Monte Carlo derived absorbed fractions for a voxelized model of Oncorhynchus mykiss, a rainbow trout

Simple, ellipsoidal geometries have long been the standard for estimating radiation dose rates in non-human biota (NHB). With the introduction of a regulatory protection standard that emphasizes protection of NHB as its own endpoint, there has been interest in improved models for the calculation of dose rates in NHB. Here we describe the creation of a voxelized model for a rainbow trout (Oncorhynchus mykiss), a freshwater aquatic salmonid. Absorbed fractions (AFs) for both photon and electron sources were tabulated at electron energies of 0.1, 0.2, 0.4, 0.5, 0.7, 1.0, 1.5, 2.0, and 4.0 MeV and photon energies of 0.01, 0.015, 0.02, 0.03, 0.05, 0.1, 0.2, 0.5, 1.0, 1.5, 2.0, and 4.0 MeV. A representative set of the data is made available in this publication; the entire set of absorbed fractions is available as electronic supplementary materials. These results are consistent with previous voxelized models, and reinforce the well-understood relationship between the AF and the target’s mass and location, as well as the energy of the incident radiation.This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Springer and can be found at: http://link.springer.com/journal/411Keywords: Monte Carlo, Dosimetry, Non-human biota, Voxel phanto

Modelling the exposure of wildlife to radiation: key findings and activities of IAEA working groups

The International Atomic Energy Agency (IAEA) established the Biota Working Group (BWG) as part of its Environmental Modelling for Radiation Safety (EMRAS) programme in 2004 (http://www-ns.iaea.org/projects/emras/emras-biota-wg.htm). At that time both the IAEA and the International Commission on Radiological Protection (ICRP) were addressing environmental protection (i.e. protection of non-human biota or wildlife) within the on-going revisions to the Basic Safety Standards and Recommendations respectively. Furthermore, some countries (e.g. the USA, UK) were already conducting assessments in accordance with national guidelines. Consequently, a number of assessment frameworks/models had been or were being developed. The BWG was established recognising these developments and the need to improve Member State’s capabilities with respect to protection of the environment from ionizing radiation. The work of the BWG was continued within the IAEA’s EMRAS II programme by the Biota Modelling Group (http://wwwns. iaea.org/projects/emras/emras2/working-groups/working-group-four.asp)

Dose-effects relationships in non-human biota : development of field sampling, dosimetric and analytic techniques through a case study of the aquatic snail Campeloma decisum at Chalk River Laboratories

In the last decade regulatory bodies have begun to implement standards to protect populations of non-human biota (NHB) from the consequences of radiation exposure. This is a departure from previous regulatory frameworks which were concerned only with protecting man. The implementation of these new standards has started an ongoing discussion concerning appropriate dose-rate limits for NHB. For the most part, the data utilized for estimating appropriately protective dose-rate limits has come from data collected via the irradiation of NHB in a laboratory setting. While some dose-effects studies have been performed under field conditions, such experiments represent a minority of the available data. This deficit in the literature has resulted in challenges to the established paradigm, with researchers reporting increased radiosensitivity in NHB under field conditions. However, many such studies overlook critical components of dose-effects analysis: lacking either robust ecological technique or dosimetric rigor. This study serves as a template for future in-depth study of the relationship between radiation dose and ecological health. It utilizes sound field, dosimetric, analytic and statistical techniques to study dose-effects relationships in the aquatic snail, Campeloma decisum, at Chalk River Laboratories in Ontario, Canada. Multiple benchmarks (number of snails, mass of individuals, etc) were employed as proxies for snail population health, which was assessed after accounting for two dozen environmental variables. Dose-rates were calculated via a novel voxelized model, developed for this study to estimate internal dose rates for the species of interest. A linear model was employed to tease out the relationship between individual snails, their environment, and radiation dose rate. There was no evidence that snail population health was influenced by radiation exposure (p=0.70) at the observed dose rates. Of the environmental variables tested, water concentration of Ca was well correlated with snail mass size (p<0.001), while water concentration of P was well correlated with the number of snails lured to a trap (p<0.001). The protocols and procedures developed as a part of this study represent novel, robust techniques for evaluating the relationship between radiation dose and population effects in NHB

Radiological Dose Rates to Marine Fish from the Fukushima Daiichi Accident: The First Three Years Across the North Pacific

A more complete record is emerging of radionuclide measurements in fish tissue, sediment, and seawater samples from near the Fukushima Daiichi Nuclear Power Plant (FDNPP) and across the Pacific Ocean. Our analysis of publicly available data indicates the dose rates to the most impacted fish species near the FDNPP (median 1.1 mGy d−1, 2012−2014 data) have remained above benchmark levels for potential dose effects at least three years longer than was indicated by previous, data-limited evaluations. Dose rates from 134,137Cs were highest in demersal species with sediment-associated food chains and feeding behaviors. In addition to 134,137Cs, the radionuclide 90Sr was estimated to contribute up to approximately one-half of the total 2013 dose rate to fish near the FDNPP. Mesopelagic fish 100−200 km east of the FDNPP, coastal fish in the Aleutian Islands (3300 km), and trans-Pacific migratory species all had increased dose rates as a consequence of the FDNPP accident, but their total dose rates remained dominated by background radionuclides. A hypothetical human consumer of 50 kg of fish, gathered 3 kmfrom the FDNPP in 2013, would have received a total committed effective dose of approximately 0.95 mSv a−1 from combined FDNPP and ambient radionuclides, of which 0.13 mSv a−1 (14%) was solely from the FDNPP radionuclides and below the 1 mSv a−1 benchmark for public exposure

A comparison of the ellipsoidal and voxelized dosimetric methodologies for internal, heterogeneous radionuclide sources

Non-human biota dosimetry has historically relied on ellipsoidal dosimetric phantoms. In 2008, the International Commission on Radiological Protection (ICRP) presented a set of ellipsoidal models representative of wildlife, including dosimetric data for homogeneously distributed internal radionuclide sources. Such data makes it possible to quickly and easily estimate radiation dose rate. Voxelized modeling, first developed for use in human medical dosimetry, utilizes advanced imaging technologies to generate realistic and detailed dosimetric phantoms. Individual organs or tissues may be segmented and dosimetric data derived for each anatomic area of interest via Monte Carlo modeling. Recently, dosimetric data derived from voxelized models has become available for organisms similar to the ICRP's Reference Animals and Plants in 2008. However, if the existing ellipsoidal models are conservative, there may be little need to employ voxel models in regulatory assessments. At the same time, existing dosimetric techniques may be inadequate to resolve recent controversies surrounding the impact of ionizing radiation exposure on wildlife. This study quantifies the difference between voxel-calculated and ellipsoid-calculated dose rates for seven radionuclides assumed to be heterogeneously distributed: 14C, 36Cl, 60Co, 90Sr, 131I, 134Cs, 137Cs, and 210Po. Generally, the two methodologies agree within a factor of two to three. Finally, this paper compares the assumptions of each dosimetric system, the conditions under which each model best applies, and the implications that our results have for the ongoing dialog surrounding wildlife dosimetry

Radiological dose rates to marine fish from the Fukushima Daiichi accident: the first three years across the north Pacific

A more complete record is emerging of radionuclide measurements in fish tissue, sediment, and seawater samples from near the Fukushima Daiichi Nuclear Power Plant (FDNPP) and across the Pacific Ocean. Our analysis of publicly available data indicates the dose rates to the most impacted fish species near the FDNPP (median 1.1 mGy d−1, 2012−2014 data) have remained above benchmark levels for potential dose effects at least three years longer than was indicated by previous, data-limited evaluations. Dose rates from 134,137Cs were highest in demersal species with sediment-associated food chains and feeding behaviors. In addition to 134,137Cs, the radionuclide 90Sr was estimated to contribute up to approximately one-half of the total 2013 dose rate to fish near the FDNPP. Mesopelagic fish 100−200 km east of the FDNPP, coastal fish in the Aleutian Islands (3300 km), and trans-Pacific migratory species all had increased dose rates as a consequence of the FDNPP accident, but their total dose rates remained dominated by background radionuclides. A hypothetical human consumer of 50 kg of fish, gathered 3 km from the FDNPP in 2013, would have received a total committed effective dose of approximately 0.95 mSv a−1 from combined FDNPP and ambient radionuclides, of which 0.13 mSv a−1 (14%) was solely from the FDNPP radionuclides and below the 1 mSv a−1 benchmark for public exposure