Mercury Levels in Sushi: Is Your Tuna Sashimi Safe to Eat?

If sushi is among your favourite foods, you could be ingesting more ?mercury than is good for you?

Credit: Flickr/Quasimime

Mercury levels are highest in bluefin 
and bigeye tuna, considered the premium species for sushi

A new study suggests restaurant sushi is higher in mercury than grocery store sushi-grade fish

We west coasters love our sushi and we all have our favourite sushi restaurants. So it’s concerning that a new study suggests folks who prefer getting their sushi from restaurants rather than their local supermarket could be getting a little something extra with that meal: a higher intake of mercury.

Scientists with the American Museum of Natural History and Rutgers University found that sushi sold in grocery stores may have a lower mercury content than that served in restaurants. That’s because grocery-store sushi tends to use yellowfin tuna, which has lower levels of mercury than other species of tuna.

Mercury Levels Vary by Type of Fish

In the study published in the peer review journal Biology Letters, the researchers analyzed the mercury content of sushi samples taken from 54 restaurants and 15 supermarkets in New York, New Jersey and Colorado.

The level of mercury in sushi can depend on the species. The researchers found that levels were highest in bluefin and bigeye tuna, considered the premium species for sushi and usually sold in restaurants.

Mercury accumulates more in muscle than in fatty tissue, so the leanest fish tend to have the highest concentrations. Bluefin and bigeye are larger fish and eat more often, which can slowly increase the level of toxins in their tissues over time. Yellowfin tuna are typically smaller and harvested at a young age.

Most Fish Exceed Safe Mercury Levels

Perhaps what’s more concerning, the researchers found that all the species examined in their study exceeded or approached the maximum daily dose considered safe by Canadian, EU, U.S. and World Health Organization standards, if a 130-pound woman ate a single order of sushi.

Mercury levels can accumulate in the body over time causing damage to the nervous, cardiovascular and immune systems and the kidneys. It takes about 45 to 70 days for methyl mercury levels in the blood stream to halve in concentration.

Restaurants and fish merchants are not required to identify species, either. The researchers suggest that proper labelling may help consumers decide which tuna sushi to purchase and which to pass by.

Health Canada advises Canadians to limit their consumption of fresh or frozen tuna (in combination with other mercury-containing fish) to no more than 150 grams (5.3 ounces) per week. Pregnant and nursing women and children should only eat up to 150 grams in one month. Get more Health Canada advice on mercury in fish.

A great resource on what’s considered safe, as well as good alternatives and fish to avoid on the basis of sustainability or mercury content, the Monterey Bay Aquarium produces brochures for different geographical locations.

Originally published in TV Week. For daily updates, subscribe to the free TV Week e-newsletter, or purchase a subscription to the weekly magazine.