News Excerpt:

The study, conducted by scientists at Columbia University in New York and published in Proceedings of the National Academy of Sciences, profiled individual plastic particles to bridge the knowledge gap that exists in the analysis of nanoplastics, as a result of effective techniques.

About Nano Plastics:

• A litre of bottled water can contain more than one lakh particles of micro- and nano-plastics, with 90% of those being the latter, a new study has reported. 
• Nanoplastics are minute, with dimensions ranging from 1 nanometre to 1 micrometre. The new findings indicate bottled water contains a much greater concentration of these minuscule plastic particles than previously expected.

Key takeaways of the study:

• The investigation revealed the presence of around 2.4 lakh micro- and nano-plastic particles per litre of bottled water (give or take 1.3 lakh).
• As it pertains to the estimation of human exposure, these values are substantially higher than those currently reported in the literature, resulting from the newly detected nanoplastic fraction of plastic particulate. 
• The tiny particles previously invisible under conventional imaging actually dominate in number and account for [approximately] 90% of the entire population of plastic particles detected. 
• The remaining 10% identified as microplastics have a concentration of around [30,000] particles per litre, with the majority of them in the size below 2 µm. 
• Larger particles (>2 µm), which are easier to identify under regular optical microscopy, are in the same order of magnitude as the reported microplastic analysis depending on the detection limited reported based on different technologies.
• The study also revealed the presence of particles in the sample that did not match any standards, suggesting the particulate composition of bottled water could go beyond plastic ‘contaminants’. 
• These standards refer to international rules that classify different plastic materials based on their physical and chemical properties. 
• Particles that do not match any of these standards imply the presence of other particulate inhabitants.

How was the study conducted?

• Nanoplastics are difficult to analyse, mainly due to their size and also due to the ability of different diagnostic techniques to identify them.
• In their experiment, the researchers addressed these challenges using a custom hyperspectral stimulated Raman scattering (SRS) imaging platform. 
  • This setup could capture multiple images of an object’s molecules at different wavelengths, allowing the scientists a comprehensive picture with which they could piece together the composition of the object.
  • SRS microscopy uses the Raman effect, a.k.a. Raman scattering.
    • When light of a certain frequency is beamed at a group of atoms or molecules, the latter absorb some of the energy in the beam and scatter it in different directions. 
    • This is a form of inelastic scattering. 
      • In elastic scattering, the scattered light still has the kinetic energy, and the atoms or molecules haven’t absorbed any of it.
• The research team used the SRS imaging platform along with an automated algorithm the team had devised to identify plastics. 
  • The algorithm extracted detailed information — i.e. at the single-particle level — about the chemical makeup from the data produced by the SRS platform.

Which plastics are in the water?

• The algorithm the research team used to track the presence of plastics in bottled water could spot following the types: 
  • polyamide 66, 
  • polypropylene (PP), 
  • polyethylene, 
  • polymethyl methacrylate, 
  • polyvinyl chloride (PVC), 
  • polystyrene, 
  • polyethylene terephthalate (PET).

What are the study’s implications?

• The study confirmed the fragmentation of the plastic content of real-world water samples beyond the micrometre scale. 
• Its findings are distinguished by the research team’s use of the SRS platform, which revealed a ‘hidden world’ of even smaller plastic particles that have eluded conventional imaging techniques.
• The researchers also reported that counting the plastic particles in the model system revealed a complex relationship between the compositions, shapes, and sizes of plastic particles. 
  • For example, according to them, polystyrene particles are around 100-200 nanometres in size, whereas PET particles have a size of around 1-2 micrometres.
• Studies have also found that plastic items can break down into sub-micrometre pieces, meaning they can breach biological barriers and enter different parts of the bodies of living beings.