Cocaine has found its way into sharks at sea, a new study has found.
Researchers dissected 13 Brazilian sharpnose sharks (Rhizoprionodon lalandii) caught by artisanal fishers in the waters off Brazil between September 2021 and August 2023. All 13 sharks had trace amounts of cocaine, while 12 were positive for benzoylecgonine, one of the metabolites that cocaine breaks down into within human bodies.
“Like many toxicology studies, this illustrates an important point – what we release into the environment can ‘come back to haunt us.’ Dilution is not the solution to pollution,” James Gelsleichter, an ecotoxicologist at the University of Florida, U.S., who wasn’t involved in the study, told Mongabay.
With cocaine consumption increasing globally in the past decade, researchers are finding the illegal drug in a variety of aquatic animals, from crabs and shrimps to fish. This is partly because you excrete what you consume. And like a lot of other pharmaceutical waste, cocaine and its metabolites reach water bodies through sewage that’s either partially or completely untreated.
Brazil, one of the world’s largest consumers of cocaine, has the additional problem of inadequately treated sewage. So biologist Rachel Ann Hauser-Davis, a co-author of the study from Brazil’s Oswaldo Cruz Foundation, wasn’t surprised to find cocaine in the muscle or liver tissues of all the sharks they examined. However, the sharpnose shark is routinely consumed by residents of southeastern Brazil, and the presence of cocaine may pose a concern.
“The fact that cocaine was detected may comprise an indirect conservation tool, as consumers may think twice about consuming a cocaine-contaminated species,” Hauser-Davis told Mongabay.
While the researchers found only trace amounts of cocaine in the shark’s tissues, the levels were much higher than those found in other aquatic animals in previous studies.
As animals near the top of most marine food chains, sharks bioaccumulate environmental pollutants more than many if not most other fish, Gelsleichter said.
“The results demonstrated evidence for biomagnification of cocaine in sharks, which suggests that we need to look at this more closely in the future since many sharks are much higher on the food chain than the species that was examined in this study,” he added.
The sample size of 13 sharks is low. But Gelsleichter noted that as a pilot study, the project has “strong value” for being the first to detect cocaine in sharks and demonstrate that the drug bioaccumulates in their bodies.
“It is also relevant to note that these analyses can often be expensive to conduct so it is not uncommon for pilot studies to begin with a smaller number of individuals to first determine if this is an issue that requires greater study,” he said.
How the drug affects sharks isn’t known yet. However, most shark and ray species are threatened with extinction. “So further studies on these animals are required to detect the extent of contamination and attempt conservation efforts,” Hauser-Davis said.
Banner image of Brazilian sharpnose shark by Ross Robertson (Public domain).