Development of an easy and cost-effective method for assessing radionuclide
concentration in airborne dust and their behavior using “Moss Bags”

Research purpose and contents

In the surrounding area of the Fukushima Daiichi Nuclear Power Station (FDNPS), dust samplers has provided data about the radionuclide concentration in the atmosphere. However, as they are expensive and need an electric power supply, the number of samplers and locations in which they can be installed have been limited. To solve this problem, we started to examine "moss bags" technique in evacuated areas of Fukushima. It can be freely installed anywhere we would like to investigate radionuclide airborne for any desired period; they are also easy to handle during installation and maintenance, along with being low-cost.

Moss bags have been studied in Europe as a method to assess air pollution. Moss have the ability to capture contaminants in the air and retain particles such as soil due to their morphology. They also accumulate elements with their large surface area and tissue roughness. The aim of this study is to apply moss ability in “moss bag” for assessing the radionuclide concentration in airborne dust and their behavior. For this purpose, we carried out exposure test of moss bags in Fukushima.

Moss bags can be fixed and suspended street lamp posts, trees and etc. around FDNPS site. For instance, we install moss bags there for any period and measure their radionuclide concentration, we will be expected to know the radionuclide concentration in the air at the location. "Carring out investigation is possible anywhere and at any time" provides a means of knowing the radioactivity level around us. This will help to enhance a feeling of security to radioactive contamination and exposure for people living and/or working in the vicinity of FDNPS site.

Investigation of atmospheric radioactive airborne concentration using moss bag

“Moss bag”, is a mesh bag filled with dried mosses, as its name indicates. We examined Hypnum species which is studied for air pollution assessment in Italy, and the genus Hypnum and Sphagnum that they are widely distributed in Japan. We focused that moss has no root, no vascular system, large surface area and simple shape. It means that moss is an easily handled organism to assess the characteristic and amount of substances uptake in moss from atmosphere. Moreover, this "natural air filter" that captures the airborne dust, is easy to prepare (cultivation) and dispose after using it. With this background, we launch a research project to develop the novel methodology for assessment of radioactive airborne concentration using “Moss bag” in the Fukushima prefecture in collaboration with the University of Naples, Federico II, in Italy (Dr. Anna Di Palma and Prof. Paola Adamo), who have the expertise and experience of “Moss bag” assessment for air pollution.

As a pre-exposure treatment, water washing and oven drying lead to death of the moss. After that step, the dry moss are loosely packed in nylon mesh; the moss bag is approximately 3 centimeters in diameter. We have examined moss bag exposure tests for over three weeks at several sites in the evacuated area (composed of three replicate moss bags per exposure test condition). The results showed a linear increase in the radionuclide concentration (radiocaesium, 137Cs) in moss bags with increasing the exposure time, regardless of the exposure test sites. This tendency suggest that moss bag has the potential to be used for quantitative assessment. We will investigate as further study, (1) the difference in radiocaesium activity concentrations in moss bags among the moss species, and depend on weather conditions, such as precipitation (difference in dust capture mechanism, its efficiency and other factors), (2) the relationship between the local conditions (e.g. with or without pavement) and the radadiocaesium activity concentration in moss bags. Because the condition will be one of factor about the amount of resuspension soil and dust in the air., and (3) the relationship between the radiocaesium activity concentrations in dust filter collected by dust sampler and in moss bags. We expect these answers will indicate that suitable moss species for moss bag, reproducible radionuclide concentration result to reflect local condition, and complementarity between dust sampler and moss bag. Then, clarifying these answers would the future that the moss bag can be widely used for practical purposes as quantitative assessment of radionuclide concentration in airborne dust.

Related information

Researcher	Terumi Dohi（researchmap）