Microplastics and nanoplastics form as larger plastic items weather, fragment, and degrade during use and disposal. These small synthetic particles have now been documented across the environment, including in the nation's waterways, prompting concern about how common they are in drinking water sources.
In the study, researchers collected water samples from the treatment plants and from popular bottled water products, then quantified the plastic particles present. They determined that bottled water contained roughly three times as many nanoplastic particles as the treated drinking water samples.
Lead author Megan Jamison Hart, a PhD candidate in environmental sciences at Ohio State, said the results underline how everyday choices can influence exposure. "We can make educated choices to try and reduce our daily exposure to these harmful chemicals," Hart said. "For the average person who is thirsty and wants a drink, the best way to do that would be drinking it straight out of the tap rather than grabbing pre-bottled water."
Previous investigations have mainly focused on microplastics and have often struggled to characterize nanoplastics because of their extremely small size. To overcome this challenge, the Ohio State team combined scanning electron microscopy for imaging with optical photothermal infrared spectroscopy for chemical identification, allowing them to detect and classify plastic particles at very small size scales.
The analysis revealed that more than half of all particles detected in the samples were nanoplastics, underscoring how pervasive these tiny contaminants can be, even in finished drinking water. In bottled water, the most common plastic types originated from the packaging, consistent with the idea that bottles and caps shed particles into the liquid during production, storage, and handling.
By contrast, the sources of plastics in treated drinking water were less clear. Particles may enter through source waters, aging infrastructure, or contact with plastic materials used in treatment and distribution, but the study did not pinpoint specific pathways. The findings indicate that tap water systems can still contain microplastics and nanoplastics, even when conventional treatment steps are in place.
Senior author John Lenhart, a professor of environmental engineering at Ohio State, said the concentrations they measured exceeded expectations once nanoplastics were included in the counts. "The concentrations we saw were higher than anticipated, which, unlike prior studies, we were able to attribute to the inclusion of the nanoplastics," Lenhart said. "That emphasis validates a lot of the information we have learned."
The study appears in the journal Science of The Total Environment and, according to the authors, highlights how important it is to account for nanoplastics when assessing overall plastic contamination. Because smaller particles are more likely to cross biological barriers and interact with tissues, understanding their abundance is especially important for evaluating potential health risks.
Scientists still do not fully understand how chronic exposure to microplastics and nanoplastics affects human health. Many experts, including the authors of this study, suggest that the particles and the chemicals associated with them may pose long-term risks as they accumulate in the body and the environment. Hart noted that, although uncertainties remain, it makes sense for people and policymakers to pursue ways to reduce exposure wherever possible.
The research also suggests that treatment and remediation strategies should explicitly target nanoplastics, not just larger particles that are easier to see and filter. By characterizing the types and sizes of plastics present in drinking water, the team believes utilities and engineers will be better positioned to evaluate which processes remove plastics most effectively and where improvements are needed.
Lenhart said that understanding the basic composition of materials in water and the reactions that control that composition is key to designing better treatment systems and environmental cleanup strategies. "By understanding the basic composition of the materials in water and the reactions important for controlling that composition, we can make better design decisions for future treatment or for remediation," he said. "That is why analyses like these are so promising."
The work was supported by the U.S. National Oceanic and Atmospheric Administration through its Ohio Sea Grant College Program and by the National Science Foundation. The authors emphasize that their findings provide a snapshot of conditions in selected systems and brands, and that broader surveys will be needed to capture how plastic levels vary across regions and over time. Even so, the study adds to growing evidence that bottled water, in particular, can be a significant source of nanoplastic exposure compared with drinking water supplied through municipal systems.
Research Report:What's in your water? A comparative analysis of micro- and nanoplastics in treated drinking water and bottled water
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