Biological Effects Of Radiation

The Biological Effects of Radiation

Whether the source of radiation is natural or man made, whether it is a small dose of radiation or a large dose, there will be some biological effects. Radiation causes ionizations of atoms, which will affect molecules, which may affect cells, which may affect tissues, and so on. Although most people tend to think of biological effects in terms of the effect of radiation on living cells, in actuality, ionizing radiation, by definition, interacts only with atoms by a process called ionization (Chandra p. 205). Thus, all biological damage effects begin with the consequence of radiation interactions with the atoms forming the cells.

Even though all subsequent biological effects can be traced back to the interaction of radiation with atoms, there are two mechanisms by which radiation ultimately affects cells. These two mechanisms are commonly called direct and indirect effects.

If radiation interacts with the atoms of the DNA molecule, or some other cellular component critical to the survival of the cell, it is referred to as a direct effect. Such interaction may affect the ability of the cell to reproduce and, thus, survive. If enough atoms are affected in such a way that the chromosomes do not replicate properly, or there is a significant alteration in the information carried by the DNA molecule, then the cell may be destroyed by “direct” interference with its life-sustaining system.

Indirect effects are caused by the reaction of radiation with the water that makes up the majority of the cells volume. When radiation interacts with water, it may break the bonds that hold the water molecule together. This produces fragments of hydrogen and hydroxyls. These fragments may recombine or they may interact with other fragments to form compounds, such as water, which would not harm the cell. It is when these fragments combine to form toxic substances, such as hydrogen peroxide, that the destruction of the cell results.

Biological effects of radiation are typically divided into two categories. The first category consists of exposure to “high doses of radiation over brief intervals of time” producing acute effects (Hall p. 15). The second category represents exposure to “low doses of radiation over extended periods of time” producing chronic or long term effects (Hall p.15). High doses tend to kill cells, while low doses tend to damage or change them. High doses can kill so many cells that tissues and organs are damaged.