Brazilian shark tests positive for surprising contaminant: cocaine
Cocaine detected in sharks for the first time, but scientists aren’t sure about its effects
Researchers found cocaine in filefish sharks off the coast of Brazil, the same genus as the Atlantic filefish pictured with student researchers near Cape Lookout on North Carolina’s Outer Banks.
Tegan Johnston/Raleigh News & Observer/Tribune News Service via Getty Images
Sharks swimming off the coast of Brazil have a somewhat surprising substance floating around in their bodies: cocaine.
The drug had never been found in wild sharks before, but that doesn’t mean these fish are unique; scientists had just never tested sharks for cocaine before. The experiment was a huge success, with the 13 sharks tested showing no signs of cocaine. all New studies have shown that the drug tested positive in the muscles and liver. Comprehensive Environmental Science.
What this means for sharks is an open question, say study co-authors Enrico Mendes Saggiolo, an ecotoxicologist at Brazil’s Oswaldo Cruz Foundation, and biologist Rachel Ann Hauser-Davis. Hauser-Davis says that while no one has ever studied the behavioral or physiological effects of cocaine on sharks, her ongoing research into environmental contamination of apex predators suggests that the notorious drug is just one thorn in sharks’ woes.
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“High levels of metals were found in more than 30 species of sharks and rays, as well as ‘forever chemicals’ (per- and polyfluoroalkyl compounds, or PFAS), pesticides, polycyclic aromatic hydrocarbons, PCBs and PBDEs,” says Hauser-Davis. PCBs, or polychlorinated biphenyls, are carcinogenic chemicals banned in the U.S. in 1976 and by signatories to the U.N. Stockholm Convention in 2001. PBDEs, or polybrominated diphenyl ethers, are flame retardants that may disrupt brain development and hormones.
Researchers became interested in drug testing sharks after Mendes Saggiolo found cocaine while investigating river water pollution in the Brazilian state of Rio de Janeiro. According to the 2020 World Drug Report, Brazil has an estimated 1.5 million cocaine users. And in many parts of the country, poor sewage treatment means drug-contaminated urine flows directly into waterways. Drug traffickers sometimes dump large amounts of cocaine into the ocean to avoid detection. A 2023 Discovery Channel Shark Week special explored the possibility of sharks gnawing at floating chunks of cocaine, revealing sharks examining dummy packets dropped near the Florida Keys. But researchers don’t think that’s the main way drugs get into sharks’ systems. A 2007 study in Florida found bull sharks contaminated with prescription drugs due to a faulty sewer system. Sharks could be exposed to contaminants directly in the water or ingest these compounds through their diet, since other fish that are very common prey for sharks are also known to be contaminated. Given the ubiquity of legal pharmaceuticals in aquatic animals, “it’s kind of crazy to think that we wouldn’t find cocaine or other illegal drugs in sharks,” says Chris Lowe, a marine biologist and director of the Shark Lab at California State University, Long Beach, who was not involved in the new study.
The researchers of this study found that the Brazilian sharkRhizoprionodon larandiiThe team caught small sharks (stingrays) that live near the coast off the coast of Rio de Janeiro. The average concentration of cocaine in the sharks’ tissues was 23 micrograms per kilogram, and the average concentration of benzoylecgonine (the compound cocaine is metabolized into) was 7 micrograms per kilogram. This is a fairly low concentration; studies of cocaine’s effects on humans tend to use doses of about 0.4 milligrams (1 milligram is 1,000 micrograms) per kilogram of body weight. However, female sharks had higher concentrations of cocaine than males, and half of the females caught were pregnant. Previous research on stingrays, a type of shark, has suggested that they can transmit environmental contamination to developing fetuses.
“Adults may have more developed immune systems and enzyme systems to metabolize some of these substances, but the developing fetus may not,” Rowe says. “We really don’t know what the effects on development are.”
Mendes Saggiolo plans to continue drug testing sharks in the area and expand testing to rays in nearby estuaries to see how widespread the contamination is. He and his team also want to look at cocaine levels in migratory fish that spend only a short part of their lives near shore.
As researchers unravel the effects of cocaine-tainted sharks, two big lessons have emerged: The first, by Mendes Saggiolo and Hauser-Davis, is that sharks are overfished and their bodies are full of unwanted compounds, so you shouldn’t eat them.
“Don’t throw trash in the water, including illegal drugs,” says David Shiffman, a marine conservation biologist at Arizona State University, pointing to another lesson focused on the sharks’ own health.
