Understanding Mercury Levels in Canned Tuna: A Safety Guide

If you've ever hesitated before adding canned tuna to your shopping trolley, wondering about mercury safety, you're not alone. Mercury in seafood is one of the most common concerns among Australian consumers, and it's an important topic that deserves a thorough, science-based explanation. The good news is that with proper knowledge, you can confidently enjoy canned tuna as part of a healthy, balanced diet.

In this comprehensive guide, we'll explore what mercury is, why it accumulates in fish, the actual risks involved, and how to make informed choices about your tuna consumption. By the end, you'll have all the information you need to enjoy this nutritious protein source with confidence.

What Is Mercury and How Does It Get Into Fish?

Mercury is a naturally occurring element found in the earth's crust. It enters the environment through volcanic activity, weathering of rocks, and human activities such as coal burning and industrial processes. When mercury reaches waterways, bacteria convert it into methylmercury, a form that can be absorbed by living organisms.

Fish absorb methylmercury primarily through their gills and by eating contaminated prey. This is where the concept of bioaccumulation becomes important. Small fish absorb mercury, and when larger fish eat many smaller fish, the mercury concentrates in their bodies. This process continues up the food chain, which is why larger, longer-lived predatory fish typically contain higher mercury levels than smaller species.

Mercury Levels in Different Tuna Species

Not all canned tuna is created equal when it comes to mercury content. The species of tuna used significantly affects the mercury levels you'll encounter:

Skipjack Tuna (Light Tuna)

Skipjack is the most common tuna species used in Australian canned products, particularly those labelled as "light tuna" or "chunk light." These fish are smaller, typically weighing 3-5 kilograms, and have a shorter lifespan of about 8-12 years. As a result, skipjack contains significantly less mercury than larger tuna species—approximately 0.12 parts per million (ppm) on average.

Yellowfin Tuna

Yellowfin tuna are medium-sized fish that grow larger than skipjack but smaller than bigeye or bluefin. They're often used in premium canned products. Mercury levels in yellowfin average around 0.35 ppm, making them a middle-ground option.

Albacore Tuna (White Tuna)

Albacore, often marketed as "white tuna," is prized for its mild flavour and firm texture. However, these fish live longer and grow larger than skipjack, resulting in higher mercury concentrations—typically around 0.35-0.40 ppm. Food Standards Australia New Zealand (FSANZ) recommends consuming albacore in moderation.

Australian Guidelines for Safe Tuna Consumption

Food Standards Australia New Zealand (FSANZ) provides specific guidance on fish consumption to help Australians enjoy seafood safely. These guidelines take into account both the benefits of eating fish (protein, omega-3 fatty acids, vitamins, and minerals) and the need to limit mercury exposure.

For the General Adult Population

Most Australian adults can safely consume 2-3 serves of canned tuna per week without exceeding recommended mercury limits. A standard serve is considered to be approximately 150 grams, which is roughly equivalent to one large can or two small cans of tuna.

For Pregnant Women and Women Planning Pregnancy

FSANZ provides more conservative recommendations for pregnant women due to mercury's potential effects on fetal development. Pregnant women can safely consume:

• 2-3 serves of canned tuna (skipjack/light) per week, OR
• 1 serve of albacore (white) tuna per week

It's important to note that these guidelines are designed with significant safety margins. Occasional consumption above these levels is unlikely to cause harm, but consistent overconsumption should be avoided.

For Children

Children's serves should be adjusted based on their body weight. Generally, children can safely eat proportionally smaller portions following the same frequency guidelines as adults. For more specific advice, particularly for infants and toddlers, consulting with a paediatrician or dietitian is recommended.

The Health Benefits That Outweigh the Risks

When consumed within recommended guidelines, the nutritional benefits of canned tuna far outweigh the minimal risks from mercury exposure. Tuna provides:

• High-quality protein: A 95g can provides approximately 20-25 grams of complete protein
• Omega-3 fatty acids: EPA and DHA support heart health, brain function, and reduce inflammation
• Vitamin D: Essential for bone health and immune function
• Selenium: An antioxidant that may actually help protect against mercury's harmful effects
• B vitamins: Including B12, niacin, and B6 for energy metabolism

Research consistently shows that the cardiovascular and neurological benefits of eating fish, including tuna, are substantial when consumed as part of a balanced diet. The key is moderation and variety.

Practical Tips for Minimising Mercury Exposure

Here are some evidence-based strategies to enjoy canned tuna while keeping mercury intake low:

Choose Skipjack When Possible

Look for products labelled "light tuna" or check the ingredients list for skipjack. Most Australian supermarket brands like John West, Greenseas, and Safcol offer skipjack options.

Vary Your Seafood Choices

Don't rely solely on tuna for your seafood intake. Rotate between different fish species, including low-mercury options like salmon, sardines, and Australian whiting.

Practice Portion Awareness

Be mindful of serving sizes. If you're eating tuna regularly, opt for the 95g cans rather than the larger 425g cans, which can lead to overconsumption.

Consider Your Overall Diet

A diet rich in selenium (found in Brazil nuts, eggs, and sunflower seeds) may help your body process and eliminate mercury more effectively.

The Bottom Line

Mercury in canned tuna is a legitimate consideration, but it shouldn't prevent you from enjoying this nutritious, convenient, and affordable protein source. For most Australians, consuming 2-3 serves of canned tuna per week—preferably skipjack or light varieties—is perfectly safe and provides significant health benefits.

The key is to make informed choices: understand the differences between tuna species, follow the guidelines appropriate for your situation, and maintain variety in your diet. By doing so, you can confidently include canned tuna as part of a healthy eating pattern for you and your family.

If you have specific health concerns or are in a higher-risk category (pregnant, planning pregnancy, or feeding young children), consulting with a healthcare professional can provide personalised guidance based on your individual circumstances.