Before the industrial revolution, the mercury present in the sea was not significant, since it only reached it by natural processes. The situation changed when this substance began to be used in industry and its waste began to reach the sea. There, its structure changes and becomes methylmercury, a molecule that sticks to fish and molluscs and that is toxic to humans. However, the amount that reaches each fish is not the same, since it depends on several factors such as the level of exposure to them and the composition of each fish. Thus, a fish that feeds on other fish that have a small amount of mercury, will have more of this substance. In addition, mercury seems to adhere better to fatty tissues, so blue fish usually have more.
For all this, there are fish whose level of mercury is much higher than that of others. Does that mean we should eliminate its consumption? According to the European Food Safety Authority (EFSA), no. This is so because, although a weekly consumption above 1.3g (micrograms of methylmercury) per kilo body and 4g of inorganic mercury is harmful, these fish contain large health benefits. In this way, the solution is to limit the consumption of species with a high content of methylmercury, but not to eliminate them.
However, this recommendation is not valid for everyone, since in the case of pregnant or breastfeeding women, as well as children under three years, it is advisable to avoid consumption. And in children between 3 and 12 years limit it to 50g per week, as indicated by AECOSAN. For this group, which is more vulnerable to toxicity, the best is increase the consumption of low fish in methylmercury and leave aside the high content ones. Well, what are those fish?
The swordfish is a very fast predator that consumes a large amount of fish per day, so the amount of mercury that accumulates in your body on a daily basis is high. In return, this semi-porous fish is low in calories and is a good source of vitamin B12 and B6.
It is the main predator of the sea, in fact, its only threat is the human being. This makes their mercury intake one of the highest. It is a semi-fatty fish with interesting levels of vitamin A and E, but in general, its nutritional properties are not remarkable compared to other fish.
The bluefin tuna is one of the fastest hunters of the sea and feeds on smaller fish, crustaceans and cephalopods. In addition, it is blue fish, so its fat composition may allow greater accumulation of methylmercury. Perhaps it is the most worrisome of the list because the consumption of this is higher, however, if limited to the recommendations already indicated, it does not have to be a problem. In fact, it is a great strength of omega 3 fatty acids and proteins, as well as vitamin D and B12. In addition, it is important to note that it is the largest bluefin tuna, and not other tuna such as the clear, whose mercury content is lower.
This river fish is of great dimensions and like the previous ones, it is a great predator. In fact, it feeds on all types of species, so in addition to containing high doses of mercury, in Spain it is considered an invasive exotic species.
In short, it is about reducing the consumption of fish with more methylmercury and consuming other fish with less quantity (salmon, hake, sardines, sole …), as they explain from AESAN, is an important part of the diet for its protein intake, omega 3 fatty acids and vitamin A, D, E, B6 and B12.
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