Marine debris pollution in mangrove at Cua Hoi, Thanh Hoa: Status and Source assessment

Marine debris pollution in mangrove at Cua Hoi, Thanh Hoa: Status and Source assessment | 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 Marine debris pollution in mangrove at Cua Hoi, Thanh Hoa: Status and Source assessment Tran Quan Dang, Thi Lim Duong, Tran Dinh Nguyen, Thi Lan Huong Nguyen, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8565242/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 This study investigates the status and sources of marine debris pollution in mangrove ecosystems of the Cua Hoi estuarine area, Thanh Hoa Province, Vietnam. Marine debris was surveyed at three sites, including two mangrove forests (S1 and S2) and one adjacent beach site (S3), following standardized international monitoring protocols. A total of 1,192 debris items were collected from 27 sampling units. Mangrove site S1 exhibited the highest average marine debris density (8.68 n/m²), while S2 showed a much lower density (0.67 n/m²), and the beach site S3 recorded the lowest value (0.052 n/m²). Plastic debris dominated the material composition, accounting for 92.79% of all items, with LDPE, PE, and PS being the most common polymer types. The dominant size class across all sites was 5–25 mm, though mangrove areas retained a higher proportion of larger debris compared to the beach. Source analysis revealed that public litter was the primary contributor (78.27%), followed by fisheries debris (21.14%), indicating strong land - based and nearshore influences. Overall, the results highlight the role of mangrove forests as natural traps for marine debris and provide scientific evidence to support improved waste management and conservation strategies in estuarine mangrove ecosystems. Marine debris Mangrove forests Cua Hoi estuarine area Source Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Mangrove forests are coastal vegetated ecosystems widely distributed in tropical and subtropical regions worldwide, serving as important ecological buffer zones between terrestrial and marine environments (Rodin & Bazilevič, 1966 ). This unique ecosystem provides a wide range of important ecological and economic benefits, including serving as feeding and nursery grounds for commercially valuable species, providing habitats for endangered species, storing carbon in both biomass and sediments, supplying timber for construction and fuel, and playing a crucial role in ecosystem nutrient cycling (Jerath et al., 2016 ), support livelihoods (Donato et al., 2011 ) and protect coastlines from storms and tsunamis (Teh et al., 2009 ). However, due to their coastal distribution, mangrove forests are particularly vulnerable to impacts from marine debris (Not et al., 2020 ). According to the United Nations Environment Programme (UNEP), marine debris is defined as any persistent solid material that is manufactured or processed by humans and deliberately or unintentionally discarded, disposed of, or abandoned in the marine and coastal environment (GESAMP & PJ, 2019 ). They cause numerous negative impacts, including entanglement of marine organisms and accumulation within the food web, thereby affecting the structure and functioning of marine ecosystems (Wright et al., 2013 ). Marine debris, including plastic waste, enters the marine environment primarily as a result of inadequate management and disposal practices, accidental releases, as well as the influence of natural processes (Li et al., 2021 ). Plastics are among the most widely used materials today, and the management and disposal of plastic waste have become a global environmental concern (Mallik et al., 2021 ). Of the approximately 275 million tonnes of plastic waste generated in 2010, an estimated 4.8 to 12.7 million tonnes were discharged into the global ocean (Jambeck et al., 2015 ). Plastics are widely distributed throughout the marine environment (Moore, 2008 ), and from the ocean they can be readily transported by ocean currents, wind, and tides to adjacent areas (Mallik et al., 2021 ), where they subsequently accumulate. In this context, mangrove forests account for approximately 0.5% of the total global coastal area (Alongi, 2014 ). These forests develop in shallow waters and intertidal zones, where the exchange of organic nutrients in and out of the system plays a key role (Su et al., 2016 ). Marine debris, together with anthropogenic pollutants, has exerted and continues to exert significant impacts on estuaries and mangrove ecosystems (Martin et al., 2019 ). Hydrodynamic processes and ocean currents govern the dispersion of marine debris (Fig. 1 a), whereas the complex root systems of mangrove vegetation act as natural traps, effectively retaining and accumulating various types of debris (Fig. 1 b). In recent years, marine debris has been recognized as an important indicator of environmental pollution and poses numerous risks to marine organisms (Roman et al., 2019 ). Marine debris pollution has become a major public concern and is widely regarded as a clear manifestation of anthropogenic impacts on the marine environment (Zhou et al., 2011 ). Similarly, mangrove ecosystems are currently facing multiple threats from marine debris pollution, including visual impacts and the presence of hazardous substances such as heavy metals, organic pollutants, and pathogens, which can be transported by debris or enter the ecosystem through uptake by marine organisms (Li et al., 2021 ). Therefore, this study was conducted to assess the current status and identify the sources of marine debris pollution. Specifically, the study focuses on investigating the characteristics of marine debris within mangrove ecosystems by determining debris density, size, material composition, and plastic types, as well as analyzing the sources of marine debris. The findings provide insights into the extent of marine debris pollution in mangrove ecosystems in the Cua Hoi area, thereby offering a scientific basis for waste management, source control, and the sustainable conservation of coastal mangrove ecosystems 2. Research area and methods 2.1. Research area: The mangrove forests in the Cua Hoi area, Thanh Hoa Province, are located at the mouth of the Ma River, where freshwater and marine ecosystems intersect, creating a distinctive environment characterized by high biodiversity and important ecological functions. According to available statistics, Thanh Hoa Province currently has approximately 1,000 ha of mangrove forests, mainly distributed in coastal and estuarine districts (Thanh Hoa Newspaper and Radio – Television Station, 2024 ). In addition, Cua Hoi is the estuarine area where the Ma River discharges into the sea, and is directly influenced by coastal tidal regimes and tropical depressions (Thi Lim et al., 2024 ). Marine debris samples from the intertidal mangrove areas were collected at three sites based on spatial distribution, including two mangrove sites (S1 and S2) and one beach site (S3), as shown in Fig. 2 . Specifically, 15 sampling units were collected at S1, 9 sampling units at S2, and 3 sampling units at S3 2.2. Research Methods: 2.2.1. Marine debris sampling method The determination of marine debris density and distribution was based on established methodologies adapted from the NOAA (National Oceanic and Atmospheric Administration) Shoreline Survey Field Guide (Opfer et al., 2012 ), the European Commission’s Guidance on Monitoring of Marine Litter in European Seas (Hanke et al., 2013 ), and the UNEP/IOC Guidelines on Survey and Monitoring of Marine Litter (Anthony Cheshire, 2009 ). S1 is characterized by mangrove vegetation dominated by Sonneratia alba (Primavera, 2004 ). At this site, a fringe mangrove area shows signs of degradation, including poor growth and standing dead trees in Fig. 3 a. The intertidal substrate in this area is predominantly sandy, while the upper intertidal zone is covered by a layer of plastic debris, mainly white expanded polystyrene foam (Fig. 3 b). This layer is densely accumulated with an average width of approximately 3 m, and the area of this zone was measured and determined using GPS. In this area, the intertidal zone was divided into 5 transects perpendicular to the shoreline, spaced 20 m apart. Along each transect, 3 sampling units were established at the mangrove fringe (near the waterline), the mid-intertidal zone, and the upper intertidal zone. In total, 15 sampling units were collected, each with an area of 4 m² (2m × 2m) S2 is an intertidal area adjacent to the Ma River, characterized by mangrove forests dominated by Avicennia and Rhizophora species, with muddy substrates. The mangrove vegetation in this area is well developed (Fig. 3 c). A total of 9 sampling units were established, each with an area of 100 m² (10m × 10m), spaced approximately 200 m apart. Areas deeper within the mangrove forest were densely vegetated and therefore difficult to access for sampling. S3 is a beach area without vegetation, characterized by predominantly sandy substrates (Fig. 3 d). As no mangro ve forest is present at this site, three sampling units were established, each covering a sampling area of 420 m² along the shoreline for all types of marine debris, following the method described (Wenneker & Oosterbaan, 2010 ). 2.2.2. Marine debris classification method During the survey, all visually identifiable marine debris larger than 5 mm was recorded. Plastic debris was directly collected at each sampling site, placed in separate bags for preservation, and transported to the laboratory for further analysis. The results were recorded as the total number of marine debris items, as well as the abundance of each debris category classified by material type and size. The collected marine debris samples were subsequently categorized into 8 main material groups, including plastics, glass, metal, rubber, textiles, paper, and other materials in Fig. 4 . This classification method was adopted based on the guidelines of OSPAR – the Convention for the Protection of the Marine Environment of the North-East Atlantic (Wenneker & Oosterbaan, 2010 ). In addition, marine debris was classified by size into meso (5–25 mm), macro (25–100 mm), and mega (> 1 m) categories; it was also identified according to product types such as cups, bowls, ropes, footwear, tarpaulins, and similar items (Anthony Cheshire, 2009 ). 2.2.3. Method for identifying the sources of marine litter Marine debris present in mangrove forests may originate from various production sectors (Veiga et al., 2016 ), as detailed in Table 1 . Table 1 Classification of marine debris sources Sources of marine debris Description Public litter Items that are discarded or left behind by humans on the coast or inland can be carried into the marine environment by wind and rivers Fisheries debris Fisheries debris, including aquaculture activities, such as nets, buoys, fishing lines, and sinkers Shipping Items lost or discarded from vessels Fly tipted Illegal waste, including furniture, ceramics, and construction materials Medical Including medical-related items such as inhalers, adhesive patches, and syringes Non – sourced Items that are too small or damaged to identify their specific sources 2.2.4. Method for determining plastic composition: Marine debris samples collected from the study sites were rinsed with distilled water, dried at 60 o C, and allowed to cool to room temperature. Samples suspected to be plastic debris were subsequently identified using Fourier Transform Infrared - Attenuated Total Reflectance spectroscopy (FTIR-ATR; Agilent Technologies, model: CARY 630, Malaysia). Each polymer was identified using a spectral library (Agilent polymer Handheld ATR Library) (Löder et al., 2015 ). The spectral range of the instrument was set from 4,000 to 650 cm − 1 , with 8 scans per sample and a spectral resolution of 4 cm − 1 , consistent with the measurement conditions of the spectral library. All polymer types, including PE (polyethylene), PS (polystyrene), PP (polypropylene), PVC (polyvinyl chloride), LDPE (low-density polyethylene), and HDPE (high-density polyethylene), were confirmed by comparison with the spectral library, with correlation coefficients (R) ranging from 0.7 to 1.0 (Compa et al., 2022 ). 2.3. Laboratory conditions The study on marine debris pollution in the mangrove forests in the Cua Hoi area, Thanh Hoa Province, was conducted under controlled laboratory conditions following strict contamination control protocols. The laboratory was thoroughly cleaned, and all personnel wore 100% white cotton laboratory coats and disposable nitrile gloves throughout the experimental procedures. All working surfaces were wiped with 70% ethanol before use to minimize airborne and environmental contamination. All laboratory equipment used in the analyses was made of stainless steel and glass. 2.4. Data analysis method: Data on marine debris density, size, and polymer composition were analyzed using Microsoft Excel. The number of marine debris per sampling unit in the intertidal mangrove areas was expressed as item counts (n), while marine debris density was expressed as the number of items per unit area (n/m²). The proportions of marine debris classified by material type, size, polymer composition, and source were expressed as percentages (%) 3. Results and Discussion 3.1. Marine debris in mangrove forests: 3.1.1. Density and size of marine debris A total of 1,192 marine debris (n) were collected from 27 sampling units. Among the study sites, S1 exhibited the highest average debris density, reaching 8.68 n/m² and accounting for 51.93% of the total marine debris collected. This result indicates a pronounced accumulation of marine debris at S1, which is consistent with the dense root systems and the “natural trap” structure characteristic of mangrove ecosystems (Martin et al., 2019 ). Due to the high and dense accumulation of marine debris, the surveyed area at S1 was limited to 60 m² to ensure representative sampling while remaining operationally feasible (Fig. 3 b). In contrast, S2 exhibited a lower average marine debris density (0.67 n/m²), accounting for 35.98% of the total debris collected. This indicates a lower level of pollution or a reduced debris retention capacity compared to S1; therefore, the surveyed area at S2 was expanded to 900 m². At S3, the average marine debris density was the lowest (0.052 n/m²), accounting for 13.09% of the total debris collected. This is consistent with the open beach environment, which has a limited capacity to retain floating debris (Fig. 3 d). Therefore, the sampling area at S3 was expanded to 1,260 m² to ensure a sufficient number of samples for detailed analysis in Table 2 . Table 2 Marine debris density and total sampled area Location Plastic debris density (n/m 2 ) Total sampling area (m 2 ) S1 Average density: 8.68 60 S2 Average density: 0.67 900 S3 Average density: 0.052 1,260 The marked differences in marine debris density between the two substrate - based areas in Table 2 (mangrove forests and beach) can be explained by the dominant southeastward flow of the Ma River from inland areas toward the sea (Doan Van Long et al., 2015). Accordingly, S1 located in the estuarine zone, is directly influenced by this transport pathway and thus becomes a convergence area for marine debris. In addition, large river systems commonly serve as major transport routes conveying land-based waste to the marine environment, with domestic waste constituting a substantial proportion (Schmidt et al., 2017 ). In addition, the topographic and geomorphological characteristics of the estuarine area, including channel curvature, uneven depth distribution, and sediment accretion trends, create favorable conditions for the formation of low-energy flow zones and localized eddies (Quan & Hung, 2016 ). These zones are considered “natural traps”, with the capacity to retain sediments and floating solid objects over extended periods (Wolanski & Elliott, 2015 ). This mechanism has been documented in many estuaries worldwide and is considered a primary driver of marine debris accumulation in estuarine and adjacent coastal areas (van Emmerik et al., 2019 ). In summary, marine debris tends to be retained in estuarine and nearshore zones before being transported further offshore or redistributed along the coastline (van Emmerik & Schwarz, 2020 ); Accordingly, Site S1 functioning as a “natural trap” may help reduce marine debris pollution pressure on the adjacent beach area (S3), which is more strongly influenced by wave action and coastal currents.” The average marine debris density at the study site shows clear differences compared with mangrove regions worldwide, as summarized in Table 3 . At S1, the average marine debris density reached 8.68 n/m², which is comparable to that reported for mangrove ecosystems in Mumbai, India (8.8 n/m², Kesavan et al., 2021 ); and in Kupang, Indonesia (9.62 n/m², Paulus et al., 2020 ). Where debris accumulation is at a moderate level, mainly influenced by tidal processes (do Sul et al., 2014 ) and nearby human activities. However, it should be noted that the sampling units used in other studies generally covered relatively large areas, ranging from 40 to 154 m². In contrast, at S1 in the present study, a very small sampling unit of only 4 m² already yielded an average marine debris density of 8.68 n/m². This result reflects a concerning level of pollution in the Cua Hoi mangrove forest, indicating a substantially higher debris accumulation capacity compared to many comparable mangrove ecosystems worldwide. Table 3 Marine debris density in different regions worldwide Location Area of each sampling unit (m 2 ) Marine debris density (n/m 2 ) Common size classes of marine debris Ref S1 4 Average density: 8.68 5–25 mm [In this study] S2 100 Average density: 0.67 5–25 mm S3 420 Average density: 0.052 5–25 mm Mangroves in Mumbai, India 40 Average density: 8.8 - (Kesavan et al., 2021 ) Mangroves in Kupang (ecotourism area), Indonesia 100 Average density: 9.62 - (Paulus et al., 2020 ) Mangroves in Kendari Bay, Indonesia 25 Average density: 261.25 - (Rahim et al., 2020 ) Mangroves in Ambon Island, Indonesia 100 Average density: 92 5–25 mm (Suyadi & Manullang, 2020 ) Mangroves in Ciénaga Grande de Santa Marta, Colombia 100 Density ranger: 0.054 > 25 mm (Garcés-Ordóñez et al., 2019 ) Mangroves in Saudi Arabia Belt transect, between 2 and 8 m wide, and 4–60 m long Average density: 0.66 > 25 mm (Martin et al., 2019 ) In contrast, S2 recorded a much lower average marine debris density of 0.67 n/m², which is relatively low compared to many international studies and may indicate a greater self-cleaning capacity or lower anthropogenic pressure in this area. In comparison, some mangrove forests such as Kendari Bay and Ambon Island, Indonesia, have reported extremely high debris densities, reaching 261.25 n/m² and 92 n/m², respectively (Rahim et al., 2020 ; Suyadi & Manullang, 2020 ). Indicating strong influences from urbanization, tourism activities, and upstream debris transport (Eriksen et al., 2014 ). In contrast, areas such as Ciénaga Grande de Santa Marta, Colombia, and mangrove forests in Saudi Arabia have reported very low debris average densities (0.054–0.66 n/m², Garcés-Ordóñez et al., 2019 ; Martin et al., 2019 ), comparable to or lower than those observed at S2. These low levels are often associated with reduced development pressure, more effective waste management systems, or geographic settings that are less prone to the accumulation of marine debris. Overall, in comparison with global findings, S1 falls within the moderate pollution category, whereas S2 belongs to the low pollution category. This contrast reflects differences in vegetation structure, flow direction, and the degree of anthropogenic influence across the mangrove areas (Eriksen et al., 2014 ). In Table 3 , the beach site (S3) was not compared with the other sites due to differences in substrate characteristics. S3 is evaluated in subsequent sections to elucidate the role of the two mangrove sites (S1 and S2) in protecting and influencing adjacent beach areas (S3). The results reveal clear differences in the size distribution of plastic debris between the mangrove sites (S1 and S2) and the beach site (S3), as shown in Fig. 5 . The 5–25 mm size class dominated across all sites, but its proportion was markedly higher at S3 (78.79%) compared to S1 (45.68%) and S2 (54.38%). This pattern can be explained by the dense root systems of the mangrove sites (S1 and S2), which act to retain larger debris items (Martin et al., 2019 ), thereby maintaining a higher proportion of the larger size class (25–1000 mm), accounting for 40.31% at S1 and 32.23% at S2, compared with only 18.18% at S3. The > 1 m size class accounted for the smallest proportion across all three sites; however, its contribution was still considerably higher at S1 (14.01%) and S2 (13.39%) than at S3 (3.03%). This indicates that land-derived marine debris tends to become trapped and accumulate within mangrove ecosystems, whereas the open beach environment has a limited capacity for long - term retention (do Sul et al., 2014 ). Overall, these differences confirm the important role of mangrove ecosystems as natural traps for large-sized marine debris. At the two mangrove sites (S1 and S2), the dominant marine debris size class ranged from 5 to 25 mm, which is consistent with findings reported for Ambon Island, Indonesia (Suyadi & Manullang, 2020 ). This may be attributed to the fact that most marine debris, particularly plastic waste, has been directly exposed to solar radiation - one of the primary factors weakening plastic structure - so that by the time of collection, the materials had already fragmented into smaller debris and plastic particles (Weinstein et al., 2016 ). In comparison with other regions worldwide, many studies have reported dominant marine debris size classes larger than 5 mm or exceeding 25 mm (Garcés-Ordóñez et al., 2019 ; Martin et al., 2019 ; Riascos et al., 2019 ), indicating greater accumulation of large marine debris due to differing environmental characteristics. 3.1.2. Material composition of marine debris and types of plastics Material-based classification results indicate that marine debris in the study area was predominantly composed of plastics, accounting for an overwhelming 92.79% of the total samples collected (Fig. 6 a). Other material categories, including textiles (4.36%), rubbers (0.92%), metals (0.84%), glass (0.58%), papers (0.41%), and other materials (0.08%), contributed only minor proportions. This pattern is consistent with numerous studies worldwide, in which plastics consistently represent the dominant material category in marine debris (Garcés-Ordóñez et al., 2019 ; Kesavan et al., 2021 ; Martin et al., 2019 ; Paulus et al., 2020 ; Rahim et al., 2020 ). The predominance of plastics reflects a widespread pattern of marine debris pollution across many coastal ecosystems, where single-use plastic products and durable polymer materials tend to persist and accumulate over long periods due to their resistance to degradation (Pearce et al., 2019 ). The dominance of plastics also suggests a high potential for fragmentation into microplastics (Weinstein et al., 2016 ), thereby increasing risks to ecosystems and food webs. Polymer-type analysis revealed that marine debris in the study area mainly consisted of common polymer groups, with LDPE being the most dominant (55%), followed by PE (19%) and PS (18%) in Fig. 6 b. Other plastic types, such as PP (6%) and HDPE (2%), were present at lower proportions, while PVC was rarely detected. The dominance of LDPE and PE reflects their common origin from flexible packaging, plastic bags, and single - use wrapping materials, which are lightweight and easily transported and accumulated in coastal environments (Pearce et al., 2019 ). These materials are easily transported and dispersed in coastal environments. The presence of PS (e.g., expanded polystyrene foam and food containers) further indicates a substantial influence of coastal domestic activities and tourism (Feld et al., 2022 ). The low proportions of HDPE and PP, together with the absence of PVC, suggest that plastics with higher durability or more rigid structures are less prevalent, possibly due to their lower fragmentation rates or lower emission sources. Overall, this polymer composition reflects the characteristics of plastic debris in the study area and is consistent with global trends observed in many coastal ecosystems, where flexible packaging and single-use plastic items constitute the dominant sources of pollution (Garcés-Ordóñez et al., 2019 ; Kesavan et al., 2021 ; Martin et al., 2019 ). 3.1.3 Assessment of the sources of marine debris Source classification results of marine debris across the three study sites indicate that public litter accounted for the highest proportion (78.27%), clearly reflecting the influence of coastal community activities such as daily household practices, tourism, and inadequately managed waste disposal (Fig. 7 ). Fisheries debris constituted the second largest category (21.14%), indicating a significant contribution from coastal fishing activities, including fishing lines, nets, buoys, and other gear that are lost or abandoned during fishing operations (Selvam et al., 2021 ). These results show strong agreement with previous studies (Debrot et al., 2013 ; Kesavan et al., 2021 ; Seeruttun et al., 2021 ). Notably, (Kesavan et al., 2021 ) reported that 54% of marine debris was associated with coastal and recreational activities, while 30.4% originated from fisheries-related sources, including fishing gear and ropes. Other source categories, such as fly-tipped waste and medical debris, accounted for only very small proportions (0.42% and 0.17%, respectively), while debris from shipping activities and items of unidentified origin (non-sourced) were virtually absent. This source composition indicates that marine debris in the study area predominantly originates from land-based and nearshore activities (Kesavan et al., 2021 ), whereas contributions from maritime activities are negligible. This reflects the characteristics of estuarine - mangrove systems, where domestic waste tends to be transported by riverine flows and accumulate over prolonged periods, and where debris particles are gradually buried within mangrove sediments over time (Martin et al., 2020 ). This also highlights the importance of local community waste management in mitigating marine debris pollution. Conclusion This study confirms the widespread presence of marine debris in the mangrove ecosystems of the Cua Hoi estuarine area, with pronounced spatial differences in debris density, size distribution, material composition, and sources. Among the study sites, mangrove area S1 exhibited the highest debris accumulation, reflecting its location at the river mouth and the strong trapping effect of dense mangrove root systems, whereas S2 showed considerably lower levels, indicating reduced anthropogenic pressure or greater self-cleaning capacity. The adjacent beach site (S3) recorded the lowest debris density, highlighting the contrasting retention capacities between mangrove forests and open beach environments. Plastics overwhelmingly dominated the debris composition, with flexible polymers such as LDPE, PE, and PS being the most prevalent, consistent with the predominance of single-use packaging and coastal domestic activities. Size analysis revealed that the 5–25 mm class was most common across all sites, while mangrove areas retained a higher proportion of larger debris, confirming the role of mangrove ecosystems as effective natural traps for marine litter. Source identification further demonstrated that land-based inputs, particularly public litter and fisheries debris, were the primary contributors, whereas inputs from maritime activities were negligible. Overall, these findings emphasize the critical ecological function of mangrove forests in intercepting and retaining marine debris before it is redistributed to adjacent coastal areas. The results also underscore the urgent need for improved waste management at the community level, stricter control of land-based sources, and targeted conservation strategies to protect estuarine mangrove ecosystems. Future research should incorporate long-term and seasonal monitoring, integrate hydrodynamic modeling, and assess buried debris and microplastics within mangrove sediments to better understand the full role of mangroves as sinks for marine debris and their implications for coastal environmental health. Declarations Author contributions Dang Tran Quan: project administration, funding acquisition, methodology, investigation; Duong Thi Lim: project administration, funding acquisition, methodology, writing – original draft; Nguyen Tran Dinh: formal analysis, software, data curation, writing – original draft; Nguyen Thi Lan Huong: investigation, formal analysis; Nguyen Thi Hue: investigation, formal analysis; Nguyen Thi Huong Thuy: conceptualization, methodology; Tran Thu Thuy: conceptualization, methodology; Nguyen Viet Cuong: conceptualization, methodology. Availability of data and materials All data and materials generated or analyzed during this study are included in this published article and supplementary information file and are available from the corresponding author upon reasonable request. Conflicts of interest The authors declare no conflict of interest. Acknowledgements: This research is funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 105.08 – 2021.09. Funding declaration: Dang Tran Quan, Duong Thi Lim, Nguyen Thi Lan Huong, Nguyen Thi Hue received funding from the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 105.08 – 2021.09. The authors declare that they have no other financial relationships or financial interests that could be perceived as influencing the work reported in this manuscript. References Alongi, D. M. (2014). Carbon cycling and storage in mangrove forests. Annual Review of Marine Science , 6 (1), 195–219. Anthony Cheshire. (2009). (PDF) UNEP/IOC Guidelines on Survey and Monitoring of Marine Litter . ResearchGate. https://www.researchgate.net/publication/256186638_UNEPIOC_Guidelines_on_Survey_and_Monitoring_of_Marine_Litter Compa, M., Alomar, C., Morató, M., Álvarez, E., & Deudero, S. (2022). 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Scientific Reports , 9 (1), 916. Schmidt, C., Krauth, T., & Wagner, S. (2017). Export of Plastic Debris by Rivers into the Sea. Environmental Science & Technology , 51 (21), 12246–12253. https://doi.org/10.1021/acs.est.7b02368 Seeruttun, L. D., Raghbor, P., & Appadoo, C. (2021). First assessment of anthropogenic marine debris in mangrove forests of Mauritius, a small oceanic island. Marine Pollution Bulletin , 164 , 112019. Selvam, K., Xavier, K. M., Shivakrishna, A., Bhutia, T. P., Kamat, S., & Shenoy, L. (2021). Abundance, composition and sources of marine debris trawled-up in the fishing grounds along the north-east Arabian coast. Science of the Total Environment , 751 , 141771. Su, L., Xue, Y., Li, L., Yang, D., Kolandhasamy, P., Li, D., & Shi, H. (2016). Microplastics in taihu lake, China. Environmental Pollution , 216 , 711–719. Suyadi, & Manullang, C. Y. (2020). Distribution of plastic debris pollution and it is implications on mangrove vegetation. Marine Pollution Bulletin , 160 , 111642. https://doi.org/10.1016/j.marpolbul.2020.111642 Teh, S. Y., Koh, H. L., Liu, P. L.-F., Ismail, A. I. M., & Lee, H. L. (2009). Analytical and numerical simulation of tsunami mitigation by mangroves in Penang, Malaysia. Journal of Asian Earth Sciences , 36 (1), 38–46. Thanh Hoa Newspaper and Radio – Television Station. (2024, October 15). Mướt xanh những cánh rừng ngập mặn . Thanh Hoa Newspaper and Radio – Television Station. https://baothanhhoa.vn/muot-xanh-nhung-canh-rung-ngap-man-227686.htm Thi Lim D., Thi Huong Thuy N., Tran Quan D., Thi Lan Huong N., Thi Hue N., Thi Minh Trang T., Thu Thuy T., Thi Dung P., Viet Cuong N., & Duc Manh V. (2024). Ảnh hưởng của kỹ thuật lấy mẫu đến tính chất vi nhựa vùng cửa sông, ven biển: Thí điểm tại cửa Hới, tỉnh Thanh Hóa. Journal of Hydro-meteorology , 10 (766), 43–52. https://doi.org/10.36335/VNJHM.2024(766).43-52 van Emmerik, T., Loozen, M., Oeveren, K., Buschman, F. A., & Prinsen, G. (2019). Riverine plastic emission from Jakarta into the ocean. Environmental Research Letters , 14 . https://doi.org/10.1088/1748-9326/ab30e8 van Emmerik, T., & Schwarz, A. (2020). Plastic debris in rivers. WIREs Water , 7 (1), e1398. https://doi.org/10.1002/wat2.1398 Veiga, J. M., Fleet, D., Kinsey, S., Nilsson, P., Vlachogianni, T., Werner, S., Galgani, F., Thompson, R., Dagevos, J., Gago, J., Sobral, P., & Cronin, R. (2016). Identifying Sources of Marine Litter . JRC Publications Repository. https://doi.org/10.2788/956934 Weinstein, J. E., Crocker, B. K., & Gray, A. D. (2016). From macroplastic to microplastic: Degradation of high-density polyethylene, polypropylene, and polystyrene in a salt marsh habitat. Environmental Toxicology and Chemistry , 35 (7), 1632–1640. https://doi.org/10.1002/etc.3432 Wenneker, B., & Oosterbaan, L. (2010). Guideline for Monitoring Marine Litter on the Beaches in the OSPAR Maritime Area. Edition 1.0. OSPAR Commission. https://repository.oceanbestpractices.org/handle/11329/1466 Wolanski, E., & Elliott, M. (2015). Estuarine Ecohydrology: An introduction . Wright, S. L., Rowe, D., Thompson, R. C., & Galloway, T. S. (2013). Microplastic ingestion decreases energy reserves in marine worms. Current Biology , 23 (23), R1031–R1033. Zhou, P., Huang, C., Fang, H., Cai, W., Li, D., Li, X., & Yu, H. (2011). The abundance, composition and sources of marine debris in coastal seawaters or beaches around the northern South China Sea (China). Marine Pollution Bulletin , 62 (9), 1998–2007. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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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-8565242","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":584882904,"identity":"0fafb293-f78e-4b04-ace1-a0be8bb676aa","order_by":0,"name":"Tran Quan Dang","email":"","orcid":"","institution":"Vietnam Academy of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Tran","middleName":"Quan","lastName":"Dang","suffix":""},{"id":584882905,"identity":"4a6e6c84-4359-4dc9-a168-8c2b953e61c1","order_by":1,"name":"Thi Lim Duong","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4ElEQVRIiWNgGAWjYDCCAyCiQILB/ngziCkhQ6QWAwkGhjPHEkBaeIjVAsQ3ckAkA2EtfDeSjz38YmARzTgj5/OrGzUWPAzsh49uwKdF8kZaurGMgURuM8/bbdY5x4AO40lLu4FPi8GNHDNpCaCWNvbcbcY5bEAtEjxmxGnpYch5Zpzzj0gtkh+AWmZw5DA/zm0jQovkmWdp0sBAzt3Ac8yMObdPgoeNkF/4jicfk/xRUZe7gb358eecb3Vy/OyHj+HVAgLM0LhgkwCThJSDAOMPqNYPxKgeBaNgFIyCkQcAUnxH03JZ4cQAAAAASUVORK5CYII=","orcid":"","institution":"Vietnam Academy of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Thi","middleName":"Lim","lastName":"Duong","suffix":""},{"id":584882906,"identity":"42b03543-0b42-4e65-88b2-41abdaf6183d","order_by":2,"name":"Tran Dinh Nguyen","email":"","orcid":"","institution":"Vietnam Academy of Science and 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03:23:28","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8565242/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8565242/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":101879748,"identity":"70942e7c-3704-4228-9247-f6f407abdc15","added_by":"auto","created_at":"2026-02-04 14:55:09","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":953503,"visible":true,"origin":"","legend":"\u003cp\u003eMangrove trees act as natural traps\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8565242/v1/708e2c49013ff76c1b52b5ab.png"},{"id":101880023,"identity":"0ba1a496-4edd-4d4a-8592-d52883e84c06","added_by":"auto","created_at":"2026-02-04 14:56:08","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":278612,"visible":true,"origin":"","legend":"\u003cp\u003eSampling area\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8565242/v1/2963450034cd446124631216.png"},{"id":101879927,"identity":"7bdce621-3534-4619-99ae-d05d7969f972","added_by":"auto","created_at":"2026-02-04 14:55:49","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1750759,"visible":true,"origin":"","legend":"\u003cp\u003eCharacteristics of the three sampling areas\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8565242/v1/d4fa662d7c92ccbc8bdbb130.png"},{"id":101879860,"identity":"741c0cbb-a836-4407-835b-c7ffcc7659ba","added_by":"auto","created_at":"2026-02-04 14:55:37","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2542829,"visible":true,"origin":"","legend":"\u003cp\u003eClassification based on material properties\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8565242/v1/0cbbe3cd64ada18cc32ae936.png"},{"id":101880215,"identity":"8e0a5db3-eaa7-4be2-ad56-e4db89f2fb2a","added_by":"auto","created_at":"2026-02-04 14:56:40","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":97504,"visible":true,"origin":"","legend":"\u003cp\u003eSize distribution of marine debris\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8565242/v1/426844bc9a98daac02701136.png"},{"id":101880078,"identity":"9d8b3264-147e-40a1-b63c-559613b4e477","added_by":"auto","created_at":"2026-02-04 14:56:19","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":241211,"visible":true,"origin":"","legend":"\u003cp\u003eMaterial composition of marine debris and types of plastics\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8565242/v1/81435e23a0081caa4c5d7743.png"},{"id":101879910,"identity":"bdf99591-ba4a-4070-938d-de06583b88d6","added_by":"auto","created_at":"2026-02-04 14:55:43","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":120487,"visible":true,"origin":"","legend":"\u003cp\u003eSources of marine debris\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8565242/v1/964b8b9a481f2980d3b1198e.png"},{"id":103927214,"identity":"4c43f4f3-7412-4cf5-83d5-82f2bdb47341","added_by":"auto","created_at":"2026-03-04 15:42:02","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6855052,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8565242/v1/41a3d956-27e7-4e5f-a467-5d47948b074d.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Marine debris pollution in mangrove at Cua Hoi, Thanh Hoa: Status and Source assessment","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eMangrove forests are coastal vegetated ecosystems widely distributed in tropical and subtropical regions worldwide, serving as important ecological buffer zones between terrestrial and marine environments (Rodin \u0026amp; Bazilevič, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1966\u003c/span\u003e). This unique ecosystem provides a wide range of important ecological and economic benefits, including serving as feeding and nursery grounds for commercially valuable species, providing habitats for endangered species, storing carbon in both biomass and sediments, supplying timber for construction and fuel, and playing a crucial role in ecosystem nutrient cycling (Jerath et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), support livelihoods (Donato et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) and protect coastlines from storms and tsunamis (Teh et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). However, due to their coastal distribution, mangrove forests are particularly vulnerable to impacts from marine debris (Not et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAccording to the United Nations Environment Programme (UNEP), marine debris is defined as any persistent solid material that is manufactured or processed by humans and deliberately or unintentionally discarded, disposed of, or abandoned in the marine and coastal environment (GESAMP \u0026amp; PJ, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). They cause numerous negative impacts, including entanglement of marine organisms and accumulation within the food web, thereby affecting the structure and functioning of marine ecosystems (Wright et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Marine debris, including plastic waste, enters the marine environment primarily as a result of inadequate management and disposal practices, accidental releases, as well as the influence of natural processes (Li et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Plastics are among the most widely used materials today, and the management and disposal of plastic waste have become a global environmental concern (Mallik et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Of the approximately 275\u0026nbsp;million tonnes of plastic waste generated in 2010, an estimated 4.8 to 12.7\u0026nbsp;million tonnes were discharged into the global ocean (Jambeck et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Plastics are widely distributed throughout the marine environment (Moore, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), and from the ocean they can be readily transported by ocean currents, wind, and tides to adjacent areas (Mallik et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), where they subsequently accumulate.\u003c/p\u003e \u003cp\u003eIn this context, mangrove forests account for approximately 0.5% of the total global coastal area (Alongi, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). These forests develop in shallow waters and intertidal zones, where the exchange of organic nutrients in and out of the system plays a key role (Su et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Marine debris, together with anthropogenic pollutants, has exerted and continues to exert significant impacts on estuaries and mangrove ecosystems (Martin et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Hydrodynamic processes and ocean currents govern the dispersion of marine debris (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea), whereas the complex root systems of mangrove vegetation act as natural traps, effectively retaining and accumulating various types of debris (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn recent years, marine debris has been recognized as an important indicator of environmental pollution and poses numerous risks to marine organisms (Roman et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Marine debris pollution has become a major public concern and is widely regarded as a clear manifestation of anthropogenic impacts on the marine environment (Zhou et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Similarly, mangrove ecosystems are currently facing multiple threats from marine debris pollution, including visual impacts and the presence of hazardous substances such as heavy metals, organic pollutants, and pathogens, which can be transported by debris or enter the ecosystem through uptake by marine organisms (Li et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Therefore, this study was conducted to assess the current status and identify the sources of marine debris pollution. Specifically, the study focuses on investigating the characteristics of marine debris within mangrove ecosystems by determining debris density, size, material composition, and plastic types, as well as analyzing the sources of marine debris. The findings provide insights into the extent of marine debris pollution in mangrove ecosystems in the Cua Hoi area, thereby offering a scientific basis for waste management, source control, and the sustainable conservation of coastal mangrove ecosystems\u003c/p\u003e"},{"header":"2. Research area and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Research area:\u003c/h2\u003e \u003cp\u003eThe mangrove forests in the Cua Hoi area, Thanh Hoa Province, are located at the mouth of the Ma River, where freshwater and marine ecosystems intersect, creating a distinctive environment characterized by high biodiversity and important ecological functions. According to available statistics, Thanh Hoa Province currently has approximately 1,000 ha of mangrove forests, mainly distributed in coastal and estuarine districts (Thanh Hoa Newspaper and Radio \u0026ndash; Television Station, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In addition, Cua Hoi is the estuarine area where the Ma River discharges into the sea, and is directly influenced by coastal tidal regimes and tropical depressions (Thi Lim et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMarine debris samples from the intertidal mangrove areas were collected at three sites based on spatial distribution, including two mangrove sites (S1 and S2) and one beach site (S3), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Specifically, 15 sampling units were collected at S1, 9 sampling units at S2, and 3 sampling units at S3\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Research Methods:\u003c/h2\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1. Marine debris sampling method\u003c/h2\u003e \u003cp\u003eThe determination of marine debris density and distribution was based on established methodologies adapted from the NOAA (National Oceanic and Atmospheric Administration) Shoreline Survey Field Guide (Opfer et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), the European Commission\u0026rsquo;s Guidance on Monitoring of Marine Litter in European Seas (Hanke et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), and the UNEP/IOC Guidelines on Survey and Monitoring of Marine Litter (Anthony Cheshire, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eS1 is characterized by mangrove vegetation dominated by \u003cem\u003eSonneratia alba\u003c/em\u003e (Primavera, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). At this site, a fringe mangrove area shows signs of degradation, including poor growth and standing dead trees in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. The intertidal substrate in this area is predominantly sandy, while the upper intertidal zone is covered by a layer of plastic debris, mainly white expanded polystyrene foam (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). This layer is densely accumulated with an average width of approximately 3 m, and the area of this zone was measured and determined using GPS. In this area, the intertidal zone was divided into 5 transects perpendicular to the shoreline, spaced 20 m apart. Along each transect, 3 sampling units were established at the mangrove fringe (near the waterline), the mid-intertidal zone, and the upper intertidal zone. In total, 15 sampling units were collected, each with an area of 4 m\u0026sup2; (2m \u0026times; 2m)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eS2 is an intertidal area adjacent to the Ma River, characterized by mangrove forests dominated by \u003cem\u003eAvicennia\u003c/em\u003e and \u003cem\u003eRhizophora\u003c/em\u003e species, with muddy substrates. The mangrove vegetation in this area is well developed (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). A total of 9 sampling units were established, each with an area of 100 m\u0026sup2; (10m \u0026times; 10m), spaced approximately 200 m apart. Areas deeper within the mangrove forest were densely vegetated and therefore difficult to access for sampling. S3 is a beach area without vegetation, characterized by predominantly sandy substrates (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). As no mangro ve forest is present at this site, three sampling units were established, each covering a sampling area of 420 m\u0026sup2; along the shoreline for all types of marine debris, following the method described (Wenneker \u0026amp; Oosterbaan, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2. Marine debris classification method\u003c/h2\u003e \u003cp\u003eDuring the survey, all visually identifiable marine debris larger than 5 mm was recorded. Plastic debris was directly collected at each sampling site, placed in separate bags for preservation, and transported to the laboratory for further analysis. The results were recorded as the total number of marine debris items, as well as the abundance of each debris category classified by material type and size. The collected marine debris samples were subsequently categorized into 8 main material groups, including plastics, glass, metal, rubber, textiles, paper, and other materials in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThis classification method was adopted based on the guidelines of OSPAR \u0026ndash; the Convention for the Protection of the Marine Environment of the North-East Atlantic (Wenneker \u0026amp; Oosterbaan, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). In addition, marine debris was classified by size into meso (5\u0026ndash;25 mm), macro (25\u0026ndash;100 mm), and mega (\u0026gt;\u0026thinsp;1 m) categories; it was also identified according to product types such as cups, bowls, ropes, footwear, tarpaulins, and similar items (Anthony Cheshire, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.2.3. Method for identifying the sources of marine litter\u003c/h2\u003e \u003cp\u003eMarine debris present in mangrove forests may originate from various production sectors (Veiga et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), as detailed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eClassification of marine debris sources\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSources of marine debris\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDescription\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePublic litter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eItems that are discarded or left behind by humans on the coast or inland can be carried into the marine environment by wind and rivers\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFisheries debris\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFisheries debris, including aquaculture activities, such as nets, buoys, fishing lines, and sinkers\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eShipping\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eItems lost or discarded from vessels\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFly tipted\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIllegal waste, including furniture, ceramics, and construction materials\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMedical\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIncluding medical-related items such as inhalers, adhesive patches, and syringes\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNon \u0026ndash; sourced\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eItems that are too small or damaged to identify their specific sources\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.2.4. Method for determining plastic composition:\u003c/h2\u003e \u003cp\u003eMarine debris samples collected from the study sites were rinsed with distilled water, dried at 60 \u003csup\u003eo\u003c/sup\u003eC, and allowed to cool to room temperature. Samples suspected to be plastic debris were subsequently identified using Fourier Transform Infrared - Attenuated Total Reflectance spectroscopy (FTIR-ATR; Agilent Technologies, model: CARY 630, Malaysia). Each polymer was identified using a spectral library (Agilent polymer Handheld ATR Library) (L\u0026ouml;der et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The spectral range of the instrument was set from 4,000 to 650 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, with 8 scans per sample and a spectral resolution of 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, consistent with the measurement conditions of the spectral library. All polymer types, including PE (polyethylene), PS (polystyrene), PP (polypropylene), PVC (polyvinyl chloride), LDPE (low-density polyethylene), and HDPE (high-density polyethylene), were confirmed by comparison with the spectral library, with correlation coefficients (R) ranging from 0.7 to 1.0 (Compa et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Laboratory conditions\u003c/h2\u003e \u003cp\u003eThe study on marine debris pollution in the mangrove forests in the Cua Hoi area, Thanh Hoa Province, was conducted under controlled laboratory conditions following strict contamination control protocols. The laboratory was thoroughly cleaned, and all personnel wore 100% white cotton laboratory coats and disposable nitrile gloves throughout the experimental procedures. All working surfaces were wiped with 70% ethanol before use to minimize airborne and environmental contamination. All laboratory equipment used in the analyses was made of stainless steel and glass.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Data analysis method:\u003c/h2\u003e \u003cp\u003eData on marine debris density, size, and polymer composition were analyzed using Microsoft Excel. The number of marine debris per sampling unit in the intertidal mangrove areas was expressed as item counts (n), while marine debris density was expressed as the number of items per unit area (n/m\u0026sup2;). The proportions of marine debris classified by material type, size, polymer composition, and source were expressed as percentages (%)\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Marine debris in mangrove forests:\u003c/h2\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1. Density and size of marine debris\u003c/h2\u003e \u003cp\u003eA total of 1,192 marine debris (n) were collected from 27 sampling units. Among the study sites, S1 exhibited the highest average debris density, reaching 8.68 n/m\u0026sup2; and accounting for 51.93% of the total marine debris collected. This result indicates a pronounced accumulation of marine debris at S1, which is consistent with the dense root systems and the \u0026ldquo;natural trap\u0026rdquo; structure characteristic of mangrove ecosystems (Martin et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Due to the high and dense accumulation of marine debris, the surveyed area at S1 was limited to 60 m\u0026sup2; to ensure representative sampling while remaining operationally feasible (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). In contrast, S2 exhibited a lower average marine debris density (0.67 n/m\u0026sup2;), accounting for 35.98% of the total debris collected. This indicates a lower level of pollution or a reduced debris retention capacity compared to S1; therefore, the surveyed area at S2 was expanded to 900 m\u0026sup2;. At S3, the average marine debris density was the lowest (0.052 n/m\u0026sup2;), accounting for 13.09% of the total debris collected. This is consistent with the open beach environment, which has a limited capacity to retain floating debris (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). Therefore, the sampling area at S3 was expanded to 1,260 m\u0026sup2; to ensure a sufficient number of samples for detailed analysis in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMarine debris density and total sampled area\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLocation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePlastic debris density (n/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTotal sampling area (m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAverage density: 8.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAverage density: 0.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e900\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAverage density: 0.052\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1,260\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe marked differences in marine debris density between the two substrate - based areas in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (mangrove forests and beach) can be explained by the dominant southeastward flow of the Ma River from inland areas toward the sea (Doan Van Long et al., 2015). Accordingly, S1 located in the estuarine zone, is directly influenced by this transport pathway and thus becomes a convergence area for marine debris. In addition, large river systems commonly serve as major transport routes conveying land-based waste to the marine environment, with domestic waste constituting a substantial proportion (Schmidt et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In addition, the topographic and geomorphological characteristics of the estuarine area, including channel curvature, uneven depth distribution, and sediment accretion trends, create favorable conditions for the formation of low-energy flow zones and localized eddies (Quan \u0026amp; Hung, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). These zones are considered \u0026ldquo;natural traps\u0026rdquo;, with the capacity to retain sediments and floating solid objects over extended periods (Wolanski \u0026amp; Elliott, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). This mechanism has been documented in many estuaries worldwide and is considered a primary driver of marine debris accumulation in estuarine and adjacent coastal areas (van Emmerik et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). In summary, marine debris tends to be retained in estuarine and nearshore zones before being transported further offshore or redistributed along the coastline (van Emmerik \u0026amp; Schwarz, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2020\u003c/span\u003e); Accordingly, Site S1 functioning as a \u0026ldquo;natural trap\u0026rdquo; may help reduce marine debris pollution pressure on the adjacent beach area (S3), which is more strongly influenced by wave action and coastal currents.\u0026rdquo;\u003c/p\u003e \u003cp\u003eThe average marine debris density at the study site shows clear differences compared with mangrove regions worldwide, as summarized in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. At S1, the average marine debris density reached 8.68 n/m\u0026sup2;, which is comparable to that reported for mangrove ecosystems in Mumbai, India (8.8 n/m\u0026sup2;, Kesavan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e); and in Kupang, Indonesia (9.62 n/m\u0026sup2;, Paulus et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Where debris accumulation is at a moderate level, mainly influenced by tidal processes (do Sul et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) and nearby human activities. However, it should be noted that the sampling units used in other studies generally covered relatively large areas, ranging from 40 to 154 m\u0026sup2;. In contrast, at S1 in the present study, a very small sampling unit of only 4 m\u0026sup2; already yielded an average marine debris density of 8.68 n/m\u0026sup2;. This result reflects a concerning level of pollution in the Cua Hoi mangrove forest, indicating a substantially higher debris accumulation capacity compared to many comparable mangrove ecosystems worldwide.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMarine debris density in different regions worldwide\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLocation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eArea of each sampling unit (m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMarine debris density (n/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCommon size classes of marine debris\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRef\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAverage density: 8.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u0026ndash;25 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e[In this study]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAverage density: 0.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u0026ndash;25 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e420\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAverage density: 0.052\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u0026ndash;25 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMangroves in Mumbai, India\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAverage density: 8.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e(Kesavan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMangroves in Kupang (ecotourism area), Indonesia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAverage density: 9.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e(Paulus et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2020\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMangroves in Kendari Bay, Indonesia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAverage density: 261.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e(Rahim et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2020\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMangroves in Ambon Island, Indonesia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAverage density: 92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u0026ndash;25 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e(Suyadi \u0026amp; Manullang, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2020\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMangroves in Ci\u0026eacute;naga Grande de Santa Marta, Colombia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDensity ranger: 0.054\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;25 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e(Garc\u0026eacute;s-Ord\u0026oacute;\u0026ntilde;ez et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMangroves in Saudi Arabia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBelt transect, between 2 and 8 m wide, and 4\u0026ndash;60 m long\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAverage density: 0.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;25 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e(Martin et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn contrast, S2 recorded a much lower average marine debris density of 0.67 n/m\u0026sup2;, which is relatively low compared to many international studies and may indicate a greater self-cleaning capacity or lower anthropogenic pressure in this area. In comparison, some mangrove forests such as Kendari Bay and Ambon Island, Indonesia, have reported extremely high debris densities, reaching 261.25 n/m\u0026sup2; and 92 n/m\u0026sup2;, respectively (Rahim et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Suyadi \u0026amp; Manullang, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Indicating strong influences from urbanization, tourism activities, and upstream debris transport (Eriksen et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In contrast, areas such as Ci\u0026eacute;naga Grande de Santa Marta, Colombia, and mangrove forests in Saudi Arabia have reported very low debris average densities (0.054\u0026ndash;0.66 n/m\u0026sup2;, Garc\u0026eacute;s-Ord\u0026oacute;\u0026ntilde;ez et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Martin et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), comparable to or lower than those observed at S2. These low levels are often associated with reduced development pressure, more effective waste management systems, or geographic settings that are less prone to the accumulation of marine debris.\u003c/p\u003e \u003cp\u003eOverall, in comparison with global findings, S1 falls within the moderate pollution category, whereas S2 belongs to the low pollution category. This contrast reflects differences in vegetation structure, flow direction, and the degree of anthropogenic influence across the mangrove areas (Eriksen et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the beach site (S3) was not compared with the other sites due to differences in substrate characteristics. S3 is evaluated in subsequent sections to elucidate the role of the two mangrove sites (S1 and S2) in protecting and influencing adjacent beach areas (S3).\u003c/p\u003e \u003cp\u003eThe results reveal clear differences in the size distribution of plastic debris between the mangrove sites (S1 and S2) and the beach site (S3), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The 5\u0026ndash;25 mm size class dominated across all sites, but its proportion was markedly higher at S3 (78.79%) compared to S1 (45.68%) and S2 (54.38%). This pattern can be explained by the dense root systems of the mangrove sites (S1 and S2), which act to retain larger debris items (Martin et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), thereby maintaining a higher proportion of the larger size class (25\u0026ndash;1000 mm), accounting for 40.31% at S1 and 32.23% at S2, compared with only 18.18% at S3. The \u0026gt;\u0026thinsp;1 m size class accounted for the smallest proportion across all three sites; however, its contribution was still considerably higher at S1 (14.01%) and S2 (13.39%) than at S3 (3.03%). This indicates that land-derived marine debris tends to become trapped and accumulate within mangrove ecosystems, whereas the open beach environment has a limited capacity for long - term retention (do Sul et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Overall, these differences confirm the important role of mangrove ecosystems as natural traps for large-sized marine debris.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAt the two mangrove sites (S1 and S2), the dominant marine debris size class ranged from 5 to 25 mm, which is consistent with findings reported for Ambon Island, Indonesia (Suyadi \u0026amp; Manullang, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). This may be attributed to the fact that most marine debris, particularly plastic waste, has been directly exposed to solar radiation - one of the primary factors weakening plastic structure - so that by the time of collection, the materials had already fragmented into smaller debris and plastic particles (Weinstein et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). In comparison with other regions worldwide, many studies have reported dominant marine debris size classes larger than 5 mm or exceeding 25 mm (Garc\u0026eacute;s-Ord\u0026oacute;\u0026ntilde;ez et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Martin et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Riascos et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), indicating greater accumulation of large marine debris due to differing environmental characteristics.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2. Material composition of marine debris and types of plastics\u003c/h2\u003e \u003cp\u003eMaterial-based classification results indicate that marine debris in the study area was predominantly composed of plastics, accounting for an overwhelming 92.79% of the total samples collected (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea). Other material categories, including textiles (4.36%), rubbers (0.92%), metals (0.84%), glass (0.58%), papers (0.41%), and other materials (0.08%), contributed only minor proportions. This pattern is consistent with numerous studies worldwide, in which plastics consistently represent the dominant material category in marine debris (Garc\u0026eacute;s-Ord\u0026oacute;\u0026ntilde;ez et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Kesavan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Martin et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Paulus et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Rahim et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The predominance of plastics reflects a widespread pattern of marine debris pollution across many coastal ecosystems, where single-use plastic products and durable polymer materials tend to persist and accumulate over long periods due to their resistance to degradation (Pearce et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The dominance of plastics also suggests a high potential for fragmentation into microplastics (Weinstein et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), thereby increasing risks to ecosystems and food webs.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePolymer-type analysis revealed that marine debris in the study area mainly consisted of common polymer groups, with LDPE being the most dominant (55%), followed by PE (19%) and PS (18%) in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb. Other plastic types, such as PP (6%) and HDPE (2%), were present at lower proportions, while PVC was rarely detected. The dominance of LDPE and PE reflects their common origin from flexible packaging, plastic bags, and single - use wrapping materials, which are lightweight and easily transported and accumulated in coastal environments (Pearce et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). These materials are easily transported and dispersed in coastal environments. The presence of PS (e.g., expanded polystyrene foam and food containers) further indicates a substantial influence of coastal domestic activities and tourism (Feld et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The low proportions of HDPE and PP, together with the absence of PVC, suggest that plastics with higher durability or more rigid structures are less prevalent, possibly due to their lower fragmentation rates or lower emission sources. Overall, this polymer composition reflects the characteristics of plastic debris in the study area and is consistent with global trends observed in many coastal ecosystems, where flexible packaging and single-use plastic items constitute the dominant sources of pollution (Garc\u0026eacute;s-Ord\u0026oacute;\u0026ntilde;ez et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Kesavan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Martin et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e3.1.3 Assessment of the sources of marine debris\u003c/h2\u003e \u003cp\u003eSource classification results of marine debris across the three study sites indicate that public litter accounted for the highest proportion (78.27%), clearly reflecting the influence of coastal community activities such as daily household practices, tourism, and inadequately managed waste disposal (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). Fisheries debris constituted the second largest category (21.14%), indicating a significant contribution from coastal fishing activities, including fishing lines, nets, buoys, and other gear that are lost or abandoned during fishing operations (Selvam et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). These results show strong agreement with previous studies (Debrot et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Kesavan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Seeruttun et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Notably, (Kesavan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) reported that 54% of marine debris was associated with coastal and recreational activities, while 30.4% originated from fisheries-related sources, including fishing gear and ropes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOther source categories, such as fly-tipped waste and medical debris, accounted for only very small proportions (0.42% and 0.17%, respectively), while debris from shipping activities and items of unidentified origin (non-sourced) were virtually absent. This source composition indicates that marine debris in the study area predominantly originates from land-based and nearshore activities (Kesavan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), whereas contributions from maritime activities are negligible. This reflects the characteristics of estuarine - mangrove systems, where domestic waste tends to be transported by riverine flows and accumulate over prolonged periods, and where debris particles are gradually buried within mangrove sediments over time (Martin et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). This also highlights the importance of local community waste management in mitigating marine debris pollution.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study confirms the widespread presence of marine debris in the mangrove ecosystems of the Cua Hoi estuarine area, with pronounced spatial differences in debris density, size distribution, material composition, and sources. Among the study sites, mangrove area S1 exhibited the highest debris accumulation, reflecting its location at the river mouth and the strong trapping effect of dense mangrove root systems, whereas S2 showed considerably lower levels, indicating reduced anthropogenic pressure or greater self-cleaning capacity. The adjacent beach site (S3) recorded the lowest debris density, highlighting the contrasting retention capacities between mangrove forests and open beach environments.\u003c/p\u003e \u003cp\u003ePlastics overwhelmingly dominated the debris composition, with flexible polymers such as LDPE, PE, and PS being the most prevalent, consistent with the predominance of single-use packaging and coastal domestic activities. Size analysis revealed that the 5\u0026ndash;25 mm class was most common across all sites, while mangrove areas retained a higher proportion of larger debris, confirming the role of mangrove ecosystems as effective natural traps for marine litter. Source identification further demonstrated that land-based inputs, particularly public litter and fisheries debris, were the primary contributors, whereas inputs from maritime activities were negligible. Overall, these findings emphasize the critical ecological function of mangrove forests in intercepting and retaining marine debris before it is redistributed to adjacent coastal areas. The results also underscore the urgent need for improved waste management at the community level, stricter control of land-based sources, and targeted conservation strategies to protect estuarine mangrove ecosystems. Future research should incorporate long-term and seasonal monitoring, integrate hydrodynamic modeling, and assess buried debris and microplastics within mangrove sediments to better understand the full role of mangroves as sinks for marine debris and their implications for coastal environmental health.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDang Tran Quan: project administration, funding acquisition, methodology, investigation; Duong Thi Lim: project administration, funding acquisition, methodology, writing \u0026ndash; original draft; Nguyen Tran Dinh: formal analysis, software, data curation, writing \u0026ndash; original draft; Nguyen Thi Lan Huong: investigation, formal analysis; Nguyen Thi Hue: investigation, formal analysis; Nguyen Thi Huong Thuy: conceptualization, methodology; Tran Thu Thuy: conceptualization, methodology; Nguyen Viet Cuong: conceptualization, methodology.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data and materials generated or analyzed during this study are included in this published article and supplementary information file and are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eThis research is funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 105.08 \u0026ndash; 2021.09.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding declaration:\u0026nbsp;\u003c/strong\u003eDang Tran Quan, Duong Thi Lim, Nguyen Thi Lan Huong, Nguyen Thi Hue received funding from the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 105.08 \u0026ndash; 2021.09. The authors declare that they have no other financial relationships or financial interests that could be perceived as influencing the work reported in this manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAlongi, D. M. (2014). Carbon cycling and storage in mangrove forests. \u003cem\u003eAnnual Review of Marine Science\u003c/em\u003e, \u003cem\u003e6\u003c/em\u003e(1), 195\u0026ndash;219.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAnthony Cheshire. (2009). \u003cem\u003e(PDF) UNEP/IOC Guidelines on Survey and Monitoring of Marine Litter\u003c/em\u003e. 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The abundance, composition and sources of marine debris in coastal seawaters or beaches around the northern South China Sea (China). \u003cem\u003eMarine Pollution Bulletin\u003c/em\u003e, \u003cem\u003e62\u003c/em\u003e(9), 1998\u0026ndash;2007.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"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":"Marine debris, Mangrove forests, Cua Hoi estuarine area, Source","lastPublishedDoi":"10.21203/rs.3.rs-8565242/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8565242/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigates the status and sources of marine debris pollution in mangrove ecosystems of the Cua Hoi estuarine area, Thanh Hoa Province, Vietnam. Marine debris was surveyed at three sites, including two mangrove forests (S1 and S2) and one adjacent beach site (S3), following standardized international monitoring protocols. A total of 1,192 debris items were collected from 27 sampling units. Mangrove site S1 exhibited the highest average marine debris density (8.68 n/m\u0026sup2;), while S2 showed a much lower density (0.67 n/m\u0026sup2;), and the beach site S3 recorded the lowest value (0.052 n/m\u0026sup2;). Plastic debris dominated the material composition, accounting for 92.79% of all items, with LDPE, PE, and PS being the most common polymer types. The dominant size class across all sites was 5\u0026ndash;25 mm, though mangrove areas retained a higher proportion of larger debris compared to the beach. Source analysis revealed that public litter was the primary contributor (78.27%), followed by fisheries debris (21.14%), indicating strong land - based and nearshore influences. Overall, the results highlight the role of mangrove forests as natural traps for marine debris and provide scientific evidence to support improved waste management and conservation strategies in estuarine mangrove ecosystems.\u003c/p\u003e","manuscriptTitle":"Marine debris pollution in mangrove at Cua Hoi, Thanh Hoa: Status and Source assessment","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-04 14:53:17","doi":"10.21203/rs.3.rs-8565242/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":"4ae800ef-acc6-4eb3-ab2d-812a993880c1","owner":[],"postedDate":"February 4th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-03-04T15:41:40+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-04 14:53:17","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8565242","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8565242","identity":"rs-8565242","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}