The blood of great white sharks found in the waters off the coast of South Africa has been found to contain quantities of heavy metals that would be dangerously toxic to other forms of marine life, according to a newly published study. The results suggest that the apex predators have an inbuilt ability to tolerate the negative effects of the heavy metals, and that the blood analysis could be used as an indicator for the health of the marine ecosystem in which they live.

A great white shark is without doubt one of the most imposing denizens of the deep that you could ever hope to not encounter. Thanks largely to their portrayal on the big screen, they have essentially become the bogeymen of the ocean, and outwardly at least, they fit the bill. White sharks can grow up to 20 ft (6 m)long, and are famed for their large dead eyes, and rows upon rows of jagged teeth.

While this is definitely a package to be wary of, the reality is that the oceanic heavyweights rarely attack humans, and the same is true for sharks in general. According to the Florida Museum's International Shark Attack File,there were just 130 incidents of shark-human interaction reported in the entirety of 2018.

White sharks play an important role in their ecosystem, and their decline in population over recent years is a cause for serious concern. Alongside environmental degradation, the predators often get trapped in fishing nets, and are actively hunted by humans who prize their fins and teeth.

The blood used in the study was drawn from 43 great white sharks that were captured off the coast of South Africa back in 2012. Each predator was carefully raised on a special platform, which allowed scientists to take blood samples and other measurements before tagging the sharks and returning them unharmed to their ocean habitat.

In the new study, researchers screened the blood samples for concentrations of 12 trace elements and 14 heavy metals. The results showed high concentrations of the metals, including mercury and arsenic, which did not correlate to a shark's sex, body size or condition.

High concentrations of heavy metals in the blood of marine animals can lead to a wide array of health problems, including neurological decline, or a weakening of the immune system. However, while the high heavy metal levels in the shark blood samples would have been toxic to many other marine vertebrates, the researchers could find no negative effects on the great whites.

"The results suggest that sharks may have an inherent physiological protective mechanism that mitigates the harmful effects of heavy metal exposure," said Liza Merly, study lead author and senior lecturer at the University of Miami Rosenstiel School of Marine and Atmospheric Science.

The analysis of the shark blood could also potentially be used as an indicator for the health of the marine ecosystem that the predators inhabit. Great whites feed on fish lower down the food chain, and the toxins found in the new study are likely to have been absorbed from their food, some of which is also fished and consumed by humans.

The team believes that the research has set a baseline for heavy metal levels in the blood of great white sharks, and opened the door for further studies of the oceanic leviathans.

The study has been published in the Marine Pollution Bulletin.