Nutrition Diet: What foods contain mercury?

October 21, 2025 •

4 min read

While seafood offers excellent sources of lean protein and heart-healthy omega-3s, nearly all fish and shellfish contain trace amounts of methylmercury. This fact makes it crucial for consumers to understand what foods contain mercury to make informed and healthier dietary choices.

Quick Summary

Mercury levels vary significantly among seafood types, with larger, predatory fish generally containing the highest amounts due to bioaccumulation. Consumers can minimize their exposure by choosing smaller, lower-mercury fish and adhering to recommended serving guidelines.

Key Points

High-Mercury Seafood: Large, predatory fish like shark, swordfish, and king mackerel contain the highest levels of mercury due to bioaccumulation and should be avoided or limited.
Low-Mercury Choices: Smaller fish and shellfish such as salmon, shrimp, sardines, and canned light (skipjack) tuna are low in mercury and are considered safe for regular consumption.
Vulnerable Populations: Pregnant and breastfeeding women, along with young children, are most susceptible to the neurotoxic effects of mercury and must pay close attention to consumption advisories.
Non-Seafood Exposure: While less common, non-seafood sources like vegetables and grains grown near industrial pollution sites can contain mercury, though seafood is the primary dietary source.
Informed Choices: Use resources like the FDA and EPA guidelines to identify safer seafood options and diversify your diet to minimize overall mercury intake.
Mercury Persists: Mercury is stored in the muscle tissue of fish and cannot be removed by cooking or any other preparation method.

The Science of Mercury in Food

Mercury is a naturally occurring element that is released into the environment from both natural sources (such as volcanic activity) and human activities, with coal-burning power plants and waste incineration being major contributors. Once in the atmosphere, it can settle into bodies of water where microorganisms convert it into methylmercury, a highly toxic organic compound. It is this form of mercury that enters the aquatic food chain and is a primary concern for dietary exposure.

How Mercury Accumulates

Methylmercury is efficiently absorbed by small organisms like plankton, which are then consumed by small fish. As larger predatory fish eat these smaller fish, the concentration of methylmercury accumulates in their bodies over time, a process known as bioaccumulation. This means that the larger and older the fish, the higher its mercury content tends to be. This process of increasing concentration up the food chain is called biomagnification.

High-Mercury Seafood: Choices to Avoid

Based on guidance from the U.S. Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA), certain species of fish are known to have the highest levels of mercury. It is particularly important for pregnant women, women who are breastfeeding or planning to become pregnant, and young children to avoid these fish.

High-mercury fish typically include:

Shark: A top predator with a long lifespan, leading to very high mercury concentrations.
Swordfish: Another large, predatory species high on the food chain.
King Mackerel: This species, especially from the Gulf of Mexico, contains significant mercury levels.
Tilefish: The FDA specifically warns against eating tilefish from the Gulf of Mexico, which has exceptionally high mercury levels.
Bigeye Tuna: Often used for sushi, this species has higher mercury content than other types of tuna.
Orange Roughy: A long-lived deep-sea fish that accumulates mercury over many decades.

Safer Seafood Choices: Low-Mercury Options

Many types of seafood are low in mercury and can be enjoyed as a regular part of a healthy diet, even for vulnerable populations. The FDA and EPA provide a list of recommended 'Best Choices' to help consumers make informed decisions.

Some of the best low-mercury options include:

Salmon (wild and farmed): A nutritious source of omega-3s with low mercury levels.
Shrimp: One of the lowest mercury seafood options, it can be consumed frequently.
Sardines: A small, oily fish known for being low in mercury.
Canned Light Tuna (Skipjack): A popular and accessible option with lower mercury than albacore tuna.
Catfish: Often farmed, catfish has relatively low mercury levels.
Pollock: A mild, flaky fish frequently used in fish sticks and other products.
Scallops and Oysters: Both shellfish species have minimal mercury content.

Beyond the Ocean: Non-Seafood Mercury Sources

While seafood is the most common dietary source of methylmercury, other foods can be affected by environmental contamination, especially near industrial areas. A 2020 study by the EPA, for instance, found that non-seafood consumers had lower blood mercury levels, but acknowledged that other dietary items could still contribute to exposure. Mercury from industrial emissions can settle on soil and be absorbed by plants.

Vegetables and Grains: Crops grown near coal-fired power plants have been shown to have elevated mercury levels, with leafy vegetables and rice particularly susceptible. In some cases, mercury concentrations exceeded food safety standards in study samples.
Wine and Liquor: The EPA study also noted that consumption of wine and liquor was associated with higher mercury biomarker concentrations among non-seafood eaters.

This highlights the importance of environmental regulation to protect the broader food supply, not just aquatic ecosystems. However, for most people, the mercury levels from these sources are minor compared to regular consumption of high-mercury fish.

Managing Mercury Intake for a Balanced Diet

The FDA and EPA provide a useful advisory for navigating seafood choices, particularly for sensitive groups. For most adults, moderate consumption of a variety of seafood is perfectly safe and beneficial. The key is mindful consumption.

Here are some tips for managing mercury intake:

Diversify your seafood: Don't rely on just one or two types of fish. A varied intake helps distribute any mercury exposure and provides a wider range of nutrients.
Follow guidelines for canned tuna: Opt for canned 'light' or skipjack tuna over albacore ('white') tuna, as it contains significantly less mercury. The FDA recommends limiting albacore to one serving per week for pregnant women.
Be aware of local advisories: If you consume fish caught recreationally, check for local advisories, as contamination can vary by waterbody.
Choose smaller, younger fish: As bioaccumulation occurs over time, selecting smaller, younger fish of the same species can result in lower mercury exposure.
Don't cut out fish entirely: The health benefits of seafood, such as omega-3 fatty acids, can outweigh the risks of mercury when choosing low-mercury options. Fish is an important part of a healthy diet.

Mercury Levels in Common Seafood: A Comparison


Mercury Level	Fish Examples	Recommended Consumption (for at-risk groups)
Highest	Shark, Swordfish, King Mackerel, Gulf of Mexico Tilefish, Bigeye Tuna	Avoid entirely.
High	Marlin, Orange Roughy, Chilean Sea Bass, Grouper, Halibut	Limit to one serving per week.
Moderate	Albacore Tuna (canned, fresh), Mahi Mahi, Snapper, Atlantic Tilefish	Up to one serving per week for some (check specific guidelines).
Low	Canned Light Tuna, Salmon, Shrimp, Sardines, Scallops, Tilapia, Catfish	Two to three servings per week.

Conclusion

Understanding what foods contain mercury is vital for safeguarding your health, especially for sensitive groups like pregnant women and young children. While certain large, predatory fish carry high levels of mercury due to bioaccumulation, most common seafoods like salmon, shrimp, and canned light tuna are low in mercury and offer substantial nutritional benefits. By making mindful choices, diversifying your diet, and following health authority recommendations, you can enjoy a nutrient-rich diet while minimizing your exposure to this environmental contaminant. The health benefits of consuming low-mercury fish should not be overlooked, and a balanced approach is recommended for optimal health. More information on seafood safety can be found from authoritative sources such as the FDA and EPA.

Frequently Asked Questions

Seafood with the lowest mercury levels generally includes smaller species and shellfish, such as shrimp, scallops, sardines, salmon, and canned light tuna. These are often categorized as 'Best Choices' by health authorities.

No, cooking fish does not remove mercury. The metal is bound to the protein in the fish's muscle tissue, meaning it remains present even after it has been cooked.

Mercury enters aquatic ecosystems primarily from industrial emissions and natural sources. In the water, bacteria convert it into a toxic form called methylmercury, which is then absorbed by marine life and accumulates up the food chain.

Mercury levels in canned tuna vary by type. Canned light tuna (typically skipjack) is significantly lower in mercury than canned albacore ('white') tuna. The FDA recommends limiting albacore consumption, especially for pregnant women and children.

Long-term, high-level exposure to methylmercury from food can lead to neurological and behavioral issues, including numbness, tremors, memory problems, and impaired motor skills. These effects are most dangerous for developing fetuses and young children.

While seafood is the most common dietary source, some studies have found minor mercury contamination in foods like rice and certain vegetables grown in areas with high environmental pollution from sources like coal plants.

For most people, the health benefits of eating fish—such as omega-3 fatty acids and protein—outweigh the risks of mercury, especially when choosing low-mercury options. A balanced approach and adherence to consumption guidelines are key.