Radiation and Health Effects

Ionizing radiation consists of electromagnetic waves or atomic particles with the capacity to strike an electron with sufficient force to strip it from its atom, thus creating an ion. This type of radiation cannot be detected, even at lethal levels, without the use of specialized devices; therefore, the effects of exposure to humans have been extensively explored in large, retrospective population studies. These studies were conducted after large populations were exposed to harmful levels of radiation. In individuals from Hiroshima and Nagasaki, the major health effect observed at the lowest doses of exposure has been cancer, while heart, digestive, and other systemic complications have been noted at higher doses of exposure. Over the previous decades, identification of markers of radiation effects has focused mostly on malignant tumor responses to irradiation. In recent years, due to the risk of radiation disasters from nuclear terrorism or accidents, the identification of early biomarkers of radiation injury has become a high priority of biomedical research. Identifying markers of exposure and finding a unique biomarker profile for toxicity in exposed individuals are complex tasks. Because radiation injury is a continuum of complex biological responses, the complex toxicities of radiation exposure can begin within hours and progress over weeks, months, or even years. These efforts are complicated by the organ-specific nature of effects, the variation of intensity of some toxicity over time, and significant variation in an individual’s sensitivity to these effects. The objectives of this chapter are to describe common types of ionizing radiation, discuss the biological consequences and toxicity in humans, and provide some information on different types of biomarkers for monitoring radiation exposure, which also can serve as future tools for diagnosis and prognosis and as targets for therapy.