Background: After the Chernobyl nuclear power plant accident in April 1986, a large increase in the incidence of childhood thyroid cancer was reported in contaminated areas. Most of the radiation exposure to the thyroid was from iodine isotopes, especially ¹³¹ I. We carried out a population-based case–control study of thyroid cancer in Belarus and the Russian Federation to evaluate the risk of thyroid cancer after exposure to radioactive iodine in childhood and to investigate environmental and host factors that may modify this risk. Methods: We studied 276 case patients with thyroid cancer through 1998 and 1300 matched control subjects, all aged younger than 15 years at the time of the accident. Individual doses were estimated for each subject based on their whereabouts and dietary habits at the time of the accident and in following days, weeks, and years; their likely stable iodine status at the time of the accident was also evaluated. Data were analyzed by conditional logistic regression using several different models. All statistical tests were two-sided. Results: A strong dose–response relationship was observed between radiation dose to the thyroid received in childhood and thyroid cancer risk ( P <.001). For a dose of 1 Gy, the estimated odds ratio of thyroid cancer varied from 5.5 (95% confidence interval [CI] = 3.1 to 9.5) to 8.4 (95% CI = 4.1 to 17.3), depending on the risk model. A linear dose–response relationship was observed up to 1.5–2 Gy. The risk of radiation-related thyroid cancer was three times higher in iodine-deficient areas (relative risk [RR]= 3.2, 95% CI = 1.9 to 5.5) than elsewhere. Administration of potassium iodide as a dietary supplement reduced this risk of radiation-related thyroid cancer by a factor of 3 (RR = 0.34, 95% CI = 0.1 to 0.9, for consumption of potassium iodide versus no consumption). Conclusion: Exposure to ¹³¹ I in childhood is associated with an increased risk of thyroid cancer. Both iodine deficiency and iodine supplementation appear to modify this risk. These results have important public health implications: stable iodine supplementation in iodine-deficient populations may substantially reduce the risk of thyroid cancer related to radioactive iodines in case of exposure to radioactive iodines in childhood that may occur after radiation accidents or during medical diagnostic and therapeutic procedures.

More than a decade has passed since a complete revision was initiated of the radiation doses received by survivors of the Hiroshima and Nagasaki atomic bombings. The new dosimetry system (DS86) was completed in 1986 and adopted shortly thereafter. Overall, DS86 was noted to be a clear improvement over the old dosimetry system. However, based on limited validation measurements, troublesome inconsistencies were suggested for neutrons. Since 1986, a substantial number of additional neutron activation measurements have been made in mineral and metal samples from Hiroshima. Importantly, a large number of measurements have now been made at distances beyond 1 km. Here, inconsistencies between neutron activation measurements and DS86 calculations for Hiroshima are examined using all available measurement data, including new measurements for 36Cl which extend the measurement range to more than 1.7 km from the epicenter, and Monte Carlo modeling calculations for each sample measured. Results show that thermal neutron activation measured beyond approximately 1 km in Hiroshima (at distances most relevant for radiation-risk evaluation) is two to 10, or more, times higher than that calculated based on DS86. Similar trends observed when comparing results by several independent measurement laboratories, using different analytical methods, suggest that the DS86 calculations for low-energy neutrons are in error. Because of the importance of the Hiroshima data in radiation risk evaluation, this large discrepancy is in need of resolution.

We present a feasibility study for using 236U as an oceanic circulation tracer based on depth profiles of 236U and 137Cs in the Japan/East Sea. The concentration of the predominantly anthropogenic 236U, measured with Accelerator Mass Spectrometry (AMS), decreased from (13±3)×106 atom/kg in surface water to (1.6±0.3)×106 atom/kg close to the sea floor (2800 m). The profile has a smooth trend with depth and concentration values are generally proportional to that of 137Cs for the same water samples, but with a slightly lower ratio of 137Cs/236U below 2000 m. The cumulative inventory of dissolved 236U in the water column was estimated to be (13.7±0.9)×1012 atom/m2, which is similar to the global-fallout level (17.8×1012 atom/m2) in Japan. Additional analyses of suspended solids (SS) and bottom sediments yielded negligible amounts of 236U. Our results suggest that 236U behaves as a conservative nuclide in seawater, with potential advantages over other tracers of oceanic circulation.

Since the atomic bomb explosions in Hiroshima and Nagasaki, high incidences of leukemia, thyroid cancer and other tumors have been reported as atomic