TCS Daily

Mothers, Babies and Mercury

By Sandy Szwarc - April 16, 2004 12:00 AM

Whether they come from the U.S. Food and Drug Administration or special interest groups, warnings about methylmercury-contaminated fish endangering the health of our babies and children are alarming. Although advisories have become more frequent and exigent over recent years, the evidence contrasts greatly from the fearmongering -- regardless of the source.

Dose Makes the Poison

The possible dangers of methylmercury to babies were first highlighted during several large-scale poisonings halfway around the world. The poisonings happened in Iraq with contaminated grain during the 1970s and in Japan from contaminated fish in the 1950s. For months to years, the Japanese had been eating tainted fish which had methylmercury concentrations as high as 40 parts per million -- astoundingly elevated compared to typical concentrations of 0.01-0.50 ppm in the fish we buy.1-6 The mercury levels discovered in the Iraqi mothers' hair after their poisonings were as high as 674 ppm -- shockingly higher than even the highest percentiles among American women of childbearing age, measuring a mere 1.4 ppm.7

While these poisonings were heartwrenching illustrations that high methylmercury exposure in utero could leave some children with tragic neurological deficits, they also verified the axiom that the "dose makes the poison" as even some babies born to mothers with hair concentrations exceeding 100 ppm were normal. The lowest mercury level associated with any neurological effects among the Japanese was 50 ppm in their hair and 200 mcg/Liter (parts per billion) in their blood. Using a figure many times lower than that to ensure public safety, the FDA established its original 1979 action level of 1 ppm methylmercury in fish (a tolerable daily intake of 0.4 mcg/kg) to ensure the public's safety.

Certainly no one wants to take chances with the lives of babies. Fish and seafood are the main dietary sources of methylmercury and nearly all fish have at least trace amounts, although most are exceedingly small.8,9 Since women have been eating fish forever and delivering healthy babies, researchers wanted to pinpoint a safe low-level of exposure for them. So, the National Institute of Environmental Health Sciences funded two large, well-designed, prospective longitudinal studies of prenatal methylmercury exposures -- one in the Faroe Islands and another in Seychelles Islands. Both locations offered populations with a broad range of exposures that would enable the clearest picture of the dose-response curve.

What's the Evidence?

After over a decade, those two studies failed to find conclusive evidence that low-levels of exposure from mercury in fish put babies at risk. But the researchers arrived at contradictory conclusions and the FDA Food Advisory Committee set out to determine why and held scientific meetings in July 2002 to critically evaluate the evidence on methylmercury.

The Harvard-led Faroe Island study had followed more than 800 children born in 1986 and 1987 and reported an association between prenatal methylmercury exposure and "subtle and small neuropsychological changes" in the children.10 However, Dr. Philippe Grandjean from Odense University in Denmark admitted to the FDA Committee that testing children's development proved "complicated to do the same way every time" and while they saw a mercury effect in the children examined by one neuropsychologist, they didn't when they adjusted for different examiners. Still he believed "our results would translate to a loss of about 1.5 IQ points every time you double the exposure."

The FDA Committee and attending scientists, however, noted other problems with the study -- confounding factors of concern. The Scandinavian population of the Faroe Islands ate fish three times a week on average, but that wasn't all. They also ate pilot whale. In fact, it was their main dietary source of methylmercury and had higher levels than almost any other fish, at 2 ppm. Grandjean noted the people ate pilot whale all the time, dried like jerky as well as occasional feasts, giving them large bolus doses. But pilot whale is also high in PCBs. In fact, Dr. Christopher DeRosa of the U.S. Department of Health's Agency for Toxic Substances and Disease Registry (ATSDR) cautioned, "PCBs are at levels 10 times higher than in the U.S. population in the Faroes, and at three times the level of FDA's tolerable daily intake." Grandjean admitted they didn't "really know" what the effects of PCBs might have been.1

The longest, longitudinal study ever done on mothers and children is the Seychelles study. Led by researchers from the University of Rochester, they used interscore reliability -- where regularly two testers score the same child independently and the results are compared -- the "gold standard" to eliminate variances with different examiners. The FDA Committee noted they also used more global tests and evaluated 21 endpoints for children's neurocognitive, language, memory, motor, perceptual-motor, and behavioral functions and have followed them for nearly 10 years. The mothers on these East African islands eat 12 fish meals a week -- the highest per capita consumption of fish in the world, according to DeRosa. That compares to an average of one serving a week in the U.S.

Yet while the methylmercury exposures of Seychelles children are 10 to 20 times higher than here, the researchers' findings reported last May in Lancet concluded: "There is no evidence of neurodevelopmental risk from prenatal methylmercury exposure resulting solely from ocean fish consumption." In an accompanying letter, Dr. Constantine Lyketsos of Johns Hopkins Hospital said: "The existing evidence suggests that methylmercury exposure from fish consumption during pregnancy, of the level seen in most parts of the world, does not have measurable cognitive or behavioral effects in later childhood...For now, there is no reason for pregnant women to reduce fish consumption below current levels, which are probably safe."11

"The [evidence for possible risk] has been, at best, unconvincing," said Charles Lockwood, MD, former chair of the American College of Obstetricians and Gynecologists.1

Fear Factor

Lockwood noted there's considerable disagreement among scientists if you can even set "a specific exposure level that would...represent the lower limit of absolute risk"1 But just after the Iraqi poisonings, the EPA used that toxic-dose data to extrapolate their own risk assessment. Dr. Joseph Jacobson, a member of the National Academy of Sciences Committee on Methylmercury, explained the EPA first calculated a "benchmark dose" (BMDL) for the most sensitive population of children: the lowest dose at which they thought they might see any effect over a lifetime of exposure. They then added in a ten-fold safety factor to arrive at their "exposure reference dose" (RfD) -- a figure they want the target for regulation.1

Hence, the EPA determined a BMDL of 58mcg/L in the blood which corresponds to hair values greater than 12 ppm --- ten times that of most American women eating fish. Their RfD safety factor was then one-tenth of that, or 5.8 mcg/L. It was never changed later when data came in from those commissioned studies.

In the EPA's pursuit of zero risks, its RfD is the most restrictive of any in the world. No scientific agency evaluating the evidence, however, has agreed with the EPA's RfD -- except one: the National Academy of Sciences. But for their statistical risk model the NAS chose to ignore the Seychelles findings and instead used data from the Faroe Islands and an unpublished study from New Zealand. Their conclusion released July 2000 stated: "The risk of adverse effects from current methylmercury exposures in the majority of the population is low...but the EPA's current RfD...[is] scientifically justifiable...for the protection of public health."12

In contrast, other scientific bodies around the world -- such as: the U.S. ATSDR, the Joint Food and Agriculture Organization of the United Nations and World Health Organization Expert Committee on Food Additives, Health Canada, and the UK's Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) -- have established minimal exposure levels multiple times higher than the EPA's.1,13-15 COT's findings last year stated: "Dietary exposures to mercury do not give rise to toxicological concerns for consumers.... [P]opulation exposures to mercury have decreased since 1976 (0.005 milligrams per day), with the current dietary exposure at its lowest level (0.0015 milligrams per day)."16

Reality Check

Let's put the EPA's numbers into perspective. The CDC's 1999 National Health and Nutrition Examination Survey (NHANES 1999) of American women found NO measurements of blood or hair values over the EPA's BMDL.1,7 All women were well under the lowest levels the EPA even theorized might risk detrimental effects to their babies.

But that's not the spin being used to frighten expectant mothers. You've seen the headlines: "8% of women of childbearing age have unsafe levels of mercury in their blood," the Environmental Working Group, a nonprofit special interest lobbying group, has repeatedly announced. The facts: NHANES found that at the highest percentiles, 7.8% of women had blood mercury levels at or above the EPA's arbitrary safety cushion -- RfD. That's the origin of the misinterpreted claims being made by alarmists that "60,000 newborns annually are born at risk."17

It's "become sort of an urban legend," said Dr. James Heimbach, former U.S. Dept of Agriculture associate administrator of the Human Nutrition Information Services. But none of these babies is anywhere near values associated with actual risk.1

In fact, the Human Nutrition Information Services analyzed the diets of American women of childbearing years -- including heavy consumers of fish or those who prefer relatively high methylmercury-containing fish, their frequency of eating the same fish, and the methylmercury in a range of fish samples. Heimbach told the FDA Committee their analysis concluded: "They [American women] simply are not exposed to levels of methylmercury that would place the newborn children at risk."


1. Dept. of HHS, FDA, CFSAN. Food Advisory Committee - Methylmercury. Transcripts of meeting July 23-4, 2002.

2. Milloy S. FDA's Mercurial Fish Story. FoxNews, Jan 19, 2001.

3. Elemental or Metallic Mercury & Methylmercury. University of Minnesota,

4. Wheeler M. Mercury. Environmental Health Perspectives; August 1996; 104 (8)

5. US Dept. of Health and Human Services FDA and EPA. Mercury Levels in Commercial Fish and Seafood.

6. Foulke JE. Mercury in Fish: Cause for Concern? FDA Consumer Magazine, Sept 1994.

7. Blood and Hair Mercury Levels in Young Children and Women of Childbearing Age -- United States, 1999. CDC MMWR Weekly, March 02, 2001; 50(08): 140-3.

8. Dalton LW. Methylmercury Toxicology Probed.Chemical and Engineering News, January 19, 2004; 82 (3): 701.

9. Barber M. Survey of metals and other elements. Food Standards Agency. Food Survey Information Sheet 48/04, March 2004.

10. Murata K, etal. Delayed brainstem auditory evoked potential latencies in 14-year-old children exposed to methylmercury. J Pediatrics; Feb 2004; 144 (2).

11. Myers GJ, Davidson PW, Cox C, Shamlaye CF, Palumbo D, Cernichiari E, Sloane-Reeves J, Wilding GE, Kost J, Huang LS, Clarkson TW. Prenatal methylmercury exposure from ocean fish consumption in the Seychelles child development study. Lancet. 2003; 361(9370):1686-92.

12. National Academy of Sciences. Toxicologic effects of methylmercury. Washington, DC: National Research Council, July 11, 2000.

13. Koenig HM. Mercury in the Environment: The Problems, the Risks, and the Consequences. Annapolis Center for Science-Based Public Policy.

14. WHO. Summary and conclusions of the 61 st meeting, Methylmercury, 2003.

15. Ogilvie K. Mercury in the Environment - A Primer. Pollution Probe. June 2003.

16. Barber M. Survey of metals and other elements. Food Standards Agency. Food Survey Information Sheet 48/04, March 2004.

17. CSPI letter to FDA Commissioner Jane Henney, Re:Petition to Set A Regulatory Limit for Methylmercury In Seafood That Reflects the Risk to Pregnant Women and Children From the Intake of Seafood Containing Methylmercury, July 17, 2000.

© 2004


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