Appearances of Fukushima Daiichi Nuclear Power Plant-Derived ¹³⁷Cs in Coastal Waters around Japan: Results from Marine Monitoring off Nuclear Power Plants and Facilities, 1983–2016

Monitoring of ¹³⁷Cs in seawater in coastal areas around Japan between 1983 and 2016 yielded new insights into the sources and transport of Fukushima Daiichi Nuclear Power Plant (FDNPP)-derived ¹³⁷Cs, particularly along the west coast of Japan. Before the FDNPP accident (1983–2010), the activity concentrations of ¹³⁷Cs, mainly from fallout, were decreasing exponentially. Effective ¹³⁷Cs half-lives in surface seawater ranged from 15.6 to 18.4 yr. After the FDNPP accident (March 2011) ¹³⁷Cs activity concentrations in seawater off Fukushima and neighboring prefectures immediately increased. Since May/June 2011, ¹³⁷Cs activity concentrations there have been declining, and they are now approaching preaccident levels. Along the west coast of Japan remote from FDNPP (i.e., the Japan Sea), however, radiocesium activity concentrations started increasing by 2013, with earlier (May/June 2011) increases at some sites due to airborne transport and fallout. The inventory of ¹³⁷Cs in the Japan Sea (in the main body of the Tsushima Warm Current) in 2016 was calculated to be 0.97 × 10¹⁴ Bq, meaning that 0.44 × 10¹⁴ Bq of FDNPP-derived ¹³⁷Cs was added to the estimated global fallout ¹³⁷Cs inventory in 2016 (0.53 × 10¹⁴ Bq). The net increase of ¹³⁷Cs inventory in the Japan Sea through the addition of FDNPP-derived ¹³⁷Cs accounts for approximately 0.2% of the total ¹³⁷Cs flux from the plant to the ocean from the accident

Appearances of Fukushima Daiichi Nuclear Power Plant-Derived ¹³⁷Cs in Coastal Waters around Japan: Results from Marine Monitoring off Nuclear Power Plants and Facilities, 1983–2016

Monitoring of ¹³⁷Cs in seawater in coastal areas around Japan between 1983 and 2016 yielded new insights into the sources and transport of Fukushima Daiichi Nuclear Power Plant (FDNPP)-derived ¹³⁷Cs, particularly along the west coast of Japan. Before the FDNPP accident (1983–2010), the activity concentrations of ¹³⁷Cs, mainly from fallout, were decreasing exponentially. Effective ¹³⁷Cs half-lives in surface seawater ranged from 15.6 to 18.4 yr. After the FDNPP accident (March 2011) ¹³⁷Cs activity concentrations in seawater off Fukushima and neighboring prefectures immediately increased. Since May/June 2011, ¹³⁷Cs activity concentrations there have been declining, and they are now approaching preaccident levels. Along the west coast of Japan remote from FDNPP (i.e., the Japan Sea), however, radiocesium activity concentrations started increasing by 2013, with earlier (May/June 2011) increases at some sites due to airborne transport and fallout. The inventory of ¹³⁷Cs in the Japan Sea (in the main body of the Tsushima Warm Current) in 2016 was calculated to be 0.97 × 10¹⁴ Bq, meaning that 0.44 × 10¹⁴ Bq of FDNPP-derived ¹³⁷Cs was added to the estimated global fallout ¹³⁷Cs inventory in 2016 (0.53 × 10¹⁴ Bq). The net increase of ¹³⁷Cs inventory in the Japan Sea through the addition of FDNPP-derived ¹³⁷Cs accounts for approximately 0.2% of the total ¹³⁷Cs flux from the plant to the ocean from the accident

The Contribution of Sources to the Sustained Elevated Inventory of ¹³⁷Cs in Offshore Waters East of Japan after the Fukushima Dai-ichi Nuclear Power Station Accident

We have evaluated the contribution of sources of ¹³⁷Cs to the inventory of radiocesium in waters (surface area: 6160 km², water volume: 753 km³) off Fukushima Prefecture and neighboring prefectures from May 2011 to February 2015. A time-series of the inventory of ¹³⁷Cs in the offshore waters revealed a clearly decreasing trend from May 2011 (283.4 TBq) to February 2015 (1.89 TBq). The ¹³⁷Cs inventory about four years after the accident was approximately twice the background inventory of 1.1 TBq. The magnitudes of the ¹³⁷Cs influxes from sources into offshore waters for periods of 182–183 days were estimated from the first period (1 October 2011 to 31 March 2012: 15.3 TBq) to the last period (1 October 2014 to 31 March 2015: 0.41 TBq). We assumed that three sources contributed ¹³⁷Cs: continuous direct discharge from the Fukushima Dai-ichi Nuclear Power Station (FNPS) even after the massive discharge in late March 2011, desorption/dissolution from sediments, and fluvial input. Quantification of these sources indicated that the direct discharge from the FNPS is the principal source of ¹³⁷Cs to maintain the relatively high inventory in the offshore area

DataSheet_1_Floating microplastic inventories in the southern Beaufort Sea, Arctic Ocean.pdf

The microplastics inflow into the Arctic Ocean may increase environmental stress on the Arctic marine ecosystem on the Pacific side, where sea ice has been significantly reduced because of global warming. However, quantitative data on microplastics are very limited in the Beaufort Sea, which is covered by sea ice for most of the year, even in summer. We therefore observed microplastic concentrations over a wide area of the southern Beaufort Sea using a neuston net from 30 August to 10 September 2022 to estimate the total number (particle inventory) and mass (mass inventory) of microplastics in the entire water column. The particle inventory during the sampling period ranged from 937 to 28,081 pieces km−2 (mean ± standard deviation, 7570 ± 7600 pieces km−2). The mass inventory of microplastics ranged from 22 to 664 g km−2 (179 ± 180 g km−2). Relatively high microplastic inventories (>6500 pieces km−2) were observed off Utqiaġvik and the mouth of the Mackenzie River, suggesting that some microplastics originate not only in the Pacific but also in the Arctic. These values indicate that waters in the southern Beaufort Sea is contaminated with microplastics to the same order of magnitude as the Chukchi Sea.</p