When it comes to the fish we eat like tuna and salmon, mercury levels are an important concern. Heavy metals like lead and mercury from industrial operations and human activities can enter waterways and make their way up the food chain.
Now, a new study has found that sharks have high concentrations of mercury as well as other dangerous heavy metals like arsenic and lead in their blood and yet somehow, the sharks seem to be relatively healthy and unimpacted.
While great whites seem resistant to the toxicity of some heavy metals, concerns remain about the mercury concentrations in the shark’s prey, fish we ourselves eat.
The study was published in the journal Marine Pollution Bulletin and is the first of its kind to measure blood concentrations of heavy metals in wild great white sharks.
“As top predators, sharks bio-accumulate toxins in their tissues via the food web from the prey they eat,” said Neil Hammerschlag, a study co-author. “So by measuring concentrations of toxins, such as mercury and arsenic, in the blood of white sharks, they can act as ‘ecosystem indicators’ for the health of the ecosystem, with implications for humans.”
The researchers analyzed blood samples that were collected during a 2012 Ocearch expedition to South Africa. During the expedition, sharks were captured, had blood taken and tracking tags put on before being released.
Blood screening results showed concentrations of 12 trace elements and 14 heavy metals, but the researchers didn’t find any indicators that these concentrations were negatively impacting the shark.
“The results suggest that sharks may have an inherent physiological protective mechanism that mitigates the harmful effects of heavy metal exposure,” said Liza Merly, the lead author of the study.
Potential immunity to heavy metals in sharks is something that researchers say should be studied further.