Last April, at the first federally sponsored symposium on mercury and public health, Dr Jane Hightower of San Francisco's California Pacific Medical Center presented some alarming findings: nine out of 10 Bay Area residents who ate fish regularly had elevated blood-mercury levels and associated health complaints.
"People are having symptoms just like the hatters," says Hightower alluding to the 19th and early 20th century "mad hatters" who were exposed to mercury nitrate used to process fur pelts. "They have weakness, headache, stomach upsets, hair loss, allergy symptoms, and there's a question of autoimmune disease."
Hightower is not the only medical professional who is worried about mercury. Recently, many Bay Area physicians have begun questioning their patients about fish intake and measuring blood-mercury levels. Dr. Laurie Green of the Pacific Women's Obstetrics and Gynecology Medical Group now asks her patients to record not only what fish they eat but how much: "I've been astounded at how many patients have high mercury levels and underestimate their fish intake," she writes. Green was amazed to discover "how much better they feel once they cut out the contaminated food."
Public Health Crisis?
Concern over toxic mercury levels in the general population is growing. The dangerous poison is showing up everywhere: not just in smokestacks, lakes and oceans, fish, dental amalgams and vaccines, but also in Arctic sunrises, wildfire smoke, landfill emissions and homes. Coal-burning power plants – the largest source of industrial mercury pollution – spew out mercury that ends up in lakes and oceans, where bacteria convert it to methylmercury.
This potent neurotoxin bioaccumulates in freshwater fish and seafood and is especially dangerous to the developing fetus. The Environmental Protection Agency warned in January that one in six children born annually may be at risk from high exposure to methylmercury in the womb.
"We have some exposures occurring now in the United States that have produced blood mercury a lot higher than anything we would have expected to see," says Kate Mahaffey of the EPA's Office of Prevention, Pesticides and Toxic Substances. "And this appears to be related to consumption of larger amounts of fish that are higher in mercury than we had anticipated."
How Much Fish is Safe?
Everyone agrees that mercury is toxic. The question is how much mercury poses a risk? Scientific uncertainty has spawned heated debate over whether the EPA's March 19 advisory to pregnant and nursing women is adequate. The advisory cautions against eating shark, swordfish, king mackerel and tilefish because of their high mercury content but allows up to 12 ounces a week of shrimp, canned light tuna and salmon.
While no one doubts the benefits of eating fish, evidence is mounting that methylmercury not only harms the developing fetal brain but could also play a role in common adult complaints like insomnia, fatigue, and serious heart and autoimmune diseases.
Dr. Paul Dantzig of Columbia University's School of Medicine has linked a distinctive skin rash to mercury exposures at levels well below the EPA "safe" limit. Dantzig (who encounters two or three patients a week with mercury poisoning) reports that the rash disappears when people stop eating fish or undergo chelation therapy to reduce mercury levels. "When it comes to mercury," Dantzig says, "there is no safe level."
The EPA had set the "safe" exposure level at 5.8 micrograms of mercury per liter of blood, which is thought to be protective of fetal development. Some scientists think the level should be higher although a recent analysis of umbilical cord blood suggests it should be lower. And so far no one knows exactly what blood mercury level triggers problems in adults.
Mercury's toxicity was vividly illustrated in the 1950s by the deaths and deformities resulting from the release of methylmercury into Minamata Bay in Japan. Hundreds more died in Iraq in 1972 after eating bread made from seeds treated with methylmercury.
How dangerous is methylmercury harbored by seafood today? How much fish is it safe to eat? Guidelines for pregnant women, nursing mothers and young children, based on a long-term study, are outlined in a March joint-advisory by the EPA and Food and Drug Administration. The study, conducted in the North Atlantic Faroe Islands, shows that the more mercury children were exposed to in the womb, the worse they score on neuropsychological tests, with measurable damage still showing up in 14-year-olds.
But critics say the advisory – aimed at keeping mercury intake below the "safe" level – is ambiguous; acan of albacore tuna, three times as high in mercury as "light" tuna, consumed once a week could put some women's mercury over the limit.
David Acheson of the FDA's Center for Food Safety and Applied Nutrition says the "safe" limit is not a "bright line" but contains a tenfold uncertainty factor. It's also true that the EPA's exposure limit is among the lowest (and therefore most restrictive) worldwide, set at less than half the World Health Organization guideline. "We know that people are going to get a little bit above the limit sometimes," says Acheson "But we've got to be thinking of the risk-benefit message."
Fish, a healthful high-protein, low-fat, low-cholesterol alternative to meat, is recommended for pregnant women because it contains omega-3-fatty acids that are beneficial for fetal brain development. Given the current debate over the harmful effects of mercury, Dr. Hightower recommends that everyone choose low-mercury, high-omega-3 fatty acid fish such as salmon.
But blood-mercury concentrations that should set off alarm bells for obstetricians just plummeted from 5.8 to 3.5 micrograms/liter, after a recent Japanese study discovered that mercury in umbilical cord blood was 1.6 times as high as in maternal blood. This prompted the EPA in January to revise the estimate of newborns annually at risk from mercury from 300,000 to 650,000.
A Fishy Study
To further muddy the waters, a long-term study of youngsters in the Seychelles Islands found no damage to children whose mothers ate an average of 12 fish meals a week when pregnant. The fish had about the same concentration of methylmercury found in US fish.
"We do not really understand why the Seychelles population has not shown effects that tend to be consistent with most of the rest of the literature," says Mahaffey. "But we hope that, over time, it will become clearer why this study is unusual."
Others, like Hightower, are troubled that the Seychelles study received close to half-a-million dollars in funding from the Electric Power Research Institute, the National Tuna Foundation and the National Fisheries Institute – a fact that lead author Gary Myers failed to disclose in his testimony to Congress when he vouched for the safety of unrestricted fish consumption.
More worrisome still is that those doctors who rely upon the profession's "Bible," the New England Journal of Medicine, are getting only one-sided and deceptively authoritative guidelines. In an October 2003 NEJM article "Review of the Toxicology of Mercury," the same Seychelles study authors write: "Fish consumption has clear health benefits, and the risk posed by exposure to mercury is currently speculative."
Informing the Public
Many women remain in the dark over mercury's potential dangers. Surveys show that over one-third of women of childbearing age don't know that eating mercury-tainted fish could harm their offspring. "Clearly the message is still not getting out," says Michael Bender of the Mercury Policy Project.
Several consumer and environmental groups suggest that mercury concentrations should appear on fish packaging, especially canned tuna.
California supermarkets now post cautionary statements: "Warning! Nearly all fish and seafood contain some amount of mercury and related compounds, chemicals known to the State of California to cause cancer, and birth defects or other reproductive harm. Certain fish contain higher levels than others. Pregnant and nursing women, women who may become pregnant, and young children should not eat the following fish: swordfish, shark, king mackerel, tile fish. They should also limit their consumption of other fish, including fresh or frozen tuna."
It's a warning that many consumer and environmental groups believe should appear nationwide.
EPA limits are calculated to protect developing fetal and newborn brains but what about dangers to adults? Pregnant women who gave birth to deformed offspring in Japan appeared normal, but follow-up studies show that Minamata residents experienced more fatigue, stomach problems, muscle stiffness, insomnia and memory loss than those living elsewhere.
Jane Hightower sees similar symptoms in her practice. Eighty-nine percent of the patients she tested, who ate fish regularly, had mercury levels above the EPA limit. Her subjects ate 30 different kinds of fish, and most patients' symptoms disappeared when they stopped eating high-mercury fish such as swordfish (their mercury levels also declined). All but two patients reduced their mercury levels to below the EPA limit by 41 weeks.
Both Hightower and Dantzig think mercury exacerbates autoimmune diseases. Animal studies confirm that, depending on genetic predisposition, mercury can trigger such disorders. People accidentally exposed to mercury in the workplace also show up with immune disturbances. "It definitely affects the immune system," says Dantzig. Hightower speculates that some people could be more sensitive to higher levels of mercury. Others agree the hypothesis warrants testing.
Mercury In the Environment
Health officials are worried not just about supermarket shoppers who eat fish frequently, but other groups too – sport, commercial and subsistence fishermen, as well as the elderly. Fish consumption advisories warn of high mercury levels and other contaminants in one-third of all lake water in the US. "The higher exposures we're seeing are often in males and sports fishermen," says Henry Anderson MD, Chief Medical Officer of the Wisconsin Division of Public Health.
Older people are vulnerable because their bodies have more difficulty eliminating toxins. They are also more susceptible to heart disease. The American Heart Association credits omega-3-fatty acids in fish with lowering heart disease risk, but European studies suggest mercury may counter that benefit.
The Healthy Californians Bio-monitoring Program, a bill introduced by Senator Deborah Ortiz (D-Sacramento) and sponsored by the Breast Cancer Fund and Commonweal called for the nation's first-ever statewide program to measure the concentration of chemical pollutants in breast milk, blood and urine. It failed to pass the Assembly Health Committee in late June by just one vote. Such a law "would help to understand how our communities in California are exposed to toxic chemicals," says Erin Malec of the Breast Cancer Fund. "And how effective the chemical regulatory process is."
While it's true that limiting fish consumption can reduce mercury levels in human blood, the environment poses a graver long-time threat. Mercury doesn't vanish. If it's not captured and isolated, it will continue to accumulate in the environment. And it may be an even bigger health problem than most people anticipate.
"The trouble is doctors don't know anything about it. Mercury is a major, major problem. This stuff keeps building up and building up and it's becoming a real nightmare," says Paul Dantzig. "This is one of the most important things in medicine right now and nobody cares. That's the whole problem."