Environmental hazards of solar radiation

Sunburn
Ultraviolet radiation as a hazard
Ictus solaris

Nature

Ultraviolet radiation represents that portion of the spectrum between X-rays and visible light. The greatest natural source is the sun, which makes sunlight is a broad-spectrum destroyer of large molecules. The ozone layer in the earth's atmosphere screens out much solar ultraviolet radiation; but thermal and chemical pollution of the atmosphere diminishes its screening ability, thus exposing the biosphere to a potential hazard of global extent.

UV radiation causes sunburn and skin cancer and accelerates skin ageing. Overexposure to UV radiation can lead to inflammations of the cornea and the conjunctiva in the eye and causes or accelerates cataract development. It may reduce the effectiveness of the immune system.

Background

The sun emits energy in the forms of light and heat. The light energy is called ultraviolet radiation (UV rays) and it ranges in intensity. We measure UV light in nanometers of wavelength. There are three types of UV rays: UVC, UVB and UVA:

Ultraviolet C is the shortest wavelength UV radiation (around 250 nanometres) and barely reaches the surface of the earth because the upper levels of the atmosphere absorb their energy.
Ultraviolet B (UVB, 380 nanometres) causes sunburn and generally increases the risk of skin cancer. It causes snow blindness and glare. Ultraviolet A (UVA, 380 nanometres) can penetrate clouds, water, and clothing. It the part of sunlight that tans.
Ultraviolet A (UVA) pass through the skin into the tissues that contain pigment-containing cells which make melanin. It converts melanin into a photocarcinogen, increasing the risk of melanoma, the most deadly form of skin cancer. These rays can get absorbed into the lens of the eye and damage the retina.

Incidence

Many people in industrialized countries are exposed to additional ultraviolet radiation because of their use of a wide range of apparatus in homes, industries, places of entertainment, health clubs and research establishments. Typical apparatus emitting ultraviolet radiation includes therapeutic lamps, sterilization and welding equipment. An increase in popular outdoor activities and changed sunbathing habits often result in excessive UV exposure. Skin cancer has frequently been reported in people whose recreation or occupation requires them to be exposed for long periods to direct solar radiation. Occupational exposure to ultraviolet radiation occurs constantly in arc welding and in the use or proximity to a large variety of testing and quality control machines using ultraviolet radiation, in industries as varied as food processing and machine assembly. Other occupational exposure occurs among attendants at health spas, beauticians and similar places where sun lamps are used. Such radiation mainly affects the eyes, causing intense conjunctivitis and keratitis (welder's flash). Symptoms are redness of the eyes and pain, which usually disappears in a few days. No permanent disability appears to result from this occupational disease; however, during periods of eyesight impairment, driving and other accidents may be caused.

Suntan parlour tanning beds, which deliver about 99% UVA to the skin, present a significant danger to users. A 1994 study found that young women aged 18 to 30 who went to a suntan parlour 10 times or more a year had seven times the incidence of melanoma than women who did not go to suntan parlours. The increase in risk for those who use tanning beds occasionally was 3 times.

The market for protective suntan creams in the UK in 1986 was £37 million.

Claim

Ultraviolet is the major known cause of skin cancer. If we all lived underground the rate of cancer would be much lower so in one sense it is a preventable tumour. The question is how should people alter their lives?

It is not disputed that exposure to sun increases the risk of skin cancer. It is believed that the riskiest types of exposure are sunburn, particularly during childhood, and intermittent exposure – such as office workers taking two-week holidays in the sun. Such intermittent exposure is thought to increase the risk of malignant melanoma by 70 per cent, while sunburn is supposed nearly to double the risk. But studies of sunburn and cancer have been disputed because people with skin cancer are more likely to remember having had sunburn.