Tiger sharks off the southern coast of Brazil are ingesting large amounts of contaminants found in cellphones, electric cars and other kinds of technology.
The contaminants include rare earth elements, a set of 17 naturally occurring metals that power our world. Finding them in sharks is alarming at a time when international regulatory bodies are considering giving the green light to deep sea mining projects for rare earth elements, and electrical waste is increasingly finding its way into the ocean. It’s the first published discovery of these types of technology-critical elements in sharks, the authors say.
“No one is talking about this,” says Natascha Wosnick, lead scientist of the sharks research and conservation program at the Cape Eleuthera Institute in the Bahamas, about increasing rare earth elements in the environment. “We know nothing about how it might affect their health.”
Wosnick has previously analyzed heavy metals and cocaine in sharks off the Brazilian coast. Curious about how increasing amounts of rare earth elements and other substances critical in technology might be getting into apex predators, she and her team analyzed 12 tiger sharks captured by artisanal fishers off the coast of southern Brazil in the state of Paraná in 2021 and 2022.
In the brains, eyes, kidneys, gills, skin, teeth, muscles, hearts and livers of the sharks, researchers looked for a subset of nine rare earth elements as well as titanium and rubidium. Rare earths’ unique properties have made them important ingredients in high-tech devices. “Pretty much all the devices we use these days contain at least one of those elements,” Wosnick says. Meanwhile, rubidium is used in certain medicines, and titanium has a number of medical, aerospace and other technological applications.
All 11 of these elements showed up in all the analyzed tiger shark parts, the researchers reported this month in Environmental Pollution.
“It’s unsurprising [that] we’re starting to see the pollution from one of these longer-term chemicals in one of these long-lived animals,” says Mark Bond, a marine biologist at Florida International University who wasn’t involved in the study.
How are sharks ingesting these metals?
Exactly how sharks pick up these elements remains a mystery, partly due to the paucity of data on rare earths in marine environments, and partly due to the unpredictable movements of tiger sharks in general.
While some shark species are migratory and others tend to stick around in the same areas, tiger sharks do both. Some will live in the same area all their lives, while others will suddenly pick up and travel great distances between continents.
“It’s hard to study tiger sharks because they do not follow the traditional patterns of other sharks,” Wosnick says.
As a result, it’s difficult to determine whether these tiger sharks caught off the coast of southern Brazil are ingesting the elements there or picking them up elsewhere before moving to Paraná.
In any case, there are two possible human sources of the rare earth elements found in the sharks. One has to do with mining—rare earths and other elements mined inland may be getting into the ocean via rivers and streams. Mining is a possible but unlikely source in this area, says Wosnick. It’s more likely that the elements come from the unregulated disposal of technology, due to the high human population along the coast of Paraná.
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The sharks might be absorbing rare earths directly through their gills or eating a lot of contaminated prey. Since tiger sharks are known to eat pretty much anything, including boots, license plates or tires, they may even be eating discarded cellphones and other devices that contain these elements, Wosnick says.
Finally, it’s also possible that some of the rare earths might not come from human industries. Since the elements occur in nature—they are relatively common in the Earths’ crust—they may just show up in water at certain levels, says Marc Amyot, a biologist at the University of Montreal and the Canadian research chair in ecotoxicology and global change who was not involved in the study.
How do rare earths and other elements affect sharks?
The effects of these elements on wildlife isn’t well understood—especially in sharks.
Rare earth element concentrations would likely need to be a lot higher to be lethal in the sharks, says Amyot, who previously found high levels of rare earths in Canadian arctic fish. But he is glad to see work like this on “data poor” contaminants. “These are elements that we really need to study because we need guidelines,” he says. “This [study] really fills a gap.”
Even if these elements aren’t killing the sharks, Wosnick and Bond worry about the sublethal impacts. The rare earths, and particularly titanium, could be causing oxidative stress in the liver, Wosnick says. The energy the sharks use to cope with this stress could affect their ability to hunt prey or reproduce.
Scientists know a little more about titanium than the other elements, Bond says. Titanium can have “really adverse effects” on the kidney and the barrier where oxygen passes from the blood to the brain. If oxygen starts to have trouble getting to the brain, it can cause a host of problems, including disorientation that could also impair the hunters, he says.
The titanium news isn’t all bad. The researchers found “extremely high concentrations” of titanium in the teeth. But Wosnick says this may be the sharks’ way of ridding themselves of this element, since sharks replace their teeth more frequently than other animals.
Human food and future mining
Sharks are consumed in Brazil—often by children. So theoretically, these rare earths could make their way into humans. “All elements that are not essential have the potential to harm people,” Wosnick says. Humans may also be more sensitive to their toxic effects than sharks because mammals usually have more fat than fish. Metals tend to stick to fat, and hence, accumulate faster.
The research didn’t find high enough levels of the elements in the tiger sharks’ muscles, which would most likely be consumed, to harm humans, Amyot thinks. Sharks near rare earth mining areas might contain higher levels, though. “You must be near a source if there would be a problem for human consumption,” he says.
Wosnick and her colleagues worry about the lack of regulatory guidelines on what constitutes healthy levels of rare earths and other elements in sharks and other marine life.
The problem is likely to increase as rare earths, and the devices that require them, increase in prevalence. Bond is also worried that the International Seabed Authority, an intergovernmental agency that makes rules concerning the ocean floor, is currently considering allowing deep sea mining, which would include rare earth extraction.
“As conservationists, we are protesting vehemently about this,” he says, adding that the underwater mining of rare earths could exacerbate the problem of contamination in sharks and other marine life.
