Why does cell phone pollution appear in tiger sharks?

Even if these elements don’t kill sharks, Wosnick and Bond worry about sublethal effects. Rare earths, especially titanium, can cause oxidative stress in the liver, Wosnick says. The energy sharks use to cope with that stress could affect their ability to hunt prey or reproduce.

Scientists know a little more about titanium than about other elements, Bond says. Titanium can have “really adverse effects” on the kidneys and the barrier through which oxygen passes from the blood into the brain. If oxygen starts having trouble getting to the brain, it can cause a range of problems, including disorientation, which can also weaken hunters, he says.

The titanium news isn’t all bad. Scientists have found “extremely high concentrations” of titanium in the teeth. But Wosnick says it could be the sharks’ way of getting rid of the element, since sharks shed their teeth more often than other animals.

Human Food and the Future of Mining

Sharks are eaten in Brazil—often by children. Theoretically, these rare earth elements could enter the human body. “Any elements that are not essential could potentially harm humans,” Wosnick says. Humans may also be more sensitive to their toxic effects than sharks, because mammals tend to have more fat than fish. The metals tend to stick to the fat, so they accumulate more quickly.