Standardization of micro-FTIR methods and applicability for the detection and identification of microplastics in environmental matrices

Chayanika Rathore; Mahua Saha; Priyansha Gupta; Manish Kumar; Akshata Naik; Jacob de Boer

doi:10.1016/j.scitotenv.2023.164157

Standardization of micro-FTIR methods and applicability for the detection and identification of microplastics in environmental matrices

Chayanika Rathore, Mahua Saha^*, Priyansha Gupta, Manish Kumar, Akshata Naik, Jacob de Boer

^*Corresponding author for this work

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Abstract

The ubiquity of microplastics (MPs) in the various environment is of increasing concern. Although micro Fourier Transform Infrared Spectroscopy (μ-FTIR) represents an ideal method for the detection of MPs, this technique lacks a standardized mode to be followed for MPs in diverse environmental matrices. The study focused on the optimization, application, and validation of μ-FTIR techniques for the identification of smaller-sized MPs (20 μm-1 mm). In order to assess the validity of the various detection modes in μ-FTIR (reflection and transmission), a confirmatory test with known standard polymers, viz., polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA), and polyvinyl chloride (PVC) were executed. Subsequently, for the validation and accuracy of the method, the polymer spectra of standard polymers acquired in μ-FTIR (smaller-sized) were compared with spectra of larger-sized particles (same standards) in FTIR-ATR (Attenuated Total Reflectance). The spectra were comparable and highlighted the similar pattern of the polymeric composition. The spectral quality and matching score (>60 %) with the reference library was taken into account to accentuate the authenticity of the different methods. This study highlighted the reflection mode (particularly diffuse reflection) as more effective for the quantification of smaller-sized MPs in complex environmental samples. The same method was successfully applied to a representative environmental sample (sand), supplied by the EURO-QCHARM for inter-laboratory study. Two polymers (PE and PET) were correctly identified out of three spiked polymers (PE, PET, and PS) in the given sample. Similarly, in terms of matching algorithms, the results for diffuse reflection (PE-71.7 % and PET-89.1 %) were found satisfactory as compared to micro-ATR (PE-67 % and PET-63.2 %) reflection mode. Overall, this study illustrates an extensive perspective of different μ-FTIR techniques, recommending the most reliable, easy, and non-destructive method to unambiguously characterize diverse types of polymers of smaller MPs in complex environmental matrices.

Original language	English
Article number	164157
Pages (from-to)	1-14
Number of pages	14
Journal	Science of the Total Environment
Volume	888
Early online date	16 May 2023
DOIs	https://doi.org/10.1016/j.scitotenv.2023.164157
Publication status	Published - 25 Aug 2023

Bibliographical note

Funding Information:
The authors are grateful to Prof. Sunil Kumar Singh, the Director of CSIR-NIO, Goa, India for his support and for providing necessary research facilities. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Chayanika Rathore and Priyansha Gupta are thankful to the Department of Science and Technology, Government of India for a doctoral research fellowship under the DST-INSPIRE scheme (Sanction no. DST/ INSPIRE Fellowship/ IF180280 and IF180238). We are also thankful to Dr. Aninda Majumdar and Dr. Mandar Nanajkar for providing us with instruments as and when required. Sincere thanks to Dr. Narsinh Thakur and Dr. Suneel Vasimalla for their constant support. This represents CSIR-NIO, Goa contribution number 7073.

Funding Information:
The authors are grateful to Prof. Sunil Kumar Singh, the Director of CSIR-NIO, Goa, India for his support and for providing necessary research facilities. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Chayanika Rathore and Priyansha Gupta are thankful to the Department of Science and Technology, Government of India for a doctoral research fellowship under the DST-INSPIRE scheme (Sanction no. DST/ INSPIRE Fellowship/ IF180280 and IF180238). We are also thankful to Dr. Aninda Majumdar and Dr. Mandar Nanajkar for providing us with instruments as and when required. Sincere thanks to Dr. Narsinh Thakur and Dr. Suneel Vasimalla for their constant support. This represents CSIR-NIO, Goa contribution number 7073.

Publisher Copyright:
© 2023 Elsevier B.V.

Funding

The authors are grateful to Prof. Sunil Kumar Singh, the Director of CSIR-NIO, Goa, India for his support and for providing necessary research facilities. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Chayanika Rathore and Priyansha Gupta are thankful to the Department of Science and Technology, Government of India for a doctoral research fellowship under the DST-INSPIRE scheme (Sanction no. DST/ INSPIRE Fellowship/ IF180280 and IF180238). We are also thankful to Dr. Aninda Majumdar and Dr. Mandar Nanajkar for providing us with instruments as and when required. Sincere thanks to Dr. Narsinh Thakur and Dr. Suneel Vasimalla for their constant support. This represents CSIR-NIO, Goa contribution number 7073. The authors are grateful to Prof. Sunil Kumar Singh, the Director of CSIR-NIO, Goa, India for his support and for providing necessary research facilities. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Chayanika Rathore and Priyansha Gupta are thankful to the Department of Science and Technology, Government of India for a doctoral research fellowship under the DST-INSPIRE scheme (Sanction no. DST/ INSPIRE Fellowship/ IF180280 and IF180238). We are also thankful to Dr. Aninda Majumdar and Dr. Mandar Nanajkar for providing us with instruments as and when required. Sincere thanks to Dr. Narsinh Thakur and Dr. Suneel Vasimalla for their constant support. This represents CSIR-NIO, Goa contribution number 7073.

Funders	Funder number
CSIR-NIO
Department of Science and Technology, Ministry of Science and Technology, India	IF180238, IF180280
Department of Science and Technology, Ministry of Science and Technology, India

Keywords

Detection modes
Micro-FTIR
Microplastics
Polymer identification
Spectroscopy

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10.1016/j.scitotenv.2023.164157

Standardization of micro-FTIR methods and applicability for the detection and identification of microplastics in environmental matricesFinal published version, 6.84 MBLicence: Article 25fa Dutch Copyright Act

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title = "Standardization of micro-FTIR methods and applicability for the detection and identification of microplastics in environmental matrices",

abstract = "The ubiquity of microplastics (MPs) in the various environment is of increasing concern. Although micro Fourier Transform Infrared Spectroscopy (μ-FTIR) represents an ideal method for the detection of MPs, this technique lacks a standardized mode to be followed for MPs in diverse environmental matrices. The study focused on the optimization, application, and validation of μ-FTIR techniques for the identification of smaller-sized MPs (20 μm-1 mm). In order to assess the validity of the various detection modes in μ-FTIR (reflection and transmission), a confirmatory test with known standard polymers, viz., polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA), and polyvinyl chloride (PVC) were executed. Subsequently, for the validation and accuracy of the method, the polymer spectra of standard polymers acquired in μ-FTIR (smaller-sized) were compared with spectra of larger-sized particles (same standards) in FTIR-ATR (Attenuated Total Reflectance). The spectra were comparable and highlighted the similar pattern of the polymeric composition. The spectral quality and matching score (>60 %) with the reference library was taken into account to accentuate the authenticity of the different methods. This study highlighted the reflection mode (particularly diffuse reflection) as more effective for the quantification of smaller-sized MPs in complex environmental samples. The same method was successfully applied to a representative environmental sample (sand), supplied by the EURO-QCHARM for inter-laboratory study. Two polymers (PE and PET) were correctly identified out of three spiked polymers (PE, PET, and PS) in the given sample. Similarly, in terms of matching algorithms, the results for diffuse reflection (PE-71.7 % and PET-89.1 %) were found satisfactory as compared to micro-ATR (PE-67 % and PET-63.2 %) reflection mode. Overall, this study illustrates an extensive perspective of different μ-FTIR techniques, recommending the most reliable, easy, and non-destructive method to unambiguously characterize diverse types of polymers of smaller MPs in complex environmental matrices.",

keywords = "Detection modes, Micro-FTIR, Microplastics, Polymer identification, Spectroscopy",

author = "Chayanika Rathore and Mahua Saha and Priyansha Gupta and Manish Kumar and Akshata Naik and {de Boer}, Jacob",

note = "Funding Information: The authors are grateful to Prof. Sunil Kumar Singh, the Director of CSIR-NIO, Goa, India for his support and for providing necessary research facilities. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Chayanika Rathore and Priyansha Gupta are thankful to the Department of Science and Technology, Government of India for a doctoral research fellowship under the DST-INSPIRE scheme (Sanction no. DST/ INSPIRE Fellowship/ IF180280 and IF180238). We are also thankful to Dr. Aninda Majumdar and Dr. Mandar Nanajkar for providing us with instruments as and when required. Sincere thanks to Dr. Narsinh Thakur and Dr. Suneel Vasimalla for their constant support. This represents CSIR-NIO, Goa contribution number 7073. Funding Information: The authors are grateful to Prof. Sunil Kumar Singh, the Director of CSIR-NIO, Goa, India for his support and for providing necessary research facilities. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Chayanika Rathore and Priyansha Gupta are thankful to the Department of Science and Technology, Government of India for a doctoral research fellowship under the DST-INSPIRE scheme (Sanction no. DST/ INSPIRE Fellowship/ IF180280 and IF180238). We are also thankful to Dr. Aninda Majumdar and Dr. Mandar Nanajkar for providing us with instruments as and when required. Sincere thanks to Dr. Narsinh Thakur and Dr. Suneel Vasimalla for their constant support. This represents CSIR-NIO, Goa contribution number 7073. Publisher Copyright: {\textcopyright} 2023 Elsevier B.V.",

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AU - Rathore, Chayanika

AU - Saha, Mahua

AU - Gupta, Priyansha

AU - Kumar, Manish

AU - Naik, Akshata

AU - de Boer, Jacob

N1 - Funding Information: The authors are grateful to Prof. Sunil Kumar Singh, the Director of CSIR-NIO, Goa, India for his support and for providing necessary research facilities. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Chayanika Rathore and Priyansha Gupta are thankful to the Department of Science and Technology, Government of India for a doctoral research fellowship under the DST-INSPIRE scheme (Sanction no. DST/ INSPIRE Fellowship/ IF180280 and IF180238). We are also thankful to Dr. Aninda Majumdar and Dr. Mandar Nanajkar for providing us with instruments as and when required. Sincere thanks to Dr. Narsinh Thakur and Dr. Suneel Vasimalla for their constant support. This represents CSIR-NIO, Goa contribution number 7073. Funding Information: The authors are grateful to Prof. Sunil Kumar Singh, the Director of CSIR-NIO, Goa, India for his support and for providing necessary research facilities. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Chayanika Rathore and Priyansha Gupta are thankful to the Department of Science and Technology, Government of India for a doctoral research fellowship under the DST-INSPIRE scheme (Sanction no. DST/ INSPIRE Fellowship/ IF180280 and IF180238). We are also thankful to Dr. Aninda Majumdar and Dr. Mandar Nanajkar for providing us with instruments as and when required. Sincere thanks to Dr. Narsinh Thakur and Dr. Suneel Vasimalla for their constant support. This represents CSIR-NIO, Goa contribution number 7073. Publisher Copyright: © 2023 Elsevier B.V.

PY - 2023/8/25

Y1 - 2023/8/25

N2 - The ubiquity of microplastics (MPs) in the various environment is of increasing concern. Although micro Fourier Transform Infrared Spectroscopy (μ-FTIR) represents an ideal method for the detection of MPs, this technique lacks a standardized mode to be followed for MPs in diverse environmental matrices. The study focused on the optimization, application, and validation of μ-FTIR techniques for the identification of smaller-sized MPs (20 μm-1 mm). In order to assess the validity of the various detection modes in μ-FTIR (reflection and transmission), a confirmatory test with known standard polymers, viz., polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA), and polyvinyl chloride (PVC) were executed. Subsequently, for the validation and accuracy of the method, the polymer spectra of standard polymers acquired in μ-FTIR (smaller-sized) were compared with spectra of larger-sized particles (same standards) in FTIR-ATR (Attenuated Total Reflectance). The spectra were comparable and highlighted the similar pattern of the polymeric composition. The spectral quality and matching score (>60 %) with the reference library was taken into account to accentuate the authenticity of the different methods. This study highlighted the reflection mode (particularly diffuse reflection) as more effective for the quantification of smaller-sized MPs in complex environmental samples. The same method was successfully applied to a representative environmental sample (sand), supplied by the EURO-QCHARM for inter-laboratory study. Two polymers (PE and PET) were correctly identified out of three spiked polymers (PE, PET, and PS) in the given sample. Similarly, in terms of matching algorithms, the results for diffuse reflection (PE-71.7 % and PET-89.1 %) were found satisfactory as compared to micro-ATR (PE-67 % and PET-63.2 %) reflection mode. Overall, this study illustrates an extensive perspective of different μ-FTIR techniques, recommending the most reliable, easy, and non-destructive method to unambiguously characterize diverse types of polymers of smaller MPs in complex environmental matrices.

AB - The ubiquity of microplastics (MPs) in the various environment is of increasing concern. Although micro Fourier Transform Infrared Spectroscopy (μ-FTIR) represents an ideal method for the detection of MPs, this technique lacks a standardized mode to be followed for MPs in diverse environmental matrices. The study focused on the optimization, application, and validation of μ-FTIR techniques for the identification of smaller-sized MPs (20 μm-1 mm). In order to assess the validity of the various detection modes in μ-FTIR (reflection and transmission), a confirmatory test with known standard polymers, viz., polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA), and polyvinyl chloride (PVC) were executed. Subsequently, for the validation and accuracy of the method, the polymer spectra of standard polymers acquired in μ-FTIR (smaller-sized) were compared with spectra of larger-sized particles (same standards) in FTIR-ATR (Attenuated Total Reflectance). The spectra were comparable and highlighted the similar pattern of the polymeric composition. The spectral quality and matching score (>60 %) with the reference library was taken into account to accentuate the authenticity of the different methods. This study highlighted the reflection mode (particularly diffuse reflection) as more effective for the quantification of smaller-sized MPs in complex environmental samples. The same method was successfully applied to a representative environmental sample (sand), supplied by the EURO-QCHARM for inter-laboratory study. Two polymers (PE and PET) were correctly identified out of three spiked polymers (PE, PET, and PS) in the given sample. Similarly, in terms of matching algorithms, the results for diffuse reflection (PE-71.7 % and PET-89.1 %) were found satisfactory as compared to micro-ATR (PE-67 % and PET-63.2 %) reflection mode. Overall, this study illustrates an extensive perspective of different μ-FTIR techniques, recommending the most reliable, easy, and non-destructive method to unambiguously characterize diverse types of polymers of smaller MPs in complex environmental matrices.

KW - Detection modes

KW - Micro-FTIR

KW - Microplastics

KW - Polymer identification

KW - Spectroscopy

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Standardization of micro-FTIR methods and applicability for the detection and identification of microplastics in environmental matrices

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