Mercury Advisories for Commercial Fish

In recent years, environmental policymakers have supplemented traditional pollution regulations with information disclosure programs to better inform the public about the health and other environmental risks of products and firm activities. One example of this approach is alerts about the health hazards from mercury contamination in certain food products. But just how effective are these mercury advisories, do they have any unintended consequences, and do they remove the need for direct regulation of mercury emissions? These are the important policy questions discussed in this week’s commentary by Jay Shimshack, who has done valuable research on this topic.

Next week’s commentary by Charles Howe discusses whether water laws in the western states lead to efficient use of water resources.

In the last several years, concern has arisen that mercury from commercial fish consumption may pose a significant threat to children’s neurological development. In 2001, the Food and Drug Administration (FDA) responded to increasing risk information by releasing a national advisory. It warned pregnant women, women who may become pregnant, and households with young children to limit their fish consumption. An advisory update was issued in 2004. Both advisories instructed at-risk groups to eliminate consumption of certain types of fish and cap consumption of all seafood, including canned fish.

To better understand this ongoing public health issue, it is useful to provide some context. Levels of mercury circulating in the environment have increased considerably over the last century. Coal-fired power plants are currently the largest source of anthropogenic mercury. When atmospheric mercury is deposited into surface water, bacteria convert the mercury into organic methylmercury. This then enters a fish’s bloodstream from water passing over their gills and accumulates in tissues. It also bio-accumulates up the food chain. Even in water where ambient mercury levels are extremely low, methylmercury concentrations may reach high levels in predatory species like tuna, king mackerel, swordfish, and shark.

For the general public, fish consumption is the primary source of exposure to mercury. Cooking and other forms of food preparation do not mitigate the risks. The FDA and other government agencies maintain that even modest mercury concentrations pose a risk of significant harm to the developing neurological systems of fetuses, infants, and young children. Consequences may include reduced IQ, learning and attention disorders, and generally slowed intellectual and behavioral development. Severe neurological illnesses, like cerebral palsy, may result from unusually high exposure. In adults, abnormally high mercury concentrations may contribute to brain damage, heart disease, blurred vision, slurred speech, and other neurological ailments, although such high concentrations are rare.

Despite the theoretical advantages of mercury advisories for managing risks, the big question is whether those advisories actually work in practice. Recent research suggests there may be serious limitations. Since a moderate amount of fish consumption provides significant health benefits to both adults and children – particularly in the form of IQ, stroke, and heart disease benefits from omega-3 fatty acid intakes – crude advisory responses or overreactions may mitigate advisories’ net public health effects. In short, there is a tension between mercury risks and seafood’s health benefits. Some members of the scientific community have even speculated that mercury advisories may have caused net harm if at-risk consumers responded to the advisories by reducing consumption of all fish rather than high-mercury fish alone.

A colleague and I have shown that this speculation is justified (Shimshack and Ward 2008). We found that at-risk consumers did reduce mercury intakes in response to the 2001 commercial fish advisory. In isolation, this is positive for public health. However, we also found that at-risk consumers substantially reduced their intake of beneficial omega-3 fatty acids. Further explorations revealed that at-risk consumers did not substitute high-mercury fish with low-mercury fish, nor did they differentially avoid high-mercury fish. They simply reduced consumption of all fish in response to the advisory. When we interpreted our results from a public health perspective, we found that the benefits of mercury reductions were approximately offset by the negative health effects of reduced overall fish consumption. In other words, on net, we found no public health benefits of the mercury advisory.

There are other concerns about mercury advisories as well. Co-authors and I found that advisories affect households differently (Shimshack, Ward, and Beatty 2007). Important groups of at-risk consumers, including the least educated, did not seem to react to mercury advisories at all. This may be a notable public health issue, since this group of consumers may be particularly poorly equipped to withstand negative health outcomes. Unintended spillover effects of these advisories are another factor. We found that some consumers not considered at-risk also reduced consumption in response to the advisory. This outcome is not consistent with policy goals.

In sum, the evidence justifies strong cautionary notes about commercial fish advisories. While the theoretical advantages of information policies for managing mercury in seafood are significant, the practical realities highlight important disadvantages. More research is needed, but the best available evidence suggests that national commercial fish advisories have no net public health benefits. Advisories must be more carefully crafted and disseminated. Mercury mitigation strategies might also appropriately begin to rely more on emissions reductions than consumption advisories alone.

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Views expressed are those of the author. RFF does not take institutional positions on legislative or policy questions.

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