Sharks in Brazil test positive for unexpected contaminant: cocaine
Cocaine detected in sharks for the first time, but scientists are concerned about its impact
By Stéphanie Pappas
Researchers have discovered cocaine in sharpnose sharks off the coast of Brazil. These sharks are in the same genus as the Atlantic sharpnose shark, shown here with a student researcher near Cape Lookout on the Outer Banks of North Carolina.
Tegan Johnston/Raleigh News
Sharks swimming off the coast of Brazil have something unexpected circulating in their system: cocaine.
The drug has never before been discovered in wild sharks. But that doesn’t mean those fish are unique; Scientists had simply never looked at the presence of coca in a shark. The effort was a success, and all thirteen sharks tested positive for the drug in their muscles and livers, according to a new study published in Science of the Total Environment.
What this means for sharks is an open question, say co-authors Enrico Mendes Saggioro and Rachel Ann Hauser-Davis, an ecotoxicologist and biologist at the Oswaldo Cruz Foundation in Brazil, respectively. No one has ever studied the behavioral or physiological effects of cocaine on sharks, Hauser-Davis says, yet his ongoing studies on the environmental contamination of those top predators suggest that this infamous drug is just one of the animals’ concerns.
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“We detected high levels of metals, as well as ‘forever chemicals’ [perfluoroalkyl and polyfluoroalkyl substances, or PFAS], insecticides and polycyclic aromatic hydrocarbons, PCBs and PBDEs in more than 30 species of sharks and rays. ” explains Hauser-Davis. PCBs, or polychlorinated biphenyls, are carcinogenic chemicals banned in the United States in 1976 and through signatories to the United Nations Stockholm Convention in 2001. PBDEs, or polybrominated diphenyl ethers, They are flame retardants that can alter brain progression and hormones.
Researchers have become interested in drug testing sharks after Mendes Saggioro detected cocaine while investigating contaminants in river water in the Brazilian state of Rio de Janeiro. Brazil has about 1. 5 million cocaine users, according to the World Drug Report 2020. Many parts of the country do not have wastewater treatment, meaning urine infected with the drug goes directly into the water. in water courses. Drug traffickers would also possibly sell shipments of cocaine into the ocean to avoid seizure. A Discovery Channel Shark Week special in 2023 explored the concept that sharks could bite into floating bales of cocaine and revealed that sharks had investigated fake packages dumped near the Florida Keys. But researchers don’t believe this is the main direction through which drugs enter sharks’ bodies. A 2007 study in Florida found that bull sharks had been infected with prescription drugs through faulty sewage systems. Other fish, which are not unusual prey for sharks, have also been shown to be infected. Therefore, it is possible that sharks are exposed directly in the water or absorb these compounds in their diet. Given the ubiquity of legal prescription drugs in aquatic animals, “to think that cocaine or other illegal drugs wouldn’t be found in sharks is a little crazy,” says Chris Lowe, a marine biologist and director of the California State Shark Laboratory. University, Long Beach, which was not involved in the new study.
The researchers in this study tested Brazilian sharp-nosed sharks (Rhizoprionodon lalandii), a small species that lives near the coast, in the waters off Rio de Janeiro. They discovered an average cocaine concentration of 23 micrograms per kilogram in the sharks’ tissues. as well as an average concentration of seven micrograms per kilogram of benzoylecgonine (the compound into which cocaine is broken down during metabolism). This is a fairly low level: studies on the effect of cocaine on humans tend to use doses of about 0. 4 milligrams per kilogram of body weight (one milligram equals 1,000 micrograms). However, female sharks had higher cocaine concentrations than males, and some of the captured females were pregnant. Previous studies on shark-related rays suggest that they can transmit environmental pollution to future fetuses.
“Adults would probably have a more evolved immune formula or enzyme formulas to metabolize some of those things, but not a developing fetus,” Lowe says. “We don’t know what the effects of progression might be. “
Mendes Saggioro plans to continue testing sharks in the domain and expand testing with rays living in the nearby estuary to see how pollution increases. He and his team also need to examine cocaine concentrations in migratory fish that spend less time in close proximity. to the coast.
As researchers examine the consequences of contaminating sharks with cocaine, there are two important things to remember. One comes from Mendes Saggioro and Hauser-Davis: Don’t eat sharks because those animals are overexploited and full of compounds you don’t need in your body.
David Shiffman, a marine conservation biologist at Arizona State University, points out the other conclusion, which centers on the fitness of the sharks themselves: “Please don’t dump their garbage into the water, adding illegal drugs,” he says. “
Stephanie Pappas is a freelance science journalist in Denver, Colorado.
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