Microplastics in wastewater are shielding pathogens from being destroyed by treatment, study

Microplastics could prevent wastewater treatments from being effective and could spread viruses and bacteria pathogens to humans, a new study published on Thursday has found.

The findings highlight the importance of effective wastewater treatment, as without it, wastewater could act as a vehicle for transferring plastic-associated pathogens into the food chain, the study said. 

Wastewater treatment plants are designed to remove contaminants, but microplastics often persist and they can harbour a sticky microbial biofilm - which experts dubbed “plastisphere” - including pathogens dangerous to human health.

The team that conducted the research, led by Ingun Lund Witsø of the Norwegian University of Life Sciences, submerged the most common plastic found in the environment in wastewater. 

Some pieces were placed in untreated wastewater and others in wastewater at the final processing stage before being released into the environment. 

Researchers swabbed each piece of plastic and spread the samples on agar plates to grow and identify bacteria. 

“Plastics in wastewater treatment plants are colonised by microbial biofilms, or “plastispheres,” which can harbour pathogens, including Listeria, E. coli, Klebsiella pneumoniae, and Acinetobacter spp., that persist through treatment processes,” the study’s authors said in a statement.

This bacteria can lead to foodborne illnesses or infections like pneumonia.

“This study highlights the potential for plastispheres to contribute to the spread of pathogens from treated wastewater, posing challenges for environmental health and water reuse efforts,” they added. 

Their findings, published in the journal PLOS ONE, suggest that the plastisphere biofilms shield these pathogens from standard wastewater treatment processes “although their abundance was low,” at less than one per cent, authors noted.

Plastisphere poses new public health challenges

Another study published earlier this year also underlined the potential for plastispheres, in this case in freshwater, to be hotspots for horizontal gene transfer, including antibiotic resistance genes (ARGs).

Antimicrobial resistance was ranked as one of the top global public health threats by the World Health Organization (WHO). 

The study’s researchers highlighted the need for further research and innovation to prevent microplastics and the pathogens linked to them from re-entering the ecosystem.