A primary health concern among residents and evacuees in affected areas immediately after a nuclear accident is the internal exposure of the thyroid to radioiodine, particularly I-131, and subsequent thyroid cancer risk. In Japan, the natural disasters of the earthquake and tsunami in March 2011 destroyed an important function of the Fukushima Daiichi Nuclear Power Plant (F1-NPP) and a large amount of radioactive material was released to the environment. Here we report for the first time extensive measurements of the exposure to I-131 revealing I-131 activity in the thyroid of 46 out of the 62 residents and evacuees measured. The median thyroid equivalent dose was estimated to be 4.2 mSv and 3.5 mSv for children and adults, respectively, much smaller than the mean thyroid dose in the Chernobyl accident (490 mSv in evacuees). Maximum thyroid doses for children and adults were 23 mSv and 33 mSv, respectively.

Several United Nations organizations sought to dispel the uncertainties and controversy that still exist concerning the effects of the Chernobyl accident. A Chernobyl Forum of international expertise was established to reach consensus on the environmental consequences and health effects attributable to radiation exposure arising from the accident. This review is a synopsis of the subgroup that examined the radiological effects to nonhuman biota within the 30-km Exclusion Zone. The response of biota to Chernobyl irradiation was a complex interaction among radiation dose, dose rate, temporal and spatial variation, varying radiation sensitivities of the different taxons, and indirect effects from other events. The radiation-induced effects to plants and animals within the 30-km Exclusion Zone around Chernobyl can be framed in three broad time periods relative to the accident: an intense exposure period during the first 30 d following the accident of 26 April 1986; a second phase that extended through the first year of exposure during which time the short-lived radionuclides decayed and longer-lived radionuclides were transported to different components of the environment by physical, chemical and biological processes; and the third and continuing long-term phase of chronic exposure with dose rates<1% of the initial values. The doses accumulated, and the observed effects on plants, soil invertebrates, terrestrial vertebrates and fish are summarized for each time period. Physiological and genetic effects on biota, as well as the indirect effects on wildlife of removing humans from the Chernobyl area, are placed in context of what was known about radioecological effects prior to the accident.

The thyroid dose due to 131 I releases during the Chernobyl accident was reconstructed for children and adolescents in two cities and 2122 settlements in Belarus, and in one city and 607 settlements in the Bryansk district of the Russian Federation. In this area, which covers the two high contamination spots in the two countries following the accident, data on thyroid cancer incidence during the period 1991–1995 were analysed in the light of possible increased thyroid surveillance. Two methods of risk analysis were applied: Poisson regression with results for the single settlements and Monte Carlo (MC) calculations for results in larger areas or sub-populations. Best estimates of both methods agreed well. Poisson regression estimates of 95% confidence intervals (CIs) were considerably smaller than the MC results, which allow for extra-Poisson uncertainties due to reconstructed doses and the background thyroid cancer incidence. The excess absolute risk per unit thyroid dose (EARPD) for the birth cohort 1971–1985 by the MC analysis was 2.1 (95% CI 1.0–4.5) cases per 10 4 person-year Gy. The point estimate is lower by a factor of two than that observed in a pooled study of thyroid cancer risk after external exposures. The excess relative risk per unit thyroid dose was 23 (95% CI 8.6–82) Gy −1 . No significant differences between countries or cities and rural areas were found. In the lowest dose group of the settlements with an average thyroid dose of 0.05 Gy the risk was statistically significantly elevated. Dependencies of risks on age-at-exposure and on gender are consistent with findings after external exposures. © 1999 Cancer Research Campaign

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