Mercury FAQs

What is methyl mercury?
Methyl mercury is not the shiny stuff in thermometers (what scientists call "elemental" mercury), but it sometimes starts out that way. When mercury is deposited into water (usually by natural sources like underwater volcanoes), certain bacteria convert it into methyl mercury. Then it enters the food chain in fish. Larger fish usually contain more methyl mercury than smaller fish, because the substance "accumulates" as big fish eat their smaller prey.

Although methyl mercury can be toxic at very high doses, the World Health Organization has concluded that "the general population does not face a significant health risk from methyl mercury" in the fish we eat. This is because eating fish -- even the fish with the most mercury -- doesn't expose us to enough methyl mercury to be harmful.


But the U.S. government says tuna and other fish could be unsafe to eat. Won't my kids' IQ drop if they eat too much tuna?
Americans whose blood-mercury concentrations are slightly above the government's recommended levels are nowhere near any actual danger.

The Food and Drug Administration (FDA) has an "Action Level" for methyl mercury in fish, and the Environmental Protection Agency (EPA) has a "Reference Dose" for mercury in the human bloodstream. And both of these measures have a built-in ten-fold "Uncertainty Factor." That means that there's a 1,000-percent difference between the amount of methyl mercury that might be harmful and the amount government agencies (and a growing faction of opportunistic activists) want you to consider "unsafe."

Applying this logic, it would make sense for a policeman to give you a speeding ticket for going 7 miles-per-hour in a 65-mph zone! Even though the Department of Transportation says it's unsafe to go faster than 65, no one would take a "6.5 mph" speed-limit sign seriously. Especially if the sign were erected by Greenpeace.


Even so, shouldn't we be a little bit scared of crossing that "Reference Dose" line?
The Japanese eat far more fish than we do. According to a 2004 study published in the Journal of Health Science, fully 87 percent of Japan's population -- including 74 percent of Japanese women of childbearing age -- have enough mercury in their bloodstream to be considered above the U.S. EPA's reference dose. But Japanese children routinely outscore American kids on standardized tests. The same is true of over-achieving Chinese children in Hong Kong, whose blood-mercury levels are between 10 and 18 times as high as their counterparts in the United States.

The U.S. Food and Drug Administration understands this. At a July 2003 EPA/FDA meeting, Dr. Michael Bolger (Chief of the FDA's Contaminants Branch) said that "92 percent of women of child-bearing age already consume below [the EPA's mercury] reference dose, while the top 8 percent still have a safety margin of about eight-fold."

The CDC's most recent National Health and Nutrition Examination Survey (NHANES) showed that absolutely no American men, women, or children had mercury levels near the government's theoretical risk level -- which, again, is 10 times greater than the "reference dose."


But I've heard that mercury, in the amount of fish we typically eat, is harmful. I've heard it from so many sources that I assumed it was true.
That's understandable. Activist groups, regulators, and politicians have jumped on this bandwagon in recent years, so it's become hard to discern who's telling the truth.

The bigger picture involves environmental groups who are unhappy about U.S. power companies that burn coal -- emitting small amounts of mercury into the air -- in order to generate electricity. According to research published in the journal Atmospheric Environment, only about one percent of global mercury emissions comes from U.S. power plants (61 percent comes from natural sources, and the rest originates from outside the United States). But activists hope that scaring Americans about the fish they eat and feed their children will produce a groundswell of opposition to fossil-fuel-based power generation.

The U.S. groups running mercury scare campaigns include Environmental Defense, the Environmental Working Group, Friends of the Earth, Greenpeace, the Natural Resources Defense Council, Oceana, the Sierra Club, the Turtle Island Restoration Network, the Water Keeper Alliance, and over a dozen more.


What's the harm in being extra careful? Why should we risk our health, especially those of us who are pregnant?
The real risk is in eating less fish, not more -- especially in the case of pregnant women. There's a broad scientific consensus that the Omega-3 fatty acids found in fish (including swordfish and tuna) are crucial for both fetal brain development and maternal health.

The mercury health scare for pregnant women began in earnest in 2002, after a National Research Council committee claimed that fetuses could be damaged by mercury in fish eaten by their mothers. But soon afterward Dr. Charles Lockwood, OB/GYN chairman at the Yale School of Medicine, told a Scripps Howard reporter: "There is some junk science at work here. They can say whatever they want; we've reviewed the basis for their findings and there isn't a lot of substance to it."

The sad irony is that U.S. government guidelines, which are intended to safeguard the health of pregnant women and young children, result in lower fish consumption by everyone. This can actually put our health (especially women's health) at risk. And activist groups are magnifying the damage with reckless scare campaigns.

Alaska's state epidemiologist has said that "limiting consumption of fish and seafood may do more harm than good by reducing the consumption of health benefits." And Harvard's Dr. Eric Rimm told The New York Times in 2004: "The message of fish being good has been lost, and people are learning more about the hypothetical scare of a contaminant than they are of the well-documented benefits."


So is there a level of mercury that's harmful to humans or not?
Yes, but it's so high that Americans aren't likely to ever reach it -- even by eating frequent, generous portions of fish. Our bodies contain trace amounts of hundreds of chemical compounds that would be fatal in higher doses. Even Vitamin C can cause death in large enough amounts. Concentrated chlorine gas can be fatal, but we swim in pools of chlorinated water. And our brains require a tiny amount of arsenic in order to function properly. In higher doses, of course, arsenic is rat poison. The important thing to remember, as known for centuries, is that "the dose makes the poison."
In Iraq from 1971 to 1972, grain treated with a mercury-containing fungicide led to 6,000 hospitalizations and 500 deaths. The mercury levels measured in the hair of mothers from this region were as high as 674 parts-per-million. By comparison, the highest hair-mercury concentrations measured in American women of childbearing age are only 1.4 parts-per-million. That's a difference of over 48,000 percent.

And in the case of Japan's Minamata Bay, 111 people living near this body of water during the 1950s ate large amounts of fish that were artificially contaminated when a plastic factory dumped mercury-laden waste into the Bay. These fish had mercury concentrations as high as 40 parts-per-million, which is more than 20 times higher than the average found in the most mercury-heavy U.S. fish. And besides, the Japanese were undoubtedly eating more fish than Americans are accustomed to. A similar case ten years later involved 120 residents of Niigata, Japan who ate industrially contaminated fish. According to the University of Rochester's Dr. Thomas Clarkson, these Japanese poisonings are the only clinical cases anywhere in the scientific literature that document mercury poisoning from fish.


The Environmental Working Group, the Natural Resources Defense Council, and the Turtle Island Restoration Network all have websites with frightening "tuna calculators" showing how much fish is "safe" to eat. Are they wrong?
Yes, they're wrong. These propaganda exercises suggest that the EPA's "Reference Dose" is the level at which real harm occurs. But it's not. If they were more sincere, these activist groups would multiply their results by ten to account for the EPA's creative "Uncertainty Factors." Click here for a mercury calculator that shows the real risk in a wide variety of fish species.


Why do environmental groups scare the public with trumped-up claims about fish?
Two reasons: generating public outcry and raising money.

Most green groups that engage in food scare campaigns have hidden agendas. Those who are interested in limiting the use of coal-burning power plants to generate electricity are using fish in their campaigns. Even though these plants contribute less than two percent of the mercury in our environment, environmentalists hope the fear of mercury will scare the public enough to appeal to Congress for action. But most people don't obsess about the source of the electricity in their homes and offices, as long as the lights stay on. So scaremongers are attacking the fish we eat instead, reasoning that Americans will be more easily excitable about the food on their families' dinner tables.

In the world of activist fundraising, there's no denying that fear is a powerful tool. And environmental charities are using the public's fear of mercury in fish, mad cow disease, genetically modified foods, and farm pesticides (despite the lack of science to back up their claims) to raise tens of millions of dollars. Groups like Environmental Defense, the Environmental Working Group, Greenpeace, the Sierra Club, and the Water Keeper Alliance have put the mercury-in-fish issue front and center in frightening financial pitches to countless Americans. And until the public understands that the trace amounts of mercury in fish pose no real health danger, these shameless pleas for money will continue to bear fruit.

Even the animal-rights lunatics at People for the Ethical Treatment of Animals (PETA) have gotten into the act. In 2005 PETA began claiming on its website that fish contain "poison." In a candid moment on an animal-rights mailing list, PETA campaign director Bruce Friedrich admitted his strategy: "For people who don't care about the suffering of fish, I suspect this will terrify them into not eating them."