Understanding Mercury Levels in Seafood
Why Some Fish Have Higher Mercury
Mercury, naturally present in the environment, accumulates in marine life in the form of methylmercury. The levels in a particular fish depend primarily on its position in the food chain, its lifespan, and its diet. Larger, older, and more predatory fish tend to have higher concentrations of mercury due to a process called bioaccumulation. As larger fish consume smaller fish, the mercury they contain builds up, leading to significantly higher levels at the top of the food chain. This is why apex predators like swordfish and shark are known to have the highest levels of mercury.
The Safest Choices: A Comprehensive Low-Mercury List
To enjoy the nutritional benefits of seafood, such as protein, essential vitamins, and heart-healthy omega-3 fatty acids, it is best to focus on species known for their low mercury content.
Low-Mercury Finfish
- Salmon: Especially Wild Alaska salmon, is an excellent source of omega-3s with very low mercury levels.
- Sardines: These small, oily fish are rich in nutrients and consistently rank among the lowest in mercury.
- Anchovies: Similar to sardines, they are small and have low mercury content.
- Tilapia: U.S.-farmed tilapia is a popular, mild-flavored freshwater fish that is low in mercury.
- Catfish: Also a freshwater fish, farmed catfish is a safe and common low-mercury choice.
- Cod: Known for its flaky white meat, cod is a relatively low-mercury option.
- Pollock: Often used in fish sticks and fast-food fish sandwiches, wild Alaska pollock is a very low-mercury option.
- Trout: Freshwater trout is a healthy, low-mercury fish.
- Atlantic Mackerel: This type of mackerel is lower in mercury than its larger cousin, King Mackerel.
Low-Mercury Shellfish and Others
- Shrimp: One of the most consumed seafoods, shrimp is very low in mercury.
- Scallops: These shellfish are prized for their sweet flavor and have extremely low mercury levels.
- Oysters and Mussels: Both are bivalves that filter feed and are very low in mercury.
- Clams: Another filter-feeding bivalve with low mercury content.
- Crab: Domestic crab, including Dungeness, King, and Stone varieties, is a safe, low-mercury choice.
- Squid (Calamari): This mollusk is low in mercury and a popular culinary ingredient.
Navigating Canned Tuna
Canned tuna is a convenient and affordable protein source, but mercury levels differ by type. To minimize exposure, the U.S. Environmental Protection Agency (EPA) and Food and Drug Administration (FDA) recommend choosing canned light tuna, which comes from smaller species of tuna and has significantly less mercury than canned albacore tuna. They advise limiting canned albacore tuna to no more than 6 ounces per week for women of childbearing age and young children.
Mercury Comparison Table: Low vs. High
| Seafood Type | Mercury Level | Typical Source | Health Recommendations |
|---|---|---|---|
| Sardines | Very Low | Smaller fish | Best Choice; Eat freely |
| Shrimp | Very Low | Shellfish | Best Choice; Eat freely |
| Salmon | Low | Smaller, fatty fish | Best Choice; Eat freely |
| Cod | Moderate | White fish | Good Choice; Limit intake |
| Bigeye Tuna | High | Large, predatory fish | Avoid or limit heavily |
| Swordfish | Very High | Large, predatory fish | Avoid entirely |
| King Mackerel | Very High | Large, predatory fish | Avoid entirely |
| Shark | Very High | Large, predatory fish | Avoid entirely |
Guidelines for Sensitive Populations
Pregnant Women and Young Children
These groups are particularly sensitive to mercury's effects on the developing nervous system. The FDA and EPA provide specific guidance to ensure safe consumption. The recommendations state that women who are pregnant or might become pregnant, nursing mothers, and young children should eat 8 to 12 ounces of a variety of low-mercury fish each week. It is critical for them to completely avoid the four fish highest in mercury: shark, swordfish, king mackerel, and tilefish.
Why Low-Mercury Fish Is Important for Development
Consuming fish with healthy omega-3 fatty acids, like salmon and sardines, provides crucial nutrients that support brain growth, nerve function, and overall development in infants and children. These benefits are so significant that avoiding fish altogether is not recommended; instead, making informed, low-mercury choices is the best strategy. In fact, some studies show that the omega-3s in fish may even help protect the developing brain from the harmful effects of mercury.
Conclusion
While mercury in seafood is a valid concern, it doesn't mean you have to stop eating fish. The benefits of consuming fish, particularly low-mercury varieties rich in omega-3s, far outweigh the risks for most people. By choosing from the extensive list of low-mercury options like salmon, sardines, and shrimp, and by being mindful of your canned tuna choices, you can enjoy seafood as a regular and healthy part of your diet. Prioritizing smaller, non-predatory species ensures you get essential nutrients while minimizing your exposure. Making informed choices is the most effective way to manage your mercury intake and promote a healthy lifestyle. For more specific information, consult the FDA Advice about Eating Fish.
Frequently Asked Questions
Can I eat any seafood if I'm pregnant?
Yes, pregnant women can and should eat seafood, but they need to be mindful of which types they choose. The FDA recommends eating 8 to 12 ounces per week of a variety of low-mercury options like salmon, cod, and canned light tuna.
Is canned tuna high in mercury?
It depends on the type. Canned albacore ("white") tuna has a higher mercury concentration than canned light tuna. For this reason, it's recommended to limit albacore tuna intake, especially for sensitive populations.
Why do some fish have more mercury than others?
Mercury levels are higher in larger, older, and predatory fish due to bioaccumulation. This means mercury builds up in their bodies as they consume smaller, mercury-containing fish.
Is mercury from fish a real danger?
For most people, the levels of mercury in average seafood consumption are not dangerous. However, excessive consumption of high-mercury fish can be risky, especially for unborn babies and young children. Choosing a variety of low-mercury fish is the key to safety.
Do wild-caught fish have less mercury than farmed fish?
Not necessarily. Mercury levels are species-dependent, not primarily determined by wild vs. farmed status. While wild fish can accumulate mercury from their environment, farmed fish have mercury levels influenced by their feed.
What are the main benefits of eating low-mercury seafood?
Low-mercury seafood is an excellent source of high-quality protein, essential vitamins, and heart-healthy omega-3 fatty acids (EPA and DHA), which are vital for brain and nervous system function.
What are some high-mercury fish to avoid?
According to the FDA, some fish to avoid due to high mercury levels include shark, swordfish, king mackerel, and tilefish.
