Radioactivity and the associated radiation exposures are sometimes thought of as environmental problems that have been created by modern science and technology. However, substantial amounts of radioactivity exist in nature and have existed on Earth since its original formation. All biological species evolved on Earth, for better or worse, in this radioactive environment. Radioactivity could be plausibly termed the oldest “pollutant” if one chooses to describe an integral part of the natural world as a pollutant.
With the advent of controlled nuclear fission, we have obtained the ability to create concentrations of radioactivity that far exceed those encountered in the natural environment. An effort is made to minimize human exposure by isolating this material or surrounding it with shielding, but some exposure nonetheless occurs. To gain perspective on the seriousness of the potential resulting problems, we consider in this chapter the sources and amounts of artificial and natural radioactivity. Natural radioactivity here provides a reference or benchmark by which to gauge the significance of the man-made radioactivity.
Human awareness of the existence of ionizing radiation dates only to the period around 1900. Wilhelm Roentgen discovered X-rays in 1895, and within the next 5 years, Henri Becquerel and Marie and Pierre Curie discovered the previously unsuspected ionizing radiations from uranium ore. These were the newly named alpha particles, beta particles, and gamma rays from the radioactive decay of uranium and its associated products. The nature of these radiations and of radioactivity was quickly elucidated by investigators in France, Great Britain, and elsewhere.
The particles from radioactivity and cosmic rays constitute natural ionizing radiation. “Man-made” ionizing radiation comes from X-ray machines, nuclear accelerators, and nuclear reactors, as well as from artificial radionuclides produced by accelerators and reactors. The significant safety and environmental issues that arise in the consideration of nuclear power are related to the radionuclides produced in nuclear reactors. The benefits of X-rays for medical diagnostic purposes were recognized almost immediately after their discovery and the purported benefits of radium, extracted from uranium ore, were proclaimed soon after. The belief that radium had curative properties continued into the 1920s, with horrors such as the sale of “medicines” laced with radium. Surprisingly, underground sites that feature enhanced exposure to radon persist in the United States and elsewhere to this day. At the same time, radium—and later other radionuclides—have been used for better justified purposes, including many applications in medicine and industry.
Along with a growing use of X-rays and natural radioactive materials, there arose a recognition of the health risks of excessive exposure to ionizing radiation. These were recognized following exposures of radiologists, X-ray technicians, and, in a particular tragedy, radium watch dial painters. The dangers were first widely recognized in the 1920s and serious attempts to establish safety standards date from the late 1920s, starting with occupational hazards. Since the 1950s, the setting of standards has been expanded to apply to the general population, usually with criteria that are substantially stricter than those for occupational exposures.