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Fight Over Mercury Risks Muddied by Bad Science
Bizarre judgments by government bodies put bad science at center of mercury-seafood fight
12/7/2006By Craig Weatherby
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It’s been interesting for us to view the ongoing fight over the relative risks and rewards of seafood from a position of neutrality.

As a company that sells only seafood that is extraordinarily low in mercury and all other contaminants, we have no dog in this fight.

Key Points
  • The debate over safe seafood intake is hobbled by the government’s reliance on flawed studies.
  • Both sides in debate distort science to some degree, but surprisingly, consumer advocates seem to engage in the most spin.
  • The mineral selenium is an overlooked factor in seafood safety, as it blocks damage from mercury and is abundant in most fish.
But we share public health experts’ concern that the fight between consumer groups and industry interests might lead people to reduce fish consumption out of sheer confusion.

We were dismayed when we first discovered that governmental guidelines for seafood safety are based on dubious decisions that confuse the issue and may underplay the safety of most seafood.

Before we get started on our examination of this contentious issue, let’s get some basic facts on the table.

Mercury and seafood: the basics
Last December we attended a landmark scientific conference in Washington D.C., titled “Seafood and Health '05: Issues, 
Questions and Answers,” which clarified the science underlying the issue of mercury in seafood: an education we’ve continued to pursue.

Lake fish in certain regions—and, to a far lesser extent, ocean fish—are the leading dietary sources of “methyl” mercury: a form more toxic to humans than the elemental mercury (“quicksilver”) used in old thermometers.

Elemental mercury from forest fires, underwater geothermal vents, and coal-burning power plants becomes methyl mercury via a series of complex steps involving bacteria in lakes, rivers, and oceans.

Almost everyone involved in this health-policy fight agrees that most fish are both safe and positively healthful to consume in moderate amounts (two to five times a week).

This is because methyl mercury occurs at relatively high levels in only a few commercial ocean species: swordfish, shark, Gulf tilefish, king mackerel and (to alesser extent) to older, larger tuna, which constitute the bulk of the fish used for mass market brands of “light” and albacore tuna (Mercury accumulates over time in predatory species like tuna and swordfish, which is why we offer only young, low-weight, minimal-mercury albacore tuna).

Government guidelines on seafood safety take two forms:
  1. The US Environmental Protection Agency (EPA) and Food & Drug Adminstration (FDA) offer joint fish intake guidelines for infants, young children, and pregnant/nursing women, which advise these groups to avoid swordfish, shark, king mackerel, and Gulf of Mexico tilefish entirely, and to limit total weekly fish intake to 12 ounces (2 average meals) and favor fish and shellfish that are low in mercury. The guidelines cite salmon, shrimp, canned light tuna, pollock, and catfish as low in mercury, but other species and small albacore and halibut are also very low in mercury.
  2. The FDA set a so-called “action” level of mercury in fish (one part per million), above which fish should not be sold. Common commercial fish virtually never exceed this level. The exceptions are swordfish, shark, and king mackerel, which often come close to it, and Gulf of Mexico tilefish, which typically exceed it.
Interestingly, even the conference speaker most concerned about increasing the prominence of mercury warnings to pregnant/nursing mothers and young children—Caroline Smith DeWaal of the Center for Science in the Public Interest (CSPI)—expressed no particular concerns about ample fish consumption by older children or adults.

Public health experts anxious about overblown fears
All of the health researchers who spoke at the Seafood and Health '05 conference voiced concern that exaggerated fears about the dangers of mercury in seafood—anxieties fueled deliberately by advocacy groups for political reasons--could prevent a beneficial increase in fish intake among the general population.

At the Seafood and Health '05 conference, Ms. DeWaal of CSPI noted that mercury scares have not prevented seafood consumption from rising in recent years.

But compared with fish consumption in countries that enjoy lower rates of heart disease, dementia, and depression/anxiety disorders, the American’s average fish intake remains at very low levels even after these recent increases.

Americans still eat far less fish than the amounts government agencies and health experts recommend to reduce the risk of heart attacks and strokes, and to promote optimal brain development in infants and mental and heart health in adults (See “New Report Finds Americans Need Far More Omega-3s”).

And it is unclear how much more fish Americans would have eaten, absent issuance in 2001 of the federal government’s seafood-and-mercury advisory for pregnant/nursing mothers and young children.

Subsequent surveys showed that very few Americans—especially women
understood that the federal advisory did not apply to everyone.

The mercury-coal connection
Environmental organizations have leveraged legitimate concerns about fish-borne mercury’s potential threat to children to help force tighter restrictions on mercury emissions from coal-burning power plants.

This strategy has impacted the policy debate very effectively, despite persuasive evidence that coal-related mercury emissions from coal-burning power plants in the US account for only a tiny percentage of mercury emissions worldwide, and no more than a very minor amount of the methyl mercury measured in ocean waters.

In fact, most of the methyl mercury in ocean waters comes from forest fires and undersea volcanoes and geothermal vents.

This situation could change, since China is building one new coal-burning power plant every week. In fact, China’s race to burn more coal is one reason US utility companies view tighter mercury emissions restrictions as relatively meaningless moves (We disagree with this fatalistic position, since coal-plant mercury emissions are proven to pollute nearby lakes and rivers).

Evidence for the natural origins of most oceanic mercury comes from measurements of mercury levels in preserved fish from the 1870’s and early 1970’s, which show that the concentrations of mercury in ocean fish have, if anything, decreased over the past 120 years.

Unfortunately, some advocacy groups seek to achieve a worthy end—reduced mercury emissions from coal-burning power plants—via exaggerated mercury-in-fish concerns that may put public health at risk by suppressing seafood consumption.

We support tighter restrictions on industrial mercury emissions, but having heard how the story of the boy who cried "wolf" ends, we cannot support distortion of science to achieve that or any other public policy end.

Mercury and fish: bad science fuels mercury fears
The ongoing battle over safe levels of seafood consumption rests in large part on the hotly disputed evidence that the US FDA relied on in setting the maximum allowable mercury levels in fish, which the US EPA also used to establish fish-intake guidelines for pregnant/nursing mothers and young children.

In the late 1990’s, the US Environmental Protection Agency (EPA) asked the quasi-governmental National Research Council (NRC) to undertake a review of the extant evidence, to help the agency set seafood intake guidelines for pregnant/nursing mothers and young children: a report the NRC issued in 2000.

Of the three relevant epidemiological (human population) studies conducted to date—in the Faroe Islands, New Zealand, and the Seychelles Islands—the NRC chose to rely exclusively on the Faroe Islands Study, solely for reasons of expediency that do not pass scientific scrutiny.

The independent academic scientists whom we heard and spoke with at the Seafood & Health ’05 conference considered the Seychelles Study—which found no harm to children despite eating extremely fish-heavy diets--the best-designed and most credible of the three available investigations. (It was conducted by a team of researchers from the University Of Rochester Medical Center, led by Dr. Gary Meyers, who we spoke with and heard speak at the conference.)

Even the seriously flawed Faroe Islands Study, which is cited, selectively, by consumer and environmental advocacy groups, found only a minuscule possibility of minuscule effects on brain performance. In fact, the alleged adverse effects were so small that they fell within the margin of statistical error.

Note: While the reference dose for methyl mercury set by the EPA flowed primarily from the NRC report, it was also influenced by analysis of data from a poisoning episode in Iraq in which mothers consumed seed grain treated with methyl mercury during pregnancy.  The mercury exposures in the Iraq incident were short term and at much higher levels than those that could result from heavy fish consumption, making them even less relevant than the Faroe Islands Study’s findings.

The flawed Faroe Islands Study
The Faroe Islands Study suffers from flaws so serious many expert observers believe that they render it unreliable as a basis for supporting the EPA’s fish-intake safety standards.

The Faroe Islands Study involved a population whose seafood consumption consists largely of Pilot whale: a predatory marine mammal that, unlike most commercial fish species, is very high in mercury and PCBs and very low in mercury-blocking selenium.

These facts alone made the NRC report authors’ decision to use the Faroe Islands population as a model for setting mercury standards appear dubious, to say the least.

The NRC report on mercury and fish was published in 2000 when the Seychelles study was still three years from official completion. It continues to this day, and the researchers still find no significant associations between extremely high fish intake and adverse brain effects.

Government and advocacy orgs ignore superior Seychelles study
The Seychelles Study, which the National Research Council (NRC) chose to ignore, was conducted by researchers from the University of Rochester, and was scientifically superior to the Faroe Islands Study in critically important respects.

In fact, the NRC admitted it could find no methodological flaws in the Seychelles Study, before dismissing it as irrelevant to the task of setting baseline mercury intake standards.

The NRC rejected the Seychelles Study because its failure to find evidence of harm made it much less useful as the basis for the panel's task of setting mercury blood-level standards: a bizarrely unscientific stance.

The NRC committee's position was predicated on the literally baseless assumption that the as-yet-undetermined level at which mercury damages brain development must lie below the relatively high mercury intake levels of the children in the Seychelles Study.

A biology 101 student who proposed this absurd paradox as a scientifically credible position would flunk out. We should expect better from supposedly authoritative institutions entrusted with serious public health decisions.

We encourage you to read the discussion on our Purity page, and learn about the FDA's 2008 study, which analyzed the epidemiological evidence and found no risk to children who eat lots of fish.

Prominent consumer org distorts Seychelles Study
Folks who want to whip up fears of mercury in fish to force tighter mercury emissions regulations cite the NRC’s strangely unscientific decision to justify ignoring the Seychelles Study and focusing only on the deeply flawed Faroe Islands Study. But this stance only undermines their credibility.

For example the Environmental Working Group (EWG)—a leading advocate of enhanced regulation of mercury emissions--and a real power on Capitol Hill
blasts the tuna industry for citing the Seychelles Study, using the following headline: “Follow Up to Utility Industry-Funded Study Leads to Finding that Mercury in Fish No Problem, Scores of Independent Studies Suggest Otherwise: Seafood Industry Hypes Lone Study Criticized by National Academy of Sciences.”

However, this headline is completely misleading, for three reasons:
  • While there have been hundreds of studies related to mercury toxicity in animals, and a handful in humans, the studies relevant to relevant to the effects of fish on child development studies are the three studies the NRC considered.
  • The NRC’s mercury-seafood panel did not criticize the Seychelles Study: they ignored it because it didn’t show harm and therefore didn't serve their narrow purpose.
  • The Seychelles Study was not “industry-funded”. It was funded by the National Institute of Environmental Health Sciences, NIH, the U.S. Food and Drug Administration, and the Republic of the Seychelles.
Far from being an industry-friendly exercise, the Seychelles study came about as a result of previous work by the same Rochester team, which reported the first data showing that pre-natal exposure to mercury could harm a developing child.

In fact, it was the Rochester team’s study of accidental mercury poisoning in Iraq more than 30 years ago that spurred them to start the Seychelles Study, which was intended to pinpoint the levels at which mercury poses a danger. Unexpectedly, its findings suggest that those levels must be considerably higher than some consumer organizations would have us believe.

Seychelles Study finds no harm: is selenium the reason?
The Seychelles Study has found no evidence of damage to children after 12 years of follow up, even though they eat 10-12 times more fish than American children and the average mercury content of the fish they eat is closely comparable to the average mercury content of America’s most commonly consumed species.

As Seychelles Study lead author Gary J. Myers said upon its release in 2003, “This study indicates that there are no detectable adverse effects in a population consuming large quantities of a wide variety of ocean fish. These are the same fish that end up on the dinner table in the United States and around the world.”

One reason that the Seychelles Study found no harm from very heavy fish consumption could come down to the mercury-blocking effects of selenium, which is abundant in almost all commercial fish. There is ample evidence that dietary selenium prevents the body from suffering damage from dietary mercury.

As University of North Dakota mercury-selenium expert Dr. Nicholas Ralston told Environment News Service in 2005, “Commercial ocean fish are uniformly rich in selenium and therefore protect humans from any mercury toxicity [from fish consumption].”

(For more on this topic, see our accompanying article, “Mercury-Fighting Mineral in Fish Overlooked in Heated Debate.”)

While commercial fish are very rich in this essential mineral, selenium is very scarce in the Pilot whales that made up most of the seafood diet in the Faroe Islands, where children are alleged to have suffered very subtle mental deficits.


Sources
  • Committee on the Toxicological Effects of Methylmercury, Board on Environmental Studies and Toxicology, National Research Council. Toxicological Effects of Methylmercury: Executive Summary. Accessed online December 6, 2006 at http://newton.nap.edu/execsumm_pdf/9899.pdf
  • Moore L. Follow Up to Utility Industry-Funded Study Leads to Finding that Mercury in Fish No Problem, Scores of Independent Studies Suggest Otherwise: Seafood Industry Hypes Lone Study Criticized by National Academy of Sciences. May 15, 2003. Accessed online December 6, 2006 at http://www.ewg.org/issues/mercury/20030521/index.php
  • MercuryFacts.com. Accessed online December 6, 2006 at http://www.mercuryfacts.com/
  • van Wijngaarden E, Beck C, Shamlaye CF, Cernichiari E, Davidson PW, Myers GJ, Davidson PW, Myers GJ, Weiss B, Shamlaye CF, Cox C. Prenatal methyl mercury exposure from fish consumption and child development: A review of evidence and perspectives from the Seychelles Child Development Study. Neurotoxicology. 2006 Apr 15; [Epub ahead of print]
  • Axtell CD, Cox C, Myers GJ, Davidson PW, Choi AL, Cernichiari E, Sloane-Reeves J, Shamlaye CF, Clarkson TW. Association between methylmercury exposure from fish consumption and child development at five and a half years of age in the Seychelles Child Development Study: an evaluation of nonlinear relationships. Environ Res. 2000 Oct;84(2):71-80.
  • Myers GJ, Davidson PW, Palumbo D, Shamlaye C, Cox C, Cernichiari E, Clarkson TW. Secondary analysis from the Seychelles Child Development Study: the child behavior checklist. Environ Res. 2000 Sep;84(1):12-9.
  • 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 May 17;361(9370):1686-92.
  • Palumbo DR, Cox C, Davidson PW, Myers GJ, Choi A, Shamlaye C, Sloane-Reeves J, Cernichiari E, Clarkson TW. Association between prenatal exposure to methylmercury and cognitive functioning in Seychellois children: a reanalysis of the McCarthy Scales of Children's Ability from the main cohort study. Environ Res. 2000 Oct;84(2):81-8.
  • Davidson PW, Myer GJ, Shamlaye C, Cox C, Gao P, Axtell C, Morris D, Sloane-Reeves J, Cernichiari E, Choi A, Palumbo D, Clarkson TW. Association between prenatal exposure to methylmercury and developmental outcomes in Seychellois children: effect modification by social and environmental factors. Neurotoxicology. 1999 Oct;20(5):833-41.
  • van Wijngaarden E, Beck C, Shamlaye CF, Cernichiari E, Davidson PW, Myers GJ, Clarkson TW. Benchmark concentrations for methyl mercury obtained from the 9-year follow-up of the Seychelles Child Development Study. Neurotoxicology. 2006 Jun 2; [Epub ahead of print]
  • 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 May 17;361(9370):1686-92.
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