Understanding Mercury in Wild Caught Tuna: Species, Risks, and Safe Consumption

While all tuna contains some level of mercury, a 2018 study found that mercury levels in Pacific yellowfin and albacore were increasing at a rate of 3.8% annually, while levels in the Atlantic were declining. This guide explores how much mercury is in wild caught tuna and how to choose safer options.

Quick Summary

Mercury levels in wild-caught tuna vary significantly by species, with larger fish accumulating more over their lifespan due to bioaccumulation. Choosing smaller varieties like skipjack helps minimize exposure.

Key Points

• Species Matters: Larger, long-lived tuna like bigeye and albacore contain more mercury than smaller, short-lived skipjack tuna.

• Bioaccumulation is Key: Mercury builds up in tuna over their lifetime as they consume smaller contaminated fish.

• Vulnerable Groups: Pregnant women, breastfeeding mothers, and young children are most at risk and should limit high-mercury tuna consumption.

• Consume in Moderation: For most healthy adults, eating a variety of fish in moderation is safe, but it's wise to favor low-mercury species.

• Look for Skipjack: When choosing canned tuna, opt for 'canned light tuna' which is typically skipjack, a lower-mercury option.

• Low-Mercury Alternatives: Incorporate other healthy seafood like salmon, sardines, and shrimp into your diet to reduce overall mercury exposure.

What Is Mercury and How Does It Get Into Tuna?

Mercury is a naturally occurring element, but its levels in the environment have been significantly increased by human activities, such as burning fossil fuels. When released into the atmosphere, it eventually settles into oceans and waterways. Aquatic bacteria then convert this element into methylmercury, a potent neurotoxin that is readily absorbed by marine life.

The methylmercury then enters the food chain. Smaller fish absorb it and are consumed by larger fish, which are in turn eaten by even larger predators, such as tuna. This process is known as bioaccumulation, and because mercury is not easily excreted, it builds up in the tissues of fish over time, leading to the highest concentrations in apex predators like bigeye tuna.

The Mercury Difference: Species and Size

Not all tuna species have the same mercury content. The amount largely depends on the fish's size, age, and position in the food chain. Smaller, shorter-lived species tend to have significantly lower mercury levels than larger, longer-lived ones. This is a critical distinction for consumers to understand when making choices about which tuna to eat.

Comparing Mercury in Wild Albacore vs. Skipjack

• Skipjack Tuna: Often labeled as 'canned light tuna', skipjack is a smaller, shorter-lived species with the lowest mercury concentration among common tuna varieties. This makes it a better choice for regular consumption and for vulnerable groups.
• Albacore Tuna: Also known as 'canned white tuna', albacore is a larger species and typically contains about three times more mercury on average than skipjack. Due to its higher mercury level, consumption is more restricted, especially for pregnant women and children.
• Bigeye Tuna: This large species, often used for sushi (ahi), has the highest mercury levels and should be consumed only occasionally, if at all. The FDA explicitly advises pregnant women and young children to avoid bigeye tuna.

Potential Risks and Health Concerns

While the nutritional benefits of fish, including tuna, are well-documented, excessive mercury exposure carries risks. Mercury is a neurotoxin that, in high amounts, can affect the nervous system. The most vulnerable populations are pregnant women, breastfeeding mothers, and young children, whose developing brains are particularly susceptible. For adults, high mercury levels can lead to fine motor coordination issues, speech problems, and neurological damage. However, for most healthy adults consuming tuna in moderation and choosing lower-mercury varieties, the risks are generally minimal.

Comparison of Tuna Species by Mercury Content

To help you make informed decisions, here is a comparison of mercury levels in different tuna species, based on FDA data from 1990-2012.

Species	Mercury Concentration Mean (PPM)	Mercury Concentration Median (PPM)
Tuna (Canned, Light)	0.126	0.077
Tuna (Fresh/Frozen, Skipjack)	0.144	0.150
Tuna (Canned, Albacore)	0.350	0.338
Tuna (Fresh/Frozen, Yellowfin)	0.354	0.311
Tuna (Fresh/Frozen, Albacore)	0.358	0.360
Tuna (Fresh/Frozen, Bigeye)	0.689	0.587

Actionable Steps to Reduce Your Mercury Intake

By being a mindful consumer, you can enjoy the nutritional benefits of seafood while minimizing mercury exposure. Here are some practical steps to take:

Choose Wisely

• Opt for Skipjack: This is the safest choice for regular consumption due to its lower mercury content. Many cans labeled 'light tuna' contain skipjack.
• Limit Albacore and Yellowfin: If you prefer these varieties, restrict your intake to once or twice a week, following guidelines from health authorities like the FDA.
• Avoid Bigeye: For sushi enthusiasts, be aware that bigeye (ahi) tuna is very high in mercury and best avoided, especially by vulnerable groups.

Follow Official Guidelines

• The FDA recommends 8 to 12 ounces of seafood per week for most adults. Women who are pregnant or breastfeeding should follow specific, often more conservative, recommendations.
• Children should also follow age-appropriate serving size guidelines, typically favoring the 'best choice' (lower mercury) fish.

Diversify Your Seafood Choices

• Incorporating a wider variety of seafood can help reduce your overall mercury exposure. Some excellent low-mercury alternatives include salmon, sardines, shrimp, and tilapia. These options still provide valuable omega-3 fatty acids and other nutrients.

Conclusion: Balancing Benefits and Risks

While is there a lot of mercury in wild caught tuna is a valid question, the answer is nuanced and depends heavily on the specific species. Larger, longer-lived varieties like bigeye and albacore do contain significantly higher levels of mercury due to bioaccumulation, while smaller species like skipjack have much lower concentrations. By being informed about these differences and following sensible consumption guidelines, consumers can confidently enjoy the nutritional benefits of tuna while effectively managing their mercury intake. The key lies in moderation, variety, and making informed choices based on scientific evidence. For the most accurate and up-to-date information on mercury in commercial fish, refer to the U.S. Food and Drug Administration (FDA) guidelines.

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Low-Mercury Alternatives to Tuna

• Salmon: Excellent source of omega-3s with low mercury levels.
• Sardines: Small, oily fish with very low mercury and high omega-3 content.
• Shrimp: A popular and versatile seafood choice that is low in mercury.
• Tilapia: A low-mercury freshwater fish that is widely available.
• Catfish: Another low-mercury option.

The Role of Selenium

Some studies suggest that tuna contains a high amount of selenium, which binds to mercury and may help neutralize its potential toxic effects. However, this is not a substitute for following recommended consumption guidelines, as high levels of methylmercury can still pose a risk.

Wild vs. Farmed Tuna Mercury Levels

While the focus is often on wild-caught fish, some research has compared mercury levels between wild and farmed tuna, with interesting results. One study on Atlantic Bluefin tuna found that farmed specimens had lower mercury levels than wild ones of the same size. This was likely due to the controlled, lower-mercury diet fed to the farmed fish. This does not apply to all species or farming practices, but it highlights how environmental factors and diet influence mercury content.

Frequently Asked Questions

Which type of wild tuna has the least mercury?

Wild-caught skipjack tuna, which is typically used for canned light tuna, contains the lowest amount of mercury compared to other tuna species.

Should pregnant women or children avoid wild caught tuna completely?

Pregnant women and children are generally advised to limit consumption of higher-mercury species like albacore and bigeye tuna. They can still enjoy lower-mercury skipjack in moderation according to guidelines from health organizations.

Is fresh wild tuna higher in mercury than canned wild tuna?

The mercury level depends on the species, not whether it is fresh or canned. For instance, canned light (skipjack) tuna often has lower mercury than fresh albacore or bigeye tuna.

Does the wild caught status affect mercury levels?

Yes, but indirectly. The mercury level is more dependent on the fish species, its size, and age. Some studies show farmed tuna can have lower mercury due to controlled diets, but this is not a universal rule.

What happens if you eat too much mercury from tuna?

High levels of mercury exposure can lead to health issues such as neurological damage, impaired motor skills, and in severe cases, more serious nervous system problems, especially in vulnerable populations.

How often can a healthy adult safely eat tuna?

For most healthy adults, consuming a moderate amount of low-mercury tuna (like skipjack) as part of the recommended 8 to 12 ounces of seafood per week is considered safe. Consumption of high-mercury species should be limited.

Does selenium in tuna neutralize mercury?

While some evidence suggests selenium can bind to mercury and potentially mitigate its toxic effects, it does not completely eliminate the risk. Following recommended consumption guidelines based on mercury levels is still the safest approach.

How can I check the mercury content of a specific brand of tuna?

Some brands, like Safe Catch, test every fish for mercury, but most do not. Your best bet is to check the can's label to identify the species and consult FDA guidelines for typical mercury levels.