Thirteen Sharks Test Positive for Cocaine Off the Coast of Brazil

It might sound like science fiction, but researchers have discovered real “cocaine sharks” off the coast of Brazil.

Thirteen wild Brazilian sharpnose sharks (Rhizoprionodon lalandii) caught near Rio de Janeiro tested positive for the drug, according to a study published last week in the journal Science of the Total Environment. The team is still teasing out the implications of this finding, but they say it adds to the growing body of evidence that humans’ illegal drug consumption is affecting wildlife and the environment.

Previous research has detected cocaine in wastewater and rivers. Last year, researchers in England identified a chemical produced by the liver after cocaine use in seawater. Studies have also found the drug in other marine creatures, including shrimp, mussels and eels.

But researchers were curious to know whether cocaine might be affecting sharpnose sharks that spend their entire lives in coastal waters near Brazil, which is a major exporter of the drug to Europe. In addition, people in Brazil and elsewhere often eat sharks, which raises questions about possible contamination up the food chain.

So, the team purchased 13 sharpnose sharks from small fishing vessels between September 2021 and August 2023. The sharks were all juveniles or small adults that measured roughly 20 inches long and weighed less than two pounds. Three were male, and ten were female; five of the female sharks were pregnant.

They dissected the creatures in the lab, then tested their liver and muscle tissues. All the tissue samples came back positive for cocaine and its metabolites, with concentrations up to 100 times higher than what had previously been found in other marine animals. When the team saw the results, they were “actually dumbfounded,” study co-author Rachel Ann Hauser-Davis, a biologist at the Oswaldo Cruz Foundation, which is affiliated with Brazil’s Ministry of Health, says to the New York Times’ Sarah Hurtes.

“We were excited in a bad way, but it’s a novel report,” she adds. “It’s the first time this data has ever been found for any top predator.”

Many questions remain unanswered. For starters, how were the sharpnose sharks exposed to cocaine? The researchers don’t know for sure, but they have a few theories. It’s possible they ate packs of cocaine that had been dumped by traffickers. Cocaine also might have reached coastal waters as drainage runoff from illegal refining labs. More than likely, untreated sewage entering the ecosystem could have contained cocaine in waste from drug users. From there, the sharks either ingested it directly through their gills or acquired it by eating smaller, contaminated fish.

“Regardless of where the drug came from—which is still not possible to determine—the results show that cocaine is being widely traded and moved in Brazil,” says study co-author Enrico Mendes Saggioro, a biologist at the Oswaldo Cruz Institute, to the Guardian’s Tiago Rogero. “Cocaine has a low half-life in the environment so, for us to find it in an animal like this, it means a lot of drugs are entering the biota.”

It’s also unclear whether or how the cocaine might have affected the sharks’ behavior or health, or whether it affected the fetuses of the pregnant females. Past studies have suggested that cocaine can be toxic or cause health problems for aquatic creatures. Researchers note that the amount of cocaine found in the sharks was a fairly low concentration, though females had higher levels than males.

The International Union for Conservation of Nature lists Brazilian sharpnose sharks as “vulnerable,” primarily because of overfishing.

Another big question is whether humans could be harmed by eating “cocaine sharks.” That may be fodder for future studies, along with tests of other shark species, estuary-dwelling rays and migratory fish, Mendes Saggioro tells CNN’s Jack Guy.

In addition, external researchers note that the study’s sample size was small and that the team did not take water samples from the area where the fish were caught. These limitations further support the need for additional research.

Despite the cocaine’s mysterious origins and its still-murky effects on humans and animals, the findings serve as a wake-up call about “the increasing danger of cocaine pollution,” says Anna Capaldo, an endocrinologist at the University of Naples Federico II in Italy who was not involved in the research, to Science’s Erik Stokstad.

And while the presence of cocaine may be shocking and attention-grabbing, it’s far from the only harmful human-produced substance that’s polluting the world’s waters.

“Cocaine gets people interested,” says Tracy Fanara, an environmental engineer in Florida who worked on the 2023 documentary “Cocaine Sharks,” to the New York Times. “But we have antibiotics, antidepressants, pharmaceuticals, sunscreen, insecticides, fertilizers. All of these chemicals are entering our ecosystem.”

Sarah Kuta | READ MORE

Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.