In Japan, a nation that eats prodigious amounts of seafood, one question sits high on the list of public concerns: Is seafood caught after the Fukushima nuclear catastrophe safe for human consumption?
In the wake of the disaster, coastal fisheries in Fukushima and all neighboring precincts were quickly closed. Within two weeks, the Japanese government began monitoring radioactivity in fish, shellfish, and edible seaweeds. More than a year later, not because of new scientific findings or any changes in offshore conditions, but in an attempt to further reassure consumers, the government lowered the acceptable limit for radiation in fish from 500 becquerels per kilogram—already among the strictest standards in the world—to 100 Bq.
Last fall, Ken Buesseler, a marine geochemist at Woods Hole Oceanographic Institution, combed through a year’s worth of data released by the Japanese fisheries agency. His analysis, published Oct. 26, 2012, in the journal Science, showed that the “vast majority” of fish being caught off Fukushima and surrounding areas had radiation levels below the tightened safe-consumption limit. Among bottom-dwelling species, however, 40 percent came in over that limit. Most important, levels of radiation in the ocean and in seafood did not appear to be declining in the 12 months following the accident.
To Buesseler and others, this persistence is strong evidence of a continuing source of radiation leaking into the environment. Fish naturally lose cesium quite quickly, about 3 percent per day, if they are not re-exposed to some additional cesium source. At the same time, Buesseler acknowledged, the remaining concentrations of radionuclides in fish are generally quite low—lower than limits in force in the United States, and lower than the amount of radiation naturally present in seawater.
Still, public anxiety in Japan remains high. With the exception of a few unaffected species such as whelk and octopus, fisheries remain closed off Fukushima prefecture. And disturbing outliers—individual fish with exceedingly high levels of radiation—continue to turn up. At the Fukushima and the Ocean conference in Tokyo in November 2012, experts drawn from various fields examined the issues surrounding seafood safety. Their spirited conversation ranged well beyond the science...