April 19, 2024

I, Science

The science magazine of Imperial College

by Molly Rains (14 June 2023)

Plastic debris on beaches worldwide may be laden with infectious bacteria, according to a new study. 

Researchers from the University of Stirling found that pathogens living on microplastics were able to survive harsh environments for weeks on end. Even after being subjected to changing conditions meant to simulate the journey from a wastewater treatment plant to the sea, the bacteria lived on for another week in the sand. 

“Plastics can facilitate the movement of pathogens from wastewater treatment plants, where humans aren’t likely to come into contact with them, into environments – such as bathing water beaches – where there is a high likelihood of humans coming into contact with them,” said Rebecca Metcalf, lead researcher on the study. 

Bacteria from sewage can live on almost any surface, but it is the longevity and buoyancy of plastics that make their contamination particularly concerning. “Natural materials, such as wood, are likely to break down, whereas plastics are becoming more and more prevalent in the environment,” said Metcalf. Instead of decomposing, plastics fragment into smaller and smaller pieces, which can float along currents for long distances before washing up on far-flung beaches – potentially with bacterial hitchhikers in tow. 

Unlike free-swimming bacteria, pathogens on plastic surfaces benefit from the “protective environment” of a colony, said Metcalf. This helps them endure the dramatic changes in conditions that occur along the journey between wastewater treatment plants and beaches. In this way, plastic pollution – millions of tonnes of which is already afloat in the world’s oceans – may be contributing to the spread of infectious disease. 

Plastic pollution may also be facilitating the rise of more dangerous strains of bacteria. By offering “a new surface for bacteria to interact [on],” Metcalf warned, plastics allow pathogens to mingle and swap genes for dangerous traits, including drug resistance and toxicity. This is a particular concern with wastewater from hospitals, where multi-drug resistance is more common in dangerous strains like P. aeruginosa and MRSA.

Microplastics are released by a wide variety of sources, but single-use plastics – especially those that are often flushed, like cotton-bud sticks and wet wipes – are of particular concern when it comes to wastewater bacteria. Avoid flushing these materials, Metcalf said; doing so “just makes the problem worse.” 

Beachgoers don’t need to avoid the shore this summer – instead, they can help control the problem. “Don’t be afraid to be involved in beach cleans,” said Metcalf. “Just be aware, wash your hands, and maybe wear gloves.”