New revelations about leaks of hundreds of gallons of radioactive water from the tsunami-damaged Fukushima nuclear facility in Japan have stoked fears across the Pacific Ocean. And while there are valid reasons to be concerned, the claim that thousands of people in the United States have already been fatally poisoned by Fukushima radiation in seawater is not one of them. Let's put that conspiracy theory to rest.

PHOTOS: Japan Earthquake and Tsunami: Before and After

“If there were thousands here there would be millions in Japan, and we're not seeing that,” said Ken Buesseler, an oceanographer who specializes in studying natural and man-made radioactivity in the oceans. The current radioactivity levels leaking into the sea are a thousand times lower than they were in 2011, when three of the nuclear reactors melted down, he said.

That's not to say there is no hazard. Intensive monitoring of sea water and fish show a severe radioactive cesium problem near the leaks, and fish from that area are no longer being caught or sold. But dilution causes the radiation levels to drop quickly in the open ocean, Buesseler said. In fact the radiation from Fukushima cesium a few kilometers away is less than that of naturally occurring polonium (210-Po) in seawater.

“We don't want to add to it,” said Buesseler, “but not every atom kills.”

In fact studies on migratory blue fin tuna that cross the Pacific show the fish have detectable amounts of Fukushima radiation. But they don't pose any more danger than a person would get from a single dental x-ray, according to Nicolas Fisher, a researcher at SUNY-Stonybrook who has been studying the radiation in fish.

“We showed that doses in all cases (from blue fin tuna) were dominated by the naturally occurring alpha-emitter 210-Po and that Fukushima-derived doses were three to four orders of magnitude below 210 Po-derived doses,” wrote Fisher and colleagues in a June paper in the Proceedings of the National Academy of Science.

“Doses to marine biota were about two orders of magnitude below the lowest benchmark protection level proposed for ecosystems.... Such doses are comparable to, or less than, the dose all humans routinely obtain from naturally occurring radionuclides in many food items, medical treatments, air travel, or other background sources,” the authors wrote.

ANALYSIS: Avoid Pacific Bluefin Tuna, Radioactive or Not

On the other hand, the Fukushima radiation problem is far from over and it's changing, Buesseler said. He is watching, in particular, the radionuclide strontium-90, which has a much longer half-life than the radioactive cesium. Strontium has the additional worrisome habit of getting locked up in bones, which allows it to irradiate tissues around it for years, he said. Strontium was not initially a big worry at Fukushima, as cesium was present in much larger amounts. But that could be changing in the Fukushima groundwater, he said.

"If that gets into the food supply and in the fish, then it's a much bigger hazard," said Buesseler. "I do have a concern."

Still, he emphasized, it will be largely a local hazard, not an ocean-wide or even a Japan-wide concern. He and his colleagues will be continuing to monitor the situation independently, including getting more water samples from the ocean near Fukushima to see if the strontium reaches the ocean.