Popular in Brazilian dishes, dogfish and tuna can accumulate heavy metals – News

Popular in Brazilian dishes, dogfish and tuna can accumulate heavy metals – News

Popular in Brazilian dishes, dogfish — as shark and ray meat is known — and tuna, although tasty, may contain heavy metals above the recommended level and should be consumed in moderation.

Shark and tuna are predators classified as top of the chain, that is, they are at the highest levels of the food chain. This means that they feed on other fish, which have already eaten smaller fish, and so on.

“There is this whole issue of the ecological chain, in which one feeds on the other, but as the shark is at the top, it accumulates all these pollutants, these heavy metals, which have already passed through the entire chain. We call them bioaccumulators [porque]literally, accumulate all these heavy metals that have already passed through the body of the animals they ingested”, explains Amanda Gomes, doctoral student in oceanography and member of the Zoommundo channel on YouTube.

The environment also favors this accumulation, since the seas and rivers are increasingly polluted with waste and heavy metals.

This situation becomes harmful to human beings for a reason: we are also bioaccumulators.

“Some sharks accumulate more heavy metals than tunas, as they feed on a greater number of prey, and large prey, such as seals, which also feed on fish. So the accumulation of heavy metals adds up”, reports Amanda.

And he adds: “If a person is going to feed on many marine animals or, mainly, on dogfish, we are accumulating this in our body as well.”

Anvisa (National Health Surveillance Agency), through Resolution No. 42, of August 29, 2013, defines the limit of contaminants that can be found in these foods.

Some examples of them are:

• Arsenic: 1 mg/kg

• Chumbo: 0,30 mg/kg

• Cadmium: 0.05 mg/kg

• Mercury: predatory fish 1 mg/kg or fish 0.5 mg/kg

However, a study released by Fiocruz (Oswaldo Cruz Foundation), in September 2022, found that rays on the coast of Rio de Janeiro (Rio de Janeiro) had high levels of arsenic.

In 20 butter ray scientists found, on average, 15 mg/kg. One of the samples even showed 79 mg/kg — almost 80 times over the permitted limit.

In 2014, researchers had already analyzed muscle tissue samples from 27 blue sharks captured in the Atlantic Ocean (south and southeast coast of Brazil) and found that mercury concentrations ranged from 0.44 to 2.37 mg/kg.

Health damage occurs when there is excessive consumption of these contaminated meats.

“Specifically, the accumulation of mercury in our body can cause damage, for example, neurological damage: reasoning problems, memory problems, tremors, headaches and can [até] make the kidney stop. Depending on how it happens, it can even affect the lungs”, says infectologist Mirian Dal Ben, from Hospital Sírio-Libanês.

For this reason, it is a recommendation by the WHO (World Health Organization) that dog meat, for example, is not part of the menu for pregnant women, nursing mothers and children (up to 12 years old).

“It is a very crucial phase of development of the nervous system, in which heavy metals can act and cause some damage”, adds Amanda.

For the general population, these meats do not need to be completely discarded, but they should appear less frequently in dishes.

“It is an extremely important source of food. We know that ideally a healthy diet should have fish at least two or three times a week, so you can have sources of omega 3 and a series of nutrients, which are present in this type of food “, clarifies Miriam.

Another option is to choose fish that are less bioaccumulators, that is, those that are not at the top of the food pyramid. Two good examples are salmon and tilapia.


For Amanda and Mirian, one way to prevent dogfish meat and tuna from being sold with large proportions of heavy metals is to have stricter legislation and surveillance.

“First, we would need to have legislation on access to information, so that we really know the origin, where it came from and what it is. And then, suddenly, Anvisa [pode] certify the companies that are distributing [essas carnes] and demand that these quantity measures be taken”, says the doctoral student.

These steps are even more essential if we consider that dogfish meat, for example, is any type of shark and ray, of any size and of any species.

“Sometimes, we don’t even know what species is on our plate, let alone the amount of heavy metals”, laments Amanda.

A study conducted by researchers from UFRGS (Federal University of Rio Grande do Sul), in 2018, investigated the presence of dogfish meat in markets in the southern region of Brazil.

They found 63 products sold as dogfish, corresponding to 20 species. Among these were two species of teleosts—which are neither sharks nor rays.

That is why it is important to pay attention to the origin and quality of the fish market where these products are sold.

threat of extinction

Sharks, in particular, are still an endangered species. According to research published in the scientific journal Current Biology in 2021, on a global scale, 32.6% of sharks are threatened with extinction — the equivalent of 391 species.

“This environmental problem is gigantic”, warns Amanda.

This is also reflected in the control of marine fauna.

“Sharks are at the top, they control the amount of their prey and generally also feed on prey that is sick and on animals that could become pests. If they start to disappear, many of their prey can become pests, proliferate too much and end up harming other species”, explains the doctoral student.

For these and other reasons, conscious consumption is important. Dogfish meat will still be sold, but consumers can make different choices.

“At the fish market, at least, you know the fish that are there, because they put the name, then research, ‘Corvina? Is the corvina a fish that is endangered or is it a fish that already has research and it is more or less contaminated?'”, recommends Amanda.

*Intern at R7under the supervision of Fernando Mellis

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