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Chemometric analysis of microplastics in tropical beach sediments of Bali, Indonesia: distribution, polymer composition, and coastal processes


Citation

Abdull Manap, Mohd Rashidi and Mohd Fadil, Nur Fariesya Athierah and Mukhni, Nur Hayatna and Imizan, Muhammad Ibadurrahman and Martinho, Herculano and Alape, Julian and Dams, Jannik Werner and Marangoni, Bruno S. and Senesi, Giorgio S. and Azis, Ramizah and Julyantoro, Pande Gde Sasmita and Nakano, Haruka (2026) Chemometric analysis of microplastics in tropical beach sediments of Bali, Indonesia: distribution, polymer composition, and coastal processes. Regional Studies in Marine Science, 99. art. no. 105123. pp. 1-16. ISSN 2352-4855

Abstract

Microplastic (MP) contamination in tropical coastal sediments remains poorly constrained, particularly in regions influenced by complex hydrodynamics and intense human activity. This study presents the first process-informed baseline of plastic particles in beach sediments from three morphologically contrasting beaches in Bali, Indonesia (Keramas, Balangan, and Nyang Nyang). Sediments collected in August 2024 were processed using dry sieving and density separation, followed by microscopy and polymer identification via ATR-FTIR spectroscopy supported by DFT vibrational analysis. Multivariate chemometric tools (PCA and PLS-DA) were applied to resolve compositional differences among beaches. Of 44 suspected particles, 15 were confirmed as plastics, including 10 MPs ('5 mm) and 5 macroplastics ('5 mm). Fragments dominated (91%), with most particles occurring within the 1–5 mm size range. MP abundances were low (0.61 ± 1.37–2.54 ± 2.30 MPs/kg dw), with Keramas exhibiting the highest levels. Polypropylene (40%) and polystyrene (20%) were the dominant polymers, while polymethyl methacrylate, polyvinyl alcohol, polyurethane, and synthetic styrene-based and butyl acrylate-based copolymers contributed smaller fractions, indicating inputs from consumer goods and maritime activities. Chemometric analyses revealed beach-specific spectral groupings: Balangan formed a distinct cluster, whereas Keramas and Nyang Nyang partially overlapped, suggesting mixed sources and alongshore connectivity. VIP bands highlighted an amide I signal that may be associated with organic material and biofouling, implying differences in environmental processing among sites. Despite a size-detection floor of 212 µm, this integrated analytical framework provides a transferable tool for regional MP monitoring in tropical marginal seas.


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Additional Metadata

Item Type: Article
Subject: Ecology, Evolution, Behavior and Systematics
Subject: Ecology
Subject: Aquatic Science
Divisions: Faculty of Science
DOI Number: https://doi.org/10.1016/j.rsma.2026.105123
Publisher: Elsevier
Keywords: ATR-FTIR spectroscopy; Bali beach; Chemometrics; Microplastic pollution
Sustainable Development Goals (SDGs): SDG 14: Life Below Water, SDG 11: Sustainable Cities and Communities, SDG 12: Responsible Consumption and Production
Depositing User: Ms. Siti Radziah Mohamed@mahmod
Date Deposited: 21 Jul 2026 07:33
Last Modified: 21 Jul 2026 07:33
Altmetrics: https://www.altmetric.com/details.php?domain=psasir.upm.edu.my&doi=10.1016/j.rsma.2026.105123
URI: http://psasir.upm.edu.my/id/eprint/127187
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