2022 Volume 2 Issue 2 Pages 28-42
In May 2020, street dust, bryophytes (mainly mosses) and Sumatran fleabane (Asteraceae family) were collected from the south exit of Shinjuku Station to the Imperial Palace, mainly along Route 20 in Tokyo and were analyzed radioactive cesium in an attempt to reveal the distribution of radioactive cesium around urban road sides environment. The highest concentration of radioactive cesium in this area at the time of the survey was 3,020 Bq kg-1 dry weight of 137Cs in street dust, suggesting the existence of potential hotspot areas in Tokyo. Among four types of samples analyzed, mosses rhizosphere soils, street dust, mosses, and shoot of Sumatran fleabane, in that order, showed the highest concentrations. The variability of concentrations varied among samples. Among the four types of samples, the roadside dusts, Sumatran fleabane, rhizosphere soil, and mosses showed the greatest variability, in that order. From these results, it was concluded that mosses and their rhizosphere soils accumulate radioactive cesium at high and stable concentrations and that their use for monitoring is effective. In the survey area, a peculiarly high concentration was found in front of Shinjuku Gyoen, and relatively high levels of radioactive cesium were also detected in Shinjuku 3-chome, Yotsuya Station overpass, and in front of Hanzomon. The roads at those sites were relatively narrow, suggesting that local geographical conditions may have played a role in the accumulation.
