Of particular concern to public health and environmental officials is the deposition of mercury in aquatic ecosystems where it can be transformed into methylmercury. In this form, mercury readily bioaccumulates up the food chain, providing a pathway of exposure to animals and humans as they consume contaminated fish. Efforts to monitor mercury levels in fish have been underway in the U.S. since the 1970s. The results of these monitoring programs indicate that elevated levels of mercury are present in certain fish species and water bodies. Consistent with mercury's ability to bioaccumulate, predatory fish that are high on the food chain, older, and larger tend to have higher mercury concentrations. Conversely, smaller, younger, fish that feed lower on the food chain generally have lower mercury levels.

In 2004, the U.S. Food and Drug Administration (FDA) and U.S. Environmental Protection Agency (EPA) issued a joint statement of advice concerning mercury in seafood for women that are pregnant, women that may become pregnant, nursing mothers, and young children. If this guidance is followed, women and their young children can still receive the benefits of eating fish while confident that they have reduced their exposure to mercury. The purpose of the three recommendations noted below is for selecting and eating fish that are lower in mercury.

1. Do not eat shark, swordfish, king mackerel, or tilefish because they contain high levels of mercury.
2. Eat up to 12 ounces (2 average meals) a week of a variety of fish and shellfish that are lower in mercury.
   • Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish.
   • Another commonly eaten fish, albacore ("white") tuna has more mercury than canned light tuna. When choosing your two meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of albacore tuna per week.
3. Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to 6 ounces (one average meal) per week of fish you catch from local waters, but do not consume any other fish during that week.

This advice is based on the EPA reference dose (RfD) for mercury of 0.1 microgram/kilogram per day (0.1ug/kg-day).

Because some uncertainty exists about the health risks associated with low levels of methylmercury exposure, states use different approaches in developing fish consumption advisories. Most states believe methylmercury is of concern and have issued consumption advisories for fish starting at contamination levels ranging from 0.3 to 1 part per million (ppm). The advisories are intended to protect sensitive individuals (i.e., pregnant women, nursing women, and children) and segments of the population that frequently consume freshwater sport fish, as well as the general public.

According to the EPA's National Listing of Fish Advisories (NLFA) website, there were 3,080 fish consumption advisories for mercury contamination in 2006. And 80 percent of all fish consumption advisories were based at least partly on mercury. In total, 48 states, 1 U.S. territory, and 2 tribes have issued mercury advisories. Currently, 35 states have statewide fish consumption advisories for mercury either in freshwater lakes and rivers, coastal waters, or both.

Sources: EPA/FDA, "What you need to know about mercury in fish and shellfish: 2004 EPA and FDA Consumer Advice": http://www.epa.gov/waterscience/fish/advice/
The National Listing of Fish Advisories Website: http://www.epa.gov/waterscience/fish/advisories/

Last Updated: 11/06/08