Biological effects

In moderate amounts ultraviolet radiation has beneficial effects for life on earth. It is a powerful germicide, for example, and triggers the production of Vitamin D in the skin. Vitamin D allows the body to fix the calcium necessary for proper bone development; lack of it may cause rickets, particularly in growing children. High intensities of ultraviolet radiation, however, are harmful to all forms of life.

Lifeforms have evolved in such a way that they can cope with existing levels of ultraviolet radiation. They are also quite capable of surviving the increases in radiation caused by short-term fluctuations in ozone levels. Most organisms would be unable to cope with the cumulative effects of progressive thinning of the ozone layer, however, and the biological consequences would be far-reaching.

The most serious concern is over rising levels of UV-B—the radiation recognized as causing most biological damage. Intense UV-B rays alter the basic foundations of life, such as the DNA molecule and various proteins (Crutzen 1974). They also inhibit photosynthesis. Growth rates in plants such as tomatoes, lettuce and peas are reduced, and experimental exposure of some plants to increased ultraviolet radiation has produced an increased incidence of mutation (Hammond and Maugh 1974). Insects, which can see in the ultraviolet sector of the spectrum, would have their activities disrupted by increased levels of ultraviolet radiation (Crutzen 1974).

Most of the concern for the biological effects of declining ozone levels has been focused on the impact of increased ultraviolet radiation on the human species. The potential effects include the increased incidence of sunburn, premature ageing of the skin among white populations and greater frequency of allergic reactions caused by the effects of ultraviolet light on chemicals in contact with the skin (Hammond and Maugh 1974). These are relatively minor, however, in comparison to the more serious problems of skin cancer and radiation blindness, both of which would become more frequent with higher levels of ultraviolet radiation. Skin cancer had a prominent role in the SST and CFC debates of the 1970s (Dotto and Schiff 1978), and it continues to evoke a high level of concern. The number of additional skin cancers to be expected as the ozone layer thins is still a matter of debate, but a commonly accepted estimate is that a 1 per cent reduction in ozone allows an increase in UV-B of 1-2 per cent. This in turn leads to a 2-4 per cent increase in the incidence of non-melanoma skin cancers (Concar 1992). Hammond and Maugh (1974) have suggested that a 5 per cent reduction in ozone levels would cause an additional 20,000 to 60,000 skin cancers in the United States alone. The US National Academy of Sciences has also estimated that a 1 per cent decline in ozone would cause 10,000 more cases of skin cancer per year (Lemonick 1987). Many skin cancers are non-malignant and curable, but only after painful and sometimes disfiguring treatment. A relatively small proportion—the melanomas—are

Figure 6.7 Incidence of melanoma in Scotland, 1979-89

Figure 6.7 Incidence of melanoma in Scotland, 1979-89

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Survival Basics

Survival Basics

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