UNEP: Environmental Effects of Ozone Depletion, 1994 Assessment


                           EPA 430/K-94/030
           UNITED NATIONS
       ENVIRONMENT PROGRAMME
ENVIRONMENTAL  EFFECTS
  OF  OZONE  DEPLETION:

     1994   ASSESSMENT
     Pursuant to Article 6 of the Montreal Protocol
      on Substances that Deplete the Ozone Layer
           under the Auspices of the
    United Nations Environment Programme (UNEP)
             November 1994
                           Recycled/Recyclable
                           Printed with Soy/Canola Ink on paper that
                           contains at laast SO«fc recycled fttwc

-------

-------
The UNEP Environmental Effects Panel was sponsored by the Netherlands
Ministry of Housing, Physical Planning and the Environment, the Federal
Ministry for Research and Technology (BMFT) of the Federal Republic of
Germany, and the United States Environmental Protection Agency.  Additional
staffing support was provided by the College of Natural Sciences, University of
Hawai'i at Manoa.
Copies of the report are available from:
      United Nations Environment Programme (UNEP)
      P.O. Box 30552
      Nairobi
      KENYA                        —- -

      J.C. van der Leun
      Institute of Dermatology
      State University Hospital Utrecht
      Heidelberglaan 100
      NL-3584 CX Utrecht
      THE  NETHERLANDS

      M. Tevini
      Botanisches Institut  II der Universitat Karlsruhe
      Kaiserstrasse  12
      D-7500 Karlsruhe 1
      FEDERAL REPUBLIC OF GERMANY

      A.H. Teramura
      College of Natural Sciences
      2545 The Mall, Bilger Hall 102
      Honolulu, Hawai'i 96822
      USA
 ISBN  92-807-1457-0

-------

-------
                          CONTENTS


                                                               Page

 INTRODUCTION AND EXECUTIVE SUMMARY                          j

 CHAPTER 1.  CHANGES IN ULTRAVIOLET RADIATION REACHING THE
    EARTH'S  SURFACE                                             -|
    S. Madronich (USA), R.L McKenzie (New Zealand), MM. Caldwell (USA), and
    L.O. Bjorn (Sweden)

 CHAPTER 2.  EFFECTS OF INCREASED SOLAR ULTRAVIOLET
    RADIATION ON HUMAN HEALTH                                23
    J.D. Longstreth (USA), F.R. de Guijl (The Netherlands), M.L. Kripke (USA), Y.
    Takizawa (Japan), and J.C. van der Leun (The Netherlands)

 CHAPTER 3.  EFFECTS OF INCREASED SOLAR ULTRAVIOLET
    RADIATION ON TERRESTRIAL PLANTS                          49
    MM. Caldwell (USA), A.M. Teramura (USA), M. Tevini (FRG), J.F. Born man
    (Sweden), L.O. Bjorn (Sweden), and C. Kuiandaivelu (India)

 CHAPTER 4.  EFFECTS OF INCREASED SOLAR ULTRAVIOLET
    RADIATION ON AQUATIC ECOSYSTEMS                         65
    D.-P. Hader (FRG), R.G. Worrest (USA), H.D. Kumar (India), and R.C. Smith
    (USA)

 CHAPTER 5.  EFFECTS OF INCREASED SOLAR ULTRAVIOLET
    RADIATION ON BIOGEOCHEMICAL CYCLES                      79
    R.G. Zepp (USA), T. V. Callaghan (UK), and D.J. Erickson

 CHAPTER 6.  EFFECTS OF INCREASED SOLAR ULTRAVIOLET
    RADIATION ON TROPOSPHERIC  COMPOSITION  AND  AIR
    QUALITY                                                     95
    X. Tang (China) and S. Madronich (USA)

 CHAPTER 7.  EFFECT OF INCREASED SOLAR ULTRAVIOLET
   •RADIATION ON MATERIALS                                    101
. •  . A.L /.'•:': cJy (USA), M.B. Amin (Saudi Arabia), S.H. Hamid (Saudi Arabia),
    X. Hu (China), and A. Torikai (Japan)

 APPENDIX A.   LIST OF AUTHORS AND CONTRIBUTORS

 APPENDIX B.   LIST OF EXPERT REVIEWERS

 APPENDIX C.   LIST OF ABBREVIATIONS USED

-------

-------
ENVIRONMENTAL EFFECTS OF
OZONE DEPLETION:
1994 ASSESSMENT
INTRODUCTION

The Montreal Protocol on Substances that Deplete the Ozone Layer requires, in Article 6 periodic
assessments of available scientific, environmental, technical and economic information. The assessments
oo!i n* fnLCf \ CVery f°Ur years> In fact' assessments were made in 1989, 1991 and, the present one
in 1994. This 1994-Assessment on Environmental Effects is written so that it can be read without having'
the earlier reports at hand. °

The provisions in the Montreal Protocol and its amendments in London (1990) and Copenhagen (1992)
nave brought about a marked decrease in production and use of ozone depleting chemicals. However the
ozone layer is still becoming thinner, and this is expected to continue until about 1998 Thereafter' a
gradual recovery is predicted, but the layer will be damaged for half a century to come. These predictions
were made by the Atmospheric Science Panel on the basis of a fairly optimistic scenario, including the
assumptions that there will be full and worldwide compliance with the Copenhagen amendments that no -
ozone depleting chemicals were overlooked, and that there will be no new threats to the ozone layer.

The present assessment deals with the consequences during the coming decades: the changes in solar
ultraviolet radiation reaching the Earth's surface, and the effects on humans, animals, plants micro-
organisms, air quality and materials. A welcome new element, compared with the earlier assessments is a
special chapter on biogeochemical cycles. The main questions from a policy point of view are now- what
will be the most important effects, and what can be done to prevent or mitigate these?

These questions are more difficult to answer than those posed initially when the problem of ozone
depletion arose Then the question was, will there be any effects so detrimental as to necessitate
protection of the ozone layer? In principle, this could be answered by giving one or two clear-cut
examples The present questions are much broader, and require quantitative knowledge on all effects of
potential importance.

Organized science recently paid special attention to the problems posed by ozone depletion SCOPE
the Scientific Committee on Problems of the Environment (formed by the International Council of
S?* noo!oT)J)r0dLlCed^V? fe^°rtS °n Effccts of Increased Ultraviolet Radiation, one on Biological
Systems (1992) and one on Glo^l i-o-.; :-..-rr.< (1993). SCOPE urges that thr-c i-.ortan* and
complicated problems require r. '•_ •• :;;...':..n •..••• •;-:,.^ y: .,x.:], .-•_.,-iiv. ;ill,' a ^a;o- e\.x>.n;i..,i.

Reality is far from these gr ' . -, ...wh on effect. . .: • , p, ,,.' •• • ,n i0,v
that !t does not even allow ful' : ' . rt ,.:arch capacit) , -ialie. Uiis mu.l^d 7?rmvers to
urgent questions cannot be give. ... ,.. ;,! !,{ [,. possible. We are glad that in spite of'il.ese
limitations, saenufic understand ,
-------
-------
EXECUTIVE SUMMARY

A change in the composition of the stratosphere becomes relevant to society only if it has noticeable
effects. This places the assessment of effects in a pivotal role in the problem of ozone depletion.

Decreases in the quantity of total-column ozone, as now observed in many places, tend to cause
increased penetration of solar UV-B radiation (290-315 nm) to the Earth's surface. UV-B radiation is
the most energetic component of sunlight reaching the surface. It has profound effects on human health,
animals, plants, microorganisms, materials and on air quality. Thus any perturbation which leads to an -
increase in UV-B radiation demands careful consideration of the possible consequences. This is the topic
of the present assessment made by the Panel on Environmental Effects of Ozone Depletion.

The assessment is given in seven chapters, summarized as follows:

Changes in Utraviolet Radiation

The quality and quantity of UV measurements has increased greatly in the last few years. Variations
among measurements from different instruments are diminishing toward the 5% level. Long-term trend
detection is still a problem, with little historical data available for baseline estimation.

Measurements in Argentina, Chile, New Zealand, and Australia show relatively high UV levels
compared to corresponding northern hemispheric latitudes, with differences in both stratospheric ozone
and tropospheric pollutants likely to be playing a role. Tropospheric ozone and aerosols can reduce global
UV-B irradiances appreciably. At some locations, tropospheric pollution may have increased since
pre-industrial times, leading to decreases in surface- uVTadiation. However, recent trends in tropospheric
pollution probably had only minor effects on UV trends relative to the effect of stratospheric ozone
reductions.

Global ozone measurements from satellites over 1979/93 imply significant UV-B increases at high
and mid-latitudes of both hemispheres, but only small changes in the tropics. Such estimates however
assume that cloud cover and tropospheric pollution have remained constant over these years. Under the
current CFC phase-out schedules, global UV levels are predicted to peak around the turn of the century in
association with peak loading of chlorine in the stratosphere and the concomitant ozone reductions. The
recovery to pre-ozone depletion levels is expected to take place gradually over the next 50 years.

Effects on Human and Animal Health

The increase in UV-B radiation associated with stratospheric ozone depletion is likely to have a
substantial impact on human health. Potential risks include increases in the incidence of and morbidity
from eye diseases, skin cancer, and infectious diseases. Quantitative estimates of risk are available for
some effects, (e.g., skin cancer), but other (e.g., infectious diseases) are associated with considerable
uncertainty at the present time.

UV radiation has been shown in experimental systems to damage the cornea and lens of the eye. Chronic
exposure to UV-B (resulting in a high, cumulative, lifetime dose) is one of several factors clearly
associated with the risk of cataract of the cortical and posterior subcapsular forms. The 1989 Report
noted that a 1% increase in stratospheric ozone depletion has been predicted to be associated with a 0.6 to
0.8% increase in cataract; this estimate, although crude, has not been improved upon in the intervening
years.

Some components of the immune system arc present in the skin, which makes the immune system
accessible to UV radiation. Experiments in animals show that UV exposure decreases the immune
response to skin cancers, infectious agents, and other antigens and can lead to unresponsiveness upon
repeated challenges. Studies in human subjects also indicate that exposure to UV-B radiation can suppress
the induction of some immune responses. The importance of these immune effects for infectious diseases
in humans is unknown. However, in areas of the world where infectious diseases already pose a significant
-------
challenge to human health and in persons with impaired immune function, the added insult of UV-B
induced immune suppression could be significant.

In susceptible (light-skinned) populations, UV-B radiation is the key risk factor for development of
non-melanoma skin cancer (NMSC). Using information derived from animal experiments and human
epidemiology, it is estimated that a sustained 1% decrease in stratospheric ozone will result in an increase
in NMSC incidence-of approximately 2%. The relationship between UV-B exposure and melanoma skin
cancer is less well understood and appears to differ fundamentally from that of NMSC. Epidemiologic
data indicate that the risk of melanoma increases with sunlight exposure, especially during childhood.
There is, however, uncertainty about the relative importance of UV-B radiation, which directly determines
the magnitude of the increase in melanoma that would result from ozone depletion.

Effects on Terrestrial Plants

Response to UV-B also varies considerably among species and also cultivars of the same species. In
agriculture, this will necessitate using more UV-B-tolerant cultivars and breeding new ones. In forests and
grasslands, this will likely result in changes in species composition; therefore there are implications for
the biodiversity in different ecosystems.

Indirect changes caused by UV-B (such as changes in plant form, biomass allocation to parts of the
plant, timing of developmental phases and secondary metabolism) may be equally, or sometimes more,
important than damaging effects of UV-B. These changes can have important implications for plant '
competitive balance, herbivory, plant pathogens, and biogeochemical cycles. These ecosystem-level effects
can be anticipated, but not easily predicted or evaluated. Research at the ecosystem level for solar UV-B
is barely beginning. Other factors, including those involved in climate change such as increasing CC>2 also
interact with UV-B. Such reactions are not easily predictedr^ut are of obvious importance in both
agriculture and in nonagricultural ecosystems.

Effects on Aquatic Ecosystems

More than 30% of the world's animal protein for human consumption comes from the sea, and in many
countries, particularly the developing countries, this percentage is significantly higher. As a result, it is
important to know how increased levels of exposure to solar UV-B radiation might affect the productivity
of aquatic systems.

Phytoplankton form the foundation of aquatic food webs. Marine phytoplankton are not uniformly
distributed throughout the oceans of the world. The highest concentrations are found at high latitudes
while, with the exception of upwelling areas on the continental shelves, the tropics and subtropics have 10
to 100 times lower concentrations. In addition to nutrients, temperature, salinity and light availability,
the high levels of exposure to solar UV-B radiation that normally occur within the tropics and subtrop'ics
may play a role in phytoplankton distributions.

Phytoplankton productivity is limited to the euphotic zone, the upper layer of the water column in
which there is sufficient sunlight to support net productivity. The position of the organisms in the
euphoric zone is influenced by the action of wind and waves. In addition, many phytoplankton are capable
of active movements that enhance their productivity and, therefore, their survival. Exposure to solar UV-B
nul.'t.on has been shown to affect both orientation mechanisms and motility in phytoplankton, resulting in
reduced survival rates for these organisms.

Researchers have measured the increase in, and penetration of, UV-B radiation in Antarctic waters, and
have provided conclusive evidence of direct ozone-related effects within natural phytoplankton
communities. Making use of the space and time variability of the UV-B front associated with the
Antarctic ozone hole, researchers assessed phytoplankton productivity within the hole compared to that
outside the hole. The results show a direct reduction in phytoplankton production due to ozone-related
increases in UV-B. One study has indicated a 6 - 12 % reduction in the marginal ice zone.

iv
-------
Solar UV-B radiation has been found to cause damage to early developmental stages offish, shrimp,
crab, amphibians and other animals. The most severe effects are decreased reproductive capacity and
impaired larval development. Even at current levels, solar UV-B radiation is a limiting factor, and small
increases in UV-B exposure could result in significant reduction in the size of the population of
consumer organisms.

Although there is overwhelming evidence that increased UV-B exposure is harmful to aquatic
ecosystems, the potential damage can only be roughly estimated at the present time.

Effects on Biogeochemical Cycles

Increases in solar UV radiation could affect terrestrial and aquatic biogeochemical cycles thus altering
both sources and sinks of greenhouse and chemically-important trace gases e.g., carbon dioxide (COo),
carbon monoxide (CO), carbonyl sulfide (COS) and possibly other gases, including ozone. These potential
changes would contribute to biosphere-atmosphere feedbacks that attenuate or reinforce the atmospheric
buildup of these gases.

In aquatic ecosystems solar UV-B radiation also might have significant impacts. Studies in several
locations have shown that reductions in current levels of solar UV-B result in enhanced primary
production, and Antarctic experiments under the ozone hole demonstrated that primary production is
inhibited by enhanced UV-B. In addition to its effects on primary production, solar UV radiation can
reduce bacterioplankton growth in the upper ocean with potentially important effects on marine
biogeochemical cycles. Solar UV radiation stimulates-dae. degradation of aquatic dissolved organic matter
(DOM) resulting in loss of UV absorption and formation of disolved inorganic carbon (DIG), CO, and
organic substrates that are readily mineralized or taken up by aquatic microorganisms. Aquatic nitrogen
cycling can be affected by enhanced UV-B through inhibition of nitrifying bacteria and
photodecomposition of simple inorganic species such as nitrate. The marine sulfur cycle may be affected
by UV-B radiation resulting in possible changes in the sea-to-air emissions of COS and dimethylsulfide
(DMS), two gases that are degraded to sulfate aerosols in the stratosphere and troposphere, respectively.

New research on the environmental fate and impact of the hydrofluorocarbon (HFC) and
hydrochlorofluorocarbon (HCFC) substitutes for CFCs has focused on trifluoroacetate (TFA), a
tropospheric oxidation product of certain HFCs and HCFCs. TFA is mildly toxic to most marine and
freshwater phytoplankton. The results indicate that TFA, although it may become globally distributed with
increased usage of alternative fluorocarbons, is not likely to accumulate in soils and organisms. Although
resistant to chemical degradation, very recent evidence indicates that TFA can be broken down by
microorganisms.

Effects on Air Quality

Reductions of stratospheric ozone and the concomitant increases of UV-B radiation penetrating to the
lower atmosphere result in higher photodissociation rates of key trace gases that control the chemical
reactivity of the troposphere. This can increase both production and destruction of ozone (03) and related
oxidants such as hydrogen peroxide (H2O2), which are known to have adverse effects on human health,
terrestrial plants, and outdoor materials. Changes in the atmospheric concentrations of the hydroxyl
radical (OH) may change the atmospheric lifetimes of climatically important gases such as methane
(CH4) and the CFC substitutes.

Trends in the photodissociation rate coefficient of tropospheric 03, of about +0.36±0.04% per year
in the northern hemisphere and +0.40+0.05% per year in the southern hemisphere, have been estimated
from satellite measurements of the ozone column between 1979 and 1992. The corresponding model-
calculated changes in tropospheric chemical composition are non-linear and sensitive to the prevailing
levels of nitrogen oxides (NOX). In polluted regions (high NOX), tropospheric 03 is expected to
increase, reaching potentially harmfula concentrations earlier in the day, and leading to more frequent
-------
exceedance of oxidant standards for air quality in urban areas where 03 levels are routinely near such air
quality thresholds. In more pristine regions (lower NOX), 03 increases can be lower or even negative.
Other oxidants, such as H2O2 and OH, are projected to increase for both polluted and pristine regions.
Changes to H2O2 concentrations may have some impact on the geographical distribution of acid
precipitation. Rural regions may become more urban-like and the percentage of areas with remote
tropospheric conditions may decline.

Increases in OH concentrations cause a nearly proportionate decrease in the steady state tropospheric
concentrations of CH4 and CFC substitutes such as the HCFCs and HFCs. Thus, the measured reductions
in the ozone column (TOMS, 1979-92) are likely to have moderated CH4 increases over the past decade,
and may account for about 1/3 of the slowing of the global CH4 trends.

Increased tropospheric reactivity could also lead to increased production of particulates such as cloud
condensation nuclei, from the oxidation and subsequent nucleation of sulfur of both antropogenic and
natural origin (e.g. carbonyl sulfide and dimethylsulfide). While these processes are still not fully
understood, they exemplify the possibility of complex feedbacks between stratospheric ozone reductions,
tropospheric, chemistry, and climate change.

Effects on Materials

Synthetic polymers, naturally occurring biopolymers, as well as some other materials of commercial
interest are adversely affected by solar UV radiation. Application of these materials, particularly
plastics, in situations which demand routine exposure to sunlight is only possible through the use of light-
stabilizers and/or surface treatments to protect them from sunlight. Any increase in solar UV-B content
due to partial ozone depletion will therefore accelerate the photogradation rates of these materials,
limiting their service lifetimes outdoors.

The nature and the extent of such damage due to increased UV-B radiation in sunlight is quantified in
action spectra. In spite of the several polymer action spectra available in the research literature the
information is often inadequate to make reliable estimates-©f-the increased damage. However, it is clear
from the available data that the shorter UV-B wavelengths processes are mainly responsible for
photodamagc ranging from discoloration to loss of mechanical integrity. The molecular level
interpretation of these changes remain unclear in many instances.

The use of higher levels of conventional light-stabilizers in polymer formulations will undoubtedly be
attempted as a means of mitigating the effects of increased UV levels in sunlight. However, such an
approach assumes that a) these stabilizers continue to be effective under spectrally-altered sunlight
conditions; b) they are themselves photostable on exposure to UV-rich sunlight; and c) they can be
sufficiently effective at low enough concentrations to serve the purpose. Experimental data bearing on
these issues is sparse. Ongoing research, particularly that relating to extreme-environment exposure of
polymers, is expected to shed more light on these questions. Substitution of the affected materials by more
photostable plastics and other materials also remains an attractive possibility. Both these approaches will
add to the cost of plastic products in target applications.

Key areas of uncertainty

• Effects on human health (infectious diseases, vaccination efficacy, cataract, melanoma)
• Effects on food production (fisheries, agriculture.) and on natural ecosystems (aquatic, terrestrial)
• Links between ozone depletion and global warming by interactions between atmosphere and biosphere
(phytoplankton, forests)
The increases in UV-B radiation already observed and expected in the future will have consequences of
significant magnitude in several respects. This applies to the UV-B increases predicted on the basis of the
niost favorable scenario of ozone depletion; it applies even more if ozone depletion would be greater, for
instance, due to incomplete compliance to the phaseout agreed for ozone depleting chemicals. This
strongly supports continued determination to protect the ozone layer.

In many areas the uncertainties about effects are still so great that quantitative predictions are not
possible. Incompleteness of knowledge does not diminish the concerns for the consequences, e.g., an
increase in infectious diseases or disturbance of natural ecosystems. Some of these consequences of ozone
VI
-------
depletion may well be more serious than the effects now quantifiable. Further investigations are necessary
in order to achieve more certainty about such effects and, if necessary, about possibilities for protection
"- mitigation.
or
VII
-------
-------
CHAPTER 1
CHANGES IN ULTRAVIOLET RADIATION
REACHING THE EARTH'S SURFACE

S. Madronich (USA), R. L McKenzie (New Zealand),
M. M. Caldwell (USA), and L O. Bjorn (Sweden)
Summary

The quality and quantity of UV measurements has increased greatly in the last few years. Variations
among measurements from different instruments are diminishing toward the 5 percent level. Long term trend
detection is still a problem, with little historical data available for baseline estimation.

Enhanced UV levels are clearly associated with the Antarctic springtime ozone reductions.
Measurements show that maximum UV levels at the South Pole are reached well before the summer
solstice, and DNA-damaging radiation at Palmer Station, Antarctica (64°S) during the springtime ozone
depletion can exceed maximum summer values at San Diego, USA (32°N). UV increases at mid-latitudes are
smaller. However, increases associated with the record low ozone column of 1992/93 in the northern
hemisphere are evident when examined on a wavelength-specific basis.
Measurements in Argentina, Chile, New Zealand, and Australia show relatively high UV levels
compared to corresponding northern hemispheric latitudes, with differences in both stratospheric ozone
and tropospheric pollutants likely to be playing a role. Tropospheric ozone and aerosols can reduce global
UV-B irradiances appreciably. At some locations, tropospheric pollution has increased since pre-inclustrial
times, leading to decreases in surface UV radiation. However, recent trends in tropospheric pollution
probably had only minor effects on UV trends relative to the effect of stratospheric ozone reductions.
Global ozone measurements from satellites over 1979/93 imply significant UV-B increases at high and
midlatitudes of both hemispheres, but only small changes in the tropics. Such estimates however assume
that cloud cover and tropospheric pollution have remained constant over these years. Under the current
CFC phase-out schedules, global UV levels are predicted to peak around the turn of the century in
association with peak loading of chlorine in the stratosphere and the concomitant ozone reductions. The
recovery to pre-ozone depletion levels is expected to take place gradually over the next 50 years.
Introduction

Reductions in stratospheric ozone (O3) allow more solar ultraviolet (UV) radiation to reach the earth's
lower atmosphere and surface. UV radiation affects many chemical and biological processes, and its
increases are of concern because of potential adverse effects on the biosphere, on tropospheric air quality,
and on materials such as wood and plastics. The UV wavelengths most affected by Os reductions are in the
UV-B (280-315 run) band with some effect also in the UV-A (315-400 nm) (see Figure 1.1). Radiation at
shorter wavelengths is absorbed completely by even relatively small amounts of O$ and by atmospheric
oxygen (O2).
-------
280
300 320 340
Wavelength, nm
Ffg. 1.1. Increases in UV radiation in response to a 1 percent decrease in the total ozone column near 300 DU (1 DU =
2.69x1016 molec cm'2). Solid lines (right scale) give spectral irradiance changes, dotted lines (left scale) give
percent changes. Values are for overhead sun (thick lines) and for a solar zenith angle of 70° (thin lines) From
Madronich [1993c].

Accurate characterization of environmental UV radiation is difficult because of large geographical and
temporal variations. However, significant progress has been made in recent years. Geographical and
seasonal variations are now better understood in terms of earth-sun geometric factors, 0% amounts,
cloudiness, various local and regional pollutants, and surface elevation and reflectivity. UV increases
associated with recent 0$ reductions have also been detected.

This update to the UNEP [1989,1991] reports addresses the state of knowledge on environmental UV
radiation as of August 1994, emphasizing the sensitivity to 03 changes for different biological and
chemical photo-processes, the measurements of UV radiation at ground level and possible causes for its
variations, and the implications of measured global 0$ trends for UV radiation.

The Biological Effectiveness of UV Radiation

Weighted UV Radiation and its Sensitivity to Ozone Changes

Various biological and chemical photo-processes respond differently to different parts of the UV
spectrum. The relative effectiveness of different wavelengths must be known in order to assess the responses
to O3 changes. The effective UV irradiance, E, or dose rate (exposure), is given by

E = jF(X)W(X)d?v
where W(X) is the weighting function, or action spectrum, for a specific biological or chemical effect, and F(A)
is the spectral irradiance, either computed or measured, for a given time and location. Hourly, daily, and
yearly weighted doses may then be computed by time-integration of the dose rates.

The weighting procedure is required because solar UV-B increases steeply towards longer wavelengths,
whereas the biological effectiveness often increases toward shorter wavelengths. As a result, weighted UV
irradiances computed with different action spectra have different responses to atmospheric O3 changes. A
commonly used measure of this dependence is the radiation amplification factor (RAF), defined by

AE/E = -RAF (AO3/O3) (percent rule)
where AO3/O3 is the percent change in the ozone column, and AE/E is the corresponding percent increase in
weighted irradiance (instantaneous or an a time-integrated basis e.g., daily, yearly). The RAFs give the
-------
increase of available effective radiation in response to Os reductions. They do not however measure the
ultimate biological response, since this often depends non-linearly on the radiation exposure, and other
factors, such as repair, time in the life cycle, whether the cell is dividing, etc., may also be important.

A compilation of RAFs for different biological and chemical processes is given in Table 1.1. The RAFs
are useful for comparing the sensitivity of different processes to 03 changes. Action spectra that decrease
strongly with increasing UV-B wavelengths have larger RAFs, while spectra with a significant UV-A tail
tend to be less sensitive.

Several uncertainties in RAF values exist. In many cases, the original data used to derive action spectra
are highly variable. For many spectra, insufficient data exist at the longer wavelengths, and if an
exponential tail is used for extrapolation, the RAFs are significantly reduced (as indicated by the
bracketed values in Table 1.1). The RAFs depend somewhat on the total O3 column, the altitude of the 03
perturbation, and the solar zenith angle (and therefore on latitude and season). They are, however,
essentially independent of cloud cover, surface albedo, or local pollution.

The simple "percent rule" given above is valid only for small 03 changes. For large 03 changes, a more
accurate relation is

E2/Ei = [ (03)i / (03)2 I8** (power rule)
where EI and £2 are the weighted irradiances corresponding respectively to ozone columns (03)1 and (03)2-
Figure 1.2 demonstrates the non-linear dependence of erythemal radiation on ozone reductions.
0)
9)
Q.
200
150
100
5 50
O
-50
— Power RAF
D Measured
1.1
a a
a
-60 -50 -40 -30
Ozone Change,
-20
•10
Fig. 1.2. Dependence of erythemally weighted UV radiation on O3 column changes. Measuremurib i
February 1991 to 12 December 1992. Adapted from Booth and Madronich [1994].
0
: V;uirt Poie, 1
-------
Table 1.1. Radiation Amplification Factors (RAFs) at 30°N.
Effect

Skin
•Erythema reference
•Skin cancer in SKH-1 hairless mice (Utrecht)
"SKH-1 corrected for human skin transmission
Elastosis
Photocarcinogenesis, skin edema
Photocarcinogenesis (based on STSL)
Photocarcinogenesis (based on PTR)
Melanogenesis
Erythema
•Melanoma in fish
DNA Related
'Generalized DNA damage
Mutagenicity and Fibroblast killing

Fibroblast killing
Cyclobutane pyrimidine dimer formation
(fr-4) photoproduct formation
HIV-1 activation
Eyes
Damage to cornea
Damage to lens (cataract)

January
(290DU)

1.1
1.5
1.2
1.1
1.6
1.5
1.6
1.7
1.7
0.1
2.2
[1.7] 2.2

0.3
[2.0] 2.4
[2.3] 2.7
[0.1] 4.4

1.2
0.8
DAP
July
(305DU)

1.2
1.4
1.1
1.2
1.5
1.4
1.5
1.6
1.7
0.1
2.1
[2.7] 2.0

0.6
[2.1] 2.3
[2.3] 2.5
[0.1] 3.3

1.1
0.7
— — . .

McKinlay and Diffey, 1987
deGruijl et al., 1993
deGruijl and van der Leun, 1994 —
Kligman and Sayre, 1991
Cole et al., 1986
Kelfkens et al., 1990
Kelfkens et al., 1990
Parrish et al., 1982
Parrish et al., 1982
Setlow et al.., 993
Setlow, 1974
Zoizer and Kiefer, 1984; Peak
etal.,1984
Keyse et al., 1983
Chan et al., 1986
Chan et al., 1986
Stein et al, 1989

Pitts et al, 1977
Pitts et al, 1977
Other effects on animal cells
'Occupational exposure limit
Immune suppression
•Cell mortality in Chinese hamster
•Substrate binding in Chinese hamster
1.4 1.5 ACGIH, 1991
[0.4] 1.0 [0.4] 0.8 • DeFabo and Noonan, 1983
_____ Banrud et al, 1993
Banrud et al, 1993
Membrane Damage
Glyrine leakage from E, coli
Alanine leakage from £. coli
Membrane bound K*-stimulated ATPase inactiv.
Plants
Generalized plant spectrum
Inhibition of growth of cress seedlings
Isoflavonoid formation in bean
Inhibition of phytochrome induced anthocyanin
synthesis in mustard
Anthocyanin formation in maize
Anthocyanin formation in sorghum
Photosynthetic electron transport
Photosynthetic electron transport
Overall photosynthesis in leaf of Rumex patientia
•DN'A damage in Alfalfa
Phytoplankton
Inhibition of motility (Euglena graalis)
'Inhibition of photosynthesis (Phaeodactylum sp.)
•Inhibition of photosynthesis (Prorocentrum micans)
'Inhibition of photosynthesis, in Antarctic community
•Inhibition of photosynthesis
(NoJtilaria spitmigeiia cyanobacteria)
Tropospherlc photolysis
•O3 + hv -> O(fD) +• O2
•O3 + hv -> O(3P) + O,
•H,O2 +• hv -» OH + OH
•HNO3 •(- hv -» OH + NO2
*NO2 + hv -» O(3P) + NO
•HCHO + hv -> H + CHO
•HCHO+ hv -^ H2-f CO

0.2
0.4
[0.3] 2.1
2.0
[3.6] 3.8
[0.1] 2.7

1.5
0.2
1.0
0.2
0.2
0.2
0.5

1.9
0.2
0.3
0.8
0.2
2.1
0.1
0.4
1.1
0.0
0.5
0.2

0.2
0.4
[0.3] 1.6
1.6
3.0
• [0.1] 2.3

1.4
0.2
0.9
0.1
0.2
0.3
0.6

1.5
0.3
0.4
0.8
0.2
1.8
0.1
0.4
1.0
0.0
0.5
0.2

Sharma and Jagger, 1979
Sharma and Jagger, 1979
Imbrie and Murphy, 1982
Caldwelletal, 1986
Steinmetz and Wellmann, 1986
Wellmann, 1985

Wellmann, 1985
Beggs and Wellmann, 1985
Yatsuhashi et al, 1982
Jones and Kok, 1966
Bornman et al., 1984
Rundel, 1983
Quaite et al, 1992

Hader and Worrest, 1991
Cullen et al, 1992
Cullen et al, 1992
Boucher and Prezelin, 1994
Hader et al, 1994
Madronich and Granier, 1994
Madronich and Granier, 1994
Madronich and Granier, 1994
Madronich and Granier, 1994
Madronich and Granier, 1994
Madronich and Granier, 1994
Madronich and Granier, 1994
-------
Table 1.1. Radiation Amplification Factors (RAFs) at 30°N. (Continued)
Effect
RAF —
January July
(290DU) (305DU)
Reference
Aqueous photochemistry
*CO production (Suvvannee River)
•COS production (Gulf of Mexico)
•COS production (North Sea)
*Photodegradation of nitrate ions
•Photodegradation of DOC (Biscayne Bay)
•Photoproduction of H2O2 in freshwater
Materials damage
Yellowness induction in poly vinly chloride
Yellowness induction in polycarbonate
Other weighting functions
Temple U. Robertson-Berger meter
•Solar Light Robertson-Berger meter (Model 501)
•ozone cross section (273 K)
•UV-A (315-400 nm)
•UV-B (280-315 nm)
•UV-B' (280-320 nm)
•simple exponential decay, one decade per 14 nm.
0.3
0.2
0.6
1.1
1.3
0.1
0.2
0.4
0.8
1.2
0.8
0.03
1.25
0.87
1.00
0.3
0.2
0.6
1.0
1.1
0.1
0.2
0.4
0.7
1.1
0.8
0.02
0.99
0.71
1.00
Valentine and Zepp, 1993
Zepp and Andreae, 1994
Zepp and Andreae, 1994 --
Zepp et al., 1987
Kieber et al., 1990
Cooper et al., 1988
Andrady et al., 1989
Andrady et al., 1989
Urbach et al., 1974
M. Morys, priv. comm. 1994
Updated from UNEP (1991). (') denotes change or new entry. Values in brackets show effect of extrapolating original data to
400 nm with an exponential tail, for cases where the effect is larger than 0.2 RAF units. RAFs computed on basis of daily
integral.

Limitations of Biological Action Spectra

Commonly used weighting functions are based on biglogical action spectra. Frequently a weighting
function at the effects level is the composite of more than one spectrum at the molecular level, and is
modified by absorbing molecules filtering the radiation before it reaches its target. Therefore the
weighting functions, and data derived from them such as the RAFs of Table 1, depend on various
independent factors and should be used with caution, taking into account the conditions under which the
experiments were performed. When labels such as "DNA-effective radiation" are used, this simply
describes the integrated irradiance potentially effective in causing effects (e.g., naked DNA damage) but
does not necessarily mean that the effect (DNA damage) will ensue. The actual effect will depend on the
sensitivity of the particular organism and several other factors.

Traditionally, action spectra have been developed for very different purposes than evaluating
biological effects of 03 reductions. Action spectra allow the photobiologist to draw some conclusions
regarding the biological pigment or molecule that absorbs the radiation and mediates the effect within an
organism. The criteria often used to develop action spectra are directed to this traditional use in
photobiology and these, along with many technical constraints, limit the usefulness of action spectra as
weighting functions. A photobiologist may v.'ish to know how an absorbing molecule is acting, with as little
interference by other substances in the organ;v.;-. -••- < »-^:.iMe, e.g., how DNA is ?Hso:bing radiation and
acting to mediate an effect. However, for evaV .,j.t. t!cr:, c '•,'-, n.;.:ction it is more
important to know how a molecule such as P'\ -\ Li I'- ".•:>!n.;.-.! stat-j within the c-, •;.-;- is affected by the
radiation and how its effect nry be ?'*,.-d b) ll - :r.:tmly of other absorbing rr.v. ,. ui-=

Action ,;--,cU-a are usually developed by exposing the biological material to radiation of only one
waveleii£lh (o: a ".arrow range of wavelengths) at a time and then measuring the effect. Again, for
traditional photobiological purposes this is quite suitable. However, organisms in nature are exposed
simultaneously to radiation at all wavelengths in the entire solar spectrum reaching the earth's surface,
and the radiation in the UV-A and visible wavebands is orders of magnitude more intense than in the LIV-
ES. Under such conditions several chromophores may be acting to cause interacting effects in the organism.
For example, the UV-A and visible radiation can ameliorate the effects of UV-B in many organisms [e.g.,
Caldwell and Flint, 1994]. For practical purposes, action spectra are usually developed with only hours of
irradiation at each wavelength: whereas in nature organisms are usually exposed over periods of days,
months or longer to the full sunlight spectrum. This too can cause interacting effects that might not be
predicted from an action spectrum.
-------
Another limitation of UV-B action spectra is that they may be arbitrarily restricted to a certain
waveband where data were collected. While these still serve the traditional photobiological purposes,
they can limit the usefulness for the 03 reduction question. For example, if data for action spectra are
restricted to the UV-B, but in reality there is some, even very low, effectiveness in the UV-A, this can
change the resulting radiation amplification factors when these action spectra are used as weiehtine
functions. ' 6

These limitations and qualifications of weighting functions based on action spectra must be borne in mind
when considering the significance of biologically effective radiation. Use of such weighting functions is
still more appropriate than the use of unweighted UV-B radiation, but qualification is required. In this
chapter, several weighting functions are employed in considering the effect of O3 reduction on the global
distribution of "effective" UV radiation. While these are illustrative, they need to be interpreted with a
knowledge of the uncertainties inherent in the weighting functions.

Measurements of Environmental UV Radiation

Data Quality

Measurements of environmental UV radiation still present some difficulty, especially for the detection
of long-term trends since high accuracy and stability are required. Significant advances have been made
recently in assessing data quality through instrument characterizations, intercomparisons, and data re-
analysis.

Several intercomparisons among different spectre-radiometers showed substantial differences among
instruments [Gardiner et al, 1993; McKenzie et al, 1993; Kirk et al, 1994], especially at the shortest
wavelengths where the solar spectrum is steepest, and therefore problems of dynamic range, stray light
rejection, and wavelength calibration are most severe. At the present time, agreement to no better than
about ±5 percent can be expected for wavelengths longer thaa-ca, 310 run, and the agreement is worse at
shorter wavelengths.

Intercomparisons with broad-band and filter instruments are more difficult, due in part to calibration
ambiguities that arise when the spectral shape of the solar spectrum changes under different solar zenith
angle, O3 column, and other atmospheric conditions [DeLuisi and Harris, 1983]. Extensive re-examination
has been carried out for the most commonly used broad-band instrument, the Robertson-Berger (RB) meter.
Its temperature coefficient (ca. 1 percent K'1) has been determined [Johnsen and Moan, 1991; Dichter et al.,
1993; Blumthaler, 1993], and a new generation of temperature-stabilized instruments is now available. The
spectral response of the RB instruments was found to be stable over more than a decade, although with some
differences between different instruments [DeLuisi et al., 1992]. A review of calibration records by Kennedy
and Sharp [1992] did not identify any significant problems. However, DeLuisi [19937 found calibration
shifts in the long-term data record of the RB meter located at Mauna Loa. The magnitude, timing, and
direction of these shifts are such as to produce an apparent negative trend in UV comparable to the
decreasing UV trends reported by Scotto et al. [1988] for RB meters located in the continental USA over
1975-85. Smith and Ryan [1993] have also identified substantial variations between different RB
instruments. Until a full re-analysis of the calibrations of the RB meter network is carried out, trends
derived from RB meters must be viewed with caution.

Geographical and Seasonal Variations

High Latitudes

Very little UV irradiance data in the Antarctic are available before the discovery of the springtime O3
hole. Baker-Blocker et al. [1984] reported measurements over 1979-81, but because their broad-band
instrument was heavily weighted in the UV-A, no conclusions can be drawn about the pre-ozone hole UV-B
record. The number of Antarctic UV measurements has increased greatly in recent years [Lubin and
Frederick, 1989, 1991; Lubin et al, 1989, 1992; Stamnes et al, 1990, 1992; Frederick and Alberts, 1991; Smith
et al., 1992a,b; Beaglehole and Carter, 1992a,b; Booth et al, 1993, 1994; Roy et al, 1994; Frederick and
Lubin, 1994; Helbling et al, 1994]. The effect of the O3 hole on UV levels is now clearly established. Figure
1.3 shows the UV radiation in two different wavelength bands, 298-303 run (very sensitive to O3) and 338-
342 run (relatively insensitive to O3), measured at the south pole between early 1991 and early 1994. While
-------
the 338-342 run band maximizes near summer solstice as expected, the 298-303 run values reach their highest
values in November, and show clearly the effects of the 03 hole. Figure 1.4a shows that 1991 springtime
DNA-damage-weighted UV radiation measured at the south pole was much higher than measurements
obtained in Barrow, Alaska, for the same solar zenith angle. Visible radiation measurements at the same
locations (Figure 1.4b) effectively demonstrate that the higher UV at the south pole was not due to other
atmospheric factors such as less cloud cover. Although the natural UV levels at high latitudes are usually
smaller than at low latitudes, measurements now show (see Figure 1.5) that during the springtime ozone
depletion the DNA-damaging radiation at Palmer Station, Antarctica (64°S) can exceed maximum summer
values at San Diego, USA (32°N).
1.4

S 1.2

8 1.0
I
TJ
g 0.8
i
2 0.6
!
g 0.4
00
o>
CM
0.2
0.0
Jan-91

180
Jan-92
Jan-93
Jan-94
160 -
140 -
I 12° '
£ 100 •
•o
80 -
£
(N
«?
ee
M
rt
60

0
Jan-91
Jan-92
Jan-93
Jan-94
Fig. 1.3. Hourly irradiance integrated over 298-303 nm (top) and over 338-342 nm (bottom), at the South Pole between
1991 and 1994. Vertical dotted lines mark the summer solstices. From Booth et al. [1994].
-------
65
70 75 80 86

Solar Zenith Angle (Dagrat)
00
100
14000
TO
75 80 «S

Solar Zenith Angl* (D*gr««)
100
Rg. 1.4. Comparison of 1991 springtime radiation at South Pole and Barrow (Alaska), (a) DNA-weighted UV irradiance' (b)
400-600 nm integrated irradiance. From Booth et al. [1993].

Northern hemisphere polar regions experienced anomalously low O3 levels in 1992 and 1993 (see below).
Spectral measurements obtained at Barrow during the spring of 1991-94 show the expected increases in UV
radiation associated with low O3/ and a return to more normal levels in 1994 [R. Booth, private
communication, 1994].

Other Latitudes

Measurements at many locations are providing a more clear characterization of the geographical
variations of ground-level UV. The RB meter network [Scotto et al, 1975, 1988; Cotton, 1990] has confirmed
the general higher UV-B levels al lower latitudes in the US. Other RB meter mo-r-fuiements also confirm
the broad latitudinal differences, e.g., in Russia [Garadzha and Nezval, 1987], Switzerland [Blmnthaler
and Ambach, 1990], Malaysia [Ilyas, 1987], and New Zealand [Zheng and Basher, 1993], though detailed
comparisons of local effects (e.g., pollution, cloudiness) has not yet been carried out. Multifilter
measurements at 39°N, 77°W have been made since 1975 by Correll et al. [1992] and are continuing, but direct
comparison to other instruments is difficult because of the different spectral response.
-------
10
20
30
40
50
60
70
80
Solar Zenith Angle (degrees)
Fig. 1.5. DNA-weighted noon irradiances measured in 1993 at Palmer Station, Antarctica (64°S) and in San Dieqo USA
(32°N). (Courtesy R. Booth, 1994). '

Spectral measurements show higher summertime values of UV-A and UV-B radiation in Lauder (New
Zealand) and Melbourne (Australia) compared to Neuherberg (Germany) [Seckmeyer and McKenzie, 1992;
McKenzie et al., 1993], due to the yearly cycle of the suivearth distance, and to lower stratospheric O3
levels in the southern hemisphere and higher tropospheric pollutant levels (O3 and aerosols) in Germany.'
Enhanced southern hemisphere UV-B levels are also evident from measurements in Ushuaia, Argentina
(55°S) [Diaz et al, 1991,1994; Frederick et al, 1993b], where in December 1991 the average noontime clear
sky radiation at 306.5 nm was 45 percent larger than calculated from the O3 climatology of the previous
decade.

Additional mid-latitude spectral measurements [Bais et al., 1993,1994; Gardiner et al., 1993;
Blumthaler, 1993; Blumthaler et al., 1993, 1994; Seckmeyer et a/.,'1994; Booth et al., 1993; /to, 1993; Kerr
and McElroy, 1993; Kirk et al., 1994; Cabrera et al, 1994} have recently contributed to a growing UV data
base, and systematic compilation of the data, though not yet achieved, should provide a reasonable picture
of mid-latitude UV distributions.

Other Factors Affecting UV

Clouds

The importance of clouds to surface UV is well established. Analysis of the long-term RB meter data
from various locations in the US shows that monthly average UV levels are red^.-rd by 10-50 percent,
depending on season and location [Frederick and Snell, 1990; Frederick et a}., If .J..j. Empirical
parameterizations based on the fraction of occluded sky observed frci.; HIL s-iilv.ce have been developed in
Malaysia, the United States, Sweden, and Australia [llyas, 1987; Cutc'tM, 19SO; Josefsson, 1986; Paltridge
and Barton, 1978; Ito, 1993]. The results are scattered and non-linear, with as much as 70-80 percent
reductions at full cover, and average reductions in the 10-50 percent range. The parameterizations should be
viewed as highly approximate and applicable only to the cloud types that are characteristic of the
different locations of the studies.

Aerosols

Tropospheric aerosols, e.g., sulfate, reduce UV levels significantly in polluted regions [Liu et al., 1991].
Seckmeyer and McKenzie [1992J estimated that aerosols had only a minor effect in the contrast between UV
irradiances in New Zealand and Germany. However, Seckmeyer et al. [1994] measured substantial UV-A
-------
and UV-B reductions on a day with high turbidity, compared to a day with low turbidity. Cabrera et al.
[1994] found larger UV-A gradients with elevation in relatively polluted areas compared to pristine
regions of Chile. Justus and Murphey [1994] analyzed RB meter data over 1980-84 for Atlanta, Georgia, and
attributed the observed 10 percent decrease to local or regional aerosols. Thus, although an effect appears
to exist, its magnitude is still not well defined.

The effect of stratospheric sulfate aerosols on surface UV irradiance has been of increased interest since
the eruption of Mt. Pinatubo in June 1991. Scattering of the incoming UV radiation by the aerosol may
decrease surface irradiance at long wavelengths, but may also change the photon pathlengths through
stratospheric Oj, resulting in increased surface irradiance under some conditions (short wavelengths, large
solar zenith angle [Michelangeti et al., 1992; Davies 1993]). The net effect on biologically weighted
radiation is expected to be a relatively small decrease [Madronich et al, 1991; Vogelmann et a!., 1992].
Spectral measurements show a marked increase in the diffuse/direct UV ratio but little effect on the total
radiation [McKenzie, 1993; Blumthaler and Ambach, 1994]. Stratospheric aerosols also influence surface
UV levels indirectly through their effects on stratospheric O3 chemistry.

Tropospheric Ozone and other Gaseous Pollutants

Bruhl and Crutzen [1989] suggested that tropospheric O3 may be a somewhat more effective absorber of
UV radiation than stratospheric O3/ due to enhancement of photon pathlengths by scattering in
tropospheric air. Frederick et al. [1993a] found a negative correlation between surface O3 concentrations and
RB meter readings in Chicago (USA). Cabrera et al. [1994] found larger increases with surface elevation for
UV-B than for UV-A, consistent with a larger tropospheric O3 column at the lower elevations. Other
tropospheric gases (especially NO2 and SO2) may attenuate UV in some urban areas [Frederick et al.,
1993a; Bais et al., 19937, but are probably not important in less polluted regions.

Surface Albedo and Elevation

Surface reflections affect UV radiation both through direct reflections toward a target, and by
enhancing the diffuse down-welling radiation. The relatively sparse measurements of surface reflectivity
(albedo) in the UV range have been reviewed recently by Madronich [1993a,b] and Blumthaler [1993].
Values usually fall below 10 percent for vegetation, but are highly variable for ice (7-75 percent) and snow
(20-100 percent). High reflections may be of some importance to the geographical and seasonal UV
distributions because they apply preferentially to colder climates.

_ UV levels are expected to be increase with increasing surface elevation above sea level because of the
thinner overhead atmosphere. Measurements at remote locations in Chile show increases of 4-10 percent per
km [Cabrera et al., 1994], in agreement with model calculations for unpolluted air [Madronich, 1993a].
Other locations show much larger vertical gradients, up to 40 percent per km near Santiago, Chile [Cabrera
et al., 1994], and 9-23 percent per km in the Swiss Alps [Blumthaler, 1993], presumably because the lower
elevations experience more tropospheric ozone, aerosol turbidity, and possibly lower surface albedo.

Detection of Long-Term UV Changes

Several long-term records have been obtained using RB meters, and are subject to the cautions mentioned
above. In Moscow, Garadzha and Nezval [1987] found a 12 percent decrease in the RB meter measurements of
UV radiation over 1968-83, with a concurrent 15 percent increase in turbidity and a 13 percent increase in
cloudiness. RB meter measurements taken over 1974-85 at eight different sites in the USA showed UV
decreases of 0.5 percent and 1.1 percent per year [Scotto et al., 1988]. RB meter data obtained at a station in
the Swiss Alps (3.6 km above sea level, 47°N) showed increases of 0.710.2 percent per year over 1981-89
[Blumthaler and Ambach, 1990], persisting at 0.7±0.3 percent per year over 1981-91 [Blumthaler, 1993].
Zheng and Basher [29937 have found increases of about 0.6 percent per year in RB meter data over 1981-90 in
New Zealand, anticorrelated with O3 column data. Increases at high elevations and southern latitudes,
together with possible decreases in industrialized northern hemisphere regions, are consistent with a role
of local pollution, although RB meter calibration shifts may have also played a role (see above).
10
-------
Multi-filter measurements by CorrelLet al. [1992] dver 1975-90 at a single site in Maryland (USA)
indicate that the maximum monthly mean UV-B irradiance was 13 percent higher in 1983-89 than for the
entire data record, with an overall increase of 35 percent from 1977/78 to 1985, much larger than expected
from actual 03 reductions. However lower values were observed after 1987, and may be indicative of the
role of the atmospheric factors such as cloud variability.

Kerr and McElroy [1993] monitored spectral UV radiation in Toronto (Canada) from early 1989 through
August 1993, a period during which ozone levels changed by -4.1 percent per year during winter (December-
March) and by -1.8 percent per year in summer (May-August). The corresponding UV changes were strongly
wavelength-dependent, as shown in Figure 1.6, with the greatest increments occurring at the shortest
wavelengths as expected from ozone reductions. Using a similar instrument, Zerefos et al. [1994] found
statistically significant increases of +9.7 percent per year at 305 run and +0.1% per year at 325 nm at
Thessaloniki (Greece) between November 1990 and November 1993. These large increases span a relatively
short time and are influenced by the anomalously low ozone of 1992/93, so that they are better interpreted
as a perturbation rather than a trend [Michaels et al., 1994; Kerr and McElroy, 1994], but they demonstrate
that ozone-induced changes in UV can be detected over a period of several years despite variability due to
cloudiness and local pollution, particularly at the shortest wavelengths.

Seckmeyer et al. [1994] found larger UV-B and simultaneously lower UV-A levels in 1993 relative to
1992 in Germany. The UV-A changes were attributed to the different average cloud cover, and the UV-B
enhancements are consistent with independently measured lower 03 values, 322 Dobson Units (DU) in 1993
compared to 342 DU in 1992, May-July averages. Enhanced peak RB meter values, measured in Innsbruck
(Austria) during 1993 winter/spring, were also found by Blumthaler et al. [1994].

Limited evidence for long-term changes in the spectral distribution of surface UV radiation comes also
from data collected by ground-based O3 monitoring networks (see above). Most of these determine O3
through a measurement of the ratio of UV at several wavelengths, either from the direct solar beam or the
zenith sky. Long-term negative trends in O3 reported by such networks are therefore indicative of long-term
shifts of surface UV towards shorter wavelengths. —°— -

Trend detection remains a problem due to the sparsity of reliable long-term data. It is likely that the
opportunity to measure the historical natural UV baseline levels (i.e., pre-ozone depletion) has already
been lost over most of the globe, and will not return until the ozone layer returns to its natural state.

Evaluation of Radiative Models

The geographical coverage possible with radiative transfer models is limited only by the available
atmospheric data which, if derived from satellites, can span the entire globe. Therefore, such models are
an important complement to UV measurements. Models are also an essential aid in identifying the causes of
observed UV changes, to carry out sensitivity studies, and ultimately to predict future UV environments
under different atmospheric Oj reduction scenarios.

The theory of scattering and absorption of atmospheric radiation is well established, and there is no
scientific doubt that, all other factors being held constant, 03 reductions are accompanied by predictable
increases in surface UV radiation. However, models require as input the optical characteristics of the
atmosphere, and if these are poorly known, as is often the case with pollutants and clouds, model-
calculated irradiances can be in serious error.

For cloud-free and low-aerosol sky conditions and known O3 column, model irradiances generally fall
within the experimental errors of both broad-band meters [e.g., Jokela, 1993] and spectroradiometers [e.g.,
McKenzie et al., 1993; Kirk et al., 1994; Zeng et al, 1994; Wang and Lenoble, 1994]. The theoretical
relationship between O3 reductions and UV increases has also been confirmed in numerous studies [Stamnes
et al., 1988, 1990, 1992; Roy et al., 1990, 1994; McKenzie et al., 1991; Smith et al, 1992b; Seckmeyer and
McKenzie, 1992; Bais et al., 1993; Frederick et al, 1993b; Holm-Hansen et al, 1993].
11
-------
~ 10 -
SUMMER1M3

WINTER.wz-o.
WINTER RATIO
SUMMER RATIO
WINTER RATIO
020NE ABSORPTION 1
i-rr-
300 305
] I I I ! j ( i I ~
310 315 320 325
WAVELENGTH (nm)
Fig. 1.6. Impact of low ozone over Toronto, Canada in 1992/1993 compared with earlier years. The top panel shows the
median daily UV spectral irradiance for the summers of 1989 and 1993, and the winters of 1989-90 and 1992-93
I <£o dle .panel shows sPectral irradiance ratios for summer (1993 divided by 1989) and winter (1992-93 divided
by 1989-90). The bottom panel compares the observed changes as a function of wavelength with the ozone
absorption spectrum; the log of the winter ratio is used because the transmission of UV radiation depends on the
exponent of the ozone absorption coefficient. Adapted from Kerr and McElroy [1993].
12
-------
Validation of the models is still a problem in the presence of clouds and tropospheric pollutants.
Commonly used UV models are incompatible with the empirical formulations based on fractional cloud
cover discussed in section above, either because they don't consider clouds at all, or idealize them as hori-
zontal layers of homogeneous vertical optical depth that do not allow for partial coverage nor for realistic
cloud morphology [Frederick and Lubin, 1988; Madronich 1990, 1993a,b]. Use of satellite images to estimate
both areal coverage and optical depths is promising [Lubin et al, 1994; Gautier et al, 1994] but requires
additional development and evaluation. Other highly variable factors such as aerosols and gaseous pollu-
tants are seldom well characterized, which presents some difficulty for accurate modeling [Liu et al., 1991].

Trends in Ozone and Implications for UV Radiation

Ozone Trends

The recent changes observed in atmospheric O3 are described in the WMO [1994] report and summarized
only briefly here. Measurements of the total O3 column are made mainly by optical means from ground-
based and satellite-based instruments. In addition, vertical profiles of O3 concentrations are made from
balloon-borne instruments. The rather large data set has elucidated the geographical and seasonal
distribution of O3. Ground-based Dobson instruments, developed in the 1920's, have increased in number and
have been providing fairly wide geographic coverage since the 1960's. Other instruments, including the M-
83 and M-124 filter ozonometer, the Brewer, and the SAOZ spectrometer, have shorter data records. True
global coverage began in the late 1970's with the deployment of the Nimbus 7 satellite carrying the Total
Ozone Mapping Spectrometer (TOMS) and the Solar Backscatter Ultraviolet spectrometer (SBUV). The
SBUV instrument ceased functioning in June 1990 and the TOMS in May 1993. The Nimbus 7 TOMS data
have been analyzed extensively, and the version 6 data appear to be reliable at least through May 1990,
but there is concern about additional calibration drifts after that date. SBUV/2 (on the NOAA-11
satellite) was launched in January 1989 and another TOMS instrument was launched in August 1991 (on the
Russian Meteor 3 satellite). Both of these instruments ase-still functioning. The combined SBUV and
SBUV/2 data records appear to be suitable for trend determinations. The Meteor 3 TOMS data have not yet
been properly assessed for consistency with the earlier systems. Other satellite O3 monitoring systems
(TOVS, LIMS, SAGE I and n) are at the present time less suitable due to incomplete detection of the total
O3 column, and some still unresolved calibration issues.

Statistically significant negative trends in total O3 are found at all latitudes except possibly in the
tropics, where ground-based measurement show no trend. Recent Dobson trends are larger (more negative) than
long-term trends, suggesting greater O3 reductions in the more recent years. The years 1992 and 1993, in
particular, exhibited large negative anomalies in O3/ possibly related to the eruption of Mt. Pinatubo, with
record low values measured at northern mid-latitudes. Total O3 in early 1994 has largely returned to the
trends observed before the Pinatubo eruption. The springtime Antarctic O3 loss, first observed in the late
1970's, has continued as an annual event, and record low values (for the first time less than 100 DU) were
observed at the South Pole in late September and early October 1993. The 1992 and 1993 O3 holes appeared
earlier and covered larger areas than those of earlier years.

Tropospheric O3 accounts for about l/10th of the total O3, and tends to be highly variable, being
associated with more polluted regions. Surface O3 concentrations in Europe may have increased '.-4 fold since
last century, and doubled since the 19.50's. However, surface values may not be representative of the free
troposphere. Analysis of vertical profiles from O3 sondes indicates increases of about 10 percent per decade in
the northern mid-latitudes, with strong regional patterns and largest increases over European and Japanese
stations [WMO, 1994]. There is also some evidence for a slowing of the trends during the 1980's. In-the
southern hemisphere, surface O3 levels show little or no trends, except for the polar regions where a decrease
of about 7 percent per decade has been reported.

Calculated UV Radiation Trends

The Nimbus-7 TOMS O3 data (version 6) over 1979/92 have been analyzed by Madronich and de Gruijl
[1993,1994] to infer the corresponding changes in UV radiation weighted by several biological action
spectra. The TOMS data after May 1990 may be affected by a calibration drift which is not considered in
the version 6 data. Here, the calculations of biologically weighted UV changes are repeated using the
combined SBUV and SBUV/2 data, from January 1979 through December 1993.

13
-------
The procedure to calculate trends in biologically effective doses is essentially unchanged. Briefly, the
atmosphere is taken to be cloudless and aerosol-free, with 10 percent surface albedo, and standard ve'rtical
profile of O3 scaled to the total column from SBUV(/2). The down-welling spectral irradiance is calculated
at 1 run intervals (279.5-399.5 run), then integrated over wavelength using several biological action spectra
to compute dose rates. This is repeated every 15 minutes for the 15th day of each month of the O3 data
record flanuary 1979-December 1993) in 10° latitude increments from 70°S to 70°N. The results are time-
integrated to compute daily and yearly doses, and trends with their standard deviations are calculated by
linear least-squares fitting.

Figure 1.7 shows the trends in daily doses for UV radiation weighted by the action spectrum for in vitro
DNA damage [Setlow, 1974]. The results are generally similar to those obtained with TOMS data over
1979-89 [Madronich, 1992] and over 1979-92 [Madronich and de Gruijl, 1993, 1994]. Relative increases
(percent per decade, Figure 1.7a) are significant in both hemispheres at middle and high latitudes, and are
largest in winter and spring. The relative increases in the tropics are small and probably not significant
Daily dose increments (J m"2 day-1 per decade, Figure l.Tb) are shifted toward summer and lower latitudes
i.e., toward higher natural UV levels.

Table 1.2 summarizes the increases over the 15-year SBUV(/2) data record for the annual doses for DNA
damage, erythema induction in humans [McKinlay and Diffey, 1987], and skin cancer induction in
laboratory mice [de Gruijl et al, 1993] (see also Table 1.1). The largest increases are observed at high
latitudes of the southern hemisphere. Significant increases are also found in the northern high latitudes
and the mid-latitudes of both hemispheres.

Some regions, particularly in the Northern Hemisphere, have experienced increased tropospheric
pollution (mostly sulfate aerosol and ozone) during the last century. It has been estimated that the
corresponding UV (DNA-weighted) could have been reduced by 6-18 percent from the sulfate aerosol
increases [Liu et al, 1991] and by 3-10 percent from the tropospheric ozone increases [UNEP, 1991] in some
industrialized regions. However, no direct information exists on pre-industrial stratospheric ozone,
precluding accurate estimates of the net UV changes. More-recent tropospheric ozone trends in
industrialized regions are estimated to contribute at most 2 percent per decade to the DNA-weighted UV
compared to +5 to +11 percent per decade from mid-latitude ozone reductions f UNEP, 1991]. Sulfur emissions
nave recently decreased in some regions while increasing in others [NRC, 1986], and the corresponding UV
changes are expected to reflect such local variations.
DHA dally don twnd, X/d««dt, SBUV(/2)79-93
-60 -
-90
a.
234567
Month
8 9 10 11 12
14
-------
DMA dally dec* f«nd. J m-'/d«cad«, SBUV(/2)70-93
-90
b.
234567
Month
8 9 10 11 12
Fig. 1.7. Trends in daily DNA-damaging radiation based on SBUV(/2) total O3 measurements over 1979-93. Heavy shading
indicates regions where trends differ from zero by less than one standard deviation (1a), light shading by more
than 10 but less than 2a (a) Fractional trends, in percent per decade relative to 1979-93 average values; (b)
energy trends, J m'2 day1 per decade with action spectrum normalization at 300 nm.

Table 1.2: Annual UV exposures estimated from stratospheric ozone measurements between 1979 and
1993(a).
Latitude
65N
55 N
45 N
35 N
25N
15 N
5N
55
15 S
255
355
45 S
55 S
655
Erythema
annual
dose
(MJ m-2)
0.47
0.68
1.01
1.46
1.94
2.35
2.58
2.58
2.34
1.95
1.49
1.06
0.73
0.51
Percent
Erythema
induction
5.6±2.1
6.6±1.8
8.6±1.9
7.9±1.9
6.0±1.9
4.0+1.5
2.6+1.7
3.2+1.5
1.8+1.4
5.4±1.5
8.0±1.5
8.0+3.9
10.7+2.8
20.4+4.4
Percent increase during 1979-1993
DNA
damage
10.3±3.8
11.6+3.3
14.5±3.3
13.0+.3.1
9.6±3.0
6.3±2.4
4.1±2.7
5.1±2.3
2.8+2.1
8.7+2.4
13.2+2.4
13.6+3.2
18.815.1
37.2+8.2
Skin
cancer
7.9+2.9
8.9±2.5
11.1+2.4
9.8±2.3
7.1+2.2
4.7+1.7
3.0+2.0
3.0+1.7
2.0±1.6
6.4±1.8
9.8±1.8
10.2+2.4
14.2±3.8
27.1+6.1
(a) Computed using monthly and zonally averaged ozone column data measured from SBUV and SBUV/2
satellite instruments between January 1979 and December 1993. Annual doses (only erythemal is
shown) are 1979-93 averages. Percent changes are expressed relative to the 1979-93 annual
averages. Uncertainties are one standard deviation.
Long term changes in cloud cover may also affect ground-level UV radiation. Surface observations at a
few continental and marine locations suggest some long term cloudiness increases, but there is yet no
confidence that such changes have occurred on global scales [IPCC, 1991]. The implications of such changes
for surface UV levels have not been quantified. Global space-based observations of clouds [e.g., Rossow et
O.L, 1991] are becoming available, but the record is still of insufficient length for trend detection.
15
-------
Future Trends

With continued full compliance to the Montreal Protocol and its amendments, it is expected that
stratospheric chlorine will peak around the year 1998, with a slow recovery over the subsequent 50 years
IWMO, 1994]. Model simulations of stratospheric ozone indicate that the peak global ozone depletions will
also occur in the next several years, with recovery over the next half-century. Relative to 1960, the
maximum ozone depletion expected at northern mid-latitudes is 12-13 percent in winter/spring, and 6-7
percent in summer/fall. The depletion at southern mid-latitudes will be approximately 11 percent (all
seasons). However, it should be noted that there are some differences among the predictions of different
models, and between modeled and observed trends to date. Furthermore, model predictions may be altered
significantly by events such as volcanic eruptions of magnitude comparable to that of Mt. Pinatubo.

The corresponding changes in biologically-weighted UV irradiances can be estimated using the RAFs in
Table 1.1. The estimated UV increases for erythema induction and DNA damage are, respectively, 15-17
and 29-32 percent (northern hemisphere mid-latitudes, winter/spring), 8-9 and 12-15 percent (northern
hemisphere mid-latitudes, summer/fall), and 15 and 25 percent (southern mid-latitudes, all seasons).

References

ACGIH, 1991-1992 Threshold Limit Values, American Conference of Governmental and Industrial
Hygienists, 1992.

Andrady, A. L., A. Torikai and K. Fueki, Photodegradation of rigid PVC formulations III. Wavelength
sensitivity to light-induce yellowing by monochromatic light, /. Applied Polymer Sci., 37, 935, 1989.
Bais, A. F., C. S. Zerefos, C. Meleti, I. C. Ziomas, K. Tourpali, V. Karaouza and D. Balis, Variability of
solar UV-B radiation at high and middle latitudes during EASOE 1991/92, /. Geophys. Res 98 5199-
5204,1993.

Bais, A. F., C. S. Zerefos, C. Meleti, I. C. Ziomas and K. Tourpali, Spectral measurements of solar UV-B
radiation and its relations to total ozone, SO2, and clouSs," Geophys. Res. Lett., 21, 1403-1406, 1994.
Baker-Blocker, A., J. J. DeLuisi and E. Dutton, Received ultraviolet radiation at the South Pole Sol
Energy, 32, 659-662,1984.
Banrud, H., K. Berg, T. Platou and J. Moan, An action spectrum for UV-induced attachment of V79 Chinese
hamster cells to a substratum, Int. J. Rod. Bio/., 64, 437-444,1993.
Beaglehole, D. and G. G. Carter, Antarctic Skies 1: Diurnal variations of the sky irradiance, and UV
effects of the ozone hole, spring 1990, /. Geophys. Res., 97, 2589-2596, 1992.
Beaglehole, D. and G. G. Carter, Antarctic Skies 2: Characterization of the intensity and polarization of
skylight in a high albedo environment, /. Geophys. Res., 97, 2597-2600, 1992.
Beggs, C. J. and E. Wellmann, Analysis of light-controlled anthocyanin formation in coleoptiles of Zea
mays 1.: The role of UV-B, blue, red and far-red light, Photochem. Photobiol., 41, 481-486, 1985.
Blumthaler, M. and W. Ambach, Indication of increasing solar ultraviolet-B radiation flux in Alpine
regions, Science, 248, 206-208,1990.
Blumthaler, M., Solar UV measurements, pp. 17-69 in Environmental Effects of UV (Ultraviolet)
Radiation, M. Tevini, (ed.), Lewis Publisher, Boca Raton, 1993.
Blumthaler M. M. Huber and W. Ambach, Measurements of direct and global UV spectra under varying
turbidity, in proc. International Symposium on High Latitude Optics, European Optical Society and
International Society for Optical Engineering, Tromso, Norway, 28 June-2 July 1993.
Blumthaler, M. and W. Ambach, Changes in solar radiation fluxes after the Pinatubo eruption, Tellits 46B
76-78,1994. v

Blumthaler, M., W. Ambach, R. Silbemagel and J. Staehelin, Erythemal UV-B irradiance (Robertson-
Berger sunburn meter data) under ozone deficiencies in winter/spring 1993, Photochem. Photobiol., 59,
657-659,1994.

Booth, C. R., T. Mestechinka, T. Lucas, J. Tusson and J. H. Morrow, Contrasts in southern and northern
hemisphere high latitude ultraviolet irradiance, in proc. International Symposium on High Latitude

16
-------
Optics, European Optical Society and International Society for Optical Engineering, Tromso, Norway,
28 June-2 July 1993.
Booth, C. R., T. Lucas, J. H. Morrow, C. S. Weiler and P. A. Penhale, The United States National Science
Foundation's polar network for monitoring ultraviolet radiation, pp. 17-37, in Ultraviolet Radiation in
Antarctica: Measurements and Biological Effects, C. S. Weiler arid P. A. Penhale, (eds.), AGU Antarctic
Research Series, volume 62, American Geophysical Union, Washington, DC, 1994.
Booth, R. C. and S. Madronich, Radiation amplification factors - improved formulation accounts for large
increases in ultraviolet radiation associated with Antarctic ozone depletion, pp. 39-42 in Ultraviolet
Radiation in Antarctica: Measurements and Biological Effects, C. S. Weiler and P. A. Penhale, (eds.),
AGU Antarctic Research Series, volume 62, American Geophysical Union, Washington, DC, 1994.
Bornman, J. F, L. O. Bjorn and H.-E. Akerlund, Action spectrum for inhibition by ultraviolet radiation of
photosystem II activity in spinach thylakoids, Photobiochem. Photobiophys., 8, 305-313, 1984.
Boucher, N. P. and B. B. Prezelin, Biological weighting function for the UV inhibition of carbon fixation in
a natural Antarctic phytoplankton community, United States Antarctic J., in press, 1994.
Briihl, C. and P. J. Crutzen, On the disproportionate role of tropospheric ozone as a filter against solar UV-
B radiation, Geophys. Res. Lett., 16, 703-706, 1989.
Cabrera, S., S. Bozzo and H. Fuenzalida, Latitudinal and altitudinal variations of UV radiation in Chile,
Photochem. Photobiol., submitted, 1994.
Caldwell, M. M., L. B.Camp, C. W. Warner and S. D. Flint, Action spectra and their key role in assessing
biological consequences of solar UV-B radiation chance, pp. 87-111 in Stratospheric ozone reduction,
solar ultraviolet radiation and plant life, R. C. Worrest and M. M. Caldwell, (eds.), Springer-Verlae
Berlin, 1986.
Caldwell, M. M. and S. D. Flint, Stratospheric ozone reduction, solar UV-B radiation and terrestrial
ecosystems, Climate Change, in press, 1994.
Chan, G. L., M. J. Peak, J. G. Peak and W. A. Haseltine, Action spectrum for the formation of endonuclease-'
sensitive sites and (6-4) photoproducts induced in a DNA fragment by ultraviolet radiation. Int. J
Radiat. Bio/., 50, 641-648, 1986.
Cole, C. A., D. Forbes and R. E. Davies, An action spectrum for UV photocarcinogenesis, Photochem.
Photobiol., 43, 275-284, 1986.
Cooper, W. J., R. C. Zika, R. G. Petasne and J. M. Plane, Photochemical formation of hydrogen peroxide in
natural waters, Environ. Sci. Tech., 22, 1156-1160, 1988.
Correll, D. L., C. O. Clark, B. Goldberg, V. R. Goodrich, D. R. Hayes Jr., W. H. Klein and W. D. Schecher,
Spectral ultraviolet-B radiation fluxes at the earth's surface: long-term variations at 39°N, 77°W, /.
Geophys. Res. 97, 7579-7591, 1992.
Cotton, G. F., Robertson-Berger UVB meter, in Summary Report 1989, Climate Monitoring and Diagnostics
Laboratory Report No. 18, National Oceanic and Atmospheric Administration, Boulder, Colorado,
December 1990.
Cullen, J. J., P. J. Neale and M. P. Lesser, Biological weighting function for the inhibitkn of phytoplankton
photosynthesis by ultraviolet radiation, Science, 258, 646-649, 1902.
Cutchis, P., A Formula for Comparing Annual Damaging Ultravir-kr (nriv; R.-H;. ::...•; L1.-..,
and Mid-Latitude Sites, Federal Aviation Administrate:; K;.;.'.,. •'-;/,/ ; \ £." .•,(.. S. ;. •
Transportation, Washington, DC, 1980.
Davies, R., Increased transmission of ultraviolet radiation to the suiia-.e due to stratospheric scattering, /.
Geophys. Res., 98, 7251-7253, 1993.
De Fabo, E. C. and F. P. Noonan, Mechanism of immune suppression by ultraviolet radiation in vivo. I.
Evidence for the existence of a unique photoreceptor in skin and its role in photoimmunoloey, /. Exv. Med
158,84-98,1983.
de Gruijl, F. R., H. J. C. M. Sterenborg, P. D. Forbes, R. E. Davies, C. Cole, G. Kelfkens, H. van Weelden, H.
Slaper and J. C. van der Leun, Wavelength dependence of skin cancer induction by ultraviolet
irradiation of albino hairless mice, Cancer Res., 53, 53-60, 1993.
17
in-ill o
-------
de Gruijl, F. R. and J. C. van der Leun, Estimate of the wavelength dependency of ultraviolet carcinogenesis
and its relevance to the risk assessment of a stratospheric ozone depletion, Health Phys., 4, 317-323,

DeLuisi, J. J. and J. M. Harris, A determination of the absolute radiant energy of a Robertson-Berger meter
sunburn unit, Atmos. Env., 17,751-758,1983.
DeLuisi, J. J., J. Wendell and F. Kreiner, An examination of the spectral response characteristics of seven
Robertson-Berger meters after long-term field use, Photochem. Photobiol, 56, 115-122, 1992.
DeLuisi, J. J., Possible calibration shift in the U.S. surface UV network instrumentation 1979 to 1985, paper
presented at the U.S. Department of Energy UV-B Critical Issues Workshop, Cocoa Beach, Florida 24-
26 February 1993.
Diaz, S. B., C. R. Booth, T. B. Lucas and I. Smolskaia, Evolution of the ultraviolet radiation on Ushuaia
since November 1988, paper presented at 6th Argentinian Congress on Meteorology, Buenos Aires,
Argentina, September 23-27,1991.
Diaz, S. B., C. R. Booth, T. B. Lucas and I. Smolskaia, Effects of ozone depletion on irradiances and
biological doses over Ushuaia, Archiv fur Hydrobiologie, in press, 1994.
Dichter, B. K., D. J. Beaubien and A. F. Beaubien, Effects of ambient temperature changes on UV-B
measurements using thermally regulated and unregulated fluorescent phosphor ultraviolet
pyranometers, in Proc. Quadriennial Ozone Symposium, Charlotsville, Virginia, June 1992, in press 1993.
Frederick, J. E. and D. Lubin, The budget of biologically active ultraviolet radiation in the Earth-
atmosphere system, /. Geophys. Res., 93, 3825-3832, 1988.
Frederick, J. E. and H. E. Snell, Tropospheric influence on solar ultraviolet radiation: the role of clouds /
Climate, 3, 373-381, 1990.
Frederick, J. E. and A. D. Alberts, Prolonged enhancement in surface ultraviolet radiation during the
Antarctic spring of 1990, Geophys. Res. Lett., 18, 1869-18ZL. 1991.
Frederick, J. E., A. E. Koob, A. D. Alberts and E. C. Weatherhead, Empirical studies of tropospheric
transmission in the ultraviolet: broadband measurements, /. Appl. Met, 32,1883-1892,1993a.
Frederick, J. E., P. F. Soulen, S. B. Diaz, I. Smolskaia, C. R. Booth, T. Lucas and D. Neuschuler, Solar
ultraviolet irradiance observed from southern Argentina: September 1990 to March 1991 / Geovhvs
Res., 98,8891-8897,1993b.
Frederick, J. E. and D. Lubin, Solar ultraviolet irradiance at Palmer station, Antarctica, in Ultraviolet
Radiation in Antarctica: Measurements and Biological Effects, C. S. Weiler and P. A. Penhale, (eds.),
AGU Antarctic Research Series, volume 62, pp. 43-52, American Geophysical Union, Washington, DC'

Garadzha, M. P. and Ye. I. Nezval, Ultraviolet radiation in large cities and possible ecological
consequences of its changing flux due to anthropogenic impact, pp. 64-68 in Proc. Symp. on Climate and
Human Health, World Climate Programme Applications, WCAP Report No. 2, Leningrad, 1987.
Gardiner, B. G., A. R. Webb and A. F. Bais, European intercomparison of ultraviolet spectroradiometers
Environ. Tec!;., 25-43, 1993.

< , ;- ^ ( f '"> ^ Yang and D. Lubin, Role of clouds arid o/.one on spectral ultraviolet-B radiation and
l" ' «.'•• ".• _<"-";'>'': 7-:V dose over Antarctica, in Ultraviolet Radiation in Antarctica: Measurements and
//£.%•:»/ UjL^-it, C. S. Weiler and P. A. Penhale, (eds.), AGU Antarctic Research Series, volume 62,
pp. 83-91, American Geophysical Union, Washington, DC, 1994.
Hader, D.-P. and R. C. Worrest, Effects of enhanced solar ultraviolet radiation on aquatic ecosystems
Photochem. Photobiol., 53, 717-725, 1991.
Hader, D.-P., R. C. Worrest, H. D. Kumar, and R. C. Smith, Effects of increased solar UV-B irradiation on
aquatic ecosystems, in Environmental Effects of Stratospheric Ozone Depletion, J. van der Leun and M.
Tevini, (eds.), United Nations Environmental Programme, Nairobi, Kenya, in press, 1994.
Helbling, E. W., V. Villafane and O. Holm-Hansen, Effects of ultraviolet radiation on Antarctic marine
phytoplankton photosynthesis with particular attention to the influence of mixing, in Ultraviolet
Radiation in Antarctica: Measurements and Biological Effects, C. S. Weiler and P. A. Penhale, (eds.),
18
-------
AGU Antarctic Research Series, volume 62, pp. 207-227, American Geophysical Union, Washington, DC,
1994.
Holm-Hansen, O., E. W. Helbling and D. Lubin, Ultraviolet radiation in Antarctica: inhibition of primary
production, Photochetn. Photobiol., 58, 567-570, 1993.
Ilyas, M., Effect of cloudiness on solar ultraviolet radiation reaching the surface, Atntos, Environ., 21,1483-
1484,1987.

Imbrie, C. W. and T. M. Murphy, UV-action spectrum (254-405 nm) for inhibition of a K+-stimulated
adenosine triphosphatase from a plasma membrane of Rosa damascena, Photochem. Photobiol., 36, 537-
542,1982.
IPCC, Intergovernmental Panel on Climate Change, Climate Change, the IPCC Scientific Assessment, J. T.
Houghton, G. J. Jenkins, and J. J. Ephraums, (eds.), Cambridge University Press, Cambridge, 1991.
Ito, T., UV-B observation network in the Japan Meteorological Agency, in Frontiers of Photobiology, A.
Shima et al., (eds.), Elsevier Science Publishers, 1993.
Johnsen, B. and J. Moan, The temperature sensitivity of the Robertson-Berger meter, /. Photochem,
Photobiol. B: Bio/., II, 277-284, 1991.
Jokela, K., K. Leszcynski and R. Visuri, Effects of Arctic ozone depletion and snow on UV exposure in
Finland, Photochem. Photobiol, 58, 559-566, 1993.
Jones, L. W. and B. Kok, Photoinhibition of chloroplast reactions. I. Kinetics and action spectrum, Plant
Physiol, 41, 1037-1043, 1966.
Josefsson, W., Solar Ultraviolet Radiation in Sweden, National Institute of Radiation Protection in
Stockholm, SMHI Report-53, Norrkoping, Sweden, 1986.
Justus, C. G. and B. B. Murphey, Temporal trends in surface irradiance at ultraviolet wavelengths, /.
Geophys. Res., 99, 1389-1395, 1994.
Kelfkens, G., F. R. de Gruijl and J. van der Leun, Ozone depletion and increase in annual carcinogenic
ultraviolet dose, Photochem. Photobiol., 52, 819-823, 1990.
Kennedy, B. C. and W. E. Sharp, A validation study of the Robertson-Berger meter, Photochem. Photobiol.,
56,133-141,1992.
Kerr, J. B. and C. T. McElroy, Evidence for large upward trends of ultraviolet-B radiation linked to ozone
depletion, Science, 262,1032-1034,1993.
Kerr, J. B. and C. T. McElroy, reply to Analyzing ultraviolet-B radiation: is there a trend?, Science, 264,
1342,1994.
Keyse, S. M., S. H. Moses and D. J. G. Davies, Action spectra for inactivation of normal and xeroderma
pigmentosum human skin fibroblasts by ultraviolet radiation, Photochem. Photobiol, 37, 307-312, 1983.
Kieber, R. J., X. Zhou and K. Moper, Formation of carbonyl compounds from UV-induced photodegradation
of humic substances in natural waters: Fate of riverine carbon in the sea, Limnol. Oceanog., 35,1503-
1515, 1990.
Kirk, J. T. O., B. R. Hargreaves, D. P. Morris, R. Coffin, B. David, D. Frtdiickson, D. Karentz, D. Lean, M.
Lesser, S. Madronich, J. H. Morrow, N. Nelson and N. Scully, Mcasuremcnls of UV-B fdu Ui'.ion in
freshwater ecosystems, Archiv filr Hydrobiologie, 1994, in press.
Kligman, L. H. and R. M. Sayre, An action spectrum for ultraviolet induced elastosis in hairless m ;••
-------
Lubin, D. and J. E. Frederick, The ultraviolet radiation environment of the Antarctic peninsula: the roles of
ozone and cloud cover, /. Appl. Met., 30,478-493,1991.
Lubin, D., B. G. Mitchell, J. E. Frederick, A. D. Alberts, C. R. Booth, T. Lucas and D. Neuschuler, A
contribution toward understanding the biospherical significance of Antarctic ozone depletion, /.
Geophys. Res., 97, 7817-7828, 1992.
Lubin, D., P. Richiazzi, C. Gautier and R. H. Whritner, A method for mapping Antarctic surface ultraviolet
radiation using multispectral satellite imagery, in Ultraviolet Radiation in Antarctica: Measurements
and Biological Effects, S. Weiler and P. A. Penhale, (eds.), AGU Antarctic Research Series, volume 62,
pp. 53-81, American Geophysical Union, Washington, DC, 1994.
Madronich, S., Changes in biologically damaging ultraviolet (UV) radiation: effect of overhead ozone and
cloud amount, pp. 30-31 in Effects of Solar Ultraviolet Radiation on Biogeochemical Dynamics on
Aquatic Environments, Report of a Workshop held in Woods Hole, October 23-26 1989, N. V. Blough and
R. G. Zepp, (eds.), Woods Hole Oceanographic Institution, Woods Hole, 1990.
Madronich, S., L. O. Bjorn, M. Ilyas and M. M. Caldwell, Changes in biologically active ultraviolet
radiation reaching the earth's surface, pp. 1-13 in UNEP Environmental Effects Panel Report - 1991
Update, J. C. van der Leun, M. Tevini and R. C. Worrest, (eds.), United Nations Environmental
Programme, Nairobi, Kenya, 1991.
Madronich S., Implications of recent total atmospheric ozone measurements for biologically active
ultraviolet radiation reaching the Earth's surface, Geophys. Res. Lett., 19, 37-40, 1992.
Madronich, S., The atmosphere and UV-B radiation at ground level, pp. 1-39, in Environmental UV
Photobiology, A. R. Young, L. O. Bjorn, J. Moan, and W. Nultsch (eds.), Plenum Press, New York, 1993a.
Madronich, S., UV radiation in the natural and perturbed atmosphere, pp. 17-69, in Environmental Effects
of UV (Ultraviolet) Radiation, M. Tevini, (ed.), Lewis Publisher, Boca Raton, 1993b.
Madronich, S., Trends and predictions in global UV, pp. 463-471 in The Role of the Stratosphere in Global
Change, M. L. Chanin, (ed.), NATO ASI Series I: GloBaf Environmental Change, Vol. 8, Sprineer-
Verlag, Berlin, 1993c.
Madronich, S. and F. R. de Gruijl, Skin cancer and UV radiation, Nature, 366, 23,1993.
Madronich, S. and F. R. de Gruijl, Stratospheric Ozone Depletion between 1979 and 1992: Implications for
Biologically Active Ultraviolet-B Radiation and Non-Melanoma Skin Cancer Incidence, Photochem
Photobiol. 59, 541-546, 1994.
Madronich, S. and C. Granier, Tropospheric chemistry changes due to increases in UV-B radiation, in
Stratospheric Ozone Depletion/UV-B Radiation in the Biosphere, H. R. Biggs, (ed.), NATO ASI
Series, vol. 118, pp 3-10, Springer-Verlag, 1994.
McKenzie, R. L., W. A. Matthews and P. V. Johnston, The relationship between erythemal UV and ozone,
derived from spectral irradiance measurements, Geophys. Res. Lett., 18, 2269-2272, 1991.
McKenzie, R. L. M. Kotkamp, G. Seckmeyer, R. Erb, C. R. Roy, H. P. Gies and S. J. Toomey, First southern
hemisphere intercomparison of measured solar UV spectra, Geophys. Res. Lett., 20, 2223-2226, 1993.
McKenzie, R. L., UV spectral irradiance in New Zealand: effects of Pinatubo volcanic aerosol, in Proc.
Quadricnnial Ozone Symposium, Charlotsville, Virginia, June 1992, in press 1993.
McKinlay, A. F. and B. L. Diffey, A reference action spectrum for ultraviolet induced erythema in human
skin, in Human Exposure to Ultraviolet Radiation: Risks and Regulations, W. R. Passchler and B. F. M.
Bosnajokovic, (eds.), Elsevier, Amsterdam, 1987.
Michelangeli, D. V., M. Allen, Y. L. Yung, R.-L. Shia, D. Crisp and J. Eluszkiewicz, Enhancement of
atmospheric radiation by an aerosol layer, /. Geophys. Res., 97, 865-874, 1992.
Michaels, P. J., S. F. Singer and P. C. Knappenberger, Analyzing ultraviolet-B radiation: is there a trend?
Science, 264,1341-1342,1994.
NRC, Acid Deposition Long Term Trends, National Research Council, National Academy Press
Washington, 1986.
20
-------
Paltridge, G. W. and I. J. Barton, Erythemal Ultraviolet'Radiation Distribution over Australia - the
Calculations, Detailed Results and Input Data Including Frequency Analysis of Observed Australian
Cloud Cover, Division of Atmospheric Physics Technical Paper-33, Commonwealth Scientific and
Industrial Research Organization, Australia, 1978.
Parrish, J. A., K. R. Jaenicke and R. R. Anderson, Erythema and melanogenesis action spectra of normal
human skin, Photochem. Photobiol, 36, 187-191, 1982.
Peak, M. J., J. G. Peak, M. P. Moehring and R. B.Webb, Ultraviolet action spectra for DNA dimer induction,
lethality, and mutagenesis in Escherichia coli with emphasis on the UVB region, Photochem.
Photobiol., 40, 613-620, 1984.
Pitts, D. G., A. P. Cullen and P. D. Hacker, Ocular effects of ultraviolet radiation from 295 to 365 run, Invest.
Ophthalmo. Visual ScL, 16, 932-939, 1977.
Quaite, F. E., B. M. Sutherland and J. C. Sutherland, Action spectrum for DNA damage in alfalfa lowers
predicted impact of ozone depletion, Nature, 358, 576-578, 1992.
Rossow, W. B., L. C. Gardner, P.-J. Lu and A. Walker, Documentation of Cloud Data, Report WMO/T
International Satellite Cloud Climatology Project (ISCCP), 1991.
Roy, C. R., H. P. Geis and G. Elliott, Ozone depletion, Nature, 347, 235-236,1990.
Roy, C. R., H. P. Geis, D. W. Tomlison and D. Lugg, Effects of ozone depletion on the ultraviolet radiation
environment at the Australian stations in Antarctica, pp. 1-15 in Ultraviolet Radiation in Antarctica:
Measurements and Biological Effects, C. S. Weiler and P. A. Penhale, (eds.), AGU Antarctic Research
Series, volume 62, American Geophysical Union, Washington, DC, 1994.
Rundel, R. D., Action spectra and the estimation of biologically effective UV radiation, Physiol.
Plantarum, 58, 360-366,1983.
Scotto, J., T. Fears and G. B. Gori, Measurements of ultraviolet radiation in the United States and
comparisons with skin cancer data, U.S. Dept. of_Health, Education, and Welfare, Report No. (NIH)
76-1029, November 1975.
Scotto, J., G. Cotton, F. Urbach, D. Berger and T. Fears, Biologically effective ultraviolet radiation.
Surface measurements in the United States, 1974 to 1985, Science, 239, 762-764,1988.
Seckmeyer, G. and R. L. McKenzie, Elevated ultraviolet radiation in New Zealand (45°S) contrasted with
Germany (48°N), Nature, 359,135-137,1992.
Seckmeyer, G., B. Mayer, R. Erb and G. Bernhard, UVB in Germany higher in 1993 than in 1992, Geophys.
Res. Lett., 21, 577-580, 1994.
Setlow, R. B., The wavelengths in sunlight effective in producing skin cancer: a theoretical analysis,
Proceedings of the National Academy of Science, 71, 3363-3366, 1974.
Setlow, R. B., E. Grist, K. Thompson and A. D. Woodhead, Wavelengths effective in induction of malignant
melanoma, Proc. Natl. Acad. Sci. USA, 90, 6666-6670, 1993.
Sharma, R. C. and J. Jagger, Ultraviolet (254-405 nm) action spectrum and kinetic studies of alanine uptake
in Escherichia coli B/R, Photochem. Photobiol., 30, 661-666, 1979.
Smith, R. C., B. B. Prezelin, K. S. Baker, R. R. Bidigare, N. P. Boucher, T. Coley, D. Karentz, S. Maclntyre,
H. A. Matlick, D. Menzies, M. Ondrusek, Z. Wan and K. J. Waters, Ozone depletion: ultraviolet
radiation and phytoplankton biology in Antarctic waters, Science, 255, 952-959, 1992a.
Smith, R. C., Z. Wan and K. S. Baker, Ozone depletion in Antarctica: modeling its effects on solar UV
irradiance under clear sky conditions, /. Geophys. Res., 97, 7383-7397, 1992b.
Smith, G. J. and K. G. Ryan, The effect of changes or differences in Robertson-Berger radiometer
responsivity on solar ultraviolet-B measurement, Photochem. Photobiol., 58, 512-514, 1993.
Stamnes, K., K. Henriksen and P. Ostensen, Simultaneous measurements of UV radiation received by the
biosphere and total ozone amount, Geophys. Res. Lett., 15, 784-787,1988.
Stamnes, K., J. Slusser, M. Bowen, C. Booth and T. Lucas, Biologically effective ultraviolet radiation, total
ozone abundance, and cloud optical depth at McMurdo Station, Antarctica September 15 1988 through
April 15 1989, Geophys. Res. Lett., 17, 2181-2184, 1990.

21
-------
Stamnes, K., Z. Jin, J. Slusser, R. C. Booth and T. Lucas, Several-fold enhancement of biologically effective
ultraviolet radiation levels at McMurdo station Antarctica during the 1990 ozone 'hole', Geophys. Res.
Lett., 19, 1013-1016, 1992.
Stein, B., H. J. Rahmsdorf, A. Steffen, M. Litfin and P. Herrlich, UV-induced DNA damage is an
intermediate step in UV-induced expression of human immunodeficiency virus type 1, collagenase, c-fos,
and metallothionein, Mol. Cellular Biol., 9, 5169-5181, 1989.
Steinmetz, V. and E. Wellmann, The role of solar UV-B in growth regulation of cress (Lepidium sativum L.)
seedlings, Photochem. Photobiol., 43, 189-193, 1986.
UNEP, Environmental Effects Panel Report, J. C. van der Leun, M. Tevini and R. C. Worrest, (eds.), United
Nations Environmental Programme, Nairobi, Kenya, 1989.
UNEP, Environmental Effects of Stratospheric Ozone Depletion -1991 Update, J. C. van der Leun, M. Tevini
and R. C. Worrest, (eds.), United Nations Environmental Programme, Nairobi, Kenya, November 1991.
Urbach, F., D. Berger and R. E. Davies, Field measurements of biologically effective UV radiation and its
relation to skin cancer in man, in Proceedings of the Third Conference on Climatic Impact Assessment
Program, A. J. Broderick and T. M. Hard, (eds.), US Dept. of Transportation, February 1974.
Valentine, R. and R. G. Zepp, Formation of carbon monoxide from photodegradation of terrestrial organic
matter, Environ. Sci. Technol., 27, 409-412, 1993.
Vogelmann, A. M., T. P. Ackerman and R. P. Turco, Enhancements in biologically effective ultraviolet
radiation following volcanic eruptions, Nature, 359, 47-49,1992.
Wang, P. and J. Lenoble, Comparison between measurements and modeling of UV-B irradiance for clear sky:
a case study, Appl. Optics, 33, 3964-3871,1994.
Wellmann, E., UV-B-Signal/Response-Beziehungen unter naturlichen und artifiziellen Lichtbedingungen,
Ber. Deutsch. Bot. Ces., 98, 99-104, 1985.
WMO, Scientific Assessment of Ozone Depletion, World Meteorol. Org., in press, 1994.
Yatsuhashi, H., T. Hashimoto and S. Shimizu, Ultraviolet action spectrum for anthocyanin formation in
broom sorghum first internodes, Plant. Physiol., 70, 735-741,1982.
Zeng, J., R. McKenzie, K. Stamnes, M. Wineland and J. Rosen, Measured UV spectra compared with discrete
ordinate method simulations, /. Geophys. Res., in press, 1994.
Zepp, R. G., J. Hoigne and H. Bader, Nitrate-induced photooxidation of trace organic chemicals in water,
Environ. Sci. Tech., 21, 443-450, 1987.
Zepp, R. G. and M. O. Andreae, Factors affecting the photochemical formation of carbonyl sulfide in
seawater, Geophys. Res. Lett., 1994, in press.
Zerefos, C. S., A. F. Bais and C. Meleti, A comment on the recent increase of solar UV-B radiation over
northern middle latitudes, Science, submitted, 1994.
Zheng, X. and R. E. Basher, Homogenisation and trend detection analysis of broken series of solar UV-B
data, Theor. Appl. Climatol, 47, 189-203, 1993.
Zolzer, F. and J. Kiefer, Wavelength dependence of inactivation and mutation induction to 6-thioguanine-
resistance in V79 Chinese hamster fibroblasts, Photochem. Photobiol., 40, 49-53, 1984.
22
-------
CHAPTER 2

EFFECTS OF INCREASED SOLAR ULTRAVIOLET
RADIATION ON HUMAN HEALTH

J.D. Longstreth (USA), F.R. de Gruijl (The Netherlands), M.L Kripke (USA),
Y. Takizawa (Japan), and J.C. van der Leun (The Netherlands)
Summary

The increase in UV-B associated with stratospheric ozone depletion is likely to have a substantial
impact on human health. Potential risks include increases in the incidence of, and morbidity from, eye
diseases, skin cancer, and infectious diseases. Quantitative estimates of risk are available for some effects
(e.g., skin cancer), while for others (e.g., infectious diseases), quantitative estimates are not possible due
to a lack of sufficient data.

UV radiation has been shown in experimental systems to damage the cornea and lens of the eye. Chronic
exposure to UV-B (resulting in a high, cumulative, lifetime dose) is one of several factors clearly
associated with the risk of cataract of the cortical and posterior subcapsular forms. Estimates of the
effect of ozone depletion on cataract have been made, but are still highly uncertain. (As stated in the 1989
report, [van der Leun, et al., 1989] these estimates predict an approximately 0.5 % increase in cataract for
each 1% sustained decrease in ozone.)

Some components of the immune system are presentjn the skin, which makes the immune system
accessible to UV radiation. Experiments in animals show that UV exposure decreases the immune
response to skin cancers, infectious agents, and other antigens and can lead to unresponsiveness upon
repeated challenges. Suppressed immunity may occur either locally in sun-exposed skin or systematically,
at non-exposed sites. Studies in human subjects also indicate that exposure to UV-B radiation car.
suppress the induction of some immune responses and may cause systemic alterations in immune function.
The importance of these immune effects for infectious diseases in humans in unknown. However, in areas of
the world where infectious diseases already pose a significant challenge to human health, and in persons
with impaired immune function, the added insult of UV-B-induced immune suppression could be
significant.

In susceptible (light-skinned) populations, the cumulative lifetime exposure to UV-B radiation is the
key risk factor for development of non-melanoma skin cancer (NMSC). This knowledge has permitted the
development of quantitative risk estimates for increases in the incidence of NMSC resulting from ozone
depletion. Using information derived from animal experiments and human epidemiology, it is estimated
that a sustained 1% decrease in stratospheric ozone will result in an increase of NMSC'incidence of
approximately 2.0% The relationship between UV-B exposure and melanoma skin cancer is less well
understood and appears to differ fundamentally from that of NMSC in that it is not apparently a function
of cumulative lifetime dose but may be related to the accumulation impact of multiple high dose
exposures such as those received in sunburns. Epidemiologic data indicate that the risk of melanoma
increases with an increase in episodes of intense sunlight exposure, (i.e. sunburn) especially during
childhood. There is, however, unceirrnLy about hosv the relationship between these exposures and
melanoma should be modeled so tVu die estimates of the increase in melanoma that would result from
ozone depletion arc much less certain.
Introduction

As presented in detail in chapter 1, solar ultraviolet radiation (UVR) illuminates nearly everything and
everyone on the earth's surface not covered or shadowed. With stratospheric ozone depletion, increases in
the ambient levels of a particular type of ultraviolet radiation known as UV-B are likely to occur. In
humans and animals, the primary (i.e., direct) effects of increases in UV-B on health are manifest through
23
-------
those organs which are exposed to sunlight, i.e., eyes and skin. These effects occur because of the
absorption of UV-B photons by molecules in these organs and the resulting tranfer of energy to produce
changes that may be either beneficial or adverse. A direct beneficial influence of exposure is the formation
of Vitamin D in the skin, a process important to the maintenance of bone tissue. Direct adverse effects of
exposure to UV-B include snow blindness, cataract, sunburn, "aging" of the skin, photodermatoses and skin
cancer. Some effects may have both beneficial or adverse elements, depending on how they are expressed.
This applies, for instance, to the influences of UV-B radiation on the immune system. The resulting
suppression of immune reactions in the skin is beneficial in patients suffering from psoriasis, (a
hyperproliferativc skin disorder) but adverse when it affects the immune defense against skin tumors or
infectious agents. In addition, there may be indirect beneficial or adverse effects. An example indirect
adverse effect could be the increase in disease associated with the potential decrease in food production
discussed in chapter 3.

The question to be addressed by the present chapter is, what will be the human health consequences of an
increase in the UV-B radiation reaching the surface of the earth? One cannot simply say that all effects of
UV-B radiation will change in proportion to the increase in radiation, because in many cases, the
relationship between the amount of exposure and effect is non-linear. For example, expos!.:.--; of the skin
to UV-B radiation results in a hyperproliferation of skin cells and increased piumrru production
providing the skin with efficient protection against sunburn through the increase" in the UV absorbing
molecules, keratin and melanin. The hyperproliferation of skin cells may, however, also render the skin
more susceptible to cancer. In some instances, the modifying influences may be so strong that greater doses
of radiation lead to smaller effects.

For example, photodermatoses are skin diseases where the skin lesions are caused by light. Solar UV-B
radiation is the predominant causative agent for several of these diseases. Although many patients and their
doctors expect an aggravation of these diseases with a decreased ozone layer, there are reasons to question
this expectation. In the first place, these diseases generally occur less frequently and with less severity in
sunny areas of the world. Second, many patients with photodermatoses are treated effectively by regular
exposures to low-dose UV-B radiation during winter. Because depletion of the ozone layer will increase
UV-B irradiance, especially in winter, this may improve the patients' condition [van der Leun and de
Grttijl, 1993]. ~^~ '

Due to such complications, and due to the limited knowledge we have on some of the effects of UV-B
radiation on humans, the overall consequences of an increase of UV-B irradiance on health cannot be
predicted in a straightforward manner. This section, therefore, presents both qualitative and quantitative
answers to the question of what the consequences of stratospheric ozone depletion and its accompanying
increase in UV-B may be for human health. Quantitative estimates of UV-B effects are presented for
non-melanoma skin cancer; however, the impact of UV-B exposure on other effects has been treated
qualitatively. It should be stressed that the dependence on qualitative estimates for some effects does not
imply that these are less significant; indeed, the quantitative estimates should be treated very cautiously
because they involve many assumptions, are based on data mainly from the United States, and may not be
representative of all regions of the world.

Ocular Effects

Background
,!Vrl',a".* Vlc bcst d°cumented short-term ocular effect of exposure to UV radiation (especially UV-B
f • ' % \ C) !<•{>' .'.toLeratoconjunctivitis ('snow blindness' and 'welder eyes'), i.e., an inflammatory
1 , •' •"«• H\',u!:mg) of the surface of the eyeball. Extraordinarily painful, one episode should be
si::.Ki<'ht tu induce behavior modification to prevent recurrences, e.g., the use of proper eye protection.
The effects of long-term or chronic exposures, e.g., pterygium or cataract, are less well documented in
part because they result after many years of exposure, and, in part, at least for cataract, because many other
factors are known to have etiologic role. For such endpoints, as with endpoints such as NMSC, causality
has to be inferred from epidemiological studies supported by animal experiments. For a much more
detailed review of this subject, the reader is referred to Pitts and Kleinstein [1993].

Epidemiological Data

Epidemiological data indicate that chronic sunlight exposure is associated with pterygium, an
outgrowth of the conjunctiva (outermost mucous layer) over the neighboring cornea (overlying the lens),
and with climatic droplet keratopathy, a degeneration of the cornea! stroma (fibrous layer of tissue of the
cornea) with droplet-shaped deposits [Doughty and Cullen, 1989, and Hollows, 1989J. Climatic droplet

24
-------
keratopathy can be a major cause of blindness. Both of these conditions are common in certain
geographical locations, especially in snowy or sandy areas.

Sun exposure is also thought to be a contributing factor in the development of cataract, an opacity in
the crystalline lens of the eye (for an extended analysis, see Dolin 1994). The World Health Organization
(WHO) estimated in 1985 that cataract was the main cause of avoidable blindness, responsible for 17
million cases of blindness worldwide (about half of the total) [Maitchouk, 1985}.

The etiology of cataract in humans is multifactorial; increased relative risks are associated not only_
with increased exposure to UV-B, but also with increasing age, diabetes, renal failure, severe diarrhea,
heavy smoking, hypertension, high alcohol consumption, excessive heat, and malnutrition [e.g., Harding
and. Van Heyningen, 1987J. The increase in relative risk associated with increased UV-B exposure is 1.3
to 3.5-fold, compared to diabetes which has a relative risk increase of approximately 10-fold. However,
because of the nearly universal exposure of humans to solar UV radiation, the size of the population
likely to be affected by this factor is significantly, greater than for any of the other factors (except age)
listed above.

In comparing epidemiologies! studies, two things must be kept in mind: 1) there are differences in the
precise definition of cataract since the form of the disease can vary from small opacities which do not
impair vision to a completely opaque lens with severe loss of vision, (furthermore, there can be variation
between clinicians, and techniques; future studies would benefit from standardization of classifications)
and 2) there are different types of cataract that show differing associations to the factors discussed above.
Exposure to solar UV radiation appears specifically to increase the risk of cortical opacities (including
opacities not impairing vision): a clear UV dose-related trend in risk was established in a well designed,
cross-sectional study of Chesapeake Bay watermen [Taylor et al., 1988]. This UV exposure-associated
increased risk of cortical opacities was confirmed for the male population in the Beaver Dam Eye Study
(an odds ratio of 1.36 between numbers with 'high versus low exposures', 95 percent confidence interval
1.07-1.79), but the risks of other types of lens opacities, i.e., nuclear and posterior subcapsular cataract,
were not detectably increased by UV exposure [Cruickshanks et al., 1992].

The relationship between sunlight exposure and vision-impairing cortical cataract was confirmed in a
large case-control study drawn from three Italian optKaTmology clinics [Italian-American Study Group, '
1991]. Increased odds ratios for cortical cataract were found for working outdoors (1.75, 1.15-2.65) and
spending leisure time in sunlight (1.45, 1.09-1.93); these increased odds ratios were also found for the
mixed cataract, but not for posterior subcapsular and nuclear cataract. However, posterior subcapsular
cataract is relatively rare, making detection of risk in a small population difficult. In a special
case-control study in the Chesapeake Bay area on 168 surgical cases involving this type of cataract, a
highly significant (p = 0.006) positive trend was established between risk and exposure to ambient UV
radiation [Bochow et al., 1989].

The relationship between geographical location (latitude) and prevalence of cataracts has also been
attributed to ambient UV radiation; e.g., in Aborigines [Hollow and Moran, 1981] and in the North
American population [Hiller et al., 1983J. The latter study provided the basis for the USEPA risk estimates
for increases in cataract from ozone depletion [USEPA 1987].

Experimental Data

There is ample experimental evidence that UV radiation can damage the lens and that in rabbits the
active portion of the solar spectrum lies in the UV-B region [Pitts et al., 1977]. In albino mice, regular
UV-B exposure (1 to 2 months of daily exposure) can disrupt the anterior (frontal) part of the lens,
resulting in opacities [Jose and Pitts, 1985]. Hi<<.h dose, daily UV-A exposure also induced opacities in the
anterior lens of nocturnal animals ?nd squirrels [Zi^an ct al., 1991]. However, experimentally-induced
opacities in animals are located cent rally i" »::•;• aiuu-'or lens (the irradiated zone), whereas human
anterior cortical cataracts tend to form in the periphery (the equatorial region) of the lens. Also,
microscopic examination of experimental cataract commonly shows marked disruption of the lens
epithelium and inward folding of the underlying cortical fibers, which is not seen in human cataract. These
differences, while possibly attributable to differences between animals and humans in geometry, level of
exposure and/or ocular structure, contribute to the uncertainty associated with extrapolating from data in
mice to human cataract risk.

Solar UV Exposure of the Human Eye

The exposure of the unprotected eyes to solar UV radiation is significantly influenced by the shielding
from the eyebrows and eyelids (through squinting) and is strongly dependent on the direction of the line of
25
-------
sight. Highly reflecting surfaces increase the exposure dramatically; for example, the risk of
photokcratoconjunctivitis is strongly increased over snow surfaces [Sliney, 1987J. This variability in
exposure can seriously complicate studies in which eye exposures in different environments are compared
unless careful exposure measurements are made. [Rosenthal et al., 1991].

In humans, the anterior eye is not only exposed to light entering along the line of sight, but also to
light impinging from very oblique angles. Coroneo [1993] drew attention to the phenomenon in which
impinging (UV) light, especially that entering the eye at a very oblique angle, can be focussed onto the
overlying periphery of the cornea and the lens; this would intensify the light while it is traversing the
cornea and the lens in a direction roughly perpendicular to the line of sight. This phenomenon could
explain not only the sites of preference for pterygium and climatic droplet keratopathy, but also why many
conical cataracts occur in the nasal quadrant of the lens [Schein et al., 1994, Adamson et al., 1991, Hollow,
1989, and personal communication with Dr. B. Klein for the Beaver Dam Eye Study].

Impact of Ozone Depletion on Eye Conditions

In view of present data, it is prudent to consider that a depletion of the ozone layer could be associated
with an increase in the incidence of cataract and other ocular effects of UV-B, e.g., pterygium and snow
blindness. It is, however, difficult to estimate the magnitude of the increase without adequate information
on the wavelength dependence of these effects and proper dose-response relationships. In the case of
cataract, by assuming a certain wavelength dependence and with some additional assumptions, one can
produce an estimate based on epidemiological data (e.g., an estimate from EPA based on Killer et al.,
[1985], cited in van der Leun [1989], and one from van der Leun and de Gruijl, [1993], based on Taylor et al.,
[1988], and Pitts et al. [1977]: 0.3-0.6% and 0.5% increase in cataract, respectively, for every 1% decrease
in ozone) but such an estimate has a high degree of uncertainty. A similar quantitative estimate is not yet
possible for snow blindness, pterygium and climatic droplet keratopathy because of the inadequacy of
cpidemiologic information and experimental data. Nevertheless, it is prudent public health policy to
indicate to medical personnel and the lay public that these are effects which may well increase with
increased exposure to UV-B.

Immunologlcal Effects ~*~'

Background

Through a variety of complex, delicately balanced mechanisms, the immune system helps maintain
health by protecting the host against infectious diseases and some cancers. The two most important of
these mechanisms arc 1) humoral immunity, involving the production of antibodies that can neutralize
toxins, kill microorganisms, prevent infection, and assist in the elimination of infectious agents, and 2)
cellular immunity, involving the production of chemical mediators (cytokines) by lymphocytes which
activate other cells of the lymphoid system to kill pathogens, virus-infected cells, and cancer cells. These
two arms of the immune response, humoral and cellular, are delicately balanced, and some cytokines
involved in activating one pathway tend to inhibit the other. A severe imbalance in either direction can lead
to pathological conditions, such as allergies and inflammatory and autoimmune diseases.

Because skin is an important immunological organ, the immune system is vulnerable to modification by
environmental agents, including UV-B radiation. Demonstrations that systemic immunity can be perturbed
by exposing skin to UV-B radiation raise the concern that ozone depletion might adversely influence
immunity to infectious diseases.

Immunomodulaiory Effects of UV-B Radiation

_ There is nov. ,>it,p!e evidence that exposure of humans and experimental animals to UV-B radiation
from a.rilficial or lutHiral sources, can modify the immune system both at the site of exposure (locally) as
well as sy.temicaliy, mainly by decreasing cellular immune responses [Hersey et al., 1983; Morison, 1989;
Kripke, 19S4, 1990; DeFabo and Nooncm, 1993; Cruz and Bergstresser, 1988]. The immunosuppressive effects
of UV-B radiation have been shown to play an important role in determining the outcome of both
melanoma [Donawbo and Kripke, 1991] and non-melanoma skin cancer [Kripke, 1984; 1990; Fisher and
Kripke, 1982], certain infectious diseases [Jeevan and Kripke,, 1993], and some forms of autoimmunity
[Ansel et al., 1985} and allergy, e.g., delayed type hypersensitivity [Kripke, 1984; Cruz and Bergstresser, 1988,
Noonan et al., 1981] in laboratory animal models of these diseases. Furthermore, introduction of a foreign
substance (antigen) during a critical period after UV irradiation can lead to immunological tolerance,
rendering the host unresponsive to re-introduction of the same antigen at a later time [Kripke, 1984].
26
-------
CHAPTER 2
EFFECTS OF INCREASED SOLAR ULTRAVIOLET
RADIATION ON HUMAN HEALTH

J.D. Longstreth (USA), F.R. de Gruijl (The Netherlands), M.L Kripke (USA),
Y. Takizawa (Japan), and J. C. van der Leun (The Netherlands)
Summary

UV radiation has been shown in experimental systems to damage the cornea and lens of the eye. Chronic
exposure to UV-B (resulting in a high, cumulative, lifetime dose) is one of several factors clearly
associated with the risk of cataract of the cortical and posterior subcapsular forms. Estimates of the
effect of ozone depletion on cataract have been made, but are still highly uncertain. (As stated in the 1989
report, [van der Leun, et al., 1989] these estimates predict an approximately 0.5 % increase in cataract for
each 1% sustained decrease in ozone.)

Some components of the immune system are presenijn_the skin, which makes the immune system
accessible to UV radiation. Experiments in animals show that UV exposure decreases the immune
response to skin cancers, infectious agents, and other antigens and can lead to unresponsiveness upon
repeated challenges. Suppressed immunity may occur either locally in sun-exposed skin or systematically,
at non-exposed sites. Studies in human subjects also indicate that exposure to UV-B radiation can
suppress the induction of some immune responses and may cause systemic alterations in immune function.
The importance of these immune effects for infectious diseases in humans in unknown. However, in areas of
the world where infectious diseases already pose a significant challenge to human health, and in persons
with impaired immune function, the added insult of UV-B-induced immune suppression could be
significant.

In susceptible (light-skinned) populations, the cumulative lifetime exposure to UV-B radiation is the
key risk factor for development of non-melanoma skin cancer (NMSC). This knowledge has permitted the
development of quantitative risk estimates for increases in the incidence of NMSC resulting from ozone
depletion. Using information derived from animal experiments and human epidemiology, it is estimated
that a sustained 1% decrease in stratospheric ozone will result in an increase of NMSC incidence of
approximately 2.0% The relationship between UV-B exposure and melanoma skin cancer is less well
understood and appears to differ fundamentally from that of NMSC in that it is not apparently a function
of cumulative lifetime dose but may be related to the accumulation impact of multiple high dose
exposures such as those received in sunburns. Epidcmiologic data indicate that the risk of melanoma
increase: with an increase in episodes of intense sunlight exposure, (i.e. sunburn) especially during
childhood. There is, however, uncertainty about how the relationship between these: exposures and
melano.T.A should be modeled so that the estimates of the increase in melanoma that would result from
ozone depletion are much less certain.
Introduction

As presented in detail in chapter 1, solar ultraviolet radiation (UVR) illuminates nearly everything and
everyone on the earth's surface not covered or shadowed. With stratospheric ozone depletion, increases in
the ambient levels of a particular type of ultraviolet radiation known as UV-B are likely to occur. In
humans and animals, the primary (i.e., direct) effects of increases in UV-B on health are manifest through
23
-------
those organs which are exposed to sunlight, i.e., eyes and skin. These effects occur because of the
absorption of UV-B photons by molecules in these organs and the resulting tranfer of energy to produce
changes that may be either beneficial or adverse. A direct beneficial influence of exposure is the formation
of Vitamin D in the skin, a process important to the maintenance of bone tissue. Direct adverse effects of
exposure to UV-B include snow blindness, cataract, sunburn, "aging" of the skin, photodermatoses and skin
cancer. Some effects may have both beneficial or adverse elements, depending on how they are expressed.
This applies, for instance, to the influences of UV-B radiation on the immune system. The resulting
suppression of immune reactions in the skin is beneficial in patients suffering from psoriasis, (a
hypcrproliferative skin disorder) but adverse when it affects the immune defense against skin tumors or
infectious agents. In addition, there may be indirect beneficial or adverse effects. An example indirect
adverse effect could be the increase in disease associated with the potential decrease in food production
discussed in chapter 3.

The question to be addressed by the present chapter is, what will be the human health consequences of an
increase in the UV-B radiation reaching the surface of the earth? One cannot simply say that all effects of
UV-B radiation will change in proportion to the increase in radiation, because in many cases, the
relationship between the amount of exposure and effect is non-linear. For example, exposure of the skin
to UV-B radiation results in a hyperproliferation of skin cells and increased pigment production
providing the skin with efficient protection against sunburn through the increase in the UV absorbing
molecules, keratin and melanin. The hyperproliferation of skin cells may, however, also render the skin
more susceptible to cancer. In some instances, the modifying influences may be so strong that greater doses
of radiation lead to smaller effects.

Due to such complications, and due to the limited knowledge we have on some of the effects of UV-B
radiation on humans, the overall consequences of an increase of UV-B irradiance on health cannot be
predicted in a straightforward manner. This section, therefore, presents both qualitative and quantitative
answers to the question of what the consequences of stratospheric ozone depletion and its accompanying
increase in UV-B may be for human health. Quantitative estimates of UV-B effects are presented for
non-melanoma skin cancer; however, the impact of UV-B exposure on other effects has been treated
qualitatively. It should be stressed that the dependence on qualitative estimates for some effects does not
imply that these arc less significant; indeed, the quantitative estimates should be treated very cautiously
because they involve many assumptions, are based on data mainly from the United States, and may not be
representative of all regions of the world.

Ocular Effects

Background

Perhaps the best documented short-term ocular effect of exposure to UV radiation (especially UV-B
and UV-C) is photokeratoconjunctivitis ('snow blindness' and 'welder eyes'), i.e., an inflammatory
reaction (a reddening) of the surface of the eyeball. Extraordinarily painful, one episode should be
sufficient to induce behavior modification to prevent recurrences, e.g., the use of proper eye protection.
The effects of long-term or chronic exposures, e.g., pterygium or cataract, are less well documented in
part because they result after many years of exposure, and, in part, at least for cataract, because many other
factors arc known to have etiologic role. For such endpoints, as with endpoints such as NMSC, causality
has to be inferred from epidemiological studies supported by animal experiments. For a much more
detailed review of this subject, the reader is referred to Pitts and Kleinstein [1993].

Epidemiological Data

Sun exposure is also thought to be a contributing factor in the development of cataract, an opacity in
the crystalline lens of the eye (for an extended analysis, see Dolin 1994}. The World Health Organization
(WHO) estimated in 1985 that cataract was the main cause of avoidable blindness, responsible for 17
million cases of blindness worldwide (about half of the total) [Maitchouk, 1985J.

The etiology of cataract in humans is multifactorial; increased relative risks are associated not only
with increased exposure to UV-B, but also with increasing age, diabetes, renal failure, severe diarrhea, ~~
heavy smoking, hypertension, high alcohol consumption, excessive heat, and malnutrition [e.g., Harding
and Van Heyninjen, 1987]. The increase in relative risk associated with increased UV-B exposure is 1.3
to 3.5-fold, compared to diabetes which has a relative risk increase of approximately 10-fold. However,
because of the nearly universal exposure of humans to solar UV radiation, the size of the population
likely to be affected by this factor is significantly greater than for any of the other factors (except age)
listed above.

In comparing epidemiological s'udies, two things must be kept in mind: 1) there are differences in the
precise definition of cataract since the form of the disease can vary from small opacities which do not
impair vision to a completely opaque lens with severe loss of vision, (furthermore, there can be variation
between clinicians, and techniques; future studies would benefit from standardization of classifications)
and 2) there are different types of cataract that show differing associations to the factors discussed above.
Exposure to solar UV radiation appears specifically to increase the risk of cortical opacities (including
opacities not impairing vision): a clear UV dose-related trend in risk was established in a well designed,
cross-sectional study of Chesapeake Bay watermen [Taylor et al., 1988]. This UV exposure-associated
increased risk of cortical opacities was confirmed for the male population in the Beaver Dam Eye Study
(an odds ratio of 1.36 between numbers with 'high versus low exposures', 95 percent confidence interval'
1.07-1.79), but the risks of other types of lens opacities, i.e., nuclear and posterior subcapsular cataract,
were not detectably increased by UV exposure [Cruickshanks et al., 1992].

The relationship between sunlight exposure and vision-impairing cortical cataract was confirmed in a
large case-control study drawn from three Italian optEatmology clinics [Italian-American Study Group, '
1991]. Increased odds ratios for cortical cataract were found for working outdoors (1.75, 1.15-2.65) and
spending leisure time in sunlight (1.45, 1.09-1.93); these increased odds ratios were also found for the
mixed cataract, but not for posterior subcapsular and nuclear cataract. However, posterior subcapsular
cataract is relatively rare, making detection of risk in a small population difficult. In a special
case-control study in the Chesapeake Bay area on 168 surgical cases involving this type of cataract, a
highly significant (p = 0.006) positive trend was established between risk and exposure to ambient UV
radiation [Bochow et al., 1989].

The relationship between geographical location (latitude) and prevalence of cataracts has also been
attributed to ambient UV radiation; e.g., in Aborigines [Hollow and Moran, 1981] and in the North
American population [Hitter, et al., 1983J. The latter study provided the basis for the USEPA risk estimates
for increases in cataract from ozone depletion [USEPA 1987].

Experimental Data

There is ample experimental evidence that UV radiation can damage the lens and that in rabbits the
active portion of the solar spectrum lies in the UV-B region [Pitts et al., 1977]. In albino mice, regular
UV-B exposure (1 to 2 months of daily exposure) can disrupt the anterior (frontal) part of the lens,
resulting in opacities [Jose and Pitts, 1985]. High dose, daily UV-A exposure also induced opacities in the
anterior lens of nocturnal animals and squirrels [Zigman et al., 1991]. However, experimentally-induced
opacities in animals are located centrally in the anterior lens (the irradiated zone), whereas human
anterior cortical cataracts tend to form in the periphery (the equatorial region) of the lens. Also,
microscopic examination of experimental cataract commonly shows marked disruption of the lens
epithelium and inward folding of the underlying cortical fibers, which is not seen in human cataract. These
differences, while possibly attributable to differences between animals and humans in geometry, level of
exposure and/or ocular structure, contribute to the uncertainty associated with extrapolating from data in
mice to human cataract risk.

Solar UV Exposure of the Human Eye

25
-------
sight. Highly reflecting surfaces increase the exposure dramatically; for example, the risk of
photokcratoconjunctivitis is strongly increased over snow surfaces [Sliney, 1987]. This variability in
exposure can seriously complicate studies in which eye exposures in different environments are compared
unless careful exposure measurements are made. [Kosenthal et al., 1991].

In humans, the anterior eye is not only exposed to light entering along the line of sight, but also to
light impinging from very oblique angles. Coroneo [1993] drew attention to the phenomenon in which
impinging (UV) light, especially that entering the eye at a very oblique angle, can be focussed onto the
overlying periphery of the cornea and the lens; this would intensify the light while it is traversing the
cornea and the lens in a direction roughly perpendicular to the line of sight. This phenomenon could
explain not only the sites of preference for pterygium and climatic droplet keratopathy, but also why many
cortical cataracts occur in the nasal quadrant of the lens [Scbein et al., 1994, Adamson et al., 1991, Hollow,
1989, and personal communication with Dr. B. Klein for the Beaver Dam Eye Study].

Impact of Ozone Depletion on Eye Conditions

In view of present data, it is prudent to consider that a depletion of the ozone layer could be associated
with an increase in the incidence of cataract and other ocular effects of UV-B, e.g., pterygium and snow
blindness. It is, however, difficult to estimate the magnitude of the increase without adequate information
on the wavelength dependence of these effects and proper dose-response relationships. In the case of
cataract, by assuming a certain wavelength dependence and with some additional assumptions, one can
produce an estimate based on epidemiological data (e.g., an estimate from EPA based on Hiller et al.,
[1985], cited in van der Leun [1989], and one from van der Leun and de Gruijl, [1993], based on Taylor et al.,
[1988], and Pitts ct al. [1977]: 0.3-0.6% and 0.5% increase in cataract, respectively, for every 1% decrease
in ozone) but such an estimate has a high degree of uncertainty. A similar quantitative estimate is not yet
possible for snow blindness, pterygium and climatic droplet keratopathy because of the inadequacy of
epidemiologic information and experimental data. Nevertheless, it is prudent public health policy to
indicate to medical personnel and the lay public that these are effects which may well increase with
increased exposure to UV-B.

Immunological Effects ~"~

Background

Through a variety of complex, delicately balanced mechanisms, the immune system helps maintain
health by protecting the host against infectious diseases and some cancers. The two most important of
these mechanisms are 1) humoral immunity, involving the production of antibodies that can neutralize
toxins, kill microorganisms, prevent infection, and assist in the elimination of infectious agents, and 2)
cellular immunity, involving the production of chemical mediators (cytokines) by lymphocytes which
activate other cells of the lymphoid system to kill pathogens, virus-infected cells, and cancer cells. These
two arms of the immune response, humoral and cellular, are delicately balanced, and some cytokines
involved in activating one pathway tend to inhibit the other. A severe imbalance in either direction can lead
to pathological conditions, such as allergies and inflammatory and autoimmune diseases.

Immunomodub.tory Effects of UV-B Radiation

flive is now ample evidcn • i!i.-t exposure of humans and experimental animals to UV-B radiation
fti, ! ar.ifiual or natural sources ca: modify the immune system both at the site of exposure (locally) as
v-.!i as systemically, mainly by decreasing cellular immune responses [Hersey et-al, 1983; Morison, 1989;
Kripke, 1984, 1990; DeFabo and Nosnan, 1993; Cruz and Bergstresser, 1988]. The immunosuppressive effects
Ot UV-B radiation have been shown to play an important role in determining the outcome of both
melanoma [Donavrbo and Kripke, 1991] and non-melanoma skin cancer [Kripke, 1984; 1990; Fisher and
Kripke, 1982], certain infectious diseases [Jeevan and Kripke, 1993], and some forms of autoimmunity
[Ansel et al., 1985] and allergy, e.g., delayed type hypersensitivity [Kripke, 1984; Cruz and Bergstresser, 1988,
Noonan et al., 1981] in laboratory animal models of these diseases. Furthermore, introduction of a foreign
substance (antigen) during a critical period after UV irradiation can lead to immunological tolerance,
rendering the host unresponsive to re-introduction of the same antigen at a later time [Kripke, 1984].
26
-------
In addition to these systemic effects on immune responses, UV-B irradiation can also inhibit local
inflammatory responses within UV-irradiated skin; thus, the response elicited by injection of antigen into
the skin of sensitized individuals (delayed hypersensitivity response) may be diminished in UV-irradiated
skin [Morison, 1989]. Such local effects of UV irradiation can also decrease resistance to the growth of
cancer cells, including melanomas [Donawho and Kripke, 1991].

Information on the UV-induced alterations in immune function in humans is fairly limited and is drawn
principally from experimental studies of the impact of UV exposure on natural killer cell activity,
contact allergy (e.g., poison ivy) and delayed hypersensitivity responses (e.g., the tuberculin skin test -
reaction) [Hersey et al., 1983; Morison, 1989; Toshikawa et al., 1990; Cooper et nl., 1992].

Mechanisms

In recent years, many advances have been made in our understanding of the cellular and molecular
mechanisms involved in modulation of immune responses by UV-B exposure. Studies with mice provide
strong evidence that at least some of the immunomodulatory effects of UV irradiation result from the
production and release of immunologically-active cytokines and other substances from cells in the skin
Interlcukins 1 and 10 (IL-1, IL-10), tumor necrosis factor (TNF)-alpha, urocanic acid (UCA), and
prostaglandins have all been suggested as contributors to the altered immune responses observed in
UV-irradiated animals [DeFabo and, Noonan, 1983, 1993; Rivets and Ullrich, 1992, 1994a; Noonan et al
1988; Vermeer and Streilein, 1990; Luger cm A Schwartz, 1990J.

The ability of UV-irradiated keratinocytes to produce IL-10 [Rivas and Ullrich, 1992] is particularly
noteworthy, because this cytokiue preferentially decreases delayed hypersensitivity responses, leaving
humoral responses undiminished [Mossman et al., 1991 J. IL-10 is thought to alter the cells that initially
take up antigens (mainly macrophages, epidermal Langerhans cells, and dendritic cells in lymphoid organs)
and inhibit their ability to stimulate the subset of murine helper T lymphocytes responsible for generating
delayed hypersensitivity responses (Thl cells), while leaving intact their ability to stimulate Th2
lymphocytes, which are involved in antibody formation and suppression of Thl'cells [Ullrich, 1994; Rivas
and Ullrich, 1994]. Figure 2.1 presents one possible model for how these various factors and events may
operate in UV-B induced immunosuppression. —-—
UV

SKIN
LOCAL
ENVIRONMENT
DNA
tUCA
CYTOKINES

(IL-10)

Other
Mediators

c-UCA
LC, altered antigen
presentation

inflammatory cells
DISTANT
SITES
Altered antigen
presentation
DTH suppress!;-:. r.,..
antibodies

Fig. 2.1. Model for UV-B Induced Immunosuppression. (See text for details; Cm and Dotysiresser, 1988' Kripke 1984'
DeFabo andNoonan, 1993; Lugerand Schwartz, 1990; Rivas and Ullrich, 1994)

There is also evidence that the cis-photoisomer of UCA can alter the ability of antigen-presenting
cells to stimulate T lymphocytes [Noonan et al., 1988] and that TNF-alpha [Vermeer and Streilein, 1990]
can alter the migration pattern of antigen-presenting cells in the skin (epidermal Langerhans cells). Direct
exposure of epidermal Langerhans cells to UV-B radiation may also alter their antigen-presenting activity
[Stmon et at., 1990; 1991], and UV irradiation of the skin induces an inflammatory response that attracts
other types of antigen-presenting cells into the UV-irradiated site [Cooper et al. 1993].
27
-------
Thus, UV radiation appears to alter the induction of immune responses by perturbing the balance of
factors that normally regulate the immune response and by altering the activity and distribution of the cells
responsible for triggering these immune responses. The mechanisms involved in the local inhibition of
delayed hypersensitivity and tumor resistance are unknown, but they are likely to involve local
modifications of cytokines and other mediators [Luger and Schwartz, 1990] and changes in the expression
of adhesion molecules on cells of various types in the skin [Krutmann et al., 1992J.

The molecular events that initiate photoimmunological effects are incompletely understood. Studies in
the mouse [Kripke et at., 1992; Tarosh et al., 1994] and the opossum [Applegate et al., 1989] demonstrated -
that increasing the repair of UV-specific lesions in DNA abrogated the suppression of contact allergy and
delayed hypersensitivity reactions, implying that UV-induced DNA damage is an essential initiating step.
These authors hypothesized that DNA damage may trigger the production of immunoregulatory cytokines in
the skin [Kripke et al., 1992].

Another mechanism by which UV irradiation could initiate immunosuppression is by converting
trans-UCA to its cis-isomer. Trans-UCA is present in large quantity in mammalian epidermis; the more
soluble cis-isomer is formed upon absorption of UV radiation. There is considerable evidence that
cis-UCA suppresses certain immune reactions in mice, suggesting that UCA may also mediate some of the
immunomodulatory effects of UV irradiation [DeFabo and Noonan, 1983, 1993].

Wavelength Dependence of Immune Suppression

The two molecular mechanisms proposed for initiating immune suppression (DNA damage and UCA
isomerization) imply different wavelength dependencies, which in turn, give different Radiation
Amplification Factors (RAFs); see Chapter 1). If DNA damage were the sole mechanism by which UV
radiation caused immune suppression, then the percent increase in innumosuppressive UV radiation per
percent ozone depletion (RAF) would be between 1.2 and 1.7. On the other hand, if UCA isomerization
were the sole mechanism, the RAF would be between 0.4 and 0.8 (See Table 1, Chapter 1). The most
detailed action spectrum for immune suppression was determined for systemic suppression of contact
allergy in the BALB/c (albino) mouse strain, using wavelengths between 254 and 320 nm [DeFcibo and
Noonan, 1983] (See Figure 2.2). Another action spectrum-for local suppression of contact allergy in a
different mouse strain has also been measured [Elmets et al., 1985]. However, neither action spectrum can
distinguish among the two proposed mechanisms or a composite mechanism with absolute certainty, partly
because of a lack of detailed information concerning the effect of wavelengths >320 nm. At present, there
is no information available on the action spectrum for immune suppression in humans.
28
-------
10
$ 0.01
0.00 i
0.0001
_L
suppression DTH
absorption UCA
in vivo t- •*• c-UCA
in vivo pyr. dimers
250 260 270
280 290 300 310 320

wavelength (nm)
330 340 350 360 370
Fig. 2.2. Action spectra of possible importance to immunosuppression: suppression of CH (-o-) and absorption UCA (....)
[DeFabo and Noonan, 1983], in vivo trans- --> cis-UCA (*) [Gibbs et al., 1993], pyrimidine dimers in skin
[Freeman et al., 1989]

Infectious and Other Diseases — =--

The finding that UV-B irradiation of laboratory animals and humans could impair the induction and
elicitation of certain types of immune responses raised concerns that immunity to infectious agents might
also be impaired. Theoretically, UV-B irradiation could affect the pathogenesis of infectious diseases by
modifying the defense mechanisms of the host to a microbial pathogen or by directly activating an
infectious organism present within exposed skin. Evidence for both effects has been provided in model
systems, but data in humans are still very limited.

Effects of UV in Experimental Models

Viral diseases

Because of the ability of UV radiation to activate herpes simplex virus (HSV) infection in humans
[Perna et al. 1991], experimental models of this infection have been studied extensively. Exposure to UV
radiation triggered active disease in mice with latent HSV infection, decreased the delayed hypersensitivity
response, induced suppressor T cells to HSV, and impaired resistance to initial infection [reviewed in
Jeevan and Kripke, 1993 J. UV irradiation also decreased cellular immunity to reovirus infection in mice;
however, clearance of systemic virus was unimpaired, suggesting that antibody may be more important than
cellular immunity in controlling this infection [Letvin et al., 1981]. Reports that the AIDS virus could be
detected in epidermal Langerhans cells in the skin of HIV+ persons [Tschachler et al, 1987] raised concern
that UV-B irradiation might accelerate the course of this disease. Although there is no evidence to
support this possibility in humans, one study in mice suggested that the course of an AIDS-like immune
deficiency was accelerated by chronic UV irradiation [Brozek et al., 1992]. The study showed that
UV-irradiated mice developed antibodies against a murine retrovirus earlier than non-irradiated control',
suggestive of more rapid disease progression.

Virus activation by UV

In addition to decreasing host resistance to infection by means of its immunomodulatory effects, UV-B
radiation has the ability to activate latent viruses contained within cells exposed directly to UV. This
phenomenon, which has been demonstrated in vitro [Zmudzka and Beer, 1990; Schmitt et al., 1989], would
be expected to affect viruses present in cells of the skin, such as papillomaviruses, herpes simplex virus,
and perhaps HIV, which can be present in epidermal Langerhans cells [Tschachler et al., 1987]. In vivo
29
-------
activation of HIV in the skin has been demonstrated in transgenic mouse models, in which UV irradiation
turned on genes involved in virus activation and replication in the skin [Morrey et al., 1991; Vogel er al.,
1992]. These studies have raised the concern that exposure of HIV-infected persons to UV radiation early
in the course of infection, when the virus is present in the skin, might accelerate the course of AIDS.
However, there is at present no experimental evidence to support this possibility. Thus, the likely impact
of increased UV-B radiation on HIV infection resulting from viral activation remains unknown.

Parasitic infections

UV-B induced immunosuppression has been shown to have an impact on leishmaniasis [Ginnnini, 1986;
Gio-nnini and De Fabo, 1987], malaria (B. Ward, personal communication) and trichinosis [Goettsch et al.,
1994J, but not on schistosomiasis [Jeevan et al., 1992]. Leishmaniasis, a tropical parasitical disease has
been studied in some depth using a mouse model. In humans, the parasites are deposited intradermally by
infected sandflies, where they induce ulcerating, cutaneous lesions. The infection may be limited to the skin
or can progress to a systemic disease, which may be fatal. In different mouse strains, the organism can
produce either a self-limiting disease controlled by cellular immunity or a progressive, lethal infection.
The outcome depends upon what type of immune response the particular strain of mouse mounts against the
parasite: a Thl response leads to immunity, whereas a Th2 response leads to disease progression. UV
irradiation of mice before and after infection through exposed tail skin improved the appearance of the
resulting skin lesions, but decreased the delayed hypersensitivity (Thl-type) response to the parasites
thereby decreasing clearance of the organism [Giannini, 1986]. The mortality rate was increased in infected
and UV-irradiated mice, which also exhibited decreased resistance to reinfection with the parasite
[Giiir.nini and DeFabo, 1987]. Thus, in this model, although there was a reduction in the size and severity of
the skin lesions in UV-irradiated mice, the pathogenicity of the disease was increased. Similar decreases
in the clearance of parasites have also been observed in rodent models of both trichinosis and malaria, but
not in schistosomiasis [Goettsch et al., 1994; B. Ward, personal communication; Jeevan et al. 1992].

Bacterial infections

The impact of UV-B exposures on immunity to mycobacterial infection in mice has been studied
extensively. Infection of UV irradiated mice in the hind footpad with Mycobacterium bovis BCG or M.
lefruemurium resulted in a decreased delayed hypersensitivity response and delayed the clearance of
bacteria from the lymphoid organs. Furthermore, macrophages from the spleen and peritoneal cavity of
UV-irradiated mice had a reduced ability to ingest M. bovis. A single high dose of UV radiation given 3
days before infection accelerated the rate of death from M. lepraemurium [Jeevan and Kripke, 1993J.
Similar results were obtained in a mouse model of Lyme disease. UV-irradiated mice infected with
Borrelia. burgdorfcri exhibited a decreased delayed hypersensitivity response, decreases in certain subclasses
of anti-Borre/w antibodies, and increased numbers of organisms in the joints [Brown et al., 1994; E. Brown,
unpublished data,].

Fungal Infections

The only model of fungal infection studied to date is systemic Candida, albicans infection in mice.
Candida is an opportunistic fungus normally present on the skin, which causes systemic disease in
immunosuppressed persons. Exposure of mice to a single high dose of UV-B radiation one day before a
lethal intravenous injection of Candida significantly reduced their survival time. Lower doses of UV
response to this organism, but lud no effect on the
' J9Q3; D ;:/;/», ci fi!., 1989].
.... injection __
radiation decreased the delayed hyper;
outcome of systemic disease [Denkins

Autoimmune and other diseases

The possibility exists that UV-B could reduce some R of rutuirnmunity, by virtue of its ability to
attenuate cell-mediated immunity. However, studies in exp"i!;n;'niul models of autoimmune diseases are
quite limited and only serve to underscore the complexity t>f the situation. In a study of the effects of
UV-B irradiation on the development of autoimmune hemolytic anemia in autoimmune strains of mice,
UV-B irradiation accelerated and exacerbated the disease process [Ansel et al., 1985J. In another study
using a different strain of autoimmune mice, chronic UV irradiation seemed to have no effect on the
pathogcncsis of this disease [Strickland, 1984].

In humans, UV-B is used therapeutically for the treatment of certain skin diseases, such as psoriasis,
which seem to have an immunological component. On the other hand, one autoimmune disease, systemic
lupus erythematosis is aggravated by UV exposure, and UV is involved in the pathogenesis of some
photoallcrgic and photosensitivity diseases. Thus, increased UV-B radiation is likely to have varied, and
30
-------
even opposing, effects on autoimmune ahd: other diseases, and it is presently not possible to make any
predictions as to its impact.

Effects of UV on Human Diseases

Of course, the crucial question regarding the significance of increased UV-B radiation is whether the
findings in animal studies apply to humans. It is clear that exposure of humans to natural or artificial
sources of UV-B radiation impairs the activity of T lymphocytes, decreases the activity of natural killer
cells, decreases the number of epidermal Langerhans cells, and abrogates the induction of the contact ~"
allergy response to chemicals applied onto the irradiated skin [Morison, et al., 1979; Hersey, et al., 1983;
Toshikawa, et al., 1990; Cooper, et al., 1992]. Furthermore, most of these immunological effects occur even
in persons with darkly pigmented skin, implying that pigmentation does not confer complete protection
against UV-induced immune suppression [Scbeibner, et al., 1986; Vermeer et al., 1991J so that the
population potentially at risk for an impact on infectious diseases is far greater than that for skin cancer.

There is evidence both in murine models [Streilein and Bergstresser, 1988; Noonan and Hoffman, 1994]
and humans [Yoshikawa et al., 1990] for genetic differences in susceptibility to UV-induced immune
suppression unrelated to pigmentation. Such differences may be important determinants of risk for skin
cancer development and susceptibility to UV-induced modifications of infectious diseases. .

The effects of UV-B radiation on infectious disease processes are likely to be complex and
unpredictable. Historically, UV radiation was used to treat a variety of skin diseases, most notably skin
tuberculosis, and in recent years, UV-B radiation has been used to treat psoriasis, acne, and other
cutaneous diseases. On the other hand, sunlight exposure was thought to aggravate pulmonary tuberculosis
and scarring from smallpox [van der Leun and de Gruijl, 1993J. There is also considerable evidence that
exposure to sunlight and to UV radiation can trigger the appearance of cutaneous lesions caused by herpes
simplex virus types 1 and 2 in persons already harboring a latent infection [Klein and Linnemann, 1986;
Spruance, 1985; Wheeler, 1975], and exposure to UV radiation has been reported to increase the severity
of skin lesions associated with herpes zoster infection [Szigeti et al., 1976J. UV radiation may also be a
contributing factor to papillomavirus infections in immunosuppressed patients, since such individuals have
a high incidence of viral warts on sun-exposed body s'i&r"[Boyle et al., 1984; Dyall-Smith and Varigos,
1985J. Whether these effects are a result of virus activation or immune suppression by UV or both is not
clear.

One approach to addressing the effect of UV-B radiation on resistance of humans to infection is to
analyze the effect of UV on a cell-mediated immune response against microbial antigens. Healthy
contacts of leprosy patients often exhibit a delayed hypersensitivity response upon intradermal injection
of lepromin, an antigen prepared from leprosy bacilli. Exposure of the injection site to UV-B radiation
before and after inoculation of lepromin markedly reduced the size of the skin test reaction and
granulomatous response and decreased the number of T lymphocytes within the reaction site, compared to
the reaction site in unexposed skin of the same subject [Cestari et al., 1994]. This study demonstrates that
exposure to UV-B radiation can diminish the cutaneous immune response to an infectious microorganism
in humans; however, it does not address the question of whether UV-B irradiation would also exacerbate
the disease process in persons suffering from leprosy or other mycobacterial infections.

Obviously, it will be very difficult to assess the role of UV-B radiation on natural infections in human
populations. Based on current knowledge, we would predict that an effect of UV-B radiation would
manifest itself as an increase in the severity or duration of disease and not necessarily as an increase in
disease incidence except possibly where reactivation of a latent virus is reflected as incidence. Since
infectious diseases are influenced by many host and environmental factors, the effect of UV-B radiation on
a given disease process may be difficult to discern from epidemiological studies. Clearly, more
information is needed on this subject. The growing evidence that the balance of Th?L- and Th2-type immune
responses plays an important role in dcu-nnining the outcome of various infectious diseases, and the
suggestion from animal studies that UV irradiation may shift this balance toward a Th2-type response
suggests that Uv radiation may indeed influence the pathogenesis of some diseases. It may also influence
the outcome of vaccination against infections. Whether this influence is beneficial or harmful will
probably depend on what type of immune response is most effective in protecting against a particular
microorganism. Thus, it is presently difficult to predict both the direction and magnitude of an effect of
UV-B radiation on a particular disease process.

This possibility is borne out in a study in mice demonstrating that UV irradiation could prevent the
induction of an autoimmune demyelinating disease, experimental allergic encephalomyelitis, in mice
[Hauser et al., 1984] which is a Thl-dependent disease.
31
-------
For example, photodermatoses are skin diseases where the skin lesions are caused by light. Solar UV-B
radiation is the predominant causative agent for several of these diseases. Although many patients and their
doctors expect an aggravation of these diseases with a decreased ozone layer, there are reasons to question
this expectation. In the first place, these diseases agenerally occur less frequently and with less severity in
sunny areas of the world. Second, many patients with photodermatoses are treated effectively by regular
exposures to low-dose UV-B radiation during winter. Because depletion of the ozone layer will increase
UV-B irradiancc, especially in winter, this may improve the patients' condition [van der Lettn and de
Gruijl, 1993].

UV dose-response and wavelength studies for immunosuppressive effects of UV radiation in humans are
essential for making quantitative predictions. More important still is understanding the significance of
these immunological effects for the pathogenesis of human diseases. In spite of its central importance to
the analysis of the consequences of stratospheric ozone depletion for human health, information to address
the latter issue is difficult and expensive to obtain and is thus almost totally lacking.

Skin Cancer

Background

UV radiation damages DNA (i.e., is genotoxic). This may lead to faulty replication of DNA in a
daughter cell, i.e., fixation of a mutation. Mutations in certain key genes (proto-oncogenes or tumor
suppressor genes) that regulate the cell cycle, cell differentiation, and cell death (apoptosis) can lead to
formation of a cancer cell. Recent research is beginning to reveal how these steps relate to the course of
UV-induced tumor formation.

Animal data and human epidemiologic studies clearly indicate that excessive exposure to UV radiation
is associated with skin cancer in humans. (See IARC [1992] for a comprehensive overview). The involvement
of DNA damage, for instance, was elegantly demonstrated in opossums (Monodelphis domestica] which have
an enzyme (photolyas) that reverses certain types of UV-induced DNA damage (cyclobutane pyrimidine
dimers) upon exposure to UV-A and visible light; UV-A plus visible light treatments counteracted the UV
induction of skin tumors (both squamous cell carcinomas and-melanomas). It is also known that xeroderma
pigmcntosum (XP) patients whose cells are deficient in the repair of UV-induced DNA damage have
dramatically increased risks of skin cancer (both squamous and basal cell carcinomas, and melanoma). [This
observation is, however, complicated by the fact that individuals with other kinds of defects in DNA repair
(e.g., Cockayne's syndrome and trichothiodystrophy), do not have an increased risk of skin cancer.] One
interpretation of this seeming contradiction is that deficiencies in the repair of genes that are normally
inactive, e.g., XP, leads to skin cancer, whereas deficient repair of active genes, as in Cockayne's
syndrome, is related to developmental and degenerative effects.

Non-Melanoma Skin Cancer

There are two main types of non-melanoma skin cancer (NMSC): basal cell carcinoma (BCC) and
squamous cell carcinoma (SCC). In most countries, reporting of these tumors to a cancer registry is either
not required or inadequately standardized, resulting in inadequate cancer registry data and an inability to
track trends in incidence or mortality. Where good medical care is available, the overall mortality is
thought to be less than 1 percent. Although BCC typically represents 80 percent of NMSC, the mortality
is mainly due to SCC.

SCC has a convincing and clear-cut relationship to UV-B radiation, whereas that for BCC is somewhat
less compelling. The causative role of sunlight in SCC is supported by the observations that a) SCC occurs
predominantly on the most sun-exposed parts of the skin, face, neck and hands; and b) in comparable
populations the incidence of SCC is highest in geographic areas with the most sunlight. The observation
that SCC occurs predominantly in fair-skinned people is consistent with this conclusion. The risk of
developing SCC appears strongly related to the total dose of sunlight received in the course of a lifetime.
In addition, in animal models, exposure to UV radiation is associated with the development-of SCC and
not BCC.

The evidence is less clear-cut with BCC, which rarely appears on the well-exposed backs of the hands,
but instead occurs more on the face and neck areas, with a fair percentage developing on the trunk. Also,'a
person's most recent history of sun exposure (the preceding 10 to 20 years) relates better to the risk of
developing SCC than BCC. [Vitasa, et al., 1990]. This may be interpreted to mean that UV radiation is
somehow related to an "early event" in the development of BCC, after which other "events" (including
growth) must occur before the tumor develops.
32
-------
I -3
o.oi-
0.001-
| 0.0001

0.00001
0.000001-
\ melanoma
SCUP-m
250
300
350
wavelength (nm)
400
•450
Fig. 2.3. Action spectra for cancer in animal models: Melanoma in fish [Setlow et al., 1993], non-melanoma skin cancer in
mice - SCUP-m [DeGruijI et al., 1993], and in humans -SCUP-h [DeGruijI and van der Leun, 1994]
Important molecular evidence for the role of UV-B in the induction of these tumors is that large
percentages (>50 percent) of SCC and BCC in humane-bear UV-specific mutations (i.e., at dipyrimidine •
sites where cytosine is replaced by thymine, a C-to-T transition) in their p53 tumor suppressor gene. This
constitutes the most direct evidence that UV radiation causes skin cancer in humans. Furthermore, it was
found that in mice these types of mutations already exist in the precursor lesions of SCC, implying that
UV irradiation can be an early event in the development of the tumor. Strikingly, it has recently' been
shown that certain UV-related mutations (tandem transitions of CC-to-TT) can be detected in sun-exposed
skin of skin cancer patients (17/24 in Australia), but are virtually non-existent in unexposed skin (1/20).
et al., 1994].
Information on the wavelength dependence of the UV induction of cancer is crucial for quantitative
risk assessments; however, it would be both impractical and unethical to derive such information from
experiments in humans. Several groups have developed such action spectra based on tumorigenesis in
hairless mice, with the most complete spectrum being that published by De Gruijl and his colleagues
[1993], and presented as the Skin Cancer Utrecht-Philadelphia (SCUP) action spectra (see Figure 2.3).
The carcinogenicity for wavelengths over 340 nm was somewhat higher than expected from constructed
action spectra (mutagenicity corrected for epidermal transmission), which could be due to an increased
level of indirect-, radical-mediated damage in vivo. More recently, the SCUP action spectrum has been
cwc-ctcd for differences in epidermal transmission between mouse and human, thus a SCUP-h was derived
ft ... the SCUP-m action spectrum ('h' standing for human and 'm' for nuuine). [De Gruijl and van der
Lcitn, 1994]. This correction nv.:.o U- c;-;::;u',_. ;! to represent a crude average, because the epidermal
transmission will vary both, in In...,...-, ?,ud incuse from one individual to another, and it will decrease under
regular UV exposure.

In relation to a depletion of the ozone layer, it is important to quantify how much more carcinogenic
UV radiation reaches the ground level for each percent decrease in ozone. For NMSC, annual doses are
assumed to be an appropriate measure, and personal doses are assumed to be proportional to ambient
doses. This increase in carcinogenic dose is expressed by the Radiation Amplification Factor (RAF), which
equals 1.4 for SCUP-m-weighted UV doses and 1.2 for SCUP-h-weighted UV doses (i.e., 1.4 or 1.2
percent more carcinogenic UV radiation for each percentage decrease in ozone; see also Chapter 1).
Next, the relationship between skin cancer incidence and an increase in carcinogenic UV radiation must be
determined. For stationary situations, this is estimated from incidence data in comparable populations
living at different geographical locations under different levels of solar UV exposure comparable in
genetic composition, lifestyle, etc.). Estimates for the white population in die United States predict that
for every 1 percent increase in annual carcinogenic UV radiation, the SCC incidence over a human

33
-------
lifetime will ultimately rise by 2.5±0.7 percent, and the BCC by 1.4±0.4 percent, based on SCUP-h (for
SCUP-m-weighted doses, the numbers are virtually the same). These latter numbers are referred to as the
Biological Amplification Factors (BAF). Multiplying the RAF and BAF gives the overall Amplification
Factor (AF), the ultimate, predicted increase in skin cancer for each percent decrease in ozone. For SCC,
AF equals 3.0±0.8 percent; for BCC, AF is 1.7±0.5 percent, and for all nonmelanoma skin cancers
combined, AF is 2.0±0.5 percent. With approximately 1.2 million new cases each year worldwide
[Longstreth et al., 1991], this would amount to 250,000 additional cases each year from a sustained 10
percent decrease in average ozone concentration [for more detail, see Madronich and De Gruijl, 1993].

It is also worth noting here that there are subpopulations of individuals at very high risk of developing
NMSC, who will be greatly affected by an increase in ambient UV-B radiation. As noted above, persons
with the rare genetic disorder XP are exquisitely susceptible to the development of UV-induced NMSC
early in life and often die of this disease. A much larger population at high risk are renal allograft
recipients and other immunosuppressed individuals, who tend to develop multiple, aggressive, and often
fatal SCC on sun-exposed skin at a relatively young age. Increased UV-B radiation is likely to be
especially hazardous for such high-risk persons [Glover et al., 1994].

In reality, the projections suggest not a sustained decrease, but rather a transient seasonal decrease in
ozone that will vary substantially over the globe, reaching its maximum in early spring at the poles. The
concentration of ozone in the stratosphere is projected to reach a minimum around the year 1998, and will
normalize to 1980 levels around the middle of the next century (see Chapter 1). Increases in UV-B
associated with these ozone losses are likely to cause a delayed transient increase in skin cancer incidence.
Besides knowledge of the UV dose dependency, information on the time dependency of the response after
changes in the ambient UV load is also needed. Such information is not ^available for human populations,
and additional hypotheses must be introduced to extend the model to time-dependent responses. To a
certain extent, animal experiments can assist in providing this extension of the model [De Gruijl and, van
der Leun, 1991], however, certain assumptions as to how the animal data translate to human responses are
still required. Although more work should be done in this area, a plausible model estimates that a steady
increase in nonmelanoma skin cancers will occur even under the most recent international agreement with
regard to the phase-out of ozone-depleting substances, reaching a 25 percent higher level in the year 2050
in comparison to 1980 at approximately 50 degrees NL [Slater et al., 1992] see Figure 2.4.

Melanoma

Cutaneous melanoma (CM) is the result of the neoplastic transformation of melanocytes, the
pigment-producing cells in mammalian epidermis. There are four different categories of CM in humans: 1)
superficial spreading melanoma (SSM) 2) nodular melanoma (NM) 3) lentigo maiigna melanoma (LMM)
also known as Hutchinson's melanotic freckle) and 4) unclassified melanoma.

The etiology of LMM appears to be similar to that of NMSC in relation to sun exposure, whereas that
of SSM and NM appears to be different in that it appears linked more with intermittent, intense
exposures (i.e., severe sunburns) and/or exposures in childhood (for a comprehensive overview, see IARC
1992; USEPA, 1987; IBMC, 1992; or Elwood, 1993).
34
-------
700
600
500
'
.400
s
§ 300
-200
CO
1 100
Montreal
London

Copenhagen
1950
2000
2050
2100
year
Fig. 2.4. Estimated increase in NMSC incidence under 3 CFC-phaseout scenarios. [Slaper et al,, 1993]

In the case of SSM and NM, evidence supporting an etiologie relationship with solar (UV) radiation
includes: *

1) the fact that in general, people light-skinned individuals who are more sensitive to sunburn run a higher
risk; in such individuals irregularities in pigmentation, i.e., freckles, a high number of moles (nevi),
and/or atypical nevi, contribute especially strongly to the risk.
2) high levels of solar exposure during childhood (before ages of 15-20 years, and possibly especialiv
intense intermittent exposures) is strongly associated with increased risk (e.g., Holman and Armstrong,
1984), and increases the number of nevi (potential precursor lesions) that a person develops (Gallagher
et al., 1990).
3) the risk is often higher for indoor workers than for outdoor workers, and can be associated with
(intense) intermittent exposure to the sun in leisure time.
4) positive correlations between ambient UV levels (e.g., latitudinal gradients) and CM in sensitive
populations.
5) high risk in XP patients who are deficient in repairing DNA damage inflicted by UV radiation (see
£ 11) . J. ).
6) mutations in the N-ras gene at di-pyrimidine sites (the target sites, of UV-B radiation in DNA) in
SSM and NM occurring in sun-exposed skin (Van't Veer et al., 1989).

The hypothesis that intermittent UV exposure is important for the risk of CM was largely inferred
from the locations of CM over the body (relatively large numbers on irregularly exposed sites) and more
occurences in indoor workers than in outdoor workers. Later confirmation of this hypothesis is, however,
. solely based on studies in which patients and control groups were retrospectively interviewed; thus, these
studies are vulnerable to recall-bias-after having contracted a CM, people tend to remember more
sunburns than before [Weinstock et al., 1991].

In the U.S., incidence rates for CM among white-skinned populations during the decade from 1974 to
1986 increased at an average yearly rate of 34 percent (varying from -2 to -7 1/4 %. Increases in mortality
during that time period showed a similar trend, although a slower rate. More recently, Scotto et.al. [1991]
have analyzed trends in skin melanoma death rates by cohort for fair-skinned ("white") males and females
over a 35-year period (1950-1984) and observed upward trends for older men and women (over 40) and
downward trends for the younger cohorts. Assuming no life-style changes and constant UV radiation levels,
these authors project that the 2 to 3 percent upward trend in mortality per annum observed since 1950 will
discontinue and bend downward by the second decade of the 21st century.
35
-------
This information is critical to assessing the risks of stratospheric ozone depletion, which would clearly
need to incorporate cohort data and age-specific trend analyses into the baseline data used in such an
activity. This same sort of cohort analysis information is also critical to estimating the potential
increases in non-melanoma skin cancer; unfortunately most countries are not collecting sufficient data on
non-melanoma skin cancer to be able to perform such trend and cohort analyses.

Animal Models for Melanoma

In the past few years, several animal models have been developed in which primary cutaneous melanomas '
can be induced by UV radiation alone or in combination with cancer-inducing chemicals. The most
interesting of these involves the induction of melanoma by UV-B radiation in Monodelpbis domestic^, the
grey, short-tailed, South American opossum [Ley et aL, 1989J; see below.

Another animal model in which melanomas can be induced with UV radiation is the tropical fish model
of Sctlow [Setlow et aL, 1989]; see below.

As described in the 1991 UNEP panel report [Longstreth et al., 1991], primary melanomas can be
induced in mice using a combination of UV radiation and chemicals, but UV radiation alone has so far
been ineffective [Romerdahl et al., 1989]. These and more recent studies [Donawho and Kripke, 1991;
Hasan et al.s 1992] indicate that UV radiation may play several different roles in the induction of murine
melanomas, including that of an initiator, a tumor promoter, and a co-carcinogen that contributes to
melanoma development by means of its immunosuppressive effects.

The animal models are instructive because they demonstrate that UV radiation can contribute to the
induction of melanotic tumors in a variety of ways. However, they are not very helpful for assessing
increases in melanoma incidence in humans exposed to increased UV-B radiation. In the opossum model,
the dose-response and wavelength data are inadequate for making such calculations, and extrapolation of
the information from the fish model to humans is obviously fraught with difficulties.

Wavelength Dependency of Melanoma

Animal experiments have not yet yielded results that unambiguously indicate mechanism(s) by which the
UV radiation may be causing CM in humans. The wavelength dependence of the induction of CM is
important for risk assessments, but conclusive data are not available, and the wavelength dependence cannot
be confidently constructed from presumed mechanisms.

In hybrid fish of the genus Xiphophorus a single, early in life UV-A exposure is quite efficient in
evoking melanomas; a UV-B exposure is only 10 to 50 times more effective (per J/m^, i.e., this action
spectrum is relatively flat when compared with the SCUP action spectra, see Figure 2.3; Setlow et al.,
1993). These experiments were, however, contaminated by the aquarium lighting. This lighting contributed
to a high background occurrence of melanomas (in about 25% of the fish), and possibly even counteracted
the induction of melanomas by UV-B radiation the fish have photolyase). In the opossum Monodelpbis
domcstica, melanomas can be induced by chronic broadband combined UV-B/UV-A exposure; such tumors
do not develop when the animals are kept solely under yellow light. Visible light exposure after each UV
exposure counteracts the development of the UV-induced melanomas, which would indicate that UV-
induccd di-pyrimidine dimers cause melanom:-:. If th'-se dinars are the main DNA lesions causing mela-
nomas in human skin, then the reversal b, ;'. ' '. ':'••'' : '•- nr<: !i'--'?ly to occur (humans appear not to have
photolyase, [Li et al, 1993] although thi> i, ;. . ".; of:, . •. :.L,,;vcrsy). The action spc-ii.um in humans
could then follow the induction of ihc.,; ];NA lesions in '.I... >!;-\, and would presumably i-.-•-. ' :. \
SCUP action spectra more than the one found for the ni.-.'.Miomas in fish (for comparis.,:i ;,cc i ,>••• ,'..-'...

It is conceivable that UV radiation may contribute in various ways to the induction of melari'. .••:,.:
that the specific mechanisms differ in the two animal models. Although it is difficult to induce > ' 's...;un
in mice by UV irradiation, it can be done quite efficiently with exposure to chemical carcinogens, and
concomitant UV exposure can then promote the melanomagenesis.

How these experimental data should be extrapolated to humans is, of course, very much an open
question. CM in humans may well have a multifactorial etiology. Although UV radiation is likely to play a
dominant role, (e.g., initiating precursor lesions during youth and suppressing immunity to the tumor cells
as a result of a sunburn in the final stage of tumor development), other factors may affect expression of
the UV effect.
36
-------
Related Issues

The majority of this chapter has been devoted to a review of the potential human health effect of the
increased ultraviolet radiation which may result from stratospheric ozone depletion. There are, however,
other health issues associated with this stratospheric ozone depletion. This section addresses four such
issues. First, animal populations beyond humans are potentially affected by increased UVR which can lead
to impacts on agricultural productivity. Second, the effects on human health of increased UVR, can be
potentially mitigated by appropriate changes in behavior. Third, although most ozone depleting substances
(ODSs) are scheduled for complete phase out by 1995, methyl bromide is not yet subject to complete "~
phase out. Its toxicity is of some concern, so has been included in this dicussion. Fourth, the chemicals
which replace ODSs may themselves have toxicity, so a brief synopsis of information known about them is
also presented.

Effects on Animals

Animals of several species develop skin cancer, mainly SCC, in sparsely haired, light-colored areas of
the skin. This includes cows, goats, sheep, cats and dogs [Etnmett, 1973; Dorn et al, 1971; Nikula et al.,
1992]. The body distribution is consistent with sunlight as the etiologic agent; UV-B is implicated by
extrapolation from studies with laboratory animals. Cancers of the eye also occur in many animal species,
including horses, sheep, swine, cats, and dogs, and are particularly frequent in cattle [Harris, 1981]. In rats,
mice, hamster, and the opossum (Monodelphis domesticus), studies on the induction of skin cancer with
mainly UV-B radiation have sometimes induced ocular tumors as well [Ley et al., 1989]; [Blum, 1943];
[Freeman and Knox, 1964]. Photokeratitis and cataract have been induced experimentally in rabbits, with
the most effective wavelengths falling mainly within the UV-B range [Pitts et al., 1977]. Bovine infectious
keratoconjunctivitis, an eye infection caused by the bacterium Moraxella bovis, is triggered and aggravated
by UV-B irradiation of the eye [Hughes, et al., 1965].

In animals in which these effects occur under natural conditions, an increase in UV-B irradiation would
be expected to exacerbate them. However, it is not possible to estimate the magnitude of such effects
because of the paucity of information on dose-response_arid wavelength dependence and on possible
behaviorial modifications.

Mitigation/Amelioration

The effects of increased UV-B exposure on human health may, in principle, be mitigated by reducing
the exposure time to sunlight. Being indoors gives a practically complete protection. Limiting exposure
during the hours of maximal UV-B irradiance, that is, between 2 hours before and 2 hours after solar noon
is especially effective.

Even while outdoors, there are still possibilities for protection. An important protection is offered by
constitutional skin pigmentation. Dark-skinned people are better protected against skin cancer and sunburn
than light-skinned individuals, but their pigment does not seem to protect them against some of the
suppressive effects of UV-B radiation on the immune system.

Changes in behavior also offer many possibilities for mitigation. Many clothing fabrics give good
protection. Hats are especially effective because they offer some protection of the facial skin and the
eyes, two body sites at comparatively high risk. Sun glasses of appropriate material also provide good
protection for the eyes. Being in the shade of buildings or trees also reduces the UV-B dose received.

Sunscreens may be a useful addition, especially for occasions when an unusually high exposure is
expected, such as a holiday in a sunnier area. Sunscreens are effective against sunburn. To some extent, they
may also be protective against skin cancer, as long as they are not used to prolong the exposure. Several
experimental results suggest that the effectiveness of sunscreens against the effects of UV-B radiation on
the immune system is limited. Continuous use of sunscreens with a high protection factor is sometimes
advocated, but it may be counterproductive; such "sunblocks" also block both the formation of Vitamin
D3 in the skin and the body's own defense systems, such as adaptation to the UV environment by thickening
of the outer skin layers and tanning.

Methyl Bromide

Methyl bromide (MeBr) is discussed here because of its potential contribution to ozone depletion and
its adverse effects on living organisms. Despite its ozone-depletion potential, current revisions to the
Montreal Protocol do not require phase-out of MeBr, rather production is limited to the amount
produced in 1991. A variety of countries have taken unilateral action which range in level of severity; for

37
-------
example, the Netherlands banned all soil uses in 1992, Denmark and Italy plan a total phase out in 1998
and 2000, respectively, the US will ban production and importation in January 2001, and Canada plans a
25% reduction in 1998 [US EPA, 1994]

McBr is a colorless, generally odorless, ozone-depleting gas which is widely used for fumigation of soil
(77%), commodities and quarantine facilities (12%) and sub-surface structures (5%). Current uses result in
significant releases to the atmosphere. Methyl bromide is toxic by all routes of exposure. Immediate
effects from acute exposures show a dose-dependent increase in severity ranging from dizziness, headache,
nausea, contact burns to the eyes and skin, respiratory irritation, venticular fibrillation, pulmonary edema -
(sometimes delayed for several days), convulsions, coma and death. The Time-Weighted Average
occupational limit recommended in the United States by the American Conference of Government
Industrial Hygienists is 5 ppm. Signs of toxicity in humans following chronic exposure have included
persistent numbness in the hands and legs, impaired superficial sensation, muscle weakness, unsteadiness of
gait, and depressed or absent distal tendon reflexes; however, once exposure has ceased, symptoms generally
disappear and recovery is complete [HSDB 1994].

Animals show similar signs of toxicity. Studies on horses, goats, cows and cattle fed hay or food
contaminated with various levels of MeBr (ranging from 170 to 8400 ppm) displayed symptoms which
ranged in a dose-dependent fashion and included difficulty in walking, incoordinate^ movement and gait,
listlcssness, inability to rise, and even death. MeBr is also toxic to aquatic species with acute and chronic
toxicity to salt water species occurring at levels as low as 11 and 6.4 mg/1, respectively. A similar level
for acute toxicity was found for fresh water species [HSDB 1994].

Toxicity of CFC Substitutes

As the production of fully halogenated chlorofluorocarbons (CFCs) ceases pursuant to the provisions
of the Montreal Protocol and the London and Copenhagen Amendments, a variety of potential CFC
substitutes arc likely to be introduced into the environment. The toxicity of these chemicals is of interest:
clearly, we do not want to introduce chemicals as replacements which are more problematic than those we
are replacing. Table 2.1 summarizes what is currently known about the toxicology of the more common
/9.S . stitutcs: hydrofluorocarbons (HFCs) and hydrochterofluorocarbons (HCFCs), and terpenes. Most
of this information has been drawn from references found either in the open literature or submitted to EPA
under the requirements of TSCA. In those cases with a sufficient database, EPA has derived a Reference
Concentration (RfC), which is the concentration, at which exposure for a lifetime should be without
adverse effect. The process of deriving these numbers basically involves selection of a No Observed Adverse
Effect Level (NOAEL) and dividing it by an uncertainty factor that reflects differences in individual
sensitivity, differences in species responsiveness, and inadequacies in the database (such as the lack of a
two-generation reproduction study or a Lowest Observed Adverse Effect Level [LOAEL]).

Several chemicals have been the focus of extensive animal studies. The conclusions of such studies can
promote a basis for determining the adverse human effects of these compounds. For example, HCFC-141b
/!TMO J?ined t0 decrcase reproductive performance; HCFC-124 has had transient central nervous system
(CNS) effects; and HCFC-22 exposure has increased liver, kidney, adrenal, and pituitary weights On the
Other hand, HFC-134a, HCFC-142b, and HCFC-152a have shown no signs of adverse effects.

TABLE 2.1. Update on Potential CFC Substitutes
UntMIUAL
d-Limonene
CASRN: 5989-27-5
alpha-Pinene
CASRN: 80-56-8
ADVERSE EFFECTS
according to 'he EPA_documgntatjon an ! ioview;_qf_jho in^.ljtion RfC
EPA revicv/sd the date for this chemical and determined that the requirements for
the m/-- •••'. di.l-t.jS3 n^ces^ary to develop an inhalation reference concentration
(RfC) \\--j •••:>' b-en me1, (EPA 1993). The compound is listed on FDA's Generally
Rega.-.J •; as Uafo (GRAS) list and is approved for use as a food additive (Opdyke
1975). A chronic bioassay involving exposure via oral administration resulted in
kidney damage in the male rats (NTP 1990); however, the mechanism involves
alpha2uglobulin which has been judged an inappropriate endpoint for effects
occurring in humans (USEPA 1991)
EPA reviewed the data for this chemical and determined that the requirements for
the minimal database necessary to develop an inhalation reference concentration
(RfC) have not been met (EPA 1993). The compound is listed on FDA's Generally
Regarded as Safe (GRAS) list and is approved for use as a food additive (Opdyke
1975). EPA has judged that there are no chronic studies by inhalation or oral
routes of exposure which are adequate to the development of an RfC. Contact
hypersensitivity studies in humans suggest that this compound is a contact
allergen. (Cachao et al. 1986)
38
-------
beta-Pinene
CASRN: 127-9193
EPA reviewed the data'for this chemical and determined that the requirements for
the minimal database necessary to develop an inhalation reference concentration
(RfC) have not been met (EPA 1993). The compound is listed on FDA's Generally
Regarded as Safe (GRAS) list and is approved for use as a food additive (Opdyke
1975). EPA has judged that there are no chronic studies by inhalation or oral
routes of exposure which are adequate to the development of an RfC. Contact
hypersensitivity studies in humans suggest that this compound is a contact
allergen. (Cacnao et al. 1986)
1,1-Dich!oro-2,2,2-
trifluoroethane
HCFC-123
CASRN: 306-83-2
EPA reviewed the data for this chemical and derived a verified inhalation -
reference concentration (RfC) of 10 mg/cu m (1.6 ppm)(EPA1992) based on a
chronic inhalation bioassay in which rats were administered the compound at 0,
300,1,000 or 5,000 ppm 6 hours/day 5 days/week for 2 years (Malley 1990). The
study identified a NOAEL (1,000 ppm) and a LOAEL (5,000 ppm) with the critical
effects being increased relative liver weight, focal histopathology in the liver, an
effect on lipid metabolism, and at high concentrations (5,000 ppm), CNS
depression. The European Center for Ecotoxicology and Toxicology has
completed a review of this chemical (ECETOC I994).
Chlorod'rfluoromethan e
HCFC-22
CASRN: 74-45-6
EPA reviewed the data for this chemical and derived a verified inhalation
reference concentration (RfC) of 50 mg/cu m (14 ppm)(EPA1992; EPA1994)
based on a chronic inhalation bioassay in which rats were administered the
compound at 0,1,000, 10,000 or 50,000 ppm 5 hours/day 5 days/week for slightly
more than 2 years (Tinston et al. 1981). The study identified a NOAEL (10,000
ppm) and a LOAEL (50,000) with the critical effects being increased liver, kidney,
adrenal and pituitary weights.
2-Chloro-1,1,1,2-
tetrafluoroethane
HCFC-124
CASRN: 2837-89-0
EPA reviewed the data for this chemical and derived a verified inhalation
reference concentration (RfC) of 300 mg/cu m (143 ppm)(EPA1992; EPA1994)
based on a subchronic inhalation bioassay in which rats were administered the
compound at 0, 5,000, 15,000 or 50,000 ppm 6 hours/day, 5 days/week for 90
days (Malley 1991). The study identified a NOAEL (15,000 ppm) and a LOAEL
(50,000 ppm) with the critical effects being transient CNS effects. The European
Center for Ecotoxicology and Toxicology has completed a recent review of this
chemical (ECETOC 19941. .
1,1,1,2-Tetrafluoro-ethane
HFC-134a
CASRN: 811-97-2
EPA reviewed the data for this chemical and derived a verified inhalation ref-
erence concentration (RfC) of 100 mg/cu m (71 ppm)(EPA1992; EPA1994) based
on a chronic inhalation bioassay in which rats were administered the compound at
0, 2,500,10,000 or 50,000 ppm 6 hours/day, 5 days/week for 2 years (Hext and
Mould 1991). The study identified a NOAEL (50,000 ppm) but not a LOAEL.
1,1 -Dichloro-1 -f luoroethane
HCFC-141b
CASRN: 1717-00-6
1 -Chloro-1,1 -difluoroethane
HCFC-142b
CASRN: 75-68-3
EPA reviewed the data for this chemical and derived a verified inhalation
reference concentration (RfC) of 100 mg/cu m (21 ppm)(EPA1992; EPA1994)
based on the interim report of a 2 generation reproduction study in which rats were
administered the compound by inhalation at 0, 2,000, 8,000 or 20,000 ppm 6
hours/day, 7 days/week for 10 weeks prior to first mating, unexposed for a short
interval around parturition, then exposed with the same regiment through a
second mating and delivery until the F1B offspring were 4 days old (Brooker et al.
1992). The study defined a NOAEL (8,000 ppm) and a LOAEL (20,000 ppm) with
the critical effect being decreased reproductive performance.
1,1-Difluoroethane
HCFC-152a
CASRN 75-37-6
EPA reviewed the data for this chemical and derived a verified Inhalation ref-
erence concentration (RfC) of 50 ing/eu m (12 ppm)(EPA1992; EPA1994) based
on a chronic inhalation bioassay in which rats were administered the compound at
0, 1,000, 10,000 or 20,000 ppm 6 hours/day, 5 days/week for 80 weeks (Seckar et
al. 1986). The study jdgntjfied_a_NOAEL jgO.OOgppm) but not a LOAEL.
EPA reviewed the data for this chemical and derived a verified JiVfel
reference concentration (RfC) of 40 mg/cu m (15 ppm)(EPA199^; EPA1994)
based on a chronic inhalation bioassay in which ra;s were administered the
compound at C, 2.CCO, 10,000 or 25,000 ppm 6 hours/day, 5 days/week for 2
years (McAlc: '* and Schneider 1992). The study identified a NOAEL (25,000 ppm)
but not a LOALl.
Pentafluoroethane
HFC-125
CASRN: 354-33-6
EPA reviewed the data for this chemical and determined that the requirements for
the minimal database necessary to develop an inhalation reference concentration
(RfC) have not been met (EPA 1993). The acute inhalation toxicity of
pentafluoroethane is very low with a 4 hour LC50 of 709,000 ppm (Panepinto
1990). Developmental toxicity studies in rats and rabbits have revealed no
toxicity at 15,000 ppm and only slight anesthetic effects in rats at 50,000 ppm
(Masters et ai. 1992; Masters et al. 1992) The compound is a cardiac sensitizer in
dogs at concentration above 100,000 ppm (Hardy et al. 1992). The European
Center for Ecotoxicology and Toxicology cf Chemicals has completed a recent
review of this chemnical (ECETOC 1994).
39
-------
1,3-D!chloro-1,1,2,2.3-
pentafluoropropane
HCFC225cb
CASRN: 507-55-1
EPA reviewed the data for this chemical and determined that the requirements for
the minimal database necessary to develop an inhalation reference concentration
(RfC) have not been met (EPA 1993). Several short-term inhalation studies either
of HCFC-225cb in rats at concentrations as high as 41,216 ppm for four hours
(Jackson et al. 1992) or of the mixed isomers (HCFC-225cb;HCFC-225ca) in mice
at concentrations as high as 13,000 ppm for four weeks (Frame et al. 1992)
induced changes in lipid and carbohydrate metabolism at several concentrations.
However, these effects were reversible after a 14 day recovery period.
1,1-Dichlor-2,2,3,3,3-
pentafluoropropane
HCFC225ca
CASRN: 507-55-1
EPA reviewed the data for this chemical and determined that the requirements for
the minimal database necessary to develop an inhalation reference concentration
(RfC) have not been met (EPA 1993). Several short-term inhalation studies either
of HCFC-225cb in rats at concentrations as high as 46,527 ppm for four hours
(Jackson et al. 1992) or of the mixed isomers (HCFC-225cb;HCFC-225ca) in mice
at concentrations as high as 13,000 ppm for four weeks (Frame et al. 1992)
induced changes in lipid and carbohydrate metabolism at several concentrations.
However, these effects were reversible after a 14 day recovery period.
Trifluoromethane
HFC-23
CASRN: 75-46-7
EPA reviewed the data for this chemical and determined that the requirements for
the minimal database necessary to develop an inhalation reference concentration
(RfC) have not been met (EPA 1993). A subchronic inhalation study in rats at
10,000 ppm or dogs at 5,000 ppm 6 hours/day 7 days/week for 90 days showed no
adverse effects in either species (Leuschner et al. 1983). Cardiac sensitization
testing in dogs at concentrations as high as 300,000 ppm revealed no activity
(Hardy 1992)
Difluoromethane
R-32; FC-32
CASRN: 75-10-5
EPA reviewed the data for this chemical and determined that the requirements for
the minimal database necessary to develop an inhalation reference concentration
(RfC) have not been met (EPA 1993). Exposure of rats to 200,000 ppm 6
hours/day, 5 days/week for 2 weeks revealed no treatment related effects (Moore
1976). Cardiac sensitization testing in dogs revealed that rare individuals were
sensitive at concentrations of 250,000 (1/12) (Mullin 1993).
1,1,1-Trifluoroethane
HCFC 143a
CASRN: 420-46-2
EPA reviewed the data for this chemical and determined that the requirements for
the minimal database necessary to develop an inhalation reference concentration
(RfC) have not been met (EPA 1993). Exposure of rats to 1, 2,000,10,000, or
39,000 ppm 6 hours/day 5 days/week for 4 weeks showed testicular effects in
animal exposed nose-only but no effects in animals given whole body inhalation
exposures leading to the conclusions that the finding with nose-only exposures
may be related to stress (Warheit et al. 1991,1992)
1,1.1,2,3.3,3-
Heptafluoropropane
(HCF-227ea)
CASRN: 43-89-0
EPA reviewed the data for this chemical and determined that the requirements for
the minimal database necessary to develop an inhalation reference concentration
(RfC) have not been met (EPA 1993). No data were found.
Perfluorobutane
FC-3-1-10
CASRN: 355-35-9
Perfluorohexane
FC-5-1-14
CASRN: 355-42-0
EPA reviewed the data for this chemical and determined that the requirements for
the minimal database necessary to develop an inhalation reference concentration
(RfC) have not been met (EPA 1993). A subchronic (90 day) inhalation exposure
of rats to 0, 5,000,15,000 or 50,000 ppm 6 hours/day, 5 days/week induced no
exposure related adverse effects (Kenny et al. 1992) suggesting that 50,000 ppm
is a NOAEL for this compound. Cardiac sensitization testing in dogs at
concentrations as high as 170,000 ppm reveal no activity as a sensitizer (Hardy
and Kieran 1992)
EPA reviewed the data for this chemical and determined that the requirements for
the minimal database necessary to develop an inhalation reference concentration
(RfC) have not been met (FPA 1993). Acute exposures as high as 79,000 ppm for
4 hours were not lethal to rats (Jackson et al. 1992) nor is the compound a cardiac
sensitizer in dogs at levels as high as 400,000 ppm (Hardy and Kieran 1992).
Bromodifluoromethane
FM-100
CASRN: 1511-62-2
EPA reviewed the data for this chemical and determined that the requirements for
the minimal database necessary to develop an inhalation reference concentration
(RfC) have not been met (EPA 1993). However, in a developmental toxicity study
of rats exposed to 0, 1,000, 4,000, or 10000 ppm 6 hours/day on gestation days
6-15, a NOAEL of 4,000 and a LOAEL of 10,000 ppm were observed for both
developmental and maternal toxicity (Nemec 1991b). A similar NOAEL for rabbits
can be derived from Nemec (1991c). Cardiac sensitization potential testing in
doqs revealed a NOAEL of 3,000 com.
40
-------
References -; .>/.>•?•' ' ^v;->••-.-,;

Adamson, I., B. Munoz, C. Enger, and H.R. Taylor (1991) Prevalence of lens opacities in surgical and
general populations, Arch. Ophthalmol.. 109:993-997.
Ansel, J. C., J. Mountz, A. D. Steinberg, E. DeFabo, and I. Green (1985) Effects of UV radiation on
autoimmune strains of mice: Increased mortality and accelerated autoimmunity in male mice, J. Invest
Dermatol. 85:181-186.
Applegate, L. E., R. D. Ley, J. Alcalay, and M. L. Kripke (1989) Identification of the molecular targeffor
the suppression of contact hypersensitivity by ultraviolet radiation, J. Exp. Med. 170:1117-1131.
Blum, H.F., (1943) Wavelength dependence of tumor induction by ultraviolet radiation, J. Nat'l Cancer
Inst. 3:533-537.

Bochow, T. W., S. K. West, A. Azar, B. Munoz, A. Sommer, and H. R. Taylor (1989) Ultraviolet light
exposure and risk of posterior subcapsular cataracts. Arch. Ophthalmol. 107:369-372.
Boyle, J., R. M. MacKie, J. D. Briggs, B. J. R. Junor, and T. C. Aitchison, (1984) Cancer, warts and
sunshine in renal transplant patients: A case-control study, Lancet I 702-704.
Bradl, M., A. Klein-Szanto, S. Porter, and B. Mintz (1991) Malignant melanoma in transgenic mice
Proc. Natl. Acad. Sci. USA 88:164-168.
Brooker, A. J., R. J. Brown, D. M. John, T. J. Kenny, and D. W. Coombs (1992) The effects of HFC 125 on
pregnancy in the rabbit, Huntingdon Research Ctre, Report No. ALS 10/920856.
Brooker, A. J., S. M. Fulcher, C. A. Parker, J. M. Offer, D. W. Coombs, and C. J. Hardy (1992) The effect
of HCFC 141b on reproductive function of two generations in the rat. Interim report: FO generation,
Huntingdon Research Ctre, Report No. ALS 2/911643.
Brown, E. L., and M. L. Kripke (1994) The effects of UV radiation on delayed type hypersensitivity and
antibody production in CgH miceimmunized with various doses of Borrelia burgdorferi, Proc. Am.
Assoc. Immunol. (Abstr.) 150: 25A.

Brozek, D. M., G. M. Shopp, D. L. Ryan, P. M. Gillespie,-D. F. Kusewitt, M. S. Rajagopalan, K. D. Ley,.
and R. D. Ley (1992) In vivo exposure to ultraviolet radiation enhances pathogenic effects of murine
leukemia virus LP-BM5, in murine acquired immunodeficiency syndrome, Photochem. Photobiol. 56-
287-295.
Cachao, P., F. Menezes Brandao, M. Carmo, S. Frazao, and M. Silva (1986) Allergy to oil of turpentine
in Portugal. Contact Dermatitis, 14(4): 205-208.
Cestari, T. F., C. D. Bucana, and M. L. Kripke (1994) Influence of ultraviolet radiation on the
granulomatous response to lepromin in humans, J. Invest. Dermatol. (Abstr.) 102: 650.
Cooper, K. D., L. Oberhelman, T. A. Hamilton, O. Baadsgaard, M. Terhune, G. LeVee, T. Anderson, and H.
Koren (1992) UV exposure reduces immunization rates and promotes tolerance to epicutaneous
antigens in humans: Relationship to dose, CDla-DR+ epidermal macrophage induction and Langerhans
cell depletion, Proc. Natl. Acad. Sci., USA89: 8497-8501.
Cooper, K. D., N. Duraiswamy, C. Hammerberg, E. Allen, C. Kimbrough-Green, W. Dillon, and D. Thomas
(1993) Neutrophils, differentiated macrophages, and monocyte/macrophage antigen presenting cells
infiltrate murine epidermis after UV injury, J. Invest. Dermatol 101:155-163.
Coroneo, M. T. (1993) Pterygium as an early indicator of ultraviolet insolation: a hypothesis, Br J
Ophthalmol. 77:734-739.
Cruickshanks, K. J., B. E. K. Klein, and R. Klein (1992) Ultraviolet light exposure and lens opacities: the
Beaver Dam Eye Study, Am. J. Public. Health 82:1658-1662.
Cruz, P. D., and P. R. Bergstresser (1988) The low-dose model of UV-B-induced immunosuppression
Photodermatol 5:151-161.
de Gruijl, F. R. and J. C. van der Leun (1991) Development of skin tumors in hairless mice after
discontinuation of ultraviolet radiation, Cancer Res. 51:979-984.
de Gruijl, F.R., and J. C. van der Leun (1994) Estimate of the wavelength dependency of ultraviolet
carcinogenesis in humans and its relevance to the risk assessment of a stratospheric ozone depletion
Health Physics 67:317-323.
de Gruijl, F. R., H. J. C. M. Sterenborg, P. D. Forbes, R. E. Davies, C. Cole, G. Kelfkens, H. Van
Weelden, H. Slaper, and J. C. van der Leun (1993) Wavelength dependence of skin cancer induction by
ultraviolet irradiation of albino hairless mice, Cancer Res. 53:53-60.
41
-------
DeFabo, E. C., and F. P. Noonan (1983) Mechanism of immune suppression by ultraviolet irradiation in
vivo: I. Evidence for the existence of a unique photoreceptor in skin and its role in photoimmunology,
J. Exp. Med. 157:84-98.
DeFabo, E. C. and F. P. Noonan (1993) UV-induced immunosuppression, In: Environmental UV
Photobiology, Eds. A. R. Young et al., Plenum Press, New York, pp. 113-148.
DeFabo, E.G. and M. L. Kripke (1980) Wavelength dependence and dose-rate independence of UV
radiation-induced immunologic unresponsiveness of mice to a UV-induced fibrosarcoma, Photochem.
Photobiol. 32:183-188.
Dcnkins, Y. M., I. J. Fidler, and M. L. Kripke (1989) Exposure of mice to UV-B radiation suppresses
delayed hypersensitivity to Candida albicans. Photochem. Photobiol. 49:615-619.
Denkins, Y. M. (1991) The effect of ultraviolet radiation on the pathogenesis of Candida albicans in mice.
Ph.D. Thesis, Graduate School of Biomedical Sciences, University of Texas, Houston.
Denkins, Y. M. and M. L. Kripke (1993) Effect of UV irradiation on lethal infection of mice with
Candida albicans, Photochem. Photobiol. 57:266-271.
Dolin, P. J. (1994) Ultraviolet radiation and cataract: a review of the epidemiological evidence, Brit. J.
Ophthalmol. 78:4788-482.
Donawho, C. K, and M. L. Kripke (1991) Evidence that the local effects of UV radiation on the growth of
murinc melanomas is immunologically mediated, Cancer Res. 41:4176-4181.Dyall-Smith, D., G.
Varigos (1985) The malignant potential of papillomavirus, Austral. J. Dermatol. 26:102-107.
Dorn, C. R., D. O. Taylor and R. Schneider (1971) Sunlight exposure and risk of developing cutaneous and
oral squamous cell carcinomas in white cats, J National Cancer Institute. 46: 1073-1078.
Doughty M. J. and A. P. Cullen (1989) Long-term effects of a single dose of ultraviolet-B on albino rabbit
cornea - I in vivo analysis, Photochem. Photobiol. 49:185-196.
Dyall-Smith, D. and G. Varigos (1985) The malignant potential of papilloma virus Sustralas J. Dermatol.
26: 102-107.
ECETOC (1994) Joint Assessment of Commodity Chemicals" No. 24 Pentachlorofluorethane (HFC 125),
Europeans Centre for Ecotoxicology and Toxicology of Chemicals, Brussels, Belgium.
ECETOC (1994) Joint Assessment of Commodity Chemicals. No. 12, 1 Chloro, 1,2,2,2
•Tetrafluoroethane (HFA 124), Europeans Centre for Ecotoxicology and Toxicology of Chemicals,
Brussels, Belgium.
ECETOC (1994) Joint Assessment of Commodity Chemicals No. 13, 1,1 Dechloro, 2,2,2,
Trifluroroethane (HFA-123), Europeans Centre for Ecotoxicology and Toxicology of Chemicals,
Brussels, Belgium.
Elmcts, C. A., M. J. LeVine, and D. R. Bickers (1985) Action spectrum for induction of immunologic
unresponsiveness to dinitrofluorobenzene following in vivo low dose ultraviolet radiation, Photochem.
Photobiol. 42:391-397.
Emmett, E. A. (1973) Ultraviolet radiation as a cause of skin tumors, Critical Reviews in Toxicology.
2:211-2S5;.
Fi&hci, M. S. and M. L. Kripke (1982) Suppressor T lymphocytes control the development of primary sk.;n
cancers in ultraviolet irradiated mice, Science 216:1133-1134.
Frame, S. R., M. C. Carakostas, and D. B. Warheit (1992) Inhalation toxicity of an is.-,r... -i -,.,: . ..."
hydrochlorofluorocarbon (HCFC) 225 in male rats, Fundam. Appl. Toxicol., 18(4): 590' :••.-.,.
Freeman, R. G. and J. M. Knox (1964) Ultraviolet induced corneal tumors in different species and strains
of animals, J. Invest. Dermatol. 43: 431-436.
Freeman, S. E., H. Hacham, R. W. Gange, D. J. May turn, J. C. Sutherland, and B. M. Sutherland (1989)
Wavelength dependence of pyrimidine dimer formation in DNA of human skin irradiated in situ with
ultraviolet light, Proc. Natl. Acad. Sci. USA 86:5605-5609.
Gallagher, R. P., D. I. McLean, C. P. Yang, A. J. Goldman, H. K. B. Silver, J. J. Spinclli, and M. Beagrie
(1990) Suntan, sunburn, and pigmentation factors and the frequency of acquired melanocytic nevi in
children. Similarities to melanoma: the Vancouver mole study, Arch. Dermatol. 126:770-776.
Giannini, M. S. H. (1986) Suppression of pathogenesis in cutaneous leishmaniasis by UV irradiation,
Infect. Immun. 51:838-843.
42
-------
Giannini, M. S. H. and E. C. DeFabo, (19,87) Abrogation'of skin lesions in cutaneous leishmaniasis, in
Leishmaniasis: The First Centenary (1885-1985) New Strategies for Control, D. T. Hart (ed.), NATO
ASI Series A: Life Sciences, Plenum Publishing Company, London, 1987.
Gibbs, N. K., M. Norval, N. Traynor, M. Wolf, B. E. Johnson, and J. Crosby (1993) Action spectra for the
trans to cis photoisomerization of urocanic acid in vitro and in mouse skin, Photochem. Photobiol
57:584-590.
Glover, M. T., N. Niranjan, J. T. Kwan, and I. M. Leigh (1994) Non-melanoma skin cancer in renal
transplant recipients: the extent of the problem and a strategy for management Br J Plast Surg. 47: 86-
89,

Goettsch, W., J. Garssen, A. Deijns, F. R. de Gruijl, and H. van Loveren (1994) UV-B exposure impairs
resistance to infection by Trichinella spiraiis, Envir. Health Perspec. 102:298-301.
Harding, J. J., and R. Van Heyningen (1987) Case-control Study of cataract in Oxford, Dev. Ophthal
15:99-103.
Hargis, A. M. (1981) A review of solar-induced lesions in domestic animals, The Compendium on
Continuing Education 3: 287-300.
Hardy, C. J. (1992) Halon 13B1, Freon 23, Mixture of Freon 23 and HFC 125. Assessment of cardiac
sensitisation potential in dogs, Huntingdon Research Ctre, Report No. DPT 273/921009.
Hardy, C. J. and P. E. Kieran (Final draft) T-5333 and T-5411, Assessment of cardiac sensitisation
potential in dogs, Huntingdon Research Ctre, Report No. MIN62/920851.
Hardy, C. J., P. C., Kiernan, I. J., Sharman, and G. C. Clark (1992) Assessment of cardiac sensitisation
potential in dogs. Comparison of HFC 125 and Halon 13B1, Huntingdon Research Ctre Report No
ALS 11/920116.
Hauser, S. L., H. L. Weiner, M. Che, M. E. Shapiro, F. Gilles, and N. L. Letvin, (1984) Prevention of
experimental allergic encephalomyelitis (EAE) in the SJL/J mouse by whole body ultraviolet
irradiation, J. Immunol 132:1276-1281.
Hersey, P., G. Haran, E. Hasic, and A. Edwards (19834-Alteration of T cell subsets and induction of
suppressor T cell activity in normal subjects after exposure to sunlight, J. Immunol 131:171-174.
Hext, P. M. and A. P. Mould (1991) HFC 134a: Two-year inhalation toxicity study in the rat. Interim
report after 52 weeks, ICI Central Toxicology Laboratory, Report No. CTL/P/3317.
Hiller, R., R. D. Sperduto, and F. Ederer (1983) Epidemiological associations with nuclear, cortical, and
supcapsular cataracts, Am. J. Epidemiol. 124:916-925.
Hollows, F. C. (1989) Ultraviolet radiation and eye diseases, in Transactions of the Menzies Foundation
15:113-117.
Hollows, F. C. and D. Moran (1991) Cataract_the ultraviolet risk factor, Lancet 2:1249-1250.

HSDB, (1994) Methy Bromide file in the Hazardous Substances Data Bank, on the National Library of
Medicine's TOXNET system, Bethesda, MD.
Hughes, D.E., G.W. Pugh, and T.S. McDonald (1965) Ultraviolet radiation and Moraxella bovis in the
etiology of bovine infectious conjunctivitis Am. J Vet. Res. 26: 1331-1338.
Husain, Z., M. A. Pathak, T. Flc.Lic, and M. M. Wick (1991) Role of ultraviolet radiation in the
induction of melanocytic tu--">f L\ hinrkss mice following 7,12-dimethylbenz(a)anthracene
'.inuon, Cancer Res. 51:4964-4970.
'••-,.;!..• lion of carcinogenic risk to humans Vol. 55, Solar and ultraviolet
, f ••• Research on Cancer, Lyon.
\';j\) Risk Factors for age-related cortical, nuclear, and posterior
r.pidemi..!. 133:541-553.
application and uhnuioler
lAIxC (K-'i^'Monogi.1;-'.-. p"
radJ:.uio:i. Inteuhiti.- ' -V
Italian-American Sti'.1 C.":1. -..•••
subcapsular catani^i-;. Am.

Jackson, G.C., C. J. Hardy, II. Singh, J. M. Offer, and C. Gopinath (Final draft) T-5411, Acute inhalation
toxicity in rats, 4-hour exposure, Huntingdon Research Ctre, Report No. M1N 58/920833.
Jackson, G. C., C. J. Hardy, H. Singh, and J. M. Offer (1992) HCFC 225cb. Acute inhalation toxicity
study in rats, 4-hour exposure, Huntingdon Research Ctre, Report No. ALS 7/911567.
Jeevan, A., R. Evans, E. L. Brown, and M. L. Kripke (1992) Effect of local ultraviolet irradiation on
infections of mice with Candida aibicans, Mycobacterium bovis BCG, and Schistosoma mansoni, J.
Invest. Dermatol. 99:59-64.
43
-------
Jcevan, A., and M. L. Kripke (1993) Impact of ozone depletion on immune function, World Resource
Revciw 5 (2):141-155.
Jose, J. L., and D. G. Pitts (1985) Wavelength dependence of cataracts in albino mice following chronic
exposure, Exp. Eye Res. 41:545-563.
Kanjilal, S., W. E. Pierceal, K. K. Cunnings, M. L. Kripke, and H. N. Ananthaswamy (1993) High
frequency of p53 mutations in UV-induced murine skin tumors: evidence for strand bias and tumor
heterogeneity, Cancer Res. 53:2961-2964.
Kenny, T. J., D. W. Coombs, C. J. Hardy, D. Crook, W. A. Gibson, R. L. Gregson, and J. M. Offer (Final
draft) T-5333, 90-day inhalation study in rats, Huntingdon Research Ctre, Report No. MIN
59/920819.
Kenny, T. J., D. W. Coombs, C. J. Hardy, J. Morrow, D. J. Lewis, C. Gopinath, and L. F. Chasseaud (1992)
HCFC 225cb. 4-week repeat dose inhalation toxicity study in the rat, Huntingdon Research Ctre,
Report No. ALS 8(225cb)/920070.
Klein, K. L., and C. C. Linnemann, Jr. (1986) Induction of recurrent genital herpes simplex virus type 2
infection by ultraviolet light, Lancet I 796-798.
Kress, S., C. Sutter, P. T. Strickland, H. Mukthar, J. Schweizer, and M. Schwartz (1992)
Carcinogen-specific mutational pattern in p53 gene in ultraviolet B radiation-induced squamous cell
carcinomas of mouse skin, Cancer Res. 52:6400-6403.
Kripfce, M. L. (1990) Effects of UV radiation on tumor immunity, J. Natl. Cancer Inst. 82:1392-1396.
Kripke, M. L. (1984) Immunological unresponsiveness induced by ultraviolet radiation, Immunol. Rev.
80:87-102.
Kripke, M. L., P. A. Cox, L. G. Alas, and D. B. Yarosh (1992) Pyrimidine dimers in DNA initiate systemic
immunosuppression in UV-irradiated mice, Proc. Natl. Acad. Sci. USA 89:7516-7520.
Krutmann, J., W. Czech, F. Parlow, A. Kapp, E. Schopf, and T. A. Luger, (1992) Ultraviolet radiation
effects on human keratinocyte ICAM-1 expression, J. Invest. Dermatol 98:923-928.
Larue, L., N. Dougherty, and B. Mintz (1992) Genetic predisposition of transgenic mouse melanocytes to
melanoma results in malignant melanoma after exposure to a low ultraviolet B intensity
nontumorigenic for normal melanocytes, Proc. Nad. Acad. Sci. USA 89:9534-9538.
Lctvin, N. L., R. S. Kauffman, and R. Finberg (1981) T lymphocyte immunity to reovirus: Cellular
requirements for generation and role in clearance of primary infections, J. Immunol 127:2334-2339.
Lcuschner, F., B. W. Neumann, and F. Hubscher (1983) Report on sabacute toxicological studies with
several fluorocarbons in rats and dogs by inhalation, Arzneim.-Forsch./Drug Res., 33(11) (10): 1475-
1476.
Ley, R. D., L. A. Applegate, R. S. Padilla, and T. D. Stuart (1989) Ultraviolet radiation-induced
'malignant melanoma in Monodelphis domestica, Photochem. Photobiol. 50:1-5.
Ley, R. D. and D. F. Kusewitt (1994) Dietary saturated fat reduces the susceptibility of the opossum
Monodelphis domestica to ultraviolet radiation (UVR)-induced cutaneous melanotic lesions,
unpublished abstract.
Li, Y. W., S. T. Kim, and A. Sancar (1993) Evidence for lack of DNA photoreactivating enzyme in humans,
Proc. Natl. Acad. Sci. USA 90:4389-4393.
Longstreth, J. D., F. R. de Gruijl, Y. Takizawa, and J. C. van der Leun (1991) Human Health. Chapter 2 in
Environmental effects of ozone depletion: 1991 update, JC van der Leun, M Tevini and RC Worrest
(Eds.), pp. 15-24. United Nations Environment Programme, Nairobi, Kenya.
Luger, T. A. and T. Schwarz (1990) Evidence for an epidermal cvtokine network, J. Invest. Dermatol. 95
(Suppl.):100S-104S.
Madronich, and S., F. R. de Gruijl (1993) Skin cancer and UV radiation, Nature 366:23.
Maitchouk, I. F. (1985) Trachoma and cataract: two WHO targets, Int. Nurs Rev. 32:23-25.
Mallcy, L. A. (1990b) Combined chronic toxicity/oncogenicity study with HCFC-123. Two-year
inhalation study in rats (one-year interim report), E. I Du Pont de Nemours Company, Haskell
Laboratory for Toxicology and Industrial Medicine, Haskell Laboratory Report No. 260-90.
Mallcy, L. A. (1991) Subchronic inhalation toxicity: Ninety-day study with HCFC-124, E. I. Du Pont de
Nemours and Company, Haskell Laboratory for Toxicology and Industrial Medicine, Haskell
Laboratory Report No. 79-91.
44
-------
Masters, R. E., R. J. Brown, D. M. John, and D. W. Coombs. (1992) A study of the effect of HFC 125 on
pregnancy of the rat (inhalation exposure), Huntingdon Research Ctre, Report No. ALS 9/920434.
McAlack, J. W., and P. W. Schneider, Jr (1982) Two-year inhalation study with ethane, 1,1-difluoro (FC-
152a) in rats, E. I. Du Pont de Nemours and Company.
McGregor, J. M., C. C-W Yu, D. A. Dublin, D. A. Levison, and D. M. MacDonald (1992) Aberrant
expression of p53 tumorsuppressor protein in nonmelanoma skin cancer, Br. J. Dermatol.
127:463-469.

Moore, B. L. (1976) Subacute two-week inhalation toxicity, E. I. Du Pont de Nemours and Company,
Haskell Laboratory for Toxicology oand Industrial Medicine, Haskell Laboratory Report No. 159-76.
Morison, W. L., J. A. Parrish, K. J. Bloch, and J. I. Kragler (1979) In vivo effect of UV-B on lymphocyte
function, Br. J. Dermatol. 101:513-519.
Morison, W. L. (1989) Effect of ultraviolet radiation on the immune system in humans, Photochem.
Photobiol. 50:515-524.
Morrey, J. D., S. M. Bourn, T. D. Bunch, M. K. Jackson, R. W. Sidwell, L. R. Barrows, R. A. Daynes, and C.
A. Rosen (1991) In vivo activation of human immunodeficiency virus type 1 long terminal repeat by UV
type A (UV-A) plus psoralen and UV-B light in the skin of transgenic mice. J. Virol//.
65:5045-5051.
Morrison, H., C. Bernasconi, and G. Pandey (1984) A wavelength effect on urocanic acid E/Z
photoisomerization, Photochem. Photobiol. 40:549-550.
Mossman, T. R., J. H. Schumacher, N. F. Street, R. Budd, A. O'Garra, T. A. T. Fong, M. W. Bond, L. W.
M. Moore, A. Sher, and D. F. Florentine, (1991) Diversity of cytokine synthesis and function of mouse
CD4+ T cells, Immunol. Rev. 123:209-229.
Mullin, L. S. (1973) Cardiac sensitization potential of difluoromethane, E. L Du Pont de Nemours and
Company, Haskell Laboratory for Toxicology and Industrial Medicine, Haskell Laboratory Report No
257-73.

Nagano, T., M. Ueda, and M. Ichihashi (1993) Expression, of p53 protein is an early event in ultraviolet
light-induced cutaneous squamous cell carcinogenesis, Arch. Dermatol. 129:1157-1161.
Nagazawa, H., D. English, P. L. Randel, K. Nakazawa, N. Martel, B. K. Armstrong, and H. Yamasaki
(1994) UV and skin cancer: specific p53 gene mutation in normal skin as a biologically relevant
exposure measurement, Proc. Natl. Acad. Sci. USA 91:360-364.
National Toxicology Program (1990) Toxicology and carcinogenesis studies of d-limonene (GAS No.
5989-27-5) in F344/N rats and B6C3F1 mice (gavage studies), US Department of Health and Human
Services, National Institutes of Health, NTP Technical Report Series No. 347, NIH PB No. 90-
2802.
Nemec, M. D. (1991b) An inhalation developmental toxicity study of FM-100 in rats, WIL Research
Laboratories, WIL Project No. WIL-12228.
Nemec, M.D. (1991c) An inhalation range-finding developmental toxicity study of FM-100 in rabbits,
WIL Research Laboratories, WIL Project No. WIL-12229.
Nikula, K. J., S. A. Benjamin, G. M. Angleton, W. J. Saunders, and A.C. Lee (1992) Ultraviolet Radiation,
Solar dermatosis, and cutaneous neoplasia in beagle dogs, Radiation Research 129:11-18.
Noonan, F. P., E. C. DeFabo, and H. Morrison (1988) Cis-urocanic acid, a product formed by ultraviolet
B irradiation of the skin initiates an antigen presentation defect in splenic dendritic cells in vivo, J.
Invest. Dermatol 90:92-99.
Noonan, F. P., E. C. DeFabo, and M. L. Kripke (1981) Suppression of contact hypersensitivity by UV
radiation and its relationship to UV-induced suppression of tumor immunity, Photochem. Photobiol
34:683-689.
Noonon, F. P., and H. A. Hoffman (1994) Susceptibility to immunosuppression by ultraviolet B radiation
in the mouse. Immunogenetics. 39:29-39.
Opdyke, D. J. L. (1975) Special Issue II:> Monographs on fragrance raw materials, Food Cosmet.
Toxicol., 13: 825-826.
Panepinto, A. S. (1990) Four-hour inhalation approximate lethal concentration (ALC) of HFC-125 in
rats, E. I. Du Pont de Nemours and Company, Haskell Laboratory Report No. 582-90.
45
-------
Pcrna, J. J., M. L. Mannix, J. F. Rooney, A. L. Notkins, and S. E. Straus (1991) Reactivation of latent
herpes simplex virus infection by ultraviolet light: A human model, Journal of the American Academy
of Dermatology 17(3):473-478.
Pitts, D. G., A. P. Cullen, and P. D. Hacker (1977) Ocular ultraviolet effects from 295 to 365 nm in
rabbit eye, Invest. Ophthalmol. Vis. Sci.16:223-240.
Pitts, D. G. and R. N. Kleinstein (1993) Environmental Vision,Butterworth-Heineman, Stoneham, MA.
Rivas, J. M., and S. E. Ullrich, (1994) Antibodies against IL-4 and IL-10 block the activity of ultraviolet
radiation-induced suppressor T cells, submitted for publication.
Rivas, J. M. and S. E. Ullrich, Ultraviolet B radiation and skin immunology, In Immunotoxkology and
Immunopharmacology, Raven Press, 1994a, in press.
Rivas, J. M. and S. E. Ullrich (1992) Systemic suppression of delayed-type hypersensitivity by supernatants
from UV-irradiated keratinocytes. An essential role for keratinocyte-derived IL-10, J. Immunol
149:3865-3871.
Romerdahl, C. A., L. C. Stephens, C. Bucana, and M. L. Kripke (1989) The role of ultraviolet radiation in
the induction of melanocytic skin tumors in inbred mice, Cancer Commun. 1:209-219.
Roscnthal, F. S., S. K. West, B. Munoz, E. A. Emmett, P. T. Strickland, and H. R. Taylor (1991) Ocular
and facial skin exposure to ultraviolet radiation in sunlight: a personal exposure model with
application for a worker population, Health Physics 61:77-86.
Scheibner, A., D. E. Hollies, W. H. McCarthy, and G. W. Milton (1986) Effects of sunlight exposure on
Langerhans cells and melanocytes in human epidermis, Photodermatol. 3:15-25.
Schein, O. D., S. West, B. Munoz, S. Virale, M. Maguire, H. R. Taylor, and N. Bressel (1994) Cortical
lenticular opacification: distribution and location in a longitudinal studv, Invest. Ophthalmol. Vis.
Sci.35:363-366.

Schievcn, G. L., J. M. Kirihara, L. K. Gilliland, F. M. Uckun, and J. A. Ledbetter (1993) Ultraviolet
radiation rapidly induces tyrosime phosphorylation and calcium signaling in lymphocytes. Mol. Biol.
Cell 4:523-530. __ .

Schmitt, J., J. R. Schlehofer, K. Mergerer, L. Gissman, and H. zur Hausen, Amplification of bovine
papillomavirus DNA by N-methyl-N'-nitro-N-nitrosoguanidine, ultraviolet irradiation, or infection
with herpes simplex virus, Virology, 172: 73-81, 1989.
Schneider, R., C. R. Dorn, and M. R. Klauber, (1968 Cancer in households. A human-canine retrospective
study, J National Cancer Inst. 41: 1285-1292.
Seckar, J. A., H. J. Trochimowicz, and G. K. Hogan (1986) Toxicological evaluation of
hydrochlorofluorocarbon 142b, Fd. Chem. Toxicol., 24(3): 237-240. (Several volumes of the original
study were consulted and are part of the literature file for this compound.)
Setlow, R. B., E. Grist, K. Thompson, and A. P. Woodhead (1993) Wavelengths effective in induction of
malignant melanoma. Proc. Nad. Acad. Aci. USA 90:6666-6670.
Scdow, R. B., A. D. Woodhead, and E. Grist (1989) Animal model for ultraviolet radiation-induced
melanoma: Platyfish-swordtail hybrid, Proc. Natl. Acad. Aci. USA 86:8922-8926.
Simon, J. C., R. E. Tigelaar, P. R. Bergstresser, D. Edelbaum, and P. D. Cruz (1991) Ultraviolet B
radiation converts Langerhans cells from immunogenic to tolerogenic antigen presenting cells.
Induction of clonal ancrgym CD4+ T helper 1 cells, J. Immunol. 146:485-491.
Simon, J. C., P. D. Cruz, P. R. Bergstresser, and R. E. Tigelaar (1990) Low dose ultraviolet B-irradiated
Langerhans cells preferentially activate CD4+ cells of the T helper 2 subset, J. Immunol.
145:2087-2091.
Simon, M. M., Y. Aragane, A. Schwarz, T. A. Luger, and T. Schwarz (1994) UV-B light induces nuclear
factor kB (NFkB) activity independently from chromosomal DNA damage in cell-free cytosolic
extracts, J. Invest. Dermatol. 102:422-427.
Slapcr, H., M. G. J. Den Elzen, H. J. van der Woerd, and J. De Greef (1992) Ozone depletion and skin
cancer incidence: an integrated modeling approach. Report 749202001, National Institute of Public
Health and Environmental Protection (RTVM), Bilthoven, the Netherlands.
Sliney, D. H. (1987) Estimating the solar ultraviolet radiation exposure to intraocular lens implant, J.
Cataract Refrac. Res.

Spruancc, S. L. (1985) Pathogenesis of herpes simplex labialis: Experimental induction of lesions with
UV light, J. Clin. Microbiol. 22:366-368.
46
-------
Streilein, J. W. and P. R. Bergstresser (1988) Generic:'basis of ultraviolet-B effects on contact
hypersensitivity. Immunogenetics. 27: 252-258.
Strickland, P. T. (1984) Photocarcinogenesis and influence of UV radiation on autoimmune disease in
NZB/N mice, J. Nad. Cancer Inst. 73:537-541.
Szigeti, B., J. Chapiro, and J. M. Saint-Girons (1976) Traitement du zona par actinotherapie
ultraviolette, J. Radiol. Electrol. 57:549-551.
Taylor, H. R., S. K. West, F. S. Rosenthal, B. Munoz, H. S. Newland, H. Abbey, and E. A. Emmett (1988)
Effect of ultraviolet radiation on cataract formation, New Engl. J. Med. 319:1429-1433.
Tinston, D. J., I. S. Chart, M. J. Godley, C. W. Gore, M. H. Litchfield, and M. Robinson (1981b) HCFC-
22 (CFC 22): Long term inhalation study in the rat, Imperial Chemical Industries Limited, Central
Toxicology Laboratory, CTL Study No. PRO 132.
Tschachler, E., V. Groh, M. Popovic, D. L. Mann, K. Konrad, B. Safai, L. Eron, F. D. Veronese, K. Wolff,
and G. Stingl (1987) Epidermal Langerhans cells—a target for HTLV-III/LAV infection, J. Invest.
Dermatol. 88:233-237.
Ullrich, S. E. (1994) Mechanism involved in the systemic suppression of antigen-presenting cell function
by UV irradiation, J. Immunol. 152:3410-3416.
USEPA, (1987) Assessing the Risks of Trace Gases that can Modify the Stratosphere, 3: Chapts. 6-18,
EPA 400/1-87/001C, U.S. Environmental Protection Agency,'Washington, DC.
USEPA, (1991) Alpha2u-globulin: Association with chemically-induced renal toxicity and neoplasia in
the male rat, US Environmental Protection Agency, EPA/625/3-91/O19F.
USEPA, (1994) Personal Communication from William Thomas, Division of Stratospheric Ozone
Protection, Office of Air and Radiation, U.S. Environmental Protection Agency.
van der Leun, J. C. and F. R. de Gruijl (1993) Influences of ozone depletion on human and animal health,
in UV-B Radiation and Ozone Depletion, M. Tevini (ed.), Lewis Publishers, Boca Raton, pp. 95-123.
van der Leun, J. C., Y., Y. Takiyawa and J. D. Longstreth (1989) Human Health, Chapt 2 in Environmental
effects of ozone depletion; J. C. van der Leun, M. Tfevini and R. C. Worress (Eds), 11-24, United
Nations Environment Programme, Nairobi, Kenya.
Van Kranen, M. J., F. R. de Gruijl, P. W. Wester, H. C. M. Senden, A. De Vries, A. Sienus-van Hasten, Y.
Sontag, and C. J. Van Kreijl (1992) p53 alterations in UV-B induced skin tumors of hairless mice.
Proc. 6th p53 Workshop, Tiberias, Israel, Nov. 1992, p. 166.
Van't Veer, L. J., B. M. T. Burgering, R. Versteen, A. J. Boot, D. J. Ruiter, S. Osanto, P. I. Schrier, and J.
L. Bos (1989) N-ras mutations in human cutaneous melanoma from sun-exposed body sites, Mol. Cell
Biol. 9:3114-3116.
Vermeer, M., and J. W. Streilein (1990) Ultraviolet B light-induced alterations in epidermal Langerhans
cells are mediated in part by tumor necrosis factor-alpha, Photodermatol. Photoimmunol. Photomed.
7:258-265.
Vermeer, M., G. J. Schmeider, T. Yoshikawa, J.-W. van der Berg, M. Metzman, J. R. Taylor, and J. W.
Streilein (1991) Effects of ultraviolet-B light on cutaneous immune responses in humans with deeply
pigmented skin, J. Invest. Dermatol. 97:729-734.
Vitasa, B. C., H. R. Raylor, P. T. Strickland, F. S. Rosenthal, S. West, H. Abbey, S. K. Ng, B. Munoz, and
E. A. Emmett (1990) Association of nonmelanoma skin cancer and actinic keratosis with cumulative
solar ultraviolet exposure in Maryland watermen, Cancer 65:2811-2817.
Vogel, J., M. Cepeda, E. Tschachler, L. A. Napalitano, and G. Jay (1992) UV activation of human
immunodeficiency virus gene expression in transgenic mice, J. Virol. 66:1-5.
Warheit, C. B. (1991) Four-week inhalation toxicity study with HFC-143a in rats, E. I. Du Pont de
Nemours and Company, Haskell Laboratory Report No. 99-91.
Warheit, C. B. (1992) Four-week inhalation toxicity study with HFC-143a in rats, E. I. Du Pont de
Nemours and Company, Haskell Laboratory Report.
Wheeler, C. E. Jr. (1975) Pathogenesis of recurrent herpes simplex infections, J. Invest. Dermatol.
65:341-346.
WHO/UNEP (1994) Monograph.
Weinstock M. A., G. A. Colditz, W. C. Willet, M. J. Stamfer, B. Rosner, and F. E. Speizer (1991) Recall
(report) bias and reliability in retrospective assessment of melanoma risk, Am. J. Epidemiol.
133:240-245.

47
-------
Wojno, T., D. Singer, and R. Schultz (1983) Ultraviolet light, cataracts, and spectacle wear Ann
Ophthal. 15:729-732.

Yarosh, D. B., C. Bucana, P. Cox, L. Alas, J. Kibitel, and M Kripke, (1994) Localization of liposomes
containing a DNA repair enzyme in murine skin, J. Invest. Dermatol, in press.

Yoshikawa, T., V. Rac, W. Bruins-Slot, W. Van den Berg, J. R. Taylor, and J. W. Streilein (1990)
Susceptibility to effects of UV-B radiation on induction of contact hypersensitivity as a risk factor for
skin cancer in humans, J. Invest. Dermatol. 95:530-536.

Zicgler, A., D. J. Lefell, S. Kunala, H. W. Sharma, M. Gailani, J. A. Simon, P. E. Shapiro, P. E. Bale, and '
D. E. Brash (1993) Mutation hotspots due to sunlight in the p53 gene of nonmelanoma skin cancers
Proc. Nad. Acad. Sci. USA 90:4216-4220.

Zigman, S., T. Paxia, T. McDaniel, M. F. Lou, and N-T Yu (1991) Effect of chronic near-ultraviolet
radiation on the gray squirrel lens in vivo, Invest. Ophthalmol. Vis. Sci. 32:1723-1732

Zmudzka, B. Z. and J. B. Beer (1990) Activation of human immunodeficiency virus by ultraviolet radiation
Photochem. Photobiol. 6:1153-1162.
48
-------
CHAPTER 3
EFFECTS OF INCREASED SOLAR ULTRAVIOLET
RADIATION ON TERRESTRIAL PLANTS
MM. Caldwell (USA), A.H. Teramura (USA), M. Tevini (FRC ), J.F. Bornman (Sweden),
LO. Bjorn (Sweden), and G. Kulandaivelu (India)
Summary

Physiological and developmental processes of plants are affected by UV-B radiation, even by the
amount of UV-B in present-day sunlight. Plants also have several mechanisms to ameliorate or repair
these effects and may acclimate to a certain extent to increased levels of UV-B. Nevertheless, plant
growth can be directly affected by UV-B radiation. Response to UV-B also varies considerably among
species and also cultivars of the same species. In agriculture, this will necessitate using more UV-B-
tolerant cultivars and breeding new ones. In forests and grasslands, this will likely result in changes in
species composition; therefore there are implications for the biodiversity in different ecosystems. Indirect
changes caused by UV-B (such as changes in plant form, biomass allocation to parts of the plant, timing of
developmental phases and secondary metabolism) may be equally, or sometimes more, important than
damaging effects of UV-B. These changes can have important implications for plant competitive balance,
herbivory, plant pathogens, and biogeochemical cycles-JThese ecosystem-level effects can be anticipated,
but not easily predicted or evaluated. Research at the ecosystem level for solar UV-B is barely beginning.'
Other factors, including those involved in climate change such as increasing CO2 also interact with UV-B.
Such reactions are not easily predicted, but are of obvious importance in both agriculture and in
nonagricultual ecosystems.
Introduction

Since the first reports of potential stratospheric ozone reduction over 20 years ago (e.g., [Johnston,
1971; Crutzen, 1972]}, UV-B (280-315 nm) effects on higher plants have been the subject of considerable
research. Approximately 350 papers have appeared, but the majority of these deal with herbaceous,
agricultural plants under laboratory or glasshouse conditions. Fewer than 5% of the studies have been
conducted under field conditions, and fewer still with plants from forests and other nonagricultural
systems. While the laboratory and glasshouse studies provide information on mechanisms and processes of
L'V-B action, only the field studies can provide realistic assessments of what will happen as the
stratospheric ozone layer thins.

Several reviews of this literature have appeared in the last five years [Bornman, 1989; Caldwell et al.,
1989; Tevini and Teramura, 1989; Krupa and Kickert, 1989; Tevini, 1993; Bornman and Teramura, 1993;
Caldwell and Flint, 1993, 1994a, 1994b; Tevini, 1994; Teramura and Ziska, 1994; Teramura and Sullivan,
1994]. The present chapter provides an overview with interpretation of the results for both agriculture and
other ecosystems such as forests, grasslands, etc. It also includes a brief consideration of the potential
effects of the breakdown products of new man-made chemicals being brought into use which are less
offending to the ozone layer.

Figure 3.1 shows some of the effects of UV-B radiation on plant processes.
49
-------
Whole Plant Growth
Rg.3.1. The influence of UV-B radiation on plant processes.

The Biological Effectiveness of Changes in Sunlight

As explained in Chapter 1, the biological effectiveness of UV-B solar radiation needs to be considered
in assessing what ozone reduction, and the resulting changes in solar radiation, potentially mean for plants
and other organisms. The biological weighting functions used for this purpose often come from action
spectra. Action spectra assumed to be relevant for plants (Figure 3.2) all indicate that the shorter UV-B
wavelengths arc the most important. However, the relative importance of shorter vs longer UV-B
wavelengths (the slopes in Figure 3.2) vary considerably. Depending on these slopes, the Radiation
Amplifications Factors (discussed in Chapter 1) vary enormously. Action spectra that do not decrease
sharply with increasing wavelength result in small RAF values. Thus, the evaluation of weighting functions
(and therefore action spectra) is critical. There is evidence that action spectra for many plant functions
arc steep indicating that ozone reduction translates into large increases in effective solar UV-B
[Caliiwcll, 1971; Setlow 1974]. Some more recent spectra developed specifically for evaluating the ozone
reduction problem show flatter slopes (and therefore lower RAF values) than the earlier work [Caldwell et
ill,, 1986; Steinmueller, 1986; Quaite et a,L, 1992]. Still, these spectra are sufficiently steep so that ozone
reduction must be taken seriously. Biological weighting functions also are needed to relate solar UV to
UV from artificial sources used in experiments.
50
-------
PLANT
380 DU
DNA
180DU
Plant
growth
Alfalfa
100 -r
0)

I
C
as
CT

0.0001
T 1000
100 ^
E
v
N '
0.1 --
-- 10
8
001 --
0.001 --
-• 1
0.1
280 290 300 310 320 330 340 350 360
Wavelength [nm]
Fig.3.2. Action spectra for DNA damage [Setlow, 1974], DNA dimer formation (a type of DNA damage) in alfalfa seedlings
[Quaite etal., 1992a], growth inhibition in seedlings [Steinmuller, 1986], and generalized plant responses
[Caldwell, 1971]. The generalized plant action spectrum was developed from action spectra available in 1971 for
several processes of higher and lower plants. It has been widely used for calculating UV irradiance in
experiments with higher plants. Solar spectral irradiance at 360 and 180 Dobson Units (DU) of atmospheric
ozone is also shown. (A Dobson Unit is an expression used for describing thickness of the ozone layer at
standard temperature and pressure; 1 mm ozone layer thickness is equivalent to 100 DU.) The solar irradiance is
calculated for latitude 49° N at solar noon on Julian date 173 using the model of Green et al., [1980].
Apart from action spectrum considerations, it is important in experiments to maintain a realistic
balance between different spectral regions since both UV-A (315-400 nm) and visible (400-700 nm)
radiation can have strong ameliorating effects on responses of plants to UV-B [Caldwell et al., 1994]. In
growth chamber and greenhouse experiments, the visible and UV-A radiation is usually much less than in
sunlight. Thus, even if realistic levels of UV-B are used in simulating ozone reduction, the plant response
may be exaggerated relative to field conditions. Even under field conditions, if applied UV-B is not
adjusted downward during cloudy periods, the UV-B sensitivity may be unduly pronounced. Unfortunately,
the most expensive and difficult experiments, i.e., those conducted in the field with UV-B supplements'
adjusted for cloudiness and other atmospheric conditions, are seldom undertaken.
51
-------
As indicated in subsequent sections, another approach which achieves appropriate spectral balance is to
filter existing solar radiation to modify the UV-B component. This has been done either with materials
such as plastic filters or using ozone gas as a filter [Tevini et al., 1990]. For the latter system, in identical
growth chambers, different UV-B levels can be achieved by filtering sunlight using ozone (the ozone gas is
passed through an envelope of UV-transparent Plexiglas). In these growth chambers other factors such as
temperature and CO2 can be controlled. This is a considerable technical improvement on other UV-B
modification experiments using filtering materials such as glass, plastic films, etc. Growth and other
responses of intact seedlings can be evaluated in these chambers, but they are too small for larger plants.
Of course, all these UV-B filtering approaches can only result in lowering, but not increasing, solar UV-
B under the particular conditions experienced.

Plant Growth Responses

General Effects in Individual Plants

Enhanced UV-B radiation can have many direct and indirect effects on plants including inhibition of
photosynthesis, DMA damage, changes in morphology, phenology, and biomass accumulation. Most of the
work to date has concentrated on crop plants from temperate regions, whereas little has been done on
tropical and nonagricultural plants. Sensitivity to UV-B radiation, defined as the relative change induced
by UV-B on plant growth, morphology, or yield, depends on plant species, cultivar, developmental stage
and experimental conditions.

Plant Growth

In many plant species reduced leaf area and/or stem growth have been found in studies carried out in
growth chambers, greenhouses and in the field [Tevini and Teramura, 1989; Johanson et al., 1994]. Studies
where the ozone filter technique with special growth chambers -under solar radiation (in Portugal at 39°
latitude) showed that higher solar UV-B (close to ambient levels) can result in smaller plants with reduced
leaf area compared with plants under reduced UV-B levels [Tevini etui., 1990, 1991a; Mark, 1992]. These
observations correspond with results obtained in other studies with artificial UV-B in greenhouses, growth
chambers [Tevini and Iwanzik, 1986] and in the field [Teramura and Murali, 1986]. To provide differently
filtered solar UV-B on a relatively larger scale, different thicknesses of UV-transparent Plexiglas have
been used in greenhouses. The greenhouses (also located in Portugal) were covered with either 3 or 5 mm
Plexiglas, providing a 10% difference in weighted solar UV-B. Even with this small difference in solar
UV-B attenuation, reductions in growth of different cultivars of bean were observed under the higher level
of solar UV-B (with the 3-mm Plexiglas).

Two studies on rice cultivars from different geographical regions were carried out in greenhouses with
an enhanced daily dose of UV-B radiation using lamps [Teramura et al., 1991J. Of 16 rice cultivars native
to the Philippines, India, Thailand, China, Vietnam, Nepal and Sri Lanka, about one third showed
statistically significant decreases in total biomass and leaf area. Tiller number, correlated with yield, was
reduced in 6 of the cultivars (Figure 3.3). The Sri Lanka cultivar, Kurkaruppan, however, showed increases
in both total biomass and tiller number, indicating that selective breeding might be a successful tool for
obtaining UV-B tolerant cultivars [Teramura, et al., 1991]. In another study with rice cultivars from the
Philippines, total biomass changes were different among cultivars, with IR74 being the most sensitive and
IR64 the least sensitive [Figure 3.3; Barnes et al., 1993]. Field experiments are currently underway in the
Philippines using modulated UV-B lamp systems which should provide some realistic estimates of rice
cultivar response to UV-B radiation.
52
-------
Biomass
Leaf Area
Tiller Number
Fig. 3.3.A. Summary of a greenhouse study examining 16 rice cultivars grown with and without UV-B radiation simulating a
20% ozone depletion over the equator. The proportion of cultivars which has significantly reduced biomass,
leaf area, and tiller number are shown in peroents [Teramura et al,, 1991].
Biomass
Leaf Area
Tiller Number
Fig. 3.3 B. Selected data from a study examining 22 rice cultivaTrgrown with and without UV-B radiation simulating a 5% -
reduction in stratospheric ozone in Spring for the Philippines. The proportion of cultivars with significantly
reduced total weight, leaf area, and tiller number are shown in percents [Barnes et al., 1993].

The molecular basis for many of the changes observed following UV-B exposure is not yet well defined.
Responses may result from direct damage to essential cell components and by UV-B absorbed by specific
photoreceptors or growth regulators [Ensminger and Schdfer, 1992; Ballare et al., In press]. Preliminary
experiments suggest that flavins may function as UV-B photoreceptors for the induction of pigment
synthesis and inhibition of elongation [Ensminger and Schdfer, 1992; Ballare et al., In press]. Elongation
growth is influenced by the auxin, indole acetic acid, which absorbs in the UV-B range and could be
photodegraded by high levels of UV-B radiation. Oxidative enzymes, such as the peroxidases, are increased
by enhanced UV-B radiation, and may be involved in plant hormone regulated growth responses, as shown in
sunflower [Ros 1990]. The levels of another plant hormone, ethylene, which causes greater radial growth and
less elongation, are increased after irradiation with UV-B in, e.g., sunflower seedlings [Ros 1990] and
cultured shoots of pear plants [Predieri ct al. 1993].

Flowering

Ultraviolet-B radiation can alter both the time of flowering [Caldwell, 1968; Ziska et al., 1992; Saile-
Mark, 1993; Staxen and Bornman, 1994] as well as the number of flowers in certain species. For example,
Rau et al., [1988] found substantial decreases in flowering from UV-B irradiation. Differences in timing '
of flowering may have important consequences for the availability of pollinators. The reproductive parts
of plants, such as pollen and ovules, are rather well shielded from solar UV-B radiation. For example
anther walls can absorb more than 98% of incident UV-B [Flint and Caldwell, 1983]. In addition, the
pollen wall contains UV-B absorbing compounds affording protection during pollination. Only after
transfer to the stigma might pollen be susceptible to solar UV-B radiation. Germinating pollen can be
sensitive at this time to UV-B [Flint and Caldvell, 1984]. The overall significance of this in the context
of the ozone reduction problem is unclear and needs to be assessed.
53
-------
Limitation of Growth Chamber Studies

In growth chambers and greenhouses the radiation conditions are usually quite different from those in
the field. For example, the visible radiation which is used in photosynthesis (400 to 700 nm,
photosynthetically active radiation, PAR) and the UV-B/UV-A/PAR ratios are different from those in
the field. As mentioned earlier, if UV-A and PAR are low, the effects of UV-B may be much more severe
(see above). In addition, other factors, such as temperature, water and nutrients differ from conditions in
the field and this can alter response to UV-B radiation. However, experiments in controlled conditions
arc usually necessary as a first step in defining plant response to specific combinations of UV-B and other
environmental factors. It is, however, important that these studies conducted under controlled conditions
be verified as much as possible under field conditions.

Translating Whole-Plant Reactions to Ecosystem Responses

Plants compose most of the living mass in terrestrial ecosystems. Although there can be effects of UV-
B directly on microbes and animal life (e.g., [Blaustein et al., 1994; Gehrke et ul., In press], see also
Chapters 2 and 4), most of the ecosystem-level responses of solar UV-B are anticipated to be mediated
through the effects on plants. As shown in Figure 3.4, the major anticipated effects of increased solar UV-
B on agricultural and nonagricultural ecosystems (such as forests, grasslands, savannahs, deserts, tundra,
etc.) may result from changes in plant growth and form and secondary chemical composition. Although the
principal processes may be the same in highly managed agroecosystems and in nonagricultural ecosystems,
their importance is thought to be different. Therefore, different schemes are presented for each in Figure
3.4. Some forest systems, such as plantations, can be considered as agricultural systems for these purposes.
Agriculture
Forests, -grasslands, deserts, etc.
species
composition
(biodiversity)
Fig. 3.4. Possible important consequences of increased solar UV-B in highly managed systems such as agricultural and
forest plantation systems and in nonagricultural, less intensively managed ecosystems.
54
-------
Competitive Balance

In forests, grasslands, etc., overall primary plant productivity may not be greatly affected by ozone
reduction even if the growth of some plants is diminished. However, since plant species differ greatly in
growth responsivity to UV-B, it is anticipated that a productivity reduction of one species will probably
lead to increased productivity of another, more UV-tolerant species. This is conceivable because more
resources (e.g., light, moisture and nutrients) will be available to the tolerant species. Thus, the overall
productivity of the system may well remain about the same while species composition may change.
However, a change in the balance of species could have far-reaching consequences for many ecosystems.
Another mechanism whereby the competitive balance of plant species can be changed by increased UV-B
is through changes in plant form. Even if plant production per se is not affected by increased UV-B,
changes in plant form can result in changes in which species can more effectively compete for sunlight.
This phenomenon has been demonstrated in several experiments. For example, in a five-year field study
using modulated UV-B lamp systems, the competitive balance of two species (wheat and a common weed,
wild oat) could be changed even though the increased UV-B had no effect on production and growth of
these species if grown by themselves [Barnes et */., 1988]. A quantitative analysis of competition for
sunlight in the mixed stands with and without supplemental UV-B showed that subtle changes in plant form
of the two species were sufficient to change the balance of competition for sunlight which is necessary for
photosynthesis [Ryel et */., 1990]. Therefore, one species can achieve some advantage over the other because
one captures more sunlight for photosynthesis. In these experiments, the wheat benefited from increased
UV-B and the weed suffered. However, in other mixtures of crop and weeds, the situation could well be
reversed. Also, other changes in plant form, such as greater allocation of biomass to roots, might change
competitive effectiveness of individual species for soil moisture and nutrients.

In grasslands and forests that are not managed intensively, similar changes in species composition may
be experienced. Of course, in forests this would take rfoTig time to be realized. Also, if there are only a -
few tree species present and they all are sensitive to solar UV-B and experience growth reduction, overall
forest productivity could decrease. Ecosystem-level experiments with nonagricultural systems are only
beginning [Johanson et al., In press].

Timing of Life Phases

The timing of life phases of plants is a combination of response to environmental factors and the
genetic constitution of the plant. This timing of events such as flowering, entering and breaking of
dormancy, and even senescence is important not only to the individual plant, but also in how plants interact
with other plants and animals. For example, a shift in the timing of flowering can mean that a plant
species might not have sufficient insect pollinators available at the new time of flowering either because
the insects are not present or because other plant species are attracting these pollinators. Such changes
could also conceivably be important in agricultural systems, but intervention with management options may
make these changes less important. As indicated earlier in this chapter, increased UV-B has been shown to
advance or delay (depending on species) the time of flowering in plants. There is little work at present on
flowering responses and virtually nothing on other potential effects of UV-B on life phase timing.

Plant Secondary Metabolism

Another pathway by which increased solar UV-B can have an influence at the ecosystem level is through
changes in secondary metabolism of plant tissues. Increased UV-B can alter secondary chemical
composition. It has been shown repeatedly that flavonoids and related phenolic compounds increase when
plants are exposed to increased UV-B. Apart from the UV-B protection afforded by increases of these
compounds, there are many other ecological implications of changes in these and related compounds.
These compounds are important for plants in deterring insects and other herbivores from consuming plant
tissues and they play a role in resistance to pathogens. For example, McCloud and Berenbaum [1994] have
shown that UV-B can increase fiiranocoumarin content of plant tissue which, in turn, results in slower
development of certain insect larvae during early life stages of the larvae. In some legume, conifer and in

55
-------
one woody dicotyledon (Vitis vinifera) UV-B has been shown to induce phytoalexin synthesis [Beggs
Wellmann 1994}; some phytoalexins are considered to be toxic to humans and many animal species, e.g.,
coumestol a compound with estrogenic properties which is induced in bean plants exposed to UV-B [Beaas
etal.1985]. •**

Secondary compounds that are important as structural materials in plants, such as lignin, are also
related to flavonoids and phenolic compounds. If the ratio of lignin to cellulose in plant tissues changes,
it can alter the rate of decomposition. This has very important implications for biogeochemical cycles as "
discussed in Chapter 5.

Overall, the consequences of increased solar UV-B in forests, grasslands and other nonagricultural
ecosystems may involve several complex pathways (Figure 3.4) rather than simply a reduction in overall
ecosystem primary productivity. However, the effects of these more involved pathways are difficult to
predict without conducting experiments with assemblages of plant species and long-term study of
ecosystem- responses. This has, thus far, received very little attention in actual research.

Further discussion of implications for specific types of ecosystems follows later in this chapter.

UV Protection and Adaptive Responses

UV Penetration

Structural and biochemical changes induced by enhanced levels of UV-B radiation ultimately modify the
penetration of UV radiation into the plant. For example, the induction of UV-screening pigments,
typically flavonoids and certain other phenolic compounds, will reduce the penetration of UV-B radiation
to underlying tissues. Increased wax on leaf surfaces also can contribute to reduced penetration of UV due
to increased reflection from the leaf surface, although reflection for most leaves is usually not more than
10% [Robberecht et al., 1980]. At the structural level, increased: length of inner leaf cells or increases in
cell number, both palisade and spongy mesophyll, influence the penetration and spectral distribution of
UV radiation across a leaf. Direct measurements of UV penetration have been done using a fibre optic
microprobc [Bornman and Vogelmann, 1988; Day et al, 1992, 1993; see also Bornman and Teramura 1993;
DcLucia et al., 1992; Cen and Bornman, 1993]. Ultraviolet radiation penetration varies among different
plant species and this should be reflected in the sensitivity of these species. Penetration of UV-B was
found to be greatest in herbaceous dicotyledons (broad-leaved plants) and was progressively less in woody
dicotyledons, grasses and conifers [Day et al. 1992]. The UV penetration also changes with leaf age;
younger leaves attenuate UV-B radiation less than do the more mature leaves, as was shown for some
conifers [DeLitcia et al. 1991, DeLucia et al. 1992].

Protection and Repair

Although different species exhibit different UV-B attenuation depending on pigments (such as
flavonoids) and leaf structure, the level of attenuation can also change as more UV-B-absorbing pigments
arc synthesized in response to UV-B exposure. Species also differ in their ability to increase UV-B-
absorbing pigment levels. Increased levels of flavonoids have been shown to directly reduce the levels of
damage by UV-B [Tevini et al., 1991b]. The link between flavonoid levels and UV-B sensitivity is most vivid
in extreme cases. For example, Li et al. [1993] showed that mutants of a mustard species, Arabidopsis
thalianti, that lacked flavonoids were extremely sensitive to the UV radiation. An anthocynanin-deficient
mutant of maize was found to be more sensitive to DNA damage by UV-B than the normal plants
[Sttipleton and Wnlbot 1994]. In cabbage leaves, flavonoids were shown to accumulate in the epidermal
layers in response to mild UV-B exposure. The flavonoids protected the underlying tissues from DNA
damage in the form of thymine dimer formation [Beggs and Wellmann 1994]. In addition to adaptive
responses involving pigment induction, changes in surface waxes and certain leaf structural characteristics
may also contribute to reducing penetration of UV into the plant tissues. Increases in scavengers of free
radicals and active oxygen species may also mitigate the negative effects of UV radiation [see Bornman
and Teramura, 1993J.
56
-------
Another characteristic of plants is the ability to repair damage. This may be exemplified by the
replacement of damaged components, e.g., proteins, or by the light and dark processes involved in repair of
DNA damage. Under illumination, the enzyme DNA photolyase repairs the UV-induced production of
pyrimidine dimers. Both visible and UV-A radiation drive this repair, underlining again the importance of
a balanced spectral regime for experiments not conducted in the field. A very effective repair capacity by
DNA-photolyase in several plant systems (cell cultures, isolated leaves, seedlings and mature plants of
several species) has been demonstrated [Buchholz et al., In press; McLennan 1987], To date, little research
has been done on induction of pyrimidine dimers in plants; a recent exception is the work of Quaite et al.
[1992 a,b] on alfalfa seedlings.

Interaction of UV-B and Other Factors

Plants in nature seldom are affected by only a single stress factor, such as UV-B radiation. Instead,
plants typically respond to several factors acting in concert. Therefore, it is important to keep in mind
that the effectiveness of UV-B radiation can be greatly modified by some of these other factors, in some
cases aggravating, and in some cases ameliorating the overall UV effect.

Water stress commonly occurs in nature. In a field study specifically designed to test the interaction
between UV-B radiation and water stress, Sullivan and Teramura [1990] demonstrated that UV-B mediated
reductions in photosynthesis and growth were observed only in well-watered soybeans. When soybeans were
water stressed, the same UV-B dose produced no significant effect on either photosynthesis or growth. The
interpretation of these observations was that water stress produced a large reduction in photosynthesis and
growth that thereby masked the UV-B effect. Furthermore, water stressed plants produced a higher
concentration of leaf flavonoids, which in turn, provided greater UV-B protection.

Increases of atmospheric CO2 and global warming are anticipated in scenarios of future climate
change. Model calculations predict that the average gk&al temperature will rise by 1.5 - 4.5° and that
atmospheric CO2 concentration will double by the latter part of the next century [Intergovernmental Panel
on Climate Change 1992]. When studied independently, plant growth responses to changes in UV-B
radiation and atmospheric CO2 concentration generally are thought to be in opposite directions, thereby
leading some to the hypothesis of a canceling of effects. To date, only a few experiments have been
specifically designed to examine this important interaction. The first such study [Teramura et al., 1990b]
included two cereal crops (rice and wheat) and one legume (soybean). In that study, the increase in growth
and seed yield resulting from a CO2 enrichment was eliminated by UV-B radiation in rice, reduced in wheat
and unaffected in soybean. This suggests that overestimates in production may be made for cereal crops if
CO2 enrichment is considered without UV-B radiation.

In loblolly pine, Sullivan and Teramura [1994] reported that the combined effects of UV-B and CO
produce changes in the proportion of dry matter in roots compared with aboveground shoots. At present-
day levels of CO2, UV-B caused more shoot production than roots, while the same UV-B dose resulted in
more roots at elevated levels of CO2. The implications of these changes is that plant competition and,
therefore, ultimately community composition might be altered by these changes in allocation patterns, as
described earlier.

As mentioned above, global climate change will likely include increased global mean temperatures in
addition to increased UV-B radiation. Unfortunately, only, very limited information is available on the
consequences of these combined effects. In a study with sunflower and maize seedlings in the ozone-filter
cuvette system mentioned earlier, Tevini et al. [1991b] found that photosynthesis was unaffected (maize) or
declined (sunflower) with higher temperature when the UV-B in sunlight was attenuated with the ozone
filter. In contrast, overall seedling production was greater at higher temperatures in both species under
conditions approaching ambient solar UV-B. This observation might be attributed to accelerated plant
development at the higher temperature.

Many metals such as cadmium, nickel, copper and lead, which can accumulate to high concentrations
from human activities, are toxic to plants. The stress imposed by high levels of metals may be further
compounded with increased UV-B radiation. Dube and Bornman [1992] showed that in spruce (Picea abies)
57
-------
with low levels of supplemental UV-B, the effect of the addition of cadmium was greater than for either
stress alone for some of the parameters measured. Mobilization of the essential trace element zinc can be
reduced by UV-B radiation [Ambler et al., 1975].

The degree of susceptibility of plants to disease and insect attack may change under elevated levels of
UV-B radiation. These effects will vary among species, cultivar and plant age. For example, certain
diseases may be less damaging to the plant under conditions of high UV-B, while the severity of others may
be increased. The latter was shown in a study where sugar beet grown under elevated levels of UV-B
radiation was infected with a fungus Cercospora beticola leading to a deleterious additive effect from the
two stress factors [Panagofoulos et al., 1992]. The timing of infection is also of importance. Plants first
exposed to UV-B radiation may be more susceptible to subsequent infection as shown in a study of
cucumber infected with Colleotrichum lagenarium and Cladosporittm cucumerinum prior to UV-B exposure
[Orth et al., 1990]. Infection after UV exposure had no effect on the severity of the disease.

Interaction of UV-B with tropospheric air pollutants is also of concern although little work has been
thus far conducted in this area. One field study of soybean plants showed them to be sensitive to ozone in
the air. However, they were not sensitive to UV-B supplements from lamps under the particular test
conditions and there were no significant interactions of supplemental UV-B and ozone [Miller et al.,
1994].

Implications for Agriculture, Forests and Other Ecosystems

Crops

One of the primary concerns of future increases in solar UV-B radiation is its potential effect on
global agriculture. Despite the enormous potential consequences, we cannot yet make a quantitative
prediction of anticipated effects resulting from stratospheric^ ozone depletion. This results from the
limitation in the controlled-environment studies as discussed earlier and the overall paucity of
experiments performed in field trials. Even in comparisons of field studies, there are large differences in
temperature, precipitation, soil types, etc. from year to year and in different locations. This adds to the
difficulty in making generalizations about the effects.

A six-year field experiment was conducted to evaluate the effects of UV-B supplementation in two
commercially grown soybean cultivars [Teramura et al., 1990a]. These cultivars were specifically selected
for their contrasting UV-B sensitivity previously determined by screening over 50 soybean cultivars under
greenhouse conditions. (For perspective, nearly 2 out of 3 of the cultivars screened for UV-B sensitivity in
the greenhouse exhibited sensitivity to UV-B.) In the field experiments, artificial lamps with selected
filters were used in addition to the normal solar radiation. Plants were exposed to either ambient levels of
solar UV-B or ambient radiation supplemented with UV-B emitted by the lamps. When evaluated over the
entire six-year period, yield in the sensitive cultivar was reduced by 19 to 25%, in four of the six years
(Figure 3.5). The other two years were characterized as hot and dry and all plants in the field experienced
considerable water stress. As shown in subsequent field and greenhouse studies, the effectiveness of UV-B
radiation is masked when the plants were subjected to other stresses such as drought (see section above).
In the same study, while the sensitive soybean cultivar exhibited decreased yield, production increased by
4 to 22% in the tolerant soybean cultivar. Such cultivar differences in the response to UV-B radiation may
be important in future plant breeding considerations, since it suggests that UV-B tolerance already
naturally exists in the modern soybean germplasm. A number of studies have shown that in addition to the
wide range of sensitivity found among species, an impressive array of cultivar responses also have been
observed. Figure 3.3 shows the proportion of sensitive rice cultivars screened under greenhouse conditions.
Note that in this example, UV-B radiation elicits both positive as well as negative responses in rice.
Similarly, wide-ranging cultivar differences have been reported in a number of plant ranging from crops
such as soybean to forest tree species such as loblolly pine.
58
-------
Year
Fig. 3.5 Summary of yields in a 6-year field study using two soybean cultivars: Essex previously identified as UV-B
sensitive and Williams, UV-B tolerant. The studies utilized filtered fluorescent sun lamps to simulate a 25%
ozone depletion over College Park, Maryland (39° NJatiiude). Values presented above represent percent
changes from control plants receiving only ambient levels of UV-B radiation [Teramura era/., 1990a] Asterisks'
represent years with drought.

In addition to quantitative changes in crop yield, evidence exists for qualitative changes as well. For
instance, in the study mentioned above, UV-B radiation also resulted in small changes on the order of 1 to
5% in the protein and oil content of the soybean seed.

A wide range of experimental protocols and methodologies have been used by different investigators
which complicates the assessment of overall effects of elevated UV-B on crops. Several experiments
reveal effects of UV-B and several do not. Because of the relatively few field studies that have been
conducted, a quantitative prediction of the potential consequences for global food production resulting
from increased solar UV-B is not now possible.

Forests

Despite the fact that over two thirds of global terrestrial productivity occurs in forest ecosystems,
little information exists on the effects of UV-B radiation on forest tree species. Tropical forests, though
representing nearly one half of global productivity and much of the total tree species diversity, have
received very little attention thus far in respect to the ozone reduction problem. Although little ozone
reduction has thus far occurred in the tropics, only a small decrease of ozone at these latitudes results in
an absolute increase of UV-B since solar UV-B is already very intense (see Chapter 1). One recent study
showed that excluding existing solar UV-B with filters can result in increased growth of some tropical'
tree species [Senrles and, Caldwell, in press]. However, for the most part, the effects of UV-B radiation on
tropical tree species have been largely ignored.

Fortunately, there is some information for midtemperate latitude tree species. Because they are long
lived, trees present a unique opportunity to observe the longer-term accumulative aspects of UV-B
exposure. In one field study using loblolly pine [Sullivan and Teramura, 1992], seedlings from several
different geographic regions were grown for three consecutive years under UV-B lamps in a field
experiment. Seedlings were exposed to either ambient solar UV-B or ambient levels supplemented with
59
-------
the UV-B from lamps, similar to the soybean study above. After only the first year of UV-B exposure,
reductions were observed in biomass of seedlings derived from several geographic areas. By the end of the
third year, these biomass reductions were several-fold larger. These overall growth reductions were
generally associated with small decreases in both roots and shoots, but not necessarily accompanied by
reductions in photosynthesis. This may be due to changes in needle growth or shifts of allocation as has
been found for some crop species. Therefore, these results suggest that the UV-B effects may be
accumulative in long-lived plants such as trees, and that even small changes in UV-B radiation might have
significant effects over the life time of the trees. Even in the absence of direct UV-B effects on tree
biomass, UV-B radiation may still have ecological implications. Changes in plant architecture or biomass
allocation could result in alterations in tree seedling competition, ultimately affecting patterns of forest
succession.

Other Ecosystems

Although absolute UV-B irradiance is naturally very low in subarctic and Arctic ecosystems such as
tundra, there is experimental evidence that the plants in such a system react to increases in UV-B
associated with realistic levels of ozone depletion. In a recent field study in northern Sweden, natural
dwarf shrub vegetation containing two evergreen species (Emfetrum hermaphroditum and Vaccinium vitis
ifaa.) and two deciduous species (V. myrtillus and V. ulijrinosum) was exposed to artificially enhanced
UV-B radiation. Leaf thickness was increased (V. vitis idaa.) or decreased (the deciduous species) while
stem growth over a two-year period was retarded more in evergreen species than in deciduous species. This
suggests that a UV-B increase over an extended time could result in species composition changes
[Johnmon et al. In press]. Not only growth inhibitions, but also species-specific morphological changes
have been observed, which, with time, may result in altered community composition.

Chemical Effects of Ozone Depleting Substances and
Breakdown Products of Replacement Substances

Trifluoroacetic acid (TFA) is a breakdown product of HFC134a, HCFC123 and 124 [WMO/UNEP
1994] that is anticipated to achieve a final average concentration less than one thousandth of that required
for toxicity of plants, making general impacts on the earth's vegetation by TFA unlikely. Substantially
higher concentrations of TFA may occur in areas with low precipitation since the same quantity of TFA
would be concentrated in less rainfall. Toxic concentrations in soils could conceivably build up in areas
with high evaporation rate or lacking runoff, where salt stress excludes vegetation except for very
specialized species. Although plants in such areas are of minor importance both economically and for
global primary production, some are essential for migratory birds and other wildlife. Further
investigations should therefore be focused on such areas and species.

Conclusion

Mechanisms of UV-B action on plant systems are reasonably well understood when compared with our
ability to assc!* potential consequences of enhanced UV-B at the level of ecosystems. As global change
involves not only increased solar UV-B, but also increased atmospheric CO; concentrations and
temperature chj-r.gcs, realistic assessments of the effect of si^iD^.-iteric ozone reduction need to consider
intending fdc:o:s. Effects of enhanced UV-B on terrcstjlr.1 i.:u;-,y.stcms are anticipated, both in
agriculture, and in nonagricultural areas such as forests, tundra, etc., but prediction of exact consequences,
and sometimes even the direction of these changes, is not currently possible.

References

Ambler, J.E., D.T. Krizek, and P. Semeniuk, Influence of UV-B radiation on early seedling growth and
translocation of Zn from cotyledons in cotton, Physiologia Plantarum 34:177-181, 1975.
Ballarc, C.L., P.W. Barnes, and S.D. Flint, Inhibition of hypocotyl elongation by ultraviolet-B radiation
in de-etiolating tomato seedlings. I. The photoreceptor, Physiologic Plantarum, in press.
60
-------
Barnes, P.W., P.W. Jordan, W.G, Gold,; S.D. Flint, and M.M. Caldwell, Competition, morphology and
canopy structure in wheat (Triticum aestivum L.) and wild oat (Avena fatua L.) exposed to enhanced
ultraviolet-B radiation, Functional Ecology 2:319-330, 1988.

Barnes, P.W., S. Maggard, S.R. Holman, and B. Vergara, Intraspecific variation in sensitivity to UV-B
radiation in rice, Crop Science 33: 1041-1046, 1993.

Beggs, C.J. and E. Wellmann, Photocontrol of flavonoid biosynthesis, pp 733-750 in Photomorphogenesis
in plants, Vol. 2, R.E. Kendrick and G.H.M. Kronenberg (eds.), Kluver Academic, Dordrecht, 1994. -

Beggs, C.J., Stolzer-Jehle A. and E. Wellmann, Isoflavonoid formation as an indicator of UV-B stress in
bean (Phaseolus vulgaris L.) leaves. The significance of photorepair in assessing potential damage by
increased solar UV-B radiation, Plant Physiology 79:630-634, 1985.

Blaustein, A.R., P.O. Hoffman, D.G. Hokit, J.M. Kiesecker, S.C. Walls, and J.B. Hays, UV repair and
resistance to solar UV-B in amphibian eggs: A link to population declines?, Proc. Natl. Acad. Sci.
91:1791-1795, 1994.

Bornman, J.F., Target sites of UV-B radiation in photosynthesis of higher plants, Journal of
Photochemistry and Photobiology B: Biology 4:145-158, 1989.

Bornman, J.F. and A.H. Teramura, Effects of ultraviolet-B radiation on terrestrial plants, pp. 427-471 in
Environmental UV-photobiology, A.R., Young, L.O. Bjorn, J. Moan and W. Nultsch (eds.), Plenum
Press, New York, 1993.

Bornman, J.F. and T.C. Vogelmann, Penetration of blue and UV radiation measured by fibre optics in
spruce and fir needles, Physiologia Plantarum 72: 699-705, 1988.

Buchholz, G., Ehmann, B. and E. Wellmann, UV-inhibition of phytochrome induced flavonoid biosynthesis
and DNA-photolyase formation in mustard cotyledons (Sinapsis alba L.) Plant Physiology (in press).

Caldwell, M.M., Solar ultraviolet radiation as an ecological factor for alpine plants, Ecological
Monographs 38:243-268, 1968.

Caldwell, M.M., Solar ultraviolet radiation and the growth and development of higher plants, pp. 131-177
in Photophysiology. Volume 6, A.C., Giese (eds.), Academic Press, New York, 1971.

Caldwell, M.M. and S.D. Flint, Implications of increased solar UV-B for terrestrial vegetation, pp.
495-516 in The role of the stratosphere in global change, M.L., Chanin (eds.), Springer-Verlag,
Heidelberg, 1993.

Caldwell, M.M. and S.D. Flint, Solar ultraviolet radiation and ozone layer change: Implications for crop
plants, pp. 487-507 (in press) in Physiology and determination of crop yield, K., Boote, J.M. Bennett,
T.R. Sinclair and G.M. Paulsen (eds.), ASA-CSSA-SSSA, Madison, WI, 1994a.

Caldwell, M.M. and S.D. Flint, Stratospheric ozone reduction, solar UV-B radiation and terrestrial
ecosystems, Climatic Change (in press), 1994b.

Caldwell, M.M., L.B. Camp, C.W. Warner, and S.D. Flint, Action spectra and their key role in assessing
biological consequences of solar UV-B radiation change, pp. 87-111 in Stratospheric ozone reduction,
solar ultraviolet radiation and plant life, R.C., Worrest and M.M. Caldwell (eds.), Springer, Berlin,
1986.

Caldwell, M.M., A.H. Teramura, and M. Tevini, The changing solar ultraviolet climate and the ecological
consequences for higher plants, Trends in Ecology and Evolution 4:363-367, 1989.

Caldwell, M.M., S.D. Flint, and P.S. Searles, Spectral balance and UV-B sensitivity of soybean: a field
experiment, Plant, Cell and Environment 17:267-276, 1994.

Cen, Y.P. and-J.F. Bornman, The effect of exposure to enhanced UV-B radiation on the penetration of
monochromatic and polychromatic UV-B radiation in leaves of Brassica napus, Physiologia Plantarum
87:249-255, 1993.

Crutzen, P.J., SSTs—a threat to the earth's ozone shield, Ambio 1:41-51, 1972.
61
-------
Dai, Q.J., V.P. Coronel, B.S. Vergara, P.W. Barnes, and A.T. Quintos, Ultraviolet-B Radiation Effects
on Growth and Physiology of four Rice Cultivars, Crop Science 32:1269-1274, 1992.

Day, T.A., T.C. Vogelmann and E.H. DeLucia, Are some plant life forms more effective than others in
screening out ultraviolet-B radiation? Oecologia 92: 513-519.

Day, T.A., G. Martin and T.C. Vogelmann, Penetration of UV-B radiation in foliage: evidence that the
epidermis behaves as a non-uniform filter, Plant Cell Environment 16: 735-741, 1993.
DeLucia, E.H., T.A. Day, and T.C. Vogelmann, Ultraviolet-B radiation and the Rocky Mountain
environment: measurement of incident light and penetration into foliage, Current Topics in Plant
Biochemistry and Physiology 10:32-48, 1991.

Delucia, E.H., T.A. Day, and T.C. Vogelman, Ultraviolet-B and Visible Light Penetration into Needles of
two Species of Subalpine Conifers During Foliar Development, Plant, Cell and Environment 15-921-
929, 1992.

Dubc, S.L. and J.F. Bornman, Reponse of spruce seedlings to simultaneous exposure to ultraviolet-B
radiation and cadmium, Plant Physiology and Biochemistry 30:761-767, 1992.

Ensminger, P.A., and E. Schafcr, Blue and ultraviolet-B light photoreceptors in parsley cells,
Photochemistry and Photobiology 55:437-447.

Flint, S.D. and M.M. Caldwell, Influence of floral optical properties on the ultraviolet radiation
environment of pollen, American Journal of Borany 70:1416-1419, 1983.

Flint, S.D. and M.M. Caldwell, Partial inhibition of in vitro pollen germination by simulated solar
ultraviolet-B radiation, Ecology 65:792-795, 1984.

Gchrkc, C., U. Johanson, T. Callaghan, D. Chadwick, and C.H. Robinson, The impact of enhanced
ultraviolct-B radiation on litter quality and decomposition processes in Vaccinium leaves from the
Subarctic, Oikos in press.

Green, A.E.S., K.R. Cross, and L.A. Smith, Improved analytic characterization of ultraviolet skylight
Photochemistry and Photobiology 31:59-65, 1980. '

Intergovernmental Panel on Climate Change. IPCC Scientific Assessment, J.T., Houghton, G.J. Jenkins and
J.J. Ephraums (cds.), Cambridge University Press, Cambridge, 1992.

Johanson, U., C. Gehrkc, L.O. Bjorn, T.V. Callaghan, and M. Sonnesson, The effects of enhanced UV-B
radiation on a subarctic heath system, Ambio (submitted), 1994.

Johnston, H.S., Reduction of stratospheric ozone by nitrogen oxide catalysts from supersonic transport
exhaust, Science 173:517-522, 1971.

Krupa, S.V. and R.N. Kickert, The Greenhouse Effect -Impacts of Ultraviolet-B (UV-B) Radiation,
Carbon Dioxide (CO2), and Ozone (O-3) on Vegetation, Environmental Pollution 61:263-393, 1989.

Li, J.Y., T.M. Oulee, R. Raba, R.G. Amundson, and R.L. Last, Arabidopsis flavonoid mutants are
hypersensitive to UV-B irradiation, The Plant Cell 5:171-179, 1993.

Mark, U., Zur VVirkung erhohter artifizieller and solarer UV-B-Strahlung in Kombination mit erhohter
Temperatur und Kohlendioxidkonzentration auf das Wachstum und den Gaswechsel von ausgewahlten
Nutzpflanzen, Karlsr. Beitr. Entw. Okofhysiol. 11:1-220, 1992. (Ph.D. dissertation).

McCloud, E.S. and M.R. Berenbaum, Stratospheric ozone depletion and plant-insect interactions: Effects
of UVB radiation on foliage quality of Citrus jambhiri for Trichoplusia ni, Journal of Chemical Ecology
ZUto20"539) 1994.

McLennan, A.G., The repair of ultraviolet light-induced DNA-damage in plant cells, Mutation Research
181:1-74

Miller, J.E., F.L. Booker, E.L. Fiscus, A.S. Heagle, W.A. Pursley, S.F. Vozzo, and W.W. Heck,
Ultraviolct-B radiation and ozone effects on growth, yield, and photosynthesis of soybean, Journal of
Environmental Quality 23:83-91, 1994. '
62
-------
Orth, A.B., A.H. Teramura, and H.D. Sisler, Effects'of;ultraviolet-B radiation on fiingal disease
development in Cucumis sativus, American Journal of Botany 77:1188-1192, 1990.

Panagopoulos, I., J.F. Bornman, and L.O. Bjorn, Response of Sugar Beet Plants to Ultraviolet-B (280-
320 nm) Radiation and Cercospora Leaf Spot Disease, Physiologia Plantarum 84:140-145, 1992.
Predieri, S., D.T. Krizek, C.Y. Wang, R.M. Mirecki, and R.H. Zimmerman, Influence of UV-B Radiation
on Developmental Changes, Ethylene, CO2 Flux and Polyamines in cv. Doyenne d'Hiver Pear Shoots
Grown In vitro, Physiologia Plantarum 87:109-117, 1993.

Quaite, F.E., B.M. Sutherland, and J.C. Sutherland, Action Spectrum for DNA Damage in Alfalfa Lowers
Predicted Impact of Ozone Depletion, Nature 358:576-578, 1992a.

Quaite, F.E., B.M. Sutherland, and J.C. Sutherland, Quantitation of pyrimidine dimers in DNA from UV-
B-irradiated alfalfa (Medicago sativa L.) seedlings, Applied and Theoretical Electrophoresis 2:171-175,
Rau, W., H. Hoffmann, A. Huber-Willer, U. Mitzke-Schnabel, and E. Schrott, Die Wirkung von UV-B auf
photbregulierte Entwicklungsvorgange bei Pflanzen, Gesellschaft filr Strahlen-und Umweltforschunn
mbH, Miinchen Abschlussbericht, 1988.

Robberecht, R., M.M. Caldwell, and W.D. Billings, Leaf ultraviolet optical properties along a latitudinal
gradient in the arctic-alpine life zone, Ecology 61:612-619, 1980.

Ros, J., Zur Wirkung von UV-Strahlung auf das Streckungswachstum von Sonnenblumenkeimlingen
(Helianthus annum L.), Karlsr. Beitr. Entw. Okophysiol. 8:1-157, 1990 (Ph.D. dissertation).
Ryel, R.J., P.W. Barnes, W. Beyschlag, M.M. Caldwell, and S.D. Flint, Plant competition for light
analyzed with a multispecies canopy model. I. Model development and influence of enhanced UV-B
conditions on photosynthesis in mixed wheat and wild oat canopies, Oecologia 82:304-310, 1990.
Saile-Mark, M., Zur Beteiligung von Phytohormonen arf Wachstum und Blutenbildung verschiedener
Bohnenkulturvarietaten (Phaseolus vulgaris L.) in Abhangigkeit von artifizieller und solarer UV-B-
Strahlung, Karlsr. Beitr. Entw. OkofhysioL. 13:1-152, 1993.

Searles, P.S., M.M. Caldwell, and K. Winter, The response of five tropical dicotyledon species to solar
ultraviolet-B radiation, American Journal of Botany, in press.

Setlow, R.B., The wavelengths in sunlight effective in producing skin cancer: a theoretical analysis
Proceedings of the National Academy of Science USA 71:3363-3366, 1974.

Stapleton, A.E., and V. Walbot, Flavonoids can protect maize DNA from the induction of ultraviolet
radiation damage, Plant Physiology 105:881-889.

Staxen, I. and J.F. Bornman, A morphological and cytological study of Petunia hybrida exposed to UV-B
radiation, Physiologia Plantarum 91: 735-740, 1994.

Steinmiiller, D., On the effect of ultraviolet radiation (UV-B) on leaf surface structure and on the mode
of action of cuticular lipid biosynthesis in some crop plants, Karlsr. Beitr. Entw. Okophysiol. 6:1-174,

Sullivan, J.H. and A.H. Teramura, Field study of the interaction between solar ultraviolet-B radiation and
drought on photosynthesis and growth in soybean, Plant Physiology 92:141-146, 1990.
Sullivan, J.H. and A.H. Teramura, The effects of ultraviolet-B radiation on loblolly pine 2 growth of
field-grown seedlings, Trees 6:115-120, 1992.

Sullivan, J.H. and A.H. Teramura, The effects of UV-B radiation on loblolly pine. 3. Interaction with
CO2 enhancement, Plant, Cell and Environment 17:311-317, 1994.

Teramura, A.H. and N.S. Murali, Intraspecific differences in growth and yield of soybean exposed to
ultraviolet-B radiation under greenhouse and field conditions, Environmental and Experimental Botany
^0:07-75, 198o,

Teramura, A.H. and J.H. Sullivan, Effects of UV-B radiation on photosynthesis and growth of terrestrial
plants. Photosynthesis Research 39:463-473, 1994.

63
-------
Teramura, A.H., J.H. Sullivan, and J. Lydon, Effects of UV-B radiation on soybean yield and seed quality: A
six-year field study, Physiologia Plantarum 80:5-11, 1990a.
Tcramura, A.H., J.H. Sullivan, and L.H. Ziska, Interaction of elevated ultraviolet-B radiation and CO on
productivity and photosynthetic characteristics in wheat, rice, and soybean, Plant Phvsioloay 94 '470-
475, 1990b. ' '

Tcramura, A.H., L.H. Ziska, and A.E. Sztein, Changes in growth and photosynthetic capacity of rice with
increased UV-B radiation, Physiologia Plantarum 83:373-380, 1991.

Tevini, M., Effects of enhanced UV-B radiation on terrestrial plants, pp. 125-153 in UV-B radiation
and ozone depletion: effects on humans, animals, plants, microorganisms, and materials, M., Tevini (eds )
Lewis Publishers, Boca Raton, Florida, 1993.

Tevini, M., UV-B effects on terrestrial plants and aquatic organisms, Progress in Botany 55:174-190 (in
press), 1994.

Tevini, M. and W. Iwanzik, Effects of UV-B radiation on growth and development of cucumber seedlings,
pp. 271-285 in Stratospheric ozone reduction, solar ultraviolet radiation and plant life, R.C., Worrest and
M.M. Caldwell (cds.), Springer-Verlag, Berlin, 1986.

Tevini, M. and A.H. Teramura, UV-B effects on terrestrial plants, Photochemistry and Photobioloay
50:479-487, 1989.

Tevini, M., U. Mark, and M. Saile, Plant experiments in growth chambers illuminated with natural
sunlight, pp. 240-251 in Environmental research with plants in closed chambers. Air pollution research
report 26, H.D., Payer, T. Pfirrman and P. Mathy (eds.), Commission of the European Communities
Belgium, 1990.

Tevini, M., J. Braun, and G. Fieser, The protective function of the epidermal layer of rye seedlings against
ultraviolet-B radiation, Photochemistry and Photobiolog£J:>3:329-333, 1991a.

Tevini, M., U. Mark, and M. Saile-Mark, Effects of enhanced solar UV-B radiation on growth and
function of crop plant seedlings, Current Topics in Plant Biochemistry and Physiology 10:13-31, 1991b.
WMO/UNEP Scientific assessment of ozone depletion: 1994, WMO global ozone research and
monitoring report no. 37.

Ziska, L.H., A.H. Teramura, and J.H. Sullivan, Physiological sensitivity of plants along an elevational
gradient to UV-B radiation, American Journal of Botany 79:863-871, 1992.
64
-------
CHAPTER 4
EFFECTS OF INCREASED SOLAR ULTRAVIOLET
RADIATION ON AQUATIC ECOSYSTEMS

D.-P. Hader (FRG), R.C. Worrest (USA), H.D. Kumar (India), and R.C. Smith (USA)
Summary
SeaweeriMn f U ' °f finfish> shellf^ and
seaweed. More than 30% of the world's animal protein for human consumption comes from the sea and in
many countries, particularly the developing countries, this percentage is significantly higher As a 'result it
is important to know how increased levels of exposure to solar UV-B radiation (280-315 nm) might '
affect the productivity of aquatic systems.

In addition, the oceans play a key role with respect to global warming. Marine phytoplankton are a
major sink for atmospheric carbon dioxide, and they have a decisive role in the development of future
trends or carbon dioxide concentrations in the atmosphere. The relative importance of the net uptake of
carbon dioxide by the biological pump in the ocean and by the terrestrial biosphere is a topic of much
current research. r

Phytoplankton form the foundation on which the very survival of aquatic food webs depends Marine
pnytoplankton are not uniformly distributed throughout the oceans of the world. The highest concentrations
are found at high latitudes while, with the exception of upwelling areas on the continental shelves the
tropics and subtropics have 10 to 100 times lower concentrations. In addition to nutrients, temperature
salinity and light availability, the high levels of exposure to solar UV-B radiation that normally occur
witrun the tropics and subtropics may play a role in phytoplankton distributions.

A major loss in primary biomass productivity may have significant consequences for the intricate food
web in aquadc ecosystems and affect food productivity. It has been estimated that a 16% ozone depiction
could result in a 5% loss in phytoplankton, which equals a loss of about 7 million tons of fish per year
Biological effects of small changes in UV-B exposure may be difficult to determine because the
biological uncertainties and variations are large, and the baseline productivity for pre-ozone-loss eras is
not well established.

Phytoplankton productivity is limited to the euphoric zone, the upper layer of the water column in
which there is sufficient sunlight to support net productivity. The position of the organisms in the
euphoric zone is influenced by the action of wind and waves. In addition, many phytoplankton are capable
of active movements that enhance their productivity and, therefore, their survival. Like humans
phytoplankton cannot perceive, and thereby avoid, UV-B radiation. Exposure to solar UV-B radiation has
been shown to affect both orientation mechanisms and motility in phytoplankton, resulting in reduced
survival rates for these organisms.

Researchers have directly measured the increase in, and penetration of, UV-B radiation in Antarctic
waters, and have provided conclusive evidence of direct ozone-related effects within natural phytoplankton
communities. Making use of the space and time variability of the UV-B front associated with the
Antarctic ozone hole, researchers assessed phvtoplankton productivity within the hole compared to that
outside the hole. The results show a direct reduction in phytoplankton production due to ozone-related
increases in UV-B. One study has indicated a 6 - 12 % reduction in the marginal ice zone.

In recent years, there has been an increased interest in UV-B effects on macroalgae and seagrasses In
contrast to the phytoplankton, most macrophytes are attached to their growing site, thereby restrictine
them to specific growth areas and the resultant exposure to UV-B radiation. Recent studies have
demonstrated that photosynthesis is inhibited in many red, brown, and green benthic algae.
rr,h radiationuhas been, found to "use damage to early developmental stages of fish, shrimp,
crab, amphibians and other animals. The most severe effects are decreased reproductive capacity and
impaired larval development. Even at current levels, solar UV-B radiation is a limiting factor', and small
increases in UV-B exposure could result in significant reduction in the size of the population of
65
-------
consumer organisms. At high latitudes (over 40°N) the late-spring increases in UV-B exposure may affect
some species because the UV-B enhancement occurs at critical phases of their development. Even small
increases or temporary fluctuations in UV-B may affect relatively sensitive species.

Recent studies have addressed the potential impact of chlorofluorocarbon substitutes and their
degradation products. Some HFCs and HCFCs, notably HFC134a, HCFC123, and HCFC124, are
degraded generating trifluoroacetic acid (TFA) as their main product. TFA is mildly toxic to most marine
and freshwater phytoplankton. It is still speculative if TFA is concentrated in the food web. Even if
produced well into the next century, TFA is unlikely to reach toxic levels for oceanic phytoplankton;
however, it could reach toxic levels in restricted aquatic systems.

Although there is overwhelming evidence that increased UV-B exposure is harmful to aquatic
ecosystems, the potential damage can only be roughly estimated at the present time.
Introduction

Aquatic ecosystems balance terrestrial ecosystems in biomass production which are assumed to
incorporate large amounts of atmospheric carbon into organic material with estimates between 90 and 100
gigatons (Gt, 10'tons) annually [Houghton and. Woodwell, 1989; Siejenthaler and Sarmiento, 1993].
Therefore it is important to know what effect increased solar UV-B irradiation has on marine productivity
and on the whole ecosystem depending on this productivity as well as climatological processes linked with
it [Smith, 1989; Prezelin etal., 1993]. As only 0.5 % of the water surface is freshwater, the marine systems
are by far the most important in the context of global carbon cycles. On the other hand, a recent workshop
on freshwater ecosystems convincingly demonstrated that lakes are excellent model systems for studying
larger marine environments, and many of these systems are locally important.

Since most macroalgae are restricted to coastal areas, the largest share in biomass production can be
attributed to phytoplankton. Phytoplankton constitute the basis for the intricate food web in the oceans
and thus arc a prerequisite for the crop of fish, crustaceans_and mollusks. Furthermore, as they are
responsible for the uptake of half of the carbon dioxide from the atmosphere, any reduction in the uptake
capacity would result in an increase in the greenhouse effect, with subsequent impacts on global climate
change. Recent investigations indicate that many aquatic ecosystems are under considerable UV-B stress
even at current levels [Hader, 1993a; Cullen and Lesser, 1991; Smith et al., 1992]. Being dependent on solar
energy for photosynthesis, phytoplankton are restricted to the upper layers in the water column where they
arc exposed to high levels of short wavelength radiation. The subject of UV-B effects on aquatic
ecosystems has been covered in a number of recent reviews [Hader, 1993b; Acevedo and Nolan, 1993; Weiler
and Penhale, 1994; Cullen and Neale, 1994; U.S. DOE, 1993; SCOPE, 1992a,b; Holm-Hansen et al., 1993a,b;
Tevtttt, 1993; Eiggs and Joyner, 1994; Williamson and, Zagarese, 1994; Karentz et al., 1994; Smith and Cullen,

Primary producers

Solar UV-B radiation has been found to affect DNA, to impair photosynthesis, enzyme activity and
nitrogen incorporation, to bleach cellular pigments and to inhibit motility and orientation [Dohler et al,
1991; Hader et al., 1989, 1991; Worrest and Hader, 1989; Hader and Worrest, 1991]. DNA is one of the
targets of radiation, but in addition a host of other chromophores and proteins are affected. Thus, UV-B
does not damage one key target in phytoplankton but has many deleterious effects which differ in their
action spectra. The action spectra are further complicated by antagonistic and repair processes stimulated
by UV-A and visible radiation. Figure 4.1 shows the action spectrum based on irradiance response curves of
UV inhibition of photosynthetic oxygen production in a mass biomass producer, the cyanobacterium
Ciodttlariti spumijjena, isolated from the Baltic Sea.

In order to evaluate the effects of solar UV-B radiation on aquatic ecosystems a number of basic
questions need to be answered:

•What is the expected spectral distribution at the surface of the water on a global basis as a function
of important physical, chemical, bio-optical, biological and environmental parameters, e.g. time of
day, season, ozone concentration, during the decades to come?

•What is the spectral penetration of solar short wavelength radiation as a function of depth in
different water types?
66
-------
•What is the vertical distributitin of the aquatic organisms in: the water column for major water types?

•What is the biologically and spectrally weighted sensitivity of the organisms affected by solar UV-B?

•What are the extent and limits of UV repair and adaptation as well as the effects of other
environmental factors in mitigating or augmenting UV effects?
x 0.00175

E 0.00150 4- T

2 0.00125 -•

> 0.00100 --
o
§ 0.00075 -•
'o
£ 0.00050 -•
o>

E 0.00025 -•
3
O
0.00000
250 275 300 325 350

Wavelength [nm]
375
400
Fig. 4.1. Action spectrum for the inhibition of photosynthesis in the cyanobacterium Nodularia spumigena

Global distribution

Phytoplankton are not uniformly distributed in the oceans of the world (Figure 4.2); the highest
concentrations are found in the high latitude regions while the tropics and subtropics show 10 to 100
times lower concentrations (with the exception of the upwelling areas on the continental shelves and near
the equator). In addition to other factors including nutrients, light availability and water column stability
UV-B radiation may play a role in this, as irradiance here is about several times higher than in
circumpolar areas [ffider, 1993b]. In temperate oceans phytoplankton blooms occur in spring and are
reduced during summer. Sometimes there is a second bloom in autumn. Judging from this general pattern
.significant increases m solar UV-B irradiation are expected to have detrimental effects on phytoplankton
productivity. Field studies conducted under the Antarctic ozone hole have demonstrated some impact on
primary productivity. Since depletions in global stratospheric ozone are expected to continue at all
latitudes well into the next century [Stolanki et */., 1992] the effects of increased UV-B on marine primary
productivity may also be relevant outside polar regions. The influence of UV-B on the abundance and
distribution of phytoplankton remains a key uncertainty.

In the last few years the role of nano- and picoplankton have been investigated. In the past their
existence was grossly underestimated because of their small size and technical problems during harvesting-
today their contribution to the total biomass is estimated to be at least 40 %. A similarly important role
and significant biomass productivity has been found for bacterioplankton which are responsible for
degradation and cycling of organic matter in the sea. UV-B has been shown to strongly affect both
,ejn^fn^°n' 3S WCil aS the extracellular enzyme activity of bacteria in subsurface waters [Herndl et
a.1., 1993J. There are also indications of large populations of viral particles (107 per ml) in the oceans the
significance of which is not yet clear. The work of several workers [Karentz et al, 1994] suggests that
small organisms (bacterial and microalgae), because of their size and short generation times are likely to
be more susceptible to UV stress than larger organisms. As a consequence, UV-B may play a key role in
niche separation, lower food web processes and species composition shifts.
67
-------
°Cean'C ^^ production based uP°n an °Ptical model and satellite derived
Vertical distribution

The transparency of the water strongly depends on the water type [Piazena and Hdder, 19941- in coastal
waters with high seston (particulate substances) and gelbstqff (yellow dissolved organic substances)
concentrations UV-B may penetrate less than 1 m to theTTl level; in contrast, in clear oceanic waters
^oo^Fc011 C°t SC KnS of meters has been shown (Figure 4.3) [Smith and Baker, 1979; Smith et al
lyy^j. Several recent papers contain information on bottom-ice algae and transmission of UV through ice
[Ryan et al., 1992; Weiler and Penhale, 1994]. Until recently there were few in-water optical sensors
wi*;.? fno^iY measuinZ UV-* as a fiction of depth in aquatic systems. Recent comparisons by
KirK et al. [1994] suggest that several commercial instruments can, with care, be used to obtain
quantitative underwater UV-B information. This is an important advance in studying the effects of solar
snort wavelength irradiation on aquatic ecosystems as it will permit more accurate estimates of the UV-B
exposures that aquatic organisms receive.
F19. 4.3.
Anjarotic wate,
S, 73- 37' W) under thin overcast, so.ar zenith ang.e
68
-------
Phytoplankton productivity is limited to the euphoric ;zbne, the top layer of the water column, the
lower limit of which is defined as the depth where photosynthesis balances respiration (typically the depth
to which incident PAR (photosynthetic active radiation) irradiance is reduced to the 0.1 % level of surface
radiation). The position of the organisms in the euphotic zone is influenced by physical processes, e.g.,
wind, waves and mixing. In addition, many phytoplankton are capable of active movements, and daily
vertical migrations of up to 15 m have been measured. Light and gravity are employed to guide the
organisms to depths of optimal irradiation resulting in typical vertical distribution patterns found in both
freshwater and marine ecosystems [Lindholm, 1992; Eggersdorfer and. Hader, 1991a,b]. Solar UV-B
irradiation has been shown to affect both motility and the orientation mechanisms in phytoplankton "
[Hader, 1993a,b]. Organisms not actively motile, such as cya'nobacteria, diatoms and even bacteria employ
buoyancy to control their vertical position in the water column by producing gas vacuoles or oil droplets
[Walsby, 1987; Walsby et al., 1992; Gosink et al., 1993].

Phytoplankton use various bands in the visible and UV-A range to orient with respect to light wh:,le
UV-B is not used for photoorientation; thus, they are in a situation similar to humans. Phytoplankton are
not able to perceive the detrimental radiation and cannot escape over-exposure if UV-B levels increase.

Field studies in Ghana showed that the percentage of motile filaments and linear velocity of several
cyanobacteria as well as their orientation mechanisms with respect to light are affected within minutes by
solar radiation. The damage was only partially repaired and only after short exposure times. In contrast, -
longer exposure times even resulted in increasing damage over a 24-h period [Donkor et al., 1993a,b].
Work carried out in India has indicated that solar UV-B affects the nitrogenase activity and carbon
dioxide uptake in rice paddy cyanobacteria [Tyagi et al., 1991, 1992]. Some cyanobacteria, however,
characterized by a brown color, seem to be better adapted to high solar radiation than closely related green
forms.

Carbon dioxide uptake and its role in global warming

The oceans play a key role with respect to global warming. A long-term global warming of surface air
temperature by 1.5 - 4.5°C is predicted for a doubling of the CO2 concentration accompanied with a 1-m
rise in sea level by 2080 [IPCC, 1990, Weaver, 1993].-te-m&rme phytoplankton are a major sink for
atmospheric CO2 they have a decisive role in future trends of carbon dioxide concentrations in the
atmosphere as well as in terrestrial and aquatic ecosystems (Figure 4.4) [Bowes, 1993; Melillo et al., 1993].

Before the onset of anthropogenic carbon release the uptake and release of atmospheric carbon were
balanced and the concentration of CO2 in the atmosphere was constant for extended periods of time. The
increase in fossil fuel burning and deforestation results in an additional release of about 7 Gt of carbon
into the atmosphere. However, long-term measurements indicate an annual deposit in the atmosphere of
only 3 Gt. It can be assumed that the remaining 4 Gt are taken out of the global atmosphere by a net uptake
by the biological pump in the ocean, a net uptake of CO2 by the terrestrial biosphere or a combination of
both. The relative importance of the two uptake modes is the topic of much current research [Lampitt et
al., 1993; Toggweikr, 1993].

Atmosphere: 735
Fig. 4.4. Annual carbon fluxes (in Gt) of natural and anthropogenic on'gin and the sizes of major reservoirs [after Houghton
andWoodwell, 1989]

69
-------
Historical Secchi disk measurements (qualitative estimate of light transmission in the water) in the
North Pacific show no evidence of a significant increase in phytoplankton biomass during this century
[Falkowski and Wilson, 1992]. Though Secchi disk measurements are a surprisingly sensitive measure for
phytoplankton biomass they do not reflect phytoplankton productivity. In contrast to terrestrial systems
phytoplankton possess a very low standing crop with a high productivity. Under optimal conditions daily
productivity may even equal the existing biomass. Therefore it is difficult to exactly predict the loss in
carbon sink from decreases in phytoplankton biornass, and this remains a key uncertainty.

Antarctic productivity

Smith et al. [1992] directly measured the increase in and penetration of UV-B into Antarctic waters
and provided the first conclusive evidence of direct ozone-related effects on natural phytoplankton
communities. Making use of the space and time variability of the UV-B front [Smith and Baker, 1989]
associated with the polar vortex-driven ozone hole, they quantitatively evaluated phytoplankton production
inside (ozone column thickness as low as 150 Dobson units, DU) compared to outside (300 DU) the hole.
These workers suggest that the ozone-related damage to phytoplankton result in reduction in primary
productivity by 6 - 12 % within the marginal ice zone of the Southern Ocean, and other estimates of
different Antarctic areas range from 6 - 23 % [Weiler and Penkale, 1994; Holm-Hansen et al., 1993a]. The
work of Smith and coworkers is distinguished by the inclusion of direct in-situ measurement of both
incident and in-water UV-B so that quantitative evaluation of biological dose as a function of depth and
time could be made [Smith et al., 1992; Prezelin et al., 1994]. An important result from this work is the
quantitative measurement of a direct ozone-related negative impact on phytoplankton production in the
Southern Ocean which is directly linked to human activities in the Northern Hemisphere. Recently, there
has also been increasing interest in the Arctic as there are indications for a potentially developing Arctic
ozone hole [Manney et al., 1994].

In situ incubations of natural phytoplankton assemblages in Antarctic waters indicated that UV-B
under the ozone hole (150 DU) impaired photosynthesis by about 4.9 % while UV-A was responsible for
about 6.2 % inhibition [Holm-Hansen et al., 1993a]. Similar ratios were found for tropical waters
[Hclbling et al., 1992], and screening of most UV <378 nmjresults in an increase in photosynthesis by 10 to
20 %. However, no significant decreases in stratospheric ozone have been detected in the tropics.
Phytoplankton from below the mixing layer in tropical waters were very sensitive to solar radiation while
surface plankton showed a high adaptation.

Recently McMinn et al. [1994], using high-resolution stratigraphic sequences from anoxic basins in
Antarctic fjords, present findings suggesting that there have been no compositional changes in diatoms
during the past 20 years of ozone hole development. They add that their findings are not necessarily
applicable to the marginal ice edge and sea-ice communities nor are they relevant to non-diatom
components of Antarctic phytoplankton communities. The ecological consequences of UV-B on
phytoplankton communities remains a key uncertainty, and high latitude regions with relatively large
decreases in ozone provide opportunities to quantitatively explore these consequences.

Screening pigments

The induction of screening pigments has been found in marine and freshwater organisms [Karentz et al.,
1991]. The pigment scytonemin has been isolated from cyanobacteria where it is induced by UV [Garcia-
Pichel and Castenholz, 1991]. IP. addition, cyanobacteria as well as eukaryotic phytoplankton use several
water soluble, UV-absorbing mycosporines as screening pigments. Other phytoplankton use carotenoids to
dissipate the excess radiation energy from the photosynthetic pigments, and some have been found to even
tolerate the unfiltered solar radiation at the water surface in tropical oceans.

Macroalgae and seagrasses

In recent years there has been an increased interest in UV-B effects on macroalgae and seagrasses. In
contrast to the phytoplankton, most macrophytes are attached to their growing site; therefore they are
restricted to certain depth zones above, below or within the tidal zone. It is thought that this zonation is
mainly caused by the visible light penetrating to this depth [tuning, 1985]. If the UV-B/PAR ratio
increases, the algae will be exposed to enhanced short wavelength radiation to which they may not be
adapted. In recent studies no effect on respiration was found while photosynthesis was inhibited in many
red, brown and green benthic algae. When using PAM (pulse amplitude modulation) fluorescence
measurements, deep-water benthic algae were most sensitive while intertidal algae were least sensitive
[HSder et al., 1994a,b; Larkum and Wood, 1993; Maegawa et al., 1993]. As in phytoplankton, the
70
-------
occurrence and induction by UV of screening pigments'lnas been recorded in tropical red aleae [Wood
1989]. -.---•

Primary and secondary consumers

Food webs

Phytoplankton are the basis for the intricate marine food webs; thus, any losses in biomass production
necessarily cause decreases in biomass at the next higher trophic levels. Eventually these losses are relayed
through all levels of the food web, ultimately leading to losses in fisheries yield [Nixon, 1988; Gucinski et
al., 1990]. In addition to these indirect effects, solar UV-B radiation has been found to cause damage to
early developmental stages of fish, shrimp, crab and other animals. The most severe effects are decreased
reproductive capacity and impaired larval development [U.S. Environmental Protection Agency, 1987]. Even
at current levels, solar UV-B radiation is a limiting factor, and small increases in UV-B exposure could
result in significant reductions in the size of the consumer community [Damkaer, 1982J.

In a recent ecosystem study an interesting effect was encountered: After some lag time, algal growth in
an artificial stream was higher under UV-B than in the control. The explanation of this surprising result
was that the grazers, larval chironomids, were more sensitive to UV-B than their food, the algae [Bothwell
et a,L, 1994]. The result of this experiment reinforces the fact that predictions of responses by ecosystems
to elevated UV-B exposure should not be based solely on single-species assessments.

Invertebrates

Marine invertebrates differ greatly in their sensitivity to UV-B radiation [Hunter et ml., 1982]. One
crustacean has been found to suffer about 50 % mortality at current UV-B irradiances at the sea surface.
Other shrimp larvae tolerate irradiances higher than those predicted for a 16 % ozone depletion
[Damkaer and Dey, 1983]. The adult crustacean Tkysanoessa raschii has a threshold sensitivity exceeding
levels expected for anticipated ozone levels in spring. However, in summer a 50 % mortality cumulative
radiation dose for about half the species examined would._be_ reached in less than 5 days assuming a 16 %
ozone depletion. UV-B kills most individuals of the common copepod Acartia clausii in culture and also
reduces fecundity in the survivors. Similar inhibitions have been found in shrimp-like crustaceans and crab
larvae in the Pacific Northwest. At high latitudes (over 40°N) the recently recorded late-spring increases
in UV-B may affect some species as the UV-B enhancement occurs at critical phases of their
development. Even sustained small increases or temporary fluctuations in UV-B may affect especially
sensitive species.

Benthic organisms are also affected by UV-B radiation: cleavage in sea urchin eggs is impaired by
ultraviolet radiation [El Sayed, 1988aj. Marine organisms associated with coral reefs, such as sponges,
bryozoans and tunicates are similarly impaired. Melanins seem to serve as absorbing pigments since, e.g.,
several colored corals withstand high levels of radiation by production of the protective pigment S-320.'
Corals differ in their UV-B. sensitivity depending on the depth at which they grow [Siebeck and Bobm,
1987J; also, the amount of the UV absorbing pigments decreases with depth [Maragos, 1972; Jokiel and
York, 1982]. UV-B radiation seems to exert an oxidative stress on these invertebrate organisms as shown in
sea anemones and octocorals [Shick et al, 1991].

Gleason and Wellington [1993] observed coral bleaching in the Bahamas that is not explained by
increases in seawater temperature. Instead they showed that UV radiation under calm, clear water column
conditions induced bleaching of reef-building corals. With increasing depth, colonies of Motastrea
annularis showed a gradual reduction in mycosporine amino acids, indicating that deeper water colonies
may be particularly vulnerable to sudden increases in UV radiation. Transplant experiments indicated that
the organisms could not adapt to higher UV levels within a period of 21 days.

Freshwater crustaceans are also affected by solar UV-B. It is interesting to note, however, that
Daphnia species from an alpine lake, where UV-B radiation is higher than in lowland lakes, are more
intensely colored and tolerate higher UV-B doses [Siebeck and Bobm, 1987; Hessen, 1994].

Vertebrates

Enhanced solar UV-B radiation directly reduces the growth and survival of larval fish [Hunter et al,
1982J. Based on these data for a region of the North American Pacific coastal shelf in June, a 16 % ozone
reduction would result in increases in larval mortality of 50 %, 82 % and 100 % at the 0.5-m depth for
anchovy larvae of ages 2, 4 and 12 days, respectively. Anchovy larvae occur in many regions coincident wi±
high radiation levels between June and August with a peak in July. Because virtually all anchovy larvae in the

71
-------
shelf areas described occur within the upper 0.5 m, a 16 % ozone reduction level could lead to large
increases in larval mortality.

Little and Fabacher [1994], comparing the sensitivity of rainbow trout and two threatened salmonids to
UV-B radiation, have shown that UV-B is an additional, and often important, environmental stress.
Inhabiting shallow headwater streams and lakes in high altitude locations, these fish showed considerable
variability in response to simulated increases in UV-B with some showing skin injury as well as apparent
suppression of their immune system.

Williamson ct al. [1994], studying the impact of short-term exposure to UV-B radiation on
zooplankton communities in north temperate lakes, suggest that UV-B in relatively clear lakes may
prevent some species of zooplankton from fully exploiting warmer surface waters during periods of
summer stratification. As a consequence, UV-B may be responsible for altering their ecological
interactions with food resources, predators and other environmental variables.

Increased UV-B radiation may be responsible for recent population declines of some amphibians
[Blaurtcin et al., 1994]. Species of amphibians differ in their ability to repair UV-B induced damage to
their eggs or oocytes. The eggs of some frog species withstand exposure to sunlight better than those of
some other frog species. The populations of certain species that lay their eggs in open water, strongly
exposed to sunlight, have suffered drastic declines [Blaustein et al., 1994]. The egg-laying behavior and
enzymatic repair activities suggest that certain amphibian species have become adapted in such a way as to
minimize exposure of their eggs to UV-B radiation.

Effects of substitutes and their degradation products

_ Some HFCs and HCFCs, notably HFC134a, HCFC123 and HCFC124, are degraded generating
trifluoroacetic acid (TFA, CF3COOH) as their main product. TFA is neither photolyzed nor does it
undergo any other physicochemical degradation. It is apparently not metabolized by plants, but
microorganisms such as methanogens, sulfate reducers and aerobic soil bacteria have been shown to degrade
TFA [Visschcr et al., 1994]. Thus, TFA may be a global contaminant persistent over long times. Current
levels in an industrialized area are 0.01 - 0.05 ng/m3 in ^(Southern Germany) and 40 times these values
are predicted for the year 2010. Further research is currently being conducted to determine whether these
results reflect the global situation. Even with the event of continued production well into the next century,
TFA is unlikely to reach toxic levels for phytoplankton in the oceans. In environmental niches such as
vernal pools, TFA could be expected to accumulate to higher levels than elsewhere. The magnitude of this
concentration effect should be similar to that observed for other solutes, which is in the ranee of 5 - 10
fold [Ckumlcy, 1994].

TFA is mildly toxic to most marine and freshwater phytoplankton tested so far (EC50 1200 to 2400
mg/1). However, the freshwater green alga, Selenastrum capricornutum, showed an EC50 of 4.8 mg/1
[Groeneveld, 1992]. Bioaccumulation factors have not been established for phytoplankton organisms; thus,
it is still uncertain whether or not TFA is concentrated in the food web.

Consequences

Though there is overwhelming evidence that increased UV-B is harmful to aquatic ecosystems,
quantitative estimates are rudimentary at this stage. There is pressing need to increase our efforts to
understand the possible long-term effects on aquatic ecosystems on a global scale. In order to evaluate the
current productivity in the oceans and a possible decrease in the future, combined satellite and surface data
arc important tools. Additional focus on important biomass producers such as diatoms, dinoflagellates
and cyanobacteria is necessary. A major loss in primary biomass productivity may have significant
consequences for the intricate food web in aquatic ecosystems and affect food productivity. It has been
estimated that a 16 % ozone depletion could result in a 5 % loss in phytoplankton which would cause a
reduction in fishery and aquaculture yields of about 7 % which equals a loss of about 7 million tons of fish
per year [Nixon, 1988]. Consequences of increased solar UV-B levels may be further complicated by
unpredicted feedback loops and other changing factors such as temperature, salinity, CO concentration
and different irradiation patterns caused by changing cloud cover.

However, biological effects of small changes in UV-B may be difficult to determine because the
biological uncertainties and variations are large and furthermore the baseline productivity for pre-ozone-
loss eras is not well established. Figure 4.5 summarizes the effects of UV-B on phytoplankton with their
expected ecosystem consequences.
72
-------
Vertical distribution
in the water column
Competition
between species ?
Reduced btomass
production?
Reduced carton
dioxide sink ?
Temperature
Increase?
Food web in
the ocean?
Species diversity ?
Global
consequences
Fig.4.5. Effects of enhanced solar UV-B on phytoplankton.

The second major impact of decreased phytoplankton productivity may be a reduced sink capacity for
atmospheric carbon dioxide which results in a faster development of the greenhouse effect and global
climate change.

Prokaryotic microorganisms such as cyanobacteria and root nodule bacteria are capable of fixing
atmospheric nitrogen in contrast to higher plants which can only utilize ammonia, nitrate or nitrite.
Decreased nitrogen assimilation by prokaryotic microorganisms may lead to a nitrogen deficiency for
higher plant ecosystems, such as rice paddies. Consequently, losses in nitrogen fixation due to increases in
UV-B radiation may need to be compensated for by artificial nitrogen fertilization.

Both macroalgae and phytoplankton release organic sulfur compounds such as dimethylsulfide (DMS)
which enter the atmosphere and serve as cloud condensation nuclei. Changes in DMS production msy affect
the atmospheric radiation balance. The time frame of the predicted changes in the ozone layer may not be
sufficient for genetic adaptation to higher UV-B levels. Since different species differ in their sensitivity
toward solar short wavelength radiation, shifts in species diversity may be a consequence. As a general rule,
UV seems to affect smaller phytoplankton more than larger organisms. As primary feeders prey by size and
not by species preference, this effect may also alter the subsequent links in the food web.

References

Acevedo, J. and C. Nolan, Environmental UV Radiation, Commission of the European Communities,
Directorate-General XII for Science, Research and Development, Brussels, 1993.

Biggs, R.H. and M.E.B. Joyner (eds.), Stratospheric Ozone Depletion/UV-B Radiation in the Biosphere,
NATO ASI Series, vol. 118, Springer, Berlin, Heidelberg, 1994.

Blaustein, A.R., P.O. Hoffman, D.G. Hokit, J.M. Kiesecker, S.C. Walls, and J.B. Hays, UV repair and
resistance to solar UV-B in amphibian eggs: a link to population declines? Proc. Natl. Acad Sci 91
1791-1795, 1994. ' '

Bothwell, M.L., D.M.J. Sherbot, and C.M. Pollock, Ecosystem response to solar ultraviolet-B radiation:
Influence of trophic level interactions, Science, 256, 97-100, 1994.

Bowes, G., Facing the inevitable: plants and increasing atmospheric CO2, Ann. Rev. Plant Phvsiol. Plant
Mol. Biol., 44, 309-332, 1993.

Byers, M., A computation of global oceanic net primary productivity from satellite derived data, UCSB Thesis
Dec. 1994.

Chumley, F.G., Workshop on the environmental fate of trifluoroacetic acid (TFA), 3-4 March 1994,
Miami Beach, FL. AFEAS Administrative Organization: SPA-AFEAS Inc., Washington, 1994.

73
-------
Cullen, J.J. and M.P. Lesser, Inhibition of photosynthesis by ultraviolet radiation as a function of dose and
dosage rate: results for a marine diatom, Marine Biol., Ill, 183-190, 1991.
Cullen, J.J. and P.J. Neale, Ultraviolet radiation, ozone depletion, and marine photosynthesis,
Photosynthesis Res., 39, 303-320, 1994.
Damkaer, D.M., Possible influence of solar UV radiation in the evolution of marine zooplankton, pp.
701-706, in The Role of Solar Ultraviolet Radiation in Marine Ecosystems, Calkins, J. (ed.), Plenum
Press, New York, 1982.
Damkaer, D.M. and D.B. Dcy, UV damage and photo-reactivation potentials of larval shrimp, Pandalus
platyceros, and adult euphausiids, Thysanoessa raschiif, Oecologia, 60, 169-175, 1983.
Dohlcr, G., Hagmeier, E., Grigoleit, E., and Krause, K.-D., Impact of solar UV radiation on uptake of
15N-ammonia and 15N-nitrate by marine diatoms and natural phytoplankton, Biol. Phys. Pfl. 187, 293-
303, 1991.
Donkor, V.A., H.A.K. Damian, and D.-P. Hader, Effects of tropical solar radiation on the motility of
filamentous cyanobacteria, FEMS Microbiol. Ecol., 12, 143-148, 1993a.
Donkor, V.A., H.A.K. Damian, and D.-P. Hader, Effects of tropical solar radiation on the velocity and
photophobic behavior of filamentous gliding cyanobacteria, Acta Protozool., 32, 67-72, 1993b.
Eggersdorfer, B. and D.-P. Hader, Phototaxis, gravitaxis and vertical migrations in the marine
dinoflagcllatc, Prorocentrum micans, Eur. J. Biophys., 85, 319-326, 1991a.
Eggersdorfer, B. and D.-P. Hader, Phototaxis, gravitaxis and vertical migrations in the marine
dinoflagellates, Peridinium faeroense and Amphidinium cater it, Acta Protozool., 30, 63-71, 1991b.
El Saycd, S Z., Fragile life under the ozone hole, Natural History, 97, 73-80, 1988.
Falkowski, P.G. and C. Wilson, Phytoplankton productivity^in the North Pacific ocean since 1900 and
implications for absorption of anthropogenic CO2, Nature, 358, 741-743, 1992.
Garcia-Pichel, F. and R.W. Castenholz, Characterization and biological implications of scytonemin, a
cyanobacterial sheath pigment, /. Phycol., 27, 395-409, 1991.
Gleason, D.F. and G.M. Wellington, Ultraviolet radiation and coral bleaching, Nature, 365, 836-838,
1993.
Gosink, J.J., R.L. Irgens, and J.T. Staley, Vertical distribution of bacteria in Arctic sea ice, FEMS
Microbiol. Ecol., 102, 85-90, 1993.
Groencveld, A.H.C., H.A.M. dc Kok, and G. van den Berg, The toxicity of sodium trifluoroacetate to the
alga Selenastrum capricorntttum, AFEAS Report No. 56635/52/92, 1992.
Gucinski, H., R.T. Lackey, and E.G. Spence, Fisheries, Bulletin Amer. Fish. Soc., 15, 33-38, 1990.
Hader, D.-P., Effects of enhanced solar ultraviolet radiation on aquatic ecosystems, pp. 155-192, in UV-
B radiation and ozone depletion. Effects on Humans, Animals, Plants, Microorganisms, and Materials,
Tcvini, M. (ed.), Lewis Publ., Boca Raton, Ann Arbor, London, Tokyo, 1993a.
HSdcr, D.-P., Risks of enhanced solar ultraviolet radiation for aquatic ecosystems, Progress in Phycological
Research, 9, 1-45, 1993b.
HSder, D.-P. and J. Schafer, Photosynthetic oxygen production in macroalgae and phytoplankton under
solar irradiation, /. Plant Physiol., in press, 1994a.
HSder, D.-P. and J. Schafer, In-situ measurement of photosynthetic oxygen production in the water
column, Environm. Monitor.Assessm., in press, 1994b.
Hiidcr, D.-P. and R.C. Worrest, Effects of enhanced solar ultraviolet radiation on aquatic ecosystems,
Photochem. PhotobioL, 53, 717-725, 1991.
HSder, D.-P., R.C. Worrest, and H.D. Kumar, Aquatic ecosystems, UNEP Environmental Effects Panel
Report, 39-48, 1989.
74
-------
Hader, D.-P., R.C. Worrest, and H.D. Kumar, Aquatic ecosystems, UNEP Environmental Effects Panel
Report, 33-40, 1991.

Helbling, E.W., V. Villafane, M. Ferrario, and O. Holm-Hansen, Impact of natural ultraviolet radiation
on rates of photosynthesis and on specific marine phytoplankton species, Marine Ecology Progress Series,
80, 89-100, 1992.

Herndl, G.J., G. Miiller-Niklas, and J. Frick, Major role of ultraviolet-B in controlling bacterioplankton
growth in the surface layer of the ocean, Nature, 361, 717-719, 1993.

Hessen, D.O., Daphnia responses to UV-light, Arch. Hydrobiol., in press, 1994.

Holm-Hansen, O., E.W. Helbling, and D. Lubin, Ultraviolet radiation in Antarctica: inhibition of
primary production, Photochem. Photobiol., 58, 567-570, 1993a.

Holm-Hansen, O., D. Lubin, and E.W. Helbling, UVR and its effects on organisms in aquatic
environments, pp. 379-425, in Environmental UV Photobiology, Young, A.R., O. Bjorn, J. Moan and W.
Nultsch, (eds.), Plenum, New York, 1993b.

Houghton, R.A. and G.M. Woodwell, Global climatic change, Sci. Amer., 18-26, 1989.

Hunter, J.R., S.E. Kaupp, and J.H. Taylor, Assessment of effects of UV radiation on marine fish larvae,
pp. 459-497, in The Role of Solar Ultraviolet Radiation in Marine Ecosystems, Calkins, J. (ed.), Plenum
Press, New York, 1982.

IPCC, Climate change 1992: The supplement report to the IPCC scientific assessment, J.T. Houghton,
B.A. Callender, and S.K. Varney (eds.), Cambridge University Press, Cambridge, 1992.

Jokiel, P.L. and H.R. York, Solar ultraviolet photobiology of the reef coral Pocillopora damicornis and
symbiotic zooxanthellae, Bull. Mar. Sci, 32, 301-315, 1982.

Karentz, D., J.E. Cleaver, and D.L. Mitchell, Cell survival characteristics and molecular responses of
Antarctic phytoplankton to ultraviolet-B radiation, /. Phycol., 27, 326-341, 1991.

Karentz, D., Bothwell, M.L., Coffin, R.B., Hanson, A., Herndl, G.J., Kilham, S.S., Lesser, M.P., Lindell,
M., Moeller, R.E., Morris, D.P., Neale, P.J., Sanders, R.W., Weiler, C.S., and R.G. Wetzel, Impact
of UVB radiation on pelagic freshwater ecosystems: Report of working group on bacteria and
phytoplankton, Arch. Hydrobiol., in press, 1994.

Kirk, J.T.O., B.R. Hargreaves, D.P. Morris, R. Coffin, B. David, D. Fredrickson, D. Karentz, D. Lean, M.
Lesser, S. Madronich, J.H. Morrow, N. Nelson, N. Scully, Measurement of UV-B radiation in
freshwater ecosystems, Arch. Hydrobiol., in press, 1994.

Lampitt, R.S., W.R. Hillier, and P.G. Challenor, Seasonal and diel variation in the open ocean
concentration of marine snow aggregates, Nature, 362, 737-739, 1993.

Larkum, A.W.D. and W.F. Wood, The effect of UV-B radiation on photosynthesis and respiration of
phytoplankton, benthic macroalgae and seagrasses, Photosynth. Res., 36, 17-23, 1993.

Lindholm, T., Ecological role of depth maxima of phytoplankton, Arch. Hydrobiol . Beih. Ergebn Limnol
35, 33-45, 1992.

Little, E.E. and D.L. Fabacher, Comparative sensitivity of rainbow trout and two threatened salmonids,
Appache Trout and Lahontan Cutthroat Trout, to UV-B radiation, Arch. Hydrobiol., in press, 1994.'
Liming, K., Meeresbotanik, G. Thieme, Stuttgart, New York, 1985.

Maegawa, M., M. Kunieda, and W. Kida, The influence of ultraviolet radiation on the photosynthetic
activity of several red algae from different depths. Jfn. J. Phycol., 41, 207-214, 1993.
Manney, G.L., L. Froidevaux, J.W. Waters, R.W. Zurek, W.G. Read, L.S. Elson, J.B. Kumer, J.L.
Mergenthaler, A.E. Roche, A. O'Neill, R.S. Harwood, I. MacKenzie, and R. Swinbank, Chemical
depletion of ozone in the Arctic lower stratosphere during winter 1992-93, Nature, 370, 429-434,
1994. ^

Maragos, J.E., A study of the ecology of Hawaiian reef corals, Ph. D. thesis, Univ. of Hawaii, 1972.
75
-------
McMinn, A., H. Heljuis, and D. Hodgson, Minimal effects of UVB radiation on Antarctic diatoms over
the past 20 years, Nature, 370, 547-549, 1994.
Melillo, J.M., A.D. McGuire, D.W. Kicklighter, B. Moore III, C.J. Vorosmarty, and A.L. Schloss, Global
climate change and terrestrial net primary production, Nature, 363, 234-240, 1993.
Nixon, S.W., Physical energy inputs and the comparative ecology of lake and marine ecosystems, Limnol.
Occanogr., 33, 1005-1025, 1988.
Piazena, H. and D.-P. Hader, Penetration of solar UV irradiation in coastal lagoons of the Southern
Baltic Sea and its effect on phytoplankton communities, Photochem. Photobiol., 60, in press, 1994.
Prezelin, B.B., N.P. Boucher, and O. Schofield, Evaluation of field studies of UV-B radiation effects on
Antarctic marine primary productivity, pp. 181-194, in Stratospheric Ozone Depletion/UV-E Radiation
in the Biosphere, Biggs, R.H. and M.E.B. Joyner (eds.), NATO ASI Series, vol. 118, Springer, Berlin
Heidelberg, 1994.
Prezelin, B.B., N.P. Boucher, and R.C. Smith, Marine primary production under the influence of the
Antarctic ozone hole, Ultraviol. Radial. Biolog. Res. Antarct., 1-62, 1993.
Ryan et al., UV radiation and photosynthetic production in Antarctic sea ice microalgae, /. Photochem.
Photobiol. B: Biol. 13, 235 - 240, 1992.
SCOPE, Effects of increased ultraviolet radiation on global ecosystems, Proceedings of a workshop
arranged by the Scientific Committee on Problems of the Environment (SCOPE), Tramariglio,
Sardinia, October, 1992a.
SCOPE, Effects of increased ultraviolet radiation on biological systems, Scientific Committee on
Problems of the Environment (SCOPE), Paris, 1992b.
Shick, J.M., M.P. Lesser, and W. R. Stochaj, Ultraviolet radiation and photooxidative stress in
zooxanthelate anthozoa: the sea anemone Phyllodiscus~sfmvni and the octocoral Clavularia sp.,
Symbio., 10, 145-173, 1991.
Siebeck, O. and U. Bohm, Untersuchungen zur Wirkung der UV-B-Strahlung auf kleine Wassertiere, BPT
Bericbt, Gesellschaft fur Strahlen- und Umweltforschung, Munchen, 1987.
Siegenthalcr, U. and Sarmiento, J. L., Atmospheric carbon dioxide and the ocean, Nature, 365, 119-125,
1993.
Smith, R.C., Ozone, middle ultraviolet radiation and the aquatic environment, Photochem. Photobiol., 50,
459-468, 1989.
Smith, R.C. and K.S. Baker, Penetration of UV-B and biologically effective dose-rates in natural waters,
Photochem. Photobiol., 29, 311-323, 1979.
Smith, R.C. and K.S. Baker, Stratospheric ozone, middle ultraviolet radiation and phytoplankton
productivity, Oceanography 2, 4-10, 1989.
Smith, R.C. and J.J. Cullen, Implications of increased solar UVB for aquatic ecosystems, U.S. National
Report to the IUGG (1991-1994), American Geophysical Union, 1995.
Smith, R.C., B.B. Prezelin, K. S. Baker, R.R. Bidigare, N.P. Boucher, T. Coley, D. Karentz, S. Maclntyre,
H.A, Matlick, D. Menzies, M. Ondrusek, Z. Wan, and K.J. Waters, Ozone depletion: Ultraviolet
radiation and phytoplankton biology in Antarctic waters, Science, 255, 952-959, 1992.
Stolarski, R., R. Bojkov, L. Bishop, C. Zerefos, J. Staehelin, and J. Zawondny, Measured tends in
stratospheric ozone, Science, 256, 342-349, 1992.
Tcvini, M. (ed.), Effects on Humans, Animals, Plants, Microorganisms, and Materials, Lewis Publ., Boca
Raton, Ann Arbor, London, Tokyo, 1993.
Toggweilcr, J.R. Carbon overconsumption, Nature, 363, 210-211, 1993.
76
-------
Tyagi, R., H.D. Kumar, D. Vyas, and A. :Kumar, Effects'of. ultraviolet-B radiation on growth, pigmentation,
NaH14CO3 uptake and nitrogen metabolism in Nostoc muscoru-m, pp. 109-124, in Impact of Global
Climatic Changes on Photosynthesis and Plant Productivity, Abrol, Y.P., P.N. Wattal, A. Gnanam,
Govindjee, D.R. Ort, A.H. Teramura (eds.) Proceedings of the Indo-US Workshop held on January 8-
12,1991 at New Delhi, India, Oxford and IBH Publishing Co. New Delhi, Bombay, Calcutta), 1991.

Tyagi, R., G. Srinivas, D. Vyas, A. Kumar, and H.D. Kumar, Differential effect of ultraviolet-B radiation
on certain metabolic processes in a chromatically adapting Nostoc, Photochem. Photobiol 55 401-
407, 1992.

U.S. Dept of Energy, Environmental Sciences Div., Wash., D.C., Overview of the DOE Atmospheric
Chemistry Program's Ozone Project, DE93-007416 DOE/ER-0575T, Jan. 1993.

USEPA (U. S. Environmental Protection Agency), An assessment of the effects of ultraviolet-B radiation
on aquatic organisms, pp. 1-33, in Assessing the Risks of Trace Gases That Can Modify the Stratosphere
EPA 400/1-87/001C, 1987. '

Visscher, P.T., C.W. Culbertson, and R.S. Oremland, Degradation of trifluoroacetate in oxic and anoxic
sediments, Nature, 369, 729-731, 1994.

Walsby, A.E., Mechanisms of buoyancy regulation by planktonic cyanobacteria with gas vesicles, pp. 385-
392, in The Cyanobacteria, Fay, P. and C. Van Baalen (eds.) Elsevier Science Publishers, Amsterdam
1987.

Walsby, A.E., R. Kinsman, and K.I. George, The measurement of gas volume and buoyant density in
planktonic bacteria, /. Microbiol. Meth., 15, 293-309, 1992.

Weaver, A.J., The oceans and global warming, Nature, 364, 192-193, 1993.

Weiler, C.S. and P.A. Penhale (eds.), Ultraviolet Radiation in Antarctica: Measurements and Biological
Effects, American Geophysical Union, Washington^J^C., 1994.

Williamson, C.E., H.E. Zagarese, eds. Impacts of UV-B Radiation on Freshwater Organisms, Arch.
Hydrobiol., in press, 1994.

Williamson, C.E., H.E. Zagarese, P.C. Schulze, B.R. Hargreaves, and J. Seva, The impact of short-term
exposure to UV-B radiation on zooplankton communities in north temperate lakes, /. Plankton Res.,
12, in press, 1994.

Wood, W.F., Photoadaptive responses of the tropical red alga Eucheuma striatum Schmitz (Gigartinales)
to ultra-violet radiation, Aquat. Bot. 33, 41-51, 1989.

Worrest, R. C. and D.-P. Hader, Effects of stratospheric ozone depletion on marine organisms,
Environmental Conservation, 16, 261-263, 1989.
77
-------
78
-------
CHAPTER 5

EFFECTS OF INCREASED SOLAR ULTRAVIOLET
RADIATION ON BIOGEOCHEMICAL CYCLES
R. G. Zepp (USA), T. V. Callaghan (UK), andD. J. Erickson (USA)
Summary

Increases in solar UV radiation could affect terrestrial and aquatic biogeochemical cycles thus altering
both sources and sinks of greenhouse and chemically-important trace gases [e.g., carbon dioxide (CC>2),
carbon monoxide (CO), carbonyl sulfide (COS) and possibly other gases]. These potential changes would
contribute to biosphere-atmosphere feedbacks that attenuate or reinforce the atmospheric buildup of these
gases. Current research discussed here focuses on effects of enhanced UV-B on biological and geochemical
processes in terrestrial and aquatic ecosystems.

In terrestrial ecosystems increased UV-B could modify both the production and decomposition of plant
matter with concomitant changes in the uptake and release of atmospherically-important trace gases.
Decomposition processes can be accelerated when UV-B photodegrades surface litter, or retarded when the
dominant effect involves changes in the chemical composition of living tissues that reduce the
biodegradability of buried litter. These changes in decomposition can affect microbial production of
carbon dioxide and other trace gases, and also may affScr the availability of nutrients essential for plant •
growth. Primary production can be reduced by enhanced UV-B, but the effect is variable between species
and even cultivars of some crops. Likewise, the effects of enhanced UV-B on photoproduction of CO from
plant matter is species dependent and occurs more efficiently from dead than living matter. The often-
individualistic response of plant species to enhanced UV-B can result in changed competitive balances
between co-occurring species such as crops and weeds. Long-lived species in natural ecosystems that can
accumulate UV-B damage may be slow to acclimate/adapt and replacement by immigration may be
restrained.

In aquatic ecosystems other investigations have shown that solar UV-B radiation also might have
significant impacts. Studies in several different locations have shown that reductions in current levels of
solar UV-B result in enhanced primary production, and Antarctic experiments under the ozone hole
demonstrated that primary production is inhibited by enhanced UV-B. In addition to its effects on primary
production, solar UV radiation can reduce bacterioplankton growth in the upper ocean with potentially
important effects on marine biogeochemical cycles. Decomposition processes can be retarded when
bacterial activity is suppressed by enhanced UV-B radiation or stimulated when solar UV radiation
photodegrades aquatic dissolved organic matter (DOM). Photodegradation of DOM results in loss of UV
absorption and formation of dissolved inorganic carbon (DIG), CO, and organic substrates that are readily
mineralized or taken up by aquatic microorganisms. The marine sulfur cycle may be affected by UV-B
radiation resulting in possible changes in the sea-to-air emissions of COS and dimethylsulfide (DMS),
two gases that are degraded to sulfate aerosols in the stratosphere and troposphere, respectively. UV-B
radiation induces the photoreaction of marine DOM to form COS, and it potentially can affect fluxes of
COS and DMS through effects on phytoplankton that produce organosulfur precursors, on bacteria that
consume DMS, and on photooxidation of DMS. Early modeling efforts to simulate these interactions have
appeared during the past two years.

New research on the environmental fate and impact of the hydrofluorocarbon (HFC) and
hydrochlorofluorocarbon (HCFC) substitutes for CFCs has focused on trifluoroacetic acid (TFA), a
tropospheric oxidation product of certain HFCs and HCFCs. These results indicate that TFA, although it

79
-------
may become globally distributed with increased usage of alternative fluorocarbons, is not likely to
accumulate in soils and organisms. Although resistant to chemical degradation, very recent evidence
indicates that TFA can be broken down by microorganisms.
Introduction

The term "biogeochemical cycles" is used here to refer to the complex interaction of biological,
chemical, and physical processes that control the exchange and recycling of matter and energy at and near
the Earth's surface. Research on biogeochemical cycles focuses on the transport and transformation of
substances in the natural environment. Global biogeochemical cycles strongly influence atmospheric
composition through their effects on the biospheric uptake and release of greenhouse gases and gases that
actively participate in atmospheric chemical reactions. The latter will be referred to as "chemically-
active" gases in this chapter. On the other hand, the Earth's climate and die nutrients derived from
atmospheric deposition are of great importance to the sustainability of the biosphere. Atmospheric
composition, climate, and the biosphere are coupled by strong interactions, including feedbacks that
reinforce or attenuate climate change. A large fraction of most greenhouse and chemically active gases in
the atmosphere is derived from biogeochemical processes in terrestrial and aquatic ecosystems
[IPCC,1992].
Solar radiation, directly or indirectly, provides the primary driving force for biogeochemical cycles.
Most of the solar radiation that reaches land or water is converted into thermal energy, but a significant
part, especially that in the ultraviolet and visible region, is diverted into photochemical and
photobiological processes that affect global biogeochemical cycles. Therefore, these processes are
sensitive to changes in ground-level solar radiation that result from global changes in stratospheric ozone,
cloud cover, aerosols, and other factors. Declines in stratospheric ozone and, by implication, increases in
solar UV-B radiation reaching the Earth's surface have been particularly pronounced during the past few
years. These changes, coupled with a number of recent findings that document the effects of UV-B
radiation on biogeochemical cycles, have prompted this new section in the UNEP report on
Environmental Effects of Ozone Depletion.
The principal goals of this section are to describe recent investigations of the effects of changing solar
UV-B radiation on terrestrial and aquatic biogeochemical cycles, but we note review papers in the text
that provide useful background information on this subject. Research related to biogeochemical cycles —
such as effects of UV-B radiation on photosynthesis, plant physiology, and aquatic trophic dynamics -- are
reviewed elsewhere in this report. In addition, excellent overviews of global biogeochemical cycles are
available as background to this section [Butcher et al., 1992; SMesinger, 1991]. The cycles of various
elements are discussed separately within this report, but it should be emphasized that biogeochemical
cycles arc tightly interwoven and are subject to significant feedback interactions, including those that
affect ozone concentration- and ground-level UV-B radiation.

Terrestria! E^ooy^,,;,^

Carbon and Ni:'ufi: ••? Cycles

Plant responses

Given the central role of plant biology in biogeochemical cycling, understanding UV-B effects on
plants is of critical importance. Here we briefly consider aspects of these effects that are relevant to
biogeochemical cycles; a much more detailed discussion of plant responses appears in Chapter 3. Most
studies of the interactions of UV-B and plants have been conducted under artificial light conditions in
growth chambers or greenhouses [Tevini and Teramura, 1991; Krufa and Kickert, 1989; SCOPE,1992;1993]
that may not mimic the spectral characteristics of ozone-dependent UV-B changes occurring in solar
radiation that reaches the ground. However, these studies have provided insights into general UV-B effects
80
-------
on physiological responses of higher plants and on alteration of growth rates and yields of crop plants.
Fewer studies address growth responses of long-lived species or primary production and phytomass in
natural ecosystems. As discussed in more detail in Chapter 3 of this report, responses to UV-B radiation
are variable between species and even between cultivars of the same species. In general, however, it seems
that those species experiencing naturally high fluxes of UV-B radiation (e.g., alpine and tropical) are
better adapted to withstand increases in UV-B than those from regions currently exposed to low levels of
UV-B. For example, growth chamber studies of various plants from the Arctic and lower latitude alpine.
regions indicated that the arctic species, living where UV-B radiation is lower, exhibited significantly
higher photosynthetic inhibition than the low-latitude species where solar UV-B flux is high [Caldwell et
al., 1982].

The few field studies that have been conducted indicate lower plant sensitivity to UV-B than that
observed under growth chamber and greenhouse conditions [SCOPE, 1993], probably in part because of the
higher flux of photorepairing solar radiation in the UV-A and other spectral regions and the plant
development effects that are prevalent in the field. Multi-season field studies of loblolly pines, however,
have shown statistically significant reductions of growth under enhanced UV-B radiation that corresponded
to 16% and 25% decreases in total ozone [Sullivan and Teramura, 1991]. Moreover, the UV-B effects on
growth accumulated over 3 years of exposure. Photosynthesis quantum yields were generally reduced in the
loblolly experiments and the effect was attributable to direct effects on photosystem II. Field studies on
Swedish subarctic heath vegetation indicated greater reductions in growth of shoots in two dominant
evergreen dwarf shrubs which accumulated damage, than in two deciduous dwarf shrubs [Johanson et al
1994].

Reviews of UV-B radiation effects on plants [Tevini and Teramura.,1991; Krupn and Kickert, 1989;
SCOPE, 1993] refer to publications that show these effects to be on plant morphology and flowering as
well as growth and photosynthesis. Particular effects _rnry_ among species, among cultivars of a species and
among local populations of a species. These changes can alter the competitive balance in mixed species
stands, resulting in significant changes in species composition and thus in primary productivity. Rapid
global warming is predicted to cause similar effects. Changes in primary production affect the flow of
CC>2 through the biosphere, but do not necessarily affect carbon storage. However, any changes in the
composition of species in plant communities driven by increased UV-B - particularly in the
representation of different life forms - could significantly affect the amount of carbon stored in
phytomass. For example, any shift from UV-B sensitive evergreens to deciduous dwarf shrubs [ implied from
work by Johanson et al. 1994] or trees could reduce carbon storage during winter while decreasing growth in
general and would increase the amount of CC>2 circulating in the atmosphere. Any sensitivity of the ground
layer to UV-B, particularly mosses [Gehrke, 1992; Sonesson and Callaghan, 1994], would alter their carbon
storage and could also increase the temperature of soil, which they insulate, thereby stimulating microbial
activity and CC>2 release to the atmosphere. Stresses caused by increased UV-B radiation, in combination
with climatic change, may affect species composition and herbivory and enhance susceptibility of plants to
insects, disease and fire. Because high latitudes are experiencing particularly large increases in solar UV-
B radiation, UV-B stresses of high-latitude forests may reinforce their transient release of carbon to the
atmosphere in response to climate change [Smith and Shttgart, 1993].
Likely UV-B increases due to stratospheric ozone depletion are not the only environmental changes.
Increases in concentrations of atmospheric CO2 are well documented and, as they generally stimulate
plant productivity, at least in the short term, the balance between UV-B and CC>2 interactions could
possibly be a particularly important determinant of carbon cycling.

Very little is known about the effects of enhanced solar UV radiation on the terrestrial nitrogen cycle.
This lack of information is of concern because changes in terrestrial nitrogen cycling would likely affect
the release of N2O, a gas that is predominantly derived from terrestrial systems [IPCC, 1992]. N^O is an
important greenhouse gas and it also participates in stratospheric processes that control the ozone layer.
The changes in species composition that are discussed above and in Chapter 3 would likely affect nitrogen
cycling in terrestrial ecosystems, e.g., possibly via UV-B effects on symbiotic association between higher
81
-------
plants with mycorrhizae and nitrogen fixing bacteria in root nodules. In the above-cited study of the
subarctic dwarf shrub, Vaccinium uliginosum [Gehrke et nl., 1994], it was found that plants exposed to
enhanced UV-B had much higher levels of leachable ammonia in the litter than the controls, indicating
possible effects on ammoniafication.

Litter decomposition

For many systems, site fertility is largely dependent on decomposition processes that release nutrients "
bound within non-living organic matter (NLOM). Therefore, changes in plant litter production and/or
subsequent degradation of litter, resulting from higher UV-B levels, may have significant impacts on
nutrient cycling. Decomposition of NLOM is carried out by saprophytic fungi and bacteria.

UV-B can potentially affect litter decomposition in several ways: (1) by changing the quantity of litter
that is available for decomposition; (2) by altering root/shoot ratios that determine where, i.e., below
ground or on the surface, and how efficiently plant matter is decomposed ; (3) by photoinhibition of biota
that decompose surface litter; (4) by photodecomposition of surface litter and; (5) by changes in chemical
composition of litter that alter its microbial decomposition. In comparison to studies of effects of
enhanced solar UV-B radiation on plant morphology and flowering, growth and photosynthesis, little is
known about the effects on decomposition.
Recent field studies in northern Sweden confirmed that enhanced UV-B radiation had significant effects
on the quality and decomposition of litter from the subarctic dwarf shrub, Vaccinium uliginosum [Gehrke et
«/., 1994; Jones et at., 1994]. The leaves of the shrub were richer in soluble carbohydrates and tannins than in
the controls and the initial decomposition rate of the leaves mixed with soil from the field site
[expressed as micrograms CC>2 per gram dry weight (g DW) per hour] was reduced (Figure 5.1). Additional
studies in microcosms further showed that leaf litter obtained from the shrubs grown under enhanced UV-B
contained more leachable ammonia and less cellulose ancHignin than did the litter from the control
shrubs. Fungal communities were affected and fungal and microbial activity was also significantly reduced
on the plant leaves that were exposed to enhanced UV-B, such that less CC>2 was emitted to the
atmosphere, i.e., soil carbon storage was increased. The changes in chemical composition of leaves may
involve photoreactions of lignocellulose materials. UV irradiation of lignocellulose materials results in
dimcrization, oligomerization, and quinone formation through photoreactions that involve carbonyl and
phenolic functional groups [see Heitner and Scaiano, 1993 for review}.
In contrast to the inhibiting effects of UV-B radiation on biotic decomposition of litter, other studies
indicate that direct exposure of litter to enhanced UV-B increases its decomposition rate [see Moorhead
and CMcighan, 1994 for review]. Moorhead and Callaghan [1994] have used ±e CENTURY model to
simulate potential effects of UV-B induced litter degradation on nutrient dynamics and soil carbon
storage. Results of the simulations indicated that the increased surface litter degradation rate substantially
decreased the surface litter and lignin pool sizes. The simulations indicated, however, that these changes
had little effect on pool sizes of the passive and slow-cycling organic matter in the soil. It was concluded,
therefore, that enhanced UV-B may have little effect on long-term nutrient cycles since it is through
formation of resistant soil organic matter (SOM) complexes that nutrients are sequestered.
In summary, decomposition processes can be accelerated when UV-B photodegrades surface litter, or
retarded when the dominant effect involves changes in the chemical composition of living tissues that
reduce the biodegradability of buried litter. These changes in decomposition can affect microbial
production of carbon dioxide and other trace gases, and also may affect the availability of nutrients
essential for plant growth. Factors that determine the net effect are poorly understood. In those
ecosystems where decomposition is retarded by increased UV-B, any additive or synergistic interactions
with increasing levels of CO2 which have also been shown to retard decomposition [Couteaux et al. 1991]
could lead to increased carbon storage in soils but lower primary production. Such effects are often
overlooked when feedbacks from warming soils due to climate change are calculated.
82
-------
o
s
ISO

180 H

110

50
30
control
UV
10
ao
30
day
40
50
60
Fig. 5.1. Respiration rates of microorganisms feeding on plant litter from Vaccinium uliginosum leaves grown under
enhanced vs. ambient UV-B radiation in the field [Gehrke era/., 1994\. Data represent 12 replicates of
experiments. Results indicate that enhanced UV-B exposure reduced the litter decomposition rate.

Trace Gas Exchange Dynamics

In the above discussions, effects of enhanced UV-B~rnrthe exchange of carbon dioxide between
terrestrial ecosystems and the atmosphere were emphasized. In addition to uptake of CC>2, plants are
known to release the chemically important gases CO and non-methane hydrocarbons (NMHCs), to the
atmosphere and to take up nitrogen oxides (NOX) and COS [7PCC, 1992},

Isoprene and other NMHCs react in the troposphere to produce ozone, other oxidants and aerosols. In
addition, CO and NMHCs are important scavengers of OH radicals in the troposphere (Chapter 6) and
changes in OH concentrations may affect the concentration of the greenhouse gases, methane and CPCs.
The- direct effects of UV-B on release of NMHCs, such as isoprene, are unknown, but it is known that
biogenic emissions from vegetation are species dependent. Thus, even if direct effects of UV-B radiation
have little effect, changes in the species composition of plant communities, driven by increased UV-B and
climatic stressors, could affect net fluxes of these chemically-important gases.

Laboratory studies have shown that senescent and dead leaves from temperate deciduous plants and
tropical grasses photoproduce CO much more rapidly than living plant leaves [Tarr et a.l.,1994].
Wavelength studies (>300 nm) indicate that UV-B radiation produces CO from the leaves with the highest
efficiency, although UV-A radiation also induces CO formation. The action spectra vary significantly
from one species to another. The flux of CO from living and non-living plant matter is sufficiently great
that it may be a major global source of this chemically active gas [IPCC, 1992]. As discussed below, UV-B
radiation also affects the production of CO in aquatic ecosystems.

Current research indicates that uptake by terrestrial plants is the major global sink for COS [Bates et
a.1., 1992]. Moreover, within-canopy uptake of the NOX from soils occurs in tropical humid forests. Based
on the known effects of UV-B on plant growth and photosynthesis that are discussed above, it is likely that
changes in UV-B radiation would selectively affect plant uptake of COS and NOX. To date, however, there
are no experimental data that confirm this possibility. COS, a gas that is considered to be one of the
major sources of sulfate aerosols in the stratosphere during periods of quiescent volcanic activity
[Crutzen, 1976], is discussed in more detail below. NOX, like NMHCs and CO, also participates in
tropospheric chemical processes that affect concentrations of tropospheric ozone, methane, and CFCs
83
-------
(sec Chapter 6). Thus, both COS and NOX, like CO, may be involved in feedbacks that affect ground-level
UV-B radiation and climate change.

Aquatic Ecosystems

Carbon and Nitrogen Cycles

Responses of photosynthetic organisms

Upper ocean carbon cycling is intimately tied to both the UV-B induced stresses to extant
phytoplankton communities as well as the complicated interaction of DOM with UV-B radiation. The
most direct effect of increased UV-B fluxes on upper ocean carbon cycling would be through changes in
phytoplankton community fecundity and structure. Other indirect effects involving trophic level
interactions may also affect ecosystem productivity [Both-well et al., 1994}. In this section we discuss the
possible role of these changes in aquatic carbon cycling. Phytoplankton responses are considered in much
greater detail in Chapter 4.
Laboratory and field studies with photosynthetic organisms obtained from aquatic ecosystems in
different locations indicate that reductions in current levels of solar UV-B result in enhanced primary
production [for recent review see Karentz et al., 1994]. Antarctic experiments under the ozone hole
demonstrated that primary production is inhibited by enhanced UV-B. Figure 5.2 shows the observed
decreased phytoplankton production associated with a 33% decrease in column ozone abundance during
austral spring of 1990 in Antarctica [Smith et al., 1992]. The net impact of a reduction in primary
production on the ocean sink for atmospheric CO2 is uncertain. Most primary production is recycled in
the upper layer of the sea. Only a fraction of the upper ocean paniculate organic carbon (POC) and
dissolved organic carbon (DOC) actually is exported from the upper ocean into intermediate and deep
water. On a global basis this "new production" is estimated, to ,be about 10 Gt C [1 gigaton (Gt) of carbon
equals 10" g] and it is believed that most of this POC and DOC is remineralized in the top km of the
sea [Sicgenthalcr and. Sarmiento, 1993]. About 0.2 Gt C of POC reaches the bottom sediments annually
where long-term carbon storage takes place. Taking into account biological removal as well as vertical
water transport of the dissolved inorganic carbon (DIG), the amount of anthropogenic CO2 taken up by
the ocean annually has been estimated to be about 2 Gt in recent years \_Siegentbaler and Sarmiento, 1993].
Additional field and modeling studies are required to come up with reliable estimates of the impacts of
enhanced UV-B radiation on this oceanic sink.

As in the case of terrestrial plants, aquatic photosynthetic organisms (algae, cyanobacteria) differ
substantially in their tolerances to UV-B exposure and changes in the ratio of UV-B:UV-A:PAR [UNEP,
1991; SCOPE, 1993; Prezelin et al., 1994; Weiler and Penhale, 1994]. Evidence has been presented that the
balance between photosynthesis, photoinhibition, and photorepair processes for natural communities of
photosynthetic organisms has been perturbed by ozone depletion over Antarctica. This perturbation may
result in changes in the competitive balance of species over time [Prezelin et al., 1994; Weiler an A Penhale,
1994]. A recent study has indicated, however, tint con positional changes in the diatom component of the
Antarctic phytoplankton community over the past 20 years h?.ve cannot be differentiated from natural
variability [McMinn et al., 1994].

Marine phytoplankton produce NMHCs [Bonsang et al., 1988; Donahue and Prinn, 1990], but the
effects of UV-B radiation on their photoproduction is unknown. As noted earlier in this chapter and
elsewhere in this report, these compounds interact with the hydroxyl radical [Donahue and Prinn, 1990]
which in turn plays a dominant role in maintenance of the oxidizing capacity of the atmosphere.
Phytoplankton, as well as higher plants and bacteria, produce other non-volatile hydrocarbons that are
highly resistant to biodegradation [for review see de Leeuw and Largeau, 1993], but the effects of enhanced
UV on production of these biomacromolecules have not been examined.
84
-------
Production [mg C nf3 h"1]
0 0.1 0.2 0.3 0.4 0.5 0.6
Fig. 5.2. Average values for in situ phytoplankton productivity versus depth (m) within the marginal ice zone of the
Beliinghausen Sea in austral spring of 1990 in which reduced productivity inside ozone hole is compared with
productivity outside hole. Integrated over depth in the water column, reductions in productivity ranged from 6 to
12%. On an annual basis, this range corresponds to an estimated annual productivity loss of 7 to 14 teragrams
which is 2 to 4% of production in the Antarctic marginaLice zone and about 0.1% of global phytoplankton •
production [Smith et al., 1992\.

A large fraction of the sea surface is covered by an organic microlayer that may have significant effects
on air-sea gas exchange. The sea surface microlayer is fully exposed to solar UV radiation and thus may be
particularly susceptible to effects of enhanced UV radiation [Duce and Liss, 1995].
As in the case of terrestrial ecosystems, few data are available on the effects of UV radiation on
aquatic biota involved in the nitrogen cycle. Changes in species composition noted above are likely to
affect nitrogen cycling, and suppression of assimilatory nitrate reduction by phytoplankton has been
demonstrated [UNEP, 1991J. The effects of UV-B on decomposition processes that are discussed below
also are likely to perturb aquatic nitrogen cycling. Moreover, solar UV-B radiation is mainly responsible
for the photodegradation of nitrate in water [Zafiriou and True, 1979; Zepp et al., 1987]; among other
species, hydroxyl radicals are produced in this photoreaction. Nitrite is also degraded by solar UV
radiation to form nitric oxide (NO), hydroxyl radicals, and other products, but this reaction is mainly
induced by UV-A radiation [Zafiriou. and Bonncau, 1987\. Effects of UV-B on marine nitrogen cycling
could affect sea-to-air exchange of N2O and NO. However, the role of the ocean as a source of
atmospheric N2O is poorly defined [IPCC, 1992; Butcher et al., 1992}.

Decomposition

Enhanced UV radiation may affect the decomposition of POC and DOC through its effects on
bacterial activity and through photodegradation of DOC. Freshwater and marine bacteria from both
freshwaters and the sea are impacted by changes in solar UV radiation [for review see Karentz et al. ,1994}
and action spectra indicate that UV-B radiation is mainly involved [Calkins and Barcelo, 1982]. This has
been confirmed by field studies which indicate that current levels of solar UV radiation reduce
bacterioplankton growth in the upper ocean [Herndl et al., 1993]. This effect may retard the decomposition
of labile organic matter in the upper ocean. Effects on other biogeochemical cycles are discussed below.
85
-------
That aquatic DOM is photoreactive has been established by numerous studies [Kouassi et al., 1990, 1992;
Frimmel and Bauer, 1987;'Kieber et al., 1990; Francko, 1990; Mopper et al., 1991; Valentine and Zepp, 1993;
Miller and Zepp, 1994]. Evidence for such photoreactivity derives in part from observed changes in the
electronic absorption spectrum of the organic matter as well as in the fluorescence intensity and spectrum.
The sunlight-induced decrease in absorbance is not accompanied by a corresponding change in dissolved
organic carbon content (DOC), although conversion to various UV-transparent products does occur (see
below). These spectral changes involve greater bleaching of the ultraviolet part of DOM spectra than the
visible part {Kouassi et al., 1992; Miller and Zepp, 1994]. Thus, photodegradation of DOM may result in
deeper penetration of solar UV (compared to visible) radiation into the sea and freshwaters.

The photoinduced fading of DOM is accompanied by the formation of a variety of organic and
inorganic compounds. The photoproducts of the biologically refractory DOM in natural waters are DIG
[Miller and Zepp, 1994]; low molecular weight compounds that are biologically labile, e.g., formaldehyde,
acctaldehyde, and the alpha-keto acid, glyoxylate [Kieber et al., 1989]; the trace gases, CO and COS; and
other unidentified species. Photoproduction rates of these compounds are greatest near the surface of
inland and coastal waters and least for open ocean waters. Francko [1990] has reviewed the rather sparse
literature on effects of solar radiation on the bioavailability of DOM. DIG is the major product from the
photodegradation of DOM derived from a coastal estuary and two rivers, including DOM in the
Mississippi River plume, Gulf of Mexico [Miller and Zepp, 1994]. The formation rate of DIG is at least
an order of magnitude greater than that of other photoproducts. Mopper et al. [1991] have argued that
photodegradation may limit the lifetime of biologically refractory DOM in the ocean.
UV-B radiation was mainly responsible for the photodegradation of DOM in Biscayne Bay (Miami),
Florida, other coastal waters and the open sea [Kieber et al., 1990; Mopper et al., 1991]. and also induces the
photoproduction of COS in near coastal seawater [Zepp and Andrcae, 1994] (Figure 5.3). Although solar
UV radiation is predominantly responsible for DOM pho_tQdegradation, the action spectra vary from one
region to another and action tails well into the UV-A region in some cases [Valentine and Zepp, 1993;
Zepp and Andreae, 1994] (Figure 5.3).

Photochemical reactions of DOM in the surface ocean produce dissolved gases that are supersaturated
with respect to an equilibrium state with observed atmospheric concentrations. This imbalance, or
'dis-cquilbria', drives the flux of these trace gases to the atmosphere from the ocean. In order to predict
quantitatively the effects of decreases in stratospheric ozone and enhanced UV-B radiation on the
photoproduction of these gases, action spectra are required. The air-sea exchange of gases also is affected
by changes in wind speed caused by climate change. Wind speed affects sea-to-air transfer coefficients as
well as vertical mixing in the upper ocean. To provide a framework for estimation of the flux and
distribution of CO and COS in the upper ocean, Najjar et al. [1994] have described a model that takes
into account photoproduction, turbulent mixing and chemical and biotic sinks for CO and COS in the
upper ocean.

DOM photoreactions are believed to be the main source of CO in seawater; its loss has been ascribed
primarily to microbial metabolism. As a result of these two processes, CO emissions from the sea follow
a diurnal pattern with maximum near surface ocean concentrations'greatly exceeding saturation during
daylight. Although the sea is thought to be a net source of CO, great uncertainty exists regarding the
strength of this source. Estimates range from 10 Tg/y up to 200 Tg/y [Erickson, 1989; IPCC, 1992].
Photodegradation of DOM in wetlands and near coastal waters may be an important regional source of CO
[Valentine and Zepp, 1993]. Action spectra and quantum yields for CO photoproduction were found to be
similar for water obtained from several wetland and near coastal sites in North America. For wavelengths >
300 nm, the greatest action for CO production was in the UV-B region, but the spectra tailed out well
into the UV-A region.

Interrelationships among biogeochemical processes in the ocean and atmosphere can sometimes lead to
feedbacks. Such a feedback relationship involving marine CO and tropospheric ozone illustrates a possible
feedback between ozone depletion and air-sea exchange of trace gases [Erickson, 1989].
86
-------
3.5E-7
3E-7

c- 2.5E-7
2E-7
iZ
8 1-5E-7
§
9- 1E7

* 5E-8

0
300 320 340 360
Wavelength, nm
380
Fig. 5.3. Comparison of action spectra for the photoproduction of COS in seawater obtained from coastal regions of the
North Sea (Q) and Gulf of Mexico (•). North Sea water was obtained near Bremerhaven, Germany (54°N, 8°E)
and Gulf of Mexico water near Turkey Point, Florida (30°N, 84.5°W). Samples used in the action spectra studios
were studied within 12 hours of the time of collection [Zepp andAndreae, 1994\.

Sulfur Cycle ~~~

Increased UV-B can influence the sulfur cycle (Figure 5.4) via impacts on both aquatic and terrestrial
ecosystems. Changes in the sea-to-air transfer of DMS and COS may influence the radiative balance of the
atmosphere. As noted in a previous section,, the growth and productivity of oceanic phytoplankton as well
bacterioplankton growth may be affected by a variety of stressors including increased UV-B. Production of
dimethylsulfonium propionate (DMSP), the precursor compound of DMS, by phytoplankton such as
coccolithophorids provides the primary source (up to 90%) of sulfur for cloud condensation nuclei in the
remote marine atmosphere. On a global scale, marine emissions of DMS account for about 15% of the
total atmospheric sulfur input [Bates et al., 1992]. Because the main sources of DMS in seawater are
particular species of phytoplankton, any alteration in the fecundity and species distribution of
phytoplankton communities could have a direct effect on the surface ocean DMS concentration and
subsequently the sea-to-air flux of DMS. In addition to its effects on phytoplankton, UV-B radiation may
affect the loss of DMS through microbial [Kiene and Bates, 1990] and photooxidative degradation. UV-B
induced changes in these various upper oceanic processes that affect DMS may result in changes in net sea-
to-air flux.
Field studies have indicated that a variety of processes affect the atmospheric concentrations of COS
[Andreae and Ferek, 1992]. These studies show that COS is formed primarily by photochemical processes in
the upper layers of the ocean. Zepp and Andreae [1994] have found that the photochemical formation of
COS from dissolved organosulfur compounds in sea water can be photosensitized by DOM. Because rates
of photosensitized reactions are generally much more rapid in coastal waters than in the open sea [Kieber
et al., 1990; Zafiriou and Dister, 1991], these results help to explain why concentrations of COS have been
observed to be highest in coastal regions [Andreae and Ferek, 1992]. Global estimates of COS production
recently have been derived using Coastal Zone Color Scanner satellite data and general circulation models
[Erickson and Eaton, 1993]. Wavelength studies of COS formation in coastal seawater samples have
confirmed that COS is predominantly formed by the action of middle UV radiation (280-340 nm), but
that action spectra for the North Sea and Gulf of Mexico differed significantly beyond 320 nm [Zepp and
Andreae, 1994] (Figure 5.3).
87
-------
Hydrolysisl Hydrogen
Sulfide
Bacteria
Fig. 5.4. Biogeochemical processes affecting the global sulfur cycle [adapted from SCOPE, 1993\

Oxygen Cycle

The previously-discussed effects of UV-B radiation on photosynthesis and microbial decomposition
also can affect the oxygen cycle in both aquatic and terrestrial ecosystems. Photooxidation of marine and
freshwater DOM leads to consumption of oxygen as it is combined with the DOM carbon. DOM
photooxidation also is accompanied by reduction of oxygen to form superoxide [Zafiriou and Dister,
1991], which dismutcs (i.e., disproportionates) to form hydrogen peroxide. Other reactive oxygen species
arc produced on absorption of UV radiation by freshwater and marine chromophores [see Waite et al., 1988
and Blough and Zepp, 1994, for reviews]. Hydrogen peroxide, through interactions with marine biota and
chemical constituents, is oxidized back to oxygen or reduced to water. Action spectra for the
photoproduction of hydrogen peroxide in sea water and freshwaters indicate that solar UV radiation is
most effective [Moore et al., 1993]. Action is most pronounced in the UV-B region, although UV-A
radiation also is involved. A model that describes the upper ocean distribution of hydrogen peroxide has
been developed [Sikorski and Zika, 1993].

Metals Cycles

Field and laboratory studies over the last 5 years have indicated that solar UV radiation enhances the
reductive dissolution of iron and manganese oxides/hydroxides in oxygenated natural waters [Faust, 1994;
Sulzbcrgcr, 1994; Waite et al., 1994]. Reductive dissolution converts the thermodynamically stable, but
biologically unavailable, oxides of these trace metals into more bioavailable forms, and thus may help
control marine productivity in parts of the ocean that are limited by iron or manganese. The action spectra
for iron photodissolution processes have not been determined and likely are variable. Light enhances the
dissolution of an amorphous manganese oxide in seawater and this process helps account for the surface
88
-------
maxima in dissolved manganese ( Mn[II]) observed in the ocean [Sunda and. Huntsman, 1990]. UV-B
radiation inhibits the microbial oxidation of soluble Mn[II] to low-solubility Mn[IV] oxides [Sunda and
Huntsman, 1990]. In most of these cases, the presence of aquatic DOM was shown to be essential for the
occurrence of photodissolution. That naturally occurring organic compounds are capable of inducing or
assisting the photodissolution of iron and manganese oxides has been confirmed in a number of laboratory
studies using organic acids that are present in fresh and marine waters, e.g. humic, fulvic and
hydroxycarboxylic acids [Watte et al., 1994].

CFC Substitutes

Considerable research on the development of suitable CFC substitutes has taken place during the past
few years. This research has included intense studies of the atmospheric fate and impact of HFC and
HCFC substitutes for CFCs [see AFEAS, 1994 and Wellington et al, 1994 for reviews]. In addition to
evaluations of the ozone depletion potentials of these substitutes, studies have included initial evaluations
of potential impacts of deposition of selected atmospheric degradation products of HCFCs and HFCs.
TFA, the major atmospheric degradation product of HCFC-123, HCFC-124, and HCFC-134a was
selected for study, because it is resistant to abiotic degradation, including atmospheric decomposition,
and likely to become globally distributed. Measurements of TFA in the present environment are sparse!
During late 1993 and early 1994, TFA was detected in the atmosphere near Tuebingen, Germany and on
spruce needles in Sweden. It is most likely that the source of this TFA was atmospheric degradation of the
anesthetic, halothane. Models indicate that most of the TFA formed from HCFCs and HFCs should be
deposited in the ocean, where it will be diluted to very low concentrations. Up to 30% may be deposited on
land. Recent field studies have shown that TFA, a hydrophilic substance, is not likely to accumulate in
most soils or biota, although accumulation in acidic organic soils may be possible. Evidence is now
emerging that TFA may be degradable by microorganisms [ Visscher et al., 1994] and that, even at high
concentrations, it appears not to significantly inhibiTthe-metabolism of acetate. Additional research is-
currently underway to better elucidate the biospheric fate and impacts of TFA and potential effects of TFA
on biogeochemical cycles.

Conclusions

Potential effects of enhanced UV-B radiation on terrestrial and aquatic carbon, nitrogen, sulfur,
oxygen, and metal cycles have been identified. These effects and companion effects on biogeochemical
cycles in the atmosphere may result in feedbacks that either reinforce or attenuate the buildup of
greenhouse gases and aerosols in the atmosphere. Radiation amplification factors shown in Chapter 1 for
some of the aquatic photochemical processes discussed in this section indicate that they are
approximately as sensitive to changes in the stratospheric ozone layer as the effects on health, plants, and
tropospheric photolysis.

Increasing UV-B radiation has the potential to change the quantities and chemical species of carbon
that are exchanged between the atmosphere and terrestrial biosphere and also the carbon that is stored in
soils and aquatic systems. The effects of UV-B on carbon storage and carbon fluxes on land are complex,
varying between ecosystems, species and even crop cultivars. In some systems, UV-B can, for example,
increase carbon storage in soils, whereas in others it can enhance the degradation of lignin in soil organic
matter and the photoproduction of chemically-important gases such as carbon monoxide.. Responses of
plants to UV-B have been shown to increase over time; impacts on natural ecosystems may be subtle but
may lead to species shifts in the long term. Consequently, there is a need for research on the impacts of
UV-B radiation on biogeochemical cycling to develop a new focus, in addition to investigations to
determine short term physiological responses. This focus should address long-term productivity responses
under natural conditions.

Laboratory and field experiments in aquatic ecosystems have shown that enhanced UV-B has a variety of
effects on biogeochemical cycles. For example, photosynthesis has been suppressed by ozone depletion
and enhanced UV-B radiation over the Antarctic. Moreover, recent studies indicate that photodegradation
89
-------
of DOM in the upper ocean has multiple effects on biogeochemical cycles, ranging from changes in the
penetration of UV-B into the sea to enhanced formation of DIG and CO. Sulfur cycling in marine systems
also might be affected by changes in UV-B radiation with resulting effects on the sea to air fluxes of COS
and DMS. Metal cycles and bioavailability, especially those of the trace nutrients, iron and manganese, are
sensitive to UV changes as well. Models designed to simulate these effects and their interactions with
changing climatic conditions are just beginning to be developed.

The results discussed here suggest that changing UV-B radiation may affect global biogeochemical
cycles and related feedback interactions. It should be emphasized that evaluations of regional and global
scale effects require the development of appropriate models and observational approaches. Earth system
models that incorporate solar UV-B radiation as a forcing variable are required in order to integrate,
evaluate and predict ecosystem effects and related feedbacks on a global scale.

References

AFEAS, Workshop on the Environmental Fate of Trifluoroacetic Acid (TFA): 3-4-1994, Miami Beach,
FL, Alternate Fluorocarbon Environmental Acceptability Study (AFEAS) Report, Chumley, F. G., Ed.,
Washington, DC, 1994.
Andreac, M.O. and R.J. Ferek, Photochemical production of carbonyl sulfide in seawater and its emission
to the atmosphere. Global Biogeochem. Cycles 6, 175-183, 1992.
Bates, T.S., B.K. Lamb, A. Guenther, J. Dignon, and R.E. Stoiber, Sulfur emissions to the atmosphere from
natural sources. /. Atmos. Chem., 14, 315-337, 1992.
Blough, X.V.and R.G. Zepp. Reactive oxygen species in natural waters, In Reactive Oxygen Species in
Chemistry and Biochemistry, C.S. Foote and J.S. Valentine (eds), Chapman & Hall, New York, 1994.
Bonsang, B., M. Kanakidou, G. Lambert and P. Monfray, The marine source of C2-C6 aliphatic
hydrocarbons, /. Atmos. Chem., 6, 3-20, 1988. _^_
Bothwcll, M.L., D.M.J. Sherbet, and C.M. Pollock, Ecosystem response to solar ultraviolet-B radiation:
Influence of trophic level interactions, Science, 265, 97-100, 1994.
Butcher, S.S., R.J. Charlson, G.H. Orians, and G.V. Wolfe (eds.), Global Biogeochemical Cycles, Academic
Press, Harcourt Brace Jovanovich, New York, 1992.
Calkins, J. and J. Barcelo, Action spectra, pp. 143-150 in The Role of Solar Ultraviolet Radiation in
Marine Ecosystems, J. Calkins (ed.), Plenum, New York, 1982.
Caldweil, M.M., R. Robberecht, R.S. Nowak, and W.D. Billings, Differential photosynthetic inhibition by
ultraviolet radiation in species from the Arctic-alpine life zone, Arctic and Alpine Research, 14, 195-
202, 1982.
Coutcaux, M.M., M. Mousseau, M.L. Celerier and P. Bottner, Increased atmospheric CO2 and litter
quality: decomposition of sweet chestnut leaf litter with animal food webs of different complexities,
Oikos, 61, 54-64, 1991.
Crutzcn, P. J., The possible importance of COS for the sulfate layer of the stratosphere, Geophvs. Res.
Lett., 3, 73-76, 1976.
De Lceuvv, J.W. and C. Largeau, A review of macromolecular organic compounds that comprise living
organisms and their role in kerogen, coal and petroleum formation, in Organic Geochemistry, M.H.
Engels and S:A. Macko (eds.), Plenum, New York, 1993.
Ducc, R. and P. Liss (eds.), The Sea Surface and Global Change, Cambridge University Press, in press,
1995.
Donahue, N. and R. Prinn, Nonmethane hydrocarbon chemistry in the remote marine boundary layer, /.
Geophvs. Res., 95, 18387-18411, 1990.
Erickson, D. J. Ill, Ocean to atmosphere carbon monoxide flux: Global inventory and climate
implications, Global Biogeochem. Cycles, 3, 305-314, 1989.
Erickson, D. J. Ill and B. E. Eaton, Global biogeochemical cycling estimates with CZCS satellite data and
general circulation models, Geophys. Res. Let., 20, 683-686, 1993.
Erickson, D.J. Ill and J.A. Taylor, 3 D atmospheric CO modeling: The possible influence of the ocean,
Geophys. Res. Lett., 19, 1S55-1958, 1992.
90
-------
Faust, B.C., A review of the photochemical redox reactions of iron(III) species in atmospheric, oceanic,
and surface waters: Influences on geochemical cycles and oxidant formation, pp.3-37 in Aquatic and
Surface Photochemistry, G.R. Helz, R.G. Zepp, and D.G. Crosby (eds.), Lewis Publishers, Ann Arbor,
MI, 1994.
Francko D.A., Alteration of bioavailability and toxicity by phototransformation of organic acids, pp.
167-177 in Organic Acids in Aquatic Ecosystems, E.M Perdue and E.T. Gjessing (eds.), John Wiley &
Sons, Limited, Chichester, 1990.
Frimmel, F. and H. Bauer, Influence of photochemical reactions on the optical properties of aquatic
humic substances gained from fell leaves. Set. Tot. Environ. 62: 139-148, 1987.
Gehrke, C., Short term effects of enhanced UV-B radiation on the moss Hylocomium splendens in northern
Swedish Lapland, Report, Department of Plant Ecology, University of Lund, Sweden, 1992.
Gehrke, C., U. Johanson, T.V. Callaghan,D. Chadwick, and C.H. Robinson, The impact of enhanced UV-B
radiation on litter quality and decomposition processes in Vaccinium leaves from the subarctic, Oikos,
in press, 1994.
Herndl, G.J., G. Mueller-Niklas, and J. Frick, Major role of ultraviolet-B radiation in controlling
bacterioplankton growth in the surface layer of the ocean, Nature, 361,717-719, 1993.
Heitner, C. and J.C. Scaiano (eds.) Photochemistry of Lignocellulosic Materials, ACS Symposium Series 531,
American Chemical Society, Washington,D.C, 223 p., 1993.
IPCC, R. Watson, L.G. Meira-Filho, E. Sanhueza, and A. Janetos, Greenhouse gases: Sources and sinks,
Chapter Al, In J.T. Houghton, B.A. Callander, and S.K. Varney, Eds., Climate Change 1992:
Supplementary Report to the IPCC Scientific Assessment, pp. 28-46, 1992.
Jones, D., T.V. Callaghan, L.O. Bjorn, C. Gehrke, U. Johanson, A. Kyparisis, J.A. Lee, and M. Sonesson,
Effects of elevated UV-B radiation and enhanced CC>2 on a subarctic heath system, European
Symposium on Effects of Environmental UV Radiation, Munich, October, 1993, in press, 1995.
Johanson, U., C. Gehrke, L.O. Bjorn, T.V. Callaghan_and_M. Sonesson, The. effects of enhanced UV-B
radiation on a subarctic heath ecosystem, Ambio, in press, 1994.
Karentz, D., M.L. Bothwell, R.B. Coffin, A. Hanson, G.J. Herndl, S.S. Kilham, M.P. Lesser, M. Lindell,
R.E. Moeller, D.P. Morris, P.J. Neale, R.W. Sanders, C.S. Weiler, and R.G. Wetzel, Impact of UV-B
radiation on pelagic freshwater ecosystems: Report of working group on bacteria and phytoplankton,
Arch. Hydrobiol., Beth. Ergebn. Limnol., 43, 31-69, 1994.
Kieber, D.J., J.A. McDaniel, and K. Mopper, Photochemical source of biological substrates in seawater:
Implications for carbon cycling, Nature, 341, 637-639, 1989.
Kieber, R. J., X. Zhou, and K. Mopper, Formation of carbonyl compounds from UV-induced
photodegradation of humic substances in natural waters: Fate of riverine carbon in the sea. Limnol.
Oceanog. 35, 1503-1515, 1990.
Kiene, R. and T.S. Bates, Biological removal of dimethyl sulphide from seawater, Nature, 345, 702-705,
1990.
Kouassi, M., R.G. Zika, and J.M.C. Plane, Photochemical modelling of marine humus fluorescence in the
ocean. Ncth. J. Sea Res., 27, 33-41, 1990.
Kouassi, A.M. and R.G. Zika, Light-induced destruction of the absorbance property of dissolved organic
matter in seawater, Toxicol. Environ. Chem, 35, 195-211, 1992.
Krupa, S.V. and R.N. Kickert, The greenhouse effect: Impacts of ultraviolet-B (UV-B) radiation, carbon
dioxide, and ozone on vegetation, Environmental Pollution, 61, 263-393, 1989.
Kuma, K., S. Nakabayashi, Y. Suzuki, I. Kudo, and K. Matsunaga, Photoreduction of Fe(III) by dissolved
organic substances and existence of Fe(II) in seawater during spring blooms, Marine Chemistry 37 15-
27, 1992.
Miller, W. L. and R.G. Zepp, Photochemical production of dissolved inorganic carbon from terrestrial
organic matter: Significance to the oceanic organic carbon cycle, Geophys. Res. Lett., submitted, 1994.
Moore, C.A., C.T. Farmer, and R.G. Zika, Influence of the Orinoco River on hydrogen peroxide
distribution and production in the Eastern Caribbean, /. Geophys. Res., 98C, 2289-2298, 1993.
Moorhead, D.L. and T.V. Callaghan, Effects of increasing UV-B radiation on decomposition and soil
organic matter dynamics. A synthesis and modeling study, Siol. and Pert, of Soils, in press, 1994.
91
-------
Moppcr, K., X. Zhou, RJ. Kieber, D.J. Kieber, R.J. Sikorski and R.D. Jones, Photochemical degradation of
dissolved organic carbon and its impact on the oceanic carbon cycle, Nature, 353, 60, 1991.
Najjar, R. G., D. Erickson and S. Madronich, Modeling the air-sea fluxes of gases formed from
decomposition of dissolved organic matter: Carbonyl sulfide and carbon monoxide, in press in Role of
Non-Living Organic Matter in the Earth's Carbon Cycle, R.G. Zepp and C. Sonntag (eds.), Wiley New
York, 1995.
Prczelin, B.B., N.P. Boucher, and R.C. Smith, Marine primary production under the influence of the
Antarctic ozone hole: Icecolors 90, In C.S. Weiler and P.A. Penhale, Eds., Ultraviolet Radiation in
Antarctica: Measurements and Biological Effects, Antarctic Research Series, 62, 159-186, 1994.
Schlcsinger, W.H., Biogeochemistry: An Analysis of Global Change , Academic Press, San Diego, 1991.
SCOPE, Effects of Increased Ultraviolet Radiation on Global Ecosystems, Scientific Committee on Problems
of the Environment (SCOPE), 51 bd de Montmorency, 75016 Paris, France, 1993.
SCOPE, Effects of Increased Ultraviolet Radiation on Biological Systems, Scientific Committee on Problems
of the Environment (SCOPE), 51 bd de Montmorency, 75016 Paris, France, 1992.
Sicgenthaler, U. and J.L. Sarmiento, Atmospheric carbon dioxide and the ocean, Nature, 365, 119-125
1993.
Sikorski, R. and R.G. Zika, Model for oceanic hydrogen peroxide, /. Geophys. Res., 98C, 2281-2288
1993.
Smith, R. C., B. B. Prezelin, K. S. Baker, R. R. Bidigare, N. P. Boucher, T. Coley, D. Karentz, S.
Maclntyre, H. A. Matlick, D. Menzies, M. Onderusek, Z. Wan and K. J. Waters, Ozone depletion:
Ultraviolet radiation and phytoplankton biology in Antarctic waters, Science, 255, 952-959, 1992.
Smith, T. and H.H. Shugart, The transient response of terrestrial carbon storage to a perturbed climate,
Nature, 361, 523-526, 1993.
Soncsson, M. and T.V. Callaghan, Short term effects of enhanced UV-B and CO2 on mosses and lichens at
different latitudes, Oecologia, submitted, 1994. -__..
Sullivan, J.H and A.H. Teramura, The effects of UV-B radiation on loblolly pine. 2. Growth of field
grown seedlings, Trees, 6, 115-120, 1991.
Sulzberger, B., H. Laubscher, and G. Karametaxas, Photoredox reactions at the surface of iron(III)
(hydr)oxides, pp. 53-74 in Aquatic and Surface Photochemistry, G.R, Helz, R.G. Zepp, and D.G. Crosby
(eds.), Lewis Publishers, Ann Arbor, MI, 1994.
Sunda, W.G. and S.A. Huntsman, Effects of sunlight and anthropogenic alterations in atmospheric solar
attenuation on manganese redox cycles in surface seawater, pp.104-107 in N.V. Blough and R.G. Zepp
(eds.), Effects of Solar Radiation on Biogeochemical Dynamics in Aquatic Environments, Woods Hole
Occanographic Institute Technical Report, WHOI-90, 1990.
Tarr, M.A., W. L. Miller, and R.G. Zepp, Direct photoproduction of carbon monoxide from plant matter,
/. Geophys. Res., in press, 1994.
Tcvini, M. and A.H. Teramura, UV-B effects on terrestrial plants, Photochem. Photobiol. 50, 479-487
1991.
UNEP, Environmental Effects of Ozone Depletion: 1991 Update, United Nations Environment Programme,
Nairobi, Kenya, 1991.
ValentinCjR. and R.G. Zepp, Formation of carbon monoxide from photodegradation of terrestrial organic
matter. Environ. Set. Technol., 27, 409-412, 1993.
Visscher, P.T., C.W. Culbertson, and R.S. Oremland, Degradation of trifluoroacetate in oxic and anoxic
sediments, Nature, 369, 729-731, 1994.
Waite, T.D. D.T. Sawyer, and O.C. Zafiriou, Panel 1. Oceanic reactive chemical transients, Appl.
Geochem., 3, 9-17, 1988.
Waite, T.D. and R. Szymczak, Photoredox transformations of iron and manganese in marine systems:
Review of recent field investigations, pp. 39-52 in Aquatic and Surface Photochemistry, G.R. Helz,
R.G. Zepp, and D.G. Crosby (eds.), Lewis Publishers, Ann Arbor, MI, 1994.
Wallington, T.J., W.F. Schneider, D.R. Worsnop, O.J. Nielsen, J. Sehested, W.J. Debruyn, and J.A. Shorter,
The environmental impact of CFC replacements - HFCs and HCFCs, Environ. Sci. Technol., 28,
320A-325A, 1994.
92
-------
Weiler, C.S. and P.A. Penhale, Eds., Ultraviolet Radiation in Antarctica: Measurements and Biological
Effects, Antarctic Research Series, 62, 159-186, 1994.
Zafiriou, O.C. and R. Bonneau, Wavelength-dependent quantum yield of OH radical formation from
photolysis of nitrite ion in water, Photochem. Photobiol., 45, 723-727. 1987.
Zafiriou, O. C. and B. Dister, Photochemical free radical production rates: Gulf of Maine and Woods
Hole-Miami transect, /. Geophys. Res., 96, 4939, 1991.
Zafiriou, O.C. and M.B. True, Nitrate photolysis in seawater by sunlight, Mar. Chem., 8, 33-42, 1979^
Zepp, R. G. and M.O. Andreae, Factors affecting the photochemical formation of carbonyl sulfide in
seawater, Geophys. Res. Lett., in press, 1994.
Zepp, R.G., J. Hoigne, and H. Bader, Nitrate-induced photooxidation of trace organic chemicals in water,
Environ. Sci. TechnoL, 21, 443-450, 1987.
93
-------
94
-------
CHAPTER 6
EFFECTS OF INCREASED SOLAR
ULTRAVIOLET RADIATION ON TROPOSPHERIC
COMPOSITION AND AIR QUALITY
X. Tang (China) and S. Madronich (USA)
Summary

Reductions of stratospheric ozone and the concomitant increases of UV-B radiation penetrating to the
lower atmosphere result in higher photodissociation rates of key trace gases that control the chemical
reactivity of the troposphere. This can increase both production and destruction of tropospheric ozone (O3)
and related oxidants such as hydrogen peroxide (H2C>2), which are known to have adverse effects on human
health, terrestrial plants, and outdoor materials. Changes in the atmospheric concentrations of the hydroxyl
radical (OH) may change the atmospheric lifetimes of climatically important gases such as methane (CHi)
and the CFC substitutes.

Trends in the photodissociation rate coefficient of tropospheric 03, of about +0.32±0.04 percent per year in
the northern hemisphere and +0.40+0.05 percent per year in the southern hemisphere, have been estimated
from satellite measurements of the ozone column between 1979 and 1992. The corresponding model-
calculated changes in tropospheric chemical composition are non-linear and sensitive to the prevailing levels
of nitrogen oxides (NOX). In polluted regions (high NOX), tropospheric O3 is expected to increase, reaching
potentially harmfully concentrations earlier in the day, and leading to more frequent exceedance of oxidant
standards for air quality in urban areas where O3 levels are routinely near such air quality thresholds. In
more pristine regions (lower NOX), O3 increases can be lower or even negative. Other oxidants, such as H2O2
and OH, are projected to increase for both polluted and pristine regions. Changes to H2O2 concentrations
may have some impact on the geographical distribution of acid precipitation. Rural regions may become
more urban-like and the percentage of areas with remote tropospheric conditions may decline.

Increases in OH concentrations cause a nearly proportionate decrease in the steady state tropospheric
concentrations of CH4 and CFC substitutes such as the HCFCs and HFCs. Thus, the measured reductions in
the ozone column (TOMS, 1979-92) are likely to have moderated Crtj increases over the past decade, and may
account for about 1/3 of the slowing of the global CHi trends.

Increased tropospheric reactivity could also lead to changes in the production of particulates such as cloud
condensation nuclei, from the oxidation and si il.-=,er»ipui i "ideation of sulfur of both anthropogenic and
rici! urcil origin (e.g., carbonyl sulftdc and dim.:-!u_> '
-------
UV-B enhancements (resulting from stratospheric O3 reductions, see Chapter 1) are expected to affect
tropospheric oxidant concentrations on many geographical scales. Tropospheric O3 is a major constituent of
the photochemical smog encountered in many polluted urban environments, and is known to have adverse
effects on human health [Lippmann, 1991] and outdoor materials [Andrady, 1993]. On broader suburban and
rural scales, oxidants including O3 and H2Q2 cause damage to vegetation and play a role in the acidification
of rain [Penkett et al., 1979; Mailer, 1989; NAPAP, 1991]. Global-scale changes in tropospheric O3 are of concern
both because O3 is a major greenhouse gas, and because it is the chemical precursor of the OH radical, the
principal cleaning (oxidizing) agent of the global troposphere. Changes in OH concentrations affect directly -
the rate of removal of many other atmospheric gases involved in climate and ozone chemistry, including
methane (CH4) and the hydrogen-containing CFC substitutes (e.g., HFCs, HCFCs) [WMO, 1994].

Photodissociation Rate Response to Increased UV-B

The rates of some chemical reactions in the troposphere depend directly on the amount of available UV-B
[Leighton, 1961]. The reaction rate coefficient, or J value, is given by the expression
J = J F(X)0(X)<)>(X) dX
where X is the wavelength (nm), F( X) is the spectral actinic flux (quanta cm-2 s'1 nnr1), c?( X) is the molecular
absorption cross section (cm2 molec'1), and <(>( X) is the photodissociation quantum yield (molec quanta'1).
The spectral actinic flux in the UV-B region is a strong function of the ozone column. The most sensitive J
values for key reactions are listed in Table 1 of Chapter 1. Comparable sensitivities have been calculated by
Madronich and Granier [1994] and Fuglestvedt et al. [19947, though for different locations and times.
Madronich and Granier [1994] calculated the trends in Ji, the O3 photodissociation rate coefficient, associated
with the 1979-1992 TOMS O3 column data record. Figure 1 shows that the global Jx has increased by about
0.36±0.04 percent per year, with slightly higher values in the southern hemisphere (0.4010.05 percent per
year) than in the northern hemisphere (0.32± 0.05 percent per year).
J0 changes relative to 1979-1992 average
10
_o
JJ
.o
O(1D) + O2,
computed using ozone column measurements from the Nimbus 7 satellite (TOMS, version 6 data). Values are
given as monthly deviations from the corresponding 1979-1992 averages. Thick solid curve is the area-weighted
global average, thin solid line and dotted line are respectively the southern hemisphere and northern hemisphere
area-weighted averages. Values next to legend are linear trends, and their corresponding uncertainties,
expressed as percent per year relative to the 1979 intercept. From Madronich and Granier [1994].
96
-------
- .
Changes in Tropospheric Chemical Composition

Changes in Os, ^262 and HOX

Translating changes in J values to changes in atmospheric chemical composition is not straightforward
because tropospheric chemistry is highly non-linear. Of special interest are the concentrations of important
oxidants such as 03, H^O^ and OH, which react with various gases in the troposphere. In particular, the OH
radical is the most important cleansing agent of the troposphere. "~

The photochemical production of tropospheric O$ is due almost exclusively to the photodissociation
NO2 + hv(X<420nm) -» NO + O(3P)
followed rapidly by recombination of the atom with molecular oxygen,

O(3P) + O2 -» Os .
Ozone loss occurs when its photodissociation,

O3 + hv(X<320nm) -> O^D) + O2
is followed by reaction of O(^D), usually with water vapor:

O(JD) + H2O -4 OH + OH
These last two reaction are also the main source of tropospheric OH radicals [Levy, 1971]. Additional loss
of 03 may occur through the catalytic cycle
OH
O3 -» HO2 + O2

HO2 + O3 -> OH + 2 O2 ~°~ "
as well as other reactions. The net ozone production/destruction depends sensitively on the amounts and
partitioning of the NOX (= NO + NC^) and HOX (= OH + HOj) species, which are in turn determined by
complex sequences of reactions involving carbon monoxide (CO) and hydrocarbons, as well as other
tropospheric compounds. Detailed discussions of these reaction sequences are beyond the scope here (but see
for example [Finlayson-Pitts and Pitts, 1986]), although some of the non-linearities that they induce may
already be evident from the well-known reactions

OH + CO +O2 -> HO2 + CO2

HO2 + NO -» OH + NO2

O3 + NO -> O2 + NO2
The HOX species are ultimately removed by termination reactions, leading to the formation of oxidants
such as hydrogen peroxide, e.g.

HO2 + HO2 -> H2O2 + O2.

Consideration of the above reactions under scenarios of enhanced UV-B radiation shows that both
increased production and increased destruction of tropospheric O3 are possible. The sign and magnitude of
the net effect are complex functions of the concentrations of various compounds (especially O3, H2O, NOX,
CO, and hydrocarbons), and may well be different for different chemical regimes (e.g., polluted vs. pristine).

Estimates of the tropospheric response to UV. changes are still a matter of active research and the results
appear to be sensitive to model formulation. Liu and Trainer [1988] used a simple zero-dimensional
chemistry model to derive the changes in O3 and OH as a function of prescribed NOX concentrations. They
found that a 20 percent loss of stratospheric ozone at northern mid-latitudes could reduce tropospheric O3 by
10-35 percent for NOx levels between 0.01 to 0.10 ppbv (parts per billion by volume), while O3 increases
substantially when NOX levels are higher than 0.1-0.2 ppbv (e.g., in many rural and most urban regions).
Different results were obtained by Thompson et al., [1991] using a one-dimensional model for different

97
-------
chemical regimes, with decreases in trope-spheric O3 concentrations for all regions considered, including
relatively polluted areas.

Modeling studies also show that OH concentrations respond to changes in Ji in a complex way. For a one
percent increase in Jj, the OH concentration increased by about 0.9 percent at low NOX and by 0.3 percent at
high NOX [Liu and Trainer, 1988]; by 0.3 percent for marine low latitudes and 0.7 percent for urban mid-
latitude regions [Thompson et al. 1991]; and by 0.5-1.0 percent when averaged globally and annually based on
a recent three-dimensional model [Fuglestvedt et al., 1994].

H2O2 levels are projected to increase globally [Thompson et al., 1989, 1991; Fuglestvedt et al., 1994]. For
scenarios with higher NO*, significantly larger H2O2 (and HO2) levels were calculated for rural and
continental conditions, while for the remote regions only a slight increase was obtained.

Thus, it may be concluded from current models that enhanced UV will increase the OH, HO2 and H2O2
concentrations, but the exact amount of the increase remains unclear, with results apparently being sensitive
to model formulation. Model-calculated changes in tropospheric 03 appear to be very sensitive to the NOX
levels of specific regions. Some O3 is also transported downward from the stratosphere, so that decreases of
stratospheric O3 could result in lower O3 input from the stratosphere to the troposphere, but quantitative
assessments of this effect have not been made. Measurements by Schnell et al. [1991] show that Antarctic
surface O3 decreased by 17 percent over 1976-89 during spring and summer, and were attributed to increased
UV-B levels associated with the O3 hole, rather than reduced downward transport from the stratosphere.

Many environmental concerns related to urban and regional air quality are likely to be affected by
increased oxidant concentrations. Urban and surrounding areas routinely experience high NOX and volatile
organic carbon concentrations due to anthropogenic emissions, which leads to very reactive chemistry and
generates high levels of ozone and other oxidants through the photo- chemical smog formation process.
Some of these oxidants, such as formaldehyde, HCHO, can produce odd-hydrogen radicals upon absorption
of UV-B [Finlayson-Pitts and Pitts, 1986], providing additional chemical channels that could contribute to
increased urban reactivity with future increases in UV-B. Increased UV-B radiation could produce even
higher levels of urban ozone, as well as potentially harmful concentrations of ozone earlier in the day, and
nearer to emission sources and population centers [Gery et al., 1987; Whitten and Gery, 1986]. It was suggested
by Gery et al. [1987] that, if UV levels are increased, significantly more stringent regulation of volatile organic
emissions will be required in urban locations to maintain photochemical oxidants below air quality standards.
De Leeuw and Van Rheineck Leyssius [19917 have similarly estimated that, given constant emissions, air
quality violations will be much more frequent in European urban areas if UV levels increase.

Because increased UV-B would make the lower troposphere more reactive, some rural regions may
become more urban-like and the percentage of areas with remote tropospheric conditions may decline; this
will change the global distribution of polluted areas [Gery, 1993]. On the global scale, the increased
tropospheric reactivity caused by UV-B radiation could lead to increases in global aerosol production,
providing additional condensation nuclei to the lower stratosphere where heterogeneous ozone destruction
processes could become more important in non-polar regions [Gery, 1993].
is the most important oxidant of sulfur(IV) in the aqueous phase when the pH is less than about 4.5
[Penkett et al, 1979] and has attracted increasing attention over the past decade, because it was identified as
one of the dominant trace species in polar ice [Neftel et al., 1984] and its concentrations have increased by 50
percent over the past 200 years, with most of the increase occurring in the past 20 years [Sigg et al, 1991].
Potential changes to H2O2 concentrations would be interesting with respect to the formation of acidic
precipitation. The predicted substantial increase in H2O2 concentrations over large geographical areas caused
by increased UV-B levels in troposphere [Gery et al, 1987; Fuglestvedt et al, 1994] may have some impact on
the geographical distribution of acid precipitation. However, no quantitative estimates of these effects are vet
available.

Changes in Cfy Lifetime
UV-related increases in tropospheric OH may affect the concentration of other important gases. Methane
is removed from the atmosphere primarily via the reaction

OH + CH4 -» CH3 + H2O
98
-------
.., .,
with a lifetime of about 10 years. Pre-industrial atmospheric CHi concentrations were near 600 ppbv, but
increased emissions (most likely due to human activities) have brought the current value near 1,800 ppbv.
Recent measurements of the rate of CHi increases show that the trend has slowed in the past decade from
about 14 ppbv per year to about 9 ppbv per year. It has been proposed that the slowing of the CHi trend may
be partly due to the increased OH resulting from tropospheric UV increases [Madronich and Granier, 1992,
1994; Fuglestvedt et al., 1994]. Increase in OH concentrations will decrease the steady state CH4 concentration
by nearly the same proportion. The time-dependent response of CH4 depends on the detailed scenario for_
OH increase. Madronich and Grainer [1992,1994J used the 1979-92 O3 column measurements (Nimbus 7
TOMS), to calculate the global increase of Ji (see Figure 6.1) and assumed a corresponding linear OH
increases at a rate of 0.36 percent per year beginning in 1979. In this scenario, in 1993 the CHj is reduced by
about 35 ppbv from the value it would have achieved without the OH increases, which may be compared
with a measured atmospheric increase of about 150 ppbv over the same time [Khalil et al., 1993; Steele et al.,
1992]. Three-dimensional model results obtained by Fuglestvedt et al. [1994] are roughly comparable,
suggesting that about 1/3 of the slowing is due to the increased UV levels.

Effects of Changes in Emissions from Natural Ecosystems

As mentioned in previous chapters, both natural terrestrial and aquatic ecosystems are likely to be affected
by UV radiation changes. For example, increased penetration of UV radiation into the oceans is expected to
affect both the viability of living organisms, and the photochemical processing of non-living organic and
inorganic matter. Thus, changes may be expected in the ocean-to-atmosphere emissions of various gases
including carbon monoxide (CO), carbonyl sulfide (COS), dimethyl sulfide (DMS), and other carbon and
sulfur compounds [Najjar et al., 1994]. Some of these species are believed to be the primary source of natural
sulfate aerosols, which have roles in the destruction of ozone, climate change, and acidification of
precipitation. For example, aerosols formed by DMS oxidation are believed to influence the ability of marine
clouds to reflect incoming solar radiation, and may thuTfnfluence climate [Charlson et al., 1987]. Another
example is COS, which is believed to be a major source of sulfur atoms to the stratosphere and of the resulting
natural stratospheric sulfate aerosol layer. Current theories of stratospheric 03 chemistry suggest that
aerosols may play a role in the destruction of 03, so that UV-induced increases in emissions of, e.g., COS, may
constitute a yet unquantified positive feedback on stratospheric Os depletion.

References

Andrady, A. L., Polymer materials, pp. 193-228, in UV-B Radiation and Ozone Depletion, M. Tevini, (ed.), Lewis
Publisher, Boca Raton, 1993b.
Charlson, R.}., J. Langner, M. O. Andreae and S. G. Warren, Oceaninc phytoplankton, atmospheric sulphur,
cloud albedo, and climate, Nature, 326,655-661,1987.
De Leeuw, F. A. A. and H. J. Van Rheineck Leyssius, Sensitivity of oxidant concentrations on changes in U.V.
radiation and temperature, Atmos. Env., 25A, 1025-1032,1991.
Finlayson-Pitts, B. J. and J. N. Pitts, Atmospheric Chemistry, Wiley-Interscience, New York, 1986.
Fuglestvedt, J. S., J. E. Jonson and I. S. A. Isaksen, Effects of reductions in stratospheric ozone on tropospheric
chemistry through changes in UV and photolysis rates, Tellus, in press, 1994.
Gery, M. W., R. D. Edmond and G. Z. Whitten, Tropospheric Ultraviolet Radiation, U.S. Environmental
Protection Agency report EPA/600/3-87/097,1987.
Gery, M.W., Tropospheric air quality, pp. 229-240, in UV-B Radiation and Ozone Depletion, M. Tevini, (ed.),
Lewis Publisher, Boca Raton, 1993.
Khalil, M.A.K., R.A. Rasmussen and F. Moraes, Atmospheric methane at Cape Mesres: analysis of a high-
resolution data base and its environmental implications, /. Geophys, Res., 98,14753-14770,1993.
Leighton, P. A., Photochemistry of Air Pollution, Academic Press, New York, 1961.
Levy, H. n, Normal atmosphere: large radical and formaldehyde concentrations predicted, Science, 173,141-
143,1971.
99
-------
Lippmarvn, M., Health effects of tropospheric ozone, Environ. Sci. Tech., 25, 1954-1962, 1991.
Liu, S.C. and M. Tranier, Response of the tropospheric ozone and odd hydrogen radicals to column ozone
change, /. Atmos. Chem., 6, 221-233, 1988.
Madronich, S. and C. Granier, Impact of recent total ozone changes on tropospheric ozone photodissociation,
hydroxyl radicals, and methane trends, Geophys. Res. Lett, 19, 465-467, 1992.
Madronich, S. and C. Granier, Tropospheric chemistry changes due to increased UV-B radiation, in
Stratospheric Ozone Depletion/UV-B Radiation in the Biosphere, Gainsville, H. Biggs (ed.), NATO ARW Series
Springer-Verlag, Berlin, 1994.
Moller, D., The possible role of H2O2 in new-type forest decline, Atmos. Environ., 23, 1625-1627, 1989.
NAPAP, Add Deposition: State of Science and Technology, Volume I, National Acid Precipitation Assessment
Program, Washington, D. C., 1991.
Najjar, R. G., D. J. Erickson and S. Madronich, Modeling the air-sea fluxes of gases formed from the
decomposition of dissolved organic matter: Carbonyl sulfide and carbon monoxide, in The Role of Non-
living Organic Matter in the Earth's Carbon Cycle, (R. Zepp and C. Sonntak, eds.), John Wiley, New York,
1994, in press.

Neftel, A., P. Jacob and D. Klockow, Measurements of hydrogen peroxide in polar ice samples, Nature, 311,
43-45, 1984.
Penkett, S. A., B. M. R. Jones, K. A. Brice and A. E. J. Eggletton, The importance of atmospheric ozone and
hydrogen peroxide in the oxidation of sulfur dioxide in cloud and rain water, Atmos. Environ., 15, 123-137,

Schnell, R. C., S. C. Liu, S. J. Oltmans, R. S. Stone, D. J. Hoffman, E. G. Dutton, T. Deshler, W. T. Sturges, J. W.
Harder, S. D. Sewell, M. Trainer and J. M. Harris, Decrease of summer tropospheric ozone concentrations
in Antarctica, Nature, 351, 726-729, 1991.
Sigg, A. and A. Neftel, Evidence for a 50% increase in ^Q^ver.the past 200 years from a Greenland ice core
Nature, 351, 557-559, 1991.
Steele, L.P., E. J. Dlugokencky, P.M. Lang, P.P. Tans, R.C. Martin and K.A. Masarie, Slowing down of the
global accumulation of atmospheric methane during the 1980s, Nature, 358, 313-316, 1992.
Thompson, A.M., M.A. Owens and R.W. Stewart, Sensitivity of tropospheric hydrogen peroxide to global
chemical and climate change, Geophys. Res. Lett., 16, 53, 1989.
Thompson, A. M., M. A. Huntley and R. W. Stewart, Perturbation to tropospheric oxidants, 1985-2035. 1.
Calculations of ozone and OH in chemically coherent regions, Atmos. Envir., 25A, 1837, 1991.
Whitten, G.Z. and M.W. Gery, The interaction of photochemical processes in the stratosphere and
troposphere, in Effects of Changes in Stratospheric Ozone and Global Climate, vol.2, Stratospheric Ozone, UNEP,
WMO, Scientific Assessment of Ozone Depletion, World Meteorol. Org., in press, 1994.
100
-------
CHAPTER 7
EFFECTS OF INCREASED SOLAR ULTRAVIOLET
RADIATION ON MATERIALS

A.L Andrady (USA), M.B. Amin (Saudi Arabia), S.H. Hamid
(Saudi Arabia), X. Hu (China,), and A. Torikai (Japan).
Summary

Synthetic polymers, naturally-occurring biopolymers, as well as some other materials of commercial interest are
adversely affected by solar UV radiation. Applications of these materials, particularly plastics, in situations which
demand routine exposure to sunlight is only possible through the use of light-stabilizers and/or surface
treatments to protect them from sunlight. Any increase in solar UV content due to partial ozone depletion will
therefore accelerate the photodegradation rates of these materials, limiting their service lifetimes outdoors.

The nature and the extent of such damage due to increased UV radiation in sunlight is quantified in action
spectra. In spite of the several action spectra for polymers, reported in the research literature, the information is
often inadequate to make reliable estimates of the increased damage. The specific formulation of the polymer
material, the damage criterion employed, and even the manner in which data is interpreted, can often influence
the results. However, it is clear from the available data that the shorter wavelength UV-B processes are mainly
responsible for photodamage ranging from discoloration to loss of mechanical integrity in polymers exposed to
solar radiation. The molecular level interpretation of thesejchanges remain unclear in many instances.

The use of higher levels of conventional light stabilizers in polymer formulations will likely be employed to
mitigate the effects of increased UV levels in sunlight. However, such an approach assumes that a) these stabilizers
continue to be effective under spectrally- altered sunlight conditions; b) they are themselves photostable on
exposure to UV-rich sunlight; and c) they can be sufficiently effective at low enough concentrations to
economically serve the purpose. Experimental data bearing on these issues is sparse. On-going research,
particularly those relating to extreme-environment exposure of polymers, is expected to shed more light on these
unresolved questions. Substitution of the affected materials by more photostable varieties of plastics and other
materials also remains an attractive possibility. Both these approaches will add to the cost of plastic products in
target applications. With plastics rapidly displacing conventional materials in numerous applications, this is an
important consideration particularly in the developing world.
Introduction

Most synthetic polymers as well as naturally - occurring biopolymers are readily affected by solar ultraviolet
(UV) radiation. The deleterious effects of UV-B on polymers (plastics and rubber) are well known, and in
applications which demand routine exposure to solar radiation, photo-stabilizers are commonly used in polymer
products to ensure adequate lifetimes. Wood and other biopolymeric materials are similarly affected; surface
coating of wood is employed to control the light-induced damage. Applications of particular interest are building
products which account for nearly a third of the plastics production in the US as well as in Western Europe. The
consistent trend towards increased use of plastics in buildings at the expense of more traditional materials of
construction such as metal, glass, mortar, and wood, is a global one and is particularly strong in developing
countries with a high demand for low-cost housing. In addition to use in building, polymeric materials are used in
numerous other applications where they are routinely exposed to solar radiation (Table 7.1).

The outdoor service lifetimes of plastics building materials, even under present exposure conditions, are
determined by their susceptibility to UV-B radiation in terrestrial sunlight. Therefore, a partial depletion of the
stratospheric ozone layer, and the resulting increase in UV-B content in sunlight reaching the earth's surface, will
have a definite impact on the use of materials in outdoor applications. As both synthetic polymers and biomaterials
will undergo light-induced chemical changes, consequent deterioration in useful properties might be expected at

101
-------
significantly fester rates under such conditions. These changes might be mitigated at least in part, however, by the
use of higher levels of conventional stabilizers in polymer formulations, by the use of new high-efficiency stabilizer
systems, and by the substitution of better UV-resistant types of polymers for outdoor applications of interest. The
effectiveness of some of these strategies have not been demonstrated for exposure conditions involving spectrally-
altered, UV-B rich sunlight. Increased cost associated with each approach, and their effectiveness, may alter the
economics of the use of plastics and rubber in building construction.

Table 7.1. Materials Routinely Exposed to Solar UV-B Radiation.
1. Building Materials: Plastics - Pipes, water storage tanks, window/door frames, siding, gutters, roofing,
glazing, exterior fascia, cable coverings, and conduits. Wood used in buildings.
2. Outdoor Furniture and Surfaces: Stadium seats, park benches, beach furniture and artificial turf.
3. Transportation Applications: Composites, other polymers, and wood, used in Aircrafts, Automobiles,
and Marine Vessels. Automotive and aircraft tires.
4. Agricultural Applications: Greenhouse coverings, mulch films, and irrigation hoses.
5. Coatings and Paints: Coatings for protection of outdoor surfaces, outdoor artwork, dyes, highway
pavement markings, and road signs.
6. Textile Products: Fabrics used outdoors (e.g. sails), geomembranes, netting and commercial fishing
gear.
7. Biopolymcrs: Wool, human hair, Chitin/Chitosan*.
8. Packaging: Heavy-duty sacs.
9. MisceUaneous: Resins for restoration of outdoor statues, leather products, solar panel materials, paper or
paperboard products used outdoors.

* Shell of crabs and shrimp is composed of Chitin, the second most abundant biopolymer. Chitosans occur
in the cell wall of fungi.
Severity of the impact of increased UV-B levels on the outdoor lifetimes of materials depend on both the
geographic location of exposure and the susceptibility of the particular material to UV-B radiation. While the
higher latitudes will experience the high levels of ozone depletion, the high ambient temperatures in the near-
equator regions will tend to severely magnify the effect of even a very marginal increase in solar UV-B in these
regions. The effects of a uniquely harsh combination of high levels of solar UV-B from spectrally altered sunlight,
and the high temperatures leading to severe heat build-up in materials exposed outdoors, on the lifetime of
building products at these latitudes is not well understood.

The cost advantage offered by durable plastic building products have made them popular in developing
countries including those in near-equator regions. Wood and natural materials have long been the conventional
building materials for dwellings in these regions. With the lifetimes of both plastics and wood affected by UV-B
increase, a partial ozone depletion will have very significant socio-economic impacts on these populations.

To make a realistic assessment of the impact of a partial ozone-layer depletion on materials, several key types of
data arc needed. These are, a) the spectral sensitivity of plastics and biomaterials of interest, b) dose -response data
to estimate the increased damage to be anticipated as a result of the UV-B increment in terrestrial sunlight, and c)
data on the effectiveness of conventional and new types of light stabilizers in specific polymers, under exposure to
spectrally-altered sunlight. Only a fraction of the needed data is currently available, and a reliable quantitative
assessment is therefore difficult at the present time. However, spectral sensitivity data on several relevant polymers,
data on high-UV desert exposures of polymers, and some preliminary information on stabilizer effectiveness, have
been reported in recent years. The availability of such data continues to increase the reliability of the assessment
process.

UV-lnduced Damage to Polymers

The chemistry of UV-induced damage to polymers is not completely understood. The basic chemical processes
that occur in key polymers exposed to solar UV-B radiation, however, have been broadly identified.

Discoloration of materials due to formation of colored chemical species from photoreactions is a primary
consequence of exposure of polymers to UV radiation. While mechanical properties also suffer on continued
exposure, the rate of discoloration often determines the service life of the product. In the case of poly( vinyl
chloride), (PVC), typical formulations used in the building applications ( for instance in siding, and in window

102
-------
frames), the predominant change caused by UV-B is the discoloration resulting from photo-dehydrochlorination
of the polymer [ Andrady et. al. ,1989, Andrady et. al. ,1990]. The yellowing obtained is uneven and gradually
increases with prolonged exposure. Adequate stabilization with an opacifier (rutile titania) controls the rate of
discoloration in white profiles used in siding, window frames and pipes [Titow, 1984 ]. Polycarbonates used in
glazing also undergoes yellowing [ Andrady et. al., 1992 ], but due to a combination of photo-Fries
rearrangement (shown below) and oxidative reactions [ Factor and Chu, 1980 ] . In this reaction the bisphenol A
units photoisomerize into phenyl salicylate units and possibly to dihydroxybenzophenone units. The use of UV
absorbers in the formulation is necessary to control rate of yellowing [ Davis and Sims, 1983 ].
UV-B
Photo-Fries Rearrangement of Polycarbonate

Wood and paper also undergo yellowing discoloration on exposure to solar UV-B [ Andrady et.al., 1991;
ForsskM et.al., 1993, Heitner, 1993], when the lignin component in wood undergoes photodegradation. In a
study involving 75 varieties of commercially important wood, 65 percent were found to discolor due to UV light
[Sanderman et.al., 1962 ]. On exposure to UV radiation, the fractions of both holocellulose and lignin reduce and
that of extractives increase, but the percent reduction in lignin is relatively higher than that of cellulose [ Hon,
1993 ]. Cellulose in wood has been shown to undergo a free radical mediated degradation on exposure to
wavelengths < 340 run. Electron spin resonance spectroscopjc data suggest scission of the GS - C6 bond in
glucose units in the molecule during irradiation [ Hon, 1981 ].

Wool readily undergoes light induced yellowing due to solar UV-B radiation. The amino acid residues,
particularly tryptophan, histidine and cystine, degrade extensively on irradiation. Some free radical mediated main-
chain scission of wool molecules also accompany photoyellowing [Launer, 1965 ]. Role of UV-B radiation in
generating free-radicals in human hair has also been reported [ Jahan et.al. 1987}. Presence of free-radicals often
leads to degradation in polymer materials.

Both photo-initiated thermooxidative processes and photodegradation reactions may lead to chain-scission in
polymers exposed to solar radiation. These are often free-radical processes and may also involve concurrent cross
linking. As the desirable mechanical properties of polymers are a consequence of their long chain-like molecular
structure, chain scission leads to deterioration of these properties. This in turn impacts their outdoor service lives.
Polyethylene films exposed to solar UV-B radiation readily loose their extensibility and strength [ Hamid et. al.
1988; ], as well as their average molecular weight [ Andrady et. al., 1993 ]. While the change in UV-induced loss
in elongation was shown to generally correlate with the development of carbonyl functionalities, it is preferable to
use both measures when predictions of weatherability of polyethylene is attempted [ Tidjani et.al., 1993 ]. In
polyethylene, photoinitiation is thought to originate from polymer-oxygen complexes while in polypropylene the
initiation is via photolysis of tertiery hydroperoxide groups [Gugumus, 1994 ]. Solar UV-B is also known to
degrade polystyrene foam [ Andrady et. al., 1991 ], a popular packaging and material. These changes in bulk
mechanical properties reflect changes in macromolecular chain scission ( and/or cross linking) resulting from
photodegradation. Changes in viscosity or gel permeation characteristics of polymers have been used [ Torikai
et.al., 1993a; Andrady et. al., 1993 ] to establish molecular level changes during photodegradation.

It has been suggested that unless the ozone losses exceed an arbitrary value of 15 percent in summer months,
the increased deleterious effects on polymers might be minimal [ Prickett, 1994 ]. These conclusions based on
biologically effective UV doses and the geographic variations of terrestrial UV currently observed, do not take into
account the synergistk effects of the temperature in polymer photodegradation. In near-equator regions (for
instance, in Dhahran, Saudi Arabia) where the ambient air temperatures can be as high as 50 C, even a very small
increase in UV-B levels can translate into significant increases in the rate of degradation. A more reliable
assessment must be based on activation spectra of relevant polymer formulations.
103
-------
Spectral Sensitivity

The spectral sensitivity of polymers is determined from exposure experiments using monochromatic radiation,
or from exposures to filtered xenon sources ( whose spectral irradiance distribution is designed to closely
approximate terrestrial sunlight at unit air mass) and a series of cut-on filters. Early experimental data is of limited
value because of incomplete descriptions of the polymer formulations and processing techniques used in sample
preparation, and because mercury vapor lamps were used as sources in these studies. Such lamps emit short
wavelength UV radiation not typically found in terrestrial sunlight.

Table 7.2 summarizes the available data on spectral sensitivity of polymeric materials. Data on UV-A sensitive
materials arc not included because ozone depletion is expected to mainly affect the UV-B region of the solar
spectrum. Data generated using a borosilicate-filtered xenon source, with cut-on filters to separate the effect of
different spectral regions allow the identification of spectral regions most effective in bringing about the damage
of interest. Such activation spectra will be source-specific, and those reported in the Table are specific for filtered -
xenon source spectrum and the indicated damage criterion only. Spectral sensitivity can also be studied in
experiments where materials are exposed to monochromatic radiation. Using either experimental approach it is
possible to estimate the damage obtained per available photon, and plot as a function of wavelength of exposure,
to obtain an action spectrum. Information from the two approaches should agree in instances where there is no
significant synergism or mutual cancellation of effects obtained at different wavelengths. In the case of PVC, the
yellowing discoloration brought about by the UV-B region of the solar spectrum is offset to some extent by the
photoblcaching of chromophores afforded by the SOOnm - 600 nm band of visible light [ Andrady et. al., 1989].
In spite of the high quantum efficiency of photobleaching reaction [ Decker et. al, 1988 ] relative to that of
yellowing, this apparantly plays only a minor role in the overall photodegradation process, and the
monochromatic wavelength sensitivity data was consistent with activation spectra for yellowing under white light [
Andradyet.nl., 1989a ]. Figure 7.1 illustrates the action spectra of common polymer formulations for yellowing.
-42.5 -
-45-
-47.5-
d
3

I
o
•3 -50-
250
D Hevsprint paper

O Leian polycarbonate

o Rigid PVC vith no TiOa

A Rigid PYC vith 2.5» TUO2
275
300
325
350
Wavelength [nm]

Fig. 7.1. Spectral sensitivity of selected polymeric materials.

Scission (and sometimes cross linking) of macromolecular chains making up the polymer, is a common
consequence of photodegradation. These changes result in a drastic reductions in the mechanical integrity of the
polymer and therefore influence their useful lifetimes outdoors. Recently' the action spectra for chain scission in
several polymers including polystyrene [ Torikai et.al., 1993b ], polyethylene [ Andrady et. al. 1994 ], and
polycarbonate [ Torikai et. al., 1993a} have been reported. Activation spectra based on tensile properties of
materials are of particular interest as the mechanical integrity of plastics is frequently measured in terms of tensile
properties. Figure 7.2 shows relevant data for (ethylene - carbon monoxide (~1 %) } copolymer film exposed to
white light from a xenon source [ Andrady et. al. 1994 ]; a sharp transition from almost no effect to drastic
deterioration is obtained around 330 nm. The standard error associated with elongation at break measurements is
generally large, and the scatter in Figure 7.2 is not unusual. A more fundamental measure of chain-scission is the
change in solution viscosity, resulting from a change in average molecular weight. Recently viscosity data on
polycarbonate [ Torikai et. al., 1993a ], and polystyrene [ Torikai et.al., 1993b ] were reported, with either 300
nm or 280 nm - 300 nm being identified as the wavelengths most effective in causing chain scission. A quantum
yield of 0 -1 x 10"^ scission events per photon was reported for polycarbonate.
104
-------
Table 7.2. Reported Spectral Sensitivity Data on Materials
POLYMER FORMULATION DAMAGE CRITERION MAXIMUM
Polyehtylene [PE]
LLDPE Base Polymer
LLDPE + Flame retardant
HDPE + Flame retardant
LDPE Base Polymer

Poly(vinyl chloride) [PVC]
Base Polymer film
Rigid PVC + titania
Base polymer film

Polypropylene [PP]
Base Polymer Film
PP + Flame retardant
PP molded pieces

Polystyrene [PS]
Base Polymer
PS + Flame retardant (I)
PS + Flame retardant (II)
Base Polymer
PS + Flame retardant (I)
PS -i- Flame retardant (II)
PS (photodegradable)

Polycarbonate [PC]
Base Polymer
PC extruded sheet
PC + photostabilizer

Poly(methyl metha-crylate)
[PMMAJ
Base Polymer

Copolymers and Blends
ECO copolymer (1% CO)

PC/PMMA Blend
EFFECT

Optical Density (UV/Vis) 260*

Optical Density (UV/Vis) 300
Discoloration 310
Discoloration (Y.I.) 320
Discoloration (Y.I.) 310 - 325
Spectroscopy (FTIR) 355 - 385
Spectroscopy (FTIR) 260 - 280
Chain Scission (GPC) 260 - 280
Extensibility (Tensile) 315 -330
Optical Density (UV/Vis) 260 - 320
Optical Density (UV/Vis) 280
Optical Density (UV/Vis) 310
Chain Scission (GPC) 280
Chain Scission (GPC) 300
Chain Scission (GPC) 300
Discoloration 320 - 345
Chain Scission (Vise.) 280 - 320
Discoloration (Y.I.) 280
Discoloration (Y.I.) 310 - 340
Chain Scission (Vise.) 300
Optical Density (UV/Vis) 280 - 340
Extensibility (Tensile) <320
Chain Scission (Vise.) <280
SOURCE

Torikai. (1993c)

Hirtet.al(1967)
Hirt (1967)
Andrady(1989)
Martin (1971)
Torikai (1993b)

Andrady(1994)
Torikai (1993b)
Andrady(1994)
Torikai (1993a)
Andrady(1994)
Andrady(1994)
Mitsuoka(1993)
Aoki (1992)
Andrady(1994)
Osawa(1991)
Biopolymers
Wood Pulp (mechanical)
Wood Pulp (refiner pulp)
Wool
Andrady(1991)
Forsskahl (1993)
Launer(1965)
Lennox (1971)
Discoloration (Y.I.) 334 -354
Brightness (UV/Vis) 450 - 500
Discoloration (Y.I.) 290 - 311
Discoloration (Y.I.) 280*
NOTES.
1. Column 1 abbreviations. LLDPE - Linear Low Density Polyethylene, HDPE - High Density Polyethylene, LDPE - Low
Density Polyethylene, PMMA - Poly(methyl methacrylate), ECO - copolymer of ethylenc and carbon monoxide.
2. Column 2 abbreviations. UV/Vis. : UV - Visible Spectroscopy, Y.I.: Yellowness Index, FTIR: Fourier Transform Infra-red
Spectroscopy, GPC: Gel Permeation Chromatography.
3. Column 3. Wavelength interval in the white light (filtered xenon - source ) spectrum at which maximum damage was
obtained. Single wavelengths refer to data from monochromatic exposure experiments, and indicate the wavelength at which
maximum damage was obtained. A '*' indicates that this was also the shortest wavelength used in the experiment.
105
-------
1000
— 800-

1
CO 600
13
a
•5 4QO
200-
260 280 300 320 340 360

Cut-on Wavelength of Filter (nm)
380
Rg. 7.2. Elongation at break for (ethylene -carbon monoxide) copolymer films exposed behind cut-on filters to a white light
source (Borosilicate-fittered Xenon source).

Activation spectra for yellowing of biopolymeric materials such as wood pulp [Andrady et.al. 1991 ] and wool
[Lennox ct.nl. 1971 ] have also been reported. With wool and paper made from mechanical pulps, premature
yellowing takes place on exposure to solar UV-B light. Figure 7.3 shows the activation spectrum for yellowing of
newsprint paper made from pinewood (Pinus taeda,) exposed to white light from a xenon source.

..&,.., .3.0
«9 300 320 310 3«p 3JQ <#p
* « * ••SpfctrBVRegrqn'ofrlrrrkiiatfonlCmd'

Fig. 7.3. Activation spectrum for yellowing of newsprint paper exposed to a white light source ( Borosilicate-filtered Xenon
source).

Increased rates of UV-B induced degradation of polymers may also affect post-consumer plastic waste
management technologies such as recycling and photodegradable polymers. Depending on the geographic
location, plastics in the litter stream will undergo higher extents of photodegradation prior to collection for
recycling. The significance of this incremental exposure on recyclate quality is not clear at this time.

Responses to increased Solar UV Radiation

In principal, there are two basic approaches to maintaining current service lives of selected materials in spite of
a moderate increase in UV levels in sunlight. One is to substitute materials; more photoresistant, albeit more
expensive, polymers or other materials might be used for those applications that demand routine exposure to
sunlight. For instance, the PVC formulations used in exterior profile (for instance in window frames) might be
replaced with better weather-resistant copolymers such as (acrylonitrile - butadiene - styrene), or with PVC -
capped \vith films or layers of selected polymers with superior weatherability [ Moore, 1994 ]. Alternatively, an
effort might be made to use conventional or novel light - stabilizers to address the problem. Polymers such as
106
-------
PVC are inherently photolabile, and their oiifijpor use is possible only due to the effectiveness of light- and heat-
stabilizer technology, with impressive classes of photostabilizers such as hindered amine systems (HALS) being
recently developed [ Al-Malaika et.al. 1983 ]. It is likely and certainly not unreasonable to expect the polymer
industry worldwide to explore the full capability of stabilizers to address the problem of increased solar UV-B
component. The cost of UV stabilizer systems is a very significant component of the cost of plastic formulations
used in outdoor applications; with polyethylene greenhouse film formulations, as much as 30 percent of the
compound cost might be ascribed to the photostabilizer. Increasing levels of stabilizer will therefore have a
definite impact on the economics of plastics use in outdoor applications.

The basic question then would be whether increasing levels of conventional photostabilizers in common
polymer formulations will result in a concomitant increase in the service life of materials exposed to spectrally -
altered, UV-rich sunlight? Early investigations of the issue in CIAP (Climatic Impact Assessment Program)
assumed that such an approach will be successful and even calculated (based on Beer - Lambert Law) factor
increases in stabilizer needed to offset a given increase in total UV radiation levels [ Shultz et.al., 1975 ]. These
calculations, however, were not based on experimental data pertaining to specific stabilizer / polymer
combinations. Some data is also available from industry sources and in technical literature on the effectiveness of
higher levels of photostabilizer in typical formulations in increasing the service life of polymers. However, this data
pertains almost exclusively to photodamage to materials from sunlight with present-day levels of UV-B. The effect
of increasing levels of a common type of photostabilizer in polyethylene film is shown in Figure 7.4 to illustrate
the efficiency of the additive in maintaining service life, and to show that the protective action can be a non-linear
function at high levels of the additive. This data is on Chimasorb 944 LD stabilized LDPE films exposed for a
three year period under desert conditions in Dhahran, Saudi Arabia [Humid et.al. 1994]. The high ambient
temperatures in desert locations will further exacerbate the problem of maintaining reasonable lifetimes for plastic
products exposed to sunlight with increased UV-B component. In an empirical study on LDPE weathering under
desert conditions Hamid et.al. [ Hamid et.al. 1991 ] found the elongation at break to be a sensitive indicator of
the extent of weathering. The study found total UV-B as well as total sunlight to correlate particularly well with
changes in properties of the polymer on exposure. Another relevant study was carried out by Bauer et.al. [ Bauer
et.al. 1990, 1992 ] on photo-degradation of organic coatings photostabilized by HALS compounds. A "Harsh"
exposure involving high-intensity short-wave UV radiation, and an "Ambient" exposure with simulated solar
radiation were used to rank a series of HALS. The rankingjaf.the effectiveness of different stabilizers was very
different under the two exposure conditions. Some commercial HALS compounds are known to be photolyzed
on exposure to short wavelength UV radiation [ Al-Malaika et.al., 1983; Chen et.al., 1988 ].
30.0
ZO.O-
10.0-
o
o o
0.0-
Percent UV St»bili»r
Fig. 7.4. Solar UV radiation needed to reduce the elongation at break by 50 percent, of LDPE films containing different
levels of UV stabilizer.

Hitherto, there was little need to address the question of spectrally-altered sunlight and its effect on
weathering of materials. The efficiency and effectiveness of conventional stabilizers under spectrally-altered
sunlight has not been studied and therefore remains essentially unknown.

Increase in levels of photostabilizers may offset the increased rate of photodegradation caused by higher solar
UV levels resulting from a partial ozone depletion. However, the effect of higher stabilizer levels on other useful
properties of the material must also be considered; at least in the case of rigid PVC profile formulations increased
107
-------
titania levels can lead to several negative consequences [ Mastro, 1983 ]. An attractive alternative is the use of
improved grades, specially coated grades, of rutile to obtain higher levels of protection at low levels of additive [
Day, 1990 ]. The relative importance of different approaches to mitigation, including the use of alternate materials
of superior UV resistance, will invariably be determined by the costs associated with each strategy. Insufficiant
data is available to estimate these costs and therefore the impact on building materials industry at this time.

In the case of biomatcrials, the mitigation of the effects of higher UV levels in sunlight is considerably more
difficult. While wood surfaces can be treated either with coatings or other stabilizers, the same is generally not
true of paper made of mechanical pulps. Light - induced yellowing and the related loss in brightness is a key factor-
limiting the use of mechanical pulpsf Hcmmingson et.al., 1989 ]. With materials such as wool, chitins, natural
fibers used in netting and cordage, die impact of damage due to increased solar UV levels has not been established
with any degree of certainty. While UV-induced degradation reactions in these materials are known, the extent to
which such changes interfere with the performance of these materials, or affect the economic value of these
materials ( specially with wool or paper) has not been comprehensively addressed.

Conclusions

Both naturally occurring biopolymer materials as well as synthetic polymers undergo degradation reactions on
exposure to solar UV-B radiation. With synthetic polymers, it is the effective photostabilization that ensures
adequate lifetimes for products used outdoors even under present exposure conditions. Any increase in the UV-B
content of terrestrial sunlight must therefore reduce the service life of products based on these materials.

Some relevant action spectra for typical formulations of common polymers are available. In spite of many
recent pertinent contributions in the literature, a complete understanding of the wavelength sensitivity of key
formulations used in building applications has not been achieved. To be useful in models assessing damage, the
action spectra have to address relevant formulations of more common polymers, and pertain to those properties
(often mechanical properties) of interest to end-users. In the case of biomaterials routinely exposed to sunlight,
even less data is available; action spectra are known only for a few of these.

With synthetic polymers there is a likelihood that either increasing the levels of conventional stabilizers, or the
use of novel stabilizers, will alleviate some of the deleterious ejects- of increased UV-B in sunlight. However,
insufficient data on weathering studies based on spectrally altered white light, precludes confirmation of the
efficacy of this strategy. Intensity - dependence of the key light stabilizers for polymers, under different and
relevant light - temperature domains has not yet been reported. Therefore the economic feasibility of this primary
industry response to stratospheric ozone depletion, cannot be realistically assessed at this time.

References

Al-Malaika, S., and G. Scott (1983). Photostabilization of Polyolefins. In "Degradation and Stabilization of
Pofyoleftns", Ed. N.S. Allen, Applied Science Publishers (New York) p 283 - 335

Andrady, A.L., K. Fucki, and A. Torikai (1989) Photodegradation of rigid PVC formulations I. Wavelength
sensitivity of light induced yellowing by monochromatic light. J. Appl. Polym. Sci. 37: 935 - 946

Andrady, A.L., N.D. Searle(1989a) Photodegradation of rigid PVC formulations. Spectral Sensitivity to light-
induced yellowing by polychromatic light. 37:2789 - 2802

Andrady, A.L., K. Fueki, and A. Torikai (1990) Photodegradation of rigid PVC formulations III. Wavelength
sensitivity of the photoyellowing reaction in processed PVC formulations. J. Appl. Polym. Sci. 39: 763 - 766

Andrady, A.L., V. Parthasarthy, Y. Song, K. Fueki, and A. Torikai 1991) Photoyellowing of Mechanical Pulps I.
Wavelength sensitivity to light-induced yellowing by monochromatic radiation. TAPPI Journal, 74(8):162 -
168

Andrady, A.L., N.D. Searle, and L.F. Crewdson (1992). Wavelength sensitivity of stabilized and unstabilized
polycarbonate to solar-simulated radiation. Polym. Deg. Stab., 35:235 - 247

Andrady, A.L. (1994). Unpublished data.

Aoki, H., M. Niregi, T. Saito, T. Akahori, S. Kobayashi, Z. Osawa and Z. Li (1992). Photodegradation behavior
of photodegradablc polymer. Ethylene-carbon monoxide copolymer. Polym. Preprints Japan XL426

Bauer, D.R., J.L. Herlock, D.F. Mielewski, M.C.P. Peck, and R.O. Carter (1990). Photostabilization and
Photodegradation in organic coatings containing a hindered amine Light Stabilizer V. Infra-red spectroscopic
measurements of hindered amine effectiveness. Polym. Deg. Stab., 28:39-51
108
-------
Bauer, D.R., J.L. Herlock, and D.F. Mielewski (1992): Phptostabilization and photodegradation in organic
coatings containing a hindered amine Light Stabilizer VII. HALS effectiveness in acrylic melamine coatings
having different free radical formation rates. Polym. Deg. Stab., 36:9 -15
Chen, J., X. Hu, L. Chu, and L. Shen, (1988). Quenching of oxygen by nitroxyl radicals, and the photostabilizing
effectiveness of hindered amines. Photogr. Sci. Photochem. (Chinese) 1: 1-10
Davis, A. and D. Sims (1983) " Weathering of Polymers ". Applied Science Publishers, New York, pp 157
Day, R.E. (1990) The role of titanium dioxide pigments in the degradation and stabilization of polymers in tne
plastics industry. Polym. Deg. Stab., 29(1):73 - 92
Decker, C., (1984) Photodegradation of PVC. In "Degradation and Stabilization ofPVC". Ed. E.D. Owen.
Elsevier Applied Science Publishers Ltd. New York, p 113
Factor, A., W.V. Ligon, RJ. May, and F.H Greenberg (1987). Recent Advances in Polycarbonate
Photodegradation. In "Advances in Stabilization and Controlled Degradation of Polymers II". Ed. A.V Patsis.
Technomic Publishing Company. Lancaster Pa. p 45 - 58.
Forsskahl, L, and H. Tylli (1993). Action spectra in the UV and visible region of light-induced changes in various
refiner pulps. In "Photochemistry ofLignocellulosic Materials ".ACS Symposium Ser., 531: 45 - 59, American
Chemical Society, Washington DC.
Gugumus, F. (1993). Re-evaluation of the stabilization mechanisms of various light stabilizer classes. Polym. Deg.
Stab, 39: 117 - 135
Hamid, S.H., A.G. Maadhah, F.S. Quereshi, and M.B. Amin, (1988) Weather-induced Degradation of
Polyethylene: Infra-red Spectroscopic Study. Arabian J. Sci., 13(4):503 - 531
Hamid, S.H., and W. Pritchard (1991) Mathematical modelling of weather-induced degradation of polymer
properties. J. Appl. Polym. Sci., 43:651 - 678
Heitner, C. (1993) Light-induced yellowing of wood-containing papers. In "Photochemistry ofLignocellulosic
Materials ". ACS Symposium Ser. 531: 2 - 25, American Chemical Society, Washington DC
Hemmingson, J.A., and H. Wong (1989) Characterization of photo-chemically degraded newsprint solubles by
spectroscopy. Holzforschung 43(2): 141 -147
Hirt, R.C., and N.D. Searle (1967). Energy characteristics of outdoor and indoor exposure sources and their
relation to the weatherability of plastics. Appl. Polym. Symp., 4:61 -83
Hon, D. N. -S. (1981) Photochemical degradation of Lignocellulosic materials. In " Developments in Polymer
Degradation -3". Ed. N. Grassie, Applied Science Publishers. London. pp229 - 281.
Hon, D. N. -S. (1991) Photochemistry of wood. In " Wood and Cellulosic Chemistry". Eds D.N.-S. Hon and N.
Shiraishi. Marcel Dekker, Inc. New York, pp 525 - 556
Jahan, M.S., T.R. Drouin and R.M. Sayre (1987) Effect of humidity on photoinduced ESR signal from human
hair. Photochem. Photobiol. 45(4):543 - 546
Launer, H.F. (1965) Effect of light upon wool. Part IV: Bleaching and Yellowing by sunlight. Textile Res. J.,
35:395 - 400
Lennox, F.G., M.G. King, I.H. 'Leaver, G.C. Ramsay, and W.E. Savige (1971). Mechanism, prevention and
correction of wool photoyellowing. Appl. Polym. Symp. 18:353 - 369.
Martin, K.G., and R.I. Tilley (1971). Influence of radiation wavelength on photo-oxidation of unstabilized PVC.
Br. Polym. J.,3: 36 - 40
Mastro, P.F., (1983). Formulation and processing of PVC fittings. J. Vinyl Tecnol. 5(2): 69 - 72
Mitsuoka, T., A. Torikai, and K. Fueki (1993). Wavelength sensitivity of the photodegradation of poly(methyl
methacrylate). J. Appl. Polym. Sci., 47:1027 -1032
Moore, S. (1994) Construction offers window of opportunity to plastics. Modern Plastics, April:46 - 48.
Nicholls, C.H. (1980). Photodegradation and Photoyellowing of wool. In " Developments in Polymer
Photochemistry" (Applied Science Publishers.) Ed. N.S. Allen. Vol. I page 125 - 144.
109
-------
Osawa,Z., and Y. Fukuda (1991). Wavelength effect on the photodegradation of polycarbonate and poly( methyl
mcthacrylatc). Polym. Deg. Stab. 34:75 - 84
Prickett, J.E. (1994) Effect of stratospheric ozone depletion on terrestrial UV radiation: a review and analysis in
relation to polymer photodegradation. Polym. Deg. Stab.,. 43:353 - 362.
Sanderman, W., and F. Schlumbom, (1962). On the effect of filtered ultraviolet light on wood. Holz Roh-
Werkst., 20:245 -285
Scarlc, N.D. (1994) Unpublished data.
Shultz, A.R., D.A. Gordon, and W.L. Hawkins. (1975) Economic and social measures of biologic and climatic
change. Climatic Impact Assessment Program (CLAP) Monograph 6, DOT-TST-75-56: 3.239 Sept.
Tidjani, A., R. Arnaud, and A. DaSilva (1993). Natural and accelerated photoaging of linear low-density
polyethylene. J. Appl. Polym. Sci., 47:211 - 216.
Titow, W.V. (1984) PVC Technology. Fourth Edition. Alsevier Apllied Science Publishers. New York.
Torikai, A., T. Mitsuoka, and K. Fueki (1993a) Wavelength sensitivity of the photo-induced reactions in
polycarbonate. J. Polymer Sci. A: Chemistry ED., 31: 2785 - 2788
Torikai, A., H. Kato, K. Fueki, Y. Suzuki, A. Okisaki, and M. Nagata, (1993b). Photodegradation of polymer
materials containing flame-cut agents. J. Appl. Polym. Sci., 50:2185 -2190
Torikai, A., K. Chigata, and K. Fueki (1993c). Photodegradation of incombustible polymer materials. Polymer
Preprints. Japan, 42: 2045 - 2047
110
-------
APPENDIX A
LIST OF AUTHORS AND CONTRIBUTORS
-------
ENVIRONMENTAL EFFECTS PANEL MEMBERS
Mohamed B. Amin, Ph.D.
Research Institute
King Fahd University of Petroleum and Minerals
Dharhran 31261
SAUDI ARABIA
TEL: 966-3-860-3239
FAX: 966-3-860-2266

Anthony Andrady, Ph.D.
Dept. of Polymer Science
Research Triangle Institute
3040 Cornwallis Road
Research Triangle Park, North Carolina 27709-
2194
USA
TEL: 1-919-541-6713
FAX: 1-919-541-5985
E-Mail: andrady@rcc.rti.org

Lars Olof Bjorn, Ph.D.
Plant Physiology
Lund University
P.O. Box 117
S-22100 Lund
SWEDEN
TEL: 46-46-107797
FAX: 46-46-104113
E-Mail: Iars_olof.bjorn@fysbot.lu.se

Janet F. Bornman, Ph.D.
Plant Physiology
Lund University
P.O. Box 117
S-22100 Lund
SWEDEN
TEL: 46-46-108167
FAX: 46-46-104113
E-Mail: janet.bornman@fysbot.lu.se

Martyn Caldwell, Ph.D.
Ecology Center
Utah State University
Logan, Utah 84322-5230
USA
TEL: 1-801-797-2557
FAX: 1-801-797-3796
E-Mail: mmc@cc.usu.edu

Terry Callaghan, Ph.D.
University of Manchester
Centre of Arctic Ecology
Williamson Building
Oxford Road, Manchester Ml 3 GP1
UNITED KINGDOM
TEL: 44-61-275-3877
FAX: 44-61-275-3938
Frank R. de Gruijl, Ph.D.
Inst. Dermatology
University Hospital Utrecht
Heidelberglaan 100
NL-3584 CX Utrecht
THE NETHERLANDS
TEL: 31-30-507386
FAX: 31-30-518328

David Erickson, Ph.D.
National Center for Atmospheric Research
1850 Table Mesa Drive
P.O. Box 3000
Boulder, Colorado 80307
USA
TEL: 1-303-497-1424
FAX: 1-303-497-1400
E-Mail: erickson@acd.ucar.edu

Donat-P. Hader, Ph.D.
Institut fur Botanik und Pharmazeutische
Biologic
der Universitat Erlangen-Niirnberg
Staudtstrafle 5
D-91058 Erlangen
"GERMANY
TEL: 49-9131-858216
FAX: 49-9131-858215
E-Mail: haeder@botanikl-pc.biologic.uni-
erlangen.de

Haleem Hamid, Ph.D.
Research Institute
King Fahd University of Petroleum and Minerals
Dhahran 31261
SAUDI ARABIA
TEL: 966-3-860-3840 or 3810
FAX: 966-3-860-2259 or 3989

Xingzhou Hu, Ph.D.
Research Institute of Chemistry
Academia Sinica
Beijing
CHINA
TEL: 86-1-256-2893
FAX: 86-1-256-9564

Margaret L. Kripke, Ph.D.
Department of Immunology
Box 178
The University of Texas
M.D. Anderson Cancer Center
1515 Holcombe Boulevard
Houston, Texas 77030-4095
USA
TEL: 1-713-792-8578
FAX: 1-713-794-1322
-------
G. Kulandaivelu, Ph.D.
School of Biological Sciences
Madurai Kamaraj University
Madurai 625021
INDIA
TEL: 91-452-85485
FAX: 91-452-85239

H. D. Kumar, Ph.D.
Centre of Advanced Study in Botany
Banaras Hindu University
C-l/1 Jodhpur Colony
P.O. Box 5014
Varanasi-221005
INDIA
TEL: 91-542-312-275 (residence)
FAX: 91-542-311693 or 312059

Janice D. Longstreth, Ph.D.
Waste Policy Institute
Quince Diamond Executive Center
555 Quince Orchard Road, Suite 600
Gaithersburg, Maryland 20878-1437
USA
TEL: 1-301-990-3034
FAX: 1-301-990-6150

Sasha Madronich, Ph.D.
Atmospheric Chemistry Division
National Center for Atmospheric Research
P.O. Box 3000
1850 Table Mesa Drive
Boulder, Colorado 80307-3000
USA
TEL: 1-303-497-1430
FAX: 1-303-497-1400
E-Mail: sasha@acd.ucar.edu

Richard L. McKenzie, D.Phil.
National Institute of Water and Atmospheric
Research
NIWA, Lauder
Central Otago 9182
NEW ZEALAND
TEL: 64-3-447-3411
FAX: 64-3-447-3348
E-Mail: mckenzie@wao.greta.cri.nz

Raymond C. Smith, Ph.D.
Center for Remote Sensing and Environmental
Optics
University of California
Santa Barbara, California 93106
USA
TEL: 1-805-893-4709 (or 4339)
FAX: 1-805-893-2579
E-Mail: ray@crseo.ucsb.edu
Yukio Takizawa, M.D.
Akita University School of Medicine
1-1-1 Hondo
Akita 010
JAPAN
TEL: 81-188-33-1166 ext. 3259
FAX: 81-188-36-2609

Xiaoyan Tang, Ph.D.
Co-chair, UNEP Effects Panel
Center of Environmental Sciences
Peking University
Beijing 100871
CHINA
TEL: 86-1-250-1925,
FAX: 86-1-250-1927
E-Mail: tangxy@bepc2.ihep.ac.cn

Alan H. Teramura, Ph.D.
Office of the Dean
University of Hawaii at Manoa
College of Natural Sciences
Bilger Hall 102, 2545 The Mall
Honolulu, Hawaii 96822
USA
TEL: 1-808-956-6451
FAX: 1-808-956-9111
E-Mail: teramura@uhunix.uhcc.hawaii.edu

-Manfred Tevini, Ph.D.
Co-chair, UNEP Effects Panel
Inst. f. Botanik II
Kaiserstrasse 12
D-76128 Karlsruhe
GERMANY
TEL: 49-721-608-3841
FAX: 49-721-608-4878
E-Mail: dbo5@ibm.3090.rz.uni-
karlsruhe .dbp.de

Ayako Torikai, Ph.D.
Department of Applied Chemistry
Faculty of Engineering
Nagoya University
Furo-Cho, Chikusa-ku
Nagoya 464-01
JAPAN
TEL: 81-52-789-3212
FAX: 81-52-789-3791

Jan C. van der Leun, Ph.D.
Co-chair, UNEP Effects Panel
Inst. Dermatology
University Hospital Utrecht
Heidelberglaan 100
NL-3584 CX Utrecht
THE NETHERLANDS
TEL: 31-30-507386
FAX: 31-30-518328
-------
Robert C. Worrest, Ph.D.
Consortium for International Earth Science
Information Network (CIESIN)
1747 Pennsylvania Ave., NW
Suite 200
Washington, DC 20006
USA
TEL: 1-202-775-6614
FAX: 1-202-775-6622
E-Mail: robert.worrest@ciesin.org

Richard G. Zcpp, Ph.D.
United States Environmental Protection Agency
Environmental Research Laboratory
960 College Station Road
Athens, Georgia 30605-2720
USA
TEL: 1-706-546-3428
FAX: 1-706-546-3636
E-Mail: rzepp@athens.ath.epa.gov
-------
APPENDIX B
LIST OF EXPERT REVIEWERS
-------
LIST OF EXPERT REVIEWERS
Prof. Mcinrat O. Andrcac
Max-Planck Institut fiiir Chemie
Postfach 3060
D-55020 Mainz
GERMANY
Phone 49 6131 305 420
Fax 49 6131 305 487

Dr. Bruce K. Armstrong
Director
Australian Institute of Health and Welfare
GPO Box 570
Canberra,- ACT 2601
AUSTRALIA
Phone 61 6 243 5001
Fax 61 6 257 1470

Dr. P. J. Aucamp
Chief Director: Forensic and Research Services
Department of Health
Private Bag X828
Pretoria 0001
SOUTH AFRICA
Phone 27 12 3120218
Fax 27 12 215392

Dr. Carlos L. Ballare
Dept. de Ecologia-IFEVA
Facultad de Agronomia, Universidad de Buenos
Aires
Avda. San Martin 4453
(1417) Buenos Aires
ARGENTINA
Phone 54 1 522 0903
Fax 54 1 51 1384
Alt (Phone and Fax) 54 1 501 4692

Dr. Safa Baydoun
Atomic Energy Commission
P.O. Box 6091
Damascus
SYRIA
Phone 963 11 6668114
Fax 963 11 6620317

Prof. Michel Boko
Laboratory of Climatology
UNB - FLASH - DGAT
B.P. 03 - 1122
Cotonou
BENIN
Fax 229 33 1981
Dr. J.P. Cesarini
INSERM
Foundation Ophtalmologique
Adolphe de Rothschild
25-29, Rue Manin _
F-57940 Paris Cedex 19
FRANCE
Phone 33 1 48036565
Fax 33 1 48036870
Telex 215306

Dr. Forrest G. Chumley
Research Manager
Environmental Biotechnology Group
DuPont Central Research and Development
The DuPont Company
P.O. Box 6101
U.S.A.
Phone 1 302 451 3336
Fax 1 302 451 9138
MCI Mail 460 0019
Internet chumley@esvax.dnet.dupont.com

Dr. Thomas P. Coohill
Ultraviolet Consultants
652 East 14th Street
"Bowling Green, KY 42101
USA
Phone/Fax 1 502 782 1351

Prof. J.E. Costa Martins
Photobiology Division, Department
of Dermatology
University of Sao Paulo
R. Peixoto Gomide, 996
Conjunto 240
CEP-01409 Sao Paulo
Brazil
Phone 55 11 289 1002
Fax 55 11 283 5409

Dr. Anthony P. Cullen
School of Optometry
University of Waterloo
Waterloo, Ontario N2L SGI
CANADA
Phone 1 519 885 1211
Fax 1 519 725 0784

Dr. S. M. Cayless
Department of the Environment
Global Atmosphere Division
43 Marsham Street
London SW1P SPY
UNITED KINGDOM
Phone 44 71 276 8396
Fax 44 71 276 8509
-------
Prof. Giinter Dohler
Botanisches Institut
Siessmayerstrasse 70
D-6000 Frankfurt
GERMANY
Phone 49 69 798 4745

Prof. Edward DeFabo
George Washington University Medical Center
Ross Hail, Room 113
2300 I St., NW
Washington, D.C. 20037
U.S.A.
Phone/Fax 1 202 994 3975

Dr. Michael J. Doughty
School of Optometry
University of Waterloo
Waterloo, Ontario N2L 3G1
CANADA
Phone 519 885 1211
Fax 519 725 0784
Telex 069 55259

Gunars Duburs, Ph.D.
Latvian Intitule of Organic Synthesis
21 Aizkraukles
LV-1006 Riga
LATVIA
Phone 371-2-551232
Fax 371-2-553493

Dr. Alex E. S. Green
ICAAS Clean Combustion Laboratory
University of Florida
P.O Box 112050
Gainesville, Florida 32611 - 2050
U.S.A.
Phone 1 904 392 2001
Fax 1 904 392 2027

Dr. R. Guicherit
TNO Institute of Environmental Studies
P.O. Box 6011
NL-2600 JA Delft
NETHERLANDS
Phone 31 15 696187
Fax 31 15 616812
Telex 38071

Dr. Mohammad Ilyas
Astronomy and Atmospheric Research Unit
University of Science of Malaysia
Pulau Pinang 11800
MALAYSIA
Phone 60 4 6572859
Fax 60 4 6576155
Dr. John Jagger
7532 Mason Dells Drive
Dallas, TX 75230
U.S.A.
Phone 1 214 692 6292

Dr. H. van Loveren
National Institute for Public Health and
Environmental Protection
P.O. Box 1
NL-3720 BA Bilthoven
NETHERLANDS
Phone 31 30 749111

Dr. All G. Maadhah
Manager
Division I, Research Institute
King Fahd University of Petroleum and Minerals
Dhahran 31261
SAUDI ARABIA
Phone 966 3 860 3319
Fax 966 3 860 2266

Mack McFarland, Ph.D.
Science Co-ordinator
Environmental Programs
DuPont Chemicals
Fluorochemicals
Wilmington, DE 19898
Phone 1-302-774-5076
Fax 1-302-774-8416

Prof. A. J. McMichael
Epidemiolody Unit
Keppel Street
London WC1E 7HT
UNITED KINGDOM
Phone 44 71 927 2254
Fax 44 71 580 6897

Dr. Giuliana Moreno
Lab. de Biophysique
INSERM U 201, CNRS URA 481
Museum National d'Histoire Naturelle
43 rue Cuvier
F-75 231 Paris Cedex 05
FRANCE
Phone 33 1 40793691
Fax 33 1 40793705

Dr. Gillian Murphy
Department of Dermatology
Beaumont Hospital
Beaumont Avenue
Dublin 9
IRELAND
Phone 353 1 8375058
Fax 353 1 8368215
-------
Mr. David Olszyk
Research Ecologist
US-EPA
Environmental Research Laboratory
200 SW 35th Street
Corvallis, Oregon 97333
U.S.A.
Fax 1 503 754 4397

Hugh M. Pitcher, Ph.D
Pacific Northwest Laboratory, Suite 900
901 D Street, NW
Washington, B.C. 20015
USA
Phone 1-202-646-7815
Fax 1-202-646-5233

Donald G. Pitts, OD, Ph.D.
6943 S. Jamestown Avenue
Tulsa, OK 74136-2611
U.S.A.
Phone 1 918 494 6779
Fax 1 918 488 9690

Dr. Barbara Prezelin
Department of Biological Sciences
University of Southern California
Santa Barbara, CA 93106
USA
Phone 1 805 893 2979
Fax 1 805 893 4724

Prof. Dr. Werner Rau
Botanischcs Institut der Universitat Miinchen
Menzinger-Strasse 67
D-80638 MQnchen
GERMANY
Phone 49 89 17861 238
Fax 49 89 1782 274

Prof. Henning Rodhe
Department of Meteorology
University of Stockholm
S-10691 Stockholm
SWEDEN
Phone 46 8 16 43 42
Fax 46 8 15 92 95

Dr. Norma D. Searle
114 Vcntnor F
Deerficld Beach, Florida 33442
U.S.A.
Phone/Fax 1 305 480 8938

Dr. Zdenek Sestak
Institute of Experimental Botany
Academy of Sciences of the Czech Repablic
Na Karlovce la
CZ-16000 Praha 6
CZECH REPUBLIC
Phone 42 2 311 1032
Fax 42 2 24310113
Dr. Richard B. Setlow
Biology Department
Brookhaven National Laboratory
Upton, Long Island, NY 11973
U.S.A.
Phone 1 516 282 3391
Fax 1 516 282 3407

Dr. Richard Soulen ~"
Technical and Management Services, Inc.
P.O. Box 388
Bloomfield Hills, Michigan 48303
U.S.A.
Phone 1 810 642 6568
Fax 1 810 258 6769

Dr. Hugh R. Taylor
Ringland Anderson Professor of Ophthalmology
Melbourne University
Department of Ophthalmology
32 Gisborne Street
East Melbourne
VIC. 3002
AUSTRALIA
Phone 613 665 9564
Fax 613 662 3859

Dr. F. Urbach
Temple University Medical Practices
"220 Commerce Dr., Suite 120
Fort Washington PA 19034
U.S.A.
Phone 1 215 643 2411
Fax 1 215 643 6188

Dr. K. Victoria
Karolinska Institute of Environmental Medicine
Box 210
S-17177 Stockholm
SWEDEN
Phone 46 8 7286400
Fax 46 8 33 6981

Prof. Alan R, Wellburn
IEBS (Biol. Sci.)
Lancaster University
Lancaster LAI 4YQ
UNITED KINGDOM
Phone 44 524 593838
Fax 44 524 843854

Prof. Dr. Eckard Wellmann
Biologisches Institut II de Universitat
Schanzlestrasse I
D-7800 Freiburg
GERMANY
Phone 49 761 203 2664
Telex 77274070 UF
-------
APPENDIX C
LIST OF ABBREVIATIONS
-------
LIST OF ABBREVIATIONS
AF Amplification Factor
AIDS acquired immunodeficiency disease syndrome
BAF Biological Amplification Factor
BCC basal cell carcinoma _
CFG chlorofluorocarbon
CM cutaneous melanoma
CO carbon monoxide. A chemically-reactive trace gas that is believed to play an important role in
controlling the oxidizing capacity of the free troposphere.
COS carbonyl sulfide. The most concentrated sulfur containing gas in the troposphere. COS is
believed to be a source of background sulfate aerosols in the stratosphere.
CO2 carbon dioxide
CZCS coastal zone color scanner
DIG Dissolved inorganic carbon. Total concentration of dissolved inorganic carbon in water,
expressed in units of grams carbon per liter
DMS dimethyl sulfide. The major volatile sulfur compound of biogenic origin emitted from the
ocean into the atmosphere. DMS reacts in the troposphere to produce sulfate aerosols.
DNA deoxyribonucleic acid
DOC Dissolved organic carbon. Total concentration of dissolved organic substances in water,
expressed in units of grams carbon per liter
DOM Dissolved organic matter. Total concentration of dissolved organic substances in water,
usually expressed in units of grams carbon per liter
DU Dobson Unit (2.69 x 1019 molecules cm-2)
EC5Q concentration resulting in 50% of specified effect
g DW Grams per dry weight
Gt Gigaton. 10$ tons (IQlS grams) —— -
HCFC Hydrochlorofluorocarbon. The class of industrially produced compounds containing carbon,
hydrogen, chlorine and fluorine. Can be used as chlorofluorocarbon substitutes.
HFC Hydrofluorocarbon. The class of industrially produced compounds containing carbon, hydrogen
and fluorine. Can be used as chlorofluorocarbon substitutes
HIV human immunodeficiency virus
HSV herpes simplex virus
ISLSCP International Satellite Land Surface Climatology Project
IL-1, 10 Interleukin -1, 10
McBr methyl bromide
NLOM Non living organic matter in the environment, e.g. litter, detritus
NMHC Non methane hydrocarbons. Volatile hydrocarbons emitted from terrestrial plants and marine
phytoplankton that participate in various tropospheric chemical reactions
NMSC non-melanoma skin cancer
NO Nitric oxide. A highly reactive trace nitrogen species that participates in a variety of
chemical reactions in the troposphere
NOX Nitrogen oxides. Reactive nitrogen-containing species, nitric oxide and nitrogen dioxide,
that play an important role in tropospheric chemistry
N2O Nitrous oxide. An important greenhouse gas that also participates in stratospheric reactions
that deplete ozone
PAM pulse amplitude modulation
PAR Photosynthetically active radiation. Generally defined as electromagnetic radiation in the
400 to 700 nm range
POC Particulate organic carbon. Total concentration of paniculate organic substances in water,
expressed in units of grams carbon per liter
RAF Radiative Amplification Factor
SBUV Solar Backscatter Ultraviolet (instrument)
SCC squamous cell carcinoma
SCUP skin cancer utrecht'- Philadelphia
SOM Soil organic matter
SP xeroderma pigmentosum

1
-------
TFA
Tg
Thl, 2
TNF
TOMS
UCA
UNEP
USEPA
UV
UV-A

UV-B

WHO
WMO
Trifluoroacetic acid. A tropospheric oxidafiorf product of certain HFCs and HCFCs
Teragrani. 1Q12 grams .'•'
T-helper 1, 2 lymphocyte
Tumor necrosis factor - alpha
Total Ozone Mapping Spectrometer
urocanic acid
United Nations Environment Programme
United States Environmental Protection Agency
ultraviolet
Ultraviolet-A radiation. Electromagnetic radiation of wavelengths in the 315 to 400 nm
range
Ultraviolet-B radiation. Electromagnetic radiation of wavelengths in the 280 to 315 nm
range
World Health Organization
World Meteorological Organization
-------
-------