Ever since the March 11 tsunami crippled Japan’s Fukushima Daiichi nuclear reactors, radioactive materials from the plant have been spreading by air, contaminating milk, vegetables, and tap water. With highly radioactive water now leaking from the reactors into the Pacific, and levels of radioactive iodine and cesium in the sea near the plant as much as 4,000 times higher than normal, the safety of seafood—and of sushi in particular—has risen on the list of concerns not only in Japan but around the world.
In the United States, upscale sushi restaurants—which are more likely than cheaper establishments to import authentic Japanese fish and nori seaweed—are suddenly looking less appetizing than they once did. Importers of Japanese seafood are cancelling orders left and right amid radiation concerns, and many sushi chefs are scrambling to incorporate more locally sourced fish into their creations.
There is little doubt, experts say, that fish and seaweed in the waters near Fukushima are absorbing radionuclides such as iodine-131 and cesium-137. Fish don’t pick up much iodine from the water, and any that they do take in decays into harmless molecules within a few weeks. But cesium may be more of a problem, says Scott Fowler, a marine radioecologist who worked for 30 years at the International Atomic Energy Agency and is now a consultant. Fish exposed to cesium concentrate it in their bodies by an average factor of 100—meaning that there would be 100 times more cesium in the animal’s tissue than in the surrounding water. And because cesium is so persistent in the environment, it accumulates up the food chain and can become even more concentrated in top predators like tuna. As such, fish from the area around Fukushima are no longer being exported. Sushi restaurateurs can easily find fish elsewhere.
Seaweed sucks up vast amounts of iodine from its environment and doesn’t discriminate between the radioactive and non-radioactive varieties.
Of greater concern is the nori seaweed that’s used to wrap sushi. Nori, a mineral-rich Porphyra algae, is a fallout magnet. The seaweed sucks up vast amounts of iodine from its environment and doesn’t discriminate between the radioactive and non-radioactive varieties, readily incorporating the radioactive form at 10,000 times its concentration in the surrounding water. The good news is that iodine-131 has a short half life, so it would decay long before any contaminated nori could make it to market. Unfortunately, nori also sucks up plutonium, concentrating it by a factor of 4,000, and cesium by a factor of 50—and those two elements are much more persistent and dangerous to humans. The world’s nori comes primarily from Japan, China, and Korea, so sushi chefs have fewer alternate suppliers than they do for fish. Tim Mousseau, a radioecologist at the University of South Carolina, says the currents and winds appear to be carrying the fallout away from nori farms in southern Japan, at least so far. China and Korea’s waters have not been affected yet.
But with exports from the affected areas banned, the key question is whether the radioactive fallout in the sea will spread widely enough and remain at a high enough concentration to impact fisheries or seaweed production in other regions of Japan or elsewhere. While there are a number of unknowns, such as how long the Fukushima plant will release radiation and where the currents and prevailing winds will take it, experts say the dilution potential of the Pacific Ocean is so vast it should make the risk negligible. “Luckily, the Pacific is a big ocean,” says David Brenner, a radiation expert at Columbia University. “The amount of dilution you get in the ocean is enormous, so the amount of radioactivity per liter of water is ultimately going to be extremely small and probably undetectable.” Barring a substantial worsening of the situation, such as a Chernobyl-style explosion and meltdown, agrees Fowler, the effects on sea life should be both local and limited.
What if radioactive fallout traveled by air and then rained down into the sea elsewhere in the world, creating hotspots of radioactivity and contaminating seafood or seaweed? Fowler says that’s not likely. “If you’re getting fallout on the grass in Washington, you’re probably getting fallout on the beach and water surface,” he says. But given the distance from Japan, levels wouldn’t be significantly higher than the low background concentration of cesium and other radioactive isotopes that remain in the environment—and in virtually all plants and animals on earth—from past nuclear testing and fallout from releases like at Chernobyl.
For the moment, scientists say that the risk of consuming radioactive seafood isn’t high enough to warrant alarm, and that health risks of chemical pollutants such as mercury or PCBs are probably much higher. “I very much doubt that this is going to have a long-term effect on the sushi industry,” Brenner says.
Ian Yarett reports on science, the environment, and health for Newsweek.