Mississippi Sound dolphins testing positive for fentanyl. What does it mean for humans?

Dolphins in the Gulf of Mexico have traces of human medications — including powerful opioids, muscle relaxants, and sedatives — in their fat, according to a new study that is sounding the alarm on pharmaceutical pollution and wastewater treatment.

The study’s findings, published last month in the journal iScience, do not suggest an immediate risk to humans, and the effects of these low drug levels on marine animals remain unclear. But study authors said it’s a concerning development that warrants monitoring.

“We should not really see any human pharmaceuticals present in dolphins and in our waters,” said study author Anya Ocampos, who conducted the study as a Texas A&M University-Corps Christi undergraduate and is now pursuing a doctorate in veterinary medicine. “Having a drug as potent as fentanyl really was concerning, and we have virtually no idea how chronic exposure to these drugs affects our marine mammals.”

Dolphins studied from Texas, Mississippi Sound

The study looked at the blubber of 89 dolphins from Redfish Bay and Laguna Madre in Texas and the Mississippi Sound, a stretch of habitat spanning Grand Isle, Cat Island, and the area from the Pearl River to Biloxi. They tested for the opioid fentanyl, a muscle relaxer called carisoprodol and a drug used to treat anxiety called meprobamate.

At least one of the three drugs was found in samples from 30 dolphins, taken as biopsies from their flanks. Fentanyl was found in over half of the 30 dolphins, including in those from the Mississippi Sound.

Fentanyl is extremely potent. About two milligrams -- the equivalent to about five to seven grains of salt -- is enough to kill an average adult.

The analysis, conducted with the help of the National Oceanic and Atmospheric Administration and Precision Toxicological Consultancy, is the first to confirm the presence of these drugs in live, free-swimming marine mammals. The findings are troubling, authors said, because dolphins are key indicators of marine health.

Twelve of the 89 dolphins were from the Mississippi Sound, but they made up 40% of the drug detections. The Mississippi samples were taken from live dolphins in 2013, then frozen for later research.

The presence of both fentanyl and a muscled relaxer in decade-old samples suggests “this is a long-standing issue in the marine environment,” said study author Dara Orbach, assistant professor of marine biology.

How did fentanyl get in dolphins?

It’s likely that dolphins are exposed to fentanyl and other drugs through their diet of fish and shrimp, which are already contaminated through the water, said Ocampo.

Pharmaceuticals can enter the waterways through insufficient treatment of wastewater, untreated discharge from drug manufacturing plants or manure runoff after animals are treated with medication. Wastewater treatment plants have pharmaceutical removal efficiencies ranging from 23% to 54%, according to study authors.

Whether the drugs are affecting the health of marine life is a more complex question, said Melissa McKinney, a Canadian researcher studying ecological change and environmental stressors and assistant professor at McGill University.

The levels of the drugs found in the dolphins were very low. These medications have half-lives ranging from two to ten hours, meaning half of the drug metabolizes within that timeframe. It’s unknown how long the medications are detectable in marine animals, so it’s hard to say what the effect is.

“It would be very hard to assess whether there was any health impact,” said McKinney.

However, both the sedative and muscle relaxer do not dissolve well in fat, making its presence in these dolphins significant. That “suggests recent exposure” to the drugs rather than long-term, said the authors.

Could humans also be accumulating the drugs?

Dolphins are considered the canary in the coal mine for aquatic health because they consume so many smaller species. Like humans, chemicals are amplified in dolphins eating prey from a contaminated environment.

“Dolphins are marine apex predators, so they’re very high up in the food chain,” said Ocampos. “And humans, we are also pretty high up in the food chain.”

So-called drug “residue” is found in other animals that humans eat – for example, chicken tissue containing antibiotics. It can cause short-term allergic reactions, according to other studies, and over the long term may contribute to cancer, DNA mutations or harm a developing fetus.

It’s possible that humans are consuming drugs through seafood or water, too. Marine mammals tend to be a good proxy for human ingestion of chemicals, said Rainer Lohmann, professor of oceanography at the University of Rhode Island.

“They eat, to some degree, similar things to what we might eat,” said Lohmann.

Seafood is among the highest routes of uptake for PFAS, the so-called forever chemicals linked to cancer, reproductive issues, liver damage, obesity and thyroid disease, said Lohmann.

“It’s especially a concern for communities that enjoy having a high seafood diet,” said Ocampos.

However, it’s unclear whether human health would be impacted. The study authors hope to continue to study these drugs and others such as caffeine, nicotine and addictive pharmaceuticals to better understand their long-term impact on aquatic life and human health.