Ionizing Radiation: (Radiation Sterilization)

Mode of Action:

Both, X rays and Gamma rays have wavelength shorter than the wavelength of ultraviolet light. X rays, which have wavelength of 0.1 to 40 nm, and gamma rays, which have even shorter wavelength, are forms of ionizing radiation, so named because it can dislodge electrons from atoms, creating ions. (Longer wavelengths comprise nonionizing radiation.) These forms of radiation also kill microorganisms and viruses and ionizing radiation damages DNA and produces peroxides, which act as powerful oxidizing agents in cells. This radiation can also kill or cause mutations in human cells if it reaches them.

Production of Gamma rays:

Gamma rays are emitted by certain radioactive elements such as cobalt, and electron beams are produced by accelerating electrons to high energies in special machines.

Production of X rays:

X rays, which are produced by machines in a manner similar to the production of electron beams, are similar in nature to gamma rays.

Advantage of Gamma rays:

Gamma rays penetrate deeply but may requite hours to sterilize large masses.

High energy Electron Beams:

Effectiveness of Electron Beam:

High energy electron beams have much lower penetration power but usually require only a few seconds of exposure.

Mode of Action of Ionizing Radiations:

The principal effect of ionizing radiation is the ionization of water, which forms highly reactive hydroxyl radicals. These radicals react with organic cellular components, especially DNA.

The so-called target theory of damage by radiation supposes that ionizing particles, or packets of energy, pass through or close to vital portions of the cell; these constitute "hits." One, or a few, hits may only cause nonlethal mutations, some of them conceivably useful. More hits are likely to cause sufficient mutations to kill the microbe.

Application of Method:

The food industry has recently renewed it interest in the use of radiation for food preservation. It can be used to prevent spoilage in seafood by doses of 100 to 250 kilorads, in meats and poultry by doses of 50 to 100 kilorads, and in fruits by doses of 200 to 300 kilorads. (one kilorad equals 1000 rads) many consumers in the United States reject irradiation foods for fear o receiving radiation, but such foods are quite safe --- free of both pathogens and radiation. In Europe, mil and other foods are often irradiated to achieve sterility. Especially high energy electron beams, is used for the sterilization pharmaceuticals and disposable dental and medical supplies, such as plastic syringes, surgical gloves, suturing materials, and catheters. As a protection against Bioterrorism, the postal service often uses electron beam radiation to sterilize certain classes of mail. These radiations can be used to differentiate between Gram positive and negative bacteria. Gram-positive bacteria are more sensitive to ionizing radiations than gram-negative bacteria. Ionizing radiations are currently used to sterilize such heat sensitive pharmaceuticals as vitamins, hormones, and antibiotics, as well as certain plastics and suture materials.

Worldwide Importance and Controversy:

Ionizing radiations have also been approved for controlling microorganisms, and for preserving foods, as noted in MIcrofocus 21.4. The approval has generated much controversy, fueled by activists concerned about the safety of factory workers and consumers. First used in 1921 to inactivate Trichinella spiralis, the agent of trichinosis, irradiation is now used as a preservative in more than 40 countries for over 100 food items, including potatoes, onions, cereals, flour, fresh fruit, and poultry. The US Food and Drug Administration (FDA) approved cobalt-60 irradiation to preserve poultry in the early 1990s, and in 1997, it extended the approval to preserve red meat such as beef, lamb and pork.