Health Effects
Intake of radioactive materials into the body tends to increase the risk of cancer, and possibly other stochastic effects. The International Commission on Radiological Protection has proposed a model whereby the incidence of cancers increases linearly with effective dose at a rate of 5.5% per sievert. This model is widely accepted for external radiation, but its application to internal contamination is disputed. This model fails to account for the low rates of cancer in early workers at Los Alamos National Laboratory who were exposed to plutonium dust, and the high rates of thyroid cancer in children following the Chernobyl accident. The European Committee on Radiation Risk calls the ICRP model "fatally flawed" when it comes to internal exposure.
The true relationship between committed dose and cancer is almost certainly non-linear. For example, iodine-131 is notable in that high doses of the isotope are sometimes less dangerous than low doses, since they tend to kill thyroid tissues that would otherwise become cancerous as a result of the radiation. Most studies of very-high-dose I-131 for treatment of Graves disease have failed to find any increase in thyroid cancer, even though there is linear increase in thyroid cancer risk with I-131 absorption at moderate doses.
Internal exposure of the public is controlled by regulatory limits on the radioactive content of food and water. These limits are typically expressed in becquerel/kilogram, with different limits set for each contaminant.
Intake of very large amounts of radioactive material can cause acute radiation syndrome (ARS) in rare instances. Examples include the Alexander Litvinenko poisoning and Leide das Neves Ferreira. While there is no doubt that internal contamination was the cause of ARS in these cases, there is not enough data to establish what quantities of committed dose might cause ARS symptoms. In most scenarios where ARS is a concern, the external effective radiation dose is usually much more hazardous than the internal dose. Normally, the greatest concern with internal exposure is that the radioactive material may stay in the body for an extended period of time, "committing" the subject to accumulating dose long after the initial exposure has ceased. Over a hundred people, including Eben Byers and the radium girls, have received committed doses in excess of 10 Gy and went on to die of cancer or natural causes, whereas the same amount of acute external dose would invariably cause an earlier death by ARS.
Read more about this topic: Committed Effective Dose Equivalent (CEDE)
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