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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Risk Assessment and Risk Management Considerations

Risk Assessment

Hazard Identification

UV rays are just beyond visible light at shorter wavelengths than the last visible ray, which is violet. Ultraviolet rays are part of the electromagnetic spectrum that can reach a high enough level on earth to be harmful to plants, animals and humans.

There are three categories of UV radiation; UV-A, UV-B and UV-C. UV-A rays have a wavelength of 320-420 nanometers (nm). UV-B rays have a wavelength of 280-320 nm, and UV-C rays have a wavelength of less than 280 nm.

UV-A radiation causes us less harm compared to the shorter wavelengths. Although, it can cause sunburn and cataracts. UV-A radiation can benefit humans by synthesizing vitamin D in the body. In addition, UV-C radiation is filtered out by ozone in the stratosphere. Only a small amount reaches the earth’s surface.

UV-B radiation poses a threat to life on earth even though some of it is filtered out by ozone in the stratosphere. UV-B radiation is capable of causing harm at the molecular level. The cumulative exposure of UV-B radiation may cause sunburn, cataracts, suppressed immune systems, premature aging including; wrinkles and skin discolorations as well as skin cancer.

The most common areas of the body to develop skin cancer are on the face or neck, ears, forearms or hands. There are three main types of skin cancer; basal cell carcinoma, squamous cell carcinoma, and malignant melanomas.

Dose-Response Evaluation

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.

Exposure Assessment

Exposure to sunlight can be enjoyable, but too much can be dangerous. Overexposure to ultraviolet (UV) radiation in sunlight can result in painful sunburn. It can also lead to more serious health effects, including skin cancer, premature aging of the skin, and other skin disorders; cataracts and other eye damage; and immune system suppression.

People whose skin tans poorly or burns easily after sun exposure are particularly susceptible to nonmelanoma skin cancer. These people in particular may benefit by following prevention methods for nonmelanoma skin cancer.

Studies have suggested that reducing exposure to ultraviolet (UV) radiation decreases the incidence of nonmelanoma skin cancer. Ultraviolet radiation is a stream of invisible high-energy rays coming from the sun. Artificial sources such as tanning booths and sunlamps also produce ultraviolet radiation.
A child's skin is more sensitive to the sun than an adult's skin and is more easily burned. Babies younger than 6 months should always be completely shielded from the sun. Children 6 months and older should wear sunscreen every day.

The best way to prevent skin cancer is to protect yourself and your family from excessive exposure to sunlight -- and not only when you go to the beach. Skin cancer prevention should be practiced every day by wearing protective clothing, avoiding the mid-day sun, and using sunscreen

Risk Characterization

  • There has been an 1,800 percent rise in malignant melanoma since 1930.
  • One American dies of skin cancer every hour.
  • One in five Americans develops skin cancer.
  • People get 80 percent of their lifetime sun exposure by the age of 18.


Risk Management

The UV index is a scale for measuring the amount of UV radiation reaching the ground and posing danger to humans. On a scale of 0-10, 0 is minimal exposure, 10 is very high exposure.

0-2 indicates little danger. Most people can stay outside one hour without burning.
3-4 is low risk. An average person can withstand a half hour without burning.
5-6 is a moderate risk. Twenty to Thirty minutes is the limit in noon sun.
7-8 is high risk. The sun should be avoided from 10am to 4pm. Thirteen to twenty minutes of exposure can lead to burning.
9-10 is very high risk. Burning can occur in less than thirteen minutes.

Using the UV Index

The UV Index can help the public be aware of the level of UV radiation exposure expected on a given day. As a result, people can use simple sun protective behaviors to reduce their lifetime risk of developing skin cancer and other sun-related illnesses. What follows is a description of each UV Index level and tips you can give to help people prepare.


0 to 2: Minimal A UV Index reading of 0 to 2 means minimal danger from the sun's UV rays for the average person: Most people can stay in the sun for up to 1 hour during the hours of peak sun strength, 10 a.m. to 4 p.m., without burning. People with very sensitive skin and infants should always be protected from prolonged sun exposure. Look Out Below Snow and water can reflect the sun's rays. Skiers and swimmers should take special care. Wear sunglasses or goggles, and apply sunscreen with an SPF of at least 15. Remember to protect areas that could be exposed to UV rays by the sun's reflection, including under the chin and nose.

3 to 4: Low A UV Index reading of 3 to 4 means low risk of harm from unprotected sun exposure. Fair-skinned people, however, might burn in less than 20 minutes: Wear a hat with a wide brim and sunglasses to protect your eyes. Use a sunscreen with an SPF of at least 15 and wear long-sleeved shirts and long pants when outdoors. Me and My Shadow An easy way to tell how much UV exposure you are getting is to look for your shadow: If your shadow is taller than you are (in the early morning and late afternoon), your UV exposure is likely to be low. If your shadow is shorter than you are (around midday), you are being exposed to high levels of UV radiation. Seek shade and protect your skin and eyes.

5 to 6: Moderate A UV Index reading of 5 to 6 means moderate risk of harm from unprotected sun exposure. Fair-skinned people might burn in less than 15 minutes. Apply a sunscreen with an SPF of at least 15. Wear a wide-brim hat and sunglasses to protect your eyes: Use sunscreen if you work outdoors and remember to protect sensitive areas like the nose and the rims of the ears. Sunscreen prevents sunburn and some of the sun's damaging effects on the immune system. Use a lip balm or lip cream containing a sunscreen. Lip balms can help protect some people from getting cold sores. Made in the Shades Wearing sunglasses protects the lids of your eyes as well as the lens.

7 to 9: High A UV Index reading of 7 to 9 means high risk of harm from unprotected sun exposure. Fair-skinned people might burn in less than 10 minutes. Minimize sun exposure during midday hours, from 10 a.m. to 4 p.m. Protect yourself by liberally applying a sunscreen with an SPF of at least 15. Wear protective clothing and sunglasses to protect the eyes: When outside, seek shade. Don't forget that water, sand, pavement, and grass reflect UV rays even under a tree, near a building, or beneath a shady umbrella. Wear long-sleeved shirts and trousers made from tightly woven fabrics. UV rays can pass through the holes and spaces of loosely knit fabrics. Stay in the Game Be careful during routine outdoor activities such as gardening or playing sports. Remember that UV exposure is especially strong if you are working or playing between the peak hours of 10 a.m. and 4 p.m. Don't forget that spectators, as well as participants, need to wear sunscreen and eye protection to avoid too much sun.

10+ Very High A UV Index reading of 10+ means very high risk of harm from unprotected sun exposure. Fair-skinned people might burn in less than 5 minutes. Outdoor workers are especially at risk as are vacationers who can receive very intense sun exposure. Minimize sun exposure during midday hours, from 10 a.m. to 4 p.m. Apply sunscreen with an SPF of at least 15 liberally every 2 hours: Avoid being in the sun as much as possible. Wear sunglasses that block 99 to 100 percent of all UV rays (both UVA and UVB). Some reduction in blue light also might be beneficial but colors should not be severely distorted. Wear a cap or hat with a wide brim, which will block roughly 50 percent of UV radiation from reaching the eyes. Wearing sunglasses as well can block the remainder of UV rays. Beat the Heat If possible, stay indoors on days when the UV Index is very high. Take the opportunity to relax with a good book rather than risk dangerous levels of sun exposure. Try not to pursue outdoor activities, whether at work or at play, unless protected with sunscreen, hat, and sunglasses.


UV Protection

Know the ABC’s of early detection

  • Away: Stay away from the sun in the middle of the day.
  • Block: Use a sunscreen with SPF 15 or higher to protect sensitive skin.
  • Cover up: Wear clothing that covers the skin, with hats on heads and sunglasses with UV protection over eyes.
  • Speak out: Teach others to protect their skin from sun damage.
  • Stay out of the sun during the peak hours of UV radiation, from 10 a.m. to 4 p.m.
  • Wear protective clothing:
    • Wide-brimmed hats that protect the face and neck
    • Tightly-woven clothing made of thick material, such as unbleached cotton, polyester, wool, or silk
    • Dark clothing with dyes added that help absorb UV radiation
    • Loose-fitting long-sleeved clothing that covers as much of the skin as possible
    • Clothing that has sun protection factor (SPF) in the fabric that does not wash out
  • Wear sunscreen with an SPF of 15 or higher summer and winter, on both cloudy and clear days:
    • SPF of 11 offers minimal protection.
    • SPF of 12 to 29 offers moderate protection.
    • SPF of 30 and above offers high protection.
  • Apply sunscreen that blocks both UVA and UVB to all exposed skin, including lips, ears, back of hands, and neck. Apply sunscreen 30 minutes before going in the sun, and reapply it every 2 hours and after swimming, exercising, or sweating.
  • Wear sunglasses that block at least 99% of UVA and UVB radiation.
  • Be careful when you are on sand, snow, or water, because these surfaces can reflect 85% of the sun's rays.

References:

http://www.epa.gov
http://www.nasa.gov/

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