Recent natural disasters in Japan led to a partial meltdown at the Fukushima nuclear power plant. A new Current Concepts article reviews the history of such accidents, along with the short-term and long-term health risks associated with environmental exposure to nuclear fission products.
The health threat from each radioisotope depends on an assortment of factors. Radioisotopes with a very short half-life (e.g., 67 hours for molybdenum-99) or a very long half-life (e.g., 24,400 years for plutonium-239), those that are gaseous (e.g., xenon-133), and those that are not released in substantial quantities (e.g., plutonium-238) do not cause substantial internal or external contamination. In contrast, iodine-131 can be an important source of morbidity because of its prevalence in reactor discharges and its tendency to settle on the ground.
• What systems tend to be most affected in acute radiation sickness?
Much of the short-term morbidity and mortality associated with a high total or near-total body dose is due to hematologic, gastrointestinal, or cutaneous sequelae. Hematologic and gastrointestinal complications are common because bone marrow and intestinal epithelium are especially radiosensitive as a result of their high intrinsic replication rate. Cutaneous toxic effects are common because external low-energy gamma radiation and beta radiation are chiefly absorbed in the skin.
• What cancers are most closely associated with nuclear-power-plant accidents?
There are important differences between the type of radiation and dose rate associated with atomic-bomb exposure and those associated with a reactor accident. These differences may explain why studies evaluating leukemia and nonthyroid solid cancers have not shown consistently elevated risks in the regions around Chernobyl. However, there is strong evidence of an increased rate of secondary thyroid cancers among children who have ingested iodine-131.
Table 3. Signs and Symptoms of Acute Radiation Sickness in the Three Phases after Exposure.
Morning Report Questions
Q: How is the dose of radiation quantified?
A: The literature on radiation refers to dose both in terms of grays (Gy), the unit of measurement of the absorbed dose, and sieverts (Sv), the unit of measurement for the effective dose, which is the absorbed dose multiplied by factors accounting for the biologic effect of different types of radiation and the radiation sensitivities of different tissues.
Q: What is the mortality associated with various ranges of radiation exposures?
A: The estimated mortality associated with exposure to radioactivity is 0% for less than 2 Gy, less than 50% for 2 to 4 Gy, 20 to 70% for exposures of 4 to 6 Gy, and 50 to 100% for exposures of 6 to 8 Gy.