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THE UVB IMPACTS REPORTER: VOLUME 3: SAMPLE ISSUE
Welcome to the Internet edition of THE UVB IMPACTS REPORTER. The Reporter brings you the latest information on the impacts of ultraviolet radiation and ozone depletion on the environment, plants, animals, human health and welfare and climate.
This is an abridged version of The UVB Impacts Reporter. The full text of The Reporter is available in hardcopy form for $55US/year in North America and $65US elsewhere (the electronic edition contains only excerpts). Those interested in receiving the complete Reporter, published bi-monthly, should see the message at the end of this text.
OZONE LOSS AND BIOLOGICALLY EFFECTIVE DOSAGES OF UV-B
Dr Steven A. Lloyd, of Johns Hopkins University believes we may be underestimating the impact of ozone layer depletion on increases in UV-B radiation incident at the Earth's surface. Part of this underestimation has resulted from the assumption that the biologically effective dosage (BED) of UV-B radiation on DNA is linearly related to the percentage of ozone column thickness loss.
In his pioneering work on the relationship between ozone depletion and biological responses in 1974, Richard B. Setlow concluded that a 1 percent decrease in atmospheric ozone resulted in a 2 percent increase in the BED. Lloyd, however, points out that "since that time both the popular press and considerable academic literature have (naively) generalized this result, concluding that the percentage increase in BED is simply twice the percentage depletion. While this 2:1 "rule of thumb" ratio is reasonably accurate for relatively small ozone losses, it is seriously in error for larger ozone losses..."
Using mathematical models developed in association with Donald E. Anderson Jr. of The Johns Hopkins University and Edward S. Im of Harvard University, Lloyd calculated that the percentage increase of BED with percentage ozone loss was linear up to about 5 percent ozone loss. At larger ozone losses, however, dosage increased exponentially. For example, a 10 percent ozone reduction results in a 24 percent increase in BED while a 30 percent loss corresponded to a doubling and a 50 percent loss a quadrupling of BED.
In light of the large decreases in the ozone layer observed annually over the Antarctic, and in the Arctic in 1993, such non-linearities have major consequences to the biosphere and human health which should not be ignored.
Lloyd's calculations also countered the belief that small decreases in the ozone layer above the equator were insignificant to UV-B dosages. His results showed that a small ozone loss at the equator provides as much additional biologically-effective UV-B as a considerably larger ozone loss at higher latitudes. For example, a 10 percent loss at the equator would produce the same annual increase in the biologically accumulated dosage of UV-B as a 30 percent loss at 50oN latitude.
UV-B radiation has many impacts on human health including immune system suppression, sunburn, skin cancer, photoaging of the skin, and eye injury. "In addition, patients taking photosensitising drugs such as tricyclic antidepressants, barbiturates, oestrogen, griseofulvin, isotretinoin, 8-methoxypsoralen, oral contraceptives, phenothiazines, sulphonamides, sulphonylureas, tetracyclines and thiazide diuretics can have an enhanced susceptibility to sunburn and blistering, and potentially also to non-melanoma skin cancers, and should be advised to exercise caution in their exposure to sunlight," warns Lloyd.
With the great concern for human exposure to UV radiation, medical and public health experts are advising people to avoid direct exposure to the sun. One of the recommended ways of sun avoidance is to "Slip on a shirt". Several companies offer "sun-protection" clothing.
Just how much can clothing protect us from UV radiation? A research team from the University of Alberta led by Dr. L. Capjack has recently summarized the current state of knowledge as to just how protective clothing is.
Obviously, heavy clothing such as leather and thick, dense cloth offer complete protection from solar UV. Such clothing, however, is impractical for the warm to hot conditions of spring and summer when most UV exposure occurs. Thus, to be effective, clothing worn to protect against the sun must also be comfortable for the prevailing weather conditions. This is especially important for children who are most at risk.
Some clothing manufacturers are quoting a sun protection factor (SPF) for clothing. Are these values comparable to the SPF factors used to rate sunscreen?
M. Pallthorpe, a textile scientist from Australia, suggests that a fabric's cover (the percent of area covered by warp and filling yarns) should be the primary factor in expressing a fabric's protectiveness from UV radiation.
Assuming that the yarns of the fabric are completely opaque, and that light only penetrates the small holes or spaces between the yarns, the transmission of UV radiation should be related to the cover factor of the fabric. Mathematically this can be expressed as:
percent UV transmission = 100 - ( percent cover factor);
SPF = 100 /( percent UV transmission).
An ideal fabric with a cover factor of 75, therefore, has an SPF of 4.
How the fabric is made has a major impact on its cover factor. Woven fabrics have higher cover factors than knit fabrics due to the more frequent interlacement of yarns. Holes or spaces are generally larger in a knit than a weave. Most light-weight summer wear has an open structure and thus a low cover factor.
Pallthorpe also noted that an ideal fabric with opaque yarns should have an increased cover factor with increasing weight of yarn per unit area. Such fabrics would have smaller holes between yarns.
Dry finishes should also alter the cover factor. Any finish which causes the yarns to shorten and thus the fabric to shrink, should also close the spaces between yarns.
Since fabrics and yarns are not ideal, the theoretical SPF is an upper limit. However, any fabric variable which decrease UV transmission would increase its protectiveness. For example, dyes and pigments which absorb UV would increase its SPF value. In contrast, bleaching and moisture content reduce the potential SPF.
If a fabric is wet, the water present in the fabric spaces may reduce the scattering of UV light and thus increase its transmission through the fabric.
The University of Alberta research team found no standardized method for measuring the UV transmission through textiles. They urged that testing be done as a function of wavelength and in relation to the relative erythemal response of the skin to the specific wavelengths. From this information and site-specific measurements of the solar UV spectrum, the SPF factor of the textile in question can be determined.
They further suggest that a standard SPF labelling system be initiated for children's wear and linked with an education program for consumers.
With the approach of Spring in the Northern Hemisphere, reports from the World Meteorological Organization (WMO) and the French Space Agency (CNES) warned of a new and significant threat to the ozone layer over the Arctic and high latitude regions after a combination of abnormally cold temperatures in the stratosphere and a build-up of pollutants.
After record low ozone levels and an extremely large ozone hole in Antarctica last September, the WMO announced February 14th that unusually low ozone values have persisted during most of January and the first half of February over the northern middle latitudes, particularly over Siberia and westward to Europe.
Dr Rumen Bojkov, Special Advisor to the Secretary-General of WMO, told journalists that ozone deficiencies during the second half of January reached 25 percent below normal over Siberia and persisted during the first half of February. During several weeks, record low ozone levels of about 250-270 Dobson Units (DU) were reported. The long-term normal monthly mean values for February are 470 DU in Eastern Siberia and 410 DU east of the Ural Mountains in Western Siberia.
A 10 percent deficiency was observed for the entire month of January over the 40-60oN latitude belt. At the same time over Europe, the deficiency from the long-term mean exceeded 10 to 12 per cent, close to the statistical limit of what is considered a normal fluctuation. Over North America, the deficiency has been 5 to 10 percent although there were also a few episodes with 20 percent depletion.
The Northern Hemisphere winter started in December 1994 with 5 to 10 per cent ozone deficiencies over the mid latitudes which is what was expected from mathematical models predicting a continuation of the ozone decline that started in the 1970s. However, during the second half of January and first half of February, the ozone deficiency was greater than 20 percent for a number of days over Europe and reached 35 percent depletion over Siberia.
Such low ozone values were not reached in these areas during the record setting January-February 1993. "At that time there was considerable speculation that the low ozone was due mainly to the ozone destruction caused by aerosols from the Mount Pinatubo eruption in 1991; however, presently there are no remnants from volcanic aerosols left in the stratosphere,"said Dr Bojkov. "But with the availability of chlorine oxide (ClO), a by-product of man-made chlorofluorocarbons (CFCs) transported from the Arctic to the sunlit areas of the 60-45oN belt over Europe and Siberia where the lower stratospheric temperatures are 8-l0C below normal, chemical ozone destruction is quite possible," he added.
The extremely low ozone thicknesses in the northern middle latitudes this winter are in part aggravated by the current westerly phase of the quasi-biennial oscillation (QBO) which is preventing the transport of ozone-rich air from the equatorial stratosphere to replace ozone-depleted air in the northern polar stratosphere. "Previous studies have shown that during this phase, the winter-spring ozone values in the northern middle and polar latitudes could be as much as 6-8 percent below long-term averages," continued Dr Bojkov. "However, now we have observed a 20 to 35 percent deficiency which could be attributed to chemical destruction."
"The conditions are all there in the region for a significant destruction of the [Arctic] ozone layer," warned Jean Pierre Pommereau of the French Space Agency (CNES). "Whether the current destruction of the ozone stops or continues depends on temperature changes in the stratosphere over the coming weeks."
Meteorologists report temperatures in the Arctic stratosphere fell to minus 89 degrees Celsius in January and February. In January, stratospheric polar clouds formed up to an altitude of 26 km according to Pommereau. He added that this year's exceptionally cold conditions made the situation in the Arctic very close to that of the Antarctic. Stratospheric polar clouds are believed to be necessary for major ozone depletion episodes in polar regions.
Near record low levels of ozone layer thicknesses have been observed by the Canadian Atmospheric Environment Service (AES) over Canada during February and early March. Average ozone levels during the period mid-February to mid-March ranged from 8.1 percent to 19.4 percent below normal over those five weeks. In March, all monitoring sites have recorded below normal thickness with most greater than 10 percent below normal. The levels are about the same as the average for this period in 1993, the worst year on record.
"Ozone levels usually vary widely from one region to another depending on weather, but currently the values are low right across the country, said Dr Jim Kerr, of AES. "There's more going on than something just related to the weather," he said. "The fact that they're all below [normal] is an indication that we're seeing somewhat less ozone this year."
ULTRAVIOLET RADIATION AND CARCINOGENESIS
The link between skin cancer and solar ultraviolet radiation (UVR) is one of the best known adverse health impacts of excessive exposure to the sun. A recent review of the cellular and molecular effects of UVA and UVB by the UK National Radiological Protection Board (Cridland and Saunders, 1994) concluded that there is now compelling evidence that ultraviolet radiation is a complete carcinogen. That is, UVR from the sun acts at all three of the major stages of carcinogenesis: initiation, promotion and progression.
UVR As an Initiating Agent
A cancer-initiating agent is an agent which acts by inducting mutations in specified genes involved in cellular regulation. In most cases, the agent acts either directly or indirectly in damaging DNA. The mutation of DNA by UVR may be increased by chemicals known as sensitisers which enhance the absorption of UVR by DNA. These may be natural components of the cell such as riboflavin, bilirubin, steroids and melanin, or chemicals coming from outside such as some dyes, drugs, cosmetics and sunscreens. Alternatively, UVR may alter a chemical into a photoexcited state which then mutates DNA.
The potential to disrupt the function of cells have been found in mutations of ras genes in non- melanoma skin cancers and some malignant melanomas. These genes are involved with the transmission of growth signals within cells. It is believed that mutations of the ras gene provides cells with a continuous growth signal. In addition, recent research by Ziegler et al. (1994) has shown that the tumour-suppressor gene p53 is a major target of solar UVR. The mutation of this gene by UVR has been found in human skin cancers, especially squamous cell melanoma.
UVR As a Promoting Agent
Promoting agents act to support the continued growth of tumours. It is believed that UVR promotes tumours through physiological actions of the body responding to skin damage from excessive UV exposure. Ziegler et al. (1995) have found that UVR can act as a promoting agent through the influence of differential selections occurring after the mutation of the p53 gene. Ultraviolet-damaged cells with a normal p53 will die as sunburned cells, while those with the mutated gene will likely survive and proliferate.
UVR As a Progression Agent
Progression agents support the continuation of the cycle of tumour growth. The progression of tumours occurs when premalignant cells in the first stages of carcinogenesis develop into malignant forms. UVR may act as a progression agent either through further genetic damage to DNA, through cellular responses which increase mutations in surrounding cells, or through immunosuppressive effects. By affecting the immune system, UVB can weaken the body's defense to the point it is helpless against tumour cells.
UV higher in New Zealand
Dunedin, 14 February 1995: Levels of ultraviolet radiation (UVR) are 50 percent higher in New Zealand than at similar latitudes in the Northern Hemisphere, according to Dr Richard McKenzie, a scientist from the New Zealand National Institute of Water and Atmospheric Research. In fact, UVR levels in mid-summer over New Zealand are about the same as those at the equator.
Recent monitoring showed that mid-latitude areas in Southern Hemisphere, including New Zealand, received 50 percent more summer UVR than locations at similar northern latitudes.
Some of the difference between the hemispheres was linked to Southern Hemisphere ozone depletion associated with the Antarctic Ozone Hole, McKenzie said. However, air pollution which absorbs much of the harmful ultraviolet-b rays in Northern Hemisphere accounts for much of the interhemisphere differences. Also, Earth is further from the Sun during the northern summer, reducing the intensity of sunlight, he said.
Scientists believed ozone depletion in the past 15 years has caused an increase of 8 percent to 10 percent in UVR reaching New Zealand. UVR levels are expected to rise another 2-3 percent, peaking about the turn of the century.
CONFERENCE PROCEEDINGS PUBLISHED
The Skies Above Foundation has published the Proceedings of the International Conference on Ozone Depletion and Ultraviolet Radiation: Preparing for the Impacts from the conference held 27-29 April 1994 in Victoria, BC Canada. The 300-page document (ISBN 1-896562-00-0) provides papers by all the Conference speakers plus an overview document and information on research published after the conference was held. The price is $35 US (plus $10 for shipping outside North America). Orders can be requested from: The Skies Above Foundation, 2701 Seaview Rd., Victoria, BC, Canada V8N 1K7; phone (604) 477-0555; fax (604) 472-0700.
Subscriptions to The UVB Impacts Reporter are $US55 annually (six issues) in North America and $US65 elsewhere. Inquiries and payments should be sent to The UVB Impacts Reporter, #302-3220 Quadra St., Victoria, BC, Canada V8X 1G3. _The UVB Impacts Reporter_ is written and edited by Keith C. Heidorn, PhD, ACM. 1995. Correspondence may be sent to #302-3220 Quadra St., Victoria, BC, Canada V8X 1G3: email - ub451@AT@freenet.victoria.bc.ca -- Keith C. Heidorn, PhD, ACM