The Spanish Agency for Food Safety and Nutrition (AECOSAN) has just updated its guide with the recommendations to consume fish safely and prevent mercury poisoning. It should be noted that fish is a very important food, a source of proteins of high biological value and that it provides numerous essential nutrients such as iodine, calcium, selenium and vitamins A and D, as well as long-chain omega polyunsaturated fatty acids. -3. Fish is a safe food and should be a prominent component in the diet, just follow the guidelines recommended by experts. But let’s go by parts:
Why is there mercury in fish?
As Pablo L. Higueras Higueras, professor in the Department of Geological and Mining Engineering at the University of Castilla la Mancha explains, to understand the problem of mercury it is necessary to talk about its biogeochemical cycle. It is a very volatile element that can enter the atmosphere from its different sources (human activity, cinnabar deposits, etc.). “Once there, part of the metal vapor is transformed into a mercury ion, which is what is called reactive mercury,” the expert explains. “Upon reaching the ground, through rain and other processes, this mercury in ionic state is transformed into methylmercury, a soluble compound that ends up in rivers and bodies of water .”
Methylmercury is a very toxic compound, but it is too dispersed in ocean water and does not pose a real risk. The problem comes in fish, which do bioaccumulate the little mercury present in the water.
What fish have the most mercury?
As indicated by the AECOSAN, the amount of mercury in fish is related to its position within the trophic chain and therefore predatory, large and long-lived fish such as swordfish or emperor, shark (dogfish, shortfin mako, dogfish, dogfish and blue shark), bluefin tuna and pike have higher concentrations. “The largest and fattiest fish accumulate the most mercury,” Higueras tells us. “Bioaccumulation occurs in the musculature of the fattiest fish, and therefore, also, blue fish contains a higher concentration of mercury than white fish.”
The AECOSAN also offers a list of fish with low mercury content , which would be pollock, anchovy, anchovy, herring, cod, blue whiting, cockle, mackerel, squid, shrimp, crab, cañada, saithe, stoker, carp, cuttlefish, chirla , clam, cuttlefish, cuttlefish, cuttlefish, crayfish, coquina, bream, sprat, prawn, horse mackerel, lobster, prawn, European sole, lime or sole, seabass, mussel, whiting, hake, whiting, razor, oyster, poppet, flounder, Squid, octopus, shrimp, salmon, sardine, sardinella, sardinopa, plaice and trout. The rest of the fish are considered to be of medium mercury content. In the case of seafood, Higueras explains that the head is the part that accumulates the most heavy metals.
What are the fish consumption recommendations to avoid mercury poisoning?
The AECOSAN guidelines, based on the latest scientific and technical information available, divide the population into “vulnerable” and “general”. The vulnerable population includes women who are pregnant or planning a pregnancy, breastfeeding women and children aged 0-10 years on the one hand, and children aged 10-14 years on the other. For the first group, it is recommended to avoid the consumption of species with high mercury content and to take three or four servings of fish with medium and low mercury content, trying to vary the species between white and blue fish.
In the case of children from 10 to 14 years old, the guidelines would be the same, but species with a high mercury content could already be consumed, of course, limiting it to 120 grams per month. For the general population, it is recommended to consume all types of fish, three or four weekly servings and varying between white and blue fish.
“The real risk is for pregnant women,” Higueras reminds us, “methylmercury can pass to the fetus through the placenta and has a teratogenic effect, it is a neurotoxic element that can affect the developing central nervous system .” The problem with all this, points out the expert, is that the toxic effects of mercury are very difficult to measure at an experimental level, as they are very difficult to separate from other factors such as genetic or socioeconomic factors, which have a demonstrated effect on variables such as the intelligence. Because of this, and as is often the case in these cases, health authorities apply the precautionary principle and recommend that fish with a high mercury content be totally eliminated from the diet of pregnant women.
Minamata disease
In the 1950s, a series of cases of mercury poisoning began to be detected in the city of Minamata, Japan. The origin was in a petrochemical company that was pouring methylmercury directly into the bay: “the element was incorporated very quickly into the fish, which quickly reached very high concentrations,” explains Higueras. “This population, impoverished after the Second World War and whose main source of income was fishing, began to become intoxicated en masse.” It is estimated that between 1932 and 1968, the company dumped 81 tons of methylmercury into Minamata Bay.
This was the most notorious case of mercury poisoning, and as a result of it, this risk began to be taken into account in the recommendations for fish consumption.
Will there ever be no mercury in fish?
Due to its toxicity, mercury has been progressively replaced by other less dangerous elements. In this sense, the regulations of the European Union are quite strict and the current regulation, applicable since January 1, 2018, prohibits the manufacture and marketing of new products with mercury and new manufacturing processes that involve the use of mercury or of mercury compounds, except where there are significant benefits, which do not involve risks to health and the environment, and there are no viable mercury-free alternatives.
Does this mean that the mercury accumulated in the fish will disappear? “You have to remember that mercury is naturally present in the earth’s crust,” Higueras tells us. “With the legislation it is intended that the concentrations of mercury in the atmosphere will be lower and lower, in this way its transformation into methylmercury will also be reduced and therefore the risk of poisoning will be limited when consuming an excess of fish that bioaccumulates it in its tissues But mercury will continue to be present in soils, water and the atmosphere. So it will always be good to continue limiting consumption in the vulnerable population ”.
In any case, the researcher reminds us that fish is a very important food at a nutritional and energy level, and that the benefits of including it in our diet are much greater than the disadvantages. The key is, as always, to moderate your consumption rather than avoid it.
