In the waters near Rio de Janeiro, scientists have discovered an alarming trend: wild Brazilian sharpnose sharks are testing positive for cocaine. Thirteen of these small coastal sharks were collected from local fishing boats, and each showed signs of cocaine in both muscle and liver tissue.

In some cases, the levels were up to 100 times higher than what’s ever been found in other aquatic animals, according to a study published in Science of The Total Environment.

These results, published by researchers from Brazil’s Oswaldo Cruz Foundation, stunned the scientific community. As The New York Times reports, the scientists expected pollutants—but not on this scale. With no known natural reason for the contamination, attention quickly turned to human sources.

Cocaine was found in all 13 Brazilian sharpnose sharks tested.

Drug Waste and Trafficking at the Root

Cocaine reaches coastal waters in Brazil from several channels. The majority comes from human waste—traces of the drug excreted in urine after consumption. Brazil, like many countries, lacks wastewater treatment systems equipped to filter out narcotics. This leaves drug residues to flow from toilets to rivers and into the ocean, Earth.com reports.

There’s also a criminal layer to the story. Drug traffickers navigating the Atlantic and Caribbean often dump cocaine bales to evade law enforcement. Some of these packages split open, dispersing high concentrations into tight coastal zones. As ClickOrlando notes, these spills happen not just in Brazil but near Florida as well, with prevailing currents sweeping the contraband into mangroves and estuaries—prime habitats for juvenile sharks.

Sharks absorb cocaine through both seawater and contaminated prey.

What Cocaine Might Do to a Shark

What happens to a shark exposed to cocaine is still being pieced together. But research on related marine animals offers clues. As explained by Indian Defence Review, cocaine alters neurological and muscular systems in species like zebrafish and eels, leading to exhaustion, poor muscle function, and slower reflexes. For sharks, this could dull their electroreception—their ability to detect prey.

If a shark can’t hunt effectively, it can’t grow, reproduce, or survive at normal rates. Over time, exposure to these invisible toxins could quietly collapse populations already under pressure from fishing, climate change, and habitat degradation.

Most cocaine pollution originates from untreated human wastewater.

Pollution Climbing the Food Chain

The impact doesn't end with sharpnose sharks. Cocaine is absorbed easily by plankton and small crustaceans—organisms that form the base of the marine food web. Sharks feeding on these species get a double dose: one from the water and one from their prey.

This process, called biomagnification, means that apex predators like larger sharks, dolphins, and seabirds could be accumulating even higher levels of toxins without any visible signs, Sky News reports.

Florida’s Test Case and Lingering Questions

The “Cocaine Sharks” phenomenon is not unique to Brazil. During Discovery’s Shark Week, researchers in Florida tested whether local sharks showed interest in mock cocaine bales. They did. Although no direct ingestion was documented, marine scientist Dr. Tracy Fanara told ClickOrlando that smaller sharks in mangrove areas could indeed face exposure if bales rupture nearby.

Fanara emphasized the broader threat, noting that antibiotics, antidepressants, insecticides, and fertilizers all wash into the ocean alongside cocaine. These mixtures could create unexpected chemical interactions, amplifying biological harm in unpredictable ways.

Drug pollution may weaken sharks' survival, growth, and reproduction.

A Global Wake-Up Call

Cocaine is only one entry in a growing catalog of pharmaceutical pollution found in marine species worldwide. Antidepressants in Great Lakes fish, methamphetamines in Czech trout, and epilepsy drugs in British otters show that the problem is both global and poorly regulated.

This isn't just a curiosity or an isolated accident—it’s a systemic issue. Drug residues slip past treatment plants, mix with other pollutants, and persist in sensitive ecosystems where animals can’t escape their effects. As Earth.com reports, this environmental footprint extends far beyond the people who use these substances.

Solutions Are Available, If We Act

Researchers at the Oswaldo Cruz Foundation believe it’s not too late. Upgrading wastewater treatment facilities with better filtration systems, deploying environmental DNA tracking, and cracking down on illegal dumping could help reduce exposure risks. But these changes require investment, coordination, and awareness.

Brazilian sharpnose sharks now serve as a grim marker of how far human pollution has reached. Their exposure isn’t just a scientific footnote—it’s a clear sign that what we flush, discard, or smuggle has a long tail. One that stretches all the way into the ocean—and back into our lives.