This is one of the most frequent questions among our readers, and it is not difficult to understand why: tuna is a food present in many of our kitchens, there are those who eat it once a week, and those who instead base their nutrition on this ingredient (see university students). The growing focus on mercury levels raises questions about whether glass packaging really makes a difference.
Mercury is everywhere, even in glass tuna
The latest investigation by BLOOM, a marine conservation organisation, reveals an inconvenient truth: all cans of tuna analyzed in Europe, regardless of packaging, were found to be contaminated with mercury. The research involved 148 packs of canned tuna coming from five European countries: Germany, England, Spain, France and Italy. These samples were tested by an independent laboratory which confirmed the presence of mercury in the 100% of the packs analyzed.
The data is alarming: over half of the cans (the 57% of the sample) exceeded the mercury limit allowed for other fish species, set at 0.3 mg/kg. Among the most striking cases, a package of the Petit Navire brand, purchased in a Carrefour City in Paris, showed a mercury content equal to 3.9 mg/kg — that is, 13 times higher than the limit applied to fish such as cod. These values reflect a Accumulation of mercury in tuna due to its position at the top of the food chain: every prey ingested contributes to increasing the concentration of heavy metals, making this fish one of the most contaminated among those commonly consumed in Europe.
Therefore, whether tuna is stored in glass or cans, the risk linked to mercury does not change. But choosing tuna in glass is still preferable since, unlike cans, it does not carry the risk of contamination from BPA, a chemical substance that can migrate from the lining of cans into food and have harmful effects on health.
Why are tuna allowed higher mercury limits than other fish?
According to BLOOM, the difference in mercury limits between fish species has no health basis. For example, the maximum mercury threshold allowed for tuna is three times higher than that of other species such as cod. This is due to economic choices, rather than real health assessments, justified to guarantee the commercialization of a species so widespread in Europe.
What are the health risks?
Even small consumptions of tuna can expose us to doses of mercury which constitute a serious risk for the human nervous system. This toxic substance, known for its ability to cross the blood brain barrier, accumulates in the body with potentially serious consequences. A study conducted by the Centers for Disease Control and Prevention (CDC) in the United States found that high levels of methylmercury in the blood are associated with a significant risk of neurotoxic effects, particularly in children and fetuses, as mercury can impair brain development.
For pregnant women, mercury intake even at low doses is concerning: research published in the “New England Journal of Medicine” highlight how prenatal exposure to mercury can cause cognitive delays, attention disorders and motor development problems in children. Other studies, including a review of theEnvironmental Health Perspectivesreport that frequent consumption of large fish, such as tuna, is associated with increased memory problems and reduced cognitive abilities in adults.
As an apex predator, tuna accumulates mercury throughout the food chain, in quantities about ten times higher than smaller fish such as sardine or cod. A meta-analysis conducted byEuropean Food Safety Agency (EFSA) estimated that for every increase in methylmercury in the human body there corresponds an increase in neurotoxic effects, with potentially irreversible consequences in cases of continuous exposure.
How to protect yourself?
BLOOM and Foodwatch are calling for an urgent review of European regulations, proposing to reduce the mercury threshold for tuna to 0.3 mg/kg and to exclude tuna from hospital, school and kindergarten canteens. Furthermore, these organizations are putting pressure on large-scale retail brands to limit the promotion of tuna, especially contaminated tuna.
