The Science of Mercury in Fish
Mercury is a naturally occurring element that, when released into the environment, can become a neurotoxin called methylmercury through bacterial processes. This form of mercury accumulates in the food chain, a process known as bioaccumulation. Smaller fish absorb methylmercury from the water and sediment, and when larger predator fish consume them, the mercury concentrates in their bodies. This is why larger, longer-living fish tend to have the highest mercury concentrations. For canned tuna, the key differentiator in mercury levels is the species of tuna being processed, as smaller species have less time to accumulate mercury.
Canned Tuna Species and Mercury Levels
Not all canned tuna is created equal. The product's mercury content is directly related to the species of tuna used, its size, and its lifespan. Understanding these differences is the most effective way to choose a lower-mercury option.
Canned Light Tuna (Skipjack and Tongol)
This type of canned tuna is your best bet for a low-mercury option. Canned light tuna is typically made from smaller, younger species, most commonly skipjack, and sometimes tongol. Due to their smaller size and shorter lifespan, these fish accumulate far less mercury than larger species. The FDA categorizes canned light tuna as a "Best Choice," meaning it can be consumed more frequently. The average mercury concentration for canned light tuna is about 0.126 parts per million (ppm), significantly lower than albacore.
Canned White Tuna (Albacore)
Labeled as "canned white" or "solid white," this tuna is exclusively albacore, a larger species of tuna. Because albacore are larger and live longer than skipjack, their mercury levels are considerably higher. The average mercury concentration in canned albacore is around 0.350 ppm—nearly three times that of canned light tuna. The FDA classifies canned albacore as a "Good Choice," recommending more limited consumption than light tuna.
Yellowfin and Other Tunas
Yellowfin tuna, a moderate-mercury option, is sometimes used in "gourmet" or "tonno" canned tuna products. Fresh or frozen yellowfin contains mercury levels comparable to albacore. For those concerned about mercury, it's best to stick to canned light tuna and avoid larger species. Fresh bigeye tuna is known to have very high mercury levels and is listed as a "Choice to Avoid" by the FDA for sensitive populations.
Choosing the Safest Canned Tuna
Beyond just the species, other factors can influence your choice. Some brands take additional measures to ensure lower mercury levels in their products.
- Brand-Specific Testing: Brands like Safe Catch have gained popularity for testing every single fish for mercury. Their claimed limit is 10 times lower than the FDA's action limit. While this may offer an extra layer of reassurance, Consumer Reports testing found that while Safe Catch had low levels, most other light or skipjack tunas also performed well.
- Fishing Methods: Some producers use pole-and-line or troll-caught methods, which often target younger, smaller fish with lower mercury content. Labels on products from brands like Wild Planet often highlight these sustainable fishing methods.
- Packed in Water vs. Oil: Mercury is stored in the fish's tissue, not the packing liquid, so draining the can does not significantly affect the mercury content. However, tuna packed in water is typically lower in calories and fat than oil-packed varieties.
Recommendations for Safe Consumption
Health recommendations vary depending on the type of tuna and who is eating it. The Dietary Guidelines for Americans generally recommend 8 ounces of seafood per week for most adults. The FDA's advice is more specific based on mercury levels:
- Canned Light Tuna: Two to three servings (8 to 12 ounces) per week for adults, including those who are pregnant or breastfeeding.
- Canned Albacore Tuna: One serving (4 ounces) per week for adults, including those who are pregnant or breastfeeding, with no other fish consumed that week from the "Good Choices" category.
Comparison of Canned Tuna Types
| Feature | Canned Light Tuna (Skipjack/Tongol) | Canned White Tuna (Albacore) |
|---|---|---|
| Mercury Levels | Lowest (avg. 0.126 ppm) | Higher (avg. 0.350 ppm) |
| Species | Skipjack or Tongol | Albacore |
| Taste Profile | Stronger, more intense flavor | Milder, less "fishy" flavor |
| Texture | Softer, flakier texture (often chunk light) | Firmer, "meatier" texture (often solid white) |
| Common Use | Tuna salad, casseroles | Recipes requiring firm, solid chunks |
| Cost | Generally more affordable | Typically more expensive |
Low-Mercury Alternatives to Canned Tuna
For those who wish to diversify their seafood intake while keeping mercury levels low, many other options are available. The FDA's "Best Choices" list includes:
- Salmon (canned or fresh)
- Sardines
- Shrimp
- Tilapia
- Cod
- Oysters
These alternatives provide valuable omega-3 fatty acids, protein, and other nutrients with less mercury risk, contributing to a balanced diet. For further guidance on seafood choices, see the FDA and EPA's detailed recommendations for eating fish.
Conclusion
When it comes to answering which canned tuna is lowest in mercury, the clear winner is canned light tuna, typically made from smaller skipjack fish. Canned albacore, while a healthy option in moderation, contains higher mercury levels and should be consumed less frequently. Consumers can make informed choices by checking product labels for the tuna species and following dietary guidelines. Opting for brands that test for mercury, like Safe Catch, and integrating other low-mercury seafoods like salmon and sardines can further reduce your overall exposure, ensuring you receive the nutritional benefits of fish with minimal risk.
