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Updated 8 February, 2004

Environmental effects of ozone depletion: Interim Summary September, 1999









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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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

  1. Ozone and UV Changes
  2. Health Effects
  3. Effects on Terrestrial Ecosystems
  4. Effects on Aquatic Ecosystems
  5. Effects on Biogeochemical Cycles
  6. Effects on Air Quality
  7. Materials Damage
  8. 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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