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Radioactive Pollution

Biological Effects Of Radioactivity

The amount of injury caused by a radioactive isotope depends on its physical half-life, and on how quickly it is absorbed and then excreted by an organism. Most studies of the harmful effects of radiation have been performed on single-celled organisms. Obviously, the situation is more complex in humans and other multicellular organisms, because a single cell damaged by radiation may indirectly affect other cells in the individual. The most sensitive regions of the human body appear to be those which have many actively dividing cells, such as the skin, gonads, intestine, and tissues that grow blood cells (spleen, bone marrow, lymph organs).

Radioactivity is toxic because it forms ions when it reacts with biological molecules. These ions can form free radicals, which damage proteins, membranes, and nucleic acids. Radioactivity can damage DNA (deoxyribonucleic acid) by destroying individual bases (particularly thymine), by breaking single strands, by breaking double strands, by cross-linking different DNA strands, and by cross-linking DNA and proteins. Damage to DNA can lead to cancers, birth defects, and even death.

However, cells have biochemical repair systems which can reverse some of the damaging biological effects of low-level exposures to radioactivity. This allows the body to better tolerate radiation that is delivered at a low dose rate, such as over a longer period of time. In fact, all humans are exposed to radiation in extremely small doses throughout their life. The biological effects of such small doses over such a long time are almost impossible to measure, and are essentially unknown at present. There is, however, a theoretical possibility that the small amount of radioactivity released into the environment by normally operating nuclear power plants, and by previous atmospheric testing of nuclear weapons, has slightly increased the incidence of certain cancers in human populations. However, scientists have not been able to conclusively show that such an effect has actually occurred.

Currently, there is disagreement among scientists about whether there is a threshold dose for radiation damage to organisms. In other words, is there a dose of radiation below which there are no harmful biological effects? Some scientists maintain that there is no such threshold, and that radiation at any dose carries a finite risk of causing some biological damage. Furthermore, the damage caused by very low doses of radiation may be cumulative, or additive to the damage caused by other harmful agents to which humans are exposed. Other scientists maintain that there is a threshold dose for radiation damage. They believe that biological repair systems, which are presumably present in all cells, can fix the biological damage caused by extremely low doses of radiation. Thus, these scientists claim that the extremely low doses of radiation to which humans are commonly exposed are not harmful.

One of the most informative studies of the harmful effects of radiation is a long-term investigation of the survivors of the 1945 atomic blasts at Hiroshima and Nagasaki by James Neel and his colleagues. The survivors of these explosions had abnormally high rates of cancer, leukemia, and other diseases. However, there seemed to be no detectable effect on the occurrence of genetic defects in children of the survivors. The radiation dose needed to cause heritable defects in humans is higher than biologists originally expected.

Radioactive pollution is an important environmental problem. It could become much worse if extreme vigilance is not utilized in the handling and use of radioactive materials, and in the design and operation of nuclear power plants.



Bock, G., G. Cardew, and H. Paretzhe, eds. Health Impacts of Large Releases of Radionucludes. John Wiley and Sons, 1997.

Brill, A.B., et al. Low-level Radiation Effects: A Fact Book. New York: The Society of Nuclear Medicine, 1985.

Carlisle, Rodney P. Encyclopedia of the Atomic Age. New York: Facts on File, 2001.

Eisenbud, M., and T.F. Gesell. Environmental Radioactivity: From Natural, Industrial, and Military Sources. Academic Press, 1997.

Eisenbud, M. Environmental Radioactivity. New York: Norton, 1987.

Matthews, John A., E. M. Bridges, and Christopher J. Caseldine The Encyclopaedic Dictionary of Environmental Change. New York: Edward Arnold, 2001.

Quinn, S. Marie Curie: A Life. New York: Simon and Schuster, 1995.


Schull, W.J., M. Otake, and J.V. Neel. "Genetic Effects of the Atomic Bombs: A Reappraisal." Science 213 (1981): 1220-1227.

Peter A. Ensminger


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Curie (Ci)

—A unit representing the rate of radioactive decay. 1 Ci = 3.7 × 1010 disintegrations per second.

Ionizing radiation

—Any electromagnetic or particulate radiation capable of direct or indirect ion production in its passage through matter.


—Two molecules in which the number of atoms and the types of atoms are identical, but their arrangement in space is different, resulting in different chemical and physical properties. Isotopes may be radioactive.

Nonionizing radiation

—Long-wavelength electro-magnetic radiation.


—A unit of absorbed ionizing radiation which results in the absorption of 100 ergs of energy per gram of medium. 1 Rad = 0.01 Gray.

Radioactive half-life

—The time required for half the atoms of a radioactive isotope to decay to a more stable isotope.


—Spontaneous release of subatomic particles or gamma rays by unstable atoms as their nuclei decay.


—A unit of the biological effectiveness of absorbed radiation, which is equal to the radiation dose in rad multiplied by a biological weighting factor, which is determined by the particular type of radiation. 1 rem = 0.01 Sievert.

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Science EncyclopediaScience & Philosophy: Quantum electronics to ReasoningRadioactive Pollution - Nonionizing Radiation, Ionizing Radiation, Sources Of Radioactive Pollution, Lifestyle And Radiation Dose, Nuclear Weapons Testing - Types of radiation