Nonionizing radiation has a wavelength longer than that or ionizing radiation, usually greater than about 1 nm. The best example of non ionizing radiation is ultraviolet (UV) light.
Mode of Action:
When microorganisms are subjected to UV light, cellular DNA absorbs the energy by purines and pyrimidine bases, and adjacent thymine molecules link together, as figure illustrates. Linked thymine molecules are unable to encode adenine on messenger RNA molecules during the process of protein synthesis. Moreover, replication of the chromosome in binary fission is impaired. The damaged organism can no longer produce critical proteins or reproduce, and it quickly dies. Ultraviolet light is especially effective in inactivating viruses. However, it kills far fewer bacteria than one might expect because of DNA repair mechanisms. Once DNA is repaired, new molecules of RNA and protein can be synthesized to replace the damaged molecules.
Conditions for Microbe control:
Ultraviolet (UV) light consists of light of wavelengths between 40 to 390 nm, but wavelength in the 200 nm range are most effective in killing microorganisms But according to some books wavelength between 260 – 265 nm is most effective.
Uses of Ultraviolet:
Ultraviolet light effectively reduces the microbial population where direct exposure takes place. It is used to limit airborne or surface contamination in a hospital room, morgue, pharmacy, toilet facility, or food service operation. In some communities, ultraviolet light is replacing chlorine in sewage treatment. When chlorine-treated sewage effluent is discharged into streams or other bodies of water, carcinogenic compounds form and may enter the food chain. The cost of removing chlorine before discharging treated effluent could add as much as $100 per year to the sewage bills of the average American family, and very few sewage plants do this. Running the sewage effluent under ultraviolet light before discharging it can destroy microorganism without altering the odor, pH, or chemical composition of the water and without forming carcinogenic compounds.
It does penetrate air, effectively reducing the number of airborne microorganism and killing them on surfaces on operating rooms and rooms that will contain caged animals. To help sanitize the air without irradiation humans, these lights can be turned on when there rooms are not in use. . Hanging laundry outdoors on bright, sunny days takes advantage of the ultraviolet light present in sunlight. Although the quantity of UV rays in sunlight is small, these rays may help kill bacteria on clothing, especially diapers.
Disadvantage of UV Light:
A major disadvantage of UV light as a disinfectant is that the radiation is not very penetrating, so the organism to be killed must be directly exposed to the rays. It is noteworthy microorganisms in the air and upper layers of the soil, but it may not the effective against all bacterial spores. Organisms protected by solids and such coverings as paper, glass, and textiles are not affected. Another potential problem is that UV light can damage human eyes, and prolonged exposure can cause burns and skin cancer in humans. And it may cause damage in human skin cells and permanent damage the eyes.
SUN--Free Source of UV:
Sunlight contains some UV radiation, but the shorter wavelengths – those most effective against bacteria – are screened out by the ozone layer of the atmosphere. The antimicrobial effect of sunlight is due almost entirely to the formation of singlet oxygen on the cytoplasm. Many pigments produced by bacteria provide protection from sunlight.