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With prevailing westerly winds over Japan, radioactive fallout from the Fukushima nuclear power plant tragedy was detected throughout North America at levels comparable to those seen 25 years earlier from Chernobyl—the only other category 7 nuclear event in history.

The highest levels of radioactive iodine in rainwater was found in Boise, Idaho, and the highest levels in milk were found in San Francisco—at levels ten times higher than the federal maximum allowed in drinking water, but below that which would be expected to pose a direct threat to U.S. public health.

A controversial paper, however, in the International Journal of Health Sciences suggested the radioactive plume from the nuclear meltdowns in Fukushima may be responsible for a subsequent bump in U.S. mortality, similar to what we saw after Chernobyl—though the authors themselves underscore their research shows merely a correlation, and potential evidence of a causal link, and that more research is necessary.

Of all the radiation released, only a tiny fraction of the fallout reached U.S. shores. Most was absorbed by the Pacific Ocean. What does that mean for seafood safety?

Researchers “report unequivocal evidence that Pacific bluefin tuna…[have] transported Fukushima-derived [radioactive fallout] across the entire North Pacific Ocean.” Tuna actually migrate from Japan to California, and appeared to have taken some radioactivity with them.

Even though there was a ten-fold spike in radioactive cesium levels in tuna, they put it in context by noting the baseline levels of radioactivity in fish—even before Fukushima—due to everything from thermonuclear weapons tests and sunken nuclear submarines, to just radioactive elements found naturally in the earth’s crust. The levels in seawater of radioactive polonium, for example, are minuscule, but it strongly bioaccumulates up the food chain into fish.

This is the same polonium used in the horrific assassination of Russian dissident Litvinenko. That’s the same polonium found in fish. It’s a by-product of uranium decay, and frequently cited as one of the reasons that tobacco is so carcinogenic—something the tobacco industry was well aware of, and could have easily removed. But, the process that could have removed the polonium affected the absorbability of nicotine. And, “[t]he loss of the nicotine “kick” sensation was found unacceptable by industry executives.” So, they kept the polonium in.

The radioactive polonium in cigarettes has been speculatively blamed for the link between smoking and male infertility. But, most of human exposure to polonium comes from diet—mostly from fish and shellfish. And, this was before Fukushima. So, what then happens if you eat seafood?

Researchers measured the increase in radioactive polonium levels in semen after a single seafood meal. It caused a 300% spike in levels. Probably not enough to cause infertility, but that was just one meal. Whether the kind of dose you can get from eating seafood would be enough to damage sperm enough still needs to be established. You may have to eat as much as a pound of seafood a month before one might realize the harmful effects of the radiation.

Interestingly, there’s eight times more polonium in cooked shrimp than in raw shrimp. Isn’t that fascinating? They think it’s because most of the polonium is in the shrimps’ internal organs, which is released into the boiling water, and contaminates the muscle. So, gutting crustaceans before cooking may decrease radiation exposure.

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