Why Are Tuna Mercury Levels a Concern?
Mercury is a naturally occurring element, but industrial pollution has increased its concentration in the ocean. In the marine environment, mercury converts into methylmercury, a highly toxic form that accumulates in the tissue of fish. As larger fish prey on smaller fish, the concentration of mercury increases up the food chain, a process known as biomagnification. Tuna, particularly larger, longer-living species like bigeye, are high-level predators, which means they tend to have higher concentrations of mercury than smaller fish. While the risk for most healthy adults is minimal when consuming tuna in moderation, excessive intake can lead to mercury poisoning, which affects the nervous system.
The Low-Mercury Champions: Skipjack and Canned Light Tuna
If minimizing mercury exposure is your goal, canned light tuna and fresh or frozen skipjack are the best choices. These are generally smaller, younger fish with a naturally lower mercury load. Canned light tuna often uses skipjack or tongol tuna, both of which are small, fast-growing species that don't have as much time to accumulate mercury as larger tuna.
- Skipjack Tuna: The champion of low mercury among tunas, skipjack is a smaller, fast-growing species. A Biodiverse Research Institute study and FDA data both confirm that skipjack consistently has the lowest mercury concentrations.
- Canned Light Tuna: Canned light tuna typically consists of smaller tuna species, most commonly skipjack. Health organizations like Health Canada advise that the mercury levels in canned light tuna are so low that most people can consume it without concern, while caution is advised for canned albacore.
- Safe Catch and Wild Planet: Specific brands like Safe Catch and Wild Planet have also gained attention for their proactive approach to minimizing mercury. Safe Catch claims to test every fish for its mercury content, offering a "Safe Catch Elite Wild Tuna" with a guaranteed low mercury level. Wild Planet also conducts third-party testing, with its skipjack products averaging very low mercury counts.
Comparison of Tuna Species by Mercury Content
To illustrate the significant difference in mercury levels, here is a comparison table using average parts per million (ppm) data from the FDA and other sources.
| Tuna Type | Average Mercury (ppm) | Consumption Guideline Notes |
|---|---|---|
| Canned Light (Skipjack) | 0.126 | Recommended for frequent consumption. Adults can typically have 2-3 servings per week. |
| Fresh/Frozen Skipjack | 0.144 | Also a great low-mercury choice, with similar recommendations to canned light tuna. |
| Canned Albacore | 0.350 | Higher in mercury than skipjack. Recommendations often limited to one 4-ounce serving per week for adults. |
| Fresh/Frozen Yellowfin | 0.354 | Mercury levels are similar to canned albacore. Consume less frequently. |
| Fresh/Frozen Albacore | 0.358 | Higher mercury content than canned due to fish size. Limit consumption. |
| Fresh/Frozen Bigeye | 0.689 | High mercury levels. Typically used in sushi. Should be consumed very sparingly, if at all. |
Mercury in Tuna and Health Risks
The primary concern regarding mercury is for vulnerable populations, including pregnant and breastfeeding women, and young children, whose developing brains are more sensitive to its effects. The FDA and EPA provide joint advice on fish consumption, recommending two to three servings of lower-mercury fish per week for these groups.
For the general population, the risk from mercury in tuna is generally low, especially when moderate intake is maintained. However, the unpredictability of mercury spikes in individual cans, even in generally low-mercury varieties like canned light, is a noted concern. Some research suggests that selenium in tuna may help neutralize mercury's toxicity, but this is not a substitute for choosing lower-mercury options.
How to Select and Consume Low-Mercury Tuna
- Prioritize canned light or skipjack: When choosing canned tuna, always opt for varieties labeled as "light" or "skipjack" over "albacore" or "white" tuna.
- Consider specialized brands: For an extra layer of confidence, explore brands like Safe Catch, which test every fish for mercury content.
- Vary your fish intake: Don't rely on tuna as your only source of seafood. Incorporate other low-mercury options into your diet, such as salmon, sardines, and shrimp, to enjoy the health benefits of fish with minimal risk.
- Eat in moderation: Even with low-mercury options, it is wise to follow recommended serving guidelines. A maximum of two to three servings per week is a common recommendation for the general population.
- Avoid bigeye and bluefin: These large, high-mercury species are often used in sushi and are best avoided, particularly for vulnerable populations.
Conclusion: Making Smarter Tuna Choices
Understanding what tuna has the lowest mercury empowers you to make informed decisions for your health. While all seafood contains some level of mercury, species like skipjack and canned light tuna are consistently the safest choices due to their smaller size and lower position on the food chain. By opting for these varieties, diversifying your seafood intake, and being mindful of consumption frequency, you can continue to enjoy the nutritional benefits of tuna while minimizing your mercury exposure. For the latest advice, consult official health and food safety websites, such as the FDA's recommendations.
