Brazilian Sharpnose Sharks Found With Cocaine in Their Systems

Brazilian sharpnose sharks living in the coastal waters of South America have been found to carry substantial amounts of cocaine and its metabolites, Brazilian researchers have reported.

Rather than the drug-addled predators portrayed in Hollywood films, the consequences of this illegal stimulant for an important part of the marine food web may be subtler, but potentially much more alarming.

An investigation headed by environmental scientist Gapriel de Farias Araujo of Brazil's Oswaldo Cruz Institute detected high cocaine concentrations in each of the 13 juvenile and young adult Brazilian sharpnose sharks (Rhizoprionodon lalandii) examined.

The researchers also identified considerable quantities of benzoylecgonine, cocaine's principal metabolite, in all but one shark.

Cocaine in Brazilian sharpnose sharks

Further work will be required to establish what these findings mean for the predators' health. However, research involving other animals offers some indication of the possible effects.

Cocaine exposure reduces cell viability and increases DNA fragmentation in zebrafish embryos. Meanwhile, a 2018 study showed that environmental concentrations of the substance altered muscle physiology in European eels.

Pharmaceutical contamination is a worldwide issue. Potentially more than one-quarter of the planet's waterways contain concentrations of active compounds - including antibiotics, synthetic oestrogen and recreational drugs - thought high enough to threaten ecosystems and perhaps human health as well.

Brazil has an especially acute issue with cocaine pollution. Water samples taken from the Bay of Santos in 2017, for example, held as much cocaine as caffeine. Caffeine is commonly used as a benchmark for pharmaceutical contamination because it is so widespread in drinks consumed around the world.

Consumers excrete both substances, which then enter waterways through sewage. Brazil is a major cocaine exporter, so illicit drug-refining sites may also be adding to the contamination. Packages lost or discarded by traffickers in the country's ports could be another source.

How cocaine moves through the marine food chain

After entering the environment, cocaine can readily be taken up by marine organisms lower in the food chain. It then builds up in those organisms, enabling higher-level consumers to absorb it at greater concentrations.

Most investigations of cocaine in the environment have focused on molluscs, crustaceans and bony fish. Consequently, little is known about its possible health effects on large predators, particularly species that live all their lives in coastal or near-coastal waters.

Between September 2021 and August 2023, fishing vessels caught three male and ten female Brazilian sharpnose sharks off Rio de Janeiro. The animals were subsequently measured and dissected.

Scientists used liquid chromatography to test muscle and liver samples for cocaine and its metabolic product, benzoylecgonine. The analysis found differing concentrations of both compounds, potentially connected to differences in the sharks' sex and reproductive status.

Cocaine and benzoylecgonine concentrations in these sharks were as much as a hundred times higher than levels recorded in published research on fish and other marine organisms. This supports the suggestion that cocaine can accumulate along the food chain.

Monitoring coastal cocaine pollution

The 2023 B-grade horror film Cocaine Shark offered the public a comic, though violent, vision of environmental drug contamination. In contrast, the researchers are urging surveillance and awareness programmes to address what may in reality be a considerably more serious issue.

Around one-third of shark and ray species are threatened with extinction, largely because of overfishing. It is therefore essential to identify and monitor every possible threat to their populations.

This study was published in Science of The Total Environment.