The issue remains unresolved, but as a matter of philosophy, it is now commonly assumed that the so-called stochastic effects, cancer and genetic effects, are nonthreshold phenomena and that the so-called nonstochastic effects are threshold phenomena. The question remained open, however, whether the health effects were threshold phenomena that would not occur below certain exposure or dose levels, or whether the risk would continue at some nonzero level until the exposure was removed altogether. These limits on radium intake or body content were designed to reduce the incidence of the then-known health effects to a level of insignificance. Shortly thereafter, experimental animal studies and the analysis of case reports on human effects focused on the determination of tolerance doses and radiation protection guides for the control of workplace exposure. This change occurred in 1925–1926 following reports and intensive discussion of short-term health effects such as ''radium jaw" in some dial painters. The first widespread effort to control accidental radium exposure was the abandonment of the technique of using the mouth to tip the paint-laden brushes used for application of luminous material containing 226Ra and sometimes 228Ra to the often small numerals on watch dials. As the practical concerns of radiation protection have shifted and knowledge has accumulated, there has been an evolution in the design and objectives of experimental animal studies and in the methods of collection, analysis, and presentation of human health effects data. Before concern developed over environmental exposure, attention was devoted primarily to exposure in the workplace, where the potential exists for the accidental uptake of radium at levels known to be harmful to a significant fraction of exposed individuals. The purpose of this chapter is to review the information on cancer induced by these three isotopes in humans and estimate the risks associated with their internal deposition.Īll members of the world's population are presumably at risk, because each absorbs radium from food and water as a working hypothesis, radiation is assumed to be carcinogenic even at the lowest dose levels, although there is no unequivocal evidence to support this hypothesis. Later, similar effects were also found to be associated with internal exposure to 224Ra. These studies were motivated by the discovery of cancer and other debilitating effects associated with internal exposure to 226Ra and 228Ra. The primary sources of information on the health effects and dosimetry of radium isotopes come from extensive studies of 224Ra, 226Ra, and 228Ra in humans and experimental animals. It has also been used for internal radiation therapy. Radium has been used commercially in luminous paints for watch and instrument dials and for other luminized objects. In communities where wells are used, drinking water can be an important source of ingested radium. Radium is present in soil, minerals, foodstuffs, groundwater, and many common materials, including many used in construction. Four isotopes of radium occur naturally and several more are man-made or are decay products of man-made isotopes.
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