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A comparison of methods to derive aggregated transfer factors: tested using wild boar data from the Fukushima prefecture

Date

2017

Authors

Anderson, Donovan, author
Johnson, Thomas, advisor
Brandl, Alexander, committee member
Hess, Ann, committee member

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Abstract

In March of 2011, the Fukushima Daiichi disaster released airborne radioactive material dominated by Cs-134 and Cs-137. When the radionuclides settled, they contaminated soil and plants, with wild boar also becoming contaminated through various pathways. An estimate of the radiocesium concentration in wild boar tissues can be obtained from an aggregated transfer factor based on soil contamination levels. The aggregated transfer factor (Tag) for purposes of this study, is the ratio of Cs-137 concentration in wild boar tissues (Bq kg-1) divided by the Cs-137 surface contamination of soils (Bq m-2). In this study, two methods were used to estimate the Tag values, and a comparison was made to determine which method reduced uncertainty. Both methods rely on harvesting and measuring radiocesium in wild boar tissues (bicep femoris muscle). The radiocesium value used for soil, however, was different in the two methods. One was obtained from a public database of samples collected by the Japanese government in 2015. Oftentimes, the soil sample paired with the wild boar trap site were not within the home range of the wild boar, reducing accuracy of the predicted radiocesium concentration levels in the animal. The other method used soil samples collected at the point of wild boar capture. The purpose of this study is to ascertain if the use of the database radiocesium soil concentration values is of sufficient granularity to provide a useful estimate of Tag values. The mean Tag value calculated in the Fukushima prefecture for wild boar were 2.3×10-3 m2 kg-1 fresh weight. The research revealed that the database radiocesium concentration values for soil (Bq m-2) used in calculating aggregated transfer factors, do not accurately represent the containment levels in the wild boar. Collecting soil samples within the home range of the animal reduces uncertainty in calculating Tag values to estimate whole body contamination levels of a wild boar. Our data complements and supports the existing monitoring programs conducted by the National and Prefecture governments in Japan by showing lower concentrations of cesium in soil and wild boar within decontaminated areas.

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2017 Spring.
Includes bibliographical references.

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