Mercury In Your Fish

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April 25, 2001 | 82,301 views

By Ken Cook, Presidentof the Environmental WorkingGroup

Fish is beyond compare as a source ofmany nutrients vital to the developing infant, some of whichmay actually enhance development of the nervous system inbabies and young children.

Widespreadcontamination of fish with toxic mercury, however, has casta shadow over the nutritional benefits of fish.

Exposure to mercury in the womb cancause learning deficits, delay the mental development ofchildren, and cause other neurological problems. Mercuryconsumed by a pregnant woman through contaminated fish cancross her placenta to damage the brain of her baby.

As a National Academy of Sciences paneldefinitively warned last year, some children exposed inutero by their mothers' fish consumption are at risk offalling in the group of children "who have to struggleto keep up in school and who might require remedial classesof special education."

Combustion in power plants of coal containingmercury is the major source of environmentalpollution.

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

Mercury pollution from coal-fired powerplants moves through the air, is deposited in water andfinds its way into fish, accumulating especially in fishthat 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 havebeen seriously polluted.

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

In this report, EWG researchers forthe first time attempt to characterize just how common suchexposures are in the U.S. population, and the associatedrisks.

One key to the analysis is a much morerefined representation of differences among women - theirsize, metabolism of mercury, blood volume, and many otherbiological variables. Government assessments use "averages"or constants for all of these factors, missing profounddifferences across the population of women of child bearingage.

EWGanalysts also assembled the most extensive database everdeveloped on mercury levels in various species of fish,drawing on federal, state and other government sources,some 56,000 records inall.

That exercise revealed major variationsin mercury contamination across fish species, yielding vital,highly practical information women can use while pregnantto reduce mercury exposure dramatically, while still enjoyingthe nutritional benefits of fish.

Earlier this year, the Food and DrugAdministration came up with its own list of fish that pregnantand nursing women, along with infants, should avoid. Basedon our analysis of much more extensive fish contaminationrecords, the list presented in this report is more complete.

By analyzing these two data sourcesin combination, the study is able to provide new insightsinto how women can avoid excessive mercury exposures duringpregnancy.

Researchers at US PIRGEducation Fund, co-authors of this study, made another vitalcontribution. PIRG painstakingly combed through hundredsof "fish advisories" issued by state agenciesto warn people about mercury levels in sport and game fishin literally thousands of US lakes and rivers.

What they found is disturbing: whilesome states are doing a better job than others, virtuallyno fish advisories for mercury contamination are adequatelyprotective of human health when judged against current scientificknowledge.

The importance of this new understandingabout mercury risks was evidenced in a landmark study onblood levels of mercury and other toxins, released by thefederal Centers for Disease Control and Prevention (CDC)in March, 2001.

While "average" blood mercurylevels among women were not of concern, the data indicatethat in fully 10 percentof American women -- roughly 7 million women -- mercurylevels were above the dose that may put a fetus at riskfor adverse nervous system effects.

Those women surely don't need more mercuryin their system, least of all if they are already pregnantor nursing. As this report recommends, the government muststart monitoring such exposures, and any possible effects,much more energetically. This is a simple, common sensematter of public health.

In the longer term, the solution isto halt mercury pollution from coal-burning power plantsand other sources so the contamination of fish is avoidedin the first place. Fuel switching -- from coal to renewableenergy sources -- along with aggressive deployment of conservationmeasures, makes sense for any number of reasons.

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


On January 12, 2001, government healthofficials issued new advisories warning women to limit fishconsumption during pregnancy to avoid exposing their unbornchildren to unsafe levels of methylmercury.

Methylmercury can cross the placentaand cause learning deficits and developmental delays inchildren who are exposed even to relatively low levels inthe womb. The principal exposure route for the fetus isfish consumption by the mother.

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

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

These restrictionsare steps in the right direction, but they need to be tightenedsignificantly to adequately protect women and their unbornchildren from the toxic effects of methylmercury.

The nutritional benefits of fish complicatethe task faced by health officials when protecting the publicfrom methylmercury. Protein, omega-3 fatty acids, VitaminD, and other nutrients make fish an exceptionally good foodfor pregnant mothers and their developing babies.

At the same time, there is no doubtthat methylmercury is toxic to the fetal brain and nervoussystem, and that many beneficial fish species are contaminated.EPA's safe exposure estimate for methylmercury has droppedtwice in the past 16 years, as new science has identifiedadverse effects in children exposed in the womb at lowerand lower doses.

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

Compounding this uncertainty is thelack of effective education and outreach to pregnant womenabout methylmercury risks and the near total absence ofinformation for pregnant women on the levels of mercuryin the fish they buy. New data from the Centers for DiseaseControl and Prevention (CDC) show that about 10 percentof all women of childbearing age have blood methylmercurylevels above the dose that may put their fetus at risk foradverse neurological effects (CDC 2001).

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

FDA's ProtectionsFall Short

FDA's methylmercury safeguards are designedto protect an average-sized woman eating an average fishcontaminated with an average amount of methylmercury thatdecays in her body at an average rate. These assumptionsrarely apply to the risks faced by any individual.

Instead, risks are unevenly distributedthroughout the population, with a small but significantnumber of pregnancies exposed to far higher and potentiallyunsafe levels of methylmercury than the average fetus. The10 percent most-heavily exposed American women already haveblood methylmercury levels that would increase health risksto their fetuses if they became pregnant (CDC 2001). FDA'shealth advisory, based on average exposures, does littleto protect these children.

The EnvironmentalWorking Group assessed fetal exposure to methylmercurytaking into account a host of real world differences inindividual exposure, including a mother's body weight andblood volume, varying methylmercury absorption and distributionrates, and variable rates of methylmercury decay in differentpregnant women (Stern 1997, CDC 2001, NAS 2000).

These biological differences were matchedup with a unique database of fish contamination that contains56,000 records of methylmercury test results from sevendifferent government sources. Fish consumption, fish contaminationlevels, and biological variables were matched thousandsof times to create a distribution of blood methylmercurylevels in women similar to that occurring in the generalpopulation.

This distribution was compared to thebenchmark dose of methylmercury recommended by the Committeeon the Toxicological Effects of Methylmercury of the NationalAcademy of Sciences (NAS 2000).
FDA's recommendation of 76 6-ounce fish meals during pregnancycould actually be detrimental to the health of unborn children.Fish are an important part of a healthy diet and women shouldbe encouraged to eat fish with low methylmercury levelsduring pregnancy.

Butif American women ate a varied diet of FDA's recommended12 ounces of fish a week (and none of the four prohibitedfish) they would expose more than one-fourth of all babiesborn each year (1 million infants) to a potentially harmfuldose of methylmercury for at least one month during pregnancy.

About20,000 of these children would be exposed to a dose of methylmercurythat increases the risk of adverse neurological effectsfor the entire pregnancy.

The EPAand state fish advisories for sport fish

EPA provides guidance on safe methylmercuryexposure levels to state officials who in turn issue consumptionadvisories for sport fish caught by recreational anglers.State authorities typically post fish advisories for individualwater bodies where fish are contaminated with methylmercuryat a level that they deem unsafe for women of childbearingage.

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

The broader issue with recreationalfish, however, is whether these advisories translate intoconscious choices by pregnant mothers to avoid eating contaminatedfish. There is a substantial body of evidence indicatingthat they do not (Golden et al 2001).


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

Federal health authorities need to takemuch stronger steps to protect a far greater portion ofthe population. They must move beyond their antiquated safeguardsdesigned to protect an average woman from an average amountof methylmercury in fish and take a realistic and protectivestance against dietary exposure to methylmercury.

Fish Advisories


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

1.The list of fish to avoidduring pregnancy must be expanded.

By advising against the consumptionof just four types of fish, FDA allows heavy consumptionof many fish that have unacceptably high methylmercury levels.To protect women and their babies from methylmercury, theFDA must add the following species to the list of seafoodthat 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 thesefish is contaminated with dangerous levels of methylmercury,the odds are greater than one in 1,000 that consumptionof a single meal of these fish will expose the fetus toa potentially hazardous amount of methylmercury for longerthan 30 days.

2. FDA'srecommendation that pregnant women eat 12 ounces a weekof any fish (except the four that are not allowed) mustbe radically revised.

Ten percent of American women enterpregnancy with elevated methylmercury levels, and currentFDA safeguards, which are based on average exposures, doalmost nothing to protect these high exposure pregnancies.If these women follow FDA's advice of 12 ounces of any fisha week, they could easily expose their fetuses to a levelof methylmercury that presents a real risk of adverse neurologicaleffects. To protect women and children, FDA must restrictconsumption of the following fish to nomore than one meal per month, for all species combined:

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 informationabout which species are leastcontaminated with methylmercury. Pregnant womenhave a right to this information, and FDA has a duty toprovide it. In addition to strengthening restrictions onfish consumption by pregnant women, FDA should promote thefollowing fish as safe options for pregnant women:

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

FreshwaterSport Fish

It was not possible for EWG to assessthe methylmercury risk from every recreational fish caughtin every lake in every state in the country. A review ofthe available data, however, shows that several large predatorsport fish are so universally contaminated that FDA shouldadd them to the list of fish that women should completelyavoid during pregnancy.

After analyzing the results of morethan 10,000 samples from 792 lakes and rivers nationwide,we recommend that FDA add the following species to theirhealth advisory: walleye,northern pike, and largemouth bass. While FDAhas no authority to regulate methylmercury levels in freshwaterfish, they do have a responsibility to provide criticalhealth information to the public. It is important that womenreceive a consistent message from one source, and the FDAis the appropriate agency to deliver this message.

Improvemonitoring of fish for methylmercury contamination

A major flaw in FDA's system is theagency's own lack of comprehensive data on methylmercuryin fish. In January 2001, FDA recommended that pregnantwomen avoid consumption of king mackerel based on methylmercurylevels from a study published in 1979. There are many otherspecies where the data on methylmercury contamination aresimilarly outdated, but where the available informationindicates a potential problem.

FDA must immediately expand its methylmercurysampling program to include a host of fish where the dataindicate that pregnant women and their babies could receivea potentially unsafe exposure from a relatively small amountof fish.

These include:

Sea bass
Atlantic cod
Grouper, black
Orange roughy
Pacific cod
Grouper, red
Sand perch
Red snapper
White perch
Dover sole
Lake trout
Flounder, various species

Improvepublic access to mercury contamination data

Consumers have a right to know aboutcontamination of the food supply, and FDA must be responsiveto this right. Currently they are not. EWG had great difficultyobtaining relatively simple information about fish contaminationfrom the agency through the Freedom of Information Act.FDA currently posts the results of its Total Diet Studyon the web, and there is no reason that all of the agency'smercury contamination information could not be posted aswell.

Improverisk assessments

FDA needs to move beyond its antiquatedand biologically implausible risk assessment methods basedon average people and average fish and adopt state-of-the-artrisk assessment techniques that provide a much more realisticpicture of mercury exposure and risk as it is distributedthroughout the population.

It is not sufficient to protect thepopulation from average exposures when it is clear thatmany individuals have far greater than average exposuresfor extended periods of time.

Reduce MercuryPollution at its Source

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


The EnvironmentalWorking Group is to be commended for their fine workin this area and for providing an answer to a more definitiveanswer to a common question I receive - "What are "safe"fish to eat?"

It is most unfortunate that the mercurypollution from the coal plants has so contaminated the waterwaysand the fish, as they are such a healthy food. One needsto be aware that all fish are potentially contaminated withmercury. However I would revise the EWGs list of safe fishby excluding the shellfish and fish without scales and includinga small safe fish, sardines. So here is my list of safefish:

Wild Pacific Salmon


Not a very big list. It is importantto note that farmed fish are very similar to commercialbeef. The fish are fed grain products and the beneficialomega 3 fatty acids (EPA and DHA) are totally distorted.Additionally, non-organic grain is used so the fish pickup the pesticides that were used on the grains and alsothat run-off from neighboring farmland.

So I would recommend limiting fishconsumption. There is another option that I will be discussingin about two weeks which does "solve" the problemand allow you to obtain the good nutrition of the fish whileavoiding the mercury and pesticides.

Stay tuned.


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