How to think about seafood choices

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Seafood is different from other foods because the main issue is not processing or coatings — it’s what builds up inside the animal over time.

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In practical terms, focus on:

• how large the fish is

• how long it lives

• where it sits in the food chain

• whether it comes from clean water or controlled farming systems

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Smaller, shorter-lived fish tend to carry less. Larger, longer-lived fish tend to carry more.

 

Where exposure comes from

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Seafood exposure mainly comes from accumulation in the water and food chain.

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As fish live and feed, they absorb compounds from their environment. Over time, these compounds can build up in their tissue.

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The longer a fish lives and the higher it sits in the food chain the more it tends to accumulate.

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This is why larger fish often carry higher levels of:

• mercury (a heavy metal)

• PCBs (polychlorinated biphenyls)

• dioxins

These compounds are persistent, meaning they do not break down easily and can remain in the body over time.

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In farmed seafood, there is an additional layer. Exposure can come from:

• the quality of the water

• the feed used in farming systems

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Lower-quality farming environments can increase the likelihood of contaminants being present in the final product.

Over time, repeated intake of these compounds is associated with effects on the nervous system, hormone balance, and long-term metabolic health.

 

Quick seafood cheat sheet

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If you want a simple way to apply this in real life, use this as a guide:

Better choices (lower buildup):

• Sardines

• Anchovies

• Wild salmon (especially smaller varieties)

• Mackerel (not king mackerel)

• Herring

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Middle ground (depends on sourcing):

• Farmed salmon (quality varies by farm)

• Shrimp (varies widely by source and country)

• Cod, tilapia, trout

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More caution (higher buildup):

• Tuna (especially albacore and larger species)

• Swordfish

• King mackerel

• Shark

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This isn’t about avoiding seafood it’s about choosing types that carry less over time.

 

What to look for when buying seafood

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You don’t need to overthink it — a few simple choices make a clear difference.

• Choose smaller fish more often
  Lower on the food chain and tend to carry less mercury, PCBs, and other contaminants

• Be more selective with larger fish
  Species like tuna, swordfish, and king mackerel tend to carry higher levels of mercury and other accumulated compounds

• Pay attention to sourcing for farmed seafood
  Water quality and feed can directly affect whether contaminants like PCBs and dioxins end up in the fish

• Mix your choices
  Rotating different types of seafood helps avoid repeated exposure from the same source

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These simple shifts help reduce overall exposure while still getting the benefits of seafood.

 

Common labels explained

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Wild-caught
Fish caught in natural environments. This does not always mean lower contamination — species and size still matter.

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Farm-raised
Fish raised in controlled systems. Quality depends heavily on water conditions and feed.

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Sustainably sourced
Focused on environmental impact and fishing practices. This does not always reflect contamination levels.

 

Bottom Line

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With seafood, the main factor is how much the animal builds up over time. Smaller, shorter-lived fish tend to carry lower levels of compounds like mercury, PCBs, and dioxins. Larger fish and poorly sourced farmed seafood are more likely to carry higher levels of these contaminants.

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The goal is to choose seafood that is lower on the food chain, comes from better sources, and carries a lower overall toxic burden.