What happens when our tiniest plastics reach the ocean? New UC Davis research tracks them
Germs are hitching rides around the world’s waterways on the tiniest of rafts — microscopic plastic fibers from human clothing and fishing nets — and contaminate the shellfish that consume them, according to research published Tuesday by scientists at the University of California, Davis.
These researchers hope to see further study on how the pathogens in these contaminated fish affect the humans and other animals eating them.
“It’s easy for people to dismiss plastic problems as something that doesn’t matter for them, like, ‘I’m not a turtle in the ocean; I won’t choke on this thing,’” said infectious disease expert Karen Shapiro. “But once you start talking about disease and health, there’s more power to implement change. Microplastics can actually move germs around, and these germs end up in our water and our food.”
Shapiro, an associate professor in the UC Davis School of Veterinary Medicine, studies the many zoonotic pathogens that travel between humans and animals and how human choices affect disease transmission. This approach to study, known as One Health, recognizes that the health of plants, animals, people and the environment are interdependent.
About the size of a grain of rice, microplastics have been found in the harshest and most remote ocean environments of the world. They even have reached the Southern Ocean where land parasites typically would never surface.
The UC Davis research, published in the journal Scientific Reports, noted two types of microplastics.
One, polyester microfibers, dislodge from fabrics and blends when they are washed or from nylon fishing nets being used to haul in the day’s catch.
The other, polyethylene microbeads, run down sink drains as people use exfoliants or cleansers to wash off their makeup.
As these microfibers mix with other human sewage, they can pick up parasites such as Cryptosporidium (Crypto) that can cause respiratory or gastrointestinal illnesses or Giardia which can cause frequent bouts of diarrhea for two to six weeks. But the largest source for these parasites is runoff from livestock farms that pours into waterways.
Yet another parasite, Toxoplasma gondii , gets into waterways as part of overland runoff from wild and domestic cat feces. When the tiny grains of plastic carrying these and other parasites sink to the bottom of the ocean, they can easily be consumed there by zooplankton, clams, mussels, oysters, abalone and other shellfish.
In research published a few years ago, Shapiro and her team directly connected strains of Toxoplasma gondii found in domestic and wild cats to nearby sea otters stranded with toxoplasmosis.
While the overall otter population was not threatened in that case, Shapiro said, toxoplasmosis has proven to be devastating to critically endangered wildlife such as Hector’s dolphins and Hawaiian monk seals.
Because toxoplasmosis can cause lifelong illnesses, as well as developmental and reproductive disorders, Shapiro and other UC Davis researchers said they definitely would like to see funding for research that can examine whether microbeads or microfibers could be carrying the devastating illness to human populations.
“This is very much a problem that affects both humans and animals,” said first author Emma Zhang, a fourth-year veterinary student at UCD. “It highlights the importance of a One Health approach that requires collaboration across human, wildlife and environmental disciplines. We all depend on the ocean environment.”
In recent years, California has taken steps to begin reducing marine plastic pollution, aiming mostly at large items like plastic bags, straws and eating utensils, but the UC Davis studies show that even microscopic plastics are a hazard.
The UC Davis researchers collaborated with scientists from the University of Toronto and the University of Nebraska. They noted that there are ways humans can keep make it harder for the pathogens to hitch rides on the microplastic rafts.
“Mitigation strategies include filters on washing machines, filters on dryers, bio-retention cells or other technologies to treat stormwater, and best management practices to prevent microplastic release from plastic industries and construction sites,” said Chelsea Rochman, a plastic-pollution expert and assistant professor of ecology at the University of Toronto
