Sharks in the waters off Brazil have tested positive for cocaine, marine biologists said in a new study, marking the first time the drug has been found in the free-ranging predators. 

Thirteen sharpnose sharks were taken from the coast off of Rio de Janeiro and tested for the cocaine and benzoylecgonine, the primary molecule in cocaine. Each shark’s liver and muscles tested positive for high levels of cocaine, the study found, and the female sharks tested had higher concentrations of cocaine in their muscles than male sharks. 

The scientists — who dubbed the study “Cocaine Shark” — posited that this may show a correlation between a shark’s weight and size and how it metabolizes cocaine, but the study noted that more research was necessary. 

CBS News partner BBC News reported that experts have multiple theories on how the illicit substances are entering the water. It’s possible that illegal labs where cocaine is manufactured could be to blame. Scientists also said that it could be entering the waterway through the excrement of drug users. A less likely theory is that packs of cocaine lost or dumped at sea could be to blame. Cocaine and other illicit drugs have previously been found in water drainage systems and in rivers. 

It’s the first study to show levels of cocaine and benzoylecgonine in free-ranging sharks. More research is necessary to see how cocaine consumption affects sharks and other wildlife, the scientists said. 

It’s not clear how the cocaine consumption affects the sharks, the study said. Some of the female sharks were pregnant at the time of the study, and it remains unclear how the illicit drugs may have affected the fetuses.  

The findings are “very important and potentially worrying,” marine eco-toxicologist Sara Novais, from the Marine and Environmental Sciences Centre of the Polytechnic University of Leiria, told Science magazine. 

Researchers have tried to study the impact of illicit drugs on sea life in other parts of the world. Last year, Discovery TV aired a show called “Cocaine Sharks” (which was also the title of a 2023 horror movie) that used experiments to show how sharks might be affected by cocaine. Tracy Fanara, an environmental engineer who worked on the show, told CBS News that the experiments and their results were preliminary, but said it’s likely that sharks are coming in contact with the illicit drug. 

“My goal of this experiment was to shed light on the real problem of chemicals in our waterways and impacting our aquatic life and then eventually impacting us,” Fanara said in 2023. “But the goal of the study was basically to see if this is a research question worth exploring more. And I would say, yes, it is.”