Ionizing Radiation

Ionizing radiation is undoubtedly one of the most intensely studied of all toxic agents. The impetus for understanding its manifold effects came from its extensive use since the beginning of the century in medical diagnosis and treating cancer. With the development of nuclear weapons and atomic energy during World War II, the field expanded dramatically. Atomic energy became one of the country's largest industrial sectors at that time. Potential health hazards from occupational and environmental sources of radiation became an important area for research; it spawned a new field in the post–World War II era of measurement and control called health physics. Practitioners in health physics created the Health Physics Society and published research findings in the Health Physics Journal.

Under the Atomic Energy Commission (AEC), a great national laboratory complex was established for research on weapons, power production, and biomedical and physics research. Long-term biomedical research was also initiated at large university-based facilities and by the support of individual faculty and institutional grants. The development and sale of radioisotopes and radiation measuring instruments was subsidized by the AEC to the great benefit of biomedical research in general. Radiation biology has its own society (the Radiation Research Society), and its own journal, the Journal of Radiation Research. Radiation has become an integral tool for understanding cellular function and the human genome. Although the level of biomedical research on radiation is much lower in the last few decades than earlier, a great deal of information on the human health effects of radiation exposure has been gleaned from epidemiologic studies.

This chapter gives toxicologists the basic features of radiation biology. However, there is a wealth of new findings currently evolving from the human genome study that is expanding our fundamental knowledge about the response of cells when exposed to radiation. For example, radiation may play a role in the formation of single nucleotide polymorphisms, DNA sequence variations that occur when a single nucleotide in the genome sequence is altered. Because of the scope of the field, only essential concepts are presented. The reader is referred to textbooks and other publications cited for more details as well as the website for the Human Genome Project (www.ornl.gov/hgmis/home.shtml).

Keywords: background radiation; carcinogenesis; cataracts; cellular level; damage; DNA; dose; electromagnetic radiation; heritable effects; in utero effects; ionizing radiation; modulation whole-body radiation syndrome; molecular level; protection; radionuclides; risk; sensitivity; tissues