Ocean Plastics

Ocean microplastics harbour parasites, study finds

27/04/2022
Written by Oceanographic Staff

A new study suggests that disease-causing parasites can quickly spread through the ocean by hitching a ride on plastic particles.

Microplastics can be found everywhere, from the deepest oceans to the highest mountains. They were recently found in human blood for the first time too. But a research team has now established that microplastics can harbour parasites as well, posing a serious risk to marine animals, public health and ecosystems.

A new study, published in the journal Scientific Reports, has found that parasites from land can hitch a ride on microplastics, giving germs the opportunity to travel to distant coastlines or the deep sea.

Parasites are known to accumulate in naturally occuring biofilms that cover surfaces in the ocean. An example of this phenomenon could be found at a dock structure on a beach. Below the surface, this structure would be covered in a sticky biofilm that is home to living organisms such as parasites. Without these biofilms, parasites would be diluted in the large water mass of the ocean.

The team of scientists behind the study wanted to find out whether this phenomenon would also occur on microplastics. Not only could parasites travel quickly around the globe if this was proven true, but it could also have human health implications. Oysters, for example, are known to ingest microplastics and if humans eat these oysters, parasites could also end up in the digestive system of humans.

For the study, the research team mixed microplastics in the form of microbeads and microfibres with parasites (Toxoplasma gondii, Giardia enterica and Cryptosporidium parvum) that are often spread via livestock, pet and human feces and often end up in ocean environments. Toxoplasma parasites, for example, can also seriously affect marine mammals such as the threatened Hawaiian monk seal or the Maui dolphin.

Over the course of seven days, the team counted the number of parasites in the water as well as on the microplastics. They found that on day one, a larger number of all parasites was still in the water, rather than attached to the microbeads or microfibres. By day seven, significantly more Giardia enterica and Toxoplasma gondii were attached to the microbeads than in the water. Interestingly, none of the parasites were attached to the microfibre in large numbers on day seven.

In essence, the study looks at the relationship between two primarily human-made issues: plastic particles and fecal pathogens. “Because of the way we live our lives, and our expansion, and that of our domestic species, we have a lot more fecal pathogens,” the study’s co-author Dr Shapiro said and continued: “And concurrently, we have relied more and more on plastics.”

The study shows that while pathogens might not be able to replicate in the sea, they can move around marine waters by hitching a ride on plastic particles. When these plastic particles float along the surface, they might be able to travel long distances, bringing parasites to areas that they usually wouldn’t reach. Plastic that sinks to the bottom could further harm filter-feeding animals such as oysters, mussels and clams.

The next part of the study will take a closer look at microplastics accumulation and the concentration of parasites within shellfish.

For more from our Ocean Newsroom, click here.
Photography courtesy of Unsplash.

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