Nanoplastics in drinking water systems may be doing more than contaminating the water directly. A Virginia Tech-led study published in the journal Water Research, led by assistant professor Jingqiu Liao, found that nanoplastics interact with bacterial communities inside water distribution systems in ways that strengthen the biofilms those bacteria form, making them thicker, heavier, and more resistant to chlorine disinfection.
The finding matters for a specific reason: biofilms, the slimy bacterial communities that coat the inside of water pipes and treatment equipment, can harbor pathogenic bacteria including Legionella, the organism responsible for Legionnaires' disease. A biofilm that resists chlorine more effectively is a biofilm that is harder for a utility's standard treatment process to eliminate.
What the Study Found
Researchers exposed biofilms made of E. coli and Pseudomonas aeruginosa, two bacteria commonly studied in water systems, to nanoplastics and observed three coordinated bacterial responses: quorum sensing, the chemical signaling bacteria use to coordinate group behavior; prophage activation, in which dormant viruses inside bacteria become active; and CRISPR antiviral defense, the bacteria's own system for fighting off those activated viruses.
Virginia Tech, published in Water Research, July 2026. The strengthened biofilm resists chlorine disinfection more effectively than untreated biofilm.
The combination of these responses produced a biofilm that was measurably thicker, heavier, and more protective than untreated biofilm exposed to the same conditions without nanoplastics present. "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," Liao said.
What This Does and Does Not Prove
It is worth being precise about what this research establishes and what it does not. The study identifies a previously undercharacterized mechanism by which nanoplastic contamination may compromise water treatment efficacy, specifically through biofilm strengthening. It does not prove that nanoplastics are currently causing measurable increases in waterborne illness in U.S. municipal water systems at today's contamination levels. Human illness attributable to this specific mechanism has not been documented.
Liao and her team noted that further research is needed to identify the molecular processes driving these responses in complex, multi-species biofilms, and that particle size likely plays a role, since microplastics are larger than nanoplastics and may affect bacteria-virus interactions differently. This is early-stage mechanistic research, not a public health alert tied to a specific outbreak.
Why This Adds to an Existing Pattern, Not a New One
This finding does not stand alone. A 2025 Boston University study found that microplastics increased antimicrobial resistance and biofilm formation in E. coli. Other research has found that charged nanoplastics alter the growth, viability, and virulence of pathogenic E. coli, and that nanoplastics can increase Salmonella virulence and biofilm formation as well, with effects that scale with nanoplastic concentration. Taken together, these studies point toward the same conclusion from multiple directions: microplastics and nanoplastics appear to influence microbial behavior in ways that could increase the persistence of pathogenic bacteria, both in water systems and in food.
Why Point-of-Use Purification Addresses a Different Layer
Municipal chlorination is designed to inactivate bacteria in water as it moves through the distribution system, and it remains effective for that purpose under normal operating conditions. This research describes a mechanism operating inside the biofilm layer coating pipes and equipment, a layer that chlorine already has a harder time penetrating than it does bacteria suspended in open water. Nanoplastics making that layer thicker and more resistant does not change what a municipal system delivers at compliant chlorine residual levels, but it does describe a pathway the system was not originally designed to counter.
A reverse osmosis system installed at the point of use operates independently of what happens inside upstream distribution infrastructure. The membrane rejects dissolved and particulate contaminants, including microplastics and nanoplastics, at the point where water reaches the dispenser, regardless of what biofilm conditions exist further back in the system.
Talk to our team about point-of-use purification for your business.
Related Guides
Frequently Asked Questions
Does this study prove nanoplastics are making people sick from tap water?
No. The study identifies a mechanism by which nanoplastics could compromise water treatment efficacy by strengthening bacterial biofilms. It does not demonstrate that nanoplastics are currently causing measurable increases in waterborne illness in U.S. municipal systems, and human illness attributable to this specific mechanism has not been documented.
What are nanoplastics, and how are they different from microplastics?
Nanoplastics range from roughly 1 to 1,000 nanometers in size, smaller than microplastics, which are generally defined between 1 micron and 5 millimeters. Their small size makes nanoplastics more difficult to remove through traditional water treatment methods and allows them to interact more directly with bacterial cells and biofilm structures.
What is a biofilm, and why does it matter for water safety?
A biofilm is a community of bacteria that attaches to a surface, such as the inside of a water pipe, and forms a protective matrix that shields the bacteria from disinfectants and other environmental stress. Biofilms in drinking water distribution systems can harbor pathogenic bacteria, including Legionella, making biofilm resistance to disinfection a genuine water treatment concern.
Does chlorine still work against bacteria in tap water?
Yes, under normal operating conditions municipal chlorination remains effective at inactivating bacteria in water moving through the distribution system. This research describes a mechanism operating within biofilm layers coating pipes and equipment, which chlorine already penetrates less effectively than open water, rather than a failure of chlorination in general.
Can point-of-use purification remove nanoplastics from drinking water?
Reverse osmosis systems installed at the point of use reject dissolved and particulate contaminants, including microplastics and nanoplastics, at the membrane level. This operates independently of biofilm conditions in upstream municipal infrastructure, addressing water quality at the point it reaches the dispenser.