Kazuhiro Ukiuchi loves his tuna sushi, and he tries to have it once a week — despite the common knowledge in Japan the popular fish can contain toxic mercury.
"I wouldn't worry about it," Ukiuchi said, strolling through Tokyo's main fish market Friday. "We're not talking about eating 10 tuna sushi every day — in which case I might be a little bit worried."
Recent reports about high mercury levels in tuna served at ubiquitous sushi restaurants in New York have been met with a collective yawn in Japan, the world's undisputed sushi capital.
Ukiuchi's relaxed attitude about mercury — which in high concentrations can cause severe brain damage — is matched by the Japanese government, which exempts tuna from its legal limits on mercury in seafood because it's not caught coastally.
Rules ban many types of seafood if the concentration of mercury exceeds 0.4 parts per million. The limit is 0.3 ppm for mercury's more dangerous derivative, methylmercury.
The restriction was set in the 1970s after outbreaks of industrial mercury poisoning in the southern town of Minamata that sickened thousands and caused hideous birth defects in the 1950s and 60s.
Victims fought for more than a decade before the government and the Chisso Corp., which contaminated fishing grounds, acknowledged the poisoning and provided widespread compensation.
Traces of mercury, which also occurs naturally, are found in nearly all fish and shellfish. The substance builds up in the animals as they feed on other fish and shellfish, so larger predator fish that have lived longer generally have higher levels.
Despite the absence of any restrictions on mercury in tuna, officials periodically check the fish. Japan consumes some 450,000 tons of it a year — more than anywhere else in the world, according to the Organization for the Promotion of Responsible Tuna Fisheries, a Tokyo-based industry group.
A Health Ministry survey in 2005, for instance, found an average of 0.7 ppm of mercury in blue fin tuna, and the highest concentration found was a startling 6.1 ppm — more than 15 times the limit for other types of seafood.
The government has issued advisories warning pregnant women and young children to limit consumption, but mercury does not seem to be a high priority for officials.
"We consider pregnant women a high-risk group, but ordinary people are fine as long as they continue a balanced, healthy diet," said Yuichiro Ejima, a ministry official in charge of food safety.
The circumspect view was a contrast to Japanese consumers' scare over mad cow disease. Tokyo shut down its imports of American beef for two years after a single case of the disease was discovered in the U.S. herd.
Shigeo Ekino, mercury expert at Kumamoto University in southern Japan, said consumers should be more cautious about mercury, since it's not clear how little it takes to cause nerve damage.
"But there is no doubt that mercury intake is harmful, and eventually destroys brain tissues," Ekino said, citing symptoms of Minamata victims, whom he has studied. "We should cut down tuna consumption to as little as possible."
The New York Times, in a story published Thursday, reported that eight of 44 pieces of sushi sampled from local restaurants and stores had mercury concentrations over 1 ppm, a level the paper reported would allow the U.S. Food and Drug Administration to take the fish off the market.
Ejima said the most dangerous thing he took from the report was that it could spread "groundless rumors."
"Seafood is an important source of nutrition," he added.
The New York City Health Department released survey findings in July that showed one in four New York City adults had elevated blood mercury levels, which they said were closely tied to fish consumption.
But the agency reported that while such levels in pregnant women could increase a risk in cognitive delays for their children, they pose little if any risk to the health of normal adults.
After the Times story was published, a spokeswoman at the office said their advice to New Yorkers about tuna sushi had not changed. They released a statement reassuring residents that "no one needs to stop eating fish, but some people may need to change the type and amount they eat."
The denizens of the fish market in Tokyo — the largest in the world — also were skeptical about the worries, expressing confidence that Japanese food safety standards would protect them.
"Where did that tuna in New York come from? I bet it's not from Japan," said fish shop owner Yoshiaki Saito. "Fresh tuna from the Japanese coast should be fine — it's the best."
Sushi lovers said it would take more than a U.S. report to take them away from their tuna rolls, and they argued a little mercury was probably harmless compared to the fats and oils in something like a hamburger and fries.
"I would think tuna sushi is much better than fast food," said Ukiuchi. "I'd have to be really unlucky if I die from eating tuna sushi."