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Micro and nano-plastics in bottled water

February 22, 2024
Plastics

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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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