Sharks off the coast of Brazil are testing positive for cocaine. Not trace amounts. Not ambiguous chemical signatures that might be something else. Cocaine — at concentrations that have startled marine biologists and raised uncomfortable questions about just how thoroughly humanity’s drug habits are polluting the ocean.
A peer-reviewed study published in Science of the Total Environment found that Brazilian sharpnose sharks captured near Rio de Janeiro carried cocaine in their muscle tissue and livers at levels up to 100 times higher than what has been documented in other marine species. Every single shark tested — all 13 specimens — came back positive. As Futurism reported, the findings represent the first confirmed detection of cocaine in free-ranging sharks, and the concentrations were striking enough to prompt concern about what chronic exposure might be doing to these animals’ neurological and reproductive systems.
The research, led by scientists at the Oswaldo Cruz Foundation (Fiocruz) in collaboration with other Brazilian institutions, wasn’t looking for a headline. The team was conducting routine ecotoxicological sampling. What they found was anything but routine.
Brazilian sharpnose sharks (Rhizoprionodon lalandii) are small coastal predators common in the waters around Rio de Janeiro — a city that also happens to be one of the largest cocaine consumption and trafficking hubs in South America. The sharks were collected from fishermen’s nets in waters near the city between September 2021 and August 2023. Researchers then tested liver and muscle tissue for cocaine and its primary metabolite, benzoylecgonine. The results showed cocaine concentrations averaging around 12 nanograms per gram in muscle tissue and roughly 23 nanograms per gram in liver tissue, with some individuals registering considerably higher. Benzoylecgonine, the compound produced when the body processes cocaine, appeared at even higher concentrations — a finding that confirmed the sharks weren’t simply carrying the drug passively but were metabolizing it.
How does cocaine end up in a shark? Multiple pathways, none of them good.
The most obvious route is sewage. Rio de Janeiro’s wastewater treatment infrastructure has long been a subject of criticism. Large volumes of untreated or partially treated sewage flow into Guanabara Bay and surrounding coastal waters. When millions of people in a metropolitan area consume cocaine — and Rio’s consumption rates are among the highest in the Southern Hemisphere — the drug and its metabolites pass through their bodies and into the sewer system. From there, it enters the ocean. Wastewater treatment plants, even functional ones, are generally not designed to filter out pharmaceutical or narcotic compounds at the molecular level. In Rio, where significant volumes of wastewater bypass treatment entirely, the problem is compounded.
But sewage isn’t the only source. Brazil is a major transit point for cocaine moving from Andean production zones to markets in Europe and Africa. Drug seizures at Brazilian ports have surged in recent years. And where there’s trafficking, there’s dumping — packages jettisoned at sea to avoid law enforcement, shipments lost overboard, clandestine processing labs discharging waste into rivers that flow to the coast. The researchers acknowledged that distinguishing between these sources in the marine environment is difficult, but the sheer concentration of cocaine in the sharks suggests sustained, not episodic, exposure.
The study noted that female sharks carried higher cocaine concentrations than males. Pregnant females showed especially elevated levels. This is particularly alarming because Brazilian sharpnose sharks are viviparous — they give birth to live young nourished through a placental connection. The implication: cocaine could be transferring from mother to pup in utero, potentially affecting fetal development in ways that haven’t yet been studied.
Researchers also pointed out that cocaine is a potent neurotoxin. In terrestrial mammals, chronic exposure damages the cardiovascular system, disrupts endocrine function, and impairs cognition. Whether sharks experience analogous effects is unknown, but the biological plausibility is there. Sharks rely heavily on electroreception and finely tuned sensory systems to hunt. Even subtle neurological interference could affect predation success, migration patterns, or mating behavior. And because sharks are apex or near-apex predators, bioaccumulation — the process by which toxins concentrate as they move up the food chain — means they’re absorbing cocaine not only from the water but from every contaminated fish and invertebrate they eat.
This isn’t the first time illicit drugs have been detected in marine life. Studies in Europe have found traces of cocaine, amphetamines, and other pharmaceuticals in mussels, eels, and river fish. A 2019 study detected cocaine in freshwater shrimp in rivers near London. But the concentrations found in Brazilian sharks dwarf those earlier findings. The gap is enormous — and it suggests that coastal waters near major population centers in Latin America may be far more contaminated with narcotics than previously understood.
The broader context matters. Pharmaceutical pollution in the world’s waterways has become an increasingly documented crisis over the past two decades. Antidepressants, birth control hormones, antibiotics, and painkillers have all been found in rivers, lakes, and oceans, with measurable effects on aquatic organisms. Fish exposed to psychiatric medications show altered behavior. Hormonal pollutants have caused sex changes in fish populations. The addition of cocaine — a powerful stimulant — to this chemical cocktail introduces yet another variable into already stressed marine environments.
And the problem isn’t confined to Brazil. Global cocaine production hit record levels in 2022 and 2023, according to the United Nations Office on Drugs and Crime. Consumption has risen across Europe, North America, and parts of Asia. Every major coastal city with a cocaine-using population is, in theory, flushing some portion of that drug into the ocean. The Brazilian study may simply be the first to look for it in sharks — and to look in the right place.
So what happens next? The researchers called for expanded monitoring of cocaine and other illicit substances in marine organisms, particularly in regions with high drug consumption or trafficking activity. They also emphasized the need for better wastewater treatment in coastal cities — a recommendation that, while scientifically sound, runs headlong into the political and financial realities of urban infrastructure in developing nations. Rio de Janeiro has been promising sewage treatment improvements for decades, most notably in the lead-up to the 2016 Olympics. Progress has been incremental at best.
There’s also the question of what this means for human health. Brazilian sharpnose sharks are commercially fished and consumed as food in Brazil, often sold under generic labels like “cação” that obscure the species. If these sharks are carrying cocaine in their muscle tissue, people are eating it. The concentrations detected are unlikely to produce a psychoactive effect in a human consumer — the doses are far too small for that — but the long-term health implications of chronic low-level cocaine ingestion through seafood are entirely unstudied.
The symbolism is hard to ignore. Sharks have survived for more than 400 million years, predating trees, dinosaurs, and every mass extinction event in the geological record. They have endured asteroid impacts, ice ages, and the rise and fall of countless species. Now they’re swimming through water laced with cocaine because of a single species’ appetite — an appetite not for food, but for a recreational high.
The study’s authors were careful to note that their sample size was small and that further research with larger populations and additional species is needed. Fair enough. But a 100 percent positive detection rate across all tested individuals is not a statistical fluke. It’s a signal. And the signal says that the chemical footprint of human drug use now extends deep into the marine food web, reaching animals that most people think of as untouchable apex predators roaming a vast and dilutive ocean.
That ocean, it turns out, isn’t vast enough.
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