Arrival of the Fukushima radioactivity plume in North American continental waters

Abstract

The large discharge of radioactivity into the northwest Pacific Ocean from the 2011 Fukushima Dai-ichi nuclear reactor accident has generated considerable concern about the spread of this material across the ocean to North America. We report here the first systematic study to our knowledge of the transport of the Fukushima marine radioactivity signal to the eastern North Pacific. Time series measurements of 134Cs and 137Cs in seawater revealed the initial arrival of the Fukushima signal by ocean current transport at a location 1,500 km west of British Columbia, Canada, in June 2012, about 1.3 y after the accident. By June 2013, the Fukushima signal had spread onto the Canadian continental shelf, and by February 2014, it had increased to a value of 2 Bq/m3 throughout the upper 150 m of the water column, resulting in an overall doubling of the fallout background from atmospheric nuclear weapons tests. Ocean circulation model estimates that are in reasonable agreement with our measured values indicate that future total levels of 137Cs (Fukushima-derived plus fallout 137Cs) off the North American coast will likely attain maximum values in the 3–5 Bq/m3 range by 2015–2016 before declining to levels closer to the fallout background of about 1 Bq/m3 by 2021. The increase in 137Cs levels in the eastern North Pacific from Fukushima inputs will probably return eastern North Pacific concentrations to the fallout levels that prevailed during the 1980s but does not represent a threat to human health or the environment.

Oceanic dispersion of Fukushima‐derived radioactive cesium: a review

“…Some of the global circulation models (Behrens et al ., ; Rypina et al ., ) also closely simulated the results of Smith et al . () and Yoshida et al . ().…”

Fukushima Daiichi–Derived Radionuclides in the Ocean: Transport, Fate, and Impacts

“…By February 2014, the 137 Cs signal had increased to 2 Bq m −3 throughout the upper 150 m, doubling the signal associated with fallout background from atmospheric nuclear weapons tests (Smith et al 2015). These activities have continued to increase over time, with offshore 137 Throughout much of the Pacific Ocean, the FDNPP plume was rapidly mixed throughout the upper 100-150 m of the water column and has only more slowly begun to penetrate to intermediate water depths , Smith et al 2015, Yoshida et al 2015). An important exception is the subsurface transport of FDNPP Cs in various Pacific mode waters that are formed through winter cooling and buoyancy loss, leading to mixing and homogenization of hydrographic properties deep in the water column .…”

“…The arrival of FDNPP-derived radionuclides off the west coast of North America was documented by measurements of 134 Cs and 137 Cs on the Canadian continental shelf in June 2013 (Smith et al 2015). By February 2014, the 137 Cs signal had increased to 2 Bq m −3 throughout the upper 150 m, doubling the signal associated with fallout background from atmospheric nuclear weapons tests (Smith et al 2015).…”

Risk assessment of radioisotope contamination for aquatic living resources in and around Japan

“…T he Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident caused by the catastrophic earthquake and tsunami on 11 March 2011 caused immense damage to human society in and around Japan by releasing large amounts of radioisotopes to the environment (1)(2)(3)(4)(5). This accident has raised great public concern about food safety.…”