A decrease of atmospheric ozone and a change of its vertical distribution will have many effects on man, animals, plants and materials. Decrease of ozone will have direct influences by an increase of the UV-B radiation penetrating to the earth's surface. This radiation has wavelengths between 290 and 320 nm and its effects are predominantly damaging. A change of the vertical distribution of ozone in the atmosphere is likely to induce changes of climate, and this in turn will influence the conditions needed for life.
It has long been known that UV-B radiation (wavelengths between 280 nm and 315 nm) is the most carcinogenic part of the solar UV spectrum reaching the earth's surface. This was established in animal experiments, and it is not possible to extract such information for humans from epidemiological data. Therefore, further animal data are needed for a proper definition of a carcinogenic UV dose. A carcinogenic UV dose has been assumed to be approximately equal to effective UV doses for other biologically detrimental effects, such as sunburn or mutations in cells. This was based on a similarity in wavelength dependence of the effects or mechanism of UV carcinogenesis (mutations leading to malignant cell proliferation).
Non-melanoma skin cancers are the most common cancers occurring in white populations. The two major forms of non-melanoma skin tumors are basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). Although the incidence of BCC is generally several times greater than the incidence of SCC, SCCs account for as much as four-fifths of all non-melanoma skin cancer deaths. Prolonged sunlight exposure is considered to be the dominant risk factor for non-melanoma skin tumors.
For every 1% depletion of ozone the incidence of BCC will ultimately increase by 2.5 percent and the incidence of SCC by 4.4 percent. For a one percent depletion of ozone, the overall incidence of non-melanoma skin cancer will increase 3 percent.
Cutaneous malignant melanoma (CMM) incidence rates throughout the world are rising at an alarming rate. During the decade from 1974 to 1983, CMM incidence has increased at an average yearly rate of between 3 and 4 percent (Sondik et al, 1985). For more than a decade, there has been serious concern that CMM is at least partially caused by UV-B radiation (NAS, 1987). There is evidence that indicates that exposure to solar radiation, and, in particular to UV-B, is a likely cause of CMM.
Evidence supporting a relationship between solar radiation and CMM includes:
Ultraviolet radiation (UVR) has been found to alter, both locally (in the skin) and systemically, the immune response to antigens administered via the skin in man and experimental animals. The effects of UV-B and solar radiation on the human immune system have not been studied in sufficient detail to allow estimation of dose-response relationships for these effects.