Understanding Mercury Contamination in Fish
Mercury is a naturally occurring element that enters oceans through both natural events and human activities, such as burning fossil fuels and industrial waste. In the water, bacteria convert this mercury into a highly toxic form called methylmercury, which is then absorbed by small marine organisms. This toxic compound climbs the food chain in a process called bioaccumulation. Since tuna are predatory fish that consume many smaller fish, they accumulate higher concentrations of methylmercury over their longer lifespans. This means that virtually all tuna, regardless of where it is caught or sold, contains some level of mercury.
Great Value Tuna: Mercury Levels by Species
Walmart's Great Value brand of canned tuna is subject to the same biological and environmental factors that affect all tuna products. The key determinant of mercury content in Great Value tuna, and any other brand, is the species of tuna used. The two most common types found on Walmart shelves are chunk light tuna and solid white (albacore) tuna.
- Great Value Chunk Light Tuna: This is typically made from smaller, faster-growing skipjack tuna. Skipjack has the lowest mercury levels of any commonly canned tuna species. This makes it a "Best Choice" for most consumers, according to FDA guidelines. The Environmental Working Group (EWG) has noted moderate contamination concerns for mercury in Great Value Chunk Light Tuna, but its levels are still significantly lower than albacore.
- Great Value Solid White (Albacore) Tuna: Albacore tuna are larger and live longer than skipjack, leading to higher levels of accumulated mercury—often three times more, on average, than chunk light. The FDA categorizes albacore as a "Good Choice," but recommends more limited consumption, especially for vulnerable populations.
Making a Safer Choice: Comparing Tuna Varieties
To help consumers navigate the options, here is a comparison of mercury levels in different types of canned tuna, based on FDA data.
| Species | Mercury (parts per million) | Typical Canned Product | FDA Designation | Recommended Consumption (Adults) |
|---|---|---|---|---|
| Skipjack | ~0.126 ppm | Canned Chunk Light | Best Choice | 2-3 servings per week |
| Albacore | ~0.350 ppm | Canned Solid White | Good Choice | 1 serving per week |
| Yellowfin | ~0.354 ppm | Some 'Gourmet' Canned | Good Choice | Limited to Albacore recommendation |
| Bigeye | ~0.689 ppm | Not typically canned | Avoid/Limit | Very occasional, if any |
It is important to note that mercury levels can spike unpredictably in individual cans, even within the same species. However, choosing chunk light over albacore remains the most reliable strategy for minimizing mercury exposure when consuming canned tuna.
Walmart Offers Lower-Mercury Alternatives
Walmart also stocks alternative brands that prioritize lower mercury content. For example, Safe Catch is a brand that specifically tests every individual fish for mercury to ensure it falls well below FDA action limits. While often pricier than Great Value, Safe Catch offers a reliable option for those who are particularly cautious about mercury intake. The availability of such brands provides consumers with a broader range of choices depending on their budget and health priorities.
How Often Can You Safely Eat Tuna?
The amount of tuna that is safe to eat depends on the type of tuna and your individual health profile. The FDA offers specific guidance for different populations, especially considering mercury's neurotoxic effects that are a concern for fetal and infant development.
- For the general population: Healthy adults can safely consume two to three servings (8 to 12 ounces) of canned light tuna per week. Consumption of albacore tuna should be limited to one serving (4 ounces) per week due to its higher mercury content.
- For pregnant or breastfeeding individuals: Due to increased risks for fetal development, it is generally advised to limit canned light tuna to two to three servings per week and to avoid albacore tuna altogether. However, some experts recommend avoiding all tuna to be fully cautious.
- For children: The FDA advises serving fish one to two times per week, with portion sizes adjusted for age. It is recommended to stick to low-mercury options like canned light (skipjack) tuna.
Other Considerations for Safer Seafood Consumption
To minimize your overall mercury intake while still enjoying the health benefits of fish, consider these steps:
- Diversify your protein sources. Don't rely solely on tuna. Incorporate other low-mercury, high-protein options like chicken, beans, or plant-based proteins.
- Choose a variety of seafood. Including a mix of low-mercury seafood can reduce your overall exposure. Lower-mercury fish options include salmon, sardines, shrimp, and tilapia.
- Check the label. Some canned products labeled as "gourmet" or "tonno" are made from larger yellowfin tuna and may have higher mercury levels than standard chunk light.
- Be aware of other contaminants. Beyond mercury, some canned seafood may contain other contaminants, such as BPA from the can lining. Check packaging for BPA-free options where available.
Conclusion: Making Informed Choices at Walmart
In conclusion, yes, Walmart's Great Value tuna, like all tuna, contains mercury. The good news is that the level is predictable based on the species inside the can. Opting for Great Value's Chunk Light (skipjack) tuna is the safest, low-mercury choice, while the Solid White (albacore) variety contains higher levels and should be consumed less frequently. By understanding these differences and adhering to recommended consumption guidelines, you can safely enjoy tuna as part of a balanced diet. For those with heightened health concerns or who want the lowest possible mercury levels, selecting a brand like Safe Catch, also available at Walmart, is a reliable alternative.
Environmental Defense Fund's Mercury Alert provides additional guidance on safe tuna consumption
