THE OZONE LAYER: NOT A FUTURE CRISIS
THE NEED FOR ACTION NOW
by
Keith C. Heidorn, Ph.D., ACM
E-mail: ub451@freenet.victoria.bc.ca
1930 Venross Place, RR#1
Saanichton, BC V0S 1M0
(604) 652-8436
Abstract:
The decline of the atmospheric ozone layer is generally linked with global warming as an
impending global environmental change. Unlike global warming, the impacts of ozone depletion are
not only projections into the future but are upon us now. The action of man-made chemicals into
the ozone layer have been active in reducing the global ozone layer for several years (Watson, et
al., 1992). In addition, recent eruptions of Mt. Pinatubo and other volcanoes have introduced
other ozone-destroying chemicals into the stratosphere (Grant, et al., 1992). The result has been
a more rapid decline in upper atmospheric ozone concentrations than previously expected with
global ozone levels the lowest on record in 1992 (Gleason et al., 1993). Preliminary reports for
1993 shows even lower ozone levels (Associated Press, 1993). Recent research has shown that the
reduction in the ozone layer and concurrent increase in ultraviolet radiation (UV) will have
major consequences to life on earth and human health and welfare (UNEP, 1991; SCOPE, 1992). This
paper reviews the recent research into impacts of ultraviolet radiation on man and the biosphere
and concludes that action to reduce the emissions of ozone-destroying compounds is not enough.
Actions must also be taken to alter life styles as a result of the increased UV radiation.
Examples of the Australian experience in public education of the dangers of increased UV
radiation will be presented.
INTRODUCTION
Much concern has been expressed in the last decade concerning changes in
the global environment and their impacts on humanity and the Earth's
biosphere. The areas of deepest concern to atmospheric scientists are global
warming and the depletion of the Earth's ozone layer. Major programs have been
undertaken around the world to determine the impact of increased releases of
carbon dioxide by man's activities on the global climate. Mathematical models
have calculated that global warming over the next century of up to 4.5oC may
result from a doubling of the atmospheric carbon dioxide concentration (Gates
et al., 1992). Although there is consensus among the scientific community that
global warming will occur as a result of the increased carbon dioxide, the
degree of warming is the subject of intense study. Those scientists not in
agreement with the consensus argue that we still know too little about the
feedback mechanisms of climate to even claim warming will be the preferred
climate change in the long term. Indeed, much debate has centred around the
question as to whether changes in global temperatures over the last century
indicate that warming has occurred in response to the concurrent rise in
carbon dioxide levels (Folland et al., 1992).
In contrast, the concerns over the depletion of the ozone layer arose
simultaneously in the mid-1970s from observed conditions and theoretical
speculation. (It is not the purpose of this paper to delve into the history of
this research; an excellent review has been published by Roan, 1989).
Measurements by the TOVS (Total Ozone Vertical Sounder) and TOMS (Total Ozone
Mapping Spectrometer) systems aboard the U.S. Nimbus satellites over the
period 1979 to 1992 indicate that there has been a significant downward trend
in the global ozone column even with known periodicities due to the solar
cycle and Quasi Biennial Oscillation removed (Gleason et al., 1993). Ozone
levels in 1992 dropped even more than expected from the previous downward
trend. While the trend has been linked with the emission of ozone-depleting
chemicals such as CFCs, additional depletion in the past few years has been
attributed to the eruption of volcanoes, especially Mt. Pinatubo in the
Philippines in 1991 (Grant et al., 1992). As chlorine and bromine abundances
continue to increase in the stratosphere, a further global decline in ozone is
anticipated (Halpert and Ropelewski, 1993).
One strong feature of the decline in the ozone layer has been the
Antarctic "ozone hole", a large region of strongly depleted ozone
concentrations arising early in the Antarctic spring. The hole has been
observed to be increasing in size with decreasing ozone concentration over the
past decade. For example, the average minimum values for the Astral spring
have decreased from 275 Dobson Units (DU) in 1979 to under 200 DU in 1992
(Halpert and Ropelewski, 1993). Recently, a Arctic ozone hole has been
observed over the Northern Hemisphere, centring on Europe and eastern North
America (Evans, 1989). In the spring of 1993, this hole reached record size
and depletion (W.F.J. Evans, Trent University, 1993, personal communication).
In their 1992 supplementary report on Climate Change, the International
Panel on Climate Change (IPCC, 1992) concluded:
Even if the control measures of the 1990 London Amendments to the
Montreal Protocol were to be implemented by all nations, the
abundance of stratospheric chlorine and bromine will increase over
the next several years. The Antarctic ozone hole, caused by
industrial halocarbons, will therefore recur each spring. In
addition, as the weight of evidence suggests that these gases are
also responsible for the observed reduction in middle and high
latitude stratospheric O3, the depletion at these latitudes is
predicted to continue unabated through the 1990s.
The Canada House of Commons Standing Committee on Environment stated
their position more bluntly: "Ozone depletion is a threat to the continuation
of life on Earth" and called on governments of the world to "declare
themselves at war with all of those elements which are responsible for
depletion of the Earth's ozone..." (SCE, 1990).
Therefore, while we may continue to debate the degree and timing of
global warming, there is no doubt that over the last fifteen to twenty years,
there has been a significant decrease in ozone in the upper atmosphere,
downward trends that were larger in the 1980s than during the 1970s (Watson,
et al., 1992). In this paper, we present a number of the impacts of this
decline in ozone on the biosphere and humankind.
ULTRAVIOLET RADIATION AND THE OZONE LAYER
Ozone is an absorber of both solar and terrestrial radiation. The active
absorption bands in the ultraviolet portion of solar radiation include 200 to
300 nm (strong), 300 to 360 nm (moderate) and in the infrared, the peak of
terrestrial radiation, ozone absorbs in a band around 9600 nm.
The overall impact on global warming of decreasing stratospheric ozone
is currently under evaluation. Preliminary results indicate its decline may
result in an overall cooling of the lower atmosphere equivalent to the warming
attributable to the greenhouse effect of the CFCs. The early model results,
however, have shown the degree of impact and even the direction of the impact,
i.e., warming or cooling, to be extremely sensitive to the amount and altitude
of the decreases in ozone concentration (Isaksen, et al., 1992).
The prime impact of a decrease in the upper atmospheric ozone layer
results in an increase in the amount of ultraviolet (UV) solar radiation
reaching the lower atmosphere and the surface of the Earth. Increases in UV
radiation have major consequences for live on Earth. In fact, life on the
planet as we know it today would not be possible without the protection of the
ozone layer above us. For the first two billion years of life on Earth, the
atmosphere contained little free oxygen. As a result, there was no ozone layer
to shield life from UV radiation. Thus, early life could only develop under
the protective cover of water (Odum, 1971).
The first aquatic, photosynthesizing organisms produced biological
oxygen as a by-product of sugar synthesis. As a result of diffusion of oxygen
from the waters to the atmosphere, an ozone layer began forming in the upper
atmosphere. As it thickened and absorbed some of the solar UV radiation, life
began to move toward the surface of the sea. By about 600 million years ago,
the oxygen content of the atmosphere and its attendant ozone layer was
sufficiently thick to lead to the second great revolution of life - the
Cambrian explosion of multicellular life. This was soon followed, geologically
speaking, by the invasion of life onto the land in the late Paleozoic period
(Odum, 1971).
CHANGES IN BIOLOGICALLY ACTIVE UV RADIATION
AT THE EARTH'S SURFACE
With the loss of stratospheric ozone, the atmosphere becomes more
transparent to solar ultraviolet radiation. Only a certain type of UV is
affected however, that UV radiation band known as UV-B (wavelengths from 280
to 315 nm). As ozone declines, the intensity of UV-B increases and the
spectral composition of solar radiation shifts toward more radiation in the
shorter wavelengths. The current estimated increase in biologically active UV
radiation in the Northern Hemisphere is 5% per decade at 30oN and about 10%
per decade in the polar regions. In the southern hemisphere, the decrease at
30oS is also 5% per decade while in the polar regions (85oS) the increase has
been 40% per decade. In contrast, little change has been found in the
equatorial regions (Mandronich et al, 1991).
Solar UV radiation incident on the Earth's surface is affected by many
factors in addition to the total atmospheric ozone column: solar elevation
angle, cloud cover, and atmospheric moisture, dust and pollutant
concentrations. These factors are quite variable in time and space. Except for
solar angle, the influences of these factors may also be dependent upon
changing global conditions. Such variations contribute to the variability of
UV measurements. For example, there has been a decrease in the total UV
measured at the surface in the United States from 1973 to 1985, between 0.5%
and 1.1% per year (Mandronich et al, 1991). Grant (1988) has suggested,
however, that local pollution may have accounted for much of the decrease
since most of the monitoring sites were in urban or near-urban locations. In
contrast, measurements in the Swiss Alps (3600 m altitude) have shown an
increase in UV radiation of 0.7% per annum between 1981 and 1989 (Blumthaler
and Ambach, 1990).
The TOMS data have been used to analyze the trends in biologically
active UV radiation during the 1979-1989 period (Mandronich, 1991). Average
daily doses of UV radiation were weighted with the generalized DNA damage
spectrum of Setlow (1974). The resulting daily dose shows statistically
significant increases of 5% to 20% per decade of clear sky UV radiation in the
30oN to 60oN latitude band during early winter and late spring, a 5% to 10%
increase in summer north of 60oN and a 5% or greater increase poleward of 30oS
from spring to late fall. The trend in UV radiation under the Antarctic ozone
hole is dramatic; increases exceeding 100% occur between August and November
from 80oS to the pole (Mandronich, 1991).
One measure of the impact of ozone depletion on changing the UV-B dosage
is the Radiation Amplification Factor (RAF). This factor is defined as the
percentage change in the effective daily dosage of UV-B radiation relative to
a 1% decrease in total column ozone. Many investigators have used an RAF of
two as a general rule of thumb. Other studies find a 2% increase in UV-B for
every 1% decrease in the ozone column thickness only at mid-latitudes in
winter. For the wavelengths specific to erythema (reddening of the skin),
however, the RAF is between 1.9 and 2.2 (Wayne, 1991). De Fabo, Noonan and
Frederick (1990) suggest an RAF of 0.6 to 1.0 for biologically effective
irradiance levels of solar UV-B. For DNA destruction, however, the RAF is much
higher, being between 2.5 and 2.8 (Wayne, 1991).
UV-B IMPACTS ON VEGETATION
UV-B and Aquatic Systems
Over the millennia, the ocean ecosystem has developed an equilibrium
with incident solar radiation. The thinning of the ozone layer disrupts this
delicate balance with serious consequences for aquatic productivity and
ecosystem function. UV-B radiation 1) affects adaptive strategies, 2) impairs
important physiological functions, and 3) threatens many marine organisms
during their development stages (Hader, Worrest and Kumar, 1991).
Phytoplankton at the bottom of the food chain are at particular risk (SCOPE,
1992). Phytoplankton presently convert 104 billion tons of atmospheric carbon
annually into organic material (Houghton and Woodwell, 1989). Therefore,
scientists have also expressed concern the ozone-induced loss of phytoplankton
may trigger a positive feedback in the global carbon cycle which would further
exacerbate the greenhouse effect (Hader, Worrest and Kumar, 1991; SCOPE,
1992).
A number of short-term studies have shown that phytoplankton production
is reduced by increasing levels of UV-B. Eggs and larvae of many marine
organisms are also sensitive to UV radiation. Marine organisms have a number
of mechanisms which increase their tolerance to ambient UV radiation, but
little is currently known about the impact of sustained increases in UV-B
(SCOPE, 1992).
Plankton orient themselves within the water column using external
factors; most, however, do not possess UV-B photoreceptors and thus cannot
avoid high levels of UV-B radiation (Hader, Worrest and Kumar, 1991). Work by
Hader and Worrest (1991) indicates that mobility/orientation mechanisms in
phytoplankton are impaired by solar UV radiation. This inability to adjust to
increased UV-B radiation may result in massive inhibition of photosynthesis.
Several studies (Hader, Worrest and Kumar, 1991) have shown that UV
penetration in Antarctic waters damaged plankton down to a depth of 65 m.
Measurements taken under the Antarctic ozone hole revealed a decrease in
phytoplankton productivity of up to 25%. Decreases in phytoplankton
productivity and populations would in turn harm the krill population which
serves as a major food source to the polar ocean biosphere. (The concentration
of phytoplankton in the subpolar seas is 103 to 104 times that found in
tropical and subtropical seas.) While qualitative knowledge of potential
impacts is growing, we are currently unable to assess quantitatively the UV-B
impact on changes in production, species composition and aquatic biomass
(SCOPE, 1992).
Some of the bacterial plankton have the capabilities to fix atmospheric
nitrogen into a form accessible to higher plants. These nitrogen compounds are
consumed by higher aquatic plants as essential nutrients. These bacteria are
also highly sensitive to UV-B radiation (Hader, Worrest and Kumar, 1991).
While the direct effect of increased UV-B radiation on the higher levels
of the food chain is unknown, UV impacts on the planktonic base may
significantly effect the oceanic trophic levels, especially in bio-rich polar
waters. Human populations may also be negatively affected by reductions in
plankton. At present, humankind derives more than 30% of its animal protein
from the sea, and further exploitation of this resource will be required to
feed ever increasing populations.
UV-B and Terrestrial Systems
Unlike aquatic plants, terrestrial vegetation evolved under conditions
of wide variations in solar UV radiation. As a result, there is a wide range
of tolerance and adaptation in terrestrial vegetation. Little is known,
however, about the manner in which agricultural and native plants in the
tropics cope with the intense UV radiation already present (Teramura, et al.,
1991). On the other hand, the degree to which such species can adapt to
increased UV-B fluxes resulting from O3 depletion is also unknown (Teramura,
et al., 1991).
The impact of UV radiation on vegetation has been extensively studied
through growth chamber studies, greenhouse studies and field studies. Impacts
on chloroplasts have been determined using in vitro techniques. These studies
conclude that UV-B radiation may affect terrestrial plants through changes in:
1) Photosynthesis and transpiration, 2) plant growth, 3) competitive balance
in a community, 4) pollination and flowering, 5) yield, 6) DNA and cellular
damage, and 7) susceptibility to disease, environmental stress and pollution
(Tevini and Teramura, 1989; Teramura et al., 1991; Stapleton, A.E., 1992;
SCOPE, 1992). Approximately two thirds of 300 plant species and cultivars
studied appear to be susceptible to damage from increased UV-B radiation
(Sullivan and Teramura, 1989). The effect of, and sensitivity to, UV-B varies
widely among species as well as among genotypes of a species (Tevini and
Teramura, 1989). Some of the specific impacts are summarized below.
1) Photosynthesis and transpiration - When plants in a growth chamber are
exposed to high UV-B levels, the effects on photosynthesis as measured by CO2-
assimilation were generally negative (Tevini and Teramura, 1989). One possible
explanation for the decrease in some species may be linked to stomatal closure
by enhanced UV-B, thereby reducing the uptake of CO2. Reductions in
transpiration in UV-B sensitive seedlings such as cucumber and sunflower also
suggest UV-B induced stomatal closure (Tevini and Teramura, 1989).
In vitro chloroplast studies indicate that damage by UV-B to
photochemical reactions is greater in C-3 plants such as wheat and beans than
to C-4 plants such as maize (Teramura et al., 1991).
Field studies of loblolly pine (Sullivan and Teramura, 1991) found a
decrease of up to 40% in photosynthetic capacity in needles exposed to
enhanced UV-B radiation simulating a 16% and 25% ozone depletion. (It must be
noted that such ozone depletions were measured over Canada during the spring
of 1993.) Seedlings in growth chamber experiments exposed to even the lowest
additional radiation levels showed reduced growth (Sullivan and Teramura,
1989). As the UV-B levels increased, there was a more rapid production of UV-B
absorbing compounds and growth was less affected. Research by DeLucia et al.
(1992) on two species of subalpine conifers showed UV-B penetration of needles
was greatest in emergent and in-bud needles and least in mature needles. The
cuticle and epicutical waxes may contain important UV-absorbing compounds
which provide a first-line of defense against enhanced UV-B light (DeLucia et
al., 1991).
2) Plant growth
UV-B radiation reduces growth characteristics such as plant height and
leaf area in sensitive species and cultivars (Tevini and Teramura, 1989).
Reduced growth rates in cucumbers continued throughout the development of the
plant whereas with soybeans, the effects varied with plant growth stage.
Three out of ten conifer species showed reduced seedling growth under
enhanced UV-B radiation (Sullivan and Teramura, 1988). After three years of
irradiation, Sullivan and Teramura (1991) found tree biomass was significantly
reduced by as much as 20%. They suggest that the effects may accumulate and
that increased UV-B radiation could significantly reduce the growth of
loblolly pine over its lifetime.
Six of sixteen rice cultivars showed a statistically significant
decrease in total biomass with increased UV-B radiation under a 20% ozone
reduction scenario over the Equator (Teramura et al., 1991). In the sensitive
cultivars, photosynthetic capacity, leaf area and tiller numbers were also
reduced.
3) Competitive balance in a community
Enhanced UV-B radiation can cause changes in the growth form of plants
without necessarily directly decreasing plant photosynthetic production
(Teramura et al., 1991). Reduction in leaf length, increased branching and
increased leaf numbers seem to be rather general impacts among different crop
and weed species. Such changes, while not important in a single species stand,
may have major consequences in a mixed community as species compete for
available light and nutrients.
For example, in a mixed wheat and wild oat field, the wheat was favoured
under enhanced UV-B radiation because wild oat showed greater reductions in
stem elongation and leaf blade lengths than the wheat. This differential
response allowed the wheat to dominate the field. In this study, neither
species showed reduced photosynthetic capacity as a result of the increased
radiation (Tevini and Teramura, 1989; Teramura et al., 1991).
4) Pollination and flowering
Pollen is well protected from UV-B radiation. Several in vitro studies
support the possibility of UV-B impacts on pollen germination; however, no in
vivo conformation of these results has been reported (Tevini and Teramura,
1989). UV-B radiation may indirectly influence pollination in some species by
detrimental effects on the pollinators and flowering.
Flowering was shown to be inhibited in some species by increased UV-B
radiation (Tevini and Teramura, 1989). In addition to reducing flower numbers,
it is suggested that the timing of floral presentation may be altered by
changes in the UV radiation flux. Advancing or delaying flower emergence may
disrupt the timing of the pollination cycle (Hale, 1993).
5) Yield reduction
Studies of yield responses to enhanced UV-B radiation in agricultural
species have shown a very wide differential between species and cultivars
(Tevini and Teramura, 1989). At present, little is know about the causes of
the differentials among agricultural cultivars.
6) DNA and cellular damage
Ultraviolet radiation, especially at the shorter wavelengths, is known
to damage DNA as well as physiological processes (Stapleton, 1992). UV damage
to DNA could be the cause of many of the other observed effects. In addition,
UV damage to cell membranes, chloroplasts and its functions, protein
destruction, and hormone inactivation may also alter a plant's biological
functions. The impact of UV radiation may result from an increase in energy
across the spectrum or, an increase in energy within a specific waveband, or
both (Stapleton, 1992). Plants have several mechanisms by which to response to
damage by normal UV radiation levels, but little is yet know concerning their
ability to respond to higher, sustained levels of UV-B.
7) Susceptibility to disease, environmental stress and pollution
Preliminary research indicates that exposure to a UV-B dose prior to
inoculation with disease led to greater disease development in cucumber
cultivars including a disease-resistant variety (Teramura at al., 1991). The
study found that the effects of the irradiation varied according to the timing
of the exposure and the tissue age. Younger tissue seems most affected.
Carrying this finding further suggests that the most critical stage for
negative impact may be in the spring when young tissue is most prevalent. This
is also the time of peak ozone depletion in the higher latitudes.
Exposure to enhanced UV-B radiation has also been shown to cause
increased impacts of air and soil pollutants and stresses induced by soil
water and mineral deficiencies (Tevini and Teramura, 1989, Teramura et al.,
1991). For example,most water-stressed plants irradiated with enhanced levels
of UV-B lost their ability to close stomata (thus reducing water loss) while
those under normal light conditions displayed expected stomatal behaviour
(Tevini and Teramura, 1989).
Plants exposed to additional UV-B radiation have shown enhanced adverse
effects when toxic pollutants such as heavy metals are present (Teramura et
al., 1991).
UV Impacts on Agricultural Crops
Much of the research concerning the impacts of UV radiation on
terrestrial vegetation has come as a result of studies on agricultural crop
species. However, because of the importance of agriculture to the human
condition, a few specific comments are presented.
Dr. Malcom Whitecross of the Australian State University has reported
that a 10% increase in UV-B radiation early in the growing season (the prime
time for high-latitude ozone depletion) can cause stunting of growth in wheat,
rice, corn, soybeans and other crops, a set-back from which the crop will not
likely recover (CBC, 1992).
Dr. Beverly Hale of the University of Guelph in Ontario feels many food
crops are at risk (Hale, 1993). Her preliminary research indicates that
elevated UV-B can initiate far-reaching changes in plants including size,
height, shape, rate of growth and productivity. Internal chemical changes in
the composition of proteins, carbohydrates and amino acids may have a
substantial impact on their nutritional content. She feels that research must
focus on the identification and development of UV-B tolerable varieties
(Personal communication, 1993).
UV Impacts on Forestry
Research on trees and forests is limited but points to major impacts on
trees and, by extrapolation, on forests. The work of Sullivan and Teramura
(1988, 1991) indicates that increased UV-B levels reduced photosynthesis and
stunted growth in species of pine. The studies of DeLucia et al. (1991, 1992)
showed that UV-B penetration into two species of subalpine conifers was
deepest in the youngest needles. This result has greater implications than may
be first evident. Conifers rely on a wide span of needle ages for their
seasonal carbon gain. Depending on the species, individual trees may retain
foliage for five to twenty years. Thus, although damage may only occur in the
early life of the needles, the damage may have impacts lasting several decades
if the tree is able to survive.
Although UV-B penetration is reduced in older needles, they may still
accumulate large lifetime doses of radiation (DeLucia et al., 1991, 1992). The
impacts of such dosages have not yet been evaluated. Trees in fairly open
subalpine forests are particularly vulnerable since they will receive
radiation from all directions including reflected radiation from sky, rock,
snow and water. Similar exposures can be experienced by trees along the edge
of clearings and within clear-cuts.
Seedlings have been shown to be the most susceptible to UV-B damage
(Sullivan and Teramura, 1988, 1991). In a natural forest setting, a seedling
is often protected from direct sunlight for a portion of the day by the
surrounding forest. However, in a clear-cut, this protection is missing, and
the seedlings are exposed to high-levels of direct and reflected UV-B
radiation. The resulting damage has serious consequences to the regeneration
of a healthy and sustainable tree yield in the future.
UV-B AND ANIMAL HEALTH
Comparatively little is known concerning the impacts of enhanced UV-B
radiation on wild terrestrial animals. This is in part due to the greater
mobility of animals in response to high levels of solar radiation and their
evolutionary adaptation to it (i.e., hair, shells, feathers, pigment and
leathery skin). However, avoidance responses have evolved over long periods of
time and generally are stimulated by a particular combination of visible light
intensity and temperature (Wayne, 1991). So long as UV-B and visible light
bear a constant intensity relationship, the avoidance response is effective.
However, depletion of the ozone layer changes the balance by enhancing the UV-
B portion of the spectrum without a compensatory increase in visible light.
The consequences of such a shift on animal health are unknown at present.
With the exception of eye cancer tumours in cattle and sheep, little or
no information is available on skin cancer, cataract formation and
immunosuppression for animals other than laboratory animals (SCOPE, 1992).
UV-B AND HUMAN HEALTH
The most well-known link between human health and exposure to UV
radiation is that of erythema or sunburn. However, skin cancer generally ranks
first on the list of UV impacts on human health in the minds of most people.
Recent research has expanded the list of negative impacts to include: eye
damage in the form of cataracts, age-related near-sightedness and damage to
the anterior lens capsule; other cancers such as cancer of the salivary gland,
and immunosuppression with impacts on both infectious disease and chemical-
sensitivities (Longstreth et al., 1991).
Erythema
The exposure of the human skin to sufficient quantities of shortwave
radiation will produce first a reddening of the skin (erythema) and ultimately
a burn. White skin is more prone to burning than black or brown skin. The fair
skin of those deriving from Northern European ancestry are the most vulnerable
to sun damage of the skin especially those receiving their exposure in the
tropical latitudes. Young children are under the greatest risk. Because of
their more transparent skin, infants should never be exposed to direct sun.
Both UV-A and UV-B cause sunburn. The degree of burn and rate at which
burning occurs is directly related to the intensity of solar UV radiation as
well as the skin type. For example, under solar UV intensities typical of
exposure to the noon-day sun in the tropics, a fair-skinned person would
typically burn in less than 15 minutes. At latitudes such as along the U.S.-
Canada border, minimum burning times are generally in excess of 17 to 18
minutes for even the fair-skinned. The thinning of the ozone layer over Canada
this year, however, has reduced burning times to as short as 14 minutes
according to Dr. Wayne Evans of Trent University (The Canadian Press, 1993b).
Excessive exposure can lead to 2nd or 3rd degree burns with the
attendant dangers of such burns in the short term. However, even minor burns
can have long-term consequences after the initial discomfort has abated. Many
researchers now feel that many skin cancers may be initiated as a result of
severe childhood burns (Longstreth et al., 1991).
Sunburn can be simply avoided by reducing exposure to the sun: avoid
being outdoors in the sun during the peak sun periods (10 a.m. to 4 p.m.) in
summer; wear long-sleeved shirts, long pants or skirt and a broad-brimmed hat,
use a sunscreen that blocks against both UV-A and UV-B. Avoiding the direct
sun does not always provide protection however. Reflected UV radiation off
clouds, buildings, and especially snow and water surfaces can increase
exposure. Even moderate overcast skies are not totally safe since as much as
half of the UV radiation may pass through a cloud layer. Indeed, UV exposure
during cloudy conditions or through reflection from snow and water may be more
damaging since the cooler conditions which often prevail during these
exposures give a false sense of security.
Skin and Other Cancers
The relation between exposure to the sun and several forms of skin
cancers has also been established for many years (Baker-Blocker et al., 1979).
UV-B radiation (wavelengths between 280 and 315 nm) is the most carcinogenic
portion of the solar spectrum reaching the earth's surface (Longstreth et al.,
1991). Non-melanoma skin cancers have been most commonly found in individuals
with outdoor occupations such as fishers and farmers. UV radiation has also
been demonstrated to enhance skin cancers which resulted from dermal contact
of chemicals. Recent research suggests that cancers afflicting the eyes, lips,
and salivary glands are also caused or induced by UV-B exposure (Longstreth et
al., 1991).
Unlike erythema which quickly occurs with excessive exposure to solar
radiation, skin cancers, both melanomas and non-melanomas only appear many
years later. It is now believed that a single acute burn, especially one
received during the early years of life, may initiate a cancers several
decades later (Garland et al., 1993). Long-term exposures at sub-erythemic
levels, however, may also result in skin cancers (Longstreth et al., 1991).
There are three types of skin cancers induced by UV radiation: basal
cell, squamous cell and melanoma. Basal cell and squamous cell are generally
classified as non-melanomas and account for 93% of all skin cancers (SCE,
1992). Basal and squamous cell cancers develop on exposed areas of the body
generally in response to UV-B. They are rarely fatal and easily cured if
treated.
Melanoma, while the rarest of the three forms, is the most deadly as it
spreads quickly to the blood, lymphatic system and other organs. Research
indicates that melanomas may be cause primarily by exposure to UV-A radiation
(Garland et al., 1993). Research suggests that melanoma is related to short,
intense exposure to sunburn-inducing sunlight, particularly in childhood (Noy
et al., 1990).
The most recent estimate of increases in non-melanomas resulting from
increased UV-B radiation suggest a 1% ozone depletion will result in an
increase in non-melanoma skin cancer of between 1.9% and 2.7%. In the United
States, this amounts to 11,500 additional cases per year (Longstreth et al.,
1991). A conservative estimate for world-wide cancer increases finds that a
10% decrease on ozone would result in 300,000 additional non-melanomas and
4,500 melanomas (Longstreth et al., 1991). Robin Marsh of the Australian Anti-
Cancer Society estimates that two of every three Australians will develop some
form of skin cancer in their lifetimes (CBC, 1992). In Queensland, Australia
the current skin cancer rate is the highest in the world.
The evidence for UV-B linkage with salivary gland cancer is still
circumstantial, being derived from co-associations between this cancer and
melanoma and lip cancers. Since the salivary gland is rarely, if ever, exposed
directly to UV-B radiation, these preliminary findings suggest a systemic
effect of UV-B (Longstreth et al., 1991). A possible link may be found in the
work on immune suppression.
Immune Suppression
The initial link between immune suppression and UV-B radiation resulted
from animal studies. However, recent studies on a number of viruses and human
subjects have confirmed the linkage between immune suppression and exposure to
UV-B radiation (Longstreth et al., 1991). De Fabo et al. (1990) have suggested
that a 1% decrease in ozone will lead to a 0.6% to 1% increase in the
biologically effective irradiance level for immune suppression. Their study
indicated that relatively low levels of sunlight activated immune suppression,
and these levels were easily obtainable over most of the populated regions of
the world. Human immune suppression has been shown to be independent of skin
pigmentation (SCOPE, 1992).
The impact of UV-B on human disease appears to work on at least three
levels. One is the increase in activation of viruses, the second is the
decrease in the immune system to respond to viral and bacterial infection, and
the third is the decrease in tolerance to chemical exposure.
In vitro studies have shown that exposure to UV-B increased the activity
of viruses such as herpes simplex, a variety of papilloma viruses, and HIV-1
(Longstreth et al., 1991; James, 1992). Increased activity of the herpes and
HIV viruses have been demonstrated in vivo (Longstreth et al., 1991). The
herpes/UV-B connection has also been demonstrated in human subjects (Rooney et
al., 1991). While it is clear that enhanced activation of HIV by UV-B is a
cause for concern, at present, no evidence as yet indicates that this will
result in an increase in human infection. Rather, the effect will likely
increase the severity of the disease (Longstreth et al., 1991).
Since UV-B is also know to damage DNA, we may also speculate the
increased UV-B may promote the development of new strains of existing viruses
and bacteria or the production of new strains injurious to humans. While no
specific studies in this area have been located, similar speculation has
suggested a link to the origin of major epidemics following large volcanic
eruptions (Gore, 1992). Recent mysterious diseases and new, more virulent,
strains of old diseases such as cholera and tuberculosis add fuel to this
hypothesis.
Cooper et al., (1992) found that even levels of UV exposure below
clinically detectible levels (i.e., no visible erythema) can impair immune
responsiveness, and a localized sunburn can alter T-cell responses at distant,
unirradiated sites. (T-cells are produced by the lymphatic system and
activated by the thymus to provide cellular immunity in response to antigens
(Tortora and Anagnostakos, 1990)). Depression of T cell response could then
result in tolerance rather than rejection of UV-induced carcinoma cells. They
also found that virtually all individuals with skin types I - III are
susceptible to the immunosuppression effects of UV, the impact is dose
sensitive, and skin absorbing subclinically detectable levels of UV (<0.75
MEDS) is affected (Cooper et al., 1992). The last finding makes it very
difficult for individuals to gauge a safe level of exposure. Brief midday
summer or high altitude exposures can easily exceed 0.75 MEDS. (An acute
weekend or vacation sunburn which results in slight peeling results from a
dosage of about 4 MEDS.)
Ocular damage
Exposure to UV radiation has been associated with damage to the cornea,
retina and lens of the eye. Ocular damage known or suspected to be caused by
UV radiation ranges from acute "sunblindness" to chronic damage such as
cataracts, tumours, presbyopia and deformation of the anterior lens capsule
((Longstreth et al., 1991). (Presbyopia is the loss of the ability of the eye
to accommodate changes in focal length and commonly requires the use of
reading glasses to view nearby objects.)
The effects of acute exposure to UV-B on the cornea and conjunctiva of
the eye are well known from occupational injury due to welder's arc flash. The
patient generally recovers within days, apparently without permanent effect
(Chou, 1992). Similar injuries have been seen in intense sunlight exposures on
fresh snow, sand and water surfaces as "sunblindness" or "snowblindness".
Very young children and individuals without lens may be very susceptible
to UV damage of the retina since their ocular media are transparent to UV
radiation (Chou, 1992).
The principal form of lens damage linked to UV radiation is cataract.
The relationship between sunlight exposure and all forms of cataracts has now
been show (Longstreth et al., 1991). The recent literature indicates that
cataract development may be related to the loss of the orderly arrangement of
densely packed lens crystalline which is required to maintain lens
transparency. Ozone depletion of 1% is estimated to result in a 0.6% to 0.8%
increase in cataract formation.
UV Protection
Many of the public health campaigns (e.g., Canadian Cancer Society's
Sunsense Programme, Environment Canada, B.C. Ministry of Health) suggest
several measures of protection against adverse impacts of UV radiation. These
are:
- Avoid being outdoors during peak sun hours (10 a.m. to 3 p.m.);
- Wear long-sleeved shirts, long pants or skirt, and a wide-brimmed
hat;
- Wear sun glasses that screen out UV-A and UV-B; and
- Use sunscreen which contains block against both UV-A and UV-B on
unprotected skin.
The issue of sunscreens has become a growing issue. According to Dr.
Daniel Saunders, head of the Dermatology Department at the University of
Toronto, people are too eager to place their trust in various products that
claim to block ultraviolet rays (Cross, 1993). Many products claim to block
ultraviolet rays but few provide full spectrum protection and some no
protection at all reports Dr. Yvon Deslauriers of Health and Welfare Canada
(Munro, 1993).
Research by Garland et al., (1993) notes the rising trend in melanoma
continuing since the 1970s and 1980s when sunscreens with high sun protection
factors became widely used. Commonly used chemical sunscreens block UV-B but
are transparent to UV-A. Garland et al. hypothesize that because these
sunscreens prevent erythema and sunburn and inhibit accommodation of the skin
to sunlight, their use may actually increase the risk of melanoma since the
deeper penetrating UV-A radiation is now able to reach the melanocytes, the
cells that turn cancerous in melanoma.
Not all spectacle or tinted lenses offer eye protection from UV
radiation. Spectacle crown glass lenses provide no protection from UV longer
than 290 nm, most of the UV-B and all the UV-A bands (Chou, 1992). Sunglass
lenses which only reduce the visible spectrum and do not block the UV bands
may actually cause more damage. Non-UV-block sun lenses cause the pupils to
dilate in response to the lowered visible light levels thus allowing more UV
radiation into the eye which may damage the delicate membranes of the retina.
In areas with high reflected sunlight such as snow or water, a wrap-around
frame with sideshields is the ideal frame design (Chou, 1992).
FACTORS AFFECTING STRATOSPHERIC OZONE CONCENTRATIONS
In its natural state, the stratospheric ozone layer remains within a
limited range and varies with the solar seasons. Natural variations in
stratospheric concentration also result from the longer term variations in
solar radiation flux and alterations in the atmosphere such as the Quasi
Biennial Oscillation. The constant production of ozone by solar radiation is
balanced by removal of ozone by other photochemical and chemical reactions.
This process has been termed the "Leaky Bucket" Analogy by Stolarski (1982).
So long as the production replenishes the ozone "leaking" from the
stratospheric reservoir, the ozone concentration remains within acceptable
limits for life on earth.
Major departures from "normal" are the result of natural factors such as
volcanic eruptions or large meteor/comet impacts and anthropogenic influences
such as emissions from high flying aircraft or releases of chlorine compounds
such as the CFCs. These factors cause destruction of ozone through chemical
reactions -- essentially punching another hole in the ozone bucket -- which
cannot be fully compensated by solar production. As a result, stratospheric
ozone concentrations begin to decline.
The impact of long-lived chlorine compounds, CFCs and related species,
on the stratospheric ozone layer was first recognized by Molina and Rowland
(1974). The stability of the CFC molecule allows it to rise high into the
stratosphere before solar radiation is strong enough to tear the molecule
apart. Once freed from the CFC matrix, chlorine atoms were able to destroy
ozone. The resulting photochemical process eventually frees the chlorine atom
thus allowing it to continue its destruction. It has been estimated that each
chlorine atom reaching the ozone layer will destroy over a million ozone
molecules during its atmospheric lifetime (Hilborn and Still, 1990).
The concern raised by the studies of Rowland and Molina and others
resulted in a 1987 international conference held in Montreal to discuss the
issue. The Montreal Protocol to reduce and eventually eliminate CFC and other
ozone-depleting emissions arose from that conference. As the rate of ozone
depletion rose, the international community further agreed in London in 1990
to accelerate the reduction in the emission of ozone-depleting substances over
the timetable set out in the Montreal Protocol. Recent measurements of the
atmospheric CFC content indicates that the rate of CFC build-up has decreased
from 3% per annum to 1% (Associate Press, 1993).
While the decrease in the rate of CFC accumulation is good news, it is
tempered by the bad news that 1992 saw the lowest ozone levels ever measured,
and 1993 would likely be lower still (Associated Press, 1993). In addition,
many of the CFC compounds have a long residence time in the atmosphere and
will likely to continue destroying ozone well into the next century.
THE NEED FOR ACTION NOW
The international community has already taken major steps toward the
reduction and elimination of emissions of ozone-depleting substances. While
these actions are among the most forward and proactive international
environmental agreements ever enacted, we are left with the fact that, even if
all emissions of ozone-depleting substances were eliminated today, we would
still be left with enough released chemicals to further deplete the ozone
layer well into the next century. Therefore, we must do more than just call
for a further increase in the rate of emission reduction. We must move quickly
to protect agriculture and human health, the two areas of society most
vulnerable to enhanced ultraviolet radiation resulting from ozone depletion as
well as he delicate balance of the biosphere. While the sword of human impacts
on the ozone layer hangs precariously over our heads, the eruption of Mt.
Pinatubo reminds us that a second sword hangs just above the first. Part of
the current reduction in ozone can be attributed to the 1991 Pinatubo
eruption, whose dust and gases are only now being cleansed from the
atmosphere. However, volcanologists have warned that Mayon, a nearby volcano
which has had several eruptions over the past year, has the potential for an
explosive eruption ten times that of Pinatubo. Such an eruption would have
major consequences for both the ozone layer and short-term weather and
climate.
The ever-growing human population and the effects of weather and climate
variability are already placing a strain on agricultural production and
fisheries. Therefore, it is essential that research be conducted to determine
which crops or which cultivars are the most resistant to increased UV-B
radiation. This knowledge must then be quickly conveyed to seed producers and
farmers so that the most resistant crops can be planted. Increased breeding
programs must also be undertaken to produce UV-B resistant crops. Research
must also be conducted on animal stocks to determine the impacts of enhanced
UV-B radiation.
Action must also be taken now to alter human lifestyles to cope with
increased UV-B radiation. These actions include alterations of lifestyles,
public education, warning systems, and provision of additional sun-shading.
Some of these changes will have major economic implications but the potential
social burden of increased illness and injury may well exceed the burden of
short-term economic disruptions.
Alterations of Lifestyle
Much of the developed world is of the opinion that a tanned body is a
healthy body, and, to achieve this look, we spend hours baking in the midday
sun. This fetish is most evident in Australia where a fair-skinned people
living in a tropical and subtropical environment, the ultimate risk
combination, have made exposure of near-naked bodies to the sun a part of
their culture. As a result, two thirds of the population are expected to
develop some form of sun-related cancer in their lifetimes (Noy et al., 1990).
While moderate exposure to the sun has many healthful benefits, we generally
far exceed prudent limits in our desire for the socially acceptable skin
colour.
Therefore, the prime required alteration of lifestyle would limit
exposure to direct and reflected solar radiation. Avoiding peak sun hours is
the best protection, but for those who cannot or will not seek shelter during
these hours, protection through additional clothing, long-sleeved shirts, long
pants and skirts and wide-brimmed hats of adequate thickness should be worn.
Eyes should be protected by wearing UV-absorbent lenses, preferably with side
protection.
Another area where alterations in lifestyle must be made is in the
setting of outdoor activity schedules such as school recesses and outdoor
sports. In Australia, New Zealand and Chile, school and recreational
activities have been altered to avoid the peak sun periods. For example,
soccer games have been scheduled for early morning or evening to avoid the
mid-day sun.
Policies and codes of practice must also be developed for outdoor
workers who are under above average risk. British Columbia, for example, has
no provision in its occupational work standards dealing with exposure to solar
radiation. Among the actions which may be taken are changes in required dress
during the high sun season. An example would be to replace baseball cap
headgear with broad-brimmed hats.
Public Education
Altering the human lifestyle is nearly impossible to legislate
effectively. Therefore, the required changes in lifestyle must be presented to
the population in the form of public education programs. Much resistance will
be encountered not only from the populace but also from those with vested
interests in the current lifestyle. Environmental education has traditionally
had to overcome obstacles placed by the fatalists on one extreme and the
disbelievers on the other. The fatalists contend that no matter what is done,
we are doomed so therefore why be concerned. The disbelievers, on the other
hand, put their head in the sand believing that any issue if ignored will go
away. (As my former neighbour called it, the "Crisis of the Month".)
Public education must be directed toward two issues: 1) the need for
reduction in the use of CFC or other ozone-depleting substances; and 2) the
need for changing lifestyles in response to increasing UV radiation. The
former has received the most attention as governments push toward phase out of
ozone-depleting chemicals. The latter has had less attention in Canada and the
United States than in Australia or New Zealand where the crisis is most at
hand. However, the need for lifestyle changes should be given at least equal
attention by government, educators, the media, and industry because, as the
subtitle of this talk indicates, the need for action is now.
Both Australia and New Zealand have promoted a protection campaign aimed
at children called "Slip, Slap, Slop" -- slip on a shirt, slap on a hat and
slop on sunscreen.
UV Warning Systems
The media have kept the issue of ozone depletion in the news for several
years now. In order to convey the immediacy of the issue, however, the public
must be kept informed as to how depletion affects everyday life. Environment
Canada has taken the lead in issuing warnings to the public of daily
variations in the UV radiation reaching the Earth's surface via the UV Index
(O'Toole, 1992). The daily UV Index forecast has been incorporated into the
regular government weather forecasts as presented via the newspapers,
television and radio and as a regular feature on The Weather Network, a
privately owned cable TV channel.
The UV Index provides a forecast of the maximum expected UV intensity
for the coming day should the sky be clear. The Index was developed by the
Atmospheric Environment Service (AES) in consultation with several health
organizations and members of the medical community. Although the Index is
intended to warn the public of all potential dangers of UV exposure, it has
been developed using human erythema as the physiological effect. Typical
tropical noon values of the Index are about 10 with an expected maximum of 12.
Under such radiation, a fair-skinned individual could burn in 15 minutes or
less of exposure.
The Weather Network uses the AES forecast of maximum UV intensity and
fits a daily radiation cycle to the maximum. The curve is presented to the
public along with the expected time to burn twice each hour (Ian Miller, The
Weather Network, 1993, pers. comm.). Realtime measurements of UV radiation
updated each hour are plotted along the expected radiation curve. While
variations from the curve may be large in very cloudy weather, the clear-sky
measurements follow the forecast curve quite well.
The Canada UV Index has been structured to be globally applicable and
has recently been adopted by the World Meteorological Organization as a world-
wide measure of UV radiation exposure (Canadian Press, 1993a).
Other warning programs have been adopted. In the United States, several
local television stations have added UV forecasts and warnings to their
broadcasts, but the practice is not yet widespread. In areas under the
Antarctic ozone hole such as Punta Arenas, Chile, New Zealand and Australia,
warnings are also issued. The frequency, method of delivery and source of
information for these warnings are not known to the author at this time. Arlen
Kruger (1993) of NASA stated in a recent paper that Canada was the only
country in the world providing a nationally released UV forecast and warning.
Site-specific warning programs should also provide information is users
of facilities such as beaches and ski hills. News reports indicated that some
local B.C. ski resorts had installed UV monitors last winter which informed
skiers of the current level of radiation.
Provision of Sunshading
The provision of shading to allow outdoor activities without long
exposure to UV radiation is an area where government, community organizations,
the private sector and individuals can all take action.
Many school yards completely lack areas where direct sun can be avoided.
New housing tracts generally suffer a similar problem where existing
vegetation is bulldozed and then re-landscaped with trees that will take
decades to mature into proper shade.
Architects have long been required to consider the negative aspects of
shading in their building designs. The time is perhaps right to consider the
positive aspects of shading as well.
AN EXAMPLE OF A PROACTIVE UV RADIATION PROTECTION PLAN
As the country with the most pressing concerns over UV exposure,
Australia has taken a number of action steps. Several of these have been
summarized in A Comprehensive Guide to Becoming A Sunsmart Council (Noy et
al., 1990) published by the Anti-Cancer Council of Victoria (Australia). This
document has received the endorsement of the Municipal Association of Victoria
and the Australian Institute of Environmental Health. The document has
designed to provide local government authorities with a framework for tackling
the problem of UV-induced skin cancer amongst residents.
The major areas for consideration in the Guide include:
Parks, gardens and other publicly owned facilities such as sports
fields and swimming pools;
Policy and work practices related to staff who work outdoors;
Publicly funded programs such as daycare, holiday programs and health
services.
Recommendations to be implemented in these areas under the categories of
education, clothing, sunscreens, shade, schedules and policy guidelines
included:
Erecting signs warning of children's risk to overexposure to the sun;
Educating parents through health education programs about the dangers
of childhood exposure;
Providing educational materials in public places;
Encouraging employees to protect themselves and thereby serve as role
models;
Ensuring sufficient shade for all users;
Selling sun-protective clothing and broad-spectrum sunscreen on site;
Allowing users to leave at midday and return later without extra
charge;
Scheduling outdoor sporting competitions for early morning or late
afternoon hours;
Incorporation of shade provisions in any new development plans;
Erecting, where practical, temporary shade structures for short-term
events;
Changing any rules which prevent people from being adequately
protected.
As of the 1990 printing of the Guide, a number of municipalities had
adopted all or portions of the recommended strategy. A few examples are
provided below.
The Shire of Myrtlewood erected a protective roof of 60-75% shade cloth
over their toddlers pool and surrounding concrete.
The City of Sandringham planted established shade trees in parks and
playgrounds with some trees becoming an extension of the play equipment.
The City of Bendigo's Occupational Health and Safety Committee
recommended a policy on sun protection for outdoor workers which included
provision of sunscreen, sunglasses and a wide-brimmed hat to employees.
The City of Warrnambool altered the schedule for beach cleaning staff
away from midday exposure. During midday hours they were transferred to a more
shady playground environment.
CONCLUSIONS
The reduction of the planet's protective ozone layer has reached
dangerous levels and continued reductions seem inevitable. The dangers to
which this loss of ozone exposes humankind and the biosphere are frightening
in their consequences. Even the most extreme program to eliminate emissions
of ozone destroying chemicals, however, will have no impact on this decline
for many decades. We must therefore take the appropriate steps to reduce the
impacts of increased ultraviolet radiation while the emissions of ozone-
depleting substances are eliminated. The need for action is now.
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Keith C. Heidorn
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