Understanding Mercury in Seafood
Mercury is a naturally occurring element that enters our oceans and waterways from industrial pollution and natural events like volcanic eruptions. In aquatic environments, bacteria convert elemental mercury into a highly toxic form called methylmercury. Fish and shellfish absorb this methylmercury, and it accumulates in their tissue.
The process of bioaccumulation and biomagnification means that fish higher up the food chain, or those that are larger and older, tend to have higher concentrations of mercury. This is the key reason for the variation in mercury levels between different fish species and even within the same species.
The Mercury Comparison: Cod vs. Tuna
When comparing cod and tuna, it is important to specify the type of tuna, as different species have vastly different mercury levels. Cod, a relatively smaller and shorter-lived fish, consistently falls into the low-mercury category. In contrast, tuna varieties range from low to high mercury, largely depending on their size and diet.
Cod Mercury Levels
Cod is consistently listed as a low-mercury fish. The FDA places cod in its "Best Choices" category, recommending 2–3 servings per week for most populations, including pregnant women and young children. The FDA's data shows that cod has an average mercury concentration of around 0.111 ppm. This relatively low level makes cod a safe and nutritious choice for regular consumption.
Tuna Mercury Levels
The mercury concentration in tuna varies dramatically by species and how it is processed. Understanding these differences is crucial for making healthy choices.
- Canned Light Tuna (Skipjack): This is one of the safest tuna options. Skipjack tuna are smaller and younger, so they accumulate less mercury. The FDA classifies canned light tuna as a "Best Choice" with an average mercury concentration of 0.126-0.128 ppm, a level comparable to cod,.
- Canned Albacore Tuna: Known as "white" tuna, albacore is a larger species than skipjack and therefore contains significantly more mercury. It is categorized as a "Good Choice" by the FDA, with an average mercury concentration of around 0.35 ppm. The recommended consumption is much lower than for canned light tuna, especially for vulnerable groups.
- Fresh/Frozen Yellowfin Tuna: This larger, predatory tuna species is also categorized as a "Good Choice" with an average mercury concentration of around 0.354 ppm.
- Fresh/Frozen Bigeye Tuna: As one of the largest tuna species, bigeye has the highest mercury concentration and is placed in the "Choices to Avoid" category by the FDA for sensitive populations,. Its average mercury level is reported at 0.689 ppm.
Comparison of Mercury Levels (ppm)
| Fish Type | FDA/EPA Category | Mean Mercury Concentration (ppm) | Consumption Advice (for general population) |
|---|---|---|---|
| Cod | Best Choice | 0.111 | Eat 2-3 servings per week |
| Tuna (Canned Light) | Best Choice | 0.126 | Eat 2-3 servings per week |
| Tuna (Canned Albacore) | Good Choice | 0.350 | Eat 1 serving per week |
| Tuna (Yellowfin) | Good Choice | 0.354 | Eat 1 serving per week |
| Tuna (Bigeye) | Choices to Avoid | 0.689 | Avoid for sensitive groups |
Official Guidance on Safe Fish Consumption
The FDA and Environmental Protection Agency (EPA) provide joint advice to help consumers, particularly pregnant women, breastfeeding women, and young children, make safer choices. The guidance is based on balancing the nutritional benefits of fish, such as omega-3 fatty acids, with the risks of mercury exposure. For these vulnerable groups, the advice is to eat 8 to 12 ounces of seafood per week from a variety of low-mercury fish.
Choosing Low-Mercury Alternatives
For those looking to diversify their seafood intake while keeping mercury levels low, many other delicious options are available. Some of the best choices include:
- Salmon: An excellent source of omega-3s with very low mercury levels.
- Sardines: Also rich in omega-3s and considered a low-mercury fish.
- Pollock: A flaky whitefish often used in fish sticks, with very low mercury content.
- Shrimp, Scallops, and Oysters: Most shellfish are very low in mercury,.
Balancing Health and Safety
The key to safe fish consumption is variety and moderation. Eating a wide variety of seafood from the "Best Choices" and "Good Choices" categories helps minimize your exposure to any single contaminant, while still allowing you to reap the many health benefits fish provides.
Conclusion
In conclusion, cod generally has less mercury than most varieties of tuna, making it a reliable low-mercury option. The popular perception that all tuna is high in mercury is inaccurate; canned light tuna has a comparable mercury level to cod and is also considered a "Best Choice" by the FDA. To maintain a healthy balance, consumers should favor these lower-mercury options and be mindful of consuming larger tuna species, like albacore and bigeye, in moderation. For the most up-to-date and comprehensive recommendations, always consult official health advisories.
For more detailed guidance on safe fish consumption based on mercury levels, consult the official FDA Advice on Eating Fish.
