Stratospheric Ozone Depletion - The Changing Arctic Environment: The Arctic Messenger - page 111

The Biological Effects of UV Radiation and Trends in
UV Exposure
Despite the fact that the Arctic and Antarctic have experienced the most intense episodes
of increased UV irradiance resulting from ozone depletion, there has been (with a few ex-
ceptions) a dearth of information on what this means to human and environmental health
in these two polar regions. Therefore, in this section, we will have to resort to observations
made largely at other latitudes and from experimental studies.
We have already noted that human health and environmental scientists are worried
about the thinning of the stratospheric ozone layer. This is because before thinning occurred,
the layer absorbed much (but not all) of the incoming solar UV-B and some of the UV-A
radiation. Therefore, most of the UV that is encountered by plants, animals and near-surface
aquatic life is UV-A. In humans, excessive UV-A exposure first results in congested blood
capillaries in our skin, called erythema (sunburn), and localized oxidative stress. The result
is a pigment-darkening effect (tanning) caused by redistribution of the pigment melanin that
is stored in skin cells, called melanocytes . Overexposure to UV-A is associated with a num-
ber of human medical outcomes, including cataract formation, premature aging and tough-
ening of the skin and immune system suppression.
UV-B is more likely to produce erythema than UV-A. It also results in an effect on
the melanocytes, but this time, it involves the production of new melanin. The main cause
for concern is that UV-B is sufficiently energetic that it can cause photochemical damage to
DNA. When DNA absorbs UV-B radiation, some of the bonds that maintain the shape of the
DNA molecule are broken and the shape can change. If this happens, it can interfere with
the way in which protein-building enzymes interpret the DNA code. DNA has always been
exposed to a certain amount of UV-B radiation. Consequently, it has evolved mechanisms
to recognize and repair such damage. However, when some damage is not repaired, aberrant
reading of the DNA code may result in serious health effects, including skin cancer.