Temporal Variation of Radionuclide Contamination of Marine Plants on the Fukushima Coast after the East Japan Nuclear Disaster

Abstract

As a result of the Great East Japan Earthquake and associated tsunami in March 2011, the Fukushima Daiichi Nuclear Power Plant (FDNPP) released a large amount of radioactive material into the environment, resulting in contamination of many marine organisms. In this study, 15 marine algal species and a seagrass species were collected from the sublittoral zone of the Iwaki Coast of Fukushima Prefecture from May 2012 to June 2015 and analyzed for variations in 110mAg, 134Cs, and 137Cs over time. The results indicated that (1) 110mAg, 134Cs, and 137Cs were present in all marine plants collected in May 2012, (2) the concentration of 110mAg in the seagrass Phyllospadix iwatensis decreased significantly over time while the ecological half-life of 110mAg in P. iwatensis was longer at locations closer to the FDNPP, and (3) the 110mAg/137Cs radioactivity ratio of P. iwatensis was remarkably high until 2015, indicating that detectable 110mAg was present in the coastal environment 4 years after the accident. The concentration of 110mAg in P. iwatensis was higher than those in other marine algae, demonstrating a species-specific mechanism of accumulation.

Contamination of sea urchin Mesocentrotus nudus by radiocesium released during the Fukushima Daiichi Nuclear Power Plant accident

“…Because the organic matter in sea sediment contains high 137 Cs that would gradually translocate to the lithogenic fraction [ 14 ] which might be ingested by sea urchin. In another study, Shigeoka et al (2019) reported that the 137 Cs activity concentrations in some seagrasses, which are important food source for sea urchins, were higher at Ena station than at the Yotsukura station [ 9 ]. Thus, the spatial difference in the T eco might be attributed by deposited 137 Cs in sediment which was transferred through food uptake (e.g., organic matter and marine plants) by the sea urchins.…”

“…Types of kelp or seaweed, the main foods of sea urchins, contribute to the contamination in the edible part of sea urchins. Of 16 species of marine plants contaminated by radiocesium [ 9 ], 2 species ( Eclonia bicyclis and Phyllospadix iwatensis ) may have contributed to the contamination of sea urchins when ingested [ 21 , 31 ]. The uptake of 137 Cs will differ depending on the species of seaweed consumed as food.…”

“…Various researchers have reported the concentrations of 137 Cs in seaweed along the Fukushima coast after the accident [ 9 , 14 , 16 ]. Shigeoka et al (2019) investigated the 137 Cs activity concentrations in 15 species of algae and 1 seagrass species and found that the 137 Cs activity concentrations in algae at 500 and 1000 days after the accident were 2.86–12.3 Bq/kg-WW and 0.22–0.58 Bq/kg-WW, respectively ( S3 Fig ) [ 9 ]. The 137 Cs activity concentration in food calculated in this study ( S4 Fig ) was 20–2554 times higher than the concentration in algae.…”

“…Radioactive Cs amounting to 3.5 PBq was transported directly out into the ocean [1]. The water mass with high levels of radioactive cesium flowed south from the FDNPP [1,[3][4][5] and contaminated many marine biota and seabed sediments along the southern coast and offshore area of Fukushima Prefecture [6][7][8][9][10][11][12]. Numerous researchers have observed temporal change in the radiocesium contamination of various marine organisms, including fish [13][14][15], invertebrates [16,17], and algae [9,18].…”

“…The water mass with high levels of radioactive cesium flowed south from the FDNPP [1,[3][4][5] and contaminated many marine biota and seabed sediments along the southern coast and offshore area of Fukushima Prefecture [6][7][8][9][10][11][12]. Numerous researchers have observed temporal change in the radiocesium contamination of various marine organisms, including fish [13][14][15], invertebrates [16,17], and algae [9,18]. From monitoring data, these researchers showed that the concentrations tended to decrease over time, and that the radioactive concentrations in marine invertebrates decreased more quickly, such that the concentrations in many species were below the level of detection within three years of the FDNPP accident.…”