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They could threaten marine ecosystems and food supply chains.
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 mix 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 a test. He and his colleagues wanted to know which of the myriad microbes living in the ocean would glom on to these introduced materials.
Vos and his colleagues’ chief 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 had let the plastics stew 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 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 were also carrying a wide range of genes for antimicrobial resistance. “Plastics that you find in the water are rapidly colonized by bacteria, including pathogens,” says Vos. “And it doesn’t really matter what plastic it is.”
It’s not just bacteria that are hitching a ride on plastics. Biofilms on marine plastics can also harbor parasites, viruses, and toxic algae. With marine plastic pollution so ubiquitous—it’s been found everywhere from the bottom of the Mariana Trench to Arctic beaches—scientists are concerned that plastics are transporting these human pathogens around the oceans.
But whether plastics are bearing pathogen populations dense enough to actually be dangerous and whether they are carrying them to new areas are difficult questions to answer.
There are good reasons 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 novel ecosystem plastics create, says plastic is different from other hard surfaces one often finds in the ocean—such as logs, shells, and rocks—because plastic is durable, long-lived, and a lot of it floats. “That gives it mobility,” she says.