Bottled Water Contains Thousands of Nanoplastics

Microplastics – tiny fragments of plastic measuring less than five millimeters in length – are increasingly now being recognized as a major environmental issue and a potential health concern. Water is a big focus of this research, with scientists keen to characterize the volume and types of microplastics that people might be ingesting through drinking water out of plastic bottles.

Now, researchers have taken these investigations a step futher. For the first time, they have been able to count and identify nanoplastics – plastic particles measuring less than one micrometer in size – in samples taken from bottled water using a technique called stimulated Raman scattering microscopy.

The research team, led by scientists from Columbia University, found that 1 L of bottled water contained ~240,000 detectable plastic fragments on average – a value that is orders of magnitude greater than previously reported in studies using other methods. The research is published in the Proceedings of the National Academy of Sciences.

Studying microplastics using lasers

The exact effects of human exposure to microplastics on our health are still undetermined, though early studies have suggested links to kidney and testicular cancers as well as long-term fertility issues and thyroid function problems.

Unlike most microplastics, nanoplastic particles are so small that they can pass directly through the intestinal barrier and enter the bloodstream. As a result, it is important that human exposure to nanoplastics is properly quantified. Although, this is a harder task than it might appear.

“While previous studies have utilized well-established techniques like FTIR [Fourier-transform infrared spectroscopy]  or traditional Raman [spectroscopy] for measuring microplastics, the study of nanoplastics (less than one micron) has been limited, mainly due to the lack of sensitive instruments,” said study co-author Dr. Beizhan Yan, an environmental chemist at Columbia University’s Lamont-Doherty Earth Observatory.

To overcome this barrier, the researchers in this study used a technique called stimulated Raman scattering microscopy (SRS). The technique was co-invented by Dr. Wei Min, a co-author of the paper and a professor of chemistry at Columbia University.

“SRS uses two synchronized laser beams, a pump beam and a Stokes beam, to excite the sample,” Yan explained. “The frequency difference between these lasers is tuned to match the vibrational frequency of specific molecular bonds in the sample, which enhances the Raman scattering signal. This allows for detailed visualization and chemical analysis of the sample at a molecular level.”

By selectively tuning this frequency and targeting seven common plastics as a reference, the researchers developed a data-driven algorithm that could interpret the SRS results for nanoplastics found in water.

“Microplastics, being diverse in chemical composition and often present in complex environmental matrices, pose significant challenges for analysis,” Yan said. “SRS microscopy's label-free and non-destructive nature enables the detection and identification of these tiny plastic particles without altering their chemical state.”

1 liter of bottled water can contain up to 370,000 plastic particles

The researchers tested 3 common brands of bottled water sold in the United States using the SRS method, which was able to detect particles down to just 100 nanometers in size.

Their tests detected between 110,000-370,000 plastic particles per liter of water, of which ~90% were nanoplastics that had not been observed in previous studies.

Polyethylene terephthalate (PET) was one of the most common plastic types observed in the experiments. This is unsurprising, the researchers said, as most water bottles are made from PET and plastic particles may fall into the water when the bottle is agitated or exposed to warmer temperatures.

The researchers also noted particularly high levels of polyamide – a type of nylon – in the water samples. This was more of a surprise to the researchers, who suggested that these particles could have originated from the use of plastic water purification filters before the water was bottled. The tests also found other plastics common to industrial processing, including polystyrene, polyvinyl chloride and polymethyl methacrylate.

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“Our previous research has highlighted the widespread presence of microplastics in New York City's waters and air, and their capacity to transport pollutants like PCBs, pharmaceuticals and pathogens. In comparison, nanoplastics are expected to have an even greater ecological and health impact due to their higher partitioning rate and associated nanotoxicity,” Yan said.

“While degradation experiments using pure plastics have confirmed their existence, as identifiable by SEM and TEM, much remains unknown about [nanoplastics’] distribution, abundance, types in our environment and exposure levels,” Yan said. “The new tool refined in this study basically opens a new window for us to uncover the invisible nanoplastic world.”

Beyond bottled water

According to the researchers, this new study is important because it unambiguously confirms the presence of nanoplastics in real-world drinking water samples. The fact that they were also able to characterize some of these nanoparticles is also a significant breakthrough.

However, the researchers noted that the chemical fingerprints for many of the nanoparticles identified using the SRS measurements did not match any of their seven plastic reference spectra. In fact, just 10% of the total particles imaged under SRS microscopy matched with this library of common plastics, leaving a significant majority unidentified.

This identification rate is on par with that reported for vibrational microscopy in studying microplastics, the researchers pointed out in the paper, with some proportion of the unidentified particles also likely to be due to particles aggregating together and creating more complex chemical signatures.

Equipped with this new technique, the researchers are eager to continue investigating the world of nanoplastics.

“In the future, our plan is to expand our research platform to include a broader range of environmental samples. This will involve analyzing tap water, air samples and biological tissues,” Yan said. “The aim is to deepen our understanding of the presence and impact of nanoplastics in these environments. We also intend to investigate potential adverse health outcomes that may arise from exposure to nanoplastics.”

Dr. Beizhan Yan was speaking with Alexander Beadle, Science Writer for Technology Networks.

Reference: Qian N, Gao X, Lang X, et al. Rapid single-particle chemical imaging of nanoplastics by SRS microscopy. Proc Natl Acad Sci USA. 2024;121(3):e2300582121. doi: 10.1073/pnas.2300582121