New Yorkers were choking on their beloved sushi yesterday after reading that eating only six pieces of raw tuna a week could put them above government safety levels for mercury.

Laboratory tests performed by The New York Times found so much mercury in tuna sushi from 20 Manhattan shops and restaurants that a regular weekly diet of six pieces would exceed the maximum set by the Environmental Protection Agency.

Sushi from five of the twenty outlets had such high mercury levels that the Food and Drug Administration (FDA) could take legal action to remove the fish from the market.

“No one should eat a meal of tuna with mercury levels like those found in the restaurant samples more than about once every three weeks,” Michael Gochfeld, Professor of Environmental and Occupational Medicine at the Robert Wood Johnson Medical School, New Jersey, told the newspaper.

Professor Gochfeld, who treats patients suffering from mercury poisoning, analysed sushi with Joanna Burger, a professor of life sciences at Rutgers University.

Tuna samples from the popular Manhattan restaurants Nobu Next Door, Sushi Seki, Sushi of Gari and Blue Ribbon Sushi and the grocery shop Gourmet Garage all had mercury above the “action level” of one part per million, at which the FDA can take food off the market.

“I'm startled by this,” Drew Nieporent, a managing partner of Nobu Next Door, told the newspaper. “Anything that might endanger any customer of ours, we'd be inclined to take off the menu immediately and get to the bottom of it.”

In 2004 the US Government warned women who might become pregnant, and children, to limit their consumption of canned tuna because the mercury it contained could damage developing nervous systems. Recent studies have suggested that high mercury levels can also cause health problems for adults, such as an increased risk of cardiovascular disease and neurological symptoms.

The Government did not issue a warning about fresh tuna. But the New York Times analysis found that most of its sushi samples contained much more mercury than did canned tuna.

Most of the sushi in the study was bluefin tuna, which generally has much more mercury than other species, such as yellowfin and albacore.

The Centre for Consumer Freedom, a food and restaurant industry group, said that the New York Times story was exaggerated, and asked the newspaper to retract it. It noted that the FDA's action level had a tenfold safety cushion, meaning that a consumer would have to ingest ten times as much before hitting a level associated with adverse effects. David Martosko, the research director of the centre, said: “Study after study shows that the documented health benefits of eating fish far outweigh any hypothetical risks.”

But the Environmental Defence advocacy group recommended that no one should eat bluefin tuna.

Professor Gochfeld said: “I like to think of tuna sushi as an occasional treat. A steady diet is certainly problematic. There are a lot of other sushi choices.”

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