Since the ozone layer absorbs most of the harmful ultraviolet-B (UV-B) radiation from the sun. If the ozone layer depletes, more harmful UV-B radiation will reach the earth through the damaged ozone layer. These changes are of interest because more UV-B radiation means more skin cancers, more diseases and eye cataracts, less yield from plants, less productivity from oceans, damage to plastics.
Effects on Human Health
The cells of three different organ systems can be directly exposed to UV radiation-the eyes, the skin, and the immune system.
The effects of UV radiation on the eye may be acute (occurring often after a short, intense exposure usually after a latent period of several hours) or long-term after an acute exposure. The commonest acute effect, photokeratitis (snow blindness) leaves few or no permanent effects, whereas cataract due to chronic exposure is irreversible and ultimately leads to blindness.
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Figure: Soft UV radiation-absorbing
contact lens covering the entire cornea
Potential acute and chronic effects of exposure to UV-B on the eye and adjacent tissues
Lid and peri-ocular skin
Sunburn: erythema (redness), blistering, exfoliation (peeling)
Lentigines (age spots) Hypomelanosis (vitiligo) Non-melanoma skin cancer
Pinguecula (local degeneration)
Dyskeratosis (abnormal epithelial cell differentiation) Intraepithelial neoplasia
Endothelial damage (swelling)
Reactivation of latent herpes viruses
Climatic droplet keratopathy (epithelial degeneration)
Pterygium (see text)
Anterior subcapsular opacities
Age-related cataract (see text)
For acute exposure, sunburn is the effect most frequently experienced by the human due to excessive solar UV-B exposure. It is an inflammatory reaction to a toxic assault on the skin. Fair-skinned people are most susceptible to sunburn, and they correspondingly run a higher risk of long term adverse effects, such as premature aging( the skin become thick, wrinkled, and leathery) and skin cancer.
The UV irradiation causes skin cancers by altering critical genes that control cell division and cell death. Altered genes result from the ability of UV to make chemical alterations in DNA, the building block of genes. Some of the genes involved in skin cancer development have been identified.
The majority of skin cancers is non-melanoma skin cancers (NMSC) which consisting of basal cell carcinomas (BCC) and squamous cell carcinomas(SCC), the malignant potential is low which also reduces death from these diseases. This is not the case for the most malignant form of skin cancer, melanoma, that arises from pigment cells (melanocytes), and is responsible for most of the deaths from the skin cancer.
It is predicted that a 10 percent decrease in the ozone in the stratosphere could cause an additional 300,000 non-melanoma and 4,500 (more dangerous) melanoma skin cancers worldwide annually.
The immune system
The immune system can be altered by UV irradiation, leading to diminished immune
responses to infectious agents and skin cancers.
Some cells of the immune system, called antigen-presenting cells, reside in the skin.
Their function is to survey the skin for foreign challenges, such as invading microorganisms
or tumour proteins. They capture any molecules they find and carry them to the nearest lymph node where the active immune response is initiated. Exposing the skin to UV-B radiation causes several changes
- leads to a change in the antigen-presenting cells so that the immune response may induce suppression.
- to stimulate the production of a particular range of immune mediators in the skin that also favour suppressing immune responses.
Numerous laboratory animal models of infectious diseases demonstrate that exposure to UV radiation at a critical time during infection can increase the severity and duration of the disease.
Effects of increased UV-B radiation on plants
Only a small proportion of the UV-B radiation striking a leaf penetrates into the inner tissues. When exposed to enhanced UV-B radiation, many species of plants can increase the UV absorbing compounds in their outer leaf tissues. Other adaptations include increased thickness of leaves, thereby reducing the proportion of inner tissues exposed to UV-B radiation and changes in the protecting waxy layer of the leaves. Several repair mechanisms exist in plants, including repair systems for damage to DNA and other vital biomolecules. Despite mechanisms to reduce or repair these effects and a limited ability to adapt to increased levels of UVB, plant growth can be directly affected by UVB radiation
Possible changes in plant characteristics
Reduced water-use efficiency
Enhanced drought stress sensitive
Reduced leaf area
Reduced leaf conductance
(either inhibited or stimulated)
Reduced dry matter production
Enhanced plant fragility
Effects on aquatic life
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Phytoplankton is at the start of the aquatic food chain, which account for 30 per cent of the world's intake of animal protein. Phytoplankton productivity is restricted to the upper layer of the water where sufficient light is available. However, even at current levels, solar UV-B radiation limits reproduction and growth. A small increase in UV-B exposure could significantly reduce the size of plankton populations, which affects the environment in two ways. The first, less plankton means less food for the animals that prey on them and a reduction in fish stocks, already depleted by overfishing. Furthermore, with less organic matter in the upper layers of the water, UV radiation can penetrate deeper into the water and affect more complex plants and animals living there. Solar UV radiation directly damages fish, shrimp, crab, amphibians and other animals during their early development. Pollution of the water by toxic substances may heighten the adverse effects of UV radiation, working its way up the food chain.
Effect on environmental processes and cycles
UV radiation influences the biological productivity of oceans, including the production of gases at their surfaces and their subsequent transfer to the atmosphere. Once in the atmosphere, trace gases such as carbon dioxide (CO2) interact with the physical climate system resulting in alterations to climate and feedbacks in the global biogeochemical system. Since atmospheric CO2 plays a central role in the distribution of heat in the atmosphere, its increasing concentrations may affect many components of the physical climate system, such as wind, precipitation and the exchange of heat and energy between the air and the oceans. There are also similarly complex interactions between biogeochemical cycles on land and the integrated climate system that may have important implications for organisms on Earth. At this stage, it is not possible to predict the overall environmental effects of these complex interactions between changes in climate and UV radiation.
Figure : Conceptual model illustrating the potential effects of enhanced UV radiation and climate change on biogeochemical cycles: OM organic matter; DOM dissolved organic matter; CDOM colored (chromophoric) DOM; CO2 carbon dioxide; CO carbon monoxide; DMS dimethylsulfide; OCS carbonyl sulfide; VOCs volatile organic hydrocarbons; CH3Br methyl bromide.
Effect on plastics and wood products
Available data on the degradation of plastics by the UV in sunlight show that for common polymers a portion of the damage that occurs over time is attributable to the UV-B radiation component.
Plastics materials, Rubber products, Coatings, Natural polymers (e.g. wood)
Absorption of UV radiation by material
Chemical reactions that degrade the materials. Reduction in useful properties
Reduced service lifetimes outdoors. Under high UV exposure unexpected failure of products
UV Absorbers and opacifiers prevent material from absorbing harmful UV radiation
Light stabilizer chemicals prevent the damaging chemical reactions
Service life maintained using higher levels of stabilizer. Cost of product increased
Figure : The effect of stabilizers on the degradation of polymers.