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The Tōhoku earthquake and tsunami of March 11,2011, resulted in unprecedented radioactivity releases from the Fukushima Dai-ichi nuclear power plants to the Northwest Pacific Ocean. Results are presented here from an international study of radionuclide contaminants in surface and subsurface waters, as well as in zooplankton and fish, off Japan in June 2011. A major finding is detection of Fukushima-derived ¹³⁴Cs and ¹³⁷Cs throughout waters 30-600 km offshore, with the highest activities associated with near-shore eddies and the Kuroshio Current acting as a southern boundary for transport. Fukushima-derived Cs isotopes were also detected in Zooplankton and mesopelagic fish, and unique to this study we also find ¹¹⁰mAg in Zooplankton. Vertical profiles are used to calculate a total inventory of ~2 PBq ¹³⁷Cs in an ocean area of 150,000 km². Our results can only be understood in the context of our drifter data and an oceanographic model that shows rapid advection of contaminants further out in the Pacific. Importantly, our data are consistent with higher estimates of the magnitude of Fukushima fallout and direct releases [Stohl et al. (2011) Atmos Chem Phys Discuss 11:28319-28394; Bailly du Bois et al. (2011) J Environ Radioact, 10.1016/j.jenvrad.2011.11.015]. We address risks to public health and marine biota by showing that though Cs isotopes are elevated 10-1,000× over prior levels in waters off Japan, radiation risks due to these radionuclides are below those generally considered harmful to marine animals and human consumers, and even below those from naturally occurring radionuclides.

Initial estimates suggest that Fukushima's reactors have emitted one-tenth of all the radioactive material released during the Chernobyl disaster in 1986, and prevailing winds have swept most of the radioactivity over the Pacific Ocean. Austria's Central Institute for Meteorology and Geodynamics in Vienna estimated last week that although Fukushima's radioactive plume has now dispersed across the Northern Hemisphere, negligible levels of volatile radioisotopes such as iodine-131 and caesium-137 (the major components of the plume) have hit countries outside Japan.

Dosimetic uncertainties, particularly those that are shared among subgroups of a study population, can bias, distort or reduce the slope or significance of a dose response. Exposure estimates in studies of health risks from environmental radiation exposures are generally highly uncertain and thus, susceptible to these methodological limitations. An analysis was published in 2008 concerning radiation-related thyroid nodule prevalence in a study population of 2,994 villagers under the age of 21 years old between August 1949 and September 1962 and who lived downwind from the Semipalatinsk Nuclear Test Site in Kazakhstan. This dose-response analysis identified a statistically significant association between thyroid nodule prevalence and reconstructed doses of fallout-related internal and external radiation to the thyroid gland; however, the effects of dosimetric uncertainty were not evaluated since the doses were simple point “best estimates”. In this work, we revised the 2008 study by a comprehensive treatment of dosimetric uncertainties. Our present analysis improves upon the previous study, specifically by accounting for shared and unshared uncertainties in dose estimation and risk analysis, and differs from the 2008 analysis in the following ways: 1. The study population size was reduced from 2,994 to 2,376 subjects, removing 618 persons with uncertain residence histories; 2. Simulation of multiple population dose sets (vectors) was performed using a two-dimensional Monte Carlo dose estimation method; and 3. A Bayesian model averaging approach was employed for evaluating the dose response, explicitly accounting for large and complex uncertainty in dose estimation. The results were compared against conventional regression techniques. The Bayesian approach utilizes 5,000 independent realizations of population dose vectors, each of which corresponds to a set of conditional individual median internal and external doses for the 2,376 subjects. These 5,000 population dose vectors reflect uncertainties in dosimetric parameters, partly shared and partly independent, among individual members of the study population. Risk estimates for thyroid nodules from internal irradiation were higher than those published in 2008, which results, to the best of our knowledge, from explicitly accounting for dose uncertainty. In contrast to earlier findings, the use of Bayesian methods led to the conclusion that the biological effectiveness for internal and external dose was similar. Estimates of excess relative risk per unit dose (ERR/Gy) for males (177 thyroid nodule cases) were almost 30 times those for females (571 cases) and were similar to those reported for thyroid cancers related to childhood exposures to external and internal sources in other studies. For confirmed cases of papillary thyroid cancers (3 in males, 18 in females), the ERR/Gy was also comparable to risk estimates from other studies, but not significantly different from zero. These findings represent the first reported dose response for a radiation epidemiologic study considering all known sources of shared and unshared errors in dose estimation and using a Bayesian model averaging (BMA) method for analysis of the dose response.

In Japan itself, critics were already questioning whether the nation's 54 nuclear power reactors were adequately prepared to handle earthquakes, an issue raised in 2007 after a massive quake struck the Kashiwazaki- Kariwa nuclear plant (see Nature 448, 392-393; 2007). [...] it's a success,\" Grimes says, then adds: \"Although do I think the general public will be able to see that? I think the answer is, sadly, no.

Beta radiation from nuclear weapons fallout could pose a risk of cutaneous radiation injury (CRI) to evacuating populations but has been investigated only cursorily. This work examines 2 components of CRI necessary for estimating the potential public health consequences of exposure to fallout: dose protraction and depth of dose. Dose protraction for dry and moist desquamation was examined by adapting the biological effective dose (BED) calculation to a hazard function calculation similar to those recommended by the National Council on Radiation Protection and Measurements for other acute radiation injuries. Depth of burn was examined using Monte Carlo neutral Particle version 5 to model the penetration of beta radiation from fallout to different skin tissues. Nonlinear least squares analysis of the BED calculation estimated the hazard function parameter θ1 (dose rate effectiveness factors) as 25.5 and 74.5 (Gy-eq)2 h-1 for dry and moist desquamation, respectively. Depth of dose models revealed that beta radiation is primarily absorbed in the dead skin layers and basal layer and that dose to underlying tissues is small (<5% of dose to basal layer). The low relative dose to tissues below the basal layer suggests that radiation-induced necrosis or deep skin burns are unlikely from direct skin contamination with fallout. These results enable future modeling studies to better examine CRI risk and facilitate effectively managing and treating populations with specialized injuries from a nuclear detonation. (Disaster Med Public Health Preparedness. 2019;13:463-469).

Some Japanese scientists have grown so frustrated with the slow official response that they have teamed up with citizens to collect data and begin clean-up. Because radiation levels can vary widely over small distances, the latest government maps are too coarse for practical use by local people, says Shin Aida, a computer scientist at Toyohashi University of Technology.

The risk to the roughly 140,000 civilians who had been living within a few tens of kilometres of the plant seems even lower. Because detailed radiation measurements were unavailable at the time of the accident, the WHO estimated doses to the public, including radiation exposure from inhalation, ingestion and fallout. After Chernobyl, evacuees were more likely to experience posttraumatic stress disorder (PTSD) than the population as a whole, according to Evelyn Bromet, a psychiatric epidemiologist at the State University of New York, Stony Brook.

The study also suggests that, contrary to government claims, pools used to store spent nuclear fuel played a significant part in the release of the long-lived environmental contaminant caesium-137, which could have been prevented by prompt action. Anti-nuclear activists have long been concerned that the government has failed to adequately address geological hazards when licensing nuclear plants (see Nature 448, 392-393; 2007), and the whiff of xenon could prompt a major rethink of reactor safety assessments, says Yamauchi.

Even as the damaged reactors at the Fukushima Daiichi nuclear power station continue to leak radiation, researchers have begun laying the groundwork for studies that will look for any long-term effects on public health. Iodine-131, which has a half-life of just 8 days but accumulates quickly in the thyroid gland, is still the major component of the emissions from the nuclear plant and remains the greatest acute radiation health threat to the public, says Richard Wakeford, an epidemiologist at the Dalton Nuclear Institute, University of Manchester, UK.