Researchers Assess Radioactivity Released to the Ocean from the Fukushima Dai-Ichi Nuclear Power …

[OKIsItJustMe]

http://www.whoi.edu/page.do?pid=7545&tid=282&cid=123049&ct=162

News Release : Researchers Assess Radioactivity Released to the Ocean from the Fukushima Dai-Ichi Nuclear Power Facility

December 6, 2011
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December 6, 2011
Source: Media Relations

With news this week of additional radioactive leaks from Fukushima nuclear power plants, the impact on the ocean of releases of radioactivity from the plants remains unclear. But a new study by U.S. and Japanese researchers analyzes the levels of radioactivity discharged from the facility in the first four months after the accident and draws some basic conclusions about the history of contaminant releases to the ocean.

The study, conducted by Woods Hole Oceanographic Institution chemist Ken Buesseler and two Japanese colleagues, Michio Aoyama of the Meteorological Research Institute and Masao Fukasawa of the Japan Agency for Marine-Earth Science and Technology, reports that discharges from the Fukushima Dai-Ichi nuclear power plants peaked one month after the March 11 earthquake and tsunami that precipitated the nuclear accident, and continue through at least July. Their study finds the levels of radioactivity, while quite elevated, are not a direct exposure threat to humans or marine life, but cautions that the impact of accumulated radionuclides in marine sediments is poorly known.

The release of radioactivity from Fukushima—both as atmospheric fallout and direct discharges to the ocean—represent the largest accidental release of radiation to the ocean in history. Concentrations of cesium-137, an isotope with a 30-year half life, at the plants's discharge point to the ocean, peaked at over 50 million times normal/previous levels, and concentrations 18 miles off shore were much higher than those measured in the ocean after the Chernobyl accident 25 years ago. This is largely due to the fact that the Fukushima nuclear power plants are located along the coast, whereas Chernobyl was several hundred miles from the nearest salt water basins, the Baltic and Black Seas. However, due to ocean mixing processes, the levels are rapidly diluted off the Northwest coast of Japan.

The study used publically available data on the concentrations of cesium-137, cesium-134, and iodine-131 as a basis to compare the levels of radionuclides released into the ocean with known levels in the sea surrounding Japan prior to the accident. Impacts of the Fukushima Nuclear Power Plants on Marine Radioactivity is published in the latest issue of Environmental Science & Technology and is available on the journal's website. Buesseler received funding support for this work from the Gordon and Betty Moore Foundation and the National Science Foundation’s Chemical Oceanography program.

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http://dx.doi.org/10.1021/es202816c

[caraher]

1. Interesting study

But I think the main takeaway is that they don't really know enough about where the cesium and other isotopes will go to make a full assessment of the harm. The key paragraph in the paper is probably this one (following one that calculated external exposure rates for immersion in the ocean):

This dose assessment does not, however, consider bioaccumulation and consumption of seafood and seaweeds and possible impacts on humans. The waters immediately adjacent to Japan remain a continued source of radionuclides that is keeping the discharge waters elevated in Cs-137, and thus likely other Fukushima-derived radionuclides that have not yet been reported. Locally elevated marine sediment concentrations are expected and this would imply possible additional pathways for assimilation in biota near shore by filter feeding shellfish and benthic marine biota. Brown seaweeds are of particular concern as they are a major crop in Japan and highly efficient at concentrating I-131 (concentration factors of 10 000), though with an 8-day half-life, the I-131 activities have rapidly declined. The provisional regulatory value in fish established by the Fisheries Agency of Japan is 500 Bq/kg for radioactive Cs. Early reports off Japan’s coast suggest that the only seafood concentrations above safety limits were for sand eels, though a few seafood samples above these levels continue to be found (see for example the July 2011 Japanese Fisheries Agency report). With a Cs concentration factor of 100 for fish, one would approach unacceptable levels of Cs in fish if in equilibrium with ocean activities>5000 Bq/m^3 for combined Cs isotopes, which we see at the discharge point in July. Also specific pathways such as preferential uptake of Sr-90 (not yet measured) in fish bones will need to be considered if whole small fish are consumed. Continued monitoring and bans on fishing in Fukushima impacted waters is thus warranted given the steady elevated levels near the NPPs. Given that Japan has the highest seafood consumption rate in the world, understanding concentrations and assimilation in marine biota is an important task.

[kristopher]

2. NHK testing of affected areas...

Radiation on the ship: 0.14 microsievert/hr, in the water 0.025 microsievert/hour. The number increases as it gets deeper. On the rock 1 microsievert/hour. Maximum number at the bottom of the ocean 1.74 microsievert/hour. Fine-grained sands at the bottom. The radiation level at the bottom of the ocean was max 70 times that of the ocean surface. (from this tweet)

Bioconcentration of radioactive cesium seen 10 to 20 kilometers off the coast of Fukushima. At the bottom of the ocean, 200 to 300 becquerels/kg . The radiation level at the bottom 1 microsievert/hour. The area is an abalone fishery. 40 becquerels/kg in the sea water, 420 becquerels/kg in arame (type of seaweed that abalones eat), 2000 becquerels/kg in abalone. 50-fold concentration .

Radioactive silver (Ag-110m) in abalone 410 becquerels/kg, in abalone liver 1800 becquerels/kg. (these two points from this tweet)

Effect of ocean currents is not what you may think. The Kuroshio Current, which comes up from south, may generally prevent the contaminated water from Fukushima from spreading further south. But the coastal current behaves totally different, and radioactive cesium has actually being transported south from Fukushima along the coast. In addition, as rivers reach the Pacific Ocean and discharge water, that creates their own micro-currents. As it turned out, a location off Ibaraki (Kajima) measured lower in radiation of the ocean soil than a location off Chiba (Inubozaki), which is much further south from Fukushima than the Ibaraki location. (from this and this tweets)

Abalone liver is a gourmet food in Japan....

http://ex-skf.blogspot.com/2011/11/radioactive-ocean-nhk-survey-shows-174.html

[kristopher]

3. This too is significant...

"Also specific pathways such as preferential uptake of Sr-90 (not yet measured) in fish bones will need to be considered if whole small fish are consumed."

Japanese are not historically a milk drinking culture and a significant percentage of the population is lactose intolerant. As a source of calcium many pregnant women munch on whole small dried fish like they are popcorn.