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Is fish dangerous to eat?

Sea-River Newsletter No. 129

26th January 2004

Periodically the authorities and consumer associations advise pregnant women and nursing mothers to consume only moderate quantities of fish to avoid contaminating their children with mercury. Is there a real danger?

Mercury accumulates in the flesh and fat of fish in the form of methyl mercury. Mercury present in the water is absorbed by algae and then levels build up all along the food chain following consumption of plankton, larger invertebrates eaten in turn by even larger fish, finally ending up with the very large predators. Each time there is a build up in concentrations. In tunas which are at the end of the chain the levels recorded are 500 000 times those found in the water!

From time to time, Canada (2002), USA (2001), Great Britain (2003) communiqués are issued advising pregnant women and nursing mothers to avoid eating carnivorous fish with long life-spans such as tuna and sea bream in order to avoid mercury contamination. This advice also applies to some freshwater fish, perch and pike in particular. The Health Canada Agency advises against consuming the flesh of large fish more than once a week at the most. The American Agency advises young people not to eat tinned fish and shellfish more than 2 or 3 times a week. The French Agency for food safety has not followed its counterparts and recommends the consumption of fish 2 or 3 times a week. The French nutritional programme does however warn against the effects of consuming large quantities of some species (tuna, swordfish, marlin, shark, sea bream, in particular). You will have to choose between essential amino acids and non saturated fats, which are excellent for the prevention of heart disease and the accumulation of toxic mercury in the body! Annual consumption of fish in France does not expose French people to any particular threat. Some point out shortcomings in both the recommendations and the findings of toxicity levels.

The first case of intoxication from mercury was seen in Minamata in Japan in 1956 and caused the death of several dozen people, 43 stillborn babies and 22 cases of malformation. The second case took place in 1971, in Iraq, with flour containing methyl mercury; over 1000 people were poisoned. In French Guyana and elsewhere, illegal gold extraction causes high-level mercury pollution.

Studies and monitoring are carried out regularly throughout the world. Opinions are mixed but the upgrading of standards and checks is envisaged (the well known precautionary principle), in particular in regions where the diet of the population consists mainly of fish. However, elsewhere the recovery of industrial or household mercury (batteries) is under way and closer monitoring is being set up. The only problem is that in many countries it is a choice between not eating fish and being contaminated, or not eating at all. An additional problem is that monitoring in these regions is very much a hit-and-miss affair.