This ecosystem toxicologist is tracking microplastic consumption in dolphins
Austin Gray’s research has led him and fellow team members to find an average of 1,400 microplastics, including small polymers from tires, particles from fishing lines, and even foam particles from discarded cups, in the gastrointestinal tracts of dolphins in Charleston Harbor.
Charleston Harbor’s mix of microplastic pollution reflects the South Carolina coastal city specializing in seafood, shipping, and tourism and one ballooning in population and infrastructure, ecosystem toxicologist Austin Gray has found.
The ecosystem toxicologist cites tire wear particles dusting the Arthur Ravenel Jr. Bridge, which connects downtown Charleston to Mount Pleasant. Bits of plastic polymer from tires are washed into drains along the bridge, and then into ponds that feed into the harbor. Discarded fishing lines can also shed polypropylene particles and fibers into the water. And then there are foam particles that may come from discarded cups likely once filled with popular sweet tea. Gray and his collaborators have referred to this possibility of pollution as the “sweet tea hypothesis.”
If you were to walk along the shoreline of Charleston Harbor, you’d encounter a piece of plastic every two steps, according to a 2014 survey of plastic debris conducted by a team that included Gray at the start of his research on microplastics. Gray joined the Virginia Tech College of Science as an assistant professor of biological sciences in 2021.
Now, he’s taking a closer look at the impact of microplastic pollution on marine life in the area. Alongside collaborators at the Hollings Marine Laboratory, Gray is working to learn which microplastics are making their way into the guts of an apex predator that can be found throughout Charleston’s waters: the bottlenose dolphin.
In a five-year project supported by the National Oceanic and Atmospheric Administration’s National Centers for Coastal Ocean Science (NCCOS), Gray and Wayne McFee, head of coastal marine mammal assessments at NCCOS, are leading a team in measuring and identifying microplastics from the gastrointestinal tracts of deceased bottlenose dolphins found stranded in Charleston Harbor.
Gray hopes to eventually compare his team’s measurements of microplastics in dolphins to the rich body of data on microplastics found in Charleston Harbor. “Charleston Harbor itself is a well-documented site, compared to other areas of the world,” said Gray, who is also an affiliated faculty member of the Global Change Center, part of the Virginia Tech Fralin Life Sciences Institute.
“We’ve documented microplastics in tidal creeks, beach sediment, surface water, its sea surface microlayer — and we’ve profiled the toxicological impacts of microplastics on shrimp and oysters. But to discover which plastics make it into the bodies of organisms of varying trophic levels that’s something we’re still teasing apart. Is what we’re finding in the water also what we’re finding in these organisms?”
As apex predators, dolphins can give us a good indication of what microplastics are moving up the food chain, Gray said. As microplastics are consumed by bigger and bigger fish, by the time they’re ingested by an animal at the top of the food chain, we may be able to learn how different microplastics are distributed and accumulated once they’ve reached their final consumers.
The first study measuring microplastics in dolphins was published in 2020, focusing on the plastics’ presence in the animal’s gastrointestinal tract. Gray and McFee aim to build on that work by monitoring microplastics retained by the dolphins’ gastrointestinal tracts over a long period of time. Their team, including microplastics researcher Bonnie Ertel, are extracting microplastics from the intestines of dolphins and analyzing their chemical composition to identify the specific polymers that make them up.
Gray’s team found an average of over 1,400 microplastics in the gastrointestinal tracts of the four dolphins they studied throughout 2022. They’ll continue to gather data from stranded dolphins this year.
“That is something I wasn’t exactly expecting,” Gray, who’s originally from North Charleston, said of the data. “I was pretty shocked to see levels that high within an organism. It leads us to start asking more detailed questions: What about these particles is influencing anything we’re seeing in regard to mortality? Are they higher depending on where the dolphin is stranded? Does abundance change throughout different seasons, or years? The more data we get, the more we can do to make inferences about what we find.”
Because the study will run over a five-year period, Gray is hopeful that his team’s data will capture change over time in a way that other studies have yet to do. Studies of this kind more often provide shorter snapshots of microplastics, maybe a year at most. With recent legislation banning microbeads kicking in, a longer study could reveal how policies on plastic waste and release correspond to microplastics detected in organisms over the next few years, Gray said.
With this long-term data will come a sense of the impact we have on our coasts, Gray hopes.
“If you’re in an area with a lot of microplastic pollution and a lot of discarding of waste, then it’s not just going to be impacting you, it’s going to be impacting organisms that live there,” he said. “Their exposure to microplastics is directly influenced by us.”