About 800 tera becquerel of Cesium- 137 is going to reach West Coast of North America by 2016, equivalent to 5 percent of the total Cs-137 amount discharged to the pacific ocean after the Fukushima nuclear disaster, [Michio Aoyama, a professor at Fukushima University] was quoted by Kyodo recently… However, Cs-137 levels detected at U.S. beaches were 1 to 2 bq per cubic meter, much lower than the safety limit… "Even if all the 800 tera bq Cs-137 have arrived, the radiation levels will stay at relatively low level that aren’t expected to harm human health,” said Aoyama.

1-2 Bq/m3 of Cs-137? The West Coast samples with Fukushima radioactive material have contained levels several times that amount. Off the coast of California, levels were 8.6 Bq/m3 (Cs-137 @ 6.9; Cs-134 @ 1.7). Levels on Vancouver Island were 7.2 Bq/m3 (Cs-137 @ 5.8; Cs-134 @ 1.4).

Aoyama’s estimate of 800 terabecquerels of Cs-137 reaching the West Coast is about the same as the total amount of Cs-137 estimated to have been deposited on Japan (1.0 petabecquerels or 1,000 terabecquerels, Source: TEPCO).

Michio Aoyama (Fukushima University) et al. (pdf), European Geosciences Union General Assembly in Vienna, Austria, Apr 2015: [W]e and our collaborators continue to collect seawater samples in 2013 and 2014 in the North Pacific Ocean… The 137Cs activity through the end of September 2014 remain higher than expected, ca. 1000 Bq m-3, implying continued releases from the reactors… In the North Pacific Ocean main body of radiocaesium surface plume of which activity exceed 10 Bq m-3 had been travelling along 40 ºN, and reached International Date Line on March 2012… the radiocaesium plume was confined along 40 ºN when the plume reached International Date Line. A zonal speed of the radiocaesium plume was estimated to be about 8 cm s-1… After that, main body of radiocaesium surface plume continued to travel eastward and reached off west coast of US continent in August 2014 which implies the zonal speed of the radiocaesium plume was maintained at similar speed.

During a TV interview last year, Aoyama announced a somewhat different scenario — Al Jazeera Transcript: "Aoyama calculates that the radiation will slow, sink, and then harmlessly decay over decades, as Pacific currents turn most of it toward Southeast Asia and the Indian Ocean. Prof. Aoyama: ‘So I can say that the people in the Western Coast are safe.’”