Mercury In Your Fish

By Ken Cook, President of the Environmental Working Group Fish is beyond compare as a source of many nutrients vital to the developing infant, some of which may actually enhance development of the nervous system ...

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By Ken Cook, President of the Environmental Working Group

Fish is beyond compare as a source of many nutrients vital to the developing infant, some of which may actually enhance development of the nervous system in babies and young children.

Widespread contamination of fish with toxic mercury, however, has cast a shadow over the nutritional benefits of fish.

Exposure to mercury in the womb can cause learning deficits, delay the mental development of children, and cause other neurological problems. Mercury consumed by a pregnant woman through contaminated fish can cross her placenta to damage the brain of her baby.

As a National Academy of Sciences panel definitively warned last year, some children exposed in utero by their mothers' fish consumption are at risk of falling in the group of children "who have to struggle to keep up in school and who might require remedial classes of special education."

Combustion in power plants of coal containing mercury is the major source of environmental pollution.

40 Tons of Mercury are released into the US EVERY year by this method.

Mercury pollution from coal-fired power plants moves through the air, is deposited in water and finds its way into fish, accumulating especially in fish that are higher up the food chain. Fish like tuna, sea bass, marlin and halibut show some of the worst contamination, but dozens of species and thousands of water bodies have been seriously polluted.

As a result, women who eat a lot of fish during pregnancy, or even as little as a single serving of a highly contaminated fish, can expose their developing child to excessive levels of mercury. The toxic metal can cross the placenta to harm the rapidly developing nervous system, including the brain.

In this report, EWG researchers for the first time attempt to characterize just how common such exposures are in the U.S. population, and the associated risks.

One key to the analysis is a much more refined representation of differences among women - their size, metabolism of mercury, blood volume, and many other biological variables. Government assessments use "averages" or constants for all of these factors, missing profound differences across the population of women of child bearing age.

EWG analysts also assembled the most extensive database ever developed on mercury levels in various species of fish, drawing on federal, state and other government sources, some 56,000 records in all.

That exercise revealed major variations in mercury contamination across fish species, yielding vital, highly practical information women can use while pregnant to reduce mercury exposure dramatically, while still enjoying the nutritional benefits of fish.

Earlier this year, the Food and Drug Administration came up with its own list of fish that pregnant and nursing women, along with infants, should avoid. Based on our analysis of much more extensive fish contamination records, the list presented in this report is more complete.

By analyzing these two data sources in combination, the study is able to provide new insights into how women can avoid excessive mercury exposures during pregnancy.

Researchers at US PIRG Education Fund, co-authors of this study, made another vital contribution. PIRG painstakingly combed through hundreds of "fish advisories" issued by state agencies to warn people about mercury levels in sport and game fish in literally thousands of US lakes and rivers.

What they found is disturbing: while some states are doing a better job than others, virtually no fish advisories for mercury contamination are adequately protective of human health when judged against current scientific knowledge.

The importance of this new understanding about mercury risks was evidenced in a landmark study on blood levels of mercury and other toxins, released by the federal Centers for Disease Control and Prevention (CDC).

While "average" blood mercury levels among women were not of concern, the data indicate that in fully 10 percent of American women -- roughly 7 million women -- mercury levels were above the dose that may put a fetus at risk for adverse nervous system effects.

Those women surely don't need more mercury in their system, least of all if they are already pregnant or nursing. As this report recommends, the government must start monitoring such exposures, and any possible effects, much more energetically. This is a simple, common sense matter of public health.

In the longer term, the solution is to halt mercury pollution from coal-burning power plants and other sources so the contamination of fish is avoided in the first place. Fuel switching -- from coal to renewable energy sources -- along with aggressive deployment of conservation measures, makes sense for any number of reasons.

Fish free of mercury -- the way they used to be -- is just another one.

Executive Summary

Government health officials issued new advisories warning women to limit fish consumption during pregnancy to avoid exposing their unborn children to unsafe levels of methylmercury.

Methylmercury can cross the placenta and cause learning deficits and developmental delays in children who are exposed even to relatively low levels in the womb. The principal exposure route for the fetus is fish consumption by the mother.

The Food and Drug Administration (FDA), which regulates commercially sold fish, recommends that pregnant and nursing women and young children not eat any shark, swordfish, tilefish, or king mackerel, but then recommends 12 ounces per week of any other fish.

The Environmental Protection Agency (EPA), which makes recommendations to states about safe mercury levels in sport fish, allows up to 8 ounces of any fish per week for pregnant women with no prohibitions on consumption of any individual fish caught recreationally.

These restrictions are steps in the right direction, but they need to be tightened significantly to adequately protect women and their unborn children from the toxic effects of methylmercury.

The nutritional benefits of fish complicate the task faced by health officials when protecting the public from methylmercury. Protein, omega-3 fatty acids, Vitamin D, and other nutrients make fish an exceptionally good food for pregnant mothers and their developing babies.

At the same time, there is no doubt that methylmercury is toxic to the fetal brain and nervous system, and that many beneficial fish species are contaminated. EPA's safe exposure estimate for methylmercury has dropped twice in the past 16 years, as new science has identified adverse effects in children exposed in the womb at lower and lower doses.

Emerging evidence indicates that the safe dose may drop even lower in the future (NAS 2000). Just how long a fetus can tolerate a dose of methylmercury above a "safe level' with no observable adverse effects is a matter of ongoing debate.

Compounding this uncertainty is the lack of effective education and outreach to pregnant women about methylmercury risks and the near total absence of information for pregnant women on the levels of mercury in the fish they buy. New data from the Centers for Disease Control and Prevention (CDC) show that about 10 percent of all women of childbearing age have blood methylmercury levels above the dose that may put their fetus at risk for adverse neurological effects.

If these women were to increase their consumption of certain fish species in hopes of benefiting their babies during pregnancy, they could expose their fetuses to potentially hazardous levels of methylmercury.

FDA's Protections Fall Short

FDA's methylmercury safeguards are designed to protect an average-sized woman eating an average fish contaminated with an average amount of methylmercury that decays in her body at an average rate. These assumptions rarely apply to the risks faced by any individual.

Instead, risks are unevenly distributed throughout the population, with a small but significant number of pregnancies exposed to far higher and potentially unsafe levels of methylmercury than the average fetus. The 10 percent most-heavily exposed American women already have blood methylmercury levels that would increase health risks to their fetuses if they became pregnant (CDC 2001). FDA's health advisory, based on average exposures, does little to protect these children.

The Environmental Working Group assessed fetal exposure to methylmercury taking into account a host of real world differences in individual exposure, including a mother's body weight and blood volume, varying methylmercury absorption and distribution rates, and variable rates of methylmercury decay in different pregnant women.

These biological differences were matched up with a unique database of fish contamination that contains 56,000 records of methylmercury test results from seven different government sources. Fish consumption, fish contamination levels, and biological variables were matched thousands of times to create a distribution of blood methylmercury levels in women similar to that occurring in the general population.

This distribution was compared to the benchmark dose of methylmercury recommended by the Committee on the Toxicological Effects of Methylmercury of the National Academy of Sciences.
FDA's recommendation of 76 6-ounce fish meals during pregnancy could actually be detrimental to the health of unborn children. Fish are an important part of a healthy diet and women should be encouraged to eat fish with low methylmercury levels during pregnancy.

But if American women ate a varied diet of FDA's recommended 12 ounces of fish a week (and none of the four prohibited fish) they would expose more than one-fourth of all babies born each year (1 million infants) to a potentially harmful dose of methylmercury for at least one month during pregnancy.

About 20,000 of these children would be exposed to a dose of methylmercury that increases the risk of adverse neurological effects for the entire pregnancy.

The EPA and state fish advisories for sport fish

EPA provides guidance on safe methylmercury exposure levels to state officials who in turn issue consumption advisories for sport fish caught by recreational anglers. State authorities typically post fish advisories for individual water bodies where fish are contaminated with methylmercury at a level that they deem unsafe for women of childbearing age.

Some states have done a better job than others in protecting their populations from methylmercury, but an analysis by US PIRG and the State PIRGs shows that only Massachusetts has adopted health safeguards that protect all women and children.

The broader issue with recreational fish, however, is whether these advisories translate into conscious choices by pregnant mothers to avoid eating contaminated fish. There is a substantial body of evidence indicating that they do not.


Fish provide important health benefits to the developing fetus, and pregnant women should be encouraged to eat fish with consistently low methylmercury levels. With too many species, however, these nutritional pluses are outweighed by the hazards of methylmercury.

Federal health authorities need to take much stronger steps to protect a far greater portion of the population. They must move beyond their antiquated safeguards designed to protect an average woman from an average amount of methylmercury in fish and take a realistic and protective stance against dietary exposure to methylmercury.

Fish Advisories


There are three ways that the FDA methylmercury health advisory must be improved:

1. The list of fish to avoid during pregnancy must be expanded.

By advising against the consumption of just four types of fish, FDA allows heavy consumption of many fish that have unacceptably high methylmercury levels. To protect women and their babies from methylmercury, the FDA must add the following species to the list of seafood that should not be eaten by pregnant women, nursing women, and women considering pregnancy:

Tuna steaks
Sea bass
Oysters (Gulf of Mexico)
White croaker
Largemouth bass

While not every serving of any of these fish is contaminated with dangerous levels of methylmercury, the odds are greater than one in 1,000 that consumption of a single meal of these fish will expose the fetus to a potentially hazardous amount of methylmercury for longer than 30 days.

2. FDA's recommendation that pregnant women eat 12 ounces a week of any fish (except the four that are not allowed) must be radically revised.

Ten percent of American women enter pregnancy with elevated methylmercury levels, and current FDA safeguards, which are based on average exposures, do almost nothing to protect these high exposure pregnancies. If these women follow FDA's advice of 12 ounces of any fish a week, they could easily expose their fetuses to a level of methylmercury that presents a real risk of adverse neurological effects. To protect women and children, FDA must restrict consumption of the following fish to no more than one meal per month, for all species combined:

Canned tuna
Mahi mahi
Blue mussels
Eastern oyster
Salmon from the Great Lakes
Blue crab from the Gulf of Mexico
Channel catfish (wild)
Lake whitefish

3. Women who want to eat fish during pregnancy must have information about which species are least contaminated with methylmercury. Pregnant women have a right to this information, and FDA has a duty to provide it. In addition to strengthening restrictions on fish consumption by pregnant women, FDA should promote the following fish as safe options for pregnant women:

Trout (farmed)
Catfish (farmed)
Shrimp * (see sidebar)
Fish Sticks
Flounder (summer)
Salmon (wild Pacific)
Blue crab (mid Atlantic)

Freshwater Sport Fish

It was not possible for EWG to assess the methylmercury risk from every recreational fish caught in every lake in every state in the country. A review of the available data, however, shows that several large predator sport fish are so universally contaminated that FDA should add them to the list of fish that women should completely avoid during pregnancy.

After analyzing the results of more than 10,000 samples from 792 lakes and rivers nationwide, we recommend that FDA add the following species to their health advisory: walleye, northern pike, and largemouth bass. While FDA has no authority to regulate methylmercury levels in freshwater fish, they do have a responsibility to provide critical health information to the public. It is important that women receive a consistent message from one source, and the FDA is the appropriate agency to deliver this message.

Improve monitoring of fish for methylmercury contamination

A major flaw in FDA's system is the agency's own lack of comprehensive data on methylmercury in fish. In January 2001, FDA recommended that pregnant women avoid consumption of king mackerel based on methylmercury levels from a study published in 1979. There are many other species where the data on methylmercury contamination are similarly outdated, but where the available information indicates a potential problem.

FDA must immediately expand its methylmercury sampling program to include a host of fish where the data indicate that pregnant women and their babies could receive a potentially unsafe exposure from a relatively small amount of fish.

These include:

Sea bass Atlantic cod Grouper, black Orange roughy
Bluefish Pacific cod Grouper, red Sand perch
Bonito Pollock Red snapper White perch
Porgy Yellowtail Rockfish Dover sole
Halibut Lake trout Flounder, various species

Improve public access to mercury contamination data

Consumers have a right to know about contamination of the food supply, and FDA must be responsive to this right. Currently they are not. EWG had great difficulty obtaining relatively simple information about fish contamination from the agency through the Freedom of Information Act. FDA currently posts the results of its Total Diet Study on the web, and there is no reason that all of the agency's mercury contamination information could not be posted as well.

Improve risk assessments

FDA needs to move beyond its antiquated and biologically implausible risk assessment methods based on average people and average fish and adopt state-of-the-art risk assessment techniques that provide a much more realistic picture of mercury exposure and risk as it is distributed throughout the population.

It is not sufficient to protect the population from average exposures when it is clear that many individuals have far greater than average exposures for extended periods of time.

Reduce Mercury Pollution at its Source

Mercury emissions from coal-fired power plants, the largest man-made source of environmental mercury, are currently completely unregulated. Federal decision-makers should require power plants to reduce their mercury pollution by 90% and ultimately move away from polluting sources of power.


Dr. Mercola's Comment:

The Environmental Working Group is to be commended for their fine work in this area and for providing an answer to a more definitive answer to a common question I receive - "What are "safe" fish to eat?"

It is most unfortunate that the mercury pollution from the coal plants has so contaminated the waterways and the fish, as they are such a healthy food. One needs to be aware that all fish are potentially contaminated with mercury. However I would revise the EWGs list of safe fish by excluding the shellfish and fish without scales and including a small safe fish, sardines. So here is my list of safe fish:

Summer Flounder
Wild Pacific Salmon

Not a very big list. It is important to note that farmed fish are very similar to commercial beef. The fish are fed grain products and the beneficial omega 3 fatty acids (EPA and DHA) are totally distorted. Additionally, non-organic grain is used so the fish pick up the pesticides that were used on the grains and also that run-off from neighboring farmland.

So I would recommend limiting fish consumption. There is another option that I will be discussing in about two weeks which does "solve" the problem and allow you to obtain the good nutrition of the fish while avoiding the mercury and pesticides.


Articles of interest from Dr Jay Dooreck D.D.S. P.C. in areas of holistic health reprinted with permission from

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