What foods have the most mercury in them?

December 18, 2025 •

4 min read

A 2008 model estimated the total amount of mercury deposited into the oceans annually to be 3,700 metric tons, much of which is converted into a toxic form that contaminates the marine food chain. This accumulation process means that certain foods, particularly some fish, contain significantly higher levels of mercury than others.

Quick Summary

Certain large, predatory fish such as shark, swordfish, and specific types of tuna contain the highest levels of mercury due to bioaccumulation up the marine food chain.

Key Points

Top Offenders: The foods highest in mercury are typically large, long-lived predatory fish like shark, swordfish, and Gulf of Mexico tilefish.
Bioaccumulation Explained: Mercury levels increase up the food chain, a process called biomagnification, meaning larger, older predators accumulate the most.
Choose Your Tuna Wisely: Canned light tuna (skipjack) is significantly lower in mercury than canned albacore or fresh bigeye and yellowfin varieties.
Safer Choices: Fish like salmon, shrimp, tilapia, and sardines are excellent, low-mercury seafood options.
Sensitive Groups: Pregnant women, those planning pregnancy, nursing mothers, and young children should strictly limit high-mercury fish consumption.
Cooking Doesn't Help: Mercury is stored in a fish's muscle tissue and cannot be removed through cooking.

The Science Behind Mercury in Fish

Mercury is a naturally occurring element that is also released into the environment from industrial processes like coal burning. Once in the environment, microorganisms in water bodies convert it into a highly toxic organic compound called methylmercury. This is the form of mercury that builds up in fish and shellfish, posing a health risk to humans who consume them. The process through which mercury levels increase up the food chain is called biomagnification.

Understanding Bioaccumulation and Biomagnification

Fish absorb methylmercury from the water they live in and the food they eat. Because they excrete it very slowly, the mercury accumulates in their tissues over time. This means that the larger and older a fish is, the higher its mercury content is likely to be. The effect is magnified as smaller fish containing mercury are eaten by larger, predatory fish, which then accumulate even higher concentrations of the toxin. This explains why fish at the top of the food chain are often the most contaminated.

Highest Mercury Seafood to Limit or Avoid

For most people, it's recommended to limit or avoid the consumption of certain types of fish to keep mercury intake low. This is especially important for pregnant women, those who may become pregnant, nursing mothers, and young children, who are more vulnerable to mercury's neurological effects.

Here are some of the foods consistently identified as having the highest mercury levels:

Tilefish (especially from the Gulf of Mexico): Often cited as the highest source of mercury, with a mean concentration of 1.123 ppm.
Shark: A large predator at the top of the food chain, with average mercury measurements around 0.979 ppm.
Swordfish: Another top predator with an average mercury load of 0.995 ppm.
King Mackerel: Contains an average of 0.730 ppm of mercury.
Bigeye Tuna: Fresh and frozen Bigeye tuna have high average mercury levels of 0.689 ppm.
Orange Roughy: This long-lived fish has an average mercury level of 0.571 ppm.
Marlin: Contains an average of 0.485 ppm of mercury.

The Mercury in Tuna: A Closer Look

Tuna consumption is a common source of mercury exposure in many countries, but mercury levels vary significantly by species and preparation. Canned light tuna, often made from smaller skipjack tuna, has much lower mercury levels than canned albacore or fresh tuna varieties.

Bigeye Tuna: High mercury levels.
Albacore Tuna (canned): Higher mercury levels than light tuna, and should be limited.
Canned Light Tuna (Skipjack): Lower mercury content, making it a safer option.

Safer, Low-Mercury Seafood Choices

Many types of seafood are low in mercury and are a healthy part of a balanced diet, offering valuable omega-3 fatty acids, protein, and minerals. The FDA and EPA recommend eating 2 to 3 servings a week of low-mercury fish for the general population.

Examples of low-mercury seafood include:

Shrimp
Salmon (Fresh/Frozen and Canned)
Catfish
Sardines
Anchovies
Tilapia
Scallops
Haddock
Pollock

Mercury Levels Comparison Table

This table categorizes common fish and shellfish based on average mercury concentration, informed by FDA data.


Mercury Level Category	Example Species	Average Mercury (ppm)
Highest	Tilefish (Gulf of Mexico)	1.123
	Swordfish	0.995
	Shark	0.979
	King Mackerel	0.730
	Tuna (Bigeye)	0.689
Moderate	Tuna (Albacore, canned)	0.350
	Tuna (Yellowfin)	0.354
	Halibut	0.241
	Cod	0.111
Lowest	Tuna (Light, canned)	0.126
	Salmon (Fresh/Frozen)	0.022
	Shrimp	0.009
	Sardine	0.013
	Tilapia	0.013

How to Reduce Your Mercury Exposure

Practical Tips for Lowering Intake

Vary your seafood choices: Don't rely on just one type of fish. Opting for a variety helps diversify your nutrient intake while minimizing exposure to contaminants that might be higher in a single species.
Eat smaller, younger fish: Because of biomagnification, smaller fish tend to have lower mercury levels.
Check local advisories: If you fish in local waters, consult state or local health departments for advisories, as some areas have specific consumption warnings.
Understand canned tuna labels: Choosing canned light or skipjack tuna over albacore or white tuna can significantly reduce your mercury consumption.

The Limits of Cooking

It is important to note that cooking methods, such as broiling or grilling, do not reduce the mercury content in fish. Unlike contaminants stored in fat (like PCBs), mercury is stored in the muscle tissue (the meat of the fish) and remains even after cooking.

Conclusion

While fish is a valuable source of nutrients, it's crucial to be mindful of mercury levels, particularly in large predatory species like swordfish, shark, and certain tunas. Understanding the process of biomagnification and identifying safer, low-mercury options allows you to enjoy the health benefits of seafood with minimized risk. Choosing a variety of low-mercury fish and paying attention to portion sizes are the most effective strategies for reducing overall mercury exposure for both adults and vulnerable populations.

For more detailed information, consult the U.S. Environmental Protection Agency's guidance on mercury and health: EPA on Mercury.

Frequently Asked Questions

Bigeye tuna, whether fresh or frozen, has the highest mercury levels. Canned albacore tuna contains more mercury than canned light tuna, which is often made from the smaller skipjack tuna.

No, cooking or preparing fish does not remove mercury. Mercury is absorbed into the fish's muscle tissue, so grilling, baking, or frying will not reduce the mercury concentration.

High mercury exposure can harm the nervous, digestive, and immune systems, as well as the kidneys, skin, and eyes. It is particularly dangerous for unborn babies and young children, whose developing brains and nervous systems are more vulnerable to damage.

Yes, but with caution. Pregnant women should eat 2-3 servings of low-mercury fish per week, such as salmon and shrimp, while avoiding or strictly limiting high-mercury species like shark, swordfish, and tilefish.

Mercury enters the atmosphere from natural and industrial sources. It settles in bodies of water, where microorganisms convert it into methylmercury. This methylmercury is then absorbed by smaller aquatic life and accumulates up the food chain through larger predatory fish.

Most common shellfish, such as shrimp, clams, and scallops, are considered low in mercury. However, it is always wise to choose a variety of seafood options to minimize any potential risk.

For most adults, the FDA suggests eating 2 to 3 servings (8 to 12 ounces) of low-mercury fish per week to gain the health benefits of fish while keeping mercury exposure low.