Great White Sharks Appear Perfectly Healthy Despite Lead, Arsenic, And Mercury Coursing Through Their Veins

Photo: Fallows C, Gallagher AJ, Hammerschlag N (2013)

Great white sharks aren’t the unstoppable killing machines of Hollywood’s imagination, but studies have continuously shown that they’re definitely badasses of evolution. A new paper out this week adds to that resume, finding that great whites can easily withstand levels of heavy metals that would kill most other animals, all without any apparent health problems.

Marine biologists at the University of Miami and elsewhere studied blood samples from 43 great white sharks that were captured and released during a 2012 expedition to the coastal waters of South Africa. These samples were tested for the presence of 14 heavy metals like lead, as well as 12 trace elements such as arsenic and mercury. Along with the samples, they also had detailed recordings of the sharks’ overall health, based on measurements of their body size and immune system taken at the time.

The sharks on average had high amounts of lead, arsenic, and mercury in their blood, including levels of the latter two that would be enough to outright kill or seriously harm other vertebrates. But there was no link between higher heavy metal levels and the sharks’ body size and weight, indicating that they had no influence on growth and development. There was seemingly no effect on their immune systems either, judging by the sharks’ stable levels of certain types of immune cells.

“The results suggest that sharks may have an inherent physiological protective mechanism that mitigates the harmful effects of heavy metal exposure,” lead author Liza Merly, a marine biologist and senior lecturer at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science, said in a statement.

Other research has shown that while great white sharks aren’t completely immune to things like cancer, their bodies are especially good at self-healing and avoiding age-related ailments, thanks to a very impressive set of genes.

Indeed, their greatest weakness is actually humans, since hunting and overfishing have dwindled their population over the years (shark fins are a popular alternative medicine treatment).

Still, while heavy metals might be not a concern for great whites, they definitely are for the many other species of marine life that they feed on. So the researchers say it’s possible we could use these sharks as an aquatic canary in the coal mine, one that can tell us how polluted the surrounding ecosystem really is. This pollution could then have consequences for the humans who poisoned the environments in the first place.

“Basically, if the sharks have high levels of toxins in their tissues, it is likely that species they eat below them will also have toxins, including fishes that humans eat,” co-author Neil Hammerschlag, a research associate professor at UM’s Rosenstiel School and Abess Center for Ecosystem Science & Policy, said in a statement. And unlike sharks, we humans tend to fare poorly when exposed to a lot of lead, arsenic, and mercury. 

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