microplastics have infiltrated virtually every corner of the planet. From Arctic sea ice to the air over Antarctica, traces appear in tap water and bottled water, in house dust, and in wildlife ranging from birds and fish to mammals. They are an emerging health concern, and many microplastics carry living organisms such as algae, protists, parasites, viruses, fungi, and bacteria.
Marine microbial biologist Linda Amaral-Zettler of the University of Chicago Marine Biology Laboratory describes these rich communities of plastic dwellers as a “plastic sphere.”
Thirteen years ago, a team led by Amaral-Zettler identified bacteria from the genus Vibrio, some strains of which can affect human health.
Animals, including humans, can inhale or ingest pathogen-coated microplastics and contract infectious diseases.
Researchers once could not determine whether these bacteria posed a real threat, but recent work by the Marine Biological Laboratory and the Royal Netherlands Institute for Sea Research shows solid reasons for continued vigilance.
Animals, including humans, can inhale or ingest microplastics carrying pathogens and potentially develop infections.
“Evidence suggests that microplastics may influence antibiotic resistance,” notes Carolyn Beats, a biologist and science reporter, in the Proceedings of the National Academy of Sciences.
A forecast released recently estimates that between 82 and 358 trillion microplastic particles, about 5 millimeters in size, could be present in the world’s oceans. Scientists worry that pathogens might hitch rides on these particles to travel long distances through water and air.
Countless pathogens
“We’re swimming in a mess of our own making,” warns Randi Rotjan, a marine ecologist at Boston University.
While it remains unclear how much of a role microplastics play in disease spread, researchers are shifting from questions of concern to demonstrations of potential pathways. Microbial ecologists and infectious disease specialists study microplastics-associated microbes in the sea and among marine life, exposing laboratory animals and human cells to substantial amounts of pathogen-coated plastics.
The challenge lies in the sheer variety of microplastic sizes, shapes, and chemical compositions. The success of colonizing microbes may depend on their genetic variation and the materials they encounter.
Translation: microplastics have the potential to infect both humans and wildlife, but the likelihood is still under study.
Plastics often carry toxic chemicals and can draw them from the environment. Some studies examine how these toxins and the physical structure of plastic harm living things.
In May this year, a research team from the United Kingdom and Australia coined the term plasticosis to describe fibrotic disease observed in seabird stomachs caused by plastic-induced scarring.
Infections in humans
Proving that microplastics enable infectious disease is not straightforward. Researchers must show that pathogens colonize microplastics and remain viable long enough to reach a host. An expert from the French National Center for Scientific Research notes the importance of distinguishing pathogenic strains from harmless ones.
Then, it must be shown that these bacteria can survive the journey to a potential host and cause disease. A team led by Rotjan demonstrated, in a controlled setting, that corals exposed to microplastics carrying a pathogenic strain of Escherichia coli fared much worse than those exposed to clean microplastics.
In natural habitats, corals ingest substantial amounts of microplastics. An average coral polyp can contain more than 100 particles, but whether these particles trigger disease remains uncertain.
Theoretically, inhalation or ingestion of environmental microplastics could release pathogens that cause human infections. In March this year, a Chinese study showed in vitro that Influenzavirus A can colonize polystyrene microplastics and be transported into human lung cells via endocytosis. Once inside, the virus’ replication could be hampered by the plastic particle’s interference.
Plastic production continues
It remains unclear whether microbes colonize microplastics more readily than other natural debris such as wood. Some studies suggest microplastics harbor more potential pathogens in certain environments, while a meta-analysis published in 2020 challenges that view, indicating microplastics are not inherently more likely to carry pathogens than natural surfaces.
World plastic production is exhausted: it now reaches about 400 million tons per year
Plastic tends to persist longer than many natural substrates, enabling the spread of associated organisms. Various studies indicate plastic is dispersing to new regions, bringing non-native species and pathogens along.
Since the 1950s, plastic production has surged. Global production is now around 400 million tons annually. About half of these plastics, such as Styrofoam and shopping bags, are disposable and most are not recycled. When discarded, plastics can endure for centuries, gradually breaking into smaller pieces. While some plastics erode within months or weeks at coastal or ocean surfaces, others persist far longer. The industry also produces microplastics for direct consumer use, including beads in exfoliating cleansers and fibers in synthetic fabrics. Even if production stopped, microplastics will continue to accumulate as existing plastics degrade.
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