Study assesses the level of mercury in fish and seafood that humans can digest

Abridged version in English: Diana Taborda

A study published in the journal “Marine Pollution Bulletin” points out the need for the implementation of a universal methodology to estimate the bioaccessibility of mercury (Hg), a toxic heavy metal, in fish and seafood commonly present in the Mediterranean diet, and highlights the importance of integrating bioaccessibility measurements in food safety legislation.

Bioaccessibility is about what the human body can absorb from the food we eat and is a particularly relevant tool in determining what maximum values for contaminants can be consumed over a lifetime without risk to health. At very low levels, mercury poses no danger to human health, but its long-term accumulation can have harmful effects.

This study, led by Filipe Costa, from the Centre for Functional Ecology of the Faculty of Sciences and Technology of the University of Coimbra (FCTUC), assessed the fraction of bioaccessible mercury in fish and seafood present in the Mediterranean diet, namely black scabbard, tuna, swordfish, blue shark, salmon and mullet; mussels and clams.

The choice of species was based on the main fish and seafood consumed in southern Europe and included species caught in the ocean (black scabbard, tuna, swordfish and blue shark), aquaculture species (salmon and mussels) and estuarine species (mullet and clams). To assess the level of bioaccessibility of the species under study, the team, which also includes Pedro Coelho and Cláudia Mieiro, from the University of Aveiro (UA), used three different forms of in vitro extraction, which "simulate in lab the effect of saliva, gastric juice and bile during the digestion process", explains Filipe Costa, noting that, in the case of black scabbard, three different cooking methods were also used: boiling, frying and grilling, to assess the impact of cooking processes on the bioaccessibility of mercury.

Overall, the results of the study indicate that the "bioaccessible Hg found in these fish and seafood species, especially after cooking, is well below the levels set by current safety risk assessment legislation. These results highlight the importance of integrating bioaccessibility measures into food safety legislation.", adds Filipe Costa.

The current food safety legislation only considers the total concentration of contaminants in fish and seafood, not taking into account the contaminant bioaccessibility during the digestion process nor the effect of cooking methods on the digestive solubilisation of the contaminant.

The scientific article may be found at: https://doi.org/10.1016/j.marpolbul.2022.113736