In the past, there has been a concern about the mercury levels in our seafood supply. The information below has been gathered from the U.S. Department of Health and Human Services (USDHHS), the U.S. Environmental Protection Agency (EPA), and the Academy of Nutrition and Dietetics to better help you understand the issue.
Mercury is a natural substance in the environment and also permeates the air through industrial pollution. When mercury is transferred to waterways, it becomes a more toxic form of methylmercury, and is absorbed by fish, with greater absorption levels for fish with longer lifespans and feeding cycles. Food processing, preparation, or storage will not significantly reduce the amount of mercury in fish.
Pregnant women are at the greatest risk, since babies developing in the uterus appear to be the most vulnerable to the effects of mercury on the nervous system. A general recommendation for women who are pregnant or may become pregnant, nursing mothers, and young children is to avoid some types of fish and opt for shellfish and other fish that are lower in mercury. The effects of mercury on babies and children may not be noticed until development occurs, such as walking or talking. These stages may be delayed due to high levels of mercury exposure. Memory, language, and attention span also may be affected. Effects on adults may include headaches, fatigue, numbness in the hands and feet, problems with concentration, and possibly even risk of heart attack.
See the following lists for fish mercury concentration. Note that mercury levels vary in commercial fish and shellfish and that not all fish are the same.
Large predator fish, which are higher on the food chain, have higher mercury levels:
- King mackerel (mean .073 ppm (parts per million))
- Shark (.99 ppm)
- Swordfish (.97 ppm)
- Tilefish - Gulf of Mexico (1.45 ppm)
Small or short-lived species have lower mercury levels:
- Anchovies (.04 ppm)
- Butterfish (.06 ppm)
- Catfish (.05 ppm)
- Cod (.11 ppm)
- Haddock (.03 ppm)
- Lobster - spiny (.09 ppm)
- Sardine (.02 ppm)
- Tilapia (.01 ppm)
- Tuna - canned, light (.12 ppm)
- Bass -saltwater (.27 ppm)
- Tuna - canned, albacore (.35 ppm)
Note, however, that there can also be many nutritional benefits to consuming fish when it is part of a healthy diet. Fish is high in protein, low in saturated fat, high in unsaturated fat, and, most of all, high in EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) omega-3 oils. EPA and DHA are needed to build the structures of a person's brain up until they are 20 years of age. General recommendations are to consume between 8 and 12 ounces per week of a variety of seafood. Women who are pregnant or may become pregnant and children should avoid larger fish with high mercury levels, such as shark, swordfish, king mackerel or tilefish, ray, barramundi, gemfish, orange roughy, and southern bluefin tuna, and limit eating canned albacore (white) tuna to 6 ounces per week. Seafood naturally lower in mercury includes shrimp, prawns, lobster, oysters, canned light tuna, salmon, pollock, and catfish. In addition, check with your local government agencies about the safety of fish caught by family and friends at nearby lakes, rivers, and coastal areas.
Sources:
Academy of Nutrition and Dietetics. Safe Sources of Omega-3 Fats for Pregnant Women. http://www.eatright.org/resource/health/pregnancy/what-to-eat-when-expecting/pregnant-safe-sources-of-omega-3-fats. Accessed July 2, 2015.
Food and Drug Administration. Fish: What Pregnant Women and Parents Should Know. http://www.fda.gov/Food/FoodborneIllnessContaminants/Metals/ucm393070.htm. Accessed July 2, 2015.
United States Department of Agriculture. Dietary Guidelines for Americans 2010. http://health.gov/dietaryguidelines/dga2010/DietaryGuidelines2010.pdf. Accessed July 2, 2015.
United States Environmental Protection Agency. Fish Advisories. http://www.epa.gov/ost/fish/.