Update: Tracking the arrival of Fukushima derived contamination in the Pacific off North America

By Jay T. Cullen

Previously unpublished data results from research expeditions in 2014 and 2015 are summarized here.  Overall the data indicate that:

  1. Fukushima derived radiocesium was first detected 1500 km west of British Columbia Canada in June 2012
  2. Contamination was detected on the continental shelf (near coastal waters) in June 2013
  3. By February 2014 Fukushima radiocesium was present at levels similar to preexisting weapons testing derived 137Cs
  4. The timing of the arrival and levels of radiocesium in the contaminated plume are in reasonable agreement with existing ocean circulation model predictions
  5. 134Cs, a unique indicator of Fukushima impact given its ~ 2 year half life, increased in 2014 and 2015 relative to previous years indicating that peak concentrations are likely to arrive in 2016
  6. Maximum combined radiocesium activities (137Cs + 134Cs) offshore as of summer 2015 are 11 Bq m-3 of seawater are about 8-10 fold less than maximum activities measured in the 1960’s due to weapons testing fallout. Current levels do not represent a significant risk to ecosystem or public health

This short post summarizes new data from 2014 and 2015 reporting results from the Integrated Fukushima Ocean Radionuclide Monitoring (InFORM) project and our partner organization Our Radioactive Ocean which are tasked with documenting the arrival of ocean borne Fukushima derived contamination along the North American Pacific coast. This post is part of an ongoing effort to communicate the best science available on the impacts of the Fukushima Dai-ichi meltdowns on the environment. High quality measurements to look for Fukushima derived radiocesium have been made in seawater in the North Pacific and Arctic Oceans from 2011 to summer 2015. Previous data was summarized in an earlier post .

A news release today by Dr. Ken Buesseler’s citizen science monitoring program Our Radioactive Ocean posted 110 new analyses of surface seawater samples collected in the North Pacific.  Measurements of 137Cs and 134Cs were made on the samples to determine the location of waters contaminated by the 2011 Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident.  A map summarizing their results for 134Cs is shown below:

Map shows the location of seawater samples taken by scientists and citizen scientists that were analyzed at the Woods Hole Oceanographic Institution for radioactive cesium as part of Our Radioactive Ocean. Cesium-137 is found throughout the Pacific Ocean and was detectable in all samples collected, while cesium-134 (yellow/orange dots), an indicator of contamination from Fukushima, has been observed offshore and in select coastal areas. (Figure by Jessica Drysdale, Woods Hole Oceanographic Institution)

Regarding the maximum levels of radiocesium detected offshore thusfar the press release states:

The level of radioactive cesium isotopes in the sample, 11 Becquerel’s per cubic meter of seawater (about 264 gallons), is 50 percent higher than other samples collected along the West Coast so far, but is still more than 500 times lower than US government safety limits for drinking water, and well below limits of concern for direct exposure while swimming, boating, or other recreational activities.

2014 measurements of 137Cs and 134Cs activities in surface seawater by the InFORM and ORO projects are shown below. These results build on a monitoring program initiated by Canada’s Department of Fisheries and Oceans in 2011 to track contamination of Fukushima contamination in the Pacific and Arctic Oceans. To do this seawater samples were collected at specific stations in the summer of 2014 indicated on the following maps which summarizes radiocesium activities:

aug14cs134_edit-01.png
Activity of 134Cs (Bq m-3) in surface seawater samples collected in the North Pacific in 2014 by ORO and InFORM projects which shows the location of waters contaminated by the FDNPP accident.

 

aug14cs137_edit-01.png
Activity of 137Cs (Bq m-3) in surface seawater samples collected in the North Pacific in 2014 by ORO and InFORM projects which shows the location of waters contaminated by the FDNPP accident and vestige contamination from atmospheric weapons testing and Chernobyl in the 20th century.

Given that other isotopes of concern with respect to environmental and public health (e.g. 90-Sr and Plutonium isotopes) were released in very low amounts relative to radiocesium the general conclusion reached for Cs can likely be extended to these isotopes as well. The levels of radiocesium expected and being measured offshore do not represent an environmental or public health threat. Ongoing monitoring will help to improve models of North Pacific circulation and keep the public up to date with respect to expected impacts on ocean and human health. Look for continued monitoring from the InFORM project and for new results to be written about here as they become available.

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