Microplastics pose a risk to human health in several ways. A new study confirms that microplastics present in the environment do not reach the sea, rivers or beaches alone. They come accompanied: pathogenic and antimicrobial-resistant bacteria settle on their surface, forming dense and persistent communities. The scientific team calls for advances in waste management and recommends something as simple as wearing gloves when cleaning beaches.
Not to cause alarm, but purely as a precaution. Microplastics — particles smaller than 5 mm — are everywhere. More than 125 billion are already floating or resting in the ocean (from the surface to the seabed). They also appear in soils, rivers, lakes, wildlife and, increasingly, in the human body. An uncomfortable reality, but one that is impossible to ignore.
Within this problem, a growing concern arises: the Plastisphere, those microbial biofilms that quickly adhere to plastic and are not always harmless. Evidence suggests that bacteria capable of causing disease or resisting essential antibiotics thrive there.
Microplastics, antimicrobial resistance and wastewater
Treatment plants and landfills may be inadvertently acting as accelerators of these resistant communities. This is not a deliberate process, of course, but a predictable side effect when infrastructure fails to fully retain microplastics or neutralise the associated bacteria. Certain laboratory studies had already shown that common plastic materials favour the selective growth of AMR (antimicrobial resistance) bacteria, as well as pathogens that are dangerous to humans and animals. But there were still important gaps: what actually happens in natural conditions? How do these communities change as they travel from hospitable waters to coastal areas? Which materials pose the greatest risk?
A study along a “sewer to sea” route
The study “Sewers to Seas: Exploring Pathogens and Antimicrobial Resistance on Microplastics from Hospital Wastewater to Marine Environments”, published in the journal Environment International, attempts to answer these questions. Led by Emily Stevenson and researchers from Plymouth Marine Laboratory and the University of Exeter, the team developed a unique experimental setup: supports on which to place five different substrates (bio-beads, nurdles, polystyrene, wood and glass) along a watercourse with a clear gradient of human contamination. A kind of environmental timeline.
What are these materials?
- Bio-beads: pellets used by UK water companies to promote the growth of bacteria that degrade nutrients in treatment plants.
- Nurdles: virgin plastic pellets, the raw material for manufacturing virtually any plastic object.
- Wood and glass serve as comparisons: one natural, the other inert.
After two months of immersion, the biofilms of each substrate were analysed using metagenomics, a technique that allows the DNA of the entire set of organisms present to be examined.
Main results
The findings are disturbing, to say the least:
- Pathogens and resistant bacteria appeared in all substrates and at all sampling points.
- Polystyrene and nurdles posed the greatest risk, perhaps due to their ability to adsorb antibiotics and favour biofilms that facilitate the exchange of antimicrobial resistance genes (ARGs).
- More than 100 unique ARG sequences were identified in biofilms on microplastics, a higher number than on wood or glass.
- The bio-beads carried resistance to essential antibiotics such as aminoglycosides, macrolides, and tetracyclines.
- Unexpectedly, some pathogens increased their presence the further downstream they were found, always associated with microplastics.
- Environmental location had a huge impact on the composition of biofilms.
- Near aquaculture facilities, colonised particles can pose a direct risk to filter-feeding organisms.
In a nutshell: microplastics act as invisible vehicles, transporting bacteria from wastewater to beaches, bathing areas and shellfish production areas.
Voices from the study
Lead researcher Emily Stevenson recalls the recent episode of bio-beads (small plastic balls) accidentally released in Sussex: an incident that highlighted a risk that has been warned about for years. For Stevenson, identifying the most problematic substrates will allow them to be better monitored or even replaced with safer alternatives. From the Plymouth Marine Laboratory, Pennie Lindeque emphasises the role of microplastics as platforms that protect pathogens and facilitate their survival on the journey from treatment plants to the coast. A kind of “shield” that should be of concern to both water management and marine sectors.
For her part, Aimee Murray highlights something fundamental: microplastics are not just visually unpleasant waste; they may be contributing to the global spread of antimicrobial resistance, one of the most serious health challenges of the century. The team also highlights the urgency of investigating how microplastics interact with other contaminants — medicines, disinfectants, hospital waste — to reduce the spread of resistant bacteria in the environment.
