This short blog summarizes an open access paper published today reporting results from a Canadian monitoring program tasked with documenting the arrival of ocean borne Fukushima contamination along the North American Pacific coast. This diary 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 were made in seawater in the North Pacific and Arctic Oceans from 2011 to early 2014. The authors concluded that:
Fukushima derived radiocesium was first detected 1500 km west of British Columbia Canada in June 2012
Contamination was detected on the continental shelf (near coastal waters) in June 2013
By February 2014 Fukushima radiocesium was present at levels similar to preexisting weapons testing derived 137-Cs
These same models predict that total radiocesium levels from weapons testing fallout and Fukushima will likely reach maximum values of ~3-5 Becquerel per cubic meter (Bq m-3 of seawater in 2015-2016 and then decline to fallout background level of ~1 Bq m-3 by 2021
Fukushima will increase northeastern Pacific water to levels last seen in the 1980’s but does not represent a threat to environmental or human health
The purpose of this post is to compare the concentrations of Sr-90 and Cs-137 in the North Pacific Ocean over the last 50 years to the concentrations predicted to arrive on the west coast associated with waters affected by release of radionuclides from the Fukushima-Daiichi Nuclear Power Plant. Given present levels that are being measured in the eastern Pacific and barring release rates that significantly exceed past rates in March-April 2011, when release rates were 10,000-100,000 times greater than ongoing releases at the plant, the impact on marine organisms and the marine environment is likely to be less significant than impacts owing to radioactivity in the 20th century. What follows is a comparison of the concentrations measured and predicted over much of the Pacific owing to Fukushima to the concentrations that were present in the mid-1960s from the fallout of atmospheric weapons testing that is free from any discussion of safe doses or models of radiation exposure to organisms.
This post is part of an ongoing series that endeavors to provide useful and accurate information about: 1) the fate of Fukushima derived radionuclides in the Pacific Ocean, and, 2) the impact of these radionuclides on the marine ecosystem and the west coast of North America. The purpose of this diary is to draw attention to a number of poorly researched posts about a recently published study (unfortunately this study is behind a publisher pay-wall) in a Chinese journal that predicts a concentrated plume of radioactive elements from Fukushima arriving on the west coast. It is an unfortunate but common example of how news aggregation sites can misinterpret the results of a scientific study and misinform the public.
What models can and cannot say about the Fukushima plume
The study in question by Fu and co-workers published in the Journal of Ocean University of China in 2014 (behind pay-wall unfortunately) is wholly incapable of describing the behavior of dissolved radionuclides in the plume that is now arriving on the west coast of North America.
From the paper the authors themselves state in the methods that:
“In the study, the radioactive pollutant in the ocean is treated as a mixture of multiple Lagrangian particulates, and each particulate represents a radioactive element. The particulates can move in both horizontal and vertical directions, but cannot diffuse and mix with surrounding seawater.”
What this means is that rather than being allowed to mix and diffuse (or decay or sink after becoming associated with particles) the radionuclides are treated as neutrally buoyant drifters. The model, therefore, greatly overestimates the concentrations of radionuclides reaching the west coast of North America in the plume.
For those interested in models using accurate physics that will allow for an accurate prediction of radionuclide concentrations consult the following studies:
The Behrens et al. study is open-access while the Rossi et al. study is not. Measurements taken in the North Pacific by Canada’s Department of Fisheries and Oceans and InFORM team member Dr. John Smith indicate that the Rossi et al. study predicts the arrival time of the plume on the west coast but overestimates the activity of the Fukushima derived radionuclide 137-Cs. Behrens et al. predict a too late time of arrival but with lower activities that appear to more realistic. It important to note that these models carry the own simplifications and assumptions (e.g. see section 3.4 Caveats of the Behrens et al. (2012) study) and that recent measurements suggest that some of the Fukushima plume is being dispersed to the south rather than to the east in the Pacific (e.g. Kumamoto et al. (2014) open-access; more on this study in a forthcoming post).
Articles that confuse the conclusions of the Chinese study are a good example of poor reporting on an important subject. The example here was originally spawned by Energy News who have a history of inaccurate reporting on Fukushima and then propagated through the web by uncritical followers of the site.