How to Measure Mercury in Fish

Levels of mercury in fish can vary depending on the species and their age.

When used in household products, as an electricity conductor and in the mining industry, mercury has been valuable time and time again. When humans are exposed to it directly, however, the metal acts as a toxic substance. As an environmental and industrial contaminant which can settle into the flesh of certain seafood, mercury can impair brain and nervous system development if consumed in large doses. Since children, pregnant women, and women who may become pregnant are at the greatest risk for these impairments, it is especially important that mercury intake is kept as low as possible. Despite some mercury content, fish also offers the health benefit of Omega 3 fatty acids, which are necessary for pregnant women since they help to develop the brain of developing babies while supporting developing vision and nerve function. Instead of avoiding fish altogether, avoid those with the highest mercury content when possible.

Instructions

1. Consider the size and age of fish. Since fish that have been exposed to more mercury can store more, older fish often have higher mercury content than younger fish of the same family. The muscle tissue of fish that are older and bulkier is often more substantial, allowing more tissue for storing mercury. Ingesting younger, smaller fish is a way to estimate that less mercury is being consumed. Clams, Flounder, Atlantic Haddock, Oysters, Salmon, Shrimp, Squid/Calamari and Tilapia are low mercury choices.

2. Consult local advisory committees. Fish may be contaminated due to environmental contamination or industrial pollution, making the contamination levels area-specific. Since mercury levels in fish can vary based on region, local advisory boards are the most reliable for measuring how much mercury is in locally-caught seafood. A list of advisories is available through the Environmental Protective Agency, which gives suggestions specific to certain regional bodies of water.

3. Research official measurements.The procedures used to measure fish are complex laboratory procedures, so visit the websites of governing bodies such as the Food and Drug Administration or the Environmental Protection Agency (see Resources) for official measurements. While the U.S. Food and Drug Administration does not allow seafood with more than 1 mg/kg to be sold after inspection, consumers should still know which fish may carry a risk. Those who are pregnant may wish to avoid fish with even moderate levels altogether. According to the American Pregnancy Association, fish with extremely high levels include Grouper, Marlin, Orange Roughy, Tilefish, Swordfish, Shark and Mackerel. Bluefish, Spanish & Gulf Mackerel Sea Bass, and canned Albacore & Yellowfin Tuna also have high mercury levels, while moderate levels of mercury are found in common seafood such as Bass, Carp, Halibut, Lobster, Mahi Mahi, Freshwater Perch, Snapper and Canned Chunk Light Tuna.

References

• The Washington Post: Benefits of Fish Exceed Risks, Studies Find
• University of Maryland Medical Center: Omega-3 Fatty Acids
• Wisconsin DNR: Questions and Answers About Eating Fish
• New York State Department of Health: Health Advice on Eating Sportfish and Game
• Lab Manager: Measuring Mercury Levels in Fish
• Natural Resources Defense Council: Mercury in Fish

Resources

• Read this Article in Spanish
• What You Need to Know about Mercury in Fish and Shellfish
• FDA.gov: Mercury Levels in Commercial Fish and Shellfish