If you consume just six pieces of tuna sushi per week your mercury blood levels could easily exceed US government safety limits, according to a recent study carried out by The New York Times which examined 20 shops and restaurants in Manhattan, New York.

In fact, The New York Times (NYT) reports that levels in five of the outlets were so high that authorities might be legally forced take the fish off the market. Michael Gochfeld, Professor of Environmental and Occupational Medicine at the Robert Wood Johnson Medical School, New Jersey, told the NYT that mercury levels found in these restaurant samples were such that a human should not consume a sushi tuna meal more than once every 21 days.

Mercury levels in the tuna sushi at these outlets were significantly higher than that found in regular canned tuna. The researchers report that most of the tuna at these shops and restaurants is bluefin tuna. Bluefin tuna usually has higher mercury levels than other types of tuna.

Drew Neiporent, a managing partner of Nobu Next Door, one of the outlets found to have high tuna sushi mercury levels said he was "startled" at the findings. He added that anything which may pose a hazard to his customers' health should be taken off the menu immediately.

Should We Be Concerned About Mercury in Fish?

Swordfish and shark are sought after in many restaurants, especially when grilled or broiled. Some people are concerned that large predatory fish, the ones at the top of the food chain, may have high levels of methyl mercury - in some cases levels higher than the 1 part per million limit for human consumption which is recommended by the Food and Drug Administration (FDA).

Scientists who work for the FDA and are responsible for seafood safety say that these large predatory fish are safe, as long as you don't eat them too frequently - not more than once a week.

According to Mike Bolger, Ph.D., FDA, about 2,700 to 6,000 tons of mercury are released into the atmosphere each year naturally by degassing from the Earth's crust and oceans. Add to this up to 3,000 tons which are released naturally into the atmosphere are a result of mankind's activities, such as burning household and industrial waste.

Methyl mercury binds tightly to the proteins in fish tissue, including muscle. Cooking does not significantly bring down methyl mercury levels in fish. Most fishes contain trace amounts of methyl mercury. Those found in/near areas where there is industrial mercury pollution can have significantly higher mercury levels.

Fortunately, most fishes rarely have levels of mercury that could pose a hazard to human health if they are consumed. The larger the fish, or the higher up it is in the food chain, the higher its mercury levels are likely to be, say experts. This does not mean larger fishes have dangerous levels of mercury, it just means they are more likely to have higher mercury levels than smaller fishes.

-- Mercury in Fish - Cause for Concern? (FDA)
-- High Mercury Levels Are Found in Tuna Sushi (New York Times)
-- Mercury Poisoning Information (Wikipedia)

Written by - Christian Nordqvist