Nutritionist Korobkina named the most harmful fish species with high mercury content

Fish is an important part of a healthy diet. It is rich in protein, omega-3 fatty acids and other essential nutrients, and is low in harmful saturated fats.

Experts recommend eating two to three servings of fish per week. However, keep in mind that some types of fish may contain high levels of mercury.

Health hazards of mercury

Mercury is a natural element that can enter the environment either through natural processes (volcanic eruptions and forest fires) or through human activity (burning coal, oil or wood for fuel). When a substance enters the air, it can fall to the ground as raindrops, snowflakes, dust or gravity, contaminating soil or water.

When mercury ends up in lakes, oceans and rivers, it undergoes a process known as methylation, in which certain microorganisms in the water convert mercury compounds to the form methylmercury. It is absorbed through the gills and also accumulates when fish eat smaller fellow fish. As it moves up the food chain, this natural element becomes more concentrated in the animal’s body.

Consumption of high doses of mercury in humans can lead to serious health problems, especially affecting the brain and nervous system, including:

• tingling or numbness in the mouth, hands or feet;
• impaired vision and hearing;
• loss of peripheral vision;
• muscle weakness and inability to coordinate movements.

In pregnant and breastfeeding women, mercury exposure can also affect the development of the baby’s brain and nervous system. It can also lead to impaired cognitive thinking, memory, attention, speech, fine motor and visual-spatial skills in the baby.

Fish with high levels of mercury

Mercury levels vary among different species of fish. This is due to factors such as vertebrate type, size, location, habitat, diet, and age.

Predatory fish (which eat other smaller relatives) are larger and at the top of the food chain, so tend to store more of this dangerous element for humans.

Doctor of nutrition, sports nutritionist, nephrologist of the Hadassah Clinic branch office

“However, the main source of heavy metals and carcinogens for humans is not food, but smoking and environmental conditions (exhaust fumes, for example).”

Fish that contain higher levels of mercury include:

• shark;
• marlin;
• swordfish;
• king mackerel;
• Atlantic largemouth;
• bigeye tuna.

The U.S. Food and Drug Administration has issued advisories that divide fish into three categories and, depending on the category, indicate the possible frequency of consumption.

For example, the “best choice” column includes anchovies, mackerel, sea bass, herring, all kinds of small fish, salmon, sardines, squid, crab and so on. Such species can be consumed two or three times a week without fear.

The next column – “good choice” (or “caution, may contain mercury”) includes carp, Chilean sea bass, lufferfish, snapper, white and yellowfin tuna. It is recommended to eat such fish no more than once a week.

And the third group – fish that should be avoided. We have already listed its types above.

How is the mercury content controlled?

The content of metals, including mercury in the food industry is controlled at different levels (technical regulations on the safety of the food industry). For different fish, uniform sanitary requirements and technical regulations set certain limits of permissible norms, and they depend on the fish’s ability to accumulate it.

For example, for sprat it will be very low figures, no more than 0.5 mg/kg, but for tuna the threshold is higher, because the longer the fish lives, the more mercury it will accumulate. Therefore, in tuna the permissible limit of mercury reaches 1 mg/kg (twice as much as for other species).

But there are also more “mercury-intensive” fish, such as shark, swordfish, marlin, king mackerel, bigeye tuna. They can accumulate up to 5 mg of mercury.