Heavy Metals: The Primary Concern
Among the various chemicals potentially found in canned tuna, heavy metals—especially mercury—are the most well-documented and concerning. Mercury is a naturally occurring element, but industrial activity has increased its presence in the marine environment. Once in the ocean, it's converted by bacteria into methylmercury, a highly toxic form that accumulates in fish tissue.
Bioaccumulation and Tuna Species
Tuna's position high on the marine food chain means it accumulates more methylmercury than smaller fish. Larger, older tuna species, like albacore and bigeye, have had more time to bioaccumulate significant levels of the toxin, resulting in higher concentrations. Smaller, younger species like skipjack and tongol, which are commonly used for 'light' canned tuna, contain lower mercury levels.
High exposure to methylmercury can cause neurological damage, particularly affecting the brain and nervous system. This makes it a serious concern for sensitive populations, including young children and pregnant or breastfeeding women, as mercury can impact fetal and early childhood development.
Can Lining Chemicals
Beyond the fish itself, the can's packaging is a source of chemical exposure. The linings of many metal cans contain bisphenol A (BPA), an industrial chemical used to prevent corrosion and keep the food fresh.
BPA and Its Alternatives
BPA is an endocrine disruptor, and while the FDA maintains its use is safe at current levels, some studies suggest regular exposure could pose health risks. As a result, many companies have switched to BPA-free linings, using alternatives like bisphenol S (BPS) or acetyltributylcitrate (ATBC). However, some research suggests that these alternatives may not be entirely benign. Consumers concerned about BPA and related compounds should look for cans explicitly labeled 'BPA-free' or opt for alternative packaging like pouches or glass jars.
Other Additives and Contaminants
Canned tuna is not just fish and can lining. Manufacturers add several ingredients during processing. The liquid packed with the tuna—either oil or water—is a key ingredient. Sodium is almost always added for preservation and flavor, and some products include additional seasonings or broths.
Common Additives
- Sodium: Canned tuna typically contains high levels of sodium. For those monitoring their intake, 'no salt added' or low-sodium varieties are available.
- Vegetable Broth/Hydrolyzed Protein: Some canned tuna products, especially chunk light, may contain vegetable broth or hydrolyzed proteins to enhance flavor and texture. This can also increase water retention.
- Spices and Flavorings: Ingredients like garlic, lemon flavoring, and spices are often added for taste.
- Sodium Acid Pyrophosphate: This additive is sometimes used to maintain a consistent color in the fish.
Other Contaminants to be Aware of
While less common or regulated, other contaminants can appear. A 2024 study detected glycidol in canned tuna, a processing contaminant associated with oils, with higher levels in olive oil varieties. Other heavy metals like cadmium and lead have also been detected in some products, though usually within regulatory limits. A study published in 2023 also highlighted carcinogenic risks associated with inorganic arsenic in some brands.
Choosing Safer Canned Tuna
To minimize exposure to unwanted chemicals, consumers can take a few simple steps. The most impactful is choosing the right type of tuna. Smaller species, like skipjack, have less accumulated mercury. You can also be mindful of the can and its contents.
Comparison of Mercury Levels in Canned Tuna
| Tuna Type | Typical Species | Average Mercury Level (ppm) | FDA Consumption Recommendation |
|---|---|---|---|
| Light Tuna (Canned) | Skipjack | ~0.118 | 2-3 servings (4oz each) per week |
| Albacore (White) Tuna | Albacore | ~0.350 - 0.407 | 1 serving (4oz) per week |
| Bigeye Tuna | Bigeye | ~0.689 | Avoid |
How to Reduce Chemical Exposure
- Choose light over albacore: Opting for skipjack-based 'light' tuna dramatically reduces mercury intake.
- Look for BPA-free cans: Select brands that advertise BPA-free linings or use alternative packaging.
- Check the sodium content: Choose 'no salt added' or low-sodium options to manage dietary sodium intake.
- Diversify your seafood: To reduce reliance on one type of fish, consider including other low-mercury seafood like salmon, sardines, and shrimp in your diet.
- Buy from reputable brands: Some companies, like Safe Catch, test every fish for mercury, offering added assurance.
Conclusion
While canned tuna is a convenient and nutritious source of protein and omega-3s, its potential chemical contaminants warrant an informed approach. Mercury poses the most significant health risk, especially with larger species like albacore. Additionally, chemicals from can linings, such as BPA, and various additives like sodium, are common in canned products. By choosing smaller species like skipjack, opting for BPA-free containers, and consuming in moderation, consumers can enjoy the nutritional benefits of canned tuna while effectively minimizing chemical exposure. For more information on mercury levels in fish and updated consumption advisories, refer to the FDA's official guidance.
