Dolphins near Charleston Harbor are full of microplastics. What does it mean for you?

Researchers have identified thousands of microplastics in the gastrointestinal tracts of four bottlenose dolphins that once swam near the Charleston Harbor.

Found inside the dolphins were clear fibers from fishing lines, plastic tire particles, and tiny pieces of Styrofoam.

Each of the four stranded dolphins had about 1,400 microplastic items inside their gastrointestinal tracts, according to a group of researchers supported by the National Oceanic and Atmospheric Administration’s National Centers for Coastal Ocean Science.

Beyond the sheer number of microplastics caught in the dolphins’ stomachs and intestines, the research sends a message about what increasing development and a growing population are doing to marine health, said Austin Gray, head researcher and assistant professor of biological sciences at Virginia Tech. It also raises questions about whether problems suffered by marine life indicate threats to humans as well.

“If we are polluting our waterways and different organisms, whether certain people value them or not, we are being impacted,” Gray said.

What’s clear is that if something doesn’t change to reduce the amount of microplastics ending up in waterways, the number ending up in the stomachs of everything from fish to large mammals will increase, researchers say.

Breaking down the process

In 2020, former College of Charleston graduate student Francesca Battaglia was the first to report microplastics in North American bottle nose dolphins.

Years before, local research had indicated that a person walking along the Charleston Harbor shore would encounter a piece of plastic every two steps, according to Gray. Plastic makes its way into the water, breaks down and ultimately ends up in in the stomachs of fish, dolphins and other marine life.

Gray said that of the fish tested in the Charleston Harbor, 99% had microplastics in their guts. Studying dolphins was the next move to see what microplastics were moving up the food chain.

Gray and research partner Wayne McFee, who is the head of coastal marine mammal assessments at NOAA’s National Centers for Coastal Ocean Science, joined forces to continue looking at the effects of dolphins’ microplastic consumption. In a five-year study, they’re tracking whether there is an increase of plastics in the animals’ stomachs over time and what the foreign objects could be doing to marine mammals’ physiology.

Their work begins with finding stranded, dead dolphins. NOAA contractor and University of South Carolina graduate student Bonnie Ertel collects the mammals and brings them to the Hollings Marine Lab in Charleston, where the dolphins’ intestinal tracts are removed.

Researchers then apply a potassium hydroxide solution to the intestines and let it sit for a few days, which works to break down organic matter. What’s left behind is what doesn’t degrade — inorganic matter. Gray said most inorganic matter they are finding are plastic polymers.

They count, characterize and look at the leftover particles under a microscope to see which shapes and sizes are most prevalent. Gray takes a sharper look at his lab at Virginia Tech, selecting a subset to analyze to identify the type of plastic polymers lodged in the dolphin’s gut.

In the first year of the study, they’ve found one microplastic that makes up 35% of those found in the dolphins: polypropylene.

The plastic fiber, magnified, shows up clear and string-like, and it mostly comes from fishing line and gear.

How’d it get there? The dolphin either ate fish that were full of the microplastic, or the mammal consumed it directly from the water.

McFee anticipates researchers will see a rise in the number of microplastics in the dolphins’ intestinal tracts. He pointed to several factors: Climate change, and increased population and development.

With more flash flooding predicted as the climate changes, whatever is on land will wash into the water, McFee said. Charleston’s growing population also contributes.

“The more people you put out there, the more people use plastics, the more chance of plastics getting into the water,” he said.

More people means more cars. As they are driven, tires break down, shedding little pieces of rubber that inevitably gets washed from a street or a bridge and into the Cooper and Ashley rivers.

While they found 1,400 microplastic particles on average in their first round of dolphin testing, Gray said preliminary results are trending closer to 2,000 microplastic particles.

Dolphin and human impact

McFee and Gray can’t draw definitive conclusions about how dolphins are affected by microplastic consumption, as their research mostly focuses on microplastic consumption over time as Charleston’s population and development grows.

However, McFee said microplastics are known to potentially hurt reproduction. He’s found that female dolphins who ate microplastics while pregnant passed those particles to their fetuses.

Microplastics have also been found in unweaned dolphins, who are only drinking their mother’s milk, McFee said. However researchers are uncertain if the unweaned dolphins are getting microplastics from the milk, which they are just beginning to test.

While there is no research on it, McFee suspects that if unweaned dolphins are getting microplastics from their mother’s milk, the same could potentially be true of humans.

“Dolphins are the closest marine animal we can study as far as being a good surrogate for human health as well,” McFee said. “We eat the same food that they do as far as seafood is concerned.”

In March 2022, Environment International reported for the first time that microplastics were identified in human blood at a concentration of 1.6 micro grams per milliliter.

“That tells you there’s an abundant amount of microplastics that have been documented with the human blood,” Gray said. “One of the major routes of exposure is through ingestion ... and ingestion typically tied to seafood items.”

How do we lessen the amount of plastics that ends up in waterways? Gray said an outright ban isn’t realistic. But putting mechanisms in place to capture microplastics before they’re released into water sources is possible.

He pointed to legislation proposed in California requiring new washing machines to have microfiber filtration by 2029. Something like a single nylon fleece jacket can leave behind about 100,000 microfibers in one wash, which is ultimately disposed into the environment.

A washing machine microfiber filter, whose cost ranges between $30 and $150, can capture those fibers.

Beyond collecting microplastics before they leak into waterways, people can work harder to collect plastic waste and debris that, when discarded, break down into microplastics.

“What we do as humans in our activities has a direct impact on the environment,” Gray said.