Biofilm-mediated interactions between plastics and radiocesium in coastal environments

Battulga, B.; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Otosaka, Shigeyoshi*; Koarashi, Jun

Environmental Science and Pollution Research, 31, p.60080 - 60092, 2024/10

https://doi.org/10.1007/s11356-024-35164-y

A ubiquitous distribution of plastic debris has been reported in aquatic and terrestrial environments; however, the interactions between plastics and radionuclides and the radioactivity of environmental plastics remain largely unknown. Here, we characterize biofilms developing on the surface of plastic debris to explore the role of plastic-associated biofilms as an interaction medium between plastics and radiocesium (Cs) in the environment. Biofilm samples were extracted from plastics (1-50 mm in size) collected from two contrasting coastal areas in Japan. The radioactivity of plastics was estimated based on the Cs activity concentration of the biofilms and compared seasonally with surrounding environmental samples (i.e., sediment and sand). Cs traces were detected in biofilms with activity concentrations of 21-1300 Bq kg biofilm (dry weight), corresponding to 0.04-4.5 Bq kg plastic (dry weight). Our results reveal the interaction between Cs and plastics and provide evidence that organic and mineral components in biofilms are essential in Cs retention in environmental plastics.

Records of the riverine discharge of I in riverbank sediment after the Fukushima accident

Nakanishi, Takahiro; Sakuma, Kazuyuki; Oyama, Takuya; Hagiwara, Hiroki; Suzuki, Takashi

Environmental Pollution, 355, p.124213_1 - 124213_7, 2024/08

https://doi.org/10.1016/j.envpol.2024.124213

This study investigated the transport behavior of I by riverbank surveys conducted from 2013 to 2015 in a watershed where the I/Cs activity ratio is low in the mountainous area and high in the plain as of 2011. Until 2015, the I/Cs activity ratio of the levee crown in the studied watershed was similar to that of the surrounding area in 2011. However, the I/Cs ratios of the surface riverbank sediments were all low, indicating that radionuclides transported from the mountainous area were deposited on the riverbank in the plain. The vertical distribution of the I/Cs ratio in the riverbank sediments indicated that some I and Cs deposited during the accident remained in the lower layers, but most were eroded immediately after the accident. Based on the I/Cs ratios of sediments deposited on the riverbank, which remained constant until 2015 after the accident, the amount of I discharged to the ocean was determined from the previously evaluated Cs discharge. It was calculated that 1.810 Bq and 1.210 Bq of I were discharged with sediment from the studied watershed and the contaminated river watersheds (Abukuma River and Fukushima coastal rivers, including the study river), respectively. The results of this study indicate that the continuous I discharge from the river contribute little to their amount in the seafloor sediments along the Fukushima coast.

Evaluation of the impact of the Cs supply from rivers to coastal waters off Fukushima on the Cs behavior in seabed sediment

Ikenoue, Tsubasa; Nakanishi, Takahiro; Shimadera, Hikari*; Kawamura, Hideyuki; Kondo, Akira*

E3S Web of Conferences (Internet), 530, p.02005_1 - 02005_10, 2024/05

https://doi.org/10.1051/e3sconf/202453002005

The accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) caused a radioactive contamination in seabed sediment. The Cs supply from rivers could be an important process for the long-term behavior of Cs in seabed sediment. In this study, a ten-year simulation of the Cs behavior in seabed sediment was conducted using an oceanic dispersion model combined with a prediction model of Cs behavior in land and river. In the waters north of FDNPP, the simulation results suggested that the Cs supply from rivers had a great impact on the concentrations in coastal sediment due to the initial low concentrations in seabed sediment and the large supply of Cs from rivers. In the waters near FDNPP and south of FDNPP, the simulation results suggested that the impact of the Cs supply on the temporal variation of Cs concentration in coastal sediment was relatively small due to the large initial adsorption from seawater. Overall, these results indicated that Cs supply from rivers had an impact on the spatiotemporal distribution of Cs concentrations in seabed sediment on a decadal time scale and the impact was especially great in the waters north of FDNPP.

Behavior of radiocesium (Cs) on the coastal seafloor near the Fukushima Daiichi Nuclear Power Plant inferred from radiocesium distributions in long cores

Nakanishi, Takahiro; Tsuruta, Tadahiko; Misono, Toshiharu; Shiribiki, Takehiko; Urabe, Yoshimi*; Sanada, Yukihisa

Journal of Coastal Research, 116(SI), p.161 - 165, 2024/01

https://doi.org/10.2112/JCR-SI116-033.1

Continuous data of Cs-137 concentration in surface seabed sediment around the Fukushima Daiichi Nuclear Power Plant (FDNPP) from 2012 to 2022 was compiled and its temporal change was fitted by exponential function. In general, Cs-137 concentrations were gradually declining with time. However, at some monitoring points in shallow region, long half-lives and/or large deviations of Cs-137 concentrations were noticed. To gain insight into cesium dynamics in shallow seafloor, long sediment cores were collected at shallow region near the FDNPP, and the vertical profiles of Cs-137 concentration and particle size distribution were determined. At the beach, Cs-137 concentration and particle size distribution were very homogenized from several tens of cm to more than 1 m deep, probably due to strong vertical mixing by wind waves and tides. Therefore, beach sediments have significant Cs-137 reserves in deeper layers at present. It was suggested that the Cs-137 supply from deep layers as well as the land area might suppress the decline of surface Cs-137 concentration in this area. At sampling points located at the bases of cliffs and depressions at the offshore zone, the vertical distributions of Cs-137 concentration were highly heterogeneous, showing the particle size dependency. Moreover, Cs-137 profiles obtained at the same point for several years were quite different. Therefore, it might cause the large fluctuation of Cs-137 concentration at surface sediment over time.

Thirty-year prediction of Cs supply from rivers to coastal waters off Fukushima considering human activities

Ikenoue, Tsubasa; Shimadera, Hikari*; Nakanishi, Takahiro; Kondo, Akira*

Water (Internet), 15(15), p.2734_1 - 2734_18, 2023/08

https://doi.org/10.3390/w15152734

The Fukushima Daiichi Nuclear Power Plant accident caused an accumulation of Cs in coastal sediment. The Cs supply from rivers to the ocean can affect the long-term fate of Cs in coastal sediment. Since the Fukushima coastal river basins include large decontaminated and evacuation order areas, considering the decontamination work and resumption of agriculture is important for predicting the Cs supply. We conducted a 30-year prediction of the Cs supply from the Fukushima coastal rivers to the ocean using a distributed radiocesium prediction model, considering the effects of human activities. In river basins with decontaminated and evacuation order areas, human activities reduced the total Cs outflow from agricultural lands, urban lands, and forest areas to the rivers and the Cs supply to the ocean by 5.0% and 6.0%, respectively. These results indicated that human activities slightly impacted the Cs outflow and supply. The Cs supply from rivers impacted by the accident to the coastal sediment was estimated to correspond to 11-36% of the total Cs in the coastal sediment in the early phase of the accident. Therefore, the Cs supply from rivers to the ocean is important for the long-term behavior of Cs in coastal sediment.

Simulation study on H behavior in the Fukushima coastal region; Comparison of influences of discharges from the Fukushima Daiichi and rivers

Sakuma, Kazuyuki; Yamada, Susumu; Machida, Masahiko; Kurikami, Hiroshi; Misono, Toshiharu; Nakanishi, Takahiro; Iijima, Kazuki

Marine Pollution Bulletin, 192, p.115054_1 - 115054_10, 2023/07

https://doi.org/10.1016/j.marpolbul.2023.115054

Effect of radioactive cesium-rich microparticles on radioactive cesium concentration and distribution coefficient in rivers flowing through the watersheds with different contaminated condition in Fukushima

Tatsuno, Takahiro*; Waki, Hiromichi*; Kakuma, Minato*; Nihei, Naoto*; Takase, Tsugiko*; Wada, Toshihiro*; Yoshimura, Kazuya; Nakanishi, Takahiro; Ote, Nobuhito*

Journal of Environmental Management, 329, p.116983_1 - 116983_13, 2023/03

https://doi.org/10.1016/j.jenvman.2022.116983

Dynamics of radiocesium in coastal areas following river flood

Misono, Toshiharu; Nakanishi, Takahiro; Shiribiki, Takehiko; Nagao, Seiya*; Ochiai, Shinya*; Sanada, Yukihisa; Tsuruta, Tadahiko

Gekkan Kaiyo, 54(11), p.558 - 561, 2022/11

Sediment traps were set up around estuaries and in coastal areas to collect sinking particles at the time of river discharge. Around the estuary, changes in radiocesium concentration and mass flux of sinking particles linked to the discharge of radiocesium from the river were observed.

Cesium-rich microparticles runoff during rainfall; A Case study in the Takase River

Tatsuno, Takahiro*; Waki, Hiromichi*; Kakuma, Minato*; Nihei, Naoto*; Wada, Toshihiro*; Yoshimura, Kazuya; Nakanishi, Takahiro; Ote, Nobuhito*

Radiation Protection Dosimetry, 198(13-15), p.1052 - 1057, 2022/09

https://doi.org/10.1093/rpd/ncac052

Migration processes of radioactive cesium in the Fukushima nearshore area; Impacts of riverine input and resuspension

Misono, Toshiharu; Nakanishi, Takahiro; Tsuruta, Tadahiko; Shiribiki, Takehiko; Sanada, Yukihisa

Marine Pollution Bulletin, 178, p.113597_1 - 113597_9, 2022/05

https://doi.org/10.1016/j.marpolbul.2022.113597

It is essential to evaluate secondary migration caused by riverine input and resuspension from seabed sediments to estimate the future distribution of radioactive cesium (Cs) in the coastal area off Fukushima Prefecture. In particular, the inflow from rivers cannot be ignored because most of the Cs inflow from rivers is deposited on the coast without elute into seawater. Two mooring systems were installed near the Ukedo River's mouth (Fukushima Prefecture) from February 2017 to February 2018. The first contained a sediment trap system, collecting sinking particles during the period. The second comprised a turbidity sensor and a current sensor. The contribution of resuspension and inflow from the river to the mass flux was quantitatively evaluated using multiple regression equations. The results showed that resuspension caused 79%-83% of secondary Cs migration in nearshore areas, whereas the influence of riverine Cs input on the sediment was only 7% per year.