In a shocking revelation, marine biologists have discovered that wild Brazilian sharks off the coast of Rio de Janeiro have tested positive for cocaine.
Researchers for the Oswaldo Cruz Foundation tested 13 of the Brazilian sharpnose sharks taken from the South Atlantic Ocean and found they all had high levels of the illegal substance in their muscle and liver.
The team say the drug could reduce their life expectancy, with cocaine damaging their eyesight and affecting their hunting skills.
Experts emphasised the need for further research to understand the impact of cocaine on shark behaviour, as previous findings suggest that drugs may affect animals similarly to humans.
Dr Tracy Fanara, an expert in ecotoxicology and environmental engineering from the University of Florida claims that: ‘They may not be going nuts from the cocaine but it could reduce their life expectancy.’
The paper, published in Scientific American, suggests the drug is likely getting into their system from illegal cocaine labs, or from drug user waste flushed into the waters via untreated sewage.
The team of researchers also looked into whether the sharks could be nibbling on cocaine that had been dumped into the ocean by smugglers, but said this was unlikely.
Cocaine-Exposed Sharks
The study, which took place off Recreio dos Bandeirantes, was conducted on wild sharks that were bought from small fishing boats, dissected and then tested. All female sharks tested were pregnant, raising concerns about the consequences of cocaine exposure on developing fetuses.
‘We were actually dumbfounded,’ said Rachel Ann Hauser Davis, a co-author of the study and a biologist at the Oswaldo Cruz Foundation. ‘We were excited in a bad way, but it’s a novel report. It’s the first time this data has ever been found for any top predator.’
This was the first study to analyse cocaine in sharks, following various studies on smaller species, including mollusks, crustaceans and eels. All 13 sharks examined were found to have unfiltered cocaine in much higher concentrations than in previous studies, with some reported to be as much as 100 times higher than in previously observed marine life.
The study in Brazil was conceived earlier this year after researchers discovered high levels of cocaine in the rivers that form Rio de Janeiro’s watershed.
Other marine experts had looked into whether sharks in the Gulf of Mexico were ingesting cocaine from the numerous packages lost or dumped in the waters in a 2023 documentary titled Cocaine Sharks, which served as an inspiration for the title of the recent study.
Hauser Davis said there were several hypotheses as to how cocaine found its way to the marine creatures, including illegal labs refining cocaine or cocaine packages lost or dumped by traffickers. But she believes these account for only a small amount of the drug found in the ocean.
She explained: ‘We feel that the major source would be excretion through urine and feces from people using cocaine,’ adding that most wastewater treatment plants worldwide cannot effectively filter these substances, leading to their release into the ocean.
João Matias, a scientific analyst at the European Union Drugs Agency, was part of a team that analysed cocaine levels in wastewater from more than 100 cities, including in Brazil. Their findings revealed that the levels of cocaine in Brazil’s wastewater were similar to those in the European cities with the highest levels.
This concern is not isolated to Brazil; last year, benzoylecgonine, a byproduct of cocaine use, was discovered in seawater samples collected off the south coast of England, highlighting the widespread issue of drug pollution in our oceans.
