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The United Nations Environment Programme
Assessment Panel on the Environmental Effects of Ozone Depletion
produced this interim summary. The assessment is given in
seven sections: changes in ultraviolet radiation, effects on human
and animal health, effects on terrestrial ecosystems, effects on
aquatic ecosystems, effects on biogeochemical cycles, effects on
air quality, and effects on materials.
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UNITED
NATIONS
ENVIRONMENT PROGRAMME
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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)
Table of Contents
- Ozone and UV Changes
- Health Effects
- Effects on Terrestrial Ecosystems
- Effects on Aquatic Ecosystems
- Effects on Biogeochemical Cycles
- Effects on Air Quality
- Materials Damage
- Panel Members and UNEP Representatives
Ozone and UV Changes
Since publication of the 1998 UNEP Assessment,
there has been a continuation of the rapid expansion of the literature
on UV-B radiation.
- Measurements at a southern mid-latitude site have clearly demonstrated
that long-term increases in peak summertime UV-B radiation have occurred
in recent years as a result of ozone depletion. In the summer of
1998-99 the peak levels of sunburning UV in New Zealand (45oS)
were about 12% more than in the first years of the decade. Larger increases
were seen for DNA-damaging UV and for plant-damaging UV, whereas UV-A
radiation, which is not affected by ozone, showed no increase. These
findings are in agreement with model calculations and provide the strongest
evidence yet of increases in UV-B radiation due to ozone depletion,
in a region where baseline levels were already relatively high. Because
the downward trends in ozone had already been occurring for several
years before the UV radiation measurements became available, one could
infer that even larger increases in UV radiation might have occurred
at this site since 1979. The results from this unpolluted site are probably
representative of a wide region of southern mid-latitudes.
- Although the rate of decline in stratospheric ozone has slowed
in recent years, in some geographical regions and seasons this is not
the case, despite the stratospheric loading of ozone-depleting substances
being close to its expected maximum. For example, in the above data
from a southern mid-latitude site, there is little evidence of abatement
in summertime ozone depletion. Further, the depleted mass of ozone in
Antarctica was at an all-time maximum in the preceding spring of 1998.
These results are not inconsistent with recent studies that suggest
that interactions between global warming and ozone depletion could delay
the recovery of the ozone layer. However, further analyses, including
data from other locations, are required to understand the extent of
these continuing ozone declines.
- There have been continuing improvements in the determination of
UV-B radiation at the Earth's surface, enhancing our ability to estimate
the risks of ozone depletion. These include expansion of the geographic
coverage of measurements, improvement in calibration procedures, and
determination of UV radiation fluxes, which are relevant to environmental
effects such as the photochemistry of air pollution. Attempts are being
made to understand the effects of partial cloud cover on UV-B radiation,
and of inhomogeneities in neighboring terrain (e.g. snow cover, altitude).
Some progress has been made in verifying satellite retrievals of UV
radiation by comparison with measurements at the Earth's surface. However,
more work is still needed in this area. Global climatologies of UV radiation
are now available on the Internet.
Health Effects
- The concern that exposure of children to UV-B radiation may be
more damaging than exposure of adults has received support from recent
findings in animals exposed as newborns. Using opossums, researchers
have shown that low-dose UV-B exposure early in development (suckling
young) can lead to widespread melanoma in later life. The exposure regimen
used involved several doses that resulted in a total dose that was less
than that needed to cause sunburn in these animals.
- It is now quite clear that in the opossum UV-B radiation induces
lesions that progress to malignant melanoma, whereas UV-A induces only
precursor lesions that do not become malignant. This is in contrast
to certain fish where either UV-A or UV-B can experimentally induce
melanoma. It is not possible on the basis of current information to
definitively identify, which of these two experimental animal systems
is the more relevant to the development of melanoma in humans.
- There is now quantitative evidence that the exposure to
the UV in sunlight is detrimental for patients suffering from systemic
lupus erythematosus (SLE). Researchers have shown that regular sunscreen
use by SLE patients was associated with a significant improvement in
the course of the disease. Patients who consistently used sunscreens
had fewer SLE-related renal problems, fewer incidences of clotting disorders,
fewer hospitalizations and a lower requirement for immunosuppressive
drugs.
- The number of diseases identified as definitely affected by UV-B
radiation is steadily increasing. New this year from studies in
humans is the discovery that critical mutations in the late stages of
cutaneous lymphomas are of a form considered the hallmark for UV-B damage.
Effects on Terrestrial Ecosystems
- Solar UV-B radiation increases which are directly linked to stratospheric
ozone reduction have been shown to cause damage to the DNA of intact
plants under natural conditions. Variations in solar UV-B caused
by changes in stratospheric ozone have been found to relate to DNA damage
in intact plants at high latitudes in the Southern Hemisphere. At these
latitudes, stratospheric ozone reduction is pronounced and varies from
day-to-day as the ozone layer undergoes changes, which are in part associated
with the Antarctic ozone "hole". This link between solar UV-B
and DNA damage was further validated with experiments in which the UV-B
component of sunlight was modified by selective filters.
- The DNA damage in plants from field studies is indicative of a
large increase in DNA-damaging solar UV-B radiation with each unit of
ozone reduction. The biological effectiveness of
solar UV-B related to changes in atmospheric ozone depends on how different
wavelengths of UV-B affect plants, animals and microbes. The same reduction
in ozone can result in large or small changes in effective solar UV-B
(in this case, DNA-damaging radiation) depending on the nature of this
wavelength dependency. These recent experiments of plant DNA damage
in nature are consistent with a large sensitivity to ozone change. That
is, each drop in ozone results in a large increase in DNA-damaging UV
radiation.
- More evidence is accumulating showing that the attractiveness of
plants for insect consumption depends on how solar UV-B radiation affects
the chemical composition of the plant foliage. However, recent information
also shows that the insects can respond directly to solar UV-B radiation.
Increases in solar UV-B will be associated with many indirect, yet important,
changes in how plants, animals and microbes interact in nature. Recent
research is adding evidence that increased solar UV-B can lead to changes
in how plants compete with one another and how effectively insects,
including pests, consume plants. The latter is thought to be largely
due to alterations in the chemical composition of plant foliage caused
by solar UV-B, leading to either increased or decreased insect consumption
of plant tissues. Recent evidence also indicates that insects can perceive
and avoid solar UV-B radiation. All these lines of research point to
the complexity of ecosystem change with ozone reduction.
- Continuing research conducted under field conditions by either
supplementing or decreasing the normal solar UV-B radiation showed a
variety of effects on plant growth and production at different latitudes.
There are now over 100 field studies with plants in which either the
normal solar UV-B was supplemented with lamp systems, or the solar UV-B
component of sunlight was excluded or reduced. These studies have shown
a wide range of response in growth and production due to the UV-B radiation
manipulations and occasionally sizeable decreases caused by UV-B radiation.
Effects on Aquatic Ecosystems
- Numerous recent studies have reconfirmed that solar UV adversely
affects aquatic primary producers (phytoplankton and macroalgae) even
at current levels. Photosynthesis, growth, development and reproduction
are affected in the top layer of the water column where these organisms
are located. Recent studies concentrating on the ecosystem level have
indicated that short wavelength solar radiation alters the community
structure and development, and the succession of species because of
differences in organism sensitivity. Loss in biomass productivity in
aquatic ecosystems due to solar UV is still controversial.
- Bacterioplankton and small non-photosynthetic flagellates that
feed on bacteria cannot utilize screening pigments because of their
small size and are highly affected by solar UV radiation, which can
cause DNA damage. The UV-inflicted damage can be repaired by light-dependent
enzymatic processes and be offset by high reproductive rates. Bacterioplankton
have a central role in the food web by mineralizing organic matter.
Bacteria are also under attack from aquatic viruses, which occur at
high abundance in the water as well as their predators, which in turn
are taken up by the next level in the food web. The effects of UV on
viruses and small flagellates still need to be elucidated.
- In cyanobacteria, growth, differentiation, photosynthesis and
nitrogen incorporation have been found to be affected by solar UV radiation,
even in extreme environments such as Antarctic rocks. Cyanobacteria
can constitute up to 40 % of the marine biomass. These photosynthetic
organisms are unique in their capacity to take up atmospheric nitrogen
and convert it into a form that can be incorporated by phytoplankton
in aquatic habitats and by higher plants, e.g. in tropical rice paddies.
- Continuous monitoring has been developed to measure solar radiation
above and in the water column. A monitoring network has been installed
in Europe and other continents to continuously monitor solar radiation
in three wavelength bands (visible radiation, UV-A and UV-B) above and
within the water column. Satellite monitoring is increasingly used to
quantify the biomass production in the oceans by color imaging.
- Further mechanisms have been identified by which aquatic organisms
protect themselves from excessive solar UV. Many primary producers
synthesize UV-screening pigments that intercept short wavelength radiation
before it reaches the DNA. In addition to substances already known,
phenolic compounds and yet unidentified chemicals have been found. Primary
and secondary consumers take up these substances and utilize them as
screening devices. Other protective mechanisms include effective DNA
repair and vertical migration (e.g. in microbial mats) to escape UV-induced
damage.
- In clear lakes, UV-B radiation is a potentially important factor
in the success of early life history stages of some freshwater fish
species. UV-B radiation was shown to affect components of freshwater
and marine ecosystems. The depth at which some fish construct their
breeding nests appears to be related to the penetration of UV-B radiation
into the water column.
Effects on Biogeochemical Cycles
- During 1999, improved knowledge has been obtained on the effects
of enhanced UV-B radiation on biogenic emissions and uptake of greenhouse
and other important gases. Field observations in Antarctica provide
corroborative evidence of the important role of UV-B radiation in sea-air
exchange of carbon and sulfur gases that affect global warming and atmospheric
chemistry. Laboratory studies have shown that enhanced UV-B in aquatic
ecosystems can stimulate photochemical oxygen demand and emission of
carbon dioxide. These recent results have shown that the effects of
UV-B on trace gas exchange are closely linked to changes in the composition
of freshwater and marine environments, such as shifts in organic carbon
and iron concentrations, that are known to be sensitive to changes in
climate and human activities.
- Additional research since the last report has confirmed that UV-absorbing
dissolved organic substances primarily control penetration of UV-B radiation
into freshwater and marine environments. Consequently, environmental
factors that affect concentrations of these substances, such as UV-induced
photodecomposition, acidification, and changes in climate can interact
with ozone depletion to strongly affect underwater UV exposure. Efforts
are now underway to develop algorithms that can use satellite observations
of ocean color or in-water fluorescence measurements to estimate large-scale
spatial and temporal changes in UV penetration into the sea.
- New efforts to better define the effects of solar UV radiation
on microbial activity and carbon and nutrient cycling in lakes and the
sea have accelerated over the past year. Continued research in this
area indicates that the photochemical breakdown of persistent, UV-absorbing
organic matter can stimulate biomass production or microbial activity
several fold. Other studies in lakes and marine ecosystems provide new
evidence that exposure to UV radiation can also inhibit bacterial growth
on algal-derived, biologically available substances.
- Long-term experiments on terrestrial biogeochemical cycles show
effects of enhanced UV-B radiation on litter decomposition. New
results obtained at sites in southern and northern Europe suggest that
the effects of enhanced UV-B on plant litter decomposition are significant
but small and species dependent.
- New approaches are being developed to assess and integrate the
interactions and feedbacks between climate change and UV-B-induced alterations
in marine and terrestrial biogeochemical cycles. Models that describe
the biogeochemistry of the upper ocean and lower atmosphere are being
assembled to integrate both climate change and ozone depletion. These
models take into account temperature and radiation distributions, human
activities, such as excessive nutrient enrichment in coastal waters,
and the concurrently changing ocean and atmospheric circulation patterns.
Effects on Air Quality
- There has been a strong increase in interest regarding how UV-B
radiation affects air quality, especially under polluted urban conditions.
Several studies have been carried out or are planned to help quantify
effects of UV-B radiation on atmospheric photochemistry and smog production.
These research efforts include instrument and model intercomparisons
and well as field observations. Such studies will help establish the
sensitivity of tropospheric oxidants to UV-B levels under conditions
of different emissions of pollutant hydrocarbons and nitrogen oxides.
Materials Damage
- At higher ambient temperatures UV-B radiation is considerably more
effective in causing photodamage to materials. The observation of
synergy between the effects of solar UV radiation and temperature was
extended to several types of common polymers. Thus climate-related increases
in global temperature can increase the extent of damage to materials
resulting from exposure to solar UV radiation levels.
- Flame retardant additives in polystyrene were recently reported
to significantly increase the susceptibility of the polymer to damage
by UV radiation. These additives, commonly used in products made
from polystyrene, tend to increase the efficiency of the photodegradation
in polystyrene and several other polymers. The enhancing effect was
more pronounced at the longer wavelengths within the UV-B region of
the solar spectrum.
- The efficiency of some types of UV-induced photodegradation processes
in wood and plastics tends to be intensity-dependent. It is well
established that the larger doses of UV-B radiation lead to correspondingly
greater damage to materials. However, at the same dose, more efficient
photodamage was obtained at the lower intensity of monochromatic radiation
in laboratory experiments. The finding suggests that significant amounts
of photodamage can occur when some materials are exposed to low intensities
of UV radiation over long periods of time.
- Several new classes of additives that protect materials against
damage by UV-B radiation were reported in 1999. Some of these can
be used with common plastics and are more effective than conventional
light stabilizers against damage from exposure to solar radiation. In
general, more effective stabilizers could make it easier to maintain
present service lifetimes of plastics in the event of increased UV-B
levels in solar radiation.
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