Graduate School of Science and Engineering, Kindai University, Higashiosaka, Osaka, Japan.
Faculty of Science and Technology, Ryukoku University, Otsu, Shiga, Japan.
PLoS One. 2018 Mar 1;13(3):e0193414. doi: 10.1371/journal.pone.0193414. eCollection 2018.
A monitoring survey was conducted from August 2011 to July 2016 of the spatiotemporal distribution in the 400 km2 area of the northern part of Tokyo Bay and in rivers flowing into it of radiocesium released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The average inventory in the river mouth (10 km2) was 131 kBq⋅m-2 and 0.73 kBq⋅m-2 in the central bay (330 km2) as the decay corrected value on March 16, 2011. Most of the radiocesium that flowed into Tokyo Bay originated in the northeastern section of the Tokyo metropolitan area, where the highest precipitation zone of 137Cs in soil was almost the same level as that in Fukushima City, then flowed into and was deposited in the Old-Edogawa River estuary, deep in Tokyo Bay. The highest precipitation of radiocesium measured in the high contaminated zone was 460 kBq⋅m-2. The inventory in sediment off the estuary of Old-Edogawa was 20.1 kBq⋅m-2 in August 2011 immediately after the accident, but it increased to 104 kBq⋅m-2 in July 2016. However, the radiocesium diffused minimally in sediments in the central area of Tokyo Bay in the five years following the FDNPP accident. The flux of radiocesium off the estuary decreased slightly immediately after the accident and conformed almost exactly to the values predicted based on its radioactive decay. Contrarily, the inventory of radiocesium in the sediment has increased. It was estimated that of the 8.33 TBq precipitated from the atmosphere in the catchment regions of the rivers Edogawa and Old-Edogawa, 1.31 TBq migrated through rivers and was deposited in the sediments of the Old-Edogawa estuary by July 2016. Currently, 0.25 TBq⋅yr-1 of radiocesium continues to flow into the deep parts of Tokyo Bay.
从 2011 年 8 月到 2016 年 7 月，对福岛第一核电站事故释放的放射性铯在东京湾北部 400 平方公里区域及流入该湾的河流中的时空分布进行了监测调查。2011 年 3 月 16 日，经放射性衰变修正后，河口（10 平方公里）处的平均活度为 131kBq·m-2，中心湾（330 平方公里）处为 0.73kBq·m-2。流入东京湾的大部分放射性铯源自东京都的东北部地区，该地区土壤中 137Cs 的最高沉积区与福岛市几乎处于同一水平，然后流入并沉积在东京湾深处的旧江户川河口。在高污染区测量到的放射性铯最高沉积量为 460kBq·m-2。2011 年 8 月事故发生后立即，旧江户川河口附近沉积物中的活度为 20.1kBq·m-2，但到 2016 年 7 月增加到 104kBq·m-2。然而，福岛第一核电站事故发生后的五年内，东京湾中心区域的沉积物中放射性铯扩散极小。河口附近的放射性铯通量在事故发生后立即略有减少，几乎完全符合基于放射性衰变预测的值。相反，沉积物中的放射性铯活度有所增加。据估计，在江户川和旧江户川流域地区从大气中沉降的 8.33TBq 中，有 1.31TBq 通过河流迁移，并于 2016 年 7 月沉积在旧江户川河口的沉积物中。目前，有 0.25TBq·yr-1的放射性铯继续流入东京湾的深部。
