Microplastics are spreading superbugs from sewage to the sea

Microplastics drift through rivers and coasts while gathering countless microbes on their surfaces. Many people still see them as simple fragments, yet scientists keep uncovering deeper risks tied to these particles.

A new study provides fresh insight into how microplastics shape microbial life from hospital wastewater to open seas, revealing worrying patterns that demand attention.

Plastic particles transport chemicals

Microplastics appear across almost every habitat. They collect bacteria within hours and form dense biofilms known as the Plastisphere. These biofilms include disease-causing and drug-resistant species.

According to the new study, microplastics may enrich resistance because they act as stable surfaces for biofilm growth, support intense gene exchange, and hold adsorbed chemicals that influence microbial activity .

The researchers noted that microplastics can carry antibiotics, heavy metals, and other pollutants within their structure. These trapped chemicals may push microbes to gain resistance.

The particles also travel far because they degrade slowly. This gives biofilms time to grow, shift and move across long distances.

Tracking real environments

The scientists created a new approach for studying natural colonization. They built free-floating structures that held five materials. These included bio beads, nurdles, polystyrene, wood and glass.

The structures were placed along a pollution gradient starting at untreated hospital wastewater and ending at marine waters.

The design ensured full exposure to real conditions rather than enclosed bags or cages that can alter biofilm behavior .

After two months, the team analyzed DNA from each biofilm. They also examined free living microbial communities and measured environmental conditions like pH and temperature.

The researchers wanted to determine how location, not just material, shaped the microbial groups.

Shifting microbial risks

The experts found thousands of microbial species across all samples. Location shaped the community far more than the material itself.

The hospital site showed the highest abundance of bacteria but the lowest diversity. Downstream and marine samples showed richer but less dense communities.

Pathogens appeared across all materials, yet patterns changed with distance. Some groups declined downstream, but others rose in biofilms, not in free water. These included Flavobacteriia, Fusobacteriia, Mollicutes and Sphingobacteriia.

Many members of these groups cause disease in fish and can resist several antibiotic classes. Their rise within biofilms near aquaculture zones raises concern for seafood safety .

The researchers also detected Vibrio species linked with risks to shellfish and human health.

Some showed higher abundance in downstream sites than in the wastewater source, suggesting that microplastics help these bacteria thrive in new locations.

Rising resistance genes

The experts also explored drug resistance genes. Microplastics carried over 100 unique sequences, far more than wood, glass or free living communities.

The team explained that microplastics may speed up horizontal gene transfer because biofilms create tight, crowded conditions for DNA exchange. The plastic surfaces also trap antibiotics, creating tiny hotspots that favor resistant strains.

Surprisingly, the relative abundance of resistance genes often increased downstream rather than decreasing. Genes linked to aminoglycosides, tetracyclines, oxazolidinones and other classes appeared at higher levels in downstream and marine waters.

The researchers suggest that agricultural run off, antibiotic residues and adsorbed chemicals may contribute to this pattern.

Polystyrene and nurdles showed particularly high resistance gene levels. Their surfaces seem to support strong biofilms and may bind antibiotics more effectively.

This combination increases the likelihood that resistance genes will survive and spread on these particles .

Urgent next steps

“Following the recent concerning release of sewage bio-beads in Sussex, this timely study highlights the pathogenic and AMR risk posed by microplastic substrates littering our ocean and coasts,” said Dr. Emily Stevenson, the study’s lead author.

“By identifying high-risk substrates, we can improve the monitoring of those, or even phase them out for safer alternatives.”

The team built their work around real environments rather than controlled tanks. They wanted to see how microbes behave when exposed to pollution gradients, shifting pH and natural flow. This approach helped them capture patterns that older methods often missed.

Dr. Stevenson pointed out that the research used a specifically-designed incubation structure that helped reduce bias from biofilm communities growing on cages, bags or boxes used to secure microplastics in traditional studies.

“Our study fixed these news structures along a transect from the clinic to marine waters and our findings clearly show the importance of this multiple environment transect,” she said.

“Previous studies have detected AMR and pathogen colonization high pollution zones but we show that other surface waters can harbor communities with a high proportion of AMR.”

Growing concerns about microplastics

As the study expanded across hospital, river and coastal waters, the team saw new risks for wildlife and volunteers.

“As this work highlights the diverse and sometimes harmful bacteria that grows on plastic in the environment, we recommend that any beach cleaning volunteer should wear gloves during clean ups, and always wash your hands afterwards,” said Professor Pennie Lindeque from the University of Exeter.

She explained that the plastic particles serve as persistent carriers. They travel long distances and shield harmful microbes from harsh conditions.

The spread of antimicrobial resistance

According to Professor Pennie Lindeque, the research shows that microplastics can act as carriers for harmful pathogens and antimicrobial-resistant (AMR) bacteria, enhancing their survival and spread.

“This interaction poses a growing risk to environmental and public health and demands urgent attention,” she noted.

“By tracking a source to sea pathway influenced by hospital and domestic wastewater discharges, our study shows how antimicrobial-resistant pathogens colonized all substrates.”

Dr. Aimee Murray said the study shows that microplastics aren’t just an environmental issue – they may also play a role in the dissemination of antimicrobial resistance.

“This is why we need integrated, cross-sectoral strategies that tackle microplastic pollution and safeguard both the environment and human health,” she concluded.

Steps for protection

The study calls for closer monitoring of microplastics and their interactions with antibiotics, metals and other contaminants.

The research also highlights the need to reduce microplastic pollution and improve waste management. Volunteers and researchers should handle plastic debris carefully and always use gloves.

As microplastics keep moving through natural systems, their biofilms will move with them. Understanding how they change, grow and carry risk across environments is essential for protecting ecosystems, food chains and human health.

The study is published in the journal Environment International.

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