What is Bioaccumulation?

Aside from the slow reproductive rate of sharks (which makes populations very slow to bounce back from overfishing), we should not be consuming these animals due to the toxic levels of heavy metals and other potential pollutants found in their tissues. Sharks have a much higher concentration of heavy metal toxins and other substances because of their high position on the food chain, a process that can be explained by “bioaccumulation and biomagnification.”

Okay, so what is bioaccumulation and biomagnification? Bioaccumulation is a process by which substances such as heavy metals, chemicals, and organic compounds are consumed by an organism. These substances accumulate in the tissues of the organism over time and can continue to build up if the organism consumes these substances faster than they can eliminate them. When this organism is consumed, the predator acquires all of the substances accumulated by their prey. In other words, concentrations of these substances can increase exponentially as they climb the food chain, a process known as biomagnification. Not only are sharks filled with these toxins and organic compounds, but they can also offload them into their pups. As a result, they may have a high threshold of toxic substances in their bodies from an early age. Substances such as heavy metals, chemicals, and even plasticizers, which are additives used to increase the plasticity of materials such as PVC, can all be found in these animals. Sharks are not immune to chemicals such as pesticides either. Juvenile Great White Sharks have actually been found to have some of the highest levels of DDT ever reported for a shark.

Heavy metals naturally occur on our planet and are a part of the Earth’s crust. These elements cannot be broken down into simpler forms. Heavy metals such as arsenic, lead, and mercury can be toxic when consumed. When mercury is obtained by microorganisms it is converted into Methylmercury. Methylmercury, according to the World Health Organization, is the most toxic of all mercury compounds. Unfortunately for us humans, this compound is extremely common in the ocean, and therefore our seafood. It tampers with our nervous system and can potentially cause memory loss, insomnia, motor and cognitive dysfunction and can strongly affect child development during pregnancies. 

So why are these toxic elements found in our water? The simple answer is that when the elements are worn off of rocks, they seep into the groundwater and eventually enter bodies of water via waste dumps, sewage, rain, runoff, etc. The bioaccumulation and biomagnification of harmful substances by organisms is further exacerbated by humans, who release substances such as chemicals (including pesticides) and plasticizers into the air and oceans. This occurs via littering, dredging, and dumping of sewage, industrial waste, and radioactive materials. It goes without saying that much of this is due to the burning of fossil fuels and the need for waste relocation, all kicking off with start the Industrial Revolution.