A Call for Tougher Standards on Mercury Levels in Fish

In response to industry pressure, the U.S. Food and Drug Administration has failed to set adequate restrictions on mercury levels in fish. Now the Obama administration must move forcefully to tighten those standards and warn the public which fish are less safe to eat.

Nine years ago, dozens of patients — some my own, some referred by fellow San Francisco physicians — began showing up in my office with similar symptoms that included fatigue, hair loss, headache, muscle and joint pain, and various neurological ailments. My effort to solve this medical mystery, and discover the thread that united these people, has led to a decade-long investigation of one of the most toxic substances on the planet — methylmercury — and a slowly growing realization that the U.S. government has taken woefully inadequate steps to safeguard Americans from this health threat.

The common link among all these patients was a regular diet of fish — and an inordinately high level of mercury in their bodies. When they stopped eating fish, their mercury levels returned to normal, and nearly all reported that their symptoms disappeared.

FDA inaction has exposed the public to a roulette game of mercury doses and leaves the heavy fish consumer at risk.

Yet even today, after other cases of mercury toxicity from consumption of predatory fish, the public remains largely in the dark about the dangers of methylmercury and the government is considering loosening, not tightening, its already weak standards on mercury in fish. The U.S. Food and Drug Administration (FDA) has issued only one advisory on the subject, which recommends that women of childbearing age, pregnant women, nursing mothers, and infants limit their consumption of fish to 12 ounces a week. The FDA has decreed that fish is safe to eat if its flesh contains less than 1 microgram per gram of mercury — a level that many scientists consider too high and that was established using questionable data. In Japan, for example, where per capita fish consumption is high, the government has advised consumers who regularly eat fish to restrict their fish consumption to species with less than 0.3 micrograms per gram of mercury.

And even as the American public is being urged to eat more fish as a heart-healthy alternative to meat, the FDA still has not issued any guidelines about which types of fish are relatively low in mercury — sardines, anchovies, herring, sole, wild salmon — and which have high levels: swordfish, shark, sea bass, tilefish, and some species of tuna. This failure has exposed the public to a roulette game of mercury doses and leaves the heavy fish consumer at risk for excess mercury and adverse health effects. Scientists from the Environmental Protection Agency (EPA) estimate that as many as 600,000 babies are born each year at risk of neurological and developmental problems because their mothers have high blood mercury levels from fish consumption.

The Obama administration now has a chance to take action on an important environmental and public health issue that has only worsened in recent years. During the Bush administration, the fishing industry and the utility industry — whose coal-burning power plants emit most of the mercury that winds up in the nation’s waterways and oceans — fought hard to loosen standards governing methylmercury. Under industry pressure, the EPA ignored its own independent scientific study about the risks of mercury poisoning to human health and issued rules that effectively exempted mercury emissions from the Clean Air Act, launching instead a system that would have allowed power plants to slowly reduce mercury emissions over decades. Fortunately, last year the U.S. Court of Appeals for the District of Columbia Circuit overturned the EPA rule, saying it ignored scientific studies and endangered human health.

During the Bush administration, the fishing and utility industries fought hard to loosen standards governing methylmercury.

In the final weeks of the Bush administration, the FDA attempted to weaken its lone mercury advisory by issuing a draft report saying that the benefits of omega-3 fatty acids in fish far outweigh the risk of mercury and that pregnant women should eat more fish than the currently recommended 12 ounces per week. That risk assessment did not rely heavily on the current literature, nor did it fully address the extent of mercury effects on human health. In fact, the report stated that the FDA’s risk assessment relied “heavily” on data from a massive mercury poisoning in Iraq in 1972, studies of which recommended levels of mercury in humans that far exceed what doctors now consider safe.

That FDA draft report on weakening mercury standards for pregnant women is still under consideration. And if President Obama intends, as he promised in his inaugural address, to “restore science to its rightful place,” one of the first steps his FDA regulators should take is to shelve that draft as part of a sweeping effort to at last begin reducing mercury emissions from power plants and establishing safe mercury levels in fish and in humans.

When the first mercury poisoning patients arrived in my office nine years ago, little did I know that my efforts to diagnose and cure them would lead to a decade-long odyssey during which I would discover just how little our public health system has done to protect the American people from mercury. I am an internal medicine specialist and diagnostician known by my colleagues as someone who likes the challenge of solving medical riddles. This mystery, however, was not that difficult to unravel. When I took a history of the patients, the common denominator among them was their high consumption of certain kinds of fish — swordfish, sea bass, halibut, ahi tuna, and other larger, long-lived species — that accumulate mercury over the years from the smaller prey they consume.

Knowing how mercury “bio-accumulates” in fish, I of course began to suspect the toxic substance as a culprit and ordered blood tests. Nearly all the patients had high mercury levels, with one woman showing blood levels more than 20 times the accepted standard and one boy with mercury levels in his hair 15 times the safe standard. When the patients removed fish from their diets, the symptoms gradually receded in nearly all cases.

When the patients removed fish from their diets, their symptoms gradually receded in nearly all cases.

Conflicting information about methylmercury in fish was so extensive, it piqued my interest. I therefore went on a quest, which I describe in Diagnosis: Mercury: Money, Politics and Poison, to find out why no one really could agree on what symptoms constituted mercury toxicity, what the treatment was, and how much mercury a person could tolerate before he or she sustained irreversible damage. I initially recognized that my patients had generally shown mild to moderate symptoms of mercury poisoning, but soon learned that other conditions can also be linked, including tremors, permanent brain damage, cardiovascular disease, infertility, and autoimmune antibodies.

The harmfulness of mercury has long been known — the expression “mad as a hatter” stems from brain damage sustained by 19th-century hatmakers who used mercury to soften felt — but when it comes to regulating a product or practice, history indicates that little or nothing is often done for years.

The most severe instance of mercury poisoning from ingesting fish occurred in Minamata and Niigata, Japan in the 1950s and 1960s, when chemical plants dumped mercury-contaminated waste into a bay where people caught and ate fish, killing scores and leaving hundreds with grave neurological illnesses. In Canada, the Ojibway people of Ontario were poisoned with methylmercury when chemical factories and pulp and paper mills dumped their effluent into the lakes and streams.

The largest mercury poisoning to date occurred in Iraq in 1972 when Saddam Hussein, then vice president of Iraq, oversaw the delivery of a huge shipment of grain — which had been sprayed with a mercury-laced fungicide — to restive Iraqi provinces, particularly Kirkuk. The initital death toll from the suspicious poisoning, which the Ba’athist government said was an accident, was 450. But my book research showed that the death toll was far higher, with thousands more sickened.

In 1969, the FDA set a standard for safe levels of mercury in fish at below 0.5 micrograms per gram. Because the amount of methylmercury in swordfish on average was 1.0 microgram per gram, most swordfish were deemed unfit for sale.

Our current action level of 1.0 microgram of mercury per gram of fish is based on data from a poisoning that occurred at the hands of Saddam Hussein.

The fishing industry set to work to loosen the standard to 1.0 microgram and helped fund studies of mercury toxicity. Scientists traveled to Iraq to research the poisoning, and at a 1977 trial to determine safe levels of mercury in fish, the main evidence presented by the fishing industry was from the study in Iraq. The judge presiding in the case accepted that evidence and ruled to loosen the standard, which means that our current action level of 1.0 microgram of mercury per gram of fish is based entirely on data from a poisoning that occurred at the hands of Saddam Hussein and his Ba’ath government, and that allows for a human blood mercury level of 400 micrograms per liter — a level 80 times that currently recommended by the EPA.

The biggest blowback to the notion that methylmercury in fish can be harmful to human health has come from lobbying groups affected by mercury regulation. These include the National Fisheries Institute (NFI), the U.S. Tuna Foundation, and the Electric Power Research Institute (EPRI), which represents operators of coal-fired power plants. These organizations have their own set of scientists and have funded studies that, not surprisingly, have routinely recommended lax action levels for mercury in fish.

With the arrival of the Obama administration and a hoped-for revival of respect for science at the FDA and EPA, I recommend the following steps:

  • Draw up, and widely publicize, a simple chart for consumers that ranks the mercury content of fish, with the most contaminated species (such as swordfish) at the top and the least contaminated (such as sardines) at the bottom. Establish a conservative, interim mercury standard — such as 0.3 micrograms of mercury per gram of fish — and recommend that fish with high mercury levels be consumed infrequently or not at all.
  • Launch efforts to sharply reduce mercury pollution from coal-fired power plants in the U.S. and work to help major, coal-developing countries, such as China, slash their emissions.
  • Conduct scientifically rigorous studies of populations with high mercury levels from eating fish — such as in the Faroe and Seychelles islands — and use this data to revise the current standard, which is not protective.
  • Instruct physicians to monitor mercury levels in patients who are high consumers of fish, and make sure doctors are advised that safe blood levels are less than 5 micrograms per liter — far lower than the standard the FDA used to establish an action level for fish.

If the fishing industry continues to push its product, regardless of mercury content, as a “miracle nutrient,” and the FDA fails to advise consumers about mercury content, we will see many more victims. But I am hopeful that, with thorough scientific study and responsible regulation, we will finally come up with a rational solution to this serious public health issue.