Excessive consumption can be detrimental
Concerns about high mercury levels in canned tuna, a popular choice on many tables, have reignited. What are the dangers, and who is most vulnerable?
Canned tuna is a readily available and affordable source of protein; however, excessive consumption can be detrimental. Investigations by environmental organizations Bloom and Food Guardians in 2022 and 2024 revealed widespread mercury contamination in tuna, the most commonly consumed fish in Europe. Tests on 148 cans purchased across five European countries showed mercury contamination in all samples. Over half the samples exceeded the 0.3 mg/kg mercury level, and some reached up to four times the European standard of 1 mg/kg.
Last month, eleven cities in France—including Paris, Lyon, Marseille, and Nice—banned the sale of tuna in school cafeterias. The ban will remain until its mercury content is reduced from 1 mg/kg to 0.3 mg/kg, the stricter World Health Organization standard already applied to fish such as cod.
Dr. Irit Harmesh, deputy director of the Gastroenterology Institute at Rambam Health Care Campus and chairperson of the Department of Clinical Nutrition at the Israeli Gastroenterological Association, explains the risks associated with excessive consumption.
A young child can easily ingest four times the recommended limit of mercury
The problem is not only whether the legal limits are met, but rather that the limits themselves do not account for actual consumption. Proportionate to their body weight, a young child can easily ingest four times the recommended limit of mercury, just by eating larger quantities of fish.
Mercury exposure depends on dose and duration. “In the case of tuna, exposure is often small but continuous,” explains Harmesh. “Age is critical—the younger one is, the greater and more irreversible the damage, especially among toddlers and children.”
Children may suffer severe and lasting neurological damage, including cognitive impairments, vision and hearing disorders, and behavioural issues. In adults, long-term exposure may lead to tremors, sensory disturbances, difficulties with memory and concentration, and sleep disorders.
It accumulates in the body and is difficult to eliminate
Mercury, a heavy metal, is listed by the World Health Organisation as a public health concern. A potent neurotoxin, it accumulates in the body and is difficult to eliminate. The main sources of contamination are coal and other fossil fuel combustion, which releases thousands of tons of mercury into the atmosphere each year. Another source is illegal gold mining, which introduces additional mercury into rivers and oceans. Once in the ocean, bacteria convert mercury into methylmercury, a highly toxic form that is easily absorbed by marine life. Fish such as tuna cannot eliminate it, and when humans consume contaminated fish, mercury builds up in their organs and blood vessels, increasing the risk of kidney and lung disease as well as mercury poisoning.
Pregnant women are advised to avoid tuna
The public typically views tuna as a health food rich in protein, but is unaware of the health risks associated with high mercury levels. From the ocean to the canneries, safety regulations should be closely monitored by manufacturers and health authorities to protect the public. Pregnant women are advised to avoid tuna due to the risk of harm to the developing fetus, and consumers should also monitor their intake. However, these health risks can be mitigated: children should not eat tuna more than twice a week, and adults should limit their consumption to no more than three or four times a week. This way, they can reduce their exposure to mercury while still enjoying the benefits of fish as a source of high-quality protein, omega-3 fatty acids, and essential vitamins and minerals.
