prunus sp,
"Legipont"
"Conference"
Mountain ash
(Sorbus aucuparia L.)
131
131
131
262
262
1310
1310
655
1310
1310
1258
1258
1336
1415
2175
(0.05)
(0.05)
(0.05)
(0.10)
(0.10)
(0.5)
<0.5)
(0.25)
(0.5)
(0.5)
(0.48)
(0.48)
(0.51)
(0.54)
(0.83)
Exposure
time, hr
1
2
3
1
2.5
4
4
4
4
4
6
6
6
3
3
Effect'
Needle injury
rating of 3
Needle injury
rating of 5
Needle injury
rating of 8
Needle injury
rating of 5
Needle injury
rating of 8
5% leaf
injury
19% leaf
injury
6% leaf
injury
4% leaf
injury
None
Leaf injury
rating of 6
Leaf injury
rating of 4
Leaf injury
rating of 5
Leaf injury
rating of 3
Leaf injury
rating of 7
Conditions
Branch
exposure
chamber
in greenhouse
Greenhouse
exposure
chambers
Same
Branch
exposure
chambers in
natural stands
Same
Same
Refer-
ence
127
70
70
128
128
128
'The vegetation was observed or exposed when growing under environmental conditions that made it most sensi-
tive to SO2.
bAverage concentrations over the reported time periods. Inaccuracies associated with instrumentation result in de-
viations a* great as ±10 percent.
cThe effects are reported differently in each reference. Their definition is briefly described.
I. Reference 127 The needle injury rating is based on a 1 Io8 scale with 7 as no injury and 8 as 2 to 3 cm of
tip necrosis.
2. Reference 70: The values reflect the average percentage foliar injury on the three most severely injured leaves.
3. Reference 128: The leaf injury rating is based on a 0 to 10 scale with 0 as no injury and 10 as the entire leaf
surface injured.
18
-------
Table 5-6. SULFUR DIOXIDE CONCENTRATIONS CAUSING INJURY
TO AGRICULTURAL AND FOREST SPECIESa
Species
Buckwheat
(Fagopyrum sp.)
Barley
(Hordeum vulgare L.)
Red clover
(Trifolium pratense, L.)
Radish
(Raphanus sativus, L.)
Oats
(A vena sativa, L.)
Peas
(Pisum sativum, L.)
Rhubarb
(Rheum rhaponticum, L.)
Timothy
(Phleum pratense, L.)
Swiss chard
(Beta vulgaris var. cicla, L.)
Beans
(Phaseolus sp.)
Beets
(Beta vulgaris, L.)
Turnips
(Brassica rapa, L.)
Carrots
(Daucus carota, L.)
Cucumbers
(Cucumis sativa, L.)
Lettuce
(Lactuca sativa, L.)
Maximum average concentrations^*
1 hr, 2 hr, 4 hr, 8 hr,
3 (ppm) jug/m3 (ppm) ;ug/m3 (ppm) jug/m3 (ppm)
Agricultural
1467 (0.56) 1022 (0.39) 681 (0.26) 393 (0.15)
1651 (0.63) 1153 (0.44) 629 (0.24) 314 (0.12)
1834 (0.70) 1205 (0.46) 707 (0.27) 367 (0.14)
1991 (0.76) 1415 (0.54) 760 (0.29) 367 (0.14)
1651 (0.63) 1546 (0.59) 891 (0.34) 445 (0.17)
1651 (0.63) 1546 (0.59) 891 (0.34) 445 (0.17)
1651 (0.63) 1546 (0.59) 891 (0.34) 445 (0.17)
1729 (0.66) 1415 (0.54) 1048 (0.40) 550 (0.21)
2306 (0.88) 1677 (0.64) 1074 (0.42) 707 (0.27)
1205 (0.46) 1179 (0.45) 1127 (0.43) 550 (0.21)
3432 (1.31) 2017 (0.77) 1179 (0.45) 603 (0.23)
3432 (1.31) 2017 (0.77) 1179 (0.45) 603 (0.23)
2830 (1.08) 2070 (0.79) 1310 (0.50) 655 (0.25)
2830 (1.08) 2070 (0.79) 1310 (0.50) 655 (0.25)
1677 (0.64) 1467 (0.56) 1126 (0.43) 996 (0.38)
1677 (0.64) 1467 (0.56) 1126 (0.43) 996 (0.38)
Tomatoes
(Lycopersicon esculcntum, Mill.)
Potatoes 1677 (0.64) 1467 (0.56) 1126 (0.43) 996 (0.38)
(Solanum tuberosum, L.)
Raspberry 1939 (0.74) 1651 (0.63) 1389 (0.53) 1022 (0.39)
(Rubus idaeus, L.)
Celery 2279 (0.87) 1939 (0.74) 1441 (0.55) 760 (0.29)
(Apium graveolens, L.)
Spinach 3511 (1.34) 2384 (0.91) 1310 (0.50) 891 (0.34)
(Spinacea oleracea, L.)
19
-------
Table 56. SULFUR DIOXIDE CONCENTRATIONS CAUSING INJURY
TO AGRICULTURAL AND FOREST SPECIES3 (Continued)
Maximum average concentrations15
Species
Ihr,
Mg/m3 (ppm) /ug
2 hr, 4 hr,
;/m3 (ppm) Mg/m3 (ppm) Mg/
8hr,
m3 (ppm)
Forest
Cabbage 2463 (0.94) 2332 (0.89) 1834 (0.70) 1179 (0.45)
(Brassica oleracea, L.)
Corn -
(Zea mays, L.)c
Bracken fern 1179 (0.45) 891 (0.34) 625 (0.25) 550 (0.21)
(Pteridium aquilinum, L.)
Large tooth aspen 1729 (0.66) 1126 (0.43) 969 (0.37) 524 (0.20)
(Populus grandidentata Michx)
Willow 1074 (0.41) 996 (0.38) 865 (0.33) 786 (0.30)
(Salix sp.)
Trembling aspen 1100 (0.42) 1022 (0.39) 681 (0.26) 341 (0.13)
(Populus tremuloides Michx)
Jack pine 1362 (0.52) 1153 (0.44) 760 (0.29) 524 (0.20)
(Pinus banksiana Lamb.)
White pine 1179 (0.45) 917 (0.35) 655 (0.25) 550 (0.21)
(Pinus strobus L.)
Alder 1205 (0.46) 1126 (0.43) 1126 (0.43) 550 (0.21)
(Alnus sp.)
Red pine 2043 (0.78) 1809 (0.69) 1153 (0.44) 786 (0.30)
(Pinus resinosa Ait)
Balsam poplar 2149 (0.82) 1703 (0.65) 1179 (0.45) 681 (0.26)
(Populus balsamifera L.)
Austrian pine 1729 (0.66) 1179 (0.45) 1153 (0.44) 865 (0.33)
(Pinus nigra Arnold)
Witch hazel 2987 (1.14) 1965 (0.75) 1179 (0.45) 603 (0.23)
(Hamametis virginiana, L.)
Red oak 2332 (0.89) 2149 (0.82) 1598 (0.61) 1074 (0.41)
(Quercus sp.)
Sugar maple 2149 (0.82) 1703 (0.65) 1624 (0.62) 1205 (0.46)
(Acer saccharum Marsh.)
White spruce 2279 (0.87) 2070 (0.79) 1834 (0.70) 1310 (0.50)
(Picea glauca (Moench) (Voss)
Cedar -- .- - -
f
(Thuja occidentalis, L.)c
aThe vegetation was observed when growing under environmental conditions that made it most sensitive to SO2.
''Average concentrations over the reported time periods. Inaccuracies associated with instrumentation result in
deviations as great as ±10 percent.
cNever injured near recorder stations.
20
-------
Table 5-7. VEGETATIONAL RESPONSE TO SULFUR DIOXIDE IN COMBINATION
WITH EITHER OZONE OR NITROGEN DIOXIDE3
Species
Concentration
ratio, b
Mg/m3 (ppm)
Exposure
time
Effect,0
percent
foliar
injury
Refer-
ence
Tomato
(Lycopersicon esculentum Mill.)
Alfalfa
(Medicago sativa L.)
Broccoli
(Brassica oleracea var. botrytis L.)
Cabbage
(Brassica oleracea var. capitata L.)
Spinach
(Spinacia oleracea L.)
Tobacco
(Nicotiana tabacum L.)
BelW3
Bel W3
BelB
BelB
Sulfur dioxide/ozone
262/196
655/490
1310/980
2620/1960
(0.1/0.1)
(0.25/0.1)
(0.5/0.1)
(1.0/0.1)
1310/98 (0.5/0.05)
262/196 (0.1/0.1)
655/196 (0.25/0.1)
1310/196 (0.5/0.1)
2620/196 (1.0/0.1)
4hr
4hr
4hr
4hr
4hr
4hr
4hr
4hr
4hr
-25d
- 3
4
-33d
-17
19d
21d
55d
1310/98
262/196
655/196
1310/196
(0.5/0.05)
(0.1/0.1)
(0.25/0.1)
(0.5/0.1)
4hr
4hr
4hr
4hr
17d
34d
11
14
1310/98
262/196
655/196
1310/196
2620/196
(0.5/0.05)
(0.1/0.1)
(0.25/0.1)
(0.5/0.1)
(1.0/0.1)
4hr
4hr
4hr
4hr
4hr
4
12
14
47d
-42d
-48d
70
70
70
70
70
655/59
655/98
1310/98
262/196
685/196
1310/196
655/59
655/98
(0.25/0.03)
(0.25/0.05)
(0.5/0.05)
(0.1/0.1)
(0.25/0.1)
(0.5/0.1)
(0.25/0.03)
(0.25/0.05)
2hr
4hr
4hr
4hr
4hr
4hr
2hr
4hr
15d
16d
55d
8
75d
73d
9d
3d
67
70
67
70
21
-------
Table 5-7. VEGETATIONAL RESPONSE TO SULFUR DIOXIDE IN COMBINATION
WITH EITHER OZONE OR NITROGEN DIOXIDE3 (Continued)
Species
Concentration
ratio, b
jug/m3 (ppm)
Exposure
time
Effect,c
percent
foliar
injury
Refer-
ence
Bromegrass
(Bromus inermis L.)
Radish
(Raphanus sativus L.)
White pine
(Pinus strobus L.)
Radish
(Raphanus sativus L.)
Bean
(Phaseolus vulgaris L.)
Oats
(A vena saliva L.)
2620/196 (1.0/0.1)
4hr
-6 Id
1310/98
262/196
655/196
1310/196
262/196
131/98
131/98
(0.5/0.05)
(0.1/0.1)
(0.25/0.1)
(0.5/0.1)
(0.1/0.1)
(0.05/0.05)
(0.05/0.05)
4hr
4hr
4hr
4hr
4 to 8 wk,
5 days/wk,
4 to 8 hr/day
10 to 30 days,
12 hr/day
5 wk,
5 days/wk,
8 hr/day
6
31d
22d
45d
9
Trace -ex ten-
sive necrosis
Reduced
growth
70
70
Sulfur dioxide/nitrogen dioxide
131/188 (0.05/0.1) 4hr 0
262/188 (0.1/0.1) 4hr 11
262/282 (0.1/0.15) 4 hr 24
655/282 (0.25/0.15) 4 hr 4
524/376 (0.2/0.2) 4 hr 16
655/94
131/188
262/188
262/282
655/282
524/376
(0.25/0.05)
(0.05/0.1)
(0.1/0.1)
(0.1/0.15)
(0.25/0.15)
(0.2/0.2)
4hr
4hr
4hr
4hr
4hr
4hr
3
0
27
12
0
10
68
69
40
71
71
22
-------
Table 57. VEGETATIONAL RESPONSE TO SULFUR DIOXIDE IN COMBINATION
WITH EITHER OZONE OR NITROGEN DIOXIDE3 (Continued)
Species
Concentration
ratio,b
/ig/m3 (ppm)
Exposure
time
Fffprt c
percent
foliar
injury
Refer-
ence
Radish
(Raphanus sativtts L.)
262/188 (01/0.1) 4hr 27
262/282 (0.1/0.15) 4 hr 24
655/282 (0.25/0.15) 4 hr 4
131/470 (0.05/0.25) 4 hr 13
71
Soybean
(Glycine max L.)
Tomato
131/94
524/94
655/94
262/188
262/282
655/282
524/376
131/470
ntum Mill.) 655/94
131/188
262/188
262/282
655/282
131/470
(0.05/0.05)
(0.2/0.05)
(0.25/0.05)
(0.1/0.1)
(0.1/0.15)
(0.25/0.15)
(0.2/0.2)
(0.05/0.25)
(0.25/0.05)
(0.05/0.1)
(0.1/0.1)
(0.1/0.15)
(0.25/0.15)
(0.05/0.25)
4hr
4hr
4hr
4hr
4hr
4hr
4hr
4hr
4hr
4hr
4hr
4hr
4hr
4hr
2
6
7
35
20
1
9
2
1
0
1
17
0
0
71
71
aThe vegetation was grown under greenhouse conditions such that the plants were most sensitive to the pollutants
and pollutant mixtures.
b Average concentration of pollutants. Inaccuracies associated with instrumentation result in deviations as great as
±10 percent.
c The effects are reported differently in each reference. Their definition is briefly described:
1. References 67, 68, and 70: Percentages are expressed as the difference between the percent of foliar injury
from the SO2/03 mixture and the additive percent injury of the single gas exposures. Minus signs indicate
that injury from the mixture was less than the additive injury from single gas treatments.
2. Reference 69: Descriptive only.
3. Reference 40: Growth reductions from the mixture were either less than additive or equal to the additive
effects of single gas treatments.
4. Reference 71: Foliar injury from the S02/NO2 mixtures occurred at pollution levels below the threshold
injury concentration for SO2 (0.5 ppm) or NO2 (2.0 ppm) when used alone.
dPercentage differences are significant at the 0.05 level.
23
-------
Table 58. PROJECTED SULFUR DIOXIDE CONCENTRATIONS
THAT WILL PRODUCE THRESHOLD INJURY TO
VEGETATION FOR SHORT TERM EXPOSURES3
Concentration producing injury in three
susceptibility groups of plants
Time,
hours
0.5
1.0
2.0
4.0
8.0
Sensitive,
Mg/m3 (pPm)
2620
1310
655
262
131
to
to
to
to
to
10,480
7860
5240
2620
1310
(1.0
(0.5
(0.25
(0.1
(0.05
to 4.0)
to 3.0)
to 2.0)
to 1.0)
to 0.5)
Intermediate,
Mg/m3 (ppm)
9170 to
6550 to
3930 to
1310to
524 to
3 1 ,440
26,200
19,650
13,100
6550
(3.5 to
(2.5 to
(1.5 to
(0.5 to
(0.2 to
12)
10)
7.5)
5)
2.5)
Resistant,
Mg/m3 (ppm)
^26,200
^20,960
^15,720
^10,480
^ 5240
(^10)
(^ 8)
£ 6)
(^ 4)
£ 2)
a Values were developed from subjective evaluations of injury reported in the literature where both time and con-
centration were considered. The concentrations and times shown for each susceptibility grouping are reasonable
only when the plants are growing under the most sensitive environmental conditions and stage of plant maturity.
24
-------
Table 59. LISTS OF PLANTS IN THREE SUSCEPTIBILITY GROUPS
BY SENSITIVITY TO SULFUR DIOXIDE3
Species Reference
Sensitive
Aceraceae
Maple (Acer pseudoplatanus L.)
Amaranthaceae
Pigweed (Amaranthus retroflexus L.)
Begoniaceae
Begonia (Begonia sp.)
Bignoniaceae
Catalpa (Catalpa sp.)
Carophyllaceae
Bouncing bet (Saponaria officinalis L.)
Sweet William (Dianthus baratus L.)
Chenopodiaceae
Beet (Beta vulgaris L.)
Lamb's quarters (Chenopodium album L.)
Spinach (Spinacia oleracea L.)
Swiss chard (Beta vulgaris var. cicla L.)
Convolvulaceae
Sweet potato (Ipomea batata L.)
Compositae
Aster (Aster sp.)
Bachelor's buttons (Centaurea cyanus L.)
Cocklebur (Xanthium sp.)
Cosmos (Bidens sp.)
Dandelion (Taraxacum officinale Weber)
Endive (Cichorium endivia L.)
Marigold (Tagetes sp.)
Prickly lettuce (Lactuca scariola L.)
Ragweed (Ambrosia sp.)
Zinnia (Zinnia sp.)
Cruciferae
Broccoli (Brassica oleracea var. botrytis L.)
Brussels sprouts (Brassica oleracea var. gemmifera L.)
Cabbage (Brassica oleracea var. capitata L.)
Kale (Brassica oleracea var.acephala DC.)
Mustard, black (Brassica sp.)
Mustard, hedge (Sisymbrium sp.)
Nasturtium (Nasturtium sp.)
128
131
28
28
28
28
28
131
28,50
28,50
28,47
28
28
28,131
28,132,50
28,131
50,47
28
28
28
28
70
28
70
28
28
28
28
25
-------
Table 5-9. LISTS OF PLANTS IN THREE SUSCEPTIBILITY GROUPS
BY SENSITIVITY TO SULFUR DIOXIDE3 (Continued)
Species
Reference
Cruciferae (continued)
Radish (Raphanus sativus L.)
Turnip (Brassica rapa L.)
Curcurbitaceae
Cucumber (Cucumis sativus L.)
Pumpkin (Cucurbita pepo L.)
Squash (Cucurbita maxima Duchesne)
Euphorbia ceae
Rubber (Hevea brasiliensis Muell.)
Fagaceae
Beech (Fagus silvatica L.)
Gramineae
Barley (Hordeum vulgare L.)
Bentgrass (Agrostis palustris Huds.)
Bluegrass (Poa annua. L.)
Bromegrass (Bromus sp.)
Fescue, red (Festuca rubra L.)
Junegrass (Poa pratensis L.)
Oats (Avena sativa L.)
Orchardgrass (Dactylis glomerata L.)
Rye (Secale cereale L.)
Ryegrass (Lolium sp.)
Wheat (Triticum aestivum L.)
Iridaceae
Gladiolus (Gladiolus Sp.)
Iris (Iris sp.)
Labiatae
Coleus (Coleus blumei Benth.)
Leguminosae
Alfalfa (Medicago sativa L.)
Bean (Phaseolus vulgaris L.)
Bean, lima (Phaseolus lunatus L.)
Pea (Pisum sativum L.)
Sweet clover (Meliotus sp.)
Sweet pea (Lathyrus odoratus L.)
Soybean (Glycine max. Merr.)
Vetch (Vicia sp.)
70,50
28
131
28
28
133
131
28,47
132
132
70
132
28
9,50,47
28
28,50,47
28
28
131
131,28
131
70,89,50,47
51,134
70,28
28
28,47
28,50
70
131
26
-------
Table 5-9. LISTS OF PLANTS IN THREE SUSCEPTIBILITY GROUPS
BY SENSITIVITY TO SULFUR DIOXIDE3 (Continued)
Species
Reference
Liliaceae
Leek (Allium porrum L.)
Onion (Allium cepa L.)
Malvaceae
Cotton (Gossypium hirsutum L.)
Hollyhock (Althaea sp.)
Mallow (Malva sp.)
Nyctaginaceae
Four o'clock ( Mirabilis jalapa L.)
Pinaceae
Larch (Larix sp.)
White pine (Pinus strobus L.)
Plantaginaceae*
Plantain (Plantago sp.)
Polygonaceae
Buckwheat (Fagopyrum sp.)
Rhubarb (Rheum rhaponticum L.)
Smartweed (Polygonum sp.)
Sorrel (Rumex sp.)
Rosaceae
Apple (Malus sp.)
Apricot (Prunus sp.)
European cherry (Prunus padus L.)
Mountain ash (Sorbus aucuparia L.)
Pacific ninebark (Physocarpus capitatus (Pursh) Ktze.)
Peach (Prunus sp.)
Pear (Pyrus sp.)
Prune (Prunus sp.)
Saskatton seniceberry (Amelianchier alnifolia Nutt.)
Saxifragaceae
Gooseberry (Ribes sp.)
Hydrangea (Hydrangea sp.)
Solanaceae
Eggplant (Solanum melongena L.)
Nightshade (Solanum sp.)
Petunia (Petunia sp.)
Tobacco (Nicotiana tabacum L.)
28
70
28,131
28
28
28
89,129
129
28
129,131,
50,47
28
28,47
128,28,131
131,128
128
87
28
128
128
131
87
28
28
28,47
28
135
70,136
27
-------
Table 5-9. LISTS OF PLANTS IN THREE SUSCEPTIBILITY GROUPS
BY SENSITIVITY TO SULFUR DIOXIDE3 (Continued)
Species
Reference
Ulmaceae
Chinese elm (Ulmus parvifolia Jacq.)
Elm {Ulmus sp.)
Umbellifereae
Carrot (Daucus carota L.)
Celery (Apiwn graveolens L.)
Parsley (Petroselinum crispum Nym.)
Parsnip (Pastinaca sp.)
Vitaceae
Wild grape (Vitis labrusca L.)
137
28
28
131
28
28
131
Intermediate
Aceraceae
Box elder (Acer negundo L.)
Maple (Acer sp.)
Norway maple (Acer platanoides L.)
Anacardiaceae
Sumac (Rhus sp.)
Asclepiadaceae
Milkweed (Asclepias sp.)
Begoniaceae
Begonia (Begonia sp.)
Betulaceae
California hazel (Corylus califomica (A.D.C.) Rose.)
Cannaceae
Canna (Canna sp.)
Caprifoliaceae
Columbia snowberry (Symphoricarpos rivularis Suks.)
Honeysuckle (Lonicera sp.)
Snowball (Viburnum sp.)
Compositae
Chrysanthemum (Chrysanthemum sp.)
Cruciferae
Horse-radish (Armoracia rusticana Gaertn., B Bay. and Scherb)
Shepherd's purse (Capsella bursa-pastora L.)
28
28
137
28
28
138
87
28
87
28
28
28
28
28
28
-------
Table 5-9. LISTS OF PLANTS IN THREE SUSCEPTIBILITY GROUPS
BY SENSITIVITY TO SULFUR DIOXIDE3 (Continued)
Species
Reference
Cucurbitaceae
Cucumber (Cucumis sativa L.)
Euphoribiaceae
Castor bean (Ricinus communis L.)
Fagaceae
Pin oak (Quercus palustris L.)
Ginkgoaceae
Ginkgo (Ginkgo sp.)
28
47,28
137
137
Gramineae
Kentucky bluegrass (foa pratensis L.)
Salt grass (Spartina sp.)
Iridaceae
Gladiolus (Gladiolus sp.)
137
28
28
Labiatae
Salvia (Salvia sp.)
Leguminosae
Wisteria (Wisteria sp.)
Liliaceae
Onion (A Ilium cepa L.)
Malvaceae
Hibiscus (Hibiscus sp.)
Oleaceae
Lilac (Syringa vulgaris L.)
Pinaceae
Douglas fir (Pseudotsuga taxifolia Brit.)
Fir (Abies sp.)
Pine, lodgepole (Pinus.contorta Dougl.)
Pine, ponderosa (Pinus ponderosa Law)
Pine, western white (Pinus monticola Dougl.)
Portulacaceae
Purslane (Portulaca sp.)
47
28
28
28
28
87
9
87
9
87
28
29
-------
Table 5-9. LISTS OF PLANTS IN THREE SUSCEPTIBILITY GROUPS
BY SENSITIVITY TO SULFUR DIOXIDE3 (Continued)
Species
Reference
Roseaceae
Plum (Prunus sp.)
Rose (Rosa sp.)
Sweet cherry (Prunus avium L.)
Salicaceae
Poplar (Populus sp.)
Saxifragaceae
Mock-orange (Philadelphus sp.)
Mock-orange, Lewis (Philadelphus lewisii Pursh.)
Scrophulariaceae
Snapdragon (Antirrhinum sp.)
Solanoceae
Potato, Irish (Solarium tuberosum L.)
Tobacco (Nicotiana tabacum L.)
28
28
28
28
28
87
139
28
140
Vitaceae
Virginia creeper (Parthenocissus quinquefolia Planch.)
28
Resistant
Caryophyllaceae
Dianthus (Dianthus sp.)
Cucurbitaceae
Cantaloupe (Cucumis melo L.)
Ericaceae
Rhododendron (Rhododendron sp.)
Fagaceae
Oak (Quercus sp.)
Oak, live (Quercus virginiana Mill.)
Oak, pin (Quercus palustris L.)
Oak, white (Quercus alba L.)
Gramineae
Corn (Zea mays L.)
139
28
139
141
28
137
141
129
30
-------
Table 5-9. LISTS OF PLANTS IN THREE SUSCEPTIBILITY GROUPS
BY SENSITIVITY TO SULFUR DIOXIDE3 (Continued)
Species Reference
Liliaceae
Lily (Lilium speciosum Thunb.) 47
Oleaceae
Privet (Ligustrum sp.) 28
Orchidaceae
Orchid (Cattleya sp.) 50,139,47
(Cymbidium sp.) 50,141,47
(Odontoglossum sp.) 50,141,47
(Oncidium sp.) 50,141,47
Pinaceae
Arb'or-vitae (Thuja sp.) 28
Cedar (Thuja occidentalis L.) 129
Rubiaceae
Gardenia (Gardenia sp.) 139
Rutaceae
Citrus (Citrus sp.) 28
Umbellifereae
Celery (Apium graveolens L.) 28
aPlants were placed into the three susceptibility groups as defined in Table 5-7. The time-concentration data were
obtained for each plant by Checking the appropriate reference.
31
-------
K. SUMMARY
Plant species and varieties vary in sensi-
tivity to SO2. This is the result of the
interaction of environmental and genetic
factors that influence plant response.
Temperature, humidity, light, other air pol-
lutants, edaphic conditions, the stage of plant
growth and the selective pressures between
and within species all interact in affecting the
sensitivity of plants to injury from sulfur
dioxide. (Section D.I, 2, and 3.) Since
ambient air is composed of many pollutants,
interaction with other pollutants must be
considered in analyzing the effects of SO2 on
vegetation. In this regard, adverse foliar and
growth effects from pollutant mixtures may
be of a larger magnitude than effects from
exposures to SO2 alone. (Section D.l.e.)
The response of a given variety or species
of plants to a specific air pollutant cannot be
predetermined on the basis of the known
response of related plants to the same pol-
lutant. Neither can the response be predeter-
mined by a given response of a plant to
similar doses of different pollutants. The
interplay of genetic susceptibility and
environmental influences must be considered
for each plant and pollutant. (Section D.)
The responses of vegetation to sulfur
dioxide may be classified into two general
categories — visible effects and subtle effects.
Visible effects are visually identifiable
pigmented or necrotic foliar patterns that
result from major physiological disturbances
to plant cells. Subtle effects are those that
produce measurable growth or physiological
changes in plants but do not cause visible
injury. (Section B.)
Visible effects can be subdivided into acute
and chronic injury. Acute injury is severe
injury that occurs within a few hours after
exposure to SO2 and is characterized by the
collapse of cells with the subsequent develop-
ment of necrotic patterns. It is associated
with high, short-term SO2 concentrations. In
broad-leaved plants, it is characterized by
white or brown interveinal and marginal
necrosis of the leaf. Red to brown colored
necrotic lesions occur in conifers. This
necrotic response usually involves the needle
tip, but other portions of the needle may also
be affected. Acute injury patterns are general-
ly more characteristic of a specific pollutant
than chronic injury patterns. (Section B.I.a.)
Chronic injury results in light to severe
injury that develops from exposure over an
extended time period. It is associated with
long-term exposures where the pollutant con-
centration is sufficiently high to produce
some cell destruction or disruption.
Symptoms are usually in the form of leaf
chlorisis, but necrotic areas may also develop.
Foliar injury is followed by leaf abscission,
and the response may resemble normal
senescence. Acute and chronic injuries may
develop on the same leaves. (Section B.l.b.)
Subtle effects implies that SO2 can
interfere with physiological and/or bio-
chemical processes, and with plant growth
and yield without attendant development of
visible symptoms. Processes that have been
studied include photosynthesis, stomatal
behavior, chemical composition, and reduc-
tions in growth and yield. (Section B.2)
The term physiological effects includes
both subtle and visible effects. Physiological
changes in plants precede the visible expres-
sions of injury; however, visible injury may
not occur at all. Changes in the plant
processes, enzyme systems, and chemical com-
position may result in growth and yield
reductions in the absence of visible injury.
(Section B.3.)
The mechanism by which plants are injured
by SO2 is not understood. Acute injury does
not occur if the rate of SO2 absorption does
not exceed the capacity of the plant to
oxidize sulfite to sulfate ions. Under long-
term SO2 stress, sulfate thus formed may
accumulate, with the subsequent development
of chronic injury symptoms. (Section C.)
In assessing SO2 damage to plants, the
most significant question is whether or not
the plant has been so altered by the pollutant
that its growth, survival, yield, or use has been
impaired.
Except in those instances where damage to
the plant foliage results in decrease in the
value of the product, economic damage is
extremely difficult to assess. (Section E.)
Growth and/or yield reductions may occur
without visible injury to plants. (Section
B.S.d) Laboratory studies demonstrated that
32
-------
reduced root weights of radishes occurred
with exposure to SO2 at concentrations of
131 to 160 Mg/m3 (0.05 to 0.06 ppm), 40
hr/week for 5 weeks. Reduction in the growth
of tobacco occurred with exposure to SO2
concentrations of 262 Mg/m3 (0.1 ppm), 40
hr/week for 4 weeks. (Section B.S.d., Table
5-3) The conditions under which the studies
were conducted, however, would probably
seldom, if ever, be reached in the ambient air.
More studies are needed before a definitive
statement can be made.
Most reports, however, have considered
that visible injury is required for reductions in
growth and yield. Many studies have shown
that the reduction in crop yield from
exposure to SO2 is proportional to the
percentage of leaf area destroyed. The
relationship between the percentage of leaf
destroyed and reduction in crop yield has
been expressed in the equation y = a - bx,
where y = the yield expressed as the per-
centage of the control and x - the percentage
of leaf area destroyed. The constant a is about
100 percent, and b is the slope of the
yield/leaf-destruction curve. (Section I, Equa-
tion 5-1.)
Foliar injury of agronomic crops and trees
was reported at SO2 concentrations of 1074
to 1650 Mg/m3 (0.41 to 0.63 ppm) for 1-hour
exposure periods when these exposure periods
were within 8-hour time periods with average
concentrations of 314 to 786 Mg/m3 (0.12 to
0.30 ppm). Concentrations of 314 Mg/m3
(0.12 ppm) injured barley after 8-hour periods.
(Tables 5-5 and 5-6.) In Germany, growth
reductions of several forage plants were
demonstrated after field exposures of 2489
Mg/m3 (0.95 ppm) SO2 for 8 hours. (Table
5-3.) For Italian rye, growth was also affected
at this concentration in exposure periods of
12 hours, but when this species was grown in
combination with red clover, growth was not
affected by SO2 exposure. (Table 5-3.) In
contrast, reduced growth of rye grass
occurred when average daily SO2 concentra-
tions were less than 262 Mg/m3 (0.1 ppm) for
about 96 percent of the experimental periods
and no greater than 524 Mg/m3 (0.2 ppm)
during the remaining periods of time. (Section
B.3.d, Table 5-3.)
Growth, yield, and quality effects have also
been related to growing season average emis-
sions from single sources. In Germany,
reductions in these parameters were demon-
strated for spinach and gooseberry at growing
season averages of 26 to 37 Mg/m3 (0.010 to
0.014 ppm) SO2. A larger number of
agronomic species were affected at averages of
45 to 66 Mg/m3 (0.017 to 0.025 ppm) SO2.
In this study, the effects were associated with
maximum 30-minute values of 2096 to 4978
Mg/m3 (0.8 to 1.9 ppm) SO2. (Table 5-1.)
Laboratory and field chamber studies are
essential if qualitative and quantitative models
of pollutant effects upon vegetation are to be
developed. Since it is impossible to include all
parameters, laboratory and field chamber
studies do not simulate ambient field condi-
tions. The following results were obtained
through field chamber studies. Several forage
plants exhibited growth reductions after field
exposures of 2489 Mg/m3 (0.95 ppm) SO2 for
8 hours. (Table 5-3.) Injury to the foliage of
varieties of apple and pear trees occurred after
6-hour exposures to 1258 Mg/m3 (0.48 ppm)
SO2 ; however, foliar injury of mountain ash
occurred after exposure to 1415 Mg/m3 (0.54
ppm) SO2 for 3 hours. (Table 5-5.)
The interrelations of time and the con-
centration of a pollutant are extremely impor-
tant in determining the amount of injury that
will be produced by a given pollutant. Several
attempts have been made to develop rational
models that express time-concentration-
response results of plants to acute exposures
of SO2. (Section J.I.)
Since ambient air contains many pol-
lutants, interaction with other pollutants
must be considered in analyzing the effects of
SO2 on vegetation. In this regard, adverse
foliar and growth effects from pollutant
mixtures may be of a larger magnitude than
effects from single SO2 exposures. (Section
J.2.) Foliar injury of three of six agronomic
crops (alfalfa, broccoli, and radish) was
greater after 4-hour exposures involving
SO2/O3 mixtures of 262/196 Mg/m3 (0.1/0.1
ppm) for each pollutant than for ozone alone.
No injury was observed after exposure to SO2
33
-------
alone. (Table 5-7.) In addition, growth reduc-
tions of radish, occurring after exposures to
SO2/O3 mixtures of 131/94/xg/m3 (0.05/0.05
ppm) 8 hr/day, 5 days/week for 5 weeks,
were greater than reductions from single SO2
exposures. (Section B.l.f.)
Foliar injury to four of five agronomic
crops (beans, oats, radish, and soybeans)
developed after 4-hour exposures to
SO2/NO2 mixtures of 262/188 Mg/m3
(0.1/0.1 ppm) of each pollutant. The con-
centration used was below the injury thres-
hold for each of the gases. (Table 5-7.)
Lichens and bryophytes are very sensitive
to the presence of SO2. Lichens have been
used in the recognition and monitoring of
SO2. The presence of several fungal pathogens
has been reduced in SO2 polluted areas.
(Section F.)
Another effect of SO2 involves the
acidification of precipitation. The oxidation
and solution of SO2 in precipitation has
increased the acidity of soil and water in
many parts of the world. This increase in
acidity may reduce populations of micro-
organisms and affect the process of de-
composition and mineralization. Acid
precipitation may also contribute to the
leaching of nutrients from plant foliage and
from the soil. (Section G.) Further studies of
the effects of acid rainfall in the United States
are needed.
Sulfuric acid mists may occur when heavy
air pollution is accompanied by fog. These
mists result in necrotic spots, usually on the
upper surface, which may then develop
progressively through to the lower epidermis.
(Section H.2.)
Reduced growth of white pine occurred
with average SO2 concentrations of 45 Mg/m3
(0.017 ppm) associated with peak 30-minute
maximums of 3249 jug/m3 (1-24 ppm) during
growing seasons over a 10-year period. (Table
5-2.)
Since short-term concentrations are
probably more important than long-term
averages in the development of vegetational
injury, growing season or annual averages as
well as the maximum concentrations must be
shown if they are to have any value in
determining causal relationships. In this
regard, there is a need for the development of
mathematical equations to express relation-
ships between short-term concentrations,
long-term averages, and vegetational response
to sulfur dioxide. (Section J.I.)
L. CONCLUSIONS
The final chapter of Air Quality Criteria for
Sulfur Oxides includes summaries of the
preceding chapters of that document and
conclusions based upon them. The summary
of vegetation effects presented in that chapter
(Chapter 10, Section A.6) no longer
represents the best information currently
available, and the reader is referred instead to
the preceding section of this report. The
conclusions related to vegetation in that
document (Chapter 10, Section B.4) also are
superseded by those presented in this section,
as is the brief statement in the "Resume"
(Chapter 10, Section C).
The conclusions that follow are derived
from a careful evaluation by the Environ-
mental Protection Agency of the foreign and
American studies cited herein. They represent
the Agency's best judgment of the effects that
may occur when various levels of pollution
are reached in the atmosphere. The data from
which the conclusions were derived, and the
qualifications that should be considered in
using the data, are identified by section or
table reference in each case.
In applying the guidelines presented in the
following paragraphs, factors other than
pollutant concentration that affect a plant's
response to pollution, including the sensitivity
of the given variety or species to the pol-
lutant, duration of exposure, temperature,
humidity, interaction with other pollutants,
edaphic conditions, and state of plant de-
velopment, should be kept in mind. Since
short-term concentrations'are probably more
important than long-term averages in the
development of vegetational injury, maximum
concentrations as well as growing season or
annual averages must be specified in evalua-
tion of long-term exposures. In this regard,
there is a need for the development of
mathematical equations that express relation-
ships between short-term concentrations,
long-term averages, and vegetation response to
sulfur dioxide.
34
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For plants such as maple trees, spinach, and
sweet potatoes that are sensitive to sulfur
dioxide, damage or reduction in growth or
yield may result from short-term exposures as
low as 131 to 1316 ME/m3 (0.05 to 0.5 ppm)
over periods of 8 hours or 2620 to 10,480
Aig/m3 (1.0 to 4.0 ppm) over periods of !/2
hour. More resistant plants such as oak trees
and corn may require exposures of over 5240
Mg/m3 (2 ppm) for the 8-hour period or over
26,000 Mg/m3 (10 ppm) for the '/--hour
period. (Section J.2, Tables 5-8 and 5-9.)
Growing season average concentrations as
low as 26 to 66 ng/m3 (0.010 to 0.025 ppm)
have been reported to affect a large number
of agronomic species. These averages were
associated with maximum 30-minute values of
2096 to 4978 /ag/m3 (0.8 to 1.9 ppm).
(Section 1, Table 5-1.)
Foliar and growth affects of mixtures of
SO2 with other pollutants may be greater
than the effects of SO2 alone. Mixtures of
both SO2 and ozone and SO2 and nitrogen
dioxide have been found to produce greater
effects than either pollutant alone.
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40
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dversuche zur Ermittlung von Schwefel-
dioxidwirkungen auf die Vegetation.
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Germany. No. 1920. 1968. 114 p.
(Typescript Trans.)
116. Brisley, H. R., C. R. Davis, and J. A.
Booth. Sulfur Dioxide Fumigation of
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1959.
41
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117. Guderian, R. Zur Methodik der
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fuer land-und forstwirtschaftliche
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Tolerance Limits for Agricultural and
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script Trans.)
118. Stratmann, H. Freilandversuche zur
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Measurement and Evaluation of SO2
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43
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BIBLIOGRAPHIC DATA
SHEET
1. Report No.
EPA-R3-73-030
3. Recipient's Accession No.
4. Title and Subtitle
EFFECTS OF SULFUR OXIDES IN THE ATMOSPHERE ON VEGETATION;
Revised Chapter 5 for Air Quality Criteria for Sulfur Oxides
5- Report Date
September 1973
6.
7. Author(s)
8- Performing Organization Kept.
No.
9. Performing Organization Name and Address
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
10. Project/Task/Work Unit No.
11. Contract/Grant No.
12. Sponsoring Organization Name and Address
13. Type of Report & Period
Covered
14.
15. Supplementary Notes
16. Abstracts
Limitations in the criteria for secondary standards in the publication "Air Quality
Criteria for Sulfur Oxides," which became apparent since the adoption of Air Quality
Standards, prompted review and revision of Chapter 5, "Effects of Sulfur Oxides in the
Atmosphere on Vegetation." This document presents the revision to Chapter 5, and also
includes revised portions of Chapter 10,"Summary and Conclusions," that relate to
effects on vegetation. The document, based primarily on a thorough review of available
literature, summarizes current scientific knowledge of air pollution effects by sulfur
oxides upon vegetation and also points up the major deficiencies in that knowledge.
17. Key Words and Document Analysis. 17o. Descriptors
Air pollution
Pollution
Vegetation*
Sulfur dioxide*
Air quality criteria*
Agriculture*
17b. Identifiers/Open-Ended Terms
*Air pollution effects
17c. COSATI Field/Group
18. Availability Statement
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Report)
UNCLASSIFIED
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UNCLASSIFIED
21. No. of Pages
54
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