How Mercury in Fish Is Regulated

When it comes to fish and shellfish, there is widespread consensus -- as evidenced by the recommendations of the 2005 Dietary Guidelines for Americans-- that seafood is an important part of a healthy diet. That is because fish and shellfish contain high-quality protein and other essential nutrients, are low in saturated fat, and contain omega-3 fatty acids.

But most fish also contain trace amounts of methylmercury, the organic form of mercury found in bodies of water. At high levels, methylmercury may harm an unborn baby or young child's developing nervous system, which is why the federal government has stringent regulations regarding mercury levels in the fish consumed in the U.S.

Which agencies are responsible for regulating mercury levels in seafood and what are their specific roles? The following provides an overview of how fish and seafood are regulated in the United States.

Who Regulates Seafood in the United States?

In the U.S., the responsibility for regulating mercury levels in fish and seafood is shared by the U.S. Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA). Specifically, the FDA regulates fish and seafood that is sold in food stores and restaurants. The EPA regulates the emissions of pollutants such as mercury into the environment and works with state governments to develop fresh water fish advisories as needed.

Whereas FDA is responsible for monitoring mercury levels in commercially sold fish, it is EPA’s responsibility to monitor the amount of mercury in fish caught recreationally in local rivers and streams. As part of this responsibility, EPA works with the states which also have the authority to issue local advisories, depending upon pollution and contamination levels.

EPA’s basis for regulating levels of methylmercury in fish is the reference dose – or RfD. The RfD is used as the standard for developing seafood consumption advice in the United States. Defined as an estimate of the highest daily dose of a chemical that the most sensitive in the population can be exposed to over a lifetime of exposure without experiencing an adverse effect, the reference dose for mercury in fish is 0.1 microgram per kilogram of body weight (bw) per day (µg/ kg-day) or 0.7 µg/kg bw/week. This regulatory standard was based on calculating the lowest dose at which a subtle subclinical effect was thought to occur (meaning the effect was not actually observed) and then building in a ten-fold safety factor.

This approach to regulating mercury levels in fish makes EPA’s reference dose the most stringent standard in the world. For example, the United Kingdom’s Food Standards Agency (FSA) uses the safety standard applied by the World Health Organization (WHO) -- called the Provisional Tolerable Weekly Intake (PTWI) -- that allows 3.3 micrograms of methylmercury per kilogram of body weight a week (ug/kg bw/week) for the general population and 1.6 micrograms of methylmercury per kilogram of body weight (ug/kg bw/week) for pregnant and nursing women.

Besides being the most stringent regulatory standard, EPA’s reference dose is based solely on calculating possible risks, and does not factor in potential health benefits. As a result, EPA cautions the public not to confuse the reference dose with the term “safety factor.” In its paper “Reference Dose: Description and Use in Health Risk Assessments,” EPA states: “The term ‘safety factor’ suggests, perhaps inadvertently, the notion of absolute safety (i.e. absence of risk). While there is there is a conceptual basis for believing in the existence of a threshold and ‘absolute safety’ associated with certain chemicals, in the majority of cases a firm experimental basis for this notion does not exist.”

Protecting Special Populations

In addition to these regulatory safeguards, both FDA and EPA recognize the need to give special advice to pregnant and nursing women, women who might become pregnant and young children about how to receive the benefits of fish while reducing their exposure to mercury levels. Accordingly, on March 19, 2004, FDA and EPA issued a joint advisory for these special populations based on calculating a 10-fold safety factor -- meaning that if pregnant and nursing women follow this advice, they will be consuming levels of mercury in fish that are at least ten times lower than the lowest level for any known risk.

Intended to protect the public health while still allowing pregnant and nursing women to reap the health benefits of eating fish during pregnancy, the FDA/EPA advisory has identified 5 commonly eaten fish with very low mercury levels: shrimp, salmon, pollock, catfish and canned light tuna. According to the government’s advisory, pregnant and nursing women, women who might become pregnant and young children can safely eat up to 12 ounces a week of these fish. The government advisory also tells these special groups that they can safely eat up to 6 ounces a week of canned albacore tuna. In general, there are 2 ounces of albacore in a typical serving.

In contrast, the advisory identifies those types of fish that have higher levels of methylmercury and should be avoided by pregnant and nursing women, women who might become pregnant and young children. These fish are shark, swordfish, tilefish and king mackerel.

Science Supporting How Mercury Is Regulated

Because mercury in the environment has become a national concern, many interest groups question whether the way in which FDA and EPA regulate mercury levels in fish is adequate. A key question posed by activists is how many mothers and babies are actually at risk from exposure to high levels of methylmercury.

To answer this question, the federal Centers for Disease Control and Prevention (CDC) used its ongoing National Health and Nutrition Examination Survey (NHANES) to analyze the amount of mercury in the blood of more than 3,600 women of childbearing age and 1,500 children aged one to five years. Published in the November 5, 2004 issue of the Morbidity and Mortality Weekly Report, the CDC’s new study confirms that mercury levels from fish consumption for women and young children in the United States are below the level of concern.

This CDC study has added significance because it showed that the concentrations of mercury in the blood of American women have actually declined over a four-year period (1999-2002). Compared to 1999 when the CDC estimated that 8 percent of U.S. women had mercury levels at or slightly above the EPA’s reference dose, this number has dropped to 6 percent. CDC concluded that women with mercury concentrations at this level are not at risk because EPA built in a ten-fold safety factor when it established its reference dose.

At the same time, the new CDC report confirms previous findings that children in the United States have mercury levels below the EPA’s reference dose and are not at risk from consuming seafood.

Besides CDC’s findings, the U.S. Department of Agriculture (USDA) has analyzed the diets of American women of childbearing age using several surveys. USDA researchers examined several factors that could increase the amount of mercury a woman could ingest through seafood consumption: 1) heavy consumption of fish and shellfish, 2) consumption of fish that contain relatively high levels of methylmercury, 3) frequency of eating a specific type of fish, and 4) the methylmercury in a range of commercial fish samples. Based on this analysis, USDA concluded that American women are not exposed to levels of methylmercury that would place their unborn children at risk.

Also supporting this view is the Agency for Toxic Substances and Disease Registry, part of the Department of Health and Human Services. ATSDR published the Toxicological Profile for Mercury following a thorough review of the peer-reviewed literature examining the substance’s hazardous properties. Based on this analysis, ATSDR concluded that the vast majority of fish purchased in the market in the United States do not have mercury levels that pose a risk to anyone, including pregnant women.

Beyond this review by U.S. government agencies, several other countries where the populace consumes significantly more fish, have weighed in with similar conclusions. In Japan, a 2004 study found that the vast majority of Japanese women and their offspring are not at risk by mercury levels that exceed the EPA’s reference dose. Conducted by researchers at the National Institute for Minamata Disease, the study examined the concentrations of mercury in the hair of 3,686 adults in five Japanese districts and found that 72 percent of all Japanese women and two-thirds (66 percent) of those considered of childbearing age (15 to 49 years) exceeded EPA’s reference dose.

In addition to the Minamata study, the United Kingdom’s Food Standards Agency (FSA) also published a report in 2004 that reached similar conclusions. The U.K. report cited a recent study conducted by the Medical Research Council (MRC) that tested 1,320 adults. The MRC report concluded that there is no evidence that people consuming large amounts of fish have increased health risks from exposure to methylmercury.

Supporting this view is another important study of British women that was reported in the July 2004 issue of Epidemiology. Conducted by researchers at the U.S. National Institute of Environmental Health Sciences (NIEHS), this study demonstrated that the children of pregnant women who consumed between one to three fish meals per week had significantly higher scores on a battery of tests measuring language, communications and motor skills than the children whose mothers did not consume fish at all. Further, the study showed no adverse developmental effects associated with the low mercury levels found in the U.K., which is consistent with the mercury levels documented in the U.S.