Cesium-137 and 137Cs/133Cs atom ratios in marine zooplankton off the east coast of Japan during 2012–2020 following the Fukushima Dai-ichi nuclear power plant accident. (15th October 2022)

• Record Type: Journal Article
• Authors: Ikenoue, Takahito; Yamada, Masatoshi; Ishii, Nobuyoshi; Kudo, Natsumi; Shirotani, Yuhei; Ishida, Yasuo; Kusakabe, Masashi
• Is Part Of: Environmental pollution. Volume 311(2022)
• Publication Date: 2022-10-15
• Subjects: Long-term monitoring -- Stable cesium -- Autoradiography -- Highly radioactive cesium-bearing particles -- Suspended particles -- Microplastics; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2022.119962
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: We measured the concentrations of cesium isotopes ( 133 Cs, 134 Cs, and 137 Cs) in zooplankton samples collected in waters off the east coast of Japan from May 2015 to June 2020. By combining these data with those obtained previously from May 2012 to February 2015, we evaluated the long-term impacts of the Fukushima Dai-ichi Nuclear Power Plant accident on marine zooplankton. Relatively high 137 Cs concentrations in zooplankton, exceeding 10 Bq/kg-dry weight, were sporadically observed until June 2016, regardless of year or station. After May–June 2017, 137 Cs concentrations decreased to below 1 Bq/kg-dry at most stations, and by May 2020, concentrations were below 0.5 Bq/kg-dry except those off Fukushima Prefecture. Since the accident, the 137 Cs/ 133 Cs atom ratios of zooplankton samples were higher than those of ambient seawater until 2019, but in May–June 2020 the ratios matched those of seawater except off Fukushima Prefecture. Highly radioactive particles were not detected in zooplankton samples by autoradiography using imaging plates after May–June 2017, although they were before. Therefore, the persistence of elevated 137 Cs/ 133 Cs ratios in zooplankton relative to seawater for nine years after the accident was probably due to the incorporation of highly radioactive particles (cesium-bearing particles or clay-mineral aggregates with highly adsorbed radiocesium) onto/into zooplankton for several years after the accident. However, since at least May–June 2017, these elevated ratios have likely been caused by small highly radioactive particles (or larger particles disaggregated into small pieces) entering the ocean from land via rivers or directly discharged from the Fukushima Nuclear Power Plant. Microplastics enriched with radiocesium with higher 137 Cs/ 133 Cs ratios than seawater may have also contributed 137 Cs to the zooplankton. Graphical abstract: Image 1 Highlights: 137 Cs and 137 Cs/ 133 Cs from the 2011 FDNPP accident are tracked in zooplankton to 2020. It took nine years for 137 Cs concentrations to return to pre-accident levels. 137 Cs/ 133 Cs atom ratios in zooplankton remained high compared to seawater. High 137 Cs/ 133 Cs ratios prior to 2017 mainly due to highly radioactive particles. High 137 Cs/ 133 Cs ratios after 2017 mainly from low-radioactivity suspended particles.