A study reports fentanyl has been found in Gulf of Mexico dolphins, providing what the authors say is the first evidence of human pharmaceuticals stored in the blubber of live, free-swimming marine mammals. Experts say the findings have important implications for ecosystem health and human food safety. Aside from fentanyl, which is an opioid analgesic 100 times stronger than morphine, carisoprodol, a muscle relaxant, and meprobamate, a sedative, were detected in dolphin fat.

The findings were described in “Pharmaceuticals in the Blubber of Live Free-Swimming Common Bottlenose Dolphins,” a study conducted by seven scientists at Texas A&M University-Corpus Christi in the United States. Published Dec. 20 in the journal iScience, the targeted analysis used samples collected from 89 live, free-swimming and postmortem common bottlenose dolphins (Tursiops truncatus). Pharmaceuticals were found in 30 of the 89 specimens tested. Of those 30, fentanyl was found in 24, 18 of which were alive and 6 dead.

Dolphins are apex predators, considered a sentinel species, meaning they are good indicators of the health of a marine ecosystem. “Their lipid-rich blubber is a biological matrix because a lot of contaminants have an affinity towards fatty tissues,” says Dana Orbach, Assistant Professor of Marine Biology at Texas A&M University-Corpus Christi’s Department of Life Sciences and lead author of the study.

Remote biopsy sampling

The study was conducted in partnership with the National Oceanic and Atmospheric Administration (NOAA). NOAA staff trained Orbach in remote biopsy sampling, which involves firing a crossbow from a moving vessel. A modified dart hits the dolphin, takes a 10-millimeter sample of tissue, pops out, and floats.

In designing the study’s methodology, coauthor Makayla Guinn determined only 150 milligrams of blubber is sufficient to carry out the analysis. The samples, some of which came from dolphins that had died before the study began, were sourced from three regions of the U.S. coast of the Gulf of Mexico: Redfish Bay, Texas; Upper Laguna Madre, Texas; and Mississippi Sound, Mississippi.

Postmortem dolphin-tissue samples were collected from the Redfish Bay and Upper Laguna Madre vicinities in 2022–23. These included blubber samples from dolphins that died in 2012-2014, revealing that pharmaceuticals in the marine ecosystem are likely a longstanding phenomenon. Says Orbach: “It’s alarming that this has been a problem for over a decade, and no one has looked for it before.”

For now, the research does not indicate how much fentanyl would be lethal, nor is there clarity on whether fentanyl was to blame for the deaths of dolphins that tested positive.

The study found a higher contaminant load in male dolphins than in females. Researchers say one explanation could be that the transplacental and lactation-related transfer of drugs effectively lowers drug levels in females to some degree. This transfer is among possible explanations offered for the fact that, in general, firstborn dolphin offspring often do not survive.

Dolphins with the highest concentration of fentanyl were from Redfish in Corpus Christi Bay—the largest port in the United States in terms of total revenue tonnage. The busy port has constant vessel traffic, noise pollution, dredging and has been impacted by occasional oil spills. Scientists say such stressors can overwhelm dolphins. “We know the area is high risk for animals in terms of anthropogenic disturbances,” says Orbach. “Could it be that these dolphins are so susceptible because of the environmental and human co-stressors? Fentanyl could be the last element that tips the scales and surpasses the animals’ ability to survive.”

High-tech analysis

The targeted analysis of blubber was carried out using ultra-performance liquid chromatography coupled with Orbitrap Fusion Tribrid mass spectrometry, an approach designed by Christiana Wittmaack, an ecotoxicologist, and Hussain Abdulla, a biochemist. Orbach says the findings have prompted the U.S. government to support broader research targeting a greater array of marine animals and substances. She says her team is now searching across trophic levels to determine what species are contaminated and the extent of the problem.

Scientists believe dolphins likely ingest pharmaceuticals in fish and shrimp that are their staple, as they don’t routinely drink water. If confirmed, this would be worrisome for a region where seafood is an important part of the local diet and export economy. Researchers say study is needed to determine the role of “point source” pollution such as untreated wastewater from pharmaceutical labs or treated wastewater that is not screened for certain contaminants.

A range of substances is being eyed in the testing of marine species. In a July 2024 study, researcher Enrico Saggioro of Brazil found cocaine in the livers of sharks living in waters near Rio de Janeiro. (See "Cocaine found in tissue of sharks caught off Rio" —EcoAméricas, July 2024.) He too is following up with research to document the presence of cocaine elsewhere in the marine food chain.