EPA-600/1-76-027b
August 1976                         Environmental Health Eilects Research Series
   OZONE  AND OTHER  PHOTOCHEMICAL  OXIDANTS
                             Volume 2 (Chapters  8-15.)
                                         .{*»

                                       "Health Effects Research Laboratory
                                          .   , n     .  . n  ,
                                          ice of Research and Development
                                       U.S. Environmental Protection Agency
                                  Research Triangle Park, North Carolina 27711

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Ozone
and Other
Photochemical
Oxidants
Volume 2 of 2 Volumes
Subcommittee on Ozone and Other Photochemical Oxidants
Committee on Medical and Biologic
Effects of Environmental Pollutants
National Research Council

NATIONAL ACADEMY OF SCIENCES  \J,
Washington, D. C.     1976

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                            NOTICE






       The  project reported on here was approved by the




 Governing  Board of the National Research Council, whose




 members are drawn from the Councils of the National




 Academy of Sciences, the National Academy of Engineering,




 and  the Institute of Medicine.  The members of the comrait'-




 tee  responsible for the report were chosen for their




 special competences and with regard for appropriate repre-




 sentation  of experience and disciplines.  The findings and




 conclusions presented are entirely those of that committee.






      This report has been critically reviewed according to




 procedures approved by a Report Review Committee consisting




 of members of the National Academy of Sciences, the National




Academy of Engineering, and the Institute of Medicine.  Only




after completion of the review process has it been released




for publication.






      The work on which this publication is based was performed




pursuant to Contract No.  68-02-1226 with the Environmental




Protection Agency.

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                                 CHAPTER 8

                                TOXICOLOGY*


      The toxicologic aspects of oxidant  air pollution have most often

 been examined through  laboratory studies of individual constituents of

 the complex mixture of air contaminants  that characterizes the ambient

 air environment.  Photochemical air pollution  (with automobile exhaust

 as  the primary emission  source) can be chemically characterized as

 oxidizing in reaction, and the chemical  species that contribute to this

 oxidizing property are varied.  Among the strongest of the photochemically

 formed oxidants that are present in "oxidant smog" and are stable enough to

 be  identified and measured is ozone.  Because ozone is also known to be

 among the most toxic of  gases, it is logical that most toxicologic

 research related to the  potential health effects of photochemical air

 pollution has focused  on it.  It has become almost a reflex to think of

 ozone toxicity when "oxidant toxicity" is mentioned.  Nitrogen dioxide

 is  another  toxic gas present in "oxidant smog," but, by most conventional

 indexes,  it is less toxic than ozone, especially when compared in the

 same proportions as their concentrations  in ambient air.  Indeed, ozone

 and nitrogen dioxide share many common toxicologic properties.  Nitrogen

 dioxide will be discussed in another monograph in this series, so its

 toxicology will not be reviewed here, except for specific comparisons.

Other chemical species—e.g., the peroxyacylnitrates and hydroxyl free


 *Most experimental toxicology studies of  inhaled vapors and gases report
 concentrations as parts per million.  That convention is used in this
 chapter.  See Chapter  6  for relations of various measurement units.

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 radicals, which undoubtedly contribute to the oxidizing properties of the


 total mixture of oxidant air pollution—may also contribute to the total


 biologic activity of this mixture.   However, there have been too few


 controlled toxicologic studies to permit an evaluation of their contrib-


 ution to the toxicologic actions of photochemical oxidant mixtures.  For


 example, the single toxicologic study on PAN that has been reported


 indicated that it. is much less acutely toxic than ozone (Campbell et al.,
       27

 1967).


      The review of the experimental toxicology of photochemical oxidants


 in this chapter is therefore primarily a review of the toxicology of


 ozone.  The reader should bear in mind that what is said about ozone may


 not apply in every case to the broader term "photochemical oxidants",


 but, given the current state of knowledge, ozone toxicology is the best


 approximation of the toxicology of  the class.  With this in mind, it is


 of value to review briefly the experimental toxicology of complex


 mixtures of ambient or laboratory simulated photochemical smog.


      Investigations of the potential biologic actions of a complex photo-


 chemical reaction mixture, produced by irradiating mixtures of air and


auto exhaust under laboratory conditions that simulated real driving


 patterns and solar irradiation, were first conducted in the laboratories


 of the Division of Air Pollution, U.S. Department of Health, Education,

                    105,106,109,147,150
 and Welfare (DHEW).                     The effects of both nonirradiated


 and irradiated exhaust mixtures were studied.  Clearly, irradiation of the


 air-exhaust mixture led to the formation of photochemical reaction products


 that were biologically more active.  The changes in chemical qualities of


 the mixture
                                     8-2

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that accompanied the increased biologic activity were an increase in the

concentration of total oxidant and an increase in the formation of irritant

aldehydes.  The relative proportions of the suspect biologically active

chemical species varied with the total concentration of exhaust gases in
                                                            147,150
the irradiated mixture and with the duration of irradiation.

Single-inhalation exposure studies lasting a few hours demonstrated in

laboratory animals that irradiation of exhaust mixtures led to greater

effects on respiratory mechanics in guinea pigs, greater reduction in

voluntary running activity of mice, and slightly greater carboxyhemoglobin

formation in rats, compared with animals exposed to the same total con-

centration of exhaust gases that were not irradiated.  The concentration

of total oxidant in these experiments ranged between 0.33 and 0.80 ppm

in the irradiated-exhaust mixtures; only a trace or no oxidant was detected

in the unirradiated exhaust.  The irritant aldehydes, formaldehyde and

acrolein, were also present in higher concentrations in the irradiated

atmospheres.  The effects that were noted during the period of exposure

(usually 4-6 h)  were reversible within a few hours when the animals were

returned to clean air.  The effects in animals exposed to the irradiated-

exhaust mixture are not necessarily uniquely characteristic of ozone,

but most of them could have been produced by ozone.

     The nature of changes in respiratory mechanics in guinea pigs exposed

to irradiated exhaust varied somewhat according to the ratio of oxidant

to aldehyde concentrations (formaldehyde and acrolein were measured), and

this ratio in turn varied with the duration of irradiation of the air-
                147
exhaust mixture.     Thus, when the oxidant:aldehyde ratio was low, the
                                    8-3

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pattern of effects on guinea pig respiration resembled that produced by
                                                        6,149,152
such upper airway irritants as formaldehyde and acrolein          and was

characterized by increased pulmonary flow resistance, increased tidal

volume, and decreased frequency of breathing.  Increasing the ratio

resulted in a shift in the pattern of respiration toward that produced by
                                                      153
deep-lung irritants (e.g., ozone and nitrogen dioxide)    —namely, de-

creased tidal volume and increased frequency—although the increased flow

resistance typical of the aldehyde effect persisted.  This interactive

effect  of an oxidant-aldehyde mixture could be reproduced by a simple
                              147
mixture of ozone and acrolein.     Concentration-response relationships

of these effects and other actions in laboratory animals exposed to mixed

or single components of oxidant air pollution are summarized in Table 8-1.

     From the data in Table 8-1, the conclusion could be drawn that all

the functional effects observed in short-duration experiments with lab-

oratory-produced photochemical smog mixtures could have been due to ozone

alone if one considers total oxidant concentration of the mixture equiv-

alent to ozone concentration.  A possible exception is the increase in

respiratory flow resistance in guinea pigs, which is more characteristic

of and probably due, at least in part, to the irritant aldehydes in the

exhaust mixtures.  The increase in respiratory frequency in guinea pigs

is most probably due to the oxidant (or ozone) content of the mixture.

Comparison of the concentrations for equal effectiveness in decreasing

the spontaneous running activity in mice also suggests that this action

of the mixture may be largely due to ozone; and the oxidant content of

irradiated auto exhaust appears to explain adequately the increase in
                                    8-4

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susceptibility to respiratory infection in mice exposed to the mixture.

These conclusions must, of course, be qualified by the possibility that

other chemical species, such as hydroxyl free radicals, that were not

measured or reported might also have produced the same effects and led

to the same conclusions.  Nevertheless, it is reasonable to conclude that

many of the functional effects produced by short-duration exposures to

complex photochemical oxidant mixtures are due to ozone.
                  109
     Hueter et al.    exposed animals to irradiated automobile exhaust

(simulated photochemical smog) for periods up to 23 months.  The concen-

trations were cycled, to simulate daily peak and trough pollution concen-

trations in urban centers.  Peak daily concentrations of carbon monoxide

were 20, 50, 60, and 100 ppm in four sets of exposure chambers.  There

was considerable loss of ozone and nitrogen dioxide on chamber walls,

cages, and animal fur, so the concentrations of chemically reactive gases

to which the animals were exposed probably ranged from about 0.04 to 0.2

ppm for ozone and about 0.15 to 0.5 ppm for nitrogen dioxide.  Pulmonary

flow resistances, tidal volumes, and respiratory frequencies of guinea

pigs were measured (while the animals were breathing clean air for brief

test periods)  at 16-week intervals during the experiments and were not

affected by the chronic exhaust exposures.  Exhaust-exposed mice showed

a decrease in running activity for the first few weeks of exposure, but

then recovered to control activity.  A decrease in mouse fertility rate

and a decrease in infant survival rate occurred in the exhaust chambers,

and there was an increase in the rate of spontaneous pulmonary infection

in exhaust-exposed animals.  There were no significant effects of exhaust
                                   8-7

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exposures on mortality, histopathology, growth rate, or hematologic

indexes.  Interpretation of these studies is difficult, because of surface

loss of contaminants in the chambers.  The decrease in mouse fertility
                                  125
(duplicated in a second experiment   ), the decrease in mouse physical

activity, and the increase in susceptibility to infections suggest that

some functional measurements were more sensitive for detecting effects

than conventional histologic, hematologic, or growth measurements.  It is

doubtful, however, whether any of the observed changes could be considered

chronic effects, i.e., irreversible or progressive in the absence of

continued exposure.
                       216
     Wayne and Chambers    reviewed the findings of studies on experimental

animals exposed throughout their lifetimes to ambient Los Angeles atmosphere.

The control animals were kept in rooms that were ventilated with special

filters that removed most of the ambient air pollutants.  No clear evi-

dence of chronic injury from the ambient air pollution was observed.

There was sane suggestion from pulmonary function tests, electron-microscopic

examinations, and pulmonary adenoma incidence that aged animals were

adversely affected by ambient smog; and some reversible changes in pul-

monary function of guinea pigs were noted during peak periods of air

pollution.  Increased 17-ketosteroid excretions suggested that breathing

polluted ambient air was stressful for guinea pigs.  Not only were the

reported effects marginal, but some of them may have been due to variations

in temperature and humidity.  Although the information obtained is of

little value in the quantitative assessment of the health hazards of air

pollution, some subjects for possible future consideration were revealed:
                                   8-8

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the effects of air pollutants on aged animals in which physiologic repair

processes are less active and the effects of other stressful stimuli on

the response to air pollutants.
                   55
     Qnik and Plata   reported on studies of the effect  of breathing

ambient oxidant-polluted air in Riverside, California, on spontaneous

running activity of mice, as recorded over a 1-year period.  The controls

were mice that were exposed to highly filtered air.  Monthly peak oxidant

concentrations in the unfiltered ambient air were 0.05-0.24 ppm; peak

nitrogen dioxide concentrations, 0.04-0.07 ppm; and peak total hydrocarbon

concentrations, 2.7-4.4 ppm.  The daily activity of mice breathing filtered

air was consistently higher than that of those breathing ambient air, and

the differences between the two groups were greatest during the months

when peak oxidant concentrations were highest.  Other environmental vari-

ables, especially temperature, may also have contributed to the magnitude

of differences between the groups.
                    160
     Nakajima et al.    studied histopathologic changes in the lungs of

mice that were exposed to irradiated auto exhaust and oxidant-fortified

exhaust-gas mixtures for 2-3 h/day on 5 days/week for a month.  Histopa-

thologic changes resembling tracheitis and bronchial pneumonia were observed

in mice exposed to atmospheres containing oxidant at 0.1-0.5 ppm, but not

in those exposed to atmospheres containing 0.1-0.15 ppm.  The changes were

minimal in the latter group; the main finding reported was irregular

arrangement of the epithelial cells of the relatively thick bronchioles.

     As will be shown in greater detail, ozone alone can produce many of

the effects of complex mixtures of photochemical oxidant air pollution
                                   8-9

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that have been reported from studies on experimental animals.  Studies of

the response of animals to these complex mixtures have the advantage that

they should detect the gamut of potential toxicity of photochemical oxi-

dant smog.  However, the study of complex mixtures has limited value for

mechanism studies, the most useful type of research for laboratory animal

experimentation.  The mere demonstration of similarity in quality of

response to complex mixtures and selected individual constituents does

not ensure that the constituents studied are the only or even the primary

biologically active ones.  At the same time, lack of similarity, both

qualitative and quantitative, between effects of a mixture and effects

of individual constituents may reflect interactive effects, both synergistic

and antagonistic.  The prime disadvantage of attempting to study the complex

mixture of photochemical smog—either ambient smog or a realistic laboratory

simulation—is the difficulty of obtaining reproducible, controlled

atmospheres.


EFFECTS IN THE LUNGS

Disposition and Uptake

     There is little information on the exact disposition and sites of

uptake of ozone.  However, because it is relatively insoluble in water,

it can reach the periphery of the lung and hence has the opportunity to

exert damage to both the central airways and terminal lung units.  Ozone

is highly reactive, and, given the concentrations found in ambient air, it

is highly unlikely to be exhaled as ozone under conditions of normal breathing.
                         70,222
     Frank and colleagues       have attempted to define the amount and

site of uptake of ozone in the lung, by two methods:  direct measurement
                                  8-10

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of the drop in concentration of the gas across the upper airway (nose and

pharynx) or the remainder of the airways, and predictions based on a

computer model.  In their animal experiments, they used anesthetized,

paralyzed, mechanically ventilated beagles.  The upper airways were

surgically isolated, and ozone at two concentrations (0.7-0.85 and 0.2-

0.4 ppm) was administered by nose or mouth.  Flow rates were either high

(35-45 liters/min) or low (3.5-6.5 liters/min).  Each exposure lasted

20-30 min; but, because of the slow response of the mast ozone meter,

measurements of respiratory uptake were useful only during the last 4-5

min of exposure.  The following observations were made:  nasal uptake

exceeded oral uptake at both high and low flow rates (p<0.01); uptake of

ozone, both nasally and orally, was inversely related to flow rate (p_<0.01),

except when the gas was directed through the mouth at the high flow rate;

and a decrease or increase in nasal resistance induced by drugs did not

significantly change the uptake.  The same investigators have developed

a computer model for predicting uptake of ozone, with some assumptions

related to solubility coefficient, an idealized version of the morphometry
            217
of the lungs    and a fixed set of ventilatory parameters.  Computer

analysis has shown that the dosage of ozone is greater to the peripheral
                                        70
airways than to the alveolar structures.

Effects of Short-Term Exposure to Ozone

     Morphologic Effects.  Gross autopsy findings of puJinonary edema and

hemorrage after acute exposure to ozone have been known for some time.

Several studies have shown that edema and an acute inflammatory response

occur in several species after brief exposures to ozone.  The minimal
                                  8-11

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concentration of ozone that causes the responses that have been demon-

strated depends very much on the methods used for the detection of edema.
                  191
     Scheel et al.    provided histopathologic evidence of injury caused

by a single acute exposure to ozone at 1.0 or 3.2 ppm for 4 h in mice and

by repeated intermittent exposures (8-45 ppm for 1 h) in rabbits.  No

gross pulmonary edema was observed in mice killed immediately after

exposure to 1 ppm, but moderately engorged blood vessels and capillaries

containing an excess of leukocytes were found.  Mice killed 20 h after

exposure showed mild edema and migration of the leukocytes into the

alveolar spaces.  Inhalation of 3.2 ppm produced grossly visible edema

during or shortly after exposure.  The perivascular lymphatic vessels

were distended and filled with edematous precipitate.  Hyperemia (excess

blood), mobilization of leukocytes, and various degrees of extravasation

of red cells accompanied the edema.  Damage to the respiratory tract

consisted of loss of epithelium from the bronchioles; sheets of desquamated

epithelial cells were seen in the lumen.  The technique for measuring the

gross edema produced (wet and dry lung weights) that was used in earlier

studies was not sufficiently sensitive to detect a mild edematous reaction.

More refined methods, based on the recovery of radiolabeled blood albumin

in pulmonary lavage fluid, indicate that the ozone-exposure threshold
                                                    5
for edema formation in rats is 0.25-0.5 ppm for 6 h.

     The use of sophisticated techniques of light and electron microscopy

have enabled several investigators to describe in detail the nature of
                                          16
the inflammatory response.  Boatman et al.   observed a desquamation of

the ciliated epithelium throughout the airways of cats exposed to ozone
                                  8-12

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 at 0.25,  0.5, and 1.0 ppm for 4-6 h.  The intensity of the response

 appeared  to be dose-related.  Ultrastructural changes in the airways

 consisted of cytoplasmic vacuolization of ciliated cells and condensed

 mitochondria with abnormal cristae configuration.  The latter occurred

 most often in the medium-sized airways, 0.8-1.2 mm in diameter.  Alveolar

 ultrastructural changes included swelling and denudation of the cytoplasm

 of Type I cells, swelling or breakage of capillary endothelium, and lysis

 of red blood cells.  Type II pneumocytes appeared normal.  There was a

 considerable variation in the degree of response, both within a single

 lung and  from animal to animal.
                    197
     Stephens et al.    have shown that, in rats, the degenerative changes

 in Type I alveolar cells occur after exposure to ozone at concentrations

 as low as 0.2 ppm for 3 h and that the cells are replaced by Type II

 alveolar cells beginning a day after the exposure.  By electron microscopy,
    11
 Bils   noted that the swelling of the epithelial alveolar lining cells of

mice occurred after exposure to ozone at 0.6-1.3 ppm for 4 h.  These changes

were not accompanied by fluid accumulation in the alveolar space.  There

was also a focal swelling of the endothelial cells and an occasional

break in the basement membrane.

     Electron microscopy has also shown that, in rats exposed to ozone at

3 ppm for 4 h and in mice exposed to 4 ppm for 3 h, acute inflaninatory
                          174,220
bronchiolar lesions occur.         These concentrations were high enough

to produce alveolar edema, and the observed changes were similar to those

found in earlier studies that used standard histologic techniques.
                                  8-13

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     Effects on Pulmonary Function.  Changes in pulmonary function have

been observed in a variety of species after short-term exposure to ozone,

including alterations in the elastic behavior of the lungs, increased

resistance to flow, and decreased carbon monoxide diffusion capacity.
                  191
     Scheel et al.    exposed 75 rats to ozone at 2 ppm for 3 h and

measured pulmonary function immediately after removal of the animals

from the exposure chamber.  Decreases in minute ventilation, tidal

volume, and oxygen uptake occurred immediately after exposure and reached

minimal recorded values after 8 h.  At 20 h after exposure, all measure-

ments had returned to normal.  Pulmonary edema may have been responsible

for the observations reported.
                  153
     Murphy et al.    exposed guinea pigs to ozone at 0.34-1.35 ppm for

2 h.  Respiratory rates increased and tidal volumes decreased during

exposure to all concentrations.  The maximal changes were significantly

different (p_ <0.05) frcm preexposure control values for every concentration

used.  Once a maximal response was reached, the effects tended to remain

constant for the remainder of the test period.  Respiratory rates and

tidal volumes tended to return to preexposure: control values when the

animals were returned to clean air.  Total respiratory flow resistances

were not significantly altered during inhalation of ozone at 0.34 and

0.68 ppm, but increased by 47% during exposure to 1.08 ppm.
                      52
     Easton and Morphy   observed up to a threefold increase in flow

resistance within an hour in guinea pigs during exposure to ozone at 5-7

ppm0  There was a 50% increase in frequency of breathing and a small

increase in tidal volume.  Lung compliance decreased by 50%.  After
                                  8-14

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exposure, all measurements returned to preexposure values within 3 h.

These responses did not result in an increase in the work of breathing,

in contrast with the response of guinea pigs to other irritants (formal-

dehyde and sulfur dioxide), in which the observed changes in pulmonary
                                                          7
function resulted in an increase in the work of breathing.
                              215
     Recently, Watanabe et al.    observed changes in respiratory

mechanics and single-breath diffusing capacity in cats exposed to ozone

at 0.26-1.0 ppm for an average of 4-6 h.  The animals were anesthetized,

paralyzed, and mechanically ventilated through a tracheal cannula.

Increased pulmonary flow resistance was the most sensitive index of ozone

exposure in this species and occurred in almost all the animals exposed

to 1.0 and 0.5 ppm and in two cats exposed to 0.25 ppm.  Although the

magnitude of the change was dose-related, it appeared that the concen-

tration of ozone was more critical than the duration of the exposure.

The mechanism of the response to ozone at 1.0 ppm appeared to differ

from that to the lower concentrations in that there was a pulsatile

increase in resistance that was superimposed on a more progressive change.

The underlying increase in resistance was approximately exponential with

respect to time.  Changes in dynamic compliance and capacity for diffusing

carbon monoxide were less frequent and less marked than the change in

resistance.  Vital capacity did not change.  The shape of the volume-

pressure curve during deflation did not change, and that suggests that

alveolar stability was not affected.  In cats, therefore, exposure to

ozone affects airway caliber at concentrations lower than those which

affect transfer of carbon monoxide across the alveolar-capillary membrane
                                  8-15

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or alveolar surface forces in the absence of pulmonary edema.  Unlike

the increase in pulmonary flow resistance that results from exposure to

sulfur dioxide, the response to ozone is not mediated entirely via reflex

bronchoconstriction, inasmuch as it was only partially reversed by atropine

in these experiments.  About half the response persisted after the admin-

istration of the drug.  Thus, the small airways are implicated in the

persistent increases in pulmonary flow resistance in response to ozone.

This implication is further supported by the following observations:

vagal innervation ends short of the peripheral airways, ozone can pene-

trate to the periphery of the lung, and postmortem studies show that

inflammatory changes occur in the peripheral airways.

     Unilateral exposure of the lung may be achieved in rabbits, because

they have an intact mediastinum, which permits the unexposed lung to

serve as a control for the exposed lung.  The control lung may be collapsed,

and ozone inhaled in a normal fashion by the noncollapsed lung; or, by

selective catheterization, one lung can be made to breathe ozone through

an airtight system while the other breathes ambient air.  Rabbits so

exposed to ozone at 12 ppm had increases in respiratory rate and minute
                                                                      4
volume and bilateral decreases in tidal volume and dynamic compliance.

Pulmonary function measurements were not significantly different in the

ozone-exposed lung until edema developed, as determined by an increase in

the wet weight of that lung.  After edema formation, tidal and minute

volumes, inspiratory and expiratory flow rates, and dynamic compliance

decreased and pulmonary flow resistance increased in the lung exposed

to ozone, relative to the unexposed lung.
                                  8-16

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     Studies have been performed on the effects of ozone exposure on
                  69
excised dog lungs.    This preparation offers the advantages of providing

information on changes in pulmonary function in the absence of intra-

alveolar edema and vagal innervation.  High concentrations of ozone were

used  (6.8-10.3 ppm for 2.5 h and 5-10 ppm for 3 h).  The changes in static-

deflation volume-pressure relationships were barely detectable, whether

measured in air or saline.  The data suggest that exposure to ozone does

not produce significant depletion or degradation of either surface-active

material or tissue elastic elements in the absence of edema.  Thus, it

seems that the changes in elastic behavior, as determined by changes in

dynamic lung compliance, are secondary to the formation of edema, unevenly

distributed changes in flow resistance or compliance, and a change in

tidal volume or end-expiratory lung volume.

     There is evidence that ozone has a delayed effect on elastic behavior.

Excised lungs of rabbits that were unilaterally exposed to ozone at 1.0

ppm for 3 h and then allowed to breathe ambient air for up to 2 weeks

showed a depression in the volume-pressure curves.  This change was present

during most of the postexposure test period.  The mechanism underlying
                                 70
this response was not determined.
                 71,72
     Frank et al.      exposed the right lung of rabbits to ozone at 2.2-

12.1 ppm for 3 h, the left lung having been collapsed before exposure.

When edema occurred in the right lung, changes in surfactant behavior

(as determined by in vitro measurements of the surface tension of washings

from the left lung)  were observed in some animals.  No such changes were

observed in the absence of edema in the right lung.  These results suggest
                                  8-17

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not only that ozone can induce chemical changes in exposed lungs, but

that the products of such changes can cause deleterious effects in non-

exposed lungs.

Effects of Prolonged Exposures to Ozone
                            199
     According to Stokinger,    at least three effects of long-term

exposure to ozone have been recognized:  effects on morphology and

function of the lung, lung-tumor acceleration, and aging.  An additional

effect, the development of tolerance after exposure to low concentrations

of ozone, may also be related to chronic toxicity.
                     204
     Stokinger e_t al.    reported that chronic bronchitis, bronchiolitis,

and emphysematous and fibrotic changes in the lung tissues occur in mice,

hamsters, and guinea pigs exposed daily to ozone at a concentration

slightly above 1 ppm.  These irreversible changes also develop in animals

that have developed tolerance to acute inflammatory effects.
                   75
     Freeman et al.   used tissue fixation and electron microscopy and

reported on the morphologic changes that occurred in the lungs of dogs

exposed to ozone at 1-3 ppm for 5-24 h/day for up to 18 months.  In general,

the effects reported tended to increase in severity with the concen-

tration used, rather than with the duration of the exposure.  There was

no evidence of pulmonary edema.  The most noticeable change was a

thickening of the bronchioles and respiratory bronchioles.  This change

was barely noticeable at the lowest concentrations used, but at the

highest concentrations it was accompanied by infiltration of lymphocytes,

plasma cells, and fibroblasts that formed peribronchiolar collars, thus

reducing the caliber of the small airways.  Bronchiolar changes included

an increase in the proportion of mucus-forming cells and squamous metaplasia
                                  8-18

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 of columnar and cuboidal cells.   In addition, there was an  increase  in the

 average number of macrophages per field along the peripheral airways.

     In developing rats  exposed to ozone at 0.54 or 0.88 ppm for up  to

 3  weeks, morphologic changes were seen in the respiratory bronchioles

 and distal  portions of the terminal bronchiolar epithelium, the entire

 alveolar duct,  and the associated alveoli.  These changes started to

 occur after 24  h of exposure; but,  after several days of exposure, the

 hypertrophic bronchiolar epithelium tended to recede and was replaced  by

 cuboidal or squamous cells.  The  lungs of growing rats exposed to ozone

 at 0.9 ppm were approximately 38%  heavier than those of normal animals
                                                                           74
 of the  same  age; within  3 weeks,  50% had died with grossly  inflated  lungs.

     Mice exposed to ozone at 2.5  ppm for 120 days showed progressive

metaplasia along the tracheal bronchial tree.  Return of these animals

 to clear air resulted in a reversal of these changes after  a further 120
     170
 days.
                    10
     Bartlett et al.   exposed 194 young rats (3-4 weeks old)  continuously

to ozone at  0.2 ppm for  28-32 days and observed that there was no effect

on respiratory  frequency, weight gain, tail-length increase, and external

appearance in the ozone-exposed group and that, although both ozone-

exposed and control groups looked healthy, 12 ozone-exposed and 11 control

animals had pneumonitis  at the end of the exposure period.  The results

with the latter animals were discarded in the later data analysis.  The

lung volumes of the ozone-exposed group were 16% greater than those of

the control group.   Air or saline static volume-pressure deflation curves

at 95% or 100% of total  lung capacity showed that transpulmonary pressure
                                  8-19

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was significantly lower in the ozone-exposed group, thus confirming that

exposed lungs were over distended at high transpulmonary pressures.  The

fact that this occurred in both air- and saline-filled lungs suggested

a small change in tissue elasticity, rather than abnormal surface tension.

There were no apparent morphologic differences between the two groups

detected by conventional staining techniques, but more sensitive electron-

microscopic techniques might have revealed some differences.

     Acceleration of lung tumorigenesis (adenoma) in a lung-tumor-

susceptible strain of mice occurred after daily exposures to ozone at

about 1 ppm.  At 15 months, an incidence of 85% was seen in the ozone-

exposed animals, compared with 38% in the controls; the average number
                                                               199
of tumors per mouse was 1.9, compared with 1.5 in the controls.

     There is some suggestive evidence that exposure to ozone accelerates
                                 12                          13
the aging process (es).  Bjorksten   and Bjorksten and Andrews   have

presented evidence that aging is due to irreversible cross-linking

between macromolecules, principally proteins and nucleic acids.  Aldehydes

were included in the list of cross-linking agents, and these can be
                                                    26
produced in the lung  as a result of ozone exposure.

Tolerance

     One feature of the response to oxidants (in particular, ozone) that

has stimulated considerable interest is the apparent development of

tolerance to the acute effects of short-term exposure to these agents
                                 59
in laboratory animals.  Fairchild   reviewed possible mechanisms of this

phenomenon.  Tolerance has been defined as the increased capacity of an

organism that has been preexposed to oxidant to resist the effects of
                                  8-20

-------
later exposures to ordinarily lethal  (or otherwise injurious) doses of

the same agent or of different agents  (cross-tolerance) with similar

toxicologic properties.

     Development of tolerance to the acute toxicity of ozone in experi-

mental animals has been demonstrated after a single, brief  (1 h or less)

exposure to low concentrations (0.3-3 ppm).  Rats can develop a tolerance

that lasts for a month or longer.  In mice, a tolerance lasting up to

14 weeks has been observed.  Ozone is not the only lung edematogenic

agent that can produce tolerance.  This phenomenon is also observed with

nitrogen dioxide, phosgene, and phenylthiourea.  The tolerance evoked by

one agent can provide cross-protection against other irritants.  For

example, a single exposure of rats or mice to ozone (0.5-5 ppm for 1-5 h)

will induce protection against the acute pulmonary effects of nitrogen

dioxide, hydrogen peroxide, ketene, phosgene, hydrogen sulfide, and
                  59
nitrosyl chloride.    The development of pulmonary edema is the toxic

effect of all these compounds.  Although pretreatment by injection of

phenylthiourate will provide tolerance to inhalation of an ordinarily lethal

dose of ozone, the reverse is not true.  Inhalation of ozone will not

provide cross-tolerance to the lung edema produced by injection of

thiourate.
                                104
     Studies by Henschler et al.     on the development of tolerance to

nitrogen dioxide in mice provided some insight into the significance of

this phenomenon.  They found that mice that had been exposed only once

to nitrogen dioxide were almost totally protected from effects of later

exposures to high, usually fatal concentrations, whereas those which were
                                  8-21

-------
repeatedly exposed were only partially protected.  It was concluded that

the first exposure protected from the effects of the following exposures,

thus inhibiting increased tolerance buildup.  It is significant that, in

another experiment, mice tolerant to nitrogen dioxide were exposed to a

concentration high enough to cause lethality, but none of the mice died

with pulmonary edema.  The predominant gross finding was massive

hemorrhage.

     In animals made tolerant to ozone and later exposed to ordinarily

injurious concentrations, the usual increase in lung water and other

pathologic changes associated with edema were either reduced or absent,

and the usual ozone-induced changes in activity of serum alkaline

phosphatase and adrenal succinic dehydrogenase were absent or slight.

In addition, there was significantly less oxidation of lung reduced
                                    59
glutathione in the tolerant animals.   It should be pointed out that

there may be species differences in tolerance development.  Quilligan
      182
et al.    used several different conditions of exposure and challenge

and were unable to demonstrate tolerance to ozone in baby chicks; and

it is not known whether humans develop tolerance to ozone.

     Tolerance appears to be a local phenomenon, in that experiments

with unilateral exposure showed that a lung is not protected from pulmonary

edema unless it has been exposed itself.  Thus, no tolerance was produced

in the contralateral, unexposed lung; this suggested that there is no
                                                               77
evidence of a circulating humoral agent that confers tolerance.    The

same investigators also attempted to show whether induction of tolerance

affected the cytotoxic effects of ozone on alveolar macrophages  (discussed
                                  8-22

-------
 in the next section).  They used unilateral exposure and lavage and

 observed no differences in the cytotoxicity of ozone between tolerant

 and nontolerant lungs.  A twofold increase in the number of polymor-

phonuclear neutrophilic leukocytes occurred in the tolerant lung.  Alveolar-

macrophage enzyme activities were equally depressed in both tolerant and

nontolerant lungs.  This study suggested, therefore, that tolerance does not

protect the antibacterial defense mechanisms of the lung from the effects of
                                  153
ozone.  In addition, Murphy et al.    found that exposure to ozone, which

produced tolerance in guinea pigs to the edema produced by later exposure

to high concentrations, failed to produce tolerance to the effects of low

concentrations of ozone on respiratory frequency and tidal volume.

     It appears that the development of tolerance is a useful tool to

determine the mechanism of ozone-induced pulmonary edema.  However, in

the light of the findings that repeated intermittent exposures of mice

to nitrogen dioxide produced less protection from the effects of a lethal

dose than a single preexposure and the failure to produce tolerance to

the effects of ozone on antibacterial defense mechanisms or on the

respiratory patterns of guinea pigs, it is unlikely that tolerance

development provides significant protection in human populations con-

tinuously exposed to low concentrations of oxidants.

Defense Mechanisms

     It has been observed that animals challenged with aerosols of

infectious organisms suffer a higher incidence of infection if they have

been previously exposed to ozone, irradiated auto exhaust, or other

common pollutants.  The suggested explanation for this is that the various
                                  8-23

-------
polutants inhibit, inactivate, or otherwise impair two distinct functions:

raucociliary streaming, the action of cilia in the nasal and upper respi-

ratory passages that clears particles and thus prevents them from entering

the lungs; and phagocytosis by alveolar macrophages.
                       139
     Miller and Ehrlich    determined the effect of exposure to ozone on

the susceptibility of mice and hamsters to respiratory infection caused

by inhalation of Klebsiella pneumoniae aerosol.  The ozone exposures

used were 1.3-4.4 ppm for 3 h and 0.84 ppm for 4 h per day, 5 days/week

for 2 weeks.  The observation period for this experiment was 2 weeks.

Mortality and survival time were measured.  The mortality due to K._

pneumoniae infection was significantly greater (p< 0.05) for every

exposure regimen in which animals were exposed to ozone than in their

paired controls.  No deaths were caused by ozone exposure alone.  Autopsy

of the animals exposed to K._ pneumoniae that died within the 14-day

holding period showed the infectious organism in the lungs and heart.

K._ pneumoniae was absent in animals that survived the 14-day holding

period.  It was concluded that exposure to ozone significantly reduced

the resistance of mice and hamsters to later respiratory infection due

to K^ pneumoniae.  Statistical evaluation of the data indicated higher

mortality, shorter survival time, and a lower LD   (for K. pneumoniae)
                                                50      — _———
in animals exposed to ozone than in controls.
                                                                   181
     In a similar series of experiments conducted by Purvis et al.,

mice were exposed to ozone at 3.8-4.1 ppm for 3 h, 1-27 h before and

3-27 h after challenge with K._ pneumoniae aerosol.  Within 19 h after

exposure to ozone, the resistance of mice to respiratory infection
                                  8-24

-------
 ijnitiated by challenge with the. aerosol was significantly reduced.  The

 same effect was observed in infected animals exposed to ozone up to 27 h

 after challenge with the aerosol.
                       36
     Coffin and Blorrmer   have shown that mice exhibit increased mortality

 from Streptococcus aerosol after exposure to ozone at 0.08 ppm for 3 h.

 This concentration of ozone also produced a decrease in the rate of kill

 of bacteria deposited in the lungs and hence an increase in their later
               35
 multiplication.    This effect was noted 4 days after exposure, but not

 4 h after exposure.
                     95
     Goldstein et al.   studied the effect of ozone on the in vivo rate

 of bacterial killing in the mouse lung.  They used male Swiss mice infected

 with aerosols of Staphylococcus aureus labeled with phosphorus-32.  The

 animals were sacrificed immediately or after exposure to ozone at 0.62-

 4.25 ppm for 4 h, and the radioisotope concentration in the lungs was

determined.  Increased numbers of bacteria  were consistently cultured

 from the lungs of animals exposed to ozone, compared with controls, and

 the magnitude of the effect was dose-related up to 2.58 ppm.  Some mice

 exposed to 2.2 ppm or greater yielded more staphylococci than were inhaled

 initially; thus, intrapulmonary bacterial multiplication had occurred.

The difference between control and infected animals was significant

 (p< 0.05)  at 1.10 ppm, when individual aerosol experiments were compared.

When the data from all the experiments were pooled, there were significant

differences in bacterial activity between control and treated mice for

 each ozone exposure (p< 0.05).  Inasmuch as the ozone-exposed mice vrere

 able to remove the same number of bacteria as control mice via mucociliary
                                  8-25

-------
streaming, the investigators concluded that the inhibition of bactericidal

activity resulted from the toxic effect of ozone on the alveolar macrophages.
                     3
     Alpert and Lewis  used unilateral exposure to study the effect of

ozone on the defense mechanisms of the lungs.  Rabbits were exposed unilat-

erally  to ozone at 0.5, 0.75, and 3 ppm for 3 h.  The alveolar macrophages

were harvested by pulmonary lavage.  Although there was a statistically

significant reduction in the viability of the cells from the ozone-exposed

lung, compared with the air-exposed lung, the differences were small.

There was also a dose-related inhibition of the intracellular hydrolytic

enzymes acid phosphatase, lysosyme, and 6-glucuronidase.  The fraction

of total cells present as polymorphonuclear neutrophilic leukocytes in

the lavage fluid from the exposed lung increased in a dose-related fashion

from approximately 2% at 0 ppm to approximately 28% at 3 ppm.  Associated

with the increase in the fraction of polymorphonuclear neutrophilic

leukocytes was a reciprocal decrease in the fraction of alveolar macro-

phages, although the total number of macrophages per gram (dry wt) remained

unchanged.  The authors suggested that the depression of the intracellular

hydrolytic enzymatic activity by ozone may contribute to the ozone-caused

impairment of lung defense mechanisms.

Interactions with Bronchoactive Agents

     The lung is relatively rich in Mstsinine-containing mast  cells, so

it is not surprising that a number of investigators have assessed the

role of histamine in the pulmonary toxicity observed after ozone exposure.

     Among the many effects of histamine are edematogenic alterations

in vascular endothelium and bronchoconstriction.  The latter may be
                                  8-26

-------
particularly pertinent, in view of its being a central manifestation of

asthma attacks and of the reported association of asthma attacks with

photochemical air pollution.  Bronchoconstriction has also been observed

in animals and man experimentally exposed to ozone or photochemical air

pollution.
                       49
     Dixon and Mountain   reported that exposure of mice to ozone at

1 ppm for 5 h resulted in a depletion of lung histamine content to as

low as 75% of the control value 5 days later.  They also observed that

pretreatment with promethazine, an antihistaminic agent, resulted in a

decrease in the amount of pulmonary edema produced by a sublethal dose of

ozone.  However, promethazine, in addition to being a potent antihistaminic

agent, is a phenothiozine derivative and thus might act as a free-radical-

trapping or membrane-stabilizing agent.

     Other investigators have been unable to demonstrate lung histamine
                                                   41
depletion in rats exposed to ozone at 4 ppm for 4 h   or guinea pigs
                                    52
exposed to ozone at 1-5 ppm for 3 h.    In the latter study, it was

observed that exposure to ozone at 5 ppm for 2 h followed by challenge

with histamine at 0.9-1.4 mgAg (injected 1.5-2.0 h after the end of

exposure) resulted in increased mortality, compared with that in an air-

exposed control group.  The increased susceptibility to histamine was

detectable for 120 h after the end of exposure to ozone at as low as 0.8

ppm.  This concentration is about one-twentieth of that required to

produce death from pulmonary edema due to ozone alone.  It was found that

the increased susceptibility occurred only when exposure to ozone took

place before challenge with histamine.  There was no increase in suscepti-

bility in guinea pigs that received histamine before exposure.
                                  8-27

-------
     Potentiation of the action of acetylcholine, another bronchoconstrictive

agent implicated as a mediator in asthma, has also been reported in guinea

pigs exposed to ozone at at least 2 ppm for 30 min before inhalation of
              128
acetylcholine;    the effect was observed intermittently for up to 23 h

after ozone exposure.

     The reported potentiation by ozone of the membrane damage produced
                                     88
by the indirect pathway of complement   might also play a role if it

occurs in vivo, inasmuch as this complement pathway apparently mediates
                                                 127
the allergin-reagin-induced release of histamine.     In view of the

fact that asthma attacks usually occur at night, whereas ozone peaks in

ambient air occur late in the morning, it might be more reasonable to

ascribe the epidemiologic association of photochemical oxidants with

asthma (if such exists—see Chapter 10) to an ozone-induced alteration

of the respiratory tract, either potentiating an otherwise subclinical

effect of an allergen or increasing the reactivity of smooth muscle to

bronchoactive compounds.

     The vasoactive compound serotonin has also been suggested to be
                                                                196
responsible for ozone-induced pulmonary edema by Skillen et al.,    who

noted a decrease in lung serotonin after ozone exposure.  Prostaglandins

may also be involved in ozone toxicity, in view of a report that aspirin,
                                                        49
a prostaglandin inhibitor, protects from ozone toxicity.    Prostaglandins
                                                                         173
are released from injured lungs, possibly as a result of membrane damage.
                    206
Recently, Tan et al.    demonstrated that injection of hydroperoxides,
                                                                         39
which results in lung damage similar to that caused by injected ozonides,

appeared to interfere with lung prostaglandin synthesis.

     In a study of the mechanism whereby Bordetella pertussis vaccine
                                       60,209         208
increased acute ozone toxicity in rate,       Thompson    ascribed the

effects to g-adrenergic blockade, and not to an immune-mediated response.

It was further noted that both atropine and reserpine reduced mortality,

                                     8-28

-------
which suggested that the acute lethal effects of ozone were due to  shock

and circulatory collapse, rather than pulmonary edema.

     The release of bronchoactive compounds may result from immune

reactions.  A possible role for the immune system in chronic ozone
                                       191                             203
toxicity was suggested by Scheel et al.    and by Stokinger and Scheel,

who hypothesized that ozone altered lung protein, making it immunogenic

to the host.  Presumably, the resulting antibody would cross-react with

normal lung tissue and produce damage.  Although some indirect evidence
                                                                 25
to support this hypothesis was presented, it has been questioned.

In addition, the suggestion that neonatal thymectomy altered ozone
        98                        209
toxicity   has not been confirmed.


BIOCHEMICAL ACTIONS AND MECHANISMS

Molecular Reactions

     Free-Radical Effects of Ozone:  The idea that ozone toxicity is

expressed through the formation of reactive free-radical intermediates

was originally derived from studies that noted the similarity of the

effects of ozone to those of radiation.  Earlier studies included the

observation of a similar and generally additive effect of ozone and
                                                                       64
x irradiation in producing chromosomal aberrations in Vicia fava seeds;

radiation-like effects on the deoxygenation of hemoglobin in the occluded
                                                     20
digits of humans breathing ozone at 1 ppm for 10 min;   the protective
                                                          62
effects of thiol radioprotective agents in ozone toxicity;   the ability

of ozone to produce mutations and chromosomal damage; and an increase in

the radiation-induced sphering of human and animal red cells in vitro
                       21
after ozone inhalation.    These studies and the idea of free-radical
                                                 201         213        134
effects of ozone have been reviewed by Stokinger,    Veninga,     Menzel,
            223
Zelac et al.    and others.   As discussed in more detail later, Zelac
      223,224
et al.         have also demonstrated a nearly additive effect of ozone
                                  8-29

-------
and x irradiation in producing lyrrphocytic chromosomal breaks in Chinese

hamsters.  Furthermore, other antioxidant and radical-trapping agents—

including various quinones, ascorbic acid, and a-tocopherol—have been
                                        87,89,129,135,164,184
reported to protect from ozone toxicity.

     The exact radicals produced by ozone in vivo are not fully under-
                      1
stood.  Alder and Hill  proposed that the aqueous decomposition of ozone

produced both hydrogen and hydroxyl free radicals and that the reaction
                              64
was catalyzed by base.  Fetner   suggested that hydroxyl and peroxyl

radicals were responsible for the observed radiomimetic effects.  It

should be noted that the peroxyl radical dissociates to form the superoxide
                                                          157
anion radical at physiologic pH.  Recently, Mustafa et al.    noted an

increase in lung superoxide dismutase after ozone exposure, which indirectly
                                                                   201
suggested the presence of the superoxide anion radical.  Stokinger,

noting the lability of sulfhydryl groups in the presence of ozone and

radiation, hypothesized that free radicals might be derived from the

interaction of ozone with sulfhydryls.  A similar reaction pathway has
                               45
been proposed by DeLucia et al.    That ozone-induced free radicals are

derived from the oxidative decomposition of unsaturated fatty acids has
                                           84        134                 185
been suggested by B. Goldstein and Balchum,   Menzel,    and Roehm et al.
                   86
B. Goldstein et al.   used electron paramagnetic resonance to demonstrate

free-radical signals in ozonized linoleic acid.  It is also conceivable

that singlet oxygen is derived directly from ozone or via the decomposition

of an ozonide.     Furthermore, hydrogen peroxide, which may be formed in

aqueous solution by ozone or these intermediates, has been indirectly
                                                          82
identified in the red cells of animals that inhaled ozone.
                                  8-30

-------
     All these rapidly reacting intermediates are potentially harmful to

the cell and might play a role in ozone toxicity.  Furthermore, the

potential for ozone-induced free-radical chain reactions exists.  It

appears likely that more than one radical is formed, either directly

from ozone or as a result of the interaction of ozone with normal cellular

constituents.

     The implications of various oxidative free-radical reactions for

biologic processes are being studied.  Many of these reactions appear to

play a role in normal cellular processes and may be of pathologic signif-

icance only if not contained by normal defense mechanisms.  It is of
                          194
interest that Shoaf et al.    have suggested on the basis of energetics

that ozone might be derived from superoxide anion radical.  Inasmuch as

superoxide is formed during some intracellular processes, ozone might be

a normal transient intermediate in vivo.  Ozonides have also been produced

in the absence of ozone by the photooxidation of diazo compounds in the
                      155
presence of aldehydes.     Further information concerning the inter-

relationships of ozone, free radicals, peroxides, ozonides, and singlet

oxygen in biologic systems would be useful.

     Sulfhydryl Compounds and Pyridine Nucleotides;  In view of the

oxidant nature of ozone, a number of investigators have evaluated its

effects on intracellular compounds that are normally active in cellular

redox reactions.  Attention has focused particularly on reduced pyridine

nucleotides—reduced nicotinamide adenine dinucleotide (NADH)  and reduced

nicotinamide ademine dinucleotide phosphate (NADPH)—and on sulfhydryl

compounds, specifically reduced glutathione (GSH).
                                  8-31

-------
          143             145        133                161
     Mudd,    Mudd et al.,    Menzel,    and Nasr et al.    have reported

that ozonization of aqueous solutions of NADH or NADPH results in their

oxidation.  However, there is a difference in their findings as to whether

the resulting product is a biologically active oxidized pyridine nucleotide
                                      133
(NAD or NADP), as suggested by Menzel,    or is molecularly disrupted to

the extent that it is unable to participate in enzymatic processes.

Inasmuch as more drastic effects are likely to be observed in vitro, it

is more likely that oxidation of intracellular reduced pyridine nucleotides

proceeds mainly to NAD or NADP after ozone inhalation, but further

resolution of this question would be of value.
                161
     Nasr et al.    failed to observe a change in the ratio of NADPH to

NADP in the tracheal epithelium of rats exposed to ozone at 33 ppm for an

hour.  This apparently negative in vivo finding is not surprising, inasmuch

as NADP will be rapidly reduced back to NADPH if ozone does not disrupt

the structural integrity of pyridine nucleotides.  In addition, de_ novo

synthesis of pyridine nucleotides may also occur.  The intracellular ratio

of reduced to oxidized pyridine nucleotides is under fine cellular control,

in that the oxidation of NADPH or NADH results in the stimulation of

enzymatic activity, which restores the initial ratio.  In the case of

NADPH, its oxidation increases the activity of the hexose monophosphate

shunt; this also occurs after the oxidation of glutathione.  The relevant

enzymatic steps are depicted in Figure 8-1.  The direct interrelationship

of glutathione and NADPH occurs in the reduction of oxidized glutathione

to reduced glutathione by glutathione reductase.  NADPH is required in

this step and is itself oxidized to NADP.  Accordingly, the oxidation of
                                  8-32

-------
2GSH  +   [0]  G. peroxidase     GSSG  +
GSSG  +  2NADPH  G. reductase   2GSH + 2NADP
G-6-P  +  NADP  G-6-PD	  6-P-G  +  NADPH
                (HMP shunt)>
GSH=reduced glutathione

GSSG=oxidized glutathione

G. peroxidase=glutathione perioxidase

G. reductase=glutathione reductase

G-6-PD=glucose-6-phosphate dehydrogenase

6-PG=6-phosphogluconate

G-6-P=glucose-6-phosphate

[0]=oxidizing moiety, e.g., hydrogen peroxide, free radical, lipid peroxide

HMP shunt=hexose monophosphate shunt

NADP=nicotinamide adenine dinucleotide phosphate

NADPH= reduced nicotinamide adenine dinucleotide phosphate



Figure 8-1.  Some enzyme processes active in defending against oxidant stress,
                                   8-33

-------
either NADPH or GSH conceivably accounts for the apparent increase in

hexose monophosphate shunt enzymes after repeated ozone exposure.
                         44
     de Koning and Jegier   also measured pyridine nucleotides in a study

in which exposure of Euglena gracilis to ozone at 0.8 ppm for an hour in

the presence of light produced a 9-12% decrease in NADH formation.

Histochemical studies have demonstrated an alteration in NADPH- and NADH-

diaphorase activity in the lungs of rats exposed to 0.8-ppm ozone for 7
     30
days.

     A possible interaction of ozone with sulfhydryl groups in vivo was
                                         58,62
originally suggested by Fairchild et al.,      who noted that protection

from lethal concentrations of ozone was conferred by the injection or

inhalation of sulfhydryl or disulfide compounds.  Other investigators have
                                                                  20,73,110,133
also noted protection from ozone toxicity by sulfhydryl compounds.
         142
Mountain     observed a decrease in lung glutathione and in the activity

of the sulfhydryl-containing enzyme succinic dehydrogenase after ozone

exposure.  The possible toxicologic implications of the reaction of ozone
                                                                201
with sulfhydryl compounds were discussed in detail by Stokinger.

     Exposure of aqueous solutions of GSH to ozone results in the formation

not only of GSSG, but also of higher oxidation states, including the
          133
sulfoxide.     This is important, in that, although the enzymes shown in

Figure 8-1 are capable of recycling GSSG back to GSH, the production of

the sulf oxide or the sulf one may lead to irreversible loss of glutathione.

By analogy, a similar oxidation of protein sulfhydryl groups to the

sulfoxide would also presumably prevent reduction by a disulfide-

exchange mechanism with glutathione and therefore lead to irreversible
                                  8-34

-------
 inactivation.  However, the ozone-induced production of sulfoxides or

 sulfones has not been reported in vivo.
                   45
     DeLucia et al.   reported that exposure of rats to 2-ppm ozone for

 4-8 h resulted in a statistically significant decrease in both protein

 and nonprotein lung sulfhydryl groups.  Bu1^ rats  exposed to 0.8-ppm ozone

 for 10 days showed no change in lung sulfhydryl concentrations.  As

 pointed out by the authors, this finding suggests lung adaptation and is

 consistent with their observation that chronic ozone exposure resulted

 in an increase in glucose-6-phosphate dehydrogenase (G-6-PD) concentration,

 despite a decrease in its activity after acute exposure.  Glutathione

 reductase, and NADH and succinate cytochrcme c reductase concentrations

 were also decreased after acute ozone exposure; this was ascribed to an

 effect on protein sulfhydryl groups.  However, there is no  firm evidence

 that free sulfhydryl groups are involved in the active sites of any of

 these enzymes in the lung.  The cytochrome c reductases and glutathione

 reductases both contain flavins, which are relatively readily oxidized

 intermediates.  Further studies on the sensitivity of flavin compounds

 to ozone appear warranted.  In addition, there is evidence  of an effect

 of ozone on cytochrome heme compounds, which might explain  the decrease
                                                    45
 in cytochrome c reductase observed by DeLucia et al.
                                  46
     More recently, DeLucia et al.   reported that the bulk of the

 glutathione oxidized in rat lung after exposure to 4-ppm ozone for 6 h

was in the form of mixed disulfides with lung protein sulfhydryl groups.

No increase in the concentration of oxidized glutathione was noted.  Peak

oxidation of nonprotein sulfhydryl groups did not occur until about 24 h
                                  8-35

-------
after exposure, and recovery was evident at 48 h.  Effects of exposure

to lower concentrations (0.8 ppm for 24 h and 1.5 ppm for 8 h) were not

observed.

     Further detailed studies of the effect of ozone on enzymes active

in the defense against intracellular oxidation were performed by Chow and
           31-33
co-workers.       Chronic ozone exposure resulted in an increase in the

activity of G-6-PD and 6-phosphogluconic dehydrogenase, two constituents

of the hexose monophosphate shunt, and an increase in glutathione

peroxidase and glutathione reductase concentrations (see Figure 8-1).

Of particular note is a study in which groups of rats were exposed to

ozone at 0.2, 0.5, or 0.8 ppm continuously for 8 days.  The increases in

G-6-PD, glutathione peroxidase, and glutathione reductase were linearly

related to dose.  Statistically significant differences were present

after exposure to ozone at 0.2 ppm.  In an additional study, exposure of

rats to ozone at 0.75 ppm resulted initially in a decrease in the activity
                                                             32
of these enzymes and then an increase, as exposure continued.    As

discussed below, the authors related their findings to the action of

glutathione peroxidase in detoxifying lipid peroxides, rather than to an

ozone-induced intracellular aqueous radical or hydrogen peroxide.  However,

if the latter processes do occur, a similar increase in these enzymes

after chronic exposure might be expected.

     Lipids.  Unsaturated fatty acids (UFA) are readily oxidized cellular

macromolecules whose oxidative breakdown has been observed in a number of

situations analogous to ozone toxicity, including radiation, exposure to
                  132                                    210
hyperbaric oxygen,    and inhalation of nitrogen dioxide.     The classic
                                  8-36

-------
mechanism by which free radicals and oxidative states interact with the

carbon-carbon double bonds of UFA is the formation of peroxides.  Their

decomposition may result in further free-radical production capable of

initiating peroxidation of additional UFA.  The resulting breakdown of

the UFA molecule results in various addition and decomposition products,

including peroxides and carbonyl compounds, which may themselves be

toxic to the cell.  Ozonization of UFA appears in many ways similar to

lipid peroxidation in the resulting products and biologic implications.

However, the initial attack on the double bond proceeds by a different

mechanism.  This has been studied in ozonized fatty-acid methyl ester
                                         184,185
emulsions and thin films by Roehm et al.,        whose findings support
                                                    40
the general mechanism originally proposed by Criegee   (Figure 8-2).

In this scheme, ozone directly attacks carbon-carbon double bonds; this

results, after decomposition of the double bond, in the formation of a

zwitterion and aldehyde.  These recombine to produce the ozonide.  As
                            184
pointed out by Roehm et al.,    in the presence of water the zwitterion

may form peroxides that can then catalyze the peroxidation of additional

molecules of UFA.  The ozone-induced oxidative decomposition of UFA in
                                                                      135
model membranes and emulsions has also been evaluated by Menzel et al.
                 207                                             134
and Teige et al.,    and the subject has been reviewed by Menzel.

     It is not clear from cellular and in vivo experiments whether the

observed ozone-induced breakdown of UFA proceeds through the direct

attack of ozone on UFA, through the effects of an ozone-induced free

radical that result in lipid peroxidation, or through a combination of

these processes.  Inasmuch as phenolic antioxidants are not as effective
                                  8-37

-------
                          0-0-0
               o          /        \
R-CH = CH-fT - i-> R-CH -    CH-R'
           o-o-o                o-o
                 ,  ff                     \                  multiple
       R-CH .   + R - CH -     R-CH     XH-R   - ^> deconposition
                                                             products
         (A)        (B)                   (C)
Figure 8-2.  Mechanism of ozonolysis.  A, Criegee  zwitterion; B,  aldehyde;

            C, ozonide.
                                8-38

-------
 in protecting against the direct attack of ozone on double bonds as they
                                                    185
 are in the autocatalytic lipid peroxidation process,    the finding that

 vitamin E protects against ozone toxicity might indirectly indicate that
                                                                     136,137
 ozone-induced lipid peroxidation does occur.  However, Menzel et al.,

 in a series of studies with preformed fatty-acid ozonides, have concluded

 that such compounds may be responsible for a significant proportion of

 ozone toxicity.  Because "lipid peroxidation" is the term commonly used

 in the literature and the biologic implications of lipid ozonization and

 lipid peroxidation appear to be relatively similar, we will use the latter

 term in discussing the effects of ozone on UFA.

     Evidence of a role of lipid peroxidation in the cellular toxicity of

 ozone has been obtained in in vitro studies in which human red cells were

 exposed to this oxidant gas.      The possibility that lipid peroxidation

 is responsible for altered permeability of bacterial cell walls after
                                               193
 ozone exposure was proposed by Scott and Lesher    and has since been
                                                          207
 confirmed by others.  Of note is the study of Teige et al.    in which

 red cells were lysed more readily by incubation with ozonized liposomes
                                                         137
 than they were by ozone itself.  Similarly, Menzel et al,    noted that

 incubation of red cells in ozonized serum produced more toxicity than did

direct ozonization of the red cells in the absence of serum.  Menzel
      137
 et al.    also demonstrated that incubation of human or mouse cells with

 fatty-acid ozonides produced Heinz bcdies, methemoglobin formation,

 oxidation of thiol groups, and formation of mixed disulfides with hemoglobin.

Oral administration of vitamin E protected against Heinz-body formation

 in vitro.  Heinz bodies were also observed in the red cells of mice
                                  8-39

-------
exposed to ozone at 0.85 ppm for 48 h.  Lung toxicity that mimicked that
                                                                  39
observed after ozone exposure has been seen by Cortesi and Privett

in rats that received intravenous injections of fatty-acid hydroperoxides

or ozonides.

     Lung lipid peroxidation during ozone inhalation was suggested by

the finding of conjugated diene bonds in an extract of the lungs of mice
                                        90
exposed to ozone at 0.4-0.7 ppm for 4 h.    The presence of thiobarbituric

acid reactants, predominantly malonaldehyde (another index of lipid

peroxidation), has been observed in the lungs of rats exposed to ozone at
                                      33
0.7-0.8 ppm continuously for 5-7 days.    The malonaldehyde concentration

was linearly related to the concentration of glutathione peroxidase, and

animals given a-tocopherol supplements did not have as great an increase

in either malonaldehyde or glutathione peroxidase.  The authors suggested

that the increase in glutathione peroxidase concentration reflected the

activity of this enzyme in detoxifying lipid peroxides, rather than a

more direct ozone-induced intracellular radical or oxidizing species.

This is a crucial point, particularly because in later studies there was
                                                                  31
no apparent threshold for the increase in glutathione peroxidases.

Lipid peroxidation is primarily a cell-membrane event, whereas GSH and

its related enzymes are intracellular.  Therefore, although an increase

in these enzymes would presumably protect intracellular constituents

against oxidation that is secondary to lipid peroxidation, direct protection

of the cell membrane might not be expected.  Accordingly, a lack of

threshold for a lipid peroxidation-induced increase in glutathione

peroxidase implies that any concentration of ozone produces lung lipid
                                  8-40

-------
peroxidation.  However, such an interpretation must be viewed with caution,

for at least two reasons:  the assumption of linearity in the enzyme data

is open to question, particularly because the findings are not inconsistent
                            31
with a curvilinear function;   and lung lipid peroxidation at low con-

centrations of ozone (e.g., 0.2 ppm) has still not been documented, and

it is possible that the observed enzyme increases, rather than reflecting

lipid peroxidation, are in response to other intracellular ozone effects.

If the latter is true, then the increase in glutathione peroxidase could

be considered an adaptive response with no pathologic consequences to

the lung, although this is open to debate.  In this respect, it is of
                      180
interest that Prinsloo    has reported an increase in lung hexose

monophosphate shunt enzymes after inhalation of quartz dust4



     Further indirect evidence of a role of lipid peroxidation in ozone

toxicity has been obtained in studies in which animals deficient in

vitamin E were found to be more susceptible to lethal concentrations of

ozone and sublethal concentrations led to a more rapid utilization of
                         87,135
this antioxidant vitamin.        Although vitamin E deficiency potentiates

the effects of ozone, it is not completely clear whether supranormal

concentrations of vitamin E protect against ozone toxicity.  Mice given

tocopherol supplements were not protected against lethal concentrations
         164
of ozone,    and the specific activity of lung hydrolases was found to
                                                48
be unrelated to dietary vitamin E concentration.    However, other

investigators have reported that additional supplementation with vitamin E

above usual dietary concentrations lessens the extent of toxicity in
                          31,33,159
animals that inhale ozone.
                                  8-41

-------
                   158
     Mustafa et al.    were unable to detect lung lipid peroxides after

short-term or subacute ozone exposures (0.8-2.0 ppm), but noted their

presence after in vitro exposures of mitochondrial preparations.  Dowell
      51
et al.   saw no evidence of lipid peroxidation in an alveolar macrophage

preparation obtained from rabbits acutely exposed to ozone at up to 10 ppm.

     The implications of an ozone-induced breakdown of UFA extend beyond

the destruction of these integral components of cellular membranes.  Lipid

peroxides can produce hydrogen peroxide and oxidize sulfhydryl groups and

other amino acid constituents, and this results in enzyme inactivation.

In addition, lipid peroxidation has been implicated in one of the many

theories that attempt to explain the aging process—that based in part

on the apparent similarity of "normal" age pigments to the products of

the reaction of lipid peroxides with proteins.  In particular, proteins

cross-linked by the dicarbonyl lipid peroxide breakdown product malonaldehyde
                                                                    47
have fluorescent spectra similar to that of lipofuchsin age pigment.
                     22
Bruch and SchlipkOter   noted lipofuchsin granules in the lungs of mice

exposed to ozone at 0.86 ppm for up to 10 months.  Inasmuch as acceleration
                                                        191
of aging has been reported after chronic ozone exposure,    it is con-

ceivable that this is mediated through lipid peroxidation.  In addition

to free radicals and peroxides, the end products of the oxidative decom-

position of UFA include carbonyl compounds that may also have toxic effects.
            26
Buell et al.   reported the presence of carbonyl compounds in the lungs of

rabbits exposed to ozone at 1 ppm for 1 h and suggested that these compounds

can cross-link collagen or elastin and so lead to altered lung function.

Increased cross-linking of collagen has also been suggested as a mechanism
                                  8-42

-------
of the deterioration of lung function with age.  Recently, Sugihara and
      205
Martin    reported simulation of lung aging after exposure to formaldehyde,

a cross-linking agent.

     Proteins.  As described above, sulfhydryl groups are relatively

susceptible to oxidation by ozone, and a decrease in lung-protein

sulfhydryl groups has been reported as a consequence of ozone exposure.

Free sulfhydryl groups are important constituents of many enzymes, and

oxidation results in a loss in activity.  In addition, cell-membrane

sulfhydryl groups play an important role in the transport of water and

ions, and it is conceivable that their oxidation in the lung is a factor

in ozone-induced pulmonary edema.

     The oxidation of cysteine, as well as other amino acids, was studied
              144
by Mudd et al.     Individual amino acids in aqueous solution were exposed

to ozone; the reported order of susceptibility was cysteine, methionine,

tryptophan, tyrosine, histidine, cystine, and phenylalanine.  Other amino

acids were not affected.  This order is similar to that for the relative

susceptibility of amino acids to radiation and to lipid peroxides.

Evaluation of the ozonization products revealed that cysteine was con-

verted to cysteic acid, as well as cystine; methionine to methionine

sulfoxide; tryptophan to a variety of products, including kynurenine and

N-formylkynurenine; tyrosine also to a variety of products, including

dihydroxyphenylalanine; histidine to ammonia, proline, and other compounds;

and cystine in part to cysteic acid.  In sane cases, the rate and end

products depended on the pH of the solution.
                                  8-43

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     Somewhat different oxidation products were observed by Previero
       178,179
et al.,        who performed the ozonization in anhydrous formic acid,

rather than aqueous solution.  This raises the possibility that in vivo

effects on protein may depend on the relative hydrophobicity of the

location of the susceptible amino acid, particularly in cell-membrane

lipoproteins.

     A number of investigators have studied the effect of ozone on the

ultraviolet absorption spectra of proteins and amino acids.  A decrease

in the absorption of 280-nm light in a number of proteins was originally
                        79
reported by Giese et al.   to be a consequence of ozone exposure; they

suggested that this was due to an interaction of ozone with the ring

structures of tyrosine and tryptophan.  Exposure of a solution of

tryptophan to ozone resulted in a decrease in 280-nm absorption, whereas

the extinction coefficient of tyrosine increased.  Similar results with
                                        191
tyrosine were reported by Scheel et al.,    who also noted alterations

in the ultraviolet spectra of egg albumen, perhaps representing dena-

turation by ozone.
                                             91
     MDre recently, B. Goldstein and McDonagh   demonstrated that the

native protein fluorescence (280-nm excitation, 330-nm emission) of red-

cell membranes exposed in vitro to ozone at 1 ppm was a somewhat more

sensitive indicator of ozone effect than other characteristics measured

in the same system, including oxidation of cell-membrane sulfhydryl

groups, loss of acetylcholinesterase activity, and formation of lipid

peroxide breakdown products.
                                  8-44

-------
     Among the specific enzymes whose activity has been reported to be

decreased after in vitro ozone exposure are papain, glyceraldehyde-3-
                        133          107              144
phosphate dehydrogenase,    lysozyme,    ribonuclease,    and acetyl-
               83,167
cholinesterase.        The latter enzyme appears to be particularly

susceptible to free-radical and oxidative states.  A loss in acetyl-
                                                                    23
cholinesterase activity has been reported in the red cells of humans
        92
and mice   that inhaled ozone.  However, there are only minimal amounts

of this enzyme in lung tissue, and, although it has been suggested that
                                                                      26
acetylcholinesterase is important in bronchial tract ciliary activity,

there is no direct evidence to support this conjecture.

     As described elsewhere in this chapter, alterations in the activity

of a number of lung enzymes have been described after acute and chronic

ozone exposure.  With the possible exceptions of the sulfhydryl-containing

enzyme succinic dehydrogenase and the cytochrome P-450 enzyme benzopyrene

hydroxylase, it is difficult to determine whether these findings are due

to a direct oxidative effect of ozone or are secondary to changes in

protein synthesis, concentrations of intermediates, or destruction of

cells or organelles.

     Nucleic acids.  Less is known about the interaction of ozone with

other macromolecules.  Alterations of nucleic acids in solution have
                                      34
been reported by Christensen and Giese,   and in Escherichia coli by
           177
Prat et al.     in studies with relatively high concentrations of ozone.

Both purines and pyrimidines are attacked by ozone.  However, the detailed

chemistry of the reaction, including the intermediates and end products,

has not been fully elucidated.  This may be important, in view of the
                                  8-45

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chronosonal effects of ozone, although such effects are most likely

due to the interaction of an ozone-induced intermediate with DNA, rather

than to ozone itself.

     Studies of DNA synthesis in lung after ozone exposure have yielded
                              191
varied results.  Scheel et al.    exposed rats to ozone at 9.2 ppm for

45 min and reported an initial decrease in lung DNA content, which

returned to normal in 6 h.  In contrast, lung RNA content was found to

increase sharply (as fraction of body weight)  an hour after exposure.
               41
Cronin and Giri   found no change in DNA content per lung in rats exposed
                                        56
to ozone at 4 ppm for 4 h.  Evans et al.   used a more sensitive auto-

radiographic procedure and reported a decrease in the fraction of mouse

lung cells that synthesized DNA immediately after exposure to ozone at

0.5-3.5 ppm for 6 h.  DNA synthesis had returned to normal or above
                                                                   219
normal within 72 h after exposure.  More recently, Werthamer et al.

studied the uptake of tritiated thymidine, uridine, and leucine in lung

homogenates obtained from mice exposed to ozone at 2.5 ppm for 2 h/day

for up to 120 consecutive days.  Both DNA and RNA synthesis initially

declined, but protein synthesis was greatly increased.  By 30 days of

exposure, DNA synthesis was above normal, but RNA synthesis remained low.

     Carbohydrates.  Even less is known about the effects of ozone on
     ~26
carbohydrates.  Buell et al.   observed a decrease in the depolymerization

of hyaluronic acid after treatment of the lungs of ozone-exposed rabbits
                                                        88
(1 ppm for 1 h) with hyaluronidase.  B. Goldstein et al.   reported a

loss in membrane neuraminic acid of red cells exposed in vitro to high

concentrations of ozone.  It would be important to study the effects of
                                  8-46

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ozone on respiratory tract mucus, which is rich in carbohydrates, including

neuraminic acid.  This could include determination of the extent to which

ozone is able to penetrate mucus that is unreacted, whether the reaction

of ozone with mucus results in the formation of cytotoxic intermediates,

and evaluation of the interaction in mucus of ozone with other air

pollutants, particularly sulfur dioxide.  Of possible pertinence is a
                     63
study by Falk et al.,   who observed that ozone produced a loss in the

viral hemagglutinating ability of snail mucus.

Subcellular Components

     Current approaches to understanding the biochemistry of organ

systems depend heavily on fractionation procedures designed to separate

various cellular and subcellular components.  The lung is a very complex

organ, which contains many cell types that presumably function in dif-

ferent ways and may well have different key biochemical processes.

Unfortunately, the lung is difficult to homogenize and fractionate, and

this, along with the multiplicity of cell types, has greatly retarded

understanding of normal lung biochemistry.

     Many studies have evaluated the biochemical effects of ozone and

other pollutants with whole-lung homogenates.  This is a somewhat

unsatisfactory approach, inasmuch as a toxic effect at a specific target

site may be obscured by reciprocal adaptive changes in other pulmonary

cells or organelles, as well as by an influx of leukocytes and the

presence of edema.  Of interest in this regard is the observation of an
                                                        22,170
ozone-induced increase in the number of lung Clara cells      and a

shift from type 1 to type 2 pneumocytes, which has been hypothesized
                                   8-47

-------
                                     42
to be related to antioxidant defense.    The biochemical concomitants

of these morphologic alterations are unknown and are unlikely to be

ascertained by using whole-lung homogenates.  For a full understanding

of the effects of ozone in the lung, and in particular for a determination

of the lowest ozone concentrations that affect specific important indexes

of toxicity, more information on normal lung biochemistry is necessary.

     In general, the lung has been considered to be the major site of

ozone toxicity, if for no other reason than because it is the first organ

to come into contact with inhaled ozone.  It is therefore of interest
                                      39
that, in a study by Cortesi and Privett/  intravenous injection of a fatty-

acid ozonide in rats resulted in lung, edema and hemorrhage and that on

gross examination the lung was the only organ noted to be affected.
                                                                            206
Similar results were observed after injection of a fatty-acid hydroperoxide.

Other systemic agents that are relatively specific to the lung and whose
                                                                       118
toxicity is perhaps mediated by free-radical reactions include paraquat
                   28
and 3-methylindole.    These findings raise the possibility that there

is some unknown biochemical aspect of the normal lung that, in comparison

with other organs, makes it relatively susceptible to oxidative free-

radical-including agents like ozone.

     Membranes.  The possibility that pulmonary membranes are a primary

site of ozone toxicity is suggested by a number of lines of evidence,

most of which are indirect.  These include observations that the membrane
                                             171              193
is the major site of ozone toxicity in plants    and bacteria;

morphologic evidence of pulmonary membrane damage after ozone exposure

in a number of studies; and in vitro experiments with human red cells

and artificial lipid membranes.
                                  8-48

-------
     As discussed above, UFA which are present primarily in cellular

membranes, appear to be particularly susceptible to oxidative degradation

by ozone.  Various studies of membrane lipid peroxidation have implicated

this process in damage to organelles, including mitochondria, microscmes,

and lysosomes, as well as to the cell membrane itself.  By analogy, it

is conceivable that many of the findings in cells and subcellular

components described in other sections of this chapter are secondary to

ozone-induced lipid peroxidation.  However, this remains conjectural.

Furthermore, the effects of ozone on the cell membrane do not appear to

be limited to UFA.  Protein is also affected, particularly cell-membrane

sulfhydryl groups and aromatic amino acids.  Whether these protein

effects are secondary to cell-membrane lipid peroxidation or arise as a

direct result of ozone is not clear.

     No studies of the effect of ozone on a lung plasma membrane fraction

have been reported.  However, a few studies have evaluated the activity

in whole-lung homogenates of enzymes that are believed to be associated
                              191
with membranes.  Scheel et al.    reported a decrease in both 51-

nucleotidase and alkaline phosphatase concentrations (expressed as

amount per milligram of tissue)  in rats exposed to ozone at 16.9 ppm
                                           219
for 1 h or 6 ppm for 4 h.  Werthamer et al.    exposed mice to ozone at

2.5 ppm for 2 h/day on consecutive days.  No effect on the concentration

of alkaline phosphatase in lung homogenates was observed after the first

day of exposure, and enzyme activity rose after 3 days of exposure.  This

was followed by a precipitous decrease in alkaline phosphatase activity

(expressed as amount per milligram of lung protein)  to about 50% of
                                  8-49

-------
 control values,  which persisted  for  30 consecutive days of exposure.
                41
 Cronin and Girl    reported  a decrease in  lung adenosine triphosphatase

(ATPase)  concentration (expressed as  fraction of total lung weight)  in

 rats exposed to  ozone at  4  ppm for 4 h.   However, this appeared to  be

 due to the edema,  inasmuch  as  recalculating the data in relation to

 total DNA revealed no difference between  control and ozone-exposed  lung

 ATPase concentrations.

      Microsomes.   An  effect of ozone on lung microsomes has been suggested

 by morphologic studies that indicated alterations in the endoplasmic
           11,75,108
 reticulum.          Biochemical  evidence  of an effect on microsomal
                                                                 166
 enzymes  was originally obtained  in the studies of Palmer et al.,

 who demonstrated that ozone exposure (0.75-LO ppm for 3 h) resulted in a

 decrease in activity  of Syrian hamster lung benzopyrene hydroxylase,  a

 mixed-function oxidase that depends  on cytochrome P-450.  No  change in

 hepatic  activities of this  enzyme were observed, and the results were

 similar  in animals in which high activities of benzopyrene hydroxylase

 had been induced.   The maximal effect was not observed until  a few  days
                                               165
 after the single ozone exposure.  Palmer  et al.    also reported a  decrease

 in rabbit tracheobronchial  mucosal benzopyrene hydroxylase activity after

 exposure to similar ozone concentrations.
                                  93
      Recently, B.  Goldstein et al.   observed a decrease in microsomal

 cytochrome P-450 concentrations  in the lungs of rabbits exposed to  ozone

 at 1 ppm for 90  min.   Again, the nadir of the cytochrome P-450 was  not
                                                                         85
 reached until a  few days  after ozone exposure.  B. Goldstein  and Balchum

 had previously obtained indirect evidence that microsomal cytochrome  P-450
                                   8-50

-------
played a role in the expression of ozone toxicity.  Rats given inducing

regimens  of phenobarbital, which are reported to increase cytochrane

P-450, were more susceptible to lethal concentrations of ozone; but

injection of allylisopropylacetamide, which destroys cytochrome P-450,

resulted in protection.  The finding that mixed-function oxidase
                                              119
inhibitors protect plants against ozone injury    may be analogous.

Other known free-radical-trapping agents shown to protect against ozone

toxicity have often been given in multiple daily doses before acute

ozone exposure and may also be active through alteration of microsomal

intermediates.  However, lung cytochrome P-450 concentrations have not

been measured in conjunction with any of these agents.

     Liver cytochrome P-450 has been shown to be destroyed by lipid
          190
peroxides,    and in vitro exposure of lung microsomes to ozone is
                                                                             93
accompanied by a loss in cytochrome p-450 and the formation of malonaldehyde.

Evidence of a possible effect of inhaled ozone on hepatic microsomes has
                                76
been obtained by Gardner et al.,   who demonstrated that mice exposed

to ozone at 1 ppm for 3 h on 2 or 3 successive days developed a prolongation

of pentobarbital  sleeping time.  No effect was observed immediately after

exposure on the first day, nor was there any significant difference from

the control after 4-7 days of exposure.  The latter finding appeared to

be due to tolerance, inasmuch as increasing the dose to 5 ppm after 7

days at 1 ppm again resulted in a prolongation of pentobarbital sleeping

time.  The authors suggested that their findings reflect a decrease in

hepatic microsomal metabolism of pentobarbital, perhaps due to an oxidizing

circulating intermediate.
                                  8-51

-------
     Mitochondria.  Numerous ultrastructural studies have noted lung
                                                                     11,15,
mitochondrial swelling and degenerative changes after ozone exposure.
16,170,174-176,192,197,198
                            Mitochondrial swelling occurs in vitro in

association with lipid peroxidation of the mitochondrial membrane.

However, the biochemical concomitants of ozone-induced damage to lung

mitochondria have not been extensively studied.
              73
     Freebairn   noted a decrease in oxygen uptake of plant and bovine

liver mitochondria that was reversible by glutathione and ascorbic acid.

The activity of some mitochondrial enzymes, including succinic dehydrogenase

and cytochrome oxidase, has been found to be susceptible to ozone.

     Mustafa and colleagues have performed a series of studies on the

effect of ozone on rat lung mitochondrial oxygen consumption.  Acute-

exposure studies (2 ppm for 8 h and 3 ppm for 4 h) revealed that an initial

decrease in succinate dependent oxygen consumption was followed by a

rebound in which increase  in the utilization of succinate, as well as
                            156,158
other substrates, was noted.         This increase persisted for at least

3 weeks.  No difference in the yield of mitochondria between control and

exposed lungs was noted immediately after ozone exposure, but there was

a definite increase in the number of mitochondria in the exposed lungs

within 48 h of recovery.  The authors concluded that increased lung

mitochondrial oxygen consumption during recovery from ozone was due to

both enzyme activation and mitochondrial proliferation, but primarily

the latter.  Continuous exposure to ozone at 0.8 ppm for 10 or 20 days

resulted in a significant increase in lung-homogenate oxygen consumption.

In a further experiment, rats were exposed continuously for 7 days to
                                  8-52

-------
                              158
ozone at 0.2, 0.5, or 0.8 ppm.     The observed increase in oxygen con-

sumption was statistically significant at all concentrations of ozone

and varied directly with dose.
                           159
     More recently, Mustafa    studied succinate-dependent mitochondrial

oxygen consumption in rats fed either a diet containing vitamin E at

approximately the normal American dietary intake or one with 6 times as

much vitamin E.  A statistically significant increase in oxygen consumption

was observed in rats that received the diet lower in vitamin E when

exposed to ozone at either 0.1 or 0.2 ppm for 7 days.  In rats on the

diet higher in vitamin E, ozone at 0.2 ppm for 7 days also produced a

significant increase, but ozone at 0.1 pprn was without effect.  Unfortunately,

serum vitamin E concentrations were not given.

     Lysosomes.  The effect of ozone on lysosomal enzymes has been

studied by a number of investigators0  Ozone has been clearly shown to

inactivate lysozyme in vitro, but the effects of inhaled ozone on the

activity of lysozyme appear to depend on the pulmonary fraction under
                      107
study.  Holzman et ajl.    reported that exposure of rabbits or mice to

ozone resulted in a decrease in the lysozyme activity of bronchopulmonary

lavage samples.  The effect was linearly related to the product of ozone

concentration and duration of exposure, although relatively high concen-

trations of ozone (2.0-5.5 ppm)  were used in this acute-exposure experiment

(1-4 h).  The authors also reported that alveolar cells present in the

bronchial lavage of rabbits exposed to ozone at 10 ppm for 3 h had a

decrease in the rate of lysosomal release when incubated in vitro.  The

inference that this is due to in vivo oxidation of intracellular lysozyme
                                  8-53

-------
is questionable, in view of the different cell populations present in

the ozone-exposed and control bronchial lavage specimens.  Of interest,

however, is a reported decrease in the release of lysozyme from a peritoneal

polymorphonuclear leukocyte sample obtained from the ozone-exposed rabbits.
                                          4,111
     In further studies by the same group,     depression in the activity

of lysosomal enzymes—acid phosphatase, g-glucuronidase, and lysozyme—

was observed in alveolar macrophages obtained from rabbits exposed to

ozone at as low as 0.25 ppm for 3 h.  Enzyme concentrations returned

toward normal 24 h after exposure.  An ozone-induced redistribution of

lysosomal enzyme into the cytosol was suggested by a fractionation study

that demonstrated a smaller fraction of enzyme activity in the alveolar

macrophage lysosomal pellet, compared with the supernatant, with increasing
                                 110
doses of ozone.  In vitro studies    of rabbit alveolar macrophages in

tissue culture revealed an ozone-induced decrease in lysosomal acid

hydrolase activity, which was prevented when sulfhydryl compounds or

serum were added to the tissue-culture medium.  A decrease in lysozyme

has also been reported in the tears of humans reacting to photochemical
     189
smog.

     In contradistinction to the decrease in lysosomal enzyme activity

observed in alveolar macrophages and bronchial lavage fluid, Dillard
      48
et al.   reported that continuous ozone exposure (0.70-0.79 ppm for 5-7

days) resulted in an increase in the activity of some lysosomal hydrolases

in rat whole-lung hcmogenates and lung fractions, including the soluble

supernatant.  The tocopherol concentrations of the diet had no effect

on the findings.
                                  8-54

-------
                           31
     Similarly, Chow et al.   observed an increase in the lysozyme

activity of a soluble lung fraction and of plasma after continuous

exposure of rats to ozone at 0.8 ppm for 8 days.  However, no difference

in lung or plasma lysozyme activity from control values was present in

rats continuously exposed to 0.2 or 0.5 ppm or intermittently exposed

 (0.2-0.8 ppm, 8 h/day for 7 days).  Histochemical evidence of an increase
                                                                     29
in lung acid phosphatase, a lysosomal enzyme, has also been reported.

     The apparently conflicting data on lysozyme may perhaps be explainable

by considering three distinct effects of ozone:  an irritative response

that produces an influx into the lung of leukocytes, including the

alveolar macrophage, which contain lysozyme at relatively high concen-

trations, thereby leading to an increase in whole-lung lysozyme concen-

tration; a disruption  of lung lysosomal membranes, resulting in the

release of acid hydrolases; and oxidation of lysosonal protein, producing

enzyme inactivation.  Evidence to support each of these processes is

available, and it appears that the net observed effects will depend on

the ozone dose and the lung fraction that is evaluated.
                                             48                       141
     As discussed in detail by Dillard et al.   and by Mittman et al.,

the possible relationship of lysosomal proteases to chronic lung disease

has been inferred from the finding of an increased incidence of emphysema

in subjects deficient in serum a -antitrypsin factor, an a -globulin
                                1                         1
that can inhibit lysosomal proteases.  (No effect of ozone on serum

a -antitrypsin inhibitor was noted in rabbits chronically exposed to
 1    168
ozone.    )   Thus, an ozone-induced increase in concentrations of such

enzymes in the lung might produce excess proteolysis and result in

eventual chronic lung disease.   However, the available evidence is

inadequate to support the belief that such a process

                                  8-55

-------
occurs in humans intermittently exposed to ozone that results from photo-

chemical smog formation.  Further studies of this potential hazard would

be of value.

     Connective Tissue.  Despite physiologic evidence that chronic ozone
                                    10
exposure may affect lung elasticity,   there is very little information

concerning the biochemical effects of ozone on lung collagen.  Buell
      26
et al.   obtained a collagen-containing fraction from the lungs of

rabbits exposed to ozone at 1 ppm for 1 h.  A number of dinitrophenylhydrazine-

reacting carbonyl compounds were obtained after digestion with collagenase

or elastase.  The authors suggested that such carbonyls might result in

intramolecular or intermolecular cross-linking of collagen with an

attendant decline in lung function.  On the basis of present information,

these carbonyl compounds are most likely derived from lipdLd.
                                         112
     In a recent abstract, Hussain et al.    presented evidence that

exposure of rats to ozone at 0.8 ppm for up to a week resulted in an

increased rate of collagen synthesis.  Such a finding might be relevant

to ozone-induced fibrosis.  Obviously, further study of the biochemical

effects of ozone on lung collagen and elastin are in order, particularly

in conjunction with chronic-exposure experiments.

Alveolar Macrophages

     Alveolar macrophages represent a major line of pulmonary defense

against exogenous material, including infectious agents and particles.

Although the origin of these phagocytic cells is still not completely

clear, recent information suggests that they are derived from the bone
       24
marrow,   but are capable of further division and replenishment in the
                                  8-56

-------
     81
lung.   As discussed below, a number of investigators have reported

alterations in alveolar macrophage function and biochemistry after ozone

exposure.  Before a description of their observations, one potential

difficulty in interpreting the effect of ozone inhalation on alveolar

macrophages should be mentioned.  Inhalation of ozone or other irritants

results in an alteration of the number of alveolar macrophages obtained

in a bronchial lavage.  Presumably, this is due to a combination of cell

destruction and an influx of younger alveolar macrophages in response

to the irritant stress.  It is well known that immature human granulocytes

have functional capacities and concentrations of biochemical intermediates

different from those of mature polymorphonuclear leukocytes.  Unfortunately,

there is no readily available morphologic indicator of alveolar macrophage

maturity, as there is for granulocytes.  Accordingly, observed differences

between alveolar macrophages obtained after ozone exposure and those

present in normal lungs may simply reflect relative immaturity secondary

to pulmonary irritation, rather than a direct effect of ozone on bio-

chemistry or function.

     Interest in the effects of ozone on alveolar macrophages has been

spurred by the observation that relatively low concentrations of ozone

potentiate respiratory infections in animals and perhaps man.  Coffin
      37
et al.   observed a decrease in the number of bacteria phagocytized by

alveolar macrophages obtained from rabbits exposed to various concen-

trations of ozone as low as 0.3 ppm.  Some suggestion of a lack of

threshold is present, but it is not clear whether the difference from

the controls at lower ozone concentrations is statistically significant.
                                  8-57

-------
     These findings in rabbits are similar to those of E. Goldstein
       94-97
et al_.,      who have related increased bacterial infectivity in mice to

an ozone-induced impairment in the bactericidal capabilities of alveolar

macrophages.  They used radioactively labeled bacteria and observed a

decrease in mouse lung bactericidal activity after a 4-h exposure to

ozone at about 0.3-0.4 ppm.  With this technique the effects of ozone
                                          97
and nitrogen dioxide are roughly additive,   and silicotic mice are no
                                                94
more susceptible to ozone than are control mice.
                  51
     Dowell et al.   reported an increase in the osmotic fragility of

alveolar macrophage preparations obtained from rabbits acutely exposed

to ozone at 10 ppm for 3 h or intermittently exposed to ozone at 2 ppm

for 8 h/d for 7 days.  Similar intermittent exposure to ozone at 0.5 ppm

was without effect.  A test for malonaldehyde formation was negative,

but this lipid peroxide breakdown product may have been lost during the

preparatory procedure.

     Additional studies related to the alveolar macrophage include that
                      218
of Weissbecker et al.,    who demonstrated that in vitro exposure to

ozone at as low as 0.06 ppm resulted in alveolar macrophage cell death.
                 183
However, Richmond    observed only a slight decrease in bacterial

phagocytosis during in vitro incubation of alveolar macrophages with an

initial ozone concentration of 0.8 ppm.  Inasmuch as ozone was not

administered continuously, the dose to the cells may have been minimal.
                   78
     Gardner et al.   noted the ozone-induced loss of an alveolar

macrophage protective component in lung lavage fluid after acute ozone

exposure (10 ppm).  This factor appears to stabilize alveolar macrophages
                                  8-58

-------
in lung fluid, and its loss would result in a decrease in cell viability.

As pointed out by the authors, this finding might indicate that the

reported effects of ozone on alveolar macrophages are, at least in part,

due indirectly to an action on an alveolar fluid component, rather than

on the macrophage itself.  The substantial decrease in recoverable

alveolar macrophages after ozone inhalation does suggest that ozone has

a direct effect on alveolar macrophages, as does the study of Huber
       108
et al.,    who noted nonspecific ultrastructural alterations in rabbit

alveolar macrophages after exposure to ozone at 5 ppm for 3 h.  However,

other investigators have failed to observe morphologic abnormalities in
                                               16,176
alveolar macrophages after inhalation of ozone.

     Mechanisms by which ozone might interfere with bactericidal function

include an alteration in cell-membrane function that produces a loss in
                                                             116
phagocytic ability and is perhaps mediated by lipid peroxides    and a

decrease in the ability of alveolar macrophages to kill phagocytized

bacteria.  Leukocytes in general appear to have a multiplicity of

mechanisms for destroying ingested bacteria.

     Ozone might interfere with the intracellular bactericidal capabilities

of alveolar macrophages by inactivating lysosomal hydrolases, or perhaps

through the destruction of heme-containing enzymes that are apparently

involved in producing superoxide anion radical.  Further evaluation of

the process by which relatively low concentrations of ozone potentiate

bacterial infection would be of value.
                                  8-59

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Extrapulmonary Effects

     An appreciable body of evidence has accumulated to indicate that

ozone has extrapulmonary effects.  Although some of the reported effects

may be secondary to the reaction of ozone with intrapulmonary neural

receptors or to release of humoral substances from the lung, other

findings appear to be more directly related to an oxidizing effect of

ozone.  The biochemical basis for the latter is unclear, particularly

because the reactivity of ozone and its short-lived intermediates would

make it unlikely for them to penetrate the pulmonary parenchyma.  Earlier

studies on the subject of extrapulmonary effects have been reviewed by
          201
Stokinger.

     Industrial and epidemiologic evidence associating ozone exposure

with headache and drowsiness are relatively nonspecific and do not clearly
                                            124
indicate extrapulmonary effects.  Lagerwerff    noted changes in a number

of indexes of vision at ozone concentrations of 0.2-0.5 ppm during short-
                                                   20
term exposures.  In addition, Brinkman and Lamberts   reported a 50%

decrease in the rate of desaturation of oxyhemoglobin in the skin

capillaries of a tied-off finger during inhalation of ozone at 1 ppm

(the experimental procedure was not given in detail).  Neither of these

studies, which have been in the literature for some time, has been

replicated.
                             23
     Recently, Buckley et al.   have described statistically significant

changes in a number of constituents and properties of red cells and serum

in human volunteers experimentally exposed to ozone at 0.5 ppm for 165

min.  Their findings included an increase in red-cell osmotic fragility
                                  8-60

-------
and a decrease in red-cell acetylcholinesterase and glutathione, all of

which were consistent with previous in vitro or animal studies.  They

also observed an increase in serum thiobarbituric acid reactants con-

sistent with lipid peroxidation and an increase in serum vitamin E that

they attributed to its mobilization.  The thiobarbituric acid assay is

predominantly a measure of malonaldehyde.  Increased serum malonaldehyde

concentrations have usually been reported in man only in association

with significant red-cell lipid peroxidation, such as occurs in hemolytic

vitamin E deficiency, presumably because malonaldehyde is rapidly

metabolized and cleared from the serum.  Also consistent with acute

hemolysis is the observation by Buckley et al. in the same subjects of

increases in serum lactic dehydrogenase and in red-cell G-6-PD.  In

contrast with those in the lung, G-6-PD increases in the anucleate red

cell are thought to represent solely a decrease in mean red-cell age

consistent with reticulocytosis, which (to explain the extent of the

G-6-PD increase in this study)  would be consistent with a relatively

significant acute hemolysis.  Data necessary to interpret this possibility
                                                               99
were not fully presented.  A more recent report from this group

evaluating dose-response data for human 2-h exposures to ozone at 0.25,

0.37, and 0.50 ppm showed a no-effect concentration of 0.25 ppm for mean

change in red-cell acetylcholinesterase activity and osmotic fragility

and a linear dose-related effect on these two characteristics at the

higher ozone concentrations.

     A number of animal studies have revealed extrapulmonary effects.

Again, there is some question as to which of these may represent an effect
                                  8-61

-------
of ozone, or a direct ozone-induced intermediate, rather than a more

indirect response to pulmonary toxicity, perhaps mediated by neurohumoral

factors.  Thus, for instance, the observations of altered hepatic nucleic
                    191                                              50
acid concentrations,    shifts in the content of metals in the liver,
                          102
alterations in urinary pH,    increases in liver weight and alkaline
                       148
phosphatase activities,    and variations in the circulating white-cell
     17
count       in ozone-exposed animals conceivably represent nonspecific

responses to lung injury.

     Of interest is the experimental approach whereby ozone is delivered

solely to one lung.  The observation of pulmonary effects in the unexposed
    71
lung   indicates that there are extrapulmonary effects of ozone at

edematogenic concentrations.  However, only the exposed lung appears to

develop tolerance to later ozone exposure and to exhibit impairment of
                             2,3,72
bacterial defense mechanisms.

     Evidence of a direct oxidizing effect on the blood of mice and rats

inhaling ozone was obtained in a study in which an increase in an in vivo
                                                                  B7
red-cell catalase-reacting compound, presumably hydrogen peroxide,   was

noted.  Although this was observed only at ozone concentrations of 5 ppm

or greater, the indirect assay for red-cell hydrogen peroxide used in

this study is relatively insensitive and would not detect smaller degrees

of ozone-induced oxidant stress.  A significant decrease in the activity

of red-cell acetylcholinesterase, a membrane constituent known to be

sensitive to lipid peroxides, has been reported in mice exposed for 4 h
                  92
to ozone at 8 ppm.    However, only a slight decrease in red-cell

acetylcholinesterase was noted in rabbits chronically exposed to ozone
                                  8-62

-------
           114                                     21
at  0.4 ppm.     An earlier study by Brinkman et al.   noted that 30-60

min of inhalation of ozone at 0.2 ppm potentiated the sphering of animal

and human red cells irradiated in vitro.  The contention that this

intriguing effect is related to an increase in aging by ozone is open to

question.  Ozone effects in blood also include chromosal aberrations in
                                        223,224
the circulating lymphocytes of hamsters,        an increase in plasma
         31                                                         169
lysozyme,   higher serum concentrations of trypsin protein esterase,
                                          136,137
and Heinz bodies in circulating red cells.         Earlier studies by
              140
Mittler et al.    failed to reveal any change in the hemoglobin or

hematocrit of young rats chronically exposed to ozone at 2.4 ppm.

     Biochemical changes in animal central nervous systems have been
                           195
reported by Skillen et al.,    who noted a decrease in brain 5-hydrox-

ytryptamine (serotonin) in rats exposed to ozone at 6 ppm for 4 h, and
                211
by Trams et al.,    who observed decreases in catecholamines and catechol-

0-methyltransferase in dogs chronically exposed to ozone at 1, 2, or 3

ppm.  Electroencephalographic (EEC) measurements in the same dogs were
                                     115
recently presented by Johnson et al.,    who noted alterations in EEC

patterns at 9 months of ozone exposure, but not after 18 months of
                                      221
exposure.  Previously, Xintaras et al.    had observed alterations in

the visual evoked electric response in rats acutely exposed to 0.5-1.0
                                       115
ppm.  As pointed out by Johnson ejt al.,    it is not clear whether these

findings indicate a direct neurotoxic action of ozone or are secondary

to damage in other organs.

     Other reported systemic effects of ozone include histologic changes
                                                                         8
in the parathyroid glands of rats exposed to ozone at 0.75 ppm for 4-8 h,
                                  8-63

-------
variations in rat thyroid function that depend on the concentration and
                           61
duration of ozone exposure,   alterations in myocardial histology in
                                            21
mice exposed to 0.2 ppm 5 h/day for 3 weeks,   ECG changes in dogs

chronically exposed to irradiated auto exhaust (containing oxidants at
            14
0.4-0.8 ppm), inhibition of gastric motility in rats exposed to ozone at
                186
0.5 ppm for 2 h,    and a decrease in the release of lysozyme frcm
                                                 107
peritoneal granulocytes in ozone-exposed rabbits.
                                             169
     An interesting report by P'an and Jegier    noted an increase in

serum trypsin protein esterase in association with pulmonary vascular

lesions in rabbits chronically exposed to ozone at 0.4 ppm.  This serum

a-2-macroglobulin, which is synthesized in the liver, has been reported

to be increased in human vascular disorders, but its physiologic

significance is unknown.

     In summary, the current evidence appears to support the contention

that ozone or an oxidizing derivative is able to penetrate the alveolar

basement membrane into the pulmonary circulation.  Recent evidence,

which requires replication, suggests that red-cell changes consistent

with an oxidizing effect can be detected in the blood of humans exposed

to ozone at ambient concentrations.  There is also evidence that ozone

affects other extrapulmonary organ systems, but it is not clear whether

this is due to oxidizing intermediates—such as ozonides, peroxides, and

the resulting carbonyl compounds carried in the circulation—or whether

it is secondary to reflex arcs or to humoral processes initiated in the

lung.
                                  8-64

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MJTAGENIC AND CARCINOGENIC ACTIONS

     The supposition that ozone is mutagenic or carcinogenic in man is

based primarily on information on the biochemical mechanism of ozone

toxicity and to a lesser extent on in vitro and animal studies.  The

biochemical evidence is for the most part indirect and depends on an

analogy between the free-radical nature of ozone toxicity and of radiation

and other carcinogenic agents.

     The production of chromosomal abnormalities by ozone was first
                             64
observed in plants by Fetner,   who noted abnormal anaphases in the root

tips of Vicia fava seeds exposed to ozone.  Bacterial mutagenesis by
                                                     43,214
ozone has been reported by a number of investigators.        Hamelin and
     100,101
Chung        noted an increased mutation rate in Escherichia coli

exposed to ozone at as low as 0.05 ppm for 5 min and observed that  the

mutants were sensitive to ozone and x irradiation.  They suggested  that

ozone might interact in DNA repair processes.  Other studies indicating

ozone-induced chromosomal effects include the observation of mitotic
                                     66
inhibition in grasshopper neuroblasts   and abnormalities in the eggs of
                                       126
oysters treated with ozonized seawater.
           65
     Fetner   has also demonstrated chromatid breaks in a human tissue-

culture cell line exposed to ozone at 8 ppm for 5 min.  Other tissue-
                                                    187
culture studies include that of Sachsenmaier et al.,    who noted

tetraploidy and other chromosomal abnormalities in embryonic chick

fibroblasts exposed to ozone and a decrease in transplantability of
                                                    163
mouse ascites tumor cells.  In addition, Pace et al.    demonstrated an

interference by ozone with mitotic activity in two tissue-culture cell
                                  8-65

-------
                                    19
lines.  More recently, Booher et al.   reported that lung cells exposed

in culture to ozone concentrations as low as 0.3 ppm demonstrated an

inhibition in growth that was proportional to the ozone concentration.
                                                           223,224
     Of particular interest are the studies of Zelac et al.        in

which Chinese hamsters exposed to ozone at 0.2 ppm for 5 h had an increased

number of chromosomal breaks in their circulating lymphocytes.  Blood

samples for study were obtained inmediately after exposure and 6 and 15.5

days later.  The highest break frequency was observed after the longest

delay.  The authors compared the effects of x irradiation and ozone

singly and combined, in their system.  The combined effects were less

than additive; this suggested some protective mechanism, perhaps analogous
                                  103
to that observed by Hattori et al.     When the authors extrapolated their

data to acceptable industrial-hygiene exposures to ozone and radiation,

ozone was found to be much more likely than x irradiation to produce

chromosomal breaks in such exposures.
                                138
     More recently, Mertz et al.    has studied the circulating lymphocytes

of humans experimentally exposed to ozone at 0.5 ppm for 6-10 h.  A

statistically significant increase in the number of minor chromosomal

abnormalities (not breaks)  was observed; it reached a peak about 2 weeks

after exposure and later returned to normal.  This delay in the development

of chromosomal abnormalities observed after ozone exposure in both hamsters

and humans differs from that observed in human radiation studies, in

which aberrations tend to remain roughly constant over 3-4 weeks.  This

raises the possibility that the ozone-induced abnormality is related to

a postreplication repair process.
                                  8-66

-------
     Carcinogenic or mutagenic effects of ozone have also been suggested
                                               199
by a number of other animal studies.  Stokinger    noted that ozone

exposure resulted in an increased incidence of pulmonary adenomas in a

strain of mice prone to develop these benign neoplasms.  Howerver, the

experimental findings were not reported in detail.  A combination of

ozone and gasoline has also been shown to cause an increased incidence
                                     121,122
of lung tumor in two strains of mice,        only one of which is prone

to develop pulmonary adenomas.

     A mutagenic effect of ozone on germ cells was suggested by the study
                   21
of Brinkman et al.,   in which female mice exposed to ozone at 0.1-0.2

ppm 7 h/day 5 days/week for 3 weeks before birth, demonstrated a fourfold

increase in neonatal mortality.  A further report of this study noted
                                                                           213
increased blepharophimosis and jaw anomalies and a decrease in litter size.

An artificial oxidant smog mixture derived from irradiated auto exhaust

has also been reported to cause an increase in neonatal mortality in
     109,125
mice.

     The toxicologic evidence indicating a possible role of ozone in

human cancer may be summarized as follows:

     •  The biochemical mechanism of ozone toxicity appears to have many

        similarities with those of other agents, particularly ionizing

        radiation, that are known human carcinogens.

     •  In vitro studies with tissue-culture cell .lines and bacteria have

        demonstrated ozone-induced chromosomal effects.

     •  Some animal studies with ozone or synthetic photochemical smog

        have shown chromosomal defects in circulating lymphocytes, a
                                  8-67

-------
        more rapid appearance of benign pulmonary tumors, and an increase



        in neonatal mortality consistent with a mutagenic effect.



     •  One study of humans experimentally exposed to ozone showed



        transient development of minor chromosomal abnormalities in



        circulating lymphocytes.



     The toxicologic studies must be considered in the perspective of an



absence of epidemiologic evidence that links photochemical air pollution



with human cancer.  Despite the presence of significant concentrations of



ozone in southern California for three decades, no associated increase in



cancer has been observed.  However, the relatively recent arrival and the



peripatetic nature of Los Angelenos might obscure, for the present, a



carcinogenic or mutagenic effect of ozone.  Furthermore, it is necessary



to consider the possible toxicologic interaction between ozone and other



airborne carcinogens.  The reported ozone-induced decrease in lung



benzopyrene hydroxylase and cytochrome P-450 concentrations could be



interpreted as protecting against aromatic hydrocarbon carcinogerisis in



which in vivo activation appears necessary.  Alternatively, it could be



hypothesized that ozone would directly activate aromatic hydrocarbon



carcinogens (e.g., by conversion to epoxides or other free-radical



intermediates) and therefore promote the presumed carcinogenic process.



This speculative discussion is presently solely to illustrate the potential



complexities of the problem of ozone-induced carcinogenesis.  Obviously,



far more information is needed on the biochemical action of ozone and



the interaction of ozone with other potential carcinogens.  This would



allow more confident assessment of the possible role of ozone in human



carcinogenesis until definitive epidemiologic information is available.
                                  8-68

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EFFECTS ON REPRODUCTION

     As noted previously, exposure of mice to simulated photochemical

smog produced by irradiating diluted auto-exhaust mixtures resulted in
                                                              109
reduced fertility and fecundity and decreased infant survival.     Lewis
      125
et al.    pursued this observation in greater depth and showed that the

nonpregnancy rate was significantly  (p< 0.02) greater  (20 of 153) in

female mice that were mated with male mice that had been exposed for 46

days to irradiated auto exhaust than in females that were mated with

males that were in clean-air chambers  (nine of 159).  No differences in

the groups with respect to the presence of copulatory plugs and absence

of implantation scars in the nonpregnant females supported the authors

conclusion that the differences in pregnancy rates were due to reduced

fertility.  In pregnant females that had been mated with irradiated-

exhaust males, there were fewer uterine implantation scars and fewer

pups per litter (p_< 0.05) than in females mated with clean-air males.

In addition, offspring viability was reduced in litters that were kept

in irradiated-exhaust chambers.  The concentration of oxidant (ozone)

varied during each day of exposure, with peaks as high as 1.0 ppm.

Daily nitrogen dioxide and carbon monoxide concentration peaks were about

1.5 ppm and 100 ppm, respectively.  The results of these experiments

suggested a possible mutagenic effect in male germ cells resulting from

exposure to the oxidant mixture.

     In an earlier study of a simpler oxidant smog mixture made by reacting

ozone with gasoline vapors (oxidant concentration, 1.25 ppm in the mixture
                                                     123
by neutral potassium iodide method), Kotin and Thomas    exposed male and
                                  8-69

-------
female mice to the synthetic oxidant mixture, to Los Angeles air, and to

washed air.  Significant differences from controls in reproduction effects

were noted only in mating pairs in the synthetic smog mixture.  These

consisted of reduced conception rates, litter size, and survival of

newborn (that were held in the exposure chambers until weaning).  These

authors also alluded to possible mutagenic effects associated with organic

peroxides that would be expected in the synthetic mixture; however, they

felt that their data on fecundity reflected an effect primarily on the

females.
                    21            213
     Brinkman et al.   and Veninga    exposed mated pairs of their

laboratory's inbred gray mice and CSV black mice to ozone at 0.1 or 0.2

ppm 7 h/day 5 days/week for 3 weeks.  There was little or not effect on

litter size, compared with air-exposed controls; however, there was a

greater incidence of neonatal mortality during the first 3 weeks of life

in the litters of ozone-exposed parents.  Offspring (C57 blacks exposed,

in addition, for 3 weeks postnatally) from the 0.2-ppm-ozone groups had

increased incidence of blepharophimosis and increased incidence of jaw

abnormalities.  The authors concluded that this was further evidence of

a similar action of ozone and ionizing radiation (which produced the same

effects at a dosage of 20 r/day).

     These studies, although few, suggest that exposure to photochemical

oxidants can influence fertility and fecundity in animals and that the

general health of newborn animals is much more likely to be impaired by

exposure to oxidants than that of their parents.  Whether the changes

observed in reproduction variables can be related to mutagenic actions of
                                   8-70

-------
ozone, discussed earlier, remains to be determined.  In any event, it

seems logical that effects of low concentrations of ozone and other

photochemical oxidants on reproduction must be indirect and may be

mediated by endocrine or ozone-biologic reaction products.


CENTRAL NERVOUS SYSTEM AND BEHAVIORAL EFFECTS

     It is somewhat surprising that possible central nervous system  (CNS)

or behavioral responses to ozone exposure have not been subjected to

greater investigation, in view of the reports of headache and drowsiness

in humans exposed to ozone and the apparent CNS depression that occurs
                                                 200,201
as an early sign of ozone interaction in animals.         Xintaras
       221
et al.,    in an application of the evoked-response technique, found a

depression in the specific visual cortex and in the superior colliculus
                                                                 53
of rats exposed to ozone at 0.5-1.0 ppm for 1 h.  However, Eglite   found

no change in rat behavior or chronaxial muscle ratios after 93 days of
                                         124
exposure to ozone at 0.6 ppm.  Lagerwerff    demonstrated in human

volunteers that repeated exposure to ozone at concentrations of 0.02-0.05

ppm resulted in psychophysiologic or sensoriphysiologic changes, including

decreased visual acuity, increased peripheral vision, altered extraocular

muscle balance, lethargy, and difficulty in concentrating.

     As mentioned previously, decreased voluntary running activity of

mice was one of the most sensitive indexes of an effect of ambient photo-
                              55
chemical oxidant air pollution   or simulated oxidant smog that was
                                                                      109,147
produced in the laboratory by irradiating diluted auto-exhaust gasses.

Whether this effect of the mixtures was due to only ozone or other oxidant

is not certain.  It is plausible to conclude that ozone was the effective
                                  8-71

-------
                                             153
agent, in view of the fact that Murphy et al.    shaved that ozone at as

low as 0.20 ppn  (during a single 6-h exposure) reduced voluntary running

activity of mice by 50%..  The 6-h exposure used in those studies coincided

with the maximaL activity period of the animals (i.e., darkness, in

adapted mice), so it seems that the effect of ozone overcame strong

natural motivation for running activity.  Furthermore, Konigsberg and
       120
Bochman    noted a concentration-related reduction in the gross motor

activity of rats exposed to ozone at 0.1-1.0 ppm.  As reported for oxidant
         109
mixtures,    mice exposed continuously to ozone at 0.3 ppm adapted and
                                            153
returned to normal activity in about a week.     However, the same mice

were still susceptible to the activity-reducing effect of higher concen-

trations (0.6-0.8 ppm), and adaptation to control activity did not occur
                                           153                     68
for at least 7 days of continuous exposure.     Fletcher and Tapell

reported that the voluntary running activity of rats was reduced by 84%

during continuous exposure to ozone at 1 ppm for a week.  Boche and
         18
Quilligan   also demonstrated that the oxidant mixture produced by

ozonizing gasoline vapors (ozone content, 0.4 ppm or greater) caused a

decrease in running activity in mice.

     These studies, although demonstrating that reduction of voluntary

running activity in mice is a very sensitive biologic indicator of oxidant

and ozone, did not reveal the mechanism of the effect.  It is possible

that this effect represents only a precautionary reaction of the organism

to avoid moving about when its senses detect  (by odor or irritation) a

strange and unpleasant stimulus.  This would be consistent with the

observation of avoidance, by mice, of a cage ventilated with ozone at
                                  3-72

-------
                                               172
 0.6-1.1 ppm in preference for a clean-air cage.     Reduction of voluntary

 running activity might also be secondary to lung irritation or inflaimation;

 however, the concentrations for activity reduction are below those

 generally associated with edema or other signs of local injury in the

 lung.  Finally, one could evoke a systemic mechanism of action as a direct

 effect of circulating ozone  (which seems unlikely) or of a CNS-depressant

 oxidant-biologic reaction product formed locally in the lung.  Further

 studies would be required to determine whether these or other mechanisms

 are involved.


 SUMMARY OF DOSE-RESPONSE RELATIONSHIPS

     The acute lethal action of ozone is due to its capacity to produce

 pulmonary edema.  The LC   for rats and mice exposed for a single 4-h

 period is approximately 6 ppm, and cats, rabbits, guinea pigs, and dogs
                                                                  199
 (in that order)  are decreasingly susceptible to the lethal action.

 Numerous reviews have considered the toxicity of ozone at lethal and
                     113,146,162,199-202,212
 lower concentrations.

     In the foregoing discussion and in Table 8-2, attention has focused

 on studies in laboratory animals that have been exposed to ozone concen-

 trations of about 1 ppm or less, because results of studies conducted

with such concentrations are thought to be more directly relevant to

 ambient oxidant air pollution, which is the source of exposure for large

human populations.  In Table 8-2, no attempt has been made to list all

 studies;  more comprehensive summaries can be found in some of the mono-

graphs cited.  Instead, the table cites studies thought to be most useful

 for evaluating the health implications of exposure to low concentrations
                                  8-73

-------
of ozone, and the concentrations listed are the lowest at which the



described effects have been observed.  Unfortunately, many studies have



not included a sufficient range of experimental concentrations to permit



construction of reliable dose-response curves or to determine what, if



any, would be a "no-observed-effect" concentration for the experimental



conditions used.  Although it is understandable that research scientists



find little stimulation in conducting exposure experiments at concen-



trations that fail to produce changes in the biologic system in which



they are interested, the conduct (and reporting)  of such experiments is



extremely important for a pragmatic evaluation of the implications of



positive findings for human health.



     The table illustrates the wide variety of biologic effects produced



in laboratory animals exposed to relatively low concentrations of ozone.



Obviously, some effects have more serious health implications than others.
                                   3-74

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RED3MMENDATIONS FOR RESEARCH



     Enhanced susceptibility to respiratory exposure to infectious agents



is of considerable potential public health significance.  This has been



reported to occur in mice exposed to ozone at as low as 0.08 ppm, the



lowest reported "effect" concentration in laboratory animal studies.



It seems essential, therefore, to continue and expand research on the



effect of ozone and other photochemical oxidants on physiologic protective



mechanisms of the lung.  Appropriate dose-response studies should be



included to confirm or establish the exposure concentration-time rela-



tionships that result in increased susceptibility to inhaled microorganisms,



and studies of the cellular responses and mechanisms should be conducted



with a view to providing methods that are applicable to epidemiologic



studies in oxidant-exposed human populations.



     Research designed to elucidate the pathophysiologic implications of



reversible changes in lung function, histology, and biochemistry that



have been observed at concentrations of 0.2-0.5 ppm would be especially



valuable in evaluating the significance of these changes for health.  In



particular, it would be useful to determine what, if any, causal or



correlative relationships exist between different effects detected by



various experimental assay systems and between reversible changes and



more chronic effects, such as reduced lung elasticity, fibrosis, and



adencma formation.  Studies on laboratory animals are particularly



suited to this type of mechanism-correlative research; but, with appropriate



experimental designs, such research should be very useful in determining




which methods or biologic changes can be usefully applied to clinical or
                                 8-80

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epidemiologic studies.  At the same time, such research could determine



whether sane of the changes  (e.g., increased activity of enzymes involved



in cell redox systems) are indicative of injury or are homeostatic



adaptive responses.  This information will have value in predicting



potential injury in the "average" population and possible help to identify



people who are hypersusceptible by virtue of some deficiency in adaptive



protective mechanisms.  Related to these research efforts, further



investigation of the influence of oxidant exposure on enzymes that bio-



transform other inhaled chemicals (e.g., aromatic hydrocarbons) and the



interaction effect of dietary antioxidants (e.g., vitamin E) should be



pursued, particularly in relation to oxidant-induced oxidation of membrane



lipids and free-radical formation.



     There are several scattered reports of extrapulmonary effects of



ozone exposure in laboratory animals.  Some (e.g., chromasomal aber-



rations in hamster lymphocytes) occur at or near concentrations that



cause local effects in the lung and portend serious and long-term health



implications.  Others(e.g., reduction of voluntary activity) may be



transient or reversible, but nevertheless contribute to decrements in



performance or well-being.  It is particularly important that further



research be conducted to confirm (or refute)  these reported extrapulmonary



actions of ozone and the exposure concentrations at which they occur.



If confirmation of their occurrence is obtained at or below the currently



reported effective exposure concentrations, useful research efforts could



be directed toward determining whether they are direct or secondary



effects and toward identifying the chemical species responsible.  More
                                  8-81

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importantly, confirmation of an isolated effect on cell genetic material



would demand a thorough expert evaluation of its significance on the



basis of existing knowledge of the long-term implication of the effect



and, accordingly, intensified laboratory and epidemiologic research.






DISCUSSION



     During the last decade, toxicologic research on the effects of ozone




in laboratory animals has demonstrated that exposure for a few hours to



airborne concentrations of less than 1 ppm produces numerous changes in



cell and organ structure and function.  The limiting concentrations



required to produce these changes appear to differ somewhat among different



species of laboratory animals and with the particular type of effect under



investigation.  However, there seems to be little doubt that several



functional and morphologic indexes of response to ozone are altered with



exposures to ozone concentrations of about 0.2-0.5 ppm.  Many of the



functional and morphologic changes produced in experimental animals



exposed to ozone as a single contaminant gas have also been demonstrated



to occur with exposure to complex mixtures of laboratory-produced or



ambient photochemical oxidant air pollution.



     Most research has focused on the effects of ozone on lung function,



morphology, and biochemistry.  Altered lung function, observed in studies



of the mechanical behavior of lungs of several species, has been noted



as the result of a few hours of exposure to ozone at 0.2-0.3 ppm.



Improved techniques for detecting minimal pulmonary edema and for examining



the microstructure of cells of the respiratory tract indicate that structural



alterations also occur with short exposures to this range of concentrations.
                                  8-82

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Furthermore, altered activities of various lung enzymes or enzyme systems,



particularly those involved in defending against oxidant stress, have



been noted by several investigators to occur at concentrations of 0.2



ppm.  Although all these effects appear to be accentuated by higher con-



centrations of ozone, indicating a dose-response relationship, most



investigations have not determined (or have failed to report) whether



lower concentrations fail to produce such changes.  In spite of the fact



that biochemical, functional, and morphologic effects have all been



detected at about the same low exposure concentrations, there has been



little systematic investigation to determine whether these effects are



causally related.  Some effects noted in these experiments might be



considered adaptive, rather than injurious.  For example, the increased



activities of lung glutathione peroxidase and glutathione reductase that



have been demonstrated after exposure to 0.2 ppm may represent an adaptation



or compensation to an injurious effect, such as lipid peroxidation, which,



although detected only at exposures to 0.4 ppm and above, may go undetected



at lower exposure concentrations because of the insensitivity of current



assay methods.  In spite of these unknowns, it is noteworthy that, in the



one case in which it is possible to make direct comparisons of the effects



of ozone in laboratory animals ard in humans in controlled experiments—



i.e., lung-function studies—the minimally effective concentrations are



nearly identical, around 0.3 ppm.  It is tempting, therefore, to speculate



that humans might also sustain the biochemical and morphologic changes



observed in laboratory animals exposed to this concentration; but such



a conclusion must await mechanistic information concerning the relationships
                                  8-83

-------
between the different types of effects or independent demonstration of



these effects in man.



     Recent studies involving repeated or prolonged exposures of



laboratory animals to ozone suggest that changes that are indicative of



chronic lung diseases (such as decreased elasticity of the lungs, hyper-



trophy of bronchiolar epithelium, and deposition of connective tissue)



also require concentrations of 0.2-0.5 ppm.  At slightly higher concen-



trations, fibrotic changes in the lungs have been observed histologically;



this is consistent with a reported increased rate of collagen synthesis



in the lung.  It appears, therefore, that the changes observed with short-



duration exposures, although generally reversible on cessation of exposure,



are as sensitive in evaluating the injury potential of exposure to ozone



as are long-term exposure studies.  There have been, however, very few



truly chronic exposure studies (i.e., covering a major part of the life-



time of the species) on which to base conclusions.



     Another subject of active investigation concerning the effects of



ozone is related to the mechanisms of defense against inhaled micro-



organisms.  It has been shown that exposure of a few hours results in a



marked increase in the susceptibility of animals to controlled doses of



infectious organisms introduced into the lung.  In fact, this criterion



of an effect is the most sensitive of any that nave been reported, with



significantly increased susceptibility of mice to one microorganism



occurring after exposure to an ozone concentration as low as 0.08 ppm.



Other reports referring to different microorganisms or different species



suggest that somewhat higher concentrations are required, but clearly



this effect is noted at less than 1.0 ppm.  Research in the mechanism of
                                   8-84

-------
ozone's effectiveness in decreasing resistance to infectious agents



suggests an action on the numbers and viability of lung macrophages.



Aside from the obvious practical implication of these findings for



carefully planned epidemiologic studies on the incidence of lung



infection in human populations exposed to oxidant air pollution, they



have stimulated more basic research in the physiology and biochemistry



of lung macrophages that may have implications beyond the question of




oxidant toxicity.



     Earlier toxicity studies had suggested that the hazard from repeated



ozone exposure might be reduced, inasmuch as animals became tolerant to



the acute pulmonary edematogenic action of ozone.  However, more recent



studies, which demonstrate that tolerance to the ordinarily ozone-induced



increase in susceptibility to infectious microorganisms or to the effects



on respiratory mechanics does not develop, suggest that the tolerance



phenomenon would have little protective value with respect to repeated



exposure to ambient oxidant smog.



     There are several reports of noteworthy extrapulmonary effects in



laboratory animals with concentrations of about 0.2 ppm.  These include



reduced voluntary activity, chromosomal aberrations in circulating



lymphocytes of hamsters, increased neonatal mortality, and greater



incidence of jaw abnormalities in offspring of ozone-exposed mice.  The



mechanisms of these reported effects and whether they are due to direct



actions of absorbed ozone, some secondary reaction product, or secondary



responses to the stress of local actions in the lung are largely unknown.



However, reported analogous effects in humans exposed to ozone, such as
                                  8-85

-------
changes in visual acuity and headache (possibly related to the reduced



activity in animals) and minor chromosomal  abnormalities in circulating



lymphocytes, require that these extrapulmonary effects be considered in



the evaluation of the hazard of ozone exposure.  Furthermore, the



chromosomal aberrations in hamsters and the reports of mutagenic activity



of ozone in a variety of microorganisms, tissue cultures, plants, and



insects raise the questions of the possibility of a genetic or carci-



nogenic hazard of this gas.  Indeed, earlier studies at higher concen-



trations of ozone or mixtures of ozone with hydrocarbons have suggested



a tumorigenic action in the lungs of mice.  Although present evidence



does not justify a definitive conclusion that exposure to ozone implies



a mutagenic or carcinogenic hazard, prudence requires that this possibility



should not be dismissed until it has been definitively tested experimentally



and epidemiologically.



     The possibility of interactions of ozone with other environmental



stresses has received relatively little recent attention.  Two exceptions



are noteworthy, however:  reports of increased susceptibility to some of



the actions of ozone in animals that are deficient in vitamin E or the



converse (protection conferred by administration of vitamin E) and



observations that exposure to ozone at less than 1.0 ppm reduces activity



of the cytochrome P-450 mixed-function oxidase activity of lungs.



Although the implications of these observations are not yet clear, they



remind us that nutritional variations or exposure to foreign chemicals



that are metabolized by lung mixed-function oxidases may provide bases



for unanticipated qualitative or quantitative effects associated with



oxidant exposures.
                                  8-86

-------
     On the basis of the foregoing discussion, it appears that, if



traditional criteria for hazard evaluation are applied to the toxicologic



data on experimental animals, there is little room for complacency re-



garding current ambient concentrations of ozone.  Functional, biochemical,



and structural effects in both pulmonary and extrapulmonary systems have



been reported by numerous investigators at or near concentrations that



are at least occasionally achieved in some polluted urban centers.




Unfortunately, there are no adequate methods for extrapolating data to



obtain reliable quantitative estimates of population risk at environmental



concentrations near the standard, and there is no assurance that the risk



is zero.
                                  8-87

-------
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29.  Castleman, W. L., D. L. Dungworth, and W. S. Tyler.  Cytochemically detected
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                            8-92

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 52.  Easton,  R.  E.   and S. D. Murphy.  Experimental  ozone preexposure and




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 53.  Eglite,  M.  A  contribution to the hygienic assessment of atmospheric ozone.



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56.  Evans,  M.  J. ,  W.  Mayr,  R.  F.  Bils,  and C.  G.  Loosli.   Effects of ozone

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    Delete 58--same as 57.

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61.  Fairchild,  E.  J., II, S. L. Graham, M.  Kite,  R.  Killens, and L. D.  Scheel.
                             I 0-1 f
          Changes  in thyroid Iiji  activity in ozone-tolerant and ozone-susceptible

          rats.  Toxicol.  Appl.  Pharmacol.  6:607-613, 1964.

62.  Fairchild,  E.  J.,  S. D. Murphy,  and H.  E.  Stokinger.  Protection by sulfur

          compounds against  the  air  pollutants  ozone  and nitrogen dioxide.

          Science  130:861-862,  1959.

63.  Falk, H. L.,  P. Kotin,  W.  Rowlette.  The response of mucus-sec ret ing

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          608,  1963.
                                ••>-»-•     f t f t r • / r > t     ,   . *     »   •     ^
64.  Fetner, R. H.  Chromosome breakage in Vicia faba by ozone.  Nature  181:

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65.  Fetner, R.  H.   Ozone-induced chromosome breakage in human cell cultures.

          Nature 194:793-794, 1962.
                               8-94

-------
 66.    Fetner,  R. H.  Mitotic Inhibition Induced  in  Grasshopper Neuroblasts




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            Brooks Air Force Base, Texas:  USAF School  of Aerospace Medicine,




            Aerospace Medical Division  (AFSC), June  1963.





       Delete  67 (omitted)





 68.   Fletcher, B. L.,  and A. L.  Tappel.   Protective effects of dietary alpha-




            tocopherol  in  rats exposed to  toxic levels of ozone and nitrogen




            dioxide.  Environ. Res.  6:165-175,  1973.





 69 0  Frank, R., J.  P.  Flesch,  and J.  D. Brain.  Effect of ozone on  elastic




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 70.   Frank, N.  R.  Pulmonary functional changes:   Animal studies, pp. 185-204.




           In National  Research  Council of Canada.  NRC Associate Committee on




           Scientific Criteria  for Environmental Quality.  Report No. 12.




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 71.   Frank, N.  R.,  J.  D.  Brain,  and D.  E.  Sherry.  Unilateral lung  exposure to




           ozone.  Fed.  Proc. 27:279,  1968.  (abstract)




 72.   Frank, N.  R.,  J.  D.  Brain,  and D.  E.  Sherry.  Unilateral tolerance and




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73.   Freebaim,  H. T.  Reversal  of  inhibitatory effects of ozone on oxygen




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74.   Freeman, G., L. T. Juhos,  N.  J.  Furiosi,  R.  Mussendett, R. J.  Stephens,




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                                 8-95

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             Mauseaseites-tumorzellen und auf Huhnerfibroblasten in der




             Gewebekultur.   Z. Krebsforsch.  67:113-126,  1965.



188.    Said, S.  I.   The lung in relation, to vasoactive hormones.  Fed. £roc. 32":




             1972-1976, 1973.




189.    Sapse, A. T.,  B.  Bonavida,  w.  Stone,  Jr., and  E.  E.  Sercarz.   Human




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             subjects  with  somg  eye irritation.   Amer.  J. Ophthalmol. 66:76-




             80,  1968.



190.    Schacter, B. A., H. S. Marver,  and U.  A.  Meyer.   Hemoprotein  catabolism




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-------
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193.    Scott, D. B. M., and E. C. Lesher.   Effect of ozone on survival and

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194.   Shoaf,  A.  R., R.  C.  Allen,  and  R.  H. Steele.   Electronic excitation state

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195.   Skillen,  R.  G., C.  H. Thiertes, J. Cangelosi,  and L. Strain.  Brain

            5-hydroxytryptamine in ozone-exposed  rats.  Proc.  Soc. Exp.  Biol.

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196.   Skillen, R. G., C.  H. Thienes,  J.  Cangelosi,  and 1. Strain.  Lung 5-

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            1962.

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                              CHAPTER 9




                      CONTROLLED STUDIES ON HUMANS









       Most standards for safe concentrations of oxidants and other photo-




chemical pollutants are based on information about their effect on human




health.   Such information is acquired through the interplay of different




fields of scientific endeavor, including epidemiologic investigation of




pollutant-exposed human groups and controlled experimental study of




animals or volunteer human subjects.  Epidemiologic studies of humans can




be used to obtain dose-response information on polluted ambient air, but




they are limited by cost factors, dose-range availability, the presence of




interfering pollutant substances, and the problems caused by the presence




of many uncontrolled variables.  Most controlled experimental investigations




have been conducted with animals.  However, there is no rigorous way of




extrapolating animal dose-response data to humans.  There is a need, then,




for comprehensive human experimental studies that are carefully controlled




and documented to ensure reproducibility and to withstand challenge by




proponents of other standards of safe concentrations.  Such studies can




establish the presence and importance of acute health responses in normal




and hyperreactive people.   Dose-response information, including minimal-




measurable-effects concentrations,  can be determined.  Hypotheses can be




developed and then subjected to animal or epidemiologic investigation.   Typi-




cally,  controlled human studies on the health effects of specific pollutants




use fixed concentrations,  an absence of interfering pollutants,  controlled




environmental conditions,  and well-characterized volunteer subjects.  Risk




is inherent in any research involving humans,  and it is axiomatic that




reasonable and proper care should be taken.      Prudence in the design of

-------
controlled human experiments requires that, when available, information from



animal and epidemiologic work be used to delineate ways in which critical


human studies are likely to be most useful.


        The purposes of this chapter are to review available test methods



and protocol designs for controlled human studies, to review and discuss


published data, and to make recommendations for future studies.




EXPERIMENTAL METHODS



        The basic design of studies on effects of pollutants should seek



to maximize information relevant to public health.  Tests must be reliable



and sensitive, the experimental air environment must be rigorously controlled,


and the manner in which subjects are exposed to this environment must simu-



late ambient exposure.   These constraints impose complications and necessi-



tate a focus on environmental control and monitoring, physiologic testing,


and evaluation of symptoms and clinical observations.




Controlled-Enviromnent Chambers



Construction and Monitoring Equipment.  A survey of the environmental control

                                                              1 7 8 9 32
and monitoring technology used in several experimental studies


indicated significant limitations in experimental control capability.  There



are seven controlled-environment chambers or clean-room facilities in the United


States for human exposure (community air pollution inhalation) from which studies


have been reported.   Another is under construction at the University of North



Carolina in association with the EPA at Chapel  Hill.  There are three chambers



in Canada of similar design.



        Table 9-1 lists design features of the exposure chambers in the



United States that have air-cleaning equipment.  The facility at the
                                 9-2

-------
                                      TABLE 9-1

               Controlled-Environment  Chambers or  Clean-Room  Facilities  for

               Community Air  Pollution Short- Or Long-Term  Human Exposure,

                                 United States"" Facility—

                                                                               c
 Item or  Condition         H.S.C.     U. Md.  U. Pa.  R.L.A.     St. V      St.  B~    N.Y.U.

 Temperature  Control           +        +       +       +         +          +         +

 Humidity Control              +        +       +       +         +          +         +

 Pressure Control              +        -       +       -         -          -         -

 Sound Control                 +        -       +       +         -          +         -

 High-Efficiency Particle
   Filter

 Laminar  Flow-

 Charcoal Filter

 Catalytic Filter—
+
-
+
+
+
+
+
	
+
-
+
_
+
e
+
+
+
-
+
_
+
+
+
_
 Scrubber^
Purafil filter-               -        -       -       +

Active—                       -        +       -       +         -         +


—   Based in part on information from an EPA - sponsored workshop on  controlled-
     environment-chambers, April 26-27, 1971, Research Triangle Park,  N.C.
b
—   H.S.C.  =  Hospital for Sick Children, Washington, B.C.
     U. Md.  =  University of Maryland Hospital, Baltimore,
     U. Pa.  =  University of Pennsylvania Hospital, Philadelphia.
     R.L.A.  =  Rancho Los Amigos Hospital, Bowney, Ca.
     St. V.  =  St. Vincent's Hospital, New York, N.Y.
     St. B.  =  University of California, Santa Barbara.
     N.Y.U.  =  New York University, New York, N.Y. (Clean-room facility has
                                                       been dismantled).
r»
-    More than one chamber available.  This describes the plexiglass chamber used
     for ozone and peroxyacetylnitrate studies.

~L   Refers to use of an intake plenum to ensure fairly uniform air flow and
     negligible gas concentration gradients within the region of the exposure
     chamber occupied by subjects.

—   Can be operated with intake flow either through or bypassing the  plenum.

—   Heated or nonheated bed designed to oxidize carbon nonoxide and light
     hydrocarbons (not removed by activated charcoal) to carbon dioxide and water.

                                           9-3

-------
g
     The liquid acid gas scrubber is packed with, polypropylene and uses sodium
     carbonate solution.
•L
—    Aluminum oxide pellets impregnated with potassium permanganate.

—    As judged by personal communication or recent publication.
                                          9-4

-------
University of Maryland Hospital, Baltimore,   has a chamber with activated-


charcoal and high-efficiency particle filters and controlled temperature


and humidity.  St. Vincent's Hospital and New York University, New York


City, each have a clean-room facility.  The University of Pennsylvania Hospital,

             25
Philadelphia,   has a self-contained, reinforced-concrete climate-controlled


chamber, with pressure controls from 28 to 32 in. Hg (about 710 to 810 mm


Hg, or 95 to 108 kilopascals).  Rancho Los Amigos Hospital, Downey, California,


has a totally enclosed steel chamber.  Inlet air is heated and passed through


a Hopcalite catalyst bed, filtered by high-efficiency particle filters,


activated charcoal, Purafil (aluminum oxide pellets impregnated with potassium

                                                                   28a
permanganate), and a Mine Safety Appliance catalytic adsorbent bed.     The


controlled-environment facility at the Hospital for Sick Children, Washington,


B.C., is a self-contained, reinforced-concrete structure that can provide


clean or specifically polluted air of monitored composition along with con-


trolled temperature, pressure, and humidity.  The living area for the


subjects is a two-room apartment with bath and minimal kitchen facilities

       2          7  53
(600 ft ,   or 56 m ).     The University of California at Santa Barbara


has two chambers for temperature - and humidity-controlled environmental


studies.  A third chamber is used for altitude simulation, and a fourth


for ozone and peroxyacetylnitrate (PAN)  studies.  The latter chamber is


6.5 ft (2m)  wide, 10 ft (3m) long,  and 19 ft (5.8m)  high and is constructed


of plexiglass.   A chamber complex at the University of Wisconsin in Madison

                                                                        55
is designed primarily for studies of occupational inhalation toxicology.


       A description of the environmental-control chamber for human


experimental studies at McGill University,  Montreal,  exemplifies the other


two Canadian facilities — at the Gage Research Institute, Toronto, and
                                    9-5

-------
McMaster University, Hamilton, Ontario.  It is a transparent chamber, 12 ft


(3.7 m) long, 8 ft  (2.4 m) wide, and 6 ft (1.8 m) high constructed of 14 6x4-


ft (1.8 x 1.2-m) panels of plexiglass held together with angled metal.


The chamber is built within an ordinary air-conditioned working labora-


tory, with a door in the middle of one of the 12-ft (3.7-m) sides.  Near


the bottom of the chamber a hole has been cut to accommodate a 9-in.


window fan, which gives the desired incoming atmosphere.   Air from the


laboratory is not purified before entering the chamber.  At the end of


the chamber opposite the fan, two outlet pipes, 6.5 and 3.75 in. (16.5


and 9.5 cm) in diameter, run from the chamber ceiling to a fume hood.

                                                         3         3
Air passes through the chamber at approximately 12,000 ft /h (336 m /h) ,


resulting in about 20 volume changes hourly.   The temperature and humidity


controls are those for the building in which the chaff,', er is housed.


       For the most reliable results, chamber environment should be


monitored continuously with instruments and techniques equivalent to


those used in ambient-air monitoring networks.  Calibration of instruments


should follow recommendations by appropriate agencies and be checked by


cross comparisons with those in other analytic laboratories.


       Ideally,  two monitoring instruments,  each operating on a different


principle, should be used for each gaseous pollutant under study.   Ozone and


nitrogen oxides can be monitored with chemiluminescence analyzers, which


provide fast response and freedom from interference by other pollutants.


Total oxidants can also be monitored by the neutral potassium iodide solution


and Saltzman reagent methods with continuous-flow colorimetric analyzers.


A nondispersive infrared analyzer and an oxidative electrochemical analyzer
                                    9-6

-------
 can be used for monitoring carbon monoxide, and light-scattering counters


 for monitoring particles.




 Environmental Variables.  In human experimental studies, variables to be



 considered and controlled include pollutant gas concentration, humidity,



 temperature, light intensity, noise, particles, and the presence of other



 gases.



        The relative humidity, air temperature, noise, and artificial


 lighting must be controlled in environmental exposure chambers, because


 they can influence a subject's response directly or indirectly.  At high


 temperature, heat stress can dominate the symptomatic and physiologic


 responses of human subjects.  The rates of some chemical reactions of


 exposure gases depend heavily on temperature, so temperature should be


 controlled.  This can be done with refrigerated cooling coils in the



 air-conditioning section of air supply systems, heaters, and thermo-


 couple sensors.  Extremes of relative humidity are known to cause dis-


 comfort in humans.   The equilibrium size of hygroscopic aerosol parti-


 cles,  the degree of conversion of sulfur dioxide to sulfurous acid  in

                         41
 sodium chloride droplets,   and the extent and rate of chemical reaction


 of mixtures of such pollutant gases as sulfur dioxide, ozone, and ammonia


 depend on the relative humidity of the chamber air.  Cooling coils in air-


 conditioning units,  and the injection of purified steam can be used to


 regulate relative humidity.   Artificial lighting within human-exposure


 chambers should be designed to ensure proper illumination,  but to avoid


potential experimental complications.   If the intensity is  too high,  the


air may overheat.   Ultraviolet irradiation should be avoided to prevent


photochemical reactions from forming uncontrolled and unknown reaction
                                   9-7

-------
products in the chamber.  If ultraviolet irradiation of gases is desired




to form specific oxidant compounds for human exposures, it should be carried




out in separate chambers to avoid contamination of the human-exposure chamber




with intermediate products and to prevent the subjects from being directly




exposed to harmful radiation.  Conventional tungsten and fluorescent lighting




meet the illumination requirements of human-exposure chambers.




       High levels of noise known to cause discomfort to humans are




unacceptable.   Moderate noise also becomes undesirable in some experimental




situations, if it is distracting or interferes with speech communication.




       During controlled exposures of human subjects to specific compounds




like ozone, the concentrations of suspended particles and trace gases must




be known and minimized to ensure that health effects can be attributed solely




to ozone.   The air purification units for the environmental chambers are




designed to remove most of the particles and pollutant gases from the ambient




air.  Prefilters and efficient absolute filters are used to remove 99% of




the particles with diameters of 0.3 jm or more.  Catalytic beds, adsorption




beds, and activated-carbon and chemical filters are used to convert carbon




monoxide to carbon dioxide and to remove most of the other gaseous hydro-




carbons, sulfur  dioxide, nitrogen dioxide, nitric oxide, and ammonia.




Condensation nuclei counters, which are commercially available, can be used




to monitor the total number of particles with diameters greater than 20A.




Light-scattering nephelometers can approximate the total number concentration




of particles with diameters of 0.1 - 1/im.  Single-particle optical counters




with multichannel analyzers can be used to monitor the number of particles




in finite size intervals between 0.2 and 10 >mi.  Alternatively, cascade




impactors and particle filters can be used to monitor the total mass






                                  9-8

-------
concentration and the size distribution of the aerosol in the chamber.




Gas monitors are commercially available for sulfur dioxide, nitrogen



dioxide, nitric oxide, carbon monoxide, and ozone.  Ammonia and these




other gases can also be collected by bubblers and analyzed by wet chemical




methods if proper precautions are taken to account for interferences.




Trace hydrocarbons can be monitored by taking bag samples and analyzing




them by gas chromatography, mass spectrometry, or infrared spectropho-




tometry.




       In the design of controlled exposures to gases and particles,




separately or in combination, extreme care is needed to avoid formation




of interfering species.   For example, in a study of the effect of a



                                                             39
mixture of nitrogen dioxide and ferric oxide aerosol in dogs,   signifi-




cant quantities of ammonium and nitrate ions were found in particles




filtered from the air of the exposure chamber.  Ammonia and trace hydro-




carbon gases also emanate from sedentary and exercising humans.   To




prevent these contaminant gases from building up in the chamber,  a continuous




flow of fresh air through the chamber must be maintained.




        In exposures of humans to artificially generated aerosols, where




the information is to be relevant to ambient aerosols, several factors are



important: the particle diameter distribution must be fairly constant and




fall within size ranges typical for the given compound in the ambient air,




the chemical composition of the aerosol must be stable and predictable, and




the electric charge distribution of the aerosol must simulate that of




normal atmospheric aerosols.






Selection and Characterization of Subjects




        A minimal group size is difficult to specify.  Studies on similar




subjects could be expected to give the least variability in results; thus,





                                9-9

-------
dose-response information on relatively small groups of medically characterized



subjects could provide a basis for extrapolating to essentially similar



population groups.  Useful results have been obtained with as few as eight


         31
subjects.    Healthy, young males probably should be studied initially because



some variations are known to accompany aging and some problems are peculiar



to females (e.g., the estrus cycle and pregnancy).  Later studies of older



males and females will,  however, be required for complete information.



       Volunteers with disease who can give informed consent and for



whom some expected benefit balances the expected risk can be considered



as potential subjects.  If those selected for the study are smokers, this



information and an estimate of the degree of smoking are needed, because

                                                                      32,38

systematic differences between smokers and nonsmokers have been found.



       People with known or suspected cardiopulmonary disease who are



referred by a physician for diagnostic environmental stress-testing may



also serve as subjects.   Testing under environmental stress of persons



who are suspected hyperreactors to pollutants is analogous in concept to



exercise stress-testing of suspected cardiac patients.   However, in



contrast with the general availability of exercise stress-testing laborato-



ries, the expense involved in an operational facility for environmental



stress-testing limits its availability to research centers.  Accordingly,



a person who is referred for clinical testing by his physician may well



become part of investigative programs and be asked to volunteer for



additional procedures.



       In selection of subjects, ethical considerations are dominant



and limit the deliberate exposure of minors or of others who are unable



legally to be volunteer subjects.
                                 9-10

-------
       Among the criteria for selecting subjects with close similarities,



socioeconomic status cannot be ignored any more than nutritional status



or genetic background.  Finally, place of residence and prior occupational



pollution exposure may be important.





Measurement of Human Response



       In addition to the visual monitoring of subjects during testing,



clinical assessment can be accomplished by having the project physician



interview each subject concerning symptoms, with a standard questionnaire



immediately after exposure.  Also, subjects can keep a record, on a standard



form, of symptoms experienced during and after exposure.  It is well to



note here that caution should be exercised in interpreting symptoms, because



these are unlikely to be "blind" studies.



       Much progress has been made in recent years in the measurement and



understanding of lung physiology.  Usually, several methods are available



for the measurement of each characteristic of lung function of interest.



Comprehensive descriptions of the various pulmonary function tests are


                  6 12 20 29
readily available,  '  '   '   so a complete review will not be attempted



here.



       Because the respiratory tract is an initial target of any air



pollutant challenge, it usually receives primary attention in tests to



determine irritant effects of exposure.  Other aspects of interest include



hematology,  blood enzyme biochemistry,  eye irritation,  and psychomotor



performance.   Constriction of the large airways,  maldistribution of ventila-



tion due to narrowing in some small airways,  constriction of peripheral



lung units,  and mechanical or gas diffusion impairment due to edema
                                 9-11

-------
are possible effects of insult by pollutants.  A variety of pulmonary tests



are required to examine the possibilities.

                          13
       Flow-volume curves:    The characteristics measured by the maximal



expiration are forced vital capacity (FVC),  1-s forced expiratory volume

                                   c
(FEV..), peak expiratory flow rate (Vmax),  and flow rates at 50% and 25%

                      •    *
of the remaining FVC (V  , V  ) for partial and maximal flow-volume curves.



These measurements give an easily obtained,  relatively reproducible



evaluation of overall pulmonary mechanical performance, but provide little



information on the mechanisms responsible for any observed changes.


                                                             22 23
       Airway resistance (R  ) and thoracic gas volume (TGV):   '     The



measurement of R   is probably more sensitive than maximal flow measurements



for constriction of large airways, but it is also more difficult to perform



and is less stable.  These problems similarly affect the measurement of



TGV, which, however, may be useful for detecting gas trapped as a consequence



of airway dysfunction (in combination with a gas-dilution lung-volume



determination).

                                        24,26,29
       Total respiratory resistance(R ):          Resistance can be measured



at pressure perturbation frequencies of 3, 6, 9, and 12 Hz.  Unfortunately,


this measurement is affected by changes in upper-airway configuration, which may



complicate the detection of changes in pulmonary airways per se.   As predicted


        43
by Otis,    the method is believed capable of detecting asynchronous mechanical



behavior (unequal regional ventilatory time  constants), which otherwise can



be documented only by the considerably more  difficult measurement of dynamic



lung compliance.

                           3»16                i6
       Closing volume (CV):       Buist and Ross   measured the lung volume



at which closure of a significant number of  small airways presumably occurs,




                                   9-12

-------
 as well as  estimating of residual volume  (RV) and total lung capacity  (TLC)


 through the expired nitrogen concentration.  In another study,   they  presented


 a method to estimate the uniformity of ventilation distribution by measuring


 the slope of the alveolar nitrogen plateau.

                                                                       40
       Static lung compliance  (C  ) and dynamic lung compliance (C^  )


 are measured from recordings of transpulmonary pressure and respiratory flow


 and volume.  Dynamic compliance in the tidal range is measured in a series


 of breaths  each at normal frequency and at other frequencies — such as 20,


 40, 60, 80, and 100 breaths/min — with total volume monitored and kept constant.


 Static compliance is measured by interrupting airflow intermittently during


 an inspiration from functional residual capacity (FRC) to TLC, followed by


 an expiration to RV.   Each determination is preceded by an inspiration to


 TLC to give a consistent volume history.  Compliance measurements are  indis-


 pensable for documentation of changes in the mechanical characteristics of


 the lung, particularly the development of unequal time constants.   Unfortunate-


 ly, the measurements are somewhat unstable and require considerable effort on


 the part of subjects and investigators.  In some studies,  these tests are


 performed only on a subgroup of subjects selected for motivation and performance.


       Pulmonary diffusing capacity (Dj  ) can be determined by the single-
                                       JL(U

 breath carbon monoxide method according to a technique developed by Ogilvie

      42
 e_t a\^.    For example, a test gas containing 0.15% carbon monoxide and 10% helium in


 air can be used.  In calculating D^  ,  correction is made for backpressure of


 carbon monoxide due to significant concentrations of blood carboxyhemoglobin.


Helium is measured with a thermal conductivity meter,  and carbon monoxide with


 an infrared detector  or an electrochemical analyzer.   Reproducibility of this


 test may be poor under some conditions  and it is affected by changes in ventila-
                                  9-13

-------
tion diffusing capacity ratios, but the test offers the potential of detecting




changes in the blood-air interface (such as alveolar edema) that might




otherwise go undetected.




       Oxygen consumption can be measured at rest and during exercise on




a constant-load bicycle ergometer or a treadmill at a level producing a


                                                             4

specified percentage of predicted maximal oxygen consumption.    Expired




air is collected and measured with a spirometer to determine total expired




volume, and samples are analyzed for oxygen and carbon dioxide.




       Carboxyhemoglobin concentration [COHb] can be estimated with the




method of Jones and co-workers.    The subject holds a deep breath for 20 s




to allow equilibration of carbon monoxide between alveolar air and blood and




then expires a sample of that air into a container.  The air carbon monoxide




concentration may be directly related to [COHb].  The test can be performed




before exposure in an environmental chamber to help to verify that the subject




has not received inordinate ambient pollutant exposure.




       Biochemical studies on human blood samples have been used to measure


                           15

response by Buckley e_t al. ,   who reported changes in red cells and serum




of men after a single acute exposure to ozone at 0.50 ppm for 2.75 h.  Red-




cell membrane fragility and glucose-6-phosphate dehydrogenase and lactate




dehydrogenase activities were increased,  and red-cell acetylcholinesterase




activity and reduced gluathione were decreased.  Red-cell glutathione reduc-




tase (GSSRase)  activity was not significantly altered; however,  serum GSSRase




activity was significantly decreased, and serum vitamin E content and lipid




peroxidation were significantly increased.



                                11 46 48
       A number of investigators  '  '   have argued that behavioral




changes are more prevalent than frank physiologic or clinical changes as






                                   9-14

-------
 effects  of air pollutants.  If  the ability to perform routine tasks, such



 as  operating an automobile or a complex piece of machinery, is compromised



 by  pollutant exposure, the setting of air pollution standards should take



 such effects into consideration.


                    28
       In one study,   human subjects were tested in a controlled-



 environment chamber with a high (summer) temperature and with ozone, nitrogen



 dioxide, and carbon monoxide as pollutants.  Performance on a divided-atten-



 tion task given at the end of the exposure period and the subjects' heart-



 rate variability (as a potential psychophysiologic measure of attention) were



 evaluated.  The subjects displayed a significant decrement in peripheral



 attention associated with increased ambient temperature.  Effects attributable



 to  pollutant gases were variable.



       Subjects exposed to ambient oxidant pollution or to controlled



 oxidant pollution in a test chamber express their response by symptoms, as



well as by physiologic changes.  Because of their subjective nature, little



 attention has been given to symptoms in overall assessments of effects;



however, with systematic collection, these experimental data lend themselves



to  semiquantitation.


                                     28a
       In the study by Hackney  et al,    the investigators proposed a



method for consistent gathering of symptom data by means of a checklist,



wherein symptoms are scored (according to predetermined criteria of severity)



for three different periods during and after exposure.   The sum of the



scores for all symptoms from all periods gives a total symptom score,  or



discomfort index,  for the 24-h period after the start of exposure.  In their



study, symptom scores for 42 subjects exposed to ozone at 0.25,  0.37,  and





                                  9-15

-------
0.5 ppm revealed a dose-response relationship for higher doses that approxi-




mated the relationship demonstrated by objective pulmonary function.  These




results suggest that semiquantitation of symptoms is feasible in controlled




pollution-exposure studies and may be a useful clinical investigative tool.






Experimental Design Considerations




       Multiple stresses may be important in assessing functional and adaptive




capabilities or people.  An exposure protocol can be designed to simulate




as closely as possible the ambient exposure of a group likely to have signifi-




cant exposure, such as people working outdoors on a smoggy summer day.  A




2-h exposure period is realistic, in that high ambient pollutant concentra-




tions usually persist about that long.  Other exposure periods should be




chosen to simulate different pollutant episodes.  Specified amounts of




exercise can serve as a tool in experimental design to provide additional




stress.  Intermittent light exercise (sufficient to approximate a doubling




of minute volume) during exposure produces a realistic degree, of ventila-




tion (to which pollutant dose is approximately proportional) during typical




work.  Increased temperature is another stress factor that is often present




during oxidant air pollution episodes and so can be introduced into the




experimental situation.  The design can provide for successive days' exposures,




in that deleterious effects of exposure may be cumulative.  These require-




ments can be incorporated into a protocol in a cost-effective manner that




tests several subjects on a given day.  However, with a single chamber of




limited size, this requires staggered exposure and testing periods, precluding




"blind" studies or control measurements on the same day.  Thus, sham control




runs (identical protocols with exposure to purified air) precede the pollutant




exposure, so  that reliable baseline values of the measured  characteristics



can be obtained.






                                   9-16

-------
        "Blind" studies with chemical substances that have a characteristic


 odor or irritant effect are difficult to manage.  If, as with ozone, the odor


 sense  tends  to diminish, then "odor sham" protocols are possible.  However,


 keeping the  subjects and the investigators (other than the safety officer)


 truly  uninformed about the nature of a particular experiment is not a trivial


 problem.

                                                                   37
        Cyclic variations in measurements are potentially important.


 Adequate information is not available, for example, on normal variation


 over time in tests of human physiologic function.  This presents a problem


 in designing not only short-term experiments, but especially longer-term


 studies.  Detailed data on stability of a given measurement over periods of


minutes, hours, days, weeks, months, and even years would improve rational


 experimental designs.  Variations in measurements with changing seasons,


 especially summer versus winter, might be expected, because of the effect


 of large temperature differences on physiology and life style.  Interactions


may be  important in design and data interpretation.  The likelihood of


 recent  prior exposure to high oxidant concentration is clearly a function


 of the  summer season and geographic location.


       There is a definite need for dose-response information on specified


groups of people, if frequency distributions of responses are to be estimated.


Obtaining and using such information present numerous problems,  such as


selection of appropriate groups and their size; the need to include persons


with disease, as well as the very young and very old; and extrapolation of


the data to the total population.  With separate dose-response information


on representative samples of major population groups, a frequency distribution


of responses at each pollutant concentration might be determined by weighting




                                   9-17

-------
the mean change for each group according to the general populations they

represent.  Information on frequency distribution of responses is necessary

for any cost-benefit analysis that will require quantitative estimates of

effects in terms of dollars.

       With due regard to the factors just discussed, a test series may

reasonably be designed to support or reject the hypothesis that no effects

of realistic pollutant exposure will be detected in volunteer subjects.

Results supporting the hypothesis would be useful to regulatory agencies in

setting air pollution standards.  If minimal effects are found in a group

of "normal" subjects, an effective experimental strategy is to test a group

of specified "hyperreactive" subjects, characterized by a prestudy history

of cough, chest discomfort, or wheezing associated with allergy or exposure

to air pollution.

       Experimental data can be subjected to repeated one-way variance analyses.
                                               CO
Post hoc comparisons with the Newman-Kuels test   are made when significant

differences among test conditions are found.  A few significant differences

due to random variation may be found, because of the number of statistical

comparisons usually being made; therefore, all observed, statistically

significant changes must be examined critically for physiologic significance.


Ambient-Air Studies

       Experiments can be conducted with well-specified ambient air, if

a suitable chamber is in a highly polluted area and if ambient air can be

introduced into the chamber without significant pollutant losses.  Other runs

with clean air and matched temperature and humidity serve as controls.  Alter-

natively, mobile health-testing laboratories with air monitoring capabilities

can go to polluted areas of interest.


                                   9-18

-------
       Detection of short-term cardiopulmonary effects of ambient oxidant




pollutant exposure is complicated by several factors.  The physiologic




measures of such effects exhibit significant inherent variability, which may




mask the relatively small changes expected.  The atmosphere contains many




potentially hazardous materials, both natural and man-made, in continuously




varying concentrations.  Not all these substances have been identified,




and many that have been identified cannot be adequately monitored.  Other




environmental factors, such as temperature and humidity, may influence




physiologic function independently and thus complicate the detection and




interpretation of pollutant effects.  Variations in concentration of any




given pollutant are usually closely linked to variations in concentrations




of other pollutants., and this makes it difficult to assess the toxicity




of a single component of the ambient mixture.  These problems have led




to the assertion that ambient-exposure study results cannot be interpreted




reliably,  owing to the incompleteness of both the atmospheric and the




biologic information and the inability to control or allow for all inter-




fering variables.  This assertion is correct in principle, but neglects the




possibility of obtaining valuable partial answers to health-effects questions




through ambient studies.  Such improved understanding of the effects of




ambient oxidants should be attainable through improved atmospheric monitoring;




improved physiologic,  biochemical,  and clinical evaluation of exposed subjects;




application of findings from concurrent controlled-exposure studies; and




combination of ambient- and controlled-exposure studies.







REVIEW AND DISCUSSION OF PUBLISHED DATA




       The data base on health effects of photochemical oxidants and ozone




was reviewed by the Subcommittee on Ozone and Other Photochemical Oxidants







                                   9-19

-------
in a report prepared in September 1974 for the Committee on Public Works,

            2
U.S. Senate.   The following discussion repeats some of the material in


that report, to exemplify the need for further work, including controlled


human studies.


       The federal primary ambient air quality standard for photochemical

                    3
oxidants is 160 ug/m  (0.08 ppm), a maximal 1-h average concentration not


to be exceeded more than once per year.    Air Quality Criteria for Photo-


chemical Qxidants  catalogs and describes the overall data base for present


standards.  In information received by the Subcommittee (February 23-24,  1974),


the following evidence was cited as the basis on which the EPA set the


standards:


       •  When high-shcool cross-country runners were exposed for 1 h to


          photochemical oxidants at 0.03 - 0.3 ppm,  their performance


          decreased with increasing concentration.     A statistical test


          for threshold values (regression using "hockey stick" functions)


          applied to these data gives a threshold estimate of 0.12 ppm, with


          a 95% confidence interval of 0.067 - 0.163 ppm.1'5'30'44'57

                                                                      3
       •  At short-term maximal peak oxidant concentration of 490 >ig/m


          (0.25 ppm),  subjects with asthma begin to  experience significantly


          more attacks.  These maximal daily peaks may occur with a maximal

                                                         o
          hourly average concentration as low as 300 jig/m  (0.15 ppm).   Eight


          people sensitive to smog experienced increased attacks at oxidant


          concentrations corresponding to those at which plant damage occurs

                                3               1,49
          (8-h average, 200 ug/m , or 0.10 ppm).

                                                              o
       •  At short-term peak oxidant concentration of 196 >ug/m  (0-10 ppm)


          and above, humans begin to experience eye  irritation.  These
                                  9-20

-------
          peaks would be expected to occur with maximal hourly average

                                       3                  45,47
          concentrations of 50-100 jug/m  (0.025-0.05 ppm).


       •  At short-term ozone concentration of 160 ;ug/m3 (0.08 ppm) for


          3 h, experimental animals (mice) exhibited increased susceptibility


          to laboratory-induced bacterial infections.  A firm dose-response


          relationship was established for this effect.

                         14
       •  Brinkman j|t^ .al-   found that, at short-term ozone concentration

                     3
          of 392 Aig/m  (0.20 ppm) for 1-2 h, experimental animals had


          increased sphering of red blood cells.  Similarly, humans had

                                                                 o
          increased sphering after 30 min of exposure to 490 >ig/m  (0.25 ppm).

                         14
       •  Brinkman et al.   also found that, at long-term ozone concentra-

                          3
          tion of 392 jug/m  (0.20 ppm) for 5 h/day for 3 weeks, structural


          changes in the nuclei of heart muscle fibers were produced in


          adult rabbits and mice.  The fibers reverted to normal a month after


          exposure.


       The EPA used the data from the first three studies listed to obtain

                     3
the value of 200 ug/m  (0.1 ppm) for a maximal 1-h concentration—the lowest


concentration at which measurable human effects are generally observed.  No


formal methodology was used in making this selection; it was derived as a best


judgment by EPA officials.


       Similarly, no published record exists to describe the procedure used


in selecting 0.08 ppm as the national primary standard for photochemical


oxidants.  It is the recollection of EPA officials that the standard was


set midway between the highest average background concentration of ozone


(0.06 ppm) and 0.1 ppm,  giving a 20% "margin of safety."



                                  9-21

-------
       There are obvious Inadequacies in the established values.  First,




it was assumed that the oxidant standard is a surrogate standard for




photochemical oxidants, with ozone as the indicator.  However, it is clear




that very low concentrations of specific irritants, such as peroxyacetyl-




nitrate (PAN), are sufficient to cause eye irritation.  Second, some of the




statistical techniques used to determine the lowest concentration at which




effects are observed were inconsistent and undocumented.  A "hockey stick"


        5 44
function '   was sometimes used to find an effect threshold.




       The inadequacy of the technical data base on photochemical


                                                                   5

oxidants was realized from the start by EPA officials; Earth &t^ aJ.. , describing




the situation in 1971, stated that "many bits of information required to




place the present National Ambient Air Quality Standards on an irrefutable




and unassailable scientific basis are not yet available."






Exposure to Ozone




       Studies before 1970 are reviewed in Air Quality Criteria for Photo-




chemical Oxidants.   Details of selected controlled human studies repeated




later are given below.


                        lOa

       Bates and Hazucha    measured significant changes in lung function




(decrease in maximal flow rate at 50% of the vital capacity, maximal transpul-



monary pressure, and increase in total pulmonary resistance) in 10 normal




male subjects aged 23-35 years Concluding two smokers) exposed to pure ozone




at 0.75 ppm for 2 h.  Two of the three subjects who exercised intermittently




at twice the resting volume showed accentuated effects.  In a separate study



                 32
by Hazucha et ad.   on effects of short-term exposure, significant changes in




lung function (decreases in forced vital capacity,  forced expired volume at 1 s,





                                  9-22

-------
maximal flow rate at 50% of vital capacity, and maximal midexpiratory


flow rate; and increases in closing capacity and residual volume) were


found in 12 normal males aged 23.6 + 0.7 years (including six smokers)


exposed to pure ozone at 0.75 and 0.37 ppm for 2 h during alternating rest


and exercise periods.  The higher concentration affected smokers more than


nonsmokers, whereas the lower concentration affected smokers and nonsmokers


similarly.  In these two studies, most subjects complained of cough, chest


tightness, and substernal soreness.  A few also had pharyngitis, dyspnea,


and wheezing.

              31
       Hazucha   also measured small decreases in the same lung functions


as above in three normal male subjects of mean age 20 years (nonsmokers)


exposed to pure ozone at 0.25 and 0.56 ppm for 2 h during alternating


15-min periods of rest and exercise.  Although these decreases were not


statistically significant,  in view of the small number of subjects involved,


they were consistent and in general agreed in value with dose-response


curves drawn from data at 0.75 and 0.37 ppm (Figure 9-1).  The subjects


coughed and complained of chest tightness, substernal soreness,  increased

                                                                   9 31 32
salivation, and expectoration of mucus.  The studies just described


were conducted in the Montreal chamber facility with general conditions


of:  temperature,  21-23 C;  humidity, 42-49% inside background air; and


two or more Mast coulombic meters for oxidant monitoring.

                                28a, 28b, 28c
       Studies by Hackney et al.               used a protocol designed to


simulate summer exposure in the Los Angeles southern coastal air basin and


included the additional stresses of heat, intermittent exercise, and


repeated exposures.   Careful attention was given to environmental control,


pollutant monitoring and generation, and subject selection.  Four  male
                                 9-23

-------
subjects aged 36-49 years (including one cigarette smoker)  judged by subject-




ive criteria to have normally reactive airways completed this protocol.




No obvious effects — as assessed by clinical response and  measures of




respiratory, cardiac, and metabolic functional change — were noted after




exposure for 4-5 h to 0.5-ppm ozone, 0.5-ppm ozone and 0.3-ppm nitrogen




dioxide, or 0.5-ppm ozone, 0.3-ppm nitrogen dioxide,  and 30-ppm carbon




monoxide.  A second group of four, aged 29-41 years (including two cigarette-




smokers) , who had previously experienced clinical bronchospasm and were




judged by subjective criteria to have hyperreactive airways (history of




developing symptoms during light activity in smog or history of asthma)




developed clinical discomfort and were unable to complete the protocol.




Exposed to ozone at 0.5 ppm for 4-5 h, this group developed marked changes




in pulmonary mechanics and gas distribution.  Some effects  were later




found after exposure to ozone at 0.37 ppm,  but not at 0.25  ppm.  In light




of the marked clinical effects, the protocol was modified,  and a third




group of seven subjects, aged 22-36 years (including two smokers), judged to




have normally reactive airways, were studied.  This group,  exposed to ozone




at 0.5 ppm for 2 h, showed only minimal effects on the first day of exposure;




however, five of the seven showed significant effects on a  second exposure




day.   A fourth group of seven subjects, aged 22-41 years (including three




cigarette-smokers), exposed for 2 h to 0.25-ppm ozone, 0.25-ppm ozone and




0.3-ppm nitrogen dioxide, or 0.25-ppm ozone, 0.3-ppm nitrogen dioxide, and




30-ppm carbon monoxide showed no obvious effects.  Of seven subjects, three




were judged on the basis of subjective criteria to have hyperreactive airways




and four were deemed to have normally reactive airways.  A fifth group of



five subjects, aged 27—41 years (including  one cigarette-smoker), was exposured to




0.37-ppm ozone for 2 h.  Important changes  with exposure were found in most phy-




siologic measures.  However, one subject showed substantial changes in measures of




                                   9-24

-------
 lung  mechanical  function, which became worse on the second day of exposure.



 Findings from this series of studies indicate that there is a wide range of




 sensitivity to photochemical  pollutants and that more sensitive people




 develop significant symptoms, biochemical changes, and respiratory function




 decrease under exposure conditions similar to those experienced during
                                                      i 0 ft /-»

pollution episodes.  The studies just described   '   '    were conducted




in the Rancho Los Amigos Hospital chamber facility with general conditions of:




temperature, 31C; humidity, 35%; purified background air; and chemilumine-




scence and neutral potassium iodide mentoring for oxidants.




       Comparison of health effects of exposure to ozone '   '   '




suggests that Canadians are more reactive than southern Calif ornians. These




results are summarized in Figure 9—1.  Experimental methods and subject




responses were compared further in a cooperative investigation of this




apparent reactivity difference.  In studies conducted in California, four




Canadians and four Calif ornians were exposed to ozone at 0.37 ppm in purified




air at 21 C and 50% relative humidity for 2 h with intermittent light exer-


     27a
cise.     Exposures to purified air alone served as controls.  Methodologic




differences sufficient to explain different results of previous studies were




not found.   Subject responses were similar to those observed previously —




Canadians on the average showed greater clinical and physiologic reactivity




to exposure than did Calif ornians, who were no more than minimally reactive.




Canadians also showed larger increases in red-cell fragility after exposure.




These results support the existence of a real difference in reactivity between




the Calif ornians and Canadians studied to date.  Although the number of




subjects tested in the cooperative study is small, the good agreement between




these results and previous results in the separate laboratories allows




considerably increased confidence in direct comparison of the previous results
                                  9-25

-------
from Los Angeles and Canada, providing a considerably larger data base


from which to judge relative reactivity.


       If the difference in response to ozone between Canadians and


southern Californians studied is accepted as real, a hypothesis of


adaptation in southern Californians is supported.  Further support of the


hypothesis requires demonstration that the subjects tested are truly


representative of larger population groups residing in the same areas and


that identifiable factors other than adaptation are not sufficient to


explain the observations.

                                 38
       In studies by Kerr et al.,    20 healthy adults — nine males and


one female,  aged 21-60 years (including 10 smokers and 10 nonsmokers) —


were exposed to ozone at 0.5 ppm for 6 h in an environmental chamber.


During this period, they engaged in two 15-min medium exercise sessions


(100 W at 60 rpm) on a bicycle ergometer.  Symptoms of dry cough and


chest discomfort, after ozone exposure, were more commonly noted in


nonsmokers.   They also had a significant decrease in dynamic compliance


after exposure.  Subjects who experienced symptoms, in general, were the ones


who developed objective evidence of decreased pulmonary function.  Chest


discomfort ranged from tightness on full inspiration to generalized chest pain


accentuated by exercise, cough, and irritation of the nose and throat.


Significant changes from control values for the group as a whole after ozone


exposure were observed for several pulmonary function tests:  specific


airway conductance (SGaw), pulmonary resistance (RL), FVC, and FEVo.   No


significant change was observed with respect to diffusing capacity (D^  ),
                                                                      CO

static lung compliance (Cgt), or the various tests derived from the nitrogen


elimination rate.  When the smokers were considered as a separate group,


no significant decrease in pulmonary function was observed, although some



                                   9-26

-------
                                                                      38
 individual smokers had decreases in pulmonary function.  These studies


 were  conducted in the Baltimore chamber facility with general conditions of:


 temperature, 24 C; humidity, 45%; purified background air; and two Mast


 coulombic meters for oxidant monitoring.

                       64
       Folinsbee et al.   tested the response of 28 subjects after ozone


 exposure to three stages of ergometer exercise with loads adjusted to 45,


 60, and 75% of maximal aerobic power.  The subjects were exposed to ozone


 at 0.37, 0.40, or 0.75 ppm for 2 h, at rest or while exercising inter-


 mittently — 15 min of rest alternated with 15 min of exercise at a


 workload sufficient to increase ventilation by a factor of 2.5.  These


 studies were conducted in a plexiglass chamber (Toronto).  Oxidant monitoring


 was with a coulombmetric analyzer (Mast), which was checked periodically


 against neutral buffered potassium iodide.  Neither submaximal exercise


 oxygen consumption nor minute ventilation was significantly altered after


 ozone exposure at any concentration.  The primary response was an alteration


 of exercise ventilatory pattern.  An increase in breathing rate (r=0.98)


 and a decrease in tidal volume (r=0.91) were correlated with the dose of


 ozone, calculated as the volume of ozone inspired during exposure.  It was


 concluded that through its irritant properties,  ozone modified normal


ventilatory response to exercise and that this effect was dose-dependent.

                   48a
       Rummo et al.     exposed 22 male volunteers,  aged 19-27, for up


 to 4 h to ozone at 0.4 ppm in relatively clean ambient air or to ambient


 air alone.   Subjects were seated during exposure,  except for two 15-min


 exercise periods on a bicycle ergometer at 700 kg-m-min exercise that about


 doubled the heart rate and quadrupled the ventilation volume.  After 2 h of


ozone exposure, there was a significant change (_p_ < 0.05)  in FVC,  MMF, and


 airway resistance (Raw).   Several other measures (FEV-p  VCQ,  and ^25)  were


 lower after 2 h of exposure,  but the statistical significance was borderline.



                                  9-27

-------
However, after 4 h of exposure, all flow measures were significantly decreased,



compared with controls.  After 4 h, Raw increased, FVC decreased further,



and FEV, decreased significantly.  Residual volume, functional residual



capacity, and total lung volume did not change as a result of the ozone



exposure.



       Kagawa and Toyama   have reported on the results of limited studies



involving four normal male subjects exercising while exposed to ozone at 0.9



ppm for 5 min.  A significant decrease in SGaw was found during exposure



and after 5 min of recovery.


                               9,28a,b,c,31,32,38,48a,64         .   .
       In all reported studies,                          an association



between symptoms and changes in lung function was usually found.  In general,



people who noticed cough and substantial tightness first were the ones who



developed the greatest defect in function.  Ozone-induced defects in function



were not usually found in the absence of definite symptoms of ozone-induced



respiratory irritation.



       It would be desirable at this point to discuss mechanistic interpreta-



tion of the lung function measures — such as FEB-^, delta nitrogen, and airway



resistance — that have been reported to change with ozone challenge.   Unfortu-



nately, although such measurements as FEV.. give an easily obtained, relatively



reproducible evaluation of overall lung mechanical performance, they provide



little information on the mechanisms responsible for any observed change.



Also, the measurement of the slope of the alveolar nitrogen plateau (delta



nitrogen) cannot be interpreted beyond saying that it reflects the uniformity



of ventilation distribution.  Airway resistance and specific airway conductance



are thought to be sensitive measures of constriction of large airways.  Results



of animal experiments provide additional information about mechanisms of action



of oxidant pollutants on the respiratory system.  These are discussed in Chapter 8.





                                   9-28

-------
       In interpreting the results of human experimental studies with pure



ozone in relation to the oxidant standard, it must be remembered that the



other oxidants ordinarily  present in smog were absent.  Conceivably, a larger



difference may be necessary between the lowest concentration of pure ozone



at which an observed effect occurred and the air quality standard than between



the lowest concentration of oxidant mixtures and the standard.


       „.              .     ,  _ ,.   ,    .,   ,  ,    10,28a,28b,28c,31,32,36,38,
       The newer experimental studies described above

48a,64

       show that significant adverse health effects occur in humans at ozone



concentrations of 0.37 ppm and higher.  Some limited studies   show evidence



of human health effects of exposure to pure ozone at concentrations as low as



0.25 ppm (see Figure 9-1).  The uncertainties of extrapolating ozone effects



to oxidant effects, of dose estimation,  of measurement, and of subject



sensitivity must be kept in mind when comparing the new data with the standard.





Exposure to Ozone and Other Pollutants



       Hazucha   and Bates and Hazucha   reported an enhanced effect between



ozone and sulfur dioxide in controlled-exposure studies of airway responses



in humans.   Hazucha studied subjects only in the resting state; Bates and Hazucha



during rest and exercise.  With various tests of ventilatory function—including



FEV,,  midmaximal flow rate, and maximal expiratory flow rate at 50% of vital



capacity — the investigators showed that healthy male college students



experienced no effect of sulfur dioxide at 0.37 ppm,  a 10% decline in function



with ozone at 0.37 ppm,  and a 20-40% decline in function with a combination



of sulfur dioxide at 0.37 ppm and ozone at 0.37 ppm.   The effect of ozone



alone on human function was not clearly mainifested until subjects had been



exposed for 2 h;  the effect of the  combination of ozone and sulfur dioxide was



apparent within 0.5 h.   The maximal effect was observed in the first 30 min



                                  9-29

-------
Figure 9-1.  Behavior of FEV  in response to ozone expressed as percentage


             change from the appropriate control (SHAM)  experiment.   Smokers


             and nonsmokers combined.   Exposures 2 h,  with intermittent light


             exercise,  except some Los Angeles exposures at 0.5 ppm for 4 h


             with intermittent exercise.   Points of error bars represent mean


             response (AFEV  postexposure vs.  control) +1 standard error.


             Curves represent best second-order polynominal fit to mean points.


             Numbers adjacent to points represent sample sizes: L.A., 7 at


             0.25 ppm,  13 at 0.37 ppm, 15 at 0.5 ppm;  Montreal, 3 at 0.25 ppm


             and 0.56 ppm (error bars  not given, because of small sample


             size), 12  at 0.37 ppm and 0.75 ppm.  Mean values for L.A. and


             Montreal 0.37 ppm x 2 h exposures are significantly different.


             t = 4.15.   2.  <  0.01.   Equations for dose-response curves:


             L.A.,  second-order fit to 3  data points,  (AFEV %) =  -7.524 +

                                                2
             46.546 (ppm 03)  -  81.795 (ppm 03)"; Montreal, second-order


             fit to 4 data points, (AFEV^) = 2.147 -  13.229 (ppm 03) -

                            2
             35.383 (ppm 0.,) .  NOTE:   These equations are only for the


             concentration ranges of the data.
                                    9-30

-------
                           FIGURE 9-1
OWtGE  IN FEVj
 10,0
 -10.0
r-20,0
,-30.0
                       PPM  03  ( BY  NEUTRAL  BUFFERED  KI  PETHQD )
                                                  -6              ,8
                          9-31

-------
after cessation of exposure.  Care was taken to use scrubbers on the instru-



ments that were used to measure each gas concentration.   The effect of the



combined gases was greater than the sum of the effects of the two gases



administered separately.


       AJ n.   i    i                    A       .*> A  •   28a,28b,28c
       Adult male volunteers were exposed to purified air,



to ozone alone, or to ozone in combination with nitrogen dioxide and carbon



monoxide.  No additional effects were detected when nitrogen dioxide at



0.3 ppm was added to ozone.  The addition of carbon monoxide at 30 ppm to



the ozone-nitrogen dioxide mixture produced no additional effects, other



than a slight increase in blood carboxyhemoglobin content and small decreases



in psychomotor performance, which were not consistent in different subject



groups.





Exposure to Peroxyacetylnitrate


                     52
       In 1965, Smith   reported increased oxygen uptake during exercise



in college students exposed to PAN at 0.3 ppm.  The average increase was

                                       21                 62
2.3%.  More recently,  Drinkwater et al.   and Ravin et al.   found no



significant physiologic change attributed to PAN exposure.  They tested 20



young men (smokers and nonsmokers) for maximal aerobic power (treadmill walk)



in a 35 C environment under four ambient air conditions:   filtered air,



carbon monoxide at 50 ppm, PAN at 0.27 ppm, and carbon monoxide and PAN.



No significant physiologic effects were noted during the PAN exposure for



smokers or nonsmokers.  Maximal aerobic power was not affected by any



pollutant condition.  Heat stress was more effective than any pollutant



condition in reducing work capacity, and a 4.3% decrease in maximal aerobic


power in a 35 C environment, compared with a 25 C environment, was greater



than the differences in aerobic power found between filtered air and any of



the pollutant conditions.



                                    9-32

-------
 Other Experimental Studies

                      34
        Holland et^ a]^.    studied 14  subjects  under  conditions  of  short-term


 exposures to irradiated  automobile  exhaust.   The environmental conditions


 simulated the "moderate" smog episodes  in  the Los  Angeles  air basin.   Oxidant


 concentrations were reported  as 0.22-0.27  ppm (on  the basis of the alkaline


 potassum iodide method).   No  significant changes attributed to exposure were


 found in reaction time,  vital capacity, work performance,  or  oxygen consump-


 tion.

                60
        Henschler    reported that the  characteristic  pungent odor  of ozone


 was  detected instantaneously  at low concentrations (less than 0.02 ppm),


 depending on individual  sensory perception acuity, and perceived  at higher


 concentrations (0.05 ppm)  for an average of  5 min.   At higher concentrations,


 the  odor was perceived as  stronger  and  persisted for an average of 13  min.


        Eye irritation has  been a common complaint  of people exposed to

                           33
 photochemical  air  pollution.    Attempts to investigate this experimentally


 have encountered  problems, because  of the subjective nature of the human


 response and the multiphasic  photochemical reactions involved.  Human  studies


 conducted until 1970 on  eye irritation  are cataloged and discussed in  National


 Air  Pollution  Control Administration Publication AP-64, Air Quality Criteria


 for  Hydrocarbons.


        Several studies indicate  that the major photochemical  products  that


 cause eye  irritation are acrolein,  PAN, and peroxybenzoylnitrate  (PBzN).   '  '


 Ozone,  the principal contributor  to ambient oxidant  concentrations, is not an


 eye  irritant.  This is an  important observation, because it might  have been


 assumed  that lacrimation would  correlate with  respiratory effects.  In fact,


 however,  ozone concentrations  can be high enough to cause considerable respira-


 tory effects without any irritation of the eyes having been noted.  Heuss


and Glasson   state that the potency of PBzN as an eye irritant  is 200 times


                                    9-33

-------
                                                 33
that of formaldehyde.  In studies by Heuss et al,   PBzN was formed in


parts-per-million amounts by irradiating automobile exhaust in laboratory


apparatus.  When some aromatics were added to a low-aromatic gasoline,


PBzN and greatly increased eye irritation resulted.

                    63
       Wilson et al.   measured irradiated automobile exhaust and pure


organic compounds and found that the addition of sulfur dioxide, although


it increased aerosol formation, decreased eye irritation in many of the


hydrocarbon - NOx systems studied.


       A number of components of ambient oxidant mixtures are discussed


in Chapter 3.  Further detailed characterization studies of ambient particulate


pollution may suggest that some of these compounds are present in the organic


fraction in quantities likely to be detrimental to human health.  Further


controlled health-effects studies might be accomplished with irradiated and


diluted automobile exhaust or exposure to pure specific compounds.




Limitations of Controlled Human Studies


       It is apparent that controlled human experimental studies are


needed, but are cumbersome and costly.  Other limitations include restrict-


ions as to the number of measurable responses and the fact that individual


pollutants are usually studied, rather than ambient mixtures.   In addition,


healthy subjects are usually studied, rather than sensitive population


groups.  The results of these studies are applicable to acute effects; but


their relation, if any, to chronic effects is not known.


       Ethical considerations impose design requirements that increase


the cost and complexity of controlled human studies.  For example, prudent


operational guidelines for such studies could include:



                                    9-34

-------
       •  The Investigators serving as the first subjects for each series




          of exposure studies.




       •  Pollutant exposure concentrations selected so as not to exceed




          documented ambient concentrations.




       •  The exposure environment constantly monitored by the technician




          who is operating the pollutant generating equipment.




       •  The presence of a physician.




       •  Monitoring of subjects electrocardiograpaically from outside




          the chamber.




       •  Direct observation of subjects at all times by viewport or




          closed-circuit television.




       •  Frequent checks by the attending physician and the chamber




          engineer for hazardous conditions and, if they encounter any,




          application of corrective measures  or halting of the study.




       •  Physician screening of prospective  volunteers.




       •  Obtaining of informed consent after the subject is given a




          full explanation of the experimental procedures, including




          known risks and discomforts.  The form would describe the




          procedures and risks fully and specify that the subject may




          withdraw from the study at any time.








SUMMARY




        Convincing new information on the health effects of oxidant




exposure has emerged from controlled studies on humans, from which tentative




dose-response curves have been constructed.  The new data show statistically




significant reduced pulmonary function in healthy smokers and nonsmokers




at ozone concentrations at and above 0.37 ppm for 2-h exposures.   Other  gases






                                   9-35

-------
and aerosols found in an urban atmosphere were not present in these experiments.




Some studies suggest that mixtures of sulfur dioxide and ozone at a




concentration of 0.37 ppm are more active physiologically than would be




expected from the behavior of the gases acting separately.




       Wide variation in response among different individuals is a general




finding in studies of oxidants, as well as other pollutants.




       Undesirable health effects of oxidant air pollution exposure are




increased by exercise,  and many people apparently limit strenuous exercise




voluntarily when oxidant pollution is high.




       Safety,  ethical, and legal considerations require that the utmost




care be exercised in human experimentation.   The risk inherent in this work




can be minimized by taking reasonable precautions while ensuring the satis-




factory performance of the study.






RECOMMENDATIONS




       Further studies are needed to give better dose-response information




and to provide a frequency distribution of the population response to oxidants




alone and in combination with other pollutants at various concentrations.




Such studies should include the effects of mixed pollutants over ranges




corresponding to the ambient atmosphere.   With combinations of ozone and




sulfur  dioxide, the mixture should be carefully characterized to be sure




of the effects of trace pollutants on sulfate aerosol formation.  The design




of such studies should consider the need to use the information for cost-




benefit analysis and for extrapolation from animals to humans and from small




groups of humans to populations.   Recent research has indicated the possibility




of human adaptation to chronic exposure to oxidants.   Further study is




desirable.
                                    9-36

-------
       Studies are needed to clarify the importance of age, sex, ethnicity,




familial elements, nutritional factors, and pharmacologic agents in determining




response to oxidants.  Because people with lung disease are thought to be more




susceptible to oxidant pollutants, exposure studies are needed to quantify this.




Better methods for measuring or estimating the actual dose of oxidants absorbed




by each subject are needed.  The usual time variation in measures of human




response should be evaluated per se, because this information is needed to




optimize experimental design.




       More information is needed before rational guidance can be given about




limiting exercise during periods of high oxidant pollution.




       Standards for the exposures of humans to controlled atmospheres




should be discussed by national groups and agencies, such as the National




Academy of Sciences,  the American Medical Association,  and the National




Institutes of Health.
                                 9-37

-------
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 57.   Wayne, W.  S. ,  and P. F. Wehrle.  Oxidant air pollution  and  school absenteeism.




           Arch. Environ.  Health 19:315-322, 1969.




 58.   Winer, B\  J.   Statistical Principles in Experimental Design.   (2nd ed.)  New



           York:  McGraw-Hill Book Company, 1971.  907 pp.



 59.   Yamashiro,  S.  M.,  S.  K. Karuza,  and  J. D.  Hackney.   Phase  compensation of




           Fleisch  pneumotachographs.   J.  Appl.  Physiol.  36:493-495,  1974.




 60.   Henschler,  D.",  A.  Stier, H, Beck, and W. Neumann.   Geruchsschwellen einiger




           wichtiger  Reizgase (Schwefeldioxyd, Ozon,  Stickstoffdioxyd) und




           Erscheinungen bei  der Einwirkung Geringer  Konzentrationen  auf den Menschen,




           Arch.  Gewerbepathol.  Gewerbehyg.  17:547-570,  1960.





 61.   Heuss, J/M., and W. A. Glasson.  Hydrocarbon reactivity and eye  irritation.




           Environ. Sci. Technol.  2:1109-1116, 1968.
                                   9-46

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62.   Raven,  P.  B. ,  B. L.  Drinkwater,  R.  0.  Ruhling,  N.  Bolduan,  S.  Taguchi, J.




           Gliner, and S.  M.  Horvath.   Effect  of carbon  monoxide  and peroxyacetyl




           nitrate on man's maximum  aerobic  capacity.  J.  Appl. Physio1.  36:288-




           293,  1974.




63.  Wilson, W.  E.,  Jr., A.  Levy, and E. H. McDonald.   Role of S02  and photochem-




          ical aerosol in eye irriation from photochemical smog.  Environ.  Sci.




          Technol.  6:423-427, 1972.




64. Folinsbee, 1. J., F.  Silverman, and R.  J. Shephard.   Exercise responses follow-




         ing ozone  exposure.  J. Appl. Physiol.  38:996-1001,  1975.
                                 9-47

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                                 Chapter 10




                        EPIDEMIOLOGIC STUDIES






       A variety of epidemiologic studies attempting to associate various




characteristics of human health and functioning with daily concentrations of




photochemical oxidants have been carried out during the last two decades,




primarily in the Los Angeles air basin.  A  few of these have shown clear-cut




associations involving large segments of the population.  Other studies related




to both the same and different health indicators have failed to demonstrate  any




consistent association.  Failure to establish clear-cut associations may well be




inherent in some aspects of the epidemiologic method.  Epidemiologic studies




have the advantage of being focused on the real -world, using human populations




in their normal setting.   This permits identification of both long-term and




short-term variations in health and function that can be correlated with pol-




lutant exposures.  It also permits identification of susceptible groups within




the general population that may be at greater risk.  Epidemiologic studies,




however, have two main disadvantages:  the health indexes used must inevitably




be relatively crude, as opposed  to controlled laboratory conditions; and it is




extremely difficult in the real world to isolate the effect of one environmental




factor  in the presence of numerous other independent and dependent variables,




•which may be synergistic with or antagonistic to the  environmental factor under




study--e. g. , other air pollutants, meteorologic factors, socioeconomic status,




occupational exposures, personal health habits, and  cigarette-smoking.   Within




these limits, some definite conclusions can be drawn as  to the association  (or




lack of it) of some health indicators with photochemical oxidant pollution.




Because of the lack  of epidemiologic information in some critical areas,  use

-------
must be made of clinical and toxicologic studies  on photochemical oxidants,




both in setting ambient air standards and in planning future epidemiologic




studies.






MORTALITY




        Death is obviously the most clear-cut and significant  end point for




determining  the effect of an environmental challenge on health.  It rarely has




a single,  isolated cause, however,  even in apparently simple events like




automobile accidents, homicide,  and suicide.  Careful investigation -will




usually reveal a constellation of factors that contributed to the final event.




Documented  episodes of deliberate  or inadvertent exposure of a sizable pop-




ulation to a high concentration of a  known toxic substance are extremely rare,




and all attempts to link death with ambient air pollution at normal concen-




trations must consider a multitude  of factors.  Furthermore, these factors




often vary from person to person and from situation  to situation.  Among the




factors that must be considered are the age and state of health of the person




affected,  the presence of    coexisting  disease states (likely for many




people), the  activity being pursued  by the person at the time  of and just




before death, and individual biologic variation in response to different




types of stress.  Other factors that must be  considered in relation to the




specific challenge are the type  of pollutant,  the presence  of other pollutants




(always a factor in epidemiologic studies of populations in natural envi-




ronments), the duration of exposure at  various concentrations,  the frequency




and degree of previous exposures to similar pollutants that may initiate either




tolerance or  hypersensitivity to the offending agent,  and the meteorologic




conditions under which exposure may take place.  The  last factor is  often shown




to play an overwhelming  role in determining the  outcome  of the  challenge.




                                      10-2

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       Several mortality studies on different population groups have been

conducted, principally in the Los Angeles area.  Studies by the California

Department of Public Health (reported in  1955,  1956,  and  1957)   showed a

marked increase in daily mortality among Los Angeles County residents aged

65 and older during a period of high photochemical oxidant concentrations in

a 2-week period in September 1955.  An examination of temperatures during

this period showed that the increase  in deaths occurred immediately after a

marked increase in temperature; mortality returned to normal before oxidant

concentrations had returned to  those prevailing before the episode. Although

the photochemical oxidant concentrations were high immediately before,

during, and after the heat wave, the  daily mortality decreased when temper-

atures dropped.  During other periods when daily mortality in citizens  over

65 was compared with both temperature and oxidant concentrations, no con-

sistent pattern could be discerned, nor could a pattern be  seen at other times

when  oxidants rose to medium and high concentrations without an accompanying

increase in temperature.  It must be concluded that heat rather than photo-

chemical oxidant exposure,  precipitated the increase  in fatalities in the

population studied.   Nevertheless, the possibility cannot be dismissed that

the concomitant high oxidant concentrations increased the  death toll. Such
                                                                    2
synergistic actions between  air pollutants and weather are well known.

       Heat has long been known to be one of the greatest  stresses to which

an elderly person can be subjected, and heat waves in New York,  as well

as Los Angeles, have been regularly shown to be followed  by  a tripling

or quadrupling of daily deaths among persons over 65, especially before

air conditioning became prevalent.  Unfortunately, high temperatures are

often  associated with high  oxidant concentrations in the Los Angeles basin.

                                     10-3

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In an attempt to isolate the effects of these two environmenta character -
                           3
istics Oechsli and Buechley  studied the mortality associated -with three

Los  Angeles heatwaves,  in 1939,  1955,  and  1963.  It was assumed that

less photochemical oxidant pollution was present in 1939  (although no

measurements were made at that time),  and  yet there was an equally high

mortality among elderly persons in 1939 and 1955. Temperatures were

similar in each of the three heat waves.  A lessened mortality was

observed during the 1963 heat wave, perhaps because of the  increasing

use of air conditioning between 1955 and 1963.  The authors  concluded

that  the high photochemical oxidant concentrations did not augment the

mortality effect of high temperatures.

       Residents of nursing homes were a special group  included in the
                                             1
California Department of Public Health study.    They were considered of

special interest because of the assumed presence of chronic illness in most

of them and their possible greater susceptibility  to photochemical oxidant

pollution.  All  nursing homes in Los Angeles County containing 25 or more

beds were included, and daily mortality, transfer to a hospital because of

worsening disease, maximal daily temperatures,  and the occurrence of smog-
                                                3
alert days with ozone  concentrations of 590 yg/m  (0. 3 ppm) or higher were

considered.  Again, the striking effect on mortality during heat waves was

noticed,  but no correlation with smog-alert days could  be demonstrated.
                                   4
       Massey, Landau,  and Deane  conducted a study on two synthetic

communities within the Los Angeles air basin.  These communities, -with a

combined population of 944, 391 persons, -were divided into high-pollution

and low-pollution areas.   The two areas had  similar temperatures.  The

mean number of daily deaths in the low-pollution area was subtracted from

                                      10-4

-------
the mean number in the high-pollution area,  and the difference was examined

by correlation and regression analyses with  respect to differences in pollution.

The observers were unable to detect any significant correlation between

mortality and difference in oxidant, sulfur dioxide, or carbon monoxide content

in the ambient air.

       Studying specifically the effect of pollutant concentrations on cardiac
                                                                       5
and  respiratory diseases in Los Angeles County, Hechter and Goldsmith

compared daily mortality from these  causes  with fluctuations in oxidant and

carbon monoxide concentrations and temperature.  The authors removed the

statistical effect of season by fitting Fourier curves to the data, which were

presumed to be independent of season.  When residua from the fitted curves

were analyzed,  no significant correlations between pollutants and mortality

from cardiorespiratory diseases could be found.  The authors also applied

lags of 1-4 days,  but again were unable to demonstrate any significant cor-

relations.  It is possible that some additive effect of pollutants on mortality

occurred but -would not be detected by  this analysis.

       Another attempt to compare cardiorespiratory deaths with photo-
                                                  6
chemical oxidant pollution was carried out by Mills,  who compared seasonally

adjusted nursing-home deaths in Los Angeles with measures  of photochemical

oxidant pollution.  He found  a suggestive positive association between photo-

chemical oxidant concentration and excess deaths when pollution rose
              3
above 390 ug/m   (0. 2 ppm).  Although heat and. seasonal    variability

were considered,  the  statistical analyses used make it questionable

whether  their effect could be suppressed.

       A variety of methods have been used to assess a relationship between

mortality from chronic illness and photochemical oxidant pollution, but none

has been able to demonstrate a clear-cut relationship.   The possibility of a

                                      10-5

-------
synergistic effect has not been ruled out, although the experience of

areas  other than the Los Angeles basin with lower concentrations of

photochemical oxidant pollution suggests that temperature is an over-

whelming factor in these deaths.

       Further studies  on mortality in relation to photochemical oxidant

pollution are needed to delineate differences in susceptibility (especially

in children and the elderly), to assess the additive effects of various

weather conditions, to examine geographic variations in mortality in

relation to pollution, and to determine whether excess mortality is

attributable to specific diseases (e. g. , emphysema),  which may have

been overlooked in examinations of total mortality.  Populations should

also be more  carefully categorized to determine whether  specific sub-

samples are at greater  risk.


HOSPITAL ADMISSIONS

       Several studies have attempted to correlate increased numbers of

hospital admissions with variations in photochemical oxidant pollution.
                                                 1
The California Department of Public Health study  of excess mortality

also investigated hospital admissions as a possible health indicator  of

oxidant pollution. Admissions  to Los Angeles County General Hospital in

September through December 1954 for childhood asthma,  tuberculosis,

other respiratory diseases, and all other causes were examined.  No

significant association with oxidant concentrations was found.

       Two other investigators have attempted to relate hospital admis-
                                                                  7, 8
sions to increased photochemical oxidant pollutants.   Sterling et al.

studied admissions to Los Angeles hospitals for a 7-month period in


                                      10-6

-------
 1961.  They grouped diseases into "highly relevant," "relevant," and

 "irrelevant" categories.  The "highly relevant" -were allergic disorders,

 inflammatory diseases of the eye, acute upper respiratory infections,

 influenza,  and bronchitis.  "Relevant" disorders included diseases of

 the heart,  rheumatic fever, vascular diseases, and all other respiratory

 diseases.  All other diseases were considered "irrelevant. "  Because

 both hospital admissions  and photochemical oxidant concentrations

 varied by day of -week, corrections for both-were introduced into the

 analysis.  Although there was  a statistically significant correlation

 coefficient between hospital admissions for "highly relevant" and

 "relevant" conditions  and photochemical oxidant pollution, the differences

 were extremely smallT

 Both "highly relevant" and  "relevant" diseases showed some  correlation

 with carbon monoxide and ozone, and nitrogen oxides and particles

 correlated with "highly relevant" diseases.  Even if the  relationships

 claimed  by this study  are valid, they are small, and confirmation by

 studies over a long period is needed.
                     9, 10
       Brant and Hill     also examined the number of patients who had

 respiratory and cardiovascular diseases and were admitted to Los

Angeles  County General Hospital for a 4. 5-month period in 1954.

 These months--generally regarded as the "smog season"--included the

highest photochemical oxidant  concentrations of the year.  Because he

accepted into his study group only persons who had resided for at

least 3 years within 13 km  of downtown Los Angeles and excluded

the extremely old and  children under 9, the numbers he dealt with

were rather  small for this  brief period.   Complex statistical analyses

                                     10-7

-------
were used to compare admissions with photochemical oxidant pollution,

as measured at a monitoring station not quite 6 km from the hospital.

The methods used have been questioned by many competent statis-

ticians, and the claims of a significant correlation between periods

of photochemical oxidant pollution and hospital admissions are  dif-

ficult to accept.  Even more difficult to accept is the claim of a positive

correlation bet-ween high concentrations of photochemical oxidants and

hospital admissions 4 weeks later. No reasonable medical explanation

can be given for the latter correlation.

       Studies to date have demonstrated an extremely weak correlation

(if any) between photochemical oxidant pollution and hospital admissions.

If such correlations do exist, observations must be carried out over

considerably longer periods with adequate provisions for controlling

confounding variables, such as meteorologic factors.


ACUTE RESPIRATORY INFECTION

        The possibility that chronic exposure to photochemical  oxidant

pollution alters host resistance and thus  increases susceptibility to

acute respiratory infection is a challenging one.  An opportunity to

examine this thesis occurred in  1968 and  1969,  when an epidemic  of

A2/Hong Kong influenza occurred in southern California.  Pearlman
      11
et al.   had the opportunity to observe five southern California

communities that varied from high to low oxidant concentrations during

this period.  Because other pollutants, especially oxides of nitrogen

and particles,  have shown associations with influenza attack rates, an

association with photochemical oxidant pollution was carefully  inves-

tigated.  Pearlman ^t al. examined the morbidity among 3, 500

                                      10-8

-------
elementary-school children in five communities.  Although these

communities showed a definite gradient in chronic  oxidant exposure,

there -was no significant difference in oxidant concentrations imme-

diately before or during the epidemic. Questionnaires to parents of

the children followed between November  1968 and January 1969 asked

about the presence of influenza-like illness or  symptoms.   Blood

specimens were later obtained from the children whose parents  reported

upper  respiratory symptoms.  Titration was performed by hemagglu-

tination inhibition and complement fixation against A 2 influenza antigen.

Although more children  reported illness in low-pollution cities,  no

statistically significant difference in illness  rates could be correlated

with exposure to chronic oxidant air  pollution.  Inasmuch as acute oxidant

concentrations were roughly similar in all five communities, it may be

that the children did not receive  an oxidant dose sufficient to impair host

defense mechanisms  immediately before or during  their exposure to the

virus.  In statistical  manipulation, the investigators were able to minimize

other significant covariants, but concluded that "oxidant exposure. . . .did

not alter host defense mechanisms enough to cause morbidity differences. "

       School absenteeism is known  to be due in large part to  acute
                                          12
respiratory illness, so Wayne and Wehrle   followed daily absenteeism

rates in schoolchildren in Los Angeles, but were unable to detect any

relationship between  variations in ambient photochemical oxidant con-

centrations  and school absenteeism.

       In a  long-term study, Hammer etal.  recorded daily symptoms

in healthy young student nurses for a period of  nearly 3 years  (October
                13
1961-June 1964).    An average  of 61 student nurses in two nursing

                                      10-9

-------
schools in Los Angeles completed a daily dairy for 868 days on the

incidence of cough,  chest discomfort, eye discomfort,  and headache--

all symptoms that might be expected to accompany an acute respiratory

infection.  Other recorded information included incidence of gastroin-

testinal symptoms,  physician visits, restricted activity, and menses.

Daily maximal hourly concentrations of photochemical oxidants, carbon

monoxide, and nitrogen dioxide and daily  temperatures were also measured

at monitoring stations within 2 miles of the schools.  As expected, eye

discomfort showed the strongest correlation with photochemical oxidant

concentrations, with one-third of the total population reporting the symptom

when oxidant concentration reached 0. 5 ppm.  However, cough and chest

discomfort also increased with maximalhourls oxidant concentration.

Headache showed a positive association with photochemical oxidant con-

centration, but the increase in the number reporting the symptom  (3-8%)

was considerably less than for other symptoms.   Temperature and carbon

monoxide and nitrogen dioxide concentrations  could not explain the

associations found.  Cigarette-smoking history, allergies,  and bias in

reporting were supressed as variables in  the analysis.  It is of particular

interest that the authors were able to compute the thresholds of which the

prevalence of the symptoms began to increase and found them  close to the

present U.S. national primary standard for photochemical oxidant, indicating

little or no margin of  safety.   The eye  irritation threshold was calculated
                          3
at approximately 294 Mg/m  (0. 15 ppm).   Because these were  all young

healthy adults, relatively free from chronic disease, the same effects in

elderly persons or in  those with chronic   heart or lung diseases could be

expected to result in greater physiologic  embarrassment.

                                   10-10

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       Although  the observed threshold for eye discomfort is comparable




•with reported results of human experimental exposure-chamber studies,




it is recognized that current methods for measuring photochemical




oxidants  primarily measure ozone, •which is not known to be an eye




irritant.   The authors  therefore assumed that the measured concen-




trations of ozone  reflected the concentrations of such known eye irritants




as peroxyacylnitrate, peroxybenzoylnitrate, formaldehyde, and acrolein--




all of which have  been  shown to be present in Los Angeles basin air.




However, the symptoms of cough, chest discomfort,  and headache have




all been associated -with occupational exposure to  ozone,  so it is possible




that ozone itself is the offending agent for these symptoms.  It is interesting




that the observed daily maximal hourly carbon monoxide  concentrations




in this study -were below those which have been reported to cause headache




experimentally.  Nevertheless, inasmuch as a significant number of




student nurses did report headache associated -with increased oxidant




concentration,  an interaction  between carbon monoxide and oxidants




cannot be excluded.
                                   10-11

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AGGRAVATION OF PREEXISTING DISEASE

        The best-documented health effect of general urban air pollution

is the aggravation of preexisting disease.  In the notorious Donora

episode and in the many we 11-documented episodes  of excess mortality

in London's "smogs," most of those who died had had marked impairment

of cardiac or  pulmonary reserve.  Similarly,  the majority of epidemiologic

studies demonstrating an association of health impairment with increased

air pollution were carried out in areas where the atmosphere was

characterized by a particulate-sulfate (and preponderantly chemically

reducing) type of pollution. Several investigators have attempted to

determine whether similar health effects are produced  by exposure to

atmospheres that have photochemical oxidants as the  characteristic

pollutants.
                              14
       Studies by Motley ^t al_.    on 66 volunteers, 46  of whom had

pulmonary emphysema,  were conducted in a "filtered room" from which

oxidants •were removed by activated-char coal filters.  Pulmonary

function studies  demonstrated improvement in emphysematous patients

who remained in the room for 40 h or more, if they had entered it on

a day when the ambient air in Los Angeles was considered "smoggy"

by the investigators and the Los Angeles Air Pollution Control District.

Normal subjects showed no change in pulmonary function in the filter ed-

air chamber,  compared with measurements taken when they were

breathing ambient "smoggy" air.  Emphysematous  patients also showed

no improvement if they entered the  room on a "nonsmoggy" day.  The

study, although  widely cited, is difficult to evaluate, because the

number of patients was relatively small.  Some improvement was noted

                                   10-12

-------
 in the emphysematous patients who entered on "smoggy days" in vital

 capacity, FEV  , and maximal breathing capacity.  The most marked
               3
 change,  however, was a decrease in residual lung volume.
                             15
       Remmers and Balchum    used a specially constructed room at

 Los Angeles County Hospital with an air-conditioning filter system

 and filters that  could be used at the discretion of the investigator to

 remove photochemical oxidants and nitrogen oxides  from ambient air.

 Particulate matter could also be partially removed.  They carried

 out studies  during September and October 1964 and from March to

 November 1965.  Pulmonary function studies were performed one or

 more times a day during the approximately 1 week that each patient

 spent in  the room with no filtration and again for a week with

 filtration.   Temperature and humidity were kept constant in both cases.

 Airway resistance, diffusing capacity, other pulmonary functions, blood

 oxygen tension,  and oxygen consumption were measured when the subjects

 •were at rest and exercising.  Examination of the data indicated  that

 airway resistance was affected by increased oxidant concentration over
                        3
 a range of 100 - 450  ug/m   (0.05 - 0. 23 ppm).   Unfortunately, the

 data are  difficult to interpret,  because many of the subjects were

 cigarette-smokers,  the subjects were exposed to ambient air con-

 taining many substances in addition to oxidant,  and the  observed

 improvement with filtered air may have been caused by the  removal

 of other pollutants, such as aerosols, aldehydes,  and particles.

A more elaborate analysis of these data was carried out by Ury and
       16
Hexter.    It demonstrated that oxygen consumption, in most cases,

increased with oxidant concentration.  Unfortunately,

                                   10-13

-------
the oxidant concentration was measured only twice a day at a station

some distance from the site of the subjects' exposure.  Oxidant was

also measured as ozone,  so the concentrations of other irritant oxidant

compounds could not be determined.
                                                           17
       A much larger group of men was followed by Shoettlin   in an

attempt to study the long-term effects of community air pollution  on

persons with and without  symptoms of pulmonary disease.   These two

groups were  veterans who lived in the domiciliary unit and in the

chronic-disease annex of the Los  Angeles Veterans' Administration

Center.  A group of 528 veterans  in the domiciliary unit who had no

symptoms of respiratory disease  were used as the control population.

A group  of 326 men -were  selected on the  basis of at least two symptoms

of respiratory disease for 2 years or longer.  The symptoms included

cough, sputum production ,  shortness of breath, wheezing, and abnormal

breath sounds.  The two groups were matched by age and smoking history,

and the resulting pairs were studied weekly by repeated pulmonary

function  tests and response to a standardized respiratory-symptom

questionnaire.  An analysis of variants showed no statistically significant

effects of air pollution on incidence or prevalence of respiratory symptoms

or on tests of pulmonary function. Nevertheless,  the maximal oxidant

and oxidant precursor concentrations consistently accounted for more of

the variation in frequency of symptoms and clinical signs in the group

with pulmonary disease than in the control group.  Up to 30% of the

variation in symptoms in  the group with pulmonary symptoms appeared

to be correlated with the maximal oxidant precxirsor concentrations,

•whereas  no association could be demonstrated in the control group.

                                   10-14

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ASTHMA

       Asthma, a. disease featuring sudden and dramatic variations

in respiratory symptoms and pulmonary function, is •well known to be

related to environmental factors in many cases. Many other factors,

however, may play a significant role in the precipitation of asthmatic

attacks,  including meteorologic factors, emotional factors,  infection,

allergy,  and physical activity.  It has also been demonstrated that

there is  a significant ethnic  variation in factors associated with acute
                  18
asthmatic attacks.    Nevertheless, between 2  and 5% of the popu-

lation is subject to asthmatic attacks,  so it has been examined as  an

indicator of health effects of photochemical oxidant pollution.
                     19
Schoettlin and  Landau   carried out one of the earliest studies to

determine whether aggravation of asthma could be related to increases

in oxidant concentrations.  They followed 137 asthmatics in  Pasadena

with known asthma for at least 5 years.  Over at least a 3-month

period in late 1956--the usual peak oxidant period of the year--

weekly reports were  obtained from each patient as to the number of

attacks.  Of the 3,435 attacks reported by these patients,  less than

5% were spontaneously associated by the patient with "smog."

Although most reported  attacks on days with high enough oxidant

concentrations to cause  eye  irritation and plant damage,  the majority

of attacks occurred between midnight and 6:00 a.m., whereas peak

oxidant concentrations occurred between 10:00 a.m.  and 4:00 p.m.

This lag, however, would not necessarily rule out a causative role of

oxidants in asthmatic attacks.   The conclusion of the authors was  that

only 8 of the  137 patients could be characterized as "smog reactors."

                                    10-15

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                                                                20
 The oxidant concentrations later reported by Renzetti and Marcus

 •were a peak of 0. 25 ppm and, for the same period and same station,

 a maximal hourly concentration of about 0. 02 ppm.  It is of interest

 that one-third of the attacks spontaneously associated with "smog" were

 reported by a single patient.  However, in spite of the small number

 of people who spontaneously associated their attacks with "smog, "

 this study suggests that there are probably some people who do

 experience asthmatic attacks related to increased  concentrations of

 photochemical oxidants.  Further studies  to confirm this,  sponsored

 by the EPA, are underway in the Los Angeles air basin.


 EFFECTS OF PHOTOCHEMICAL OXIDANTS ON HEALTHY POPULATIONS

Athletic Performance
                   21
       Wayne ei^ al.    related athletic performance of high-school

 cross-country runners over a 5-year period from  1959 to 1964 to  oxidant

measurements for the hour of the race and 1, 2, and 3 h before the

 race.  Temperature, relative humidity, wind velocity and direction,

and oxides  of nitrogen were also considered, but showed no relation

to the running times.  A "training effect"  that might be expected to

improve performance  on each succeeding  race was also considered.

A significant relationship, however,  was observed between high

oxidant concentrations and the percentage  of runners whose performance

decreased, compared with their performances in the previous home

meet.  It is of interest that the deterioration in performance of these
                                          3
21 runners was noted beginning at 130 ug/m   .  With increasing oxidant

concentration, there was a manifest deterioration  in team performance


                                   10-16

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                             3
over a range of 60  - 590 Mg/m  .   This deterioration

in performance began well below the national photochemical oxidant
                    3
standard of 160 yg/m  (0.08 ppm).  The authors readily admitted

that "the observed  effects may be more related to the lack of maximal

effort due to the increasing discomfort than to decreased physiologic

capability."  Nevertheless, although they  discussed the possibility

that decreasing performance might be due to the detrimental effect

of discomfort from eye irritation,  the data provide convincing

evidence that some components of  the air  that were measured as

oxidant had an effect on team performance.

       Although no threshold effect was specified by Wayne et al.
                                   22
a later analysis by Hasselblad et al.    suggested a threshold estimate
            3
of 235 yg/m   (0. 012 ppm).  A similar study was carried out over a
                         23
shorter period by Koontz   in Seattle, where oxidant concentrations

were approximately one-third those in Los Angeles.  A decrease  in

performance of long-distance  runners was noted with increasing

oxidant concentrations, but these were also associated with marked

temperature increases,  and it was impossible to separate their

relative contributions.


Automobile Accidents
       Another association of oxidant concentrations with potentially

serious implications is the increase in automobile accidents noted by
     24
Ury.    He recorded accidents in each daylight hour of each weekday

in the "high-smog" 3-month period between August and November for

2 years and found a statistically significant relationship between oxidant
                                   10-17

-------
concentrations and the number of automobile accidents.  He was

unable to demonstrate a similar relationship with nitrogen dioxide.

Because the  study compared hours -with presumably similar traffic

density,  the  likelihood that traffic density accounted for the association

is probably small.   The data  suggest that photochemical oxidant pol-

lution impairs driving performance, either directly by interfering with

oxygen transport or utilization or indirectly by causing eye discomfort

or respiratory irritation.  It  is also possible that other pollutants,

such as carbon monoxide emitted from the automobile tailpipe,

account for some or all  of the excess accidents.


Discomfort

       Additional evidence of an association of discomfort or more

severe health effects with increased oxidant concentrations was

published by the Committee on Air Pollution of the Los Angeles
                             25
County Medical Association.    The organization circulated a

questionnaire to a sample of  every sixteenth physician registered to

practice in the County.  Although air pollution was not specifically

mentioned in the questionnaire, the fact that it was sponsored by an

air pollution committee  probably  suggested to the physicians that air

pollution was the principal environmental concern.  The physicians

were asked how many patients they had advised to move from Los

Angeles County for health reasons before December I960.  By

extrapolation from these questionnaires, it was estimated that over

10, 000 persons had been advised  by their physicians to move from the

County for health reasons and,  for two-thirds of these, air pollution

was given as the reason.  Because this was a study of  attitudes,it

cannot be categorically  cited  as indicative  of a definite health effect.

                                    10-18

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Pulmonary Function

        Children have  often been considered to be particularly sensitive

indicators of environmental challenge and therefore to constitute a group

in -which adverse health effects of air pollution might be detected at lower

concentrations than in adults.   Two groups of elementary-school children

living in the Los Angeles basin were assessed twice a week by McMillan
      26
et al.   with a Wright peak-flow meter to measure ventilatory performance.

One group of 50 children lived in an area exposed to high oxidant concen-

trations,  and the other group of 28 children lived in a less polluted area.

During  11 months  of the study,  no correlation could be  found  between acute

changes in oxidant concentration and ventilatory performance in either

group.  Unfortunately, there were significant differences between the two

groups, in that the group in the more highly polluted area was ethnically

mixed and had an incidence of upper  respiratory tract infection 3 times

greater than that reported in the other group. Pulmonary function studies,

as part of the  Community Health Effects Surveillance Studies  (CHESS)

program, are underway in  seven communities with graduated concentrations

of photochemical oxidants in the Los Angeles basin.  It is hoped that these

will yield more  definitive results.

       A  similar study on the  relations between pulmonary function and
                                                                         27
exposure  to photochemical  oxidant pollution was carried out by Cohen et al.

To eliminate the effects of  smoking,  the study was confined to Seventh Day

Adventists who abstain from tobacco.  They were  divided into two groups:

one living in the San Gabriel Valley (a high-oxidant-pollution area),  the

second  living in San Diego,  which was then considered to represent a

relatively low-pollution area.  Each participant was

                                   10-19

-------
interviewed by a physician, underwent a battery of pulmonary function

tests,  and completed a standardized respiratory-disease questionnaire.

Daily maximal hourly average oxidant concentrations in the San Gabriel

Valley -were twice those in San Diego during the time of the study (San
                        3                                       3
Gabriel, about 274 \ig/m  ,  or 0. 14 ppm; and San Diego,  137yg/m ,

or 0. 07 ppm).  In  spite of the marked difference between the oxidant

concentrations in the two areas,  no significant differences could be

found in pulmonary function studies, the prevalence  of chronic

bronchitis,  or the occurrence of respiratory-disease symptoms,  as

determined by the questionnaire.  In this study, the  differences may

have been due to the absence of cigarette-smoking in both groups;

some investigators have suggested that smoking is an additive factor
                                     28
in the effects  of ambient air pollution.   It must also be noted that,

although the peak values of oxidant pollution in the more polluted

area were twice those in the less polluted area, the  mean yearly

averages were essentially the same.
                          29
       Kagawa and Toyama   in Tokyo followed 20 normal  11-year-

old  schoolchildren once a week from June to December 1972 with a

battery of pulmonary function tests.  Environmental factors studied

included oxidant, ozone, hydrocarbon, nitric oxide,  nitrogen dioxide,

sulfur dioxide, particles, temperature, and relative humidity.

Temperature was  found to be the most important environmental

factor affecting respiratory tests.   The observers noted that pulmonary

function tests of the upper airway were more susceptible to increased

temperature than those of the lower airway.  Although the effect of

temperature was the most marked,  ozone concentration -was significantly

                                    10-20

-------
associated with air-way resistance and specific airway conductance.

Increased ozone concentrations usually occur  at the same time as

increased temperature, so their relative contributions could not be

determined.


Eye Irritation and Lacrimation

       Eye irritation and lacrimation are by far the most widespread

and common symptoms clearly associated with increased photochemical

oxidant pollution.  Although photochemical oxidant is customarily

measured as ozone, ozone  itself is not a primary eye irritant.  Thus,

the eye irritation associated with increased photochemical oxidants

is probably due to some or many of the complex organic oxidants
                                                             31, 32
produced in photochemical  "smog."  Richardson and Middleton

noted nearly 20 years ago that eye  irritation could be expected in a

considerable portion of the population when the oxidant concentration
                 3
reached 200yg/m
                           33
       Renzetti and Gobran   carried out a controlled study on two

groups of 20  female telephone-company employees working in adjacent

rooms for a period of 120 days.  Filters  to remove eye irritants were

switched periodically between  the rooms,  so that the two groups  were

alternately exposed to test  and control conditions.   Subjects were

unaware  of whether air was filtered or unfiltered at any  given time,

but they consistently reported  eye irritation when the oxidant concen-
                         3
tration exceeded 200 yg/m  .   Eye irritation has also

been previously cited as the most commonly reported symptom in the
                                     13
student-nurse study of Hammer et al.
                                   10-21

-------
        That the problem of eye irritation in urban environments is not
                                                                    34,35
confined to  Los Angeles is indicated by the studies  of McCarroll et al.
                   36
and Mountain et_ al_.  on a population in the lower east side of Manhattan.

This population of approximately 2, 000 persons of all ages  representing

the major ethnic  groups of New York City was followed for  a period of 3

years with weekly interviews.   Participants were queried about the

occurrence of many different diseases, disease symptoms,  aggravation

of preexisting diseases, and a variety  of other health factors.  Frequency

of reports of new eye  irritation increased concomitantly with increases

in oxidant concentrations in the neighborhood.  Exact oxidant concen-

trations could not be measured in the study, because of the presence

of high  concentrations of interfering substances, including  sulfur

oxides,  particles, and carbon  monoxide.  Substances other than  oxidants

might have  contributed to the eye irritation reported by this population.

        For the two most prevalent symptoms  related to photochemical

oxidant  exposure — eye irritation and lacrimation--no method of

quantification has been developed.   Eye irritation, although undoubtedly

real,  is a purely subjective response of the  subject, and no measurement,

other than the complaint itself, has yet been developed.  Similarly, a

routine  objective measure of lacrimation remains to be developed.

However, studies on tears have demonstrated that,  when a  person

is experiencing eye  irritation, the  lysozyme content of  the tears is
                   37
lower than normal.    Measuring lysozyme  content of tears or the

related  pH variation appears promising, but more feasibility studies

are necessary  before  the usefulness of the method is known.
                                   10-22

-------
       A survey of the state of knowledge of eye irritation and

lacrimation in response to photochemical oxidant pollution was  carried

out by Wilson of the Copley International Corporation for the Coordinating
                  38
Research Council.     After  reviewing the studies cited above and related

toxicologic work,  the  report concludes:  "In many ways,  the under-

standing of eye  irritation produced by photochemical smog has not kept

pace with the understanding  of other smog manifestations.  Part of this

is no doubt due  to the  fact that air pollution control agencies are not

set up to collect data from human panels but rely exclusively on

instruments.  If an objective measure were available for measuring

eye irritation,  and if this measure were sensitive enough to be

useful below the threshold of most humans,  then a straightforward

study could be done on natural smog."

       Nevertheless,  in spite  of the many gaps  in our knowledge of

the components  that produce eye irritation,  there is  remarkable

uniformity in the findings of several epidemiologic studies cited,  in

the prevalence of the symptoms as oxidant concentrations increase,

in the distress that oxidants  cause the affected subjects,  and in the

threshold concentration at which the symptoms appear (0. 15-0. 2 ppm).


PHOTOCHEMICAL OXIDANT POLLUTION AS A CAUSE OF CHRONIC
DISEASE

       Several  studies attempting to relate  aggravation of preexisting

chronic disease to increases in photochemical oxidant pollution have been

discussed. The  possibility has also been raised that photochemical oxidant

pollution plays a role in the initiation of some chronic diseases. In part,

this possibility was suggested  by  laboratory studies demonstrating some

                                    10-23

-------
radi.omim.etic properties of ozone. Although ozone may mimic ionizing

radiation in some respects, it carries by no means all the carcinogenic

implications.  Nevertheless,  experiments have indicated chromosomal
                              39
damage to living cells by ozone   and to human cells in vitro by organic
           40                               41
peroxides.     Work of Palmer and colleagues   has  suggested that

ozone is a potential cocarcinogen--a  finding that carries great impli-

cations during a time of increasing rates of human lung cancer.

        To assess the possible contribution of photooxidant pollution
                                    42
to lung-cancer mortality, Buell je_t a_l.   carried out a prospective

study of lung cancer among 69, 160 members  of the American Legion--

residents of Los Angeles County, the San Francisco Bay area, San

Diego County, and all other California counties.  This study was

carefully adjusted for cigarette-smoking habits, occupation, and

duration of residence in the same county.   Death certificates for the

first 5-year period were checked for mortality from cancer of the

lung and from other chronic lung conditions for a total of 336, 571

man-years of observation.  As would be expected, residents of the

urban counties of Los Angeles,  the San Francisco Bay area, and San

Diego had considerably higher mortality, both from lung cancer and

from other cronic pulmonary disease.  Even when adjusted for

cigarette-smoking,  these differences persisted, but they are compatible

with other observations on the well-known "urban factor"  in increased

death rates from lung cancer, other  cancers, and other chronic pulmonary

disease. When  heavy smokers  (more than  one pack a day) were examined,

the relative risk of lung cancer was found to  be greater in Los Angeles

County  than in other areas of California. For nonsmokers, however,

                                   10-24

-------
the rate in the San Francisco Bay area and San Diego County was

slightly higher than the rate  in Los Angeles County.  From these

data, it was not possible to demonstrate any effect of oxidant pollution

on lung-cancer mortality,  if one assumes  that in the years of observation

(i958-1963) oxilant concentrations were higher in Los Angeles.  However,

because it is well known that the development of overt lung cancer

is an indolent process that takes many years, the period of observation

may not have been long enough to detect an environmental effect.

       When the same observers examined mortality from chronic

respiratory diseases  other than cancer of  the lung,  the death rates

were found to be somewhat higher in Los Angeles than in the San

Francisco Bay area and San  Diego County, particularly among persons

•who  had lived for 10 or more years  in the  same area.  It is well

known, however, that socioeconomic class is an important factor
                                             43
in mortality from chronic respiratory disease,    and no data are

available  to show such differences among the  groups examined in this

study.
                                                                   44
       With standardized respiratory-survey techniques,  Deane et al.

examined a. group of West Coast  outdoor telephone-company employees

whose work and medical and  social status were comparable with those

of similar groups examined on the East Coast, in the United Kingdom,

and in Japan.  They noted that, in the group over 50  years old,  respiratory

symptoms were more frequent in the Los Angeles and in the San

Francisco population  than in  the  other areas  studied.  Twice as many

telephone-company workers  in Los Angeles complained  of persistent

cough and phlegm as in San Francisco. The groups were controlled

for smoking habits.  Surprisingly,

                                   10-25

-------
in spite of the difference in reporting of symptoms,  there were no

important differences in the results of pulmonary function tests

between residents of the two areas in this occupational group.
                                                     50
These findings are at variance with those of Hackney,     •who noted

seasonal differences,  which were greater in San Francisco than in

Los Angeles.


DISCUSSION

        The EPA is conducting a major study in  the Los Angeles basin

on the effects of photochemical oxidants on health.  It  is a survey

of schoolchildren in seven communities representing a gradient  of oxidant

exposure.  In addition to comprehensive  environmental monitoring data,

specific health characteristics will be followed,  including chronic

respiratory disease in adults, lower respiratory disease in children,

acute respiratory disease  in both children and adults,  pulmonary function

in children, aggravation of asthma, irritation of mucous  membranes,

and tissue  residues of trace metals.   Complete  data from this study

will not be available for another 3 years,  but data from the first 2

years may become available sooner.

       A second study by the EPA will attempt to correlate the effects

of photochemical oxidants  and cigarette-smoking in promoting chronic

respiratory signs and symptoms in cohorts of adolescents and their

families.   Pulmonary function tests will  be included, and this  study

should do much to answer  the vexing questions of the relationship  of

chronic pulmonary disease and photochemical air pollution.
                                    10-26

-------
        The abovementioned    studies are being carried out by the EPA




as part of the CHESS program.  Although some of these  studies have




produced useful information, others are apparently not fulfilling their




objectives.  Specifically, these  studies are designed entirely in-house




by full-time employees  of the EPA at Research Triangle Park,  North




Carolina.  The studies -would have benefited by the presentation of




experimental design and proposals to knowledgeable and experienced




scientists outside the federal establishment for comment and criticism.




Furthermore,  some of the  information collected in    past studies




and much that is now being collected is retained by the EPA  to be




used ultimately in standard-setting, without first being subjected  to the




scrutiny of the scientific community outside the federal government.




To date,  there has been relatively little publication in the usual




scientific journals,  and most data have been issued by the  EPA in




the form  of monographs; hence,  external scientific input, although




sought, had little effect on  the published scientific product.  Because




most of these studies have  been  related to disease or symptom




prevalence, before-and-after studies of the effects of approved air




quality have been impossible to  carry out.  This criticism applies not




only to the CHESS studies,  but to virtually all epidemiologic  studies




cited in this chapter, inasmuch  as adequate environmental monitoring




was  rarely carried  out in studies before the last decade.  The




epidemiologists and statisticians undertaking the CHESS  studies are




extremely competent and are supported by well-trained engineers,




chemists,  and meteorologists.   Personnel turnover, however, has




inevitably affected the continuity of direction of the program.




                                     10-27

-------
       In addition to these much-needed studies,  others  should be

designed to seek information on human populations on points already

raised by important toxicologic and clinical studies.  Although

epidemiologists have been unsuccessful in relating infectious diseases
                                     45
to oxidant pollution, Coffin and Garner    showed that ozone exposure

before or after exposure to pathogenic bacteria strikingly increases

mortality in mice.  They found that ozone  not only affected host

resistance by inhibiting clearance rates,  but also permitted uncontrolled

growth of streptococci.  This and much other toxicologic evidence

that ozone  interferes with host defense mechanisms in animals suggest

that a similar phenomenon may go unrecognized in humans.
                                                        41
       The evidence that ozone is a potential cocarcinogen   has grave

implications.  If the radiomimetic properties of ozone are confirmed,

we may well be dealing with a nonthreshold dose-response situation in

which no standard can be considered to represent a completely innocuous
                                                               46,47
concentration of pollutant.  The recent work of Bates and Hazucha

showing a synergistic  effect of ozone and sulfur dioxide encourages the

belief that pollutants cannot be considered separately when standards

are promulgated and that the complex interrelationships  among them

must be considered.  It is important to know -whether other phenomena
                                                48
well demonstrated in animals, such as tolerance,    also occur in humans.

And there are suggestions that some type  of cross-protection may occur,

whereby exposure to ozone provides  some protection against other irritant
         49
oxidants.    Analogues for all these phenomena should be sought in human

populations, and methods should be devised for assessing their significance

for human health.

                                    10-28

-------
RECOMMENDATIONS




       Modification of the method in which the CHESS studies are




designed and in -which the data are displayed would add considerably




to their value.  The scientific data collected in all the CHESS studies




should be made available through accepted scientific publications




to the scientific community as a whole.




       The continuation of epidemiologic studies, including those of




the CHESS program, is vital to our understanding of the effects of air




pollution on health.  There  is no other way to determine the needed




dose-response (exposure-response) relationships between the complex




urban atmospheres and specific health effects.  No animal  or clinical




experiment can duplicate the full range of variables to be found in




ambient urban air.  For this reason,  all necessary support should




be given to qualified scientists to conduct epidemiologic studies




designed to answer these questions.  Although such studies are




expensive and time-consuming, the data they produce can be  produced




in no other way and are essential in the development of useful air




quality standards.




       It is important to know whether such phenomena as tolerance




and cross-protection,  well demonstrated or suggested in animals,




occur in man.  Analogues for all these phenomena should be sought




in human populations,  and methods should be devised for assessing




their significance for human health.
                                     10-29

-------
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          Los Angeles.  Arch.  Environ.  Health  10:323-331, 1965.
                                 10-34

-------
45.  Coffin, D. L., and D. E. Gardner.  Interaction o£ biological agents and chem-

          ical air pollutants.  Ann. Occup. Hyg. 15:219-234, 1972.


46.  Bates,  D., and M. Hazucha.   The short-term effects of ozone on the human

          lung, pp. 507-540.  In National Research Council.. Assembly of Life

          Sciences.   Proceedings of the Conference on Health Effects of Air

          Pollutants,  October 3-5,  1973.  Senate Committee on Public Works Print

          Serial No. 93-15.  Washington, D. C. :   U. S. Government Printing

          Office,  1973.
                i           (    •  .   .
47.  Hazucha, M.,  and  D.  V.  Bates.   Combined effect of ozone and sulphur dioxide

          on human pulmonary function.   Nature  257:50-51,  1975.

48.  Stokinger, H.  E.,  and  L.  D.  Scheel.  Ozone  toxicity.   Immunochemical  and

          tolerance-producing  aspects.   Arch. Environ.  Health 4:327-334,  1962.


49.  Stokinger,  H.  E.,  W.  D. Wagner,  and 0.  J. Dobrogorski.  Ozone toxicity

          studies.   III.   Chronic injury to lungs of animals following exposure

          at a  low level.   A.M.A. Arch.  Ind.  Health 16:514-522,  1957.


50.  Hackney, J.   Final Report to California State  Air Resources Board on Contract

          No. N01-HR3-2901.   Smoking and Chronic Airways  Obstruction., 1975.

          (UNVERIFIED)
                              10-35

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                                 Chapter 11

                     PLANTS AND MICROORGANISMS


        The intent of this chapter is to give a critical review of all research

related to the effects of photochemical oxidants,  including ozone and the

peroxyacylnitrates, on plants and microorganisms.

        Injury to vegetation -was one of the earliest indicators of photochemical
                                                                        369
air pollution.  Injury was first observed in the Los Angeles area in 1944.

Since then,  there has been  a slow but steady increase in research efforts to

understand the effects of these pollutants on vegetation.  In the late 1960's

and early 1970's,  there has been a flood of published information.

        In attempting to understand the effects of pollutant-pathogen interactions,

investigators looked at the  effects of oxidant pollutants on individual micro-

organisms and on these organisms as they infected host plants.  Ozone has been

tried as a fumigant to protect stored plants and plant parts against infection

by parasitic  and saprophytic fungi and bacteria.  Research on ozone as a

sterilant for water supplies and  sewage systems  is also related to effects on

bacteria.  Some studies have simply used bacteria as models for the action of

ozone in biologic systems.

        The  chemical composition of the photochemical oxidant complex is dis-

cussed  in Chapter 2. The major phytotoxic components are ozone, nitrogen

dioxide, and the peroxyacylnitrates.  The latter homologous series of compounds

includes peroxyacetylnitrate (PAN),  peroxypropionylnitrate (PPN), peroxybutyryl-

nitrate  (PBN),  peroxyisobutyrylnitrate (PisoBN),  and peroxybenzoylnitrate

(PBzN). The first four of these  are known to be  toxic to plants, but only PAN

and PPN have been reported in sufficient quantities in ambient air to cause  visible

-------
           506
symptoms.      The effects of the nitrogen oxides (NO  ) are included in
                    80                              x
another NAS report.     Discussion of the quantitative effects of ozone

and PAN will be limited to laboratory and controlled field exposures,

because, under ambient conditions, the effects of these compounds are

difficult to differentiate. Although ozone is, quantitatively,  the primary

oxidant component of photochemical air pollution, the term "oxidant" is used

to include ozone and PAN in discussing  biologic effects under ambient conditions.

However, some studies  suggest that phytotoxicants in addition to ozone and
                                               209
PAN are present in the photochemical complex.     Regardless of the number

of phytotoxicants present,  ozone is the most important, it has received the

greatest amount of study, and its effects are better understood.  The major

thrust of this chapter covers  research with ozone.
                    225,461          496
       Before  ozone          and  PAN     were identified as  specific phytotoxic

components of  the photochemical  complex,  researchers used  a number of

artificial chemical reaction systems to  simulate the ambient photochemical

oxidant situation.  These efforts involved a number of irradiated and non-

irradiated reaction systems (unsaturated hydrocarbon-ozone mixtures,

unsaturated hydrocarbon-NO   mixtures, and dilute auto exhaust).  Most
                           x
research before I960 involved one or  more of these reaction systems.  This
                                102, 103, 132, 209,210, 215,  365, 368,401, 505,
research has been well reviewed
515,553
         and thus  is not  extensively covered here.  Although the work is dif-

ficult to correlate with research on individual pollutants or  combinations of

pollutants, many of our  present concepts were first enunciated on  the basis

of these photochemical oxidant simulation systems.  Any researcher con-

cerned with the effects of oxidant pollutants on vegetation or microorganisms

should be familiar -with this early work.

                                   11-2

-------
        A number of reviews of varied quality cover general or special
                                                                     515
 effects of photochemical oxidants on vegetation (Table  11-1).  Thomas

 fairly comprehensively covered the available information on the effects of
                                            365
 photochemical oxidants on plants.  Middleton     gave the first comprehensive

 coverage of the phytotoxic effects of photochemical oxidants in 1961.  A
                                                            453
 number of excellent reviews have appeared since 1961.  Rich      presented
                                                        131, 132
 an early review of ozone effects.  Dugger and associates          presented
                                                                  210
 the physiologic and biochemical effects of oxidants on plants.  Heck
                                                                         196
 covered factors that influenced the expression of oxidant damage.   Heagle

 discussed oxidant problems with respect to interactions between air pol-

 lutants and  plant parasites.   Three chapters in  the air pollution atlas
                                                                   215,235, 510
 (Recognition of Air Pollution Injury to Vegetation;  A Pictorial Atlas)

 stressed  components of the  photochemical oxidant complex in terms of symptom
                                                               447
 development and relative  susceptibility of plants.   Reinert et aj..     presented

 an excellent treatment of interactions between several of the photochemical

 oxidant pollutants and sulfur dioxide.   The American Phytopathological Society
                                                                           12
 published a glossary of terms that should be useful to any research worker.

 In addition,  several recent review articles have discussed the effects of
                                               211,223,     505,567
 photochemical oxidants or ozone on vegetation.                       Three

 recent books on air pollution effects on vegetation cover subjects of concern
                                                  128a,390, 398
 to anyone interested in the photochemical oxidants.                There

 are two criteria documents:  one for the Canadian Ministry of  the  Environ-
            318
ment in 1975     and the other for the former U.  S. National Air  Pollution
                               401
 Control Administration in 1970.      Both focus on the  development of criteria

useful for the setting of ambient air quality standards.  These two reviews

pertain primarily to dose-response effects and attempt to define threshold

                                     11-3

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                               Table  11-1

                Selected Review Articles - A Subject Listing
Subject
References
General
Criteria documents

Symptoms and susceptibility

Photochemical oxidants

Ozone

PAN

Physiologic and  biochemical

Effects  of various factors

Plants as monitors

Glossary of terms
51, 101, 103, 128a, 175, 211, 222,
223, 251, 317, 351a, 364, 365, 367,
368,  390,   398,  505, 515, 516, 517,
565, 566, 571, 584

318, 401

215, 235, 475, 510, 515

103, 215

235, 390, 453, 567

79, 390, 510

128a, 131,  132, 390

196, 210, 447

28, 209

12
                                    11-4

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dose or specific concentration and time combinations that produce specific

response measures.  Neither document contains  sufficient information on

microorganisms to enable the development of useful dose-response information.
                    318
The Canadian review     is generally more comprehensive than the U. S.
          401
document,     in that it presents a threshold dose-response  curve for

use with ozone and,  by implication, with ambient oxidant measurements.


RESPONSES OF VASCULAR PLANTS

       Injury to vegetation from photochemical oxidants was first characterized
       369
in 1944    as a glazing,  silvering,  or bronzing of the lower leaf surfaces

of broadleaved plants.  These symptoms were first identified in the Los

Angeles area,  but were soon recognized over a large segment of southern
                                            367
California and in the San  Francisco Bay area..     Photochemical oxidants

are known to injure plants in most,  if not all, major metropolitan areas

of the United States, Canada,  and Mexico and probably affect vegetation in

major metropolitan areas throughout the world.

       Ozone is generally recognized as the  most important phytotoxicant
                                                           300
in the oxidant complex.   Early studies were  reported in  1864,     The
                                           285a
phytotoxicity was firmly established in 1914,      and this was  confirmed
                             246
in laboratory studies in 1937.     It was  first shown as a  phytotoxic component
                                                    461
(causing  grape stipple)  of the oxidant complex in  1958     and later as the
                                 225
cause of weather fleck of tobacco.       Ozone is  now known to cause

injury to a multitude of broadleaved plants and to explain  several types of

needle  injury in both eastern and -western conifer species.
                                   11-5

-------
                                                         496
        The peroxyacylnitrates were first identified in 1961    as the primary

cause of the undersurface glazing and bronzing on some broadleaved plants.

PAN has since been implicated in numerous pollution episodes in southern

California.  Its importance in other metropolitan and rural areas in the

United States and throughout the world is uncertain,  although symptoms have
                         428
been reported elsewhere.      This is because oxidant concentrations in

other parts of the world are much lower than those reported in California,

and monitoring networks have not looked for PAN or its homologues.
                           436
The report by Penkett £t al_.     is the first to come from Europe.

       Research on photochemical oxidants including ozone was  confined

primarily to California during the 1950's.  By 1959, ozone was known to

be an important pollutant in the eastern United States and southern Canada.

It is now known as a ubiquitous pollutant and has been widely studied through-

out the United States and Canada.   By 1972, several other countries had

recognized the potential effects of photochemical oxidants on vegetation and

initiated research.

       We shall stress three  areas of methodology that are of special concern

for the study of air pollution effects on vegetation: growth of the test organisms,

exposure facilities,  and instrumentation.  First, to determine the effects of

air pollutants  on many plant species, one must have a good understanding of

the best cultural conditions for a given test crop; some results reflect the

use of poor test specimens.  Second, dynamic air-flow designs are  required

in  chamber construction and exposure  conditions must be similar to those

•which occur in the field.  The method of preference would be a dynamic,
                    218
single-pass system,     to avoid reactions of reactive oxidants with materials

of  chamber construction or emanations from the plants. Several useful chamber

                                     11-6

-------
                                             24,204,232,332, 592
 designs have been reported in the literature.

 For routine  experiments, temperature,  light, and relative humidity should

 approach ambient conditions,  and nutrient status should be conducive to

 good growth.  Third,  one should not assume instrument accuracy without

 adequate  calibration,  either initially or later. Most plant scientists have

 used the Mast  oxidant instrument to measure ozone and ambient oxidants.

 One should be  aware of the inherent variability among instruments  and

 routinely calibrate them.  Calibration of all instruments should be  with the

 EPA standard  1% neutral potassium iodide method,  and the values  should

 be so reported.  When this is  not done, the actual values may be  50-100%

 greater than the reported values.  Most papers do  not state the  calibra-

 tion procedure, if any, and some do not mention the monitoring instrument.

 Investigators who use the  Mast instrument over long periods without an

 adequate maintenance program may also report erroneous values.  Cali-

 bration and instrumentation problems are reviewed in Chapter 6.  For
                                                                    3
 comparison,  ozone at 1 ppm is equivalent to ozone at about 1, 960 yg/m  .

       The foliar response of plants is discussed in terms of the visible

 or subtle  effects on individual plants.   Visible effects may be defined as

 identifiable, pigmented,  chlorotic,  or necrotic foliar patterns

 that result from major physiologic disturbances.  Subtle effects do not produce

 visible injury,  but may include transitory metabolic disturbances,  such as

 changes in rates of respiration, photosynthesis,  transpiration, and enzymatic

processes.  Subtle effects may be measurable in terms of growth or long-term

biochemical changes.   Both visible and subtle effects are induced by physiologic

and biochemical changes in the plant.   Subtle  changes may also affect repro-

ductive or genetic systems.  If cumulative changes  occur within individual

                                     11-7

-------
plants as a result of visible or subtle effects, these changes may affect plant

populations and communities, and this could have adverse effects on eco-
          194,568
systems.          Community and ecosystem responses are discussed and

quantified in Chapter 12.

        In general,  the direct response of plants to all oxidant pollutants

has been  in the foliage.  In several cases of long-term exposure (grape-

fruit after several months of exposure to ambient oxidants) or high ozone
                                           371       490
concentration over a shorter period (apple,      peach    ),  injury has

been reported on fruit itself.


Visible Symptoms

        Visible symptoms are useful in characterizing the  response of vegeta-
                                                   565
tion to a variety of stresses,  including air pollution.      Similar symptoms,

induced by different stresses, have been well described and may confuse the
          60,227,235
diagnosis.            On the basis of studies to date, diagnostic  techniques

that use indicators other than visible injury (e.g., respiration) are less

reliable than the subjective judgment of an experienced observer. Thus,

it is important that researchers  become familiar -with injury symptoms

caused  by oxidants and those caused by  other stresses.  This section briefly

describes the injury symptoms used for diagnostic purposes.

        The terms "acute injury" and "chronic injury" are often confused with

"acute exposure" and "chronic exposure. "  Their historical use and  the need

for brief descriptive terminology suggest that they are still useful terms.

Acute injury  may affect  only a small part of a given leaf.   It is a result of

destruction of cell contents and always causes cell death.  The necrotic

patterns in acute injury may be characteristic of a given oxidant.   These


                                     11-8

-------
patterns at least demonstrate the presence of a chemical toxicant.  Acute

injury is usually associated -with short exposures (hours) to specific oxidants

or pollutant mixtures at concentrations that cause acute  injury and usually

appears within 24 h after exposure.  Chronic injury, whether mild or severe,

is usually associated with long-term or intermittent exposures to low con-

centrations of oxidants that do not produce acute injury.  Normal cellular

activity is  disrupted, and the chlorosis or other color  or pigment change that

follows may eventually cause cell death.   Chronic oxidant injury patterns are

generally not characteristic  and may be confused with  symptoms caused by

normal senescence, biotic diseases, insects, nutritional disorders,  or other

environmental stresses.  These patterns may appear as  early leaf senescence

with or without leaf abscission.  Repeated short-term  exposures to ozone

may cause physiologic changes that are responsible for chronic symptoms.

However, such exposures may produce small but additive amounts of acute

injury that are mistakenly referred to as chronic injury.

        Before the identification of ozone  and PAN as two major phytotoxic

oxidants in photochemical air pollution, simulated "smog" (a variety of chemical

mixtures) and ambient pollution were the test atmospheres used.  The most

complete morphologic and developmental studies were  conducted during
                                           35-38, 60,  179
this time by Bobrov (Glater) and associates.               These were

classic studies that covered  a  range of plant species, including table beet,

annual bluegrass, oat, and tobacco.  From these early studies has come our

basic understanding of microscopic changes and developmental patterns.

These workers first suggested that membrane injury may have led to the

initial effects on  the chloroplasts.  They  also defined developmental patterns

and showed that leaves near maximal expansion were more sensitive than

                                    11-9

-------
 young leaves (or leaf tissue) or older leaves.  They suggested that maximal

 sensitivity -was related to stomatal function, volume of intercellular spaces,

 and the extent of suberization of mesophyll cells.  Other work has  since
                           148,361, 524, 529, 542
 substantiated their studies.
                      60
        Bystrum _et al.   first described morphologic changes in leaf surface

 waxes of table beet exposed to photochemical oxidants; these changes were

 different from those associated with aphid feeding.   Comparison of oxidant

 injury with that produced by insects has since received attention from
        227
 Hibben,     who found that ozone  injury to the leaves of four tree species

 produced smaller flecks, randomly spaced and darker than fleck injury

 along veins induced by a mesophyll-feeding leafhopper.

       Although ozone and PAN are considered the  two primary phytotoxic

 oxidants in the photochemical complex,  the specific response of plants to

 many simulated atmospheres suggests the existence of other phytotoxic
         209
 oxidants.      The symptoms associated with many of these reactant mixtures
                                                    208,215
 are closely related to those caused by ozone and PAN.         In some tests,

 the mixtures used would not have  produced either ozone or PAN. In other

 cases, leaf age or the pattern of injury on sensitive test plants suggested

 one or more pollutants other than ozone or PAN.  Field injury symptoms

 often  resemble those reported  for ozone or PAN, but the response  pattern

 is sufficiently different that accurate diagnosis is difficult.  Brennan
      50
 et al.    correlated development of oxidant symptoms with aldehyde con-

 centrations in New Jersey and  suggested that aldehyde may be a major

phytotoxic component of the photochemical oxidant complex.  The symptoms

were  probably not responses to the aldehyde, but rather to some compound
                                                                        237a
 or group of compounds present under  the same conditions as the aldehyde.

                                     11-10

-------
        The most complete description of ozone injury symptoms is found
             235
in the Atlas.     However,  several of the review articles, including the
                       318,401
two criteria documents,         have injury descriptions.  A concise
                                          211
description is found in Heck and Brandt.

        The classic ozone symptoms  on angiosperms are  the upper surface
                225                     461
fleck of tobacco    and stipple of grape.      These classic symptoms were

described in plants with differentiated mesophyll and are especially significant,

because they were identified with palisade cells,  and not  with spongy cells.

        The two classic symptoms are still more widely associated with the

response of dicotyledonous plants to  ozone than are other symptoms.  Many

plants  (e. g. , pinto bean,  cucumber,  tomato,  soybean,  and sycamore) may have

the entire upper surface covered with a bleached appearance as a result of

ozone exposure, with no observable injury on  the lower surface.  On closer

examination, the bleached area is seen  to be made up of many small groups

of palisade cells that are dead and contain no pigment.  In other plants or

under different  conditions, the palisade cells may accumulate dark alkaloid

pigments (stipple) coincidentally with cell death.  After exposure to higher

ozone concentrations or after longer periods of exposure, injury extends

to the spongy cells,  producing bifacial necrosis.  Plants exposed to a high

concentration of ozone or to  a high concentration of ambient pollution during

a pollution episode usually develop dark watersoaked areas in the leaf within

a few hours. Leaves may show partial recovery, or these areas may form

light-tan bifacial necrotic lesions within 24-48 h. Individual lesions may

be small,  but groups of them can extend and affect a considerable portion

of the leaf.
                                     11-11

-------
       In monocotyledonous plants (grasses and cereals) and some others,

there is no division of mesophyll tissue,  and injury normally appears as a
              35
bifacial fleck.    Some plants, after extended exposure to low concentrations

of pollution (either continuously or intermittently),  produce chlorotic patterns

that may be distinctive of oxidant pollution or similar to symptoms of normal

senescence.  The early senescence seen in some plants may be a result of

long-term exposure to ambient oxidants.

       The  foregoing discussion is not descriptive of effects noted in con-

iferous trees,  such as pine.  It is -worth discussing two classic oxidant  (ozone)

syndromes of pine--one eastern, the other •western.  Ozone is the probable
                                                                    23
cause of emergence tipburn in -white pine (white pine needle dieback).    The

injury is characterized as a tip dieback of newly elongating needles and occurs

throughout the  range of eastern white pine.  Affected trees are found at random

in a stand, and symptoms develop in discrete episodes in successive years.

Primary roots  of affected trees often die after repeated needle injury.
                     85
Costonis and Sinclair   reported silvery or chlorotic flecks,

chlorotic mottling, and tip necrosis of  needles as results of ozone exposure.
                                                                    314
Ozone may be associated with semimature-tissue needle blight (SNB),     but
       315
Linzon   found that both SNB-sensitive and SNB-tolerant-white pine  were first

injured -with ozone at about 0. 6 ppm for 2 h,  and the symptoms were  not like
             315
SNB.   Linzon found that ozone injury began in young tissue -with newly functional
                          313
stomates, whereas in SNB     the necrosis begins in semimature leaf tissue

and then spreads through the  older needle tissue toward the tip.  Needle

injury resulting in a disease called "chlorotic decline" of ponderosa pine
                                                                       426
was first noticed in 1953 and was related to oxidant air pollution by 1961.

The chlorotic decline was characterized by a progressive reduction in terminal

                                    11-12

-------
and diameter growth,  retention of only the current season's needles, reduc-

tion in number and size  of these needles,  yellow mottling of the needles,

deterioration of the primary roots,  and eventual death of the tree.   The
                                                                  425
chlorotic decline was not associated with stresses other than ozone.

These symptoms were reproduced by exposing ponderosa pine  to ozone at
                                  380
0. 5 ppm for 9 h/day for 9-18 days.      Similar symptoms were noted by
                462
Richards £t al_. ,     who called the  disease "ozone needle mottle of pine."
                 149,150,151                       374
Evans and Miller              and Miller and Evans      have conducted

histologic investigations on injury development in ponderosa pine.  They found

that chlorotic needle mottle caused  by ozone or ambient oxidants was easily
                                 374
distinguished from "winter fleck. "     A  comparison of needle anatomy in four

pines of differing sensitivity suggested that sensitivity was related to the
                                       150
number of mesophyll cells per stomate.      They also reported an accumulation

of chloroplasts and carbohydrate stain in peripheral portions of mesophyll

cells of ponderosa needles before development of visible injury that was
                                149
not related to stomatal presence.     These changes were not shown sufficiently
                               151
to be specific for ozone  effects.

       Injury from PAN was first described as smog injury by Middleton
      369
ei^ al_.     on spinach,  garden beet,  romaine lettuce, and chard.  They

reported a collapse of spongy mesophyll tissue with the development of large

air pockets,  especially near the stomates. The air spaces gave  the leaf the

appearance  of a glaze and were responsible for this classic PAN symptom.
                                                             35-38,60, 179
Most of the  descriptive work reported by Bobrov and associates

from simulated atmospheres and ambient exposures  resulted from  PAN

injury.   The classic injury pattern for PAN is glaze  followed by a bronzing

of the lower leaf surface.  Young expanding leaves are normally more

                                     11-13

-------
sensitive to PAN than more mature leaves.   Physiologic maturity is

important, as shown by the banding appearance on many susceptible leaves

that do not mature uniformly.  If the -whole leaf has a similar physiologic

age, it may be uniformly injured (e. g. , pinto bean).  In case of severe

injury, bifacial necrosis  can occur.  Early senescence and leaf abscission

are often associated with PAN injury.  The most complete description of
                                     510
injury is that by Taylor and MacLean.      Symptoms associated with PPN

and PEN are similar to those for PAN.
                                                                  79, 506, 566
       In several cases,  symptoms have been associated with dose.

At a high dose  (0. 5 - 1.0 ppm for 0. 5 h),  sensitive plants show complete

collapse. As the dose  is reduced,  the plants may show necrotic banding,

then bronzing and glazing with slight collapse. At 0. 1 ppm, chlorosis is the
                                            79
major symptom.  In some unpublished work,   an upper-surface light-yellow

to white  stippling has been described on alfalfa after exposure to PAN

at 0. 02 - 0. 1 ppm for 2-6 h.  The injury was intercostal on the tip of young
                                                128
leaves and on the base  of old leaves.  Drummond     reported a necrotic

fleck  and an upper-s\irface stipple  on petunia after a  1-h exposure to  PAN

at 0. 15 ppm.


Physiologic and Biochemical Effects;  Mechanism of Action

       Many reports on the effects  of ozone and PAN on physiologic processes

(net photosynthesis, stomatal response, and water relations) and on metabolic

activity (including in vivo and in vitro studies of individual enzymes,  enzyme

systems, metabolic pathways, metabolic pool relationships, cell organelles,

and plant tissue studies) have appeared since  1964.
                                     11-14

-------
        Stomata are the  principal entry sites for ozone and PAN into plant
                                                                      347
 leaves, and stomatal closure effectively protects the plant from injury.
                                                                 259,289,
 Several studies suggest that oxidants may cause stomatal closure.
 326,457
          Stomatal closure was associated with a genetic factor in onion
                                                    142
 wherein the stomata of sensitive plants did not close.       The effect of ozone

 and PAN  on stomatal opening depends on many interacting  factors; those
                                                                116
 representing water stress appear to be the most important.  Dean     related

 stomatal  density to the difference in sensitivity between two tobacco cultivars.
                153
 Evans and Ting     found that maximal sensitivity of b«an  primary leaves

 was not associated with changes in  stomatal number o>r leaf resistance.

 Ozone exposure caused a decrease  in relative  water content,  but no  change

 in resistance.   Bean leaf sensitivity seemed more a function  of internal

 activities.

        Isolated enzymes and enzyme systems  are affected by exposure to PAN

 and ozone.  It is now recognized that strong oxidants interfere with various

 oxidative  reactions within plant systems.  Metabolic pools, including nitrogen

 and carbohydrate,  appear to have some controlling influence  on the response

 of plants to these pollutants.  Sulfhydryl groups are primary  targets of oxidant

 pollutants and may be a key to understanding the mechanism of action.

 Unsaturated lipid components of some membranes are  sites of early action of

 both ozone and PAN.


       Ozone.   Ozone  is  the most nearly ubiquitous of  the photochemical

 oxidants,  at least in concentrations that cause  measureable effects.   It has

been studied more  extensively than  the other oxidants.

       • Physiologic effects:  The physiologic  effects  of ozone depend on

its entry into the internal leaf spaces through the stomata.  If the plant

                                     11-15

-------
is resistant to ozone even when stomata remain open, mechanisms of

resistance, other than stomatal closure, must be operative.   The

physiologic effects measureable with the intact tissue include effects

on respiration and photosynthesis.
             551
        Todd     reported that the respiration of pinto bean leaves was

stimulated by exposure to ozone  (at 4 ppm for 40 min) . The first

measurements were 4 h after the ozone exposure.  The respiration rate

later declined to the control value.  In all cases,  increased respiration
                                              321
correlated well with visible injury.  Macdowall     confirmed these

results, but made an additional observation: during the first hour after

ozone exposure (at 0. 7 ppm for 1  h), and before visible symptoms

appeared,  respiration was inhibited.  The increase in respiration took
                                                                      129
place only later, when visible  symptoms appeared.  Dugger and Palmer

reported an increase in respiration in lemon leaf tissue after 5 days

of exposure to ozone at 0. 15-0. 25 ppm for 8 h/day.   They reported no
                                                       11
morphologic  changes at that time. Anderson and Taylor    found that

ozone induced carbon dioxide evolution in tobacco callus tissue.   The

threshold for evolution was about 0. 1 ppm for 2 h in the sensitive Bel W .
                                                                      3
The  ozone concentration required for maximal carbon dioxide evolution

was  about twice as much  in the more resistant cultivar.   Formation of

roots decreased sensitivity.
            551                      554
        Todd     and Todd and Probst     also measured the effects of

ozone (at 4 ppm for 40 min) on photosynthesis and found that development

of symptoms was associated with  inhibition  of carbon dioxide fixation.
                                             321
This effect was also confirmed by Macdowall,     who reported that the

inhibition of photosynthesis was greater than that which could be accounted

                                     11-16

-------
                                                  234
for by chlorophyll destruction.  Hill and Littlefield     associated decreased

net photosynthesis  caused by ozone (at 0. 06 ppm for 1 h) with both stomatal

opening and rates of transpiration.   These studies have generally shown

that net photosynthesis can decrease without visible injury.
                        431
       Pell and Brennan    found an initial decrease  in net photosynthesis

and an increase in  total adenylate concentration after a 3-h exposure to an

injurious concentration of ozone.  Net photosynthesis returned to normal

within 24 h.  Respiration was usually not immediately stimulated,  but it

was  within 24 h.  The authors concluded that the stimulation of respiration

was  a consequence of  cellular injury, whereas the changes in photosynthesis

and adenylate content  -were early events  leading to the appearance of ozone

injury.

       The photosynthetic rate  is an important indicator of vigor in

ponderosa pine.  A reduction in this rate may occur at the threshold dose
                                                379
of ozone without visible symptoms.   Miller ei^ aL      found that a daily

9-h exposure to ozone at 0. 15 ppm reduced apparent photosynthetic rates
                                                                   40
by 10% after  30 days,  without typical ozone symptoms. Botkin et al.

found that a threshold ozone dose for suppression of net photosynthesis in

eastern white pine was a 4-h exposure to 0. 50 ppm.

       Ozone causes both quantitative and  qualitative changes in carbon
                                                590
dioxide fixation patterns.  Wilkinson and Barnes,     using carbon
        14
dioxide-   C, found a reduction  in radioactivity in soluble sugars and

increases in free amino acids and sugar phosphates in white pine after a
                                              372
10-min exposure to ozone at 0.  10 ppm.   Miller     observed a decrease
                 14
in carbon dioxide-   C  fixation in ponderosa pines that  correlated with

loss  of chlorophyll,  after exposure to ozone at 0. 30 -  0. 35 ppm.  The

Hill  reaction rates  of  chloroplasts isolated from healthy and ozone-injured

                                     11-17

-------
ponderosa pine indicated that both light and dark reactions of the chloroplasts
                                                  15
from ozone-injured plants -were depressed.  Barnes   found depressed

photosynthesis and stimulated respiration in seedlings of four pine species

of the southeastern United States after exposure to  ozone at 0. 15 ppm.

       It is commonly observed that leaves exposed to ozone develop dark

green areas--sometimes referred to as a "•waterlogging" effect.  If

symptoms develop, they will be in these "waterlogged" areas,  but

symptoms are not always a consequence of the "waterlogging."  In other

words, there is sometimes recovery from this initial effect.  The effect

is due to leakage of cell contents into the intercellular spaces and, to

some extent, is reversible.  Many experiments with radioactive inorganic

ions and  organic substances have  confirmed that plant cell permeability is
                              154                         437
affected by exposure to ozone.      Perchorowicz  and Ting     found that,

immediately after ozone exposure (at 0.4 ppm for 1 h),  there was no uptake
           14
of glucose-  C,  but the uptake slowly increased for a period of hours.

However, the metabolism  of the glucose into various products (organic

acids, lipids,  carbon dioxide) was not changed by the ozone exposure.

       Although it is widely believed that the effects of ozone on cell perme-
                                     533
ability are the basis of  ozone  toxicity,     the chemical basis of the effects

on membranes is still arguable.   It  is still not clear whether the first

effect of  ozone is on the protein or lipid components of the cell.
                    133
       Dugger 
-------
 Susceptibility was regained by supplying sucrose through the petiole.

 However,  susceptible leaves could be made resistant by supplying more

 sucrose through the petiole.  They concluded that the leaf was resistant

 when the soluble-sugar content was either above or below the range of
                                                                      302
 1. 0  - 4. 0 mg/g of fresh weight.  These results  were confirmed by Lee,

 who concluded that the protective action of high  sugar  content could be

 partly,  but not completely, explained by causing closure  of stomata (ozone
                                       16
 at 0. 8 ppm for 5 h).  Barnes and Berry   reported seasonal changes in

 the soluble sugars of white pine that may  relate low sugar contents to a
                                                  189
 prolonged  sensitivity to ozone.   Hanson and Stewart    found that several

 species exposed to noninjurious concentrations of ozone retained higher

 starch concentrations in their tissue after 12-36 h of darkness.
                 320
       Macdowall     found that tobacco leaves were most susceptible to

 injury by ozone (at 0. 035 ppm for 5 h) just after full leaf expansion.  This

 point corresponded to the beginning of the decline in protein content.
    303
 Lee     modified the nitrogen content of tobacco leaves by supplying urea

 and found a positive  correlation of injury caused by ozone (at 1 ppm for 5 h)

with nonprotein nitrogen,  but not with protein.  This result is in contrast
                             531
with that of Ting and  Mukerji,     who found that,  in cotton leaves  (in which

 the period  of maximal susceptibility was at about 75% of full leaf expansion),

 the amino acid pool was low at the time of maximal susceptibility.  However,

 ozone treatment (0. 7 ppm for 1  h) increased the free amino acid pool.

       At the moment, it is  impossible to give a rational explanation of the

 relationship between ozone injury and carbohydrate and nitrogen composition

of the leaf.  The compounds measured  (protein and carbohydrate) may be

only distantly related to metabolites  that  confer  resistance or susceptibility.

                                    11-19

-------
       It seems reasonable that susceptibility and resistance of different

plant species and different varieties -within a species should depend on con-

centrations of endogenous antioxidants.   The results of such studies do
                                      191
not give a clear picture:  Hanson et^aL     concluded that the range of

susceptibility in petunia varieties depended on the ascorbic acid concen-
                    353
tration, but Menser     found that the ascorbic  acid content of  tobacco

varieties -was not related to ozone susceptibility.  Ozone resistance of

plants can be conferred by application of antioxidants.  In  the case of

•white bean, ascorbic acid, cysteine,  glutathione, and nickel N-dibutyldithio-
                          105, 170
carbamate were effective.          Field studies -with tomato and tobacco

showed that a number of antioxidants were effective protectors:  manganous

1, 2-naphthoquinone-2-oxime,  cobaltous 8-quinolate, nickel di-N-butyldithio-
                                                      454
carbamate, N-isopropyl-N-phenyl-p_-phenylenediamine.      These pre-

ventives  do not yet present an economically feasible practice for agriculture.

       •  Biochemical effects: It is usual to find some changes  in the

chemical composition of plant tissue after exposure to ozone.  One  cannot

be certain whether the changes are  associated with early reactions  to

ozone or are merely delayed consequences of cell injury.

       A number of histologic and histochemical changes in current-year

needles of ponderosa pine were detected after five to seven daily exposures
                                       149
to ozone at 0.45 ppm for  12 h each day.       Chloroplasts and carbohydrate

stain accumulated in the peripheral portions  of mesophyll  cells; con-

currently,  the homogenous distribution of proteins  and nucleic acids was

disrupted,  and acid phosphatase activity increased.  Cell wall destruction

occurred in mesophyll cells after appreciable intracellular damage.
                                     11-20

-------
              251a,  252                       255
       Howell          and Howell and Kremer    found phenol

accumulation associated with  the exposure of plants to ozone.  Menser
            356
and Chaplin     also reported an increase in the phenol content of tobacco
                                           243
leaves injured by ambient oxidants. Hoffman     reported as much as an

80% increase in nicotine in  leaves exposed to ozone at 0. 24 ppm for 4 h.

No increase was found after exposure  to 0. 06 or 0. 12 ppm.  Keen  and
       271
Taylor     found accumulation of several isoflavonoid compounds in soybean

(Harosay 63) exposed to ozone.  The presence of these compounds suggests

a defense mechanism against  ozone that is similar to  that for disease

resistance.
                           556
       Tomlinson and Rich     reported an increase in y-aminobutyric

acid in bean leaves after exposure  to ozone (at 1 ppm  for 30 min). In a
                                            531
more comprehensive study, Ting and Mukerji     repeated this finding

in cotton leaves, but found increases in many other amino acids.   The only

decreases found were in phosphoserine, phosphoethanolamine, ethanolamine,

phenylalanine, and alanine.  There are discrepancies  in the literature

regarding the time after ozone treatment before detection of changes in
                                         531
amino acid composition.  Ting and Mukerji    found the increase only
                                543
after  24 h, whereas  Tingey  et al.     reported the change to be immediate.
                                                        543
Similar differences concern soluble protein: Tingey ^t^l_.     noted a rise
                           92,94
after  24 h, whereas  Craker      found a decline in protein content.  As
                                                       543
far as specific proteins are concerned, both Tingey ei_ al.    and Leffler
           305                                      ~~           595
and Cherry    found a decrease in nitrate reductase;  Yamaga   et al.
                                                      106
reported a decrease in carbohydrase.   Dass and Weaver    found significant

increases in peroxidase and cellulase,  but no change in lactate dehydrogenase;
                 97
Curtis and Howell    reported  an increase in peroxidase isoenzyme activity.
                                                           534
Tingey has also reported an increase in the G-6-PD activity.      It is

                                    11-21

-------
 possible to fit the latter change into a rational scheme for the effects of

 ozone,  but "rational"  is not synonymous with "right."  Chang and
           72
 Heggestad    found that ozone at 0. 35 ppm for 50-80 min impaired the

 activity of photosystem II in spinach and reduced the  8-carotene of the
                                 87
 chloroplasts.   Coulson and Heath,  using isolated  chloroplasts,  found

 an inhibition of both photosystems and no penetration of the grana.  They

 suggested  that in the intact plant  ozone affects only the  first membrane

 contacted.
              69,70,71
        Chang        has made observations on the polysomes of pinto

 bean leaves exposed to ozone (at  0.  35 ppm for 20-50 min).  He found that

 the chloroplast polysomes -were more susceptible to degradation than were

 the cytoplasmic ribosomes. The sulfhydryl content of the chloroplast

 ribosomes was also much more susceptible  to oxidation than was  that of

 the cytoplasmic ribosomes. Finally, it was found that  the effects  of ozone,

 on ribosome composition could be reproduced by p_-mercuricbenzoate.

Chang's    results imply that either ozone itself or a product of ozone

 oxidation passes from the cytoplasmic membrane to the interior of the

 chloroplast before  having its effect. These  results connect with a number

 of papers on the oxidation of sulfhydryl  compounds by ozone.  Tomlinson
         557
 and Rich     have reported decreases in leaf sulfhydryl groups after ozone

 exposure (at 1 ppm for 30-60 min).  A number of investigators have found

 that reagents  that react with sulfhydryl  groups can reproduce the  symptoms
                                   105
 of ozone damage.   Dass and Weaver     reported this effect in white
                          557
 bean.  Tomlinson and Rich    reported the  same effect in tobacco, and
                   455
 Rich and Tomlinson     found  that conidiophores of Alternaria solani

 became more susceptible to ozone if they were pretreated with iodoacetamide.

                                     11-22

-------
It appears that effects on sulfhydryl content may be quite early events

in the toxic reactions initiated by ozone.  One should remember, however,

that symptoms of ozone and PAN  injury are  quite different, and one cannot

explain the effects of both pollutants as sulfhydryl oxidizers.
                           558,559
        Tomlinson and Rich         have also considered the reaction of

ozone (at 1 ppm for 30 min) •with lipid components of the leaves.  They

found that a change in the fatty  acid  composition as a result of ozone

treatment was an increase  in the  saturated fatty acid content.  It was

concluded that malonaldehyde (an index of lipid peroxidation) was formed
                                                             168
only in the later  stages of ozone damage.  Frederick and Heath     reported

that the production of malonaldehyde is correlated with loss of viability of

Chlorella sorokiana exposed to ozone (at 1. 8 ppm for 5-20 min),  but with
                                                           499
a lag after the initiation of  ozone  exposure.   Swans on et al. ,      in

agreement with  Tomlinson  and Rich, found only small changes in the  fatty

acid composition of tissue  exposed to ozone (at  0.3 ppm for  2 h) .  It is not

possible to conclude  from the available data that oxidation of lipid is the
                                                      560
primary effect of ozone  exposure.  Tomlinson and Rich      have examined

the effects of  ozone on the complex lipids  of plants.  Plants were exposed

to ozone at 0.  25 ppm until the first symptoms were seen (2. 5-3 h),  and

leaf solubles were extracted.  It was found that  there were  a decrease in

free sterol and increases in both  sterol glucoside and acylated sterol

glucoside.
                     543
        Tingey et_a±.     found an increase in reducing sugars soon after

the exposure of soybean plants to  ozone.  In experiments with ponderosa
                  379
pine, Miller e± aj.    found that the polysaccharide content of both current

and 1-year needles, treated for 33 days with ozone at 0. 30  ppm, was  lowered

                                     11-23

-------
by 40%, but there -was a slight increase of soluble sugars.  No
                                                  14
relationship -with ascorbic acid was found.  Barnes   reported  studies

•with five pine species exposed to ozone at 0. 05 pprn for 5-22 weeks.

There were significant increases in total soluble carbohydrates, re-

ducing sugars, and ascorbic acid.  At  0. 15 ppm, the effect on ascorbic

acid was not observed.  These results  do not lead one to believe that

ascorbic acid plays an important role in ozone resistance.
                      405
       Nobel and Wang     reported that the permeability of the outer mem-

branes of chloroplasts was  increased by exposure to ozone  (at 30 ppm for
                                                                       169
5 min).   They hypothesized that the effect was lipid  oxidation.   Freebairn

showed that ozone inhibited respiratory activities of isolated mitochondria,
        304
and Lee     found that the effect of ozone on oxidative phosphorylation was
                                          395
greater than on oxygen uptake.  Mudd ei_aL      reported that the metabolism

of UDP-galactose by  isolated chloroplasts was inhibited by  ozone (at 1, 000

ppm for 2 min).  There were differential affects  on  the synthesis of various

galactolipids, the synthesis of monogalactosyldiglyceride being  relatively

resistant.  This differential effect of ozone could be reproduced by chemicals

that react-with sulfhydryl groups.

       There is some information concerning the reaction of ozone with

chemicals under aqueous conditions.  The information available suggests

that double-bond  cleavage takes place,  just as it does under nonaqueous

conditions,  except that ozonides are not formed.   Instead, the zwitterionic

intermediate reacts with water, producing an aldehyde  and  hydrogen peroxide.

In addition to double-bond cleavage, a  number of other  oxidations are
                      394
possible.  Mudd je_t al_.     showed that the susceptibility of  amino acids

is in the  order cysteine,  tryptophan, methionine, histidine,  tyrosine,

                                     11-24

-------
phenylalanine, and cystine (ozone at 2,000 ppm for  2-10 min).  All
                                       550
other amino acids are resistant.  Todd     tested the susceptibility of

catalase, peroxidase, urease,  and papain to ozone.  Papain -was the

most susceptible; this result is consistent with the knowledge that a

sulfhydryl group is necessary for its activity.   The inactivation of
      394               307
avidin    and lysozyme     can be attributed to the oxidation of

tryptophan residues, although,  in the case of lysozyme, methionine is

also partially oxidized.  Enzyme  inactivation caused by ozone reaction
                                                                      394
with histidine has been indicated  in the  case  of pancreatic ribonuclease.

The reaction of nicotinamide derivatives with ozone has been studied by
                                                    392
Mudd j3jt al.  (ozone at 0. 4  - 800 ppm for 1-100  min).      The reduced

forms are quite susceptible, and  the oxidized forms quite resistant.  The

adenine moiety is quite  resistant. When NADH is oxidized by ozone, the

5, 6 double bond is broken, so the coenzyme  is no longer biologically useful.

       Studies of the reaction of  ozone  -with simplified lipid systems have
                                                               393
shown that malonaldehyde can be  produced by direct ozonolysis.      The

use of malonaldehyde assay as  an index of lipid peroxidation is therefore

invalid in ozone studies.  Liposom.es formed from egg lecithin  and  pre-

pared in aqueous media  were quite resistant to  ozone,  but the contribution
                                                                       395
of polyconcentric spheres  to this  resistance has not been fully assessed.

However, the bilayer configuration,  with  the susceptible unsaturated  fatty

acids shielded from ozone by the  hydrophilic areas of the  molecule, may

be resistant.  In hexane, where the fatty acid moieties are exposed, ozone

reacts stoichiometrically with the double  bonds. The experiments with

aqueous  suspensions of phosphatidylcholine gave no  evidence of the for-
                          528
mation of lipid peroxides,     nor did experiments with films of fatty
                       465
acids exposed to ozone.

                                     11-25

-------
        • Chemical basis of toxicity:  There is only one comprehensive

theory for the action of ozone on biologic organisms--the theory of Chow
           73
and Tappel   that the initial event is the formation of lipid peroxide and

that successive events are an attempt to detoxify this product.  The theory

was developed from experiments with animals that show that exposure to

ozone increases malonaldehyde, glutathione peroxidase, glutathione

reductase, and  G-6-PD.

                O
                3
        lipid	£ lipid peroxide (ROOH),


                       GSH peroxidase
       ROOH +  2GSH	^ROH + GSSG,


                         +   GSSG reductase                +
       GSSG + NADPH + H	> 2GSH + NADP ,


             +           G6P dehydrogenase                    +
       NADP  + G-6-P	.	^ 6PG + NADPH + H  .


        This theory is questionable on a number of points:  there is no

direct evidence  of formation of  lipid peroxide, GSH can be oxidized

directly by ozone or used to  reduce hydrogen peroxide produced from  ozone

reactions, and the increased activity of G£»P <^eh
-------
        • Physiologic effects:  Leaf age and illumination have been studied

 as physiologic and physical factors that affect the response  of plants  to
       135
 PAN.      Leaves of most plants are most susceptible when very young.

 In primary leaves of pinto bean, the period of maximal susceptibility to

 PAN precedes that for ozone by several days (about 5-7 days from seed

 for PAN, as opposed to 9-13 days for  ozone).  The example of tomato

 is particularly striking, inasmuch as the terminal leaflet of the compound

 leaf is the oldest  tissue.   Thus, the youngest susceptible leaf  is affected

 in the  terminal leaflet; but, as the leaves become older, the terminal
                                                      510
 leaflet is resistant and the lateral leaflets are injured.

        There is no reason to believe that stomatal opening is  different

 in leaves of different ages, so the entry of PAN into the intercellular

 spaces of the leaf is probably the same as the entry of ozone.   One can

 hypothesize that the chemical composition of the leaf is such that re-

 sistance is conferred at particular physiologic states.  Such a hypothesis

would lead to a search for compounds that combat the oxidizing and

 acylating properties of PAN.

       There appears to be an absolute requirement for illumination

before, during, and after fumigation with PAN (1 ppm for 30 min),  if
                              513
 symptoms are to be observed.      If the prefumigation light period is

followed by 15 min of darkness before  a 30-min exposure to PAN in the

light, no symptoms are observed.   Thus, at this time, a short dark

period before PAN exposure prevents damage.  However, the  dark period

after fumigation must be 1-2  h long, if damage is to be avoided.  The light
                                                                     506
period after fumigation must  be 3 h long,  if damage is to be maximal.

These  effects of illumination  are not understood.

                                    11-27

-------
                                                    134
        The action spectrum for the light requirement    shows maximal

quantum responsivity at 420 and 480 nm and low responsivity at wavelengths
                                                        134
characteristic of chlorophyll (PAN at 4 ppm for 15 min).       The action

spectrum suggests participation of either carotenoids or  flavins.  It should

be emphasized that the action spectrum for illumination was determined

only during fumigation.  It is possible that a different photoreceptor is

involved in the periods before and after exposure.  Photosynthesis of

intact cells of  Chlamydomonas    reinhard/  was inhibited by PAN (at 125
                180
ppm for 5 min).      Photosynthesis recovered after the  exposure, but

the recovery varied with the light quality used during the exposure.

Recovery was less when the irradiation was at 450 nm; this is roughly
                                                                   134
consistent with the work on the action spectrum in pinto bean leaves.

       Although the quantum responsivity is low at 660-700 nm, effects

of irradiance at these wavelengths are noticeable.  In a comparison of the

effects  of light at 660 and 700 nm, injury was greatest when plants were

irradiated at 660 nm during exposure and lowest when they -were exposed
                                                           130
either in darkness or at 700 nm (PAN at 1 ppm for 15 min).      The most

striking observation was that simultaneous exposure  to light at 660 and 700

nm resulted in little injury.   These results v/ere interpreted as effects  on

photo synthetic  systems I (activated at 700 nm) and II  (activated at 660 nm),

but effects  of these wavelengths on phytochrome transformation should not

be overlooked:


                             660  nm
                        P  -;	^ p
                             700 nm
where P  is the red form of phytochrome and P   is the far-red form.
        r                                      fr

                                     11-28

-------
 It is noticeable that the action spectrum for the PAN effect is similar to

 that for phytochrome and for some physiologic responses mediated by
               59,383
 phytochrome.         Interaction of PAN with the phytochrome system

 seems worthy of systematic study.  The light effects may also be related

 to the sulfhydryl content of plants,  inasmuch as illumination increases
                                                                        130
 and exposure to PAN (at 1 ppm for 15 min) lowers the  sulfhydryl content.

       It has been suggested that sulfhydryl compounds are susceptible to

 reaction with PAN (by  oxidation or acetylation), and thus that conditions that

 increase the sulfhydryl content will increase susceptibility.  This explanation

 for PAN injury is consistent -with the finding that inhibition of photo-

 phosphorylation by N-ethylmaleimide, a reagent that reacts with sulfhydryl
                                                                    350a
 radicals,  is most effective when chloroplasts are treated in the light.

 In the Calvin and Hatch-Slack pathways of carbon  dioxide fixation in photo-

 synthesis, some enzymes are activated by light (e. g. , ribulose phosphate
        59
 kinase),    and some are inactivated by light (e. g. ,  glucose-6-phosphate
                            9
 dehydrogenase or G-6-PD).   In both cases,  the effect of light can be

 replicated with sulfhydryl compounds, such as dithiothreitol.  The reaction

 of PAN with the sulfhydryl forms of these enzymes  can easily be visualized

 as upsetting the regulation of carbon dioxide fixation.   These considerations

 are consistent with the effects of PAN on various aspects  of photosynthesis

 (adenosine triphosphate, ATP,  formation; nicotinamide adenine dinucleotide

 phosphate, NADP,  reduction; and carbon dioxide fixation) and with the fact

 that the earliest injury found by the electron microscope was in the stroma
                                             525
 of the chloroplasts (PAN at 1 ppm  for 30 min).

       •  Biochemical  effects:  Several enzymes that use nicotinamide  co-
                                                               387
factors were found to be inhibited by PAN (at  125 ppm for 1 min)    in

                                     11-29

-------
in vitro studies.  These enzymes were most susceptible in the absence of

substrates.  In some cases, an enzyme was protected by the nicotinamide

cofactor (e.g., G-6-PD plus NADP), and in other cases, by the cosub-

strate (e. g. ,  isocitrate dehydrogenase plus isocitrate).   Precisely the

same protection could be obtained when compounds that react with

sulfhydryl compounds (e.g. , p_-mercuricbenzoate) were used instead of

PAN.  Thus,  the evidence indicated that PAN reacted with  sulfhydryl

groups.

       Direct evidence of the reaction of PAN with sulfhydryl compounds
                                                       306, 388, 391
has since been obtained (PAN at 115 ppm for 1-10 min).               In the

reaction with  glutathione,  the major products are oxidized  glutathione

(disulfide) and S-acetylglutathione.   Other sulfhydryl compounds (e. g. , co-

enzyme A, lipoic acid, and cysteine) yield only  oxidation products, with no

evidence of S-acetylation.   However, acetylation reactions  have been observed
             403              583
with alcohols     and amines.       Sulfur compounds other than thiols can

undergo oxidation by PAN:  methionine is converted to methionine sulfoxide,

and oxidized lipoic acid (disulfide) is converted  to sulfoxide.

       Papain is readily inactivated by PAN  (at 115 ppm for 40 min), provided
                                391
that it is in the sulfhydryl  form.       The reaction  of sulfhydryl groups of

hemoglobin with PAN is very similar to the reaction with p_-mercuricbenzoate:

there is more reaction at a pH of 4. 5 than at a pH of 7.  However, there

is one striking difference between PAN and classic compounds that react
                                                                      391
with sulfhydryl groups:  egg albumen is resistant to reaction with PAN.

Thus,  enzymes that have no free  sulfhydryl groups should be quite resistant

to PAN.   This is the case  with pancreatic ribonuclease:  the native enzyme

was not affected by a 300-fold molar excess of PAN.

                                     11-30

-------
        There is some difficulty in correlating results  of PAN exposure

 in vivo with the above types of in vitro studies.  For example,  UDP-glu-

 pyrophosphorylase is very susceptible to PAN in vitro, but in vivo there
                                                            186
 is a stimulation of enzymatic activity (at 112 ppm for 6 min).      It is

 also anomalous that, whereas phosphoglucomutase of oat seedlings is sensitive
                                                   186
 to PAN both in vivo and in vitro (at 50 ppm for 4 h),     it is generally

 considered that the  active site is serine, rather than cysteine.   Results of

 enzyme analysis after in vivo exposure to tissues to PAN are complicated,

 because direct effects on the enzyme may be overshadowed by effects on

 protein synthesis,  and these effects in turn may be directly on  the protein

 synthesizing machinery or on the regulatory mechanisms that depress or

 stimulate protein synthesis.  A  schematic representation of this dynamic

 system shows that PAN could affect the  synthetic process (site 1),  the

 enzyme itself (site 2), or  the degradation process (site 3).   If the  site of

 attack were site  2,  the synthetic process might compensate for degradation

 of the  enzyme by producing more.


                synthesis    enzyme X     degradation     degradation
 precursors     _____\                 _  _ _  _  ^    products
                  t            T           t
                site  1        site 2         site 3


If the enzyme activity were measured as a function of time after exposure,

there would be first a decrease and then recovery of activity.   (Such a

response has  been observed for the effect of ozone on respiration. )  Effects

at site 3 -would show first an increase in activity and then, if the system

were regulated, a decline to normal,  as the  synthetic process slowed down.

Effects at site 1 would cause a decrease in activity commensurate with the

rate of enzyme degradation.

                                     11-31

-------
         Experiments with chloroplasts  showed an apparent inhibition of fatty
                                                389
  acid synthesis by PAN (at 72 ppm for 10 min).       The result is difficult

  to interpret: the inhibition could be attributed  to inactivation of one of the

  enzymes of the multistep system or to oxidation of the  reductant (reduced

  NADP, or NADPH) required in the chain elongation process.

         In addition to the protein and low -molecular -weight thiols that

  react with PAN, there are several other reactive biochemicals.  Reduced

  nicotinamide derivatives are susceptible to oxidation by PAN (at 72 ppm
               389
  for  1-5 min),     whereas the  oxidized forms are resistant.  The capability

  of PAN to oxidize these compounds  rapidly dissipates in aqueous solution,

  with a half-life of 4-10 min, depending on pH.  The oxidation products appear

to be the biologically active forms of the nicotinamide derivatives.   Purines
                                                                427
  and pyrimidines react with PAN (at 1, 000 ppm  for 30-120 min).      The

  order of  sensitivity is thymine, guanine, uracil,  cytosine,  and adenine.

  Their reactions were studied at relatively  low  pH and at high PAN concen-

  tration and are probably not of biologic significance.

         Various  olefins and amines (undiluted) react with solutions of PAN
           104, 583
  in CdCl:
        z

                                        .0
         PAN + R  C = CR - ^R  C - C R  + MeONO + MeNO ;
                  2222                   2
         PAN + RNH - ^CH  CONHR+O  + HNO  .
                    23             22
  These oxidation and acetylation reactions have not yet been examined in a

  biologic context.

         •  Chemical basis of toxicity;  The toxicity of the peroxyacylnitrates

  to plants can be the result of several different processes.  Any chemical

                                       11-32

-------
explanation of the toxicity will have to explain the increasing toxicity of

the series PAN,  PPN, PEN, and PBzN.  Three hypotheses have been
       390
tested:      the more toxic homologues are more readily taken up by the

plant; all homologues  are taken up equally well, but the plant is  able to

reverse the actions of the lower homologues; and all homologues are

taken up equally-well, but the higher homologues have longer half-lives.

In testing the  first hypothesis, it was found that PAN and PPN were taken

up equallly well by plants; so that hypothesis is probably incorrect.  The

ability of the plant to hydrolyze thioesters of glutathione was tested; the

second hypothesis predicted that the higher homologues would be hydrolyzed
                                        591
more slowly;  but the opposite was found.      Thus, the second hypothesis,

although not fully tested (in that  the thioesters measured may not be the

ones formed in the cell), does not look promising.   The third hypothesis

was tested by determining the half-lives of the oxidizing power of each com-

pound in aqueous medium.  PBN had the longest half-life, as predicted,  but
                                                   390
the half-lives  of PAN  and PPN were about the same.     It seems probable

that half-life influences  the toxicity of the peroxyacylnitrates, although

definitive results have not yet been  obtained.


       Discussion.  The acute responses of plants to ozone and  PAN  result

from disruption of normal cellular mechanisms.   The initial response causes

disorganization, prehaps through an attack on sulfhydryl linkages or unsaturated

lipid linkages. Cellular water and salts are lost,  with cell plasmolysis re-

sulting.  Cell  death normally will occur; however,  depending on  dose and

environmental conditions, membrane permeability may be restored and cell

recovery take place.   The extent of recovery depends on the severity of the

external stresses and  probably on the ability of the cells to initiate  repair

                                     11-33

-------
mechanisms.  A sigmoid response has been observed in many plants

exposed to ozone and probably reflects physical resistance to gase move-
                                     544
ment within the  tissues.  Tingey ^jt aL     determined activity changes

in selected enzymes from soybean  leaves and found that the reactions

were similar to those produced by other stresses, and not to the process

of senescence.

        Chronic  injury results primarily from  secondary reactions involving

membrane injury.  The oxidants could cause the formation of free radicals

or other,  more  stable oxidants  (such as hydrogen peroxide),  -which in turn

could cause secondary reactions.  These secondary reactions could  stimulate
                                                                  1,89,539
the production of cellular ethylene, with tissue senescence resulting.

These  secondary reactions may predispose plants to increased injury from

later acute exposures by limiting their repair  capability.  This predisposition

concept has been noted in several reports.


Reproductive Systems and Life Cycles

        Ozone and PAN are both strong oxidizing agents.   Some work has

suggested that ozone  is a radiomimetic gas.  It is known to cause  chromosomal

breakage in both plants and animals at high concentrations.  Although  the

potential of ozone's mutagenic effects on vegetation at ambient concentrations
                                        491
is not understood,  Sparrow and Schairer    reported that ozone appeared

to be a weak mutagen in causing an increase in the pink somatic mutation

rates in petals of Tradescantia.
             155
       Feder     showed an effect of ozone on  tobacco pollen germination

and postulated effects on reproductive capacity of tobacco.  This work was
                            488
not substantiated by Sinclair,      but the  exposure techniques used were
                           177
questionable.  Gentile £t al_.      showed that germination of pollen from

                                    11-34

-------
 sensitive ascessions of Lycopersicon Pimpinellifolium were reduced by as
                                                155
 much as 40% with techniques described by Feder.      However, reciprocal

 cross-pollinations between ozone-exposed and -unexposed populations led
                                                                 193
 to normal fruit development and viable seeds.  Harrison and Feder

 found a migration of cell organelles from the outer layer  of cytoplasm in

 pollen grain of sensitive petunia exposed to ozone.  They  used 0. 50 ppm for
                                                              397
 3 h and found an 80% reduction in germination.   Mumford et a_l.    found

 that 0. 03-0. 06 ppm  was the threshold for an effect on  germination of corn

 pollen.   They did  extensive biochemical studies  of the  pollen and suggested

 that ozone induces autolysis of structural glycoproteins and stimulates amino
                                        62, 63
 acid synthesis.  Cameron and associates       found major reductions in

 yield of some corn varieties after high-ambient-oxidant episodes occurred

 during tasseling.  These  reductions appeared to result from poor fertilization.

 Although preliminary, those studies point to the importance of understanding

 the direct effects  of oxidant pollutants on reproductive processes within plant

 species.

       A study was  undertaken to determine the potential mutagenic effects
                                57
 of ozone on  Arabidopsis thaliana.    This plant completes its life cycle in

 about 35 days and is an excellent test  species for determining effects of ozone

 across life cycles.  Plants were exposed to acute doses for 6 h/day,  3 days/

•week, through 4 weeks of the life cycle.  Seeds were collected from control

 and exposed plants and planted over seven generations. Seed production and

 biomass were reduced within generations, but no factors  studied were carried

 over into later generations. The results showed that,  for this particular

 species and the concentrations used,  no mutagenic effects were carried via

 seed to  later generations.   This  was a preliminary study  that also  reported

                                    11-35

-------
problems with variability in plant response.  The author suggested that

similar studies be initiated to verify these results.


Biomass and Yield

       Photochemical oxidants,  including ozone and PAN, reduce  plant

biomass and yields in many plant species.  Although yield and growth reduc-

tions are normally associated with visible injury, the oxidants can cause

growth reductions with little or no injury.  This relationship is not understood

for the oxidant pollutants and probably varies with species and cultivars,

as well as with conditions of growth and exposure, including dose.   Todd
           552
and Arnold      compared injury with biomass and chlorophyll content for

pinto bean exposed to a synthetic oxidant (ozone plus hexene).  They found

a logarithmic relationship between injury and the two physiologic measure-

ments and suggested that injury was not a reliable index of growth  effects.

Their data were from acute exposures and suggest effects on growth at low
                                           4,5
injury values.  A group of Canadian workers     have used physiologic

measures exclusively for acute exposures.  Many investigators are using

physiologic measures,  instead of injury, because they are more objective.

Although physiologic responses are often better measures of chronic effects,

their variability is usually at least as great as  that of a subjective  injury

measure, and they are  sometimes not as sensitive in indicating acute effects.
                   470
Runeckles and  Resh     reported on a reflectance measure of chronic effects

that was much  less variable than chlorophyll extraction.  They did not com-

pare this with a visual  injury estimate.  This technique should be studied

further.

       Considerable information is available on growth and yield effects.

However, because it comes from scattered sources and much of it is

                                     11-36

-------
 subjective, no one has developed the data for predictive use (relating

 dose or injury to yield reductions).  This section is divided into a discussion

 of effects under ambient conditions and a discussion of effects with controlled

 additions of oxidants,  primarily ozone.  The ambient oxidant section includes

 observational information and chamber studies comparing plant response in

 filtered versus unfiltered  ambient air.


       Ambient oxidant studies.  Since the first  observations of oxidant
injury,      there have been continual reports of effects of oxidants on

vegetation.   This section does not attempt to cover all those reports, but

does give several descriptive examples.  The closing sections of this

chapter (on plants as monitors and on economics) have additional examples.
            144
Engle elb al_.     first identified ozone as the cause of onion tip burn.  They

associated the development of this condition with severe •weather fronts and

suggested that ozone,  produced in thunderstorms, may be the  culprit.

They identified both resistant and  sensitive cultivars where resistance was
                                           580
genetically controlled. Weaver and Jackson     first described bronzing

in white bean and associated this with oxidant (ozone) episodes.  They found

that ozone produced similar symptoms and that 0. 16-ppm ozone for 0. 5 h

was the threshold for  effects in their studies. This disease is known to cause
                               184
reductions in bean yields.   Haas    did a growth analysis in field plot studies.

He  selected 5 plots based on severity of bronzing symptoms and showed a

relationship between severity of bronzing and growth.   He found that the

rate of growth influenced symptom severity and that the stage of growth

determined the dose at which bronzing occurred.   He showed that physical
                                                                      42
conditions within a field could cause a variable response.  Brasher et al.

reported 10 - 95% injury to 3 cultivars and 16 seedling lines of potato

                                     11-37

-------
after 3 days of ambient oxidant that reached a maximum of 0. 15 ppm.  No
                                                  459
yield data were reported for this study.  Rich ^t al_.     reported  crop

damage from oxidants to many plants in Connecticut when  oxidant concen-

tration was above 0. 05 ppm.  There were 83 of these high-oxidant days in
                                                          451
355 days monitored over 4 growing  seasons.   Reinert ei_ al.     found similar

effects around  Cincinnati,  Ohio,  when oxidant concentrations were high. In

this  study, a group of plants was set out to monitor effects.  Generally,
                                                                   422
these studies have not included quantitative yield data.  Oshima et al.

reported a severe episode in California where injury was greater than

expected on the basis of total-oxidant measurements.  The presence of  PPN

was  suspected.  This is indicative of the episodic potential in high-pollution

areas throughout the  country. Several studies have reported on the severe
                                                                    77,375
effects of oxidants on ponderosa pine in the San Bernardino Mountains,

and quantitative work (including growth-ring analyses) is reported elsewhere
                                                                       32, 571
in this document.  Several subjective observations have  come from Europe
               588
and Australia,      but little quantitative work has come from outside the

United States and Canada.

       Several excellent studies  have reported yield data obtained by use

of filtered and nonfiltered greenhouse or field chambers.  Selected summary

data are  shown in Table 11-2.  The  first field-chamber work was  reported
                                   521
on citrus by Thompson and Taylor.      Their report summarized several

years of  detailed work on lemon and orange and considered many  combinations

of pollutants.  Reductions in fruit size,  number, and total  yields were

reported in these studies and are the basis for the projected 50% reductions
                                                               520
in citrus yields  from the Los Angeles basin.   Thompson and Kats     showed

that  some of these effects on citrus  were probably related  to concentrations

                                     11-38

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                                                     518, 519, 522
of PAN in the ambient air.  Thompson and co-workers            used

the same chambers to determine effects of oxidants on grape over 2 years.

They found nominal effects  in the first year and 50-60% reductions in the

next 2 years.   The differences were attributed to the effects of oxidants

on floral initiation in the year before the first study year.   This concept

could hold for any plants when floral structures are initiated in the prior

season.  They also reported a 41-62%  reduction in leaf chlorophyll and

a 13-17% reduction in sugars.  A wax emulsion spray gave a 20%  increase

in yield over unsprayed plants; this suggests that selected protectants may

be useful in protecting grapes grown in areas of high oxidant concentration.

These chambers were also  used in the San Joaquin Valley in California to
                                       53
determine effects  of oxidants on cotton.     Yield reductions  of 5-29% in the

lint and seed were reported at three locations over 2 years, but no effects
                                                   221
on lint quality or seed grade were found.  Heggestad    reported  reduced

yields in four potato cultivars grown in filtered versus nonfiltered green-

houses.  The results  cover a 3-year study and show up to a 50% loss in

yield from  sensitive cultivars.  He also presented an excellent description
                                                      204
of oxidant and ozone symptoms on potato.  Heagle et aj_.       reported

preliminary results on yield reduction in tobacco grown as part of a test

of an open-top field-chamber design.   They found significant reductions in

both top and root fresh weight that  compared closely with injury ratings
                              253
(Table 11-3).  Howell and Koch    reported yield reductions  of 16-40%

in four soybean cultivars with these open-top chambers. They found no

changes in the protein or oil of seed.
                                    11-41

-------
                                    Table 11-3

       Injury versus Growth Reduction in Selected Plants Exposed to Ozone
           Ozone Con-
Plant Growth    Foliar Injury
Response,  %    Response,  %
 Plant      centration,   Exposure   reduction       increase over
 Species    ppm	 Time,  h    from control    control        Reference
Bean,
cultiva r
Pinto



Corn,
sweet

Soybean,
cultiva r
Dare


Tobacco,
cultiva r
Bel W
3
Soybean (2
cultivars)

0. 30
0. 30
0. 30
0. 30
0.05
0. 10
0.05
0. 10
0. 1 (+
SO at
2
0. 1)
> 0.05a

0. 05
0. 10
0. 5/day,
14 days
1. 0/day,
14 days
2/day,
14 days
3/day,
14 days
6/day,
64 days
6/day,
64 days
6/day,
133 days
6/day,
133 days
6/day,
133 days

(Often
over
growing
season)
8/day, 5
days/wk,
3 wk
8/day, 5
days/wk,
3 wk
1 1, leaf dry wt
40, leaf dry wt
70, leaf dry wt
76, leaf dry wt
12, ave. 4 yield
responses
35, ave. 4 yield
responses
22, plant fresh wt
65, plant fresh wt
75, plant fresh wt

22, top fresh wt

2, top fresh wt
21, top fresh wt
9
46
69
78
14
25
19
37
46

17

8
19
319



206

205


204

548

a A study in field chambers with ambient photochemical
  oxidant (ozone)  concentrations.

                                       11-42

-------
        Controlled chamber studies.  Many workers have used controlled

 additions of ozone in acute or  chronic studies to determine effects on a

 variety of growth measures.   These studies  suggest results attributable to

 ambient oxidants  in field plantings.  However, in the field, there are

 probably combinations of acute,  chronic,  and predisposition effects of

 oxidants on the  susceptible species and cultivars.   Most of these  studies are

 from greenhouse  and controlled-chamber exposures, but several have used

 chambers placed  over field plantings.  Several studies have shown correlations

 between injury and yield or biomass reductions (Table  11-3).  These suggest

 that injury may be a good  criterion of yield reductions.  However, it is

 known that yield reductions occur with little or no visible injury and that

 injury may cause  no measurable yield reductions.  These  studies have been

 divided according to whether they used short- or  long-term exposures.
                                                                   413
       •  Growth  effects of short ozone exposures:  Ordin and Propst

 used high concentrations of either  ozone or PAN and reported a 50% inhibition

 in indoleacetic acid-stimulated growth in Avena coleoptile.  This  suggested

 that the oxidant  may have a direct  effect on hormonal production.  Adedipe

and associates reported reduced biomass and floral production in four bedding
      5                         4
plants   and in 2 radish cultivars   from acute ozone exposures (Table 11-4).

 They reported no  effects on marigold, celosia, impatiens, and salvia, even

at the high concentration of 0. 80 ppm for a 2-h exposure.  The radish study

included effects  of exposure temperatures on growth.  One cultivar re-

acted the  same across temperatures, but the response  of the second was
                                         540
conditioned by temperature.  Tingey et ah      exposed radish at  7, 14,  or

21 days and all combinations of these ages to ozone at  0. 40 ppm for 1. 5 h.

They found the greatest effect on root growth at 14 days for the single

                                    11-43

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exposure and at 7 and 14 days for the double exposure.   The greatest effect

•was found in the root growth from the triple exposure (7, 14, and 21 days).

The root reductions for  the multiple exposures •were equal to the additive

reductions for  single exposures.  It was  concluded that reductions were

a result of photosynthate going preferentially to top growth.  Reduced root

growth  rate was still found in the second week after exposure.

        The studies of acute effects  resulted in  interesting growth phenomena
                                        542
that require further study.  Tingey  e_t al.     related foliar sensitivity in

the first trifoliate leaf of soybean to leaf growth, stomatal resistance, and

several metabolites.   Maximal sensitivity occurred during the end of the

period of rapid leaf expansion, when stomatal resistance was low.  However,

reduced sensitivity •was  shown in older leaves when stomatal resistance •was

still low.  They found no relationship between sensitivity and concentrations

of protein, amino acids, or various carbohydrates.  This suggested that

metabolic pools •were not directly related to foliar response.  Tingey and
     536
Blum      reported a consistent reduction in root growth that was related to

reduced nodule number in soybean.   The  ozone did not affect nodular activity
               147
or size.   Evans    exposed pinto bean to acute ozone doses and found a

reduction in leaf expansion within 12 h (10%) and a 33% maximal reduction on

the day  after a  0. 20-ppm exposure.   Growth rate continued to slow  3 days

after exposure.  He used the terminal leaflet of the first trifoliate for these

studies.  A stimulation of stem elongation in tomato within 3 days after  a
                               402
2-h exposure to 0. 30-ppm ozone     and  a predisposition to increased

sensitivity from acute ozone exposure after exposure to low ozone concen-
        467
trations     have also been reported.  These are only some of the effects

seen.  Similar  results are reported elsewhere  in this chapter.

                                     11-46

-------
                                                                    512
        •  Growth effects of long-term ozone exposures:  Taylor gt al.

first reported a 52% reduction in the fresh weight of avocado seedlings
                                                                        548
exposed to a synthetic "smog" (ozone plus hexene) for 280 h.  Tingey et al.

found reduced growth in 2  soybean cultivars (Hood and Dare) after intermettent

exposure  to ozone at 0. 10  ppm over 3 weeks.  They found that root and top

growth  were equally affected, but that roots were most affected when soybean

was exposed to a mixture of ozone and sulfur dioxide.  They found similar
        545
results    with radish.  Little injury was reported in either paper.
     171
Frey     reported a 55% reduction in seed yield of soybean with a 5% de-

crease  in seed lipids and a 21% increase in free amino acids.   This is one

of the few reports on quality changes in  seed as a result  of ozone exposure.

A 30% reduction in -wheat yield occurred when wheat was exposed at anthesis
                                       481          423
to ozone at 0. 2 ppm, 4h/day for 7 days.     Oshima    reported a reduc-

tion in tomato yield at 0. 35 ppm over a long exposure period, whereas injury

effects were significant at both 0. 20 and 0. 35 ppm.   He suggested an injury-

tolerance  threshold for tomato below which one would find no yield reduction.

He also reported a decrease in kernel weight of sweet corn exposed to ozone
                    418
at 0. 20  or 0. 35 ppm.       The reduced weight was associated with a shrivel

ear condition (kernels) that might relate to the effects  of ozone  on pollen

development.
              91
       Craker    reported a reduction in petunia flower weight after a 53-day
                                                                          93
exposure to ozone at 0. 05-0. 07 ppm, but an increase in petunia flower weight

was found in a 7-day exposure to 3 different concentrations.  Carnations

continuously exposed to 0. 07-0.08 ppm produced a single deformed flower,
                                       157
but the controls had 24 normal flowers.      Poinsettia bract area was de-

creased by 39% after a 50-day exposure  (6 h/day) to ozone at 0. 10-0. 12 ppm.

                                    11-47

-------
                     22a
       Bennett e_t aL     make a case for stimulation of growth at low

concentrations of ozone.  They exposed bean (cultivar Pure Gold Wax),

barley (cultivar Brock), and smartweed to ozone at 0. 03 ppm over some

growth stage and found instances of significant growth increases.  The

concept needs further study in light of the current concern over "normal"

background ozone concentrations.
                                                                   206
       Heagle and associates found a reduction in yield  of sweet corn
            205
and soybean    after exposure to ozone at 0. 10 ppm for 6 h/day over

much of the growing season. These exposures were carried out in field

chambers set over soybean plots in the field. They suggested that a threshold

for measurable effects on these crops would lie between ozone  (oxidant) con-

centrations of 0. 05 and 0. 10 ppm for 6 h/day.   These values are  realistic

in terms of growing-season averages in the eastern United States.  More

of these studies  could help to clarify dose-response relationships for

economically important crops.

       Table 11-5 summarizes these long-term, chronic studies.
                             194
       Harwood and Treshow    exposed 15 species, representative of the

aspen plant community, to ozone at 0, 0. 05, 0.  15, and 0. 30 ppm and ambient

air during the growing season and reported effects in all species at the highest

pollution concentration (Table 11-6).  There was considerable plant variability,

and only 6 species reproduced.  However, vigor was reduced and most species
                                   441
were sensitive.  Price and Treshow     found major biomass reductions in

6 grass and 2 tree species exposed for 4 h/day to ozone  at  0.15-0.33 ppm

over a growing season.  They also  found a reduction in or loss  of some re-

productive  components.  These effects could result in subtle shifts in com-

munity composition after several years of ozone exposure.

                                    11-48

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        The results of these experiments suggest that overall economic effects

on agricultural production could be extensive, depending on the sensitivity of

cultivars used in production, and should be considered in the attempt to arrive

at valid economic-damage functions for vegetation.


Factors Affecting Plant Response

       The sensitivity of plants  to ozone and PAN is conditioned by many
                           210
interrelated factors.   Heck     reviewed these factors and found that our

understanding of the importance of any given factor  on plants was fragmentary.

Since then,  a new body of research has become available that permits a more

concise discussion of many factors that affect the response of plants.

Although the response of a given plant is not predetermined by the response

of related plants,  sufficient information to predict relative responses under

given sets  of conditions is available.  Information to predict interactions

between variables and to predict whether species respond the same way to

environmental factors under different pollutant stresses is not available.

Current research demonstrates  our inadequacies in understanding interacting

variables.

       Before we can predict the response of a plant variety to a specific

pollutant or group of pollutants,  we must understand the following factors:

genetic variability (both between and within species), climatic and edaphic

factors, interactions  with other pollutants,  interactions with biotic pathogens

and insects, and the growth and physiologic age of susceptible plant tissue.

The overall conceptualization of relationships between pollutant exposure and

ultimate effects is shown simplistically (Figure 11-1) in an adaptation from
                        572
van Haut and Stratmann.
                                     11-56

-------
                            POLLUTANT
                          CONCENTRATION
       NUMBER  OF
       EXPOSURES
       DOSE
       CLIMATIC FACTORS


       EDAPHIC  FACTORS -


       BIOTIC  FACTORS
X    t
  ^  PLANT
""^RECEPTOR
                       MECHANISM OF ACTION
                               I
                             EFFECTS
               I

             ACUTE
     CHRONIC
 DURATION  OF
EACH EXPOSURE
                      GENETIC MAKEUP
                     .STAGE OF PLANT
                       DEVELOPMENT
  SUBTLE
Figure 11-1.  Conceptual model of factors involved  in air pollution effects

            on vegetation.  Modified from van Haut and Stratmann.
                               11-57

-------
       Genetic Factors.  Knowledge concerning the influence of genetic

variability on plant response to ozone has been obtained from both field

observations and chamber experimentation since the mid-1960's.  Similar

information on PAN is scarce,  but several published reports are available.

Resistance to ozone and PAN varies  between species of a given genus and

between cultivars within a given species.  Variations in response are

functions  of genetic variability and environmental stress as they affect

morphologic,  physiologic, and biochemical characteristics.   In native

populations and in breeding experiments,  both ozone and PAN may act as

selective  pressure stresses.

       Variations in  species response to ozone and  PAN are well
            235, 236, 269, 301, 401, 506, 510, 593a
documented.                                     A  list of species suscep-

tibilities to ozone is found in Table 11-24, which was generated from results

of controlled exposures and the use of the sensitivity table, Table 11-23.
            210
       Heck     summarized variations in cultivar responses of several
                 445
species.   Reinert    developed a compendium of research papers covering

horticultural cultivar responses to ozone, PAN, and other pollutants that

is complete,  but  gives no summary of results.  A number of papers have
                                  49
been published since Brennan et_ al.    first published their results on the

separation of oat and potato cultivars exposed to ozone  and stressed the

importance of cultivar differences within species.  Additional ozone studies
                      109          5                400                 48,
are available for bean,     begonia,   morning  glory,     chrysanthemum,
284           340          338         449         449           44
    poinsettia,      spinach,      lettuce,     radish,     turfgrass,
               52        257           256          254,382,546
forage legume,    alfalfa,    safflower,     soybean,             small
                                477                    47
grain (oat, rye,  wheat, barley),     and English holly.     Petunia was
                                  162
studied with auto exhaust and PAN,      and both petunia and chrysanthemum
                                  11-58

-------
                           128, 593
have been studied with PAN.          Screens using ambient oxidant

conditions,  sometimes without pollutant concentration,  are fairly common:
      247        42,247,310          226,247,355,362         310
bean,     potato,             tobacco,                  petunia,
           310             63           273
poinsettia,     sweet corn,   and grape.      Most of these studies used

acute exposures, which may or may not relate to results from chronic

exposures.  Some reports of  ambient oxidant exposures covered part or all

of a growing season.  These screens used injury as the response measure.

We do not know whether foliar injury ranking relates to economic yield

loss  ranking.

       Cultivar variations in  three species have been intensively studied in
                                             5,67,162         75,76,177,
relation  to their sensitivity to ozone:  petunia,          tomato,
448              115,181,226,239,358,361,362
    and  tobacco.                               These studies have resulted

in recommendations that some cultivars not be used in areas of high oxidant

potential. The  susceptible Bel W  tobacco is widely used as a biologic indicator
                               3
of oxidant.

       A summary of cultivar responses to oxidants,  ozone, and PAN is given

in Table  11-7.  Summary data •were also included in the development of the

dose-response equations and  Table 11-24 on plant sensitivities.
               188
       Hanson    presented a list of 160 woody species from observations

at the Los Angeles State and County Arboretum that were  sensitive or tolerant

to oxidants.  Several recent investigations have  considered susceptibility of
                             264                                      25
tree  species to ozone. Jensen    studied nine hardwood species, Berry
                                            107, 112
looked at three pine  species,  Davis and Wood          reported on  18 con-
                           373
iferous species, and Miller     reported on 15 western conifers.  In general,

selection within natural tree species has not been studied.
                                     11-59

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-------
        Two studies have explored the mechanism of genetic resistance to
               141                         142
ozone.  Engle      and Engle and Gabelman     found that ozone sensitivity

in onion is probably controlled by a single gene pair, with dominance of the

resistant gene.  In resistant plants,  the membrane  of the guard cells was

more sensitive to ozone and lost its differential permeability, thus causing

stomatal closure.  This did not occur in the  guard cells of the sensitive
                                                      500
cultivar,  and thus the stomata remained open.  Taylor     crossed the

sensitive  Bel W   tobacco with a resistant line and found that the F was of
               3                                                 1
intermediate sensitivity.  The F   segregated into 40%  resistant,  10% sensitive,
                                2
and 50% intermediate.  He  postulated that sensitivity was controlled by at  least

two genes.  Resistance mechanisms need to  be studied in other species.
     116
Dean     reported a 50% increase in stomatal density of two sensitive

tobacco cultivars  over two  resistant cultivars.  Stomatal size was not a

factor  in this study.

       Differential susceptibility of individual clones of eastern white pine to
                                                           28              82
ozone and sulfur dioxide was shown by Berry and Heggestad   and Costonis.
                      126
When Dochinger ei_ al_.     determined that chlorotic dwarf could be caused by an

interaction of ozone and sulfur dioxide,  they used a chlorotic dwarf-susceptible
                                                 249
clone to eliminate the genotype variable.  Houston     tested the response of

tolerant and susceptible clones of eastern white pine (on the basis  of  symptom

expression under ambient conditions) to ozone or sulfur dioxide.  Injury caused

by sulfur dioxide or sulfur  dioxide plus  ozone correlated well with the earlier

field responses, but ozone  did not produce a consistent response.  They also

found that a 6-h exposure to a mixture of  sulfur dioxide and ozone  caused a

difference in needle elongation between  clones within tolerant and sensitive

groups.  This suggests that tollerance may function over a wise range of

responses.

                                     11-63

-------
       It is reasonable to suggest that a spectrum of genotypes represents

various susceptibilities to oxidants,  singly or in combination.  Although

environmental factors are important in conditioning pollutant susceptibility,

the control of environment over injury to sensitive  genotypes may be less

pronounced,  if specific biochemical or physiologic mechanisms that have

weak interactions with the environment are involved.

       Climatic Conditions.   Plant response to ozone and PAN may be

altered by climatic               conditions before,  during, and after
          210
exposure.      Plants may be sensitized to a given set of conditions after

1-5 days. It appears that the major  conditioning occurs within the first

3 days under a given set of environmental conditions.  Conditions during

exposure may be critical, and conditions after exposure are probably

important,  but less  so than those before and during exposure.  The responses

of plants to ozone and PAN under varied climatic conditions  are  studied

primarily under laboratory and  greenhouse conditions,  but field  observations

have often substantiated the results.  Most studies have  involved individual

climatic  factors and one or two  response measures, usually including injury.

Several have dealt with environmental interactions.  Sufficient information

exists  for generalizations of plant response,  but there is much uncertainty,

because  of the small number  of species studied and the  lack  of information

on the  interactions of factors.

       • Light quality:  The  quality  of light affects the  growth and development

of plants and plays some  role in determining the response of pinto bean to
      134,136
PAN.          Injury to pinto bean from PAN was maximal when exposed at

420 and 480 nm and  less than half that at 640 nm.  The response is apparently
                                                                487
associated with changes in carotenoid pigments.  Shinohara et:  a_l.     reported

                                     11-64

-------
an effect on tobacco (H-mutant) when exposed at 0.40-ppm ozone for 30 min.

They found the least injury in far red,  followed by blue, green, and white,

with the greatest effect in red.  This work was preliminary.  More information

is needed on the effects of light quality.

        •  Photoperiod; The effect of a given light period within a 24-h cycle

exerts physiologic  control over some aspects of plant development.  Research

has shown that plants are more sensitive to ambient oxidants and ozone when
                                                                      212,
grown under an 8-h photoperiod than either a  12-h or a 16-h photoperiod
268,320
         (Table 11-8).

        •  Light intensity:  The intensity of light affects many physiologic

processes within plants and is known to affect the response of plants to

oxidant pollutants.  Studies have been reported on effects of intensity before,

during, and after exposure (Table 11-9).
                    136
        Dugger et aL     found a direct correlation between the sensitivity of

pinto  bean to PAN and increasing light  intensity.  Pinto bean required light
                                                                 136, 513
just before, during, and after a PAN exposure for injury to occur.

This was not true with exposure to ozone, although some light period was

necessary.

        Generally, plants  are more sensitive to ozone when grown at lower
                                              137,138,212             137,
light intensities.  This was shown for pinto bean              and tobacco,
212,487                                     138
        but was reversed in tobacco Bel W .      The reason for this
                                          3
reversal was unclear.  In both pinto bean and  tobacco, there was greater

injury from ozone when plants were grown at lower light intensities when
                             137               136
the humidity was  60% or 80%.      Dugger et al.     found greater injury in

plants grown at 900 ft-c (about 9,  690 luces) than at 2, 200 ft-c (about 23, 680
                         138
be), but Dunning and Heck     reported no difference between 1, 000 and 2, 000

ft-c (about 10, 760 and 21, 530 Ix) for either pinto bean or tobacco exposed

                                    11-65

-------
                                Table 11-8

        Response of Plants to Ozone, as Conditioned by Photoperiod
Plant
Species
Tobaco,
cultivar White
Gold

Tobacco,
cultivar
Bel W_
Bean,
cultivar Pinto
Ozone Con-
centration,
ppm, h	  Notes
0.67, 5
0.30, 1
0.30, 1
           Response, % injury
           Photoperiod, h
           57
Control    54
conditions,
2,000 ft-c
(21,529 Ix)

Control    71
conditions,
2,000 ft-c
(21,529 Ix)
                                Reference
40
27    320
        19    212
        18    212
                                   11-66

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                       136
to ozone.  Dugger et al_.     found a relation between plant age and light

intensity.  Peak sensitivity to ozone -was about the same at both intensities,

but the  span of plant age that was sensitive was increased at 900 ft-c (about

9, 690 be).   This could have an important bearing on environmental work and

has not been seriously considered by other workers.

        Sensitivity to ozone a6 light changes during exposure generally increases
                                          138
with intensity.  This was found for tobacco     between 1, 000 and 4, 000 ft-c

(about 10, 760 and 43, 060 be), with a slight decrease at 6, 000 ft-c (about
                             137, 216
64, 580  be),  and for pinto bean        between 1, 000 and 6, 000 ft-c

(about 10, 760 and 64, 580 be).  When pinto bean was  grown at 4, 000 ft-c

(43, 060 be),  there -was an increase in  sensitivity from 1, 000 to 6, 000 ft-c

(10, 760 and 64, 580 be) during ozone exposure; but,  at lower intensity during

growth,  the 4,000- and  6,000-ft-c  (43,060- and 64,580-lx) exposure intensity
                        138       137
gave similar responses.      Heck    reported that exposure  light had

no effect on the response of tobacco or pinto bean to ozone when the relative

humidity was 80%,  but had an effect at 60%.
                       487
       Shinohara et a_L     reported that up to 10 h  of postexposure  light did
                                                                      113
not affect the response  of tobacco  (H-mutant) to ozone. Davis  and Wood

delayed symptom development in  Virginia pine when the plants were held in

the dark for extended periods after ozone exposure.   However,  the final

severity of response was unchanged.

       •  Temperature: Variations in plant response to ozone or oxidants

occur with increasing growth temperature, if a given temperature is maintained
                                               320
for 3 days or more before exposure.  Macdowall      found that a  low day or

high night temperature increased the susceptibility of White Gold  tobacco to

ozone.  He reported no interaction between day and night temperatures.

                                     11-69

-------
             268
Juhren et al_.     used eight combinations of day and night growth temperatures

with Poa annua and then exposed these plants to ambient oxidants for a day.

The sensitivity varied with plant age, showed a partial reversal after 3 days

of changed temperatures, and was greatest at the 26 C-20 C day-night
                      4,417               139
temperatures.  Radish       and pinto bean     were more sensitive if
                                                7          139
grown under cooler conditions, whereas snap bean,   soybean,      pinto
      138,139                  138,363,485               107,113
bean,         Bel W  tobacco,               Virginia pine,          and
          589       3
white ash    -were more sensitive if grown under warmer conditions.
                       486
       Shinohara et_ a_L      looked at growth, exposure and postexposure

temperatures, and their effect on the response of several tobacco  cultivars

to ozone.  Plants were grown at constant temperature (day/night) during

growth and were kept in the dark for 48 h after exposure.  These elements

of design weaken the value of this report.  However, generally they showed

an interaction between growth and postexposure temperature,  night temper-

atures were more important than day temperatures,  and  lower temper-

atures during expos\ire  increased the sensitivity of tobacco to  ozone.
                  128
       Drummond     reported increased injury to petunia (cultivar White

Cascade) with increasing temperature when exposed for 1 h to PAN at

0. 15 ppm.

       Early reports suggested a positive correlation between plant response

to ozone and increasing exposure temperature,  to about 30 C.   These results
                                                                          216
were shown for pinto bean when exposures -were under  greenhouse conditions,

but an inverse correlation was found when they were under controlled lighting in

growth chambers.  This suggested that,  under greenhouse conditions,  it was

not possible to separate light and temperature effects.  This inverse relation-
                                        64,65,138,216              159
ship has been shown for Bel W  tobacco,                Lemna minor,
                             3
                                    11-70

-------
              107,113              589
 Virginia pine,         and white ash.      Under some conditions, this does
                              138, 139
 not seem to hold for pinto bean,         in which a direct correlation was

 found from 20 to 32 C.
                            210
        It has been suggested    that higher postexposure temperatures will
                                                                107, 113
 cause an increase in  sensitivity.  This was shown for Virginia pine
                  589                                            485
 and for white ash,     but the reverse occurred in Bel W   tobacco    and in
          4                                           3
 in radish.

        Two papers have considered interactions between temperature and
                               139
 other variables.  Dunning ^t al.     studied possible interactions among

 species (Dare soybean and pinto bean), ozone dose, potassium nutrition,

 growth  temperature,  and exposure temperature.  The two species did not

 respond the same,  except that there -were  no interactions with potassium

 nutrition in either species.   Soybean showed no interactions between dose

 and temperature under either temperature design.  Pinto bean showed

 strong interactions between dose and growth temperature and  between

 exposure and growth temperatures and a mild interaction between dose and

 exposure temperature,  with  no higher-order interactions.  The dose-growth

 temperature  interaction is shown graphically in Figure 11-2.  Apparently,

pinto bean is very sensitive to a variety of stresses, and these variations

make pinto bean both  a unique test plant and one that can be very  difficult
                                           138
to handle.  In later studies,  Dunning and Heck    looked at interactions

among  growth temperature,  exposure temperature, and plant  species (Bel W
                                                                         3
tobacco and pinto bean).   They found that the two species responded differently

to the temperature conditions.  Pinto bean showed no interaction  between

growth and exposure temperatures,  whereas tobacco showed a strong inter-

action.  For  tobacco,  growth temperature  had little effect at an exposure

                                    11-71

-------
          35-4
                                  	20   PINTO BEAN
                                  	28°  PINTO BEAN
        25-4
                                                                45-1
                                                                           60-1
  50-2
Figure 11-2.
The significant interaction  of  growth temperature in C, ozone dose (con-
centration x time),  and  species on foliar response (% injury) to ozone.
Dose is shown at the end of  each of the eight axes as concentration (parts
per hundred million) and time  (hours).  Percentage injury is shown in 5%
increments along each axis.  Each value is a mean of 15 observations.
The LSD at the 1% level  is 8.3  for the injury response.  This value can
be used to compare any two points in the figure.  (Reprinted with per-
                           139
mission from Dunning et  al.    )

                          11-72

-------
temperature of  16 or 32 C, but a marked effect at 21 or 27 C (sensitivity

increased with increasing growth temperature).  These types of interactions

need further clarification as we attempt to understand the effects of a total

environmental system on the  response of plants to oxidant pollutants.

       Crops that show greater injury under cooler conditions may be more

severely injured in early spring (assuming that oxidant is present).  Feder
            159
and Sullivan    used duckweed to remove the confounding effects of stomatal

movement.   They reported similar results in light and dark fumigations with
                                       139
temperature variations.  Dunning et a_l.     found no changes in carbohydrate

content associated with sensitivity of either pinto bean or Dare  soybean.
                                  4
This was also reported for radish,   except that cultivar  Cavalier showed

an increase in carbohydrate after an ozone exposure in a single experiment.

       A summary of these temperature effects is  found  in Table 11-10.

       •  Relative humidity:  Field observations suggest  that plants are

more sensitive to oxidants  as relative humidity increases.  Davis and
    107,113
Wood    found an increase in sensitivity of Virginia pine to ozone at a

high humidity during  exposure, but reported no effects from growth or
                                               424
postexposure humidity changes.  Otto and Daines     found similar results

over a wider humidity range and over several ozone concentrations during

exposure of pinto bean and  Bel W tobacco.  They did not study  growth or
                                3           137
postexposure conditions.  Dunning and Heck     showed a significant increase

in the response  of pinto bean, but not of tobacco, to increased exposure

humidity.  For growth humidity, tobacco sensitivity decreased with an

increase in  humidity; pinto bean response was unaffected by humidity at a

growth light of 4, 000  ft-c (43, 060 be), but was increased with an increased
                                                              138
humidity at  2, 000-ft-c (21,  530-lx) growth light. In later work,      Dunning
                                  11-73

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and Heck found an increase in sensitivity of both tobacco and pinto bean to

ozone with increasing exposure humidity from 45 to 90%,  regardless of growth

humidity.  However, there was an interaction between growth humidity and

exposure humidity  such that the response of these two species  to growth

humidity was  conditioned by the exposure humidity.  Plants were  always more

sensitive when grown at 75% humidity, regardless of the exposure humidity.

Table 11-11 shows  some of these results.

       • Carbon dioxide; Stomatal activity is affected by carbon dioxide,
                                                               212
and it may affect plant  sensitivity to  oxidants.  Heck and Dunning     reported

a decrease in sensitivity of tobacco to ozone if the tobacco was exposed to

added carbon  dioxide at 500 ppm immediately before and during exposure

to ozone (22% injury with added carbon dioxide,  and 66% injury without).

If this is a general plant response, the carbon dioxide now added to green-

houses to increase  productivity may  also increase resistance of the plants

to oxidant pollutants.

       • Field observations:  Canadian workers using ambient oxidant dose
                                                        324, 396
have correlated meteorologic variables with plant injury.          A cor-

relation  was discovered when an empirical relationship involving  evapotrans-

piration  (the coefficient of evaporation) was developed and used to modify

the dose information.   This empirical relationship has been used  on a

limited basis  to predict damaging oxidant concentrations from  monitored

meteorologic  conditions.
             313
      Linzon reported SNB symptoms on white pine after  several days of

wet weather followed by a continuous  sunny period.  Symptoms were noted

several times during the 1957 - 1964  growing seasons at Chalk River,  Ontario,

Ontario, but time of occurrence did not correlate well with peak oxidant

                                     11-78

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                314                      29
 concentrations.      Berry and Ripperton   observed emergence tipburn on

 susceptible trees in West Virginia several days after oxidant peaks of 0. 065

 ppm.  They found that container-grown susceptible pine clones were protected

 from injury if placed in a chamber supplied with charcoal-filtered air.

        Such factors as windspeed and barometric pressure appear to play

 little or no role in affecting plant sensitivity to oxidant pollutants.  Air move-

 ment would be expected to play a role under ambient conditions,  because of its

 known effect on leaf boundary layers, but it probably has little effect in chamber
                                                               45, 207, 232
 •work, unless  wind velocities are greater than 1 mph (1. 6 km/h).

        It is widely believed that vegetation growing  in the humid eastern

 United States  would be severely injured, if oxidant concentrations reached

 the daily peak concentrations (0. 20-0.40 ppm) commonly experienced in the

 less humid sections of California.  An air pollution  episode that  occurred on

 July 27-30, 1970, in  the Washington,  D.C., area is indicative of what may

 happen.  During this  4-day period, the peak oxidant  concentrations ranged

 from 0. 14 to 0. 22 ppm and were accompanied by a low concentration of

 sulfur dioxide (0.04 ppm).  Oxidant injury was  observed on 31 tree,  15 shrub,
                                            2               2
 and 18 herbaceous  species in an area of 72 mi   (about  187 km ).  Increased

 emission of the precursors of photochemical oxidant formation could result

 in repeated episodes  of acute injury or even chronic injury to eastern

 vegetation.

       Several workers  have explored the relationships between ozone

 effects on vegetation and several climatic factors.  Thus, we have some

understanding of how  these factors may affect a plant's response to ozone
                                                                     137-
and probably to ambient oxidants.   The few reports on these interactions
 139
    suggest that much remains to be learned about how  these climatic

                                     11-81

-------
factors interact in causing a plant response.  Studies to date suggest that

stresses applied during exposure have their greatest effect on stomatal

activity, -whereas those applied during growth affect a physiologic basis

of resistance that is not related to  stomatal function.  Postexposure

reactions -would no doubt be physiologic.  Interactions between growth

and exposure conditions would combine these stress factors.  A physiologic

stress may be  so pronounced that the normally responsive stomatal
                                              137
mechanism would not function during exposure.      More emphasis needs

to be placed on the study of multiple-stress interactions.


       Edaphic Conditions.  Soil -water stress during growth and exposure to

oxidant is probably the most significant environmental factor  affecting  plant
                           280
response.  Khatamian et_ al_.     found  less reduction in chlorophyll content

and an increase in dry-matter production in tomato exposed to ozone at 0. 50

or 1. 00 ppm for an hour,  if plants  were grown under a -water  stress that

did not itself cause a reduction in growth.  Plants in the three-leaf stage

•were most sensitive to ozone if grown  in optimal soil moisture (Table  11-12).
                       348
Markowski and Grzesiak     found  protection from ozone in bean and barley
                                                          117, 504, 577
grown  under drought conditions.  Several early field studies

showed a close correlation between soil moisture and oxidant injury to several

tobacco cultivars.  Field  observations generally  suggest that  sensitive plants

may become resistant under drought conditions.  It is possible that drought

during growth  causes physiologic changes within  the plant that increase re-

sistance,  whereas similar conditions during exposure may reduce  stomatal
                       8
opening.  Adedipe et al_.    reported some stomatal closure in  tomato exposed

to ozone at  1. 00 ppm for  1. 5 h.  However,  closure may have  been  triggered

by the  low light intensity of exposure (50 ft-c, or about 540 Ix).  Rich and

                                      11-82

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-------
       457
Turner    found rapid stomatal closure in pinto bean during a 30-min

exposure to ozone at 0. 20-0. 25 ppm,  if plants were grown under a soil

moisture stress.  Closure under optimal water availability was slower.

They also reported rapid closure in pinto bean and Bel W  tobacco if the
                                                       3
plants were conditioned and exposed to ozone at a  relative humidity of 37%;

this was not found at 73%.  Their evidence  suggests that ozone may induce

more rapid closure when plants are already under some type of water stress.
                530
Ting and Dugger     related activitivity of two tobacco cultivars to the size of

the root systems; those with larger root systems were more sensitive.  Several

•workers have recommended withholding water from greehouse and irrigated

crops during times of high pollution potential.
              495
       Starkey    found  that a sensitive bean exposed to subacute concen-

trations  of PAN was  sensitive  to postexposure  drought,  but more resistant

plants were  not.   This -was  related to  effects of PAN on membranes.

       In perennial vegetation, adequate soil moisture in the early season

interacts to  allow open stomata, and thus oxidant injury  occurs.  When soil

moisture becomes limiting, the nonfunctional stomata of injured leaves may

remain open,  thus increasing transpiration.  The moisture stress induced

in the late season is additive with oxidant injury,  because both increase

defoliation.
             411
       Oertli     found that both salinity and low soil moisture increased  the

resistance of  sunflower to ambient oxidants.  He used four different strength

salt solutions from 0. 75 to  6 atm and  two soil moisture levels  (0. 3 and 0.  8
                      412
atm).  Ogata and Maas      exposed garden beet for  38 days to  ozone at

0. 20 ppm and varied  exposure time from 0 to 3 h/day.  The garden beet

was protected from ozone injury and yield reductions at  high soil salinity,

                                     11-84

-------
but this protection was offset by growth reductions caused by the salinity

(Table 11-12).  The storage root was the most sensitive yield indicator for

both salinity and ozone stress.   They found that yield was not affected until

the daily ozone exposure was 2 h (-40 kPa) or 3 h (-440 kPa).  Ozone had no
                                  244
effect at -840 kPa.  Hoffman e_t aL     reported similar results with pinto

bean exposed to four ozone concentrations for 2 h/day from seed to harvest.

They had three degrees of nutrient osmotic potential and used sodium chloride

to increase salinity.  The  0. 15-ppm treatment at -40 kPa gave  a 46% reduction

in bean fresh weight, whereas no yield was found at 0. 25 ppm and above.

Results for top and root dry-weights were similar (Table 11-12). Maas
      319
et. al.     studied the response of pinto bean to ozone and salinity as conditioned

by concentration and duration of exposure (Table 11-13).  They found the

injury and  growth reductions were sigmoidal at the low salinity (Tables 11-3,

11-5, and 11-13). Salinity suppressed plant growth, but extended the ozone

tolerance for both growth and injury response.  In this study, the roots

were more severely affected than the tops. However,  in contrast with their
              244
earlier  study,     the pinto beans were exposed for  only 14 days and harvested
                            319
as young plants.  Maas e_t  al.    also looked at nutritional effects; although

some redistribution of nutrient was found (with respect to calcium,  magnesium,

potassium,  and nitrogen),  no serious nutritional imbalances occurred.  In
                                                                       245
the last of a  series of excellent papers on salinity effects, Hoffman et al.

studied  the effects of four  ozone concentrations  (2 h/day for 21  days) at

four levels of salinity on biomass production in alfalfa (Table 11-14). As

in the earlier studies, the ozone effect decreased with increasing salinity.

However,  in contrast, they found that -200 kPa gave protection from ozone


                                     11-85

-------
                                 Table 11-13

              The Interaction of Ozone and Salinity on Biomass
                       of Pinto Bean Exposed to Ozone^-
                             Reduction from Control Weight of Plants Grown at
                             -40 kPa and Not Exposed to Ozone,
Osmotic Ozone
Dry Wt of Leaves
Potential, Concentration, 0 0.30 0.60 0.90
kPa ppm (ozone dose, ppm-h)
-40

-240

-440

0.
0.
0.
0.
0.
0.
15
30
15
30
15
30
0
0
25
25
59
59
14
36
31
39
65
55
28
68
41
70
60
63
67
75
50
76
67
75
Dry Wt of Roots
0 0.30 0.60 0.90
(ozone dose, ppm-h)
0
0
24
24
47
47
18
64
25
50
49
42
53
83
35
81
40
56
72
87
51
85
53
74
                      319
—Data from Maas et al.
—Specific dose was given daily for 14 days; the duration of exposure can be
 determined from ozone concentrations used.
                                   11-86

-------
                                  Table  11-14
                                                                    •a
          Interaction  of  Ozone  and Salinity  on  Top Growth  of Alfalfa-
 Ozone                          Reduction from Control Weight of Plants    c
 Concentration,                 Grown at -40 kPa and Not Exposed to Ozone,%^
 ppm 2.	                 -40 kPa    -200 kPa    -400 kPa    -600 kPa

 0                                  0          +2         24          35

 10                                16          11         29          41

 15                                26          14         33          49

 20                                39          23         31          48
                         245
a
-Data from Hoffman et al.
—Concentration shown was given 2 h/day for 21 days.
c
—Values that differ by 10 are probably significantly different.
                                   11-87

-------
with no effect of salinity on biomass production.  This suggests  that moderate

salinity, in areas of high oxidant,  could protect forage legumes  (such as

alfalfa) from yield reductions.  They also found that both high salinity and

ozone increased water use efficiency of alfalfa and leaf diffusion resistance.

These reports on salinity suggest that we are dealing -with a moisture stress

problem.  Although this may involve stomatal response,  it is more likely

that we are dealing with a changed physiologic state that increases the resistance

of the plants to  ozone  effects.  At high salinity, both phenomena may play

a role,  but salinity itself can cause major yield reductions in the crops

reported on here.

        The importance of soil fertility in the  response of plants to oxidants

is not understood.  No research has attempted to explore, in depth,  the

nutritional interactions with oxidants.  Nitrogen nutrition has received the
                                   360
most attention.   Menser and Street,     in an ambient-oxidant study,  reported

an increase in tobacco fleck with increasing application of soil nitrogen.
                                               54             311
This was also found in spinach exposed to ozone.    Leone et aJ.    reported

that nitrogen concentrations  optimal for growth produced the most sensitive

tobacco, •whereas either higher or lower nitrogen applications increased

resistance to ozone.   The opposite was reported for White Gold  tobacco,  in

which the optimal nitrogen concentration for growth gave the greatest resistance
         320                417
to ozone.      Ormrod e_t aL     found no effect of two nitrogen  concentrations

on growth of radish exposed to ozone.  It is apparent that nitrogen concen-

trations and other conditions used in these experiments were not sufficiently
                                                                 90
critical for an evaluation of nitrogen-oxidant interactions.  Craker    reported

that increased nitrogen in the nutrient increased chlorophyll loss in duckweed

exposed to ozone.  Several studies have explored the importance of phosphorus

                                    11-88

-------
                                                                       417
in controlling the sensitivity of plants to oxidants.   Work by Ormrod et al.

suggested that radish grown at 20 C is more sensitive to ozone at a  higher

phosphorus  concentration, but that phosphorus has no effect at a growth
                                         464
temperature of 30 C.  Ripaldi and Brennan     reported an increase in tissue

phosphorus  for pinto bean after exposure to ozone.  They did not determine
                                        308
nutrient phosphorus.  Leone and Brennan     reported an increased ozone

injury to tomato with increasing nutrient and tissue phosphorus  (1.5 - 62 ppm).
              54
Brewer et: al.   found an interaction bet-ween potassium and phosphorus in the

response of spinach to ozone.  They reported that,  at low phosphorus,  an

increase in  potassium tends to increase injury, but, at high phosphorus,  the
                                                  90
potassium increase  tends to reduce injury.  Craker   reported  a  similar

effect on duckweed;  chlorophyll loss increased with increasing potassium at

a medium phosphorus  content, but decreased with increasing potassium at

zero or higher phosphorus content.  There is an apparent interaction
                                                                      139
betv/een these nutrients, but its importance is not known.   Dunning et al.

found that pinto bean and soybean were more sensitive to ozone  at low
                                         7
nutrient potassium,  -whereas Adedipe je_t al.  reported that low nutrient sulfur
                                                                       351
increased the response of Blue Lake snapbeans to ozone.  Mcllveen et al.
                                                          90
reported increased injury with increasing  soil zinc.   Craker    found no

change in the response of duckweed to ozone when total salt was varied from

one-tenth to one-half of a full-strength nutrient solution.  The response in a

full-strength nutrient was about one-third  less.  Soil nutrition probably plays

a fairly important role in plant response to pollutants only in cases  of nutrient

imbalances,  although total salts should affect response under  some  conditions.

In soils with balanced fertilizer, plants may respond fairly uniformly to

oxidant stress.  Table 11-15 summarizes  several nutritional studies.

                                     11-89

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                    498
       Stolzy £t al.     found that low oxygen partial pressures over soil

(0-10 mm Hg) for 40 h effectively protected tomato from injury by ozone

(0. 35 ppm. for 3 h).  These anaerobic conditions also decreased water use
                                 497
and general vigor.  In later work,     Stolzy ^taJ.  reported that, with

anaerobic soil conditions, the photosynthetic rate stablized within 24 h, -well

below the control  (32%).  Exposure to ozone (at 0. 17 ppm for 3 h) caused no

injury, but caused a marked reduction in the photosynthetic rate of the control

with a slight increase in photosynthetic  rates in plants under anaerobic con-

ditions.  They also  showed that a 3-h period of anaerobic treatment of the

soil affected the plant response to  an ozone exposure 22 h later.  The

anaerobic treatment showed less injury and the photosynthetic rate was reduced

less than in the  control plants.  These changes were related to  carbohydrate

changes within the plants.  These experiments suggest that even passing

periods of low soil oxygen tension  could reduce plant response to ozone stress.
                        34
       Blum and Tingey    found that ozone reduction in soybean root

growth and nodulation was a function of foliar impact.   They found no direct

effect of ozone on the  roots or soil systems surrounding the roots.


       Pollutant interactions. Oxidant air pollutants exist as parts of a

complex mixture of gases,  many of which may be phytotoxic. However,

except for ambient air studies and simulated photochemical oxidant studies,

little research was done with pollutant combinations until the classic work
                                 357                                   517
of Menser and Heggestad in 1966.      It is of interest that Thomas et al.

suggested that sulfur dioxide might lessen the effect of oxidants in causing
                                            368
foliar injury to pinto bean.  Middleton et al. ,     working with ratios of

sulfur dioxide to ozone of from 4:1 to 6:1, did not observe an increase in


                                     11-92

-------
injury, although hey found that, at 4:1, ozone appeared to interfere with the
                                   209
expected sulfur dioxide injury.  Heck    found that various combinations of

ethylene,  propylene, and acetylene, when mixed -with products of irradiated

propylene-nitrogen dioxide mixtures,  did not decrease or increase  the

development of foliar injury.
                             357
       Menser and Heggestad    first reported that exposure to mixtures

of sulfur dioxide (0. 50 ppm) and ozone (0. 03 ppm) for  2 or 4 h caused 23-48%

foliar  injury to the sensitive tobacco cultivar Bel W ,  whereas the concen-
                                                  3
trations of the individual gases  produced no injury.  This study stimulated

plant scientists to develop research on pollutant combinations.
                     447
       Reinert £t aL     have  suggested the use of the terms "simultaneous"

(mixtures of pollutants),  "sequential" (one  pollutant followed  by a second

pollutant),  and "intermittent" (when there is some period between sequential

exposures) to refer  to exposures in discussing studies of pollutant combinations.

They also recommended terminology for use in describing plant  response to

pollutant combinations:  less than additive,  -; additive, 0; and greater than

additive, -f.

       Ozone and sulfur dioxide mixtures are of special interest, owing to

their widespread occurrence and to the greater than additive  effect  on Bel W
         357                                                               3
tobacco.       Concentrations of either or both that may cause foliar injury

are found around major metropolitan areas  throughout the world and are
                                                                      323
widespread throughout rural eastern United States.  Macdowall and  Cole

reported that the two-gas combination lowered the threshold for  injury of

tobacco (cultivar White Gold) by sulfur dioxide,  but not the threshold for
                              324
ozone injury.  Macdowal et_ al_.      defined the threshold in  terms of dose

when they reported the threshold at 20 pphm-h (0. 20 ppm-h).   This  has not

                                     11-93

-------
                                      357,547
appeared true in several other reports,         nor -within the results
                                323
reported by Macdowall and Cole.      Symptoms reported, -when sulfur

dioxide was below the threshold for the specific plant, are similar to those

reported for ozone.
                     547
        Tingey ^t al.      exposed 11 species to different ratios of sulfur

dioxide and ozone mixtures.  There was no general trend in terms of how

the ratios of pollutant concentrations influenced foliar injury; additive,

greater than additive, and less than additive responses were noted (Table  11-16).

They described an undersurface  silvering and collapse of epidermal tissue,

whereas the upper-surface injury was  generally an interveinal necrotic fleck
                                                         181, 239,359, 362
or stipple (pigment accumulation).  Menser and associates

determined the response  of many Nicotiana tabacum types,  several Nicotiana

species, and various cultivars within N.  tabacum to sulfur dioxide and ozone

mixtures.  They found, generally, that tobacco was more sensitive to the

sulfur  dioxide-ozone mixtures than to the  individual pollutants, but the

relative sensitivity was often similar to that shown to exposure to ozone,
                                           201
ambient oxidant, or both.  Heagle  and  Neely     compared the relative

foliar injury among  cotton and soybean cultivars exposed to  sulfur dioxide-

ozone mixtures and  to the individual pollutants.  The relative cultivar
                                                                         261
sensitivity to each pollutant was normally different.  Jacobson and Colavito

found that sulfur dioxide at 0. 04 ppm decreased the sensitivity of bean and
                                                                       331
increased that of  vetch     to ozone during a 4-h exposure.   Mandl  et al.

found that the response threshold of alfalfa to sulfur dioxide  was increased
                                                              126           83
by ozone at 0. 07 ppm during a 4-h exposure.  Dochinger et al. ,      Costonis,
           249
and Houston     presented evidence that ozone-sulfur dioxide mixtures change
                                                                      126
the response of white pine to the individual pollutants.  Dochinger et al.

                                     11-94

-------
                                  Table 11-16
                       Summary Effects of Sulfur Dioxide
                      and Ozone Mixtures on Foliar Injury
 Plant Species

 Alfalfa

 Broccoli

 Cabbage

 Radish

 Tomato

 Tobacco, Bel W
                            Response at Concentration Ratio, SO :0 ,  ppm'
                                                                2   3
0. 50:0.05
     0

     0

     0
0.10:0.10     0.25:0.10
0

0
         0.50:0.10
                        547
'Data from Tingey et al.

 + = greater than additive,  0 = additive,  - = less than additive.
                                   11-95

-------
            249
and Houston    found that the mixture increased the amount of injury, -whereas
         83
Costonis    reported less injury from the mixture than from sulfur dioxide

alone.  Both Costonis and Houston reported effects from sulfur dioxide and

its mixture -with ozone at concentrations of both gases

well below those of other reports.   It is possible that they used ultrasensitive

clonal materials.  Whatever the reason, this work needs verification.
                      13
Applegate and Durrant   reported injury to peanut at sulfur dioxide-ozone

concentrations and ozone concentrations -well below those reported for other

plants. Their work also requires substantiation.  In the latter two cases,

the concentrations reported are  close to the detection limits of the monitors

used.
                     545
        Tingey ^t aJ.     found additive inhibition of top growth of radish and

less than additive inhibition of root growth after exposure to sulfur dioxide-
                                    538                  548
ozone mixtures. Tingey and  Reinert     and Tingey etaA.     exposed soybean,

tobacco, and alfalfa to mixtures of sulfur dioxide and ozone and reported greater

than additive inhibition of root growth of soybean, additive inhibition for
                                                                 205
tobacco, and less than additive  inhibition  for alfalfa.  Heagle et al.

reported greater than additive effect on growth and yield in soybean,  grown

under field conditions, from a mixture of these  gases,  but the differences

between the mixture and the ozone treatments were  not significant.  Heagle
          203
and Trent     reported a less than additive effect on yield of peanut from a

mixture of the two pollutants.
              581
        Weber     reported reductions in  plant growth and nematode pop-

ulations from mixtures of ozone and sulfur dioxide,  but these changes were

similar to those caused by ozone alone.
                                     11-96

-------
        Other combinations of pollutants with ozone, PAN, or both may be
                                                      349
 important,  but have received little study.  Matsushima    reported additive

 foliar effects on pinto bean and tomato from a mixture of sulfur dioxide and

 PAN and a less than additive effect on tomato from mixtures of ozone and
                           174
 nitrogen dioxide. Fujiwara    reported a greater than additive effect on
                                                        290           287
 pea  from a mixture of ozone and nitrogen dioxide.  Kress    and Kohut

 studied the  response  of hybrid poplar to ozone-PAN mixtures.  Kress used

 sequential exposures and found a  greater  than additive effect after most

 exposures; after others,  he reported mixed responses.  Kohut  used  simul-

 taneous exposure and found all three  responses in three replicates of a study.

 The  reasons for these variations  are unclear.
                 174                   447
       Fujiwara    and Reinert jjt aL     have recently  reviewed the  subject

 of pollutant interaction.   Fujiwara gave a straightforward reporting  of research

 that  is fairly comprehensive, -whereas Reinert _et al. interpreted  and analyzed

 results.   Fujiwara also included some of his data  on peas and spinach.  His

 graph (Figure 11-3) showing the greater than additive  response of pea to the

 mixtures of ozone and sulfur dioxide is of interest, because  of  the linear

 responses of the two ozone concentrations across  sulfur dioxide concen-
                      447
 tration.  Reinert ^t aL      developed some useful tabular material,  some  of

which is shown in Tables 11-17 and 11-18.

       Studies of pollutant interactions are preliminary.  We are still  not

 able  to define adequately the total potential impact of pollutant combinations

 on the production of quality food,  feed,  and fiber.  We do know  that plant

 species respond  differently to pollutant combinations and  that responses can

be additive, greater than additive, or less than additive.  We still do not

understand variations in species or cultivar responses or the responses of

plants grown or exposed under a variety of environmental stresses.

                                     11-97

-------
                 4J
                 a
                 w
                      70  -
                      50  -
                      40  -
                      30  -
                      20  -
                      10
                       0
                                                       20 pphm  0,
                                                       10 pphm 0
      0-0,
                                     10
20
                                  SO  Cone,  (pphm)
Figure 11-3.  The effects of sulfur dioxide and ozone on percentage foliar injury  to

                                                                   174
              garden pea.  (Reprinted with permission from Fujiwara.   )
                                         11-98

-------
                                Table  11-17

                     Foliar Response of Selected Plants
                    to Sulfur Dioxide and Ozone Mixtures
          Concentration
          Ratio,  SO :O
Plant               2   3
Species   ppm
Exposure   Foliar
Duration,   Injury,
h           %
Response to
Mixture      Reference
Bean,
garden
Bean, lima
Broccoli
Cabbage
Tomato
Radish
Alfalfa
Eastern
white pine
Cotton (6
cultivars)
Tobacco,
cultivar
Bel W
3
Tobacco,
cultivar
Bel W
3
Tobacco,
Md (6
cultivars)
1.

0.
0.
1.
0.
0.
0.
0.

1.

0.



0.



0.


70:

25:
50:
00:
10:
50:
50:
0.

0.
0.
0.
0.
0.
0.
025:0

00:

25:



50:



50:



0.

0.



0.



0.


19

05
05
10
10
10
10
.05

30

03



10



10


0. 5

4
4
4
4
4
4
6

6

4



4



2


24 +

0 0
17 +
28 0
10
50 +
60 +
26 +

10-24 0

41 +



88 +



20 +


349

547
547
547
547
547
547
249

201

357



547



362


                        447
Data from Reinert et al.

+ = greater than additive,  0 = additive,  - = less than additive.

                                    11-99

-------
                                Table 11-18


                     Growth Response of Selected Plants
                     to Sulfur Dioxide and Ozone Mixtures
           C one entr ation
Plant
Plant
Species
Radish
Radish

Alfalfa
Soybean
Soybean
Tobacco
Ratio, SO :O , Exposure
2 3 Duration,
0.05:0. 05 8/day, 5
days/wk,
5 wk
0.45:0.45 4

0.05:0.05 8/day, 5
days/wk,
12 wk
0.05:0. 05 7/day, 5
days/wk,
3 wk
0. 10:0. 10 6/day, 5
days/wk
0.05:0.05 7/day, 5
days/wk,
4 wk
Response, Response
% reduction fa to ^
from control Mixture
10 TDW
55 RDW
16 TDW
70 RDW
18 TDW
24 RDW
24 RDW
52 TDW
63 seed wt
32 TDW
49 RDW
0
0
0
-
+
0
0
0
0
Reference
545 •
447

447
548
205
447
T>ata from Reinert et al.
                        447
 TDW = top dry wt, RDW = root dry wt.

a
+ - greater than additive,  0 = additive,  - = less than additive.
                                    11-100

-------
        Pollutant-pathogen interactions.  An important factor in the response

 of vegetation to oxidants  (primarily ozone) is the presence of biotic pathogens.

 Such responses have been studied from several perspectives  since Yarwood
              596
 and Middleton     accidentally found that rust-infected bean leaves were less

 sensitive to photochemical oxidants (probably PAN).  Several investigators

 have  looked at the protection from ozone injury afforded to plants with active

 infections; others have noted that ozone injury  increases the sensitivity of

 plants to infection; some  have studied the effects of ozone on pathogens; and

 several have found no interacting effects.
                              596
       Yarwood and Middleton    reported the first protective effects in

 1954.  Little more was done until about 1968.   Protection of plants from ozone
                                                            200
 has been shown in several instances:  rust infection of wheat;     Botrytis
                       328                                         279
 cinerea on broad bean;    Pseudomonas phaseolicola on pinto bean;    mosaic
                46,385                       443
 virus on tobacco;       three tobacco viruses;     and mosaic virus on
      110, 111
 bean.         In the latter two cases, protection was reported without visible

 symptoms of the virus.  This may be a  general phenonemon,  inasmuch as

 some protection was  reported with very mild symptoms by Brennan and
       46
 Leone.     This protective action has generally been ascribed to the production

 of a diffusible substance by the invading pathogen.  This  might be due to

an alteration in plant metabolism caused by the viral infection.

       Several investigators have reported that ozone  injury increases the

infectivity of some weak pathogens.  This was originally investigated when a

high incidence  of B. cinerea was reported on potato that  appeared to have
                   346
 severe ozone fleck.      The authors later reproduced the symptoms and

disease incidence in greenhouse exposures.  B. cinerea  also invades ozone-
                                         33£~~
injured geranium leaf tissue more  rapidly.     It was suggested that the ozone

                                    11-101

-------
                                          336
injured geranium leaf tissue more rapidly.     It was suggested that the ozone

lesions serve as infection sites for the weak pathogens.

        Plant pathologists have used the possibility of pathogen-pollutant inter-

actions to study the direct effects of ozone on  the pathogen while it is active

on plant tissue.  This is the best way to study the effects of ozone and is the

only way to study these effects on obligate parasites.   The results have
                                                  195           452
included reduced growth of crown rust  uredia  on oat     and bean,
                                                                     199
reduced hyphal growth and number of urediospores  of wheat stem rust,
                                                       202
reduced infectivity of barley by powdery mildew conidia,     and a small
                                                                  344
reduction in symptoms caused by Fusarium oxysporium on cabbage.

In general,  it is felt that the results are due to changes in the host physiology,

and not to direct effects on the pathogen.  This may not be true for reduced

infectivity of fungal spores.

        There are  several reports  of the use of ozone with biotic pathogens,

and the responses noted were independent of each other.   These reports include
                                             86
Lophodermium pinastri infection of white pine,   Fusarium infection of
          344                                       339               452
cabbage,     Botrytis infection of poinsettia bracts,     rust on bean,     and
                         335
brown root rot of tomato.      These results  could reflect the conditions used.
              196
       Heagle     has developed an excellent review of this entire subject.

He has also covered the direct effects of pollutants  on pathogenic organisms.

We have used the portion of this tabular material that covers the effects

of ozone on plant diseases (Table  11-19).

                                   494                  378
       Other factors.   Stark e_t ah       and Miller £Jbal_.       reported

that oxidant (ozone) injury to ponderosa pine predisposed the trees to later

invasion by pine bark beetles.   The beetles increase the  rate of decline and


                                    11-102

-------
                                 Table 11-19
                                                       a
                      Effects of Ozone on Plant Diseases
 Disease Affected

 Botrytis on gladi-
  olus and chrysan-
  themum petals

 Botrytis on
  geranium petals

 Oat crown rust
 Wheat stem rust

 Wheat stem rust

 Wheat stem rust

 Barley powdery
  mildew

 Barley powdery
  mildew
 Botrytis on potato
  leaves

 Botrytis on broad
  bean leaves

 Botrytis on potato
  le a ve s

 Botrytis on
  Geranium leaves
Tobacco mosaic
  virus
Effects
Fewer infections by
 conidia
Decreased patho-
  genesis

Smaller pustules
Fewer infections by
  urediospores
Decreased hyphal
  growth
Decreased urediospore
  production
Fewer infections by
   conidia

Fewer infections by
   conidia
Increased incidence
  and pathogenesis

More infections and
  pathogenesis

More infections and
  pathogenesis

More infections and
  pathogenesis


More infections on
pinto bean
Ozone  Concen-
tration and  Time

Not measured
0. 35 ppm, 4 h
0. 10 ppm, 6 h/
  day,  10 days

0.06 ppm, 6 h

0. 06 ppm, 6 h/
  day,  3 days
0. 06 ppm, 6 h/
  day,  17 days
0. 10 ppm, 24 h
  after inoculation

0. 25 ppm, 8th
  through 12th h
 after  inoculation

Ambient
0. 15 ppm,  8 h
0. 15 - 0. 25 ppm,
  6 - 8 h

0. 07 - 0. 10 ppm,
  10 h/day, 15
  days

0. 30 ppm,  6 h
Reference

 329, 330



 337


 195


 199

 199

 199

 202


 474



 346


 327


 346


 336



  46
"Under ambient conditions, pollutants often exist in mixtures.  Therefore,  some
 of the effects observed in the field (ambient) may have been caused by inter-
                                                         196
 actions of more than one pollutant.  Adapted from Heagle.      All work done
 in United States.
                                     11-103

-------
                                       77
may be the final cause of tree mortality    (see Chapter 12).   It is possible

that oxidant stress in other parts of the country contributes to insect infestation
                        581
in forest areas.   Weber    has  shown that ozone and mixtures  of ozone

w^ith sulfur dioxide (0. 25 ppm,  4 h/day) can decrease the population of four

nematodes associated with soybean.  These types of interactions may be

significant in areas of the country with significant oxidant pollution problems.
                       198
       Heagle and Heck    found that Bel W   tobacco was predisposed to
                                           3                    320
later oxidant injury by exposure to ambient pollutants.  Macdowall

reported the same -when the preexposure was to low oxidant and the  later

exposure was also low.  Antagonism was noted when both doses were high.

       Sensitivity of plants to ozone and PAN is conditioned by leaf maturity

(Table 11-20).  This has received its best documentation in the work by
        36                 368
Bobrov.    Middleton ^t a_l.      found that pinto bean primary leaves were

most sensitive  at  the age of 14 - 34 days when exposed to an ozone-hexene

mixture.  Under ambient oxidant conditions,  leaves of White Gold tobacco
                                                                 320
did not fleck until  a week or so after the logarithmic growth phase.      Ting
           529
and Dugger     found that cotton leaves were most sensitive at about 70%

expansion and that sensitivity was rapidly lost.  Stomatal resistance -was

low, even if plants -were not resistant,  all other things being equal.   Ting
            531
and Mukerji    associated this with  reduced amino acid and carbohydrate

pools.  There was a twofold increase in amino acids 24 h after a 1-h exposure

to ozone at 0. 80 ppm; it was a transient increase.  This suggests that low

pool compounds could reduce the  speed of repair mechanisms.  Tingey
      542
et a_l.     reported that the first trifoliate leaf of soybean was most  sensitive

during the latter stages  of leaf expansion.  However, their metabolite studies

suggested that metabolic pools did not directly affect foliar sensitivity.

                                    11-104

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-------
                        564
Townsend and Dochinger    did definitive work on red maple seedlings

exposed to ozone at 0. 75 ppm, 7 h/day over 3 days.   They reported that

leaves of seedlings about 90% expanded were most sensitive, but that

young leaves were tolerant.

       Generally, studies have shown that plants are most sensitive to ozone

at a physiologic age associated with nearly expanded leaves.   Sensitivity is

associated with functional  stomata,  intercellular spaces,  and rate of cutin
                        36
formation on cell walls.    This is  not true in the case of PAN, in which

leaves of a lower physiologic age, just before maximal leaf expansion, are

most sensitive. Plants  generally are more  sensitive to oxidant pollutants

during rapid growth stages and lose sensitivity as leaves mature.  When

oxidant episodes occur throughout the growing season, the older leaves,

weakened during their stage  of maximal physiologic growth,  show early

senescence.
                    190
       Hanson etaL     reported an increased tolerance in petunia cultivars

as they approach the flowering stage.  This  was true  for both sensitive and

tolerant cultivars, with  the latter more  strongly influenced.  They sug-

gested that bud development produced a  diffusible substance that moved

down the plant  and acted as a protectant.
                     6
       Adedipe _et al.   found that Bel W  tobacco leaves were more sensitive
                                       3
to ozone when attached,  rather than detached or used as leaf disks.  Effects

were seen as visual injury and change in chlorophyll content.
                      107, 114
       Davis and Wood         found that ages of Virginia pine needles

influenced their response to  a 4-h exposure  to ozone at 0. 25 ppm.  Generally,

cotyledons  were more sensitive than primary needles, which -were more

sensitive than secondary needles.  Secondary needles of seedlings were

                                     11-106

-------
about as sensitive as those of 3-year-old trees.  This suggests that seedlings

may be good test plants for determining the sensitivity of mature trees.

The cotyledons and secondary needles became  resistant after 16 and 18 weeks,

respectively, whereas  the primary needles remained sensitive  beyond 18
               27
weeks.   Berry   reported that Virginia, shortleaf,  loblolly,  and slash pines

at 2 - 6 weeks from seed were most sensitive to ozone at 0. 25 ppm for 2 h.

Most species had peak  sensitivities at about 2 weeks for the primary needles.

The species  were listed in order of sensitivity.  These results  may not be

contradictory, inasmuch as the exposures  and  growth conditions varied

greatly between the two reports.
                                                     450, 536
       Ozone is known to reduce nodulation in  soybean         and in  ladino
       286
clover.      The reduction in fixed nitrogen was related to a reduced nodule
                                     33
number, and not to nodule size.  Blum   found no direct effect  of ozone on

Rhizobium or on nodule formation.  He attributed the reduction in nodule

number to the reduction in available  energy in the root tissue.  This reduction

in nitrogen fixation could affect total biomass and agricultural production,
                                                                         286
especially in areas of high oxidant pollution and low soil nitrogen.  Kochhar

also reported an inhibition of plant growth  and nodulation of Trifolium  repens

(clover) when the plants were treated with  root exudates from fescue grass

exposed to ozone.  If these factors are widespread,  they could change  the

competitive ability of plant species, with a resulting change in plant diversity

and a possible decrease in agricultural productivity.

       Although there has been considerable interest in understanding how

various factors, including air pollutants, affect the  response  of plants  to

pesticides, especially herbicides,  very little has been done with air pol-
                               240-242
lutants.  Hodgson and associates         first showed an effect of ozone

                                    11-107

-------
on the metabolism of herbicides.   They found that ozone inhibited the

dealkylation of atrazine in corn and altered the pathway of diphenamid

metabolism in tomato.   The changes could be beneficial,  if oxidants increase

pesticide degradation,  or harmful,  if oxidants stop biologic breakdown at
                                   66
a toxic intermidiate.   Carney ^taL    reported that the herbicide

pebulate in combination with ozone gave a greater than additive response

on White Gold tobacco and that chloramben did the same with Delhi 34

tobacco.  They reported a less than additive  response of both tobacco cultivars

to the  combination of benefin and ozone.  These  and other herbicides acted
                                                                      414
independently of ozone  exposure  on tomato and white bean.  Ordin  et al.

found that Avena  coleoptile growth was less inhibited by PAN when 2, 4-D

was used in amounts giving optimal growth.  These  interactions with herbicides

need additional investigation,  to determine whether  the responses noted are

of general importance.   Research needs to be directed at possible  interactions

between atmospheric pesticides (vapors or fine particles) and oxidant air

pollutants.

       Another interaction has recently been  rt:ported between  cadmium applied
                                   100
to soil and ozone exposure of  cress.      If cadmium potentiates the ozone

response of cress, maybe other heavy metals respond in a similar fashion.


       Discussion.  A  complete understanding of the many factors that affect

the response of vegetation to oxidant pollutants is probably impossible.  An

understanding of  the individual factors is possible,  however,  and much is

already known; but the  interactions between some of these many factors are

unclear.   It is possible that, as the mechanism of response becomes better

understood, we can develop an expectation as  to how various factors will

interact.  However, a well-trained and knowledgeable investigator can

                                     11-108

-------
develop a subjective estimate of response that is repeatable.  Inherent

genetic resistance is probably the most important factor that affects the

response of a plant to an oxidant dose.  However, the factors  discussed

here will influence the severity of response of sensitive genotypes.  Even

normally resistant genotypes  can be injured by appropriate combinations

of other factors.

       Genetic  or other factors that induce stomatal closure will reduce plant

sensitivity to oxidant pollutants.  Generally, the sensitivity of plants at the

time of exposure is controlled primarily by factors  that affect the stomatal

aperture.  The  internal resistance to gas flow may also influence leaf

sensitivity.  Factors that affect sensitivity during growth usually cause

physiologic changes in the plant that tend to make it more resistant to the

added stress of oxidant.  Many of  these stresses may alter membrane

physiology and make the membranes either more or less sensitive to

oxidant stress.


Dose-Response Relationships

       The development of criteria for setting air quality standards requires

a sufficient data base  relating   a given dose (concentration of pollutant

x duration of exposure) of oxidant  (e. g. , ozone or PAN) to some meaningful

effect on plants. An understanding of dose response is also important for

a basic understanding of the mechanism of oxidant effects on plants.  Heck
           211
and Brandt     have suggested that an ideal criterion would be a set of standard

equations that would relate  response to concentration and duration of exposure

and that would reflect the effects of all other factors that control the response

of the plant.  If these equations were developed, they would be different for

acute and chronic  exposures and perhaps specific for individual species or

cultivars.  Such a depth of coverage  would have little practical value for

                                     11-109

-------
overall understanding or for ambient air quality standards.  However,  some

average equation involving groupings of plants expressed -with confidence

limits might permit a more reasonable interpretation of dose-response

functions under average ambient conditions.  Discussions of the relationship
                                                                     211,
of time, concentration, and response are found in several publications.
318,401


        Data regarding the chronic effects of oxidants (including ozone and

PAN) have not been gathered on a scale wide enough to permit the development

of usable equations in regard to concentration and duration of exposure.  Much

of the information available was discussed and tabulated earlier in this chapter.

The data suggest that chronic and acute-chronic effects with resulting yield

and biomass  reductions can occur -when average concentrations of oxidant

(ozone) are between 0. 05 and 0. 10 ppm for 2-6 h/day over a number  of days

during the  growing season.   This type of statement is not yet possible for

PAN, but in the Los Angeles basin it is always a factor in ambient-oxidant

studies.

        Even  that kind of information is not available for forest species.  Other

than chronic  injury to white pine (associated with ozone, sulfur dioxide, and

their mixtures), no clearly defined examples of chronic injury from ozone

have been reported for eastern forests, and no information  is available on

PAN.  It is of interest that both Virginia and jack pine appear more sensitive
                                        25, 112
than white  pine to acute ozone exposures,        but chronic symptoms have

not been observed in either species.  The relationship between oxidant dose
                                               507
and injury  in the San Bernardino Mountains area     suggests that ponderosa

pine is moderately to severely injured in areas that receive oxidant at above

0.08 ppm for  12-13 h each day (Chapter 12).  Ponderosa pine  seems  to be the

most  sensitive western pine, but in some areas  Jeffrey pine is about as sensitive.

                                    11-110

-------
White fir,  incense cedar, and sugar pine all appear more tolerant, even to
                                                              373
the high oxidant concentrations in the  San Bernardino Mountains.     PAN

may play some role in the chronic responses noted in the western forest

species, particularly by broadleaf deciduous  trees and some shrubs.

        The information available on exposures to PAN and its homologues
                                                        506
is not sufficient to develop dose-response curves.  Taylor    reported

comparative results from exposures  to PAN, PPN, PEN, and P   BN.
                                                              iso
He found increasing sensitivity in the  first three homologues.
           128
Drummond    found a nonlinear response of petunia to PAN that was

similar to those reported for ozone.   Representative information for
                                        108
PAN is  presented in Table 11-21.  Davis     was unable to injure

cotyledons or primary needles of ponderosa pine with PAN concentrations

of 0.08, 0. 20, or 0.40 ppm during 8-h exposures. A species-sensitivity
                                        510
table for PAN was developed in the Atlas.

        The information on acute  exposures of forest species to  ozone is
        25, 107,112,125, 227, 373,  589, 594
limited.                                 These results of these reports

suggest that many eastern deciduous  species  are sensitive to exposures to

ozone at 0. 20-0. 30 ppm for 2 - 4 h.  Generally, the eastern conifers are

somewhat more sensitive, and the western conifers, somewhat  less sensitive.

These results are included in the summary data presented in this section.
                     568
Treshow and Stewart     developed an extensive list (70 plants) from two

plant communities, but it is impossible to determine percentage effect

from their data.  They found some injury to several species at 0. 15 ppm

for a 2-h exposure.  This list of  plants should interest investigators concerned

with plant communities.
                                     11-111

-------
                                 Table 11-21

                    Effects of Time and Concentration on
                  Foliar Response of Selected Plants to PAN
Plant PAN Concen-
Species tration, ppm
Time, h
Plant Response
Ref
Controlled Exposures:
Petunia
Petunia
Petunia, cultivar
Rosy Morn
Petunia, cultivar
White Cascade

Bean, cultivar
Pinto

Bean, cultivar
Pinto
Bean, cultivar
Sanilac
Acer, Fraxinus,
Gleditsia, and
Quercus spp.
0.10
0.12
0.14

0.05
0.10
0.20
0.02
0.04
0.14
0.10

0.12

0.20-0.30


5
1
1

2
1
0.5
8
4
1
5

2

8


Severe injury
11% injury
33% injury

23% injury
19% injury
15% injury
44% injury
90% injury
55% injury
Moderate injury

64% injury

Variable symptoms;
sensitivity related
to tissue age
496
162
506

128


506


496

495

127


Ambient Exposures;

Petunia, tomato,      0.025-0.03
  swiss chard, others
Petunia, tomato

Petunia, tomato,
  Romaine lettuce,
  others

Tomato, cultivar
  Pearson
ca. 0.014

0.015-0.02



0.10
Several   Typical symptoms


   4      Acute injury

   4      Acute injury



   5      Severe injury
560


506

510



498
                                   11-112

-------
        This  section deals with published data related to short-term exposures

of sensitive plants to ozone and the resulting responses.   In most cases,  the

measure of response is a subjective estimate of visible injury.  However,

various growth measures have been reported in some research,  and cor-

relations between injury and growth measures are often possible (Table 11-3).

These acute  ozone effects have  received sufficient study to permit the con-

struction of preliminary models to relate time,  ozone concentration, and

plant response for a number of  plant species.

       A graphic expression was developed for pinto bean and Bel W  tobacco
                                       217                        3
exposure to ozone by Heck and Dunning.      Later work with a number of

plants permitted the development of a simplistic model derived as an empirical
                                                             214
relationship between ozone concentration, time, and response;     this gave

a reasonable interpretation of acute response up through a single  8-h

exposure.  It also permitted the development of a reasonable acute threshold

concentration for a number of species.  The equation was a variant  of the

O'Gara equation for sulfur dioxide and is shown as:


       C=A+AI+A  /T,
             .012


where C is concentration of ozone; I is the  response  measure, in percentage

injury or percentage  reduction from control; T  is time, in hours;  and the

constants A  , A , and A  relate to inherent and external factors affecting
           01         2   211                 318
sensitivity.   Heck and Brandt     and Linzon et al.     critically reviewed

these dose-response  relationships.  They summarized much of the available

acute-response data and analyzed the data on the basis of  the O'Gara
                          211
equation.  Heck and  Brandt     reported the 95% confidence curves for 5%


                                     11-113

-------
                               318
and 33% response; Linzon je_t al.     reported the curve for 5% response,

along with data points.  They constructed a threshold curve from the minimal

data points shown.  These reviews attempted to develop an average response

across much of the useful information on acute plant response.
                        297
       Larsen and Heck     analyzed data on the foliar response of 14 plant
                                       214                 217
species to ozone  (from Heck and Tingey     and  Heck et al.    ).   They

depicted the data using a mathematical model with two characteristics: a

constant percentage  of leaf  surface is injured by an air pollutant concentration

that is inversely  proportional to exposure duration raised to an exponent

(Figure 11-4); and, for a given exposure duration, the percentage leaf injury

as a function of pollutant concentration fits a log-normal frequency distribution

(Figure 11-5).  The  complete leaf injury equation combines the equations

shown in Figures 11-4 and 11-5.   This equation expresses pollutant concen-

tration as a function of the other  variables:
                             Zp
               c = m     s   t  ,
                     g hr  g

where c is concentration in parts per million,  m      is geometric mean con-
                                               g hr
centration for 1-h exposure, s  is standard geometric deviation, Z is number
                             g
of standard deviations from the median (injury),  t is time in hours,  and p is

slope of injury line on logarithmic paper.  From the data  for pinto bean in

Figures  11-4 and 11-5:
                             Z -0. 57
               c = (0. 31)1.44 t

Thus, c = 0. 10 ppm to give 10% injury in a 3-h exposure.   The summary

table  of Larsen and Heck for the  exposure of 14 plant species  (two cultivars

of corn) appears as Table 11-22.  From this analysis, they suggested that

averaging times of 1, 3, and 8 h  should be used in the development of

oxidant standards for the protection of vegetation.


                                    11-114

-------
        For the present report, the literature was critically reviewed for




information on the  three measures--duration of exposure, ozone concen-




tration,  and plant response.  From this review,  74 references  were  found to




have usable data.   Several criteria -were established before data were used:




the monitoring technique and method of calibration should be defined  (40%




of the references used a calibrated Mast instrument,  50% used the Mast




uncalibrated or the calibration procedure was impossible to determine,  4%




used a 20% buffered potassium iodide wet chemistry,  3% were unknown but




other procedures suggested that the data were reliable, one report used an




ultraviolet method, and one used an automated iodometric technique); the




plant response must be subject to the development of a percentage




evaluation in comparison with the control plant (about 93% of the responses




were foliar  injury--for these we often made a subjective evaluation of scales




used, on the basis  of injury description given--other responses included




a reduction in chlorophyll, yield,  leaf area, root dry weight, or top dry




weight and an increase in respiration; and the general experimental pro-




cedures used needed to conform to those  generally reported around the




country.  The data  used came from a number of laboratories where




growth and exposure conditions were highly variable and plants were




exposed at different ages, at various times of year, and under  various




soil conditions.  The investigators always attempted to  grow and expose




plants under sensitive conditions.  We have assumed that these variations




have given us  some average over environmental conditions.   The above

-------
      10
 £
 o,
 a

 c
 o
•H
-p
 TO
 O
 C
 O
 O


 Q)


 O
 N
O
0.1
                                                                3.09
                                                          2.33
                                                          1.28
                                                               -1.28
                                                                -2.33
                                                               -3.09
c
2
•5

-------
                               z. Number  of stand  deviation

                                         from median
 a
  c
  o
  03
  5-c
  •P
  C
  0)
  O
  c
  o
  o

  0)
  c
  o
  N
  O
      0.01
        0,01
                    10  16          50

                      Leaf  injury, %
                                                                                99.9
                                                                        99.99
Figure 11-5.
Percentage leaf injury in pinto bean exposed  to various ozone concentrations

for various durations—concentration versus percentage injury.   c=m  s   ,

where c=concentration in ppm,  m =geometric mean concentration for a^plrticula

exposure duration, s =standard geometric deviation, and Z=number of  standard

deviations that the percentage of  leaf  injury is  from the median.  (Z for

10% injury is -1.28.)  (Reprinted  with  permission from Larsen and Heck.297)
                                         11-116

-------
                                    Table  11-22

          Calculated  Injury Parameters  for Plants  Exposed to Ozone
297
Calculated. 1 njury Leaf injury
threshold (ppn) equation** —
for exposure of parameters

Pollutant and plant
Ozone
a. Bean, Pinto
b.
c.
d.
e.
f.
K.
h.
1.
j.
k.
'-
-..
. n.
o.
Torna to, Roma
Clover, Pennscott Red
Toba'cco, Bel U-3
Spinach, Northland
Chrysanthemum, Oregon
Begonia, Thous. Wonders
Corn, Pioneer 509
Corn, Golden Cross
Bronegrass, Sac Smooth
Oats, Cllntland Bit
Radish, Cherry Belle
Periwinkle, Bright Eyes
Wheat, Wells
Squash, Summer

1 hr
0.10
0.06
0.13
O.OS
0.17
0.21
0.11
0.11
0.08
0.10
0.05
0.05
0.3U
0.30
0.11

3 hr
0.05
0.04
0.08
0.014
0.09
0.16
0.08
0.06
0.05
0.07
0.03
O.OU
0.22
0.18
0.11

8
hr
1
0.03
0.03
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.

.05
,02
05
12
06
03
03
05
02
03
15
11
10

m
g hr
0.31
0.24
0.65
0.34
0.72
1.79
0.76
0.80
0.83
0.64
O.l»7
0.29
1.37
0.83
0.70

s p
e
l.lifc -0.57
1.53 -0.35
1.68 -O.!i3
1.60 -0.68
1.
2.
1.
1.
2.
1.
2.
1.
1.
1.
1.
60 -0.55
00 -0.27
85 -0.31
91 -0.57
11 *"0 • ^ 1*
80 -0.3S
02 -O.lil
72 -0.32
57 -O.ltO
39 -O.US
83 -0.01
Multiple
corrcl .
coeff .
0.98
0.98
0.89
0.93
0.89
0.76
0.90
0.94
0.99
0.95
0.91
0.93
0.91.
0.94
0.96

Injury cone.
ratio
Median


Threshold
3.1
3.7
It
- t
t
8
6
7
10,
6,
.9
.3
.2
.C
.7
.%
.0
.2
8.8
S.W
%.
.0
2.S
C.
5

 * The Injury threshold is arbitrarily defined here as  1 percent  leaf  injury
   in the median plant of an exposed set
            TJ
** c=m  ,  s^ tp.
      g hr g
                                    11-117

-------
data (1, 135 data points) were divided into three susceptibility groupings,

on the basis of information from Table VIII in reference 211 and Table

6-6 in reference 401.  These tables -were modified,  on the basis of the

analysis of the data used  (Table 11-23).  The three susceptibility groups

were:  sensitive (471 data points),  intermediate (373 data points),  and

resistant (291 data points).  The plants (and appropriate references) in

each susceptibility group are shown in Table 11-24.   The underlined

references (in the table) were not used in compiling  the data for the

generation of  Figure  11-6 and Table  ll-24a.

       The data developed for each susceptibility group were then analyzed
                                   214
with the  equation of Heck and Tingey     (Figure 11-6 and Table ll-24a).

This is not to say that the data generated could not be used to develop a

different or more  complex model.  However, this model presents  a

better interpretation  of data than other simple models that have been

used.  It should be emphasized that the data presented are pertinent

only to pollutant concentrations that produce an acute response  in 8 h or

less (two data points in the sensitive group were for 12 h). None of the

information should be extrapolated beyond this period.  The data from

exposure of the plants in  Table  11-24 (except for underlined references)

were used in the model.  Several rather  extensive lists of species and

cultivar  sensitivities to oxidants,  ozone,  and PAN are found in  a number
              67, 235, 236, 269,401,475, 510, 515, 568
of references.
                                     11-118

-------
                                Table 11-23

         Ozone Concentrations for Short-Term Exposures  That Produce a
         5% or 20% Injury to Vegetation Grown under Sensitive Conditions
                              Concentrations That May Produce
Exposure           	5% (or 20%) Injury, ppm
Time,  h

0. 5


1.0


2.0


4.0


8. 0
Sensitive Plants
0. 35-0. 50
(0.45-0. 60)
0. 15-0.25
(0. 20-0. 35)
0.09-0. 15
(0. 12-0. 25)
0.04-0.09
(0. 10-0. 15)
0.02-0.04
(0.06-0. 12)
Intermediate Plants
0. 55-0. 70
(0. 65-0. 85)
0. 25-0.40
(0. 35-0. 55)
0. 15-0. 25
(0. 25-0. 35)
0. 10-0. 15
(0. 15-0. 30)
0. 07-0. 12
(0. 15-0. 25)
Resistant Plants
10. 70 (0. 85)
10.40 (0. 55)
10. 30 (0.40)
10. 25 (0. 35)
10. 20 (0. 30)
a
 Data developed from analysis of acute responses shown in Table ll-24a and
 Figure 11-6.
                                    11-119

-------
                                  Table  11-24

                   List  of Plant  Species and  Cultivars by
                   Susceptibility  to Acute Ozone Exposures
                                   SENSITIVE
Alfalfa
        410
   Dawson257
   Glacier257
   Mesa-Sirsa257
   Moapa
   Vernal
257
 257
   Williamsburg257

Aspen, quaking568
Bean
   Pint089»109'136,139,147,212,216,217,
         368,433,435,464,492,513,561
   Seeway65'105
   White166
   Sanilac]
 .109, 580
Broccoli
            214
   Calabrese

Chrysanthemum
   King's Ransom2-8-^
   Mango284
   Minn White2-8-4-
   Mt. Snow284
   Red MischiefM4-
   Tranquility2-84.

Clover, red
   Kenland52

Coleus
   Scarlet Rainbow5
           r o
Corn, sweet

Cucumber1*10

Duckweed159
Grass, annual

Grass, bent
   Astoria44
   Cohansey44
   Holfior44
                                 Grass, bent
                                    Penncross
                                    Seaside44
             44
Grass, brome
   Sac Smooth214

Mustard410
                                         Oats
   329-80214
   C. I. 754049
   Clintland 62214
   MO-0-20549
   Oneida49
   Pendek214

Petunia
   Capri5
   Pink Cascade67

Pine, jack25

Pine, red25

Pine, Virginia112 113

Pine, eastern white25) 83

Radish
   Cavalier4,1*17
   Champion449
   Cherry Belle4,214,449
   Crimson Giant449
   Comet449

Safflower
   Arizona 14154256
   Biggs256
   Jordan256
   Nebraska 1-1-5-1256
   Nebraska-4051256
   Nebraska-6256
   Nebraska-8256
   Pacific-2256
   Utah 1421-9-16256
   Ute256
                                   11-120

-------
                             Table 11-24 (Cont.)
                   List of Plant Species and Cultivars by
                  Susceptibility to Acute Ozone Exposures
             a
                                  SENSITIVE
 Soybean410
    Clark382
    Clark  63382
    Cutler382
    Dare139,254,382
    Haberlandt382
    Kent251*'382
    Lee382
    Lincoln382
    Peking382
    Richland382
    Roanoke382
    S100382
    Semmes382
   Wye382

Spinach
   AmericaA3-8.
   Dark Green Bloomsdale-3-3-8-
   Hybrid 612^18.
   Virginia Blight Res. Savoy-3-3-3-

Tobacco
   Bel B214
   Bel C383
   Bel W S*11^4,139,212,214,216,217,
        3352,354,361,363,464,1+84
   Bel B,  Callus11
   Bel W ,  Callus11

   Catterton362
   Coker 187358
   Coker 187-Hicks358
   Coker 316358
   Coker 319358
   Delcrest358
   Delhi 61358
   Havana  142239
   Havana  307239
   Havana  501239
   Havana  503239
   Hicks358
   Maryland,  6 cv362
   Maryland 10362
Tobacco
   Maryland 59362
   Maryland 64362
   Maryland 609362
   McNair 30358
   NC 95358
   Reams 64358
   Samsun181
   Speight G-3358
   Speight G-7358
   Speight G-36358
   Va 115358
   White Gold214'358
   Wilson362
   Xanthi181

Tobacco, (N_. glutinosa) l 81

Tobacco, (Itf. rustica)
   Brasilia181

Tomato
   Heinz 1350448
   Marglobe448
   Pearson448'497
   Red Cherry41*8
   Roma214
   Roma VF448
   Rutgers308'311
                                  11-121

-------
                            Table  11-24  (Cont.)

                  List of Plant  Species  and Cultivars  by
                  Susceptibility  to Acute Ozone Exposures
                               INTERMEDIATE
Alfalfa
    Cherokee257
    Iroquois257
    Kanza257
    MSA-CW3An2257
    MSB-CW5An2257
    MSHp6F-An2W2257
    Saranac257
    Team2 5 7
    Vernal214

Ash, white589

Bean109
    Astro109
    Bush Blue Lake109
    Clipper105
   Pinto469
   Tempo109

Bean, lima
   Thaxter
          214
Beet
                    214
   Perfected Detroit
Begonia
   Linda5
   Thousand Wonders White214
   White-Tausendschon5
                    «

Cabbage
   All Season214

Chard, Swiss
   Fordhook Giant214

Chrysanthemum
   Baby Tears2!4.
   Chris Columbus2!!
   Corsage Cushion2!4.
   Crystal Pat284
   Gay Blade284
   Golden Arrow48
   Pancho284
   Penguin284
   Pink Chief284.
   Sleighride2!4,
 Chrysanthemum
    Tinkerbell-2-84
    Touchdown2-^4-
    Yellow Supreme^-8-4-

 Clover,  red
    Chesapeake52
    Pennscott52'214

 Clover,  ladino52

 Clover,  white sweet52

 Coleus
    Pastel  Rainbow5

 Corn
    Golden Cross214
    Pioneer 509214

 Cucumber
    Chicago Pickling433
    Long  Marketer214

 Duckweed90

 Grass, bent
    Highland44
    Kingstown44

Grass, Bermuda
   Kansas P-1644

Grass, brome
   Smooth Sac214

Grass, Kentucky blue
   Delta44
   Merion44

Grass, perennial rye
   Lamora44
   Manhattan44
                                 11-122

-------
                             Table 11-24 (Cont,)
                   List of Plant Species and Cultivars by
                  Susceptibility to Acute Ozone Exposures
             a
                                INTERMEDIATE
 Grass, red fescue
    Highlight44
    Pennlawn44

 Larch, European112

 Lettuce
    Dark Green Boston449
 Oats
    C.  I.  757549
    C.  I.  757849
    Clarion119
    Clintland 64214
    Garry49
 Onion
    SW34144

Petunia
    Comanche67


Pine, Austrian112

Pine, jack112

Pine, Virginia114

Poinsettia
   Eckespoint340
   Paul Mikkelson340

Radish
   Calvalrondo449
   Cavalier3
   Early Scarlet Globe449
   French Breakfast449
   Icicle449
   Red Boy449

Safflower
   Friozi>6
   Nebraska-10256
 Sorghum
   Martin214

 Soybean
   Amsoy546
   Arksoy382
   Chippewa 64 546
   Clark  63 546
   CNS382
   Delmar254
   Dunfield382
   Hark546
   Hawkeye546
   Kent546
   Lee546
   Ogden382
   P. I. 157474382
   P. I. 181550382
   Scott214, 546
   Traverse546
   Wayne546
   York382

Spinach
   Bounty_33j8_
   Northland214
   Winter BloomsdaleJLl8-

Spinach, New ZealandlM.

Squash, summer214

Tobacco
   56-92B352
   Ast— C352
   Bel B6-»354»361>363
   Bel
   Bel W3214

   Catterton352'361'363
   Delhi 61354
                                  11-12S

-------
                            Table  11-24  (Cont.)

                  List of Plant Species  and  Cultivars  by
                 Susceptibility to Acute Ozone Exposures6
                               INTERMEDIATE
Tobacco
   H,
   McNair 12 354
   NC-95354
   Samsun NN181
   White Gold354
Tomato
   Fireball8, 28°
   Manapal448
   Ohio WR-7448
   Ohio WR-25448
   VF 13L448
   VF 145B7879448
                                 RESISTANT
                                            Wheat
                                               Wells214
Alfalfa
   Atlantic52
   DuPuits52
   Vernal211*
Chrysanthemum
Arborvitae
          112
Azalea
   Alaska214

Bean
   Eagle109
   Harvester109
   Provider109
   Stringless Black Valentine109
   Tender Crop109

Begonia
   Christmas214

Begonia
   Scarletta5

Chard, Swiss
   .Fordhook Giant214
Chrysanthemum2^
   Ann Lady go?-8-4-
   Bonnie Jean284
   Bright Yellow Tuneful284
   Cameo48
   Dark Yellow Tokyo2!!*
   Distinctive?-8-4.
   Flair284
   Fuji Jess Williams2-84:
   Fu j i-Mef o?H
   Golden Cushion284
   Golden Peking2-8-4
   Golden Yellow Princess
   Indian Summer48
   Jessamine Williams-?-8-4.
   Larry284
   Lipstick2-^4-
   Mandalay2!4
   Muted Sunshine48
   Oregon2 l 4
   Pink Chief48
   Queens Lace
   Red Dessert 48»^i
   Redskin48.284
   Resolute48
   Rosey Nook^i
   Ruby Mound4 8^2J4
   Silver Sheen48
   SpinwheelMl
   Tinkerbell48
   Touchdown48
   Tranquility48
   Trident48
   White Grandchild2-8-^
                                    11-124

-------
                              Table  11-24  (Cont.)
                    List  of  Plant  Species  and  Cultivars  by
                   Susceptibility  to Acute Ozone  Exposures
             a
                                  RESISTANT
 Chrysanthemum
     Wildfire^84
     Yellow Jess Williams284
     Yellow Jeanette48
     Yellow Moon1*8; 284

 Clover
     Alsike52

 Corn, sweet62

 Cotton
     Acala214
     Acala  SJ-1529

 Cucumber
   Long Marketer211*

 Fir, balsam112

 Fir, Douglas112

 Fir,  white112
Grass, Orchard
    Potomac 214

Grass, zoysia
    Common 4*+
    Meyer 44

Hemlock, Easternil2

Holly. English47

Larch, Japanese 112

Lettuce
    Big Boston449
    Butter Crunch449
    Dark Green Boston214
    Grand Rapids Forcing 449
 Lettuce
    Great Lakes449
    Imperial #456449
    Romaine449
    Simpson, Black Seeded449

 Maple,  sugar229

 Oats
    Clintland 642l4

 Onion2!4

 Periwinkle
    Bright Eyes2!4

 Petunia
    Blue Danube162
    Blue Jeans162
    Blue Sea162
    Bonanza5
    Calypso162
    Canadian-all Double  Mix5
    Cherry Blossom162
    Festival162
    Lilac Time162
    Parti Pink (Pink)162
    Peach Blossom162
    Peaches & Cream162
    Red  Magic (Red)162
    Roulette162
    Victory I62
    Warrior162

Pine, pitch112

Pine, red112
Pine, Scotch112

Pine, eastern white112
Poinsettia214
   Annette Hegg68
   Dark Red Annette Hegg340
   Eckespoint C-l68
   Mikkelwhite340
   White Annette Hegg340
                                   11-125

-------
                            Table 11-24 (Cont.)

                  List of Plant Species and Cultivars by
                 Susceptibility to Acute Ozone Exposures
          a
                                 RESISTANT
Snapdragon
   Floral Carpet 5
   Rocket Mixture5
Sorghum
   Sartin21"
Soybean
   Culler2^
   Harosay546
   Hood546
   Pickett546
   Scott214
   York254
Spinach
   Viroflay!
Spruce, black112

S pruce , blue112

Spruce, Norway 1 1 2

Spruce, white112

Sultana
   White Imp214

Tobacco
   Bel C6
   Hicks354

Tomato
   Fireball280
   Heinz
   VF
                                              Vetch,  crown
                                                 Chemung52
                                                 Penngift52
Plants are listed by common generic names followed by species common
name.  Cultivars are listed under the common names.  Data from the under-
lined references were not used in developing Figure 11-6 or Table H-24a.
                                  11-126

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-------
        The equations developed and the figures shown reflect the fact

that concentration plays a greater role in the response of plants  to ozone

than does time.  Although the concept has long been accepted,  it is often
                                                                 217,
forgotten that equal doses do not necessarily give equal responses.
379
     That is, a given dose applied over a short period produces  a much

greater plant response than  an equal dose applied over a longer period.

The concept of a concentration threshold actually ensures this  basic dose

concept.  Although some disagree with the threshold concept with respect

to the oxidant pollutants, the concept must have mechanistic validity,

inasmuch as organisms have some inherent mechanism for detoxifying

oxidants. This might not be true in the case of some individuals of a given

species that might have lost the inherent protective mechanism.   However,

when we are dealing with a large number of species  of vegetation and are

attempting to develop some type of realistic oxidant dose response,  we must

use the  species as a whole,  or at least a major subdivision (cultivar) of it.

In these  cases,  in the work that has been done, there is a rational body of

data to support a threshold concept.


Plants as an Oxidant Sink
                       211
       Heck and Brandt    discussed the effectiveness of green belts in

relation to vegetation as a pollutant sink and concluded  that vegetation probably

acts as a major sink for air  pollutants,  including oxidants and  ozone, over

time, but has a relatively minor effect on oxidant concentrations during high-

pollution episodes; is more effective in some seasons than others or with some

cultural and management practices than others; and  should not be considered

an important contributor to short-term reductions in oxidant or ozone con-

centrations.

                                    11-129

-------
        The concept of vegetation as a pollutant sink is  significant to the

atmospheric chemist and meteorologist who is attempting to develop air pol-

lution material budgets.  There is a need to know the ultimate sinks of air

pollutants  released by the activities of man.  The preliminary research

results available show attempts to understand the parts played by plants,

soils, and soil organisms.
                    569
        Turner et al_.     reported that freshly turned soil exposed to air

was a significant sink for ozone.  They found that soil was about 50% as active
                                                      570
as charcoal in removing ozone  from air.  Turner e_t aL    reported ozone

flux within a maize field and a forest.  They determined that vegetation

could reduce ozone loss to  soil -when plants were under stress,  but

supported the view that vegetation and  soil could  be the primary sinks
                     322
for ozone. Macdowall    found that soil absorbed twice as much ozone

as mature field-grown tobacco  growing on the soil.  He concluded that soil

is an effective sink and may play a protective role, in that it tends to keep
                                                       2
the oxidant concentration within the canopy low.  Abeles   suggested that most

soil activity,  in relation to reduced pollutant concentration, is associated

with the metabolic  activity  of soil microorganisms.  This may not be true

with ozone, because it is such a reactive gas.  Soils may play a more  important

role than has been  suggested, but they are usually covered with  vegetation

and in general are  probably less important than vegetation in acting as pol-

lutant sinks.
                   460,527
        Two reports         based on rather gross measuring techniques

found a close  correlation between ozone uptake and transpiration.  These

studies indicated that stomatal control is the prime factor in controlling

pollutant uptake and that cuticular sorption is negligible in relation to

                                     11-130

-------
 stomatal absorption.  These findings are generally supported by past work

 that indicates that stomata are the prime sites of pollutant entry into plant

 tissues.  However, cuticular sorption may be a. small but effective sink,
                      563
 over time.  Townsend      used similar techniques and reported ozone

 sorption by nine tree species.  He did not attempt  to separate stomatal and

 cuticular sorption.  White birch showed a linear uptake from 0.  10 to 0. 80

 ppm (Figure 11-7) and only a 5% decrease in uptake rate  over an 8-h exposure

 at 0. 20 ppm.  Uptake in red maple was linear to 0. 60 ppm and was at

 only 40% of the  maximal rate after an 8-h exposure to 0. 20 ppm.  Townsend

 presented values of actual uptake rates that may be of value. Several of

 these are given in Table 11-25.  All these studies determined uptake on the

 basis of the time needed to deplete the ozone in a closed system.  This  does

 not permit a high reliability in the data given, but they are among  the best

 available.
           233
       Hill     reported pollutant uptake values for a number of gaseous

 pollutants, including ozone and PAN,  with alfalfa as his test organism (Table

 11-25).  These  values were obtained with a dynamic, but closed, exposure

 facility.   Uptake was determined by the amount of pollutant needed to maintain

 a constant chamber concentration over an alfalfa bed.  Uptake values, expressed

 on the basis of leaf area, reflect the effect of the plant canopy on the exchange

 of gases within the canopy and do not give the maximal capability of plants for

pollution sorption.   They are,  however,  representative of the agricultural

 situation.  The values  shown are an order of magnitude below those reported
            563
by Townsend     and reflect the experimental conditions used, as well as  the

test species.  Hill's use of the alfalfa canopy partially explains his lower  values,

but  the technique used  by Townsend could have  resulted in inflated  values.

                                     11-131

-------
            CM
             I
             E
             T3
             o

             s
             v_x
             0
             (B
                                                              white
                                                              birch
                   0
                                   Ozone  Conc.(pphm)
Figure 11-7.  Net ozone uptake by foliage  of red maple and white birch seedlings
             in relation to ozone concentrations.   (Reprinted with permission from
                      563
             Townsend.   )

                                      11-132

-------
                                 Table 11-25

                Rates of Oxidant Uptake by Selected Plant Species
 Plant
 Species

 White oak
Pollutant
   O
        Uptake Rate
       -2     -1        -1
(yg, dm   ,  hr   < pphm.   )    Reference
             32
563
White birch
   O
             27
563
Sugar maple
   O
             19
563
Sweet gum
   O
             14
563
Red maple
   O
             14
563
Alfalfa
  O
             1. 1
233
Alfalfa
  PAN
             1.2
                                                                  233
                                    11-133

-------
                     22
        Bennett et aL    have presented a model for gaseous pollution sorption

by plants.   The model includes all the known factors that might have  a

significant effect on pollution sorption by plant leaves, including gas  con-

centration (ambient air and internal leaf),  gas fluxes (external and internal),

resistance to flow (Leaf boundary layer,  stomatal,  and internal), nature of

leaf surfaces (stomatal presence,  cutin, and surface properties),  importance

of gas solubility and thus solute concentration -within the leaf,  and ability

of the plant to metabolize pollutants (decontaminate itself).  They  mentioned

the reactivity of ozone as another factor to consider.   They believe that

surface sorption may be important,  at least over short periods.   They

presented a possible mathematical  representation of these factors, which

they suggested is equivalent to  the mathematical statement of  Ohm's  law.
                                                                  21
This material is well integrated in  the review by Bennett and Hill.
               466
        Rogers     used a constantly stirred tank reactor  that permitted

instantaneous mixing of incoming air with air  already in the chamber.  The

system was based on a dynamic exposure design with a single-path air flow-

system. This  system, should permit the development of maximal uptake

rates under given oxidant loads and a more accurate appraisal of the  effects

of oxidants on stomatal activity.  The chamber design permits a constant

turbulence within the chamber and an average air flow over leaf surfaces.

Within bounds,  one can vary this turbulence, -while maintaining a uniform

mixture of pollutants in the chamber.  Preliminary work with this  chamber
                                                                     233
have produced  uptake rates essentially doubling those reported by Hill

for nitrogen dioxide.  However, Rogers has not yet used the design to

study other oxidants (ozone and PAN).


                                     11 -134

-------
        Oxidant uptake rates are controlled by inherent variations within plant

 species,  the effect of the oxidant on the uptake potential of the plant, the effect

 of environmental stresses  on the uptake potential, and meteorologic factors

 that affect pollutant distribution.   It is  important to know •whether both resistant

 and  sensitive plants act as oxidant sinks or whether only sensitive plants are

 major sinks.   This knowledge requires some understanding of the mechanism

 of plant resistance to oxidants.  If resistance  is associated with stomatal
                            142
 closure due to the oxidants,     then resistant plants will not act as effective

 sinks.  However, if resistance is  physiologic, these plants could act as effective

 oxidant sinks,  with little adverse effect on the plants.  Neither  resistant nor

 sensitive plants would be effective  sinks under environmental stress that caused

 stomatal  closure.

        Plants probably act as major oxidant sinks over both  time and

 distance.   However,  it is important to  remember that  plants do not respond

 in a  predictable way over time and are  not active over the  greater portion

 of the year.  The total capacity of plants as sinks with or without harm to

 the receptors is not known.


 Plant Protection

       Air pollution research in effects on vegetation has focused largely on

 symptom  identification, dose response, and mechanisms.  The  purpose has

 been to develop criteria necessary to understand effects and  to form a basis

 for the promulgation of ambient air quality standards.  Environmentalists

were not concerned with protecting plants  per  se, but in controlling emission.

 Thus,  those interested in protection of  plants received little  encouragement.

 In addition, no economical ways were suggested for control,  and research


                                     11-135

-------
leaders were not convinced of the importance of adding air pollution stress

to breeding programs.  It -was the hope of most research -workers that air

quality standards would protect vegetation from  ozone and other oxidants.

       Most research workers are now convinced that pollution abatement

will have little impact on overall pollution concentrations until clean energy

forms are  developed and  in widespread use.  Because phytotoxic concen-

trations of ozone and other  oxidants are inevitable for the foreseeable future,

researchers are seriously considering other means of protecting plants from

injurious effects of oxidants.

       For managed agricultural crops,  including forest species and other

woody perennials, the addition of air pollution stress into standard breeding

programs has begun or is being discussed.  Some workers are trying  to

develop protective sprays for the more sensitive species and cultivars.

Some consideration is also  being given to the management of cultural
                                                               415
practices and  to general land management.  Ormrod and Adedipe    have

presented an excellent review of the concepts and work to date regarding

the protection of horticultural plants from, atmospheric pollutants.


       Breeding for resistance.  Varietal studies define the genetic

variability in resistance to  oxidants within different species.  These types

of studies are necessary  to select genetic lines or accessions for breeding

programs.   Although plant-breeders have not selected for oxidant resistance,

selection probably has occurred, for two reasons: breeders normally select

plants with the highest yield and least injury, regardless of cause;  and many

breeding programs are carried  out in areas of relatively high oxidant  content.

In this regard, natural selection pressures should increase the tolerance of


                                     11-136

-------
populations of native species near urban industrial areas,  although this would

tend to reduce the genetic plasticity-within sensitive species.

        Oxidant problems are starting to be of concern to plant-breeders.

Extensive varietal  screening of tomato, petunia,  and other plants has permitted

some resistant cultivars to be recommended for use in high-oxidant areas.

None of the varietal screens have involved breeding experiments in -which

resistant lines are developed and used in the development  of resistant varieties

for new introductions.

        Growers in the Connecticut valley have probably selected wrapper

tobacco for oxidant resistance  since the  1950's.  Similar selection is  probably
                                                  472
taking place in other tobacco-growing areas.  Sand     worked with a number

of wrapper  selections and suggested a partial dominance of genes for  fleck

resistance. He found that the F hybrid between a  sensitive  and a resistant
                              1                                  440
selection was  more  resistant than the parental average. Povilaitis     used

five tobacco varieties and made six crosses with six genetic populations from

each cross, for 36  different populations.  He used injury ratings and, unlike

Sand, suggested that susceptibility may be dominant over tolerance (dominance

•was important in five of six crosses).
                     266
        Johnson .et al.     determined the variation in response of 16  sweet

corn hybrids to ambient oxidants in California.  From these observations,
                    62
Cameron and  Taylor   selected five inbreds and three of their F   hybrids
                                                              1
for further field studies  and four inbreds and two hybrids for use in ozone

exposures.  The relative effects of the polluted environments were the same.

The final data suggested an inheritance for partial dominance to ozone sus-

ceptibility.
                               564
        Townsend and Dochinger     worked with four red maple selections

and found sensitive and tolerant selections  that showed the  same relative

                                    11-137

-------
susceptibility over four growth stages and four  Leaf developmental phases.

Symptoms were similar in the four selections,  but the design should have

used lower ozone  dosages.  These results suggest a strong genetic control

that will facilitate selection of ozone-tolerant seedlings for urban use.
               248                        250
       Houston     and Houston and Stairs     did clonal repeatability analyses

to determine genetic: control of tolerance in white pine with an ozone-sulfur

dioxide mixture and a 6-h exposure.  They used needle elongation and two

injury estimates in assessing effects.  The repeatability estimates indicated

that tolerance to the pollutant mixture is under  genetic control.   The nature

of the inheritance  of tolerance is still not understood, but field selection of
                                                             122
tolerant or susceptible individuals is possible.  Demeritt e_t aj_.     reported

an evaluation system that used visible needle injury for determining resistance

of Scotch pine to ozone.  This permitted the  discrimination of phenotypic

differences in a quantitative way.  Results suggested that a few genes were

responsible for resistance in Scotch pine.  A program -was initiated to  select
                                                                          582
for ozone resistance in loblolly pine, but no  definitive  results are available.

       As genetic understanding develops, it will be incorporated into basic

breeding programs that are concerned -with such characteristics  as yield,

growth habit, insect and disease resistance, flavor,  and texture.  These

programs will be  most effective if present ambient ozone and other oxidant

concentrations  do  not increase.

                                          278
       Protectant sprays.  Kendrick ^t al_.     first reported protection

of pinto bean foliage from sprays or dusts of four fungicides.  They later
                                     11-138

-------
 reported rather extensive studies that used a number of fungicides and
                                    277
 antioxidants on selected test plants.       These tests were in general

 agreement with the earlier studies and suggested that the response was due
                                                           267
 to a surface deactivation of ozone and  other oxidants.  Jones     found

 protection of tobacco with various particulate  substances,  including charcoal.
                     170
 Freebairn and Taylor    found protection from use of ascorbate sprays

 as antioxidants.  They reported partial protection to pinto bean, petunia,

 celery, lettuce, and grapefruit from oxidant injury in the Los Angeles basin.

 Several other early studies reported various degrees of chemical protection
                            30,575                  502
 from fleck injury to tobacco.         Taylor and Rich     found that an

 antiozonant-treated cloth protected wrapper tobacco from oxidant injury.

       These early studies, along with the recognition that oxidant pollution

 will continue as a  significant problem, encouraged a number of studies

 directed at finding  chemical treatments that might serve a dual function

 with a minimum of applications.  Some selected results  of these studies are

 summarized in Table 11-26.

       The fungicides, as a group,  have received the most attention,  and

 Benomyl (methyl-l-butylcarbamoyl-2-benzimidazolecarbamate) has been most

widely studied, owing to its protective properties.  Benomyl has been used

as a foliar spray,  a soil drench, and a soil amendment.  Mixed results have

been reported when benomyl was used  as a spray.  Protection was reported
           446             334,343,479             99            276
 on tobacco,     pinto bean,              white bean,   and grape;      no
                                  433,434               433
protection was found for pinto bean,         and cucumber.      It was not

possible  to equate the Benomyl concentrations used, but most were 20  - 4, 000

ppm.   Most reports on soil applications showed protection against oxidants.

Soil drenches at 10-1,000 ppm gave complete to partial protection for


                                     11-139

-------
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           342            434,561                  284
poinsettia,     pinto bean,          chrysanthemum,     and annual
          384
bluegrass.      Soil amendments
                                          341,433,434,469,479
at 2-160 ppm were effective for pinto bean,                        annual
           384               433                  503
bluegrass,     and cucumber.      Taylor and Rich     reported that a

single soil amendment at about 25 ppm protected the first eight leaves of

tobacco, but not the younger leaves.  They also found less tobacco root

cyst nematodes from benomyl applications, and the fungicide -was not toxic
                                                                         433
to the plants at the rates used.  Benomyl does not induce stomatal closure,
503
    so an internal physiologic mechanism must be involved.  The active
                                     434,561
ingredient is the benzimidazole moiety,        which inhibits senescence
                                                                   561
in bean and also inhibits the loss of free sterols in plant membranes.
                                           493
Sterols themselves are effective inhibitors,     and the mechanism of action

may involve effects on membrane sterols  and thus membrane permeability.
             492
Spotts e_t al.    studied the effects of benzimidazole and ozone on several

water relation  effects that suggest that the protection is  due to the effect

of benzimidazole on the cell membrane.

       The fungicide Carboxin has received some study, but with varied results.
                                                             98
A 0.43 mM solution gave protection at 5-10 days in white bean,    a 0. 36%
                                                334
spray gave no protection to pinto or tempo bean,     and a 0. 01% spray
                           386
increased injury to azalea.      Soil applications of Carboxin were generally

more beneficial,  but results were still varied.  A Carboxin soil amendment
                        503               458
was phytotoxic  to tobacco     and pinto bean,      although protection -was

noted in pinto bean.   Pinto and tempo bean were protected from oxidant for
                                                                     334
36-40 days after a soil amendment with Carboxin at 8 g per 4. 6-m row,

and the sulfoxide analogue gave protection to white bean, with a 13%  yield
          99
increase.    A soil drench gave protection to soybean,  cotton,  tomato,  and

                                     11-144

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                    458
 tobacco at 9. 5 ppm,     but a soil drench at 1-100 ppm increased
                                    386
 senescence in azalea due to oxidants.      These differences in species

 or conditions of application,  but they do call for clarification of the possible

 role of this fungicide (Carboxin) in protection against oxidants.  Carboxin
                                 458
 had no effect on stomatal opening,    and its protective action appears
                                       99,458
 due to the  sulfoxide breakdown product,        -which is not fungistatic.

 Thus,  although it can  serve a dual role, the modes of action are dissimilar.

        In addition to the compounds named,  several  others have been studied
                              68
 briefly.  Cathey and Heggestad    found protection to eight cultivars of

 poinsettia after treatment with the growth retardant Ancymidol  and

 Chlormequate.      They also reported a 75% protection in petunia treated with

 the growth retardant succinic acid 2, 2-dimethylhydrazide (SADH) as a 0. 5%
        67
 spray.     This was part of a screen of 65 petunia cultivars  to ozone.

 They found that the resistant cultivars did not respond to SADH; this suggested

 that protection may be  related to modified leaf structure (reduced cell size,

 intercellular space and stomata, and thicker cell walls).  The SADH treatment

 was not effective above an ozone concentration of 0.45 ppm for 3 h.  Adedipe
            3
 and Ormrod    found that a 30-ppm spray of the growth hormone N-6-

 benzyladenine protected radish from ozone at 0. 25 ppm  (4 h),  and Fletcher
     166
£t aL    protected white bean by use of a 1-ppm abscisic acid (ABA)

 solution.  The ABA caused partial stomatal closure,  which the authors

 suggested is the mechanism of protection.   Studies with ascorbic acid on
           105                                             288
white bean,    the insecticide piperonylbutoxide on tobacco,    road dust
              573                                           435
 on pinto bean,     and a wax emulsion (Folicote) on pinto bean    all stressed

 that many compounds can act as  protectants to vegetation against oxidant

 (ozone) effects.

                                    11-145

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              296
        Larkin    injected several peroxidases at 0. 1-10 ppm into one half

of a tobacco leaf and found some protection.  He suggested that peroxidase,

which is often associated with plant stress conditions, may be important

in physiologic resistance.  It is doubtful that any one mechanism of action

exists.  It is  important that we understand the  mechanism of ozone injury

and resistance in plants, so that we can determine better what chemicals

may play a role in protecting plants against oxidants.

        We do not yet have good answers to four basic questions  that have kept

protective chemicals from practical use:  we do not know the frequency or

rate of  application needed for continued resistance,  or,  therefore, the total

cost of  application.  We have little idea of the specificity of selected chemicals

on different plants.  Little is known of possible undersirable residues  or  side

effects.  We do not have sufficient prediction accuracy for high-oxidant

days for chemicals that are not long-lived.  These basic questions need to

be answered as  chemicals are tested and promoted for use.   The ideal

chemical would be effective on several  species  (cultivars),  have multiple

uses (e.g., fungicides), have a long life (a single preemergence soil application

would be best),  and leave no toxic  residues.  Such chemicals would have

value, at  least until breeding programs can incorporate  resistance to pol-

lution stress into new cultivar introductions.

                                                            415
        Cultural practices  and land use.  Ormrod and Adedipe     have

developed an excellent presentation on edaphic  and climatic factors that play

a role in making plants more resistant to ozone and other oxidant stress.

They suggest how these environmental factors may be used in cultural and

management practices to help to alleviate the effects of  oxidant pollutants.


                                     11-146

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 These practices may be of help in greenhouse management and to some

 extent in field irrigation systems.  The association of water  stress with

 resistance to oxidant has long been recognized, and growers have been

 urged to keep this in mind during periods of high air pollution potential.

 The increased use of carbon dioxide in greenhouse management would have

 a positive effect, but the additions are made during cooler months, when

 oxidant concentrations  are  not high.   These practices are worth considering,

 but are as yet of no more than supplemental help.
                  124
       Dochinger    was able to predict chlorotic dwarf on  seedbed white pine
                                        501
 with greater than 90% accuracy.  Taylor     found that susceptible and resistant

 tobacco could be identified  in seedbeds.  Both suggested  that, for some sensitive

 plants, time could be saved by  visual screening of transplant beds and the use

 of only the more resistant members of the population as  transplants.

       Interest in land use planning--with respect to areas to be  set aside

 for agricultural use, as opposed to industrial use--needs to be considered

 as a potential ameliorating factor in the control of air pollution effects on

 vegetation.   Land use might not be as effective for the oxidant pollutants,
                                                   211
 because of their ubiquitous  nature.  Heck and Brandt     have developed

 a brief but acceptable point of view in terms of the need for land use planning

 and protection of agricultural commodities from air pollution.

       A  rational approach to land use planning for air quality maintenance

may be built on the basis of diffusion modeling.  Although the photochemical

 versions of  the models  that relate air quality to emission are only beginning

 to be applied, there has been sufficient validation  to permit their use at least

 to obtain relative assessments (in contrast with prediction of absolute pol-

 lutant concentrations).  Chapter 5 discusses the principles and performance

                                     11-147

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of models that can be used for studying the distribution of photochemical

ozone and other oxidant concentrations.  The application  of these techniques

requires a succession of forecasts, beginning with land use patterns and

continuing with transportation network usage,  vehicle  emission intensities,

stationary-source contributions, and,  finally, patterns (in space and time)

of pollutant input to the atmosphere. Meteorologic characterizations based

on detailed weather data provide the transport measures needed.  For various

scenarios, the model generates statistics on the air quality that should be

expected.  The loop is closed by adjusting the land use to achieve the desired

atmospheric pollutant concentrations.


RESPONSES OF NONVASCULAR GREEN PLANTS

       Lichenologists have long used  the presence and abundance of lichen

and moss species  to map the biologic  impact of latrge urban and industrial
       164
areas.      Early workers considered changes in the presence and abundance

of these organisms to be  related to  such factors as temperature and humidity.

More recently, most researchers have tended to relate changes in lichen

population more to industrial air pollution than to other environmental  changes.

Although most of the air pollution work lacks ambient air quality measurements,

there is strong indication that both the presence and the abundance of lichen

and moss species  are correlated with sulfur dioxide concentrations  in large

urban and industrial areas.  Such studies have not been done in areas where

oxidants  are the primary air pollutants, nor in rural areas -with relatively

high oxidant and mixtures of sulfur  dioxide and nitrogen dioxide.  Thus,

little is known about the direct effects  of ozone or  other oxidants on lichen

and moss morphology or physiology.


                                     11-148

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                            78
       Comeau and Le Blanc   found that a 4-h exposure of Funaria

hygrometrica to ozone at  0. 25-1. 00 ppm stimulated the regenerative

capacity of the moss leaves.  This •was not true for 6- and 8-h exposures.
              178
       Glater     reported oxidant injury to several species of fern in the

Los Angeles area.   Initially,  tan lesions appeared near the smaller veins,

but in no  special pattern.  Later, the entire leaf became necrotic.  Symptom

development and sensitivity of leaves were different from those noted in

vascular plants. All leaves appeared to be equally sensitive, except for the

growing tip and the youngest uncoiling leaves.   Occasionally, a young plant

was killed.

       We know little about the overall effects  of ozone or other oxidants in

the nonvascular green plants.  Although they may not be economically important,

such effects may have an adverse ecologic impact.


RESPONSES  OF MICROORGANISMS
       Heagle     reviewed the effects of ozone on fungus growth, sporulation,

and germination.  Ozone may inhibit colony growth  on artificial media, but

rarely causes death,  even at high concentrations.  Differences in species

susceptibility are known.   Exposure to ozone at 0. 10  ppm for 4 h stopped
                                                                455
conidiophore elongation and spore production in Alternaria solani.      In

several fungi, exposure to ozone at 0. 10 or 0.40 ppm for 4 h caused a 10-
                                     196        197
fold to 25 -fold increase in sporulation.     Heagle     reported effects

on three obligate fungi from low ozone exposures.  Spore germination was
                                         292
not affected in any of these studies.  Kuss     grew 30 representative fungi

on agar and often found increased spore production after exposure to  ozone.

Spore germination was decreased in most  species, but increased in others.


                                     11-149

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                   442
       Rabotonova     exposed two species of yeast to ozone: Candida

lipolytica "was sensitive, and C. auilliermondii was resistant.  The

biocidal activity of ozone was determined under  various cultural conditions

with air streams of about 150 or 5, 500 ppm (v/v for 10-30 min).  Ozone

was  an effective biocide under most conditions,  and effectiveness increased
                           270
with decreasing pH.  Kanoh    found that exposure to ozone at 30 ppm for

30 min increased oxygen uptake in slime mold (Physarum polycephalum)

homogenate.  The ozone also increased succinoxidase activity and inhibited
                                       118-121
part of glycolysis.  deKoning and  Jegier        reported  effects of ozone

on Euglena gracilis that included  reduction of net photosynthesis, increase

in respiration, and effects  on pyridine nucleotide reduction and phosphorylation.

They reported that reduction of net photosynthesis was a logarithmic function
                                        118
of ozone concentration in 1-h exposures.     They also found a 5% reduction

in oxygen evolution after a  1-h exposure to 0. 5-ppm ozone bubbled into 5 ml
                                                                         121
of solution and an additive effect with a mixture  of sulfur dioxide and ozone.
          574
Verkroost    carried out a. detailed study of the effects of ozone on

Scenedejamus obtusiusculus, Chod. with special concern over the  effects  on

photosynthesis and respiration. A major weakness in this study was the

use of an air stream  containing ozone at 150 ppm.   The report suggested

that  the primary site of  ozone action is the membrane structure, -which

produces changes in photosynthesis and respiration.

       Ozone at high concentrations has  been used in a variety of applications

for the control and suppression of fungi and bacteria.  These applications
                                                         182
have included food protection,  drinking-water purification,     and treat-
                281,350
ment of sewage.          It is generally accepted that ozone is not an

effective germicide at concentrations below the point of human sensitivity--

                                     11-150

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 0. 04 pprn.  The germicidal effectiveness depends on concentration,

 relative humidity,  and the specific organism.  In many cases, even a

 concentration of 3-5 ppm -was not sufficient to kill some bacteria.
                58
 Burleson et al.     showed inactivation of several viruses and bacteria

 after ozone exposure and a greater inactivation with simultaneous
                                    597
 sonication. Zobnina and Morkovina      related the tolerance of a

 carotinoid strain of Mycobacterium carothenum with the presence  of

 the pigment.  The dwarf mutant was much more sensitive.

        Large doses of ozone may inhibit growth and sporulation of fungi
                                                                    490
 on fruit, although most fungi tested were resistant to ozone.  Spaulding

 reported that  ozone acted as a surface biocide.  Above  0. 5 ppm, ozone

 inhibited surface growth of fungi on strawberry and peach.  At 0. 06 ppm,

 it severely injured leaves  on head lettuce after 8 days.   He  also reported
                                                                  463
 some direct injury on  peach fruits above 0. 5 ppm.  Ridley and Sims

 extended the shelf-life of strawberry and peach by exposing them to ozone,

 but stated no concentrations.  Ozone at 1-2 ppm for  1-2 h/day controlled

 the surface growth of fungi and  sporulation on apple, reduced offensive odors,
                               489          579
 and decreased the ripening rate.     Watson     found that ozone at 0.4-2.0

 ppm acted as a surface fungicide, but did not penetrate.  Thus, there was

no effect on fungal  growth within the fruit.  Sporulation and  some decay

 control of Penicillium  digitatum and P.  italicum were noted in open storage
                                                    92
boxes of lemon and orange exposed to ozone at 1 ppm.     Ozone was  more

effective than  a fungicide dip in controlling Botrytis  bud rot of gladiolus,
                                       329
but no  concentrations were determined.      In general, researchers have

 suggested that rather large dosages of ozone  are required to protect  storage

fruits from fungal infection. These concentrations may be so high as to

                                    11-151

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preclude the use of ozone in storage facilities.  The ability of ozone to

reduce spore germination in fungi apparently depends  on species,  spore
                                      196
morphology, moisture, and substrate.     Single-celled  spores and those

with thin cell walls are most  sensitive. Wet spores are more sensitive than

dry spores.
              185
       Haines    reported that ozone at 4 ppm  retarded growth of Escherichia
                                                         476
coli, whereas 10 ppm prevented growth. Scott and Lesher    found that
                     7
approximately 2 x 10  molecules  of ozone per bacterium killed 50% of the

cells of E. coli and that the primary effect was  on the cell membrane.  Only
                                                                        140
metabolites leached from the  cell were affected. Elford and van den Ende

reported that ozone at 20 ppm had a lethal effect on some bacteria deposited

from aerosol mists on various surfaces.  Relative humidity is an important

factor, particularly when ozone concentration is low.  They found  little death

at a humidity below 45%,  at concentrations of  1  ppm, as opposed to a 90%

kill in 30 min at 0. 025 ppm with a humidity of around 70%.  A 5-m.in exposure

of Bacillus cereus to ozone at 0. 12  mg/liter was the minimal lethal dose,
                                                                   56
whereas 0. 10 mg/liter was effective for B. megaterium and E.  coli.

Spores of the Bacillus sp. -were killed by ozone  at 2. 29 mg/liter.  These

responses were of the all-or-none type with ozone between 0.  4 and 0. 5

mg/liter of water.  Time of exposure, from 1 to 32 min,  was not important.

Chlorine was effective at 0. 27-0.  30 mg/liter,  with time an important con-

sideration.   These two gases  did not affect E.  coli in the same way.

       In most research on lower organisms,  there has been an attempt to

use ozone as a germicide or to understand  the interactions  of pollutants and

pathogens on the  responses of higher plants.  In few studies has  the interest

been on the effects of ozone on the organisms themselves,  except in the

studies of effects on algae.

                                     11-152

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BIOLOGIC MONITORS

        The use of biologic indicators as an early detection system for severe

air pollution episodes or for chronic air pollution problems is of interest to

many urban and industrial control officials.  Plants served as air pollution

detection systems long before it was acknowledged a problem by industry or

government.  Higher plants serve as useful detection tools, because they develop

characteristic symptoms from acute exposure,  even though the symptoms are

not necessarily specific to cause.  Cause and effect can be reliably ascertained,

when an air pollution source is identified and symptom patterns are identified

within given sensitive species.

        Plants have been used  effectively in field surveys to determine the

extent and magnitude of pollution problems and in bioassay techniques in

conjunction with field  surveys. Most general review articles (Table 11-1)

treat,  to some extent,  the use of plants as indicators of air pollution.
     585
Went     covered plant sensitivities  to pollutants and the use of plants as

indicators.  He stressed  the photochemical oxidants and recommended
                                            209
charcoal filtration for greenhouse use.   Heck    presented a detailed

discussion and review of plants as indicators in field surveys and in the
                                                          222
bioassay of photochemical problems.  Heggestad and Darley     reviewed

plants  as indicators of ozone and PAN and recommended pinto bean as the

best indicator of both oxidants.  They also suggested three variably resistant

tobacco cultivars for use in monitoring  the severity of ozone episodes.

       It may be of value to differentiate the indicating and monitoring uses

of plants.  Most reported work has used the  indicator concept, with plant

injury  (symptoms) as indicative of a problem.  Monitoring implies some

degree of reliability.  Several studies have attempted to use plant response

                                     11-153

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as a monitor of pol lution concentrations or doses, with variable but uncertain

success.  Plants could also be  considered monitors if they gave a reliable

index of the biologic effects on  biologic systems of concern to man (crops,

forests, animals, and man himself).  The latter has not been seriously

discussed.

        This section is divided into reviews  of plants in field surveys and

plants as  a bioassay technique and a brief discussion of the possible value

of biologic indicators.


Field Surveys

        Field surveys have played a significant role  in the assessment  of air

pollution problems.  Basic techniques were developed in  surveys around point

sources of sulfur dioxide and fluoride.  Similar techniques have been

developed regarding photochemical pollutants,  starting with the  early report
                   369
by Middleton et al.
             ~
       Treshow     has developed the thesis that foliar injury is a useful

criterion in the identification and analyses of air pollution effects on vege-

tation and presented some basic concepts for use in field evaluation.
                         482
       Sharma and Butler    found that white clover in a highly polluted

area (Nashville,  Tenn. ) had a lower  stomatal frequency, a higher trichome

frequency, and a greater trichome length than the same species growing in

an area of lower  pollution.   They suggested oxidants as  one of the pollutant

stressors.  It is  possible that pollutant stress (among other things) is

causing selective pressures that favor these changes; thus, a separate race

may be evolving.  This type of work  needs further evaluation  and exploration.

       Most researchers have felt that biochemical changes in plant tissues

are associated .with so many normal  growth and stress phenomena that they

                                    * 11-154

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                                                                         272
would have no relevance in field evaluations of air pollution effects.   Keller

has associated changes in peroxidase activity-with different pollution stresses

(flouride and oxidants) in apricot and -white ash growing in areas of high pol-

lution, as  opposed to those of low pollution.  This study suffers from lack

of pollution monitoring (although leaves were analyzed for flouride) and con-

sideration of other stress factors.  This is the same type of criticism that
                                                           164
has long been made of lichen studies in industrialized areas.     Lichens

may respond to the photochemical complex, although such work has not been

reported.  The larger question of the value of these studies persists.  If, in

fact, changes in some biochemical entity could be clearly associated with one

or more pollutant and if this could be separated from  other  stresses, what

would it tell an interested party?  Can it be related  to adverse yield,

quality, or genetic changes?  These approaches to understanding air pollution

effects through field surveys appear to be of doubtful value and must  rely on

statistical methodology involving many variables.

       A technique that offers greater potential is the use of remote  sensing

of injury to vegetation.  This technique was first tried with ponderosa pine as
                       586             587                 298
the species of concern.      Wert^t aL     and Larsh^t al.    found that

injury to ponderosa pine in the San Bernardino Mountains was  severe enough

for the technique to have  real potential.  They were able to identify the  severity

of diseased areas  through color  photography -with a high degree of correlation

with ground plots.  In severely affected areas where air pollution is  the

principal stressor, this approach offers a rapid and inexpensive technique

for surveying large tracts.  It is not yet possible to use remote sensing to

identify pollutant stress amid a  variety of other stressors.  However, as

these techniques are improved,  they should be applied to air pollution problems.

                                     11-155

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       Early field surveys depended on identification of a syndrome of responses

that included symptoms on both native and cultivated plant species.  Middleton
           366
and Paulus     directed the first large-scale survey to determine  the extent

and severity of photochemical oxidant effects in California on crops of agronomic

importance.  They delineated four categories of crops (field, flower, fruit,

and vegetable) and one  of weeds.  This was the most extensive survey of

oxidant effects until the late 1960's.  The information was later used as a

basis for subjective estimates of economic losses.  This type of visual

assessment of foliar injury has been attempted in many  states and has been

purposefully developed in  some for use in economic estimates of damage to

vegetation.


Plant Bioassay of Oxidant Effects

       During the 1950's,  when the phytotoxic components of the photochemical

oxidant complex were not known, plants were used extensively as a bioassay
                                                       183, 209, 238,406,408,
of many simulated reaction mixtures to indicate toxicity.
496
      Plants  were also used to help in identifying specific components of
                                                               496
photochemical reaction products, such as PAN and its analogues.

       This bioassay technique was also used to determine the phytotoxicity

of the ambient photochemical complex and to attempt to  standardize plants,

so that oxidant concentrations  could be determined from severity of injury.

Two such studies were initiated at about the same time in the Los Angeles
                       368
basin.  Middleton ejt aL    established five stations where young pinto bean

plants,  grown under uniform conditions,  were set out daily and foliar injury

intensity was compared with results from oxidant instruments.  Results

were recorded as the percentage of days showing plant injury and the average

injury index per day per station.  There  was a  relationship between injury

                                    11-156

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and oxidant values,  but the correlations were not significant and the

association was obscure.  The most detailed study was carried out over a
                                             407
period of about 4 years with annual bluegrass.     The plants
                                          268
were grown under standardized conditions,     and injury development was
                  37
concisely defined.     The plants were transported daily to  locations around

Los Angeles County, California.  They were exposed for 24 h and  returned

for a control posttreatment period before injury assessment.  The injured

leaf areas were measured and correlated with the  severity of oxidant episodes.

The procedures were time-consuming, and the results were poorly cor-

related with oxidant concentrations.  Thus, this procedure  was discontinued

as automatic instrumentation became available.

       The bioassay technique was developed to reduce the uncertainties

associated with the use of native vegetation or cultivated  crops.  Plants can

be started under controlled conditions and exposed under standardized con-

ditions.  Species and cultivars can be selected for oxidant sensitivity and

symptom characteristics.  The two studies just noted were the most closely

controlled.  Similar work has not been repeated.   However, many investi-

gators have grown plants under known cultural conditions and then transplanted

them  to field sites where they received special care.  These plants can then

be read for foliar symptoms throughout a given period, and the symptoms

related to oxidant concentrations.  The lack of apparent  correlation in the

two early studies could be due to the lack of specificity for  the monitored

oxidants, the presence of different concentrations  of interacting oxidants at

different times,  or variations in cultural conditions between exposure times.
                      50
       Brennan et al_. ,   using petunia,  found a better correlation with

atmospheric aldehydes than with total oxidants.  This appears spurious,

                                    11-157

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because researchers do not regard aldehydes themselves as important
                                            324
atmospheric phytotoxicants.  Macdowal et al_.     were able to correlate

tobacco injury with oxidant concentrations by considering ozone flux into

plant leaves.  They then predicted fleck attacks with fair consistency on

the basis of meteorologic considerations.  Several investigators have used

acknowledged plant sensitivity and emphasized the importance of accurate
                        84                         123
monitoring for pollutants   and meteorologic factors.      These aspects

must concern any investigator who is  seriously considering a plant monitoring
                26
system.   Berry   developed clonal white pine material for use with specific
                                421
atmospheric pollutants.  Oshima      has recommended pinto bean as a

reliable monitor of oxidant intensity with a subjective injury evaluation (0-5)

that has been standardized against colored photographs.   This is not as

sensitive as a percentage separation,  but is no doubt easier for an untrained

observer to use.  He did show good correlation between weekly  oxidant

concentrations and plant response.  This a relatively simple system, but

the monitoring plant is not as sensitive to low concentrations of oxidant

of oxidant as is  Bel W  tobacco.
                     3
       The most  extensively used monitoring system for photochemical oxidants
                                          224
has used the ultrasensitive Bel W  tobacco.     The technique was first developed
                      213,220  3
by Heck and associates.         The response of this tobacco variety was

used to determine the distribution, frequency of occurrence, and approximate

average concentrations of photochemical oxidants in and around Cincinnati,

Ohio, over four growing seasons.  Monitoring sites were set up at various

distances from Cincinnati,  up to 75 miles  (120 km) due east.  Injury responses

from  this monitoring network showed  that the average effective  concentration

of photochemical oxidants was as high in rural Ohio as in Cincinnati.  Although

                                     11-158

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 oxidant concentrations did not correlate well with plant injury on a weekly

 basis, the seasonal ratio  of injury to oxidants was similar over a 3-year

 period.  It was suggested that all areas east of the Mississippi have suf-

 ficient photochemical oxidants to cause injury to sensitive plants at some

 stage of their development.   This  monitoring system has  since been used

 as part of a regional study to determine the importance of oxidant pollutants
                                                                262
 with respect to sensitive crops in  the northeastern United States,     and
                                                                     176
 similar systems have been used as oxidant indicators in South Dakota,
          285                      18
 Germany,     the United Kingdom,    and other locations--including North

 Carolina, Washington State,  and Arizona.  This type of monitoring system

 was designed to provide communities with estimates of the frequency of

 occurrence of phytotoxic concentrations of oxidants,  of the relative severity

 of each episode, and of the regional distribution of oxidant pollutants.   The

 system will not give a  reliable estimate of oxidant concentrations.   Thus,

 it is an indicator of oxidant phytotoxicity, instead of a monitor  for  oxidant

 concentrations.
                    96
       Craker et a_l.   used  Bel W  tobacco  as  a relatively simple monitoring
                                  3
device whereby interested citizens in a community could develop some idea

 of the biologic  severity of oxidant pollution in their community.  There are

problems with  their study, but the concept is useful and might alert a  com-

munity to potential pollution problems.

       Several investigators have  used systems ranging in complexity from
                                            578
 simple antioxidant-impregnated cloth covers     to fairly elaborate filtered
                        145,204, 228, 237
and unfiltered chambers                  to determine the effects of ambient

oxidants on sensitive indicator (monitoring) plants.   Bel W  tobacco was
                                                         3
used in all these tests.  Such tests can  be used  to determine growth and yield

reductions,  as  well as  to identify possible problems.

                                     11-159

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Discussion

       Many investigators have discussed the use of biologic indicators as

early detection systems for air pollution problems.   Some have viewed the

possibility of a nationwide monitoring system for air pollutants and other

environmental contaminants.   Others have felt that the increased collection

of chemical data at many sites obviates biologic indicators  or monitors.

However, the chemical and meteorologic  data do not yet give a clear picture

of the biotoxicity of air pollution episodes.  Thus, agencies  should give

serious consideration to the development  of national networks. If such

interest becomes widespread,  it should be possible to correlate the  biologic

response of the monitors with  the response of important economic species,

ornamental species,  or some human health measures.  Without the ability

to correlate these factors, bioindicators are merely another index of pollution

that carries no rational value.  Without the use of the bioindicator,  we are

back to a direct assessment of the effects of a  given pollution episode on

the biologic organisms of interest to man.


ECONOMIC ASSESSMENT

       This section will bring into focus our present understanding of the
                                                                       211
economic effects of oxidant air pollution on vegetation.   Heck and Brandt

presented in depth the problems inherent  in making an economic evaluation

of the response of pla.nts to air pollutants, including ozone and other oxidants.

 They used the distinction between injury  and damage that was proposed by
                 41
German workers.    Injury is defined as  any identifiable and measurable

response of a plant to air pollution;  damage is any measurable adverse

effect on the desired  or intended use of  the plant.  Thus,  before an effect


                                     11-160

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 on a plant can be evaluated in terms of economics, the plant must have

 been altered either quantitatively or qualitatively in such a way as to reduce

 its use value.  In this context, visible symptoms or transient changes  in

 physiologic responses may not result in an economic loss.  Thus, leaf necrosis

 in soybean is injury; to be classified as damage, the injury must affect yield.

 In the  same way, a severe  oxidant episode that bronzes the leaves of romaine

 lettuce may not affect biomass, but will affect use and may result in complete

 economic loss.  Ornamental plants,  whose major use value depends on

 appearance,  may be both injured and damaged.
                                        23
        Emergence tip burn of white pine   and  other physiogenic diseases of

 white pine associated with air pollution occur throughout the natural range of

 the species.   Insular stands containing ponderosa pine are frequently injured

 in the  Southwest.  The significance of these physiogenic diseases is not

 understood because they affect only sensitive genotypes.  The disease  occurs

 randomly in the forest, and its most obvious effect is the slow selection

 and gradual elimination of genotypes that may have otherwise superior

 silvicultural characteristics.  This could be a serious loss to future tree

 improvement efforts and may be occurring in other forest species.   Economic

 considerations have not been addressed in any reasonable way.

       Early work with sulfur dioxide showed a  linear relationship between

 visible injury and reduction in yield for many crop species.  The assessment

•was made that no reduction in yield would be found unless visible injury were

noted.   Definitive research with ozone, other  oxidants, or mixtures  of these

pollutants -with other gases  has not been done.  Thus, we do not know

whether such  relationships  between visible injury and yield hold  for the

oxidants,  but data in Table  11-3 suggest that for acute exposures there may

                                     11-161

-------
be good correlations between injury and yield reductions.  Many researchers

have hypothesized that the oxidants may have an effect on plants that will

produce a yield reduction with little or no visible injury.  Such studies need

to be designed in a more definitive manner before it is concluded that yield

reductions without visible  symptoms are clearly acceptable.  Projections of
                                                               19, 370
yield losses have made use of some of the data reported earlier.
               419,4ZO
       Oshima        has developed a methodology for evaluating and

reporting economic crop losses that involves continuous air monitoring,

chamber exposures,  and monitoring plant species.  He has attempted to weld

these into a comprehensive method of determining yield  reductions.  He

has reported yield reductions for some  species, but has not fully clarified

the procedure.  He presented no economic values  in either  report.  This

type of approach needs to be considered further.
                                                                       540,
       The reports of specific effects related to sensitive growth stages,
542, 543, 545
             especially to reproductive growth stages in which the pollutant
                                                            62, 63, 155
may be affecting reproductive structures and not leaf tissues,

are probably of greater importance  to the understanding of reduced yield

without visible symptoms than to the potential of a debilitating effect caused

by chronic continuous exposure to ozone or other oxidants.  These economic

considerations have not been addressed.

       Any attempt to assess oxidant damage to agricultural crops requires
                                                         294
judgment by a competent investigator.  Landau and Brandt     believe that

the success of crop surveys is directly related to  the number of subjective

decisions required in data collection.   The first surveys were conducted in
          366, 369
California         and were used, with a general  survey of conditions on the

East Coast, to develop some of the early economic estimates of $8-10 million

                                     11-162

-------
in California and $18 million on the East Coast.  These estimates were raised

to $500 million on the basis  of increased awareness of pollution effects and

increased recognition of additional sensitive  species.  However, all early

estimates -were  subjective, with no  substantial backup data.

       Since 1969, a number of states have instituted an intensive training

program for county agricultural agents and made detailed reports of crop
                  163, 292,295,370,399,429
injury and damage                           (Table 11-27).  The first such
                               295
report came from Pennsylvania     in 1969 and gave an estimate of a $9. 6

million loss to agronomic commodities from oxidant pollutants.  This survey

included direct and some indirect cost. Similar surveys have  been conducted
                399             163,429            370
in New England,     New Jersey,          California,     and Michigan (no

report is currently available).  These  surveys considered yield reductions

on the basis of injury and made no direct growth or yield assessments,
                                                                        432
although subjective estimates of damage were obtained.  Pell and Brennan

presented a well-developed thesis on the rationale for the difference  in

estimated losses to agriculture in New Jersey between 1971 and 1972.  They

discussed this in relation to the overall problem of assessing agricultural

losses.
                                     19
       A survey \vas  initiated in 1969   by Stanford Research  Institute

(SRI)  to develop  an empirical model for assessing damage to vegetation.

This program made use  of laboratory and field data from controlles

exposures on various crops and chemical data from simulated  reaction

chambers,  so estimates of ozone and other oxidants could be made on the

basis of concentrations of primary pollutants.  Hydrocarbon was chosen

as the basic pollutant from which to develop the model for prediction of

expected oxidant values and, therefore, effects on various crops.   From

                                     11-163

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                                                                 11-164

-------
 the oxidant value, injury and damage for specific crops were calculated for




 over 100  statistical reporting areas in the United States.   The report used




 many subjective assumptions and -was related primarily to visible injury




 symptoms.  The results were preliminary,  and the approach had many




 deficiencies; but similar approaches should be contemplated in the develop-




 ment of damage functions that will give some  reliable estimates  of economic




 losses.  On the basis of the SRI model, the  1969 estimated loss to  vegetation




 from oxidants in the United States was approximately $125 million.   Con-




 sidering the increase in crop values and assuming that oxidant concentrations




 have not been significantly  reduced during the last few years,  the loss in




 1974 from oxidants could approach $300 million, on the basis of  the SRI




 study.




       A  summary of estimates derived from various surveys and assessment




 techniques is shown in Table  11-27.  These values are suggestive at best.




 As with all values developed for agricultural losses,  these have  been directed




 at losses  to the producer—not to  the consumer.




       Whereas a reduction in production may actually increase  the  aggregate




 farm income and produce serious income distribution problems,  the consequent




 reduction in marketable surplus would cause a significant rise in the cost to




 consumers, because of the  inelastic consumer demand for most agricultural




 crops.  Therefore, at the consumer level,  losses based on farm prices  are




not appropriate and are likely to be conservative.  Because of percentage




markups and fixed •wholesale and  retail marketing costs, the cost to the




 consumer of agricultural losses could be twice as great as that observed




at the farm level--i. e. , a $300 million loss at the farm level in  1974 could




 represent a $600 million loss to the consumer.




                                     11-165

-------
SUMMARY




       Oxidant injury to vegetation was first identified in 1944 in the Los




Angeles basin.  Our understanding of oxidant effects and of the widespread




nature of their occurrence has increased steadily since then. Although the




major phytotoxic components of the oxidant (photochemical) complex are ozone




and peroxyacetylnitrate (PAN),  indirect data support the contention that other




phytotoxicants are present in the photochemical complex.  Ozone is considered




the most important phytotoxic component and was first identified as the specific




cause of weather fleck on tobacco and stipple on grape.  PAN is associated




with the undersurface glazing and bronzing associated  with many of the vegetable




crops.




       Plant response to oxidants (including ozone and PAN) is often divided




into  visible and subtle effects.  Visible effects  are identifiable pigmented,




chlorotic, and necrotic foliar patterns resulting from major physiologic




disturbances. Subtle  effects  produce no visible injury, but include metabolic




disturbances and may be measured on the basis of growth and long-term




biochemical changes.  These effects may influence plant populations and




communities and could have  an adverse influence on ecosystems.  Visible




injury may be acute or chronic.  Acute injury breaks down the cell membrane




and causes cell death, with leaf necrotic patterns that  may be characteristic




for a given oxidant,  but can be confused with other stress factors.  Classic




injury from ozone is  the upper-surface fleck on tobacco and  the stipple of




grape.  Many plants show an upper-surface bleach with no lower-surface




injury.  Bifacial necrotic spotting is common and may appear flecklike.




Classic injury from PAN appears as a glaze followed by bronzing of the




lower leaf surface in many plants.   Complete collapse of leaf tissue can




                                     11-166

-------
 occur,  if concentrations are high.  Chronic injury is associated with




 disruption of normal cellular activity followed by chlorosis or other color




 or pigment changes that may lead to cell death.  Chronic injury patterns




 are generally not characteristic and may be confused with symptoms caused




 by biotic diseases, insects, nutritional disorders, or other environmental




 stresses.  Early leaf senescence and abscission may result from chronic




 exposure.




        Leaf stomata are the principal entry sites for ozone and PAN.




 Stomata, when closed by any of a number of factors, will protect plants.




 Ozone and PAN may interfere with various oxidative reactions in plant cells.




 Membrane sulfhydryl groups and unsaturated  lipid components may be primary




 targets of oxidants.  Physiologic leaf age is an important consideration in




 the response of the leaf to oxidants.   Young leaf tissue is more sensitive




 to PAN, whereas newly expanding and maturing tissue  is most sensitive to




 ozone.  Light is  required before plant tissue will  respond to PAN, but not




 to ozone.   Oxidants affect  such physiologic processes as photosynthesis,




 respiration,  transpiration,  stomatal opening,  metabolic pools,  biochemical




 pathways,  and enzyme systems.  The acute response of plants to ozone and




 PAN may result  from a saturation of  sensitive cell sites and a disruption




 of normal cellular  repair mechanisms.  Chronic injury probably results




 from  secondary reactions  involving membrane injury.




        There is  evidence that  ozone is a radiomimetic  gas.  Ozone affects




 pollen germination in some species and thus may directly affect yield.  A study




with Arabidopsis thaliana suggested no mutagenic effects from ozone on this




 plant  over five generations.




                                     11-167

-------
       Ambient-oxidant studies in filtered versus nonfiltered field chambers




have reported up to 50% reduction in citrus yield (orange and lemon), a  10 -




15% reduction in grape yield in first year and 50 - 60% reductions over the




following 2 years, and a 5 - 29% reduction in yield of cotton lint and seed in




California.  Losses of 50% in some  sensitive potato, tobacco, and soybean




cultivars have been reported from the eastern United States.  It is apparent




that ambient oxidants do reduce yields of many sensitive plant cultivars.




Growth reductions associated with acute exposure to ozone are often associated




with injury; sometimes the correlations are high.  Even multiple exposures




and sometimes chronic exposures have shown fair to good correlation between




injury and growth (biomass) reductions.  The greater reductions in root




growth than in top growth reported in several species are related to solute




transport and may be fairly common under  some conditions.   Ozone affects




nodule number,  but not nodule size or efficiency in clover, soybean, and




pinto bean.  This causes a reduction in nitrogen fixation associated with legumes




and, if widespread, could have a major impact on plant communities and




affect fertilizer needs.   The effect on nodulation is related to carbohydrate




supply.  Yield reductions with little  injury after chronic exposure are known




for several crops.  Severe injury in tomato was required before a yield




reduction -was found.  Chronic exposures to ozone at 0. 05-0. 15 ppm for  4-6




h/day will produce yield reductions  in soybean and corn grown under field




conditions.  The threshold appears to be 0. 05-0. 10 ppm for some sensitive




cultivars and is well within values monitored in the eastern United States.




Growth or flowering effects, at chronic exposures to ozone at 0. 05-0. 15




ppm for  2-24 h/day are reported for carnation, geranium,  radish,  and pinto




bean grown in greenhouse  chambers.




                                    11-168

-------
        Plant sensitivity to ozone, PAN, and other oxidants is conditioned




 by many factors.   Genetic diversity between species and between cultivars




 •within a species is well documented.  The mechanism of genetic resistance




 is known for only one onion  cultivar and is related to  the effect of ozone




 on stomatal closure.  Variants within a natural species are well known for




 several pine species, including white, loblolly, and ponderosa.  Plant




 sensitivity to oxidants can be changed by both climatic and edaphic  factors.




 A change in environmental conditions will initiate a change in sensitivity at




 once, but it will be 3-5 days before  the response of the  plant is  completely




 changed.  Plants generally are more sensitive when grown under short




 photoperiods, medium light conditions, medium temperature, high humidity,




 and high soil moisture.  Injury to PAN may increase with increasing light




 intensity.  Conditions during exposure and growth affect the response of




 plants to oxidants in similar ways.   However,  plants exposed to ozone are




 more sensitive  to increasing light intensity and, in some cases, to decreasing




 temperature during the exposure period.  In general,  growth factors that




 tend to  cause a  physiologic hardening of plant tissue make the plants more




 tolerant to ozone.   At the  time of exposure, factors that increase water




 stress tend to make plants more tolerant to ozone.  Soil moisture is probably




 the most important environmental factor that affects response during the




 normal growing season.




        Plants respond in different ways to pollutant mixtures; less  than




 additive, additive,  and greater than  additive  effects have been reported.




Mixtures of ozone with sulfur dioxide and of nitrogen dioxide with sulfur




 dioxide  can cause  oxidant-like symptoms in some  sensitive plants.  Mixtures




 can cause effects below the threshold for either gas, although there is some




                                     11-169

-------
disagreement on this in regard to ozone.  Ratios of mixtures,  intermittent




exposures,  sequential exposures to pollutants, and predisposition by one




pollutant to the effects  of a second pollutant may all be important in nature,




but little research has  been done.




       The response of some plants to oxidants is conditioned by the




presence or absence of biotic pathogens.  Depending on the plant and the




pathogen, oxidants may cause more or less injury to a given species.




Pathogens may protect their host or make it more sensitive.   The pathogens




themselves may be injured or may be protected by the host plant.  This




subject is just starting to be understood.




       Oxidant injury to ponderosa pine predisposes the trees to later




invasion by pine bark beetles.   Ozone and ozone-sulfur dioxide mixtures




may decrease the population of soybean nematodes.  Both greater and smaller




effects have been noted -when herbicides have been used in  the presence  of




high oxidant concentrations.




       The two most critical factors in terms of air quality standards are




duration of  exposure and concentration.  These two factors determine the




exposure dose for a  plant.  In determining  the response of vegetation, con-




centration is more important than time.  A given dose presented to a plant




in a short period has a  greater  effect than the same dose applied over a longer




period.  This suggests  a threshold effect for plant populations and is probably




related to the repair mechanisms inherent  in biologic  systems.  Sufficient




information is not available from long-term chronic studies, but a threshold




between 0. 05 and 0.  10 ppm is probable for ozone (oxidant). For acute effects,




an overall threshold concentration with respect to time can be determined




from Figure 11-6  and Table ll-24a.   For  pinto bean (Table 11-22), this threshold




                                     11-170

-------
 for injury is about 0.03 ppm for 8 h and about  O.lOppm for  1 h.  This




 suggests  that oxidant standards may be needed for periods up to 8 h.




        Vegetation can act as a major sink for oxidants over time, but has a




 relatively minor effect on oxidant concentrations during episodes of high air




 pollution, is more effective at some seasons or under some cultural and




 management practices  than others, and should not be considered an important




 contributor to short-term reductions in oxidant or ozone concentrations.




        Plant protection from air pollution stress has involved three types of




 programs.  Several researchers are including pollutant stress  in standard




 breeding programs -with the aim of developing resistant cultivars. Our present




 concepts of pollution effects suggest that the gene pool of all species is  large




 enough to permit the development of more tolerant cultivars. Natural selection




 •will slowly do this for native vegetation.  If pollution concentrations go  no




 higher, this should be an effective protection device.  Interim measures




 involve the use of chemical sprays.  Such sprays are not yet economically




 feasible,  but several do give adequate protection against oxidants.  Fungicides,




 such as Benomyl, may serve a dual function.  Cultural and land use practices




may also  play important roles, especially on a short-term basis.




        Little  research on the effects of oxidants on nonvascular green plants




and microorganisms has been  reported.  Lichens and mosses are responsive




to acid  gases, but there is no definite evidence that they respond to oxidants.




Ferns may be especially sensitive, but their injury response is much different




from that of higher plants.   Growth and sporulation of fungi on surfaces




are usually, but not always, affected.  Ozone does not penetrate the leaf




tissue  or  the colony and thus does not cause death of colonies.   O^one from
                                     11-171

-------
0. 1 to several milligrams per liter of solution is required to kill many




microorganisms in liquid media.  Most work with microorganisms has




been done to study the effectiveness of ozone as a biocide i-n  the  storage of




vegetation or treatment of water or sewage supplies.




       Plants have been used as biologic indicators of oxidant pollutants




for many years.  Attempts have been made to use plants as monitors, but




too many unknown variables  are involved.  Plants may be capable of




monitoring the total biologic potential for adverse effects, but no research




has been developed along these lines.




       Losses based on farm prices are  not appropriate at the consumer




level and are likely to be conservative. Because of percentage markups and




fixed wholesale and retail marketing costs, the cost to the consumer from




agricultural  losses to oxidant pollutants could be as much as $600 million per




year.
                                     11-172

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 RECOMMENDATIONS

        These recommendations are not listed in a priority order, but

 many could be followed in parallel or simultaneously. In general,  the recom-
                                   219
 mendations presented by Heck et_ al.     are still germane to research

 needs in the subject of oxidant pollutants.

        A few definitive experimental  designs are needed to further our

 knowledge of acute dose-response information on ozone.   Much of this type

 of information is still needed for PAN and its analogues.  All experimental

 designs should incorporate dose response.

        Studies to develop dose-response curves  for chronic exposures of

 crop and native species over growing seasons and under field conditions

 are needed for ozone, PAN, and other oxidants.

        Research should be continued  with filtered and nonfiltered field

 chambers to study effects of ambient  oxidants on important agronomic,

 horticultural, and native  species.  We know that there is a problem, but

 its significance and magnitude are matters  of conjecture.

        There is a critical need to understand the interaction of multiple pol-

 lutants  on individual plant species and ecosystems.  Multiple-pollutant effects

 are generally important,  but little is  known of their effects on most plants.

 Variable concentrations,  ratios of pollutants, and age of plants all affect

 response.

       Models should be  developed  to understand the relative importance  of

 other variables as they affect plant dose  response.  These include,  but are

not limited to,  climatic,  edaphic, biotic,  and genetic factors.  Considerable
                                     11-173

-------
information is available, but there are many gaps, and no comprehensive




programs are in progress to determine how these factors act and interact




to affect a plant's response.




       The mechanism of response and the biochemical systems affected




are not understood. Although plant membranes are considered the primary




sites of action for the  oxidant pollutants, there is no definitive work on




this.  An understanding  of these responses would be supportive of breeding




and spray protective programs.




       Both breeding and spray protective programs need to be




developed, so that  better-yielding and better-quality cultivars  will be pro-




tected against oxidant  pollutants.




       Some effort is  needed to explore the feasibility of using plants to




monitor  the overall biologic activity (or biomass reductions) caused by




photochemical oxidants in specific air basins or  regions.  The response




of sensitive plants  should be correlated with the response of plants  of




economic and aesthetic importance.




       Additional monitoring of multiple pollutants is needed in rural areas.




       Whenever possible, measures that vary on a continuous scale (e.g. ,




biomass) should be used with subjective estimates of injury (e. g. ,  indexes




of visible injury).
                                     11-174

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                          APPENDIX TO CHAPTER 11

                INDEX OF PLANT NAMES AND REFERENCE NUMBERSa
ALFALFA  (Medicago sativa, L.) — 79,233,245,331,447,487,538,547,548

APPLE (Malus, sp.) — 371,489

APRICOT  (Prunus armeniaca, L.) — 272

Arabidopsis thaliana, L, Britt — 57

ARBORVITAE (Thuja orientalis, L.)

ASH, white (Fraxinus  americana, L.) — 264,272

ASPEN, quaking (Populus tremuloides, Michx.) — 194

AVOCADO  (Persea, sp.) — 512

AZALEA (Rhododendron, sp.) — 386

BARLEY (Hordeum vulgare, L.) — 22a,202,348,474,477

BEAN (Phaseolus vulgaris, L.) -- 7,22a,69-71,98,99,110,111,133,134,137,
                                 138,141,143,153,170,222,244,247,261,277-
                                 279,297,319,327,328,334,341,343,344,345,
                                 348,349,421,424,434,452,457,458,479,495,
                                 496,506,517,551,552,556,573,596

BEAN, lima (P.  limensis. Macf.)  — 547

BEET, table (Beta vulgaris, L.)— 60,369,412

BEGONIA,  Christmas (Begonia socotrana, Hook, f.)

BEGONIA  (Begonia, sp.) -- 214,297

BIRCH, white (Betula alba, L.) — 563

BROCCOLI (Brassica oleracea, L.) — 214,547

CABBAGE (B.  oleracea,  L.)  — 344,547

CARNATION (Dianthus caryophyllus, L.) — 156,157

CEDAR (Juniperus, sp.) — 373,507

Chenopodium album, L. — 194
                                  11-175

-------
                       APPENDIX TO CHAPTER 11  (Cont.)




                INDEX OF PLANT NAMES AND REFERENCE NUMBERS'2
Chenopodium fremontii, L. — 194




CELERY (Apium graveolens, Linn) — 170




CELOSEA (Celosea, sp.) — 5




CHARD, swiss (Beta vulgaris. L.) — 369,560




CHRYSANTHEMUM (Chrysanthemum, sp.) — 128,297,329,330,593




CITRUS (Citrus, sp.) — 520




CLOVER, red (Trifolium pratense, L.)	297




CLOVER, white (T. repens, L.) — 286,482




CLOVER, white sweet (Melilotus alba, Desr.) — 482




COLEUS (Coleus blumei, Benth.)




CORN  (Zea mays, L.) — 63,206,240-242,266,297,397,418,509,570




COTTON (Gossypium hirsutum, L.) — 53,201,458,531




CRESS (Lepidium sativum, L.) — 100




CUCUMBER (Cucumis sativus, L.) - 416




Descurainia, sp.     — 194




DUCKWEED (Lemna minor, L.) — 158




FIR, balsam (Abies balsamea (L.), Mill.)




FIR, Douglas (Pseudotsuga menziesii (Mirb.) Franco.)




FIR, white (Abies concolor (Gord.  &  Clend.) Lindl.)




GERANIUM (Geranium, sp.) — 156,336,337




GERANIUM,  wild (£. fremontii L. Torr. ex A. Gray) — 194




GLADIOLUS (Gladiolus, sp.) — 329,330




GRAPE (Vitis,  sp.) — 273,276,461,518,519,522
                                  11-176

-------
                       APPENDIX TO CHAPTER 11  (Cont.)




                 INDEX OF PLANT NAMES AND  REFERENCE  NUMBERS
GRAPEFRUIT  (Citrus, sp.) — 170




GRASS, annual blue  (Poa annua, L.) —  268,384,407




GRASS, bent  (Agrostis palustris, Huds.)




GRASS, Bermuda  (Cynodon dactylon, L.)




GRASS, brome  (Bromus tectorum) — 441




GRASS, brome  (B. inermis, Leyss) — 297




GRASS, Kentucky blue (Poa pratensis, L.)




GRASS, orchard  (Dactylis glomerata, L.)




GRASS, perennial rye (Lolium perenne,  L.)




GRASS, red fescue (Festuca rubra, L.)




GRASS, zoysia (Zoysia japonica, Steud.)




GUM, sweet (Liquidambar styraciflua) — 563




HEMLOCK, Eastern (Tsuga canadensis (L.), Carr.)




HOLLY, English  (Ilex, sp.)




IMPATIENS (Impatiens sullanii, Hook) — 5




LARCH, European (Larix decidua, Mill.)




LARCH, Japanese (L.  leptolepis (Sieb & Fucc.) Gord.)




LEMON (Citrus, sp.)  — 92,129,192,521




Lepidium virginicum, L.  — 47,194




LETTUCE (Lactuca sativa, L.) — 170,369,490,510




LOCUST, honey (Gleditsia triacanthos,  L.) — 127




Madia glomerata — 194




MAPLE, red (Acer rubrum, L.) — 563,564
                                  11-177

-------
                        APPENDIX TO CHAPTER 11 (Cont.)

                 INDEX TO PLANT NAMES AND REFERENCE NUMBERS
 MAPLE, silver (A. saccharinum, L.) -- 127,264

 MAPLE, sugar (A., saccharuim, Marsh) — 264,563

 MARIGOLD (Tagetes patula, L.) — 5

 MORNING GLORY (Ipomoea purpurea, Roth ) — 400

 MUSTARD (Brassica pekinensis)

 OAK, red (Quercus rubra, L.) — 127

 OAK, swamp (Q.  palustris, DuRoi) — 127

 OAK, white (Q.  alba) — 127,563
 OATS  (Arena sativa, L.) -- 62,64,186,195,297,477
 ONION (Allium cepa", L.) -- 141,142,416

 ORANGE (Citrus sinensis. Osbeck) — 92,192,521

PEACH (Prunus persica, Sieb. & Zucc.) — 463,490

 PEA, cream (Pisum sativum, L.) — 174

 PEANUT (Arachis hypogaea, L.) — 13,203

 PERIWINKLE (Vinca minor, L.) -- 297

 PETUNIA (Petunia hybrida, Vilm.) — 50,91,93,128,170,190,191,193,310,
                                     496,506,510,560,593

 PINE, Austrian (Pinus nigra, Arnold)

 PINE, eastern white (P. strobus, L.) — 16,23,26,28,40,82,86,113,124-
                                         126,248-250,313,315,590

 PINE, jack (P.  banksiana, Lamb.)

 PINE, Jeffrey (P. jeffreyi) — 373,507

 PINE, loblolly (JP. taeda, L.) — 27,582

 PINE, pitch (P.  rigida. Mill.)

 PINE, ponderosa (P. ponderosa, Laws) — 77,108,149-151,298,372,374,375,
                                         378-380,426,507,586,587

 PINE, red (P.  resinosa,Ait.) — 113
                                   11-178

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                        APPENDIX TO CHAPTER 11 (Cont.)

                 INDEX OF PLANT NAMES AND REFERENCE NUMBERS
 PINE, Scotch (P. sylvestris, L.) -- 122

 PINE, shortleaf (P. echinata, Mill.) — 27

 PINE, slash (P. caribaea,  Morelet) — 27

 PINE, sugar (P. lampertiana) — 373,507

 PINE, Virginia (P.  virginiana. Mill.) — 25,27,107

 POINSETTIA (Poinsettia pulcherrima, Willd.) — 93,214,310,339,342

 Polygonum aviculare, L. — 50,194

 POPLAR,  hybrid (Populas deltoides Earth, x P_._ trichocarpa (Torr. and Gray)
      265,287,290

 POPLAR,  yellow (Liriodendron tulipifera) ~ 264

 POTATO (Solanum tuberosum, L.) 42,49,221,247,310,346,416

 RADISH (Raphanus sativus,  L.) — 297,447,540,545,547

 RYE (Secale cereale, L.) -- 477

 SAFFLOWER (Carthamus tinctorius, L.)

SALVIA (Salvia splendens, Sello) — 5

 SMARTWEED (Polygonum lapathlfolium) — 22a

 SNAPDRAGON (Antirrhinum majus, L.)

 SORGHUM  (Sorghum vulgare,  Pers.)

 SOYBEAN  (Glycine max,  Merr.) — 34,105,171,201,205,253,271,358,450,458,
                                 536,538,543,544,548,581

 SPINACH  (Spinacea  oleracea, L.) — 72,174,297,369

 SPINACH  (Tetragonia expansa)

 SPRUCE,  black (Picea glauca var. densata Bailey)

 SPRUCE,  blue  (P. pungens,  Engelm.)
                                   11-179

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                        APPENDIX TO CHAPTER 11 (Cont.)

                 INDEX OF PLANT NAMES AND REFERENCE NUMBERS
 SPRUCE, Norway (P. abies (L.), Karst.)

 SPRUCE, white (P. glauca CMoench,) Voss.)

 SQUASH, summer (Curcurbita pepo, L.) — 297

 STRAWBERRY (Fragaria, sp.) — 463,490

 SULTANA (Impatiens sultani, Hook.)

 SUNFLOWER (Helianthus annus, L.) — 411

 SWEETGUM (Liquidambar styraciflua, L.) — 563

 SYCAMORE (Platanus occideutalis, L.) — 264

 TOBACCO (Nicotiana tabacum.L.) — 30,37,46,65,66,96,115-117,137,138,145,
                                   155,198,204,222,224-226,228,237,243,247 ,
                                   267,288,296,297,303,311,320,322-324,349,
                                   353,355-357,359,360,385,424,440,443,446,
                                   447,454,458,472,485-487,500-504,530,538,
                                   547,548,557,575,577

 TOBACCO (N.  glutinosa, L.)

 TOBACCO (N.  rustica)

 TOMATO (Lycopersicon esculentum, Mill.) — 75,76,177,240-242,289,297,335,
                                            349,402,418,423,454,458,498,506,
                                            510,547,560

TOMATO (L^ pimpinellifolium) — 177

 VETCH, broad bean (Vicia faba, Linn.) — 261

 VETCH, crown (Coronilla varia, L.)

 WHEAT (Triticum duram, Desf.) — 199,200,297,477,481
 References are in addition to those found in Table 11-24 for the same
  plants.  For complete references on a single species, check both the
  Appendix and Table 11-24.
                                    11-180

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 6.   Adedipe, N. 0., R. A.  Fletcher, and  D.  P.  Ormrod.   Ozone  lesions  in  rela-




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8.  Adedipe, N. 0., H. Khatamian, and D. P. Ormord.  Stomatal  regulation  of




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9.   Anderson, L. E. , T.-C. L. Ng., and K-E. Y. Park.  Inactivation of pea leaf




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                              11-181

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       Deleti  10





 11.   Anderson, W. C., and 0. C. Taylor.  Ozone induced carbon dioxide evolution




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 12.    Glossary o£ air pollution terms and selected reference list.  Phytopath.



            News  8(8),  1974.  (insert)



 13,   Applegate,  H. G., and L.  C. Durrant.  Synergistic action of  ozone-sulfur




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 14.   Barnes, R.  L.  Effects of chronic exposure to ozone on suluble  sugar  and




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15_    Barnes, R. L.  Effects of chronic exposure to ozone on photosynthesis and




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16.    Barnes, R. L., and C. R.  Berry.  Seasonal changes  in carbohydrates  and




           ascorbic acid of white pine and possible relation  to tipburn sensi-




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18.    Bell,  J.  N.  B.,  and R.  A.  Cox.   Atmospheric  ozone and plant  damage in the




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      Delete 20
                                11-182

-------
 21.    Bennett,  J.  H. ,  and A.  C.  Hill.   Interactions of air pollutants with cano-




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 23.   Berry,  C.  R.  White  Pine Emergence Tipburn,  a Physiogenic  Distrubance.




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 24.   Berry,  C.  R.   A plant fumigation chamber suitable for  forestry needs.




            Phytopathology 60:1613-1615,  1970.
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            ozone  and  sulfur dioxide.  Phytopathology   61'.231-232,  1971.





 26.    Berry,  C. R.  The differential sensitivity of eastern white pine to three




            types  of air pollution.   J.  Can.  Forest. Res.  3:543-547, 1973.




 27.    Berry,  C. R.  Age of pine seedlings with primary needles affects sensitiv-




            ity to ozone and sulfur  dioxide.   Phytopathology 64:207-209,  1974.
28.   Berry, C. R. , and H. E. Heggestad.  Air pollution detectives, pp. 142-146.




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           D. C.:   U. S. Government Printing Office, 1968.




29,   Berry,  C.  R.,  and L.  A. Ripperton.  Ozone,  as possible cause of white pine




           emergence tipburn.  Phytopathology 53:552-557,  1963.
                                11-183

-------
 30.    Bertinuson, T. A., H. LeCoultre, and W. C. Waterman.  The inhibitory  effect

             of zinc ethylene bisdithiocarbamate dust on weather fleck of Connecti-

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        Delete  31

 32.    Blattny,  C.,  and  J.  Break.   Die Bedrohung  der Futterpflanzen durch Smog

             und  Poa  annua als  Indikator dieser Schadquelle.   Wiss.  Z.  Karl-Marx-

             Univ.  11:111-113,  1962.
 33. ,  Blum, U.   North Carolina State University,  Raleigh,   Personal Communication.
            ,1976.
 34.    Blum,  U.,  and  D.  T.  Tingey.   Effects  of  soil-ozone complex on root  growth

             and nodulation.   Environ.  Qual.   (in press)   (UNVERIFIED)
 35.     Bobrov,  R.  A.   The  effect  of  smog  on  the  anatomy  of  oat  leaves.   Phytopath-

             ology  42:588-563,  1952.

 36.     Bobrov, R. A.  The anatomical effects of air pollution on plants, pp. 129-134.

             In Proceedings of the Second National Air Pollution Symposium, Pasadena,

             California, 1952.  Los Angeles:  National Air Pollution Symposium, 1952.

 37.    Bobrov, R. A,  The leaf structure of Poa annua with observations on its Smog

             sensitivity in Los Angeles County.  Amer. J.~Bot.  42:467-474, 1955.

 38.    Bobrov, R. A.  Cork formation  in table beet leaves (Beta vulgaris) in respons

             to smog, pp. 199-205.   In Proceedings of the Third National Air Pollution

             Symposium, Pasadena, California,  1955.  Los Angeles:  National Air Pollu-

             tion Symposium, 1955.

        Delete 39

40.     Botkin, D.  B., W. H, Smith, R. W.  Carlson, and T. L.  Smith.  Effects  of

             ozone  on white pine saplings:  Variation in  inhibition  and  recovery

             of net  photosynthesis.   Environ. Pollut. 3:273-289, 1972.
                                 11-184

-------
 41.    Brandt,  C.  S.,  and  U.  Holzel.   Problems  of the  Recognition and Evaluation




             of  the Effects of Gaseous  Air Impurities on Vegetation.   Technical




             Report A61-37.   Cincinnati:   U.  S.  Department  of Health,  Education,




             and Welfare,  1961.




 42.    Brasher,  E.  P., D.  J.  Fieldhouse,  and M. Sasser.  Ozone  injury in potato




            variety trials.   Plant Dis. Rep. 57:542-544, 1972.




       Delete 43"




 44.   Brennan,  E., and p.'  M.  Halisky.  Response of turfgrass cultivars to  Ozone  and




            sulfur  dioxide  in the  atmosphere.  Phytopathology  60:1544-1546,  1970.




 45.   Brennan,  E., and  I.  A. Leone.  The  response of plants to sulfur dioxide or




            ozone-polluted  air supplied at varying flow rates.  Phytopathology  58:




            1661-1664,  1968.




 46.    Brennan,  E., and I.  A. Leone.   Suppression of ozone toxicity symptoms in




            virus-infected  tobacco.  Phytopathology 59:263-264, 1969.




 47.    Brennan,  E., and I.  A. Leone.   The response of English holly selections




            to ozone and sulfur dioxide.   Holly Lett.  37:6-7, 1970.




 48.    Brennan,  E.,  and I. A.  Leone.  Chrysanthemum response  to  sulfur dioxide  and




            ozone.   Plant Dis. Rep.     56:85-87, 1972.



 49.    Brennan,  E., I.  A.  Leone, and  R. H. Daines.  The importance of variety in




            ozone plant  damage.   Plant  Dis. Rep. 48:923-924, 1964.




 50.    Brennan,  E.  G. , I. A.  Leone, and R.  H. Daines.   Atmospheric aldehydes  related




            to petunia leaf damage.  Science  143:818-820, 1964.




51.    Brennan,  E.,  I. A. Leone, and R. H.  Daines.   Characterization  of the plant




            damage  problem by  air  pollutants  in  New Jersey.   Plant Dis.  Rep.  51:




            850-854, 1957.
                                11-185

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52.    Brennan,  E.,  I.  A.  Leone,  and P4 M. Halisky.  Response  of  forage  legumes  to




            ozone  fumigations.  Phytopathology  59:1458-1459,  1969.




53.    Brewer, R. P., and  C. Ferry.  Effects of air pollution  on cotton  in the San




            Joaquin  Valley.  Calif. Agric.  28(6) '.6-7, 1974.




54.    Brewer, R. P., P. B. Guillemet, and R, K. Creveling.  Influence  of N-P-K




            fertilization on incidence and severity of oxidant injury to mangels  and




            spinach.  Soil Sci.  92:298-301,  1961.




      Delete 55





56.   Broadwater, to, T., R. C. Hoehn,  and P.  H. King.   Sensitivity of three selected




           bacterial species to ozone.  Appl. Microbiol.  26:391-393, 1973.




57.   Bruton, V. C.   Environmental Influence  on the Growth of Arabidopsis thaliana.



           Ph.D. Thesis.  Raleigh:  North Carolina State University, 1974.  iQ5 pp<




           pp.
58.   Burleson, G. R., T. M. Murray, and M. Pollard.  Inactivation  of viruses




           and bacteria by ozone, with and without sonication.  Appl. Microbiol.




           29:340-344, 1975.
59.   Butler,  W.  L.,  H.  W.  Siegelman,  and  C,  0.  Miller.   Denaturation of phytochrome.




           Biochemistry   3:851-857,  1964.



60.    Bystrom,  B.  G., R.  B.  Glater,  F.  M.  Scott,  and  E.  S.  C.  Bowler.  Leaf sur-




            face  of  Beta vulagris--electron microscope study.   Bot.  Gaz. 129:




            133-138,  1968.




      Delete 61




62.    Cameron,  J. W., and  0.  C.  Taylor.   Injury to  sweet corn  inbreds and hybrids




            by  air pollutants  in  the  field  and by  ozone  treatments  in the green-




            house.  J. Environ. Qual.  2:387-389,  1973.
                                11-186

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 63.    Cameron,  J.  W. ,  H.  Johnson,  Jr.,  0.  C.  Taylor,  and H.  W.  Otto.   Differen-




             tial susceptibility of  sweet corn  hybrids  to field  injury  by air




             pollution.   HortScience 5:217-219,  1970.   (UNVERIFIED)



 64.    Cantwell,  A. M.   Effect  of temperature  on response  of  plants  to  ozone as




             conducted in a specially designed  plant fumigation chamber.   Plant




             Dis.  Rep. 52:957-960, 1968.




 65.   Cantwell,  A. M.   Air Pollution in Delaware and Its  Effects on Plants




             Under Ambient and Controlled Environmental Conditions.  M.S.  Thesis.




             Newark:  University of Delaware, 1969.  86 pp.  (UNVERIFIED)



 66.   Carney, A. U.,  G. R.  Stephenson,  D. P. Ormrod,  and G. C.  Ashton.  Ozone-




            herbicide  interactions  in crop plants.   Weed Sci.  21:508-511, 1973.




 67.   Cathey, H. M. ,  and H.  E.  Heggestad.  Reduction of ozone damage to Petunia




            hybrida Vilm. by use of growth regulating chemicals and tolerant




            cultivars.  J.  Amer. Soc. Hort. Sci. 97:695-700,  1972.
 68.    Cathey, H. M., and H. E." Heggestad.  Effects of growth retardants and fumiga-




            tions with ozone and sulfur dioxide on growth and flowing of Euphorbia




            pulcherrima Willd.   J. Amer. Soc. Hort. Sci.  98:3-7, 1973.
69.   Chang, C. W.  Effect of ozone on  sulfhydryl groups of ribosotnes  in  pinto  bean.




           leaves.  Relationship with ribosome dissociation.  Biochem. Biophys.  Res.




           Commun.  44:1429-1435, 1971.




70.   Chang, C. W.   Effect  of ozone  on ribosomes  in pinto  bean  leaves.  Phyto-




           chemistry 10:2863-2868,  1971.



71.   Chang, C. W.   The  influence of ozone  on growth and ribosomal  RNA in pinto




           bean plants.  Phytochemistry 11:1347-1350,  1972.
72.    Chang, C. W.,  and H. E. Heggestad.  Effect of ozone on photosystem II in




            Spinacia oleracea chloroplasts.  Phytochemistry  13:871-873, 1974.
                                11-187

-------
 73.   Chow, C. K., and A. L. Tappel.  An enzymatic protective mechanism against




            lipid peroxidation damage to lungs of ozone-exposed rats.  Lipids




            7:518-524, 1972.





       Delete  74




 75.   Clayberg, C. D.  Screening tomatoes for ozone resistance.  HortScience   &•



           396-397, 1971.




 76.    Clayberg,  C. D.   Evaluation of tomato varieties for resistance of ozone.




            Connecticult  Agricultural Experiment Station Circular 246, 1972.



            11 pp.   (UNVERIFIED)



 77.   Cdbb, P." W., Jr.,  and R." W. Stark.   Decline and mortality of smog-injured




           ponderosa pine.  J.  Forest  68:147-149,  1970.
78.   Comeau, G.,  and F.  LeBlanc.   Influence de 1'ozone et de 1'anhydride sul-




           fureaux sur la regeneration des feuilles de Funaria hygrometrica




           HEDW.  Natural. Can. 98:347-358,  1971.
79.   National Research Council.  Committee on Medical  and  Biologic  Effects  of




           Environmental Pollutants.  Vapor-phase Organic Pollutants.  Volatile




           Hydrocarbons and Oxidation Products.  Washington, D. C.:  National




           Academy of Sciences, 1976.   (in press)   (UNVERIFIED)
80.   National Academy  of  Sciences.  Committee on Medical  and  Biologic  Effects




            of Environmental Pollutants.  Nitrogen Oxides.  Washington,  D.  C.:




            National Academy of Sciences, 1976.   (in press)   (UNVERIFIED)
      Delete 81
82.   Costonis, A. C.  Acute foliar injury of eastern white pine induced by sulfur




           dioxide and ozone.   Phytopathology  60:994-999, 1970.
                               11-188

-------
  83.    Costonis, A. C.  Injury to eastern white pine by sulfur dioxide and ozone




             alone and in mixture.  Eur. J. Forest.  Path. 3:50-55,  1973.
 84.   Costonis, A. C., and S.'M.' Linzon.  Methods for measuring photochemical air



            pollution in forest areas.  Mitt. Forst.  Bundes-Versuch.  92:57-70, 1971.
 85.   Costonis, A. C., and W. A. Sinclair.  Relationships of atmospheric ozone to




            needle blight to eastern white pine.  Phytopathology  59:1566-1574, 1969.
 86.   Costonis, A. C.,  artd W. A. Sinclair.  Susceptibility of healthy and ozone-




            injured needles of Pinus strobus to invasion by Lophodermium pinastri




            and Aureobasidium pullulans.  Eur. J. For. Path. 2:65-73, 1972.
 87.    Coulson, C., and R~ L. Heath.   Inhibition o£ the photosynthetic capacity of




            isolated chloroplasts by ozone.   Plant Physiol.   53:32-38, 1974.
       Delete  88
 89.    Craker,  I.  E.   Ethylene production from ozone injured plants.   Environ.




            Pollut.  1:299-304, 1971.




 90.    Craker,  L.  E.   Effects of mineral nutrients on ozone susceptibility of Lemna




            minor.   Can.  J.  Bot.  49:1411-1414,  1971.
91.   Craker, L.' E.  Decline and recovery of petunia flower development from ozone




           stress.  HortScience  7:484, 1972.




92.    Craker,  L.  E.   Influence of  ozone on RNA and  protein content  of Lemna minor 1.



            Environ.  Pollut.   3:319-323, 1972.



93.   Craker, L. E.,  and W. A. Feder.  Development of the inflorescence in petunia,



           geranium,  and poinsettia under ozone stress.   Hortscience  7:59-60,  1972.




94.     Craker, L, E., and J,' S.' Starbuck.  Metabolic changes associated with ozone



             injury of bean leaves.  Can. J7 Plant Sci.   52:589-597, 1972.
                                11-189

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       Delete 95





  96.   Craker, I.  E. ,  J.  1.  Berube,  and P.  B.  Fredrickson.   Community monitoring




            of air pollution with plants.   Atmos.  Environ.  8:845-853, 1974.





  97.   Curtis, C.  R.,  and R.  K.  Howell.  Increases in peroxidase isoenzyme activity




            in bean leaves exposed to low doses of ozone.   Phytopathology 61:1306-




            1307,  1971.



  98.  Curtis, L. R., L. V. Edgington,  and G. Hofstra.  Relationship  of ozone




           injury to time of application of carboxin analogues.  Phytopathology




           63:200, 1973.  (abstract)
99.   Curtis, L. R., L. V. Edgington, and D. J. LittleJohns.  Oxathin chemicals




           for control of bronzing of white beans.  Can. J. Plant Sci. 55:151-




           156, 1975.



100.   Czuba,  M. ,  and D.  P.  Ormrod.   Effects of cadmium concentration on ozone-




            induced phytotoxidity in  cress.   Plant Physiol.  Ann.  Suppl.  1974:31.




            (abstract)




101.  Daines, R. H.  Air pollution and plants  response, pp. 436-453.  In  J.  E.




           Gunckel,  Ed.  Current Topics in  Plant  Science.   New York:  Academic



           Press,  1969.




102.   Darley, E.  F., E.  R.  Stephens, J.  T.  Middleton,  and P.  L.  Hanst.   Oxidant




            plant  damage  from ozone-olefin reactions.   Int.  J. Air Pollut. 1:155-



            162,  1959.
103.   Oarley, E; F., W. M. Dugger, j; B," Mudd, L. Ordin, 0.  C. Taylor,  and  E.  R.-




            Stephens.  Plant damage by  pollution derived from automobiles.   Arch.



            Environ. Health  6:761-770, 1963.
                                11-190

-------
 104.    Darnall, K.  R. ,  and J. N. Pitts, Jr.  Peroxyacetyl nitrate.   A novel  reagent




              for oxidation of organic compounds.  Chem. Commun.  1970:1305-1306.
 105.    Dass,  H.  C.,  and 
-------
 116.    Dean,  C.  E.   Stomate density and  size as  related  to ozone-induced weather
             fleck in tobacco.   Crop  Sci.  12:547-548,  1972.
 117.    Dean,  C.  E.,  and  D.  R. Davis.   Ozone  and  soil moisture  in  relation to the
            occurrence of weather  fleck  on Florida cigar-wrapper  tobacco in 1966.
            Plant Dis. Rep.  51:72-75,  1967.
 118.   de Koning, H.  W.,  and Z.  Jegier.  Quantitative relation between ozone con-
            centration and reduction of photosynthesis  of Euglena gracilis.  Atmos,
            Environ.  2:615-616,  1968.
 119.   de Koning, H.  W.,  and Z.  Jegier.  A study of the effects of ozone and sul-
            fur dioxide on the photosynthesis and respiration of Euglena gracilis.
            Atmos. Environ.  2:321-326, 1968.
120.   de Koning,  H.,  and Z.  Jegier.   Effect of ozone on pyridine nucleotide
            reduction  and phosphorylation of Euglena gracilis.   Arch. Environ.
            Health 18:913-916,  1969.
121.   deRoning, H. W.,  and  Z.  Jegier.   Effects of sulfur dioxide and ozone on
            Euglena gracilis.   Atmos.  Environ.   4:357-361,  1970.
122.   Demeritt, M. E.,  Jr.,  W.  M.  Chang,  J.  D. Murphy,  and H.  D. Gerhold.  Sel-
            ection System for Evaluating Resistance of Scotch Pine Seedlings to
            Ozone  and  Sulfur Dioxide.   Center for Air Environment Studies.  Publ.
            243-72.  University Park:   Pennsylvania State University, 1972.  21
            pp.   (UNVERIFIED)
123.  Dethier, B. E., and D," W,"' Lecher.  Atmospheric pollution by oxidants  and  its
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 124.   Dochinger,  L.  S.   U.  S.  Forest  Service,  Delaware,  Ohio.   Personal Commun-
            ications .
                                11-192

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  125.   Dochinger, L, S,, and C. E, Seliskar.  Air pollution and the chlorotie dwar£
             disease of eastern white pine.  For. Sci.  16:46-55, 1970.
  126.   Dochinger,  1.  S.,  F.  W.  Bender,  F.  I.  Fox,  and W.  W.  Heck.   Chlorotic
             dwarf  of  eastern white pine caused  by  an ozone and  sulphur dioxide
             interaction.   Nature  225:476,  1970.
  127.   Drummond,  D,  B.   Influence of high concentrations  of peroxyacetylnitrate
             on woody  plants.  Phytopathology 61:128, 1971.  (abstract)
  128.  Drummond, D. B.   The Effect of Peroxyacetyl Nitrate on Petunia  (Petunia
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            University Park:   Pennsylvania State University, 1972.  70 pp.  (UNVER.)
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 129.   Dugger,  W. M.,  Jr.,  and  R.  I.  Palmer.   Carbohydrate metabolism in leaves
            of  rough  lemon  as influenced  by ozone,  pp.  711-715.   In H.  D.  Chapman,
            Ed.  Proceedings of the  First International Citrus  Symposium.   Held
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 130.  Dugger, W. M., and I. P. Ting.  The effect of peroxyacetyl nitrate on
           plants:  Photoreductive reactions and susceptibility of bean plants
           to PAN.  Phytopathology 58:1102-1107, 1968.
131.   Dugger, W.  M.,  and I.  P.  Ting.   Physiological and biochemical effect of air
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132.   Dugger, W. M., J. Koukol, and R.  L. Palmer.  Physiological  and biochemical
           effects of atmospheric oxidants on plants.  J. Air Pollut.  Control
           Assoc. 16:467-471,  1966.
                                11-193

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 133.    Dugger,  W.  M.,  Jr.,  0.  C.  Taylor,  E.  Cardiff,  and  C.  R.  Thompson.   Rela-




             tionship between  carbohydrate content  and susceptibility of pinto




             bean plants  to  ozone  damage.   Proc.  Amer.  Soc.  Hort.  Sci.  81:304-



             314, 1962.



 134.   Dugger, W. M., Jr., 0.  C. Taylor, W. H. Klein, and W. Shropshire, Jr.




            Action spectrum of peroxyacetyl nitrate damage to bean plants.




            Nature 198:75-76,  1963.




 135.   Dugger, W. M., Jr., 0.  C. Taylor,  E. Cardiff, and C. R.  Thompson.   Stoma-




             tal  action in plants as related to damage  from photochemical oxidants,




             Plant Physiol. 37:487-491,  1962.



 136.   Dugger, W. M. , Jr.,  0.  C. Taylor, C.  R.  Thompson,  and E.  Cardiff.  The




            effect  of light  on predisposing plants  to ozone  and  PAN damage.  J.




            Air  Pollut.  Control Assoc.  13:423-428,  1963.
137.   Dunning,  J.  A.,  and W.  W.  Heck.   Response of pinto bean and tobacco to




            ozone as conditioned  by light intensity and/or humidity.  Environ.




            Sci. Technol.  7:824-826,  1973.




138.   Dunning,  J.  A.,  and W.  W.  Heck.   Agricultural Research Service.  Raleigh,




           North Carolina.  Personal Communication, 1976.
139.  Dunning,  J. A., W. W. Heck, and D. T. Tirtgey.   Foliar  sensitivity  of pinto




           bean and  soybean to ozone as  affected by  temperature,  potassium nutri-




           tion and  ozone dose.  Water Air Soil Pollut. 3:305-313,  1974.




140.  Elford,  W.  J., and  J. van  den Ende.  An investigation  of the merits of




            ozone as  an  aerial disinfectant.   J.  Hyg. 42:240-265,  1942.




141.   Engle, R. 1.   Reaction  of  Onion,  Allium cepa I., and Pinto Bean, Phaseolus




            vulgaris  L., to Ozone.   Ph.D. Thesis.   Madison:  University of Wiscon-




            sin, 1966.  54 pp.
                                11-194

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 142.    Engle,  R.  L.,  and  W.  H.  Gabelman.   Inheritance  and  mechanism for resistance




             to ozone  damage  in  onion,  Allium cepa  L.    Proc.  Amer.  Soc.  Hort.  Sci.




             89:423-430, 1966.



 143.   Engle,  R. L., and W. H. Gabelman.  The effects of low  levels of ozone on




            pinto beans, Phaseolus vulgaris L.  Proc. Amer. Soc. Hort. Sci. 91:




            304-309, 1967.



 144.   Engle, R. L., W. H. Gabelman, and R. R. Romanowski.  Tipburn, an ozone




            incited response in onion, Allium cepa L.  Proc. Amer. Soc. Hort.




            Sci. 86:468-474,  1965.
145.   U. S. Environmental Protection Agency.  Technical Report.  Mount Storm,




            West Virginia--Gorman, Maryland, and Luke, Maryland--Keyser, West




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            gations.  Air Pollution Control Office Publ. No. APTD-0656.  Research




            Triangle Park, N.  C.:   U. S. Environmental Protection Agency, 1971.
      Delete  146
147.   Evans,  L.' S.   Bean leaf growth response to moderate ozone levels.   Environ.




            Pollut.   4:17-26,  1973.



148.   Evans, L. S.  Microscopic changes in, avena and Phaseolus from ozone expos-




            ure.  Preprint.  22 pp.   (UNVERIFIED)



149.   Evans, L. S., and P. R. Miller.  Ozone damage  to ponderosa pine:   A histo-




            logical and histochemical appraisal.  Amer. J. Bot.  59:297-304,  1972.




150.   Evans, L. S., and P. R. Miller.  Comparative needle anatomy  and relative




            ozone sensitivity of four pine  species.   Can. J. Bot. 50:1067-1076,




   	     1972.	      ^	__	^



151.   Evans,  I. S., and ?. R. Miller.  Histological comparison of single and




            additive 0., and SO  injuries to elongating ponderosa pine needles.




            Amer. J. Bot. 62:416-421, 1975.
                                11-195

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        Delete  152


153.    Evans,  I. S.,  and  I. P. Ting.  Ozone sensitivity  of  leaves:   Relationship


             to leaf water content, gas transfer resistance, and  anatomical char-


             acteristics.  Amer. J. Bot. 61:592-597,  1974.

                                                          6d
154.    Evans,  L. S. ,  and  I. P. Ting.  Effect of ozone on °  Rb-labeled potassium


             transport in  leaves of Phaseolus vulgaris L.  Atmos.  Environ.  8:855-


             861, 1974.
155.   Feder, W.' A.  Reduction in tobacco pollen germination and tube elongation,


            induced by low levels of ozone.   Science  160:1122,  1968.


156.   Feder, W. A.  Plant response to chronic exposure of low levels of oxidant


            type air pollution.  Environ. Pollut. 1:73-79, 1970.


157.   Feder, W. A,, and F.  J. Campbell.   Influence of low levels of ozone on


            flowering of carnations.  Phytopathology 58:1038-1039, 1968.
158.   Feder,  W.  A.,  and  F.  Sullivan.   Ozone:   Depression of frond multiplication


            and  floral  production  in duckweed.   Science  165:1373-1374,  1969.
159.   Feder,  W.  A.,  and  F.  Sullivan.   The effect  of  ambient  temperature on the


            sensitivity of  aquatic  green plants  to low  levels  of ozone.   Paper


            72-158 Presented at  65th Annual Meeting of  the  Air Pollution Control


            Association,  1972.   9 pp.   (UNVERIFIED)


      Delete  160


161.   Feder,  W.  A.,  J. Donoghue, and  I.  Perkins.   Response of poinsettia cultivars


            to ozone.  Florogram 5:13-14,  1972.   (UNVERIFIED)


162.   Feder,  W.  A.,  F. 1.  Fox,  W.  W.  Heck,  and  F.  J. Campbell.   Varietal responses


            of petunia to several air  pollutants.   Plant  Dis.  Rep.  53:506-509, 1969.
                                11-196

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  163.    Feliciano, A.  Survey and assessment of air pollution damage  to vegetation




             in New Jersey.  Cooperative Extension Service.  New Brunswick, N. J.:




             Rutgers, The State University, 1971.  43 pp.   (UNVERIFIED)




  164.   Ferry,  B. W., M.  S.  Baddeley,  and D. L. Hawksworth,  Eds.  Air  Pollution and




             Lichens.  Toronto:  University of Toronto Press,  1973.  389 pp.




  165.   Fetner,  R.  H., and  R.  S. Ingols.  A comparison  of the bactericidal activity




             of ozone and chlorine against  Escherichia  coli  at  1  .   J. Gen.  Micro-




             biol.  15:381-385,  1956.




 166.   Fletcher, R. A.,  N.  0. Adedipe, and D. P.  Ormrod.  Abscisic  acid protects




             bean leaves  from ozone-induced phytotoxicity.   Can.  J.  Bot. 50:2389-




             2391,  1972.
       Delete 167
 168.   Frederick, P. E., and R. 1. Heath.  Ozone-induced fatty acid and viability




            changes in Chlorella.  Plant Physiol. 55:15-19, 1975.





 169.   Freebairn, H. T., Reversal of  inhibitory effects  of ozone on  oxygen uptake




             of mitochondria.   Science 126:303-304,  1957.
170.   Freebairn, H. T.,  and 0. C. Taylor.  Prevention of plant damage from air-




            borne oxidizing agents.  Proc. Amer. Soc. Hort. Sci. 76:693-699, 1960.
171.   Frey,  J.  E.  The  Effects  of  Ozone  on  the  Synthesis  and Storage of Nutrients




            in Soybean Seeds.  Ph.D.  Thesis.   Greeley:   University of Northern




            Colorado, 1972.   109 pp.





       Delete 172






       Delete 173





174.   Fujiwara, T.  Damage to plants by  combined air pollution.   Shokubutsu




            Boeki  (Plant Protection)  27:233-236, 1973.   (in Japanese)
                                11-197

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 175.   Yamazoe,  F.   Plant-damaging air pollutants.   Shokubutsu Boeki  (Plant Pro-




             tection) 27:220-223,  1973.   (in Japanese)



 176.   Gardner,  W.  S.  'Ozone injury to tobacco plants in South Dakota.  Plant Dis.




             Rep. 57:106-110, 1973.




 177.   Gentile,  A.  G.,  ft. A, Feder, R." E.  Young, arid 2. Santner.  Susceptibility of"




             Lycopersicon spp. to ozone injury.  J.  Amer. Soc. Hort. Sci.  96:94-96,




             1971.



 178.   Glater, R. A. B.    Smog, damage to ferns in the Los Angeles  area.




            Phytopathology 46:696-698, 1956.



 179.   Glater, R. B. , R.  A.  Solberg, and F. M. Scott.   A developmental study of




            the  leaves of Nicotiana  glutinosa as related to their  smog-sensitivity.




            Amer. J. Bot. 49:954-970, 1962.
180.   Gross, R.  E. ,  and W.  M.  Dugger, Jr.  Responses of Chiamydomonas reinhardtii




            to peroxyacetyl  nitrate.  Environ. Res. 2:256-266, 1969.
181.   Grosso,  J.  J., H.  A.  Menser, G.  H. "Hodges, and H. H. McKinney.  Effects




            of air pollutants on Nicotiana cultivars and species used for virus




            studies.   Phytopathology 61:945-950, 1971.
182.   Guinvarc'h, P.  Three years  of  ozone  sterilization of water in Paris.  Adv.




           Chem.  Ser. 21:416-429,  1957.




183.   Haagen-Smit, A. J., E.  F.  Darley, M.  Zaitlin,  H.  Hull, and W.  Noble.




           Investigation on injury to plants  from air pollution in the Los




           Angeles area.  Plant  Physiol.  27:18-34,  1952.



184.   Haas, J.  H.  Relation of crop maturity  and  physiology to air pollution



           incited bronzing of Phaseolus  vulgaris.   Phytopathology 60:407-410,




           1970.
                                11-198

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 185.    Haines, R. B.  Effect of pure ozone on bacteria, pp. 30-31.   In  Report  of

             the Food Investigation Board  for the Year  1936.  London:  His Majesty's

             Stationary Office, 1937.   (UNVERIFIED)                          	
 186.    Hall, M.  A.,  and L.  Ordin.   Subcellualr location of phosphoglucomutase

             and  UDP glucose pyrophosphorylase in avena coleoptiles.  Physiol.

             Plant.  20:624-633,  1967.

        Delete 187
 188.   Hanson,  G. P.  Relative  air  pollution  sensitivity of  some  Los  Angeles

            Arboretum plants.   Lasca Leaves 22:86-89,  1972.
189.   Hanson, G. P., and W." S." Stewart.  Photochemical oxidantsi  Effect on starch

            hydrolysis in leaves.  Science  168:1223-1224, 1970.
                               •            ."                      •       I '////;"
190.   Hanson, G. P., L. Thorne, and D. H. Addis.  Ozone sensitivity of Petunia

            hybrida Vilm. as related to physiological age.  J. Amer. Soc. Hort.

            Sci. 100:188-190, 1975.

191.   Hanson, G. P., L. Thorne, and C. D. Jativa.  Ozone tolerance of petunia

            leaves as related to their ascorbic acid concentration, pp. 261-

            266.  In H. M. Englund and W. T. Beery, Eds.  Proceedings of the

            Second International Clean Air Congress.  Held  at Washington, D.  C. ,

            Dec. 6-11,  1970.  New York:  Academic Press, 1971.

192.   Harding,  P.  R.,  Jr.   Effect  of ozone on penicillium mold decay and sporu-

            lation.   Plant Dis.  Rep.  52:245-247, 1968.

193.   Harrison, B.  H., and W.  A.  Feder.   Ultrastructural changes in pollen

            exposed to ozone.  Phytopathology 64:257-258, 1974.
194.    Harward, M., and M. Treshow.   Impact  of  ozone  on  the  growth  and  reproduc-

            tion of understorey plants  in the aspen zone of  western U.S.A.

            Environ. Conserv. 2:17-23,  1975.
                                11-199

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 95.   Heagle,  A.  S.   Effect of low-level ozone fumigations on crown rust of oats.




            Phytopathology  60:252-254,  1970.




196.   Heagle, A. S.  Interactions between air pollutants and plant parasites.  Ann




            Rev. Phytopath.  11:365-388, 1973.



197.   Heagle,  A.  S.   Response  of  three  obligate  parasites  to ozone.   Environ.




            Pollut.  9:91-95,  1975.
198.   Heagle,  A.  S.,  and W.  W.  Heck.   Predisposition of tobacco to oxidant air




            pollution  injury  by  previous  exposure to oxidants.   Environ. Pollut.




            7:247-252,  1974.




199.  Heagle, A4  S., and L. W. Key.  Effect of ozone on the wheat  stem rust  fungus.




           Phytopathology  63:397-400, 1973.



200.  Heagle, A.  S.', and L. W. Key.  Effect of Puccinia graminis f. sp.  tritici on




           ozone  injury  in wheat.  Phytopathology   63:609-613,  1973.




201.  Heagle, A.  S., and G. E. Neely.   Agricultural Research Service.   Raleigh,




           North  Carolina.  Personal Communication. 1976.




202.   Heagle,  A.  S.,  and A.  Strickland.   Reaction of Erysiphe graminis f. sp.




            hordei to  low levels  of ozone.   Phytopathology 62:1144-1148, 1972.
203.   Heagle,  A.  S.,  and  L.  L.  Trent.    Agricultural  Research Service.   Raleigh,




            North  Carolina.   Personal Communication.  1976.








204.   Heagle,  A.  S. ,  D.  E.  Body, and W. W  Heck.  An open-top field chamber to




            assess the impact of air pollution on plants.  J. Environ. Qual. 2:




            365-368,  1973.




205.   Heagle,  A.  S.,  D.  E.  Body, and  G. E.  Neely.   Injury and yield responses




            of  soybean to  chronic doses of ozone and sulfur dioxide in the field.




            Phytopathology 64:132-136,  1974.
                                11-200

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 206.    Heagle, A.  S.,  D.  E.  Body,  and E.  K.  Pounds.   Effect of ozone on yield of




             sweet  corn.   Phytopathology 62:583-687,  1972.




 207.    Heagle, A.  S., W. W. Heck, and D.  Body.  Ozone injury  to plants  as  influ-




            enced  by air velocity during  exposure.  Phytopathology 61:1209-1212,



            1971.




 208.    Heck, W. W.  Plant  injury induced  by photochemical reaction products  of




            propylene-nitrogen dioxide mixtures.  J. Air Pollut. Control Assoc.




            14:255-261, 1964.





 209.   Heck, W.'W.    The use of plants as indicators of air pollution.  Int.  J.  Air




            Water Pollut.   10:99-111, 1966.




 210.   Heck, W. W.   Factors influencing expression of oxidant damage  to plants.




            Ann. Rev.  Phytopath. 6:165-188,  1968.




 211.   Heck, W. W., and C.  S.  Brandt.  Impact of air pollutants on vegetation:




            Crops,  forests, native,  pp.         In.  A.  C. Stern, Ed.  Air Pollu-




            tion.  (3rd ed.)   Vol.  2.  New York:  Academic Press, (in press)








 212.   Heck, W. W.,  and J.  A.  Dunning.   The effects  of  ozone on  tobacco  and pinto




            bean  as conditioned by several ecological  factors.   J. Air Pollut.




            Control Assoc.  17:112-114, 1967.




213.   Heck, W. W.,  and A.  S.  Heagle. Measurement of  photochemical  air  pollution




            with  a  sensitive monitoring  plant.   J.  Air  Pollut.  Control Assoc. 20:




            97-99,  1970.



214.   Heck, W. W., and D.  T.  Tingey.  Ozone.  Time-concentration model  to  predict




            acute foliar injury, pp.  249-255.  In  H. M. Englund  and W. T. Beery,




            Eds.  Proceedings  of the  Second International Clean  Air Congress.




            Held  at Washington, D. C., December  6-11, 1970.   New York:   Academic




            Press,  1971.







                                11-201

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215.  Heck, W. w., R. H. Dairies, and I. J. Hindawi.  Other phytotoxic pollutants,




           pp. F1-F24.  In J. S. Jacobson, and A.  C. Hill, Eds.  Recognition of Air




           Pollution Injury to Vegetation:  A Pictorial Atlas.  Pittsburgh:  Air




           Pollution Control Association, 1970.




216.  Heck, W. W., J. A. Dunning, and  I. J. Hindawi.  Interactions o£ environmental




           factors on the sensitivity  of plants to  air pollution.  J. Air Pollut.




           Contr. Assoc.  15:511-515,  1965.




217.  Heck, W. W. ,  J. A. Dunning, and I. J. Hindawi.  Ozone:  Non-linear relation




           of dose and injury in plants.  Science 151:577-578, 1966.





218.  Heck, W. W. , J. A. Dunning, and  H. Johnson.   Design of  a Simple Plant




           Exposure  Chamber.  National Air Pollution Control Administration Publ.




            No. APTD 68-6.   Cincinnati, Ohio:   U.  S. Department of Health,




            Education, and Welfare,  1968.  24 pp.





219.    Heck,  W.  W.,  0.  C. Taylor, and  H.  E.  Heggestad.   Air pollution research




            needs:   Herbaceous  and  ornamental plants and agriculturally generated




            pollutants.  J.  Air Pollut.  Control Assoc.  23:257-266,  1973.





220.   Heck, W. W.,  F.  L.  Fox,  C. S.  Brandt,  and  J.  A.  Dunning.  Tobacco,  a




            Sensitive Monitor for Photochemical Air Pollution.  National Air




            Pollution Control Administration Publ.  No.  AP-55.   Cincinnati:




            U. S. Department  of  Health, Education,  and  Welfare, 1969.  23  pp.



221.   Heggestad, H.  E.   Photochemical air pollution injury to potatoes in the




            Atlantic  coastal states.  Amer. Potato J. 50:315-328, 1973.




222.  Heggestad, H.  E., and  E.  F. Darley.  Plants  as indicators  of  the  air pollutants




           ozone and PAN, pp. 329-335.   In Air Pollution.   Proceedings  of the  First




           European  Congress on the  Influence of Air Pollution on Plants  and Animals.




           Wapeningen,  April 22 to  27,  1968.   Wageningen, The Netherlands:   Centre




           for Agricultural  Publishing and Documentation, 1969.
                                11-202

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223.   Heggestad,  H. E.,  and W. w.  Heck.  Nature,  extent,  and variation  of  plant




            response to air pollutants.  Adv. Agron. 23:111-145,  1971.




224.   Heggestad,  H. E.,  and H. A. Menser.  Leaf spot-sensitive tobacco  strain




            Bel W-3, a biological indicator of the air pollutant ozone.  Phyto-




           pathology 52:735,  1962.  (abstract)




225.  Heggestad, H. E., and J. T. Middleton.  Ozone in high concentrations as




           cause of tobacco leaf injury.  Science 129:208-210,  1959.




226.  Heggestad, H. E,,  F.  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 Water Pollut.  8:




           1-10, 1964.




227.  Hibben,  C. R.  The  distinction between injury to tree leaves by ozone and




           mesophyll-feeding  leafhoppers.   Forest  Sci.  15:154-157, 1969.
228. Hibben, C. R.  Plant injury by oxidant-type pollutants  in the New York  City




          atmosphere.  Plant Dis. Reptr.  53:544-548,  1969.
229. Hibben, C. R.  Ozone toxicity to sugar maple.  Phytopathology  59:1423-1428,




          1969.



230. Hibben, C.  R. ,  and  M.  P.  Taylor.   The leaf roll-necrosis disorder of




           lilacs:   Etiological role  of  urban-generated air pollutants.  J.




           Amer.  Soc .  Hort.  Sci.  99:508-514,  1974.
     Delete





232.  Hill, A. C.  A special purpose plant environmental chamber for air pollution




           studies.  J.  Air Pollut. Contr. Assoc.  17:743-748, 1967.




233. Hill, A." C,  Vegetation:  A sink for atmospheric pollutants.  J. Ait Pollut.




          Control Assoc.  21:341-346, 1971.
                               11-203

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 234.  Hill, A. C.,  and N. Littlefield.  Ozone.  Effect on apparent photosynthesis,




            rate of  transpiration,  and stomatal closure in plants.   Environ. Sci.



            Technol.  3:52-56,  1969.



 235.  Hill, A. C.,  H.  E.  Heggestad,  and S.  N.  Linzon.   Ozone,  pp.  B1-B22.   In




            J.  S.  Jacobson and A. C.  Hill,  Eds.  Recognition of Air Pollution




            Injury to Vegetation:   A  Pictorial  Atlas.   Pittsburgh:   Air Pollution




            Control  Association,  1970.




 236.  Hill, A. C.,  M. R. Pack, M.  Treshow, R. J. Downs, and L. G. Transtrum.  Plant




            injury induced by ozone.   Phytopathology  51:356-363, 1961.




 237.  Hindawi, I. J.   Natural pollutants  in Staten  Island,  New York and Perth




            Amboy, New  Jersey  as  reflected  on vegetation.   Paper Presented  at




            New York/New  Jersey Air Pollution Abatement  Conference  1968.  24 pp.









237a.  Hindawi, I. J.,  and A.  P.  Altshuller.  Plant  damage caused by irradiation




            of aldehydes.   Science  146:540-542, 1964.



 238.  Hindawi,  I. J. ,  J.  A. Dunning,  and C.  S.  Brandt.  Morphological  and  micro-




            scopical changes in tobacco, bean,  and petunia  leaves exposed to




            irradiated  automobile exhaust.   Phytopathology  55:27-30,  1964.
 239.  Hodges, G. H., H. A. Menser, Jr., and W. B. Ogden.  Susceptibility of




           Wisconsin havana tobacco cultivars to air pollutants.  Agron. J.




           63:107-111, 1971.




 240.   Hodgson,  R.  H.   Alteration of triazine metabolism by ozone, p. 28.  In




            Weed Science Society of American Abstracts 1970.




 241.  Hodgson,  R.  H., K. E. Dusbabek,  and B. L.  Hoffer.  Diphenamid  metabolism




            in tomato:  Time course  of  an ozone fumigation  effect.  Weed  Sci.  22:




            205-210, 1974.
                                11-204

-------
  242.  Hodgson,  R.  H,, D.' S.' Frear, H. R.  Swanson,  and L. A. Regan.  Alteration  of




           diphenamid metabolism  in  tomato  by  ozone.  Weed Sci.   21:542-548,  1973.




  243.  Hoffmann,  A.  R.   The  Effect of Ozone  on  Nicotine  Concentration  in Nicotiana




           tabacum L. Leaves.   Ph.D.  Thesis.   Philadelphia:   Temple University,




           1974.   88 pp.




  244.  Hoffman, G.'J,, E.'  V. Maas, and S.  L, Rawlins.  Salinity-ozone  interactive




           effects  on yield and water relations of pinto bean.  J.  Environ. Qual.




           2:148-152, 1973.




 245.  Hoffman,  G.  J. , E.  V. Maas,  and S.  L. Rawlins.    Salinity-ozone inter-




           active  effects on alfalfa yield  and water relations.   J. Environ.




  	     Qual. 4:326-331, 1975.



 246. Homan,  C.   Effects of ionized air  and  ozone on plants.   Plant Physiol.  12:



           957-978, 1937.



 247. Hooker, W. J., T.  C. Yang, and H.  S. Potter.  Air pollution injury of




           potato in Michigan.   Amer. Potato J. 50:151-161, 1973.




 248.  Houston, D. B.  Physiological and Genetic Response of Pinus strobus L.




           Clones to Sulfur Dioxide and Ozone Exposures.  Ph.D. Thesis.




           Madison:  University of Wisconsin,  1971.  85 pp.
249.  Houston,  D.  A.   Response  of  selected Pinus  strobus  L.  clones  to fumigations




          with sulfur dioxide  and ozone.   Can. J.  Forest Res.  4:65-68,  1974.




25°-  Houston,  D.  B.,  and  G.  R. Stairs.   Genetic  control  of  sulfur  dioxide and




          ozone tolerance in Eastern white pine.   Forest Sci  19:267-271,  1973.




251.  Houten,  J. G.  ten.   Aspects  of air pollution in agriculture.   Landbouwkundig




          Tijdschrift  78:2-13,  1966.   (in Dutch, summary in English)
                               11-205

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251a.  Howell,  R. K.  Influence of air pollution on quantitites of caffeie  acid




           isolated  from  leaves of Phaseolus vulgaris.  Phytopathology  60:  1626-




            1629, 1970.



 252. Howell, R. H.   Phenols,  ozone,  and their involvement in pigmentation and




           physiology of plant injury,  pp.  94-105.   In M.  Dugger, Ed.  Air Pol-




           lution Effects on Plant  Growth.   American Chemical Society Symposium




           Series 3.  Washington,  D.  C.:  American  Chemical Society, 1974. (UNVER.)




 253. Howell, R. K., and E.  J. Koch.   An experimental design for open-top field




           chambers to estimate crop  losses caused  by air pollution.   (in press)










 254. Howell, R. K., and D.  F. Kremer.  Ozone injury to soybean  cotyledonary




           leaves.   J. Environ. Qual. 1:94-97, 1972.




 255.  Howell,  R. K.,  and D.  P. Kremer.   Chemistry  and  physiology of pigmentation




            in  leaves  injued by air pollution.  J.  Environ.  Qual. 2:434-438,  1973.




 256. Howell, R. K., and C.  A. Thomas.  Relative tolerances of twelve  safflower




           cultivars to ozone.  Plant Dis.  Rep.    56:195-197, 1972.



 257.  Howell,  R. K., T.  E.  Devine, and  C.  H.  Hanson.   Resistance of selected




            alfalfa  strains  to ozone.  Crop. Sci. 11:114-115,  1971.




       Delete 25S





 259. Hull, H.  M.,  and F. W. Went.   Life processes  of plants as affected by air




           pollution, pp. 122-218.   In Proceedings  of the Second National Air




           Pollution Symposium, Pasadena, California, 1962.  Los Angeles:  National




           Air Pollution Symposium,  1952.





       Delete 260




 261.   Jacobson,  J.  S.,  and  S.  Colavito.  The  effect  of SCL  on the phytotoxicity




            of  Cy   Plant  Physiol. Ann.  Suppl.  1974:31.   (abstract)
                                11-206

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 262.  Jacobson, J. S., and W, A. Feder.  A Regional Network for Environmental




            Monitoring:  Atmospheric Oxidant Concentrations and Foliar Injury -to




            Tobacco Indicator Plants in the Eastern United States.  Massachusetts




            Agricultural Experiment Station Bulletin No. 604.  Amherst:  Univer-




            sity of Massachusetts, College of Food and Natural Resources, 1974.




            31 pp.



       Delete  263




 264.  Jensen,  K. F.   Response of nine  forest  tree species  to chronic  ozone  fum-




            igation.   Plant  Dis.  Rep. 57:914-917,  1973.
 265.  Jensen, K. F\, and" L." S. Dochirtger.  Responses 6f hybrid poplar cuttings to




           chronic and acute levels of ozone.  Environ. Pollut.  6:289-295, 1974.
 266.' Johnson, H., Jr., J. W. Cameron, and 0. C. Taylor.  Air pollution resis-




           tance in sweet corn varieties.  Calif. Agric. 25(5):8-10, 1971.
 267.  Jones,  J.  L.   Ozone damage:   Protection for plants.  Science 140:1317-




           1318,  1963.
268.  Juhren, M.,  W. Noble, and F. W. Went.  The standardization of Poa annua as




           an indicator of smog concentrations.  I.  Effects of temperature,




           photoperiod, and light intensity during growth of the test plants.




           Plant Physiol. 32:576-586, 1957.
269. Kadota, M. , and K. Ohta.  Ozone sensitivity of Japanese plant  species  in




           summer, with special reference  to  a tentative  sensitivity grade  list  for




           applying to field survey on ozone  injury.  Taiki Osen Kenkyu  (J.  Jap.




           Soc.  Air Pollut.) 7:19-26, 1972.   (in Japanese, summary in English)




270. Kanoh,  F.   Ozone reaction on slime mold.  Tokyo Toritsu Eisei  Kenyssho




           Kenkyu Nempo 24:337-342, 1972.   (in Japanese)   (UNVERIFIED)







                               11-207

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271.   Keen, N.  T.,  and 0.  C.  Taylor.   Ozone injury in soybeans:   Isoflavonoid




            accumulation is related to necrosis.   Plant Physiol.  55:731-733, 1975.




272.  Keller, T.  The  use  of peroxidase activity  for monitoring  and mapping air




            pollution areas.  Eur.  J.  Forest Path. 4:11-19,  1974.
273.  Render, W. J., and S. G. Carpenter.  Susceptibility of grape cultivars and



           selections to oxidant injury.  Fruit Var. J.  28:59-61, 1974.
      Delete 274




      Delete
276. Render, w. j., E. F»" Taschenberg, and N. Jk Shaulis.  Benomyl protection of



          grapevines from air pollution injury. HortScience   8:396-398, 1973.
277. Kendrick, J.' B.5 Jr., E. F/ Darley, and J." Tf Middleton.  Chemotherapy  for




          oxidant and ozone induced plant damage.  Int. J. Air Water Pollut.   6:




          391-402, 1962.
278.  Kendrick,  J.  B.,  Jr.,  J.  T. Middleton,  and  E.  F.  Darley.   Chemical protec-




           tion  of  plants  from  ozonated  olefin  (smog)  injury.   Phytopathology




           44:494-495,  1954.   (abstract)
279. Rerr, E. D., and R. A. Reinert.  The response of bean to ozone as related to




          infection by Pseudomonas phaseolicola.  Phytopathology  58:1055,  1968.




          (abstract)
280.  Rhatamian, H.,  N. 0." Adedipe, and D,"  ?.  Ormrod.   Soil-plant-water aspects of



           ozone phytotoxicity in tomato plants.   Plant Soil  38:531-541, 1973.
281. Kinman, R. N.  Uater and wastewater disinfection with ozone:  A critical




          review.  CRC Crit. Rev. Environ. Control 5:141-152, 1975.




     Delete 282





     Delete 283
                              11-208

-------
 284. Klingaman, G. I., and C. B.  Link.  Reduction air pollution injury to foli-




           age of Chrysanthemum morifolium Ramata using tolerant cultivars and




           chemical protectants.  J. Amer. Soc. Hort. Sci. 100:173-175, 1975.
 285.  Knabe,  W.,  C.  S.  Brandt,  H.  van Haut,  and  C.  J.  Brandt.   Nachwech photochem-




            ischer Luftverunreiniqungen dutch biologische Indikatoren in der Bundes-




            republik  Deutschland,  pp.  A110-A114.   In Proceedings of the Third




            International  Clean  Air Congress.  Held  at  Dusseldorf,  Federal Repub-




            lic  of Germany,  October 8-12,  1973.   Dusseldorf:  Verlag des Vereins




            Deutscher Ingenieur,  1973.




285a.  Knight, R.  C., and  J.  H.'  Priestley.  The respiration of  plants under various




            electrical conditions.   Ann.  Bot.  28:135-161,  1914.




 286.  Kochlar,  M. Phytotoxic and Competitive Effects  of Tall  Fescue on Ladino




            Clover as Modified by Ozone and/or Rhizoctonia solani.   Ph.D. Thesis.




            Raleigh:   North Carolina State University,  1974.  71 pp. (UNVERIFIED)
 287.   Kohut,  R.  J.   Response of Hybrid Poplar to Simultaneous Exposure to Ozone




            and PAN.   Center for Air Environment Studies Publ. #288-72.  Univer-




            sity Park:   Pennsylvania State University,  1972.   26 pp. (UNVERIFIED)
 288.  Koiwai, A., H. Kitano, M. Fukuda, and T. Kisaki.  Methylenedioxyphenyl  and




           its related compounds as protectants against ozone injury  to plants.




           Agric. Biol. Chem. 38:301-307, 1974.
 289.  Koritz, H. G., and F. W. Went.  The physiological action of smog on plants.




           I.  Initial growth and transpiration studies.  Plant Physiol. 28:50-




           62, 1953.




 290.  Kress, I. W.  Response of Hybrid Poplar to Sequential Exposures of Ozone




           and PAN.  Center for Air Environment Studies,Publ. #259-272.  Univer-




           sity Park:  Pennsylvania State University, 1972.  39 pp.  (UNVERIFIED)
                                11-209

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        Delete  291




 292.    Kuss, F. R.  The Effect of Ozone on Fungus Sporulation.  M.S.  Thesis.




            Durham:  University of New Hampshire, 1950.  27 pp.  (UNVERIFIED)




 293.    Lacasse, N. I.  Assessment of Air Pollution Damage  to Vegetation  in Penn-




            sylvania.  Center for Air Environment Studies  Publ. #209-71.   Univer-




            sity Park:  Pennsylvania State University,  1971.  61 pp.  (UNVERIFIED)



 294.   Landau,  E.,  and  C."  S.  Brandt.  The use  of  surveys  to estimate  ait  pollution




            damage  to agriculture.  Environ. Res.  3:54-61, 1970.
295.  Lacasse, N. L., and T. C. Weidensaul.  A cooperative extension-based  system




           of assessing air pollution damage to vegetation:  Organization,  results,




           and recommendations for future surveys, pp. 132-136.  In H. M. Englund




           and W. T. Beery, Eds.  Proceedings of the Second International Clean




           Air Congress.  Held at Washington, D. C., December 6-11, 1970.   New




           York:  Academic Press, 1971.
296.   Larkin, R. C.  Reduction of Ozone Damage on Bean and Tobacco with Peroxi-




            dase Injections.  M. S. Thesis.  Newark:  University of Delaware,




            1973.  19 pp. (UNVERIFIED)
297.   Larsen, R.  I.,  and W.  W.  Heck.   An air quality data analysis system for




            interrelating effects,  standards, and needed source reductions--




            Part 3.   Vegetation Injury.  J.  Air Pollut. Control Assoc.  (in press)




            (UNVERIFIED)
298.  Ursh, R." N., P, R.~ Miller, and S»~ L." Wert.  Aerial photography to detect a



           evaluate air pollution damaged ponderosa pine.  J7 Air Pollut. Control




           Assoc.  20;289-292, 1970.




      Delete  299
                                11-210

-------
 300.  Lea, M. C.  On the influence of ozone and some other chemical agents on




            germination and vegetation.  Amer. J.  Sci. Arts. 37:373-376, 1864.




 301.  ledbetter,  M.  C.,  P.  W.  Zimmerman,  and  A. E.  Hitchcock.   The histopatholog-




            ical  effect  of ozone  on plant  foliage.   Contrib.  Boyce  Thompson Inst.




            20:275-282,  1959.



 302.  Lee,  T. T.   Sugar  content  and stomatal  width  as related  to ozone  injury in




            tobacco leaves.  Can. J.  Bot.  43:677-685,  1965.
 303.  Lee, T. T.  Chemical regulation of ozone susceptibility in Nicotiana tabacum.




           Can. J. Bot.  44:487-496, 1966.



 304.  Lee, T. T.  Inhibition of oxidative phosphorylation and respiration by




           ozone in tobacco mitochondria.  Plant Physiol. 42:691-696, 1967.
 305.  Leffler,  H.  R.,  and J.  H.  Cherry.   Destruction of enzymatic activities o£ corn




           and  soybean leaves exposed to ozone.   Can.  J.  Bot.   52:1233-1238, 1974.
 306.  Leh, F.,  and J.  B. Mudd.  Reaction of peroxyacetyl nitrate with cysteine,




           cystine, methionine, lipoic acid, papaj.n, and lysozyme.  Arch. Biochem.




           Biophys. 161:216-221, 1974.



 307.  Leh, F.,  and J.  B. Mudd.  Reaction of ozone with lysozyme, pp. 22-39.  In




           M. Dugger,  Ed.  Air Pollution Effects on Plant Growth.  ACS Symposium




           Series 3.  Washington,  D.  C.:   American Chemical Society, 1974. (UNVER.)
308.  Leone,  I.  A.,  and E.  Brennan.   Ozone toxicity in tomato as modified by phos-




           phorus nutrition.   Phytopathology  60:1521-1524,  1970.




      Delete  363




310.  Leone,  I.  A.,  and D.  Green.  A field evaluation of air pollution effects




           on petunia  and potato cultivars in New Jersey.  Plant Dis.  Rep.  58:



           683-687,  1974.
                               11-211

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 311.  Leone, I. A., E. Brennan, and R. H. Daines.  Effect of nitrogen nutrition




            on the response of tobacco to ozone in the atmosphere.  J. Air Pollut.




            Control  Assoc. 16:191-196, 1966.
       Delete
 313.   Linzon,  S.  N.   The  development  of  foliar  symptoms  and  the possible cause and




            origin of white  pine  needle blight.   Can.  J.  Bot   38:153-161, 1960.
 314.   Linzon,  S.  N.   Semimature-tissue Needle  Blight  of  Eastern White Pine and




            Local  Weather.   Ontario  Department  of  Forestry,  Research Laboratories




            Information  Report  O-X-1,  1965.   (UNVERIFIED)




 315.   Linzon,  S.  N.   Damage to Eastern white pine by  sulfur dioxide,  semi-mature-




            tissue needle blight, and  ozone.  J. Air Pollut. Control  Assoc.  16:




            140-144, 1966.




       Delete 316




 317.   Linzon,  S.  N.,  and A. C. Costonis.  Symptoms caused by photochemical  air




            pollution  injuries to forest trees.  Mitt. Forst. Bundes-Versuch.  92:



            71-82, 1971.
318.  Linzon, S. N., W. W. Heck, and F. D. H. Macdowall.  Effects of photochem-




           ical oxidants on vegetation, pp. 89-142.  In Photochemical Air Pollu-




           tion:  Formation, Transport and Effects.  NRC Associate Committee on




           Scientific Criteria for Environmental Quality.  Report No. 12. Publ.




           No. NRCC 14096.  Ottawa:  National Research Council of Canada, 1975.
319. Maas, E. V,, G. J. Hoffman, S. L. Rawlins, and G. Ogata.   Salinity-ozone




          interactions on pinto bean:  Integrated response  to ozone concentra-




          tion  and duration.  J. Environ. Qual. 2:400-404,  1973.



320. Macdowall,  F. D. H.  Predisposition  of  tobacco to ozone damage.   Can.  J.




          Plant Sci. 45:1-12, 1965.
                              11-212

-------
 321.   Macdowall,  F.  D.  H.   Stages  of ozone damage  to  respiration  of  tobacco  leaves.
            Can. J.  Bot.  43:419-427,  1965.
 322.   Macdowall, F. D. H.  Importance of soil in the absorption of ozone by a crop.
            Can. J.'  Soil Sci.  54:239-240,  1974.
 323.  Macdowall, F.  D.  H.,  and A. F, W.  Cole.   Threshold and synergistic damage to
           tobacco by ozone and sulfur dioxide.   Atmos.  Environ.   5:553-559,  1971.
 324.  Macdowall, F.  D. H., E.  I. Mukammal,  and A. F. W. Cole.  Direct correla-
            tion of air-polluting ozone and  tobacco weather  fleck.  Can.  J. Plant
            Sci. 44:410-417, 1964.
      Delete 325
 326.  MacKnight, M.  L.  The Effect  of Ozone on Stmatal  Aperture and Transpiration.
            M.S. Thesis.  Salt  Lake  City:  University of Utah, 1968.  80  pp.
327.  Magdycz, W. P.  The Effects of Concentration  and  Exposure Time  on  the
           Toxicity of Ozone to  the Spores of  Botrytis  cinerea.  M.S. Thesis.
           Waltham:  University  of Massashucetts, 1972.  39 pp.
328.  Magdycz, W.  P.,  and W. J.  Manning.  Botrytis cinerea protects broad bean
           against visible ozone injury.  Phytopathology 63:204,  1973. (abstract)
329.  Magie, R. 0.  Controlling gladiolus botrytis bud rot with ozone gas,  Proc.
           Flor.  State Hort. Soc. 73:373-375,  1960.
330.  Magie,  R. 0.   Botrytis disease control  on gladiolus,  carnations,  and chrysan-
           themums.  Proc. Fla.  State Hort.  Soc.   76:458-461,  1963.
331.  Mandl,  R. H.,  M.  C. O'Neill,  and  L. H.  Weinstein.   The effect of ozone on the
           phototoxicity of  sulfur  dioxide for alfalfa.   Plant Physiol.  Ann.  Suppl.
           1974:30.   (abstract)
332.  Mandle, R.  H., L.  H. Weinstein,  D. C. McCune, and M. Keveny.  A cylindrical,
           open-top chamber for the exposure of plants to air pollutants  in the
           field.  J.  Environ. Qual. 2:371-376, 1973.
                               11-213

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       Delete 333





 334.  Manning, W. J., and P. M. Vardaro.  Suppression of oxidant injury on beans by




           systemic fungicides.  Phytopathology  63:1415-1416, 1973.




 335.  Manning, W. J. , and P. M. Vardaro.  Ozone and Pyjrenochaeta lycopersici;




           Effects  on growth and development of tomato plants.  Phytopathology




           64:582,  1974.  (abstract)



 336.  Manning, W.  J., W.  A.  Feder,  and  I.  Perkins.   Ozone  injury increases infec-




           tion  of geranium  leaves  by Botrytis  cinerea.  Phytopathology 60:669-




           670,  1970.



 337.  Manning, W. J., W. A.  Feder,  and  I.  Perkins.   Ozone and infection o£ geranium




           flowers by Botrytis cinerea.  Phytopathology  60:1302, 1970.   (abstract)




 338.  Manning, W.  J., W.  A.  Feder,  and  I.  Perkins.   Sensitivity of spinach cul-




           tivars to ozone.   Plant  Dis. Rep.  56:832-833,  1972.
339.  Manning,  W.  J.,  W.  A.  Feder,  and  I.  Perkins.   Effects  of Botrytis and ozone




           on bracts  and  flowers  of poinsettia cultivars.   Plant Dis. Rep. 56:




           814-816,  1972.




340.  Manning,  W.  J.,  W.  A.  Feder,  and  I.  Perkins.   Response of poisettia culti-




           vars to several concentrations  of ozone.   Plant Dis. Rep. 57:774-775,




           1973.



341.  Manning, W.  J., W.  A. Feder,  and  P.  M. Vardaro.  Benomyl in soil and res-




           ponse of pinto bean plants to repeated exposures to a low level of




           ozone.   Phytopathology 63:1539-1540, 1973.



342.  Manning,  W.  J.,  W.  A.  Feder,  and  P.  M. Vardaro.  Reduction of chronic ozone




           injury  on poinsettia by  benomyl.   Can.  J. Plant Sci. 53:833-835, 1973.




343.  Manning, W.  J., W.  A. Feder,  and  P.  M. Vardaro.  Suppression of oxidant




           injury  by benomyl:   Effects  on yields of bean cultivars in the field.




           J. Environ. Qual. 3:1-3, 1974.
                               11-214

-------
  344.   Manning,  W.  J., W.  A.  Feder,  P. M.  Papia,  and  I.  Perkins.   Effect  of low




             levels  of ozone  on  growth  and  susceptibility of  cabbage  plants  to




             Fusarium oxysporum  F.  sp.  conglutinans.   Plant Dis. Rep. 55:47-49,  1971.




  345.  Manning, w. J4, W. A.  Feder, P.  M. Papia, and I, Perkins.  Influence of foliar-




            ozone injury on root development and root surface fungi of pinto bean




            plants.   Environ. Pollut.  1:305-312, 1971.




  346.  Manning, W. J4, W,  A,  Fedet, I.  Perkins,  and  M. Glickman.   Ozone injury  and




            infection  of  potato  leaves  by Botrytis cinerea.   Plant Dis. Rep.    53:




            691-693, 1969.



  347.  Mansfield, T. A.   The  Role of Stomata in Determining the Responses of




            Plants to  Air Pollutants.  Commentaries Plant Sci. 2:11-20, 1973.
 348.  Markowski,  A.,  and S.  Grzesiak.   Influence of sulfur dioxide and ozone on




            vegetation of bean and barley plants under different soil moisture




            conditions.   Bull. Acad.  Pol. Sci.  Ser.  Sci.  Biol. 22:875-887, 1975.




 349.  Matsushima,  J.  On composite harm to  plants by  sulfurous  acid  gas  and




            oxidant.   Sangyo  Kogai 7:218-224, 1971.   (in  Japanese)
 350.  McCarthy,  J.  J.,  and C.  H.  Smith.   A review of ozone and its application




            to domestic  wastewater treatment.  J. Amer. Water Works Assoc. 66:




            718-725, 1974.
350a.  McCarty,  R.  E.,  P.  R.  Pittman,  and  Y.  Tsuchiya.   Light-dependent inhibition




            of photophosphorylation by N-ethylmaleimide.   J.  Biol.  Chem.  247:3048-




            3051,  1972.




 351.  Mcllvenn,  W.  D. ,  R.  A.  Spotts,and D.  D.  Davis.   The influence of soil




            zinc  on nodulation,  mycorrhizae,  and ozone-sensitivity of pinto




            bean.   Phytopathology 65:645-647, 1975.
                                11-215

-------
351a.   Mellanby,  K.,  Ed.   (Issue devoted  to  effects  of pollutants  on plants.)




           Environ.  Pollut.  9(2)85:155, 1975.
      352.  Menser, H. A., Jr.  The Effects of Ozone and Controlled Environment  Factors




                on Four Varieties of Tobacco, Nicotiana tabacum L.  Ph.D. Thesis.




                College Park:  University of Maryland, 1963.  146 pp.



      353.  Menser, H. A.  Response of plants to air pollutants.  III.  A  relation




                between ascorbic acid levels and ozone susceptibility of  light-




                preconditioned tobacco plants.  Plant Physiol. 39:564-567,  1964.




      354.  Menser, H. A., Jr.  Response to ozone of five  flue-cured tobacco varieties.




                Tobacco 162:32-33, 1966.






                                    11-216

-------
 355.  Menser,  H.  A.,  Jr.   Effects of air pollution on tobacco cultivars grown




            in several states.   Tobacco 169:20-25,  1969.   (UNVERIFIED)




 356. Menser, H. A.,  and J. F. Chaplin.  Air pollution:  Effects  on  the phenol




           and alkaloid content of cured tobacco leaves.  Tobacco 169:73-74,




           1969.   (UNVERIFIED)




 357. Menser, H. A.,  and H. E. Heggestad.  Ozone and  sulfur dioxide  synergism:




           Injury to  tobacco plants.  Science 153:424-425, 1966.




 358. Menser, H. A.,  and G. H. Hodges.  Tolerance  to  ozone of  flue-cured tobacco




           cultivars  in field and fumigation chambers tests. Tobacco   169:




           19-22, 1969.  (UNVERIFIED)



 359. Menser,  H.  A.,  and  G.  H.  Hodges.   Effects  of  air pollutants  on burley




           tobacco  cultivars.   Agron.  J.  62:265-269,  1970.




 360.  Menser, H.  A.,  and 0. E.  Street.  Effects of air pollution, nitrogen levels,




           supplemental irrigation,  and plant spacing on weather  fleck and leaf




           losses of Maryland tobacco.  Tobacco 155:192-196,  1962.   (UNVERIFIED)
361.  Menser, H.  A., H. E.  Heggestad, and 0. E. Street.  Response of plants to




           air pollutants.   II.   Effects of ozone concentration and leaf matur-




           ity on injury to Nicotiana tabacum.  Phytopathology 53:1304-1308, 1963.
362. Menser,  H." A. ,  G>  H.' Hodges,  and  C.'  G." McRee.   Effects  of air pollution on




          Maryland  (Type  32)  tobacco.   J.  Environ.  Qual.   2:253-258,  1973.
363.  Menser,  H.  A.,  H.  E.  Heggestad,  0.  E.  Street,  and R.  N.  Jeffrey.   Response




           of  plants  to  air pollutants.   I.   Effects of ozone  on tobacco plants




           preconditioned by light  and temperature.   Plant  Physiol.  38:605-609,




           1963.



364.  Middleton,  J. T.   Response  of plants  to air pollution.   J.  Air Pollut.




           Control  Assoc.  6:7-9,  1956.
                               11-217

-------
365.  Middleton,  J.  T.   Photochemical air pollution damage to plants.  Ann. Rev.
           Plant  Physiol.  12:431-448, 1961.	
366.  Middleton,  J.  T. ,  and  A.  0. Paulus.  The  identification and  distribution
           of  air pollutants  through  plant response.  A.M.A.  Arch.  Ind.  Health
           14:526-532,  1956.
367.  Middleton,  J.'T,,  E. F." Darley, and  R." P.  Brewer.   Damage  to vegetation from
           polluted  atmospheres.  J7 Air Pollut.  Control  Assoc.  8:9-15,  1958.
368. Middleton,  J.  T. , J. B. Kendrick, Jr., and E. F. Darley.  Air-borne oxidants
           as plant-damaging  agents,  pp. 191-198.  In Proceedings of  the Third
           National  Air Pollution Symposium, Pasadena, California,  1955.  Los
           Angeles:   National Air Pollution Symposium, 1955.
369.  Middleton,  J.  T., J. B. Kendrick, Jr., and H. W. Schwalm.  Injury to
           herbaceous plants by smog or air pollution.  Plant Dis. Rep. 34:
           245-252,  1950.
370.  Millecan, A. A.  A Survey and Assessment of Air Pollution Damage to Califor-
           nia Vegetation in 1970.  Sacramento:  California Department of Agricul-
           ture, 1971.  (UNVERIFIED)
371.  Miller, P. M.,  and S. Rich.  Ozone damage on apples.  Plant Dis. Rep. 52:
           730-731, 1968.
372.  Miller, P.  R.   Relationship of Ozone to Suppression of Photosynthesis and
           the Cause of the Chlorotic Decline of Ponderosa Pine.  Ph.D. Thesis.
           Berkeley:  University of California,  1965.   129 pp.
373.  Miller,  P.  R.   Susceptibility to ozone of selected western conifers.
           Paper Presented at Second International Congress  on Plant Pathology,
           Minneapolis,  1973.  (abstract)   (UNVERIFIED)
374.  Miller,  P. R.,  and L. S. Evans.  Histopathology of oxidant injury and win-
           ter fleck injury on needles of Western pines.  Phytopathology 64:801-
           806, 1974.
                               11-218

-------
  375.    Miller, P. R.,  and A. A. Millecan.  Extent o£ oxidant air pollution damage  •




              to some pines and other conifers in California.  Plant Dis. Rep.  55:




              555-559, 1971.
         Delete  376




         Delete  377
 378.     Miller, P". R.,  F.'W. Cobb, Jr., and E. 2avarin.  Photochemical oxidant injury




              and bark beetle (Coleoptera:  Solytidae) infestation of ponderosa pine.




              IIlT  Effect of injury upon oleoresin composition, phloem carbohydrates,




              and phloem pH.   Hilgardia  39:135-140, 1968.
379.    Miller, P. R.,  J. R. Parmeter, Jr., B. H. Flick, and C. W. Martinez.  Ozone




             dosage response of ponderosa pine seedlings.  J. Air Pollut. Control




             Assoc. 19:435-438, 1969.



380.    Miller, P. R.,  J. R. Parmeter, 0. C. Taylor, and E. A. Cardiff.  Oaone




             injury to the foliage of Pinus ponderosa.  Phytopathology 53:1072-




             1976, 1963.




        Delete 381




382.    Miller, V. I.,  R. K. Howell, and B. E. Caldwell.  Relative sensitivity of




             soybean genotypes to ozone and sulfur dioxide.  J. Environ. Qual. 3:




             35-37, 1974.
383.    Mohr,  H.   Lectures on Photomorphogenesis.   New York:   Springer-Verlag,  1972.




             237  pp.
384.    Moyer, J.,  H. Cole, Jr., and N. L. Lacasse.  Reduction of ozone injury on Poa



             annua  by benomyl and thiophanate.   Plant Dis.  Reptr.   58:41-44, 1974.
385.     Moyer,  J.  W.,  and  S.  H.  Smith.   Oxidant injury reduction on tobacco induced




              by tobacco etch  virus  infection.   Environ.  Pollut.  9:103-106,  1975.
                                 11-219

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386.  Moyer, J. W. , H. Cole, Jr., and N. 1. Lacasse.  Suppression of naturally




           occurring oxidant injury on azalea plants by drench or foliar spray




           treatment with benzimidazole or oxathin compounds.  Plant. Dis. Rep.




           58:136-138, 1974.
387.  Mudd,  J.  B.   Enzyme inactivation by peroxyacetyl nitrate.   Arch.   Biochem.




          Biophys.   102:59-65,  1963.
388. Mudd, J. B.  Reaction of peroxyacetyl nitrate with glutathione.  J. Biol.




         Chem. 241:4077-4080, 1966.



389.  Mudd,  J.  B.,  and W.  M.  Dugger,  Jr.   The  oxidation of reduced pyridine




          nucleotides by  peroxyacyl  nitrates.   Arch.  Biochem.  Biophys.  102:




          52-58,  1963.




390.  Mudd,  J. B., and T.  E.  Kozlowski, Eds.  Responses of Plants to Air Pollut-




           ants.  New York:  Academic Press, 1975.  383 pp.  (UNVERIFIED)
391.  Mudd, J.  B.,  R.  Leavitt,  and W.  A.  Kersey.   Reaction of peroxyacetyl nitrate




           with sulfhydryl groups of proteins.   J. Biol. Chem. 241:4081-4085, 1966
392.  Mudd,  J.  B.,  F.  leh,  and  T.  T. McManus.   Reaction of  ozone with nicotinamide




           and  its  derivatives.  Arch.  Biochem.  Biophys.  161:408-419, 1974.




393.  Mudd, J.  B.,  T.  T.  McManus,  and A.  Ongun.  Inhibition of lipid metabolism




           in chloroplasts by ozone,  pp.  256-260.  In H. M. Englund  and W. T.




           Beery,  Eds.  Proceedings of the Second International Clean Air




           Congress.  Held at Washington, D.  C., December 6-11, 1970.  New




           York:   Academic Press,  1971.
394. Mudd, J. R., R. Leavitt, A. Ongun, and T. T. McManus.  Reaction of  ozone with




         amino  acids and proteins.  Atmos. Environ.  3:6'69-681,  1969.
                               11-220

-------
395.   Mudd, J.  B.,  T.  T.  McManus,  A.  Ongtm,  and T.  E.  McCullough.   Inhibition




            of glycolipid  biosynthesis in chloroplasts  by ozone and sulfhydryl




            reagents.   Plant Physiol.  48:335-339,  1971.








396.  Mukammal, E. 1.  Ozone as a cause of tobacco injury.  Agric. Meteorol.  2:




           145-165, 1965.                                                       	



397.  Mumford, R. A., H. Lipke, D. A. Laufer, and W. A.  Feder.  Ozone-induced




           changes in corn pollen.  Environ. Sci. Technol. 6:427-430,  1972.




398.  Naegele, H. A., Ed.  Air  Pollution  Damage  to Vegetation.   Advances  in  Chemis-




           try Series 122.  Washington, D. C.:   American  Chemical Society, 1973.




           137 pp.




399.  Naegele,  J.  A., W. A.  Feder,  and C.  J.  Brandt.   Assessment of Air Pollution




           Damage to Vegetation in New England:   July,  1971-July,  1972.  Final




           Report,  Suburban  Experiment Station,  University of Massachusetts,




           Amherst.   (Contract  No.  68-02-0084)




400.  Nakamura, H.,  and  S. Maisunaka.   Indicator plants  for air pollutants.   1.




           Susceptibility  of  morning  glory to photochemical oxidants:   Varietal




           difference and  effect  of environmental  factors.   Proc.  Crop Sci.  Soc.




           Jap. 43:517-522,  1974.  (in  Japanese,  summary  in  English)




401.  U. S. Department of Health, Education, and Welfare,  public Health Service.




           National Air Pollution Control Administration.  Effects  of  photochem-




           ical oxidants on vegetation and certain microorganisms,  pp. 6-1--6-23.




           In Air Quality Criteria for Photochemical Oxidants.  NAPCA  Publ. AP-63.




           Washington,  D.  C.:  U. S.  Government Printing Office, 1970.




402. Neil, L. J., D. P.'Ormrod, and G. Hofstra.  Ozone stimulation  of  tomato stem




           elongation.  HortScience  8:488-489,  1973.
                               11-221

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403.  Nicksic, S. W. ,  J.  Harkins,  and P.  K.  Mueller.   Some analyses for PAN and




           studies of  its structure.   Atmos. Environ.  1:11-18,  1967.




      Delete 404




405.  Nobel, P. S.,  and C.  T.  Wang.   Ozone increases  the permeability of isolated




           pea chloroplasts.   Arch.  Biochem. Biophys.  157:388-394, 1973.
406.  Noble,  W.  M.   The relation of plant damage to fuel composition.  Paper




           Presented at the Conference on Motor Vehicle Exhaust Emissions and




           Their Effects,  Dec.  5,  1961,  University of California,  Los Angeles,




           11 pp.




407.  Noble,  W.  M.,  and L.  A. Wright.   Air pollution with relation to agronomic




           crops:  II.   A bio-assay approach to the study of air pollution.




           Agron. J. 50:551-553, 1958.
408.  Noble,  W.  M. ,  W.  Peele,  L. Wright,  and  P.  P. Mader.   A Comparison of the




           Smog  Forming Properties  of  the Exhaust  Gases  from Two Types of Motor




           Fuels Using  Plants  as Indicators.  Los  Angeles  County Air Pollution




           Control District, 1958.  10  pp.



      Delete  409.




 410.   Nouchi, I., T. Odaira,  T. Sawada,  K. Oguchi,  and  T.  Komeiji.   Plant ozone




           injury symptoms.   Taiki Osen  Kenkyu   (J. Jap.  Soc. Air Pollut.)  8:




           113-119,  1973.   (in Japanese)





411.  Oertli, J.  J.   Effect  of salinity on susceptibility  of sunflower plants




           to smog.   Soil  Sci. 87:249-251,  1959.




412.  Ogata,  G. ,  and E.  V. Maas.  Interactive effects  of salinity and ozone on




           growth and yield  of garden  beet.   J.  Environ. Qual. 2:518-520,  1973.



413.  Ordin,  L.,  and B.  Propst.  Effect of photochemically produced  oxidants on




           growth of avena coleoptile  sections.  Plant Physiol.  36:326-330,  1961.
                               11-222

-------
  414.  Ordin, L.,  M. J.  Garber, and J.  I.  Kindinger.  Effect of 2,4-dichlorophen-
             oxyacetic acid on growth and on ^-glucan synthetases of peroxyacetyl
             nitrate pretreated Avena coleoptile sections.   Physiol.  Plant.  26:
             17-23,  1972.
  415. Ormrod, D. P., and N. 0. Adedipe.  Protecting horticultural plants from
            atmospheric pollutants:  A review.  HortScience  9:108-111,  1974.
  416. Ormrod, D. P., N. 0. Adedipe, and G. Hofstra.  Responses of cucumber,
            onion,  and potato  cultivars to  ozone.  Can. J. Plant  Sci. 51:283-
            288, 1971.
  417. Ormrod, D. P., N.  0.  Adedipe, and G.  Hofstra.   Ozone effects on growth of
            radish  plants  as influenced  by nitrogen and phosphorus nitrition and
            by temperature.   Plant Soil  39:437-439, 1973.
 418.  Oshima, R. J.  Effect of ozone on a commercial sweet corn variety.  Plant
            Dis.  Rep. 57:719-723,  1973.
 419.  Oshima,  R. J.   Development  of a System  for  Evaluating  and Reporting
            Economic Crop Losses Caused  by Air Pollution in California.   I.
            Quality  Study.   Sacramento:  California Department  of  Food and
	       Agriculture, 1973.
 420.  Oshima,  R. J.  Development  of a System  for  Evaluating  and  Reporting
            Economic Crop Losses Caused  by Air Pollution in California.   II.
            Yield Study.  Sacramento:  California  Department  of Food  and
            Agriculture,  1974.
 421. Oshima,  R.  J.   A viable system o£  biological indicators for monitoring air
           pollutants.  J.' Air Pollut.  Control Assoc.  24:576-578, 1974.
       Oshima,  R., 0.  C. Taylor, and E.  A. Cardiff,  severe air pollution episode
            in south coast basin.   Calif. Agric. 28(2):12-13, 1974.
                                11-223

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423.  Oshima, R.  J. ,  0.  C.  Taylor,  P.  K.  Braegelmann,  and  D. W.  Baldwin.   Effect




           of ozone  on a commercial variety of tomato.   J.  Environ.  Qual.  4:463-




           464,  1975.




424.  Otto,  H. W. , and R. H. Daines.  Plant injury by air pollutants:  Influ-




           ence of humidity on stomatal apertures and plant response to ozone.




           Science 163:1209-1210,  1969.




425.  Parmeter,  J. R., Jr.,  and P.  R.  Miller.   Studies relating to the cause of




           decline and death of Ponderosa pine in southern California.   Plant




           Dis.  Rep.  52:707-711,  1968.



426.  Parmeter, J. R., Jr., R. V.  Bega, and T. Neff.  A chlorotic decline of




           ponderosa pine in southern California.  Plant Dis. Rep,   46:269-273,




           1962.
427.  Peak, M. J.,  and W.  I.  Belser.  Some effects of the air pollutant, peroxy-




           acetyl  nitrate, upon deoxyribonucleic acid and upon nucleic acid bases,




           Atmos.  Environ. 3:385-397, 1969.
428.  Pearson,  R.  G. ,  D.  B.  Drummond, W.  D. Mcllveen,  and  S.  N.  Linzon.   PAN-




           type injury to tomato  crops  in southwestern Ontario.   Plant  Dis.




           Rep.  58:1105-1108,  1974.



429.  Pell, E. J.  1972  Survey and Assessment of Air Pollution Damage to Vegeta-




           tion in New Jersey.  EPA-R5-73-022.  New Brunswick:  Rutgers, The




           State University Department of Plant Biology, 1973.  44 pp.





      Delete 430
 431.  Pell.  E. L. ,  and E.  Brennan.  Changes  in  respiration,  photosynthesis,




            adenosine  5-triphosphate,  and  total  adenylate  content  of ozonated




            pinto  bean foliage  as they relate to symptom expression.   Plant




            Physiol. 51:378-381,  1973.
                                11-224

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432.   Pell, E.  J.,  and E.  Brennan.   Economic impact of air pollution on vegeta-
            tion in  New Jersey and an interpretation of its annual variability.
            Environ.  Pollut.  8:23-33,  1975.
433.   Pellissier, M.   Effect of Foliar and  Root Treatments of Benomyl in Reduc-
            ing  Ozone Injury to Pinto Bean and Cucumber.  M. S. Thesis.  Center
            for Air Environment Studies Publ. #213-71.  University Park:
            Pennsylvania State University, 1971.  29 pp.    (UNVERIFIED)
434.  Pellissier, M., N. I. Lacasse, and H. Cole, Jr.  Effectiveness  of benomyl
            and benomyl-folicote treatments in reducing ozone  injury to pinto
            beans. J. Air Pollut. Control Assoc. 22:722-725, 1972.
435.  Pellissier, M., N. L.'Lacasse,  C. D.  Ercegovich,  and H. Cole.  Jr.   Effects  6f
           hydrocarbon wax  emulsion sprays  in reducing  visible  ozone injury  to
           Phaseolus vulgaris  'Pinto  III1.  Plant Dis.  Reptr.   56:6-9,  1972.
436,  Penkett, S. A., F. J. Sandalls, and J. E. Lovelock.  Observations of per-
           oxyacetyl nitrate  (PAN) in air in southern England.  Atmos. Environ.
           9:139-140, 1975.
437.  Perchorowicz,  J.  T.,  and I.  P.  Ting.   Ozone  effects on plant cell permea-
           bility.   Amer.  J.  Bot.  61:787-793,  1974.
      Delete  438
      Delete 439
440.  Povilaitis, B.   Gene effects for tolerance to weather fleck in tobacco.
           Can. J. Genet. Cytol. 9:327-334, 1967.
441.  Price,  H.,  and M.  Treshow.  Effects  of  ozone  on  the  growth  and  reproduction
            of grasses, pp. 275-280.  In Proceedings of the International  Air
            Pollution Conference, Melbourne, Australia,  1970 or  1972.  (UNVERIFIED)
                                11-225

-------
 442.  Rabotnova, I. 1., V. S. Somov, T. S. Bobkova, I. V. Zlochevskaya, L. N.
            Chekunova, I. F. Knyazeva, and S. I. Belen'kiy.  The relationship
            between the toxic action of ozone on yeast and certain components  and
            medium pH.  Vestnik Moskovskogo Uniiver. Biol. Pochvored. 6(5):
            47-51, 1971.  (in Russian)
443.  Reinert, R. A.   Agricultural Research Service, Raleigh, N. C., Personal
           Communication, 1976.
      Delete 444
 445. Reinert, R. A.   Monitoring,  detecting,  and effects of air pollutants on
           horticultural crops.  Sensitivity of genera and species.  HortScience
           10:495-500, 1975.
 446. Reinert, R. A.,  and H. W. Spurr, Jr.   Differential effect of fungicides
           on ozone injury and brown spot disease of tobacco.  J. Environ.
           Qual. 1:450-452, 1972.
 447.  Reinert, R. A., A. S. Heagle, and W. W. Heck.  Plant response  to pollu-
            tant combinations, pp.  159-178.  In B. Mudd  and T.  E.  Kozlowski,  Eds.
            Responses of Plants to  Air Pollution.  New York:  Academic  Press,  _
            1975.  (UNVERIFIED)
 448.   Reinert,  R.  A.,  D.  T.  Tingey,  and  H.  B.  Carter.   Sensitivity to tomato
            cultivars to ozone.   J. Amer.  Soc.  Hort.  Sci.  97:149-151,  1972.
 449.  Reinert, R. A., D. T. Tingey, and H. B. Carter.  Ozone induced  foliar
           injury in lettuce and radish cultivars.  J. Amer. Soc. Hort.  Sci.
 _         97:711-714, 1972.
 450.  Reinert, R. A., D. T. Tingey, and C. E. Koons.   The early growth of soy-
           bean  as  influenced by ozone stress.   Agron. Abstr.  63:148, 1971.  (UNVER
                                11-226

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 451.  Reinert,  R. A., A. S. Heagle, J. R. Miller, and W. R.  Geckeler.   Field




           studies of air pollution injury to vegetation in  Cincinnati, Ohio.




           Plant Dis. Rep. 54:8-11, 1970.




 452. Rcsh,  H.  M.,  and  V.  C.  Runeckles,   Effects of  ozone  on bean rust  Uramyces




           phaseoli.  Can.  J.'Bot.   51:725-727,  1973.




 453. Rich, S.   Ozone damage to plants.  Ann. Rev. Phytopath. 2:253-266, 1964.





 454. Rich, S.,  and G, S, Taylor.   Antiozonants  to protect  plants  from  ozone




          damage.  Science 132:150-151,  1960.





 455. Rich,  S., and  H.  Tomlinson.   Effects of ozone  on conidiophores and conidia of




           Alternaria_ solani.   Phytopathology  58:444-446,  1968.





     Delete  456





 457. Rich,  S., and  N.  C.  Turner.   Importance of moisture  on stomatal behavior of




           plants  subjected  to ozone.   J.  Air Pollut.  Control Assoc.  22:718-721,




           1972.




 458. Rich, S.,  R. Ames, and J. W.  Zukel.  1,4-oxathin derivatives protect  plants




          against ozone.  Plant Dis. Rep,    58:162-164, 1974.




 459. Rich, S.,  G. S. Taylor,  and M. Tomlinson.  Crop damaging periods  of ambient



          ozone in Connecticut.  Plant Dis.  Rep.    53:960-973,  1969.




 460. Rich, S.,  P. E. Waggoner, and H. Tomlinson.  Ozone uptake by bean leaves.




          Science  169:79-80,  1970.



 461. Richards,  B. L., J. T. Middleton, and W. B. Hewitt.   Air pollution with




          relation to agronomic crops:  V.   Oxidant stipple  of grape.   Agron.




          J. 50:559-561, 1958.




462.  Richards, B.  L.,  Sr.,  0. C.  Taylor,  and G. F.  Edmunds, Jr.   Ozone needle




           mottle  of pines of southern California.   J. Air Pollut. Control Assoc.




           18:73-77,  1968.
                                 11-227

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463.  Ridley, J.  D.,  and E.  T.  Sims,  Jr.   Preliminary Investigations on the Use
           of Ozone  to Extend the Shelf-life and Maintain the Market Quality of
           Peaches and Strawberries.   South Carolina Agricultural Experiment
           Station Research  Series No.  70.   Clemson:   Clemson University, 1966.
           22 pp.

464.  Ripaldi, C. P., and E. Brennan.  Effect of ozone on phosphorous  levels  o£
           pinto bean stems  and  foliage.  Phytopathology 63:206,  1973.  (abstract)

465.  Roehm,  J. H. ,  J.  G.  Had'ley, and D.  B.  Merizel.   Aritidxidarits vs  lurig disease.
           Arch.  Intern.  Med. 128:88-93,  1971.
466.  Rogers, H. H.,  Jr.   Uptake  of Nitrogen Dioxide  by Selected  Plant  Species.

           Ph.D. Thesis.  Chapel Hill:  University of North  Carolina,  1975.
           140 pp.
467.  Rosen,  P. M.,  and  V. C. Runeckles.   Adaptation to  ozone.  Plant Physiol.
           Ann Suppl. 1974:31.   (abstract)
     Delete 468

469. Rufner, R., F. H. Witham, and H. Cole, Jr.  Ultrastructure  of  chloroplasts
          of Phaseolus vulgaris leaves treated with benomyl  and  ozone.   Phyto-
          pathology 65:345-349, 1975.
470. Runeckles, V. C.,  and  H. M.  Resh.   The assessment  o£  chronic  onzone injury
          to leaves by  reflectance spectr'ophotometry.   Atmos.  Environ.  9:447-
          452,  1975.
     Delete 471
472. Sand, S. A.  What  the  tobacco plant does to ozone.  Frontiers  Plant Sci.

          12(l):4-5,  8,  1959.

     Delete 473
                          11-228

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       Schuette, 1. R.  Response of the Primary Infection Process of Erysiphe




            graminis F. sp. hordei to Ozone.  Ph.D. Thesis.  Salt Lake City:




            University of Utah, 1971. 76 pp.




 475.   Scott,  D.  H.   Air Pollution Injury to Plant Live.   Washington,  D.  C.:




            National Landscape Association Guide,  1973.   12 pp.




 476.   Scott,  D.  B.  M.,  and E.  C,  Lesher.   Effect  of ozone on survival  and per-




            meability  of Escherichia  coli.   J.  Bacteriol.  85:567-576,  1963.




 477.   Sechler,  D.,  and  D.  R.  Davis.   Ozone toxicity in  small grain.   Plant  Dis.




            Rep.  48:919-922,  1964.





      Delete 478




 479.  Seem,  R.' C.,  M.  Cole, Jr., and  N.  L. Lacasse.  Suppression of ozone injury to




           Phaseolus vulgaris "Pinto  III1  with triarimol and its monochlorophenyl




           cyclohexyl  analogue.   Plant Dis. Rep.  56:386-390,  1972.





      Delete 480




 481.  Shannon, J. G., and C. 1. Mulchi.  Ozone damage to wheat  varieties  at




            anthesis.  Crop Sci. 14:335-337, 1974.




 482.  Sharma, G. K., and J. Butler.  Leaf  cuticular variations  in Trifolium




            repens L. as indicators of environmental pollution.  Environ.




           Pollut. 5:287-293, 1973.



483.  Shaulis, N. J., W. J. Kender, C. Pratt, and  W. A. Sinclair.  Evidence  for




            injury by ozone in New York vineyards.   HortScience  7:570-572,  1972.




484.  Shinohara, T. , Y.  Yamamoto,  and H. Kitano.  The relation  between ozone




           treatment and the injury in tobacco.  Proc. Crop  Sci. Soc. Jap.




           42:412-417, 1973.



485.  Shinohara, T., S. Kuroda, T. Kitamura, and K. Kunisawa.   Studies on weather




            fleck on tobacco leaves.  VI.   Effects  of temperature on the  fleck




            injury induced by air-borne oxidants.   Bull. Okayma  Tob. Exp.  Stat.




            33(Special #2):51-54, 1973.  (in Japanese, summary in English)






                                 11-229

-------
486.  Shinohara, T. , Y. Yamamoto, Y. Kitano, and M. Fukuda.  Effects of tempera-




           ture on ozone injury to tobacco.  Proc.  Crop Sci. Soc. Jap. 42:418-




           421, 1973.




487.  Shinohara, T., Y. Yamamoto, H. Kitano, and M. Fukuda.  Interactions  of




           light and ozone injury in tobacco.  Proc. Crop. Sci. Soc. Jap.  43:




           433-438,  1974.




488.   Sinclair, M. G.   The Effects  of Ozone on TVo Varieties of Tobacco Pollen




            and on the  Conidia of the Fungus Monilinia fructicola.  M.  S.  Thesis.




            Newark:  University of Delaware, 1969.   59 pp.




489.   Smock, R. M., and R. D. Watson.  Ozone in apple storage.   Refrig. Eng. 42:




            97-101,  1941.




490.  Spalding, D. H.   Appearance and Decay of Strawberries, Peaches,  and  Lettuce




           Treated with Ozone.  Marketing  Research Report  No.  756.   Agriculture




           Research  Service,  U. S. Department of Agriculture.  Washington,  D. C. :




           U.  S. Government Printing Office, 1966.  11 pp.





491.  Sparrow,  A.  H.,  and  I.  A.  Schairer.   Mutagenic  response  of tradescantia




            to  treatment with  X-rays,  EMS,  DBE,  ozone,  S02, NoO and several




            insecticides.   Amer.  Envir.  Mutagen  Soc.   26:445, 1974.




492.  Spotts,  R. A., F.  L. Lukezic,  and R.  H.  Hamilton.   The effect of benzimida-




            zole on some membrane  properties of  ozonated  pinto  bean.  Phytopath-




            ology 65:39-45, 1975.




493.   Spotts,  R.  A., F. L. Lukezic, and N. L.  Lacasse.  The effect of benzimida-




            zole,  cholestrol,  and a steroid inhibitor on leaf sterols and  ozone




            resistance  of bean.  Phytopathology 65:45-49, 1975.







                                11-230

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494.  Stark,  R.  W.,  P.  R.  Miller,  F.  W.  Cobb,  Jr.,  D.  I.  Wood,  and J.  R.  Parmeter,




           Jr.   Photochemical  oxidant injury  and  bark  beetle  (Coleoptera:




           Scolytidae)  infestation of Ponderosa pine.   I.   Incidence  of bark




           beetle  infestation  in  injured  trees.   Hilgardia  39:121-126,  1968.




495.  Starkey,  T.  D.   The  Influence of Peroxyacetyl Nitrate on  Bean (Phaseolus




           vulgaris  L)  Subjected  to Post-Exposure Water Stress.   Center for Air




           Environment  Studies Publ.  #400-75.   University Park:   Pennsylvania




           State University,  1975.  45 pp.   (UNVERIFIED)
496.  Stephens,  E.  R. ,  E.  F.  Darley,  0.  C.  Taylor,  and W.  E.  Scott.  Photochemical




           reaction products  in air pollution.   Int.  J. Air Water Pollut. 4:79-




           100,  1961.




497.  Stolzy,  L.  H. , 0.  C.  Taylor,  W.  M.  Dugger,  Jr.,  and  J.  D.  Mersereau.   Phys-




           iological changes  in and ozone susceptibility of the  tomato plant




           after  short  periods  of  inadequate  oxygen  diffusion to the roots.   Proc.




           Soil Sci. Soc. Amer.  28:305-308,  1964.




498.  Stolzy,  L.  H.,  0. C.  Taylor, J,  Letey,  and T.  E. Szuszkiewicz.  Influence of




           soil-oxygen diffusion rates on susceptibility of tomato plants to air-




           borne  oxidants.   Soil Sci.   91:151-155,  1961.



499. Swanson, E. S., W. W. Thomson, and  J. B. Mudd.   The  effect  of ozone on




           leaf cell membranes.  Can.  J.  Bot. 51:1213-1219, 1973.




500. Taylor,  G.  S.  Ozone  injury  on Bel  W-3  tobacco controlled  by at  least  two




           genes.  Phytopathology  58:1069,  1968.   (abstract)




501. Taylor,  G.  S.  Ozone  injury on tobacco  seedlings  can predict  susceptibility




           in  the field.  Phytopathology  64:1047-1048,  1974.



502. Taylor,  G.  S., and S, Rich.  Antiozonant-treated  cloth protects tobacco from




           fleck.   Science  135:928, 1962.
                               11-231

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503.    Taylor,  G.  S. ,  and  S.  Rich.   Ozone  injury  to  tobacc£«4ft- the field influ-
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504.   Taylor,  G.  S.,  H. G. DeRoo, and P.  E. Waggoner.  Moisture  and  fleck of
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506.   Taylor,  0.  C.   Importance of peroxyacetyl nitrate  (PAN) as  a phytotoxic  air
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507.   Oxidant Air Pollutant Effects on  a Western Coniferous Forest Ecosystem.
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       Delete 508
       Delete 509
510.   Taylor, 0. C., and D.  C. Maclean.  Nitrogen Oxides and the peroxyacyl rtitrati
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       Delete  511
512.   Taylor, 0. C., E. A. Cardiff, J. D. Mersereau, and J. T. Middleton.  Effect
            of air-borne reaction products of ozone and 1-N-hexene vapor  (synthetic
            smog) on growth of avocado seedlings.  Proc. Amer. Soc. Hort. Sci.
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513.   Taylor, 0. C., W. M. Dugger, Jr., E.  A. Cardiff, and E. F. Darley.   Inter-
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                                 11-232

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       Delete






 515.  Thomas, M.  D.   Effects of air pollution on plants,  pp. 233-278.  In Air




            Pollution.  World Health Organization Monograph Series No. 46.   New




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 516.  Thomas, M. D.  Photochemical Smog.  Air Quality Monograph #69-6.  New York:




            American Petroleum Institute, 1969.  40 pp.




 517.  Thomas, M.  D. ,  R.  H. Hendricks, and G.  R.  Hill.   Some impurities in the




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            (UNVERIFIED)




 518.  Thompson, C. R.  University  of  California, Riverside.  Personal  Communications,




519.  Thompson, C. R., and G. Kats.   Antioxidants reduce  grape  yield  reductions




           from photochemical smog.   Calif. Agric. 24(9):12-13, 1970.
520.   Thompson,  C.  R.,  and G.  Kats.   Effects of ambient concentrations of per-




            oxyacetyl nitrate on navel orange trees.   Environ. Sci. Technol. 9:




            35-38,  1975.




521.  Thompson,  C. R., and 0.  C. Taylor.  Effects  o£  air  pollutants  on growth  leaf




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            934-940,  1969.




522.   Thompson,  C.  R.,  E.  Hensel,  and G.  Katz.   Effects of photochemical air




            pollutants  on Zinfandel grapes.   HortScience 4:222-224, 1969. (UNVER.)




       Delete  523




524.  Thomson, W. W., W. M.  Dugger, Jr.,  and R.  L. Palmer.   Effects  of ozone on the



            fine  structure  of the palisade parenchyma  cells  of bean leaves.   Can.  J.




            Bot.  44:1677-1682,  1966.



525.   Thomson,  W. W., ft. M. Dugger,  Jr., and R.' L. Palmer.   Effects of peroxyacetyl




            nitrate  on ultrastructure of chloroplasts.  Bot.  Gaz.   126:66-72,  1965.
                                11-233

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       Delete 526





 527.  Thorne,  L.,  and  G.'P.  Hanson.   species  differences  in  rates  o£ vegetal 6z6ne




            absorption.   Environ.  Pollut.   3:303-312,  1972.



 528.  Teige, B., T. T. McManus, and J. 8. Mudd.  Reaction of ozone with phosphathyi-




            cholinc kiposomes and  the  lytic effect of products on red  blood cells.




            Chem. Phys. Lipids 12:153-171, 1974.



 529.  Ting, I. P., and W. M. Dugger,  Jr.  Factors affecting ozone  sensitivity




            and susceptibility of  cotton plants.  J. Air Pollut. Control Assoc.




            18:810-813, 1968.



 530. Ting, 1.  P.,  and W. M.  Dugger.  Ozone resistance in tobacco plants:  A




           possible relationship to water balance.   Atmos. Environ. 5:147-150,




           1971.



 531.  Ting, I.  P.,  and S. K.  Mukerji.   leaf ontogeny as a factor in susceptibil-




           ity to ozone:   Amino acid and carbohydrate changes during expansion.




           Amer.  J.  Bot.  58:497-504, 1971.
      Delete 532



533.  Ting,  I.  P.,  J.  Perchorowicz,  and 1.  Evans.   Effects of ozone on plant cell




          membrane permeability,  pp.  8-21.  In M.  Dugger, Ed.  Air Pollution




          Effects  on Plant Growth.   ACS Sympsoium Series 3.   Washington, D. C.:




          American Chemical Society,  1974.  (UNVERIFIED")
534. Tingey,  D. T.   Ozone  induced alteration in the metabolite pools  and  enzyme




           activities  of plants, pp. 40-57.  In M.  Dugger,  Ed.  Air Pollution




           Effects  on Plant Growth.  ACS  Symposium  Series 3.  Washington,  D.  C.:




           American Chemical Society,  1974.   (UNVERIFIED)





     Delete  535



536.  Tingey, D.  T.,  and  U. Blum.   Effects  of ozone on soybean  nodules.   J.




           Environ. Qual.  2:341-342,  1973.
                               11-234

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        Delete 537


 538.  Tingey, D. T., and R. A. Reinert.  The effect of ozone  and  sulfur dioxide


            singly and in combination on plant growth.  Environ. Pollut. 9:117-


    	 126,  1975.


 539.  Tingey, D. T. , and C. Standley.   Factors  influencing  ethylene  evolution


            from  ozone stressed plant.   Plant Physiol.  56(Suppl.):5 ,  1975.  (abstract)


 540.  Tingey, D.  T.  , J.  A.  Dunning, and G. M. Jividen.  Radish root growth


            reduced by acute ozone exposures, pp. A154-A156.  In Proceedings of

                                                                  11
            the Third International Clean Air Congress.  Held at Dusseldorf,


            Federal Republic of Germany, October 8-12,  1973.  Dusseldorf:   Verlag:


            des Vereins  Deutscher Ingenieur, 1973.


       Delete 541


 542.   Tingey, D. T., R.  C.  Fites, and  C. Wickliff.  Foliar  sensitivity of  soy-


            beans to ozone as related to several leaf parameters.  Environ. Pollut.


            4:183-192, 1973.


 543.   Tingey, D. T., R/ C. Fites, and  C. Wickliff.  Ozdrte  alteration  of nitrate


            reduction in soybean.  Physiol.  Plant.   29:33-38,  1973.


 544.   Tingey,  D.  T., R. C.  Fites,  and C. Wickliff.   Activity changes  in selected


            enzymes  from soybean  leaves  following ozone exposure.   Physiol.  Plant.


            33:316-320, 1975.

 545.   Tingey,  D.  T., W. U.  Heck,  and R.  A.  Reinert.  Effect  of low concentrations


            of  ozone  and sulfur dioxide  on  foliage,  growth  and  yield of radish.  J.


            Amer.  Soc. Hort. Sci.  96:369-371,  1971.

546.   Tingey,  D.  T., R. A.  Reinert,  and H.  B.  Carter.   Soybean cultivars:   Acute


            foliar response  to  ozone.  Crop  Sci.  12:368-370,  1962.

547.   Tingey,  D.  T. , R. A.  Reinert,  J.  A. Dunning,  and  W. W. Heck.  Foliar  injury


            responses of eleven plant species to  ozone/sulfur dioxide mistures.


            Atmos. Environ.  7:201-208, 1973.
                                11-235

-------
 548.    Tingey, D. T., R. A, Reinert, C. Wickliff, and W. W. Heck.  Chronic ozone or




              sulfur dioxide exposures or both, affect the early vegetative growth of




              soybeans.  Can. J".' Plant Sci.   53:875-879,  1973.




        Delete 549




 550.   Todd, G, W.  Effect  of low concentrations of ozone on the  enzymes catalase,




             peroxidase, papain and urease.  Physiol. Plant.  11:457-463, 1958.




 551.  Todd, G. W.  Effect of ozone and  ozonated 1-hexene on respiration and




            photosynthesis of leaves.  Plant Physiol. 33:416-420,  1958.




 552.   Todd, G. W., and W. N. Arnold.  An evaluation of methods used to determine




             injury to plant leaves by air pollutants.  Bot. Gaz.  123:151-154, 1961.




 553.  Todd, G. W., and M. J. Garber.  Some effects of air pollutants on the




            growth  and productivity of plants.  Bot. Gaz. 120:75-80, 1958.




 554.  Todd, G.  W., and B. Propst.   Changes in transpiration and photosynthetic




            rates of various leaves during treatment with ozonated hexene or




            ozone gas.   Physiol.  Plant. 16:57-65,  1963.





       Delete 555



 556.   Tomlinson,  H., and  S.  Rich.  Metabolic changes  in  free amino acids of bean




            leaves  exposed  to ozone.   Phytopathology 57:972-974,  1967.




 557.   Tomlinson,  H., and  S.  Rich.  The ozone resistance  of  leaves  as related  to




            their  sulfhydryl  and adenosine triphosphate content.  Phytopathology




            58:808-810,  1968.




 558.   Tomlinson,  H., and  S.  Rich.  Relating  lipid  content  and  fatty acid synthe-




            sis  to ozone injury of  tobacco  leaves.   Phytopathology  59:1284-1286,




            1969.



559.   Tomlirtson, M., and Sk  Rich.  Lipid peroxidation, a result of  injury in bean



            leaves  exposed  to ozone.   Phytopathology  60:1531-1532,  1970.
                                11-236

-------
 560.  Tomlinson, H. , arid §.' Rich.  Effect of. ozone on Sterols and sterol derivatives
             in bean  leaves.  Phytopathology  61:1404-1405, 1971.
 561.  Tomlinson, H., and S. Rich.  Anti-senescent compounds reduce  injury  and
             steroid  changes  in  ozonated  leaves  and their chloroplasts.  Phyto-
             pathology 63:903-906,  1973.
       Delete 562
 563.  Townsend,  A.  M.   Sorption of ozone by nine shade tree species.  Proc. Amer.
            Soc.  Hort.  Sci.  99:206-208, 1974.
 564.  Townsend,  A. M. ,  and  L.  S.  Dochinger.   Relationship  of  seed  source  and
            developmental  stage to the  ozone  tolerance of  Acer  rubrum seedlings.
            Atmos. Environ.  8:957-964,  1974.
 565.   Treshow, M.  Evaluation of vegetation injury as an air pollution criterion.
            J. Air Pollut. Control Assoc.  15:266-269, 1965.
 566.  Treshow, M.  Environment and Plant Response.  New York:  McGraw-Hill  Book  Co.,
            1970.  422 pp.
 567.  Treshow, M.  Ozone  damage  to plants.   Environ. Pollut.   1:155-16,  1970.
 568.   Treshow, M.,  and D. Stewart.   Ozone sensitivity of plants in natural com-
            munities.   Biol.  Conserv. 5:209-214, 1973.
 569.  Turner, M.  C., S.' Rich, and P. E. Waggoner.  Removal  of  ozone by soil.  J.
           Environ. Qual.  2:259-264,  1973.
570.   Turner, N.  C., P.  E. Waggoner, and S.  Rich.   Removal of ozone from the
            atmosphere  by soil and vegetation.   Nature  250:486-489, 1974.
571.   Turri, E., and M.  P.  Benetti.   La  "contaminazione  di fondo" dell'  atomsfera
             ("smog") e sua influenza sulla vegetazione  erbacea.   Bol.  Staz.  Pat.
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                                11-237

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 572.   van Haut,  H.,  and  H.  Stratmann.   Experimentalle  Untersuchungen liber die




            Wirkung von Stickstoffdioxid auf  Pflanzen.   Schriftenr.  Landesanst.




            Immiss.  Bodennutzungssch.  Land. Nordrheim-Westfalen  7:50-70,  1967.








 573.  Vasiloff,  G.  N.,  and D.  B.  Drummond.  The effectiveness  of road dust as a




           protective agent  on buckwheat and  pinto  bean against  sulfur dioxide




           and  ozone.   Phytopathology   64:588,  1974.     (abstract)




 574. Verkroost, M.   The effect of ozone on photosynthesis and respiration of




          Scenedesmus obtusiusculus Chod., with a general discussion of effects




          of air pollutants in plants.  Meded. Landbouwhogesch. Wag. 74:1-78,




          1974.




 575.  Walker,  E.  K.   Chemical  control  of weather fleck  in flue-cured tobacco.




           Plant. Dis.  Rep.  45:583-586,  1961.




      Delete 576




 577.  Walker,  E.  K. , and L.  S. Vickery.   Influence  of sprinkler irrigation on




           the incidence of weather fleck on  flue-cured tobacco in Ontario.




           Can.  J.  Plant Sci.  41:281-287,  1961.



 578. Walker, J.  T.,  and   J. C. Barlow.  Response of  indicator plants  to  ozone




           levels in Georgia.  Phytopathology 64:1122-1127,  1974.




579.  Watson,  R.  D.   Ozone as  a Fungicide.  Ph.D. Thesis.   Ithaca,  N.  Y. :




           Cornell  University, 1942.   74 pp.




580.  Weaver,  G.  M., and  H.  0. Jackson.   Relationship between  bronzing in white




           beans  and phytotoxic levels of  atmospheric ozone in Ontario.  Can.




           J.  Plant Sci.  48:561-568,  1968.



581.  Weber,  D.   The Effect of Ozone and/or Sulfur  Dioxide on Selected Species




           of Plant Parasites  Nematodes.  Ph.D. Thesis.  Raleigh:  North Carolina




           State University, 1975.
                               11-238

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 582.   Weir,  R.   Worth Carolina  State University,  Raleigh.   Personal  Communica-




             tion,  1975.




 583.   Wendschuh, P. H., H. Fuhr, J. S.  Gaffney, and J. N. Pitts, Jr.  Reaction of




            peroxyactyl nitrate with amines.  Chem. Commun. 1973:74-75.




 584.   Went, FV W.  Air pollution.  Sci. Amer.  192(5):63-70, 72, 1955.




 585.   Went, F. W.  Plant damage due to air pollution and the use of plants as




            indicators of air pollution.  Air Pollut. Control Assoc. News 6:




            3-6, 1958.  (UNVERIFIED)




 586.   Wert,  S.  L.   A system for using  remote sensing  techniques to detect and




             evaluate air  pollution effects  on forest stands, pp. 1169-1178.  In




             Proceedings of the  Sixth  International Symposium on Remote Sensing




             of the  Environment.   Vol. 2.  Ann Arbor, University of  Michigan,  1969.



 587.   Wert, S. L.,  P.  R.  Miller, and  R. N.  Larsh.   Color photos detect smog in-




            jury to forest trees.  J.  Forest.  68:536-539, 1970.
588.   white,  N.  H.   Observations  on air-oxidant  injuries  on plants  in the




            Sydney metropolitan area.   Paper #7 Presented  at First Clean Air




            Conference  held  at  the University of  New South Wales,  1962.   7 pp.




            (UNVERIFIED)




589.   Wilhour,  R. G.   The Influence of Ozone on  White Ash.   Center  for Air Envir-




            onment Studies Publ. #188-71.   University Park:   Pennsylvania State




            University,  1971.   86  pp.   (UNVERIFIED)



590.   Wilkinson,  T.  G.,  and  R.  L.  Barnes.   Effects  of ozone on 14C02 fixation




            patterns  in pine.   Can.  J.  Bot.  51:1573-1578,  1973.




591.  Winberry, L. K., and J. B. Mudd.  S-acyl glutathione  thioesterase  of plant




           tissue.  Plant Physiol.  53:216-219,  1974.
                                11-239

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592.  Wood,  F.  A.,  D.  B.  Drummond,  R.  G. Wilhour,  and  D.  D.  Davis.   An'Exposure




           Chamber  for Studying  the Effects  of  Air Pollutants  on  Plants.   Agri-




           cultural Experiment Station Progress  Report No. 335.   University Park:




           Pennsylvania State University,  1973.  7  pp.




593. Wood, F. A.,  and D.  B. Drummond.  Response of eight cultivars of chrysan-




          themum to peroxyactyl nitrate.  Phytopathology 64:897-898, 1974.




b93a.Wood,  F,  A.,  and J.  B. Coppolino.  The influence of ozone  on  selected woody




           ornamentals.   Phytopathology  61:133,  1971.   (abstract)




594. Wood, F. A.,  and J.  B. Coppolino.  Response of 11 hybrid poplar clones




          to ozone.  Phytopathology 62:501-502, 1972.   (abstract)



595. Yamaga, M., K. Omori, K. Abe,  and T.  Tozawa.  The  effects  of  air pollut-




           ants  on  vegetation.  The  effects  of ozone on carbohydrase.  Symp.




          Jap.  Soc. Air Pollut. Proc. 13:230,  1972.       (in  Japanese)  (UNVER.)




596. Yarwood, C. E., and J. T.  Middleton.   Smog injury and rust  infection.




          Plant Physiol.  29:393-395,  1954.
597. Zobnina, V. P., and E. A. Morkovina.  Effect of ozone on  survival  of




          carotinoid strain of Mycobacterium carothenum and  its white mutant




          obtained with nitrosoguanidine.  Microbiology 40:79-81,  1971.
                              11-240

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                               Chapter 12


                               ECOSYSTEMS




       The effects of ozone and other photochemical oxidants on indivi-


dual species of green plants and microorganisms were discussed in detail


in Chapter 11.  The purpose of this chapter is to examine the effects


of oxidant pollutant stress on both simple and complex communities of


organisms.  The human population is an integral and dependent component

                                           49
of these biotic communities, or ecosystems.


       It is usually not possible to interpret the meaning of a


stable ecosystem for man's welfare in the terms of conventional economics,


for example, as a cost-benefit analysis.  In the case of some natural


ecosystems, there may be only social and psychologic values to be

           70
considered,   which are only remotely related to monetary values through

                                               79
the recreational opportunities that they offer.    One of the most import-


ant justifications for the examination of the effects of oxidant stress


on an ecosystem is the concern that it will not revert to its prior


condition even after removal of the stress.  For example, it has been


suggested that the arid lands of India are the result of defoliation and


elimination of vegetation, which induced local climatic changes that


were not conducive to the reestablishment of the original vegetation.


       A natural ecosystem is a distinct association of plants and


animals with the physical environment that controls them.  Spatial boundaries


of ecosystems are defined when the physical and biologic parts form an


integrated unit in which there are defined paths for energy flow and


material transport or cycling.   Classes of terrestrial ecosystems called


"biomes" are distinguished by their dominant vegetation form — e.g.,

-------
grasslands and deciduous and coniferous forests.  Additional character-

istics are emphasized in Odum's more formal definition:  "any unit includ-

ing all of the organisms (i.e., the community) in a given area interacting

with the physical environment so that a flow of energy leads to a clearly

defined trophic structure,  biotic diversity, and material cycles (i.e.,

exchange of materials between living and non-living parts) within the
                                             50
system is an ecological system or ecosystem.     The agroecosystem is

defined as "a unit composed of the total complex of organisms in the crop

area together with the overall conditioning environment and as further

modified by the various  agricultural,  industrial, recreational, and
                          63
social activities of man."     The important components and processes of

natural ecosystems are summarized in Table 12-1.

       Ecosystems may be described developmentally as young (serai,

successional)  or mature (climatic).   In a young ecosystem, developmental

stages or communities are rapidly replaced by other communities.  This

succession leads ultimately to the mature stage.  The distinguishing

characteristic of the mature,  or climax stage is that the dominant species

that form the community can replace themselves; thus, the community is

in equilibrium with its normal environment.

       There are important  differences  among the components and processes

of young and mature ecosystems that result in  different degrees of response

to environmental stresses or new perturbations, such as the presence of

oxidant air pollutants (Table 12-2).  The greater diversity of a mature

ecosystem slows down the disruption of  normal structure and function.

For example,  a forest ecosystem in which many species make up the producer

community would show less immediate visible damage than a successional

stage with only a few species.   Even greater damage would be anticipated

                                12-2

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               Table 12-1




         Elements of an Ecosystem







Components:




    Inorganic substances (C,N,H20, etc.)




    Organic substances




    Climatic regime




    Autotrophs (producers)




    Phagotrophs (macroconsumers)




    Saprotrophs (microconsumers)







Processes:




    Energy flow circuits




    Food chains (trophic relationships)




    Diversity patterns in time and space




    Nutrient (biogeochemical) cycles




    Development and evolution




    Control
                  12-3

-------
                              Table 12-2

                 Characteristics of Ecosystem Development
   Agroecosystems and
Successional (Young) Stages

High production:respiration
ratio

High net production

Short food chains

Small organisms


Open nutrient cycles

Lack of stability

Maintenance cost reduced
by energy subsidies (by man);
production increased
Climax (Mature) Stages

High biomass:respiration
ratio

Low net production

Complex food webs

Great diversity in size
and numbers of organisms

Closed nutrient cycles

High stability

Maintenance cost high,
but rarely subsidized
                                   12-4

-------
In an agroecosystem (which might be considered the simplest of successional


stages, inasmuch as often only a single producer species is present).




GENERAL RESPONSES OF NATURAL ECOSYSTEMS AND AGROECOSYSTEMS TO STRESS BY


OXIDANTS


       Ecosystems subjected to oxidant air pollutants must be carefully


observed and described individually if we are to understand and predict

                                                     Q O
the complex consequences of chronic injury.  Woodwell   has summarized


some of the expected effects of air pollutants on ecosystems:  elimination


of sensitive species and reduction of diversity in numbers of species;


selective removal of larger overstory plants and a favoring of small plants;


reduction of the standing crop of organic matter, which leads to a reduc-


tion of nutrient elements held within the living system; and increase in


the activity of insect pests and in some diseases that hasten producer


mortality.  Many other effects can be suggested.


       Photochemical oxidant air pollutants have constituted a chronic


problem only during the last 20 - 25 years, at first principally in south-


ern California, where both natural ecosystems and agroecosystems have been


subjected to these pollutants for the longest period.  Citrus groves and


vineyards in the inland valleys of southern California are prime examples


of agroecosystems stressed by chronic exposure to oxidants.  Studies were

                                                 72
initiated in 1960 on lemon and navel orange trees   and in 1968 on wine

      73
grapes   to determine the economic losses due to oxidant pollutants.  Both


studies were performed under field conditions for several years.   The  lemon


and orange studies provide data that may be interpreted in an agroecosystem


context,  although they were highly oriented toward the primary producer


components.   '    '    '     There was no effort to examine the effects on


consumer and decomposer components.
                                  12-5

-------
       At two lemon groves and one orange grove near Ontario and

Upland, California, 24 trees were selected at each grove and divided

according to a randomized block design into six treatments with four

replications each.  The most important treatments for this discussion

were greenhouse-enclosed ambient air, enclosed carbon-filtered air, and

unenclosed ambient air.  The first difference noted was a lower rate of

water use by oxidant-stressed trees.  The number of irrigations required

by trees in filtered air was always significantly greater than that in

ambient-air treatments; this behavior could not be correlated well with

transpiration rates.    From a systems view, one of the major input variables,

irrigation water needed,  would be lower for this stressed ecosystem.  Com-

parisons of the apparent photosynthesis of single branches of trees in

filtered and ambient air yielded mixed results, but with a trend toward
                                                          71
reduced apparent photosynthesis in ambient-air treatments.    After five

consecutive seasons of treatment at the two lemon groves and four years

at the orange grove, there were no significant differences in tree circum-
                             74
ference among the treatments.    The lemon trees showed significantly

greater leaf drop in both ambient-air treatments;  the orange trees also

followed this trend, but the differences were not significant.   The drop

of small,  unripened fruit was a severe problem in ambient-air treatments

with orange trees, but insignificant for lemons.   The average annual yields

at both lemon groves and the orange grove were significantly reduced when

filtered versus unfiltered treatments were compared;  yield was sometimes
                          74
reduced by as much as 50%.    Additional studies with navel oranges exposed

to ambient air, carbon-filtered air, and carbon-filtered air containing

either ambient or half-ambient concentrations of ozone again showed increases

in leaf and fruit drop and decreases in yield of marketable fruit in accor-

dance with increasing ozone or oxidant dose.    None of the above studies
                                    12-6

-------
managed  to separate the different effects of ozone and peroxyacetylnitrate


or  its homologues in the photochemical oxidant mixture.


       In summary, oxidant stress reduced water use and photosynthesis,


increased leaf drop and fruit drop, and resulted in a severe reduction in


yield of marketable fruit.  All these effects occurred without the develop-


ment of plainly visible leaf symptoms.


       Several inferences can be drawn from these data that may suggest


the impacts to be expected at the consumer and decomposer levels.  Accelerated


leaf drop may influence the development of pests—namely, aphids, scale insects,


and red citrus mites.   Pest populations might be increased if injured leaves


had higher concentrations of amino acids or free sugars before abscission


(see Chapter 11) or diminished if leaves fall too rapidly.  Leaf and fruit


drop would provide a larger substrate for populations of decomposer organisms


at the soil surface.


       In southern California, the coastal chaparral ecosystem, dominated by


chamise and manzarita or woodland species (including the live oaks and big-


cone Douglas fir), and the coniferous forest ecosystem have received severe


exposure; and the desert ecosystems in the vicinity of mountain passes connect-


ing the coastal and desert regions have undoubtedly been exposed.  Injury


has been well documented only in the mixed-conifer forest ecosystem of the


San Bernardino Mountains.   Early symptoms of injury in conifer species were

                                                            42
reported in a number of California national forests in 1970.     In the south-

                                                 82
ern Sierra Nevada, Forest Service surveys in 1974   have detected increased


injury in ponderosa pine since 1970 at many locations in the Sequoia National


Forest,  Sequoia National Park,  and Kings Canyon National Park.   Particular


stands of mixed-conifer forest on the western slopes of the southern Sierra

                                                                         44
Nevada now appear to be affected by oxidants from the San Joaquin Valley.




                                  12-7

-------
The potential loss of timber growth alone in this area is a very serious


prospect.


       Injury to important primary producer species constituting forest


ecosystems is not limited to California.   In the eastern United States, a


disease  Qalled emergence tipburn of eastern white pine was related to

                             3
ozone by Berry and Ripperton.   Occurrence of similar symptoms on the same


species in eastern Canada could not be definitely related to ozone by

       38
Linzon.   The disease is characterized by bands of necrosis initiated in


the semimature tissue of elongating needles; the necrosis spreads to the


needle tip.  In other studies with ozone  fumigations at 0.07 ppm for 4 h or


0,03 ppm for 48 h, the tipburn appeared;  additional symptoms were silvery

                                           13
or chlorotic flecks and chlorotic mottling.


       Under forest conditions, the affected trees occur randomly in the


stand; the same trees are injured successively in a single season or in successive

      4
years.   Eastern white pine either forms  pure stands or occurs in mixtures


with other species in abandoned fields;  under these conditions, it is an

                       80
important pioneer tree.     In established stands, it is a major component


of four forest types and an associate in  14 other types with a range extending

                                                                       80
over 7 million acres from the lake states to the Appalachian Mountains.


Berry  reported that emergence tipburn occurs throughout the natural range


of this species; there is also evidence of a slow decline in tree vigor due


to the deterioration of feeder rootlets.


       Higher concentrations of ozone in  the forested areas of the eastern


United States would undoubtedly cause greater injury to eastern white pine


and other forest species.  Chapter 11 reported additional studies that suggested


that other conifer species, in particular Virginia pine and jack pine, may

                                                16
more sensitive to ozone than eastern white pine.    In addition, there is


a synergistic interaction between low concentrations of ozone and sulfur



                                   12-8

-------
 dioxide  that  ±s  the  cause  of  the  chlorotic  dwarf disease  of  eastern white


 pine.     A study by  Ellertsen jit  al_.     showed  10%  mortality  between  1956


 and 1965 of dominant and codominant  eastern white pines near an  industrialized


 area including several  hundred  square miles on  the  Cumberland  Plateau.   Both


 ozone and sulfur dioxide were considered responsible  for  tree  decline.   Because


 eastern  white pine represented  only  5%  of the total wood  volume  available


 for harvest,  the economic  impact  was slight.  There was no effort  to  interpret


 pollutant effects in an ecosystem context.  An  air  monitoring  network  was


 operated by Virginia Polytechnic  Institute  in 1975  at three  locations  —


 the Blue Ridge Mountains,  the Shenandoah Valley, and  the  southern  Appalachians.

                         62
 According to  J.M. Skelly,   a pollution episode occurred  during  early  July


 1975 during which total oxidant peaks as high as 0.13 ppm were observed, along


 with 43  h when concentrations were 0.08 ppm or  higher.  After  this episode,


 significant increases in oxidant  injury were observed, particularly  in the


 Blue Ridge Mountains in three categories of eastern white pine —  those


 previously without symptoms,  those with chlorotic mottle, and  those  exhibiting


 chlorotic dwarf  symptoms.  Such incidences  suggest  the need  for  more compre-


 hensive  studies  of oxidant (and sulfur  dioxide) effects in forests of  the


 eastern  United States.  In the  long  run,  the broader  question  regarding


 effects  of pollutant stress on  all ecosystems components—primary  producers,


 consumers,  and decomposers—should be addressed.  An  analysis  of the multiple


 effects  of oxidants  on  eastern  forest ecosystems will be  a much  more adequate


 measure  of their future usefulness to man than  the  small  amount  of information


 now available related mainly  to single  primary-producer species.


       The purpose of this  chapter is to examine in the greatest  detail


possible the effects  of oxidant  air pollutants  on ecosystems.  A project


is now going on to study the  effects  on a mixed-conifer forest  ecosystem in


southern California,   '   and  the  planning documents and  early  results from


this study constitute the major  source  of information for  the remainder of


                                   12-9

-------
this chapter.  Other examples of damage to agroecosystems and natural ecosystems



will be included.





ORIGIN OF INJURIOUS CONCENTRATIONS OF OZONE AND OXIDANTS AFFECTING NATURAL



ECOSYSTEMS



Advection from Urban Centers to Remote Areas



Southern California.  Descriptions of the vertical and horizontal distribu-



tions of photochemical smog in the Los Angeles basin (southern coastal air



basin) during typical summer days have recently been provided by Blumenthal


       5         20                19                 43
et al_.,  Edinger,   Edinger e_t a.1.,    and Miller e_t _al.    Important observa-



tions to be drawn from their reports are the interactions of basin and



mountain topography and local meteorology in determining the transport and



concentrations of oxidant air pollutants in relation to elevational zones



of vegetation.



       The marine temperature inversion layer that frequently forms above



the heavily urbanized Los Angeles metropolitan area often extends inland as



far as 90 miles  (144 km), depending on season and time of day.  Surface



heating of air under the inversion increases with distance eastward in



the basin and often disrupts the inversion by midmorning at its eastern edge.



The northern rim of the basin is formed by the San Gabriel and San Bernardino



Mountains, interrupted only by the Cajon Pass about 55 miles (88 km) inland



(see Figure 12-1).  The marine temperature inversion layer encounters the



mountain slopes usually below 4,000 ft (1,200 m).   In the morning, the



temperature inversion often remains intact at this juncture, and air pollu-


                                                         19   a        20
tants are confined beneath it.  Studies by Edinger et al.   and Edinger



have described how the heated mountain slopes act  to vent oxidant air



pollutants over the crest of the mountains and cause the injection of



pollutants into the stable inversion layer horizontally away from the slope.



                                12-10

-------
Oxidant concentration within the inversion is nonuniform, containing multiple


layers and strong vertical gradients.  In some cases, the inversion may serve


as a reservoir for oxidants, principally ozone, which may arrive at downwind


locations along the mountain slopes relatively undiluted, because of a lack


of vertical mixing within the inversion layer and a lack of contact with


ozone-destroying material generated at the ground.  The important result of


the oxidant's being trapped in these layers is its prolonged contact with


high terrain at night.



     The most important effect of the interaction of pollutant and inversion


layer at the heated mountain slope is the vertical venting of oxidants over


the mountain crest by upslope flow.  A gradient of oxidant concentrations


or doses is established across distinct vegetation zones ordered along an


elevational gradient—i.e., the chaparral and conifer forest ecosystems


that occupy the slopes and mountain terrain beyond the crest, respectively.


The altitudinal sequence of these ecosystems is illustrated in Figure 12-2.

                    27
According to Horton,    the  chaparral zone is  subdivided  from  lower to higher


elevations into three subzones called the chamise, manzanita, and woodland


chaparral; the mixed-conifer forest occupies  the mountain  crest.


       The daytime changes  in oxidant concentrations at  several  stations


(A, B, C, and D in Figure 12-1) along the southern slope and at  the  crest  of


the San Bernardino Mountains is illustrated in Figure 12-3.  In  the  late


afternoon, the highest  concentrations in this profile were at 3,000  - 4,000 ft


(900 - 1,200 m) and adjacent to the mountain  slope.  The oxidant was not always


confined below the inversion layer, but was present in the inversion layer

                             19
and above the mountain  crest.    An instrumented aircraft measured concentra-


tions of oxidant ranging from 0.05 to 0.11 ppm as high as 2,432 m (approximately


1,033 m above the ridge crest) during several noon and 4 p.m. flights.  At these



                                   12-11

-------
                                   r;-:v,. \
                                        t:jj, ;-,\:: : :^ :;•::::::::•::: y:::::::::::::: \::::.-..

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                                        •	^ ^  • '•". _	•    "   I •    I iLC.t 9,^^X5

                                                                       r—I wo-rcco
                                                               ?O 1/lUS
FIGURE  12-1.  Major topographic features  of the Los  Angeles basin with



               inland valleys  and mountains.  Station locations;  A, Highland;




               B,  City Creak;  C,  Mud Flat;  D,  Rim Forest.  Aircraft flight




               paths for the study area are also shown.   (Reprinted with


                                                19
               permission from Edinger et  al.   )
                                       12-12

-------
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                            12-13

-------
         0900
                                  June 19, 1970
                                                  1,000ft.
                                                    8
        Temperatur
        Tvrrain profile
                                    Rsdlands
FIGURE 12-3.  Daytime changes in oxidant  concentrations along

              a  west-to-east transect in  the southern coastal


              air  basin,  including the  slopes of the San Ber-

              nardino Mountains (see Figure  12-1).   (Reprinted

                                                   19
              with permission from Edinger et al.  )

                           12-14

-------
times, downwind diffusion of oxidant beyond the crest—on the basis of aircraft


flights approximately 500 ft (150 m) above the terrain—suggested only

                                                      19
slight dilution in the first 10 km north of the crest.     Observations on

          / Q
other days   suggested a 50-60% reduction in oxidant 10 km north of the crest.


There was no ground station at this point for comparison with the aircraft


measurements at either time.


       Total oxidant, temperature, and vapor-pressure gradient were


measured continuously during 16 days in July and August at mountain slope


and crest stations (A, B, C, and D in Figure 12-1).  In Figure 12-4, the


time of the daily peak oxidant concentration was progressively later at stations


of higher elevation.  Temperatures and vapor-pressure gradients were also


progressively lower at higher elevations at the time of oxidant peak.  The


duration of oxidant concentrations exceeding 0.10 ppm was 9, 13, 9,  and 8


h/day going from lower to higher stations.  The longer duration at City


Creek (elevation,  817 m) probably coincides with the point where the


inversion layer most often contacts the mountain slope.   The oxidant concen-


trations rarely decreased below 0.05 ppm at night on the slope of the mountain


crest, whereas it usually decayed to near zero at the basin station (Highland).


       The vegetation zones along the slope and at the crest are subjected


to oxidant exposure differently.   Even though the lower chaparral receives


longer exposure,  the peak concentrations coincide more closely with the maximal


evaporative stress for the day.  There is some support for the hypothesis that


stomates would be closed during this period and that pollutant uptake would


be lower.  There is in fact very little visible injury to the species in this


zone.   In contrast, the daily oxidant peak occurs well after the temperature


and vapor-pressure gradient maximums in the conifer forest at the mountain


crest; the oxidant injury to plant species here is severe.   These suggestions


of strong microclimatic control of the sensitivity of these native species


to ozone form a working hypothesis that needs further investigation.   •



                                   12-15

-------
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                                  12-16

-------
                                                                           42,82
The  San Joaquin Valley and Adjacent Sierra Nevada Mountains.  Field surveys



have confirmed oxidant injury to ponderosa pine and associated species at



numerous locations in the Sierra Nevada foothills east and southeast of



Fresno.  Oxidant measurements at ground stations and by instrumented aircraft



show late-afternoon peaks of "transported" oxidant on the western slopes of



the  Sierras.  Limited measurements by instrumented aircraft suggest the



development of a layer of oxidant approaching the forested mountain slopes


                                                  44
between 610 and 1,829 m during the late afternoon.   A very weak inversion



or isothermal layer may serve as a reservoir of oxidant, which is advected



to the mountain slope in the southern coastal air basin, as suggested by


        20
Edinger.



       Considerable concern has been registered about air quality in the Lake

                                                                              9
Tahoe Basin, where local development may cause adverse oxidant concentrations.



Seasonal and Daily Variations of Injurious Concentrations



Synoptic Weather Patterns Associated with Episodes of High Pollution.



McCutchan  ana Schroeder   classified 145 days during May through September 1970



with data collected on the southern slopes of the San Bernardino Mountains.



Five general weather patterns were described, with the associated synoptic



patterns at the surface and at 500 millibars (Table 12-3).  An analysis of



eight meteorologic variables was used to classify days during May through



September into the five general weather categories.   Of 123 days classified



by stepwise discriminant analysis,  10,  13,  44,  23, and 24 were correctly



categorized into classes 1-5,  respectively;  the remainder could not be



clearly placed in the five classes.   The oxidant concentrations associated



with these classes were:  1,  low;  2,  low and high;  3,  high;  4,  low;  and



5, low.  In this sample,  the sum  of days in classes 2 and 3,  namely 57 days,



suggests that about 46% of the sample days had high concentrations of oxidant



air pollutants.




                                   12-17

-------
                               Table 12-3

                 Descriptions of Meteorologic Patterns
                    for Five Classes of Spring and
                   Summer Days in Southern California-
Class
General Weather
                                               Associated Synoptic Pattern
                                             at
                                          Surface
          at
        500 mb
       Hot, dry continental air
         throughout the day
         (Santa Ana)
                              Large high pressure
                                over Great Basin
Strong northerly
  winds over area
  with trough east
  of the area
       Relatively dry forenoon;
         modified marine air in
         afternoon; very hot (heat
         wave)

       Moist, modified marine
         air; hot in afternoon

       Moist, modified marine
         air; warm in afternoon

       Cool, moist, deep marine
         air throughout the day
                              High pressure over     Subtropical closed
                                Great Basin and        high over area
                                thermal trough over
                                desert
                              Thermal trough over
                                desert

                              Thermal trough over
                                desert

                              Synoptic low over
                                desert
Ridge over area
Trough over area
Deep trough or
  closed low over
  area
a                                       40
"~  Derived from McCutchan and Schroeder.
                                   12-18

-------
       Class 2 and 3 days are both characterized by high pressure (500-


mb ridge over the area).  Descriptions of the synoptic weather patterns


(contained in the U.S. Forest Service "California Fire Weather Severity,


10-Day Summaries") for May through August 1972-1974 were compared with


episodes of severe oxidant concentration at Rim Forest and nearby Sky Forest.


For the purposes of this comparison, all days having maximal hourly concen-


trations of 0.33 ppm or higher were compared with the synoptic patterns for


those days.  In all cases, a persistent 500-mb high pressure over the area


was the most common synoptic feature.  For 8 qualifying days in 1972, the


mean of the maximal hourly concentrations for those days was 0.37 ppm; for


16 days in 1973, 0.41 ppm; and for 46 days in 1974, 0.38 ppm.  The highest


hourly concentration ever obtained was 0.60 ppm, on June 28, 1974.


       During episodes of severe oxidant pollution, the weather is generally


very hot (85-100 F or about 29-38 C) and the relative humidity may be either


low or moderately high on class 2 and 3 days, depending on the behavior of


the marine layer.  The small difference between means of maximal hourly


concentrations on high-pollution days in 1972-1974 suggests continuation of


heavy primary pollutant emission in spite of current control strategies.




Annual Trends of Total Oxidant Concentrations at a San Bernardino Mountain


Station and the Nearby City of San Bernardino.   Since 1968, total oxidant


concentrations have been measured continously with a Mast ozone meter


(calibrated by the California Air Resources Board method) from May through

                                   3 la
September at Rim Forest-Sky Forest.     The fall, winter, and early spring


months have generally been omitted until recently, because synoptic patterns


are usually not conducive to oxidant accumulation and transport.  For example,


average maximal hourly oxidant concentrations from October through April 1973

                                                                   70
and 1974 stayed below 0.10 ppm; those for April were 0.10-0.15 ppm.     The
                                   12-19

-------
main data collection period coincides with the growing season and thus

permits a  reasonable estimate of the total annual dcse of oxidant air

pollution received by vegetation.

       Two methods of documenting trends of axidant concentrations during

the 1968-1974 period at Rim Forest-Sky Forest express the accumulated

dose as a sum of all hourly values in micrograms per cubic meter and as

number of hours with a concentration of 0.08 ppm or more (the federal

standard) for each month separately, June through September (Figure 12-5).
                                                                      o
The dose excludes background concentrations — those less than 59 ug/m

(0.03 ppm).   The percentage of valid data recovered is also indicated.

The absence of some data — ranging up to 17.8% in 1970, but averaging

8.3% during the 7 years — represents an underestimate that cannot be

adjusted with any certainty.  The total number of hours with concentrations
           3
of 157 jag/m  (0.08 ppm) or more during June through September was never

less than 1,300 during each of the 7 years.  These measures of oxidant

trends indicate no improvement in air quality.

       Data are available back to 1963 from the downtown San Bernardino

station operated by the County Air Pollution Control District (APCD).  The

colorimetric potassium iodide method used to measure total oxidants was

calibrated according to the method of the California Air Resources Board.

A positive correction factor of 1.22 was used to adjust mountain data for

the decreased air pressure at the higher elevation.

       The data from the Rim Forest-Sky Forest station were compared with

published data from the San Bernardino County  APCD.  The numbers of hours
                                      n
with concentrations exceeding 392 /ig/m  (0.20 ppm) during July,  August,

and September in 1969 - 1974 were compared (Figure 12-6).  For 1963 - 1968,

data are shown only from the San Bernardino APCD.  A large part of the year-

                                  12-20

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                  12-22

-------
 to-year differences at the same station and between stations can be attributed




 to differences in synoptic and mesoscale  (local) meteorologic patterns.  For




 example, the increases in 1972, 1973, and 1974 at Rim Forest-Sky Forest are




 associated with 6, 16, and 46 days, respectively, when a persistent 500-mb




 ridge occurred over the Southwest, particularly southern California.  The




 difference between stations in the same year is probably influenced most




 by inversion height.  Lower inversions partially restrain transport upslope




 to shorter periods each day.  Higher inversions would have the opposite




 effect and also allow a greater air volume below to dilute oxidants.  The


                                                                    3
index for comparison chosen in Figure 12-6 — i.e., hours >^ 392




would be sensitive to inversion height.  The 3-year moving averages for




each station tend to remove some of the variation due to meteorology.


                                                3

In terms of hours equal to or exceeding 392 jig/m , the moving average between




1970 and 1973 at Sky Forest-Rim Forest has increased from 175 to 290.  The




increased oxidant concentrations at both these stations are the reverse of




those in upwind, urban Los Angeles County, where increased emission of NO
                                                                         X



tends to shift the chemical equilibrium to the left, toward the ozone




precursors.   The most recent data   firmly indicate that oxidant concentra-




tions will either increase annually or continue to oscillate around the




mean of present high concentrations in the foreseeable future at these




distant locations.




       The tropospheric ozone cycle   describing rural upwind, urban, and




rural downwind variations in concentration can be easily demonstrated in




the Los Angeles and connected inland basins.  The effects on both natural




ecosystems and agroecosystems also become apparent.   For example,  oxidant




doses during August 1972 at six oxidant stations — Costa Mesa,  La Habra,




Corona, Riverside,  City Creek,  and Rim Forest — extending in a line
                                   12-23

-------
northeastward from the coast to the mountains show low doses at the coast




increasing to a maximum on the chaparral-covered mountains and decreasing




beyond the mountain crest (Figure 12-7).   The oxidant dose is indicated




hy the dashed line.  A crude estimate of the relative economic value of the




products from ecosystems encountered along this transect are expressed in




a very general way by the solid line and the nomenclature on the abscissa.




Finally, the relative complexity of the ecosystems involved is shown below




the abscissa.  This conceptualization emphasizes the enormously greater




dosage received by the natural ecosystems during this month.  This pattern




of dosages is very typical of June, July, and August, but the offshore flow




typified by the Santa Ana winds may reverse the situation in September or




October; susceptible crops growing on the coastal plain may be seriously




damaged.




       In general, the permanent vegetation constituting natural ecosystems




receives much greater chronic exposure, whereas the short-lived higher-




value vegetation constituting the agroecosystems of the coastal plain can




be subject to injurious doses, but in intermittent short-term fumigations.




Each situation has measurable economic and aesthetic effects, but on diffe-




rent time scales.   The simple agroecosystem has little resiliency to pollu-




tant stress;  losses are immediate and may be catastrophic.  The complex




natural ecosystem is initially more resistant to pollutant stress, but




the longer chronic exposures cause the disruption of both structure and




function in the system.   Damage may not be reversible.







AN EXPERIMENTAL DESIGN FOR INVESTIGATING THE EFFECTS OF OXIDANT STRESS




ON ECOSYSTEMS




Techniques for Ecosystem Modeling




       The steps needed to understand the effects of oxidant air pollu-




tants on an ecosystem are description of ecosystem components or subsystems





                                  12-24

-------
                                                                    r-
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-------
and identification of the most important processes within organisms or


interactions between organisms or communities of organisms that would be


most vulnerable to pollutant stress, including an evaluation of factors


of the physical environment that may limit ecosystem processes.  This infor-


mation can be conveniently arrayed in terms of interaction tables that show


which variables are involved in various subsystems and whether the inter-


action between any two variables is positive or negative.   The next step


involves the selection of the most appropriate paradigm for the substance


or "unifying thread" that flows through the various subsystems.  Examples


of possible "flows" are energy, biomass, mineral nutrients, water, numbers


of species, population densities, or area occupied per biotic unit.


       The state of the art of ecosystem modeling has evolved rapidly in


recent years.  Discussions of various ecologic subsystem simulators are

          30, 34, 52
published.            Recently, discussions of the utility of computer


simulation modeling in ecologic research have been published by the National

                   47                                     48
Academy of Sciences   and the National Science Foundation.


       Depending on the "flows" through the ecosystem that one chooses to


study, the modeling procedures may be either deterministic or stochastic.

      58
Rochow   has described the step-by-step procedure for studying the flow


of nitrogen through a forest ecosystem.  In this case, nitrogen can be found


in a number of well-defined storage compartments.  The transfers of nitrogen


between compartments are described by transfer coefficients arrayed in a


symmetric transfer matrix.  Differential equations are written that represent


the rate of change (or flow) of nitrogen through time for each of the various


compartments.  Computer programs already exist to solve these equations.  Once


the model is running smoothly on the computer, it is possible to impose
                                   12-26

-------
various experimental conditions — e.g.,  clear-cutting or selective cutting -



and observe the effects on nitrogen flow.   Sensitivity analysis can then


be performed to study which transfer coefficients are sensitive to small



changes and which only to large changes.   The useful outputs of these manipu-


lations include a determination of how much particular transfers in the



system can be changed or stressed before the ecosystem deteriorates.   This


example uses a deterministic model; however, the flow of water through an



ecosystem may have both deterministic and stochastic mathematical proper-



ties.15


       Models of energy flow or biomass flow have been more successful when



uniform plant canopies were involved — e.g., a field of corn.  A recent



development from the field of integrated pest management has been described



in which an alfalfa growth model has been coupled with an alfalfa weevil

                          23
population dynamics model.    The plant growth model in this example might



be adaptable to air pollutant injury studies in agroecosystems.  Because the



model is built to incorporate current weather data that have direct influen-



ces on pollutant concentration and plant sensitivity, this type of model



seems to be a worthwhile departure point for simulating dose responses.



       The simulation of the population structure and dynamics of autotrophs


and phagotrophs is another important interaction that can be modeled to test



for effects of pollutant stress.  A standard approach is the use of a finite-

                            35
population-difference model.    The model assumes that the population change



of a species in a specific period is equal to the species population multi-



plied by an intrinsic coefficient of rate of change.  The rate coefficients



are difficult to define without extensive data.  The task is further compli-



cated because "a consistent feature of communities is that they contain a_



comparatively few species that are common— that is, represented by large



numbers of individuals or a large biomass—and a comparatively large number
                                   12-27

-------
                                                               49
of species that are rare at any given locus^ in time and space."   It is


Implied by this statement that adequate sampling procedures may be difficult


to design if only the spatial aspect of the problem is considered.  The


constraints of short-term research funding in the form of grants or contracts

                                                                         21
generally preclude adequate sampling of the time dimension.  Ewing et al.


have considered a related modeling constraint:   the simulation of the hierar-


chic structure inherent in a biologic population.   Through exploitation of


the structure of the biologic,  mathematical, and computer systems, a Monte


Carlo simulation of a structured population is possible.   With a nonhomo-


geneous Poisson process, events are defined and a suitable risk structure


is developed that satisfies mathematical and biologic requirements.  A


structured computer language allows one to mimic the structure and organiza-


tion of a population — different levels of organization ranging from the


individual to the complete population.


       A description of another "flow," the area occupied per biotic


unit over time, is also very important for defining and predicting long-


term successional changes in plant communities due to pollutant stress.

               61
Schugart et al.   have described a model for 250 years of succession in


the western Great Lakes Region in the absence of fire, epidemics, and

                                     6
forest management.  Botkin and Miller  predicted successional changes


during a 100-year period after logging in a northern hardwood forest.


       There are no examples of models dealing directly with oxidant


stress on communities or ecosystems.  However,  the types of models


just described may be applicable to this problem.   In view of the trend


of increasing oxidant concentrations downwind from urban areas,  a much


more precise understanding of chronic effects on both natural ecosystems


and agroecosystems is required.  Descriptive and predictive models dealing


with the responses of biologic systems can provide the best input to the



                                   12-28

-------
 decision models  needed  for  standard-setting,  land-use  planning,  and  resource


 management.



 Modeling the  Effects  of Oxidant  Stress  on a Western Mixed-Conifer  Forest


 Ecosystem


        The  recent history of  the mixed-conifer  forest  of  the  San Bernardino

                            68
 Mountains has been analyzed.     This analysis included an initial  inventory


 of  ecosystem  components and processes,  as indicated in Figures 12-8  through


 12-12.   The inventory emphasizes ponderosa and  Jeffrey pines, the  most


 dominant species in the climax community, and is  stratified according to


 organizational level  — namely,  organism or tree  (Figures 12-8 and 12-9),


 community or  stand (Figures 12-10 and 12-11), and finally a time-oriented


 analysis of plant succession  in  the aggregation of relatively distinct


 communities or stands that  collectively make up the mixed-conifer  forest


 ecosystem (Figure 12-12).   This  analysis was assembled by nearly a dozen

                                              70
 coinvestigators  representing  many disciplines.     These detailed diagrams


 are presented here to emphasize  the complexity  of ecosystem interactions


 at  each level of biologic organization.  Only the interactions considered


 to  be the most important ones guiding the course  of plant succession in the


 several forest plant  communities now constituting the  mixed-conifer  forest

                                                                        69
 have been selected by project investigators for immediate investigation.


In the case of each interaction,  it  is important to decide the time frequency


at which the selected state variables  and driving  variables will  be measured—


i.e.,  hourly,  weekly,  or annually.


       A data capture,  storage,  and retrieval system is being devised to


provide  modelers with immediate  access  to all subproject  data.   Because


 this project is  currently the most active effort  directed toward under-


 standing the effects  of ozone and other oxidants  on a  natural ecosystem, most


 of  this  chapter  is a  discussion  of its  latest progress.



                                  12-29

-------
                                      OXIDANT
                                   ;f  UAiUAM    ^
                                   [     AIR      ]
                                \}2.\  POLLUTANTS-'^;
                                               A
                                             •":i^«'v
                                                                      SOIL
                                                                  >LlCRO-
                                                                H;\ARTI!RO?ODS  J
    ^    \
                7  8  9  10    X  I3  14
        liATURAL  \
      ENEMIES  OF  ^
      BARK BEETLES^
                  A1,"D  OTHER
                  HOLE NESTING
                       BIRDS
FIGURE 12-8.
Organism-level interactions irr'a mixed-conifer forest.  Types of
interaction:  1, competition for food supply; 2, direct effect of
ozone on small-mammal physiology; 3, climatic control of oxidant
concentration in forest; 4, direct effect of ozone on soil micro-
arthropods; 5, effect of precipitation and temperature on soil
moisture and soil temperature; 6, insect damage to developing
cones; 7, small-mammal damage to developing cones and importance
of cone crop as animal food supply; 8, direct effect of ozone on
physiology of cavity-nesting birds; 9, role of fruiting bodies
of nonpathogenic fungi in nutrition of small mammals; 10, direct
effect of ozone on tree physiology; 11, role of fruiting bodies
                                    12-30

-------
of pathogens in nutrition of small mammals; 12, direct effect
of ozone on nonpathogenic fungi; 13, effect of temperature
and evaporative stress on tree growth; 14, direct effect of ozone
on pathogenic fungi; 15, interaction of nonpathogenic fungi and
soil microarthropods; 16, interaction of pathogenic fungi and soil
microarthropods; 17, effect of soil microarthropods on litter
reduction; 18, impact of predation and parasitism on bark
beetles; 19, predation of bark beetles by woodpeckers; 20, effect
of bark beetles on tree mortality and vigor and effect of phloem
thickness and moisture on bark beetles; 21, effect of phloem
moisture and thickness on natural enemies of bark beetles;
22, influence of woodpeckers on rate of parasitism; 23, effect
of nonpathogenic fungi on tree growth; 24, effect of pathogens
on tree vigor and mortality; 25, effect of soil moisture and
soil temperature on tree growth; 26, effect of soil moisture
and temperature on occurrence of nonpathogenic fungi; 27, inter-
action of pathogenic and nonpathogenic fungi;  28, effect of soil
moisture and temperature on occurrence of pathogenic fungi.
(Reprinted with permission from Taylor.™)

-------
                                                          • OX I DAN T  \!
                                                         .POLLUTANTS
                                     SYNTHESIS
                                         AND
                                     RESPIRATION
                                                  /
                                                  /  MINERAL
  WATER
 UPTAKE
    AND
TRANSPIRA-
  TION    /  [CARBOHYDRATE
                   PHLOEM Th'.CKMESS

                   PHLOEM  MOISTURE
                   RESIN DUALITY

                   RESIN QUANTITY
FIGURE 12-9.   Tree-level interactions  in a mixed-conifer  forest ecosystem.
              Types of interaction:  A,  relationship  between net photosynthesis,
              foliage age,  and foliage retention;  B,  effect of plant moisture
              stress on net photosynthesis;  C,  relationship between mineral
                                    12-31

-------
uptake and net photosynthesis; D, relationship between net
photosynthesis and carbohydrate storage; E, relationship between
water uptake and mineral nutrition; F, relationship between
carbohydrate storage and bark characteristics; G, relationship
between carbohydrate storage and cone production; H, relationship
between carbohydrate storage and cone production; 1, relationship
between cone crop and seed crop; 6, cone insect damage to develop-
ing cones; 7a, small-mammal damage to developing cones; 7b, small-
mammal predation of seeds; lOa, effect of ozone on photosynthesis
and respiration; lOb, effect of ozone on needle retention; 13,
effect of temperature, light intensity, and evaporative stress
on photosynthesis and respiration; 20a, effect of bark beetles
on water uptake and transpiration and relationships of tree
moisture stress to bark beetle attack; 20b, effect of bark
beetles on tree carbohydrate concentration and relationships of
carbohydrate concentration to bark beetle population in tree;
20c, relationships between bark characteristics and bark beetle
attack and population; 21, relationship between bark characteris-
tics and natural enemies of bark beetles; 23a, relationship bet-
ween root characteristics and mycorrhizal-forming nonpathogenic
fungi; 23b, effect of nonpathogenic fungi on mineral uptake;
24a, effect of pathogens on tree carbohydrate concentration and
relationship of carbohydrate concentrations to pathogen attack;
24b, effect of pathogens on water uptake and transpiration;
24c, relationship between stem and root characteristics and
pathogen attack; 25a, effect of soil moisture and temperature
on water uptake and transpiration; 25b, effect of soil mineral
concentration and temperature on mineral nutrition of tree.
a indicates direct influence of external factor on trees.
b and c indicate influence of tree condition on external factor.
(Reprinted with permission from Taylor.^0)

-------
FIGURE 12-10.
Community-level interactions in a mixed-conifer forest ecosystem.
Types of interaction:   1,  competition between woodpeckers and
small mammals; 2,  climate control of oxidant concentration in
different forest communities;  3,  effect of precipitation and
                                     12-32

-------
temperature on soil moisture and soil temperature in
different forest communities; 4, predation of bark beetles
by woodpeckers in different forest communities; 5, effect
of cone crop abundance on cone insect populations in different
forest communities; 6, effect of cone crop abundance on small-
mammal populations in different forest communities; 7, fruiting
bodies of nonpathogenic fungi as food for small mammals in
different forest communities; 8, smog-caused mortality and
morbity in different forest communities; 9, fruiting bodies
of pathogens as food for small mammals in different forest
communities; 10, effect of temperature and evaporative stress
on species composition in different forest communities; 11,
relationship between soil characteristics and population
density of burrowing small mammals in different 'communities;
13, relationship between soil characteristics and microarthro-
pod population; 14, bark beetle mortality caused by natural
enemies in different forest communities; 15, effect of bark
beetles on tree mortality and vigor in different forest
communities; 16, relationship between soil characteristics and
forest community composition and growth; 17, relationship
between soil characteristics and species distribution and
behavior of nonpathogenic fungi; 18,  relationship between
soil characteristics and species distribution and behavior
of pathogens;  19, influence of forest community type on
populations of natural enemies of bark beetles; 20, woodpecker
distribution and density in different forest communities;
21, effect of pathogens on tree vigor and mortality in different
forest communities; 22, relationship between nonpathogenic
fungi and forest community composition and growth.  (Reprinted
with permission from Taylor.  ^)

-------
  xl PATHOGENIC
       FUNG/
22 b
     ENEMIES CF I \
        BARK   / 2!b
      BEETLCS
                                       ABUNDANCE
                                          OF
                                     COf.'ES 0  SEEDS
   PLAN!
COMPETITION
        SOIL
       MICRO-
    ARTHROPODS
       SMALL
     MAMMALS
  FIGURE 12-11.
Stand-level interactions in a mixed-conifer forest ecosystem.
Types of interaction: A, effect of plant  competition on
abundance of cone and seeds; B, effect  of plant  competition
                                     12-33

-------
on characteristics of liying trees; C, effect of plant
competition on characteristics of shrubs; D, effect of
plant competition on characteristics of herbs; E, effect
of plant competition on tree mortality; 5, abundance of
cones and seeds and predation by cone insects; 6a, abun-
dance of cones and small-mammal predation of cones; 6b,
characteristics of forest stands and small-mammal popu-
lations; 6c, influence of shrub and herb layer vegetation
on small-mammal populations; 8a, smog-caused mortality
and morbidity in different tree species with forest stands;
8b, influence of stand conditions on concentration of
oxidants; lOa, influence of temperature and evaporative
stress on stand structure and composition; lOb, influence
of stand condition on temperature and evaporative stress;
12b, influence of stand condition on soil microarthropod
population; 15a, influence of bark-beetle-caused tree
mortality on stand condition; 15b, influence of stand
condition on bark beetle population; 16a, influence of
soil moisture and temperature on stand characteristics;
16b, influence of stand condition on soil characteristics;
19, influence of stand condition on population dynamics
of natural enemies of bark beetles; 20, relationship
between smog occurrence and woodpecker population; 21a,
influence of pathogen-caused mortality on stand condition;
21b, influence of stand condition on pathogen population;
22a, influence of mycorrhiza fungi; 22b, influence of
snags (and downed trees) on nonpathogenic fungi; 22c,
influence of stand condition on nonpathogenic fungi.
a indicates direct influence of external factor on trees
in stands,  b and c indicate influence of stand condition
on nonpathogenic fungi.  (Reprinted with permission from
Taylor.70)

-------
                                                          SOIL
                                                       CtlARACT ER-
                                                         ISTICS
COMMUNITY
STRUCTURE
#1
J
1
i
I
                                6
                            7
                            f
if) —
1 \J
I
?
I


r
c* r~i ^ f ^'^r r^ * T ' • — \*
CTPT Tp-T" '">ir
^2
8
FIGURE 12-12.
Community-succession interactions in a mixed-conifer forest
ecosystem.  Types of interaction:  1, oxidant modification
of community structure; 2, climate modification of community
structure; 3, fire modification of community structure; 4,
soil characteristics and their influence on community structure;
5, insect modification of community structure; 6, mammal
modification of community structure; 7, pathogen modification
of community structure; 8, people impact on community structure;
9, logging modification of community structure; 10, predictive
capability through integration of submodels for items 1-9.
(Reprinted with permission from Taylor.
                                    12-34

-------
                                                  25,  56,  77
       Other researchers at the University of Utah           have completed

studies to determine the ozone susceptibility of the most  prevalent species


in some major vegetation associations in the intermountain area.   These data

are intended to be combined with background information on community stability


and integrated into mathematical equations.  The equations may be able to

predict the community changes that occur after stress of various degrees.

The ozone concentrations in grassland and aspen plant communities in the


Wasatch Mountains above Salt Lake City are much lower than those in the
                                                            77
San Bernardino I-!ountains.  According to Treshow and Stewart,   "Background


ozone concentrations in the grassland communities geographically contiguous


to the Salt Lake Valley occasionally reached peaks at 15 pphm, but the

average concentration over a 1-hour period never exceeded 6 pphm at any of


the plots.  Concentrations measured in the aspen community during the study

reached 9 pphm but never for more than a few minutes at a time."  The

                               ,   .                              -, .     25, 56
present low concentrations may be important to some species or cultivars


and the plant communities of which they are members.



EFFECTS ON PRIMARY PRODUCERS (GREEN PLANTS)


       The ozone dose responses and the specific effects on the photo-

synthetic activity of both herbaceous and woody plants, principally in

controlled short exposures, are discussed in Chapter 11.  The main aim


of this section is to evaluate the effects of the chronic exposure of

vegetation in natural ecosystems to total oxidants (more than 90% ozone)


under field conditions or simulated field conditions.  The effects of


chronic exposure on agroecosystems is also discussed to a limited extent


in Chapter 11.

                  64
       H. W. Smith   has suggested three classes of ecosystem response


to air pollution:  those in which vegetation and soils serve only as  a sink


for pollutants, with no visible injury; those in which some species or


sensitive individuals within species are injured and are more subject to
                                  12-35

-------
 other  stresses;  and  those  in which high  dosages  cause  acute morbidity  or


 mortality  of  some  species.  Although  these  classes are convenient for


 discussion, in most  situations  they are  not clearly  separated in space.


 More often, these  classes  of response occur along a  gradient of decreasing


 pollutant  exposure,  as in  the San Bernardino Mountains.



 Extent  and Intensity of  Injury  to Overstory Trees in the  San Bernardino


 National Forest.—Wert (1969) used aerial photography  to  determine  the


 extent  of  oxidant  injury to ponderosa and Jeffrey pines in diameter classes


 larger  than 30 cm.   Injury was  categorized  as heavy, moderate, light or


 negligible, and  it generally decreased with distance from the source area.


 Of  the  160,950 acres  (64,380 hectares)  of  ponderosa-Jeffrey type within


 the forest boundaries, 46,230 acres (18,492 ha)  had  heavy damage, 53,920


 acres  (21,568 ha)  had moderate  damage; and  60,800 acres (24,320 ha)  had


 light or negligible  damage.  An estimated 1,298,000  trees were affected;


 of  them, 82% were  moderately affected, 15%  were  severely  affected,  and 3%


 were already dead.


        The term  "ponderosa-Jeffrey type" is a general  term that includes


 a mosaic of five subtypes described by McBride on the basis  of species

          3 la
dominance.      These subtypes are:   ponderosa pine forest, ponderosa pine-white


fir forest, ponderosa pine-Jeffrey pine forest,  Jeffrey pine forest, and


 Jeffrey pine-white fir forest.  The injury  by oxidant  air pollutants is most


 intense in the types dominated  by ponderosa pine and less intense in the


 Jeffrey pine types.  In  the field plots  of  these various  types, the average


 area covered by  shrubs is  only  3.8% in the  ponderosa types, but 26%  in the

                   31a
 Jeffrey pine types.

                     45,  68, 70
        Later studies           have expressed the amount  of injury  to


 ponderosa  and Jeffrey pines and  associated tree species  in permanent  study



                                  12-36

-------
plots as a numerical score.  The range of scores is subdivided into seven


                                                    45

categories ranging from dead to no visible symptoms.




       In 1974, all tree species at 19 permanent study plots were scored




individually by binocular inspection.  The data can be obtained from conifers




early in the fall, but the most important deciduous species, black oak, was




evaluated during 3 days, August 28-31, to prevent confusion of oxidant-injury




symptoms with natural autumn senescence of leaves.   The injury to black oak




as of August 31, 1974, at several representative study sites and the June -




August accumulated dose at nearby monitoring stations are shown in relation to




the topographic projection of the San Bernardino Mountains in Figure 12-13.




Lower scores mean greater injury.  The darkened portion of the bar represent-




ing oak injury is for leaf chlorotic mottle and interveinal necrosis.   A




score of 8 means no injury.  The remaining portion of the score is the sum of




scores for leaf complement, leaf size, and twig mortality, not shown separately.




These data suggest that oak shows no visible injury where the accumulated



                                                 5     3
June - August dose does not exceed about 2.5 x 10  jag/m -h from about  Snow




Valley eastward.




       The distribution of ponderosa and Jeffrey pines into various injury




classes with respect to the distance of the study site along the gradient




of oxidant dose (June - September) is illustrated above the topographic




projection in Figure 12-14.  It is important to realize that the 1974  distribu-




tion into injury classes is also a product of earlier years, when the  oxidant




concentrations were not always as high as in 1974 (see Figure 12-5).   The




trend toward greater numbers in the very slight (29-35) and no visible injury




(36 and greater) categories is quite evident in the eastern plots receiving




lower doses — e.g., Holcomb Valley (HV).  The assumption has been made that




ponderosa and Jeffrey pine respond similarly to oxidant.  Ponderosa pine is





                                  12-37

-------


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replaced by Jeffrey pine in the natural stands east of Camp O'ongo, and




they intermix at Barton Flats (BF).  The validity of this assumption can be




partially verified by examining the distributions of the two species into




injury classes at Barton Flats (Figure 12-14).  These data indicate reasonable




similarity at a common site; but the influence of other environmental variables




that change continuously along the oxidant gradient — such as soil moisture




availability, temperature, and humidity — must be examined more intensively




to understand the degree to which they influence oxidant susceptibility (see




Figures 12-8 through 12-12).







Trends in Oxidant Damage to Conifer Species in the 19 Major Study Plots




from 1973 to 1974.—The first evaluation of oxidant injury to all tree




species in the new study plots was completed in September and October 1973.




The second evaluation, in 1974,  offered the first opportunity to assess




trends of tree injury and mortality.  In Table 12-4, the plots are arranged




in the order of severe injury (first) to no visible injury (last), according




to the 1974 average injury score for all ponderosa or Jeffrey pine in




each plot.  Of the 12 plots categorized as severe and moderate, all but six




showed significantly lower scores (increased injury) with a probability of




0.05.  Among the remaining 6 plots classified as slight, very slight, or no




visible injury, there were three significant increases, one insignificant




increase, and two decreases (one significant and one insignificant), all at




a probability of 0.05.




       The general increase in injury in the severe and moderate plots




is probably related to the 1974  increase in June-September dose (Figure 12-5).




Tree mortality among ponderosa and Jeffrey pines was about the same in




1973 and 1974.   The largest mortality was at permanent study plots in the




moderate injury category.   Perhaps the populations in these plots still






                                  12-40

-------
                      ANNUAL GROWTH OF BRANCHES, UPPER HALF OF SAPLINGS


3S-
30-
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26-
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1 AVi.ENT AJr< OUTSIDE
2 AV3:ENT A,R HOUSE
J FILTERED AIR HOUSE








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2 3
1973
YEAR
                   32-

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                                         FIRST ORDER BRANQ< GROWTH
       l AVS1L^.T AIR OUTSIDE

       2. AMBIENT A« HOUSE
       3 FILTERED ArR HOUSE
                   :lra
                       I  2  i
                         1963
                     	jt
r"
                                   2 3
                                   1972
           Z 3
           I97J
                                         YEAR
FIGURE 12-15.
Annual  growth of the terminal shoot  (upper)  and first-
order branches (lower)  in upper half of  ponderosa pine
saplings  maintained in  filtered or unfiltered (ambient)
air greenhouses, and an outside ambient  air treatment
from 1968 through 1973.   (Reprinted with permission
from Kickert et al.31a)
                                       12-41

-------
retain greater numbers of the more susceptible genotypes.  In earlier years,


tree mortality rates for ponderosa or Jeffrey pines in several stands suffering

                                                                           68
moderate to severe injury were 8% and 10%, respectively, from 1968 to 1972,

                     45                          10
8% from 1969 to 1971,   and 24% from 1966 to 1969 .    The final cause of death

                                                  65
of weakened trees is usually the pine bark beetle.     Mortality has not been


observed in tree species other than ponderosa and Jeffrey pine.


       Data for the longest observation period of tree decline extend from


1952 to 1972 in two 5-acre (2-ha) control plots in the vicinity of Barton Flats

                                      80
in the San Bernardino National Forest.    These plots are in the Jeffrey pine-


white fir subtype and are now considered to be in an area of moderate injury


(see Barton Flats and Camp Oceola plots in Table 12-4).  All Jeffrey pines,


with a diameter breast height (dbh) of 12 in. (30.5 cm) and larger were measured and


their vigor was described by judging the risk or the probability that they would


be susceptible to attack and kill by bark bettles (Dendroctonus sp.).  Risk


classes 1 and 2 indicate low-risk trees that would definitely be preserved


if trees were being marked for a timber sale.  Classes 3 and 4 are high-risk


trees that would be marked for removal in a timber sale.  In Table 12-5, the


changes in merchantable volume in board feet (bd ft) in all four classes are


recorded for two control plots in 1952, 1963, and 1972.  The increases in


volume of high-risk trees since 1952 are remarkable; decreases in volume of



low-risk trees and total volume in the plots are very large.  The total volume


decrease is related, first, to one-by-one removal of bark-beetle-killed trees


inside the plots indicated for certain by the increase in snags and current


stumps and, second, possibly to suppressed radial growth.


       One of the objectives of the two 5-acre (2-ha) control plots was to


show what would have happened in the absence of sanitation salvage logging.


The distributions of trees in all categories in 1952, 1963,  and 1972 (Table


12-5) suggest that by 1972 in plots 1 and 2 the sanitation salvage logging



                                  12-42

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or timber sales would have removed 45% and 68% of overstory trees, respect-
ively.  The more selective tree-by-tree salvage would have removed only 8%
and 10% of the overstory trees in plots 1 and 2, respectively.  These results
must be treated as suggestions, not firm conclusions, because of the lack of
a more adequate statistical design, which should have included more plots
in additional stand types and sampling of several kinds of sites at various
distances from the pollution source.  However, because of the suggested
impact, the sanitation salvage logging practice needs careful scrutiny.
Other information is available from the ponderosa pine subtype that suggests
that biomass production of overstory species is diminished in proportion
                                             54
to the oxidant dose received.  Parmeter et al.  observed decreases in
height growth of ponderosa pine that showed injury symptoms.   Injured
trees did not respond with greater growth during years with more favorable
soil moisture content; uninjured trees (often side by side with injured
trees) did have increased height growth in these years.  McBride (in
             3 la
Kickert et al.  ) studied two populations, each including 19 ponderosa
pines dominant in their stands.  One population ranged in age from 52 to
71 years in 1972, and the other, from 20 to 39 years.  The influence of
tree age on ring width growth was minimized by comparing rings of equivalent
age in each population.  The measured rings in the older group were produced
from 1910 to 1940, before the advent of "Los Angeles smog," and in the
younger group, from 1941 to 1971, when smog was present.  After the
influence of precipitation on growth was evaluated,  there was a difference
of 0.20 cm in average annual growth attributable to oxidant air pollutant
injury.  In this sample, a 30-year-old tree subjected to air pollution would
be 24 ft (7.2 m) tall and 7.5 in.  (19 cm) in dbh, with one 16-ft (48-m) log
having a volume of 30 bd ft.  In comparison, a 30-year-old tree growing

                                  12-45

-------
 before  the  injury by oxidant air pollutants  (1910-1940) would be 30 ft  (9 m)




 tall and  12  in.  (30.5 cm) in dbh and could yield a 4.8-m log with a volume




 of  80 bd  ft.  The impact of oxidant stress on forest growth is apparent




 without further  eleboration.




        The  growth suppression of ponderosa pine saplings has been demonstrated




 by  enclosing a group of 10 naturally seeded  trees in the plastic-covered



                             72
 greenhouses used by Thompson;   enclosed trees were provided with activated-




 charcoal-filtered air (FAH) from April through October 1968 - 1973 by


                                     31a

 Miller  and McBride (in Kickert et al).    The controls consisted of two




 similar groups of trees, one in a greenhouse receiving unfiltered or ambient




 air (AAH) and another group not enclosed (AAO).  Precipitation was rare




 during  the summer enclosure period, and all  three groups received the same




 amount  of winter precipitation.  At the end  of the 1973 growing season,




 most of the saplings were harvested from each treatment for growth analysis.




 One indicator of the response to these treatments was the length of annual




 growth of terminal shoots and first-order branches in the upper half of




 the saplings (Figure 12-15).  After an initial lag in 1969 and 1970, the




 growth of shoots and branches on the FAH trees increased dramatically.  The




 retention of annual needle whorls was remarkably different by 1973;  needles




 in internodes older than 1972 were completely absent from the AAH and AAO




 trees.   The decrease in needle biomass on the AAH and AAO trees for the




 1973 whorl was 32 and 37%,  compared with that on FAH trees (Figure 12-16).




       Needle length and litter production furnish another important




measure of biomass decrease.  In field studies,  it was found that the




 average amount of litter production increased with decreasing ozone injury




 of selected ponderosa and Jeffrey pines (r = 0.55) and that the average mass




 of needles per fascicle increased with decreasing ozone injury (r = 0.96).




       Early studies   suggested that injury to ponderosa pine was similar




 in all size classes,  but Cobb and Stark   later reported higher mortality




                                12-46

-------
                      180

                      170

                     §,.50

                     uj 150-
                    KJ .33

                    S 120

                    £ MO
                    0.
                      TO
                    | 60.
                    < 50-
                    s
                    UI 40-
                    cr
                    u.
                    o ,„
           MASS OF NEEDLES RETAINED PER iNTFRNODE BY
           PONDEROSA PINE SAPLINGS M 1973
            I AW3IENT ArR OUTSIDE

            2 AMBIENT AR HOUSE

            J FILTERED AIR HOUSE

                                                        I  2 5

                             1969       1970       1971        1972

                           YEAR INTERNOOE AND NEEDLES WERE PRODUCED
                                                 I  2  3

                                                  1973
FIGURE 12-16.
Average weight of all  needle  fascicles retained in 1973
per  internode  in filtered or  unfiltered (ambient) air
greenhouses, and an outside ambient air treatment after
treatment since 1968.   (Reprinted with permission from
Kickert  et al.31a)
                                         12-47

-------
 rates  in understory ponderosa pines  (9-12 in., or 22.9 - 30.5 cm, in




 diameter)  than in larger size classes.  The probable effect of tree



 mortality  on stand composition can be anticipated to some extent from an




 example of the present species and size-class composition, as shown in


           45
 Table  12-6.    In this severely damaged stand in the ponderosa pine-white




 fir subtype, nearly 50% of the overstory and about 22% of the understory




 is ponderosa pine.  With all size classes considered, 16.1% had slight,




 33.3% moderate, 31.2% severe, and 19.4% very severe injury.  White fir




 and incense cedar are well established in the understory, but their poorer




 survivorship to 12.00-23.99 in.  (30.5 - 60.9 cm) in dbh compared with




 ponderosa pine suggests that other mortality factors have acted heavily




 on them in the past.   Incense cedar and sugar pine are the most tolerant




 to oxidant, but sugar pine is present in very low numbers.  The accelerated




mortality of ponderosa pines has particular significance in this ecosystem,




because it is the dominant member of the climax community.




       The direct effects of ozone on plant species constituting the




 shrub layer in the conifer forest are not yet sufficiently understood




to permit any conclusion to be drawn.  In many sites where the conifer




overstory is well developed,  the shrub species are excluded completely.




In more open pine stands,  some shrubs are very common,  such as skunk bush




 (Amorpha californica) and white thorn (Ceanothus cordulatus).  Of these



two species,  only skunk bush shows highly visible chlorotic mottle of




leaflets and premature defoliation where ozone dosages  are high.   A shrub




species common to the lower chaparral zone,  squaw bush  (Rhus trilobata),


                                         57

is even more susceptible to ozone injury.     In the San Bernardino Mountains,




166 herb-layer species have been identified as common to the conifer forest.
                                  12-48

-------
                                Table 12-62.

       Tree Species and Size Composition on a Study Site Affected by
                                               
-------
The phenology of these species is being studied so that growth and flowering



can be correlated with soil moisture availability and seasonal changes of



ozone dose.  Initial field observations suggest that at least 10 species are



obviously injured by total oxidant in areas receiving high dosages.  These



areas have been subject to exposure for at least 20 years, so some species

                                                        18
or subspecies may have been completely eliminated.  Dunn   reported that



smog may have acted as a selective agent to remove oxidant-sensitive



subspecies of Lupinus bicolor from the Los Angeles area.  Furthermore,



L.' latifolius appeared to have floral ontogeny inhibited without damage



to leaves, and _L. densiflorus was severely damaged by ambient total oxidant



at Claremont, California.

            56
       Price   selected six important grass species found in either the



Gambel oak or quaking aspen communities in the Wasatch Mountains of Utah.



The selected species were fumigated under greenhouse conditions with ozone



varying from 0.15 to 0.30 ppm during each experiment.  These treatments



caused a 53% reduction in top-growth biomass of the six species.  The initia-



tion of reproductive structures of all species was inhibited, and the repro-



ductive potential of Bromus tectorum and ,B_. carinatus declined to zero.



These results suggest that the species composition of affected natural



communities could be altered.   In other studies,  17 representative species



from the quaking aspen community were fumigated with ozone 3 h each day, 5



days/week, with ozone at 0.30, 0.15,  and 0.05-0.07 ppm in the first two



cases and with ambient total oxidant in the last case.  Experiments extended



through three seasons.   At concentrations of 0.15 ppm or below,  growth



reduction and stimulation were both observed in different species;  growth



was reduced in all but 2 species at 0.30 ppm.   Seed production was reduced



in 2 species at 0.15 ppm and in 3 species at 0.30 ppm, of the total of 6


                                      25
species that produced fruits or seeds.





                                  12-50

-------
                                                            77
       In a third series of experiments, Treshow and Stewart   fumigated


native plants growing naturally under field conditions.  The threshold ozone


concentrations required to injure important species in the grassland-oak and


aspen-conifer communities during 2-h exposures were determined (Table 12-7).


Three important species — Bromus tectorum, Quercus gambelli, and Populus


tremuloides — were injured by a single 2-h exposure to ozone at 0.15, 0.25,


and 0.15 ppm, respectively; over half the remaining species showed visible


injury after exposure to 0.30 ppm or less.   The implications for possible


imbalances in community stability are readily apparent if these plant


communities receive dosages similar to those typical in the San Bernardino


Mountains.

                     84
       Yonkers et al.   have tested the ozone susceptibility of 15 species


of annuals common to the Mojave Desert just north and east of the Los


Angeles basin (and San Bernardino Mountains).   Compared with the susceptible


pinto bean plants included in the experiment with ozone at 0.35 ppm, Plantago


sp., Cercidium sp.,   and Prosopsis sp. were also sensitive.  Further


interpretation of these results is complicated by the influences of plant


age and preexposure conditions.



Dose-Injury Observations with Ambient Oxidant and Native Ponderosa Pine


Saplings.—During 1969, 1970, and 1971, 10 sapling-size ponderosa pines


that received the ambient air outside (AAO) treatment for comparison with


trees enclosed in filtered- or ambient-air  greenhouses were observed


to determine the rate of current-year needle growth and appearance of

                                                               3 la
oxidant injury symptoms on both current and 1-year-old needles.    Forty


new needles on each tree were measured monthly (Figure 12-17, left); growth


leveled off in early September.  Current-year and 1-year-old needles were
                                  12-51

-------
                                                   Table 12-7-

                                  Injury Thresholds  for  2-hour-s Exposures  to  Ozone
                 Species
            Grassland -Oak Ccm.-.yjnity Species
  Injury
 thresh-
   old
 (pphm
 c:one)
                                                                                                           injury'
                                                                                                           ihrcsh-
                                                                                                            olci
 Tiees & Shrubs
     Acer gr2,*~,'d-::-:2':,(m Nutt.
     Xet/-;;^../:^L.
     Ar!-.-..--'-!J !i;J-:-'3!a Xutt
     /,/.7'.^ ••••- u r:,:5- G.Don
     Cclcckcrtt'.s r.'.mdi.i icrr.
     Cirsi'.irr. crceiise (L.) Seep.
     Ccr.in.-r: n:ocn^sliim  L.
     Ifrdyssrum boreale Nutt.
     Hclicn'ik'.is cr.nus L.
     i /"  _7*        '   y

     F>:ime.~ crisp:is L.
     Urtica grsciif:  Ait.


 Glasses
     Era:-us brizzeforrr.is Fisch. & Mcy.
     /?,-ps:c!a Piper
     O$rr.or'r.'::a cc-::dsr.lalis Torr.
     Pl'.ncelia hfliropr.ylia Pursh
     Polcmcn;:irr> fc':osisi'.m'.) O.E.Scliulr
     Gdimn bifc!:'i,i:i V.'ais.
     Guyepfiylitn: racc;rs^'.,.T, T. JL G.
     Po[/~ont:!r, dc.i\;h:i'. Gieeri

Grasses
     A$ropyron cn::'i nisi (L.) F-cauv.
     }lroir,:/s ccr,'"j'i;s Moo!<-  ^- AMI.
       25
 under 25
       15
       30
   '    25
 under-10
       30
       30
       30
       30
  over 15
 under 25
       15
  over 25
  over 25
       25
       30
  over 25
 under -40
  over 3D
       25
 under 25
       30
       30
 under 30
    "  15
  over 25"
  over 25
       25
  over 25
  over 30
under 25
under 25
       25
 over 30
       30
 over 25
 over 25
under 25
        Reprinted with  permission from  Treshow and  Stewart.77
                                                       12-52

-------
inspected monthly for amount of chlorotic mottle, necrosis,  and abscission.


Each symptom was given a descriptive rating:  0,  none;  1,  very slight; 2,


slight; 3, moderate; and 4,  severe.   In Figure 12-17,  an average of the 3


years shows that, by Julian day 250 (September 7),  the current-year needles


had a visible-injury score of 2.2, indicating slight chlorotic mottle (sig-


nifying severe injury to the trees);  there was usually no necrosis and almost


always no abscission of current-year needles.  Symptoms developed more rapidly


on 1-year-old needles; the combined score of  the current-year and 1-year-old


needles was about 9.


       The accumulated ozone dose since June  1,  which is associated with the


current-year and 1-year-old needle injury expressed on the left of Figure 12-17


can be roughly estimated by transferring the  injury score to the right.   For


example, the current-year needle score of 2.2 on September 7 is associated with

                                 5     o
a total oxidant dose of 2.75 X 10  ug/m -h.   These  results assume that all the


air monitoring data were available,  but on the average about 90% were available.


The dose-injury curve is apparently not linear as assumed, and interpretation


is further confounded by the random occurrence of injurious  doses in the


field.  Additional observations of ponderosa  and Jeffrey pine are required


to define more completely the ozone or total  oxidant dose response.   The


development of a model relating injury to dose and  important controlling


environmental variables is a high-priority need for understanding chronic-


exposure effects.



Effects on Reproduction


       The effect of ozone injury on herbaceous plant  reproduction has


been mentioned earlier in this chapter and in Chapter  11.   Seed production


by annuals is influenced mainly by the environmental conditions of the current
                                 12-53

-------
         SYMPTOMS COMFiPED TO 3ATE AND
         STAGE OF NEW NEE^IF GrC>,TH,
         JUIt THRU senrw.HsTF 195». 1570. 1971
                 JULliN  DATE
                                     INCREASE OF VIS'atE NEEDLE STMPTOMS
                                     COUPCRfO WITH TOTAL OXIMKT DOSE
                                       ERCt*. P'NE SAPLINGS
                                                     RIM FORfST. CA
                                                     JUNE- SEPTEMBER
                                                     1969,1970. 1971
                                                                             CURRENT PLUS
                                                                             OHE-TtAR-OLD
                                                                             NEEDLES
                                                                           CURRENT >TAR
                                                                           •CEDLES ALONE
                                                      OS
                                                   ACCUMULATED DOSE
FIGURE 12-17.
Development of oxidant injury symptoms  on current and
current-plus-1-year-old needles of ponderosa  pine
saplings, in  relation  to stage of current-year  needle
growth and time during the summer season (left)  and
in relation to total dose of  oxidant  (right).  „..
(Reprinted with permission from Kickert et al.    )
                                         12-54

-------
year, but perennial woody plants — particularly conifers — are erratic


seed-producers.  Intrinsic factors affecting cone production include age


and vigor; seasonal temperature and soil moisture are important environmen-

            22
tal factors.


       The effects of sulfur dioxide on cone production have been described


by Scheffer and Hedgecock   and Pelz.     Generally,  the decrease in tree


vigor caused by the pollutant may eliminate or lower the frequency of cone


production and diminish the size,  weight,  and germination of seed.   The


effects of chronic ozone injury on conifer seed production may be similar,


in that tree vigor is drastically reduced.  The effects of chronic ozone


injury on ponderosa and Jeffrey pine seed production are under investigation

                          3 la
by Luck (in Kickert at al.    )


       Seeds from individual species may constitute  the bulk of the diet


of small vertebrates, such as the deer mouse (Peromyscus sp.)  and the western


gray squirrel (Sciurus griseus anthonyi).   During periods of low seed


production due to diminished tree vigor, squirrels converge on the few


remaining vigorous ponderosa pines and consume about half the seed crop


before it matures and reaches the ground.   In the areas severely affected


by ozone, squirrels return to the same trees year after year.   After the


seed reaches the ground, other small vertebrates, such as mice, seek it out.


The habit of preferential seed use by small vertebrates may be a stress


acting additively with ozone injury to decrease seriously the regeneration


potential of ponderosa pine.




Indirect Effects


       Most indirect effects of oxidant air pollutants on primary production


and reproduction would be mediated through changes in the physical environ-

                                                                      28
ment resulting from disruption of stand structure.   For example, Hursh




                                12-55

-------
described three microclimates in the area surrounding the ore smelter at


Copper Basin, Tennessee.  These zones were distinguished by changes in air


and soil temperatures, winds, evaporation, air moisture, and rainfall.


Because sulfur  dioxide was the pollutant in this case, there were also


changes in soil pH and sulfur  content, which would not accompany oxidant


air pollution damage.  Soil erosion increased dramatically.


       Changes in such physical factors as light, temperature (particularly


maximums and minimums), relative humidity, and wind speed in forest communities


subject to structural alteration by mortality of susceptible species could


change the suitability of some sites for growth, reproduction, and reestablish-


ment of survivor species.  We can only speculate on some of the possible

                                               45
secondary effects until more data are gathered.


       Wildfire is a very important factor in western forest ecosystems.


In the San Bernadino Mountains, the fire frequencies were determined by


J. R. McBride and R. Laven (in manuscript) in two stand types before and


after 1893, when the area was first set aside as a forest preserve and


fire protection began.  Before 1893, the average interval between fires in


ponderosa stands was 12 years; after 1893, it was 24 years.  The comparable


numbers for Jeffrey pine stands were 16 and 38 years.  The buildup of heavy


fuels due to ozone-caused mortality and fire protection results in hotter


fires, and the thinning of the tree canopy results in increased rates of

            14
fire spread.    Hotter fires decrease tree survival.  Moisture interception


by condensation in living tree crowns would decrease as the stands became

                                             32
thinner,  thus causing some sites to be drier.




EFFECTS ON CONSUMER POPULATIONS


Vertebrate Populations


       The effects of oxidant air pollutants on vertebrates can be


segregated into direct and indirect categories.  Direct effects are clinical



                                 12-56

-------
and pathologic alterations of tissues that result from exposure to ambient




air.  Indirect effects result from alterations in numbers or distribution




of the plant and animal populations exposed to ambient air.  For example,




if air pollution eliminates or thins numbers of a susceptible plant species,




the food chain of the consumers that feed on it may break down.  The result




could be a simpler and less stable ecosystem,  with fewer plants and animals




in species and numbers.




       The clinical and pathologic effects of  oxidant air pollutants on




domesticated vertebrates have received little  study in the laboratory.  We




have found no major references to studies of these effects on free-ranging




native species.  It is therefore necessary to  extrapolate from laboratory




results to probable effects on wildlife in the field and forest.




       Chapter 8 indicates that oxidant air pollutants may adversely affect




the olfactory and sight senses, degree of activity, general health and vigor,




reproductive rate,  heart and kidney function,  protein synthesis,  respiratory




function, and disease resistance in domestic vertebrates in laboratory




conditions.  Many of these adverse physical responses develop at or near




the concentrations of ozone currently experienced daily in ambient air in




parts of the San Bernardino Mountains.




       Although it is risky to extrapolate from domestic species in a




laboratory to free-ranging species in the forest, it appears likely that




some wild vertebrates in the San Bernardino Mountains could be affected




adversely by their prolonged exposure to current concentrations of ozone.




Nitrogen dioxide, PAN,  ozone,  and environmental factors may act additively or syne




gistically to increase the overall stress on the individual.  Potentially, the




direct effects of oxidant air pollution on wild vertebrates within a forest




system could be great.   A reduction in visual  or olfactory acuity or other






                                  12-57

-------
 loss  of  health  or  condition  could be a  serious handicap for a predator

 whose survival  depends on overcoming prey, and equally serious for  the

 prey  that  survives by staying one jump  ahead of a predator.
       In  the San Bernardino Mountains, our goals have been to describe
 the terrestrial vertebrate community within this mixed-conifer forest,

 particularly in relation to  ponderosa and Jeffrey pine stands, and  to
 determine  the effects of oxidant air pollutants on this community.  The

 possible   interactions of vertebrates in this system are shown in Figures

 12-9  through 12-12.
       The most abundant species of small mammals were selected to  exemplify

 vertebrate interactions, because of the importance of this group as seed-

 eaters.  The results from trapping of abundant species show that the deer
 mouse  (Peromyscus spp.)  is the most numerous.    Chipmunks (Eutamias spp.),

 the golden-mantled ground squirrel (Callospermophilus lateralis), the

 dusky-footed woodrat (Neotoma fuscipes), the meadow mouse (Microtus californi-

 cus),  and the harvest mouse  (Reithrodontomys megalotus) are the other common
              33
 small mammals.    Numbers have fluctuated widely from year to year  and

 from  plot to plot, as is characteristic of small-mammal populations.  Deer

mouse numbers fluctuate the laost.  Preliminary analysis indicates that the
 same species of small mammals are present in this forest as were reported
                                    33
 from similar trappings 70 years ago.     Thus,  it appears that oxidant air
pollution has not yet resulted in a reduction in the diversity of this

 component of the vertebrate fauna.   Population numbers of the common small-

mammal species do,  however,  appear to be low,  in comparison with other
                       31a
 similar forest regions.      This is particularly true for the study plots

 in areas of heavy oxidant air pollution.  We have not yet determined whether

 these low population densities of small mammals are directly or indirectly

 related in any measure to the oxidant air pollution.   These differences

                                 12-58

-------
may result from variations in other aspects of habitat quality.  For example,


the study plots in the areas of heavy oxidant air pollution are dominated by


ponderosa pine and have sparse shrub cover, whereas the study plots in areas


of light oxidant air pollution are dominated by Jeffrey pine and have much

      u  v       31a
more shrub cover.


       When changes occur in one part of an ecosystem, the intimate nature


of the interrelationships results in changes in many other parts.  Any


factor that causes change in one component of a system potentially affects


all subsystems of that ecosystem.  The most important indirect effects of


oxidant air pollutants on vertebrates are those resulting in changes in the


habitat.  Foremost among these effects are those on the vegetation and


the successional patterns of the plant community.   Because of the high


degree of interrelationship and interaction between the vegetation,  the


fauna, and the inorganic matrix of an ecosystem,  effects of air pollution


on the vegetation potentially can result in changes throughout the ecosystem.


Damage to vegetation is probably the most important effect of chronic, low-


concentration air pollution on wildlife.  Ponderosa pine,  Jeffrey pine, and


black oak are all susceptible to damage, and these are the most important


trees within the forest as providers of food and habitat for wildlife.  A


similar selectivity by species doubtless occurs within the shrub and herb


layers of the vegetation.   The long-term effects will be reduced production


of fruits and seeds and elimination of the sensitive plant species and,


therefore,  reduction in the diversity of the vegetation.  In turn, this will


lead to a reduction in abundance and diversity of the vertebrate fauna.

                                      Q O
       Likewise,  Woodwell's prediction   of enhancement of the activity


of insect pests and some disease agents (which has been demonstrated on


this forest)  could lead to an increase in vertebrate species that feed


on invertebrates or utilize dead plants for cover.  Birds  would be the



                                  12-59

-------
most  likely  to  increase and, to a lesser extent, such small mammals as


deer  mice, which are partially insectivorous.


       Fruit and seeds make up the largest part of the diet of most of


the common small mamals on our study sites, particularly the deer mouse,


harvest mouse,  chipmunk, ground squirrel, and western grey squirrel (Sciurus


griseus).  The  grey squirrel is an excellent example of the interactions


within this forest  and of the potential effects of oxidant air pollution.


It is abundant  throughout the mixed-conifer type, depending specifically


on the pines and oaks for the majority of its food, cover, and nest sites.


This  squirrel eats or stores a major portion of the pine and oak seed crops


each  year.  On  some yellow pine trees on our study plots, grey squirrels


cut more than 2,000 cones per tree.


       Thus, tree squirrels are a major source of loss of seeds of


ponderosa, Jeffrey, and sugar pine and of black oak acorns.   Vertebrates,


then, can have a major effect on the reproduction of these species, particu-


larly because the grey squirrel is only one of numerous species in this


forest that feed on conifer seeds and acorns.


       An alteration of the balance between pine and oak,  a change in squirrel


populations, or a reduction in any of the mast crops brought about by oxidant


air pollution obviously could have a major impact on this forest, particularly


on tree reproduction and successional patterns.   Reductions in conifer seed


crops as a result of air pollution has been suggested in other forests,


where cone production was lowered and size, weight, and germination ability

                          55,  60
of the seeds were reduced.


       Another way that oxidant air  pollution could affect this subsystem


is through an alteration in forest moisture.   Elimination of vegetation cover


allows the exposed soil to dry more  rapidly,  which would affect soil-burrowing


and soil-inhabiting vertebrates.   The lower moisture content may reduce or



                                  12-60

-------
inhibit fruiting-body formation of fleshy fungi.  These fleshy fungi are an


important food source for tree squirrels, making up a third or more of their


diet in some seasons.  A reduction in this food source doubtless would result


in an even greater utilization of conifer seeds and acorns, reducing further


the reproductive capabilities of these trees and eventually limiting future


food supplies for the squirrel population.


       In summary, subtle and simple initial changes may radiate and


magnify throughout all trophic levels of the ecosystem.   Restoration of


the system may be impossible.




Kacroarthropods

                                                               2
       Laboratory studies have indicated that ozone at 196 pg/m  (0.10


ppm) was lethal to adult houseflies (Musca domestica L.) and caused them to

               2
lay fewer eggs.   Two cockroach species (Paraplaneta americana L. and


Nauphoeta cinerea, Oliver) and the red fire ant (Solenopsis invicta Buren)


were exposed to ozone at 588 ;ug/m  (0.30 ppm) for up to LO days.  There was


no unusual mortality or evidence of direct injury to individual insects.


The fire ant workers were stimulated to migrate inside their nest initially,


but further observations indicated no disruption of social behavior.    These


reports do not suggest that free-ranging insects would be directly affected


by ambient concentrations of ozone in natural ecosystems or agroecosystems.


       The indirect effects of ozone through modification of the availa-


bility of food for insects, particularly in a conifer-forest ecosystem, has


received some investigation.  '      The weakening of ponderosa pines by


chronic exposure to ozone makes them more vulnerable to successful infesta-


tion by pine bark beetles (Dendrqctonus brevicomis and _D. ponderosae).


Figure 12-18 shows a  positive relationship between degree  of  tree injury  and


frequency of bark beetle infestation and the relative frequency of attack



                                 12-61

-------
                            SF .^ f*
                            WJJftTT
           SMOG INJURY RATING
                                               I
                                               I 20
                                                    M
                                                              '.Iv^CO'-'-S CNLT

                                                              V;H-EO BY uorw :
                                                              SMOO IUJ'JflY RATING
FIGURE 12-18.
Relationship between degree  of oxidant injury to ponderosa
pines and  bark-beetle attack (left) and numbers of trees
killed by  western pine beetle, mountain pine  beetle, of
the two  species together  (right).   (Reprinted with permission
from Stark and Cobb.  )
                                     12-62

-------
by the two species of bark beetles.    The relationship (see Figures 12-9


through 12-12) between tree health and brood productivity and the population


dynamics of bark beetles and their insect associates in infested trees are

                   31a, 70
being investigated.         Pine bark beetles have been a constant threat


to ponderosa pines in the San Bernardino Mountains for many years, since

                                                     67
before the inception of oxidant air pollution injury.     Bark beetles are


a key element responsible for accelerating the modification of stand structure.
Plant Parasites and Symbionts


Parasitic Phanerogams.  Both true mistletoe and dwarf mistletoe are common


parasites of forest tree species.  The true mistletoes (Phoradendron sp.)


occur commonly on California black oak and white fir and less often on incense


cedar in the San Bernardino Mountains.  No direct effects of oxidants have


been noted on the mistletoe plant itself under field conditions.   The true


mistletoe obtains mainly water from its host and would be indirectly affected


by debilitation of the host tree.  The dwarf mistletoes (Arceuthobium sp.)


are common on ponderosa, Jeffrey, and sugar pines in the San Bernardino


National Forest.  They depend on their host for both water and carbohydrates.


Heavily infected or "broomed" branches on ponderosa or Jeffrey pines severely


injured by ozone often have more annual needle whorls retained than do uninfec-


ted branches on the remainder of the tree.   The needles are also  greener.


It can be hypothesized that the infected branch is a carbohydrate sink where


a pooling of carbohydrates occurs; higher carbohydrate concentrations may  be


instrumental in either preventing or helping to repair ozone injury to needles


on the broomed branches.  In the long term, stresses from mistletoe and ozone


are probably additive and hasten tree death.



Parasitic Fungi.  Fungi that infect  above-ground plant parts causing leaf


or stem diseases may be directly affected by ozone, as discussed  in Chapter 11.




                                  12-63

-------
Ozone  injury  to needles of eastern white pine increased infection by
                                               12
Lophodermium  pinastri and Pullularia pullulans.    These results suggest
that leaf tissue of many species may be made susceptible to fungi that are
normally saprophytes but may be low-grade parasites when circumstances permit.
       In the San Bernardino National Forest, the needle- and twig-
infecting fungus Elytroderma deformans is a common fungus disease of ponde-
rosa and Jeffrey pines.  The additive stresses of ozone and fungus on the
host may hasten tree decline in severe cases.  In some situations, it appears
that infected or broomed twigs may die sooner than uninfected twigs at the
                                                        31a
same position in the tree.  Observations are continuing.
       Root-infecting fungi, such as Armillaria mellea and Fomes annosus,
are generally more virulent pathogens when they encounter  trees already
weakened by other stresses.  This observation has been made mostly in
Europe, where sulfur dioxide was the principal pollutant; the spread and
virulence of j?.  annosus across the gradient of decreasing oxidant dosage
                                                  31a
are being studied in the San Bernardino Mountains.
       Significant increases have been reported in length of root tissue
colonized by annosus when artificially inoculated ponderosa and Jeffrey
pine seedlings were fumigated with ozone at 431 pg/m^ (0.22 ppm) and 888 fig/m
                                       3 la
(0.45 ppm)  12 h/day for 58 and 87 days.
       Beneficial mycorrhizal fungi infect the small feeder roots of
trees and other plants.   The resulting relationship is symbiotic and involves
an intimate exchange of minerals and essential metabolites.   The host tree
benefits through increased efficiency of nutrient uptake from the soil.   Any
interruption or imbalance of the exchange of materials between the host  root

tissue and the fungus mantle surrounding it can have deleterious effects on
the fungus and the host.   Such stresses as air pollution injury to the host
                                 24
undoubtedly disrupt this balance.     The feeder rootlet system of ponderosa
pines in the San Bernardino Mountains and those of  eastern white pine have

                                12-64

-------
shown remarkable deterioration involving diminished numbers of mycorrhizal

                                                                              54
rootlets, which are replaced by saprophytic fungi that decay smaller rootlets.




EFFECTS ON DECOMPOSERS


       Although some of the solar energy fixed by producing plants is


released by the respiration of these plants and of animals, much of it is


stored in dead organic matter until released by decomposer organisms at


rates that vary greatly with place, season, and kind of organic matter.


Generally, one-third or more of the energy and carbon annually fixed in

                                                                    53
forests is contributed to the forest floor as litter, mostly leaves.


Because litter is generally related to the quantity of photosynthetic


tissue in the ecosystem, it is a useful index of ecosystem productivity.


       One of the predicted effects of pollutants on ecosystems suggested

           83
by Woodwell   is a reduction in the standing crop of organic matter, which


would lead to a reduction in nutrient elements held within the living system.


The evidence discussed earlier definitely shows that primary production is


much lower in an ozone-stressed conifer-forest ecosystem.   This result


would be anticipated in all similarly stressed natural ecosystems or


agroecosystems.


       The reservoir of energy and mineral nutrients represented by


litter is a very important resource in natural ecosystems  with closed nutrient


cycles.  The growth of new green plant tissue depends on the slow release of


nutrients by decomposer organisms.  In agroecosystems geared for high


producticn, litter is often removed or burned, and fertilizer is added to


the soil; the nutrient cycle is open and subsidized.


       In a conifer forest, litter production and decomposition release


about 80% of the total minerals in the biomass of the stand; the remainder

                                            41
is retained in the living parts of the tree.    Standing dead material is


not considered litter.



                                  12-65

-------
       In terrestrial ecosystems, most decomposers occupy the mantle



of litter or the surface layers of the soil, where they supply the necessary



recycling mechanisms to convert dead plant or animal material into humus and



eventually into minerals, gases, and water.  Small animals, arthropods, fungi,



and bacteria exist as a complex in intricate food chains in which they feed



not only on dead material, but also on one another, ultimately releasing the



mineral nutrients needed by the producer populations.  Without the decomposers,



some essential elements — such as calcium, phosphorus, and magnesium — would



concentrate in the litter until the supply in the soil was depleted; growth



of green plants would then be seriously limited.





Direct Effects



       The decomposition of tree leaves is not entirely confined to the



litter layer on the forest floor.  Leaves and needles are invaded by bacteria



and fungi even as they grow; these microorganisms may be either pathogens or


            29
saprophytes.



       The first possible interaction between ozone and decomposer organisms



might be with the bacteria and fungi that occupy the surface of the living



green leaf.   The direct effects of ozone on microorganisms are discussed in



Chapter 11,  but very little conclusive information is available that can be



applied to natural conditions.



       It is not known whether ozone,  PAN, or other oxidants could have



any direct influence on decomposer organisms in the litter layer;  however,



there does appear to be a rapid flux of ozone to soil surfaces.  The ozone



flux to some kinds of surfaces constituting ecosystems—e.g., vegetation,  soil,



and water—has been determined by Aldaz;   he expressed the flux as molecules



per square centimeter per second times 10.    The relative fluxes into


                                                              o

different surfaces, assuming an ozone concentration of 40 jig/m ,  were:
                                12-66

-------
fresh water, 0.5; snow, Q.9;  grass, 1.1;  sand or dry grass,  5;  and juniper


bush, 10.  Furthermore, it was found that bare soil destroyed about 75% more


ozone when dry than when moist.  The determination of ozone flux to surfaces


may be a far more realistic measure of dose to living organisms than atmospheric

                                          46
concentration of ozone, according to Munn.



Indirect Effects


        The concentration of plant nutrients in litter influences both the


rate of decomposition and the amount of nutrients released after decomposition.


Ozone-injured foliage may be deficient in inorganic nutrients,  because of the

                                                                   54
concomitant decay of the root systems of chronically injured trees.


        Coniferous leaf litter is more resistant to decomposition than

                    41
broad-leaved litter.    Both low inorganic nutrient status and the presence


of organic compounds that are toxic to microorganisms may account for slower


decay.  Ozone injury to needles or broad leaves might result in an accumula-


tion of phenolic compounds that are toxic to bacteria and fungi.  The rate


of litter decomposition might be decreased.  A high carbon:nitrogen ratio


related  to nitrogen deficiency may also  slow decomposition.

                     31
       Katz and  Lieth   have  categorized the roles  of both microflora and


microfauna groups in litter decomposition.  They have discussed the success-


ional trends of  microflora and microfauna populations during the warm season.


A  typical problem emerges when population sampling  is attempted:  "a consis-


tent feature of  communities is that they contain a  comparatively large

                                                                      49
number of species that are rare at any given locus  in time and space."


The  task of identifying interactions  (see Figures 12-9 through 12-12) of


decomposer populations with pollutants,  particularly oxidants, is formidable.


       In the San Bernardino Mountains,  studies are going on to describe


the  effects of oxidant injury  to ponderosa and Jeffrey pines on the microar-


thropods and fungi of  the litter layer under trees with various degrees of


                                   12-67

-------
 injury.   Initial observations suggested lower population densities  of


 microarthropods in the classes Insecta, Arachnida,  and Myriapoda under  some

                        31a
 severely injured trees.


         A coincident effect  on decomposers may be from the accumulation of


 heavy metals,  such as lead,  which is  entrained in the photochemical oxidant

                                       59
 complex.   In Sweden, Ruhling and Tyler   have preliminary evidence  that litter


 decomposition  rate in a  spruce forest was limited by  increased  concentration


 of heavy-metal ions, but only during  times of the year when water and tem-


 perature were  not limiting factors.


         The  difficulties of  understanding population  changes of litter-


 decomposing  microflora and microfauna as an  index of  pollutant  effects  suggest


 that  a more  simple approach  should be used at the outset.   The  least sophisti-

                                       51
 cated expression of accepted procedure   is:


                Ax
                — =  income  for interval - loss for interval,
                At


 where Ax  is  the change in amount of litter over the interval t.   This express-


 ion describes  energy storage in litter and indicates  the balance between


 producers  and  decomposers.   Typical annual litter production, steady-state


 accumulation on the forest floor,  and associated decomposition  rate factors

                                                                      51
 have  been  estimated for  several locations and types of forest litter.


 Comparisons  of  litter  decomposition rate factors under similar  stands of trees


 subjected  to various doses of  oxidant air pollutants  could be useful for


 quantifying  the dynamics  of  ozone-induced tree  decline.   This approach  is

                                                 3 la
 being investigated  by  Arkeley  (in  Kickert et  al.    )  in  the San  Bernardino


 Mountains.



        Sophisticated  decomposition models are  being  developed.   A  simulation

                                       o

 model developed by  Bunnell and  Dowding  for tundra  sites  is  a nine-compart-


 ment  model with 23  transfers between  compartments.  This  type of  model  may


 provide the  only method for  understanding the extremely  complex  litter


decomposition process.



                                   12-68

-------
        In summary, it is anticipated that decreasing litter production by



green plants experiencing pollutant stress would result in a similar reduction



in the inventory of nutrient elements held within the system,  owing to the


                                                                         37
interruption of cycling pathways and mechanisms of nutrient conservation.





CONCLUSIONS



        The transport of injurious concentrations of ozone and other oxidants



to rural areas downwind from urban centers at numerous locations in the United



States appears to be on the increase.  '       Blumenthal j^t al.   conservatively



estimate that the urban plume from the Los Angeles area "could cause ozone



concentrations to exceed the Federal standard of 0.08 ppm at locations as



far as 260 km."  Other areas where significant rural concentrations of oxidant



have been observed are Salt Lake City, Denver, and the Blue Ridge Mountains.



        In general, the permanent vegetation constituting natural ecosystems



receives much greater chronic exposure, and the short-lived higher-value



vegetation constituting the agroecosystem of the Los Angeles coastal plain



can be subject to injurious doses, but in intermittent short-term fumigations.



Each situation  has measurable economic and aesthetic effects, but on




different time-scales.  The single agricultural ecologic system  (the



agroecosystem) has little resilience to pollutant stress; losses are



sometimes immediate and occasionally catastrophic.  The complex natural



ecosystem is initially more resistant to pollutant stress, but the longer



chronic exposures cause disruption of both structure and function in the



system that may be irreversible.


                                                                      47  52
     Simulation models of ecosystem subsystems are developing rapidly.   '



They deal with flows of energy, biomass,  mineral nutrients, water, numbers



of species, population densities, and area occupied per biotic unit.  Inter-



actions between ecosystem components must be understood before prediction can



be attempted.  Simulation models offer a bright opportunity for determining





                                   12-69

-------
the long-term effects on natural ecosystems and agroecosystems.  New knowledge




of biologic effects should suggest the importance of prevention and some means




for ameliorating damage.




        Oxidant injury to the mixed-conifer stands of the San Bernardino,




Mountains beginning in the early 1940's is well advanced.  A similar problem




is developing in the forests of the southern Sierra Nevada.  Both places




show both direct and indirect effects on all subsystems of the forest eco-




system — producers, consumers, and decomposers.  For example:




        •  Ozone injury limits biomass production by the primary




           producers and their capacity to reproduce.




        •  The decrease of biomass or energy flow to consumer and




           decomposer in the ecosystem affects the populations of




           these organisms.




        •  Essential recycling processes, such as recycling of




           nutrients, may be interrupted, further limiting primary




           production.




        •  Stand structure is altered rapidly in some areas by salvage




           logging of high-risk trees; as a result, species composition




           is changing,  and wildlife habitat is being altered.




        Oxidant injury to eastern white pine in some forest stands in




the eastern United States is a significant problem.  There is an important




concern about injury caused by a synergistic reaction between ozone and




sulfur dioxide at low concentrations.




        The relationship between man's welfare and stable natural ecosystems




and agroecosystems can be established in terms of the economic and aesthetic




values derived from them.   In some situations, where ecosystems are stressed




by oxidant pollutants, the benefits realized by present and future generations




may soon diminish.   Considerable research is required to find alternatives that




prevent stress or that may salvage some of these benefits.   New management





                                 12-70

-------
strategies should be instituted only when their consequences are predictable




within reasonable limits.






RECOMMENDATIONS




        The present knowledge of the biologic consequences of chronic




oxidant injury to both natural ecosystems and agroecosystems must be communi-




cated to groups in the public sector that work in planning and enforcement.




The indirect effects on man's health and the direct effects on his welfare




resulting from ecosystem deterioration due to oxidant injury are serious




enough to be given more thorough consideration in all decisions related to




abatement of air pollution from both mobile and stationary sources.   Land-use




planning and proper airshed classification should be used to prevent further




deterioration of air quality, particularly in prime timber-producing areas




and in remote, pristine areas, regardless of their present use designation.




        The most important research needs are related to the determination




of the responses of natural ecosystems and agroecosystems to chronic exposure




to oxidant pollutants.   In particular, chronic-dose-response models are needed




to understand the responses of the dominant primary-producer species constituting




forest ecosystems in both the eastern and the western United States.  The result-




ing alteration  of interactions with other subsystems—e.g., consumers and




decomposers—must also be investigated.
                                  12-71

-------
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63.  Smith, R.  F.,  and H. T. Reynolds.  Integrated Pest  Control.   Proceedings




          of FAO Conference,  Rome, 1965.
                                 12-78

-------
 64,   Smith, W. H,  Air pollution effects on the quality and resilience of the




           forest ecosystem, pp.      .   In Proceedings of AAAS Symposium on




           Temperate Climate Forestry and the Forest Ecosystem; An Environmental




           Issue?  Washington,  D. C. :   American Association for the Advancement




           of Science,  1972.




 65.   Stark,  R.  W.,  P.  R.  Miller,  F. W.  Cobb,  Jr.,  D.  1. Wood,  and J.  R.  Parmeter,




           Jr.   Photochemical oxidant  injury and bark beetle (Coleoptera:   Scolytidae)




           infestation  of ponderosa pine.   I.   Incidence of bark beetle infestation




           in injured trees. Hilgardia  39:121-126,  1968.




 66.   stark,  Rf Wf,  and F," W." C6bb, Jr.  Smog  injury,  ro&t  diseases, and bark  beetle




           damage  in ponderosa pine.   Calif. Agric.   23(9):13-15,  1969.



 67.   Oxidant Air Pollutant  Effects on a Western Coniferous Forest Ecosystem.




           Task R Report:  Historical  Background and Proposed Systems Study of




           the San Bernardino Mountain Area.  Riverside:  University of California,




           Statewide Air Pollution Research Center, /not dated, circa 1973_/



 68.   Oxidant Air Pollutant  Effects on A western Coniferous Forest Ecosystem.




          Task  C Report: Study Site  Selection and On-Site Collection of




          Background Information.  EPA-R3-73-043B.   Riverside:   University of




          California, Statewide Air Pollution Research Center,  1973.   /189 pp._7



69.   Taylor, 0. C., and P.  R.  Miller.  Modeling the oxidant air pollutant impact




           on a forest  ecosystem.   Calif.  Air Environ. 4:1-3, 1973.




70.   Oxidant Air Pollutant Effects on a Western Coniferous Forest Ecosystem.




           Annual Progress Report, 1973-1974, Task D.  Riverside:  University




           of California, Statewide Air Pollution Research Center, 1974.



71.   Thompson, C.  R.,  0. C, Taylor, M.  D.  Thomas,  and J.  0.  Ivie.  Effects of




           air pollutants on apparent  photosynthesis and water use by citrus




           trees.   Environ.  Sci. Technol.  1:644-650, 1967.




                                12-79

-------
 72.  Thompson, C. R.  Effects of air pollutants on lemons and navel oranges.
           Calif. Agric. 22(9):2-3, 1968.
 73. Thompson, C. R., and C. Rats.  Antioxidants reduce grape yield reductions f"roni
          photochemical smog.  Calif. Agric.  24(9):12-13, 1970.
 74. Thompson, C. R.', and 0. C. Taylor.  Effects of air pollutants  on growth  leaf
          drop,  fruit drop, and yield of citrus trees.  Environ. Sci. Technol.  3;
          934-940, 1969.
 75,   Thompson,  C.  R.,  0.  C.  Taylor,  and B.  L.  Richards.   Effects of photochemical
           smog on lemons  and  navel oranges.   Calif.  Agric.  24(5):10-11,  1970.


 76.  Thompson, C.  R.,  G.  Kats,  and E. Hensel.   Effects of ambient  levels of ozone
          on  navel oranges.   Environ. Sci.  Technol.  6:1014-1016,  1972.
 77.  Treshow, M., and D. Stewart.  Ozone sensitivity of plants in natural com-
          munities.  Biol. Conserv. 5:209-214, 1973.
 78  Tocher, R., and H. Kopp.  People and forests—the challenge of  forest recre-
         ation, pp.  91-101.  In Proceedings of 15th IUFRO Congress, 1971.

 79. U. S. Department of" Agriculture.  Forest Service.  A Model  for  the Determin-
         ation of Wildland Resource Values.  Clarke-McNary,  Sec.  2, Study Comm.,
         1971.   39 pp.
 80. U. S. Department of Agriculture, Forest Service.  Silvicultural Systems  for
         the Major Forest Types of the United States.  Agriculture  Handbook 445,
         1973.  114 pp.
81. Wert, S. I.  A system for using remote sensing techniques to detect  and
         evaluate air pollution effects on  forest stands, pp. 1169-1178.  In
         Proceedings of 6th International Symposium on Remote Sensing of the
         Environment,  1969.  Vol.  2.  Ann Arbor:  University of Michigan,  1969.
                               12-80

-------
82. Williams, W. T.. M.  Brady, and S. Willison.  Air Pollution Damage  to  forest




         Trees  in  the  Sequoia National Forest, Sequoia and Kings Canyon National




         Parks, California.  San Francisco:  U. S. Department of Agriculture,




         Forest Service,  1975.




83. Woodwell, fif M.  Effects of pollution on the Structure and physiology of eco-




         systems.   Science  168-429-433, 1970.




84p  Yonkers, T. A., F. C. Vasek,  and H.  B.  Johnson.   Seed germination and air




          pollutant sensitivity in selected  species of desert plants, pp.




          In F.  C.  Vasek, H.  B.  Johnson,  and W.  W.  Mayhew, Eds.   Biological




          Impact of the Southern California  Edison Company Proposed Generating




          Station in Upper Johnson Valley and Associated Transmission and Fuel




          Lines.  Riverside:   University of  California,  Dry Lands Research




          Institute, 1974.
                                 12-81

-------
                                  Chapter  13

                EFFECTS OF PHOTOCHEMICAL OXIDANTS ON MATERIALS


     The effect of photochemical oxidants  on materials has been investigated

by exposure of materials to ambient air containing photochemical oxidants,

including ozone, PAN, peroxybenzoylnitrate  (PBzN), and all other molecules

in ambient air that oxidize iodide ion (but not nitrogen dioxide), as pre-

scribed in the photochemical oxidant ambient air quality standard.1

Laboratory experiments for corroboration of field tests always use ozonized

air that contains no NO  if photochemical  generation is used and may contain
                       x
NO  if electric discharge is the method of ozone generation.  The reactivity
  x
of oxidizing species, such as atomic oxygen and excited electronic states of

molecular oxygen, must be assessed both in test chambers and in ambient air

before blame for damage is assigned to ozone.  On the presumption that ozone

is the damaging species in test-chamber experiments in which PAN and similar

oxidants are absent, photochemical oxidant damage is often referred to in

this discussion as "ozone" damage.  The subject has been reviewed in Air

Quality Criteria for Photochemical Oxidants2 and in a systems study by

Salmon3 and more recently by Sanderson.4  Other, rather comprehensive,

although specialized, reviews have appeared on the effects of air pollutants

on textiles and dyes,5 on rubber,6 and on paint7*8 and on their economic

effects.9  In preparing this document, the literature has been reviewed with

special emphasis on papers published since 1970, when the EPA criteria

document appeared.2

-------
TEST-CHAMBER STUDIES

     Experimental studies on the effects of ozone on materials usually

involve the laboratory generation10 of ozone by photolysis of air with a

mercury resonance lamp or by some form of electric discharge through air or

oxygen.  Several oxidizing species result, among which are the first singlet
                          1                                  3
state of atomic oxygen, 0( D);  ground-state atomic oxygen, 0( P); the lowest-
                                   1
lying singlet molecular oxygen, 0 ( A ); and ozone.  To identify the species
                                 2   g
responsible for the effect, one must know the rate constants characteristic

of the interactions of these species with the material in question and the

relative concentrations of the species at the contact surface between the

ozonized air and the damaged material.


The Photochemical Ozone Generator

     The standard ASTM test method10 (D-1149-64) for rubber damage includes
                                   3
a test chamber (volume, 0.11-0.14 m ) through which ozonized air flows at a

rate greater than 0.6 m/s.  Because the residence time of the ozonized air

in the test chamber is about 1 5, the ozone may be expected to reach the

material in about 0.1 s.  A somewhat similar test procedure10 (AATCC test

method 109-1972; ANSI L14, 174-1973) is used in testing colorfastness.  The

ozone generator is usually (but not necessarily) a mercury-vapor resonance

lamp with emission lines at 184.9 and 253.7 nm.  The 184.9-nm line is absorbed,

and two ground-state oxygen atoms are produced:

                                   3
     0   +  hv (184.9 nm)   ->•   20( P).                             (1)
      2

Each oxygen atom then reacts with diatomic oxygen to form ozone:


     0  +  0   +  M   ->   0   +  M,                                 (2)
            2              3
                                     13-2

-------
where M signifies any gaseous molecule, such as 0  or N  .  Usually,  the
                                                 2     2
253.7-nm line is more intense than the 184.9-nm line and falls in  a  very

strong absorption band of ozone:

                                   1          1
     0   +  hv  (253o7 nm)   ->   0( D)  +  0 ( A ).                  (3)
      3                                     2   g

The species produced by this photochemical reaction can be quenched  to their

ground electronic states by collisional processes:

       1                 3
     0( D)  +  M   ->   0( P)  +  M;                                  (4)

        1                   3 -
     0 ( A )  +  M   ->   0 ( T,  )  +  M.                             (5)
      2   g               2    g

In addition, the ground—state oxygen atom reacts with ozone:


     0  +  0    ->   20 .                                             (6)
            3         2

Rate constants of these reactions are summarized in Table 13-1.


     Concentrations in the Generator.  The absorbed intensity, I , is
                                                                a
obtained from the Beer-Lambert law, which relates the incident intensity,
 o
I , and the transmitted intensity, I ,
                                    t
         o
     I /I    =   exp (-ecA),                                         (7)
      t

where e is the absorption coefficient, c is the concentration of the absorbing

species, and £ is the path length.  It follows that

      o
     I  - I        I
     	t       _a   =   1 -exp (-ec£).                           (8)
         o          o
        I          I
                                     13-3

-------
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t
                                          a
                      CO
                                       m
        OO
                   CM
                               CO
                      O
                      CM
                                                        CM
                                                        60
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t

s

CM
O

~"~
o
r^ "• — '
O
CO
u~l *t~
CM
^ s
J3 +
^•^
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CO >— '
0 0
CO
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CM
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CM
+ |
"^ 60
<] O
rH
CM
0 0
                                     13-4

-------
For  ec£«l,
             o
      1=1  ECio                                                  (9)
      a

The  stationary-state expressions are:

                                          1
d[0]/dt  =  21  - k [0] [0 ]  [M]  +     [0( D)] [M] - k  [0]  [0  ] = 0;   (10)
              122                           63
     1                     1
d[0( D)]/dt  =  I  - k [0( D)][M]  =  0;                             (11)
                 3    4

d[0  ]/dt  =  k [0][0 ][M]  -  I  - k [0][0 ]  =  0;                  (12)
   3          22          363

The values of I  and I —the absorbed light intensities at  184.9 nm  and 253.7
               1      3
nm, respectively—are related to incident intensities by expressions like Eq0

8.  The incident intensities depend heavily on lamp design  and construction.

For the purpose of the stationary-state computation, we use (on the  basis of
                   17           3                17           3
experience) I  = 10   photons/cm  and I  = 3 x 10   photons/cm -s. In the
             1                         3
calculations, a 1-cm path length is assumed.  Summing Eqs.  10-12 and referring

to Table 13-1,

                           o
     I   =  k [0][0 ]  =  I  e [0 ].                                 (13)
      163       12
                                                     18              3
The oxygen concentration in air is taken to be 5 x 10   molecules/cm „

                      30
     [0]  =  1.16 x 10  /[O ].                                       (14)
                           3
                       1
The concentration of 0( D) is obtained from Eq. 11.
                            o
        1        I         I  e [0 ]             -9
     [0( D)]  =   3     =   333   =  2.1 x 10  [0 ].             (15)
                 k [M]       k [M]3
                  4           4
                                     13-5

-------
                        1
The concentration of 0 ( A ) is obtained by means of its stationary-state
                      2   g
expression:

          1
     d[0 ( A)]                  1
        2        =   I  - k [0 ( A)]M   =   0;                      (16)
        dt            352
                   o
         1        I e  [0 ]             -2
     [0 ( A)]  =   33   3   =  7.1 x 10  [0 ].                     (17)
       2            k M                     3
                     5

                                         1
Because I   =  k [0][0 ] and I   =  k [0( D)][M], Eq. 10 yields:
         163       34
     I   +  I   =  k [0][0 ][M].                                    (18)
      1322

Substituting for [0] and solving with the quadratic formula:

                                    30    o           o
     I  +1  = k [0 ][M] x 1.16 x 10   =1  e [0 ] + I e [0 ];      (19)
      1322                      112333

      o      2      o                                  30
     I e [0 ]   +  I e [0 ][0 ] - k [0 ][M] x 1.16 x 10   =0       (20)
      333        1123     22
     [0 ]  =  -b * / b  - 4ac                                       (21)
       3            2a
Evaluating a, b, and c:

     a = 3.3,
                 15
     b = 3.7 x 10  , and
                 34
     c = 8.5 x 10  ,
                                     13-6

-------
                               17             3
the solution is [0 ] = 1.6 x 10   molecules/cm .  The concentrations of the
                  3                  17             3
oxidizing species for [0  ] = 1.6 x 10   molecules/cm  are given in Table 13-2.
                        3         3
The ratio of rates of attack of 0( P) and ozone on a material in the ozone

generator is given by:

                   3        k
     R /R    =  [0( P)]   .  _0    ,                                  (22)
      0  0       [0 ]k
          330
                              3
where k  and k   are the rate constants.  A hypothetical example of a
       0      0
               3

material undergoing a damage test may be chosen to be an olefinic polymer.

In the absence of data on appropriate material, we may presume that damage

done to an olefinic material by oxygen atoms and ozone would proceed at the

same relative rates as attack on a typical olefin, e.g., butene-^l.  Rate

                                                 *-
constants for attack of various oxygen species on butene->L are presented in
                                                 A
Table 13-3.  Thus, we estimate

                        5
     k /k    =  3.5 x 10                                            (23)
      0  0
          3
                         -5           5
and  R /R    =  (4.5 x 10  ) (3.5 x 10 ) = 15.8.                    (24)
      0  0
          3

It follows that, although the ozone concentration is more than 10,000 times

that of the oxygen atom, the latter reacts so rapidly with olefins that

oxygen atoms, rather than ozone, will be the species responsible for material

damage, if the material is placed in the ozone generator.
                                     13-7

-------
                          Table 13-2

        Stationary State Concentrations of Oxidants in
                Photochemical Ozone Generator*3

                                              Concentration,
                                                          3
Oxidant                                       molecules/cm

                                                      17
0                                             1.6 x 10
 3

  3                                                   12
0( P)                                         7.3 x 10

  1                                                   8
0( D)                                         3.4 x 10

   1                                                  16
0 ( A )                                       1.1 x 10
 2   g
              o     17           3     o         17           3
a  1=1 cm, I  = 10   photons/cm -s, I  = 3 x 10   photons/cm -sc
              1                        3
                             13-8

-------
                     Table  13-3

        Rate  Constants for  Reaction of Oxygen
            Species with  trans—2—Butenea
Oxidant
0  ( A )
 2   g
 Rate Constant
        -1  3 -1
(k, molec  cm s  )
                                               -18
 4.6 x  10
                                              -17
                                      3.5 x  10
  3
0( P)
         -11
 2.3 x 10
a  Data from Demerjian et al.1!
                        13-9

-------
                       1
     Similarly, for 0 ( A )•
                     2   g
1
R 0 ( A )
2 g
R 0
3
k
A
k
0
3
1
[0 ( A)]
2
[0 ]
3
= 2.3 x
1.1 X
-18
10
-17
10
1.1 X
1.6 x
16
10
17
10
              1
Therefore, 0 ( A ) could be a significant problem in ozone damage tests on
            2   g
olefin-like materials, if the test were done in the ozone generator.  The

results in Table 13-2, although only very approximate because of the

assumptions made, show that in a photochemical ozone generator we may expect
   1
0 ( A ) concentrations to be an appreciable fraction of the ozone concen-
 2   g          1
tration.  The 0( D) concentration is negligibly small, because it is removed

in the reaction shown in Eq. 4 on almost every collision.
     Concentration Downstream from the Generator.  The ASTM method requires

that the ozone generator be outside the test chamber, and we must ask how
        1          3
long 0 ( A ) and 0( P) survive after the ozonized air leaves the generator
      2   g
on its way to the material under test.  About 0.1 s is required for the ozone

to reach the material after leaving the generator.  As the light source is

extinguished (t = 0) or as the ozonized air leaves the photolysis chamber,
                     1                                         1
the rate at which 0 ( A ) is removed is—using S to signify 0 ( A )—
                   2   g                                     2   g

       d[S]= k [S][M];                                              (26)
        dt    5
     - d£n[S]  =  k [M]dt.                                          (27)
                   5
                                     13-10

-------
 Thus, 0.1 s after the light  is  turned  off,  [S  ]  decays  to  [S]  by Eq.  5,
                                             o
 whose rate constant  is given in Table  13-1.  The concentration,  [M],  is
         19             3
 2.7 x 10   molecules/cm .   Solving Eq.  27, we  obtain
          [S]

            d£nS   =   6;                                              (28)

          [S]
      £n  [S]    =   -6;                                                (29)
         TsT
            o

                -2.6
      [S]    =   10    .                                                (30)
      FT
        o

                            1
 Therefore,  although the 0  ( A  )  is only very  inefficiently  quenched  by
                         2   g
collision, at a pressure of  1 atm quenching  is sufficiently  rapid  that only
                                       1
 a  few tenths of 1% of the original 0  ( A  ) can reach  the test material.
                                    2    g                     18
 However, when  the  pressure  is  smaller — say, 76 torr or 2.5  x  10   molecules/
   3                                                                       1
 cm — In ([S]/[S] ) = -0.6 after  0.1 s  and more than half the  original 0  ( A )
                o                                                      2   g
 molecules may  reach the test material.

      Finally,  we must ask whether the  ASTM procedure is likely to result  in

 removal of  oxygen  atoms sufficiently rapid for the observed damage to be

 attributed  to  ozone.  The rate of removal of  oxygen atoms by  the reaction of

 Eq. 2,  which is the major sink,  is given by:
     -d[0]/dt  =  k  [0][0  ][M];                                      (31)
                   2     2
                                      13-11

-------
           [o]
           [o]
              d£n[0]  =   k [0 ][M]
                           2  2
0.1

    dt;                   (32)

0
                         3
     £n[0]   =  -8.1 x 10 ;                                         (33)
       ToT
          o

                    -3500
     [0]/[0]   =  10     .                                          (34)
            o
Therefore, the ASTM test is a valid ozone damage test, inasmuch as both the
                        1
oxygen atoms and the 0 ( A ) are rapidly removed downstream from the generator.
                      2   g
The importance of having the ozone generator outside the test chamber cannot

be overemphasized.  The validity of any ozone damage test using other sources

depends very heavily on the test procedure.  If an electric discharge is used

as the ozone generator, the test chamber should be designed in accord with

such chemical kinetic considerations as indicated in the model discussed

here.  The relative concentrations of oxidizing species in a radiofrequency

or microwave discharge or a photochemical generator are subject to conditions
                                                             3         1
and to some speculation.   However,  equal concentrations of 0( P)  and 0( A )
                                                                         g
have been suggested as emerging from discharged air.17  The ratio of oxygen

atoms to ozone depends critically on the pressure.   In a microwave discharge

where the pressure may be 1  torr, 0.1 s after leaving the discharge a

substantial fraction of the  oxygen atoms remains.

     Because oxygen atom reaction rate constants can be orders of magnitude

greater than those for ozone, an experiment done on material subject to a

reduced-pressure discharge is likely to signify damage done by oxygen atoms,

rather than ozone.
                                     13-12

-------
 Oxidant  Species Concentrations in Polluted Air

     We  have  shown that, in a properly designed laboratory experiment, ozone

 is  likely to  be the only oxidant species producing damage in the test material.

 In  a real atmosphere, such photochemical oxidants as PAN and PBzN are formed

 in  complex atmospheric reactions.  Because there is no information on the

 effects  of these oxidants on materials, no consideration is given to them

 in  assessing material damage in this discussion.  Sunlight and energy transfer
                                     1                       3
 processes result in generation of 0 ( A ) and particularly 0( P).  Therefore,
                                   2   g
 it  is necessary to consider the concentrations of these species relative to

 that of  ozone in a real atmosphere.  This has been done, notably by

 Demerjian et_ al.,18 one of whose estimates, calculated from smog-chamber

 considerations, is shown in Table 13—4.  The ozone concentration assumed in

 Table 13-4 is typical of a fairly polluted atmosphere.  To estimate the

 relative contributions of each oxidizing species to oxidant damage, it is

 necessary to multiply the concentration by the rate contant for each

 individual material.  Unfortunately, there is almost no information on rate

 constants, and it is assumed in nearly all cases that the oxidizing species

 is ozone.


 EFFECTS OF OXIDANTS ON INDIVIDUAL MATERIALS

     According to the Midwest Research Institute study of 1970,3 both ferrous

 and nonferrous metals have excellent resistance to ozone.  Such materials as

building stone, building brick, cement, glass, and graphite also have excel-

 lent resistance.  Some synthetic rubbers have good ozone resistance, but

natural rubber has notoriously poor resistance.  Polyethylene, polystyrene,

 and polypropylene are believed to have only fair resistance to ozone, and
                                     13-13

-------
                     Table 13-4

        Calculated Concentrations of Oxidant
              Species in Smog Chambers'3
                                         Concentration,
                                                     3
Oxidant                                  molecules/cm

   1                                             8
0 ( A )                                  1.4 x 10
 2   g

                                                 12
0                                        3.8 x 10
 3

  3                                              5
0( P)                                    2.6 x 10

                                                 6
OH                                       1.9 x 10
HO                                               10
  2                                      1.0 x 10
a  Calculated concentrations for oxidants in smog
   chamber under conditions outlined in Chapter 2
   for 60-min irradiation (see Table 2-2).
                        13-14

-------
 acetate, nylon,  and  fibers of cotton, rayon, and cellulose esters are also




 in  the  "fair"  category„  Wood is considered fairly resistant, but little




 information  is available.  The approach used by MRI in assessing economic




 effects is that  the  value of material exposed to air pollution, Q, is the




 product of four  factors:  the annual production, P; the average economic




 life of the material, N; the fraction of material exposed to air pollution,




 F;  and the labor factor, R, which reflects the cost of putting the material




 in  place where it is used.  Hence,






     Q  =  P • N • F • R.                                           (35)







 Having defined Q, the MRI report defines the damage costs as the product of




 Q and v, the "interaction" value per year0  For example, if Q = $1 billion




 and a pollutant causes a 1% reduction in economic life per year of exposure,




 then v = 0.01,  and the economic loss, L, due to the pollutant is Qv, or $10




million/year.  The values of v for pollutant damage generally are difficult




 to obtain,  because few data are available.  For the particular pollutant,




 ozone, the values of v are almost impossible to assess.  The MRI report




points out  that "intuitive feelings" are sometimes used to assess v.  The




materials that  have been classified poor or fair in ozone resistance are




 listed in Table 13-5 in order of decreasing in-place value.  The chemical




 interaction value,  v, and the economic loss, L, are also tabulated.   Because




 it is difficult at best to estimate overall pollutant interaction, ozone




damage has  been assessed in the last column of Table 13-5 by estimating L1,




the ozone damage, as follows:  If chemical resistance has been estimated by




MRI as either poor or fair for one pollutant other than ozone for which a
                                     13-15

-------
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                                                                    13-16

-------
 national ambient air quality standard has been set,  L*  = %L;  if two other




 pollutants are in the poor or fair category,  L'  = 1/3L.   The  data in Table 13-5




 should be regarded as very rough and indicative  only of broad-brush outlines.




 For example,  paint damage is undoubtedly a very  important economic conse-




 quence of ozone pollution,  but,  as we shall see,  the estimate of rubber




 damage in Table 13-5 is  much too low.




      The most studied materials, as well as the  most important economically,




 with respect  to ozone damage are paint and elastomers (e.g.,  rubber).   Other




 materials will be reviewed  individually in cases  in  which scientific data




are available.







 Paint




      Failure  of Paint Films.   Paint formulation  consists of a binder (a




 natural or synthetic polymer or  dryingoil), a solvent,  and a  pigment or




 colorant,  including an extender, typically calcium carbonate  or a silicate.




 Because of the reactivity of organic polymers toward ozone, it is not




 surprising that ozone damage ftas been observed,  at least in laboratory




 experiments.   In 1968, paint sales of over $2.5 billion  were  recorded in




 the United States.   Table 13-6 outlines these sales.8  The failure of paint




 films takes on a variety  of  forms,  as shown in Table 13-7, and methods  for




 testing the various forms of failure have been delineated by  the ASTM.19




 These methods  are listed  in  Table 13-8.   The  paint industry has been con-




 cerned mainly  with "weatherability" of  paints, rather than specifically




 with the  effect of air pollutants.
                                     13-17

-------
                                  Table 13-6

            Trade and Industrial Paint Sales, United States, 1968a
Type of Sale
Trade:
     Interior house paints:
       Latex emulsion
       Oil and alkyd
       Primer, sealers, etc.
       Miscellaneous
     Exterior house paints:
       Latex emulsion
       Oil and alkyd
       Enamels
       Primers, sealers, etc.
       Miscellaneous
     Automotive refinishing
     Traffic
     Other

Industrial:
     Automotive, new
     Marine
     Railroad, aircraft, etc.
     Coil coating
     Prefinished wood
     Industrial maintenance
     Machinery and equipment
     Miscellaneous
Amount,
millions
of gallons

424

145
 45
 10
 25

 55
 40
 15
 10
 20
 30
 25
  4

419
 55
 20
 15
 20
 15
 45
 30
219
Cost,
$ millions

1,428
Unit Cost,
$/gal

3.37
425
170
30
100
190
155
55
35
50
150
45
23
1,159
170
85
40
80
40
160
75
509
2.93
3.78
3.00
4.00
3.45
3.88
3.67
3.50
2.50
5.00
1.80
5.75
2.77
3.09
4.25
2.67
4.00
2.67
3.56
2.50
2.32
a  Data from Spence and Haynie.8
                                      13-18

-------
                                  Table 13-7

                            Types of Film Failurea
Type Failure
Description
Chalking


Cracking or checking


Alligatoring



Peeling

Color fading


Blistering



Rusting
Formation of powdery layer on surface
of coating that is being eroded away

Shrinkage of the coating resulting in
film rupture

Film rupture resulting from the appli-
cation of a brittle film over a more
flexible coating

Poor adhesion of the coat to substrate

Reaction of binder or pigment in
presence of sunlight or environment

Projections or pimples on film that
result from trapping of solvent or
moisture between substrate and film

Oxidation of metallic substrates, such
as iron or steel, when film permits
moisture or chemicals to attack
substrates
a  Data from Spence and Haynie.8
                                     13-19

-------
                                  Table 13-8

                  ASTM Test Methods for Exterior Paint Films
Test	    Purpose
D 659-44      Evaluating degree of resistance to chalking

D 660-44      Evaluating degree of resistance to checking

D 661-44      Evaluating degree of resistance to cracking

D 662—44      Evaluating degree of resistance to erosion

D 772-47      Evaluating degree of resistance to flaking (scaling)

D 1641-59     Measuring exterior durability of varnishes

D 1543-63     Measuring color change of white architectural enamels

D 1654-61     Evaluating painted or coated specimens subjected to corrosive
              environments

D 2197-68     Measuring adhesion of organic coatings

D 2370-68     Measuring elongation and tensile strength of free films of
              paint, varnish, lacquer, and related products with tensile
              testing apparatus
                                     13-20

-------
     Probably the most definitive study of the effect of air pollutants on




paint is contained in a 1972 report of the Sherwin-Williams Company.20




Five commercially important coating systems were selected for study:




     1.  House paint—lead-titanium-zinc extender in oil with 100% rutile




         titanium dioxide.




     2.  House paint—titanium extender in acrylic latex with 100% rutile




         titanium dioxide.




     3.  Industrial maintenance coatings—titanium in alkyl with 100% rutile




         titanium dioxide.




     4.  Coil coating finishes—titanium extender in urea-alkyl with 75%




         rutile and 25% anatase titanium dioxide.




     5.  Automotive refinish lacquer—titanium in nitrocellulose-acrylic




         with 100% rutile titanium dioxide.




For each coating system, three tasks were performed:




     •   Existing exterior exposure records were reviewed with respect to




         visual erosion ratios.




     •   Short-term exposures were studied at Leeds, North Dakota; Los




         Angeles, California; Chicago, Illinois; and Valparaiso, Indiana.




         The North Dakota location was a clean,  rural site; Los Angeles




         represented a high-oxidant urban site;  Chicago was a high-sulfur




         dioxide location; and Valparaiso was considered to have moderate




         sulfur dioxide pollution and low oxidant concentrations.  Tests




         with commercial instruments included those for erosion, gloss,




         sheen,  surface roughness,  and tensile strength.
                                     13-21

-------
     •   Accelerated laboratory exposures were made at various pollutant

         concentrations:  no pollutant, 0.1-ppm sulfur dioxide, 1-ppm

         sulfur dioxide, 0.1-ppm ozone, and 1-ppm ozone.

     As measured by erosion rates (linearly related to pollutant concen-

tration) , it was found that in all cases coatings were affected more by

sulfur dioxide than by ozone.  Sulfur dioxide at: 1 ppm had the following

effects on the five paint systems:  System 1, "considerable"; systems 2

and 4, "moderate"; and systems 3 and 5, "no effect."  Both attenuated total

reflection and scanning electron photomicrographs showed that the damage

was greater in Chicago and Valparaiso than in Los Angeles and North Dakota.

     Studies have been conducted on creep compliance tests8 in which paint
                                                   2                32
films were subjected to tensile loads of 4-7 Ib/in.  (27.2—47.6 x 10  N/m )

and to 6% ozone for 505 h.  A typical result for a high-quality emulsion-

base paint is shown in Figure 13-1.   Creep compliance is reduced by exposure

to 6% ozone.  If the effect is linearly related to ozone concentration, we

might expect the same reduction in creep compliance at 0.1-ppm ozone in
      8
3 x 10 h, or some 30,000 years.  Thus, reduction in creep compliance is not

viewed as having a serious ozone contribution.


     Economic Effects.  The Midwest Research Institute Report (pp. 41 ff.)

computes L, the increased cost of cleaning or repainting per year, as the

product of Q, the consumer purchase price of a unit of material; y> the cost

of cleaning or repainting one such unit; and Af, the fractional increase in

cleaning frequency resulting from particulate pollution.


     L  =  Q«yAf, dollars/(yr. x unit).                            (36)
                                     13-22

-------
                30
              CM
                20
              «c
              _l
              D_
              i 10
              o
              CL.
              LD
              •^  «
              0=  0
              O
                        20
               40
60
80    100

TIME, minute
120
140    160
180
Figure  13-1.
Initial  creep of EM 7338  first-quality emulsion-base paint,
before and  after 505-h exposure to ozone at  60 C.  (Reprinted
from Spence and Haynie.8)
                                       13-23

-------
The cost, Y» of cleaning one unit is determined for two classes of material,

fibers and nonfibers.  For fibers, $0.10/lb is taken as the cost of cleaning;
                       2
for nonfibers, $0.10/ft  is taken as the cost of cleaning (removal of par-

ticulate material).  The purchase price is defined as the material cost

times a factor that gives the consumer purchase price including labor

(painters, outlet salesmen and their overheads, etc.).  The quantity yAf is

given by v = yAf = L/Q-yr and is called the soiling interaction:


     L  =  Qv.                                                      (37)


The determination of the quantity Af, the fractional increase in cleaning

frequency due to particulate matter, is the difficult part of the problem.

The data of Michelson and Tourin21 suggest a value of v for paint of 1.5/

year.  The value of Q is obtained as follows:  According to Noble,22 the

annual production of paint in 1968 was $2.59 billion0  Because the economic

life of paint is considered to be 4 years, $10.36 billion worth of paint is

in place, of which only 70% is exposed to atmospheric pollutants.  Thus,

$7.25 billion is the manufacturers' value of in-place paint exposed to air

pollution.  Using a labor factor of 3.3, the total in-place value of paint

is $23.9 billion.  Because v = 1.5 for particulate soiling, the cost of

pollution damage (cleaning costs) is some $36 billion per year.

     The costs associated with chemical effects of gaseous pollutants could

not be ascertained for each pollutant, because of a paucity of information.

The value of v for chemical deterioration was obtained by an educated guess

that repainting is needed every 4 years in a polluted environment and every

5 years in a pristine air environment.  Thus, v (chemical) = 0.050  The
                                     13-24

-------
 corresponding figure for chemical deterioration costs is 0.05 ($23.9



 billion) =  $1.195 billion per year.



     Spence and Haynie have attempted to assess costs of air pollution



 damage to paints without special regard to the identity of the pollutant



 doing the damage.  However, repainting frequencies have been determined in



 five American cities whose particulate concentrations have been measured.



 There appears to be a linear (although not necessarily causal) relationship


                                                                0 1
 between the maintenance frequency and particulate concentration.    Economic



 loss due to pollution was estimated by the following procedure:  The average



 service life of exterior household paint in urban areas is 3 years, and in



 rural areas, 6 years.  Thus, 0»33 and 0.17 are the replacement probabilities



 per year.  Because 60% of the surface painted is urban and 40% rural, it may



 be calculated that some 74% of the paint used over a long period is consumed



 in urban areas.   The total value of manufactured paint is $485 million, of



which 74%,  or $359 million per year, is the cost of paint consumed in urban



 areaso   Its service life is 50% less than in rural areas, so 0.50 ($359



million)   =  $180 million is the annual cost of exterior household paint



deterioration due to pollution.,  The value of loss of paint in place was



 computed  to be 3.0 ($180 million)  =  $540 million.  It is noteworthy that



 the Midwest Research Institute report estimates $1.195 billion repainting



costs due to chemical pollution.



     The  economic assessment of air pollution damage to exterior paints is



summarized  in Table 13-9.   There appears to be no definitive way to determine



the fraction of  the $225 million loss for all exterior paints that is due



 to photochemical oxidants»   According to the convention introduced by Midwest
                                     13-25

-------
                                  Table 13-9

             Economic Assessment of Air Pollution Deterioration of
             Exterior Paints (1968 Figures—Manufacturers Costs)a
                                                               Loss Due to Air
Exterior Paint          Value of Paint Exposed in Urban        Pollution,
Class	          Areas, $ million	        $ million	

Coil coatingb                           31                              8

Automotive
refinishing                            111                             22

Industrial
maintenance                             74                             15
         b
Household                              359                            180

               Total                   575                            225
a  Data from Spence and Haynie.

b  Extender Type Paints.
                                     13-26

-------
Research Institute—that repainting costs may be considered to be due to

chemical pollution—only NO , sulfur dioxide, and photochemical oxidants
                           x
seem likely to be involved in this kind of paint damage.  Sulfur dioxide

seems to attack only the extender  (e.g., calcium carbonate) component.  It

might also be expected that nitrogen dioxide would attack only extender

paints.  Sulfur dioxide has no effect on the nonextender types—industrial

maintenance and automotive refinishing paints.  Therefore, the $37 million

worth of damage done to the nonextender types each year may be attributed

to the effects of oxidants.  Of the $188 million worth of damage to extender

paints, we may expect some 80% to be caused by sulfur dioxide and nitrogen

dioxide, with $38 million worth of damage (20%) due to oxidants.  Thus, a

total of  $75 million worth of paint damage per year is caused by oxidants.

The figure of  $75 million includes only the cost at the manufacturers'

levelo  The cost at the consumer level—i.e., the total cost of the paint

applied to a surface—is obtained by multiplying by a factor of 3.0 (according

to Spence and Haynie8) or 3.3 (according to Salmon3).  Thus, the ozone

damage to paint (using a 3.3 factor) is $248 million per year.


Elastomers

     Failure of Elastomers.  Elastomers include both synthetic elastomers

and natural rubber.  The most extensive study of the effects of ozone on

elastomers (including economic effects) was done by Mueller and Stickney6

and Stickney et_ al_. ,23 and much of what follows is taken from the 1971

report.23  Table 13-10 presents the estimated elastomer production in 1975.

The effect of ozone on cracking of natural rubber was proved by Newton2lf

and by Crabtree and Kemp.25  In general, highly unsaturated elastomers are
                                     13-27

-------
                                  Table 13-10

                       Polymer Usage Projected to 1975a


                                           Estimated

Estimated
Average

Production, Price Per

Polymer
SBR — copolymer of butadiene
and styrene
Natural — natural polyisoprene
Polybutadiene— polymerized
butadiene
Neoprene — polymerized
chloroprine
Nitrile — copolymer of
butadiene and
acrylonitrile
Urethane — polymers containing
urethane linkage
Butyl — copolymer of
isobutylene and isoprene
Silicons — polydimethylsiloxane
Polyisoprene— synthetic
polyisoprene
Polyacrylate — polymer or
copolymer based on an
acrylate
EPDM — copolymer of ethyl ene,
propylene, and a diene
Polysulfide— ^polysulfide
Fluorocarbon — f luorinated
polymers
Chlorohydrin — polymer of
epichlorohydrin or
copolymer of
epichlorohydrin and
ethylene oxide
Total
1,000
tons^1
1,748

689
375

146

95


45

101

13
134

3


168

17
2

8




3,544
Pound ,
cents5
23

22
27

40

50


125

27.5

250
26

80


25

135
1,250

85





Value,
$ million
804.1

303.2
202.5

116.8

95.0


112.5

55.5

65.0
69.7

4.8


84.0

45.9
50.0

13.6




2,022.6
Portion
of Total
Polymer
Value, %
39.8

15.0
10.0

5.8

4.7


5.6

2.7

3.2
3.4

0.2


4.2

2,3
2.5

Oo7




100.0
a  Derived from Stickney et al.23
b  Chemical Week, March 18, 1970, p. 58.
o  Battelle and industry estimates.
                                     13-28

-------
more subject to ozone attack than are saturated elastomers, because ozone

attacks aliphatic double bonds.  The more highly unsaturated elastomers are

listed in Table 13-11.  Of these, neoprene is particularly resistant to

ozone, owing to the presence of the electronegative chlorine atom in its

structure.  Elastomers crack under the influence of ozone when stressed,

and the crack propogates in a direction normal to the stress direction.  The

chemical mechanism may be written:27


                          o'N,
                          I     I
     0   +  - C = C-  ->  -C  -  C-
      3       H   H       H     H
                                                                    (38)
        +
     + -C -0-0+0= C- •
        H               H


The zwitterion and aldehydic group are thought to combine,

      +       -                   0^
     -C - 0 - 0  +  0=C-  ->  -C       C-  ,                          (39)
      H               H       H\     /H
                                0—0


to form a highly oxidized structure of much lower extensibility than the

unoxidized elastomer.  Cracking is the result.

     There are two main approaches to avoidance of ozone damage.  One is

the addition of antiozonants.  The more extensively used antiozonants are

listed in Table 13-12.  These antiozonants have limited solubility in

elastomers and tend to "bloom" to the surface.  The antiozonant action is

not well understood chemically, but probably involves formation of a pro-

tective film.   Crack initiation occurs at critical stress, which is strongly

influenced by the presence of a few percent of the N,N'-dialkyl-p-

phenylenediamines.  Dithiocarbamates are a second class of antiozonants that
                                     13-29

-------
                                  Table 13-11

                        Highly Unsaturated Elastomers'2
Polymer
Use
SBR

Natural

Polybutadiene

Neoprene

Nitrile

Polyisoprene
General

General

Wear-resistant

Oil-resistant

Oil-resistant

General
Crack Growth
Rate, mm/min^
   0.37

   0.22

   ND

   0.01

   ND

   ND
1970 Cost,
cents/lb

   23

   25

   25

   40

   50

   24
a  Derived from Mueller and Stickney.
b  Data from Braden and Gent.26  ND = no datac
                                     13-30

-------
                                  Table 13-12

                            Elastomer Antiozonants
Antiozonants	     Price, cents/lb  (1970)

N-N1— Diphenyl-jD-phenylenediamine                              99

N-N'-Di-(2-octyl)-2-phenylenediamine                          90

N-N'-Di-3-(5-methylheptyl)-£-phenylenediamine                 90

N-Nf-bis-(l,4-Dimethylpentyl)-£-phenylenediamine              86

N-N'-bis-(l-Ethyl-3-methylpentyl)-£-                          90
     phenylenedlamine

 i-N'-bis-(1-Methylheptyl)-p_-phenylenediamine                  90
N
                                     13-31

-------
act by slowing crack growth rates.  The crack growth rates depend linearly

on the concentration of ozone, as shown in Figure 13-20  In addition to

antiozonants and special polymeric structures, protection against ozone

damage during storage is afforded by the use of waxes, protective coatings,

and paper wrapping.

                                                                       3
     Identity of Oxidizing Species.  It is known that atomic oxygen, 0( P),

reacts with double bonds at room temperature to produce a rupture of the

carbon—carbon chain.  Because elastomers are known to be very stable to
              3 -
ground-state ( £ ) molecular oxygen, the possible oxidants responsible for
                g                                     1
rubber-cracking in polluted air are atomic oxygen, 0 ( A ), ozone, OH, and
                                                    2   g
HO .   Relative rates of reaction are products of rate constants and concen-
  2
trations of oxidizing species.

     One elastomer, cis-polybutadiene, has been exposed specifically to
   1
0 ( A ) in the absence of ozone or oxygen atoms.28  cis-Polybutadiene forms
 2   g
hydroperoxides (-OOH) when exposed to oxygen at 5 torr that has been subjected

to an electrodeless discharge (2,450 MHz).  Oxygen atoms and ozone were
                                                                 1
removed by mercuric oxide in these experiments, leaving on!i}r 0  (  A  ).  As we
              1                                               2 _ g
have  seen, 0 ( A ) survives for a long time at the low pressures used, nearly
            2   g
half  of it surviving 1 s after leaving the discharge zone.  No measurements
                                                   1
have  been made of relative rates of reaction of 0 ( A ), ozone, atomic oxygen,
                                                 2   g
OH, and HO  with individual materials, and it is therefore not possible to
          2
know the relative importance of attack by these species.  The results in

Table 13-13 would lead to the speculation that   ozone is more important
        1
than  0 ( A ) in cis-polybutadiene damage.  Because we do not have information
      2   g
on the relative rates of reaction of the five species with elastomers, we can
                                     13-32

-------
     100
    ex
    ex
    c:
    o
    O

    o
    o
    c
    o
    M

    O
10
\
\
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t
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I
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s\
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\
                                                                                \
        I                                   10

                                      Time, minutes




Figure 13-2.  Effect of ozone concentration  on  cracking  time.   (Reprinted

              from Mueller and Stickney.6)
                                                                         100
                                     13-33

-------
                                  Table 13-13

                        Rates of Attack of Oxidants on
                   trans-2-Butene In Simulated Polluted Air
Oxidant
OH
HO
Rate constant
          -1  3 -1
(k), molec  cm s  a
Concentration,
            3 ,
molecules/cm
                              -11
  2.5 x 10
                              -11
  2.4 x 10
  1.9 x 10
                                 10
  1.0 x 10
Relative Rate
1
0 ( A )
2 g

°3

0(3?)
-18 8 -10
4.6 x 10 1.4 x 10 6.4 x 10

-17 12 -4
3.5 x 10 3.8 x 10 1.3 x 10
-11 5 -6
2.3 x 10 2.6 x 10 6.0 x 10
                                                   -5
 4.8 x 10
 0.24
a  Data from Demerjian et al.18
b  Data from Table 13-4»
                                     13-34

-------
 assume  that  the rate constants parallel those of the reactions with trans-

 butene-2  (see Table 13-3), as was done in estimating the rates of reaction

 with an olefinic polymer in the laboratory ozone generator.  Using the con-

 centrations  in Table 13-4 with the rate constants in Table 13-3, we arrive

 at  the  attack rates shown in Table 13-13.  These results suggest that HO
                                                                        2
 is  the  most  important oxidant in attack on elastomers in ambient air.


     Economic Effects.  The Battelle study5 revealed very substantial

 compounding  costs for protection against photochemical oxidants.  Table 13-14

 summarizes the results of an analysis based on responses to a questionnaire.

 These costs  include the introduction of such ozone-resistant polymers as

 butyl,  neoprene, EPDM, Hypalon, and polysulfide.  Fair agreement was obtained

 between costs obtained from the questionnaire and those from estimates of

 individual compounding costs as summarized in Table 13-15.  In addition to

 the costs outlined in Table 13-15, other costs are associated with replacement

 of entire assemblies when a part fails, labor costs for replacement, etc0

 These costs  at the retail level have been estimated by Battelle to total

 $226 million per year, of which $100 million is attributed to damage of

medical goods.  In 1969, the cost of antiozonants in automobile tires2 alone

was about $100 million,  which represents the cost of avoiding ozone damage

 to tires.   The $226 million estimate does not include labor costs for actual

 replacement.  Because antiozonants tend to discolor, they cannot be used in

white sidewall tires,  which use, instead, such costly elastomers as Hypalon

 and EPDM.   It is of interest that tires, hoses, and belts do not represent

 the only important use of rubber in automobiles.  Some $50 per car or $500

million per year in other rubber parts represents the value at the manufacturer
                                     13-35

-------
                                  Table 13-14
                        Estimate of AddedAManufacturing
                           Costsa on National Level®
Product
Passenger tires
Truck and bus tires
Other tires
Rubber belts and belting
Rubber hose and tubing
Sponge and foam-rubber goods'3
Rubber floor and wall covering
Mechanical rubber goods
Rubber soles and heels'3
Drug and medical
Footwear
Other rubber products

                      Total
Estimated
Value of
1970
Shipments,
$ million

  2,352
  1,037
    679
    300
    480
    325
     66
  1,295
    165
    100
    400
    650

  7,849
Estimated
Added Cost
per Dollar of
Production,
mils	

     12
     12
     10
      4
      2
      8
      1
      1
Total
Added
Cost,
$ million

  2802
  12.4
   6.8
   1.2
   1.0
   2.6

   0.8
   0.4
   0.7
                    54.1
a  Extra costs due to special compounding or formulation to protect against
     oxidant damage,
b  Derived from Mueller and Stickney.5
G  No protective compounding or formulation used.
                                   13-36

-------
                     Table 13-15

    Summary of Added Costs at Manufacturer Levela


Type of Cost                          Cost, $ million

Special polymers                           20.6

Antiozonant                                34.1

Wax                                         5.0

Protective Finishes
Wrapping

Compound development
26.0^
                           Total           85.7
a  Derived from Mueller and Stickney.6
b  Rough estimate.
                        13-37

-------
level.  The cost of ozone damage is summarized in Table 13-16.  An approximate

25% rise in rubber production was expected between 1969 and 1975.  Therefore

the cost of ozone damage to elastomers in 1975 should be 1.25 x 596= ~$750

million.


Textile Fibers

     It is difficult to find any definitive information that indicates ozone

damage as extensive as that suggested in the Midwest Research Institute

report.3  The latter identifies cotton, nylon, and rayon as particularly

susceptible to ozone.  The oxidation of cellulose fibers by ozone was the

subject of a study2g in 1952 that showed that dry cotton was not seriously

degraded by ambient ozone.  In more recent studies, these conclusions were

confirmed.  »31  The only information available on fibers other than cotton

addressed the effect of ozone on modacrylic, acrylic, Nylon 66 and polyester

fabrics.32  The results indicated minimal effects on these fibers.

     However, Jellinek and Chaudhuri33 exposed Nylon 66 films to nitrogen

dioxide, ozone, and ultraviolet radiation.  The degree of degradation of

polymer, a, was measured by


     a  =  _!   -  _!_ ,                                               (40)
           L      L
            t      o

where L  and L  are the number-average chain lengths at times Q and t,
       o      t
respectively0  Degradation proceeds rapidly at 19.2 ppm and stops at around

a = 0.002 after 1 h.  Lower concentrations produce lower ultimate degrees

of degradation after longer times (see Figure 13-3).  The mechanism of the

degradation is believed to be attack at the N-H bond.
                                     13-38

-------
                                  Table 13-16

                                    TV,
                 Summary of Ozone Damage Cost Per Year  (1969)
                             Mfr. Level
                             Cost,                             Retail Cost,
Type of Cost _      $ million       Labor Factor      $ million
Special formulations            85.7              3               257



Early replacements             225.7              1.5             339



                    Total                                         596
                                     13-39

-------


*0
o


20
18
16
14
12
10
e
4
a
I 1 I t I I — 1 — 1 — I — 1 — 1 — 1 — p
1 » *

„
*
x^"*
/
^S^-- 1 P 1 !' 1 I 1 i i i i .
0 1 * 3 4 9 6 7 8 9 10 I) 12 13
HOURS
Figure 13-3.
Plots of a vs. time for BI films at 35 C in presence of 1 atm
of air containing ozone;B, 19.2 ppm; A} 11 ppm;  •, 5.2 ppm0
(Reprinted with permission from Jellinek and Chaudhurio  )
                                     13-40

-------
                 OH               Q   OOOH
                 ii   i               n    •                           .  .
     0   +	C-N	 ->	C-N                           (41)
      3
                 Pi   9
                 -C-N       +       HO „

                                       2






Protection of the peptide link is afforded by the addition of hydrogen-




bonding compounds, such as benzaldehyde:
     C H   -  C  =  0


      65     |     :


              H     H
              •
              »
              *

              0


              11

             ,C	
The overall evidence of ozone damage to fibers is not compelling.






Dye Fading




     0-Fadlng.  The discovery that dyes faded under the influence of ambient




ozone was made by accident in 1955.^  The dye molecule is converted by




oxidation to much less deeply colored molecules.  The phenomenon became




known as "0-fading."  Laboratory tests had shown a new dye, Disperse Blue




27, to be resistant to attack ("gas fading") by nitrogen dioxide.  Field




tests to confirm the laboratory findings were run on acetate draperies




containing this dye in a high-nitrogen dioxide area (Pittsburgh) and a low-




nitrogen dioxide area (Ames, Iowa).  The draperies in both locations were




protected from sunlight.  The result of 12 months of exposure was opposite




to that expected—the Ames draperies had faded more than the Pittsburgh




draperies.  Ozone was identified as the damaging pollutant, and 0-fading




was found to occur only when Disperse Blue 27 was used on cellulose
                                     13-41

-------
triacetate and polyester, but not with acrylic and nylon.  The dyes most




susceptible to 0-fading were found to be anthraquinone blues, some reds,




and some azo reds.  Gas-fading inhibitors (such antioxidants as




diphenylethylenediamine and tert-butylhydroquinone) are used to retard




fading.  The American Association of Textile Chemists and Colorists Committee




on Colorfastness of Textiles to Atmospheric Contaminants (RA-33) later




conducted extensive tests,35 and these tests eventually led to the discovery




of fading problems due to the effect of ozone on permanent-press fabrics




and on nylon carpets."*  Other very extensive tests on dye fading by air




pollutants have been carried out under the auspices of the AATCC Committee




RA-33, the EPA,36,37 and others.38




     Test procedures established by Committee RA-33 include a test ribbon




intended to characterize the ozone content of air to which fabrics are




exposed.  The test ribbon is dyed to the tertiary gray shade, with CI Disperse




Blue 27.  Committee RA-33 has also established a test ribbon for nitrogen




dioxide gas fading.







     Fading of Permanent-Press Fabrics.  Permanent-press garments are blends




of polyester and cotton in a ratio of 50:50 or 65:35.  The permanent-press




formulation includes a catalyst (zinc nitrate or magnesium chloride*),  a




softener (polyethylene), a nonionic emulsifying agent, and a wetting agento




The anthraquinone blues react with the magnesium chloride catalyst to form a




chelate that is soluble in the polyethylene softener and in the emulsifying




agent, both of which, are contained in the "finish."  In the curing process




(at 320-340 F,or 160-171 C), disperse dyes (e.g., anthraquinone blues)




migrate to the "finish"—i.e., migrate preferentially to the folds and creases.
                                     13-42

-------
The dye in this substrate, at folds, fades under the influence of ozone.




Storage of garments in the summer in warehouses with open windows has




resulted in fading in as few as 10 days.^9  Remedial measures include




replacing anthraquinone dyes with azo disperse dyes, avoiding the use of




magnesium chloride catalyst, and using different surfactants and softeners,







     Nylon Carpeting.  Consumer complaints of fading nylon carpeting in the




warm, humid areas of Texas and Florida gave rise to the term "Gulf Coast




fading. "^ j1* 1  Laboratory experiments showed the fading to be due to a




combination of ozone and high relative humidity (above 65%).  It was found




that fading was reduced on nylon fibers textured by dry heat, rather than




by steam, which produces a moisture-absorbing fiber structure.  Such a




structure encourages diffusion of ozone throughout the fiber.  Measures




have been taken to mitigate Gulf Coast fading, and it is no longer considered




to be a serious problem.







     Economic Effects.  Although measures can be and have been introduced




to eliminate dye fading due to ambient ozone, these measures are expensive




and represent a minimal cost of pollution damage that would otherwise be




sustained.




     Oppenheimer42 and Waddell1*3 attribute the preliminary economic summary




in Table 13-17 to Salvin.  These figures are based on increased costs of




fade—resistant dyes, inhibitors, research, and quality control.  Also




included are costs to consumers of decreased product life.  Waddell concluded




that the "best" estimate of damage to materials for all air pollutants is




about $2.2  billion per year.
                                     13-43

-------
                                  Table 13-17

                           Cost of Dye Fading, 1970a
Pollutant
NO
  x
Material

Acetates

Rayon

Cotton

Spandex
                                              Subtotal
Cost, $ Million

       73

       22

       22

      	5

      122
Ozone
Acetates

Nylon Carpets

Permanent Press
                                              Subtotal
       25

       42

       JL7_

       84
a  Derived from Waddell.43
                                     13-44

-------
 Other Materials

      A number of rather tenuous arguments  suggest  ozone damage  to  such

 materials as recording tape,44  asphalt,45  and  dried  milk.46   However,  studies

 on such subjects are scattered  and  generally uncorroborated.  Some studies

 even discuss beneficial effects of  ozone,  such as  reduction  of  corrosion

 rates in steel47 and improvement in adhesion of ink  to  polyethylene films.

      Polyethylene is a major electric  insulating material, and  the suggestion

 that ozone may "disastrously" affect its insulating  properties48 bears

 examination.

      Laboratory studies carried out by Priest  and  his co-workers

 have demonstrated by means  of infrared and other techniques  that terminal

 double bonds in polyethylene end groups are attacked by "ozonized" oxygen

 to form carboxylic acid groups  and  by  rupture  of the polymer chain to

 produce short-chain dicarboxylic acids.  A net gain  in  weight results.

      Razumovskii5^ and his  colleagues  appear not to  have been aware of the

 work of Priest et al.  and prefer to interpret  their  own results as supporting

a mechanism  that involves attack of ozone  on the CH  -CH  unit in polyethylene.
                                                   2   2
 Rate constants for the reactions have  not  been measured, and  no assessment

 of the role of other oxidizing  species has been made.   However, it is  pre-

 sumed  that  a  high-pressure  ozonizer was used and that ozone  was the active

 species.

      It is  known that  atomic oxygen reacts with polyethylene  at room

 temperature53  to produce a  loss in  weight  and  some morphologic  changes.

 The work of Trozolo and Winslow54 and  of Kaplan and  Kelleher28  suggests that
    1
 0  ( A  )  also  interacts with polyethylene to form hydroperoxides.   Because
 2   g
                                      13-45

-------
                                                         3 -
polyethylene is known to be very stable to ground-state ( £ ) molecular
                                                           g
oxygen, the possible oxidants responsible for polyethylene damage in
                                   1
polluted air are atomic oxygen, 0 ( A ), and ozone, Off «•£ HQ .   Relative rates
                                 2   g                       2
of reaction are products of rate constants and concentrations of oxidizing

species in the real atmosphere.  Thus the relative rates of reaction of these

species with polyethylene could be assessed, if we had rate

constants for their reactions with polyethylene.  Because we do not, we

can assume that the rate constants parallel those of the reactions with

butene-yt, (see Table 13-3).  With the concentrations in Table 13-4 and the

rate constants in Table 13-3, we arrive at the attack rates shown in

Table 13-13.

     These results suggest that H02 may be the dominant oxidant  that attacks

polyethylene or other materials in ambient air.



     However, despite the known interactions of oxidants with polyethylene

and other polyolefins to form intermediate peroxy radicals,52 there is no

evidence that the chemical reactions go far beyond the surface.   In fact,

polyethylene  is specially treated with the products of a corona discharge

to improve the surface adhesion of printing ink.55  Winslow55 believes that

the effects of atmospheric ozone on polyethylene insulation and  other

polyethylene  products are negligible, compared with the embrittlement of

polyethylene  by a combination of oxygen and solar ultraviolet radiation.,

The mechanisms by which this embrittlement occurs probably involve

sensitization to oxidation by absorption of ultraviolet radiation by

residual hydroperoxy and carbonyl groups in the polymer and by surface
                                     13-46

-------
deposits of aromatic sensitizers from polluted air.  Deterioration of  the



electric insulating properties of polyethylene48 by oxidation  in  some



environments cannot be attributed to ozone.  Damage to polyethylene by



ozone suggested by the figures in Table  13-5 is undoubtedly overestimated.



     In view of the relative stability of polyethylene toward  ozone, it  is



surprising that the perfluorinated analogue  (Teflon) reacts with  ozone to



produce perfluoroformaldehyde and carbon dioxide.57  Because Teflon is



widely used to contain ozone-air mixtures, researchers are cautioned to  be



aware of this reaction.





SUMMARY



     In the context of this review, the  term "photochemical oxidants"  is



considered to be synonymous with "ozone."  In test chambers that  have



external ozone generators and that operate at or near atmospheric pressure,



ozone is the only likely oxidizing species.  In ambient air, however,



ground-state atomic oxygen, hydroxyl radicals, and especially  hydroperoxy

                         avA »*<*y ev/ei\ c(ov*\w>te

radicals can compete with ozone in attacking materials, such as rubber,
                         A


that contain olefinic bonds.  The most economically important  materials



with respect to ozone damage are paint, elastomers (rubber), and  textile



fiber-dye systems.  Damage to polyethylene by ozone is considered to be



negligible.  The ozone-specific damage in 1970 to materials has been assessed



in economic terms and is approximately as follows:  paint, $540 million;



elastomers, $569 million; and textile fibers and dyes, $84 million.  Total



material damage attributable to ozone is, therefore, $1.22 billion.  This



is to be compared with Waddell's estimate of total air pollutant material



damage of $2.2 billion.  It is clear that otidavfc &re very important molecule*"



in pollutant damage to materials.





                                     13-47

-------
RESEARCH RECOMMENDATIONS

     •  Laboratory studies of effects of photochemical oxidants  other than

        ozone—e.g.,  PAN,  peroxybenzoylnitrate,  atomic oxygen, excited
                             1
        molecular oxygen,  0 ( A ),  and hydroperoxy and hydroxyl  radicals—
                           2   g
        on specific materials should be conducted.

     •  Concentrations of  oxidants  other than ozone should  be measured in

        real atmospheres.

     •  Mechanisms of attack of oxidants on materials  should  be  investigated,

        so that distinctions can be made between effects  on a given material

        due to various pollutants.

     •  An integrated study should  be conducted  in which  relative effects

        of all major  air pollutants on materials are assessed.
                                     13-48

-------
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 46.   Kurtz, P." E.,  A. Tamsma, R." L.  Selman, and M.  J.  pallansch.   Effect of pollution




           of air  with ozone on flavor of sprayed-dried milk.   J.  Dairy Sci.   52:



           158-161,  1969.





 47,  tiaynie, F. M.,  and J.  B.  Upham.   Effects of atmospheric pollutants on corro-




          sion behavior of steel.  Mater. Protect.  Perform. 10(11):18-21, 1971.





 48.  Grassie, N.   Atmosphere on the attack.   New Scient. 45:12-15, March 19,  1970.





 49.  Keller, A., and D. J." Priest.  Experiments on the location of  chain ends in




          monolayer single crystals of polyethylene.  J. Macromol.  Sci. Phys. B.




          2:479-495, 1968.




 50.  Priest,  D.  J.   Fold  surface of polyethylene single crystals  as  assessed  by




          selective  degradation.  I.   Ozone  degradation method.   J.  Polymer Sci.




          Part  A-2   9:1777-1791, 1971.



5!.  Keller,  A., E.  Martuscelli, D. J.  Priest,  and Y. Udagawa.   Fold surface  of




          polyethylene single  crystals as assessed by selective degradation studies.




          III.   Application  of the improved  techniques  to  single crystals.   J.




          Polymer  Sci.  Part  A-2  9:1807-1837,  1971.




52,  Razumovskii,  S. D,,,  A.  A, Kefeli, and G.  E. Zaikov.  Degradation of polymers




          in reactive gases.  Eur. Polymer J.  7:275-285, 1971.
                               .13-54

-------
53.   Reneker,  D.  H. ,  and  L.  H.  Bolz.   Effect  of  atomic  oxygen on the  surface




          morphology  of polyethylene,  pp.         .In  Symposium on Plasma




          Chemistry of  Polymers, American Chemical Society Meeting, Philadel-




          phia, Pa.,  April 6-11, 1975.




54.  Trozzolo,  A.  M. ,  and  F.  H.  Winslow.  A mechanism  for  the  oxidative  photo-




          degradation  of polyethylene.  Macromolecules 1:98-100,  1968.





55.  Hansen, R. H. ,  J. V.  Pascale,  T.  DeBenedictis ,  and P. M.  Rentzepis.  Effect




          of atomic  oxygen on polymers.  J.  Polymer Sci. Part  A 3:2205-2214, 1965,




56.  Winslow, F. H.   Private communications.
57.  Daubendiek,   R. L. , and J. G. Calvert.  The reaction  of  ozone with  per-




          fluorinated polyolefins.  Environ. Lett. 6:253-272,  1974.
                                  13-55

-------
                                   CHAPTER 14.

                         GENERAL SUMMARY AND CONCLUSIONS


          The general summary and conclusions that appear below is a collage

                         taken from the individual chapters.

 CHEMICAL ORIGIN



       The major primary pollutants of importance to bxidant formation are

 nitric oxide, hydrocarbons,  aldehydes, and carbon monoxide.  A few free

 radicals are formed by photolysis  of aldehydes and nitrous acid by sunlight

 or by the reaction of traces of  ozone with reactive hydrocarbons.  These

 free radicals initiate chain reactions involving hydroperoxy and alkylperoxy

 radicals.  During these chain reactions, the nitric oxide is converted to

 nitrogen dioxide, and the hydrocarbons and aldehydes are degrated.  The

 photolysis of nitrogen dioxide by  sunlight forms a free oxygen atom,  which

 combines with an oxygen molecule to form ozone.  Because of the NO-NC^-O^
              of Chapter 2,
 cycle (Eqs. 1-3/) the ozone  concentration is determined primarily by the

 ratio [N02J : [NO] and so does not become large until most of the nitric

 oxide has been converted to  nitrogen dioxide.   The total amount of oxidant

 formed depends, in a nonlinear fashion,  on the amount of hydrocarbons

 available to continue pumping  the nitric oxide to nitrogen dioxide.   Al-

 dehydes and even carbon monoxide can also serve this pumping function.

 When some of the peroxy radicals recombine or  react with the nitrogen oxides,

many secondary products, such as hydrogen peroxide and PAN,  are formed.

       Recent chemical modeling studies  have been reasonably successful

 In reproducing the concentration — time histories of smog-chamber experi-

ments.   An  examination of  these models  shows a need  for much more detailed


 chemical knowledge.  Modeling studies also  point out  the necessity  of

 carefully defining the  initial conditions of  smog-chatr.ber  experiments.   Some

 observations that have  been made with these models  are:

                                    14-1

-------
        »  Even if hydrocarbons arc co; .\>1 c icly rwrmviHl i ro.a the air,
           aldehydes and N(\. cap ^enei.:Lc hi[',h concent) at i ons of photo-
           chemical oxidants.
       •  If both hydrocarbons and aldehydes are eliminated, carbon
          monoxide  and  NOX alone can generate significant concentrations
          of ozone.
       •  The concentration of ozone generated photochemically goes through
          a maximum as  the NOX concentration is increased.
       •  The steady-state concentration of free radicals in smog is
          approximately 0.3 ppb and is rather insensitive to primary
          pollutant concentration.
The concentrations, average lifetimes, and rates of attack of the reactive
intermediates can be calculated with chemical models.
       The effects of free radicals on biologic surfaces cannot be
ignored.
       The development of lasers has opened up several new techniques
for monitoring pollutants in the atmosphere.   Sensitivities  down  to  the
parts-per-billion range are claimed, and continuous monitoring  is possible.
The photoionization mass spectrometer has been developed as a sensitive
detector  for free radicals in the gas phase.  A high-resolution mass
spectrometer coupled to a computer is capable of detecting up to 300
compounds in air, both  in particulate form and in the gas phase.

 AEROSOLS
        Review of  the literature provides ample evidence that aerosol formation
   is  an important part  of the  atmospheric chemistry linked with photochemical
   oxidant  production.   The important  chemical  constituents of concern include
   sulfate,  nitrate,  and secondary  organic material.
        Secondary organic aerosols, formed by gas-phase reaction between
   nitrogen oxide, ozone, and hydrocarbons constitute an important fraction
   of urban photochemical smog.  Data obtained at high ozone concentrations

                                    14-2

-------
 (0.67 ppm)  can be taken as an upper limit of the contribution of secondary
 organic aerosols to the organic aerosol fraction and total suspended
 particulate material  (95% and 65%, respectively).  Most of the identified
 ambient secondary organic aerosols are difunctional compounds that bear
 carboxylic, nitrate,  aldehyde, and alcohol groups.  The same compounds
 have been identified  in smog chambers from C_  cyclic olefins and diolefins,
 with gas-to-aerosol conversion factors exceeding by more than an order of
 magnitude those measured for the ambient average conversion of all reac-
 tive hydrocarbons.  The formation of such species in the gas phase in
 excess of their saturation concentration followed by condensation on
 preexisting particles and further growth in the light-scattering range
 is the predominant physical mechanism that controls the gas-to-aerosol
 conversion process.
     Because of their very low vapor pressures, difunctional compounds
 are readily converted to the aerosol phase, whereas more volatile
 monofunctional compounds require much higher precursor and ozone concen-
 trations to reach their saturation concentration.  This explains why
 most of the'*tompounds formed from alkenes remain in the gas phase, whereas
 C   cyclic olefins and diolefins are efficient aerosol precursors.  How-
 ever, there is no known source of the latter class, so cyclic olefins,
 identified in both gasolines and auto exhaust, can be regarded as the
most important source of secondary organic aerosols.  The role of aromatics
 as aerosol precursors is essentially unknown.  Because of their accumulation
 in the submicrometer  range, all secondary organics are potentially
 dangerous.  However,  there is almost no information on health effects
 associated with the presence of such compounds in the atmosphere.
     Because the conclusions presented in this chapter rely heavily on
a few recent studies, it is extremely difficult to relate the urban con-
                                  14-3

-------
    centrations  of  secondary aerosols to the concentration of their gas-phase

    precursors.   Simple  relations of the type d(secondary aerosol)/dt = a

    (precursor)  (ozone)  have been derived from smog-chamber data for organic

    aerosol  formation in mixtures of cyclic olefins and NO  and sulfate
                                                         X

    aerosol  formation in mixtures of NO , sulfur dioxide, and C   alkenes.
                                      X                       J ^
    Such kinetic  data are consistent with the organic (a few micrograms per

    cubic meter per hour) and sulfate (up to 13%/h) aerosol formation rates

    observed in photochemically polluted urban areas.  More complex kinetic

    relations reflect certainly all the possible variations between these

    extreme  and rather simple systems.  Although control of ozone, through

    control  of NO and total hydrocarbon emission, would obviously have a
                 x
    roughly  proportional effect on the formation of organic aerosols, present

    data suggest  the identification and control of a few specific hydrocarbon

    precursors as an alternative approach.  The contribution of photochemical

    reactions involving  hydrocarbons to inorganic nitrate and sulfate aerosol
              ••s.
    formation "remains to be determined.  More data on the identification of

   hydrocarbon precursors and on the kinetics of formation, physical parameters,

   and health effects of their products would ultimately permit quantifying

    the complex relations between secondary aerosols and ozone concentrations

    in urban atmospheres.


ATMOSPHERIC  CONCENTRATIONS OF PHOTOCHEMICAL OXIDANTS


     In comparison v;ith previously available piaterial   on  atmospheric  con-

centrations  of photochemicaloxidants,  we  now have a far richer  data  baye  and

a deeper understanding  of how to interpret the reported concentrations.   The

recent information on  hydrogen peroxide and the  broader geographic  coverage

of measurements abroad  are examples of new data  that have  come  to  light.


                                     14-4

-------
      Subtleties  in  future  standard-setting must consider receptor damage in




 terms of  exposure location and  time and receptor distributions and response




 functions.   The  formula  for damage function points up the need for improved




 knowledge of spatial and temporal distribution.  The use of second-to-worst




 hourly  readings  for an ambient  air quality standard must give way to a




 specification stated in  terms of a statistically defensible higher-frequency




 event.  This will reduce substantially the uncertainty inherent in confining




 one's attention  to  the. "worst case."





      Long-term trends in oxidant concentration canrot be identified with




 nearly the degree of certainty  that we might like.  The data suggest a




 decrease  in oxidant concentrations in central-city areas and an increase in




 downwind  areas. Measurements of nonurban oxidant are exhibiting a higher




 frequency of violations of the  ambient standard than was once believed to




 occur.  Figure 4-43 shows typical ranges of concentrations in various regions




 in and out of urban complexes.




     Probably the most critical question today regarding atmospheric concen-




 trations  of ozone and other photochemical oxidants is,  "uliat fraction of the




 observed values in each locale  is susceptible to control by anthropogenic




 emission  reduction?"  As brought out in this chapter, there, is one school




 of thought embracing the idea that nature frequently presents us with con-




 centrations that exceed the U.S. national ambient air quality standards.




The other point of view is that globaJ background ozone concentrations do not




 exceed 0.05 - 0.06 pp:n at the surface and that higher concentrations than




 this have anthropogenic sources.




     The data presented in the  literature reviewed above support the second




point of view.  The observation of ozone concentrations exceeding the ambient




 standard  in nonurban areas does not demonstrate that this is of natural







                                     14-5

-------
origin.  However, the measurement£3 in remote areas of the northern hemisphere,




compared with those in the continental United States, do support the thesis




that anthropogenic soui'ces are involved in cases where the standard is




exceeded.




     This is a very broad conclusion, and additional measurements must be




made.  Some of this effort (which is goingon) should address the problem of




other pollutants and condensation nuclei that accompany the nonurban oxidant.




Interpretation of these measurements will increase the specificity of




separating anthropogenic sources from natural background sources.  Theoretical




assessments of the existing observations will shed ligh't on the relative




roles played by stratospheric injection, plant emission, background methane,




and dry deposition on surfaces in the natural portion of the tropospheric




ozone cycle.




     Geographically, our best measurements have focused on the Los Angeles,




California, region because of the severity of the problem there.  The




Regional Air Pollution Study and its extensions will, it is hoped, supply




an additional rich data base for the St. Louis, Missouri, region.  Airborne-




pollutant measurements aimed at specific experimental objectives are needed




in the central and eastern areas of the United States to broaden the foundations




of a national control strategy.  Existing ground-based continuous monitoring




networks will not provide an adequate basis for the regional control of




oxidant.  Ad hoc, one-shot aircraft measurements have led mainly to specu-




lation that can establish incorrect attitudes on the origin and fate of nonurban




ozone.  In the vigor of environmental control efforts, incomplete data sets




have stimulated hasty targeting on specific sources (for example, rural




vehicular emission, power stations, trees, and frontal passages).






                                     14--6

-------
     Another subject of recent interest has been tbe question of indoor-
outdoor oxidant concentrations.  Available measureiuc-nts and models suggest
that indoor exposures may be substantially reduced by appropriate choices
of ventilation systems, air filters, and interior surface materials.  The
cost-benefit relationships coming from these studies may well have a great impact
on future decisions based on atmospheric concentrations of oxidant pollutants.
     Much care must be exercised in comparing atmospheric concentrations
between one place and another because of differences in primary ca]ibration
techniques or in instrumentation.  Chap.er 6 summarizes these problems in
detail.

   MODELS FOR PREDICTING AIR QUALITY

        The literature contains reviews of air quality modeling that stress
   special purposes.  Some concentrate on meteorologic aspects, and others combine
   this with air chemistry.  Proceedings of several conferences are another
   information resource.  Recent surveys have been addressed specifically to
   photochemical modeling problems.  It may be concluded that, although they are
   relatively complex, the photochemical-diffusion models perform as well as, if
   not better than, available inert-species models.
        A variety of goals and objectives may be met with air quality modeling.
   They are summarized as:
        •  Scientific understanding of atmospheric phenomenology,
        •  Rational application of the regulatory process.
        •  Land-use planning within environmental constraints.
        •  Real-time control of episodes.
                                       14-7

-------
      The fundamental elements  of deterministic models involve a combination of
 chemical and meteorologic input, preprocessing with data transmission, logic
 that describes atmospheric processes, and concentration-field output tables or
 displays.  In addition to deterministic models, there are statistical schemes
 that relate precursors (or emission) to photochemical oxidant concentrations.
 Models may be classified according to time and space scales, depending on the
 purposes for which they are designed.
      Specific model applications to the oxidant problem include both the
 simple rollback (with modifications) and the photochemical-diffusion tech-
 niques.  Very little modeling  of intermediate complexity seems to have been
 attempted for the oxidant system.
      Model performance is now  receiving critical attention because of the need
 for cost-effective control measures.  Standard statistical performance de-
 scriptors can sometimes mislead a prospective user; therefore, more specialized
 tests are being devised.  Various model types are being compared for a specified
 set of initial and boundary conditions.  It is apparent from these studies
 that added fidelity is purchased at the expense of added complexity of a logical
 structure that must represent  the controlling phenomenology.

MEASUREMENT METHODS

         With the exception of  calibration, the measurement problems which
were apparent in 1970, at the time of publication of the first air quality criteria
document on photochemical oxidants,  have essentially been solved for ozone.
This  remarkable achievement  is the result of unstinting efforts by individuals
working at EPA's National Environmental Research Center,  North Carolina;
the National Bureau of Standards; private research contractors sponsored

                                    14-8

-------
primarily by EP.  ; private instrument manufacturers; the Jet Propulsion




Laboratory of the California Institute of Technology;  the Air and Industrial




Hygiene Laboratory, California Department of Health; the Air Pollution




Research Center of the University of California  at Riverside, and the Califor-ia




Air Resources Board (CARB).




         Due to  the  focus on  the problem brought  about by  the CARB  , a




significant advance  in the accurate calibration of instruments for monitoring




ozone in ambient air was achieved during  1975.  Asa result, this agency




adopted the measurement of  ozone in the ultraviolet region at 254 run as  a




primary calibration reference  standard.   They have also adopted statewide,




as a transfer standard for  calibrating ozone and  oxidant monitoring instrumer.-.3




at air monitoring  stations, a commercially available instrument (coupled with




the precise controlled  generation  of ozone in air), which  measures the dif-




ferential absorption of ultraviolet radiation.




         It is important to  separate conceptually, and in practice, the




calibration process from the monitoring process.  Photochemical oxidants




consisting primarily of ozone were first continuously measured in Southern




California by measuring the  color change  of potassium iodide solutions brought




into contact with the ambient air.   This measurement continues to yield  valic




photochemical oxidant  data in California.  However,  it has yielded questionable




data at ambient air monitoring  sites elsewhere in the United States.  For this




reason at the end  of 1971,  EPA officially adopted a continuous monitoring




process  that measures the chemiluminescence  produced when o?,one in air is




brought into contact with  the gas  ethylene.   This reference procedure  when




calibrated with the primary reference procedure using ultraviolet absorption




is widely accepted.
                                     14-9

-------
         Instruments based on differential ultraviolet absorption still




need to be evaluated,  and possibly modified,  prior  to their acceptance




for monitoring ozone in polluted atmospheres on a nationwide scale.




The California Air Resources Board and other air pollution control




agencies are currently conducting multi-year programs for evaluating




ultiaviolet absorption side-by-side with chemiluminescent and potassium




 iodide based     instruments, to determine their applicability and




needed modification, as well as to assure continuity in the data base




•while the  older monitoring instruments are being replaced.




         Thus despite the remarkable progress in the monitoring for ozone,




nitrogen oxides  and non-methane  hydrocarbons,  which has strengthened the




implementation  and evaluation of control programs, substantial research




and development is  still required to help resolve the uncertainties  in our




knowledge which 3.re inhibiting the actual achievement of desired air quality




standards.










RESPIRATORY  TRANSPORT AND ABSORPTION








     This chapter har, discussed tho.  general approach required to rood«I




 the transport and absorption of ozone and other pollutant gases in the




 respiratory tract.   For  unraactive  or very weakly reactive gases,  there




 are a  few models that are qualitative descriptions for  assessing total




 dosage and  dosage  in major regions.   However, there is  no adequate model




 for gases like  ozone, which are  strongly reactive within the mucous




 and tissue layers.
                                    14-10

-------
TOXICOLOGY
     The acute  lotlviJ  act .1.0,1 or or- :>:'_• i" due Lo its capacity to prodj.cc




pjlrnonary edema.  The  LCr.   for rats and ndce c tco",'d for a single 4-h
       is approximately C  pp:n,  cind cats,  rabbits, guinea pig.c; , and do;js




 (in that order) arc decreasing!/ .':.u:;coptible in the lethal action.




Numerous review's have  considered the tcxieity of ozone at Jetlial <:a;d




1 ox\7er cone jnt ration s .




     In the foregoing  discussion ami in Table 14-1. attention has focused




on studies in laboratory animals th.it have bacn exposed to ozone concen-




trations of about 1 ppm or less, because  results of studies conducted




with such concentrations are  thought to be irore directly relevant to




ambient oxidant air pollution,  which is the source of exposure for largo




human populations.  In Table  14-1, no attempt has been made to list all




studies; more comprehensive suirnvaries am te found JJi some of the mono-




graphs cited.  Instead,  the table cites studies thought to be most useful




for evaluating the health  ini£ilic:jtions of exposure to ]ov; concentratjc.nj



of ozone, and the concentrations listed arc the ,lo",;est at which the




described effects have been observed.  Unfortunately, m;my studies have




not included a sufficient  range of oqperin.'jntnl concoiTb"al-Jcnr> to pc-n^ilt




construction of reliable dose-response curves or to cvetermJ ne vdiat, if




any, would be a "no-observed-effcct" concenti-ation for the o:/x;rimental




conditions usad.  Zilthough it is ujvilcrstandable that research scientists




find little stimulation in conduct jng exposure experiments at concen-




trations that fail to  pro. iuce cliongcs in  the biologic system in which




they are interested, the conduct (and reporting) of such experiments .is




extremely important for a  pragrratic evaluation of the implications of




positive findings for  human health.




     The table illustrates tha wide variety of biologic effects produced




in laboratory animals  exposed to relatively low concc-ntxations of ozonoc

-------
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CONTROLLED STUDIES ON HUMANS

        Convincing new information on the health effects of oxidant
exposure has emerged from controlled studies on humans, from which tentative
dose-response curves have been constructed.  The new data show statistically
significant reduced pulmonary function in healthy smokers and nonsmokers
at ozone concentrations at and above 0.37 ppm for 2-h exposures.   Other cases
and  aerosols  found  in an urban atmosphere were not present in these experiments.
Some studies  suggest that mixtures of sulfur dioxide and ozone at a
concentration of 0.37 ppm are more active physiologically thai: would be
expected from the behavior of the gases acting separately.
       Wide variation in response among different individuals is a general
finding in studies of oxidants, as well as other pollutants.
       Undesirable health effects of oxidant air pollution exposure are
increased by exercise,  and many people apparently limit strenuous exercise
voluntarily when oxidant pollution is high.
       Safety, ethical,  and legal considerations require that the utmost
care be exercised in human experimentation.  The risk inherent in this work
can be minimized by taking reasonable precautions while ensuring the satis-
factory performance of the study.
                                        14-17

-------
 PLANTS AND MICROORGANISMS






        Oxidant injury to vegetation -was first identified in 1944 in the Los




Angeles basin.  Our understanding of oxidant effects and of the widespread




nature of their occurrence has increased steadily since then.  Although the




major phytotoxic components of the oxidant (photochemical)  complex are ozone




and peroxyacetylnitrate (PAN), indirect data support the contention that other




phytotoxicants are present in the photochemical complex.  Ozone is considered




the most important phytotoxic component and was first identified as the specific




cause of weather fleck on tobacco and stipple on grape.  PAN is  associated




with the undersurface glazing and bronzing associated with many of the vegetable




crops.




       Plant response to oxidants  (including ozone and PAN) is often divided




into visible and subtle effects.  Visible  effects  are identifiable pigmented,




chlorotic,  and necrotic foliar patterns resulting from major physiologic




disturbances. Subtle effects  produce no visible injury,  but include metabolic




disturbances and may be measured on the basis of growth and long-term




biochemical changes.   These effects may influence plant populations and




communities and could have  an adverse influence on ecosystems. Visible




injury may be acute or chronic.  Acute  injury breaks down the cell membrane




and causes cell  death, with leaf necrotic patterns  that may be characteristic




for a  given oxidant, but can be confused with other stress factors.   Classic




injury from ozone is the upper-surface  fleck on tobacco and  the stipple of




grape.  Many plants show an upper-surface bleach -with no lower-surface
                                  14-18

-------
 injury.  Bifacial necrotic spotting is common and may appear flecklike.
 Classic injury from PAN appears as a glaze followed by bronzing of the
 lower leaf surface in many plants.   Complete collapse of leaf tissue can
 occur, if concentrations are high.  Chronic injury is associated with
 disruption of normal cellular activity followed by chlorosis  or other color
 or pigment changes that may lead to cell death.  Chronic injury patterns
 are generally not characteristic and may be confused with symptoms caused
 by biotic diseases,  insects, nutritional disorders, or other environmental
 stresses.  Early leaf senescence and abscission may result from chronic
 exposure.
        Leaf stomata are the principal entry sites for ozone and PAN.
 Stomata, when closed by any of a number of factors, will protect plants.
 Ozone and PAN may interfere with various oxidative reactions in plant cells.
 Membrane sulfhydryl groups and unsaturated lipid components may be primary
 targets of  oxidants.  Physiologic leaf age is an important consideration in
 the response of the  leaf to oxidants.   Young leaf tissue is more sensitive
 to PAN, whereas newly expanding and maturing tissue is most sensitive to
 ozone.   Light is  required before plant tissue will respond to PAN, but not
 to ozone.  Oxidants affect such physiologic processes as photosynthesis,
 respiration,  transpiration, stomatal opening, metabolic pools,  biochemical
 pathways,  and enzyme systems. The acute response of plants to ozone and
 PAN may result  from a saturation of sensitive cell sites and a disruption
 of normal cellular repair mechanisms.  Chronic injury probably results
 from secondary reactions involving membrane injury.
        There is  evidence  that ozone  is a radiomimetic gas.  Ozone affects
 pollen germination in some species and thus may directly affect yield.  A study
with Arabidopsis thaliana  suggested no mutagenic effects from ozone on this
plant over  five generations.
                                  14-19

-------
        Ambient-oxidant studies in filtered versus nonfiltered field chambers




have reported up to 50% reduction in citrus yield (orange and lemon), a 10 -




15% reduction in grape yield in first year and 50 -  60% reductions over the




following 2 years,  and a 5 - 29% reduction in yield of cotton lint and seed in




California. , Losses of 50% in  some sensitive potato, tobacco,  and soybean




cultivars have been reported from the  eastern United States.  It is apparent




that ambient oxidants  do reduce yields of many sensitive plant cultivars.




Growth reductions  associated with acute exposure to ozone are  often associated




•with injury; sometimes the correlations are high.  Even multiple exposures




and sometimes chronic exposures have shown fair  to good correlation between




injury and growth (biomass) reductions.  The greater  reductions in root




growth than in top growth reported in several species are  related to  solute




transport and may  be  fairly common under some conditions.  Ozone  affects




nodule number, but not nodule efficiency in clover,  soybean, and pinto bean.




This causes a  reduction in nitrogen fixation associated -with legumes and,  if




•widespread, could  have a major impact on plant communities and affect




fertilizer needs.    The effect on nodulation is related to carbohydrate  supply.




Yield reductions •with  little  injury after chronic exposure are known for




several crops.  Severe injury  in tomato was  required before a yield  reduction




was found.  Chronic exposures to ozone at 0. 05-0.  15 ppm  for 4-6 h/day




will produce yield reductions in soybean and  corn grown under field con-




ditions.  The threshold appears to be 0.05-0. 10 ppm for some sensitive




cultivars and is well within values monitored in  the eastern United States.




Growth or flowering effects, at chronic exposures to ozone at 0. 05-0. 15




ppm for 2-24 h/day are reported for carnation,  geranium, radish, and pinto




bean grown in greenhouse chambers.






                                      14-20

-------
        Plant sensitivity to ozone, PAN, and other oxidants is conditioned




 by many factors.  Genetic diversity between species and between cultivars




 within a species is well documented.  The mechanism of genetic resistance




 is known for only one onion cultivar and is related to  the effect of  ozone




 on stomatal closure.  Variants within a natural species are -well known for




 several pine species, including white,  loblolly, and ponderosa.  Plant




 sensitivity to oxidants can be changed by both climatic and edaphic factors.




 A change in environmental conditions will initiate a change in sensitivity at




 once, but it will be 3-5 days before  the response of the plant is  completely




 changed.   Plants generally are more sensitive when grown under short




 photoperiods, medium light conditions, medium temperature, high humidity,




 and high soil moisture.  Injury to PAN may increase with increasing light




 intensity.   Conditions during exposure and growth affect the response of




 plants to oxidants in similar -ways.   However,  plants exposed to ozone are




 more sensitive  to increasing light intensity and, in some cases, to decreasing




 temperature during the exposure period.  In general,  growth factors that




 tend to  cause  a  physiologic hardening of plant tissue make the plants more




 tolerant to ozone.  At the  time of exposure, factors that increase water




 stress tend to make plants more tolerant to ozone.  Soil moisture  is probably




 the most important environmental factor that affects response during the




 normal growing season.




        Plants respond in different ways to pollutant mixtures; less than




 additive, additive,  and greater than  additive  effects have been reported.




Mixtures of ozone with sulfur dioxide and of nitrogen dioxide with sulfur




dioxide can cause oxidant-like symptoms in some sensitive plants.  Mixtures




 can cause effects below the threshold for either gas,  although there is some
                                    14-21

-------
disagreement on this in regard to ozone.  Ratios of mixtures, intermittent




exposures, sequential  exposures to pollutants, and predisposition by one




pollutant to the  effects  of a second pollutant may all be important in nature,




but little research has  been done.




        The response of some plants to oxidants is conditioned by the




presence or absence of biotic pathogens.  Depending  on the plant and the




pathogen,  oxidants may cause more or less injury to a given species.




Pathogens may  protect their host or make it more sensitive.  The pathogens




themselves may be injured or may be protected by the host plant.   This




subject is  just starting to be understood.




        Oxidant  injury to ponderosa pine predisposes  the trees to later




invasion by pine bark beetles.   Ozone and ozone-sulfur dioxide mixtures




may decrease the population of soybean nematodes.   Both greater  and smaller




effects  have been noted when herbicides have been used in the presence of




high oxidant concentrations.




        The two  most critical factors in terms of air  quality standards are




duration of exposure and concentration.  These two factors determine the




exposure dose for a plant.  In determining the response of vegetation, con-




centration is more important than time.  A given dose presented to a plant




in a  short period has a  greater  effect than the same dose  applied over a longer




period.   This suggests  a. threshold effect for plant populations and is probably




related  to the repair mechanisms inherent in biologic systems.  Sufficient




information is not available from long-term chronic studies, but a. threshold




between 0. 05 and 0. 10 ppm is probable for ozone (oxidant).  For acute effects,




an overall threshold concentration with respect to time can be determined




from Figures 11-6 and Table  ll-24a.   Fcr pinto bean (Table  11-22), this threshold
                                  14-22

-------
 for injury is about 0. 03 ppm for 8 h and about 0. 10 ppm for 1 h.  This




 suggests that oxidant standards may be needed for periods up to 8 h.




        Vegetation can act as a major sink for oxidants over time, but has a




 relatively minor effect on oxidant concentrations during episodes of high air




 pollution,  is more effective at some seasons  or under some cultural and




 management practices than others, and should not be considered an important




 contributor to  short-term reductions in oxidant or ozone concentrations.




        Plant protection from air pollution stress has involved three types of




 programs.  Several  researchers are including pollutant stress in standard




 breeding programs with the aim of developing resistant cultivars.  Our present




 concepts of pollution effects suggest that the gene pool of all species is large




 enough to permit the development of more tolerant cultivars.  Natural selection




 •will slowly do  this for native vegetation.  If pollution concentrations go no




 higher,  this should be an effective protection device.  Interim measures




 involve the use of chemical  sprays.  Such sprays are not yet economically




 feasible, but several do give adequate protection against oxidants.  Fungicides,




 such as  Benomyl, may serve a dual function.  Cultural and land use practices




may also play important roles, especially on  a short-term basis.




       Little research on the effects of oxidants  on nonvascular green plants




 and microorganisms  has been reported.  Lichens and mosses are responsive




 to acid gases,  but there is no definite evidence that they respond 1o oxidants.




Ferns may be especially sensitive, but their injury response is much different




from that of higher plants.   Growth and  sporulation of fungi on surfaces




are usually, but not always, affected.  Ozone does not penetrate the leaf




tissue or the colony and thus does  not cause death of  colonies.   Ozone from
                                     14-23

-------
 0. 1 to several milligrams per liter of solution is  required to kill many




 microorganisms in liquid media.   Most work with microorganisms has




 been done to study the effectiveness of ozone as a biocide  in the storage of




 vegetation or treatment of water or sewage supplies.




        Plants have been used as biologic indicators of oxidant pollutants




 for many years.  Attempts have been made to use plants as monitors, but




 too many unknown variables are involved.  Plants may be  capable of




 monitoring the total biologic potential for adverse effects,  but no research




 has  been developed along these  lines.




        Losses based on farm prices are not appropriate at the consumer




 level and are likely to be conservative.  Because of percentage markups and




 fixed wholesale and retail marketing costs, the  cost to the consumer from




 agricultural losses to oxidant pollutants could be as much  as $600 million per



 year.
ECOSYSTEMS






        The transport of injurious concentrations  of ozone and other oxidants




 to  rural areas downwind from urban centers at  nuir-erous  locations in the United




 States  appears to be on the increase.          Bluraenthal  et_  al.  conservative!;.




 estimate that the urban plume from the Los Angeles area "could cause ozone




 concentrations to exceed the Federal standard  of 0.08 ppm at locations as




 far as  260 km."  Other areas where significant rural concentrations of oxidant




 have been observed are. Salt Lake City, Denver, and the  lilue  Ridge Mountains.




         In general, the permanent vegetation const. Ltutlng natural ecosystems




 receives nuch greater chronic exposure, end the short-lived  higher-value




 vegetation constituting the agroe.cosypt^i o! uhc LOR Angules coastal plaLn




                                    14-24

-------
 can be subject to  injurious  doses,  but  in  intermittent  short-term  fumigations.
 Each situation  has  measurable  economac and  aesthetic effects, but on
 different time-scales.   The  simple  agroecosystem has little  resilience  to
 pollutant stress;  losses are immediate and sometimes catastrophic.  The
 complex natural ecosystem is initially more  resistant to  pollutant stress,
 but the longer chronic  exposures  cause disruption  of both structure and
 function in the system  that  may be  irreversible.
         Simulation models of ecosystem subsystems  are developing rapidly.
 They deal with flows of energy, biomass, mineral nutrients,  water,  numbers
 of species, population  densities, and area occupied per biotic unit.  Inter-
 actions between ecosystem components  must  be understood before prediction  can
 be attempted.   Simulation models  offer a bright opportunity  for determining
 the  long-term effects on natural ecosystems and agroecosystens.   New knowledge
 of biologic effects should suggest the importance of preveiition and some means
 for  ameliorating damage.
        Oxidant injury to the mixed-conifer stands  of  the  San Bernardino,
Mountains beginning in the early 1940's is  well advanced.   A  similar problem
 is developing in the forests of the  southern  Sierra Nevada.  Both places
 show both direct and indirect effects on all  subsystems  of the forest  eco-
 system — producers,  consumers,  and  decomposers.  For  example:
        e  Ozone injury  limits biomass production by the primary
           producers  and their capacity to  reproduce.
        •  The decrease  of biomass or energy  flow to consumer and
           decomposer in the ecosystem affects the  populations  of
           these organisms.
                                  14-25

-------
         0  Essential recycling processes,  such as recycling of

            nutrients, may be interrupted,  further limiting primary
            production.

         •  Stand structure is altered rapidly in some areas by salvage

            logging of high-risk trees;  as  a result,  species composition

            is changing,  and wildlife habitat is being altered.

         Oxidant injury to eastern white pine in some forest stands in

 the eastern United States is a significant problem.   There is  an important

 concern about injury caused by a synergistic reaction between  ozone and
 sulfur dioxide at low concentrations.

         The relationship between man's  welfare and stable  natural ecosystems

 and agroecosystems can be established in terms of the economic and aesthetic

 values derived from them.  In some situations, where ecosystems are stressed

 by oxidant pollutants, the benefits realized by present  and future generations

 may soon diminish.  Considerable research  is required to find  alternatives that

 prevent stress or that n.ay salvage :,o;nc of these benefits.   New management
strategies should be instituted only when  their consequences are predictable
within reasonable limits.
EFFECTS Of PHOTOCHEMICAL OXIDANTS ON MATERIALS

     In the context of this review, the term "photochemical oxidants" is

considered to be synonymous with "ozone."  In test chambers that have

external  ozone generators and that operate at or near atmospheric pressure,

ozone  is  the only  likely oxidizing species.  In ambient air, however,

ground-state atomic oxygen, hydroxyl  radicals, and especially hydroperoxy

                                      14-26

-------
radicals can compete with ozone in attacking materials, such as rubber,




that contain olefinic bonds.  The most economically important materials




with respect to ozone damage arc paint, elastomers (rubber), and textile




fiber-dye systems.  Damage to polyethylene by ozone is considered to be




negligible.  The ozone-specific damage in 1970 to materials has been assessed




in economic terms and is approximately as follows:  paint, $540 million;




eL   '
-------
                          CHAPTER 15.

              RECOMMENDATIONS FOR FUTURE RESEARCH


          The recommendations  for research that appear below is a

               collage  taken from the individual chapters.

CHEMICAL ORIGIN


•  Rate constants are needed for almost all  the reactions of H02


   and R02-

•  The homogeneous and heterogeneous reactions of the oxides of

   nitrogen with water vapor need study.

•  The yields of free radicals from -the photolysis of nitrous acid

   and of aldehydes should be established.

              of Chapter 2,
e  Equation 4/  [0-j] = k-jNC^]/k3[NO], should be tested in the real

   atmosphere,  as well as in  laboratory experiments.  Simultaneous

   measurements of the concentrations of ozone, nitric oxide, and

   nitrogen dioxide and of the intensity of sunlight for a variety of

   conditions will provide a much-needed check on this dynamic

   equilibrium.

•  A quantitative measure of  the concentration of free radicals in

   smog (probably OH or HO ) under well-defined conditions will provide

   an important test of present chemical models.

•  Strong support for fundamental gas-phase kinetics is needed.  Most

   of the reaction mechanisms and rate constants that are needed to

   construct realistic and detailed models of the polluted atmosphere

   are determined in laboratory studies under very special conditions,

   not in smog simulations at a pressure of 1 atm.  Because there are

   still very serious gaps in the present models, further research

   should be supported.


                               15-1

-------
 •   Smog-chamber studies are needed for validating both the detailed
    chemical models and the lumped models.  Many of the past chamber
    studies have not used sufficiently well-defined initial conditions.
    Measurements of more products and of the reactive intermediates
    will provide more stringent tests for models.
 •   Modeling studies are very useful in pointing out the important
    kinetic data that are lacking, in clarifying some of the past
    smog-chamber studies, and generally in making the very complex
    chemistry more comprehensible.  Accurate models can make unique
    predictions about the polluted atmosphere.  There are very useful
    interactions between the modeling studies, the smog-chamber
   experiments, and fundamental chemical kinetics;  it  is  not
   possible to ignore one without hurting progress  in  the others.
•  It seems probable that many new and  unstable compounds are
   present in the polluted atmosphere or in smog chambers.  A  care-
   ful search for some of these compounds may provide  some surprises.
•  Promising new instrumental techniques should be  supported,  both
   for monitoring pollutants  and for following reactive intermediates
   in kinetic studies.   A reliable and  accurate method of standardizing
   concentrations in the parts-per-billion range is needed.
•  The possibility that free  radicals,  particularly H0~,  have  signifi-
   cant effects on biologic surfaces exposed to the irradiated atmosphere
   should be investigated.   Sticking coefficients are  needed.   In
   experiments in which the observed biologic effects  cannot be attributed
   to the measured ozone and  PAN concentrations, the possibility of
   damage by the steady-state concentrations of free radicals  in the
   atmosphere should be considered.

                                15-2

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 AEROSOLS



      Our  present  knowledge  of  the chemical and physical processes  that


 govern  aerosol  formation  in the atmosphere is rather limited, and  further


 studies are  needed  in most  of  the relevant areas of research.  This may


 leave the reader—and the decision-maker—with a feeling of endlessness.


 However,  substantial improvements could be made in a reasonable period


 by  focusing  research efforts in the subjects most directly involved:


      •  Laboratory  (smog-chamber) studies of aerosol formation from


 aromatic  hydrocarbons;  gas-phase reaction mechanism, physical processes


 controlling  gas-to-aerosol  conversion, kinetic data on aerosol formation


 and aerosol  growth, identification of the aerosol products, and effect


 of hydrocarbon  concentration on aerosol formation (threshold).


      •  Careful search, in  the atmosphere, for aerosol precursors, such


 as cyclic  olefins and C   alkenes.
                       6+

      •  Study of  the possible health effects of exposure to difunctional


 oxygenated organics (such as dicarboxylic acids) that are present  in urban


 aerosols.


      •  Identification of organic components of ambient aerosols,  to


 permit estimation of the  relative importance of olefinic and aromatic


 hydrocarbons as aerosol precursors.


      •  Estimation of the relative contributions of photochemical and


 nonphotochemical pathways to the formation of inorganic nitrate and


 sulfate aerosols.


      Identification of organic components of ambient aerosols and esti-


mation of  the contributions of various pathways are of immediate interest


 for control strategies and could be  achieved by using the existing


monitoring networks so as to provide more information on aerosol chemical

                                15-3

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composition.  In view of the adverse effects (e.g., on health and visi-




bility) associated with submicroraeter aerosols, an air quality standard




for submicrometer particles might be more adequate than the present




standard for tot;al suspended particles.
 ATMOSPHERIC  CONCENTRATIONS OF PHOTOCHEMICAL OXIDANTS









       •  Nonmethane hydrocarbons and both oxides of  nitrogen should




 be monitored concurrently whenever photochemical oxidant or ozone




 is monitored.




       • Photochemical oxidant monitoring stations should be sited




 upwind and downwind from urban areas, as  well as within those urban




 areas, wherever possible.




        • A common primary calibration standard should be established




 for all monitoring networks.




       • Documentation should be provided in each case to outline




 the rationale for location and design of  monitoring  stations and




 the rationale for data validation for photochemical  oxidants.




        • A clear indication of what constitutes background




 concentrations of photochemical oxidants  and ozone must be made,




 in order to form the basis of emission control programs.




        • The results of monitoring data must be generalized, in




 order to relate air quality to emission in a stochastic fashion.
                                  15-4

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  MODELS  FOR PREDICTING AIR QUALITY

      Internal improvements in deterministic methods will be based on accounting
 for more physicochemical effects in the logical structure.  One challenge to
 the researcher is to do this without making something that is already complex
 still more difficult to understand, and another challenge is to avoid needless
 elaboration of detail. Both pitfalls will be avoided, first, by asking how
 accurate a modeling job is demanded and, second, by carrying out order-of-
 magnitude analytic appraisals of the omitted phenomenology.
      Perhaps the most important thing that research will contribute is-a set
 of criteria delineating the fidelity of existing models, rather than a single
 supermodel that will consider all effects.  Much remains to be done in statis-
 tical modeling.  The scientific community is on the threshold of potentially
 great strides with these methods, because of the veritable explosion of data
 from measurement programs.  It is absolutely essential for all agencies
 interested in environmental management to begin mounting analysis programs that
 are carefully designed to capitalize on the data base.  Traditionally, support
 has been more readily obtained for making additional measurements in hope
that useful information would emerge directly or that someone would sponta-
neously dig out the useful information.  Seldom has either been the case.
     Specific research subjects have emerged with respect to improved des-
criptions of specific phenomena.  Some time ago,   it was speculated that gas-
solid interactions and turbulence effects on reaction kinetics would be
Important areas of advance in the modeling art.  Gas-solid interactions include
both chemical formation of aerosols and reactions on surfaces of preexisting
suspended particulate matter.  Because of differing effects of a material in
 the gas  phase and  in  some  condensed phase, it will be important to characterize
transformation processes.  The ACHEX (Aerosol Characterization Experiment)

                                    15-5

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program   recently carried out under the direction of Hidy will provide an

extensive data base with which to test new ways of treating the gas-solid

interaction problem.

     The turbulent mixing of emitted reactant gas (such as nitric oxide) with

atmospherically formed reactant gas (such as ozone) results in macroscopic

heterogeneities, which under some circumstances can significantly change the

reaction rate from the value that the mean concentrations used in a rate

equation would predict.  Airborne measurement from some 40 operational days

from the LARPP (Los Angeles R.eactive Pollutant Program) study gives 6-s-interval

gas-phase data for six gas-phase species simultaneously.  This program (under

the field management of W. Perkins and under the direction of Coordinating

Research Council's CAPA-12 committee, chaired by J. Black) has produced archives

of these data that can serve as a test bed for theories of turbulent inter-

actions with kinetics.

     In a broader sense, the data obtained from the Regional Air Pollution

Study (RAPS) and the California Three-Dimensional Pollutant Gradient Study

Program should also serve as bases of further model development.  It is

incumbent on the agencies responsible for air quality control to identify

resources specifically aimed at using these data for improving techniques for

designing pollution abatement strategies.



      Suggested Applications  to Pollution Abatement.  Without doubt,  the  top-priority

 application of air  quality models is the determination of emission  controls  needed

 to achieve ambient  air quality standards.  With the reexamination of transportation
                                                                             beyond
 control strategies  and with  the pressures of fuel substitutions,  refinements well  /


                                     15-6

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traditional proportional models are imperative.  Where validated diffusion
models are available, they should be used to recalculate the emission require-
ments that came from initial hasty efforts to implement the Clean Air Act
Amendments of 1970.  This is the greatest national service that could be
performed by the air quality modelers at present.  Before this can be achieved,
however, the institutional apparatus must provide the impetus and resources
called for in a recent National Academy of Sciences report to the U.S. Senate.
     Much of the research work will add content to the model structures, but
future applications demand simplifications that are oriented toward the non-
specialist user.  One of the largest obstacles to the effective use of air
quality prediction schemes is the resolution of this apparent conflict.  At
least two steps can be taken by those who produce models to encourage appli-
cations and to aid the user:
     •  Compile a catalog of air quality models that describes their capa-
        bilities in terms of a common set of performance standards.
     •  Clarify data communication in the input-output interfaces between
        user and model.
      To accomplish the first step,  model standards will be evolved on the
 basis of legislative mandates and regulatory needs.  Each of the various
 types of model has undergone performance evaluation through the  application
 of a set of tests peculiar  to its own structure  or output.   For  example,
 Gaussian models that predict long-term averages  are often evaluated  by
 computing only the correlation coefficient  between measured  and  computed  con-
 centrations.   Early evaluations  of  species-mass-balance models stressed hour-
 by-hour comparison of the predicted and  observed concentrations.   Recently,
 a  broader range of descriptors has  evolved,  as evidenced  by  the work  of
 Nappo   and Whitney.
                                      15-7

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     The performance indexes must be designed with the model applications in



mind.  Will the model be used to predict local effects around a highway or a



smelter where short-term high doses are as important as long-term averages?



Will the model be called on to compare trends in air quality between two



different scenarios of urban population growth?  Will the model be used to



select a control plan that will result in a given hourly air concentration's



being exceeded only once a year?  A properly designed set of performance



standards will allow a potential user to compare models with respect to



suitability for any specific application.  The particular performance char-



acteristic of interest influences strongly the rank-ordering of models on a



scale of goodness.
                 •


     Fundamental to the definition of an optimal set of performance measures



will be the relationship of risk (of health, property, or aesthetic attributes)



to exposure (average pollutant concentration, time-integrated pollutant con-



centration, synergistic combination of pollutant dosages, or dosages integrated



with respect to space, time, and population  ).   Derived from the risk factor



will be, not a single number, but a distribution of effects for each degree of



exposure.For example, a range of pulmonary effects can be expected in a sample



population in which each individual has been exposed to ozone at an average



concentration of 100 ug/m3 for 5 years.  The expectation value of the effect



will be the risk factor that is the function of exposure described above.



The model performance index will utilize these relationships to connect a



probability density distribution output from the model (associated with imperfect



knowledge) to a probability density distribution of the threat to public health



and welfare.  Stated in a different way, each model will be assessed on the



basis of the uncertainty of damage estimate that arises from it imperfections.



This must be done in an unambiguous way for the user, who may not be a specialist.



                                  15-8

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      The second step that will be needed to ensure  ready application of air




 quality models is largely a question of  packaging and presentation.   User-




 oriented documentation will be needed for personnel  at data processing centers,




 who may not be specialists in chemistry, mathematics, or meteorology.  Expe-




 rience has shown that the user desires to operate the model in his own data




 center and wishes to understand enough about the model structure .:o explain it




 to others in his field.  Models that cannot be adapted to these requirements




 have not been widely applied.  In somo cases,  an operating manual  intended for




 persons with some knowledge of programing will need  to be rewritten to allow




 the user to supply completed data foiins  to a computer center and routinely




 receive output in return.  Other adaptations may require a user to punch data




 in on a teletypewriter and receive output on the same machine in an interactive




 mode.  This involves a network of remote terminals  served by the computer




 center, such as that under development in UNAMAP.






      Output  displays  will  be  required  to  bring  the abstract  aspects  of




voluminous output data  into  some  form  chat  appeals to  the  experience of the




user.   Isopleth maps  are useful,  as  ar
-------
model results.  The model output for a particular set of meteorologic conditions



can be on the frequency distribution of each station for which observations are



available in sufficient sample size.  If the model is validated for several



different points on the frequency distribution based on today's estimated



emission, it can be used to fit a distribution for cases of forecast



emission.  The fit can be made by relating characteristics of the distribution



with a specific set of model predictions.  For example, the distribution could



be assumed to be log-normal, with a mean and standard deviation each determined



by its own function of output concentrations computed for a standardized set



of meteorologic conditions.  This, in turn,  can be linked to some effect on



people or property that is defined in terms  of the predicted concentration



Statistics.  The diagram below illustrates this process:
 Concentration  field

 predictions

                      Statistical        Predicted          Injury or   Expected

                       module     frequency distributions  damage  te  harm to heal tl
                                                                                    '
       .  ,
Historical air^                                       - nodule      am}

quality data
        We have seen  the wide variety of methods now available to calculate air



   quality.  The priority for adapting these methods to current needs is clearly



   established.  Only through clear expositions of model performance and simple



   implementation procedures will the present techniques have a favorable impact



   on air quality management.  A growing appreciation by the specialist community



   of the policy requirements will be essential for the successful fulfillment



   of these goals.




                                      15-10

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MEASUREMENT METHODS






         Instruments based on differential ultraviolet absorption still




need to be evaluated, and possibly modified, prior to their acceptance




for monitoring ozone in polluted atmospheres on a nationwide scale.




The California Air Resources Board and other air pollution control




agencies are currently conducting multi-year programs for evaluating




ultraviolet absorption side-by-side with chemiluminescent and potassium




iodide based     instruments, to determine their applicability and




needed modification, as well as to assure continuity in the data base




while the older monitoring instruments are being replaced.




         Thus despite the remarkable progress in the monitoring for ozone,




nitrogen oxides and non-methane hydrocarbons, which has strengthened the




implementation and evaluation of control programs,  substantial research




and development is  still required to help resolve the uncertainties in our




knowledge which are inhibiting the actual achievement of desired air quality




standards.




         The areas in which further research and development are needed,




in sequence  of priority are:




         •  Evaluation of    primary calibration nrocedures applicable



nationwide  for ozone measurement.




         •  Development principles and instruments which can easily track




the sources  of those hydrocarbons reactive in the production of ozone and




those which are reactive in the production of particles.




         •  Chemical identification of both gas  and particle phase compounds




occurring in the atmosphere, which cause eye irritation and respiratory




difficulties.






                                    15-11

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         •   Methods for the direct and continual measurement of those
 chemicals in the particles of the atmospheric haze, that are known to be
 formed during photochemical pollution episodes and are already suspect
 as respiratory irritants.  By implementing such measurements it will be
 possible to find out to what extent the occurrence of such substances  can be
 reduced by various emission controls.  To assess  actual population
 exposures,  it is also necessary that these measurement methods be
 easily carried out  indoors and in vehicles.
         •   Improved measurement methods  suitable for observations from
airborne platforms so that the regional scale  impacts of urban emissions
can be accurately assessed.  This is needed because some control options
for solving the urban-scale problem have the potential of transferring
pollution from one  geographic area  to other geographic areas.


 RESPIRATORY  TRANSPORT AND ABSORPTION

      The development of models requires more  knowledge  about the  chemical,
 physical, morphologic, and flow properties of the  mucous layer; the
 kinetics of  the reactions of ozone in the mucous arid tissue layers;  and
 the molecular diffusivity of ozone in these layers.   Similar information
 is needed for the  hydroperoxy, HO  , and singlet oxygen, 02  (a   A), free
 radicals, which are reactive intermediates in photochemical smog.
      Furthermore,  a realistic model hased on such  knowledge needs to be

 verified by  measurements of uptake and tissue dosage in the various
 regions of  the respiratory tract.  These are currently  difficult  to  make,
 but are required to establish accuracy and reliability.   New methods of
 sampling and techniques using tagged gases should  be developed,  so that
 local uptake can be measured.
                                     15-12

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     An extensive effort d s needed in studies of pollutant-gas transfer,




absorption, and reaction in the respiratory tract.  After some of the




experimental questions about behavior of o/.one in the mucous layer and




adjacent tissue arc answered, available methods for calculating the local




dosage to critical airway sites can be used in new uptake models.  Gas-




absorption and particle-deposition models for the upper respiratory




tract (nose, mouth, pharynx, larynx) also need to be improved.  Experimen-




tal data now available can be used to develop seniempirical relations for




gas uptake in the nose in a procedure analogous to that used to model




particle deposition.  Development of a more refined model for nonreactive




gases requires data on gas diffusivities in the mucus and tissue,




local blood perfusion rates in the nasal epithelium, and physiologic and




pharmacologic factors affecting the mucosa and local blood flow rates.




Models need to be developed for mixtures of gases that may interact




chemically in .the gas phase, in the mucus, or in aerosol droplets to form




other species.  This requires theoretical and experimental studies of




dissolution, absorption, adsorption, and desorption of gases in or on




aerosols in the respiratory tract.




     Improved modeling is needed for the design and interpretation of




animal experiments and controlled human studies, and for the collation




of diverse data from animal and human exposures to ozone.  Calculations




of local dose at reactive tissue sites can help to explain the mechanisms




of tpxicity and are needed to extrapolate animal and human data for




assessing population rislcs under different environmental conditions.
                                    15-13

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TOXICOLOGY




     Enhanced susceptibility to respiratory exposure to infectious agents



is of considerable potential poblic health significance.  This has been



reported to occur in mice exposed to ozone at as low as 0.08 ppm, the




lowest reported "effect" concentration in laboratory animal studies.



It seems essential, therefore, to continue and expand research on the



effect of ozone and other photochemical oxidants on physiologic protective



mechanisms of the lung.  Appropriate dose-response studies should be




included to confirm or establish the exposure concentration-time rela-



tionships that result in increased suscepti-bility to inhaled microorganisms,




and studies of the cellular responses and mechanisms should be conducted



with a view to providing methods that are applicable to epidemiologic



studies in oxidant-exposed human populations.




     Research designed to elucidate the pathophysiologic implications of



reversible changes in lung function, histology, and biochemistry that




have been observed at concentrations of 0.2-0.5 ppm would be especially




valuable in evaluating the significance of these changes for health.  In



particular, it would be useful to determine what, if any, causal or



correlative relationships exist between different effects detected by



various experimental assay systems and between reversible changes and



more chronic effects, such as reduced lung elasticity, fibrosis, and




adenora formation.  Studies on laboratory animals are particularly



suited, to this type of mechanism-correlative research; but, with appropriate




experimental designs, such research should be very useful in determining




which methods or biologic changes can be usefully applied to clinical or
                                     15-14

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epidcmiologic studies.  At the came tJJne, .such research could determine



whether seme of the changes  (e.g., increased activity of enzynias involved



in cell redox systems) are indicative of injury or are honeostatic



adaptive responses.  This information will have value in predicting



potential injury in the "average" population and possibly help to identify




people who are hypersusceptible by virtue of sane deficiency in adaptive



protective mechanisms.  Related to these research efforts, further




investigation of the influence of oxidant exposure on enzymes that bio-



transform other inhaled chemicals  (e.g., aromatic hydrocarbons) and the



interaction effect of dietary antioxidants  (e.g., vitarruji E) should be



pursued, particularly in relation to oxidant-induced oxidation of membrane




lipids and free-radical formation.



     There are several scattered reports of extrapalmonary effects of




ozone exposure .in laboratory animals.  Some (e.g.r chrorrasomal aber-




rations in hamster lymphocytes) occur at or near concentrations that



cause local effects in the lung and portend serious and long-term health



implications.  Others(e.g., reduction of voluntary activity) may be



transient or reversible, but nevertheless contribute to decrements in



performance or well-being.  It is particularly important that further



research be conducted to confirm (or refute) these reported extrapalmonary



actions of ozone and the exposure concentrations at which they occur.




If confirmation of their occurrence is obtained at or below the currently




reported effective exposure concentrations, useful research efforts could




be directed toward determining whether they are direct or secondary




effects and toward identifying the chemical species responsible.  Fore
                                    15-15

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  importantly, confirmation of an isolated effect on cell genetic material



  would demand a thorough expert evaluation of its significance on the



  basis of existing knowledge of the long-term implication of the effect




  and, accordingly, intensified laboratory and epidemiologic 10search.
CONTROLLED STUDIES ON HUMANS







       Further studies are needed to give better dose-response information




and to provide a frequency distribution of the population response to oxidants




alone and in combination with other pollutants at various concentrations.




Such studies should include the effects of mixed pollutants over ranges




corresponding to the ambient atmosphere.   With combinations of ozone and




sulfur  dioxide, the mixture should be carefully characterized to be sure




of the effects of trace pollutants on sulfate aerosol formation.  The design




of such studies should consider the need to use the information for cost-




benefit analysis and for extrapolation from animals to humans and from small




groups of humans to populations.   Recent research has indicated the possibility




of human adaptation to chronic exposure to oxidants.   Further study is




desirable.




       Studies  are needed  to clarify  the  importance  of age,  so:,  ethnicity,




familial  elements, nutritional factors, and pharmacologic  agents  in  detenr.inir.:




response  to  oxidants.   Because people with Jung  disease  are  thought  to be r.or-i




susceptible  to  oxidant  pollutants,  exposure studies  are  needed  to quantify  tl.i;




Better methods  for measuring or  estimating the  actual dose of oxidants absorbe.:




by each  subject are needed.  The usual time variation in measures of human




response  should be  evaluated p_cr_ _s_e,  because  this  information  is  needed  to




optimize  experimental  design.





                                     15-16

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       More informal: ion is needed before rational guidance can be given




limiting exercise during periods oi high oxidant pollution.





                    J^                 J r ' r) 'i. t °,_c«p rr o I l_e d at-.in
                                                          as
Academy of Sciences_,_J^j^erJ£j^n^K^^c^__Aj ; socin Urn i ,_Jind__the J^TJ. i or i al




Ins t.ij:uj:_es__of_ JI oa It h .








  EPIDEMIOLOGIC STUDIES






         Modification of the method in which the CHESS studies are




  designed and in which the data are displayed would add considerably




  to their value.   The scientific data collected in all the CHESS studies




  should be made available through accepted  scientific publications




  to the scientific community as a whole.




         The continuation of epidemiologic studies, including those of




  the CHESS program, is vital to our understanding of the effects of air




  pollution on health.  There is no other way to determine the needed




  dose-response (exposure-response) relationships between the complex




  urban atmospheres and specific health effects.  No animal or clinical




  experiment can duplicate the full range of variables to be found in




  ambient urban  air.  For this reason, all necessary support should




  be given to qualified scientists to conduct epidemiologic studies




  designed to answer these questions.  Although such studies are




  expensive and time-consuming, the data they produce can be produced




  in no other way and are essential in  the development of useful air




  quality standards.




         It is important to know whether such phenomena as tolerance




  and cross-protection,  well demonstrated  or suggested in animals,




  occur in man.  Analogues for all these phenomena should  be sought




  in human populations,  and methods should be devised  for assessing




  their significance for human health.




                                    15-17

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 PLANT AND MICROORGANISMS






        These recommendations are not listed in a priority order,  but




many could be followed in parallel or simultaneously.  In general, the recom-




mendations presented by Heck jet al.     are  still germane to research




needs in the subject of oxidant pollutants.




       A few  definitive experimental designs are needed to further our




knowledge  of acute dose-response information on ozone.  Much of this type




of information is still needed for PAN and its analogues.  All experimental




designs should incorporate dose response.




       Studies to develop dose-response curves for chronic  exposures of




crop and native species over growing seasons and under field conditions




are needed for ozone, PAN,  and other oxidants.




       Research should be continued with filtered and nonfiltered field




chambers to study effects of ambient oxidants on important agronomic,




horticultural,  and native  species.  We know that there is a problem, but




its significance and magnitude are matters  of conjecture.




       There  is a critical need to understand the interaction of multiple pol-




lutants on individual plant species and ecosystems.   Multiple-pollutant effects




are generally  important,  but little is known of their effects on most plants.




Variable concentrations,  ratios of pollutants, and age of plants  all affect




response.




       Models should be  developed to understand the relative importance of




other variables as they affect plant dose response.   These include, but are
                                15-18

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  not limited to, climatic, edaphic, biotic,  and genetic factors.   Considerable

  information is available, but there are many gaps, and no comprehensive

  programs are in progress  to determine how these factors act and interact

  to affect a plant's response.

         The mechanism of response and the biochemical systems affected

  are not understood.  Although plant membranes are considered the primary

  sites of action for the oxidant pollutants, there is no definitive work  on

  this.  An understanding of  these  responses would be supportive of breeding

  and spray protective programs.

         Both breeding and spray protective programs need to be

  developed,  so that better-yielding and better-quality cultivars  will be pro-

  tected against oxidant pollutants.

         Some effort is needed to explore the feasibility of using  plants to

 monitor the  overall biologic activity (or biomass reductions) caused  by

 photochemical oxidants  in specific air basins or regions.  The response

  of sensitive  plants should be correlated with the response of plants of

 economic and aesthetic  importance.

        Additional monitoring of multiple pollutants is needed in rural areas.

        Whenever possible, measures that vary on a continuous scale (e.g.,

 biomass)  should be used with subjective estimates of injury (e. g. ,  indexes

 of visible injury).




 ECOSYSTEMS

        The present knowledge of  the biologic  consequences of chronic

oxidant injury to  both natural  ecosystems and  agroecosystc-ms must be. commuai-

cated to groups in  the public sector  that work  in planning and enforcement.

The indirect effects  on man's health  and  the direct effects on his welfare

resulting from ecosystem  deterioration due  to oxidant in-jury are serious
                                    15-19

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enough to be given more (.borough consideration in all decisions related to

abatement of air pollution from both mobile and stationary sources.   Land-use

planning and proper airshed classification should be used to prevent further

deterioration of air quality, particularly in prime timber-producing areas

and in remote, pristine areas, regardless of their present use designation.

        The most important research needs are related to the determination

of the responses of natural ecosystems and agroecosysterns to chronic exposure

to oxidant pollutants.  In particular, rhronic-dose-response models are needed

to understand the responses of the dominant primary-producer species constituting

forest ecosystems in both the eastern and the western United States.  The result-

ing alteration  of interactions with other subsystems—e.g., consumers and

decomposers—must also be investigated.


EFFECTS OF PHOTOCHEMICAL OXIDANTS ON MATERIALS
    o  Laboratory studies of effects of photochemical  oy.idants  other than

       ozone—e.g.,  PAN,  peroxybenzoylnitratc,  atomic  oxygen,  cxc.ited
                            1
       molecular oxygen,  0 ( A ),  and hydroperoxy and  hydroxy]  radicals—
                          2   g
       on specific materials should  be conducted;

    » Methods to measure concentrations of transient oxidants such as OH, HO ,

      0~  ( 0 ) in real atmospheres should be developed.

    » Mechanisms of  attack of oxidants on materials should  be  investigated,

       so that distinctions can be made between  effects on a given material

      due to  various pollutants.

    • An integrated  study should  be conducted in which relative  effects

      of all  major air pollutants on materials  are assessed.
                                     15-20

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