Deadly pathogens can hitch a ride on ocean microplastics, study finds

FILE - A fisherman paddles at the Potpecko accumulation lake covered with plastic bottles near Priboj, in southwest Serbia on Jan. 22, 2021. (AP Photo/Darko Vojinovic, File)

A new study has found that microplastics can carry land-based parasites to the ocean, affecting both wildlife and human health.

According to researchers out of the University of California, Davis (UC Davis), microplastics can make it easier for disease-causing pathogens to concentrate in plastic-contaminated areas of the ocean, reaching places a land parasite would normally never be found.

Microplastics are tiny plastic fragments or fibres produced from the breakdown of larger pieces of plastic, including from beverage bottles, packaged food wrappers and plastic bags.

"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 study author and UC Davis associate professor Karen Shapiro in a news release.

"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."

The study, which was published Tuesday in peer-reviewed journal Scientific Reports, is the first to connect microplastics in the ocean with land-based pathogens.

Previous studies have shown that people and animals were known to consume microplastics via food and water, as well as breathing them in through air pollution. They have also been found in the feces of babies and some adults, as well as in human blood.

Researchers looked at three common pathogens: Toxoplasma gondii, Cryptosporidium (Crypto) and Giardia, which can infect both humans and animals.

According to researchers, these pathogens are recognized by the World Health Organization as underestimated causes of illness from shellfish consumption and are found throughout the ocean.

Toxoplasma gondii, a parasite found only in cat feces, has infected many ocean species with the disease toxoplasmosis and has also been linked to sea otter deaths, according to the study. In humans, researchers say the pathogen can cause lifelong illnesses, as well as developmental and reproductive disorders.

Cryptosporidium and Giardia can cause gastrointestinal disease and can be deadly in young children as well as those who are immunocompromised.

Under laboratory conditions, researchers tested whether the pathogens can associate with plastics bathed in seawater using two different types of microplastics: polyethylene microbeads and polyester microfibers.

Microbeads are often found in cosmetics, such as exfoliants and cleansers, while microfibers are in clothing and are commonly shed in washing machines, reaching oceans via wastewater systems.

The study, which was funded by the Ocean Protection Council and California Sea Grant program, found that more parasites attached to microfibers compared to microbeads, though both types of microplastics can carry land pathogens.

Researchers say microplastics can make it easier for land parasites to reach the oceans, depending on whether the plastic particles sink or float.

According to the study, microplastics that float along the surface of the sea can travel long distances, spreading pathogens far from their land sources, while plastics that sink may concentrate in the benthic zone at the bottom of the sea. This zone is where filter-feeding creatures like zooplankton, sea urchins, abalone, mussels, crabs and other shellfish live, increasing the likelihood of them ingesting the microplastics and any attached parasites.

If sea life ingests such parasites, researchers say the effects could have serious impacts to food chains.

"When plastics are thrown in, it fools invertebrates," Shapiro said in the release. "We’re altering natural food webs by introducing this human-made material that can also introduce deadly parasites."

To help reduce the impacts of microplastics in the ocean, researchers suggest using filters on washing and drying machines and increasing storm water treatment, as well as implementing "best management practices" for plastic industries and construction sites.

"This is very much a problem that affects both humans and animals," said study author and UC Davis veterinary student Emma Zhang in the release. "We all depend on the ocean environment."