Royal Society of Chemistry, National Institute for Physics & Nuclear Engineering, Romania, 2015 (emphasis added): AMS analyses of I-129 from the Fukushima Daiichi nuclear accident in the Pacific Ocean waters of the Coast La Jolla, San Diego, USA — This paper presents the results of an experimental study we performed by using the Accelerator Mass Spectrometry (AMS) method with iodine 129 (Halflife = 15.7 Million years], to determine the increase of the radionuclide content in the USA West Pacific Coast waters, two years after the March 2011 Fukushima Daiichi nuclear power plant accident… The results of the experiments showed a significant increase of the radionuclide concentration during the late spring of 2013. Compared to the isotopic ratio 129I/127I, measured at a 40 km distance, offshore of Fukushima and immediately after the accident, our results show an increase on the USA West Coast that was more than a 2.5 factor higher. Also, compared with the pre-Fukushima background values [in San Diego], our results show an isotopic ratio of about two orders of magnitude higher…
The Fukushima Daiichi nuclear power plant… released an enormous amount of liquid waste of 129I and other fission isotopes directly into the Pacific Ocean that were subsequently dispersed eastwards. This paper reports on the determination of the nuclear plume impact on the West Coast of the USA that happened during April–July 2013… The determined maximum 129I concentration 
increase was in an amount of more than 2 times greater than the concentration of the isotope measured offshore of Fukushima at a 40 km distance immediately after the accident…
129I concentrations were measured… from the ocean water of the West Coast of the USA [at] La Jolla, San Diego… This work reports two sudden increases of the 129I/127I isotopic concentration in the ocean water, which were observed at the end of spring 2013…
Our exploratory measurements on the USA West Coast started on samples collected at the beginning of 2013. The lowest 129I concentrations that we measured had values between [6-20 million] atoms per L. Such values correspond to the equilibrium concentration of iodine… offshore of La Jolla, San Diego…
Our results… measured offshore of Cove La Jolla, San Diego, USA, during the spring of 2013, are presented in Fig. 5. Two high and distinct spike maxima are visible. They reveal the maximum concentration values of [1.2 billion] atoms per L measured on May 24, 2013 and [1.7 billion] atoms per L measured on June 18, 2013, with 24 days in between. Both peaks occurred in the measurement spectrum after a slow increase in concentration 
that started about 15-20 days before the main increase…
Samples collected [by Fukushima Daiichi, Jun 2011] at a distance of about 40 km away from the coast [had] a maximum concentration value of [620 million] atoms per L for 129I in the surface water of the ocean. Taking into account this value as a reference value, the maximum 129-iodine concentration reaching the USA West Coast was 2.5 times stronger than in the contaminated ocean water offshore of Fukushima after the accident. If we compare it to the equilibrium value of 129I concentration in the ocean water [near San Diego], then during the impact its concentration was about 100 times higher…
AMS measurements of 129I were performed on ocean water… offshore of Cove La Jolla, San Diego, USA, and definitely have shown an increase of the radioactivity more than two orders of magnitude over the natural level of the Pacific Ocean before the accident…
Read study for free here ($50 at Royal Society of Chemistry)