In the spring of 2012, a year after the Fukushima Daiichi nuclear disaster, there was general concern that inhalation of radiocesium-contaminated Japanese cedar pollen may have caused the general population internal exposure to radioactive material. To determine if pollen had been contaminated through uptake of radiocesium by Japanese cedar and was therefore contributing to inhaled doses, Research Associate Shogo Higaki at the University of Tokyo Radioisotope Center measured radiocesium and Japanese cedar pollen adhered to nonwoven fabric masks worn by 68 subjects residing in eastern Japan, including Fukushima prefecture, for 8 weeks in the spring of 2012 (19 February 2012 to 14 April 2012). It was discovered that the principle source of radiocesium that might bring about internal exposure was not cedar pollen but fugitive dust (small particles without a clear point of origin). The maximum cumulative Cesium-137(137Cs) and Cesium-134(134Cs) radioactivities on masks worn by an individual were 21 ± 0.36 Bq and 15 ± 0.22 Bq, respectively, and the estimated effective dose during the 8 week was 0.494 µSv. Based on these values, the internal exposure over one year was estimated at 3.2 µSv. While this value is 1/310th of the official internal exposure limit of 1 mSv/year, this
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