Answer to Question #4004 Submitted to "Ask the Experts"

How is radiation used to sterilize medical instuments?

Sterilization, the killing of bacteria (or any types of cells), on medical instruments is primarily achieved by the radiation causing severe damage to the cell's chromosomes, specifically the DNA. "Severe damage" to DNA is multiple breaks in the long DNA ladder-like structure. Radiation (for example, x rays or beta and alpha radiation) has enough energy to ionize atoms and molecules; that is, it can create charged particles and free radicals. In cells, the water can be ionized to form free radicals, somewhat like H-plus and OH-minus radicals found in acids and bases. The free radicals made inside a cell's nucleus can cause damage to (breaks in) the DNA structure (the radiation may also directly cause ionizing breaks in the DNA's chemical chain). If enough damage is done to the cell's DNA, which acts as the cell's control mechanism, the cell cannot function properly or reproduce and the result is cell death (sterilization).

Radiation is used to sterilize medical instruments by first sealing a clean, but not bacteria-free, instrument in an air-tight bag. The bag and instrument are then placed in a very large field of radiation that can penetrate the bag—for example, gamma radiation, x rays, or high-energy electrons. These ionizing-radiations can kill the bacteria (cells); and the air-tight bag will keep the instrument sterile until it is opened in the medical facility.

You may want to look at the following E-Beam Services, Inc., Web site for more information.

Hope this helps and thanks for your question.

John P. Hageman, MS, CHP