ATION
U. S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
                                 Public Health Service
                           Environmental Health Service

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                   AIR  POLLUTION
INJURY  TO  VEGETATION
                                     Ibrahim Joseph Hindawi
          U. S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
                                       Public Health Service
                                  Environmental Health Service
                        National Air Pollution Control Administration
                                      Raleigh, North Carolina

                                                  1970

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   The AP series ot  reports is  issued by  the National Air
Pollution  Control  Administration to report the results of
scientific and engineering studies, and information of general
interest in the field  of air pollution.  Information reported in
this series includes  coverage of NAPCA intramural activities
and of  cooperative studies  conducted in conjunction with
state  and local  agencies, research institutes, and industrial
organizations.  Copies  of AP reports  may be obtained upon
request,  as supplies permit,  from the Office of Technical
Information and Publications, National Air Pollution Control
Administration,  U.S.  Department of  Health, Education,  and
Welfare,  1033 Wade Avenue, Raleigh, North Carolina 27605.
   The author  wishes  to  thank the following contributors
who furnished additional color photographs contained in this
publication:
   Dr.  Howard Heggestad, U.S. Department of Agriculture
(Figure  13); Dr. Ruth Glater,  University of California (Figure
24); Misses Ida Leone and  E.  Brennan,  Rutgers University
(Figures  30 and  41);  Dr. D. F.  Adams,  Washington  State
University  (Figures 35  and 38); Dr. M.  D. Thomas, American
Smelting and Refining Co. (Figure 23); Dr.  Clyde Hill, Uni-
versity of  Utah  (Figure  36);  Dr.  J.  S.  Jacobson, Boyce-
Thompson  Institute  (Figure  39); The  American  Society of
Agronomy  and the  National Fertilizer Association (Figure
49).
                                                                                            ;    v-  :
                                                                            ••
                                    National Air Pollution  Control Administration Publication No. AP-71

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r /
                                        '••_  U
                             INTRODUCTION	   1

                             STRUCTURE AND ACTIVITIES OF PLANTS	   3

                             PHOTOCHEMICAL REACTION OF HYDROCARBONS AND NITROGEN OXIDES
                             PRODUCES OZONE AND PAN	  10

                             NITROGEN DIOXIDE CAUSES DIRECT VEGETATION DAMAGE	  18

                             SULFUR DIOXIDE CAUSES ACUTE AND CHRONIC INJURY	  20

                             SYNERGISTIC EFFECT OF OZONE AND SULFUR DIOXIDE CAN CAUSE MORE
                             SEVERE INJURY THAN EITHER POLLUTANT ALONE	  25

                             PLANT DAMAGE APPEARS FROM LOW CONCENTRATION OF FLUORIDES	  26

                             CHLORINE DAMAGE OCCURS CLOSE TO SOURCE	  30

                             ETHYLENE INJURES VEGETATION IN  URBAN AREAS	  32

                             AIR POLLUTION RETARDS GROWTH OF VEGETATION	  34

                             VEGETATION INJURY FROM OTHER AGENTS CAN BE CONFUSED WITH AIR
                             POLLUTION  INJURY	  36

                             AIR POLLUTION INJURY TO VEGETATION INDICATES DEGRADATION OF
                             ENVIRONMENT	  38
                             REFERENCES.
                                                                                              40

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©TO
                         A
    ir  pollution fouls  the  air in every community of more than
50,000 population in the United States as well as in a major propor-
tion of smaller towns.1 A number of natural variables play an impor-
tant role in the formation,  duration, and location  of air pollution.
Because of variation in wind direction and  speed,  air pollution re-
spects  no arbitrary boundaries.  Pollutants may  travel freely from
their sources, cross city and state lines, and contaminate other com-
munities  many miles away. Meteorological and topographical  condi-
tions that cause stagnant air masses may cause a buildup of pollution
at certain times and places.

   In  Los Angeles, pollution from automobile exhaust is the major
problem. In London, it is the smoke and gases from high-sulfur-con-
tent coal. In New York and New Jersey, air pollution has been traced
to petroleum  refineries, automobile exhaust, power-generating facili-
ties, waste disposal  systems, and many other sources. In  some cases
the problem arises from a series of chemical reactions in the  atmos-
phere  involving by-products of combustion and  other processes. A
chemical reaction takes place,  for instance, between hydrocarbons
and nitrogen  oxides, with  sunlight  acting as an energy source, to
produce  photochemical smog. Pollutants from these various sources
injure  crops, trees, and  property and reduce the amount of sunlight
reaching  the earth's surface.

   Since  a  threat to human health is  implicit in air  pollution,  and
since  agricultural and  other economic losses can  be attributed to
pollution,  means must be  found to detect and control atmospheric
pollutants. The study  of  the effects of  pollutants on vegetation is
important  not only because of the obvious relationship of such ef-

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fects to agricultural production, but also because many  plants can
serve as indicators of  the presence of  pollutants. The usefulness of
plants as indicators is  based primarily on the sensitivity to pollutants
of selected species or varieties.

   For the past 20 years, scientists have been growing  plants under
controlled conditions and exposing them to various concentrations
and  combinations of  certain chemicals. In this way they have been
able to determine the relative effects of these chemicals on plant life.
By now,  characteristic injuries to certain plants can be interpreted
not only  to determine the presence but even the relative concentra-
tions of aerial pollutants that cause injury.  In some instances when
analytical  techniques  and  measuring  instruments are  inadequate,
plant injury alone may be used to determine the presence of pollu-
tants.

   One variety of tobacco is used by many investigators as an effec-
tive  ozone indicator. Pinto bean plants  are used  to  detect peroxy-
acetyl nitrate (PAN); petunias, to investigate total oxidants; and glad-
ioli,  to  determine fluoride accumulations.  Dahlias, petunias, alfalfa,
and cotton are excellent detectors of sulfur  dioxide injury.

   Actual  leaf injury and its relationship to crop, losses have been
measured  quantitatively.  In  fact, alfalfa  and grain crop losses have
been shown to be directly proportional to  visible  damage caused by
sulfur dioxide.2 Field vegetation surveys and plant damage reports
have been  used  to estimate the presence,  distribution, and  general
levels of pollution.3

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  ^ir pollutants are divided into two major types, gases and particu-
lates. Gaseous pollutants account for the most widespread  injury to
plant life. Gases known to damage vegetation include: ozone, PAN,
nitrogen  dioxide,  sulfur dioxide, hydrogen fluoride, ethylene, and
chlorine. These pollutants destroy plant chlorophyll, disrupt the pho-
tosynthesis process, and consequently reduce food production.  In
severely polluted  areas, adjacent to certain industrial operations,
plant life has been  almost entirely exterminated.

  An interaction of even low concentrations of these gases can cause
injury  that  is  not readily apparent. This injury  may  show  up as
growth  suppression, dwarfing, or early  maturation or as symptoms
similar to those of  nitrogen deficiency or virus infection.

  The leaf  is the primary indicator of the  injurious effects  of  air
pollution. Its structure plays an important  role in building carbo-
hydrates and other vital plant products and foods. Some of the basic
anatomy, morphology,  and physiology  of the leaf are  discussed  on
the  following pages to facilitate understanding of leaf activity in
relation to air pollution symptoms and injuries.
  Plants and animals alike are composed of tiny cells, which may be
compared to the bricks or stones that make up the walls of a house.
Cell  sizes range from 0.01 to 0.1 millimeter in  diameter. A  typical
plant cell (Figure  1) has  three main components: the cell wall; the
protoplast, which  is the protoplasm of  one cell; and the inclusions,
which are composed of nonliving structures.

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                                         Protoplast
                                                                                Inclusions
                    Cell  Nucleus
                              Chloroplasts
                                                               Cell  Wall
                                     Figure 1. All or part of a cell may be injured by air pollutants.
   Cell walls are extremely thin when they are first formed, but they
become  relatively thick with age. The  cell  wall, produced by the
protoplast that it encloses, is made up almost entirely of cellulose.
                         Protoplasm
   Protoplasm, usually colorless, is a jelly-like substance that is found
in all living plant and animal matter.  It is considered living matter in
its simplest form.

   Protoplasm is composed of several chemical compounds. The most
important  is protein;  others are fat  and carbohydrate. The water
content of the protoplasm ranges from 60 to 90 percent. The dense
bit of protoplasm found in the center of the cell  is the nucleus, and
the protoplasm located outside the nucleus is the cytoplasm. Within
the cytoplasm are three  types of  tiny bodies,  or plastids, that per-
form vital functions in the life of  a plant: chloroplasts, leucoplasts,
and chromoplasts.

  All green  plant cells contain chloroplasts,  oval microscopic bodies
that contain the green pigment chlorophyll  plus some yellow pig-
ment. Chloroplasts are of enormous biological importance because
they are key structures in the plant's food  manufacturing process,
photosynthesis.

  Leucoplasts are colorless plastids that  convert starch  into starch
grains.  As these grains increase in  size and number, the  leucoplasts
stretch to many times their normal  size.

  Chromoplasts are responsible for the red, yellow, or orange colors
appearing in many flowers and fruits.

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                          Inclusions
  Inclusions are the nonliving structures of cells. They are seldom
found in very young cells, but appear in increasing numbers as cells
mature. They are particularly  evident in old cells with large food-
storage capacity. Inclusions may be crystals, noncrystals, or sacs con-
taining liquid mixtures. These sacs, called vacuoles, contain mixtures
of water and  substances such as nitrogen oxides, carbon dioxide,
inorganic salts, soluble protein, and simple nitrogen compounds.

                            Vascular  Bundle-
                ANATOMY OF  THE  LEAF
  Plant structure is  formed by the leaf,  stem, and  root. The  leaf
(Figure 2) is  the principal organ involved  in photosynthesis. Micro-
scopic  examination  of a typical mature leaf reveals three  primary
tissue systems: the outer epidermis, the mesophyll.and the  vascular
bundle (veins).
Air  Spaces
                                                                                          Upper Epidermal  Cells


                                                                                              11 •*  Palisade
                                                                                              j .   Parenchyma
                                 Spongy
                               Parenchyma
                                                                                                                    Mesophyll Cells
                                                                                      jf   Lower   Epidermal  Cells
                                                   Guard Cells  (enlarged)
      Figure 2.  Cross section of intact leaf shows air spaces within leaf that serve as passages lor pollutants that may subsequently
                injure leaf.

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  The epidermis covers the entire surface and protects the  tissue
within from injury caused by such things as excessive water loss and
wind  and rain.  Epidermal  cells are relatively long-lived, dying just
before the leaf falls. Chloroplasts are usually absent from epidermal
cells. Oval openings in the leaf epidermis are called stomata. Bounded
by two special cells called guard cells (Figures 3 and 4), stomata are
found  among  ordinary epidermal cells on the lower side of a leaf and
occasionally on the upper  epidermis. These openings regulate the
entrance and exit of gases. The  function of the guard cells in opening
and closing stomata  depends upon change  in the turgor (normal dis-
tention and resiliency) of the cell.
                                                                      Stem a
                                                                                      Guard  Cells
                                                                 Chloroplasts
                     Figure 3.  Cross section of leal inward from epidermis illustrates stoma through  which pollutants enter.


                                                                  6

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 Epidermal   Cells
Guard  Cells
   Figure 4.  Enlarged view of leaf surface reveals open stoma.


  The mesophyll is  the  soft tissue between  the  lower and upper
epidermis of typical leaves and is made up of two principal types of
tissue, the palisade parenchyma and the spongy parenchyma. Palisade
parenchyma consists  of one or several layers  of elongated cells lo-
                                                                   cated between  the  upper epidermis and  the spongy  cells. Spongy
                                                                   parenchyma cells are not elongated. They are formed and arranged so
                                                                   that many large spaces exist between them. The cells of both palisade
                                                                   and spongy parenchyma contain chloroplasts.

                                                                     Vascular  bundles carry water, minerals, and carbohydrates
                                                                   throughout the leaf area. The mid-rib is the largest vein.
                                                                                  ACTIVITIES OF THE  LEAF
                                                                     The  primary  functions within a typical leaf are photosynthesis,
                                                                   transpiration, and respiration.
                                                                    Photosynthesis:  Basic  Food Manufacturing Process
                                                                     The mesophyll tissue contains a large number of chloroplasts. In
                                                                   the presence of light, photosynthesis takes place in the chloroplasts.
                                                                   This involves the union of water and carbon dioxide to form sugar
                                                                   (glucose) and then starch. Photosynthesis is described by the follow-
                                                                   ing equation:
                                                                             6CO,  +
                                       6H2O
                                  C6H1206
+  6O,
                                                                     The excess oxygen generated in the process escapes from the plant
                                                                   and into the atmosphere during  photosynthesis. Light is the source
                                                                   of energy for photosynthesis, and part of this energy is stored in the
                                                                   molecules of glucose.
                                                                     Transpiration: Coo/ing  and  Nutritional Processes
  A plant suffers constant water loss to the atmosphere through
evaporation.  As shown  in Figure 5, the water is siphoned from the
soil through the roots and moves through conducting tissue or veins
to the leaves.  In the leaves, the moisture escapes in vapor form from
the moist cell walls of the mesophyll into the intercellular spaces. It
is then released through the stomata into the atmosphere. Transpira-
tion causes a continuous stream  of water to move from the roots to
the top of the plant. It transports soil minerals through the plant and
also cools the plant. These  processes increase  during hot sunny
weather and greater-than-normal  air movement.

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Figure 5.  Flow  of moisture in  the growing plant provides for transpiration and respiration
          processes.  Sunlight serves as energy source for photosynthesis.
                                                Plants breathe through  leaves.
                                                              Bark or hard case protects plant from bruises and insect damage

                                                                      Trunk, stem, and tendrils reach up into sunlight and air.
Foods manufactured

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  Blossom uses food in production of seeds.
             Carbon dioxide is absorbed.
                   Oxygen  is released.
             Chlorophyll, the green substance in the plant, absorbs energy from
             light and water.  This energy is used to make starch and sugar.
        Branches and leaves are arranged to expose greatest possible area to light.
                     Fats and proteins are made by chemical changes
                     in the sugar and starches in various parts of the plant.
in  leaves and branches are carried down stem .
        Roots anchor the plant, absorb minerals and moisture, and serve as
        food reservoir.
                                                                                     Respiration:  Energy-Producing Mechanism
   Respiration, a continuous process in the protoplasts of all living
cells,  involves the  reaction of oxygen with carbohydrates to release
energy. In  effect,  oxygen acts as a fuel to burn carbohydrates and
produce  energy. Thus, photosynthesis (see  Figure 5) is an  energy-
absorbing or storing  process and  respiration is an energy-releasing
process.

   Because  they obtain all the energy necessary for food production
and storage directly from the sun, plants form  the beginning of the
food  chain that sustains all animal life, for animals derive all their
food, and thus all their  energy, directly or indirectly from plants.
The  immediate end product of  photosynthesis in plants is glucose, ,
which, conversely, is the substrate oxidized in respiration. The equa-
tion for respiration, then, is the reverse of that for photosynthesis:
                    +  6On
                                                                                                                     6H,O  + 6CO,
                                                                                While the process of photosynthesis is taking place, plants release
                                                                              oxygen  into the air and help maintain the correct atmospheric bal-
                                                                              ance.  At night, or at other times of photosynthesis inactivity, plant
                                                                              cells take in oxygen and release carbon dioxide to the atmosphere.

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     I he i
   I he photochemical reaction of hydrocarbons and nitrogen oxides
produces ozone and PAN. When exposed to sunlight, nitrogen diox-
ide absorbs ultraviolet light, which furnishes the energy to break the
bond  between oxygen and nitrogen in the gas molecule. The result is
the formation of  nitric  oxide  and atomic oxygen.  This reaction
causes a  number of oxidations, with ozone  the principal oxidant
produced.

   Major sources of hydrocarbons and nitrogen  oxides are automobile
engines and industrial plants.
                                         AND ALTERS COLOR
      Ozone  severely injures many forms of plant life (Figures 6-15).
    "Weather flecks" on tobacco leaves have been attributed to ozone.4
    These marks appear first on mature leaves of Tobacco Bel W3 and
    then  progress to the youngest leaves. The first lesions to appear on
    tobacco leaves are dark  (Figure 7),  and remain  dark  for about 24
    hours. Then they become lighter in color (Figure 8) and finally turn
    white several days later (Figure 9).
10

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                                                                                                V- $V
                                                                                               i ^•••l^^^
                                                                   Figure  7.  Tobacco leaves exposed to ambient air in New  York City
                                                                            developed dark lesions attributed to ozone.
Figure 6.  Tobacco plant displayed oxidant (ozone} injury at Staten
          Island, New York, in 1966.  Injury progressed from oldest
          to youngest leaves.
Figure 8.  Ozone-injured tobacco  leaves develop light-colored  le-
          sions approximately 3 or 4 days alter exposure.
                                                               11

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                                                                      Figure 10. Enlarged  surface  of pinto bean leaf shows stipple (pig-
                                                                                 mentation) along veins of plant grown outside at Staten
                                                                                 Island, New York.
Figure 9.  Lesions on tobacco leaves appear white several days after
          exposure to ozone.
'•'igure 11.  Microscopic cross section of pinto bean leaf shows se-
           vere  ozone injury. Palisade  cells plasmolyzed and lost
           their integrity,  but spongy and epidermal cells remained
           intact.
                                                                   12

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Figure 12.  Fleck and symptoms of dehydration appeared on old  pri-
           mary  leaf of pinto bean plant exposed to natural pollu-
mary leal
tants.
Figure 13.  Injury on tobacco leaf exposed to ozone in laboratory did
           not develop on upper part of leaf because it was shaded
           during ozone exposure.  Severe  ozone injury appeared on
           unshaded part of leaf. Light caused the stomata to open,
           thus a greater amount of ozone entered and injured this
           portion.
  Ozone causes stipple and bleaching on the upper surface of leaves
of the pinto bean  plant (Figure 10).  Fleck and stipple caused by
ozone  also appear on the upper surface of grapevines. These symp-
toms are similar to those of ozone injury in other species of plants
and were first recognized  in 1958.5

  Ozone injures the palisade cells of plants (Figure 11). Initially, the
chloroplasts condense and accumulate at the center or at both ends
of the  cell. This is followed by collapse of the cell wall. Occasionally,
the chloroplasts granulate and  form a jelly-like mass. As the result of
pigment breakdown in the damaged cells, a reddish-brown color is
produced. When exposed to ozone, leaves of woody  plants develop
red-brown spots from the formation of new pigment.6 When small
islands of palisade tissues are injured, discrete punctate spots appear.

   Studies made at  the greenhouse facilities  of the National Air Pol-
lution Control Administration in Cincinnati revealed that sensitivity of
Tobacco  Bel W3 and  pinto bean plants to ozone exposure is influ-
enced  by  environmental  conditions and  the time of day of expo-
sure.7 Plants were significantly more sensitive during the mid-portion
of the  day. The importance of the time factor is recorded in Tables 1
and 2. Table 3 indicates the effect of light intensity during ozone
exposure tests on pinto bean plants.

  Published information  concerning tobacco varieties indicates that
test plants grown in California and Utah are not as sensitive to ozone
as are the same plant varieties when grown in the middle and eastern
regions of the United States.4 Studies in California showed that 25
parts per hundred million (pphm) of ozone for 6 hours causes injury
to plants.4  In Utah in  1961, it was found that an average of 24 pphm
of ozone for 2  hours injured tobacco  plants.8 In 1959 in New York
City, however, tobacco injury was reported at 10 pphm for 8 hours,9
and in  1962 in Beltsville,  Maryland, studies showed that Tobacco Bel
W3 was injured after 4 hours fumigation  at  an ozone concentration
of only 5 to 7 pphm.10 In 1965 it was found that greenhouse-grown
Tobacco  Bel W3 plants were injured after 4  hours' fumigation at 3.5
pphm of ozone,7 a concentration about half of that used at Belts-
ville.

  This variation suggests that the plant injury threshold of ozone in
one location may vary from day to day and that a concentration of
                                                                 13

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the gas that would not cause injury in a certain location  may be
injurious to  comparable plants in other locations. Conditions that
may cause the injury threshold to vary include light intensity, tem-
perature, humidity,  available  nutrition,  and season.  Examples of
ozone  injury to agricultural specimens are shown in Figures 14 and
15.
Figure 14.  Symptoms on spinach  leaves indicate  injury from oxi-
           dants, mainly ozone.
                                                                      Figure 15.  Injured leal shows reddish-brown bleach attributed to at-
                                                                                 mospheric oxidants.
                                                                  14

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       Table 1.  EFFECT OF TIME OF DAY OF EXPOSURE
        ON SENSITIVITY OF PINTO BEAN TO OZONE 7
    Time of day
Portion of leaf damaged, %
      9 a.m.
     11 a.m.
      1 p.m.
      3 p.m.
         39
         63
         60
         47
         Table 2.  SENSITIVITY OF TOBACCO BEL W3
               TO LOW LEVELS OF OZONE 7
Concentration, pphm
3.5
3.5
5.0
5-0
9.0
9.0
Time, hours
4
8
2
4
2
4
Portion of leaf damaged, %
12
56
1
14
11
45
Table 3.  EFFECT OF LIGHT INTENSITY ON SENSITIVITY OF PINTO
    BEAN TO OZONE EXPOSED AT CONSTANT TEMPERATURE7
 Light intensity, ft-c
     Portion of leaf damaged, %
       2,600
       1,800
        100
       Dark
               89
               73
               10
                2
                           15

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  PAN IS  HIGHLY  TOXIC TO  MANY  PLANT  SPECIES
   Peroxyacetyl nitrate, commonly called PAN, is extremely toxic to
 many plant species, especially small plants and young leaves. PAN is
 unstable, particularly at temperatures above 90° F. Visible symptoms
 of  PAN injury include bronzing, silvering, and glazing on lower leaf
 surfaces (Figures  16-19).

    In this kind of damage, some of the spongy or the lower epidermis
 cells or both become plasmolyzed, and the chloroplasts tend to lose
 their integrity. After severe damage,  additional spongy cells become
 plasmolyzed and the cytoplasm changes color to light or dark brown.
 The microscopic pattern of injury associated with PAN  is shown in
 Figure  19.
  Studies have shown that injury varies directly with concentration
and length of exposure to PAN. Exposure to high concentrations of
PAN (0.8 ppm  for 30 minutes or more) can cause  severe injury on
young pinto bean plants. A low concentration of PAN, 0.5 ppm for 1
hour or 0.1  ppm for  5 hours, caused severe injury to  pinto bean,
petunia, and tomato plants.11  Glazing or bronzing on the lower leaf
surface with little or  no symptom visible on the upper surface devel-
oped when bean leaves were exposed to  0.8 ppm for 15 minutes.12
PAN concentrations as low as 0.01 ppm  for 6 hours can cause plant
injury.
      13
  Physical  changes  have been found in the chloroplast structure of
pinto bean  leaves exposed  to 1 ppm for 30 minutes although injury
was not evident to the unaided eye.14

  The light intensity under which pinto bean plants are grown and
exposed to PAN  has a very  pronounced effect  on development of
visible symptoms. For the visible symptom to  develop light  is re-
quired by the plant for at least 3 hours preceding exposure, during
exposure, and for at  least 2 to 3 hours following exposure.1 5
Figure 16.  Triloliate leaf olpinto bean plant exposed to ambient air
           shows bronzing symptoms caused by severe PAN injury.
Figure 17.  Lower surface of primary leal ol pinto bean plant shows
           silvering.
                                                                  16

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Figure IS. Severe oxidant injury developed on lettuce plants grown
           in Los Angeles, California, area.
Figure 19.  Microscopic cross  section  ol petunia leaf exposed in
           laboratory shows  PAN injury.  Spongy cells adjacent to
           lower epidermis plasmolyzed, and chloroplasts lost their
           integrity. Upper and lower epidermis and palasade cells
           remained intact.
   Overt symptoms of injury by PAN may be indistinguishable from
those produced by other pollutants. For example, PAN causes glaz-
ing and silvering on the lower surface of young trifoliate and primary
leaves of the pinto  bean plant, but identical symptoms develop on
comparable  plants exposed to irradiated automobile exhaust fumes
and irradiated pure components such as propylene and nitrogen ox-
ide, when tested under controlled conditions.16.1 7

   Other studies demonstrated that plant injury similar to that found
on  the  lower surfaces of old leaves of pinto beans grown in  Los
Angeles could be  reproduced by exposing similar plants to a mixture
of gasoline  vapor and ozone.18  Comparable results were  obtained
with mixtures of  ozone  and certain olefins.16^ 7.19,20 Mixtures of
nitrogen dioxide and gasoline vapor also produced the same type of
injury.

   Reddening and bronzing developed on the lower surfaces of old
primary and  trifoliate leaves of pinto beans grown  and exposed to
ambient air  at Staten Island,  New York, and Perth Amboy, New
Jersey.21 These symptoms also resemble those produced by ozone-
olefin products. It has been reported that a non-irradiated mixture of
ozone and 1-pentane, 1-hexane, and 3-heptane caused typical PAN-
type injuries to 14-day-old primary  leaves of pinto beans, but did  not
injure 8-day-old bean leaves or petunia leaves.22 During the course of
the studies at Staten  Island and Perth Amboy21  in  1965 and 1966,
cloud cover  and heavy concentrations of particulate matter in  the
atmosphere were  encountered. Because light intensity was reduced,
the ozone-olefin mixture was not fully irradiated.
                                                                 17

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c
    ombustion  of  coal, fuel  oil,  natural gas,  and gasolines used in
power-generating  operations  is the source  of nitrogen dioxide. In
addition  to its  role in producing ozone and PAN in  the presence of
light and hydrocarbons, nitrogen dioxide alone injures vegetation.
Symptoms of  nitrogen  dioxide injury appear as irregular white or
brown collapsed lesions on tissue between the  veins and near the leaf
margin (Figure  20).


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r
         Figure 20. Petunia plant exposed to 13.5 ppm nitrogen dioxide lor 1
                    hour shows injury that resembles sullur dioxide damage.

            Studies indicate that visible leaf damage to tomato  seedlings is
          caused by a  concentration of 2.5 ppm nitrogen dioxide after 4 hours
          exposure.15  Pinto bean  plants are reportedly  injured  by a 3-ppm
          concentration after 4 to 8 hours exposure.3  Nitrogen dioxide injury
          to a tomato plant exposed to ambient air is shown in Figure 21.

            Acute  symptoms  found on  bean, tomato, and tobacco seedlings,
          induced by an exposure  to 2.5 ppm of nitrogen dioxide, also closely
          resemble  necrotic lesions (surface spotting) caused by sulfur dioxide
          or injuries caused by excessive concentrations of ozone.11 A nitro-
          gen dioxide concentration of 25 ppm injures most indigenous vegeta-
                                                                                    Plant growth may be inhibited by continuous exposure to 0.5 ppm
                                                                                  nitrogen dioxide or perhaps  less.1 5 When applied continuously, ni-
                                                                                  trogen dioxide in concentrations below 0.5  ppm  (and equivalent to
                                                                                  the  levels  recorded  in the Los Angeles atmosphere) cause  marked
                                                                                  chlorosis of basal leaves of tobacco.1 2
         tion.
              23
Figure 21.  Tomato plant exposed  In  ambient air  in  Chattanooga,
           Tennessee, ira.s injured hy nitrogen dioxide.
                                                                           19

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        ajor sources of sulfur dioxide are residential  and commercial
    buildings heated  by coal or fuel oil of high-sulfur content, industrial
    facilities such as  petroleum refineries and some chemical plants, and
    power-generating plants that burn sulfur-bearing fuel.

      Sulfur dioxide causes both acute and chronic plant injury (Figures
    22-29).  Acute injury  is characterized by clearly marked dead tissue
    between the  veins  or on the margins of  leaves. Chronic injury is
    marked  by brownish-red, turgid, or bleached white areas on the blade
    of the leaf. The  plant injury  threshold for  sulfur dioxide  is 0.3 ppm
    for 8 hours.

       Plant injury is thought to be caused by sulfur dioxide, sulfuric acid
    that forms as a by-product of sulfur dioxide  in the atmosphere, or a
    combination  of  both.  It has been reported that for  each 25 to 30'
    parts of sulfur dioxide formed during combustion of fossil fuel, one
    part of sulfur trioxide is formed. It continues to form as the combus-
    tion products mix  with the atmosphere. Sulfur trioxide, in turn, mav
    rapidly combine with  atmospheric moisture to  form sulfuric acid.24
    This acid may be  suspended as small droplets, which cause distinct
    punctate spots to appear on  leaves. Most often, acid aerosol damage
    occurs during foggy weather and  the  injury  develops on non-waxy
    leaves (Figure 25). This type of spotted injury  has been reported in
    the Los Angeles area  during  a period of heavy air  pollution  accom-
    panied by fog or light rain.1 4 Similar injury may also occur without
    fog, and its attendant moisture,  in an  area where there are combus-
    tion by-products containing  sulfur  oxides and  where the effluent
    dew-point permits acid droplets to form. Usually the  upper leaf sur-
    faces display  the initial  necrosis. Cellular collapse and  punctate spots
    develop progressively  through the upper epidermis, mesophyll layers,
    and the lower epidermis of the leaf.  No glazing or  bleaching  accom-
    panies this injury.
20

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Figure 22.  Rose leaves in Independence,  Missouri,  show marginal
           and interveifiaJ necrotic injury from sulfur dioxide.
Figure 23.  Laboratory-exposed potato leaves reveal typical  sulfur
           dioxide injury.
Figure 24.  Salt  bush  plant  was exposed to sulfur  dioxide  in lab-
           oratory:  this plant is excellent indicator of excess SOg.

-------
                                                                       Figure 26.  Pinto bean plant was  sprayed with water before sulfur
                                                                                 dioxide exposure in laboratory.
Figure 25.  Bindweed injury in Staten Island, New York, was caused
           by sulfuric acid droplets.
Figure 27.  Apple tree leaves near power plant in Pennsylvania shows
           typical sullur dioxide injury.
                                                                  22

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                                                                       Figure 29.  Forsythia in upper Ohio River Valley near Steubenville,
                                                                                  Ohio, was injured by sulfur dioxide.
Figure 28.  Castor bean leaf injury resulted from laboratory exposure.
Figure 30.  Necrotic injury on hydrangea leaf was caused by fly ash
           from New Jersey power plant.
                                                                  23

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   Plants are particularly sensitive to sulfur dioxide during periods of
intense light, high  relative  humidity, adequate plant moisture, and
moderate temperature. Plants are, therefore, especially sensitive to
sulfur dioxide during the  growing season  in late  spring and  early
summer.

   Time and levels  of exposure affect plant sensitivity to sulfur diox-
ide. Plants exposed to high sulfur dioxide concentrations during the
early or late daylight hours are less affected by the gas than plants
exposed from 10:00 a.m. to 2:00 p.m. At night, when the stomata of
most plants  are closed, the plants are much less susceptible to sulfur
dioxide injury.

   The degree of turgidity  of test plants  is extremely important in
sulfur dioxide sensitivity.  Soil  dry  enough  to cause a slight wilting
increases  plant resistance  to sulfur dioxide injury. Turgid  tomato
leaves are severely injured by sulfur dioxide, but slightly wilted leaves
are  uninjured by  the same concentration  of the  toxicant. Young
plants are more resistant than old plants, and middle-aged leaves are
most susceptible to injury.  These differences are probably caused by
variations in the number, size, and  activity of the stomata and the
quality of the cytoplasmic contents of the cells.

   Microscopic examination of leaf tissue injured  by sulfur dioxide
reveals that the mesophyll cells are affected and the  chloroplasts
become  plasmolyzed  or  bleached out. The spongy cells are often
more readily affected than the palisades. Under severe conditions the
epidermis  cells are also plasmolyzed. The  mid-rib  and large  veins
remain intact and green, even though most of the leaf has collapsed.

   Injury  to  agricultural crops exposed to  a given concentration of
sulfur dioxide is greater than the injury to laboratory-exposed plants
subjected to the same concentration because of possible  additional
toxicants  present in the uncontrolled ambient atmosphere.  For this
reason, injury to  agricultural  crops is usually  greater than  can be
projected  from laboratory experiments involving only one toxicant.

   Low concentrations  of  sulfur  dioxide  can  interfere with the
growth and functioning of a plant without leaving visible injury. This
injury may interfere with or reduce  photosynthesis. Grain  crops may
suffer a reduction in yield,  especially if crops are damaged by sulfur
dioxide at the blossom stage.2
                                                                    24

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0
    that t
    :one and  sulfur dioxide  together produce a synergistic action
tfiat reduces the  injury threshold of leaf tissue. It has been reported
that an ordinarily harmless concentration of ozone, when combined
with sulfur dioxide, produced ozone-type injury to Tobacco Bel W3
plants.25 No injury  developed  from exposure of similar plants to
identical concentrations of the individual gases. See Table 4.

    Table  4.  SYNERGISTIC EFFECT OF OZONE AND SULFUR
           DIOXIDE  ON TOBACCO BEL W3 PLANTS25

Duration, hr
2
2
2
4
4
4
Toxicants,
03
0.03

0-027 <
0.031

0-28 +
ppm
S02

0.24
0-24

0.26
0.28

Leaf damage, %
0
0
38
0
0
75
      Laboratory work has indicated that  a single 4 hour exposure to
    nitrogen dioxide below 2 ppm and to sulfur dioxide below 0.7 ppm
    will not injure tobacco. Exposure for 4 hours to  a mixture of 0.1
    ppm of nitrogen dioxide and 0.1 ppm of sulfur dioxide produces
    moderate injury to the older leaves of Tobacco Bel  W3. Preliminary
                                                                         experiments with ozone, nitrogen dioxide, and sulfur dioxide suggest
                                                                         that a mixture containing 0.05 ppm of each of these toxicants injures
                                                                         tobacco.26
                                                                           In 1966 it was revealed that tobacco exposed to ambient air in the
                                                                         Brooklyn Botanical Garden; Staten Island,  New York; and Bayonne
                                                                         and Roselle,  New Jersey, showed  ozone injury on  plant leaves al-
                                                                         though the ozone concentration was  far below  the  injury thres-
                                                                         hold.27. 28 Sulfur dioxide was shown to be present, however. Figure
                                                                         31  shows a tobacco leaf exposed to ambient air and  another  to a
                                                                         controlled, uncontaminated  atmosphere during the New York-New
                                                                         Jersey study.
                                                                         Figure 31.  Tobacco  Bel W3 plants exposed  to clean atmosphere
                                                                                    (le(t)andto ambient air(right) dramatize the possibility
                                                                                    of ozone • sulfur dioxide synergistic action.
                                                                                       AEROSOLS-SULFUR DIOXIDE
                                                                       The presence of an aerosol may substantially increase the toxic
                                                                     effects of sulfur dioxide. A study has indicated  that in the presence
                                                                     of dew,  mist, or very light rain, a lower level of sulfur dioxide con-
                                                                     centration than that required during a dry period  could cause plant
                                                                     injury.29  Heavy rains, however, might wash away the gas rather than
                                                                     concentrate it on leaf surfaces.
                                                                     25

-------
       _| luorides in  concentrations as low as 0.1 part per billion are toxic
     to some  plants.2  Fluorides in either gaseous or particulate form can
     accumulate outside or inside plant  leaves and  cause leaf injury (Fig-
     ures 32  through  39). Fluorides do not translocate from the leaf to
     other parts of the plant.  Even when high fluoride concentrations
     exist in the leaf tissue, the root systems, flower seeds, and all other
     plant parts remain very low in fluoride content.

        Gaseous fluoride compounds are responsible for most fluoride in-
     juries suffered  by plants. Hydrogen fluoride and  other gaseous com-
     pounds  are readily  absorbed by the leaves. An accumulation of a
     solid fluoride on its surface will not injure the leaf, however, unless
     the fluoride on the leaf is dissolved by  moisture.  Dew or light rain
     can provide the necessary moisture. The soluble fluoride then can be
     absorbed readily by the tissues.

        Principal sources of fluorides emitted  to the atmosphere are ferti-
     lizer manufacturing, aluminum reduction,  ore smelting, and ceramic
     manufacturing.
26

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                                                                                                 Figure 33.  In  advanced stage,  injury
                                                                                                            progresses  from tip to base
                                                                                                            of gladiolus leaves.
Figure 32.  Gladiolus plant shows beginning of fluoride injury on tips
           of leaves.
Figure 34.  Fluoride-injured pear leaves were collected in Staten  Is-
           land,  New York.
                                                                  27

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 Figure 35.  Prune  /eaves  (urn brown at edges when exposed to fluo-
            ride.
Figure 37.  Maple leaves from West Virginia were injured by fluoride
           from nearby industry.
Figure 36.  Italian prune leaves were injured during laboratory expo-
           sure to fluoride.
                                                                                 Figure .38.  Pine needles show sporadic  injury.
                                                                  28

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 Figure 39.  Young  needles of ponderosn pine exposed  to  fluoride
            Iright) were injured:  control on left is healthy plant.

   Vegetation closest to and downwind from a fluoride source suffers
the most  severe injury.30  Measurements taken over  the years from
such  locations have disclosed alarmingly high fluoride  concentra-
tions. Concentrations as high as 300 ppm of fluorine were found  in
vegetation  near aluminum  and  fertilizer plants in Tennessee.31   In
another case the fluoride level was 462  ppm. Nine miles from this
source the concentration  on grape leaves was still 114 ppm. In still
another investigation, concentrations of  more that 10,000 ppm fluo-
ride were found on pine trees in Montana.

   Fluoride contamination of plants is manifested in several ways.  In
gladioli, for instance, necrotic injury of  the tissue starts at the tip  of
the leaf and advances downward. On broad-leaf plants, the injury is
along the margin, and  there  is often  a sharp demarcation line be-
tween injured and intact tissue. Injury to some plants appears as spots
of injured tissue surrounded by healthy tissue.

   A study of citrus  trees exposed to 2 to 3 ppm fluoride for several
months revealed leaf  chlorosis.  Compared  with comparable  trees
growing in fluoride-free air, the trees studied produced smaller leaves
and lower fruit yields, and grew less vigorously. In other plants stud-
ied,  fluoride accumulations also caused dwarfing,  leaf  abscission,
dropping of fruit, and lower yields.32
                                                                      of fluoride pollution at  Staten  Island,  New York.21  Gladioli bulbs
                                                                      were  planted at five  sites on June 27, 1965. Tip and margin burn
                                                                      developed by July  20, and injury on the leaf blades gradually  ex
                                                                      tended downward and maintained a fairly uniform front. The gladioli
                                                                      plants were harvested September 20, 1965, and leaf  and  petal sam-
                                                                      ples from each of the five test stations were analyzed chemically. The
                                                                      results are shown in Table 5. The amount of fluoride found and the
                                                                      predominance of fluoride  injury that appeared on  the tips of the
                                                                      gladioli leaves indicated  that gaseous fluorides were  present in the
                                                                      atmosphere.


                                                                          Table 5.  RESULTS OF FLUORINE ANALYSIS OF GLADIOLUS
                                                                                               LEAF SAMPLES3

Location
Port Richmond


Willowbrook


Willowbrook (Control)


Princess Bay


Greenhouse at U. S.
Public Health Hospital

Location of sample
analyzed, inches
from blade tip
0 - 2
2 - 4
4 - 8
0 - 2
2 - 4
4 - 8
0 - 2
2 - 4
4 - 8
0 - 2
2 - 4
4 - 8
0 - 2
2 - 4
4 - 8
Fluoride
concentration, b-c
ppm
58.9
23.8
3.3
82.9
38.2
9.3
37.9
6.7
10.7
31.3
11.4
3.4
123.4
30.8
10.4
aGlodiolus petals collected from all five locations and analyzed forflu
 found to contain  3.9 ppm, calculated on a dry weight basis.
  In 1965, Snow Princess gladioli plants were used to locate
                                                         sources
 Calculated on a dry weight basis.

cValues above 10 ppm are considered
 ppm ore accurate to about ' 3 ppm.
                                                                                                        ate to about  ' 5 ppm; values under 10
                                                                  29

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   _ hlorine is found in the atmosphere primarily in those areas where
    it is being used as a disinfectant or where it is involved in a chemical
    process. For example, chlorine-injured plants are often observed near
    swimming pools and sewage disposal systems.

      Chlorine pollution causes marginal and tip necrosis, which may be
    similar to the  plant injury caused by  sulfur dioxide. Middle-aged
    leaves are most susceptible to chlorine injury, followed by the oldest,
    then the youngest leaves. Photographs of chlorine injury are shown
    in  Figures 40-43.

      The chlorine concentration required to injure plants is greater than
    that reported for hydrogen fluoride, but less than the level reported
    for sulfur dioxide.33

       In a study at Rutgers University, tomato plants were exposed for 2
    and 3 hours  at three different chlorine levels.34 Half of the plants
    were periodically sprayed with water. Response of plants, wet or dry,
    was similar. A chlorine concentration of 0.31 ppm caused no injury,
    0.61 ppm caused slight injury, and 1.38 ppm caused severe injury.
    Stanford Research Institute reported injury to alfalfa  and radishes
    that were exposed for 2 hours to 0.10 ppm chlorine.33
30

-------
Figure 40. Chlorine injury to silver maple leaves is similar to sulfur
           dioxide injury.
Figure 42.  Begonia was injured by chlorine and by hydrochloric acid
           mist in Pennsylvania.
Figure 41.  Cucumber leaf exposed to 0.75 ppm  Cl? lor 4 hours shows
           injury similar to sullur dioxide injury.
Figure 43.  Redbud leaves from
           were also injured.
same  area as  begonia  in Figure 42
                                                                  31

-------
      ethylene is one of the few hydrocarbons possessing the ability to
    injure plants without undergoing photochemical reaction with nitro-
    gen  oxides.35 Unlike PAN and ozone, ethylene is difficult to extract
    by carbon-filtering processes.

      Ethylene  is found principally in the atmospheres  of larger cities
    and  urban areas because of the high concentrations  of automobile
    and  truck exhaust, natural-gas and fuel-oil heating systems, and coal-
    burning industrial processes.

      Ethylene injury to orchids and azaleas is shown in  Figures 44 and
    45.  In the Los Angeles area and Hawaii, ethylene has been reported
    to cause the sepals of orchid flowers to become  brown or withered
    and  dry.  In  an  experimental study, the sepals of orchid  flowers be-
    came withered and dry after a 24-hour exposure to 5 ppm of ethyl-
    ene.36  Exposure to 0.3 ppm ethylene for  1 hour or 0.05 ppm for 6
    hours causes abnormalities in the sepals of cattleya orchids.

      Ethylene  interferes with  the activities  of  plant  hormones  and
    thereby causes  growth retardation.6  In addition, carnation  flowers,
    for example, failed to open properly  after  a 6-hour exposure to 0.1
    ppm.37  A  0.05-ppm  ethylene  exposure  impaired  normal develop-
    ment of marigold leaves.38  Abnormalities  of tomato  leaves  and loss.
    of flower buds  were observed after exposure of tomato  and pepper
    plants to 0.01 ppm ethylene for several hours.
32

-------
   Extensive injury to a cotton field adjacent to a polyethylene man-
ufacturing area has been reported.3?  The  pollutant traveled 1 mile
downwind from the source,  and the  damaged field suffered almost
complete loss of yield.
                                                                  Figure 45.  Contra/  azalea on left has rigorous blooms, but plant on
                                                                             right dropped blooms when exposed to ethylene.
Figure 44.  Orchid at top was  exposed to ethylene in laboratory;
           intact orchid  of same  variety is shown at bottom.
                                                                 33

-------
numi
TTC3
                                 |n addition to the visible injuries caused by toxicants in the atmos-
                                phere, atmospheric pollutants or combinations of pollutants may
                                cause considerable injuries that disturb plant function and that alter
                                or suppress growth. An example of growth suppression is shown in
                                Figure 46.
                               Figure 46. Petunia on left was grown out ol doors. Larger plant on
                                       right was grown in controlled environment.
                           34

-------
  In one experiment, the action of ozone and 1-hexane in combina-
tion  reduced  tomato plant growth, but no visible symptoms of leaf
injury were observed. Tomato plants exposed to naturally occurring
oxidants  in contaminated air had abnormally small leaves. Blossom
initiation was completely suppressed. Comparable  plants grown  in
carbon-filtered air developed  normal blossoms and set fruit.

  In 1966, it was found that growth was suppressed in Tobacco Bel
W3,  pinto beans, petunias, and geraniums when grown for 8 weeks in
ambient air at Steubenville, Weirton,  and Wheeling and for  10 weeks
in New York and New Jersey. These plants were compared to similar
plants  grown in ambient air that was passed through an activated-car-
bon  filter. Leaves on plants grown in carbon-filtered air were longer,
more vigorous, and darker  green. Root systems of plants  grown  in
carbon-filtered  air also were larger and more vigorous than  those
grown  in unfiltered air26' 27  as shown in Figure 47.
  In a later study,  chlorosis, dwarfing, and  growth suppression of
petunia, columbine, geranium, and  pinto bean plants  developed.
These plants were exposed to ambient air, and the injuries probably
were caused by the interaction of a combination of toxicants.

  It also has been shown that tree growth may be reduced by expo-
sure to ozone-olefin reaction  products and  to  naturally occurring
oxidants.40 Exposure to ozone and hexane 41 for 280 hours over a
period  of 8 weeks caused the following growth reductions in avocado
seedlings: stem growth, 56 percent; leaf width, 35 percent; and stem
diameter, 21  percent. The fresh weight of seedlings, including the
root system, was reduced 52 percent. The dry  weight of seedlings,
including the root system, was reduced 58 percent. All comparisons
were made with  comparable lots of avocados grown in carbon-fil-
tered air.
                                                                                      Figure 47.  Root  systems  of  pinto  bean plants
                                                                                                 grown with (above) and without (below)
                                                                                                 activated-charcoal-filtered air.
                                                                 35

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VEGETATION  INJURY   FROM   OTHER  AGENTS
                         CAN   BE   CONFUSED   WITH  AIR
                                             POLLUTION  INJURY
                                                          me striking similarities exist between visible injury from air pol-
                                                      ution and injury from other agents. Natural factors that may be
                                                      injurious are drought, frost, and mineral deficiencies. Other agents of
                                                      plant injury and disease include insects, nematodes, and viruses. Not
                                                      only can natural factors mimic pollution-like damage, but pollutants
                                                      themselves can sometimes mimic each other.
                                                        In 1965, injury by natural agents was thoroughly explored.42 It
                                                      was pointed out, for example, that terminal bleach disease in cereal
                                                      plants was caused by excessive water loss associated with hot winds.
                                                      Symptoms similar to sulfur dioxide  injury can be induced by frost
                                                      (Figure 48) or even by mineral deficiency (Figure 49). Symptoms of
                                                      virus or nematode attack  (Figure 50) also have to be taken into
                                                      consideration in diagnosis. Virus-like symptoms (Figure 51) are
                                                      sometimes confused with ozone injury.
                                                        In addition to the major air pollutants, other agents may  cause
                                                      extensive damage to vegetation. One such agent is the herbicide 2,
                                                      4-D. Very low concentrations of 2, 4-D cause defoliation, dwarfing,
                                                      curling, stiffening, and twisting (Figure 52). Cotton, grape, and toma-
                                                      to plants are especially sensitive to 2, 4-D.  Some insecticides are also
                                                      harmful to vegetation (Figure 53).
                                                        Because of the many possible mechanisms and sources of injury to
                                                      vegetation, investigators determining damage attributable to air pol-
                                                      lution should have extensive experience in the field.
                                                   36

-------
                                               Figure 49.  Cucumbers  and leaves  from plants with potash (center)
                                                           and nitrogen (right) deficiencies are shown with healthy
                                                           leal and cucumber (left).
Figure 48.  Frost injury
           oxide injury.
to geranium plants is similar to sulfur di-
Figure 50.  Suspected sullur dioxide injury to Texas  cotton
           rightfully identified as nematode attack.
                                           37

-------
Figure 51.  Strikingly  similar tobacco injury was  from  ozone (top)
           and mosaic virus (right). Ozone attacks old leaves first,
           then young leaves.  Mosaic  virus attacks young  leaves
           first and progresses  to old leaves.
                                                     38

-------
Figure 52.  Cotton  leaves exposed to 2, 4-D are subject to "crow/-
           footing," shown at right of photograph;  healthy leaves
           are shown on  the left.
Figure 53.  Tobacco was exposed to methyl paratnion.
                                                                  39

-------
         D       D
   _ir pollution injury  to vegetation is not only important for the
economic losses it causes agriculture, but because vegetation injury is
a  sign or forewarning of air pollution problems  that can affect man
and his well being.  Plants are  considered to be a sensitive  tool by
which the  presence  of  several  airborne toxicants in low concentra-
tions can be detected and evaluated.

   The photographs  in this document  illustrate  the damage  that air
pollution can cause  to vegetation. A number of  the  most serious
pollution offenders have been identified, and their effects have been
determined. Synergistic  effects  of multiple pollutants have also been
revealed. In most cases  injury observed in indigenous vegetation has
been reproduced in laboratory  experiments.  Table 6 is a summary of
the well-known airborne pollutants that cause vegetation injury.

   The investigator will need to use caution in diagnosing pollution
injury symptoms; and where there are uncertainties, he should obtain
help from scientific  experts. Special care must be taken to differenti-
ate between pollutant symptoms and problems associated with min-
eral deficiency, plant disease, and other agents.


   Toxicants stemming from photochemical  reactions and the injuri-
ous effects of these toxicants have been found in at least 27 states
and the District of Columbia. Canada, Mexico, and  Europe also are
known to suffer from similar problems.

   The cost of agricultural losses in the United States was recently
estimated   to  be in the  neighborhood  of  $500  million  annually.
Losses to  agronomic species  in California  alone are estimated to
amount to $132 million, with a 50 percent loss in citrus fruit.43  No
estimates  have been made of  the real economic loss caused  by sup-
pression of growth, delayed  maturity, reduction in yield, and the
attendant  increase in the cost  of crop production. Since air pollution
is  growing  in intensity in  many  areas of the country, the losses from
vegetation  damage also are undoubtedly increasing.
                                                                  40

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   Table 6. SUMMARY OF POLLUTANTS, SOURCES, SYMPTOMS, VEGETATION AFFECTED, INJURY THRESHOLDS, AND  CHEMICAL ANALYSES
Pollutants
Ozone (03)





Peroxyacetyl
nitrate (PAN)

Nitrogen
dioxide (N02)

Sulfur dioxide
(S02)




Hydrogen
fluoride (HF)



Chlorine (CI2)


Ethylene (CH2)



Source
Photochemical reaction of
hydrocarbon and nitrogen
oxides from fuel combustion,
refuse burning, and evapora-
tion from petroleum products
and organic solvents.
Same sources as ozone


High-temperature combustion
of coal, oi 1, gas, and gasol ine
combustion engines.
Coal, fuel oil, and petroleum.





Phosphate rock processing.
aluminum industry, iron
smelting, brick and ceramic
works, and fiber-glass
manufacturiag.
Leaks in chlorine storage
tanks; hydrochloric acid
mi st.
Incomplete combustion of
coal, gas, and oil for heat-
ing, and automobile and
truck exhaust.
Symptom
Fleck, stipple, bleaching
bleached spotting, pigmen-
tation, growth suppression.
and early abscission. Tips
of conifer needles become
brown and necrotic.
Glazing, silvering, or
bronzing on lower surface
leaves.
Irregular, white or brown
collapsed lesion on inter-
leaf margin.
Bleached spots, bleached
areas between veins,
bleached margin, chlorosis,
growth suppression, early
abscission, and reduction
in yield.
Tip and margin burn,
chlorosis, dwarfing, leaf
abscission, and lower
yield.

Bleaching between veins,
tip and margin burn, and
leaf absci ssion.
Sepa 1 withering, leaf
abnormalities,' flower
dropping, and failure of
flower to open properly.
Type of leaf
affected
Old,
progressing
to young



Young


Middle-aged


Middle-aged





Mature




Mature


(Flower)



Part of leaf
affected
Palisade





Spongy cells


Mesophyll
cells

Mesophy 11
cells




Epidermi s
and
mesophy 1 1


Epidermis
and
mesophy 1 1
All



Injury threshold0
ppm
0.03





0.01


2.5


0.3





0.1 (ppb)




0.10


0.05



Mg/m3
70





250


4700


800





0.2




300


60



Sustained
exposure
4 hours





6 hours


4 hours


8 hours





5 weeks




2 hours


6 hours



Reference
7





13


15


24





2




34


35



Chemical analysis
for po llutants
in plants
None





None


None


b





Distillation
and
ti tration


b


None



°Metric equivalent based on 25"C and 760mm mercury.




 Chemical analysis often is not reliable for diagnosing chloride or sulfate accumulation in leaf tissue because undamaged plants often contain higher concentrations of these pollutants tha
                                                                      41

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1. Tetzlaff,  F.  S., M.  Rogers, and  S. Edelman, "Guiding Princi-
   ples—State Air Pollution Legislation," presented at 87th meeting
   of American Public Health Association, Atlantic City, N.J., Oc-
   tober 23, 1959.

2. Thomas,  M. D., "Effects of Air Pollution on  Plants," World
   Health  Organization, Monograph Series,  No. 46, Columbia Uni-
   versity  Press, New York, 1961.

3. Middleton, J. T., J. B. Kendrick, Jr., and E. F. Darley, "Airborne
   Oxidants  as  Plant-Damaging Agent," National Air Pollution
   Symposium, Stanford Research Institute, 1955.

4. Heggestad,  H.  E., R. R. Burleson, J. T.  Middleton, and E. F.
   Darley,  "Leaf Injury on  Tobacco  Varieties  Resulting from
   Ozone, Ozonated Hexene-1. and  Ambient Air of Metropolitan
   Areas," Int. J. Air and Water Pollution, 8:1-10, January 1964.

5. Richards, B. L., J. T. Middleton, and W. B. Hewitt, "Air Pollu-
   tion  with Relation to Agronomic Crops: V. Oxidant Stipple of
   Grape," Agron. J., 50:559-561, 1958.

6. Darley, E. F., C. W.  Nicholas, and J. T. Middleton, "Identifica-
   tion  of Air Pollution Damage to Agricultural Crops," Bulletin,
   Dept. of Agriculture, State of California, Volume 55, 1966.

7. Heck, W. W., J. A. Dunning, and  I. J. Hindawi,  "Interaction of
   Environmental  Factors on the Sensitivity of Plants to Air Pollu-
   tion," JAPCA,  15:511-515, November 1965.

8. Hill,  A. C., M. R. Pack, M. Threshow, R. J. Downs, and L. G.
   Transtrum,  "Plant Injury Induced by Ozone," Phytopathology,
   51:356-363, June 1961.
 9. Ledbetter, M. C., P. W. Zimmerman, and A. E. Hitchcock, "The
    Histopathological Effects of Ozone on Plant Foliage," Contribu-
    tions of Boyce-Thompson  Institute  20(4):225-282, Oct.-Dec.
    1959.

 10. Heggestad,  H.  E., and H. A. Menser, "Leaf Spots-Sensitive To-
    bacco Strain Bel W-3, A  Biological Indicator of the Air Pollutant
    Ozone," Phytopathology, 52:735, August 1962.

 11. Taylor, 0.  C., and F. M. Eaton, "Suppression of Plant Growth
    by Nitrogen Dioxide," Plant Physiol.,  41:132-135,  January
    1966.

 12. Bush, A. F., R. A. Glater, J. Dyer, and G. Richards, "The Effects
    of Engine Exhaust on the Atmosphere When Automobiles are
    Equipped  with Afterburners," Dept. Eng.  Report  No. 62-63,
    Univ. of Calif., L. A., pp. 1-35.

 13. Darley, E. F., W.  M.  Dugger, J. B. Mudd, L. Orchi, 0. C. Taylor,
    and E. R. Stephens,  "Plant Damage by Pollution Derived from
    Automobiles," A.M.A. Arch. Environmental Health, 6:761-770,
    June, 1963.

14. Middleton,  J. T., E.  F.  Darley, and R.  F. Brewer, "Damage to
    Vegetation  from Polluted Atmospheres,"  JAPCA 8:9-15 May
    1958.

15. Taylor, O. C., "Oxidant Air Pollutants as Phytotoxicants," Pre-
    sented at 57th Annual Meeting of Air Pollution Control Associa-
    tion, Houston, Texas, June 1967.
16.  Hindawi, I. J., J. A. Dunning, and C. S. Brandt, "Morphological
    and  Microscopical  Changes in Tobacco, Bean,  and Petunia
    Leaves Exposed to Irradiated Automobile Exhaust," Phytopath-
    ology, 55:27-30, January 1965.
                                                               42

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 17. Altshuller, A. P., S. L. Kopczynski, W. Lonneman, T. L. Becker,
    T. A.  Bellar, and  I. J. Hindawi, "Air Pollution Aspects of the
    Propylene-Nitrogen Oxides Photochemical  Reaction," presented
    at 149th National ACS Meeting, Detroit, Michigan, May 1965.

 18. Haagen-Smit, A. J., and M. M. Fox, "Ozone Formation in Photo-
    chemical Oxidation of Organic Substances,"  Ind. Eng. Chem.,
    48:1484-7, September 1956.

 19. Haagen-Smit, A. J., E. F.  Parley, M. Zaitlin, H. Hull, and W. H.
    Noble, "Investigation on Injury to Plants for Air Pollution in the
    Los Angeles Area," Plant Physiol. 27:18-34, January 1952.

20. Parley, E. F., E.  R. Stephens, J. T.  Middleton, and  P. L. Hanst,
    "Oxidant Plant Damage from  Ozone-Olefin Reactions," Int. J.
    Air Pollution, 1:155-162, January 1958.

21. Hindawi, I. J., "Natural Pollutants in Staten Island, New  York,
    and Perth Amboy, New Jersey, as Reflected on Vegetation," in:
    report submitted by Abatement Branch, Division of Air Pollu-
    tion, Public Health Service, to Commissioner of the City of New
    York, 1965.

22. Stephens, E. R.,  E. F. Darley,  O. C. Taylor,  and W. E. Scott,
    "Photochemical  Reaction  Product in Air Pollution," Int.  J. Air
    and Water Pollution, 4:79-100, June 1961.


23. Air Quality  Criteria for  Sulfur Oxides, U.S.  DHEW,  NAPCA,
    Publication No. AP-50, Washington, D.C., March 1967.


24. Thomas, M.  D., and R. H. Hendricks, "Effect of Air Pollutants
    on Plants," in: Air Pollution Handbook, ed. P.  L. Magill,  F. R.
    Holden, and C. Ackley, pp. 9.1-9.44, New York, 1956.
     Synergism:  Injury to  Tobacco Plants," Science,
     153(3734):424-425, July 1966.

 26.  Heck, W. W., "Discussion of 0. C. Taylor's Paper, "Effects of
     Oxidant Air Pollutants," Occupational  Med.,  10:496-499, May
     1968.

 27.  Hindawi,  I.  J., "Injury by Sulfur Dioxide, Hydrogen Fluoride,
     and Chlorine as Observed and Reflected on Vegetation in the
     Field," JAPCA, 18:307-312, May 1968.

28.  Hindawi,  I. J. "The Product of  Photochemical Reaction as Re-
     flected on Vegetation Grown in Brooklyn Botanical Gardens,
     Willowbrook,  New York,  Roselle and Bayonne, New Jersey,"
     presented at Cooper Union Colloquium, New York, April 17,
     1967.

29.  Brewer,  R. F., R.  C. McColooch, and P. H. Sutherland, Proc.
     Am. Soc. Hort. Science, 70:259,  1957.

30.  Leone, I. A., E.  G. Brennan, R.  H. Daines, and W.  R. Robbins,
     "Some Effects of Fluorine on Peach, Tomato, and Buckwheat
     When Absorbed Through the Roots," Soil Science,  66:259-266,
     December 1948.

31.  Mclntire, W.  H., et  al., "Effects of Fluorine in Tennessee Soil
     and Crops," Ind.  Eng. Chem. 41:2466-75, November 1949.

32.  Brewer, R. F., et al., "Some  Effects of Hydrogen Fluoride Gas
     on  Bearing Navel Orange Trees," Proc.  Am.  Soc.  Hort. Sci.
     76-208-214, 1960.

33. Zimmerman, P. W., Proceedings  of the First National Air Pollu-
    tion Symposium, Los Angeles, Stanford  Research  Institute  p.
     135, 1949.
25. Menser, H. A., and H.  E. Heggestad, "Ozone and Sulfur Dioxide     34- Brennan, E.,  I. A. Leone, and  R. H. Daines, "Chlorine  as a
                                                                43

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    Phytotoxic Air Pollutant," Int.  J. Air and  Water Pollution,
    9:791-797. December 1965.

35. Brennan, E. G., I. A. Leone, and R. H. Daines, "Fluorine Toxic-
    ity  in Tomato as Modified by  Alternations with Nitrogen, Cal-
    cium, and  Phosphorus Nutrition  of the Plant," Plant Physiol.
    25:736-47, October 1950.

36. Davidson,  0. W.,  "Effects of Ethylene on Orchid Flowers,"
    Proc. Am. Soc. Hort. Sci., 53:440-446,  1949.

37. Middleton,  J. T.,  L. O. Emik,  and 0. C. Taylor, "Air Quality
    Criteria and Standards for Agriculture," JAPCA, 15:476-80, Oc-
    tober 1965.
38. Croker, W., Growth of Plants, Reingold, New York, 1948.
39.  Heck, W. W., E. G. Pires, and W. C. Hall, "The Effects of a Low
     Ethylene Concentration on the Growth of Cotton," presented at
     54th Annual Meeting of the Air Pollution  Control  Assoc., New
     York, June 1961.

40.  Todd, G. W., J. T. Middleton, and  R. F. Brewer, California Agr.
     10:7-8,  14, 1956.

41.  Taylor,  O. C., E. A. Cardiff, J.  D. Mersereau, and J. T. Middle-
     ton, Proc. Am. Soc. Hort. Sci., 71:320-25, 1958.

42. Threshow, M., "Evaluation of Vegetation Injury as an Air Pollu-
     tion Criterion," JAPCA, 15:266-269, June 1965.
43. Stern. A. C., Air Pollution and Its Effects, Academic Press, New
    York and London, 1968.
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