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Abstract: Iodine-131 is a major component of the atmospheric releases following reactor accidents, and the passage of 131I through food chains from grass to human thyroids has been extensively studied. By comparison, the fate and effects of 131I deposition onto lakes and other aquatic systems have been less studied. In this study we: (1) reanalyze 1960s data from experimental releases of 131I into two small lakes; (2) compare the effects of differences in lake trophic structures on the accumulation of 131I by fish; (3) relate concentrations in fish and fish tissues to that in the water column using empirically estimated uptake (L kg−1 d−1) and loss (d−1) parameters; and (4) show that the largest concentrations in the thyroids of trout (Oncorhynchus mykiss) may occur from 8 to 32 days after initial release. Iodine-131 concentration in trout thyroids at 30-days post release may be >1000 times that in the water. Estimates of cumulative radiation dose (mGy) to thyroids computed using an anatomically-appropriate model of trout thyroid structure within the Monte Carlo N-particle modeling software predicted cumulative thyroid doses that increased approximately linearly after the first 8 days and resulted in 32-day cumulative thyroid doses that ranged from 6 mGy g−1 to 18 mGy g−1 per 1 Bq mL−1 of initial 131I in the water depending upon fish size. The majority of this dose is due to beta emissions, and the dose varies with positions in the thyroid tissue. [Copyright &y& Elsevier]

This paper discusses the development, comparison, and application of three anatomically representative computational phantoms for the grass species Andropogon virginicus , an indigenous grass species in the Southeastern United States. Specifically, the phantoms developed in this work are: (1) a stylized phantom where plant organs (roots or shoots) are represented by simple geometric shapes, (2) a voxel phantom developed from micro-CT imagery of a plant specimen, and (3) a hybrid phantom resulting from the refinement of (2) by use of non-uniform rational basis spline (NURBS) surfaces. For each computational phantom, Monte Carlo dosimetric modeling was utilized to determine whole-organism and organ specific dose coefficients (DC) associated with external and internal exposure to 99Tc, 137Cs, 237Np, and 238U for A. virginicus. Model DCs were compared to each other and to current values for the ICRP reference wild grass in order to determine if noteworthy differences resulted from the utilization of more anatomically realistic phantom geometry. Modeled internal DCs were comparable with ICRP values. However, modeled external DCs were more variable with respect to ICRP values; this is proposed to be primarily due to differences in organism and source geometry definitions. Overall, the three anatomical phantoms were reasonably consistent. Some noticeable differences in internal DCs were observed between the stylized model and the voxel or hybrid models for external DCs for shoots and for cases of crossfire between plant organs. Additionally, uptake data from previous hydroponic (HP) experiments was applied in conjunction with hybrid model DCs to determine dose rates to the plant from individual radionuclides as an example of practical application. Although the models within are applied to a small-scale, hypothetical scenario as proof-of-principle, the potential, real-world utility of such complex dosimetric models for non-human biota is discussed, and a fit-for purpose approach for application of these models is proposed. • Modeled internal dose coefficients (DC) were similar to ICRP 136 DCs for wild grass. • Differences between modeled external DCs and ICRP 136 values were more variable. • Hybrid and voxel model DCs were consistent in all cases. • DC differences are primarily due to differences in phantom geometry. • Model utility is discussed with a proposed fit-for-purpose approach to application. [ABSTRACT FROM AUTHOR]