THE FIRST notable nuclear reactor accident occurred in 1957 at the Windscale Plant in Britain. Radioactive 131I was released from the reactor building into the surrounding area, but a 50 y follow-up of the highest-exposed group—workers involved in cleanup—found no exposure-related effects on cancer or mortality rates (McGeoghegan et al. 2010).
This presentation will focus on the three more recent reactor accidents: namely, Three Mile Island (TMI) in Pennsylvania in 1979; Chernobyl in the Former Soviet Union in 1986; and Fukushima in Japan in 2011. In all three cases, exposures to members of the public were primarily due to internal radiation, principally 131I, although concentrations varied markedly. The release and deposition of 131I at Fukushima was an order of magnitude lower than at Chernobyl, and levels at TMI were lower still (Bouville and Kryuchkov 2014). Health surveys at Fukushima are ongoing, but the results of epidemiologic studies of populations exposed at TMI and Chernobyl are reflective of their relative exposures.
Radioactive iodine is taken up by the body and stored in the thyroid gland, where it has the potential to cause benign and malignant thyroid disease (NCRP 2008). Exposure to members of the public occurs largely via ingestion of contaminated milk and other foods. Because the thyroid dose from 131I is roughly proportional to milk consumption and inversely proportional to thyroid mass, children—with their high milk consumption and small thyroid glands—generally receive the highest doses. Indeed, currently the most widely recognized adverse health effect from Chernobyl fallout is the approximately fivefold increase in thyroid cancer among exposed children and adolescents in the most affected regions of Ukraine and Belarus (Tronko et al. 2006; UNSCEAR 2011)—a risk that is comparable to that from external radiation. Risks for noncancer thyroid diseases, such as follicular adenoma (Zablotska et al. 2007) and subclinical hypothyroidism (Ostroumova et al. 2009, 2013) in children and adolescents exposed to 131I as a result of Chernobyl, have been reported as well. This presentation will cover the limited literature on effects among those exposed prenatally (Hatch et al. 2009), another potentially radiosensitive group, as well as those exposed as adults; recent evidence from a study by the International Agency for Research on Cancer suggests an increased risk in this group from ingestion doses received in contaminated residential areas (Kesminiene et al. 2012). Finally, the potential for future genetic research based on biomaterials from thyroid cancer cases in Chernobyl-affected areas will be touched upon (Abend et al. 2012; Leeman-Neill et al. 2013).
Although radiation doses from the accident at TMI were very low, health studies were conducted to respond to public concerns. Efforts to reconstruct dose and to evaluate dose-response patterns in cancer incidence and mortality in the populations living within ~8–16 km of the plant have been reported, with largely null results (Hatch et al. 1990; Talbott et al. 2000). Psychosocial stress from the accident has also been investigated, and stress levels have been found to be elevated (Dew and Bromet 1993; Bromet 2014), particularly in susceptible subgroups such as pregnant women. However, the effects of accident stress on other health outcomes are not clear. Radiation doses from the Fukushima Daiichi nuclear reactor accident were also much lower than at Chernobyl, both because of a smaller release and timely countermeasures to minimize exposure (Boice 2012). For this reason, as well as the circumstances leading to the accident (i.e., the earthquake and tsunami and the associated loss of life and dislocation of so many people), psychosocial outcomes will likely emerge as the most significant health effect of this most recent nuclear accident (Yasumura et al. 2012; Bromet 2014).
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