Ultraviolet Radiation

Characteristics of UV Radiation

Fate and Transport of UV Radiation

Monitoring UV Radiation

Exposure Pathways

Methods of Measurement of Human Exposure

Prevention of Exposure


Harmful Effects

Dose Response

Absorption, Distribution, Metabolism

Sites of Toxicity

Biomarkers of Disease

Molecular Mechanism of Action

Risk Assessment and Risk Management

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Dose Response

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.

Ultraviolet-B radiation (UV-B) damages human skin: Acute exposure causes sunburn and chronic exposure results in loss of elasticity and increased aging. Some individuals, usually those living in areas with limited sunlight and long dark winters, may also suffer severe photo-allergies to the UV-B in sunlight. Increased absorption of UV-B triggers a thickening of the superficial skin layers and an increase in skin pigmentation, which act to protect the skin against future sunburns. This protective mechanism also makes the skin more vulnerable to skin cancer, however. Strong evidence exists of a dose-response relationship between nonmelanoma skin cancer and cumulative exposure to UV-B radiation. Increased risk of malignant melanoma is associated with episodes of acute exposure that result in severe sunburns, especially those that occur during childhood. In general, the incidence of nonmelanoma and malignant melanoma skin cancer has increased significantly over the past few decades. Researchers are examining the relationship of the growing risk of skin cancer to increases in ground-level UV-B radiation due to ozone depletion. http://www.ciesin.org/TG/HH/ozskin1.html

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:
1. The fact that people who lack the protective pigmentation (which reduces penetration of solar radiation into the skin) have higher CMM incidence rates.
2. A correlation, in well-designed ecologic epidemiological studies, of higher CMM incidence rates with decreasing latitude and increasing radiation (and in particular, UV-B) levels.
3. The demonstration in several case-control studies of an association between freckling and nevus formation (risk factors for CMM) and solar exposure.
4. Differences in CMM rates found between natives and immigrants to sunny climates.
5. High rates of CMM in Xeroderma Pigmentosum (XP) patients who are genetically deficient at repairing DNA damage induced by UV-B.
6. The indication, in case-control studies, that sun exposure at early ages and of an intermittent and severe nature (e.g., sunburn) results in higher CMM risks (Green et al, 1985; Holman et al, 1986).

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.

References
1. CIESIN Thematic Guides. The Relationship of Skin Cancer Prevalence and the Increase in Ultraviolet-B Exposure Due to Ozone Depletion. Center for International Earth Science Information Network, Columbia University. http://ciesin.org/TG/HH/ozskin1.html
2. CIESIN Thematic Guides. Ozone Depletion-Implications for the Tropics. Center for International Earth Science Information Network, Columbia University. http://www.ciesin.org/docs/001-539/001-539.html
3. CIESIN Thematic Guides. United Nations Environment Program. Center for International Earth Science Information Network, Columbia University. http://www.ciesin.org/docs/001-518/001-518.html

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