Tiny plastic particles may be quietly reshaping microbial life in drinking water systems.
Nanoplastics already raise fears because people can ingest them directly. Now scientists say these tiny particles can create a different kind of danger when they end up in water: they can help bacteria become tougher and harder to remove.
A study in Water Research led by Virginia Tech’s Jingqiu Liao, working with international collaborators, found that nanoplastics can influence how environmental microbes behave in ways that may indirectly affect human health. The concern is not just what the particles might do in the body, but what they might encourage in the water systems people rely on every day.
“It is very important to better understand the adverse effects of the nanoplastics on human health, and not just in humans but also in the environment, which indirectly influences human health,” said Liao, assistant professor of civil and environmental engineering. “The nanoplastics can make the antimicrobial-resistant pathogens better survive, which could be harmful to the environment and would have public health implications.”
One major issue is disinfection. Water systems depend on treatment steps designed to control microbial growth, but the researchers report that nanoplastics can be linked to increased resistance to disinfectants. That kind of shift could make routine treatment and distribution more difficult, especially if microbes become better at persisting on pipe surfaces and reappearing downstream.
“When the nanoplastics interact with the biofilm and the bacteria inside them, they can strengthen the biofilm and make it more resistant to any kind of measures that are going to keep the water clean,” said Liao, who is also an affiliate with Fralin Life Sciences Institute’s Global Change Center.
Nanoplastics are part of the broader microplastics category, but they are even smaller, roughly one to 1,000 nanometers across, far below what the eye can see. In this work, the team focused on what happens when these particles influence biofilm formation inside drinking water systems, where bacteria often prefer to live attached to surfaces rather than floating freely.
Why Biofilms Matter
Biofilms form when different bacteria settle onto surfaces such as the inside of water pipes and build a slimy protective layer around themselves. That coating helps them withstand stress, including conditions that would otherwise kill or wash away individual cells. In some settings, biofilms can be useful by helping trap or break down undesirable substances, but in drinking water distribution systems they can be a serious liability.
Liao noted that the risk relates to which microbes are present and what they carry. Some bacteria in biofilms can be pathogenic, and bacteria can also host bacteriophages, which are viruses. Those viruses can reshape microbial communities by killing certain bacteria, pushing others to adapt, and sometimes influencing the movement of genetic material through a population. Before this study, researchers had limited insight into how nanoplastics might affect these already complex relationships inside biofilms.
“The primary process that we were particularly interested in is how the bacteria and the bacteriophages interact with each other during the process when the nanoplastics influence the biofilm as a whole,” said Liao, also an affiliate with the Fralin Life Sciences Institute’s Center for Emerging, Zoonotic, and Arthropod-borne Pathogens.
Liao’s expertise with microbial ecology and metagenomic analysis made her ideal for the study. She’s published studies on the role of soil in the spread of antibiotic resistance and recently won a Scaling Scholarship Award through the College of Engineering’s Major Grants Initiative related to her work on the Nature Communications publication, “Differential roles of deterministic and stochastic processes in structuring soil bacterial ecotypes across terrestrial ecosystems.”
How Nanoplastics Alter Biofilm Behavior
Liao said the researchers discovered that when the biofilm composed of E. coli and Pseudomonas aeruginosa is exposed to nanoplastics, several responses from the bacteria are triggered:
- Different bacteria “talk” with each other and secrete substances that make the biofilm thicker, heavier, and more protective.
- Prophages — phages that integrate their own genomes (DNA) into their bacterial hosts’ genomes — are activated, destroying the bacterial cells they live in and creating many new virus particles.
- Bacteria fight the prophages using clustered regularly interspaced short palindromic repeats (CRISPR) of DNA or RNA cells to target them as an antiviral defense system.
An illustration of the three responses from the bacteria when the nanoplastics come into contact with the biofilm. Image courtesy of Jingqiu Liao.
In the study, the authors conclude that “the increased mechanical strength of the biofilm and its resistance to the disinfectants highlight a potential challenge for water treatment and distribution systems, as nanoplastics may increase the formation of difficult-to-eradicate biofilms on the surface of some water treatment and distribution systems.”
Liao believes more research is needed to better understand the molecular mechanisms underlying the ecological responses of complex multispecies biofilms to nanoplastics. She also suggests that the size of the plastics matters. She points out that microplastics, which are larger than the nanoplastics, may have different effects on the bacteria-phage interactions within the biofilm.
“Overall, our findings provide novel insights into the interplay between nanoplastics and bacterium-phage dynamics, highlighting increased microbial risks associated with waterborne nanoplastics,” Liao said.
Reference: “Nanoplastics induce prophage activation and quorum sensing to enhance biofilm mechanical and chemical resilience” by Haibo Wang, Hui Chen, Chujin Ruan, Jingqiu Liao, Cory Schwarz, Baoyou Shi, Pedro J.J. Alvarez and Pingfeng Yu, 1 October 2025, Water Research.
DOI: 10.1016/j.watres.2025.124712
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