Land-based pathogens may hitch a ride on microplastics to oceans: Study

Land-based pathogens may piggyback on microplastics flowing into the sea, potentially posing a threat to marine life, a new study has warned.

The pathogens in question include Toxoplasma gondii, Cryptosporidium (Crypto) and Giardia, known to infect humans and animals, according to the study published in Scientific Reports.

Toxoplasma gondii, for instance, is found in cat poop. This pathogen is linked to deaths of sea otters and other critically endangered wildlife such as Hector’s dolphins and Hawaiian monk seals, the study pointed out.

Previous studies have focussed on water-loving germs such as Vibrio, which thrive in seawater, Karen Shapiro, an author of the study, told Down To Earth.

The parasites in the study by Shapiro, who is an infectious disease expert and associate professor at the UC Davis School of Veterinary Medicine in the United States, cannot multiply in the sea.

But whether these microbes attached themselves to microplastics — which form when plastics break down to form particles measuring less than five millimetres in size — was unclear, according to the study.

So, the team exposed the pathogens to two types of microplastics — polythene microbeads and polyester microfibres — that were already submerged in seawater. The former can be traced back to cosmetics, such as exfoliants and cleansers and the latter to clothing and fishing nets.

The experiment showed that pathogens attach to both microplastics, although they showed a higher preference for microfibres.

“Disease transmission must depend on the physical transport of these pathogens from the poop of infected animals and people to a susceptible host in the ocean or a human that consumes contaminated seafood,” Shapiro said.

Microplastics might ferry pathogens into the sea and impact marine life in two ways, the study noted. These particles can either float on the surface and travel long distances, spreading pathogens in the process.

Alternatively, they could sink into the oceanic depths, which are regions inhabited by filter-feeding animals like zooplankton, clams, mussels, oysters, abalone and other shellfish.

Filter-feeding animals, which swallow water to filter food, are particularly susceptible to ingesting high levels of microplastics, a previous study found.

“This is very much a problem that affects both humans and animals,” first author Emma Zhang, a veterinary student with the UC Davis School of Veterinary Medicine, said in a press statement.

The problem requires collaboration across human, wildlife and environmental disciplines as we all depend on the ocean environment, she added.

Researchers have previously detected these pathogens in shellfish. “Now, we will focus on investigating whether microplastics increase the uptake of pathogens among shellfish,” Shapiro said.

Adding filters on washing machines and dryers could control the release of microfibres into the environment, the researchers said.

Other solutions include deploying technologies to treat storm water and best management practices to prevent microplastic release from plastic industries and construction sites, the researchers added.

So far, scientists have detected microplastics in the air, water, food and in our bodies, too. In March 2022, a study identified these particles in human blood samples.

Another study published in Science in The Total Environment detected microplastics hiding deep in human lungs. These particles were fragments of polypropylene, used in plastic packaging and pipes and polyethylene terephthalate or PET, used in bottles.

While the health impacts of exposure to these human-made pollutants are not clear yet, researchers have called for more studies to investigate the link.

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