Why mercury is a concern in tuna
Mercury is a naturally occurring element that is released into the environment through both natural events, such as volcanic activity, and human activities like the burning of coal and industrial waste. Once in the water, microorganisms convert it into methylmercury, a highly toxic organic compound. This methylmercury then enters the marine food chain and, due to a process called bioaccumulation, levels magnify up the food chain. As a large predatory fish, tuna consumes smaller fish that contain mercury, causing it to accumulate in its tissues over time.
How mercury levels vary by tuna species
Not all tuna is created equal when it comes to mercury content. The larger and longer-lived the fish, the more time it has had to accumulate mercury.
- Bigeye Tuna (Ahi): This species, often used for sushi, is typically highest in mercury due to its large size and position in the food chain.
- Albacore Tuna (White): A common variety for canning, albacore has higher mercury levels than lighter tuna types, though still less than bigeye.
- Yellowfin Tuna: Mercury levels are generally moderate in this species, often found in fresh or frozen steaks.
- Skipjack Tuna (Light): The smallest and fastest-growing of the major species, skipjack is used for most canned light tuna and has the lowest mercury concentration.
Official consumption guidelines for tuna
The U.S. Food and Drug Administration (FDA) and Environmental Protection Agency (EPA) provide specific guidance to help consumers, especially sensitive populations, balance the health benefits of fish consumption with the risks of mercury exposure.
Recommended serving limits
- Canned Light (Skipjack) Tuna: Adults can typically eat 2 to 3 servings per week. For women who are pregnant or breastfeeding, and for young children, this is also considered a "Best Choice".
- Canned White (Albacore) Tuna: Because of its higher mercury content, the FDA recommends adults limit intake to one 4-ounce serving per week. It is considered a "Good Choice" but should be consumed more sparingly.
- Fresh/Frozen Bigeye Tuna: This high-mercury species is recommended for infrequent consumption by most people and should be avoided entirely by pregnant women and young children.
Choosing lower-mercury fish
Eating a variety of fish is the best way to gain nutritional benefits while minimizing mercury exposure. Other excellent, low-mercury choices include salmon, sardines, shrimp, and tilapia.
Comparison of tuna species and mercury levels
| Tuna Species | Typical Use | Average Mercury Level (PPM) | Recommended Frequency (Adults) | Notes |
|---|---|---|---|---|
| Bigeye (Ahi) | Sushi, sashimi | 0.689 | Avoid (pregnant/children); Very limited (others) | Highest mercury; top of the food chain. |
| Albacore (Canned) | Canned tuna (White) | 0.350 | Up to 1 serving per week | Higher mercury than light tuna. |
| Yellowfin | Steaks, fresh/frozen | 0.354 | Limit consumption | Moderate mercury levels. |
| Skipjack (Canned Light) | Canned tuna (Light) | 0.126 | 2-3 servings per week | Lowest mercury; smallest species. |
Conclusion
Yes, certain types of tuna are high in mercury, but the amount varies significantly by species and size. By making informed choices, consumers can continue to enjoy the nutritional benefits of tuna, such as protein and omega-3 fatty acids, without compromising their health. Opting for canned light (skipjack) tuna over albacore and limiting intake of high-mercury species like bigeye tuna are key strategies. For pregnant women, nursing mothers, and young children, following specific FDA guidelines is particularly important to mitigate risks associated with mercury exposure. Balancing tuna consumption with other low-mercury fish is the most effective approach for a healthy and safe diet. Always check specific guidance from reputable sources like the FDA or EPA before making major dietary changes.
For more detailed information on mercury levels in fish, you can consult the FDA's official data.
