March 11, 2016 will mark the fifth anniversary of the Tōhoku earthquake and tsunami that precipitated the Fukushima Dai-Ichi nuclear power plant accident.  An interesting report has just appeared on MarineLink.com.  The first paragraph notes that while the federal government still has not gotten its act together, one dedicated individual, exhibiting personal responsibility and initiative, has collected very useful data.

Five years after the Fukushima nuclear accident, there is still no U.S. federal agency responsible for studies of radioactive contaminants in the ocean. But scientific data about the levels of radioactivity in the ocean off our shores are available publicly thanks to ongoing efforts of independent researchers, including Ken Buesseler, a radiochemist with Woods Hole Oceanographic Institution (WHOI), who has led the effort to create and maintain an ocean monitoring network along the U.S. West Coast.

The initial acute threat was due to radioactive iodine, Iodine-131, which is easily absorbed into the thyroid glands of children on a milk diet.  The Centers for Disease Control advise:

If I-131 were released into the atmosphere, people could ingest it in food products or water, or breathe it in. In addition, if dairy animals consume grass contaminated with I-131, the radioactive iodine will be incorporated into their milk. Consequently, people can receive internal exposure from drinking the milk or eating dairy products made from contaminated milk. Once inside the body, I-131 will be absorbed by the thyroid gland.

Fortunately, I-131 has a radioactive decay half-life of eight days, so the threat rapidly diminishes.  In less than two months, the emitted iodine radionuclides would have decreased by a factor of over 100.

The longer-term radioactive threats are principally due to Cesium-137 and Strontium-90.  With regard to Cesium-137, Buesseler finds:

The highest level of cesium Buesseler’s team found in a sample taken off Japan in October 2015 measured 200 Becquerels per cubic meter (about 264 gallons) of seawater. (A Becquerel equals one decay event per second.) The samples were collected following a typhoon in September that delivered unusually heavy rains, which the researchers suspect may have caused elevated cesium levels in the ocean. These levels are still higher than prior to the accident but much lower than at the peak of the releases in 2011 when there were 50 million Bq/m3 in the ocean immediately off the dock at Fukushima.

With regard to strontium, Buesseler reports:

So little strontium was released relative to cesium from Fukushima in 2011, that even though Fukushima cesium is detectable, the strontium-90 signal is not detectable in these samples, at least in the eastern Pacific[.]

More detailed info on Fukushima can be found in the AT archives. See Fukushima: Better but Not Good , Easter in Fukushima -- American Exceptionalism at Work and The Pyrolysis of the Spent Fuel Rods at Fukushima.  You might wish to say a prayer of thanksgiving.