Scientists have discovered nearly a quarter of a million invisible nanoplastic particles in the average liter of bottled water. This microscopic plastic menace has been detected and categorized for the first time, thanks to a dual-laser microscope employed by researchers from Columbia and Rutgers universities.

While scientists long suspected the presence of these minuscule plastic particles, it wasn’t until the recent study that the quantity and types were unveiled. Examining samples from three common bottled water brands, the researchers found particle levels ranging from 110,000 to 400,000 per liter, with an average of around 240,000, as reported in Monday’s Proceedings of the National Academy of Sciences.

These nanoplastics are smaller than a micron in size, with 25,400 microns in an inch. For comparison, a human hair is approximately 83 microns wide. Previous studies focused on slightly larger microplastics, making this research a significant advancement.

Lead author of the study, Naixin Qian, a Columbia physical chemist, pointed to the bottle itself and the reverse osmosis membrane filter as likely sources of the plastic contamination. The study refrained from disclosing the three brands involved, emphasizing the need for more samples before singling out a specific brand.

The crucial question of whether these nanoplastic particles pose a health risk remains unanswered. Study co-author Phoebe Stapleton, a toxicologist at Rutgers, acknowledged the uncertainty, stating, “We don’t know if it’s dangerous or how dangerous.” The International Bottled Water Association expressed skepticism, citing a lack of standardized measuring methods and scientific consensus on the potential health impacts.

The global plastic pollution crisis, with over 430 million tonnes of plastic produced annually, has raised concerns about microplastics infiltrating oceans, food, and drinking water. Efforts for a global plastics treaty continue amid challenges.

The four co-authors of the study have personally reduced their bottled water consumption in light of their findings. However, as Stapleton noted, filters themselves can introduce plastics, presenting a dilemma.

Outside experts praised the study but cautioned against definitive conclusions. Duke University professor Jason Somarelli expressed concern about the additives in plastics, citing more than 100 known cancer-causing chemicals. University of Toronto biologist Zoie Diana highlighted the potential for small particles to cross unintended membranes, such as the blood-brain barrier.

The dual laser microscope technology, developed by Columbia physical chemist Wei Min 15 years ago, played a pivotal role in this discovery. While some experts lauded the advancement, others called for replication of the technique and results.

Denise Hardesty, an Australian government oceanographer, provided context, noting that the total weight of the nanoplastic found is equivalent to a single penny in the volume of two Olympic-sized swimming pools. Hardesty emphasized the privilege of having access to clean tap water.

Beizhan Yan, a study co-author, revealed plans to investigate municipal water supplies in Boston, St. Louis, Los Angeles, and other locations to determine the prevalence of plastics in tap water. Despite uncertainties about human health risks, Yan recommended using reusable bottles instead of single-use plastics for those concerned.