Why eating shark is dangerous for humans

Eating sharks not only threatens the life of our oceans, it can also be extremely harmful to humans. This is because of the various toxins found in the shark meat that then pass on to us when we eat them.  

How do toxins enter a shark’s body?

When pollutants enter the ocean, marine organisms absorb the toxins and heavy metals, unable to excrete them. A fish will eat these organisms where the toxins will accumulate in its body until it’s eaten by a bigger fish, causing the toxins to bioaccumulate through the food chain.

As the toxins travel up the food chain, their concentration increases through a process called ‘biomagnification’. Sharks are apex predators sitting at the top of the food web and so these biomagnified toxins will be stored in their body and continuously added to during its long life, eventually passing on to the human that eats it.

What toxins are found in shark meat and what are the effects on humans?

Many samples and studies have found different toxins in shark meat sold right here in Australia. These include:

  • Methyl-mercury - Many people know the health risks and presence of mercury found in seafood but this more toxic compound is caused when mercury binds with organic molecules in the environment. Sharks have been found to contain the highest concentrations of methyl-mercury than any other seafood due to bioaccumulation and their place at the top of the food chain. Cooking does not eliminate mercury.

    • Health effects on humans - methyl-mercury is one of the most dangerous poisons for a human and can cause loss of motor control, corrosion of skin and mucous membranes, blindness, deafness, impotence, sterility as well as being linked to Hodgkin’s Lymphoma, Parkinson’s disease and Alzheimer’s. A study from the German University in Mainz revealed a dangerous amount of methyl-mercury in blue shark steak, showing that a person weighing 155lbs eating a normal portion could be getting 50 times the legal amount.

  • BMAA - A neurotoxin that has been found in the flesh, cartilage and organs of sharks.

    • Health effects on humans - Linked to neurodegenerative diseases including Alzheimer’s and Parkinson’s disease.

  • Ciguatera - The most common type of seafood poisoning, although many cases are unreported or misdiagnosed. The toxins originate from a type of micro-organism which attaches to a species of algae on dead or damaged coral. As coral damage is increasing so is ciguatera outbreaks.

    • Health effects on humans - Typical food poisoning symptoms but can also be fatal. In Australia, almost all ciguatera poisoning has occurred from fish caught in Queensland or the Northern Territory.

  • DDT - A synthetic and toxic pesticide that is banned for agricultural use but is still used in certain parts of the world. Sharks are highly exposed to these toxic compounds.

    • Health effects on humans - Dizziness, convulsions and irritability with long-term exposure leading to lasting cognitive and neurological problems. As well as this, pregnant women exposed to DDT are more likely to have premature babies.

  • PCBs - Have been widely used as they are very stable and don’t degrade quickly. Though they were banned in the 1970s due to their high toxicity, they still exist in the environment today and have been found in shark meat and oils.

    • Health effects on humans - PCBs can cause liver disease and a reduced immune response. Women exposed to PCBs during pregnancy tend to have babies with a variety of problems and children exposed to these chemicals have suffered with their development. PCBs also alter estrogen levels in the body and can contribute to reproduction problems.

Both DDT and PCBs have been listed by the EPA (Environment Protection Agency) as a probable human carcinogen which causes cancer.

Dead sharks are the real threat to humans

Women who might become pregnant, are currently pregnant or are nursing are recommended by the EPA and FDA to not eat shark because of their high levels of mercury. The Environmental Defense Fund recommends women should not eat shark at all, men should eat no more than 1 meal per month and kids up to the age of 12 should not eat it at all, again because of the mercury levels.

Mercury is one of the more known toxins present in seafood, and even more prevalent in sharks. However, with so many other toxins and poisons proven to be in the shark meat sold in Australia, it’s apparent that its the dead sharks on our plates that are the real danger to humans.