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Understand how and why mercury is found in fish in different regions of the world, including Brazil

Edited and resized image by Gregor Moser is available on Unsplash

Finding mercury in fish is no lie. This metal, which is naturally found in air, soil and water, has polluted the environment through anthropogenic activities; among them, the National Resources Defense Council states that those that generate the greatest mercury pollution are mining and the burning of mineral coal by thermoelectric plants.

• What is mercury and what are its impacts?
• Protests in favor of nature and against mining
• What is coal?

Mercury

Mercury occurs in a liquid state at room temperature, however, when the temperature increases, it is easily volatilized to the atmosphere in the form of mercury vapor. Once in the atmosphere, mercury vapor can be deposited or converted to a soluble form and incorporated into the rain cycle. When soluble, it can be volatilized again and return to the atmosphere, or it can remain in the aquatic environment, where it will be transformed into methylmercury [CH3Hg]+ by microorganisms present in the sediments of the aquatic environment.

Methylmercury contaminates the entire food chain, from phytoplankton to carnivorous fish. Due to its long residence time, methylmercury remains incorporated into the body's tissue after ingested. Thus, the concentration of mercury becomes increasingly higher within the food chain as organisms feed on others that already have the mercury accumulated in their tissues. This process is called bioaccumulation.

For this reason, top-chain carnivorous fish have the highest concentrations of methylmercury. By incorporating these mercury-contaminated fish into our diet, we are including ourselves in this process and ingesting high concentrations of mercury.

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Main polluting sources of mercury in Brazil

The Ministry of the Environment points out that there is a lack of data on atmospheric concentrations of mercury. But it claims that gold mining and burning of large forest areas are the country's main mercury emissions.

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According to the report by the Ministry of Mines and Energy, currently gold production has taken place mainly in the states of Minas Gerais, Pará, Bahia and Mato Grosso, respectively.

According to the Ministry of the Environment, other forms of frequent exposure in the country are related to the activities of manufacturing chlorine-soda, manufacturing and recycling fluorescent lamps, manufacturing thermometers, manufacturing batteries and dental material.

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Intoxication

According to the World Health Organization (WHO), there is a direct relationship between high concentrations of mercury in human blood and consumption of fish contaminated by methylmercury

According to the Preliminary Diagnosis of Mercury in Brazil, prepared by the Ministry of the Environment, 90% of all mercury present in high trophic level organisms (predators at the top of the food chain) is in the form of methylmercury.

Methylmercury [CH3Hg]+ is considered one of the most harmful forms of mercury to the human body. It is a neurotoxin capable of crossing placental and blood-brain barriers, negatively affecting the developing brain. Therefore, pregnant women should be even more careful regarding the consumption of fish possibly contaminated by mercury.

Exposure of pregnant women to methylmercury [CH3Hg]+ can damage the nervous system of babies and lead to learning and cognitive impairments in childhood. In addition, the National Cancer Institute classifies methylmercury as a substance with a possible carcinogenic effect.

Human mercury poisoning is a public health problem that mainly affects riverside populations, who have fish as the basis of their diet. Even so, the subject should receive the attention of all those who regularly consume fish.

For consumer safety, the National Health Surveillance Agency (Anvisa) has an ordinance which establishes that the maximum concentration of mercury must not exceed 1mg/kg in predatory fish and 0.5mg/kg in non-predatory fish. When these values ​​are exceeded, the batch of fish is seized.

However, this initiative has no impact to reduce the risks to which riverside populations are exposed, nor to reduce the environmental damage caused by contamination. For this case, it would be necessary to act directly in the reduction of mercury emission sources.