Understanding Mercury in Tuna
Mercury is a naturally occurring element, but human activities such as burning fossil fuels have increased its presence in the environment. This heavy metal is deposited into oceans, where microorganisms convert it into a highly toxic form called methylmercury. This methylmercury enters the marine food web, concentrating in larger predatory fish through a process known as bioaccumulation. When we eat fish, we also ingest the methylmercury it contains.
The amount of mercury in a tuna depends on several factors:
- Species: Different tuna species occupy different positions in the food chain and have varying life cycles.
- Size and Age: Larger, older tuna have had more time to accumulate mercury from their diet.
- Diet: The types of smaller fish a tuna preys on affects its mercury load.
- Habitat: While less impactful than species and size, geographic location can influence mercury content.
The Tuna with the Highest Mercury Content
Based on data from the FDA and other research, bigeye tuna consistently ranks as one of the tuna species with the highest mercury levels. For example, FDA data indicates that fresh or frozen bigeye tuna has a mean mercury concentration of 0.689 parts per million (ppm). This is significantly higher than other types, including albacore and skipjack. This species is a large, deep-diving predator, which contributes to its high mercury accumulation. Bigeye is also a type of "ahi" tuna commonly used for sushi and sashimi.
Other High-Mercury Tuna Varieties
- Bluefin Tuna: Bluefin, the largest of the tuna species, is another high-mercury variety, particularly in large or older individuals. Some large bluefin tuna have been reported with mercury concentrations exceeding the FDA action level for commercial fish. While not as commonly used in everyday canned products, bluefin is a prized and expensive fish for sushi and sashimi, and its high mercury content is a significant health concern.
- Albacore Tuna: Canned "white" tuna is typically albacore. While still lower in mercury than fresh bigeye or bluefin, it has considerably higher levels than canned light tuna. FDA data shows canned albacore has a mean mercury concentration of 0.350 ppm. Consumer Reports testing also found that most albacore warrants limited consumption of just one serving per week for adults.
Lower-Mercury and Safer Tuna Options
- Skipjack Tuna: Often labeled as "canned light" or "chunk light," skipjack tuna is a smaller, fast-growing species that contains the least amount of mercury. With a mean mercury concentration of 0.126 ppm for canned light tuna, it is the safest option for more regular consumption.
- Yellowfin Tuna: Fresh or frozen yellowfin has moderate mercury levels, averaging around 0.354 ppm. However, some products labeled "gourmet" or "tonno" can be yellowfin and have mercury levels comparable to canned white tuna.
Comparison of Tuna Species by Mercury Content
| Tuna Species | Average Mercury (ppm) | Consumption Advice (Adults) | Typical Use |
|---|---|---|---|
| Bigeye | 0.689 | Limit to very occasional consumption | Sushi, Sashimi |
| Large Bluefin | >0.689, varies by size | Limit to very occasional consumption | Sushi, Sashimi |
| Albacore (Canned) | 0.350 | Up to 1 serving per week | Canned White Tuna |
| Yellowfin (Fresh) | 0.354 | Limited consumption advised | Ahi Tuna, Steaks |
| Skipjack (Canned Light) | 0.126 | 2-3 servings per week, safer option | Canned Light Tuna |
Guidelines for Safer Tuna Consumption
To minimize mercury exposure while still enjoying the nutritional benefits of fish, consider the following points:
- Prioritize Low-Mercury Species: Whenever possible, choose canned light (skipjack) tuna over albacore. For fresh tuna, consider yellowfin, but be mindful of consumption frequency.
- Vary Your Fish Intake: Don't rely solely on tuna for your fish consumption. Incorporate a variety of other low-mercury fish and shellfish like salmon, sardines, shrimp, and cod.
- Mind Your Portion Sizes: Pay attention to recommended serving sizes, especially for high-mercury options like albacore. For example, pregnant women and young children have stricter consumption limits.
- Check Local Advisories: If consuming locally caught fish, consult local health department advisories, as mercury levels can vary by specific waterways.
- Be Aware of "Ahi" Tuna: "Ahi" can refer to either bigeye or yellowfin tuna. Always ask which species is being served to understand the potential mercury levels.
Conclusion
When asking what tuna has the highest amount of mercury, the answer is clearly bigeye and large bluefin tuna. These larger, longer-lived species accumulate the most methylmercury due to bioaccumulation. For most consumers, especially pregnant women and young children, prioritizing lower-mercury options like canned light (skipjack) tuna is the safest approach. By diversifying your seafood choices and being mindful of portion sizes, you can reap the health benefits of fish while effectively managing mercury intake. Always refer to authoritative sources like the FDA for the most current guidelines.
Additional Resources
For detailed advice from the FDA on eating fish and shellfish, including guidelines for pregnant and breastfeeding women, visit the FDA Advice on Fish Consumption.
