Researchers at the Federal University of Rio de Janeiro have detected the antidepressant sertraline in the brains of hammerhead sharks caught off the coast of Rio de Janeiro state, in what they describe as the first finding of its kind in Brazil and one of only a few reported worldwide.
The study, carried out by UFRJ's EcoShark Project, examined 20 hammerhead sharks from two species: the scalloped hammerhead (Sphyrna lewini) and the smooth hammerhead (Sphyrna zygaena). The animals were accidentally caught by partner fishermen in coastal areas including Copacabana, Barra da Tijuca, Recreio and Guaratiba, according to Folha de S.Paulo.
The results have not yet been peer reviewed. Mariana Alonso, the biologist who coordinates the research, told Folha that the paper is expected to be submitted to a scientific journal by the end of July.
The team analyzed several tissues and organs, including liver, muscle, gills, brain tissue and the ampullae of Lorenzini, sensory structures located in the sharks' heads. The work took about three years, from collection of the animals to laboratory analysis and interpretation of the data.
Alonso said the finding was striking because contaminants are usually concentrated in the liver. In this case, sertraline appeared almost exclusively in the brain, the same organ where the drug acts in humans. The researchers said the compound was detected in most of the sharks analyzed, but declined to release the exact number before peer review.
The scientists have not found evidence that the contamination altered the sharks' behavior or physiology. Alonso said the next step is to test whether sertraline affects serotonin levels in sharks and whether that could change behavior.
Previous studies in zebrafish, a common laboratory species, have linked exposure to sertraline with changes such as slower swimming and learning difficulties. It is not yet known whether similar effects can occur in sharks.
The next phase of the research will expand the number of animals studied and compare contamination levels in pups, juveniles and adults. The team also plans to investigate whether the compound can be transferred from mothers to offspring during gestation.
Both shark species examined are threatened. The smooth hammerhead is classified as vulnerable, while the scalloped hammerhead is considered critically endangered, one of the highest risk categories before extinction.
Sertraline can reach marine animals through sewage discharged into the sea or through contaminated prey. Alonso said the problem is not limited to areas without sewage collection and treatment. Conventional wastewater plants often fail to remove pharmaceutical residues completely. These substances are known as emerging contaminants because they are increasingly detected in the environment but are not yet fully regulated.
The EcoShark group has previously identified other contaminants in sharks and dolphins, including sunscreen filters, insecticides, parabens and industrial residues. Alonso warned that mixtures of such substances may amplify their biological effects, although more research is needed to establish toxic impacts.
The finding adds to evidence that everyday chemical use can move through wastewater and food chains into marine predators. As Alonso put it, sharks function as sentinels of the ocean: if a contaminant reaches them, it has likely passed through several layers of the marine ecosystem.
This article is based on single-source reporting from Folha de S.Paulo. The underlying scientific results are preliminary and have not yet undergone peer review.