Heavy Metals in Fish and Seafood: Should You Avoid Eating Them?

Seafood is often considered a healthy part of a balanced diet, but concerns about mercury and other contaminants have made many people (including myself and my family) unsure about what to do.

Should you avoid fish altogether, or is it still a good option if you’re careful about type and sourcing?

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For many years, I had heard about concerns with heavy metals in fish. It didn’t affect me much at first since I’ve never been a big seafood eater, though I used to enjoy tuna salad and would occasionally splurge on swordfish when eating out.

However, my husband really enjoys fish, and I do like salmon and the occasional tuna or white fish, and the “men” in our home used to enjoy sardines fairly often, so it’s something we’ve had to figure out.

We've all been told that fish is good for us. So the question is: should we not be concerned or should we avoid it completely? Let's discuss.

What Is a Heavy Metal?

The definition of what a heavy metal is varies, however some base their definition on the density of the metal element. Copper, nickel, cadmium, iron, lead, mercury and zinc are typically considered to belong to this category.

When it comes to heavy metals in the ocean and in seafood and the effects that they might have on humans, mercury, lead, and cadmium are typically the ones that are the focus of concern.

What Heavy Metals Are Found in Fish?

Seafood can contain small amounts of naturally occurring and environmental contaminants, including:

• mercury (the main concern for most people)
• lead
• cadmium
• arsenic

Of these, mercury—especially in the form of methylmercury—is usually the biggest focus when people talk about fish safety.

Why Do Fish Contain Mercury?

Mercury enters oceans from both natural sources and pollution. Once mercury enters the water, it can be converted by microorganisms into a form called methylmercury, which is more easily absorbed by living organisms (source).

This is the form that builds up in fish (as well as in plants and microorganisms in the ocean) and is the main reason mercury is a concern when choosing seafood.

Mercury binds strongly to fish muscle tissue and proteins rather than being excreted, causing concentrations to increase with the fish's age and up the food chain. As larger fish eat smaller fish, mercury builds up over time. This process—called bioaccumulation—means that larger, long-living fish tend to have higher levels than smaller fish.

Is Seafood Still Healthy?

Even with these concerns, seafood can still be a valuable part of the diet. Many types of fish provide beneficial nutrients like:

• omega-3 fatty acids
• high-quality protein, and
• minerals like selenium.

However, the amounts can vary quite a bit depending on the type of fish. Fatty fish like salmon, sardines, and mackerel tend to be higher in omega-3s, while leaner fish provide less.

Fish Lower in Heavy Metals

In general, smaller fish that are lower on the food chain tend to have lower levels of mercury, but there are also some larger fish that still tend to have relatively low mercury levels.

Some commonly recommended options include:

• trout
• sardines
• anchovies
• herring
• wild-caught salmon

Salmon isn’t a small fish, but it’s still considered a lower-mercury option because it has a shorter lifespan and doesn’t accumulate mercury to the same extent as larger predatory fish.

Fish Higher in Mercury

Larger, long-living fish tend to accumulate more mercury due to the reason mentioned above. These are often best eaten less frequently:

• swordfish
• shark
• king mackerel
• tilefish
• larger types of tuna

What About Tuna?

Tuna is one of the most common fish people eat, but mercury levels can vary widely depending on the type.

• Lower mercury options:
  • skipjack tuna (often labeled “light tuna”)
• Higher mercury options:
  • albacore (white tuna)
  • bigeye tuna

Some brands also test for mercury levels or specialize in smaller, more sustainable species, which can be helpful if you eat tuna regularly. Safe Catch tuna is one such brand.

As a general rule, choosing smaller species of tuna and limiting higher-mercury varieties can make a big difference.

Is Seafood Safe During Pregnancy?

This is an area where many people have concerns, and for obvious reasons.

There has been research looking at mercury exposure during pregnancy, and while it’s something to be aware of, it’s also important to remember that health outcomes are influenced by many factors—not just one food or exposure.

Because of the many benefits of seafood for a mother and her growing baby, many recommendations focus on choosing lower-mercury fish and avoiding high-mercury options, rather than avoiding seafood entirely (source).

What About Radiation?

Concerns about radiation in seafood—especially after events like Fukushima—have led many people to question whether fish is still safe to eat. In fact, you can read about a funny exchange I had with a friend about this in my post about natural protection from radiation.

While trace levels of radiation have been detected in some areas, monitoring programs have generally found levels in seafood to be very low and well below safety limits for typical consumption.

For most people, this means that everyday exposure to mercury and other environmental contaminants is more of a concern to focus on.

Farmed vs. Wild Fish

There’s also some debate about farmed versus wild fish.

In general:

• wild-caught fish are often preferred for their nutrient profile
• farmed fish quality can vary depending on how they’re raised

If possible, choosing well-sourced fish—whether wild or responsibly farmed—can make a difference.

Shopping Tips for Choosing Safer Seafood

Here are some tips to make it easier for you choose lower-mercury fish for your home.

• Choose smaller fish more often, since they tend to accumulate fewer contaminants
• Opt for lower-mercury options like sardines, salmon, trout, anchovies, and herring
• Limit larger predatory fish like swordfish and shark
• When buying tuna, choose skipjack or “light tuna” over albacore
• Look for brands that prioritize testing and sourcing transparency
• Whenever possible, choose well-sourced seafood instead of relying only on labels or marketing terms

One helpful thing to know is that sardines are almost always wild-caught because they are difficult to farm commercially, so paying extra for “wild-caught” sardines is often unnecessary.

Canned fish can also still be a nutritious and affordable option, especially when choosing lower-mercury varieties. While some people have concerns about can linings, these concerns are generally considered greater with highly acidic foods like tomatoes. Still, many people prefer to choose BPA-free cans or seafood packaged in glass jars when possible.

What We Do in Our Home

While I tend to be more cautious about certain health topics, we take a balanced approach when it comes to seafood.

I’m not a big seafood eater myself just because I don't typically love it and am more in the know about contaminants, but my husband really enjoys fish (we’ve definitely had conversations about this when choosing seafood, especially when eating out). So this whole topic is something we’ve had to think through rather than just avoid altogether.

Over time, we’ve landed on a middle ground:

• We don’t rely heavily on seafood as a staple
• When we do include it, we focus on lower-mercury options like sardines and wild salmon
• We tend to avoid larger, long-living fish more often
• And we try to keep variety in our diet instead of relying too much on any one food

For us, it’s not about avoiding seafood completely—it’s about being thoughtful and selective.

Choosing Lower Mercury Fish

Category	Fish	Why
Best Choices (Lower Mercury)	Sardines, anchovies, herring, wild salmon, trout	Lower on the food chain and/or shorter lifespan
Moderate (Eat Occasionally)	Skipjack tuna (“light tuna”), cod, halibut	Moderate mercury levels
Higher Mercury (Limit)	Albacore tuna, yellowfin tuna	Larger species (more accumulation)
Highest Mercury (Avoid if Possible)	Swordfish, shark, king mackerel, tilefish	Large, long-living predators

A helpful rule of thumb is that fish lower on the food chain or with shorter lifespans tend to have lower mercury levels—even if they aren’t especially small.

This is one reason salmon is often recommended as a balanced choice—it’s relatively low in mercury while still being rich in omega-3s.

The Bottom Line

You don’t have to avoid fish completely to reduce your exposure to heavy metals.

Focusing on lower-mercury options, limiting high-mercury fish, and keeping variety in your diet can go a long way.

Like many things in nutrition and overall health, it’s less about one perfect choice and more about consistent, quality decisions over time.

Do you eat fish or do you avoid it?