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Micro and nano-plastics in bottled water

  • Context (TH): A recent study has found that a litre of bottled water may contain over one lakh particles of micro– and nano-plastics. Of these particles, 90% are identified as nano-plastics.
  • Nano plastics are hard to analyse because of their tiny size, making it challenging for diagnostic techniques.
  • The researchers used a specialised hyperspectral stimulated Raman scattering (SRS) imaging platform in their experiment.
  • SRS microscopy uses the Raman effect, a.k.a. Raman scattering.
  • This platform captured various images of an object’s molecules at different wavelengths, offering a detailed picture for understanding its composition.
  • Along with SRS imaging, an automated algorithm devised by the team was used 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.
  • Plastics in bottled water are of the following types: polyamide 66, polypropylene (PP), polyethylene, polymethyl methacrylate, polyvinyl chloride (PVC), polystyrene, and polyethylene terephthalate (PET).
  • Micro means one-millionth.
  • Nano means one-billionth.

Raman scattering

  • Raman scattering is named after Indian physicist C. V. Raman, who discovered it in 1928.
  • For his observation of this effect, Raman was awarded the 1930 Nobel Prize in Physics.
  • Raman scattering has given rise to several critical technologies, and foremost among these is Raman spectroscopy.
  • When light is irradiated on molecules, the light is scattered by molecules.
  • Most scattered light has the same frequency as incident light, but some fraction of light has different frequencies due to the interaction between the oscillation of light and molecular vibration.
  • Rayleigh scattering
    • Most light passing through a transparent substance undergoes Rayleigh scattering.
    • This is an elastic effect, which means that the light does not gain or lose energy during the scattering. Therefore, it stays at the same wavelength.
  • Raman scattering
    • It is different in that it is inelastic. The light loses or gains energy during the scattering process and, therefore, increases or decreases in wavelength respectively.
    • Raman scattered light contains various information on molecules in a substance.

A diagram of light by molecules Description automatically generated

Why is the sky blue & Sun is Yellow?

  • The wavelength of light influences the amount of scattering.
  • Shorter wavelength violet and blue light are Rayleigh scattered more than the longer wavelengths (yellow and especially red light)
  • As a result, we see blue light coming from all parts of the sky. Additionally, the scattering of blue light from the Sun’s direct path contributes to the Sun appearing yellow.
  • Which parts of the visible spectrum enter our eyes determines which colours we perceive.
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