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green@work : Magazine : Back Issues : May/June 2004 : Lifelines


What's for Dinner?
If fish is a regular part of your diet, you may want to reconsider. How much and what kind of fish you eat could cause mercury poisoning.


The warning against eating mercury-contaminated fish announced in March by the Food and Drug Administration (FDA) and the U.S. Environmental Protection Agency (EPA) is proof that we need to remove mercury from commerce, according to a top scientist at the Natural Resources Defense Council (NRDC).

Linda Greer, an environmental toxicologist at NRDC, also said the health advisory does not adequately warn parents about feeding their children albacore tuna, given the EPA’s own data.

“This advisory does not do enough to help parents ensure that their children are not exposed to harmful amounts of mercury,” said Dr. Greer. “But that obscures the larger issue. Just as we did with lead, we have to take mercury out of commerce.”
The advisory does not warn consumers about eating some of the most highly-contaminated fish, she said. For example, it does not mention grouper and orange roughy, two popular fish dinner entrées that, according to recent FDA test data, have high mercury levels. It also does not provide specific advice for parents with young children. The advisory states that children should eat less than 12 ounces of fish a week, but does not specify how much less. Based on FDA data, a 22-pound toddler who eats three ounces (one-half of a six-ounce can) of albacore tuna a week would ingest nearly four times the EPA’s safe level, and an 88-pound child eating six ounces would be exposed to twice EPA’s safe level.

Like lead, mercury damages the brain and nervous system. Mercury exposure can lead to developmental problems, learning disabilities and mental retardation. Infants and children are at most risk, according to the Centers for Disease Control and Prevention and the EPA. One in 12 American women of childbearing age have mercury in their blood above the level that could pose a risk to a developing fetus.

The NRDC reports that mercury pollution has contaminated 12 million acres of lakes, estuaries and wetlands—30 percent of the national total—and 473,000 miles of streams, rivers and coastlines. Last year, 44 states issued warnings about eating mercury-contaminated fish, a 63 percent jump from 1993, when 27 states issued such warnings. Nineteen states have issued statewide advisories for mercury in freshwater lakes and rivers, and 10 states have issued advisories for canned tuna.

In NRDC’s Mercury Contamination in Fish: A Guide to Staying Healthy and Fighting Back, a wide range of information on mercury’s effects and its sources, as well as tips for eating fish more safely, are examined. (See A brief review of guide highlights follows.

Examining the Exposure
Over the years, many companies have used mercury to manufacture a range of products including thermometers and thermostats, automotive light switches and “silver” dental fillings. Although the metallic mercury in these products rarely poses a direct health hazard, industrial mercury pollution becomes a serious threat when it is released into the air, primarily by power plants and certain chemical facilities, and then settles into oceans and waterways, where it builds up in fish that we eat.

Once mercury enters a waterway, naturally occurring bacteria absorb it and convert it to a form called methyl mercury. This transition is particularly significant for humans, who absorb methyl mercury easily and are especially vulnerable to its effects.

Mercury then works its way up the food chain as large fish consume contaminated smaller fish. Instead of dissolving or breaking down, mercury accumulates at ever-increasing levels. Predatory fish such as large tuna, swordfish, shark and mackerel can have mercury concentrations in their bodies that are 10,000 times higher than those of their surrounding habitat.

Humans risk ingesting dangerous levels of mercury when they eat contaminated fish. Since the poison is odorless, invisible and accumulates in the meat of the fish, it is not easy to detect and can’t be avoided by trimming off the skin or other parts. Once in the human body, mercury acts as a neurotoxin, interfering with the brain and nervous system.

Exposure to mercury can be particularly hazardous for pregnant women and small children. During the first several years of life, a child’s brain is still developing and rapidly absorbing nutrients. Prenatal and infant mercury exposure can cause mental retardation, cerebral palsy, deafness and blindness. Even in low doses, mercury may affect a child’s development, delaying walking and talking, shortening attention span and causing learning disabilities.

In adults, mercury poisoning can adversely affect fertility and blood pressure regulation and can cause memory loss, tremors, vision loss and numbness of the fingers and toes. A growing body of evidence suggests that exposure to mercury may also lead to heart disease.

Mercury in the Food We Eat
The most common source of mercury exposure for Americans is tuna fish. Tuna does not contain the highest concentration of mercury of any fish, but since Americans eat much more tuna than they do other mercury-laden fish, such as swordfish or shark, it poses a greater health threat. Subsistence and sports fishermen who eat their catch can be at a particularly high risk of mercury poisoning if they fish regularly in contaminated waters.
The following recommendations about eating fish issued by the NRDC are largely designed for the people most at risk from mercury poisoning: children and women of childbearing age. Other adults may not need to restrict their diets as much, but can use these guidelines to make informed choices.

* Avoid contaminated fish:
Children under six, as well as women who are pregnant or planning to become pregnant, are the most vulnerable to mercury’s harmful effects. They should restrict or eliminate certain fish from their diet, including tuna, tilefish, swordfish, shark, king mackerel, grouper and fish caught in any waters that are subject to a mercury advisory. Women with elevated mercury levels should begin avoiding or restricting their consumption of mercury-laden fish as much as a year before they become pregnant.

* Restrict your portions:
In general, a woman who is pregnant or is likely to get pregnant should eat no more than two cans of light tuna per week, or two-thirds of a can per week of white albacore tuna if she wants to be sure to stay below the EPA’s level of concern for mercury. Keep in mind that the amount of mercury in a single can varies depending on where the tuna was caught. Albacore or solid white tuna is most likely to have higher concentrations, and chunk light tuna, lower concentrations.

Raw tuna and other sushi fish are also something to watch out for. Often the apex predators of the food chain, these fish tend to be high in mercury.

Since children get most of their mercury from canned tuna, it is important for parents to limit their children’s consumption to less than one ounce of canned light tuna for every 12 pounds of body weight per week, in order to stay below the level of mercury the EPA considers safe. That means that a child who weighs 36 pounds should not eat more than three ounces (half a standard-sized can of chunk light tuna) per week. Children should avoid albacore or white tuna because the levels of mercury are higher.

* Check your mercury level:
For an accurate reading, you can request a blood mercury test from your physician. Women with a high blood mercury level who are planning to start a family may decide to postpone pregnancy for a few months until levels drop; often this occurs over a three- to six-month time frame.

* Be an activist:
The NRDC is tracking proposals by the EPA and the FDA to protect the public from mercury poisoning. To receive regular updates and participate in decision-making on these and other environmental and health issues, join NRDC’s Earth Activist Network or send a message to the EPA to get poisonous mercury out of our fish (see Lastly, urge your grocery stores, fish markets and restaurants to label fish accurately and advise consumers about the dangers of mercury in the fish they sell.

The list below shows the amount of various types of fish that a woman who is pregnant or planning to become pregnant can safely eat, according to the EPA. People with small children who want to use the list as a guide should reduce portion sizes. Adult men, and women who are not planning to become pregnant, are less at risk from mercury exposure, but may wish to refer to the list for low-mercury choices.

Certain fish, even some that are low in mercury, make poor choices for other reasons, most often because they have been fished so extensively that their numbers are perilously low or if the methods used to catch them are especially damaging to other sea life or ocean habitats. These fish are marked with an asterisk.

This list applies to fish caught and sold commercially. For information about fish you catch yourself, check for advisories in your state. Fish are listed in descending order, so those at the bottom of each category are lower in mercury than those at the top.
(more than .55 parts
per million)
(from 0.26 to 0.55 parts per million)
(from 0.12 to 0.25 parts per million)
(less than 0.12 parts
per million)
Tilefish *
Shark *
Mackerel (king)
No more than two 6-ounce servings per month
Grouper *
No more than one 6-ounce serving per week
Orange roughy *
Marlin *
Tuna (canned,
white albacore)
Sea trout
Tuna (fresh) *
About two 6-ounce servings per week
Rockfish *
Mahi Mahi
Crab (dungeness)
Haddock *
Snapper *
Crab (blue)
Crab (snow)
Cod *
Tuna (canned,
chunk light)
Sea Bass *
Trout (freshwater)
No limit
Perch (freshwater)
Crab (king)
Pollock *
Perch (ocean) *
Scallops *
Flounder *
Sole *
Trout (farm raised)
Shrimp *


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