Effects of Ionizing Radiation on Living Matter

Whereas nonionizing radiation is relatively harmless, ionizing radiation has a destructive effect on living tissue. When the atom that was ionized is part of a biological macromolecule or membrane component, the results can be devastating. 

Doses are often expressed in millirems (10 rem). The SI unit for dosage equivalent is the sievert (Sv). It is defined in the same way as the rem but with absorbed dose in grays thus, 1 rem = 0.01 Sv. 

Sources of Ionizing Radiation We are continuously exposed to ionizing radiation from natural and artificial sources (Table 23.6, next page). Indeed, life evolved in the presence of natural ionizing radiation, called background radiation. The same radiation that can alter bonds in DNA and cause harmful mutations also causes beneficial mutations that, over time, allow organisms to adapt and species to change. 

Internal radiation from minerals in tap water and daily intake of food  

The largest artificial source of radiation, and the easiest to control, is associated with medical diagnostic techniques, especially x-rays. The radiation dosage from nuclear testing and radioactive waste disposal is miniscule for most people, but exposures for those living near test sites, nuclear energy facilities, or disposal areas may be many times higher. 

Our ability to detect minute amounts of radioisotopes makes them powerful tools for studying processes in biochemistry, medicine, materials science, environmental studies, and many other scientific and industrial fields. Such uses depend on the fact that isotopes of an element exhibit very similar chemical and physical behavior. In other words, except for having a less stable nucleus, a radioisotope has nearly the same chemical properties as a nonradioactive isotope of a given element For example, the fact that is utilized by a plant in the same way 

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The effect of ionizing radiation on living matter depends on the quantity of energy absorbed and the extent of ionization in a given type of tissue. Radiation dose for the human body is measured in rem. 

We have discussed that ionization and ex tdfion are the two events that take place when radiation Interacts with matter. These events can also take place when radiation interacts with living tissues. This is (ffecfisefy the mechanism by vdilch radiation can have deleterious effects on life (see Boar 13.7. Although eveiy individual in the world is exposed to a small amount of radiation arising from natiunl and man-made sources, exposure to radiation is of more than mundane interest to a biologist who is exposed to radiations from tracer experiments which have become so common and useful. It is erefore useful for a biologist to know what are the tolerable radiation doses and to limit his/her exposure to those levels or levels even lower. 

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