What Type Of Seafood Has The Highest Mercury Content?

We have all heard to be wary about consuming too much seafood because of its mercury content, but do you really know what type of seafood to be on defense about and just why mercury can be so dangerous? Today we thought we’d share to help inform you!

Mercury is dangerous to humans due to its toxicity, especially when it accumulates in the body over time. Mercury exists in several forms, including elemental (liquid), inorganic (mercury salts), and organic (methylmercury), with the organic form, particularly methylmercury, being the most harmful to human health. When mercury is inhaled, ingested, or absorbed through the skin, it can enter the bloodstream and accumulate in vital organs, particularly the brain, liver, and kidneys. One of the most dangerous aspects of mercury exposure is its ability to cross the blood-brain barrier, a protective layer that shields the brain from toxins. This allows mercury to accumulate in the brain, where it can cause neurological damage. Chronic exposure to mercury can lead to cognitive deficits, memory loss, tremors, mood swings, and motor impairments.

Methylmercury, in particular, is highly toxic and bioaccumulative, meaning it builds up in the food chain, especially in fish and seafood. As humans consume contaminated fish, they absorb methylmercury, which is stored in the body for long periods. Over time, this can cause neurological and developmental issues, especially in pregnant women, fetuses, and young children, who are more vulnerable to mercury's effects. In addition to neurological damage, mercury can cause renal failure (kidney damage) and respiratory issues when inhaled in its elemental form. Inorganic mercury compounds can also be highly corrosive and can lead to severe damage to mucous membranes, the digestive system, and skin upon direct contact. Due to these risks, even low levels of mercury exposure over extended periods can result in long-term health issues, making it crucial to limit exposure to mercury from environmental sources, contaminated food, or industrial processes.

Mercury toxicity can cause a wide range of symptoms, which can vary depending on the type of mercury exposure (elemental, inorganic, or organic), the duration of exposure, and the amount of mercury involved. Symptoms may develop gradually or become more acute, depending on the level of exposure. Some of the most common symptoms include:

Neurological Symptoms:

• Tremors: Fine shaking or trembling, often in the hands, but it can affect other parts of the body.
  
  

• Memory problems: Difficulty with short-term memory, concentration, and cognitive function.
  
  

• Numbness or tingling: A sensation of "pins and needles" in the hands, feet, or around the mouth.
  
  

• Mood changes: Irritability, anxiety, depression, and personality changes.
  
  

• Fatigue: Chronic tiredness or weakness that is not relieved by rest.
  
  

• Headaches: Persistent or frequent headaches.
  
  

• Coordination problems: Difficulty with motor control, balance, and walking, which can resemble symptoms of a movement disorder.
  
  

Physical Symptoms:

• Muscle weakness: Reduced strength or difficulty in performing everyday tasks.
  
  

• Vision problems: Blurred vision or narrowing of the visual field.
  
  

• Speech difficulties: Slurred or unclear speech due to muscle control issues.
  
  

• Swelling: Swelling of the hands, feet, or face due to kidney damage.
  
  

• Unusual skin rashes: Itching or eruptions on the skin, particularly in cases of contact with inorganic mercury.
  
  

Kidney Damage Symptoms (from inorganic mercury exposure):

• Proteinuria: Excess protein in the urine, which can be detected through medical tests.
  
  

• Edema: Swelling, especially in the legs or ankles, caused by fluid retention.
  
  

• Reduced urine output: A noticeable decrease in the amount of urine produced, potentially indicating kidney failure.
  
  

Gastrointestinal Symptoms:

• Abdominal pain: Discomfort or cramping in the stomach area.
  
  

• Nausea and vomiting: Feeling sick and vomiting, which may be linked to ingestion of mercury or its compounds.
  
  

• Diarrhea: Frequent, watery stools that may accompany other digestive disturbances.
  
  

Respiratory Symptoms (from inhalation of elemental mercury vapor):

• Coughing and shortness of breath: Difficulty breathing and a persistent cough.
  
  

• Chest pain: Pain or tightness in the chest, which may occur with inhalation of mercury vapor.
  
  

• Metallic taste in the mouth: A distinct taste, often linked to mercury exposure through inhalation.
  
  

Symptoms in Children and Fetuses:

• Developmental delays: In young children, mercury exposure can impair cognitive and motor skills.
  
  

• Learning difficulties: Children may struggle with attention, memory, and processing information.
  
  

• Abnormal reflexes: Children exposed to high levels of mercury might show signs of abnormal or delayed reflex responses.

Mercury also has an affinity for affecting other minerals, specifically zinc and selenium, meaning it can further deplete and prevent absorption of them if one is toxic.

In terms of which seafood has the highest levels of mercury, this includes large predatory fish that are at the top of the food chain. These fish tend to accumulate more mercury because of a process known as biomagnification. As smaller fish are consumed by larger fish, the mercury they have absorbed from the environment is passed along and concentrated. Over time, this results in high levels of mercury in the tissues of larger, longer-living fish.

Fish with the Highest Mercury Levels:

1. Shark: Due to their large size and long lifespan, sharks accumulate significant amounts of mercury. They are at the top of the food chain and consume a variety of smaller fish, allowing mercury to build up in their bodies.
   
   

2. Swordfish: Swordfish also live for many years and eat other fish that have mercury in their systems, making them one of the highest offenders in terms of mercury concentration.
   
   

3. King mackerel: Known for its high mercury content, this fish is another large predator that accumulates mercury through its diet of smaller fish.
   
   

4. Tilefish (from the Gulf of Mexico): Tilefish, especially those from the Gulf of Mexico, are known for having particularly high levels of mercury due to their position at the top of the food chain and long life span.
   
   

5. Albacore tuna: Albacore tuna, especially in its larger forms (such as older, bigger fish), has higher mercury levels than smaller tunas, like skipjack. Tuna, being large and predatory, accumulates mercury over time.
   
   

6. Bigeye tuna: Like albacore tuna, bigeye tuna are large and long-living, leading to high mercury concentrations in their tissues.
   
   

Why These Fish Contain High Levels of Mercury:

Mercury, particularly in the form of methylmercury, enters aquatic ecosystems primarily through industrial pollution, atmospheric deposition, and runoff into water bodies. Once in the water, mercury is converted by microorganisms into methylmercury, which is absorbed by aquatic organisms. The mercury concentration increases as smaller fish are eaten by larger predators, leading to a higher concentration of mercury in the flesh of top predators.

Fish that are larger, longer-living, and higher in the food chain tend to have more time to accumulate mercury, resulting in higher concentrations of the toxin in their bodies. The longer the lifespan and the larger the fish, the more mercury it has been exposed to over time, which is why these species tend to be the ones with the highest mercury levels.

For this reason, it is generally advised to limit the consumption of high-mercury fish, particularly for pregnant women, young children, and people with weakened immune systems, as exposure to mercury can have harmful effects on the nervous system.

If you’re an avid seafood consumer and are potentially concerned about one’s mercury levels, we invite you to run a Hair Tissue Mineral Analysis (HTMA) which could then help distinguish if you are toxic, as well as if there are any other deficiencies that could be contributing to the toxicity. You can do so by clicking here and try not to eat too many fish!