Researchers with the EcoShark project along Rio de Janeiro's coast have detected the antidepressant sertraline in shark tissues — including hammerhead brain samples — highlighting an invisible form of ocean pollution. While detection does not prove biological harm, it raises urgent questions about exposure pathways and potential physiological or behavioural effects. EcoShark uses an integrated approach (contaminants, telemetry, genetics, diet and health markers) and partners with local fishers to build the long-term datasets needed for effective conservation. The team plans to expand studies on pharmaceutical impacts across life stages and to combine molecular tools with movement ecology to inform policy.
Invisible Pollution: Brazilian Scientists Find Antidepressant Traces in Shark Brains
People should support organizations and research groups working on marine pollution and ecotoxicology, since long-term monitoring is what turns isolated findings like "drug traces in shark tissue" into actionable policy data.Getty Images
When we imagine ocean pollution, we often picture plastic debris, oil slicks or fishing gear. But along the coast of Rio de Janeiro, researchers from the EcoShark project have been revealing a less visible — and potentially consequential — form of contamination: chemical and pharmaceutical residues that accumulate in marine predators.
Since 2018, EcoShark has studied sharks from multiple angles — movement, diet, genetics, health and contaminant exposure — and their work recently attracted international attention when they detected the antidepressant sertraline in shark tissues collected from Brazilian waters, including brain samples from hammerhead sharks.
"Honestly, my first reaction was surprise," said Adjunct Professor Dr. Mariana Batha Alonso of the Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro. "We already know sharks are exposed to sunscreen filters, insecticides and other pollutants, but finding sertraline in shark tissue — and in brain tissue — was unexpected. That raised broader questions about pathways, exposure and potential effects."
The researchers emphasize an important distinction: detection does not equal proven harm. Finding a pharmaceutical compound in tissue shows exposure, not necessarily a biological effect. Still, because sertraline acts on the serotonergic system in humans, its presence in shark brains prompts urgent questions about how the compound reaches apex predators and whether it might alter physiology or behaviour.
An Integrated, Whole-Animal Approach
EcoShark uses a multi-disciplinary strategy to understand sharks as whole animals living in human-influenced coastal ecosystems. Contaminant and tissue analyses reveal chemical burdens; satellite telemetry and acoustic tracking show movements and habitat use; genetics clarify population structure and species identity; dietary studies place individuals within food webs; and health and physiological markers indicate biological responses. Together, these methods help identify where threats overlap and which habitats are most critical for conservation.
This approach is especially important in Brazil, a country with extraordinary shark and ray diversity along roughly 7,000 miles (about 11,000 km) of coastline. But research and conservation face major challenges: overfishing and bycatch, habitat degradation, pollution, limited health assessments, fragmented funding and too few long-term monitoring programs. Movement ecology in particular requires expensive equipment and sustained investment to track animals across months and years — and sharks do not respect human-defined boundaries like protected areas or administrative borders.
People And Partnerships
Local fishing communities are central to EcoShark's work. The team partners with fishers in Marambaia, Recreio dos Bandeirantes, Barra da Tijuca, Barra de Guaratiba and Grumari, relying on bycatch and local ecological knowledge for much of their sampling. Fishers spend hundreds of days at sea and can report seasonal shifts, changes in shark abundance, size and behaviour that short scientific surveys often miss. EcoShark stresses that scientific and local knowledge complement each other, and that effective conservation must respect fishing livelihoods: building trust, listening first and pairing restrictions with socioeconomic support.
Next Steps And Why It Matters
EcoShark plans to expand sampling across life stages to determine whether contaminants transfer from mothers to offspring, investigate links between pharmaceutical exposure and changes in serotonergic systems, physiology or behaviour, and integrate telemetry, genetics, virome surveys, microbiome analysis and other molecular tools. Long-term monitoring is essential to turn isolated findings — like drug traces in shark tissue — into actionable policy data.
Call to action: People should support organizations and research groups working on marine pollution and ecotoxicology, because sustained funding and long-term datasets are what convert occasional detections into evidence that can guide policy and conservation.
Reflecting on the fieldwork, Alonso notes, "What keeps me excited is that there is always something unexpected." That unpredictability is precisely why researchers keep going: sharks' bodies archive the chemicals flowing from coastal cities into the ocean, their movements intersect with fisheries and habitats, and protecting them means protecting the broader health of the marine ecosystem we all rely on.
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