Paper IMAGING PLANT LEAVES TO DETERMINE CHANGES IN RADIOACTIVE CONTAMINATION STATUS IN FUKUSHIMA, JAPAN Hiroo Nakajima,* Mamoru Fujiwara,† Isao Tanihata,† Tadashi Saito,‡ Norihiro Matsuda,§ and Takeshi Todo* AbstractVThe chemical composition of plant leaves often re- flects environmental contamination. The authors analyzed im- ages of plant leaves to investigate the regional radioactivity ecology resulting from the 2011 accident at the Fukushima No. 1 nuclear power plant, Japan. The present study is not an evalu- ation of the macro radiation dose per weight, which has been performed previously, but rather an image analysis of the ra- dioactive dose per leaf, allowing the capture of various gradual changes in radioactive contamination as a function of elapsed time. In addition, the leaf analysis method has potential appli- cations in the decontamination of food plants or other materials. Health Phys. 106(5):565Y570; 2014 Key words: 137 Cs; Chernobyl; contamination, environmental; imaging INTRODUCTION THE UNPRECEDENTED M9 East Japan Earthquake and acci- dent at the Fukushima No. 1 nuclear power plant (NPP) occurred on 11 March 2011. The subsequent hydrogen explosion at the reactor building dispersed water-soluble radioactive materials such as highly radioactive iodine ( 131 I) and radioactive cesium ( 134 Cs and 137 Cs). Water containing these radioactive materials evaporated into the atmosphere. Pollutants were transported by wind and rain, which even- tually resulted in the deposition of high-level pollutants northeast from the Fukushima No. 1 NPP (Fujiwara et al. 2011; MEXT 2011). Fukushima has abundant natural areas, and buildings, soil, and open grounds such as fields, mountainous areas, and plant leaves suffered widespread radioactive contam- ination. Thus, by investigating plant leaves, variations in regional contamination could be identified. Because the visualization of radioactive pollution gives an intuitive perception, reports of image analyses of ra- dioactive contamination in plants (Bersina et al. 1995; Nakajima et al. 1998; Soudek et al. 2006; Sawidis et al. 2010) and animals (Yamaguchi et al. 2012) increased after the Chernobyl accident. However, certain drawbacks of the image analysis, such as its inability to measure doses of radioactivity accurately and identify radionuclides, led to the use of image analysis as a minor method. In the present work, the authors did not employ con- ventional evaluation methods, which use large numbers of samples to measure radiation levels on leaves. Instead, they performed image analysis of leaf samples to monitor tem- poral changes in contamination and showed the advantages of using image analysis. MATERIALS AND METHODS Leaf samples taken from radioactively contaminated areas were placed on a BAS imaging plate (20 cm 25 cm, 20 cm 40 cm; Fujifilm Corporation, Tokyo, Japan) and were stored in cool, dark conditions for exposure periods of 3 or 7 d. Latent imaging was conducted using a scanner-type image analysis device (Typhoon FLA 7000, GE Health- care) to visualize the distribution of radioactivity on leaf surfaces. The intensity of radioactivity was measured as the PSL (photo-stimulated luminescence) value at 50 mm pixel j1 . The PSL values ranged from 12,798 (background) to 65,535 (upper limit). In the images, areas of high ra- dioactivity on leaf surfaces were represented as darker patches (Figs. 1, 2, and 3). To visualize the semi-quantification of radioactivity on a leaf, a concentration series of 137 Cs solutions (0.5, 1, 5, 10, and 50 Bq per 5 mL) was prepared as a scale of radioactivity levels. Each solution was dropped onto www.health-physics.com 565 *Department of Radiation Biology and Medical Genetics, Grad- uate School of Medicine; †Research Center for Nuclear Physics; ‡Radioisotope Research Center, Osaka University; §Headquarters of Fukushima Partnership Operations, Japan Atomic Energy Agency. The authors declare no conflicts of interest. For correspondence contact: Hiroo Nakajima, Department of Ra- diation Biology and Medical Genetics (B4), Graduate School of Med- icine, Osaka University, 2-2, Yamada-Oka, Suita, Osaka 565-0871, Japan, or email at nakajima@radbio.med.osaka-u.ac.jp. (Manuscript accepted 26 August 2013) 0017-9078/14/0 Copyright * 2014 Health Physics Society DOI: 10.1097/HP.0000000000000020 Copyright © 2014 Health Physics Society. Unauthorized reproduction of this article is prohibited.