Summary of - Integrated LIBS-Raman spectroscopy: A comprehensive approach to monitor microplastics and heavy metal contamination in water resources

Document Type

Article

Abstract

Study Background: The article presented titled “Integrated LIBS-Raman spectroscopy: A comprehensive approach to monitor microplastics and heavy metal contamination in water resources” by Mr. Vaisakh P.S., Dr. Adarsh U.K., Dr. Amrutha K. Dr. Aneesh K.V., Dr. Kartha V.B., and Dr. Unnikrishnan V.K. is an attempt to apply combination of Laser Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy for the characterisation of microplastics based on the polymer type and surface adsorbed heavy metals from the environmental neighbourhood. The article offers a general introduction to the microplastic pollution, followed by the comprehensive description on sample pre-treatment for their analysis, and finally the application of spectroscopy for the characterization of microplastics.

Research Goals and Hypothesis: The goal of the research is to develop a combined LIBS-Raman spectroscopy based methodology to characterize microplastics. The major emphasis is to monitor environmental samples, especially water to detect and characterize microplastics and heavy metals using a unified sample pre-treatment and analysis protocol. Also, the article aims to study the heavy metal adsorption process in temporal regime by the microplastics in laboratory conditions.

Methodological Approach:

  1. The microplastic samples for the report was collected from estuary sites formed by the River Swarna near Kalmadi (Malpe) in Udupi district and River Netravathi in Mangalore, Dakshina Kannada District, Karnataka, southwest India, with a size range from 1 mm to 5 mm. The method of wet peroxide oxidation was followed for the sample pre-treatment process.
  2. A locally developed LIBS-Raman system is used for analyzing the microplastics. Raman spectroscopy is applied to identify the polymer type and LIBS is utilized to detect the surface adsorbed heavy metals.
  3. A Raman database for polymer types (PA, PC, PS, PP, and PE) were created using pure plastic samples for spectral comparison for identification of microplastics collected from the sampling sites. A LIBS emission database for heavy metals was created using standard metal samples for correctly identifying heavy metals that are adsorbed on to the identified microplastics
  4. A controlled adsorption experiment was performed to evaluate the rate of adsorption of lead (Pb) on to the polyethylene (PE) and polypropylene (PP) plastic surface.
  5. The source analysis of the heavy metals was performed by recording LIBS spectra of ambient water sample collected from the sampling sites of microplastics. The confirmation of identified heavy metals from the microplastic surface and water source was done by performing inductively coupled plasma optical emission spectroscopy (ICP-OES)

Results and Discoveries:

  1. Microplastics of three major polymer types were identified from the collected water samples-PET, PE, and PP. In River Swarna, the microplastics were under PE and PP classes, whereas in River Netravathi, all three types of microplastics were identified.
  2. The surface adsorption experiment showed a gradual adsorption of heavy metals (Pb) on to the PE and PP microplastics. The results shows the enhanced adsorption of the elements on to the plastic surface which was subjected to surface deformities.
  3. The calibration of the system using known concentrations of Pb solution showed that the system can detect Pb as low as below 10 ppm.
  4. Using LIBS analysis, heavy metals were identified from the collected microplastics. The identified heavy metals include Al, Mn, Ni, Zn, Cr, and Cu. Additional elements like Na, Mg, Li, and Ca were also detected using the methodology.
  5. The ICP-OES analysis confirmed the presence of heavy metals in the river water which was detected by the LIBS method. It showed the feasibility of the proposed system in detecting trace levels of these heavy metals from microplastic surface as well as from the source water samples.

Citation to the base paper:

Vaisakh PS, Adarsh U.K, Amrutha K, Warrier A.K, Kartha V.B, Unnikrishnan VK (2023), Integrated LIBS-Raman spectroscopy: A comprehensive approach to monitor microplastics and heavy metal contamination in water resources, Environmental Research, 231, 2, https://doi.org/10.1016/j.envres.2023.116198

Publication Date: 2023

Recommended Citation: Vaisakh PS, Adarsh U.K, Amrutha K, Warrier A.K, Kartha V.B, Unnikrishnan VK, Integrated LIBS-Raman spectroscopy: A comprehensive approach to monitor microplastics and heavy metal contamination in water resources, Environmental Research (2023),

Publication Date

2023

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