Mercury in tinned tuna: How worried should you actually be?

Tinned tuna is affordable, tasty and packed with nutrients. But concerns have been raised in the past, external about its mercury content. Before you throw your store cupboard stash away, we speak to the experts about whether it's safe to eat.

Mercury is a heavy metal that enters the ocean, external through volcanic eruptions and human activities like coal burning and industrial waste. Once in the water, mercury is transformed by bacteria into methylmercury, which is toxic and builds up in fish.

"All marine organisms will contain mercury," explains Dr Andrew Turner, associate professor in environmental sciences at the University of Plymouth.

"The further up the food chain you go the more mercury is accumulated, so when you get to the top, you find the highest levels, including in tuna but also in species like swordfish and shark."

Mercury can be found at low levels in other foods, including vegetables, external, but the World Health Organisation, which considers mercury one of the top ten chemicals of major public health concern, external, says the greatest risk comes from eating fish and shellfish.

Mercury is considered toxic to our health, particularly for pregnant women, nursing mothers, external and young children, external.

While most of us will have small amounts of methylmercury in our bodies, being exposed to high levels has been linked to effects on reproduction, concentration, speech and memory, external, and kidney damage, external.

In Great Britain and Europe, the maximum amount of mercury allowed in tuna and large predatory fish is 1.0 mg/kg, external. For smaller fish (like cod), it's 0.5 mg/kg in the UK and 0.3mg/kg in Europe, external.

"The EFSA and the FSA set these thresholds based on risk assessments, considering both the nutritional value of fish and the potential health risks," says Alex Ruani, nutrition science researcher and chief science educator at The Health Sciences Academy.

"So, instead of imposing a limit so low that it would make tuna less available, authorities set a threshold that more realistically reflects its higher mercury levels while aiming to keep it a practical and nutritionally valuable option."

The Food Standards Agency, external regularly monitors mercury levels in UK food and businesses are responsible for meeting the legal requirements. Local authorities also test products on sale to make sure they're sticking to the limits.

In the UK, the Committee on Toxicity's most recent report, external into mercury in the diets of very young children didn't identify any concerns – but professor Parvez Haris, a biomedical scientist and a fellow of the Royal Society for Public Health, believes limits should be introduced.

"Ideally, we should reduce our exposure to mercury as it's a toxic substance which isn't needed for healthy body functions," he says. "It would be good to have labels that provide information on mercury content so consumers are aware of what they are consuming."

Mercury levels in tuna vary according to the species, where it was caught and its diet, so Turner recommends looking out for skipjack, which he says can contain half the level, external of mercury found in some other varieties of tuna.

And the good news? According to the Marine Stewardship Council (MSC), external, almost 90% of tinned tuna sold in the UK and Ireland that carries the MSC mark is skipjack.

It's also worth noting that there are health benefits to eating tuna. It comes with vitamin D, vitamin B12, iodine and selenium, which are good for our health.

In the UK, the NHS recommends, external eating at least two portions of fish a week.

Those trying for a baby or pregnant should eat no more than four tins of tuna (based on a medium tin with a drained weight of 140g) or two tuna steaks (140g each) per week.

That's because tinned tuna, which typically contains smaller and younger fish, is thought to have lower levels of mercury than fresh.

"Canned tuna remains a nutritious and accessible food option," Ruani says. But people who eat tuna frequently "should be mindful of their mercury intake".

She recommends eating a variety of lower-mercury fish such as salmon, sardines, cod, and mackerel (but not king mackerel, as its mercury content is comparable to tuna).

"While tuna products are strictly regulated in the UK, consumers – especially those who are pregnant or looking to conceive, and children – should prioritise a mix of smaller fish species to reap the nutritional benefits while keeping mercury exposure in check."

Originally published February 2024. Updated March 2026.

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