244 12 J. T. 0. Kirk, A theoretical analysis of the contribution of algal cells to the attenuation of light within natural waters. II. Spherical cells, New P&tol., 75 (1975) 21-36. 13 J. T. 0. Kirk, A theoretical analysis of the contribution of algal cells to the attenuation of light within natural waters. III. Cylindrical and spheroidal cells, New Phytol., 77 (1975) 341-358. 14 J. A. Raven, A cost-benefit analysis of photon absorption by photosynthetic unicells, New Phytol., 98 (1984) 593-625. 15 J. A. Raven, Physiological consequences of extremely small size for autotrophic organisms in the sea, Photosynthetic Picoplankton, Can. Bull. Fish. Aq. Sci., 214 (1986) l-70. 16 S. Scherer, T. W. Chen and P. Boger, A new W-A/B protecting pigment in the terrestrial cyanobacterium Nostoc commune, Plant Physiol., 88 (1988) 1055-1057. 17 W. F. Wood, Photoadaptive response of the tropical red alga Eucheuma striatum Schmitz (Gigartinales) to ultra-violet radiation, Aquut. Bot., 33 (1989) 41-51. 18 B. M. Greenberg, V. Gaba, 0. Canaani, S. Malkin, A. K. Mattoo and M. Edelman, Separate photosensitizers mediate degradation of the 32 kDa photosystem II reaction centre protein in the visible and UV spectral regions, Proc. Natl. Acad. Sci. U.S.A., 86 (1989) 6617-6620. 19 G. Samuelsson, A. Lonneborg, E. Rosenqvist, P. Gustafsson and G. Cquist, Photoinhibition and reactivation of photosynthesis in the cyanobacterium Anacystis niduluns, Physiol. Plant., 79 (1985) 992-995. 20 J. A. Raven and G. Samuelsson, Repair of photoinhibitory damage in Anucystis nidulans 625 (Synechococcus 6301): relation to catalytic activity for, and energy supply to, protein synthesis, and implications for hax and the efficiency of light-limited growth, New Phytol., 103 (1986) 625-643. 21 J. A. Raven, Fight or flight: the economics of repair and avoidance of photoinhibition of photosynthesis, Functkmal Ecol., 3 (1989) 5-19. 22 K. Mopper and X. Zhou, Hydroxyl radical photoproduction in the sea and its potential impact on marine processes, Science, 250 (1990) 661-664.
Ozone holes and biological
consequences
Johan Moan Institute for Cancer Research, (umayj
Department
of Biophysics,
Montebello
0310, Oslo 3
The Antarctic ozone hole, apparent in the period September-December, is an undeniable fact [ 11. Even though the hole was deeper in 1987 than in 1988 [2], it has manifested itself more and more clearly since 1970 [l]. This situation has alarmed governments all over the world and has led to increased research activity in many countries. Is the ozone layer in the Arctic stratosphere also declining? Is there a statistically significant decreasing trend at mid-latitudes? What biological consequences will a reduced ozone layer lead to? The Ozone Trend Panel announced in 1988 a decreasing ozone trend for the period 1969-1986 over the northern hemisphere [ 31. However, this was probably a transient and random fluctuation, since the trend over a longer period, 1957-1986, is increasing rather than decreasing [4]. The truth is that we need more measurements, from more stations and for a longer period of time, before we can announce statistically significant messages.
245
However, it is very likely that the Antarctic ozone hole is produced or at least seriously aggravated - by chlorofluorocarbon (CFC) gases from human activities [ 11. Even in Arctic regions intermediate products of the CFC-catalysed degradation of ozone have been detected [5]. Furthermore, “miniholes” in the Arctic ozone layer have been observed [ 61, although it is quite clear that the conditions in the Arctic stratosphere are less favourable for an ozone reduction than those in the Antarctic region, mainly because the temperature is higher and the presence of polar stratospheric clouds is less frequent in the former region. As yet, the Antarctic ozone hole has probably had very little biological effect, although the present fluence rate of biologically efficient UV light in Antarctica is more than doubled in October-November compared with that in the same season prior to the hole formation (i.e. before 1970). It has been reported that the 1987 hole, which was a record “deep” (approximately 50% reduction), led to a decrease in the ozone layer over populated areas in Australia and New Zealand [ 71. It seems very likely that an increased UV fluence will harm terrestrial plants [S] as well as microorganisms in the ocean [9]. The latter organisms seem to be very UV sensitive and it cannot be excluded that even today, i.e. without any worldwide ozone depletion, UV radiation from the sun may be a factor of importance in the ecological balance of plankton. Increased UV radiation may change the equilibria. Notably, the ecological balance between different species may be shifted. It has been shown that, on UV exposure, different crops are out-competed by weeds [lo]. In the case .of permanent ozone depletion, human health will be more seriously challenged by UV radiation than today. The incidence rates of several diseases will increase: eye diseases such as cataracts, skin cancers and diseases related to immunosuppression. UV radiation from the sun can damage the cornea, lens and retina [ 111. A study of the relationship between cataracts and exposure to sunlight in the Himalayas showed that the prevalence increased by a factor of 2.4 when the average daily sun exposure increased from 7-S h to 1 l-12 h [ 12). It has been estimated that a 1% decrease in the ozone layer will result in a 1.2% increase in the incidence rate of cortical cataracts [ 131. All of the common forms of skin cancer (basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and cutaneous malignant melanoma (CMM)) are mainly caused by UV radiation from the sun. The risk of a person developing SCC, BCC or lentigo maligna melanoma (a form of CMM) is thought to be proportional to the accumulated dose of carcinogenic sunlight received by that person [ 141. The incidence rates of these cancer forms increase with decreasing latitude. Using epidemiological data for comparable populations living at different latitudes, it is possible to estimate that a 1% ozone depletion will lead to a 1.6%-2.3% increase in the incidence rates of SCC and BCC [ 151. The situation is more complicated for CMM since these cancers are thought to be related not only to the accumulated UV exposure, but also to the exposure pattern [ 141. Intense periods of sun exposure at
246
a young age are particularly significant. Nevertheless, increased annual UV exposures will most probably lead to an increase in the frequency of CMM. Over the last few decades there has been a steady increase in the incidence rates of skin cancer in most countries. For instance, in Norway the annual age-adjusted incidence rate of CMM was about 2.2 per 100 000 in 1955 and about 11 in 1977, corresponding to an annual increase of about 7%. The frequency of no other cancer has increased so rapidly. It is clear that this increase is related to the habits of sun exposure and not to a decrease in the ozone layer. Since 1955 the ozone layer has been constant to within a few per cent. Ozone is beneficial in the stratosphere, but dangerous in the troposphere. A decreased amount of ozone in the stratosphere will lead to a decrease in the ozone concentration in the troposphere, provided that the air is relatively clean. However, at NO, concentrations higherthan about 0.1 ppb (volume), the tropospheric ozone concentration will increase if more UV light is let through the stratosphere [ 161. Therefore it is feared that the air quality in rural areas will become poorer rather than better if the ozone layer in the stratosphere should decrease. There is one peculiar aspect related to this. It has been calculated that, in areas with increasing tropospheric concentrations of ozone, the UV exposure at the Earth’s surface may decrease rather than increase even if the total ozone column should decrease [ 171. This is related to the fact that the scattering of UV light is much larger in the troposphere than in the stratosphere. Thus, a given amount of ozone will absorb more UV light if it is in the troposphere than if it is in the stratosphere. This may explain why annual exposures to biologically effective UV radiation were found to decrease in the U.S.A. in the period 1974-1985 [ 181 during which there was a slight decrease in the total ozone level [ 41. It can be concluded that the biological effects of a decreased ozone layer will be mostly negative. Human health, as welI as plants and microorganisms in the ocean, will be adversely affected. How much we can allow the ozone level to decline before statistically significant biological effects can be measured is not exactly known, but is proposed to be of the order of 10% or less.
1 J. C. Farman, H. Gardiner and J. D. Shanklii, Large losses of total ozone in Antarctica reveal seasonal ClO,/HO, interaction, Nature, 3I5 (1985) 207-210. 2 M. R. Schoeberl, Dynamics weaken the polar hole, Nature, 336 (1988) 420-421. 3 D. Lindley, CFCs canse part of global ozone decline, Nature, 322 (1988) 293. 4 R. D. Bojkov, Ozone variations in the northern polar region, Meteurol. Atmos. Phys., 38 (1988) 117-130. 5 S. Solomom, G. H. Mount, R. W. Sanders, R. 0. Jacoubek and A. L. Schmeltekops, Observations of the nighttime abundance of OLcO in the white stratosphere above Thnle, Greenland, Science, 242 (1988) 550-555. 6 D. J. Hofmann, T. L. Deshler, P. Aimedieu, W. A. Matthews, P. V. Johnstone, Y. Kondo, W. R. Sheldon, G. J. Byrne and J. R. Benbrook, Stratospheric clouds and ozone depletion in the Arctic during January 1989, Nature, 240 (1989) 117-121.
247 7 R. J. Atkinson, W. A. Matthews, P. A. Newman and A. Plumb, Evidence of the mid-latitude impact of Antarctic ozone depletion, Nature, 340 (1989) 290-294. 8 M. Tevini and A. H. Teramura, UV-B effects on terrestrial plants, Photo&em. PhotobioZ.,
50 (1989) 479-487. 9 R. C. Smith, Ozone, middle ultraviolet radiation and the aquatic environment, Photo&em. Photobiol., 50 (1989) 459-468. 10 W. G. Gold and M. M. Caldwell, The effects of ultraviolet-B radiation on plant completion in terrestrial ecosystems, Phystil. Plant, 58 (1983) 435-444. 11 H. R. Taylor, The biological effects of UV-B on the eye, Photo&em. PhotobioZ., 50 (1989) 489-492. 12 L. B. Brilliant, N. C. Grasset, R. P. Pokhrel, A. Kostal, J. M. Lepkowski, G. E. Brilliant, W. N. Hawks and R. Pararsjasegaram, Associations among cataract prevalence, sunlight hours and altitude in the Himalayas, Am. J. Epidemiol., 118 (1983) 250-264. 13 H. R. Taylor, S. K. West, F. S. Rosenthal, M. Beatriz, H. S. Newland, H. Abbey and E. A. Emmett, Effect of ultraviolet radiation on cataract formation, Nm En.&. J. Med., 319 (1988) 1429-1433. 14 J. M. Elmwood, S. M. Whitehead and R. P. Gallagher, Epidemiology of human malignant skin tumors with special reference to natural and artificial ultraviolet radiation exposures, in C. J. Conti, T. J. Slaga and A. J. P. Klein-Szano (eds.), Skin Tumms: Experimental and Clinical Aspects, Raven, New York, 1989, pp. 55-84. 15 J. Moan, A. Dahlback, T. Henriksen and K. Magnus, Biological amplification factor for sunlight-induced skin cancer at high latitudes, Cancer Res., 49 (1989) 5207-5212. 16 S. C. Lm and M. Trainer, Responses of the tropospheric ozone and odd hydrogen radicals to column ozone change, J. Atmos. Chem., 6 (1988) 221-223. 17 C. Briihl and P. J. Crutzen, On the disproportionate role of tropospheric ozone as a filter against solar UV-B radiation, Geophys. Res. L&t., 16 (1989) 703-706. 18 J. Scotto, G. Cotton, F. Urbach, D. Berger and T. Fears, Biologically effective ultraviolet radiation: surface measurements in the United States, 1974 to 1985, Science, 239 (1988) 762-764.
Ozone holes and biological
consequences
Johan Moan Institute for Cancer Research, (umayj
Department
of Biophysics,
Montebello
0310, Oslo 3
The Antarctic ozone hole, apparent in the period September-December, is an undeniable fact [ 11. Even though the hole was deeper in 1987 than in 1988 [2], it has manifested itself more and more clearly since 1970 [l]. This situation has alarmed governments all over the world and has led to increased research activity in many countries. Is the ozone layer in the Arctic stratosphere also declining? Is there a statistically significant decreasing trend at mid-latitudes? What biological consequences will a reduced ozone layer lead to? The Ozone Trend Panel announced in 1988 a decreasing ozone trend for the period 1969-1986 over the northern hemisphere [ 31. However, this was probably a transient and random fluctuation, since the trend over a longer period, 1957-1986, is increasing rather than decreasing [4]. The truth is that we need more measurements, from more stations and for a longer period of time, before we can announce statistically significant messages.
245
However, it is very likely that the Antarctic ozone hole is produced or at least seriously aggravated - by chlorofluorocarbon (CFC) gases from human activities [ 11. Even in Arctic regions intermediate products of the CFC-catalysed degradation of ozone have been detected [5]. Furthermore, “miniholes” in the Arctic ozone layer have been observed [ 61, although it is quite clear that the conditions in the Arctic stratosphere are less favourable for an ozone reduction than those in the Antarctic region, mainly because the temperature is higher and the presence of polar stratospheric clouds is less frequent in the former region. As yet, the Antarctic ozone hole has probably had very little biological effect, although the present fluence rate of biologically efficient UV light in Antarctica is more than doubled in October-November compared with that in the same season prior to the hole formation (i.e. before 1970). It has been reported that the 1987 hole, which was a record “deep” (approximately 50% reduction), led to a decrease in the ozone layer over populated areas in Australia and New Zealand [ 71. It seems very likely that an increased UV fluence will harm terrestrial plants [S] as well as microorganisms in the ocean [9]. The latter organisms seem to be very UV sensitive and it cannot be excluded that even today, i.e. without any worldwide ozone depletion, UV radiation from the sun may be a factor of importance in the ecological balance of plankton. Increased UV radiation may change the equilibria. Notably, the ecological balance between different species may be shifted. It has been shown that, on UV exposure, different crops are out-competed by weeds [lo]. In the case .of permanent ozone depletion, human health will be more seriously challenged by UV radiation than today. The incidence rates of several diseases will increase: eye diseases such as cataracts, skin cancers and diseases related to immunosuppression. UV radiation from the sun can damage the cornea, lens and retina [ 111. A study of the relationship between cataracts and exposure to sunlight in the Himalayas showed that the prevalence increased by a factor of 2.4 when the average daily sun exposure increased from 7-S h to 1 l-12 h [ 12). It has been estimated that a 1% decrease in the ozone layer will result in a 1.2% increase in the incidence rate of cortical cataracts [ 131. All of the common forms of skin cancer (basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and cutaneous malignant melanoma (CMM)) are mainly caused by UV radiation from the sun. The risk of a person developing SCC, BCC or lentigo maligna melanoma (a form of CMM) is thought to be proportional to the accumulated dose of carcinogenic sunlight received by that person [ 141. The incidence rates of these cancer forms increase with decreasing latitude. Using epidemiological data for comparable populations living at different latitudes, it is possible to estimate that a 1% ozone depletion will lead to a 1.6%-2.3% increase in the incidence rates of SCC and BCC [ 151. The situation is more complicated for CMM since these cancers are thought to be related not only to the accumulated UV exposure, but also to the exposure pattern [ 141. Intense periods of sun exposure at
246
a young age are particularly significant. Nevertheless, increased annual UV exposures will most probably lead to an increase in the frequency of CMM. Over the last few decades there has been a steady increase in the incidence rates of skin cancer in most countries. For instance, in Norway the annual age-adjusted incidence rate of CMM was about 2.2 per 100 000 in 1955 and about 11 in 1977, corresponding to an annual increase of about 7%. The frequency of no other cancer has increased so rapidly. It is clear that this increase is related to the habits of sun exposure and not to a decrease in the ozone layer. Since 1955 the ozone layer has been constant to within a few per cent. Ozone is beneficial in the stratosphere, but dangerous in the troposphere. A decreased amount of ozone in the stratosphere will lead to a decrease in the ozone concentration in the troposphere, provided that the air is relatively clean. However, at NO, concentrations higherthan about 0.1 ppb (volume), the tropospheric ozone concentration will increase if more UV light is let through the stratosphere [ 161. Therefore it is feared that the air quality in rural areas will become poorer rather than better if the ozone layer in the stratosphere should decrease. There is one peculiar aspect related to this. It has been calculated that, in areas with increasing tropospheric concentrations of ozone, the UV exposure at the Earth’s surface may decrease rather than increase even if the total ozone column should decrease [ 171. This is related to the fact that the scattering of UV light is much larger in the troposphere than in the stratosphere. Thus, a given amount of ozone will absorb more UV light if it is in the troposphere than if it is in the stratosphere. This may explain why annual exposures to biologically effective UV radiation were found to decrease in the U.S.A. in the period 1974-1985 [ 181 during which there was a slight decrease in the total ozone level [ 41. It can be concluded that the biological effects of a decreased ozone layer will be mostly negative. Human health, as welI as plants and microorganisms in the ocean, will be adversely affected. How much we can allow the ozone level to decline before statistically significant biological effects can be measured is not exactly known, but is proposed to be of the order of 10% or less.
1 J. C. Farman, H. Gardiner and J. D. Shanklii, Large losses of total ozone in Antarctica reveal seasonal ClO,/HO, interaction, Nature, 3I5 (1985) 207-210. 2 M. R. Schoeberl, Dynamics weaken the polar hole, Nature, 336 (1988) 420-421. 3 D. Lindley, CFCs canse part of global ozone decline, Nature, 322 (1988) 293. 4 R. D. Bojkov, Ozone variations in the northern polar region, Meteurol. Atmos. Phys., 38 (1988) 117-130. 5 S. Solomom, G. H. Mount, R. W. Sanders, R. 0. Jacoubek and A. L. Schmeltekops, Observations of the nighttime abundance of OLcO in the white stratosphere above Thnle, Greenland, Science, 242 (1988) 550-555. 6 D. J. Hofmann, T. L. Deshler, P. Aimedieu, W. A. Matthews, P. V. Johnstone, Y. Kondo, W. R. Sheldon, G. J. Byrne and J. R. Benbrook, Stratospheric clouds and ozone depletion in the Arctic during January 1989, Nature, 240 (1989) 117-121.
247 7 R. J. Atkinson, W. A. Matthews, P. A. Newman and A. Plumb, Evidence of the mid-latitude impact of Antarctic ozone depletion, Nature, 340 (1989) 290-294. 8 M. Tevini and A. H. Teramura, UV-B effects on terrestrial plants, Photo&em. PhotobioZ.,
50 (1989) 479-487. 9 R. C. Smith, Ozone, middle ultraviolet radiation and the aquatic environment, Photo&em. Photobiol., 50 (1989) 459-468. 10 W. G. Gold and M. M. Caldwell, The effects of ultraviolet-B radiation on plant completion in terrestrial ecosystems, Phystil. Plant, 58 (1983) 435-444. 11 H. R. Taylor, The biological effects of UV-B on the eye, Photo&em. PhotobioZ., 50 (1989) 489-492. 12 L. B. Brilliant, N. C. Grasset, R. P. Pokhrel, A. Kostal, J. M. Lepkowski, G. E. Brilliant, W. N. Hawks and R. Pararsjasegaram, Associations among cataract prevalence, sunlight hours and altitude in the Himalayas, Am. J. Epidemiol., 118 (1983) 250-264. 13 H. R. Taylor, S. K. West, F. S. Rosenthal, M. Beatriz, H. S. Newland, H. Abbey and E. A. Emmett, Effect of ultraviolet radiation on cataract formation, Nm En.&. J. Med., 319 (1988) 1429-1433. 14 J. M. Elmwood, S. M. Whitehead and R. P. Gallagher, Epidemiology of human malignant skin tumors with special reference to natural and artificial ultraviolet radiation exposures, in C. J. Conti, T. J. Slaga and A. J. P. Klein-Szano (eds.), Skin Tumms: Experimental and Clinical Aspects, Raven, New York, 1989, pp. 55-84. 15 J. Moan, A. Dahlback, T. Henriksen and K. Magnus, Biological amplification factor for sunlight-induced skin cancer at high latitudes, Cancer Res., 49 (1989) 5207-5212. 16 S. C. Lm and M. Trainer, Responses of the tropospheric ozone and odd hydrogen radicals to column ozone change, J. Atmos. Chem., 6 (1988) 221-223. 17 C. Briihl and P. J. Crutzen, On the disproportionate role of tropospheric ozone as a filter against solar UV-B radiation, Geophys. Res. L&t., 16 (1989) 703-706. 18 J. Scotto, G. Cotton, F. Urbach, D. Berger and T. Fears, Biologically effective ultraviolet radiation: surface measurements in the United States, 1974 to 1985, Science, 239 (1988) 762-764.
