Tuna Mercury Levels: Pan-Seared Safe?

Tuna is a nutritious and protein-rich saltwater fish that is a common source of mercury in the diet. Mercury is a chemical used in industrial facilities and released into the environment, where it settles in our oceans and is consumed by small fish, which are then eaten by larger fish, such as tuna. As a result, tuna can have high levels of mercury that can build up in the human body over time and cause adverse health effects. While tuna is generally safe to eat in certain amounts, it is important to understand the risks associated with mercury consumption and to make informed choices about tuna consumption, especially for vulnerable groups such as pregnant women and young children.

Mercury levels in tuna

Tuna is a nutritious and protein-rich saltwater fish that can contain high levels of mercury. Mercury is a neurotoxin that can be harmful to both children and adults. It can cause problems with fine motor coordination, speech, sleep, and walking, and can also lead to brain cell death, impaired memory and focus, anxiety, and depression. Therefore, it is important to monitor one's consumption of tuna and choose varieties that are lower in mercury.

The term "tuna" encompasses several species of fish, including skipjack, albacore, yellowfin, and bigeye. Mercury levels can vary significantly between these species, with bigeye tuna having the highest levels. Skipjack tuna, the most commonly consumed species, generally has lower mercury levels.

Canned tuna is a convenient and affordable source of protein and omega-3 fatty acids. However, it is often a significant source of mercury in the diet. Light and skipjack varieties of canned tuna typically contain much less mercury than albacore tuna. Canned light tuna is considered a good choice for individuals who need to limit their mercury exposure, including pregnant and breastfeeding women.

The US Environmental Protection Agency (EPA) has set a maximum safe dose of mercury at 0.045 mcg of mercury per pound (0.1 mcg per kg) of body weight per day. This amount is known as a reference dose. It is important to note that mercury levels in fish are measured in parts per million (ppm) or micrograms (mcg), and a single serving of some tuna species may exceed the weekly reference dose.

The Food and Drug Administration (FDA) recommends that adults consume 3-5 ounces of fish 2-3 times a week to get enough omega-3 fatty acids and other beneficial nutrients. However, it is important to choose fish that are low in mercury, such as skipjack, canned light tuna, cod, crab, salmon, and scallops.

For pregnant women, breastfeeding women, and young children, the FDA recommends limiting the consumption of tuna and other high-mercury fish. Instead, they should aim for 2-3 servings of low-mercury fish per week. Bigeye tuna, often used in sashimi and sushi, should be avoided by these groups.

Health risks of mercury

Mercury is a naturally occurring element that is toxic to humans. Even in small amounts, exposure to mercury may cause serious health problems. People are exposed to mercury through skin contact, inhalation of mercury vapours, and consumption of contaminated fish.

The health effects of mercury exposure depend on several factors, including the form of mercury, the amount of exposure, the duration of exposure, the route of exposure, and the age and health of the person exposed.

Nervous System

Mercury is a neurotoxin, and exposure to high levels of mercury can cause adverse health effects on the nervous system. It can lead to impaired fine motor skills, memory, and focus. Studies have shown that individuals with high concentrations of mercury performed worse on fine motor, logic, and memory tests. Additionally, mercury exposure has been linked to anxiety and depression.

Brain Development

Mercury exposure is of particular concern for pregnant women as it can adversely affect the developing brains and nervous systems of their babies. High levels of mercury can impair a child's physical and mental development, including motor skills, learning capacity, and memory. The Centers for Disease Control and Prevention estimates that about 6% of child-bearing-aged women in the United States have a blood mercury level that is unsafe for a developing fetus.

Kidneys

Exposure to mercury can also cause kidney damage. Inhalation of mercury vapours and ingestion of inorganic mercury can lead to kidney toxicity.

Respiratory System

Breathing in mercury vapours can cause respiratory issues, and high exposures may result in respiratory failure and even death.

Cardiovascular System

Mercury buildup has been linked to an increased risk of heart disease. Studies have shown that individuals with high mercury concentrations were more likely to die from heart attacks and heart disease.

Other Health Effects

Other possible symptoms of mercury poisoning include loss of peripheral vision, numbness or tingling sensations in the hands, feet, and mouth, lack of coordination, impairment of speech, hearing, and walking, mood swings, memory loss, and mental disturbances.

How tuna accumulates mercury

Tuna is a nutritious and protein-rich saltwater fish that can contain high levels of mercury. Mercury is a highly toxic metal that can cause severe health issues, especially for pregnant women, nursing mothers, and young children. So, how does mercury accumulate in tuna?

Firstly, it's important to understand that mercury is present in the environment due to both natural sources and human activities. Natural sources include volcanic eruptions, while human activities, such as coal-burning power plants, industrial emissions, and waste incineration, release significant amounts of mercury into the air and water.

Now, let's break down the process of how tuna accumulates mercury:

• Absorption by Plankton: Mercury, often in the form of methylmercury, enters the ocean and is absorbed by algae and small plankton at the beginning of the food chain.
• Bioaccumulation in the Food Chain: As tuna are higher up in the food chain, they consume smaller fish that have already accumulated varying amounts of mercury. This process is known as bioaccumulation, where mercury builds up in the tissues of tuna over time.
• Slow Excretion: Tuna, like other fish, efficiently absorb methylmercury but excrete it very slowly. Methylmercury is not soluble, so instead of being excreted, it accumulates in the viscera and muscle tissue of the tuna.
• Biomagnification: This process explains why predatory fish like tuna have higher concentrations of mercury than would be expected from direct exposure alone. As tuna consume more contaminated prey, the amount of mercury in their bodies increases significantly.

It's important to note that the larger and older the tuna, the more mercury they are likely to have accumulated. This is why certain species of tuna, such as albacore and bigeye tuna, tend to have higher mercury levels than others, such as skipjack tuna.

While tuna can accumulate high levels of mercury, it's important to remember that individual cans of tuna may vary in their mercury content. This variation is due to unpredictable spikes in mercury levels, which is a concern for consumers, especially pregnant women and children. Therefore, it's recommended to consume tuna in moderation and opt for varieties with lower mercury levels, such as skipjack or canned light tuna.

Recommended tuna consumption

Tuna is a nutritious and protein-rich saltwater fish that is also a common source of mercury in the diet. Mercury is a chemical often used in industrial facilities, such as power plants and automotive light switches. When released into the ocean, it builds up in marine life over time, particularly in larger fish like tuna. As a result, regular tuna consumption may lead to health issues.

The US Environmental Protection Agency (EPA) states that 0.045 micrograms of mercury per pound (0.1 micrograms per kg) of body weight per day is the maximum safe dose of mercury. This amount is known as the reference dose. Your daily reference dose for mercury depends on your body weight, and multiplying that number by seven gives you your weekly mercury limit. For example, an individual weighing 60 kg (132 lbs) would have a reference dose of 6.3 micrograms per day and 44.1 micrograms per week.

The Food and Drug Administration (FDA) recommends that adults eat 3–5 ounces (85–140 grams) of fish 2–3 times a week to get enough omega-3 fatty acids and other beneficial nutrients. However, the FDA also recommends that children aged 1–11 and individuals who are pregnant, trying to become pregnant, or breastfeeding should select fish varieties that are low in mercury.

For adults, 4 ounces is considered one serving. For children, the serving size varies with age:

• 1 ounce for children aged 1–3 years
• 2 ounces for children aged 4–7 years
• 3 ounces for children aged 8–10 years
• 4 ounces for children aged 11 and older

Canned light tuna, such as skipjack, is low in mercury and is considered one of the best choices for individuals who need to limit their exposure. People who are pregnant or breastfeeding can consume 2–3 servings of canned light tuna per week, while children can have 2 servings per week.

White albacore tuna and yellowfin tuna contain slightly more mercury but are still good choices for adults. These varieties are not recommended for children, but those who are pregnant or breastfeeding can consume up to 1 serving per week. Bigeye tuna, often used in sushi and sashimi, is high in mercury and should be avoided by these groups.

In addition to body weight and age, the specific type of tuna and its mercury concentration are important factors in determining recommended consumption. Lab tests suggest that, depending on these factors, an individual could consume between 25 and 35 small tins (95 grams each) of tuna a week before reaching maximum mercury limits. However, it is important to note that mercury levels can vary from can to can, and unpredictable spikes in mercury content can occur. As such, it is generally recommended to eat tuna in moderation and to include other low-mercury fish in your diet, such as cod, crab, salmon, and scallops.

Mercury in other fish

Mercury is present in all fish and shellfish to varying degrees, and it is a particular concern for pregnant women, those trying to conceive, breastfeeding mothers, and young children. While the nutritional benefits of fish may outweigh the risks, it is important to be aware of the mercury content of different types of fish and to moderate consumption accordingly.

• Shrimp
• Salmon
• Scallops
• Oysters
• Sardines
• Cod
• Crab
• Tilapia
• Pollock
• Catfish
• Skipjack tuna
• Canned light tuna

The following fish are high in mercury and should be consumed in moderation or avoided:

• Shark
• Swordfish
• King mackerel
• Tilefish (especially from the Gulf of Mexico)
• Marlin
• Bigeye tuna
• Orange roughy
• Chilean sea bass
• Albacore tuna ("white" tuna)
• Tuna steaks
• Northern pike

It is recommended that pregnant women, those trying to conceive, and breastfeeding mothers eat no more than two servings (12 ounces or 340 grams) per week of low-mercury fish. For young children, the recommended amount varies depending on age:

• Ages 1-3: 2 ounces
• Ages 4-7: 4 ounces
• Ages 8-10: 6 ounces
• Age 11: 8 ounces

It is also important to check local advisories about the safety of fish caught in local lakes, rivers, and coastal areas, as mercury levels can vary depending on the levels of mercury in the water.

Frequently asked questions