JON HAMILTON: I'm Jon Hamilton, in Tokyo. Every day, hundreds of tons of fish and seaweed are bought and sold at the city's seafood markets. The markets are still bustling, despite the troubles in Fukushima, but prices have fallen sharply. People are afraid these products might be contaminated with radioactive material. To find out how likely that is, I went to see someone who should know.
Dr. MASASHI KUSAKABE (Director, Nakaminato Laboratory for Marine Radioecology): My name is Masashi Kusakabe.
HAMILTON: Dr. Kusakabe directs the Nakaminato Laboratory for Marine Radioecology not far from Tokyo. It's a research center devoted to figuring out precisely what happens to radioactive stuff that gets into the ocean.
Dr. Kusakabe says what's been getting into the Pacific Ocean near Fukushima is mostly radioactive iodine. It dissolves in water, and experiments have shown that the iodine tends to concentrate in algae. Then it gets even more concentrated as it works its way up the food chain. Dr. Kusakabe says that might sound bad.
Dr. KUSAKABE: But the iodine we're talking about now is iodine-131, which has a very short half-life at eight days.
HAMILTON: Every eight days, half of it goes away. So after a few weeks, there's not much iodine-131 left in a fish.
Kusakabe says radioactive cesium is a lot worse: Its half-life is measured in decades, not days. But so far, much less cesium has gotten into the ocean at Fukushima.
Also, the ocean is so vast that radioactive materials are heavily diluted by the time they travel even a few miles.
So the Japanese fish most likely to become contaminated are the ones that spend their entire lives right near the Fukushima power plant. And the government isn't letting fishing vessels anywhere near the place.
But what about the ocean-going fish that show up on sashimi platters, fish like salmon and tuna? I asked Dr. Kusakabe whether they might be contaminated by radioactive material from the power plant.
Dr. KUSAKABE: I don't think so, though, because tuna move everywhere. They travel, you know, maybe hundreds of kilometers. So they never stay there.
HAMILTON: A tuna might swim by the Fukushima plant. But it wouldn't hang around long enough to become seriously contaminated.
Dr. Kusakabe says the biggest threat to the Japanese fishing industry right now isn't radiation. It's fear.
Dr. KUSAKABE: Most people now think, oh, it's very dangerous to eat fish in Japan or fish around this coast. But it's - I think it's very safe. So now is your chance to eat fish, because it's cheap.
HAMILTON: You're still eating fish?
Dr. KUSAKABE: Oh, of course. Why not?
HAMILTON: Dr. Kusakabe says once people realize Japanese fish are safe, he expects the price of Pacific Bluefin to go back up.
John Hamilton, NPR News, Tokyo.