Stratospheric Ozone Depletion and its Relationship to Skin Cancer DAVID M. AMRON, MD RONALD L. MOY, MD
SUN PROTECTION
Several articles have appeared in the literature regarding the impact of stratospheric ozone depletion on the prevalence of skin cancer due to increasing ultraviolet radiation. While it has been shown that UVB radiation is related to carcinogenesis of both melanoma and nonmelanoma skin cancer, it has not definitively been shown that stratospheric ozone depletion is translating into increased penetrating ultraviolet radiation. Estimates of increasing skin cancer in the future are dependent on calculations of UVB increases drawn from data on ozone depletion. The present article describes the history of stratospheric ozone depletion, how it may afect UVB penetration and skin cancer rates, and what is currently being done to prevent man's further detrimental efects on our atmosphere. J Dermatol Surg Oncol 1991;17:370- 372.
T
here exists some controversy regarding man's contribution toward damage of the atmosphere. The issue centers around whether or not we are to blame for stratospheric ozone depletion, and if so, whether this will eventually translate into an increase in skin cancer and other deleterious consequences for us. At present, there is no definite answer, only growing data pointing to the need for thoughtful action. This article represents an effort to educate as well as inspire others with regard to the significance that anthropogenic influences on our atmosphere might have for our lives and for the lives of future generations.
History In the early 1970s, prompted by increasing production and consumption of both aerosol and non-aerosol chloroFrom the Division of Dermatology, UCLA School of Medicine, V A Wesf Los Angeles Medical Cenfer, and U.C.LA. Ionsson Comprehensive Cancer Center, Los Angeles, California.
fluorocarbons (CFCs), concern began to stir regarding the fate of these compounds, which were being released into our atmosphere at a rate exceeding one billion pounds per year. Studies showed that virtually none of the released CFCs were being degraded in the atmosphere.' Research into the effects of man-made substances on the atmosphere began to be funded by many of the chemical manufacturing companies. In 1974, it was theorized by Molina and Rowland*that man-made CFCs would find their way into the stratosphere where they would be photolyzed by ultraviolet (UV) radiation, releasing chlorine atoms. These free chlorine atoms could then act as catalysts to decrease the ozone concentration, thus possibly increasing penetration of solar radiation in the UVB range. For the decade following this hypothesis, data continued to be gathered on CFC use and ozone depletion. In 1978, the United States banned the use of CFCs in aerosol sprays. However, nonaerosol uses have become increasingly popular. Science and industry felt there was still time to deal with the possibility of ozone depletion attributable to anthropogenic causes, as no consistent trend in ozone decrease had been seen, and global production of CFCs remained essentially constant during this period. In 1985, Farman et aP published data demonstrating a dramatic decrease in early spring ozone at the Halley Bay Station, Antarctica. This "Antarctic hole" was later confirmed by satellite measurements and appeared to span the entire continent. Soon after, NASA formed the International Ozone Trends Panel, which published their report in 1988.4The panel concluded that man-made chlorine species were primarily responsible for the ozone column decrease in the Antarctic region. Satellite data also indicated that ozone had decreased about 5% at all latitudes south of 60" since 1979 and that part of the decrease was probably because of dilution from the Antarctic hole. They also estimated an approximate 2-3% average global ozone decrease during the past 20 years.
0 1991 by Elsevier Science Publishing Co., lnc. 0148-0812/91/$3.50
J Dermatol Surg Oncol 1991;I 7:370 - 372
Additionally, a National Research Council study in 1989 demonstrated that the primary active form of chlorine, chlorine monoxide, had increased 100-fold over Antarctica during the ozone decrease period from what would have been expected from natural mechanisms alone.5 Theories on the mechanism of formation of this active chlorine, involving reactive nitrogen on stratospheric clouds, have been put forth.6
CFCs and Halons: Uses and Alternatives Chlorofluorocarbons were initially developed by industry in the 1930sand have become an extremely useful group of compounds commercially, primarily owing to their high chemical stability. Chlorofluorocarbonsare inflammable, nonexplosive, and essentially nontoxic. They are used extensively in refrigeration, insulation, fire extinguishers, and air conditioners because of their low vapor pressure thermal conductivity. They are compatible with many construction materials and are excellent solvents for use in cleaning electronicand mechanical components for communications equipment, computers, and navigation instruments for aircraft.' Halons (containing Bromine, eg, CBrF3), also extremely valuable commercial agents, have been in use since the 1950s. However, because of their physical properties, both halons and CFCs are difficult to break down. They usually pass through the troposphere (the first 10 km above sea level; 10-50 km is the stratosphere, where 80-90% of atmospheric ozone resides) unchanged until they are photolyzed by UV radiation in the stratosphere to form reactive chlorine and bromine byproducts, which can then deplete ozone through catalysis. Once in the atmosphere, the CFCs and halons can last unchanged for up to 100 years. Because of growing scientificevidence (especially concerning the Antarctic ozone hole), as well as increasing public awareness of the ozone depletion problem, it became clear that specific control measures to limit worldwide production and consumption of CFCs and halons were needed. After much negotiating and compromising, the Montr6al Protocol on Substances that Deplete the Ozone Layer was signed in September 1987.'* Currently, the protocol has been ratified by over 50 countries and took effect on January 1, 1989. The main man-made substances that the protocol initially focused on were the five major CFCs (CFC-11, -12, -113, -114, and -115) and halons 1211 and 1301. While recognizing the need for immediate action with regard to these chemicals, negotiators also realized the importanceof achieving a smooth economic transition, as the commercialization of potential substitutes was still years away.
AMRON AND MOY OZONE DEPLETION/SKIN CANCER
371
The development and use of acceptable alternative compounds is a key factor in the plan to phase out CFC and halon use. At present, hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are the most promising substitutes. Because of significantly lower levels of chlorine than CFCs (HFCs contain no chlorine), and because they contain hydrogen to allow for tropospheric decomposition, both the ozone-depletingpotential and the atmospheric lifetimes of these compounds are drasticallyreduced. Dupont (the worlds largest CFC producer) estimates that about 40% of the CFC demand will be met by these substitutes and another 32% will probably be met by not-in-kind (non-fluorocarbon)substitutes by the year 2000.
Penetrating Ultraviolet Radiation Ultraviolet radiation from the sun is divided into three wavebands, UVC (200-280 nm), UVB (280-320 nm), and UVA (320-400 nm).9Penetration of UVA waves are hardly affected by ozone. UVC waves are virtually eliminated by ozone, but it is the wavelengths in the UVB region that are most sensitive to variations in the atmospheric ozone concentration. It has been demonstrated that the most biologically effective wavelength for producing erythema of Caucasian skin is 297 nm, right in the middle of the UVB waveband.'* Many have tried to translate the ozone depletion into increases in UV radiation and skin cancer rates. It has been calculated using current available data for ozone depletion that the annual UV dose for the Northern Hemisphere has increased anywhere from 0.5 - 3.1%, depending on latitude." The US. Environmental Protection Agency has also estimated that for each 1%reduction in ozone concentration, there will be a concommitant 2% increase in UVB radiation.12In 1983, Rundel and Nachtwey13projected that by even the most favorable scenario, the incidence of non-melanoma skin cancer will increase by 5% by the year 2300, and with the least favorable scenario the incidence of skin cancer will double. However, surface measurements of solar radiation during the period 1974-1985 for latitudes between 30" and 50" N (includes the United States) failed to show increases in the UVB spectrum. Scotto et all4 have suggested that climatic, meteorologic, and environmental factors in the troposphere might be acting to diffuse solar energy, and thus reduce the amount of UVB radiation reaching us. Furthermore, although there appears to be a decrease in the stratospheric ozone column, there has been a 1- 2% increase in tropospheric ozone concentrations owing to man-made pollution, and this might also be compensating for the stratospheric decrease. This increase in tropospheric ozone may partly compensate for
372 Ah4RON AND MOY
the decrease in stratospheric ozone, thus helping to minimize the potential increase in penetrating ultraviolet radiati011.I~
Conclusion The incidence of both melanoma and non-melanoma skin cancer is increasing in the United States, and it is now becoming clear that they are both related to the effects of UVB radiation. Basal and squamous cell carcinomas appear to be related to chronic UV exposure.16For cutaneous melanoma (excluding lentigo maligna melanoma, which seems to be connected to chronic sun exposure), the contribution of damaging UVB radiation has been more difficult to elucidate. It now appears that periodic bursts of sunlight leading to severe sunburn is a causative factor in the development of these melanoma^.",'^ Animal studies and in vitro models also support the role of UVB radiation in the induction of melanoma carcinogeneS~S.~ However, what is still unclear is whether the recently discovered stratospheric ozone depletion, which is likely owing, at least in part, to man, is affecting the penetration of damaging solar radiation. It is unlikely that the recent increase in skin cancers can be solely attributed to the ozone depletion. The ozone decrease is probably too recent to account for trends that began many decades However, it may contribute to an increased incidence of skin cancer in the future. The ozone depletion issue is an extremely complex and controversial one. Continuing research into man’s detrimental effects on the atmosphere needs to be pursued. How this generation deals with the ozone depletion problem will likely affect the incidence of skin cancer for future generations.
Acknowledgments. This work was supported in part by the Dermatology Foundation Research Fellowship sponsored by Herbert Laboratories.
References 1. Lovelock JE. Atmospheric fluorine-chlorine compounds as
indicators of air movements. Nature 1971;230:379. 2. Molina MJ, Rowland FS. Stratospheric sink for chlorofluoromethanes-chlorine atomic-catalyzed destruction of ozone. Nature 1974;249:810-12.
Dermntol Surg Oncol 1991;17:370- 372 3. Farman JC, Gardiner BG, Shanklin JD. Large losses of total ozone in antarctica reveal seasonal CIOx/NOx interaction. Nature 1985;315:207-10. 4. Watson RT, Prather MJ, Kurylo MJ. Present state of knowledge of the upper atmosphere 1988: An assessment report. NASA: Greenbelt, MD; Reference Publication 1208,1988. 5. Anderson JG. Ozone depletion, greenhouses gases and climate change. National Research Council. Washington, DC: National Academy Press, 1989:56-65. 6. Jackman CH. Stratospheric ozone change. Environ Sci Technol 1989;23:1329- 32. 7. McFarland M. Chlorofluorocarbonsand ozone. Environ Sci Technol 1989;23(10):1203-07. 8. Koehler J, Hajost SA. The Montr6al protocol: A dynamic agreement for protecting the ozone layer. Ambio 1990;19:82- 86. 9. Kripke ML, Pitcher H, Longstreth JD. Potential carcinogenic impacts of stratospheric ozone depletion. Environ Carcin Revs (J Envir Sci Hlth) 1989;C7(1):53- 74. 10. Koller LR. Ultraviolet radiation. 2nd ed. New York John Wiley and Sons, 1965. 11. Dahlback A, Henriksen T, Larsen SHH, Stamnes K. Biological UV-doses and the effect of an ozone layer depletion. Photochem Photobiol 1989;49:621-25. 12. Hoffman JS. An assessment of the risks of stratospheric modification. US Environmental Protection Agency, March 1987. 13. Rundel RD, Nachtwey DS. Projections of increased nonmelanoma skin cancer incidence due to ozone depletion. Photochem Photobiol 1983;38:577-91. 14. Scotto J, Cotton G, Urbach F, Berger D, Fears T. Biologically effective ultraviolet radiation: Surface measurements in the United States, 1974-1985. Science 1988;239:762-64. 15. Logan JA. Tropospheric ozone: Seasonal behavior, trends and anthropogenic influence. J Geophys Res 1985;90:46382. 16. Fears TR, Scotto J, Schneiderman MA. Mathematical models of age and ultraviolet effects on the incidence of skin cancer among whites in the United States. Am J Epidemiol 1977;105:420-27. 17. Ross PM, Carter DM. Actinic DNA damage and the pathogenesis of cutaneous malignant melanoma. J Invest Dermato1 1989;92:293S-96S. 18. Lew RA, Sober AJ, Cook N. Sun exposure habits in patients with cutaneous melanoma; A case control study. J Dermatol Surg Oncol 1983;9:981-88. 19. Kripke ML. Impact of ozone depletion on skin cancers. J Dermatol Surg Oncol 1988;14:853-57.
SUN PROTECTION
Several articles have appeared in the literature regarding the impact of stratospheric ozone depletion on the prevalence of skin cancer due to increasing ultraviolet radiation. While it has been shown that UVB radiation is related to carcinogenesis of both melanoma and nonmelanoma skin cancer, it has not definitively been shown that stratospheric ozone depletion is translating into increased penetrating ultraviolet radiation. Estimates of increasing skin cancer in the future are dependent on calculations of UVB increases drawn from data on ozone depletion. The present article describes the history of stratospheric ozone depletion, how it may afect UVB penetration and skin cancer rates, and what is currently being done to prevent man's further detrimental efects on our atmosphere. J Dermatol Surg Oncol 1991;17:370- 372.
T
here exists some controversy regarding man's contribution toward damage of the atmosphere. The issue centers around whether or not we are to blame for stratospheric ozone depletion, and if so, whether this will eventually translate into an increase in skin cancer and other deleterious consequences for us. At present, there is no definite answer, only growing data pointing to the need for thoughtful action. This article represents an effort to educate as well as inspire others with regard to the significance that anthropogenic influences on our atmosphere might have for our lives and for the lives of future generations.
History In the early 1970s, prompted by increasing production and consumption of both aerosol and non-aerosol chloroFrom the Division of Dermatology, UCLA School of Medicine, V A Wesf Los Angeles Medical Cenfer, and U.C.LA. Ionsson Comprehensive Cancer Center, Los Angeles, California.
fluorocarbons (CFCs), concern began to stir regarding the fate of these compounds, which were being released into our atmosphere at a rate exceeding one billion pounds per year. Studies showed that virtually none of the released CFCs were being degraded in the atmosphere.' Research into the effects of man-made substances on the atmosphere began to be funded by many of the chemical manufacturing companies. In 1974, it was theorized by Molina and Rowland*that man-made CFCs would find their way into the stratosphere where they would be photolyzed by ultraviolet (UV) radiation, releasing chlorine atoms. These free chlorine atoms could then act as catalysts to decrease the ozone concentration, thus possibly increasing penetration of solar radiation in the UVB range. For the decade following this hypothesis, data continued to be gathered on CFC use and ozone depletion. In 1978, the United States banned the use of CFCs in aerosol sprays. However, nonaerosol uses have become increasingly popular. Science and industry felt there was still time to deal with the possibility of ozone depletion attributable to anthropogenic causes, as no consistent trend in ozone decrease had been seen, and global production of CFCs remained essentially constant during this period. In 1985, Farman et aP published data demonstrating a dramatic decrease in early spring ozone at the Halley Bay Station, Antarctica. This "Antarctic hole" was later confirmed by satellite measurements and appeared to span the entire continent. Soon after, NASA formed the International Ozone Trends Panel, which published their report in 1988.4The panel concluded that man-made chlorine species were primarily responsible for the ozone column decrease in the Antarctic region. Satellite data also indicated that ozone had decreased about 5% at all latitudes south of 60" since 1979 and that part of the decrease was probably because of dilution from the Antarctic hole. They also estimated an approximate 2-3% average global ozone decrease during the past 20 years.
0 1991 by Elsevier Science Publishing Co., lnc. 0148-0812/91/$3.50
J Dermatol Surg Oncol 1991;I 7:370 - 372
Additionally, a National Research Council study in 1989 demonstrated that the primary active form of chlorine, chlorine monoxide, had increased 100-fold over Antarctica during the ozone decrease period from what would have been expected from natural mechanisms alone.5 Theories on the mechanism of formation of this active chlorine, involving reactive nitrogen on stratospheric clouds, have been put forth.6
CFCs and Halons: Uses and Alternatives Chlorofluorocarbons were initially developed by industry in the 1930sand have become an extremely useful group of compounds commercially, primarily owing to their high chemical stability. Chlorofluorocarbonsare inflammable, nonexplosive, and essentially nontoxic. They are used extensively in refrigeration, insulation, fire extinguishers, and air conditioners because of their low vapor pressure thermal conductivity. They are compatible with many construction materials and are excellent solvents for use in cleaning electronicand mechanical components for communications equipment, computers, and navigation instruments for aircraft.' Halons (containing Bromine, eg, CBrF3), also extremely valuable commercial agents, have been in use since the 1950s. However, because of their physical properties, both halons and CFCs are difficult to break down. They usually pass through the troposphere (the first 10 km above sea level; 10-50 km is the stratosphere, where 80-90% of atmospheric ozone resides) unchanged until they are photolyzed by UV radiation in the stratosphere to form reactive chlorine and bromine byproducts, which can then deplete ozone through catalysis. Once in the atmosphere, the CFCs and halons can last unchanged for up to 100 years. Because of growing scientificevidence (especially concerning the Antarctic ozone hole), as well as increasing public awareness of the ozone depletion problem, it became clear that specific control measures to limit worldwide production and consumption of CFCs and halons were needed. After much negotiating and compromising, the Montr6al Protocol on Substances that Deplete the Ozone Layer was signed in September 1987.'* Currently, the protocol has been ratified by over 50 countries and took effect on January 1, 1989. The main man-made substances that the protocol initially focused on were the five major CFCs (CFC-11, -12, -113, -114, and -115) and halons 1211 and 1301. While recognizing the need for immediate action with regard to these chemicals, negotiators also realized the importanceof achieving a smooth economic transition, as the commercialization of potential substitutes was still years away.
AMRON AND MOY OZONE DEPLETION/SKIN CANCER
371
The development and use of acceptable alternative compounds is a key factor in the plan to phase out CFC and halon use. At present, hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are the most promising substitutes. Because of significantly lower levels of chlorine than CFCs (HFCs contain no chlorine), and because they contain hydrogen to allow for tropospheric decomposition, both the ozone-depletingpotential and the atmospheric lifetimes of these compounds are drasticallyreduced. Dupont (the worlds largest CFC producer) estimates that about 40% of the CFC demand will be met by these substitutes and another 32% will probably be met by not-in-kind (non-fluorocarbon)substitutes by the year 2000.
Penetrating Ultraviolet Radiation Ultraviolet radiation from the sun is divided into three wavebands, UVC (200-280 nm), UVB (280-320 nm), and UVA (320-400 nm).9Penetration of UVA waves are hardly affected by ozone. UVC waves are virtually eliminated by ozone, but it is the wavelengths in the UVB region that are most sensitive to variations in the atmospheric ozone concentration. It has been demonstrated that the most biologically effective wavelength for producing erythema of Caucasian skin is 297 nm, right in the middle of the UVB waveband.'* Many have tried to translate the ozone depletion into increases in UV radiation and skin cancer rates. It has been calculated using current available data for ozone depletion that the annual UV dose for the Northern Hemisphere has increased anywhere from 0.5 - 3.1%, depending on latitude." The US. Environmental Protection Agency has also estimated that for each 1%reduction in ozone concentration, there will be a concommitant 2% increase in UVB radiation.12In 1983, Rundel and Nachtwey13projected that by even the most favorable scenario, the incidence of non-melanoma skin cancer will increase by 5% by the year 2300, and with the least favorable scenario the incidence of skin cancer will double. However, surface measurements of solar radiation during the period 1974-1985 for latitudes between 30" and 50" N (includes the United States) failed to show increases in the UVB spectrum. Scotto et all4 have suggested that climatic, meteorologic, and environmental factors in the troposphere might be acting to diffuse solar energy, and thus reduce the amount of UVB radiation reaching us. Furthermore, although there appears to be a decrease in the stratospheric ozone column, there has been a 1- 2% increase in tropospheric ozone concentrations owing to man-made pollution, and this might also be compensating for the stratospheric decrease. This increase in tropospheric ozone may partly compensate for
372 Ah4RON AND MOY
the decrease in stratospheric ozone, thus helping to minimize the potential increase in penetrating ultraviolet radiati011.I~
Conclusion The incidence of both melanoma and non-melanoma skin cancer is increasing in the United States, and it is now becoming clear that they are both related to the effects of UVB radiation. Basal and squamous cell carcinomas appear to be related to chronic UV exposure.16For cutaneous melanoma (excluding lentigo maligna melanoma, which seems to be connected to chronic sun exposure), the contribution of damaging UVB radiation has been more difficult to elucidate. It now appears that periodic bursts of sunlight leading to severe sunburn is a causative factor in the development of these melanoma^.",'^ Animal studies and in vitro models also support the role of UVB radiation in the induction of melanoma carcinogeneS~S.~ However, what is still unclear is whether the recently discovered stratospheric ozone depletion, which is likely owing, at least in part, to man, is affecting the penetration of damaging solar radiation. It is unlikely that the recent increase in skin cancers can be solely attributed to the ozone depletion. The ozone decrease is probably too recent to account for trends that began many decades However, it may contribute to an increased incidence of skin cancer in the future. The ozone depletion issue is an extremely complex and controversial one. Continuing research into man’s detrimental effects on the atmosphere needs to be pursued. How this generation deals with the ozone depletion problem will likely affect the incidence of skin cancer for future generations.
Acknowledgments. This work was supported in part by the Dermatology Foundation Research Fellowship sponsored by Herbert Laboratories.
References 1. Lovelock JE. Atmospheric fluorine-chlorine compounds as
indicators of air movements. Nature 1971;230:379. 2. Molina MJ, Rowland FS. Stratospheric sink for chlorofluoromethanes-chlorine atomic-catalyzed destruction of ozone. Nature 1974;249:810-12.
Dermntol Surg Oncol 1991;17:370- 372 3. Farman JC, Gardiner BG, Shanklin JD. Large losses of total ozone in antarctica reveal seasonal CIOx/NOx interaction. Nature 1985;315:207-10. 4. Watson RT, Prather MJ, Kurylo MJ. Present state of knowledge of the upper atmosphere 1988: An assessment report. NASA: Greenbelt, MD; Reference Publication 1208,1988. 5. Anderson JG. Ozone depletion, greenhouses gases and climate change. National Research Council. Washington, DC: National Academy Press, 1989:56-65. 6. Jackman CH. Stratospheric ozone change. Environ Sci Technol 1989;23:1329- 32. 7. McFarland M. Chlorofluorocarbonsand ozone. Environ Sci Technol 1989;23(10):1203-07. 8. Koehler J, Hajost SA. The Montr6al protocol: A dynamic agreement for protecting the ozone layer. Ambio 1990;19:82- 86. 9. Kripke ML, Pitcher H, Longstreth JD. Potential carcinogenic impacts of stratospheric ozone depletion. Environ Carcin Revs (J Envir Sci Hlth) 1989;C7(1):53- 74. 10. Koller LR. Ultraviolet radiation. 2nd ed. New York John Wiley and Sons, 1965. 11. Dahlback A, Henriksen T, Larsen SHH, Stamnes K. Biological UV-doses and the effect of an ozone layer depletion. Photochem Photobiol 1989;49:621-25. 12. Hoffman JS. An assessment of the risks of stratospheric modification. US Environmental Protection Agency, March 1987. 13. Rundel RD, Nachtwey DS. Projections of increased nonmelanoma skin cancer incidence due to ozone depletion. Photochem Photobiol 1983;38:577-91. 14. Scotto J, Cotton G, Urbach F, Berger D, Fears T. Biologically effective ultraviolet radiation: Surface measurements in the United States, 1974-1985. Science 1988;239:762-64. 15. Logan JA. Tropospheric ozone: Seasonal behavior, trends and anthropogenic influence. J Geophys Res 1985;90:46382. 16. Fears TR, Scotto J, Schneiderman MA. Mathematical models of age and ultraviolet effects on the incidence of skin cancer among whites in the United States. Am J Epidemiol 1977;105:420-27. 17. Ross PM, Carter DM. Actinic DNA damage and the pathogenesis of cutaneous malignant melanoma. J Invest Dermato1 1989;92:293S-96S. 18. Lew RA, Sober AJ, Cook N. Sun exposure habits in patients with cutaneous melanoma; A case control study. J Dermatol Surg Oncol 1983;9:981-88. 19. Kripke ML. Impact of ozone depletion on skin cancers. J Dermatol Surg Oncol 1988;14:853-57.
