Microplastics contamination detection in Swan-Canning Estuary via Raman spectroscopy: Insights from shoreline sampling

Microplastics contamination detection in Swan-Canning Estuary via Raman spectroscopy: Insights from shoreline sampling | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Microplastics contamination detection in Swan-Canning Estuary via Raman spectroscopy: Insights from shoreline sampling Xiong Xiao, Kwanghee Jeong, Aneena Sebastian, Sidharth Suresh Kumar, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6442874/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Plastic pollution along the shores of Swan-Canning Estuary (Swan and Canning Rivers) in Perth, Australia is an increasing concern, with a survey by the Western Australian Government reporting an average of 151 plastic pieces per square meter in the Swan-Canning Estuary. This study examines the origins, distribution, and concentrations of microplastics (MPs) in the Swan-Canning Estuary to inform effective mitigation strategies. Water samples were collected from 3 key locations along the Swan-Canning Estuary, including Matilda Bay, Deep Water Point Reserve, and Bardon Park. Sampling was conducted over 14 runs, with a combination of 5.6 mm (3.5 mesh) and 0.10mm (150 mesh) or 0.074 mm (200 mesh) sieves used to capture microplastics effectively. Approximately 1000 to 2000 litres of water were processed per site through sieving and chemical treatments to isolate MPs, which were subsequently analysed using Raman spectroscopy. The results revealed the highest MP concentration at Matilda Bay, followed by Bardon Park and Deep Water Point Reserve, with no MPs detected at the other sites. Seasonal variations were noted, with higher concentrations during winter compared to summer, necessitating further research to confirm this trend. Polypropylene, commonly associated with fisheries and marine activities, emerged as the most prevalent MP species. This study demonstrates the effectiveness of Raman spectroscopy for microplastic detection and identifies key pollution hotspots in the Swan and Canning Rivers. The findings offer valuable insights for targeted remediation efforts and support broader initiatives to mitigate plastic pollution in urban waterways. Microplastics Raman spectroscopy Swan River Matilda Bay Swan-Canning Estuary Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Highlights First microplastic contamination assessment in the Swan-Canning Estuary using Raman spectroscopy Seasonal variations impact microplastic distribution in the Swan River Polypropylene (PP) dominates microplastic pollution in the estuary Hydrodynamics and urban activities influence microplastic hotspots Introduction Plastics, first introduced in the 1950s, have become indispensable due to their versatility and reliability, leading to widespread use across industries and everyday life. However, their durability has also caused significant environmental challenges, particularly the emergence of microplastics (MPs). Defined as plastic particles smaller than 5 mm (Yonkos et al. 2014 ), MPs are a growing environmental and public health concern. They form through the degradation of larger plastic items and as primary pollutants intentionally added to products such as cosmetics and cleaning agents (Sun et al. 2020 ). Their widespread presence has been detected in various ecosystems and human samples, including placentas and breast milk, marking MPs as a global issue of the 21st century. MPs pose serious threats to both aquatic ecosystems and human health (Wright &Kelly 2017 ). They enter water bodies through terrestrial runoff (Li et al. 2018 ), industrial discharge (Geyer et al. 2017 ), and urban waste (Lee et al. 2024 ), breaking down further due to environmental turbulence and weathering (Andrady 2011 ). MPs are ingested by aquatic organisms, which are then consumed by humans, completing a contamination cycle that introduces MPs into food and water supplies. Studies estimate annual human ingestion of up to 250 grams of MPs per year (Li et al. 2023 ), with exposure linked to chronic inflammation, cytotoxicity, and oxidative stress due to their ability to accumulate in tissues and interact with cellular systems. The Swan-Canning Estuary in Perth, Australia, exemplifies this growing crisis. As an urban and industrially influenced waterway, it is highly susceptible to plastic pollution. Surveys have revealed an average of 151 plastic pieces per square meter in the Swan-Canning Estuary, with common pollutants including polystyrene and soft plastics (Kruijff 2022). Over time, these plastics fragment into MPs, increasing contamination levels and complicating detection and removal efforts. Despite the urgency of addressing MP pollution, detecting and analysing MPs remains a significant challenge due to their small size and the complexity of environmental samples. Traditional methods such as density separation, filtration, and Fourier Transform Infrared Spectroscopy (FTIR) are considered to be effective but often have limitations, particularly in identifying smaller MPs (Bailey et al. 2021 , Cabernard et al. 2018 ). Raman Spectroscopy has emerged as an alternative (Käppler et al. 2016 ), offering molecular characterization and the ability to detect samples in micrometer scale. This spectroscopic method detects the inelastic scattering of light induced by laser incidence to a sample, which provides detailed information about chemical composition and phase of the sample (da Silva Falcão et al. 2024 , Jeong et al. 2023 ). Enhanced techniques, such as Surface-Enhanced Raman Scattering (SERS), further extended the application of Raman characterization by enhancing signal intensities from a sample with a lower concentration. (Badillo-Ramírez et al. 2021 , Feliu et al. 2017 , Jeong et al. 2022 ) This study leverages Raman Spectroscopy to analyse MP contamination in the Swan and Canning Rivers. aiming to (i) quantify MP abundance, (ii) identify the types of plastics present and (iii) map their spatial distribution across the river. Additionally, the study seeks to investigate the potential sources of MPs, providing insights into the pathways through which plastics enter and persist in aquatic ecosystems. Beyond generating scientific data, this research highlights the need for public and governmental action to mitigate MP pollution. By raising awareness of the environmental and health impacts of MPs, the findings aim to support informed decision-making and the development of effective strategies to reduce plastic pollution in urban waterways. The Swan-Canning Estuary serves as both a case study and a microcosm of the global challenge posed by MP pollution. Through its focus on cutting-edge detection methods and comprehensive analysis, this study contributes to the broader effort to understand, manage, and ultimately mitigate the environmental and health risks associated with microplastics in Western Australia. Methods Sample Collection In this work, sampling was conducted across various sections of the Swan and Canning Rivers, targeting areas along the shoreline that traverse key urban and industrial zones. The selection of sampling locations was guided by factors such as geographical diversity, accessibility, and insights from prior studies (Wright et al. 2023 ). It was essential to include sites spanning both upstream and downstream sections of the river to capture variations in microplastic concentrations across different environmental and anthropogenic settings. Sampling was conducted at Matilda Bay (Crawley), Deep Water Point Reserve (Mount Pleasant), and Bardon Park (Maylands), where microplastics were detected. The selected sites aimed to provide a representative assessment of microplastic distribution across the Swan–Canning Estuary. A map illustrating the sampling locations is presented in Fig. 1 . Solids Extraction and Chemical Treatment The sample treatment approach in this work is based on the methods outlined by Masura et al. (Masura et al. 2015 ). The procedures involved wet sieving to extract solids from water samples, drying the collected particles, wet peroxide oxidation (WPO) to remove organic materials, density separation to isolate lower-density particles, and analysing microplastics using Raman spectroscopy. The sample collected in the bucket was poured through a stacked sieve setup, consisting of a 5.6 mm sieve placed above either a 0.10 mm (150 mesh) or a 0.074 mm (200 mesh) sieve. Larger particles such as leaves and rocks were retained on the 5.6 mm sieve and removed, while smaller particles required for analysis were captured on the finer sieve. The experiment utilized both the 0.10 mm and 0.074 mm sieves to balance the needs of effective microplastic capture and practical chemical treatment. The 0.10 mm sieve was initially used for samples collected at Deep Water Point Reserve (Mount Pleasant) and Matilda Bay (Crawley), excluding the final sampling at the latter site, to simplify chemical treatment by reducing the retention of excess debris that could hinder processing. For the sample collected at Bardon Park (Maylands) and the final run at Matilda Bay, a 0.074 mm sieve was employed to enable the capture of smaller microplastics where applicable (Priya et al. 2022 ). This dual-sieve approach ensured that an adequate sample size of microplastics was collected while maintaining the feasibility of subsequent chemical treatment. After sieving, the solids retained on the finer sieve were carefully transferred to the laboratory and placed into a 500-mL beaker using a spatula. The samples were rinsed with distilled water to remove any remaining impurities and then dried in a furnace at 90°C for at least 24 hours or until all residual moisture had evaporated. The WPO process was applied to remove organic particles while preserving inorganic microplastics. A 0.05 M Fe(II) solution was prepared by dissolving 7.5 g of FeSO 4 ⋅7H 2 O in 500 mL of water with the addition of 3 mL of 98% weight concentrated sulfuric acid. Subsequently, 20 mL of this solution was added to the beaker containing the dried sample. To initiate the WPO reaction, 20 mL of 30% hydrogen peroxide (H 2 O 2 ​) was introduced into the mixture, which was allowed to stabilize at room temperature for 5–10 minutes. The mixture was heated to 75°C with continuous stirring, avoiding boiling. Additional 30% H 2 O 2 ​ was incrementally added every 30 minutes if organic particles were still visible. This process was repeated until all organic material had been dissolved. Once organic removal was complete, 6 g of sodium chloride (NaCl) was dissolved into the solution for every 20 mL of WPO mixture. The solution was reheated to 75°C to ensure complete dissolution of NaCl, thereby increasing the density of the solution for subsequent separation steps. The prepared WPO solution was poured into a density separator, which consisted of a funnel mounted on a stand, with its bottom opening sealed using a clamp. The setup was left undisturbed overnight, with the funnel loosely covered with foil or a sheet to minimize contamination. The settled solids at the bottom of the funnel were carefully removed by gradually releasing the clamp, while the floating particles were retained for analysis. The floating particles were transferred to a 0.10 mm or 0.074 mm sieve, rinsed with distilled water, air-dried, and stored in labelled vials. Each vial was marked with the corresponding sample collection location and date to ensure traceability. Raman Experiment Here we employ Raman spectroscopy to analyse the microplastic samples. Renishaw inVia™ confocal Raman microscope, equipped with a 532 nm Nd:YAG laser (200 mW of maximum laser power), was used with a 20x lens (SLMPlan N 20x, Olympus). The WiRE 5.5 software (Renishaw) enabled the acquisition and analysis of Raman spectra. A spectral calibration was carried out using a silicon wafer (520.7 cm − 1 ) before the microplastic sample tests. To suppress potential damage on a sample by the monochromatic laser exposure, each spectrum was acquired with ten accumulation of Raman spectra acquired with a 10% of maximum laser power. The spectral data and particle concentrations obtained from Raman spectroscopy were used to identify the types (chemical species) of microplastic samples, based on established literature data and to understand distribution of microplastics across the sampling locations through the Swan-Canning Estuary. The Plastic Raman Database (Marica et al. 2022 ), which includes colour-specific spectra, was implemented to identify components in a sample particle. In cases where plastics were identified as polyblends or composites, multiple Raman peaks corresponding to different polymers were detected (Lin et al. 2015 ). Results and discussion Sample Collection Locations, Weather and Key Initial Observations Multiple water samples were collected from various locations along the Swan-Canning Estuary shoreline, with 1000–2000 litres of water collected per location. Following chemical treatment and density separation, particles were obtained for Raman spectroscopy analysis. Among all the sampling runs (in total of fourteen), eleven were conducted during hot and sunny weather, while three were carried out during the rainy season. All samples collected during the rainy season yielded particles after processing, whereas some samples collected in sunny weather did not contain any particles. Notably, the number of particles collected from Matilda Bay in a rainy day was significantly higher compared to those performed on sunny days at the same location. A similar trend was observed in Maylands, where samples were collected during rainy season, while in hot summer season, no microplastic was collected. Table 1 summarizes detailed information about the sample collection, such as sampling runs, locations, weather conditions, volume of water collected, number of particles obtained, and particle colours. Selected Raman spectra for various microplastics obtained at different locations are given from Fig. 3 to Fig. 8 . The primary types of microplastics detected in this study—polypropylene (PP), polyethylene (PE), polylactic acid (PLA), high-density polyethylene (HDPE), and polyvinyl chloride (PVC)—reflect diverse anthropogenic influences contributing to plastic contamination in the Swan-Canning Estuary. A microplastic distribution figure is exhibited in Fig. 9 . PP was the most frequently detected MP, predominantly at Matilda Bay and Bardon Park. Known for its durability and flexibility, PP is extensively used in packaging materials, textiles, ropes, fishing nets, and construction. Due to its non-biodegradable nature, PP fragments into microplastics through physical abrasion, sunlight exposure, and water currents (Dimassi et al. 2022 ). Frequent recreational boating activities at these locations, involving mechanical abrasion of ropes, nets, and mooring lines, significantly contribute to PP fragmentation and MP release. Additionally, localized recreational activities such as picnics, barbecues, and casual littering along riverbanks may introduce further PP waste, which subsequently fragments and enters the aquatic system. PE, often found blended with PP and HDPE at Matilda Bay and Deep Water Point Reserve, is the most widely used plastic globally. It is commonly found in products such as plastic bags, bottles, and food packaging. These PE blends, designed for superior mechanical strength and durability, reflect urban contamination, particularly intensified by rainfall and surface runoff (Tai et al. 2000 ). Urban contamination is particularly intensified by rainfall and surface runoff, carrying MPs from streets, parks, and nearby establishments into aquatic systems. Additionally, recreational and residential facilities adjacent to sampling locations likely contribute to plastic pollution through daily consumer activities, littering, and improper waste disposal practices, especially during community events and high-use periods. HDPE and PE are frequently combined for applications requiring enhanced material properties, particularly in industrial and commercial settings. One notable use is in the production of fabric bio-liners, which incorporate meshed layers of HDPE and PP to achieve improved tear and tensile strength. This layered structure enhances durability and mechanical resistance while maintaining flexibility under harsh environmental conditions. Such bio-liners are commonly used in applications requiring robust containment solutions, including landfill liners, agricultural covers, and protective barriers in industrial settings. The integration of HDPE and PE layers ensures that the material can withstand significant strain while maintaining structural integrity (Polyfabrics). Given the widespread use of these materials, their presence in the estuarine environment likely results from industrial runoff, construction debris, and degradation of protective coverings used in marine and urban infrastructure. PLA, specifically detected in grey particles at Matilda Bay, is a biodegradable polymer primarily utilized in 3D printing due to its adaptability and low melting point. Despite its biodegradability under controlled conditions, PLA's detection highlights limitations to its degradation in natural aquatic environments (Ainali et al. 2022 , Ranakoti et al. 2022 ). The detected PLA microplastics may originate locally from activities such as 3D printing conducted at nearby institutions, notably the University of Western Australia, restaurants, hotels, recreational facilities, and weekend recreational activities like picnics and barbecues along the grassy areas near the shoreline. Definitive attribution to specific sources, however, requires further detailed investigation. Although PVC is detected in trace amounts at Matilda Bay, it provides important insights into the broader issue of plastic pollution in estuarine environments. PVC is widely used in construction materials, plumbing, electrical insulation, and synthetic leather products. Unlike PP and PE, which are commonly associated with consumer goods and packaging, PVC is more frequently linked to industrial applications and long-term infrastructure. The presence of PVC in the estuarine environment suggests contributions from construction runoff, stormwater drainage, and degradation of plastic coatings used in marine equipment. Additionally, discarded PVC-based products such as old tarpaulins, waterproof materials, and synthetic flooring from nearby commercial and residential developments may be sources of contamination. The potential leaching of hazardous additives, including plasticizers and stabilizers, raises environmental concerns, as these compounds can introduce toxic effects to aquatic organisms (Bartl et al. 2025 ). Despite its low detection frequency in this study, the implications of PVC pollution remain significant, underscoring the need for continuous monitoring and assessment of its long-term ecological impact. The enclosed geomorphological structure of Matilda Bay significantly contributes to MP accumulation. Its curved shoreline and sheltered environment create natural collection points, enabling MPs transported by river currents to deposit along the shoreline. The relatively low water flow (Department of Biodiversity 2025, Hamilton &Turner 2001 ) in this area reduces the natural dispersal of MPs, allowing them to settle and accumulate over time. Additionally, the presence of aquatic vegetation and sediment composition may further facilitate the trapping and retention of MPs, preventing them from being transported further downstream. The combination of these physical and hydrodynamic factors suggests that Matilda Bay functions as a retention zone for MPs within the estuary system, making it a critical area for long-term microplastic monitoring and pollution mitigation efforts. Similar patterns of MP accumulation have been observed in other enclosed or semi-enclosed coastal and estuarine environments, where reduced hydrodynamic energy and shoreline morphology promote plastic retention (An et al. 2024 ). Conclusion and Future Work This study successfully identified and quantified microplastic contamination along the Swan and Canning Rivers using Raman spectroscopy, providing valuable insights into the distribution, composition, and potential sources of MPs. The findings revealed Matilda Bay as the most affected area, highlighting its role as a microplastic pollution hotspot, likely influenced by recreational activities, proximity to urban infrastructure, and hydrodynamic factors. Seasonal variation in MP concentrations, with higher levels observed during the rainy season, suggests that surface runoff and sedimentation processes significantly contribute to MP accumulation. The use of both 0.10 mm (150 mesh) and 0.074 mm (200 mesh) sieves ensured a balanced approach to sample collection, capturing a wide size range of MPs while facilitating effective chemical treatment. The application of Raman spectroscopy demonstrated reliably analysis on the MP samples, with identification of component types and their distribution across different sampling sites. These findings provide critical data for targeted remediation strategies, and underscore the need for continued monitoring and broader research efforts, including offshore and deeper water sampling. Polypropylene, widely associated with fisheries and recreational activities, was found to be the predominant MP type, emphasizing the impact of human activities on plastic pollution in the river ecosystem. This work serves as a foundation for mitigating plastic pollution in the Swan–Canning Estuary and similar urban waterways, supporting local and global initiatives aimed at addressing the environmental challenges posed by microplastics. Preliminary investigations were also conducted at several other locations within the estuary; however, no microplastics were collected at those sites during the sampling period. These results may reflect local hydrodynamic conditions or temporal variability and warrant further investigation. Future studies will adopt a more comprehensive sampling strategy that accounts for both seasonal and spatial variation. In particular, the use of the Manta net deployed from a boat is planned to enable surface water sampling across offshore and deeper regions of the estuary, which will enhance the resolution and representativeness of microplastic contamination data. Declarations Acknowledgements This work is supported by the University of Western Australia (UWA). Funding XX and KJ acknowledge UWA Riverlab and Woodside Futurelab for the funding in field and lab work. Authors’ Contributions Xiong Xiao: Conceptualization, Methodology, Software, Validation, Formal Analysis, Investigation, Resources, Data Curation, Writing – Original Draft, Writing – Review & Editing, Visualization, Supervision, Project Administration, Funding Acquisition. Kwanghee Jeong: Conceptualization, Methodology, Software, Validation, Formal Analysis, Investigation, Resources, Data Curation, Writing – Review & Editing, Visualization, Supervision, Project Administration, Funding Acquisition. Aneena Sebastian: Software, Formal Analysis, Investigation, Data Curation Sidharth Suresh Kumar: Software, Formal Analysis, Investigation, Data Curation Miaosen Liu: Software, Formal Analysis, Investigation, Data Curation Cameron McWilliams: Software, Formal Analysis, Investigation, Data Curation Ethical Approval This is not applicable Consent to Participate This is not applicable Consent to Publish This is not applicable Competing Interests The authors have no competing interests to declare relevant to this paper's content. Data Availability Statement The data that support the findings of this study are available from the corresponding author upon reasonable request. References Ainali NM, Kalaronis D, Evgenidou E, Kyzas GZ, Bobori DC, Kaloyianni M, Yang X, Bikiaris DN, Lambropoulou DA (2022): Do poly(lactic acid) microplastics instigate a threat? A perception for their dynamic towards environmental pollution and toxicity. Sci. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6442874","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":450034992,"identity":"adcf47f4-c49f-4e10-9dfd-522c397a2b5d","order_by":0,"name":"Xiong Xiao","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7UlEQVRIiWNgGAWjYDACZgjFA2QdgDAPEK+FLYFILQjAY0CcFoPjzMcefmE4LMPf3vNNmqeGQY7vRgLjZx48WiSb2dKNZRjSeCTOnN0mzXOMwVjyRgKzND4t/Mw8ZtISDDY8DDdyt0nnsDEkbriRwIBXCxtEiwSP/I2cZ9I5/xjqgVqYfxOyRfID0BaDGzls0rltDAkGNxLY8NoC9EuaNINBGo/hmWPG1n/7JAxnnnnYZjkHjxaD84ePSf6oOGwvd7z54c0Z32zk+Y4nH77xBo8WEGCGxQgQSAAxYwMBDUAlPwgqGQWjYBSMghENAIGCQQZ8b8IkAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0001-5568-4815","institution":"The University of Western Australia","correspondingAuthor":true,"prefix":"","firstName":"Xiong","middleName":"","lastName":"Xiao","suffix":""},{"id":450034993,"identity":"f74647e9-4dff-489c-aff9-cf9d45832892","order_by":1,"name":"Kwanghee Jeong","email":"","orcid":"","institution":"The University of Western Australia","correspondingAuthor":false,"prefix":"","firstName":"Kwanghee","middleName":"","lastName":"Jeong","suffix":""},{"id":450034994,"identity":"ade57498-cd56-40f1-9235-980cce4c1ab1","order_by":2,"name":"Aneena Sebastian","email":"","orcid":"","institution":"The University of Western Australia","correspondingAuthor":false,"prefix":"","firstName":"Aneena","middleName":"","lastName":"Sebastian","suffix":""},{"id":450034995,"identity":"c3f8c3a4-a31a-42d5-ad14-6ff5ebf85ecb","order_by":3,"name":"Sidharth Suresh Kumar","email":"","orcid":"","institution":"The University of Western Australia","correspondingAuthor":false,"prefix":"","firstName":"Sidharth","middleName":"Suresh","lastName":"Kumar","suffix":""},{"id":450034996,"identity":"9c0f8ef2-51f9-49b6-9a1f-41bfe811e019","order_by":4,"name":"Miaosen Liu","email":"","orcid":"","institution":"The University of Western Australia","correspondingAuthor":false,"prefix":"","firstName":"Miaosen","middleName":"","lastName":"Liu","suffix":""},{"id":450034997,"identity":"a24c97d2-3fcb-4c9c-93d6-415079d5ab9f","order_by":5,"name":"Cameron McWilliams","email":"","orcid":"","institution":"The University of Western Australia","correspondingAuthor":false,"prefix":"","firstName":"Cameron","middleName":"","lastName":"McWilliams","suffix":""}],"badges":[],"createdAt":"2025-04-14 06:16:54","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6442874/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6442874/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":81993829,"identity":"c195bb94-880a-458a-8823-3199f3e7cf8d","added_by":"auto","created_at":"2025-05-05 17:21:22","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":3201380,"visible":true,"origin":"","legend":"\u003cp\u003eUp: Location of the Swan-Canning Estuary in Australia. Bottom: Map of sampling locations: 1. Matilda Bay, Crawley; 2. Deep Water Point Reserve, Mount Pleasant; 3. Bardon Park, Maylands. The arrows indicate the river flows.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6442874/v1/edd35465090808f5ed2f33c5.png"},{"id":81994497,"identity":"efcf723c-92b6-48c0-b8f0-69c3416495e4","added_by":"auto","created_at":"2025-05-05 17:29:22","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1284370,"visible":true,"origin":"","legend":"\u003cp\u003eSummary for the sample treatment: \u003cem\u003e\u003cstrong\u003ea\u003c/strong\u003e\u003c/em\u003e, the collected sample poured on the sieves; \u003cem\u003e\u003cstrong\u003eb\u003c/strong\u003e\u003c/em\u003e, untreated sample transferred into the beaker; \u003cem\u003e\u003cstrong\u003ec\u003c/strong\u003e\u003c/em\u003e, sample after WPO treatment; \u003cem\u003e\u003cstrong\u003ed\u003c/strong\u003e\u003c/em\u003e, density separation; \u003cem\u003e\u003cstrong\u003ee\u003c/strong\u003e\u003c/em\u003e, floating particles observed during density separation.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6442874/v1/7c5e639d19614d56575acaf0.png"},{"id":81993827,"identity":"14748ee0-2927-4ca9-ab49-d67af9dfa536","added_by":"auto","created_at":"2025-05-05 17:21:22","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":187489,"visible":true,"origin":"","legend":"\u003cp\u003eA Raman spectrum of a grey microplastic particle collected at Matilda Bay, identified as PLA.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6442874/v1/0ff2f3a73543442e73581ce6.png"},{"id":81993561,"identity":"2ef30e6e-e6c0-48c7-9b50-46f7ee7599e9","added_by":"auto","created_at":"2025-05-05 17:13:23","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":500083,"visible":true,"origin":"","legend":"\u003cp\u003eRaman spectra of green microplastic particles collected at Matilda Bay, identified as \u003cem\u003e\u003cstrong\u003ea\u003c/strong\u003e\u003c/em\u003e, PP and \u003cem\u003e\u003cstrong\u003eb\u003c/strong\u003e\u003c/em\u003e, blend of PP and PE.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6442874/v1/433b594116a06fc57e4c6f3f.png"},{"id":81993831,"identity":"7f931e59-8bc8-4e07-9471-39cdc08c4f7f","added_by":"auto","created_at":"2025-05-05 17:21:23","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":834139,"visible":true,"origin":"","legend":"\u003cp\u003eRaman spectra of blue microplastic particles collected at Matilda Bay, identified as \u003cem\u003e\u003cstrong\u003ea\u003c/strong\u003e\u003c/em\u003e and \u003cem\u003e\u003cstrong\u003eb\u003c/strong\u003e\u003c/em\u003e, blend of PP and PE, \u003cem\u003e\u003cstrong\u003ec\u003c/strong\u003e\u003c/em\u003e, PP, and \u003cem\u003e\u003cstrong\u003ed\u003c/strong\u003e\u003c/em\u003e, blend of PP, PE and HDPE.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6442874/v1/7d405f56e78fb1b158596983.png"},{"id":81993563,"identity":"03160b3a-9351-4b78-946a-a57e20443d5e","added_by":"auto","created_at":"2025-05-05 17:13:23","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":689717,"visible":true,"origin":"","legend":"\u003cp\u003eRaman spectra of turquoise microplastic particles collected at Matilda Bay, identified as \u003cem\u003e\u003cstrong\u003ea\u003c/strong\u003e\u003c/em\u003e, blend of PP, PE and PVC, \u003cem\u003e\u003cstrong\u003eb\u003c/strong\u003e\u003c/em\u003e, blend of PE, PP, and HDPE, and \u003cem\u003e\u003cstrong\u003ec\u003c/strong\u003e\u003c/em\u003e, PP.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6442874/v1/3eae5001e63b8cace80de9cb.png"},{"id":81994499,"identity":"511d72af-c59d-4ea2-a25a-2d7c3e0f3a02","added_by":"auto","created_at":"2025-05-05 17:29:23","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":220104,"visible":true,"origin":"","legend":"\u003cp\u003eA Raman spectrum of a blue microplastic particle collected at Deepwater point reserves, identified as blend of PP, PE, and HDPE.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6442874/v1/bcb8feafbc963dca8c9c227f.png"},{"id":81994817,"identity":"4d25a111-78e6-44f5-ba34-474d42f2c8b8","added_by":"auto","created_at":"2025-05-05 17:37:23","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":191146,"visible":true,"origin":"","legend":"\u003cp\u003eA Raman spectrum of a blue microplastic particle collected at Bardon Park, identified as PP.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6442874/v1/2297f369bfa1f36f298c5f6c.png"},{"id":81993852,"identity":"8e5639a7-a61e-48db-a098-5f2d323182e2","added_by":"auto","created_at":"2025-05-05 17:21:24","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":3575707,"visible":true,"origin":"","legend":"\u003cp\u003eMicroplastic distribution in the Swan–Canning Estuary investigated in this work. Sampling locations: 1. Matilda Bay, Crawley; 2. Deep Water Point Reserve, Mount Pleasant; 3. Bardon Park, Maylands. The arrows indicate the river flows.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6442874/v1/3de32f56778906b538846cd6.png"},{"id":85751354,"identity":"06e3f7d2-3cf5-4aeb-b1c6-5b423fa9e2a3","added_by":"auto","created_at":"2025-07-01 10:11:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":17326524,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6442874/v1/f89c9706-ae98-4101-b74c-f4c0eb58602e.pdf"},{"id":81993556,"identity":"aa2e2aa6-34fc-47c8-934e-388781248ebc","added_by":"auto","created_at":"2025-05-05 17:13:22","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":427228,"visible":true,"origin":"","legend":"","description":"","filename":"Table1.docx","url":"https://assets-eu.researchsquare.com/files/rs-6442874/v1/40994c554bcef0bd7ac5f3fb.docx"}],"financialInterests":"","formattedTitle":"Microplastics contamination detection in Swan-Canning Estuary via Raman spectroscopy: Insights from shoreline sampling","fulltext":[{"header":"Highlights","content":"\u003cul\u003e\n \u003cli\u003eFirst microplastic contamination assessment in the Swan-Canning Estuary using Raman spectroscopy\u003c/li\u003e\n \u003cli\u003eSeasonal variations impact microplastic distribution in the Swan River\u003c/li\u003e\n \u003cli\u003ePolypropylene (PP) dominates microplastic pollution in the estuary\u003c/li\u003e\n \u003cli\u003eHydrodynamics and urban activities influence microplastic hotspots\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"Introduction","content":"\u003cp\u003ePlastics, first introduced in the 1950s, have become indispensable due to their versatility and reliability, leading to widespread use across industries and everyday life. However, their durability has also caused significant environmental challenges, particularly the emergence of microplastics (MPs). Defined as plastic particles smaller than 5 mm (Yonkos et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), MPs are a growing environmental and public health concern. They form through the degradation of larger plastic items and as primary pollutants intentionally added to products such as cosmetics and cleaning agents (Sun et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Their widespread presence has been detected in various ecosystems and human samples, including placentas and breast milk, marking MPs as a global issue of the 21st century.\u003c/p\u003e \u003cp\u003eMPs pose serious threats to both aquatic ecosystems and human health (Wright \u0026amp;Kelly \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). They enter water bodies through terrestrial runoff (Li et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), industrial discharge (Geyer et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), and urban waste (Lee et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), breaking down further due to environmental turbulence and weathering (Andrady \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). MPs are ingested by aquatic organisms, which are then consumed by humans, completing a contamination cycle that introduces MPs into food and water supplies. Studies estimate annual human ingestion of up to 250 grams of MPs per year (Li et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), with exposure linked to chronic inflammation, cytotoxicity, and oxidative stress due to their ability to accumulate in tissues and interact with cellular systems.\u003c/p\u003e \u003cp\u003eThe Swan-Canning Estuary in Perth, Australia, exemplifies this growing crisis. As an urban and industrially influenced waterway, it is highly susceptible to plastic pollution. Surveys have revealed an average of 151 plastic pieces per square meter in the Swan-Canning Estuary, with common pollutants including polystyrene and soft plastics (Kruijff 2022). Over time, these plastics fragment into MPs, increasing contamination levels and complicating detection and removal efforts.\u003c/p\u003e \u003cp\u003eDespite the urgency of addressing MP pollution, detecting and analysing MPs remains a significant challenge due to their small size and the complexity of environmental samples. Traditional methods such as density separation, filtration, and Fourier Transform Infrared Spectroscopy (FTIR) are considered to be effective but often have limitations, particularly in identifying smaller MPs (Bailey et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2021\u003c/span\u003e, Cabernard et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Raman Spectroscopy has emerged as an alternative (Käppler et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), offering molecular characterization and the ability to detect samples in micrometer scale. This spectroscopic method detects the inelastic scattering of light induced by laser incidence to a sample, which provides detailed information about chemical composition and phase of the sample (da Silva Falcão et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2024\u003c/span\u003e, Jeong et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Enhanced techniques, such as Surface-Enhanced Raman Scattering (SERS), further extended the application of Raman characterization by enhancing signal intensities from a sample with a lower concentration. (Badillo-Ramírez et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2021\u003c/span\u003e, Feliu et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2017\u003c/span\u003e, Jeong et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2022\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eThis study leverages Raman Spectroscopy to analyse MP contamination in the Swan and Canning Rivers. aiming to (i) quantify MP abundance, (ii) identify the types of plastics present and (iii) map their spatial distribution across the river. Additionally, the study seeks to investigate the potential sources of MPs, providing insights into the pathways through which plastics enter and persist in aquatic ecosystems. Beyond generating scientific data, this research highlights the need for public and governmental action to mitigate MP pollution. By raising awareness of the environmental and health impacts of MPs, the findings aim to support informed decision-making and the development of effective strategies to reduce plastic pollution in urban waterways.\u003c/p\u003e \u003cp\u003eThe Swan-Canning Estuary serves as both a case study and a microcosm of the global challenge posed by MP pollution. Through its focus on cutting-edge detection methods and comprehensive analysis, this study contributes to the broader effort to understand, manage, and ultimately mitigate the environmental and health risks associated with microplastics in Western Australia.\u003c/p\u003e "},{"header":"Methods","content":"\u003cp\u003eSample Collection\u003c/p\u003e\u003cp\u003eIn this work, sampling was conducted across various sections of the Swan and Canning Rivers, targeting areas along the shoreline that traverse key urban and industrial zones. The selection of sampling locations was guided by factors such as geographical diversity, accessibility, and insights from prior studies (Wright et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). It was essential to include sites spanning both upstream and downstream sections of the river to capture variations in microplastic concentrations across different environmental and anthropogenic settings.\u003c/p\u003e\u003cp\u003eSampling was conducted at Matilda Bay (Crawley), Deep Water Point Reserve (Mount Pleasant), and Bardon Park (Maylands), where microplastics were detected. The selected sites aimed to provide a representative assessment of microplastic distribution across the Swan–Canning Estuary. A map illustrating the sampling locations is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eSolids Extraction and Chemical Treatment\u003c/p\u003e\u003cp\u003eThe sample treatment approach in this work is based on the methods outlined by Masura \u003cem\u003eet al.\u003c/em\u003e (Masura et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The procedures involved wet sieving to extract solids from water samples, drying the collected particles, wet peroxide oxidation (WPO) to remove organic materials, density separation to isolate lower-density particles, and analysing microplastics using Raman spectroscopy.\u003c/p\u003e\u003cp\u003eThe sample collected in the bucket was poured through a stacked sieve setup, consisting of a 5.6 mm sieve placed above either a 0.10 mm (150 mesh) or a 0.074 mm (200 mesh) sieve. Larger particles such as leaves and rocks were retained on the 5.6 mm sieve and removed, while smaller particles required for analysis were captured on the finer sieve. The experiment utilized both the 0.10 mm and 0.074 mm sieves to balance the needs of effective microplastic capture and practical chemical treatment. The 0.10 mm sieve was initially used for samples collected at Deep Water Point Reserve (Mount Pleasant) and Matilda Bay (Crawley), excluding the final sampling at the latter site, to simplify chemical treatment by reducing the retention of excess debris that could hinder processing. For the sample collected at Bardon Park (Maylands) and the final run at Matilda Bay, a 0.074 mm sieve was employed to enable the capture of smaller microplastics where applicable (Priya et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This dual-sieve approach ensured that an adequate sample size of microplastics was collected while maintaining the feasibility of subsequent chemical treatment. After sieving, the solids retained on the finer sieve were carefully transferred to the laboratory and placed into a 500-mL beaker using a spatula. The samples were rinsed with distilled water to remove any remaining impurities and then dried in a furnace at 90°C for at least 24 hours or until all residual moisture had evaporated.\u003c/p\u003e\u003cp\u003eThe WPO process was applied to remove organic particles while preserving inorganic microplastics. A 0.05 M Fe(II) solution was prepared by dissolving 7.5 g of FeSO\u003csub\u003e4\u003c/sub\u003e⋅7H\u003csub\u003e2\u003c/sub\u003eO in 500 mL of water with the addition of 3 mL of 98% weight concentrated sulfuric acid. Subsequently, 20 mL of this solution was added to the beaker containing the dried sample. To initiate the WPO reaction, 20 mL of 30% hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e​) was introduced into the mixture, which was allowed to stabilize at room temperature for 5–10 minutes.\u003c/p\u003e\u003cp\u003eThe mixture was heated to 75°C with continuous stirring, avoiding boiling. Additional 30% H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e ​ was incrementally added every 30 minutes if organic particles were still visible. This process was repeated until all organic material had been dissolved. Once organic removal was complete, 6 g of sodium chloride (NaCl) was dissolved into the solution for every 20 mL of WPO mixture. The solution was reheated to 75°C to ensure complete dissolution of NaCl, thereby increasing the density of the solution for subsequent separation steps.\u003c/p\u003e\u003cp\u003eThe prepared WPO solution was poured into a density separator, which consisted of a funnel mounted on a stand, with its bottom opening sealed using a clamp. The setup was left undisturbed overnight, with the funnel loosely covered with foil or a sheet to minimize contamination. The settled solids at the bottom of the funnel were carefully removed by gradually releasing the clamp, while the floating particles were retained for analysis.\u003c/p\u003e\u003cp\u003eThe floating particles were transferred to a 0.10 mm or 0.074 mm sieve, rinsed with distilled water, air-dried, and stored in labelled vials. Each vial was marked with the corresponding sample collection location and date to ensure traceability.\u003c/p\u003e\u003cp\u003eRaman Experiment\u003c/p\u003e\u003cp\u003eHere we employ Raman spectroscopy to analyse the microplastic samples. Renishaw inVia™ confocal Raman microscope, equipped with a 532 nm Nd:YAG laser (200 mW of maximum laser power), was used with a 20x lens (SLMPlan N 20x, Olympus). The WiRE 5.5 software (Renishaw) enabled the acquisition and analysis of Raman spectra. A spectral calibration was carried out using a silicon wafer (520.7 cm\u003csup\u003e− 1\u003c/sup\u003e) before the microplastic sample tests. To suppress potential damage on a sample by the monochromatic laser exposure, each spectrum was acquired with ten accumulation of Raman spectra acquired with a 10% of maximum laser power. The spectral data and particle concentrations obtained from Raman spectroscopy were used to identify the types (chemical species) of microplastic samples, based on established literature data and to understand distribution of microplastics across the sampling locations through the Swan-Canning Estuary. The Plastic Raman Database (Marica et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), which includes colour-specific spectra, was implemented to identify components in a sample particle. In cases where plastics were identified as polyblends or composites, multiple Raman peaks corresponding to different polymers were detected (Lin et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eSample Collection Locations, Weather and Key Initial Observations\u003c/p\u003e\n\u003cp\u003eMultiple water samples were collected from various locations along the Swan-Canning Estuary shoreline, with 1000–2000 litres of water collected per location. Following chemical treatment and density separation, particles were obtained for Raman spectroscopy analysis. Among all the sampling runs (in total of fourteen), eleven were conducted during hot and sunny weather, while three were carried out during the rainy season. All samples collected during the rainy season yielded particles after processing, whereas some samples collected in sunny weather did not contain any particles. Notably, the number of particles collected from Matilda Bay in a rainy day was significantly higher compared to those performed on sunny days at the same location. A similar trend was observed in Maylands, where samples were collected during rainy season, while in hot summer season, no microplastic was collected.\u003c/p\u003e\n\u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e summarizes detailed information about the sample collection, such as sampling runs, locations, weather conditions, volume of water collected, number of particles obtained, and particle colours. Selected Raman spectra for various microplastics obtained at different locations are given from Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e to Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eThe primary types of microplastics detected in this study—polypropylene (PP), polyethylene (PE), polylactic acid (PLA), high-density polyethylene (HDPE), and polyvinyl chloride (PVC)—reflect diverse anthropogenic influences contributing to plastic contamination in the Swan-Canning Estuary. A microplastic distribution figure is exhibited in Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003ePP was the most frequently detected MP, predominantly at Matilda Bay and Bardon Park. Known for its durability and flexibility, PP is extensively used in packaging materials, textiles, ropes, fishing nets, and construction. Due to its non-biodegradable nature, PP fragments into microplastics through physical abrasion, sunlight exposure, and water currents (Dimassi et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). Frequent recreational boating activities at these locations, involving mechanical abrasion of ropes, nets, and mooring lines, significantly contribute to PP fragmentation and MP release. Additionally, localized recreational activities such as picnics, barbecues, and casual littering along riverbanks may introduce further PP waste, which subsequently fragments and enters the aquatic system.\u003c/p\u003e\n\u003cp\u003ePE, often found blended with PP and HDPE at Matilda Bay and Deep Water Point Reserve, is the most widely used plastic globally. It is commonly found in products such as plastic bags, bottles, and food packaging. These PE blends, designed for superior mechanical strength and durability, reflect urban contamination, particularly intensified by rainfall and surface runoff (Tai et al. \u003cspan class=\"CitationRef\"\u003e2000\u003c/span\u003e). Urban contamination is particularly intensified by rainfall and surface runoff, carrying MPs from streets, parks, and nearby establishments into aquatic systems. Additionally, recreational and residential facilities adjacent to sampling locations likely contribute to plastic pollution through daily consumer activities, littering, and improper waste disposal practices, especially during community events and high-use periods.\u003c/p\u003e\n\u003cp\u003eHDPE and PE are frequently combined for applications requiring enhanced material properties, particularly in industrial and commercial settings. One notable use is in the production of fabric bio-liners, which incorporate meshed layers of HDPE and PP to achieve improved tear and tensile strength. This layered structure enhances durability and mechanical resistance while maintaining flexibility under harsh environmental conditions. Such bio-liners are commonly used in applications requiring robust containment solutions, including landfill liners, agricultural covers, and protective barriers in industrial settings. The integration of HDPE and PE layers ensures that the material can withstand significant strain while maintaining structural integrity (Polyfabrics). Given the widespread use of these materials, their presence in the estuarine environment likely results from industrial runoff, construction debris, and degradation of protective coverings used in marine and urban infrastructure.\u003c/p\u003e\n\u003cp\u003ePLA, specifically detected in grey particles at Matilda Bay, is a biodegradable polymer primarily utilized in 3D printing due to its adaptability and low melting point. Despite its biodegradability under controlled conditions, PLA's detection highlights limitations to its degradation in natural aquatic environments (Ainali et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e, Ranakoti et al. \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). The detected PLA microplastics may originate locally from activities such as 3D printing conducted at nearby institutions, notably the University of Western Australia, restaurants, hotels, recreational facilities, and weekend recreational activities like picnics and barbecues along the grassy areas near the shoreline. Definitive attribution to specific sources, however, requires further detailed investigation.\u003c/p\u003e\n\u003cp\u003eAlthough PVC is detected in trace amounts at Matilda Bay, it provides important insights into the broader issue of plastic pollution in estuarine environments. PVC is widely used in construction materials, plumbing, electrical insulation, and synthetic leather products. Unlike PP and PE, which are commonly associated with consumer goods and packaging, PVC is more frequently linked to industrial applications and long-term infrastructure. The presence of PVC in the estuarine environment suggests contributions from construction runoff, stormwater drainage, and degradation of plastic coatings used in marine equipment. Additionally, discarded PVC-based products such as old tarpaulins, waterproof materials, and synthetic flooring from nearby commercial and residential developments may be sources of contamination. The potential leaching of hazardous additives, including plasticizers and stabilizers, raises environmental concerns, as these compounds can introduce toxic effects to aquatic organisms (Bartl et al. \u003cspan class=\"CitationRef\"\u003e2025\u003c/span\u003e). Despite its low detection frequency in this study, the implications of PVC pollution remain significant, underscoring the need for continuous monitoring and assessment of its long-term ecological impact.\u003c/p\u003e\n\u003cp\u003eThe enclosed geomorphological structure of Matilda Bay significantly contributes to MP accumulation. Its curved shoreline and sheltered environment create natural collection points, enabling MPs transported by river currents to deposit along the shoreline. The relatively low water flow (Department of Biodiversity 2025, Hamilton \u0026amp;Turner \u003cspan class=\"CitationRef\"\u003e2001\u003c/span\u003e) in this area reduces the natural dispersal of MPs, allowing them to settle and accumulate over time. Additionally, the presence of aquatic vegetation and sediment composition may further facilitate the trapping and retention of MPs, preventing them from being transported further downstream. The combination of these physical and hydrodynamic factors suggests that Matilda Bay functions as a retention zone for MPs within the estuary system, making it a critical area for long-term microplastic monitoring and pollution mitigation efforts. Similar patterns of MP accumulation have been observed in other enclosed or semi-enclosed coastal and estuarine environments, where reduced hydrodynamic energy and shoreline morphology promote plastic retention (An et al. \u003cspan class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e\n\n\n\n"},{"header":"Conclusion and Future Work","content":"\u003cp\u003eThis study successfully identified and quantified microplastic contamination along the Swan and Canning Rivers using Raman spectroscopy, providing valuable insights into the distribution, composition, and potential sources of MPs. The findings revealed Matilda Bay as the most affected area, highlighting its role as a microplastic pollution hotspot, likely influenced by recreational activities, proximity to urban infrastructure, and hydrodynamic factors. Seasonal variation in MP concentrations, with higher levels observed during the rainy season, suggests that surface runoff and sedimentation processes significantly contribute to MP accumulation. The use of both 0.10 mm (150 mesh) and 0.074 mm (200 mesh) sieves ensured a balanced approach to sample collection, capturing a wide size range of MPs while facilitating effective chemical treatment.\u003c/p\u003e\u003cp\u003eThe application of Raman spectroscopy demonstrated reliably analysis on the MP samples, with identification of component types and their distribution across different sampling sites. These findings provide critical data for targeted remediation strategies, and underscore the need for continued monitoring and broader research efforts, including offshore and deeper water sampling. Polypropylene, widely associated with fisheries and recreational activities, was found to be the predominant MP type, emphasizing the impact of human activities on plastic pollution in the river ecosystem.\u003c/p\u003e\u003cp\u003eThis work serves as a foundation for mitigating plastic pollution in the Swan–Canning Estuary and similar urban waterways, supporting local and global initiatives aimed at addressing the environmental challenges posed by microplastics. Preliminary investigations were also conducted at several other locations within the estuary; however, no microplastics were collected at those sites during the sampling period. These results may reflect local hydrodynamic conditions or temporal variability and warrant further investigation. Future studies will adopt a more comprehensive sampling strategy that accounts for both seasonal and spatial variation. In particular, the use of the Manta net deployed from a boat is planned to enable surface water sampling across offshore and deeper regions of the estuary, which will enhance the resolution and representativeness of microplastic contamination data.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e\n\u003cp\u003eThis work is supported by the University of Western Australia (UWA).\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eFunding\u003c/h2\u003e\n\u003cp\u003eXX and KJ acknowledge UWA Riverlab and Woodside Futurelab for the funding in field and lab work.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eAuthors\u0026rsquo; Contributions\u003c/h2\u003e\n\u003cp\u003eXiong Xiao: Conceptualization, Methodology, Software, Validation, Formal Analysis, Investigation, Resources, Data Curation, Writing \u0026ndash; Original Draft, Writing \u0026ndash; Review \u0026amp; Editing, Visualization, Supervision, Project Administration, Funding Acquisition.\u003c/p\u003e\n\u003cp\u003eKwanghee Jeong: Conceptualization, Methodology, Software, Validation, Formal Analysis, Investigation, Resources, Data Curation, Writing \u0026ndash; Review \u0026amp; Editing, Visualization, Supervision, Project Administration, Funding Acquisition.\u003c/p\u003e\n\u003cp\u003eAneena Sebastian: Software, Formal Analysis, Investigation, Data Curation\u003c/p\u003e\n\u003cp\u003eSidharth Suresh Kumar: Software, Formal Analysis, Investigation, Data Curation\u003c/p\u003e\n\u003cp\u003eMiaosen Liu: Software, Formal Analysis, Investigation, Data Curation\u003c/p\u003e\n\u003cp\u003eCameron McWilliams: Software, Formal Analysis, Investigation, Data Curation\u003c/p\u003e\n\u003ch2\u003eEthical Approval\u003c/h2\u003e\n\u003cp\u003eThis is not applicable\u003c/p\u003e\n\u003ch2\u003eConsent to Participate\u003c/h2\u003e\n\u003cp\u003eThis is not applicable\u003c/p\u003e\n\u003ch2\u003eConsent to Publish\u003c/h2\u003e\n\u003cp\u003eThis is not applicable\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eCompeting Interests\u003c/h2\u003e\n\u003cp\u003eThe authors have no competing interests to declare relevant to this paper\u0026apos;s content.\u003c/p\u003e\n\u003ch2\u003eData Availability Statement\u003c/h2\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAinali NM, Kalaronis D, Evgenidou E, Kyzas GZ, Bobori DC, Kaloyianni M, Yang X, Bikiaris DN, Lambropoulou DA (2022): Do poly(lactic acid) microplastics instigate a threat? 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Health 1, 249-257\u003c/li\u003e\n\u003cli\u003eLin J-H, Pan Y-J, Liu C-F, Huang C-L, Hsieh C-T, Chen C-K, Lin Z-I, Lou C-W (2015): Preparation and compatibility evaluation of polypropylene/high density polyethylene polyblends. Materials 8, 8850-8859\u003c/li\u003e\n\u003cli\u003eMarica I, Aluaș M, P\u0026icirc;nzaru SC (2022): Raman technology application for plastic waste management aligned with FAIR principle to support the forthcoming plastic and environment initiatives. Waste Manag. 144, 479-489\u003c/li\u003e\n\u003cli\u003eMasura J, Baker J, Foster G, Arthur C 2015: Laboratory methods for the analysis of microplastics in the marine environment: recommendations for quantifying synthetic particles in waters and sediments, NOAA Marine Debris Division, Silver Spring, MD, USA\u003c/li\u003e\n\u003cli\u003ePolyfabrics Geomasta composite HDPE bio-liner\u003c/li\u003e\n\u003cli\u003ePriya AK, Jalil AA, Dutta K, Rajendran S, Vasseghian Y, Qin J, Soto-Moscoso M (2022): Microplastics in the environment: Recent developments in characteristic, occurrence, identification and ecological risk. Chemosphere 298, 134161\u003c/li\u003e\n\u003cli\u003eRanakoti L, Gangil B, Mishra SK, Singh T, Sharma S, Ilyas R, El-Khatib S (2022): Critical review on polylactic acid: properties, structure, processing, biocomposites, and nanocomposites. Materials 15, 4312\u003c/li\u003e\n\u003cli\u003eSun Q, Ren S-Y, Ni H-G (2020): Incidence of microplastics in personal care products: An appreciable part of plastic pollution. Sci. Total Environ. 742, 140218\u003c/li\u003e\n\u003cli\u003eTai CM, Li RKY, Ng CN (2000): Impact behaviour of polypropylene/polyethylene blends. Polym. Test. 19, 143-154\u003c/li\u003e\n\u003cli\u003eWright J, Hovey RK, Paterson H, Stead J, Cundy A (2023): Microplastic accumulation in Halophila ovalis beds in the Swan-Canning Estuary, Western Australia. Mar. Pollut. Bull 187, 114480\u003c/li\u003e\n\u003cli\u003eWright SL, Kelly FJ (2017): Plastic and human health: a micro issue? Environ. Sci. Technol. 51, 6634-6647\u003c/li\u003e\n\u003cli\u003eYonkos LT, Friedel EA, Perez-Reyes AC, Ghosal S, Arthur CD (2014): Microplastics in four estuarine rivers in the Chesapeake Bay, U.S.A. Environ. Sci. Technol. 48, 14195-14202\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table 1","content":"\u003cp\u003eTable 1 is available in the Supplementary Files section.\u003c/p\u003e\n"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Microplastics, Raman spectroscopy, Swan River, Matilda Bay, Swan-Canning Estuary","lastPublishedDoi":"10.21203/rs.3.rs-6442874/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6442874/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePlastic pollution along the shores of Swan-Canning Estuary (Swan and Canning Rivers) in Perth, Australia is an increasing concern, with a survey by the Western Australian Government reporting an average of 151 plastic pieces per square meter in the Swan-Canning Estuary. This study examines the origins, distribution, and concentrations of microplastics (MPs) in the Swan-Canning Estuary to inform effective mitigation strategies. Water samples were collected from 3 key locations along the Swan-Canning Estuary, including Matilda Bay, Deep Water Point Reserve, and Bardon Park. Sampling was conducted over 14 runs, with a combination of 5.6 mm (3.5 mesh) and 0.10mm (150 mesh) or 0.074 mm (200 mesh) sieves used to capture microplastics effectively. Approximately 1000 to 2000 litres of water were processed per site through sieving and chemical treatments to isolate MPs, which were subsequently analysed using Raman spectroscopy. The results revealed the highest MP concentration at Matilda Bay, followed by Bardon Park and Deep Water Point Reserve, with no MPs detected at the other sites. Seasonal variations were noted, with higher concentrations during winter compared to summer, necessitating further research to confirm this trend. Polypropylene, commonly associated with fisheries and marine activities, emerged as the most prevalent MP species. This study demonstrates the effectiveness of Raman spectroscopy for microplastic detection and identifies key pollution hotspots in the Swan and Canning Rivers. The findings offer valuable insights for targeted remediation efforts and support broader initiatives to mitigate plastic pollution in urban waterways.\u003c/p\u003e","manuscriptTitle":"Microplastics contamination detection in Swan-Canning Estuary via Raman spectroscopy: Insights from shoreline sampling","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-05 17:13:17","doi":"10.21203/rs.3.rs-6442874/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e565c17d-127a-4259-a308-b2648455b186","owner":[],"postedDate":"May 5th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-07-01T10:03:01+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-05 17:13:17","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6442874","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6442874","identity":"rs-6442874","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}