The oceans mix fairly well over time, but how the radiating isotopes would sort out is hard to tell.
We do not know if they are dissolved, or in particulates.
There is a tremendous amount that is not known.
We do know that the radioactive increase on the west coast is quite small.
“Out of the 110 new contaminated samples detected off the US west coast, the most radioactive was collected around 2,500 km off the coast of San Francisco. It contained 11 Becquerel’s per cubic metre of seawater – which is equivalent to 50 percent higher cesium levels than other samples collected in this part of the ocean so far.
Buesseler’s research has also shown that Fukushima is still leaking radioactive material into the ocean in Japan, with the levels off the Japanese coast between 10 to 100 times higher than the levels off the US West Coast today.
“Levels today off Japan are thousands of times lower than during the peak releases in 2011,” said Buesseler. “That said, finding values that are still elevated off Fukushima confirms that there is continued release from the plant.”
Isotopes with short half-lives give off lots of radiation, but drop off very quickly, so the danger passes quickly.
Isotopes with long half-lives give off tiny amounts of radiation, but last for a long time. That is most of background radiation.
“The oceans mix fairly well over time, but how the radiating isotopes would sort out is hard to tell.
We do not know if they are dissolved, or in particulates.”
If in particulate form, then it could be deadly eating seafood contaminated by it.