Plastic garbage in the sea is a life raft for pathogens

According to studies, different human diseases are attracted to the microplastics in saltwater.

A thin coating of biofilm, a sticky mixture of mucus and microorganisms, has already formed on the surfaces of the plastics after just one week of immersion in the Atlantic near Falmouth, England. A microbiologist at the University of Exeter in England named Michiel Vos had tested this by submerging five different kinds of plastic. He and his colleagues were interested in learning which of the numerous marine bacteria might latch onto these new compounds.

Pathogenic microorganisms were the main focus of Vos and his associates. The researchers injected wax moth larvae with the biofilm to examine how far plastic may be colonized by potentially lethal bacteria. Four percent of the larvae perished after a week. Vos and his colleagues decided to repeat the test four weeks later after giving the plastics a little more time to simmer in the water. The wax moth mortality rate was 65% this time.

The plastics were coated in bacteria, including ones that are known to make us sick, when the scientists examined the biofilm. They discovered the pathogenic bacteria that cause pneumonia, infections of the skin, stomach, and urinary system, among other ailments. The fact that these bacteria also carried a variety of genes for antibiotic resistance only made matters worse. According to Vos, microorganisms, including diseases, quickly colonize plastics found in water. And it really doesn't matter what kind of plastic it is.

More than simply microbes are traveling on plastics. Additionally, parasites, viruses, and harmful algae may be present in biofilms on marine plastics. Scientists worry that because marine plastic pollution is so pervasive and has been discovered everywhere from the Mariana Trench to Arctic shores, these human infections are being transported by plastics across the oceans.

However, it is impossible to say if pathogen populations are present in plastics in sufficient numbers to represent a threat or whether they are spreading to other locations.

There are solid grounds for thinking that germs are gathering on plastics and spreading them over the globe. Plastic is distinct from other hard surfaces one frequently finds in the ocean—such as logs, shells, and rocks—because it is strong, long-lasting, and much of it floats, according to Linda Amaral-Zettler, a microbiologist at the Royal Netherlands Institute for Sea Research who coined the term "plastisphere" for the novel ecosystem plastics create. She claims, "That gives it movement."

Long distances may be covered using plastic. For instance, several items that could only have come from Japan after the earthquake and tsunami in 2011 washed ashore on the west coast of North America. This trash "has the ability to move anything tied to it," claims Amaral Zettler.

Recent laboratory research also demonstrates that several parasites that generally cause diseases on land may live in saltwater and infect marine mammals. Toxoplasma gondii, Cryptosporidium parvum, and Giardia enterica are three protozoan parasites that Karen Shapiro, an infectious disease specialist at the University of California, Davis, demonstrated may bind to microplastics in saltwater. This could be changing the times, locations, and methods by which these parasites gather in the water.

"They will end up where the plastic ends up," says Shapiro, "if they are hitching a ride on plastics that just so happen to be in the same sewage outlet, river, or overland overflow from a storm drain." That may be in bottom shellfish or adrift on currents in the middle of the ocean.

The following stage, according to Shapiro, is to search for a comparable connection between parasites and plastics outside of the lab.

For Vos, the discovery that microplastic pollution appears to be a haven for germs presents a longer-term worry: that plastics could be aiding in the spread of antibiotic resistance. He claims that because the bacteria are in close proximity to one another on the surface of microscopic microplastics, there is a high amount of horizontal gene transfer between them. Pesticides and other contaminants, which also adhere to biofilms, can come into contact with bacteria through plastics. This promotes the growth of antibiotic resistance.

There may be intriguing ways in which bacteria could be subjected to greater selection for antimicrobial resistance on plastics while also having more opportunities to exchange genes that could confer resistance, according to Vos.

Amaral-Zettler claims that plastic-borne viruses might endanger not just human health but also marine ecosystems and food supply networks. Many infections infect the fish and shellfish we consume, and while millions of people rely on seafood as a source of protein. According to Amaral-Zettler, it's possible for microplastics to spread diseases among various aquaculture and fishing areas.

These findings provide yet another strong case for regulating plastic pollution, despite the fact that we still don't completely understand the consequences, according to Vos. "Plastics with viruses floating about can't have any benefits."

This article was originally featured on Hakai Magazine, an online publication about science and society in coastal ecosystems. Read more stories like this at