Mercury in Fish and Shellfish

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What is mercury?

• Mercury is a metal found naturally in coal, rocks, and soil.
• Mercury can be released into the environment by burning coal and other fuels, and by soil erosion, mining, forest fires, and volcanic activity.

How does mercury get into fish and shellfish?

• Mercury in the air and soil makes its way into rivers, lakes, and the ocean through rain and snow runoff.
• Mercury can be released directly into water through wastewater and industrial discharges.
• Mercury passes into tiny plants and animals that live in water, and into the fish and shellfish that eat them.
• Mercury builds up in fish and shellfish in the form of methylmercury (a more toxic form of mercury).

What is the health concern for humans?

• Too much mercury can:
  • harm the brain, especially in children and babies, affecting their behavior and ability to learn.
  • damage the nervous systems of adults.
• Women can pass mercury on to their babies during pregnancy and breastfeeding.

Should I still eat fish?

• Yes!  Low-contaminant fish are an important part of a healthy, well-balanced diet.
• Fish are a good source of protein and vitamins, and are a primary source of heart-healthy omega-3 fatty acids.
• Eating two servings of fish per week is good for you, according to the American Heart Association.
• If you are pregnant, eating low-contaminant fish may help the baby’s brain develop.

Which fish have the most mercury?

• Fish that eat other fish usually have the most mercury. These include:
  • In the ocean, Shark, Swordfish, King Mackerel, Marlin, Orange Roughy, Tilefish (from the Gulf of Mexico), and Bigeye Tuna.
  • In lakes and rivers, Black Bass species (for example, Largemouth Bass), Striped Bass, Pikeminnow, and White Sturgeon.
• Larger, older fish tend to have more mercury than younger fish.

Can I reduce mercury levels in fish or shellfish to make eating them safer?

• No. There is no way to clean or prepare fish or shellfish that will reduce their mercury levels.

How can I lower my risk from mercury in fish and shellfish?

• If you catch your own fish and shellfish, follow the Office of Environmental Health Hazard Assessment’s (OEHHA) fish advisories for California water bodies.
• OEHHA has specific advice for women ages 18-49, and children 1-17.  This is because fetuses, babies, and children are especially sensitive to mercury.
• OEHHA also has advice for women ages 50 and older, and men 18 and older. 
• Mercury can stay in your body for a long time. Women who could become pregnant should always be careful to eat low-mercury fish.
• If you buy your fish and shellfish, follow advice from FDA and USEPA for women ages 16-49, pregnant and breastfeeding women, and young children.
• Try to eat small fish instead of large fish (but observe minimum legal size requirements).

Where can I learn more?

• OEHHA’s Fish Advisory Program
• Biomonitoring California
• Mercury in your Environment (USEPA)