A dozen years ago, Robert F. Kennedy Jr. – a short-lived candidate for the 2024 US presidential election, now aligned with Donald Trump – was suffering from severe cognitive problems, including mental fog and memory loss. So much so that, in addition to his recurring heart problems, he was thought to have a brain tumor. In May, the New York Times revealed that he had been found to have the remains of a parasitic worm in a corner of his brain, but that his doctors suspected that the more likely cause of his troubles was far less spectacular. It was, as he confided to the American daily, his immoderate love of tuna sandwiches – a fish that is among the most contaminated with methylmercury, a powerful neurotoxicant. How can the consumption, even excessive consumption, of such a trivial food cause effects of this magnitude? In a report published on Tuesday, October 29, the French NGO Bloom provided a series of answers that, according to its president, Claire Nouvian, amount to "an authentic health scandal."

The French NGO devoted to the protection of the oceans had nearly 150 cans of tuna analyzed. It is using the results to argue in favor of lowering the permitted levels of mercury in the flesh of this fish, the most widely consumed in Europe. One in 10 cans tested exceeded the limit value for fresh tuna, which is 1 milligram per kilo (mg/kg) in Europe. According to Bloom, this high rate is not aimed at protecting public health, but at maximizing the compliance rate of fish, in order to keep them on the market. As a result, according to Bloom, people are overexposed to the health thresholds set by the authorities, who estimate the amount of mercury that can be absorbed each week without health risk: 1.3 micrograms per kilo of body weight per week (µg/kg bw/week) for the European Food Safety Authority (EFSA). Its American counterpart goes with almost half this amount, 0.7 µg/kg bw/week.

A heavy metal resulting from coal combustion, mining and certain industrial activities, mercury is dispersed in the environment. It then continues its journey in the oceans, where it is transformed into methylmercury, and accumulates in marine organisms, particularly at the top of the food chain. It then ends up in the bodies of consumers of tuna, shark and swordfish.

In France, the biomonitoring study published in 2021 by Santé Publique France (SPF, the French public health agency) indicated that contamination of the population is widespread. Whether or not this contamination is problematic depends on the safety thresholds considered. According to the thresholds adopted by SPF, mercury levels found in hair are indicative of risk only for 0.8% of adults, 2.1% of women of childbearing age and 2.4% of children (aged 6 to 17). Applying the US authorities' thresholds, 27.4% of adults and 7.6% of 6-17 year-olds are at risk in France. The study has no data for the under-6s, the most vulnerable population.

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