Environmental Engineering Reference
In-Depth Information
of ozone-depleting substances in the upper atmosphere. Consequently, stratospheric ozone
levels are nolonger declining. Therefore, Northern Hemisphere mid-latitudes are at present
experiencing UV-B irradiances only 5% greater than in 1980. Of course, peak values are
much higher at high and polar latitudes, where ozone depletion has been larger. We will
return to projections on the levels of UV irradiance for the rest of the present century at the
end of this chapter.
Here is a closer look at some of the human health and environmental effects that have
been attributed to chronic UV-B radiation exposure. The most well-established evidence
concerns the incidence of several types of skin cancer.
There are two broad categories of cancer involved: cutaneous malignant melanomas
and nonmelanoma skin cancers (basal cell carcinoma and squamous cell carcinoma). The
latter two are the most common forms of skin cancer. A crusty area that develops on ex-
posedskin,knownasan actinic or solar keratisis ,appearstooftenbeaprecursortosquam-
ous cell carcinoma. Fair-skinned people spending much of their lives in sunny locations are
the most susceptible, but treatments are usually effective and mortality is low. Cutaneous
melanoma is less common but is much more dangerous.
According to the UNEP 2010 assessment, the incidence of all three of these tumours
has risen significantly over the past five decades, particularly in people with fair skin. For
cutaneous malignant melanoma, there has been an average increase of 1-3% per year. The
annual incidence of cutaneous malignant melanoma also varies geographically. For ex-
ample, the incidence in Europe ranges from between five and 24 per 100,000 to more than
70 per 100,000 in higher ambient UV radiation regions of Australia and New Zealand. In
Australia, melanoma is now the third-most reported cancer in men and women. The num-
ber of cases of melanoma in dark-skinned people is fewer than in fair-skinned people. It
has historically been uncommon in people under age 20, but in 2007, Lange and colleagues
reported an increase of 2.9% per year between 1973 and 2003 in the United States. How
much of this may be linked to societal trends, such as sunbathing, is unclear.
In addition to the temporal and geographical coincidence of these epidemiological
trends with corresponding trends of ozone depletion and increased UV irradiance, there are
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