LATEST NEWS Human pathogens are taking a ride on floating plastic:...

Human pathogens are taking a ride on floating plastic: Mother Jones


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Images by James Wakibia/SOPA via ZUMA Press Wire

This story was originally published by hakai magazine and is reproduced here as part of the climatic table collaboration.

The plastics had only been submerged in the ocean off Falmouth, England, for a week, but in that time a thin layer of biofilm, a slimy mixture of mucus and microbes, had already developed on their surfaces. Michiel Vos, a microbiologist at the University of Exeter in England, had sunk five different types of plastic as evidence. He and his colleagues wanted to know which of the myriad microbes that live in the ocean would latch on to these introduced materials.

Vos and his colleagues’ main concern was pathogenic bacteria. To understand the extent to which plastic can be colonized by potentially deadly bacteria, the scientists injected wax moth larvae with the biofilm. After a week, four percent of the larvae died. But four weeks later, after Vos and his team let the plastics sit in the ocean for a bit longer, they repeated the test. This time, 65 percent of the wax moths died.

The scientists analyzed the biofilm.: The plastics were covered in bacteria, including some that are known to make us sick. They found pathogenic bacteria responsible for causing urinary tract, skin, and stomach infections, pneumonia, and other illnesses. To make matters worse, these bacteria also carried a wide range of antimicrobial resistance genes. “The plastics you find in the water are quickly colonized by bacteria, including pathogens,” says Vos. “And it doesn’t really matter what plastic it is.”

It’s not just bacteria that hitchhike on plastics. Biofilms from marine plastics can also harbor parasites, virusand toxic algae. With marine plastic pollution so pervasive (it’s been found everywhere from the bottom of the Mariana Trench to the beaches of the Arctic), scientists are concerned that plastics are carrying these human pathogens through the oceans.

But whether plastics contain populations of pathogens dense enough to be truly dangerous, and whether they carry them into new areas, are difficult questions to answer.

There is good reason to believe that plastics are accumulating and spreading pathogens around the world. Linda Amaral-Zettler, a microbiologist at the Royal Netherlands Institute for Sea Research, who coined the term plastisphere for the new ecosystem that plastics create, he says that plastic is different from other hard surfaces often found in the ocean, such as logs, shells, and rocks, because plastic is durable, long-lived, and much of it floats. “That gives you mobility,” she says.

Plastics can travel long distances. After the 2011 Japan earthquake and tsunami, for example, many identifiable Japanese objects stranded on the west coast of North America. This trash, says Amaral Zettler, has “the potential to carry anything attached to it.”

Recent laboratory work also shows that some typically terrestrial disease-causing parasites can survive in seawater and infect marine mammals. Karen Shapiro, an infectious disease expert at the University of California, Davis, showed that these protozoan parasites, specifically, Toxoplasma gondii, Cryptosporidium parvumY Giardia enterica—can adhere to microplastics in seawater. This could be altering where, when and how these parasites accumulate in the ocean.

“If they are hitchhiking on plastics that are in the same sewer outlet, river, or land runoff from a storm drain, they will end up where the plastic ends up,” Shapiro explains. That could be in the shellfish at the bottom of the sea or floating in the currents in the middle of the ocean.

The next step, Shapiro explains, is to look for a similar association between parasites and plastics outside the lab.

That microplastic contamination appears to be a breeding ground for pathogens raises, for Vos, a long-term concern as well: that plastics may be promoting the spread of antibiotic resistance. Bacteria can exchange genes, and since bacteria are in close contact on the surface of tiny microplastics, the level of horizontal gene transfer between them is high, he says. Plastics can also bring bacteria into close contact with pesticides and other contaminants, which also stick to biofilms. This favors the development of antimicrobial resistance.

“We don’t know much about it,” Vos says, “but there are potentially interesting ways that bacteria can undergo stronger selection.” [for antimicrobial resistance] in plastics, but they also have more opportunities to exchange genes that could confer resistance.”

As well as posing potential risks to human health, plastic-borne pathogens could threaten marine ecosystems and food supply chains, says Amaral-Zettler. Millions of people depend on shellfish as a source of protein and there are many pathogens that infect the fish and shellfish we eat. It could be possible, says Amaral-Zettler, that microplastics spread diseases between different areas of aquaculture and fishing.

Although we don’t fully understand the risks, these studies are another good argument for limiting plastic pollution, says Vos. “There can be nothing positive in plastics with pathogens floating around.”

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