Causes and Effects of Stratospheric Ozone Reduction An Update (1982) / Chapter Skim
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5 DIRECT HUMAN HEALTH HAZARDS
5 DIRECT HUMAN HEALTH HAZARDS
Pages 75-115
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From page 75... ...
Epidemiological studies show that sunlight causes more than 90 percent of basal and squamous cell skin cancers and is a factor in melanoma. Experimental studies and theoretical considerations suggest that actually the wavelengths most affected by ozone (i.e., UV-B)
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From page 76... ...
, several new observations have heightened the awareness and broadened the understanding of the health hazards of human exposure to UV. These include a better understanding of the optical properties of skin and blood; the results of careful study of various exposure conditions that influence UV-induced skin cancer in laboratory animals; demonstration and quantification of two forms of DNA repair in viva in human skin (see Chapter 3)
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From page 77... ...
The organ most affected by UV is the skin. The optical properties of skin determine the amount of optical radiation reaching various depths in the tissue.
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From page 78... ...
In considering the effects of possible changes in the terrestrial solar spectrum resulting from ozone depletion, it is important to know the depths to which optical radiation penetrates human skin (Table 5.l)
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Biologically active UV reaches the level of cutaneous blood vessels. Endothelial cells and connective tissue elements may be directly affected by the radiation; blood cells, lymphatics, and humoral substances passing through the skin may be photochemically altered.
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From page 80... ...
Because the action spectrum, dose-response curve, and intensity-time reciprocity relationship for sunburn are known, it is possible to calculate the decrease in time required to acquire a sunburn for any given ozone depletion. If UV-B increases by 10 percent, the decrease in time required to acquire a sunburn would be about 10 percent plus a small additional decrease in time because of the spectral shift to include shorter, more effective wavelengths.
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From page 81... ...
been called "premature aging," but there is no convincing evidence that the cellular mechanisms and connective tissue alterations are the same as those that occur in natural aging. The action spectrum for solar degeneration is not known, and therefore the potential effects of ozone depletion are not known.
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From page 82... ...
The most detailed studies have been performed on experimental animals. Skin cancers induced in mice by UV-B radiation are highly antigenic, and many are rejected by an immunologic reaction even when transplanted into genetically similar mice, i.e., mice from the same highly inbred strain.
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From page 83... ...
. There are increased UV-associated skin cancers in renal transplant patients (Marshall 1974)
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The action spectrum for these changes, however, appears to be in the W-A range and therefore would not be affected by ozone depletion.
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From page 85... ...
were asked to predict whether increased exposure to W-B would be likely to increase basal and squamous cell skin cancer incidence rates. To do so, they had to make judgments on the basis of limited evidence from epidemiological studies, backed up by clinical and pathological observations and the results of animal experiments, because human experimentation was out of the question.
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From page 86... ...
. There were very few hard data on the incidence of and mortality from skin cancers when the 1976 and 1979 reports of the Committee on Impacts of Stratospheric Change (NRC 1976a, 1979a)
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From page 87... ...
to the incidence of basal and squamous cell skin cancers. The report provided a brief summary of the survey methods that are described in detail in NRC (1975)
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From page 88... ...
All known strains nave poor excision repair of DNA compared with people (see Chapter 3) , and the optical properties of mouse skin differ from those of human skin.
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From page 89... ...
We were also provided with revised estimates of predicted increases in the incidence rates of skin cancer for a range of possible percentage reductions in stratospheric ozone concentration and/or changes in R-B meter units. The new information made available to us by the NCI came from three sets of data.
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From page 90... ...
, the incidence rates were not corrected for any confounding factors other than age and sex. The incidence data from the eight geographic locations provided age- and sex-specific rates for basal and squamous cell cancers, as well as rates of occurrence on different sites of the body.
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From page 91... ...
More detailed analysis showed that basal and squamous cell skin cancers were reported at earlier ages in the South. When the new annual sex- and age-adjusted incidence rates of these skin cancers were plotted against R-B meter measurements of UV, all incidence rates were found to be lower in 500 400 ~ - ~ ~ LIJ cr UJ 300 a o J o ° 200 to to to LLJ LIJ 6 150 cr 100 30 34 · Skin Cancers Other Than Melanoma (1977-1978)
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From page 92... ...
An association between skin cancer other than melanoma and W exposure in non-Caucasians had not been found until recently. The 1977-1978 survey found 68 black patients with basal cell or squamous cell skin cancers.
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FIGURE 5.5 Annual age-adjusted incidence rates for basal and squamous cell cancers among white females and males for two surveys, 1977-1978 (closed symbols) and 1971-1972 (open symbols)
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of basal and squamous cell cancers according to anatomic site and sex (U.S. white population, 1977-1978)
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From page 95... ...
er 100,000) for Basal and Squamous Cell Skin Cancers Among U.S.
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From page 96... ...
Basal and squamous cell skin cancers from W radiation have become so common that although the fatality rate is one death in every hundred cases, the overall national mortality figures actually resemble those for melanoma (Mason et al.
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From page 97... ...
For example, after four years of follow-up, rates of basal and squamous cell skin cancer in 1373 psoriasis patients treated with photochemotherapy using W -A (P WA) were 3 times higher than were expected on the basis of age, sex, and geographic-location incidence rate data.
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From page 98... ...
(1981) plotted the age-adjusted incidence rates for basal and squamous cell cancers on a logarithmic scale against the annual W dose measured by an R-B meter (Figure 5.5)
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From page 99... ...
. The differences between the two methods of calculation reviewed above are not the result of different epidemiological data, since they both use the same incidence rates, but of different ways of estimating the change in UV dose per unit change in ozone concentration.
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(35-64) Squamous cell Minneapolis-St.
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(6-21) Squamous cell Minneapolis-St.
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From page 102... ...
estimate the overall increase in basal cell skin cancer incidence per 1 percent decrease in ozone concentration to be between 2 percent and 5 percent depending on latitude. For squamous cell cancer the values are approximately double.
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Even if it was assumed that all the cancers in blacks were squamous cell -- since in blacks this type is relatively more common than basal cell -- 92 percent of squamous cell cancers in whites would still be related to sunlight. However, given that the incidence rates in blacks have some correlation with latitude, as was suggested earlier, these values would be overestimates.
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From page 104... ...
. The argument was seen at that time to be clearly less substantial than that supporting the inferred relationship between WEB exposure and basal and squamous cell skin cancer.
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From page 105... ...
The epidemic has been affecting popula tions at many different latitudes with varying background incidence levels. ~ ~ ~ ~ ~_ ~_ The epidemiological picture ot higher Incidence rates In each successive birth cohort is reminiscent of the earlier lung cancer epidemic in those same countries, which resulted from the Progressive .
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From page 106... ...
Much of it underscores and extends the inconsistent and sometimes paradoxical findings from past epidemiological studies, and some of it provides interesting new avenues for exploration. When the 1973-1976 incidence data from the NCI SEER program are plotted against the 1977-1978 NCI R-B meter measurements of accumulated dose in eight geographic locations, the results are consistent with those of earlier analyses and show a definite relationship between melanoma and measurements of annual solar W flux (Scotto et al.
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From page 107... ...
o a ~c <0 _ at ~. c c In 0 6 z 1 a x in 1 1 1 1 1 160 180 SOLAR UV RADIATION INDEX FIGURE 5.7 Annual age-adjusted incidence rates for skin melanoma (SEER data, 1973-1976)
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From page 108... ...
Some early analysis of data collected at the University of Sydney suggests that in the women with higher incidence rates the ratio of superficial spreading melanoma to nodular and other histological types (Table 5.7) is higher than average.
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109 o Cal 3 o Ct no Ce :^ Ct .§ C)
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From page 110... ...
. These early findings could explain a number of other recent reports that note that the proportion of small and thin newly diagnosed melanomas is steadily increasing in populations with both very high and moderate incidence rates.
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From page 111... ...
nevus to a melanoma is analogous to the progression in the cervix from normal endothelial cells to squamous cell carcinoma in situ. It is also believed that on the skin, as on the cervix or in the bronchi, dysplasia is likely to occur in multiple sites.
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From page 112... ...
Other investigators expect that their results are likely to strengthen evidence favoring individual types of susceptibility and to emphasize the need to analyze melanoma incidence rates by histological type (Sober et al.
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From page 113... ...
The base line pigmentation of very dark skinned races protects against UV-B radiation 30 times better, and of moderately dark-skinned races 3 to 5 times better, than that of fair Caucasians. The range of base line pigmentation, and the capacity for tanning (i.e., for increasing melanin production)
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From page 114... ...
5. Epidemiological studies of skin cancer incidence and mortality rates have supplied valuable evidence confirming the existence of an association between basal and squamous cell skin cancers and sunlight.
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From page 115... ...
To do this, careful epidemiological studies based on reliable clinical and much more detailed histological descriptions at the time of diagnosis are needed.
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