Research Reveals Bacterial Passengers on Ocean Plastics Pose Ecosystem, Health-Related Harms
Empty soda bottles, abandoned six-pack rings and discarded fast food toys are chauffeuring deadly disease around the globe.
It’s bad enough that plastic never goes away. The Great Pacific Garbage Patch, the Earth’s largest accumulation of ocean plastics measures three times the size of France. This detritus, though, also is Ubering bacteria across the high seas, threatening delicate ecosystems and potentially endangering human health.
Take Vibrio cholera, for instance. Lillian Lowrey '19 works with several varieties of the bacterium that causes the intestinal infection cholera, which can quickly cause severe dehydration and is spread in unsafe water, typically in places without sanitation. Lowrey’s lab work this semester continues her Davidson Research Initiative (DRI) project looking at the effect of plastics-riding bacteria on coastal communities in the southeastern United States.
More than 90 percent of the plastics in the ocean are microplastics—particles at five mm or less not visible to the naked eye. They include nylon particles from clothing, which pour into the sea by way of our laundry room washing machines.
Once they infiltrate delicate ecosystems, no organism is safe—they embed in the digestive tracts of coral, fish, and other creatures; carry organic pollutants that remain in fatty tissues for the life of the organism; and provide a favorable environment for virulent bacteria to grow and disrupt natural oceanic bacteria ecosystems.
Antibiotic resistance has been found to spread faster in microplastic-attached bacteria than in those living freely in the water. "What’s living on the plastics is distinct from what’s in the water," Lowrey said, explaining how plastics over time collect a biofilm, or slime, composed of all manner of microscopic organic matter and living organisms.
Lowrey wondered whether a handful of nasty species of bacteria were prevalent on microplastics, which are particularly nimble at spreading these biofilm colonies around the globe, and if they were also present in seawater and sediment in the estuaries of the southeastern coast of the United States.
For her project, she drew inspiration from a study that found cholerae and a bunch of its other relatives in the Baltic Sea.
"This is strange, because you wouldn't really expect a lot of cholerae to be in cold areas with decent water sanitation," she said. "A fair number of studies analyzing what is living on the surface of these plastics have been done in Europe and on the open ocean, but studies on the U.S. coast have been lacking."
The biology and environmental sciences double major, and daughter of a nationally-ranked tennis player and a U.S. Marine, is used to vigorous travel like the summer field research trips she took with environmental studies professor Dave Backus and others.
"Every week or so, we’d get in the environmental studies truck and take the horrible environmental studies swamp boat down to the coast," she said, clearly relishing the memories of collecting samples in the well-worn vessel, which handled more like a fork lift than a Porsche.
They trawled their nets from Jacksonville, Florida, to Wilmington, North Carolina, and through Winyah Bay, which drains Myrtle Beach.
"I spent basically the entire time we were out in the water two steps away from being sea sick," Lowrey said. "It was unbelievably hot out because by the time we could actually start trawling, it was nearing noon and the process took hours."
Back in Biology Professor Dave Wessner’s lab, Lowrey grows cultures from the samples she took. The researchers run the samples through the lab’s Fourier Transform Infrared Spectroscopy machine—analysis suggests that the plastic contains toxins from Vibrio cholerae, a species made up of many strains. The toxins from some of those strains are what cause the acute gastrointestinal effects of cholera.
Lowrey checks for the toxic strains by analyzing a small part of the bacteria’s genome.
"These species I'm looking for aren't present in the seawater or sediment," Lowrey said. "So the plastics are supplying a niche for dangerous bacteria to grow where they were not able to or didn't prefer to previously."
As these bacteria form biofilm on the plastics, they may also begin to grow more readily in the water, Lowrey said. This poses a public safety threat not only to people in coastal communities, who ingest or use the water to cook and bathe, but also to consumers of contaminated oysters grown in estuarine environments, for instance.
"After the plastic was cleaned multiple times, the toxin was still present on the surface of the plastic and at high enough concentrations for the machine to make a decent match," she said. "This suggests that virulent forms of cholerae that produce the cholera infection are present, and the toxins that actually cause the illness can stick to the surface of these plastics."
Lowrey’s findings shed light on a global problem, and come at a time when scientists are only beginning to understand the extent of that problem. Last month, a study by Austrian scientists found microplastics in human stool samples—a first, and an indicator that microplastics may be widespread in the food chain.
Lowrey hopes to keep asking the questions that others aren’t asking as a graduate student. First, though, she’ll turn her sights toward a senior thesis on the prevalence of cholerae on microplastics in the Baltic Sea.
Meanwhile, experts say they’ve observed enough harm to the ecosystem from microplastics to sound the alarm—it’s time for humanity to clean up its act.
- November 6, 2018