©Sean Robertson via Unsplash
In recent years, the amount of mercury found in tuna fish has been getting increased attention around the world. The concern is particularly related to levels of methylmercury, a toxic form that can accumulate in fish tissue and have harmful effects on human health.
Now, a new study has been conducted in Poland that inventories the heavy metals not only in tuna, but in many other fish we consume regularly as well.
The fish analyzed
The researchers examined 20 fish species commonly available on the Polish market, including herring, cod, salmon, sea trout, trout, tuna, halibut, sole, dab, mackerel, hake, sea bream and perch. Some species were caught directly in the Baltic Sea, while others were purchased from local markets in 2021 and 2022.
For each fish species, at least 10 samples were analyzed, and for each, the concentrations of cadmium (Cd), lead (Pb), total mercury (THg), methylmercury (MeHg) and inorganic arsenic (iAs) were measured to assess the health risk to consumers.
The good news is that almost all species show reassuring values, well below the limits set by European and international regulations. The presence of heavy metals is minimal and poses no danger to regular consumers of these fish products.
The tuna problem
The situation changes dramatically when it comes to tuna. This species shows average concentrations of total mercury (THg) of 0.919mg/kg, close to the maximum permissible limit of 1mg/kg, with some samples reaching as much as 2.28mg/kg. The most alarming figure relates to methylmercury (MeHg), the form most dangerous to the human body, which in tuna reaches average levels of 0.684mg/kg, much higher than in all the other species analyzed.
The risk indicator calculated by the researchers show THQ values (an indicator used to estimate the risk of a chemical contaminant in food) for MeHg in tuna that exceed twice the recommended safe threshold. This does not mean that tuna should be eliminated from the diet, but clearly indicates that it should be consumed in moderation.
Why does tuna collect the most mercury? As is now well known, the explanation lies in tuna's position in the marine food chain. As a large, long-lived predator, tuna accumulate larger amounts of pollutants in the aquatic environment over time. This is because mercury and other heavy metals are not easily degraded and gradually concentrate higher up the food chain. Simply put, the larger and longer a fish lives, the more toxins it accumulates in its tissues.
Marine pollution has various causes - from industrial activities to emissions - and heavy metals eventually end up in sediments and waters and enter the food chain through small organisms that are then eaten by larger fish.
Who should pay more attention and how can we protect ourselves?
Methylmercury is particularly harmful to the nervous system. The most vulnerable groups are: pregnant women (mercury can cross the placenta and damage fetal brain development); nursing mothers; children and adolescents whose nervous systems are still developing; and people who consume tuna frequently and in large quantities.
Long exposure to methylmercury can cause neurological problems, learning difficulties, memory and attention disorders, and possible motor and visual impairments.
Based on the results, the researchers stress that tuna consumption should be moderate. In addition to this specific indication, there are some good practices commonly recommended by experts to continue to benefit from the nutritional properties of fish while reducing exposure to contaminants, such as varying the species consumed, preferring small fish and choosing products carefully based on origin and certifications.
The researchers also noted that tuna consumption should be moderate.
According to the data collected, the presence of heavy metals in fish has remained largely unchanged over the past decade, with no overall deterioration. The only exception is mercury in tuna, confirming that this is a species that should be monitored. This highlights the importance of monitoring for the presence of heavy metals in tuna.
(©Food and Chemical Toxicology via GreenMe.it 2026/Managing Editor: Julie Morgan - The Press Junction/Picture: ©Sean Robertson via Unsplash)