The ultraviolet (UV) region of the electromagnetic spectrum is intermediate in wavelength and frequency between the x-ray and the visible regions. UV radiation can produce damage to the eyes and skin. The wavelength of the radiation and the length of the exposure determine the type and extent of the damage. UV radiation is emitted when excited atoms make transitions from a higher to a lower energy state, thus releasing photons with energies in the UV range. The primary man-made method of generating UV radiation is to excite atoms via an electrical arc through a gas or a vapor and intense heat. Examples of sources of UV radiation are mercury vapor lamps, fluorescent lights, germicidal lamps, black light lamps, plasma torches, open arcs (such as those used in arc welding) and sunlamps used in the tanning salon industry.
The Agency currently regulates tanning facilities and mercury vapor lamps, see AAC Title 12, Chapter 1 Article 14 "The Control of nonionizing Radiation".
For more information on this topic, please visit the following sites:
EPA Ultraviolet Index
Ultraviolet Information Sheet (New Zealand National Institute of Water and Atmospheric Research at Lauder )
UV NASA (NASA)
The US National Institute of Health (Sunlight, Ultraviolet Radiation, and the Skin)
Ultraviolet Radiation DA UV-B Radiation Monitoring Program
USDA UV (USDA at Colorado State University)
MORE ON ULTRAVIOLET RADIATION
All energies that move at the speed of light are collectively referred to as electromagnetic radiation or 'light'. Various types of light differ in their wavelength, frequency and energy; higher energy waves have higher frequencies and shorter wavelengths. Pigments inside the retina of our eyes absorb wavelengths of light between 400nm-700nm, collectively referred to as 'visible light'. A "nm'' is a nanometer which is one billionth, or 10e-9, meters. Stratospheric Oxygen and Ozone molecules absorb 97-99% of the sun's high frequency Ultraviolet light, light with wavelengths between 150 and 300nm. Ultraviolet-B (UV-B) is a section of the UV spectrum, with wavelengths between 270 and 320nm.
The amount of UV-B light received by a location is strongly dependent on:
- Latitude and elevation of the location. At the high-latitude Polar Regions the sun is always low in the sky; because the sunlight passes through more atmosphere so more of the UV-B is absorbed. For this reason average UV-B exposure at the poles is over a thousand times lower than at the equator.
- Cloud cover; the reduction in UV-B exposure depends the cover's thickness.
- Proximity to an industrial area because of the protection offered by photochemical smog. Industrial processes produce ozone, one of the more irritating components of smog, which absorbs UV-B. This is thought to be one of the main reasons that significant ozone losses in the Southern Hemisphere have not been mirrored in the Northern Hemisphere.
HEALTH EFFECTS OF UV-B LIGHT
Genetic damage DNA absorbs UV-B light and the absorbed energy can break bonds in the DNA. Most of the DNA breakage’s are repaired by proteins present in the cell nucleus but unrepaired genetic damage of the DNA can lead to skin cancers. In fact one method that scientists use to analyze amounts of 'genetically-damaging UV-B is to expose samples of DNA to the light and then count the number of breaks in the DNA. For example J.Regan's work at the Florida Institute of Technology used human DNA to find that genetically significant doses of solar radiation could penetrate as far as 9 feet into non-turbulent ocean water.
The Cancer link. The principle danger of skin cancer is to light-skinned peoples. A 1% decrease in the ozone layer will cause a estimated 2% increase in UV-B irradiation; it is estimated that this will lead to a 4%increase in basal carcinomas and 6% increase in squamous-cell carcinomas.[Graedel&Crutzen]. 90% of the skin carcinomas are attributed to UV-B exposure [Wayne] and the chemical mechanism by which it causes skin cancer has been identified [Tevini]. The above named carcinomas are relatively easy to treat, if detected in time, and are rarely fatal. But the much more dangerous malignant melanoma is not as well understood. There appears to be a correlation between brief, high intensity exposures to UV and eventual appearance (as long as 10-20yrs!) of melanoma. Twice as many deaths due to melanomas are seen in the southern states of Texas and Florida, as in the northern states of Wisconsin and Montana, but there could be many other factors involved. One undisputed effect of long-term sun exposure is the premature aging of the skin due to both UV-A, UV-B and UV-C. Even careful tanning kills skin cells, damages DNA and causes permanent changes in skin connective tissue which leads to wrinkle formation in later life. There is no such thing as a safe tan.
Possible eye damage can result from high doses of UV light, particularly to the cornea, which is a good absorber of UV light. High doses of UV light can causes a temporary clouding of the cornea, called 'snow-blindness’ and chronic doses has been tentatively linked to the formation of cataracts. Higher incidences of cataracts are found at high elevations, Tibet and Bolivia; and higher incidences are seen at lower latitudes (approaching the equator).
Damage to marine life. The penetration of increased amounts of UV-B light has caused great concern over the health of marine plankton that densely populate the top 2 meters of ocean water. The natural protective-response of most chlorophyll containing cells to increased light-radiation is to produce more light-absorbing pigments but this protective response is not triggered by UV-B light. Another possible response of plankton is to sink deeper into the water but this reduces the amount of visible light they need for photosynthesis, and thereby reduces their growth and reproduction rate. In other words, the amount of food and oxygen produced by plankton could be reduced by UV exposure without killing individual organisms. There are several other considerations:
- Ultraviolet levels are over 1,000 times higher at the equator than at the polar regions so it is presumed that marine life at the equator is much better adapted to the higher environmental UV light than organisms in the polar regions. The current concern of marine biologists is mostly over the more sensitive Antarctic phytoplankton, which normally would receive very low doses of UV. Only one large-scale field survey of Antarctic phytoplankton has been carried out so far [Smith et.al _Science_1992]; they found a 6-12% drop in phytoplankton productivity once their ship entered the area of the springtime ozone hole. Since the hole only lasts from 10-12 weeks this translates into a 2-4% loss overall, a measurable but not yet catastrophic loss.
- Both plants and phytoplankton vary widely in their sensitivity to UV-B. When over 200 agricultural plants were tested, more than half showed sensitivity to UV-B light. Other plants showed negligible effects or even a small increase in vigor. Even within a species there were marked differences; for example one variety of soybean showed a 16% decrease in growth while another variety of the same soybean showed no effect [R.Parson]. An increase in UV-B could cause a shift in population rather than a large die-off of plants
- An increase in UV-B will cause increased amounts of Ozone to be produced at lower levels in the atmosphere. While some have hailed the protection offered by this 'pollution-shield' many plants have shown themselves to be very sensitive to photochemical smog.
R.Parson FAQ 111 ,UV and biological effects of UV
FDA Consumer Magazine and publications: FDA#87-8272, #81-8149 and #92-1146
M.Tevini, ed. UV-B Radiation and Ozone Depletion: Effects on humans, animals, plants, microorganisms and materials Lewis Pub. Boca Raton, 1993.
R.P.Wayne, Chemistry of the Atmospheres 2nd ed. Oxford 1991
R.Smith et al. "Ozone depletion: Ultraviolet radiation and phytoplankton biology in Antarctic waters"' Science, 255, 952. (1992)
Author: Brien Sparling
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