Anses Agence nationale de sécurité sanitaire Alimentation Environnement Travail

Fish consumption and exposure to methyl mercury

Methylmercury (MeHg) is the toxic chemical form of mercury which can be absorbed by living organisms.
Mercury is a metal present naturally in trace amounts in the environment: it is mostly released from the earth's crust into the air and is then dispersed in soil, water and sediments. It also diffuses into nature because of waste from human activities: mining, metallurgy, conversion of paste to paper, waste combustion and fossil fuels in particular.
It is very volatile in its elemental form and then becomes toxic and easily bio-accumulable following chemical transformations. It is present in low concentrations in water or sediments in the methylated form and can be very highly concentrated in aquatic organisms, tending to rise in concentration up the food chain whenever one species eats another.

Why is Afssa concerned about it?

Fish consumption is the major source of dietary methyl mercury contamination in human beings. The level of fish contamination varies according to the species. This tends to be higher as the species reaches the top of the food pyramid (major predators). Average mercury content for example in swordfish, marlin (similar to swordfish) and siki (a variety of shark) is 4 times higher than in other predatory species such as tuna, dorado, ray, monkfish or ling.
At high dose, methyl mercury is toxic to the human central nervous system particularly during in utero development and in early childhood. It may cause hypertension, mild behavioural disorders or developmental delay in children exposed in utero or after birth even in the absence of signs of toxicity in the mother.

What does Afssa recommend?

Afssa does not consider that consumption of fish presents a risk to the health of the overall population. Intake of methyl mercury from fish is less than the acceptable daily dose (1) defined by the World Health Organization.

In terms of the nutrients obtained from consuming fish (essential fatty acids, proteins, vitamins and trace elements) Afssa recommends:
- eating fish twice per week, including one oily fish (salmon, mackerel, sardines, anchovies, herring, etc.);
- eating a wide range of different species of fish.
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Afssa recommends that specific precautions be taken by pregnant and breast-feeding women and young children (1 to 30 months old)
- as a precaution, avoid eating the most highly contaminated fish: sharks, sea lampreys, swordfishs, marlins (similar to swordfish) and sikis (variety of shark)
- limit consumption of fish likely to be highly contaminated (2) to 150g per week for pregnant and breast-feeding women and to 60g per week for young children (1 to 30 months old)

(1) The acceptable daily dose is the quantity of a substance that can be ingested on a daily basis by the consumer without any harmful effects on health.
(2) monkfishes or burbots, Atlantic wolf-fish, bonito, eels and elvers, Hoplopstethus Atlanticus, orange roughy or Hoplostethus Mediterraneus, grenadier, Atlantic halibut, megrim, mullet, pike, derbio, pout, Portuguese dogfish, rays, deep sea rosefish, Atlantic sailfish, silver and black scabbardfish, gilthead seabream, progy, black or striped escolar, oilfish, snake mackerel, sturgeon, tuna

February 2009

Opinions expressed by Afssa
Afssa received a mandate from the Directorate General for Health to produce 3 opinions assessing the health risk from consuming fish contaminated with methyl mercury. As these opinions have progressed, the Agency has refined and added more detain to its recommendations in light of the changes in international guideline values and information available about mercury, the dietary consumption of different categories in the population and the contamination of different types of fish.
October 2002
For the first time in France, an opinion was produced to prevent risks of mercury poisoning from consumption of fish. Afssa recommended that pregnant and breast-feeding women and young children should diversify their consumption of fish and reduce their consumption of fish liable to be highly contaminated.
March 2004
After the World Health Organization reassessment by the of the acceptable daily dose of mercury for health, Afssa strengthened its recommendations for pregnant and breast-feeding women and young children. It recommended that they should restrict their consumption of fish liable to be highly contaminated to once per week.
July 2006
Afssa strengthened and refined its previous opinion: it recommended that pregnant and breast-feeding women and young children avoided consuming the mostly highly contaminated fish (swordfish, marlin, siki). It considered that dietary consumption surveys were required in the overseas départements and territories to assess the exposure of their populations to methylmercury.