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Potential biological effects initiated by exposure to ionizing radiation are described in some detail, including the characteristics of radiation sources, radiation fields, dosimetry, and fundamental radiation protection quantities and units. Special attention is paid to exposure pathways and the risk assessment of radiation exposure to the human body in terms of relevant health risks reflecting biological effects resulting from external and internal radiation exposure. Some particulars are presented to illustrate the nature and severity of stochastic and deterministic effects caused by the exposure. The chapter then presents an overview of pertinent radiation protection requirements and monitoring methods for the evaluation of exposure of persons in regular and emergency situations, as well as the assessment of environmental radioactive contamination inflicted by releases of radioactivity from facilities where radioactive materials are used or stored, taking into account their possible damage or destruction resulting from accidents and potential terrorist attacks, sabotage, or other malevolent actions. In all these cases, discharges of radioactive substances from various sources, including those used in medicine, industry, and research facilities, should be considered to obtain reliable information about specific radiation routes. Radioactive materials, in the form of solid particulates, aerosols, and gases, disperse in several ways known as exposure pathways. It is essential that the description of both exposure pathways and their characteristics be expressed in officially recommended and generally accepted quantities and units. In general, the final part of an exposure pathway refers to how a person can come into contact with hazardous substances, including materials containing radionuclides.

Radionuclides are present in the environment or result from human activities, such as the use of radiation or nuclear technologies. The presence of radionuclides in foods can pose certain health risks, and their toxicity depends on several factors, including the intake of radionuclides, the type of radionuclide, its concentration, and the specific characteristics of the food. Under typical situations, the contributions of internal exposure to the human body from food or water, where only trace concentrations of usually natural radionuclides are present, are minor in most cases. Slightly different situations may occur when food, due to radionuclides from man-made sources used in various applications in industry and medicine or radioactivity induced during radiation sterilization of food, shows an increased level compared with the natural background concentrations. But even here, there is no reason to consider the impact on living organisms to be serious since the increase in exposure levels is only a fraction of exposure due to the natural background.

On the other hand, however, the concentration may be higher in some cases when the food is produced from plants or animals that are heavily contaminated. Specific aspects of radioactivity or, in general, ionizing radiation (hereinafter, simply, radiation), which can be detected even at particularly small levels thanks to the availability of very sensitive instrumentation, have to be stressed here. Radiation monitors are able to measure even extremely insignificant changes within the fluctuation level of natural radiation. When the instrument shows some results close to the background level or even up to several times this level, there is no need to be concerned since the impact of such exposure on a person is almost negligible in comparison with other, much more dangerous situations we face daily in our typical living or working environment caused by many other, much more hazardous agents. The chapter will present an overview of the health risks attributed to the toxicity resulting from exposure to foods contaminated by radionuclides of various origins.