Growing concern around a cheap cupboard staple has triggered fresh questions about what really hides in our favourite tins.
For millions of households, canned tuna looks like the perfect shortcut: high in protein, low in price, endlessly convenient. A new investigation reported by French consumer magazine 60 Millions de consommateurs, and led by two NGOs, now paints a far more troubling picture of what regular tuna eaters might actually be swallowing.
The investigation that shook the tuna aisle
The report shared by 60 Millions de consommateurs pulls together testing carried out by NGOs Foodwatch and Bloom across five European countries. In total, laboratories analysed 148 tins of tuna sold in mainstream supermarkets.
Every single sample tested contained mercury, and one in ten exceeded the legal European limit for this toxic metal.
The EU currently sets the maximum mercury level for tuna at 1 milligram per kilogram of flesh. According to the NGOs’ data, around 10% of the products tested went beyond that threshold. A few tins even showed levels roughly four times higher than the limit, including certain products from the well-known brand Petit Navire, reportedly reaching up to 3.9 mg/kg in tins sold in Carrefour City stores.
These are not obscure brands tucked away on a dusty shelf. They are mainstream, heavily marketed products that many consumers assume are safe by default.
Why tuna is so heavily contaminated
Mercury is a heavy metal that ends up in the oceans mainly through industrial and mining pollution. Once there, it transforms into methylmercury, a highly toxic compound that accumulates in marine life.
Tuna sits high in the marine food chain. It is a large, long-lived predator that feeds on smaller fish, which themselves have already absorbed mercury from plankton and the surrounding water.
The higher a fish sits in the food chain, the more mercury tends to build up in its flesh over time.
This process, called bioaccumulation and biomagnification, explains why tuna, swordfish and other top predators regularly show higher mercury readings than smaller, short-lived species such as sardines or mackerel.
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Are current safety limits too generous?
The investigation has reignited debate around European safety thresholds. For tuna, the EU allows three times more mercury than for most other seafood products. In other words, tuna is given its own, far more flexible ceiling.
In information published on the website of the French National Assembly, officials state that a 70-kilogram adult could safely eat 91 grams of tuna a week if the product contains exactly 1 mg/kg of mercury. That works out at roughly 4.7 kilograms of tuna per year.
For NGOs and consumer advocates, this is where alarm bells ring.
Campaigners argue that the limit looks designed to keep most of the tuna trade flowing, rather than to build in a real margin of safety for public health.
Foodwatch and Bloom say the current threshold leaves too little protection for heavy consumers, vulnerable people and those who unknowingly buy the most contaminated brands. 60 Millions de consommateurs echoes their call for tighter rules and clearer information on packaging.
When asked whether Brussels should review the limits for tuna and other large predators, the French National Assembly published a strikingly blunt response: there was “no reason” to push for a lower maximum level at EU level. For many public health campaigners, that answer feels badly out of step with the test results.
Brands singled out: who’s at the bottom of the class?
The analysis does not treat all labels equally. Some brands appear far more frequently among the worst performers, with higher mercury readings and repeated mentions in the NGOs’ findings.
Among the canned tuna brands flagged as the least reassuring are Cora, Carrefour Discount, Petit Navire, Saupiquet and Pêche Océan.
Other names, while not mercury-free, show much lower levels across the samples tested. Among these relatively better options are Monoprix-branded tuna, Casino’s “thon blanc germon”, Connétable, and Phare d’Eckmühl.
To make the landscape easier to grasp, here is a simplified snapshot based on the report shared by 60 Millions de consommateurs:
| Category | Examples of brands | Comment |
|---|---|---|
| Brands to avoid | Cora, Carrefour Discount, Petit Navire, Saupiquet, Pêche Océan | More frequent high mercury readings, including some above EU limits |
| Less concerning brands | Monoprix, Casino thon blanc germon, Connétable, Phare d’Eckmühl | Lower average levels in tests, but still not mercury-free |
Even the “safer” category still contains mercury. The difference lies in the dose, not the presence or absence of contamination.
Health risks: who should worry most?
Mercury, especially in the form of methylmercury, is a neurotoxin. It targets the brain and nervous system. High or long-term exposure can cause coordination issues, sensory disturbances, memory problems and, in extreme cases, severe neurological damage.
Certain groups are far more at risk than the average healthy adult:
- Pregnant women, because mercury can cross the placenta and affect foetal brain development.
- Young children, whose nervous systems are still forming.
- Women planning a pregnancy, as mercury accumulates in the body over time.
- Heavy fish consumers, such as people relying on tuna several times a week for budget reasons.
For these groups, eating large predatory fish regularly can push exposure above what health agencies consider tolerable. Some national guidelines already advise pregnant women to limit tuna and avoid swordfish or shark entirely.
How often can you safely eat tuna?
Public health authorities generally work with a “tolerable weekly intake” for mercury, often around 1.3 micrograms per kilogram of bodyweight. For a 70 kg adult, this gives roughly 91 grams of tuna a week if the fish sits right at the EU limit of 1 mg/kg.
The problem is real life: many tins fall below the limit, but some shoot well above, and regular eaters have no easy way to tell which is which.
In practice, nutritionists often recommend that adults who like tuna:
- Keep canned tuna to once a week at most.
- Alternate with smaller fish such as sardines, anchovies or mackerel.
- Vary sources of protein, including plant-based options like beans or lentils.
For pregnant women, some guidelines suggest limiting canned tuna to one or two small portions per month, and avoiding large fresh tuna steaks completely.
Practical swaps: cheaper fish with less mercury
The appeal of tuna lies in price and practicality. So what can you put in your sandwich, pasta or salad instead?
From a mercury standpoint, smaller oily fish are clear winners. Sardines and mackerel tend to contain far less mercury, because they feed low in the food chain and live shorter lives.
Sardines, mackerel and herring often bring more omega‑3s and less mercury than tuna, at a similar or even lower price.
Here are a few easy swaps:
- Tuna sandwich → sardine or mackerel sandwich with lemon and herbs.
- Tuna pasta → pasta with canned sardines, garlic and cherry tomatoes.
- Tuna salad → bean and mackerel salad with olive oil and vinegar.
These alternatives still offer protein, iron and omega‑3 fats, often with the bonus of higher vitamin D levels.
Why the NGOs are pushing for rule changes
Foodwatch, Bloom and 60 Millions de consommateurs are not asking people to abandon fish altogether. Their message targets regulators and industry just as much as shoppers.
They want tighter legal limits for large predatory fish, better monitoring across brands, and clear, readable information on packaging regarding recommended consumption, especially for vulnerable groups.
The broader question is whether economic interests around tuna stocks are weighing more heavily than long-term public health.
For consumers, the investigation is a reminder that not all fish is equal from a contamination standpoint. Tuna still has a place in many diets, but occasional use, brand choice and species diversity make a real difference to long-term exposure.
Key terms and real-life scenarios
Two technical notions sit at the heart of this issue.
Bioaccumulation describes how a toxin like mercury builds up in a single organism over time. A tuna that lives for years keeps adding small doses of mercury to its tissues throughout its life.
Biomagnification refers to what happens up the food chain. Small fish eat contaminated plankton, medium fish eat lots of small fish, and large predators eat plenty of medium fish. The higher you go, the more concentrated the toxin becomes.
Consider a common scenario: a student relies on cheap canned tuna four times a week, using it in sandwiches, pasta and salads. If some of those tins sit close to or above the EU mercury limit, their weekly exposure could quickly overshoot recommended levels, even if they fall within legal sales standards.
Or picture a pregnant person who enjoys sushi, tuna steaks and canned tuna. Without tailored advice, she might unknowingly mix different high-mercury sources during the same week, increasing the risk for the baby’s developing brain. This is why NGOs urge clearer consumer messaging, beyond intricate toxicology tables buried in official documents.