The Food Journal and Food, Nutrition & Science

An alliance between The Lempert Report and The Center for Food Integrity

Mercury and Fish

Mercury and Fish

Food Safety Update

February 24, 2008

Mercury and Fish
Recent studies have raised new concerns about the content of mercury in fish, suggesting that updates are needed for the 2004 FDA’s consumer advisory guidelines regarding fish safety. The studies, which looked at the mercury content of fish samples purchased at both sushi restaurants and grocery stores, found that a large percentage of the samples contained levels of mercury beyond levels that the FDA considers safe.
One of the studies, conducted by Oceana, a marine conservation group, looked at swordfish, fresh tuna and tilapia samples purchased in 26 different cities across the country, as well as samples of nigiri or sashimi style tuna and mackerel purchased from 23 different U.S. cities. While tilapia from grocery stores and mackerel in sushi restaurants checked out as good, low-mercury alternatives, tuna and swordfish results results were considerably less favorable.
Oceana found that the mercury levels in tuna were much higher than existing FDA data suggests, with one-third of sushi tuna samples exceeding 1 part per million – the action level allowed by the FDA for fish intended for human consumption. Additionally, they found that two-thirds of swordfish tested were above the 1 part per million mark.
Another study conducted for the New York Times with Rutgers University had similar findings. Their study looked at sushi from 20 Manhattan stores and restaurants. Tuna samples from five of the 20 restaurants contained mercury levels above 1 part per million, with the highest mercury concentration, at 1.4 parts per million, found in one particular restaurant.
Grocery store mercury levels in fish tended to be lower than levels of mercury in fish from sushi restaurants in the New York Times study – a finding confirmed by the Oceana study as well. Even so, the average mercury concentration for grocery store tuna, per the Oceana study, was .68 parts per million – nearly double the FDA’s average finding of .38 parts per million for fresh or frozen tuna.
“We’re seeing higher levels at sushi restaurants partly because of the species of fish being eaten. Sushi fish tends to come from bigger, older species of fish, and these fish contain more mercury. But levels are also high for certain types of fish at the grocery level,” says Jackie Savitz, Senior Director for Oceana’s Pollution Campaign.
Mercury is a metal released into the environment. About two-thirds of mercury in the environment comes from human sources; only about one-third of it is naturally occurring. The primary industrial (human) source of mercury enters the environment through the burning of fossil fuels, especially coal. It also comes from intentional uses of mercury, such as its use in the production of chlorine and mercury-containing devices such as thermostats. Municipal waste incineration is another source.
When mercury finds its way into rivers and lakes, small fish take it up when eating algae. The ingested mercury gets biomagnified as it moves up the food chain. Larger predatory fish eat smaller fish that have eaten even smaller fish, and so on. These larger fish, like sharks and swordfish, tend to contain higher levels of mercury, but nearly all fish and shellfish contain trace amounts of the metal. Mercury can damage the organs of the central nervous system and cardiovascular systems when consumed at high levels.
Tuna is the number one source of mercury in the American diet, according to Oceana, due largely to high levels of tuna consumption. Consumption of sushi tuna and tuna steaks have peaked in popularity in recent years, as compared to consumption of the less glamorous canned light tuna – a variety that is considerably lower in mercury content. The Oceana study found that average mercury levels in sushi tuna exceeded levels in king mackerel, a fish on the FDA’s “Do-Not-Eat” list. Currently, tuna is not on this list.
“If more tests show the same, we think that the FDA should be reconsidering its advice for fresh tuna consumption,” says Savitz.
The current EPA and FDA consumer advisory, published in 2004, recommends that women of childbearing age and young children avoid eating swordfish, shark, tilefish and king mackerel. The advisory also recommends limiting the consumption of albacore tuna or tuna steaks to six ounces or less per week, while limiting other low mercury fish to 12 ounces or less per week.
To gauge the effectiveness of communicating FDA fish safety guidelines to consumers, the Oceana study also looked at the knowledge level of seafood counter attendants. Unfortunately, they found that nearly 90% of seafood counter attendants either gave a wrong interpretation of the FDA warnings, or they did not know the FDA guidelines regarding mercury in fish. Only 13% of those interviewed gave the correct information to shoppers.
To date, the FDA has not evaluated the tests conducted by Oceana or the New York Times. Meanwhile, nutritionists are concerned that these findings will scare away the general public from eating fish, which is an important source of lean protein, Omega-3 fatty acids, vitamins and minerals. The American Dietetic Association recommends eating two to three fish meals per week, and the FDA and EPA both agree that pregnant women and children can also benefit from seafood when consumed as part of a balanced diet.

Oceana recommends that major grocery store chains post the FDA guidelines about mercury and seafood at the point of sale. Nearly 5,500 grocery stores (28% of the nation’s major grocery stores) have agreed to post this information so far. They would also like the FDA to post warning signs at stores indicating which varieties of fish should be avoided by women of childbearing age and children, and work to better educate the public about potential mercury risks in fish. Retailers have a role to play too.
“When retailers post the FDA advice, their customers can make more informed choices, buy a low mercury fish, and continue to get the benefits of eating fish without mercury risks. It’s such a simple and cheap solution,” says Savitz.
But there’s more to be done, Savitz says. Retailers can also fight to stop mercury from getting in their fish to begin with by getting behind programs that fight to control mercury pollution from sea to store.
Savitz adds, “We’re hoping that this becomes the industry standard.”
For a complete FDA list of mercury levels in fish and shellfish, visit:
For a list of fish considered safe to eat, and sustainably raised, visit: