Amount of tiny plastic particles in bottled water underestimated: study

Amount of tiny plastic particles in bottled water underestimated: study

Subject: Environment

Section: Pollution

Introduction:

• As per Columbia University in New York study, published in the National Academy of Sciences:
• A litre of bottled water can contain more than one lakh particles of micro-and nano-plastics(90%) [Nanoplastics are minute, with dimensions ranging from 1 nanometre to 1 micrometre].
• Also much greater concentration than earlier estimated.

Significance of Nano-plastics presence in bottled water: 

• Bridge the knowledge gap in analysis of nano plastics
• Providing information about plastic pollution at the nanometre level.

Analysis of Nano-plastics:

• Nano plastics are difficult to analyse due to their size and inability of different diagnostic techniques to identify them.
• Diagnostic technique adopted: 
• A custom hyperspectral stimulated Raman scattering (SRS) imaging platform is a solution.
• With the use of the SRS platform, fragmentation of the plastic content of real-world water samples beyond the micrometre scale, even smaller that was unable to be detected by conventional imaging techniques.
• SRS can capture multiple images of an object’s molecules at different wavelengths, leading to a comprehensive picture.

SRS Microscopy:

SRS microscopy uses the Raman effect, a.k.a. Raman scattering.

Raman scattering: 

• When light of a certain frequency is beamed at a group of atoms or molecules, the latter both absorb some of the energy in the beam and scatter it to different direction.
• 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)

Adoption by research team: 

• The research team used the SRS imaging platform along with an automated algorithm 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.
• After test and verification researcher used combined apparatus to detect plastic particles quickly and accurately.
• Researcher used bottled water as a model system to look for micro- and nano-plastics.

Which plastics are in the water?

-In bottled water following types of plastics are found: polyamide 66, polypropylene (PP), polyethylene, polymethyl methacrylate, polyvinyl chloride (PVC), polystyrene, and polyethylene terephthalate (PET).

Interesting revelation: 

According to research, counting the plastic particles in the model system revealed

-For example, polystyrene particles are around 100-200 nanometres in size whereas PET particles have a size of around 1-2 micrometres.

Thus, PET is a more significant component when measuring [the particles] in mass while Polystyrene clearly dominates when counting the number of particles.

Relevance of study:

-In present era of Plastic pollution concern, The study has been published.

Why plastic pollution is a concern:

Microplastics is being found in all ecosystems from ocean trenches to the tops of Himalayan mountains.

-Also 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.

What were the findings?

The investigation revealed the presence of around 2.4 lakh micro- and nano-plastic particles per litre of bottled water – that is two to three orders of magnitude more than the previously reported results and as per paper —experts may have been underestimating the concentration of microplastics in bottled water.

Various particle-type analysis: 

As per research paper, obtained values are substantially higher than those currently reported-due to newly detected nano plastic part of plastic particulate, previously invisible under conventional imaging, are 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 m.

Larger particles (2 m), which are easier to identify under regular optical microscopy, are in the same order of magnitude as the reported.

Technology adopted : 

Traditional single particle chemical imaging techniques like Fourier transform infrared spectroscopy and Raman microscopy have lower instrumental resolution and detection sensitivity.

These have a limited ability to study the chemical composition of a material beyond the microscopic scale.

Also sophisticated techniques like electron microscopy and atomic force microscopy (that can track and study individual particles such as atoms and molecules) can’t differentiate between different compositions and thus uniquely identify the material.

Other particles presence: 

As per study, presence of particles that did not match any standards (international rules that classify different plastic materials based on their physical and chemical properties)-i.e. the presence of other particulate inhabitants is also obtained.