An estimated 80% of marine plastic pollution is caused by land-based activities. Obstacles to curbing land-based sources of marine plastic pollution in the Global South can be attributed to overburdened waste management facilities lacking the capacity to deal with rapidly increasing plastic waste generation. 

In India, the national government has introduced several policy regulations to promote source segregation and proper handling of all solid waste streams, including plastic. These regulations address marine plastic pollution with actions to ease the burden on waste management infrastructure and curb plastic leakage. Most notable is The Plastic Waste Management Rules, 2016 (henceforth, Rules), which was notified by the Ministry of Environment, Forests, and Climate Change of the Government of India. The Rules as per Clause 8 outline the responsibility of waste generators to minimize plastic waste, segregate at source, and ensure forward linkage of plastic waste to curb plastic leakage. The Rules also iterate the need for further alignment with The Solid Waste Management Rules, calling for decentralized waste management, where appropriate, to boost efficiency of waste management. 

Bulk waste generators, that is any entity producing more than 100 kg solid waste/day, alone account for 30-40% of the daily waste in India. This includes residential communities such as gated communities where the standard operating procedure so far has been the collection of co-mingled waste then sent to the corporation dustbins. 

The selected case study deep dives into a gated community in the city of Chennai, The Atrium, winner of the ‘Swachh Survekshan 2021’ award for efficient solid waste management to help illustrate a pathway to achieve zero-landfill status for residential communities. Through this, a framework for source segregation and decentralized waste management for gated communities in the Global South is outlined. The adoption of this framework has the collective potential to curb marine plastic pollution massively. 

How to cite: Govindarajan, G.: Framework to enable the transition to decentralized waste management in gated communities in the Global South to curb marine plastic pollution, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-76, https://doi.org/10.5194/oos2025-76, 2025.

Discussions on plastic pollution have predominantly focused on solid and water-insoluble polymers, such as polyethylene and polystyrene, spanning from large debris to microplastics. However, there is another category that has been largely overlooked: non-solid polymers used as flocculants.

Synthetic polymers used as flocculants in wastewater treatment can harm marine ecosystems in several ways: toxicity and bioaccumulation, disruption of natural aggregation processes and alteration of water quality posing a multi-faceted threat to marine ecosystems.

In recent years, there has been a growing interest in sustainable alternatives for wastewater treatment, particularly in reducing reliance on synthetic polymers as flocculants. Synthetic polymers’ environmental and potentially toxic residuals underscore the urgent need for biodegradable and eco-friendly alternatives.

 Chitosan, a biopolymer derived from shrimp shell waste, has shown potential as an effective natural flocculant.

This study evaluates chitosan’s flocculation performance compared to synthetic polymers through a series of jar tests to determine optimal dosing, turbidity reduction, and solid-liquid separation efficiency. In this study, real wastewater samples were used to evaluate chitosan’s effectiveness as a natural flocculant, ensuring practical relevance and enhancing the validity of the results. By using actual wastewater rather than simulated solutions, the research assessed chitosan’s performance under real-world conditions, which often include complex mixtures of organic and inorganic pollutants. This approach allowed for a more accurate comparison between chitosan and synthetic polymers, providing insights into chitosan’s practical feasibility and efficacy in diverse wastewater treatment scenarios. These findings suggest that chitosan is not only effective in reducing water turbidity but also supports efficient sludge management with lower moisture in the resulting dry cake.

Chitosan has demonstrated comparable efficacy to synthetic polymers in flocculation processes for wastewater treatment demonstrating chitosan's effectiveness as a feasible replacement.

Chitosan, repurposed from shrimp shell waste, embodies a circular economy approach by diverting biowaste from disposal and contributing to sustainable wastewater treatment.

As the world focuses primarily on solid plastic pollutants in oceans, this work aims to expand this dialogue to include other forms of synthetic polymers. This transition towards bio-based flocculants aligns with global sustainability goals and supports ocean health, as treated wastewater and synthetic polymers (flocculants) residues often ultimately enter marine ecosystems. By adopting chitosan, wastewater treatment facilities can reduce their reliance on non-renewable resources, mitigate pollution, and contribute to healthier aquatic ecosystems.

How to cite: Amorín, M.: Chitosan vs. Synthetic Polymers in Wastewater Treatment: Expanding the Plastic Pollution Dialogue through a Comparative Study on Performance, Environmental Impact, and Circular Economy, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-87, https://doi.org/10.5194/oos2025-87, 2025.

Freshwater inflow strictly controls the abundance of microplastic within coastal ecosystems. Sundarbans, the world’s largest contiguous mangrove ecosystem, faces the northern coastal Bay of Bengal and forms a source of anthropologic matter, including microplastics, to the ocean. In-depth spatial and temporal studies during a long-term monitoring program, SBOTS, indicated presence of high abundance of microplastics. Alongside, nearly 748 plastic-degrading enzymes (PDEs) hits were identified. These PDEs are capable of breaking down 17 types of polymers, both natural and synthetic types and notable seasonal variation. A diverse group of bacteria appear to house these PDEs within their genomes. Further genome-scale analyses revealed high numbers of heavy metals resistance genes (MRGs) and antibiotic resistance genes (ARGs). Co-occurrence network analysis suggested potential co-selection of plastic-degrading genes, MRGs and ARGs. Such co-occurrence patterns will have strong implications for disease dissemination within highly populated estuaries. Goals for SDG1 and SDG14 would both strongly be impacted should plastic pollution drive disease dissemination within high populated ecosystems such as the Sundarbans. It is thus imperative to further study such correlation patterns to understand ecosystem-level responses to microplastics within the changing ocean.

How to cite: Saini, N. and Bhadury, P.: Emergence of specialized plastic-degrading enzymes within highly dynamic coastal oceans, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-91, https://doi.org/10.5194/oos2025-91, 2025.

Since 1950 humans have introduced over 10 000 million metric tons (Mt) of plastic polymers into the Earth’s surface environment. Accounting for the dispersal and fate of mismanaged plastic waste and fragmented microplastics (MP) in the environment has been challenging. Recent studies have fueled debate on the magnitude of plastic transport from land to oceans, on the sinking and beaching of marine plastics and on the emission of marine microplastics to the atmosphere. In this study we define a global plastics cycle and budget, and develop a box model of plastics cycling, including the fragmentation and transport of MP within coupled terrestrial, oceanic and atmospheric reservoirs. We force the model with historical plastics production and waste data, and simulate global plastic and MP dispersal for different OECD policy scenarios towards 2060. Based on published observations, we suggest floating surface ocean plastics (2.1 Mt) are the tip of the marine plastics iceberg, as considerable amounts of plastics reside in the deep ocean (82 Mt), in shelf sediments (175 Mt), and on beaches (1.8 Mt). The model constrains current land to sea plastic transport to 14 Mt per year, implying 4 to 9 times larger leakage than OECD estimates. Model simulation of two ambitious policy scenarios show a peak in land to sea transport of total plastics of 23 Mt per year around 2045 and a decrease thereafter. Environmental concentrations of small MP remain high after 2060 due to continuous fragmentation of legacy mismanaged plastic waste on land and indicates the need for remediation of legacy plastic waste in policy instruments.

How to cite: Yakovenko, N., Segur, T., and Sonke, J.: A mass budget and box model of global plastics cycling, fragmentation and dispersal in the land-ocean-atmosphere system, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-150, https://doi.org/10.5194/oos2025-150, 2025.

This study presents a methodology aimed at advancing our understanding of plastic dispersion, accumulation, and stranding within the western Mediterranean basin. The approach is multi-scaled and employs the Ocean General Circulation Model NEMO coupled with the Lagrangian particle tracking simulator OceanParcels to simulate the 3D movement of plastic particles at large, mesoscale, and small scales. On a large scale, the methodology will examine the influence of major coherent current structures, such as the Northern Current to identify potential hotspots where plastics accumulate, strand, or settle on the seafloor and link them with climate indices. This large-scale perspective is essential to understand broad patterns of plastic distribution across the Mediterranean basin. Then, focusing on the mesoscale, plastic particles movement within an ocean eddy will be modelled, exploring the vertical and horizontal dynamics. This mesoscale analysis enables us to investigate how particles are trapped or redistributed within these features, shedding light on transport barriers effects. Lastly, the study narrows down to the small scale, where factors like wind and wave interactions are incorporated to enhance the model accuracy in simulating plastic and biomedia stranding events. This final stage will focus on biomedia (floating plastic discs used for wastewater treatment) stranding events to bridge model predictions with available observations from NGOs and citizen science efforts. The combined multi-scale approach will provide a comprehensive model for understanding plastic 3D dynamics from offshore to coast, enhancing targeted mitigation strategies in the Mediterranean Sea.

How to cite: Cunci, C., Molcard, A., Ourmières, Y., Barreau, C., Bencivengo, P., and Paiement, A.: Fate and 3D distribution of marine litter in the western Mediterranean basin from offshore to coast, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-154, https://doi.org/10.5194/oos2025-154, 2025.

The global transport model of marine plastics shows a disproportionate distribution of plastic pollution, estimating that approximately two-thirds of the plastic mass released from land into the ocean since the 1950s is likely to have stranded along the world’s shorelines. Furthermore, plastic debris transported by ocean currents and wind can travel vast distances across the world’s ocean far away from its source, eventually converging in one of the five subtropical gyres. The shores of Hawaiʻi are particularly impacted by plastic pollution due to its proximity to the North Pacific Subtropical Gyre, where the high concentration of floating plastic debris is known as the North Pacific Garbage Patch, NPGP. While surface surveys have documented significant concentrations of plastic pollution on Hawaiian beaches; our survey of buried plastic particles (> 0.5 mm) sampled down to 1 meter in 60 x 60 cm quadrats exposes a substantial hidden layer of pollution on the shores of Hawaiʻi. Our 1-meter sand column sampling from November 2022 to February 2024 reveals that 91% of the recovered plastic particles were buried below the surface layer (at 2-102 cm depth), with over 90% of these particles being small, brittle fragments primarily composed of polyethylene (PE) and polypropylene (PP). The recovered plastic particles, showed high brittleness and low molar mass (with particles having a molar mass < 10 kg mol^-1), signifying extensive weathering. This brittleness points to ongoing fragmentation under coastal conditions, heightening the risk of secondary microplastic formation. To better understand fragmentation behavior and rates of plastics in coastal environments, we conduct simulated swash zone tests on both weathered and unweathered PE and PP films (including the accelerated and naturally aged samples). These tests provide valuable insights into the pathways through which secondary microplastics form. High accumulation zones, such as coastal areas, could be key intervention points to prevent plastics from becoming buried or entering the marine ecosystem as secondary microplastics. Our study of buried plastics and fragmentation behaviour aims to refine models on plastic transport and accumulation, enhancing understanding of the coastal storage and re-mobilization processes of plastics between terrestrial and marine environments. Such insights into plastic fate and transformation dynamics support targeted beach cleanup prioritization in high-accumulation zones. They can inform the Legally Binding International Instrument on Plastic Pollution (LBII) and SDG 14.1 efforts, aiding global strategies to address legacy plastic pollution and refine remediation measures.

How to cite: Delorme, A. E., Le Gac, P.-Y., Lebreton, L., and Royer, S.-J.: Buried Plastic Pollution and Fragmentation Dynamics in Coastal Zones: Insights from Hawaiian Beaches, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-305, https://doi.org/10.5194/oos2025-305, 2025.

Plastics are extremely versatile materials used in a wide range of applications that support human activities and make our lives easier. However, increasing population growth, excessive consumption, and poor waste management have transformed these materials into an environmental threat. This research integrates findings from six European projects investigating sources, distribution, and impacts of plastics in aquatic and marine environments, with a particular focus on the Atlantic Ocean and on the North, Baltic, and Mediterranean Seas. The projects assessed key detection methods, pollution sources, distributions, accumulation, pathways, and impacts of plastics and microplastics, including novel aspects related to risk assessment using ecotoxicological data, nanoplastic detection in natural environments, assessment of eco-corona layers on submerged microplastics, and identification of accumulation hotspots in European waters. The geographical coverage of the projects also extended to areas along the Atlantic, African, and South American coasts. The studies investigated a range of plastic polymers, including conventional polymers and bioplastics, showing little differences in accumulation of organic and inorganic pollutants among them. Ecological risk assessment and ecotoxicology studies identified the dynamic nature of interactions between plastics and environmental matrices, and the release of leachates or adsorption of persistent organic pollutants and trace metals to the biofilm layers. The six projects identified new risks to ecosystem and human health, particularly regarding invasive species and toxicological impacts. All the projects participated in communication activities, fostering collaborations and enhancing public outreach. Policy recommendations emphasise the urgent need to regulate production and increase recycling efficiency to meet Paris Agreement targets, to regulate intentionally added chemicals to reduce potential human health risks, and to mitigate the spread of invasive species by intercepting items before they reach the open ocean. These insights support the development of policies that effectively manage marine plastic pollution and protect ocean & human health.

How to cite: Frias, J., Beck, A., Regoli, F., Vollertsen, J., Ziveri, P., and Sempere, R.: Sources, distribution and impacts of microplastics in the marine environment: an overview of the results of JPI Oceans projects, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-322, https://doi.org/10.5194/oos2025-322, 2025.

Plastic biodegradation in natural environment is performed by the microbial biofilm living on its surface (so-called “plastisphere”), whose molecular mechanisms remain a black box. Here, we present the DNA-stable isotope probing (DNA-SIP) coupled with -OMICs techniques as a powerful tool to describe the microorganisms actively involved in plastic biodegradation. We produced two types of ¹³C-labeled polyhydroxyalcanoates with short chain length (¹³C-scl-PHA) and medium chain length (¹³C-mcl-PHA), which were incubated as sole carbon source with natural marine plastispheres. Rapid biodegradation into carbon dioxide (CO₂) was found for scl-PHA, where much longer biodegradation rates were observed in the case of mcl-PHA. DNA-SIP coupled with 16S rRNA metabarcoding identified different active biodegraders according to the polymer types (mainly Marinobacter sp., Cellvibrionaceae and Alteromonas sp. for scl-PHA and Rasiella rasia and Leptonema sp. for mcl-PHA). Another study showed that metagenomics coupled with DNA-SIP identified several PHA-dehydrogenase systems according to the reconstruction of ¹³C-labeled metagenome-assembled genomes (MAGs). Finally, genomic and transcriptomic analysis of a novel bacterium Alteromonas plasticoclasticus isolated from the marine plastisphere confirmed the expression of PHA-dehydrogenase and revealed an example of entire metabolic pathways of scl-PHA biodegradation (Barbe et al. 2024). Overall, these results illustrate the potential of the stable isotope tracers to explore the functional reservoir of the plastisphere for discovering new processes involved in the plastic end-of-life in the marine environment.

Barbe et al. (2022) https://doi.org/10.1016/j.jhazmat.2024.133573

How to cite: Saint-Picq, C., Odobel, C., Hingant, M., Derippe, G., Albignac, M., Eyheraguibel, B., Cébron, A., Bruzaud, S., ter Halle, A., Barbe, V., and Ghiglione, J. F.: Revealing marine plastic degraders using stable isotope tracers, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-446, https://doi.org/10.5194/oos2025-446, 2025.

Global production of synthetic and natural textile fibres has more than doubled in the last 20 years, reaching 107 million tonnes in 2018 and is expected to reach 145 million tonnes in 2030 if business continues as usual. Synthetic fibers now account for nearly two-thirds of global fiber production and 14.5% of plastic production, although it is now clear that most of the fibers found in the environment are natural fibers of animal or plant origin, such as cotton and wool. The increasing consumption of textile products has led to the accumulation of large quantities of microfibers in the marine environment, with impacts and degradation times currently unknown. Textile fibers are now the most prevalent type of anthropogenic particle detected in microplastic pollution surveys worldwide, often accounting for 80-90% of microplastic counts. Substantial concentrations of microfibers have been detected globally in surface and subsurface waters, polar regions, deep-sea and coastal sediments, as well as terrestrial and freshwater ecosystems. Recent studies have reported the presence of these particles in atmospheric samples even in the most remote areas of the planet. Given their abundance, it is not surprising that fibers have also been found in food, drinking water, and human lungs, as well as in the digestive system of many aquatic and terrestrial organisms. The potential impacts of microfiber ingestion on marine organisms are still under investigation, but concerns exist regarding physical damage, reduced feeding, and the transfer of adsorbed pollutants. Furthermore, a wide variety of chemicals, including dyes, additives, and flame retardants, are used during natural and synthetic textile production, raising concerns about the role of fibers as carriers of hazardous substances in the environment. Future research should focus on understanding the degradation rates of different fiber types, the effects of microfibers on marine ecosystems, and the development of strategies to reduce microfiber pollution. This talk will review and summarize available information on the occurrence, sources, fate, accumulation, and transport of natural and synthetic fibers in the marine environment. Results and research experiences dealing with the distribution, movements, long-range transport, degradation, and sinking dynamics of fibers in ocean environments will be presented. The main methods used to quantify this contaminant in the marine environment and the critical knowledge gaps that require further research will also be discussed. By understanding the extent of microfiber pollution and its potential impacts on marine ecosystems, we can work towards sustainable textile production and consumption practices.

How to cite: Suaria, G.: Occurrence, sources, fate and transport of textile fibers in oceanic environments, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-507, https://doi.org/10.5194/oos2025-507, 2025.

This research, funded by the DOORS project, investigates marine plastic pollution along the Black Sea coastline, focusing on its transboundary movement and long-term environmental impacts. Through extensive field surveys on beaches in Romania, including Corbu, Mamaia, and Mangalia, the study assessed the types, sources, and quantities of marine litter, particularly plastics and microplastics. By harmonizing methodologies with European standards, such as the EU MSFD and OSPAR guidelines, this research contributes to understanding how plastic waste circulates within the Black Sea region and beyond, emphasizing the urgent need for cross-border strategies to mitigate plastic pollution. The findings highlight the significant role of human activity, tourism, and regional shipping in exacerbating plastic pollution, with implications for both marine ecosystems and human well-being. The study calls for enhanced regional collaboration and policy alignment to address the transboundary nature of ocean plastic pollution.

How to cite: Sitchinava, T.: Transboundary Tides: Investigating Marine Plastic Pollution and Its Impact on the Black Sea Coastline, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-528, https://doi.org/10.5194/oos2025-528, 2025.

This presentation will showcase the findings of the PermaGov diagnostic tool for institutional barriers identification as explored through two case studies focusing on marine plastics, namely Abandoned Lost and otherwise Discarded Fishing Gear (ALDFG) in the Baltic Sea region and agri-plastics as a source of marine pollution in the Mar Menor (Mediterranean Sea). Institutional barriers are critical obstacles to policy implementation and are symptoms of deeper governance issues. They hinder the achievement of policy targets such as those established in the European Green Deal. Within the literature, institutional barriers are described as “impasses in governance processes that are rooted in the institutional context of the adaptation situation” (Oberlack, 2017: 807; Eisenack et al. 2014). Thus, developing options to address them requires both identifying and unpacking the root causes of these barriers within their specific institutional context. Although there is a vast literature on institutional barriers, this work often fails to connect specific barriers with the institutional design attributes that cause them. For example, path dependency may arise from the rigidity of formal institutions, or from weak institutions that enable powerful actors to prevent new management practices from being implemented. Linking institutional barriers to specific institutional design attributes is key to developing solutions to overcome them.  

The PermaGov project co-developed and tested a diagnostic tool based on a literature review and insights from end-users and selected stakeholders to identify and analyze institutional barriers and design attributes within marine governance. For the Baltic Sea case study, it was identified that: insufficient data and lacking mechanisms to share and leverage information limits stakeholder understanding of the seriousness and scope of the issue as well as impedes decision makers opportunities to design targeted action; limited institutional incentives (e.g. unclear responsibilities) are potentially hindering participation of critical actors (especially amongst State bodies) within policy implementation; and conflicting interests combined with lacking economic incentives to address ALDFG in the region are slowing opportunities for cross-policy (i.e. ministries) and cross-sectoral (i.e. industries) collaboration. Within the Mediterranean Sea case study, there remains: a lack of innovative business practices to prevent plastic waste generation in line with the Extended Producer Responsibility approach; need to increase awareness raising for all citizens as well as industry-targeted trainings to reduce plastic consumption and emission; need to establish voluntary country agreements and develop mandatory requirements with the industry to reduce plastics; need to revise the current legal framework at the national levels (e.g., National Action Plans and/or Programmes of Measures); and the need to develop a database on the production and consumption of plastic products. The results demonstrate that a number of opportunities to improve marine plastics governance exist within the two case studies and offer a starting point to develop new strategies for addressing pollution within these two regions. Findings are also relevant to consider regarding further research for both institutional barriers and marine plastics more broadly.

How to cite: Boteler, B., Lafitte, A., Flannery, W., Dodd, L., and van Leeuwen, J.: Overcoming institutional barriers in marine plastics governance: lessons from the PermaGov diagnostic tool as explored in the Baltic and Mediterranean regional seas , One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-530, https://doi.org/10.5194/oos2025-530, 2025.

Plastic pollution is widely recognised as one of the biggest threats to the ocean. St Helena and Ascension Island, two of the UK’s most remote Overseas Territories (OTs), are custodians of vast ocean estates home to abundant and unique biodiversity. Their entire Exclusive Economic Zones were designated as Marine Protected Areas, in 2016 and 2019 respectively, to protect these valued marine and coastal environments: resulting in a cumulative 893,411km² of protected ocean in the heart of the South Atlantic. However, these environments, like those of many other small island nations, still suffer the pervasive impacts of plastic pollution: both from external sources and generated on the islands themselves. Currently, there are limited opportunities for people living on these islands to take positive action to protect their environment, resulting in a lack of community empowerment.  

The South Atlantic Plastic Project is a Darwin Plus and John Ellerman Foundation funded three-year project beginning in 2022, spanning across both St Helena and Ascension Island. With a focus on local actor engagement, knowledge-sharing and co-design, the project aimed to: perform a system mapping exercise to quantify and reduce plastic waste, creating a strategy to trial interventions for single-use plastic reduction and improve waste management efficiencies; research the characteristics and sources of plastic pollution and their associated threats to wildlife; and explore opportunities for international action through a new UKOTs and Crown Dependencies network.

The project will conclude and results will be finalised by the time of the One Ocean Science Congress. Representatives of the project team will present key project outputs from the following: intervention work undertaken on St Helena following extensive community engagement; a study investigating the origin of single-use plastic bottle debris on both islands; research to quantify the prevalence and composition of anthropogenic debris found in brown booby (Sula leucogaster) and green turtle (Chelonia mydas) nests on Ascension Island; and an investigation into ingested microplastics by inshore marine species in the waters of both islands.

It is hoped that the work undertaken on this project will serve not only as a catalyst to continue work addressing plastic pollution into the future locally, but will bear relevance to other small island nations in scaling of effective interventions and capacity sharing globally.

Project team: Ascension Island Government (AIG), St Helena National Trust (SHNT), St Helena Government (SHG), Zoological Society of London (ZSL).

How to cite: Austin, R. and Capel, T.: Turning the tide on plastic pollution in St Helena and Ascension Island, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-641, https://doi.org/10.5194/oos2025-641, 2025.

Plastics are recognized as an environmental threat and have been detected all over the planet.  Plastics in the environment will degrade and fragment due to physical, chemical and/or biological forces, creating smaller-sized particles, including micro- and nanoplastics. Most microplastic particles identified in the environment are secondary particles, i.e., fragments from larger pieces, and several show a level of degradation. However, information regarding how plastic degrades and fragments in the environment is lacking.

Polyethylene (PE), Polypropylene (PP), and Polylactic acid (PLA) plastic film were produced from pellets without adding additives. The films with a thickness of 40–50 μm were exposed to summer outdoor conditions for 46 days in different climate zones, including Arctic, Tropic, Nordic, and Mediterranean zones. After exposure, the films were analyzed using Fourier Transform Infrared Spectroscopy (FTIR), tensile strength, and imaged using Scanning Electron Microscopy (SEM).

Preliminary results indicate the highest degradation for PP followed by PE, and there is no sign of degradation for PLA in the tested conditions. Moreover, relationships between temperature, sun intensity, and the level of degradation occur.

How to cite: Mattsson, K., Aristéa de Lima, J., Sdiri, K., Lecchini, D., and Metian, M.:  Effects of Climate zones on plastic film degradation – Artic to tropic, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-731, https://doi.org/10.5194/oos2025-731, 2025.

Around three-quarters of oceanic plastic waste come from land-based sources and is mainly transported via rivers and estuaries.  However, not all plastics entering estuarine environments reach the open Ocean. Plastic litter and particularly microplastics, can accumulate in estuaries, creating pollution hotspots. This retention may be especially pronounced in macrotidal estuaries, where strong landward residual flows enhance trapping. The ANR PLASTINEST project aims to advance our understanding of the transport, trapping, and dispersion of microplastics within estuarine environments dominated by tides. Using innovative field measurements, controlled physical experiments, and enhanced numerical modeling, PLASTINEST offers new insights into the physical processes that govern particle transport under varying environmental conditions. Ultimately, this research contributes to the ongoing scientific debate on the assessment of plastic river input to the ocean and the existence of a “missing ocean plastic sink”, which to this day ignores the potential trapping role of tide-dominated estuaries. 

In this work, we present the methodology and key results of PLASTINEST, through three work packages:

In the first work package, laboratory experiments provided insights into the erodibility, bottom trapping, and settling dynamics of microplastics in the presence of muddy sediments characteristic of estuarine environments.  Both, bottom resuspension and settling behavior were primarily influenced by particles physical properties—shape, density, and size. The presence of cohesive sediment has a secondary influence on microplastics transport in turbid estuaries by increasing the critical shear stress of microplastics deposited on the bed and by promoting flocculation in the water column. These two processes favor the retention and accumulation of particles in turbid estuaries.

In work package 2, the spatio-temporal variability of microplastics is evaluated across a macrotidal estuary, in relation to key physico-chemical parameters, through ongoing field campaigns. A novel protocol for sampling microplastics has been implemented in the Gironde estuary, using an innovative in-situ filtration system. Data post-processing will elucidate   on the role of hydrodynamics (tides, river discharge, longitudinal tidal and salinity gradient, vertical mixing) on microplastic concentration variability and distribution patterns within the estuary.

Numerical modelling tools  for the transport of plastic debris were improved to include key microplastic transport processes in work package 3. The implementation of these in the Gironde Estuary provided key insights on the role of environmental factors and transport mechanisms on the trapping and dispersion patterns of microplastics across different temporal scales (from intratidal to seasonal) for floating and sinking particles. Beaching, convergent currents and tidal pumping were identified as key trapping mechanism retaining particles inside the estuary.   Interestingly, during wet period, the high river discharge flushes important amount of floating particles into the Ocean , while settling particles remain in the estuary.

By synthesizing insights from earlier findings, PLASTINEST will provide a comprehensive view of how plastic particles are transported, accumulate, and are periodically exported to the Ocean within tide-dominated estuarine systems.

How to cite: Ruiz-Gonzalez, V., John Kaimathuruthy, B., Defontaine, S., Sous, D., Gomit, G., Steinmetz, C., Lam-Detrait, C., Romero-Ramirez, A., Marieu, V., Jarny, S., Huybrechts, N., Rosignol, L., Lefebvre, C., Lecomte, S., Cachot, J., Sottolichio, A., and Jalon-Rojas, I.: Tide-dominated estuaries as gateways and filters of plastic pollution to the Ocean: insights from the PLASTINEST project, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-785, https://doi.org/10.5194/oos2025-785, 2025.

Plastic pollution is a major issue in marine ecosystems. Plastic items can easily be mismanaged or littered at the end-of-life, but leakage to the environment happens throughout the life cycle of any product containing plastic. The leaked and littered plastic particles can be of any shape and size, usually distinguished into micro- (smaller than 5 mm) and macroplastics (larger than 5 mm). With the ongoing, and soon to be concluded, plastic treaty, solutions and actions are required to reduce and hopefully stop macroplastics entering aquatics environment. As macroplastics are one of the major sources of microplastics through fragmentation, microplastics would be consequently reduced.

To be able to assess the magnitude of impacts from plastic pollution, we need tools that can address multiple impacts across value chains. One such tool used for decision-making is Life Cycle Assessments which can help by evaluating and comparing similar products for informing the best suitable solutions. However, plastic pollution is currently not well covered in the framework. Recently, Life Cycle Impact Assessments (LCIA) models that assess impacts from plastics that are released directly to the ocean have been developed. Although work has been done on certain impact pathways, most notably for microplastics, fate modeling, describing how plastic is transported through the environment, still needs to be improved and expanded to fill the methodological Fate Factors (FF) gaps in LCIA. One particular need is to cover how macroplastic from land-based activities will be mismanaged (MPW), transported to, and affect different marine ecosystems through environmental and hydrological processes.

Through existing conceptual and probabilistic observations-based models, our approach consists of quantifying novel FF for LCIA use. The FFs have global coverage while being regionalized per water basin. We quantify the fate of macroplastic items, by including the influence of environmental factors, such as wind, runoff, and land use. These factors affect the mobilization, transport, and accumulation of plastics pollution from land into marine environments. Transport on land is modeled based on the conceptual framework of the Plastic Pathfinder¹ using grid cells-based movement with respect to environmental factors and mapping the plastics mobilization and accumulation on the coasts or in in rivers. Once plastics have reached a river, this portion of MPW is then multiplied by the probabilities of a river to release plastics in the ocean based on observations, discharge, and Strahler order from Meijer et al. (2021)². FFs can be used to update existing LCIA models which will help accounting and assessing the regional and global impacts of plastic pollution from land to sea in marine environments ultimately improving decision making.

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(1)       Mellink, Y.; van Emmerik, T.; Kooi, M.; Laufkötter, C.; Niemann, H. The Plastic Pathfinder: A Macroplastic Transport and Fate Model for Terrestrial Environments. Front. Environ. Sci. 2022, 10. https://doi.org/10.3389/fenvs.2022.979685.

(2)       Meijer, L. J. J.; Van Emmerik, T.; Van Der Ent, R.; Schmidt, C.; Lebreton, L. More than 1000 Rivers Account for 80% of Global Riverine Plastic Emissions into the Ocean. Sci. Adv. 2021, 7 (18), eaaz5803. https://doi.org/10.1126/sciadv.aaz5803.

How to cite: Deschênes, C. E., Høiberg, M. A., Dorber, M., and Verones, F.: Is it fate? Quantifying the probabilities of mismanaged macroplastics reaching the ocean within the Life Cycle Assessment framework , One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1057, https://doi.org/10.5194/oos2025-1057, 2025.

Recycling marine (ocean and beach) plastics is essential for reducing pollution, conserving resources, and lessening the environmental impacts of plastic production and waste. Traditional recycling methods, however, struggle with the mixed, degraded, and potentially contaminated nature of ocean plastic waste, which limits the quality of recovered materials. Solvent-based recycling is emerging as a promising approach, as it selectively dissolves plastics, allowing for purification while preserving material properties, and retaining contaminants in the solvent phase. This method is applicable to various polymers, including polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and even mixed polymer waste.

In this study, a solvent-based recycling method combined with an extractive cleaning process is used to recover high-quality PE and PP from ocean plastics. Additionally, the method removes hazardous components often associated with plastic production, such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), UV stabilizers, antioxidants, bisphenol A, brominated flame retardants (BFRs), and phthalates. Some of these contaminants are listed as chemicals of high concern by the European Chemicals Agency (ECHA). Previous applications of this method have proven effective in removing flame-retardant additives from electronic waste [1] and cleaning diethylhexyl phthalates from PVC flooring waste [2], demonstrating its potential for recycling even heavily contaminated plastics

Mixed Ocean plastic waste samples for this study were harvested by The Ocean Clean Up company from the Great pacific garbage patch. Preliminary dissolution tests showed that the process could selectively separate PE or PP from the mixed waste through process adjustments such as dissolution temperature and solvent selection. HT-GPC-IR analysis of the recycled polymer showed an average molecular weight of 1.70×10⁵g mol^-1 for PE and 1.42×10⁵ g mol^-1 for PP. IR analysis of both PE and PP revealed similar C-H stretches around 2850-2950 cm^-1 and CH₂ bending around 1464 cm^-1. PP further displayed a distinctive methyl group absorption at 1375 cm^-1 and CH₃ bending at 850-889 cm^-1. Furthermore, 13C-NMR analysis of mixed plastic samples from beaches indicated up to 50% PP with no detectable copolymers. To assess organic contaminants, samples were analyzed for phthalates using gas chromatography-flame ionization detection (GC-FID), bisphenol A using high-performance liquid chromatography-mass spectrometry (HPLC-MS), and UV-328 via gas chromatography-mass spectrometry (GC-MS) prior to extractive cleaning. Initial results showed an average of 107 ng/g bisphenol A, 296 µg/g butyl benzyl phthalate (BBP), and 5323 ng/g UV-328. Preliminary extractive cleaning trials demonstrated the potential to significantly reduce contaminants ie. BBP levels by up to 85%.

This research highlights dissolution recycling as an effective method for recovering high-quality polymers while removing organic contaminants from ocean plastics. Ongoing work seeks to further optimize dissolution and cleanup conditions to target additional contaminant classes. Future research will also address the removal of potentially toxic heavy metals, ensuring the safe reuse of recycled marine plastics.

[1] Schlummer M. et al., Waste Management & Research, 2006, 24(6), 573-583.

[2] Wagner S., Schlummer M., Resources Conservation and Recycling, 2024, 211, 107889.

How to cite: Kibuta, C., Schmidt, M., Schlummer, M., Buettner, A., and Fell, T.: Can high-quality polymers be recovered from marine plastics using solvent-based recycling processes – and thus decontaminate plastic waste?, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1137, https://doi.org/10.5194/oos2025-1137, 2025.

Hamdi Ben Boubaker, Sana Ben Ismail , Emna Derouiche, Wael Koched, Hela Jaziri, Khouloud Boltane, Hajer el Maleh, Siwar Dabboub

National Institute  of Marine sciences and Technologies (INSTM), Laboratory of the marine environment - Tunisia

Abstract:

Within the scope of EU-funded initiatives like COMMON and Plastic Busters CAP ( INSTM Team) in Tunisia , I've harnessed the power of photography to document the prevalent issue of marine debris and its profound impact on ocean ecosystems. These endeavors seek to tackle marine litter through holistic management strategies and community involvement.

During field expeditions and awareness days organized in Tunisia, I've captured a diverse array of marine litter, and people. These evocative images serve as potent instruments for raising awareness and igniting action towards cleaner oceans, revealing the hidden toll of marine debris on ecosystems and biodiversity in Tunisia.

I'll delve into the challenges encountered in capturing these images, including adverse weather conditions during field work ,access limitations to polluted areas and technical challenges. Furthermore, I'll explore the diverse avenues through which these photos have been leveraged to engage the public and bolster environmental initiatives, spanning campaigns, social media outreach, and exhibitions.

Through the power of photography storytelling, we underscore the pressing need for collective action to tackle marine pollution in Tunisia . Our objective is to deepen understanding, promote sustainable behaviors, and underscore the significance of individual and community contributions in safeguarding our Mediterranean sea.

How to cite: Ben Boubaker, H., Ben Ismail, S., Derouiche, E., Koched, W., Jaziri, H., Boltane, K., El Maleh, H., and Dabboub, S.: Capturing marine debris and people through photography storytelling: Insights from COMMON and Plastic Busters CAP Projects in Tunisia, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1244, https://doi.org/10.5194/oos2025-1244, 2025.

The PLASMA project (Pollution aux microplastiques du lagon de Mayotte) is a multidisciplinary project that began in 2022. It is funded by the Mayotte National Marine Park and aims to gain a better understanding of the state of microplastic pollution in what can be considered one of the most beautiful lagoons in the world. Indeed, the Mayotte lagoon, known for its exceptional biodiversity, is currently facing major threats from human pressure and overpopulation, and the quantity of these micropollutants and their effects on the environment (fauna, marine flora, coral, etc.) need to be assessed. This project is underpinned by a key question. Where do these microplastics come from? Do they come from the local practices of local people? Or do they come from far away, transported by marine currents and accumulated in the lagoon by the particular hydrodynamic circulation of channel lagoons?

Modelling work has shown the existence of zones of accumulation and, conversely, zones of dispersion. In addition, a participatory science initiative has been launched to better understand the origin of these microplastics and to raise awareness of the consequences of their presence, first in river water and then in the lagoon. Pupils from Mayotte's secondary schools became budding researchers, sampling (and counting) microplastics in the river near their school, and carrying out ethnographic surveys of the lagoon.

How to cite: Chevalier, C., Leborgne, M., Strady, E., Marchessaux, G., Chkili, O., Mattei, C., Devault, D., Pagano, M., Rodier, M., Ruitton, S., Thibault, D., Durieux, G., Juhles, I., Jullia, H., Chevalier, A., Marco-Just, V., Bigot, L., Chabanet, P., and Roger, C.: Plasma Project, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1452, https://doi.org/10.5194/oos2025-1452, 2025.

Microplastics (MPs) contaminate all marine compartments, from the surface down to the seafloor. Despite a growing number of studies, accurately estimating MP stocks in marine environments remains challenging, as the water column and the sediment remain largely understudied. Most studies focus on MP present at the surface, leading to an observational bias that could contribute to the "Missing Plastic Paradox".

Hosting 150 million inhabitants, the Mediterranean Sea faces high and diverse anthropogenic pressures. Ranked as the sixth greatest accumulation zone for marine litter, it is assumed to concentrate 7% of all global MPs, an estimation that could be reconsidered if all marine compartments were considered. Here we present the results of an integrative survey of large MP (>300μm) distribution, performed on a biannual basis between 2020 and 2023 in the Bay of Marseille, second largest city (by population) and one of the most important ports in France. We provide quantitative data on MP contamination level and spatiotemporal distribution in (1) surface waters, (2) water column, and (3) surface sediments at 15 stations. For the first time in the area, we also provide an historical record of MP contamination since the 50's based on a short undisturbed sediment core.

Mean concentrations of 5.83±1.97 MP.m^-3 and 865±63 MP.kg dry sediment^-1 were estimated in surface waters and sediments, respectively. No spatiotemporal trends were statistically demonstrated, except in February 2020 with abnormally high concentration of MP in surface water (22.47±8.85 MP.m^-3 on average). We assume that this episodic high level of contamination results from repeated intrusions of the Rhône river plume into the bay in February 2020, as revealed by the MARS3D-RHOMA model.

In the water column, MPs were found at all depths, with concentrations averaging 1.43 ± 0.38 MP.m^-3 at 5 meters below the surface, and 0.59 ± 0.38 MP.m^-3 at the bottom (approx. 40 - 70m). Overall, MPs found below the surface represent more than 99% of the total MP mass collected in the entire water column. By contrast to surface water, vertical MP distribution exhibits a clear contrast between late winter and late summer, suggesting hydroclimatic processes exert a major control on distribution and transport in the water column (e.g., wind strength vs stratification). Interestingly, fibres with light and medium density (PP, PE, Nylon) were the dominant MP types found from the surface down to the sediment, questioning vertical transport processes at work in the area. 

Historical record of MP accumulation in the sediment matches well the global increase in plastic production since the 50's. MP burial rate increased by barely less than 500% since the 90's, and remained stable since then despite local and global plastic management policies. This original data set will enable, for the first time, to provide a quantitative estimation of MP stocks accumulated in water and sediment compartments along the 57km coastline of the Bay of Marseille. 

How to cite: Alcaïno, A., Licari, L., Vidal, L., Chevalier, C., Conrod, S., Dauvier, J., Delanghe, D., de Garidel-Thoron, T., Grelaud, M., Malengros, D., Mazur, J.-C., Montavon, V., Paillès, C., Pinazo, C., Sulpis, O., Surmont, A., and Rigaud, S.: CONTAMINATION BY MICROPLASTICS IN THE BAY OF MARSEILLE (Gulf of Lion, France): AN INTEGRATIVE DIAGNOSIS FROM THE SURFACE TO THE SEAFLOOR, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1516, https://doi.org/10.5194/oos2025-1516, 2025.

A candidate of the fate of ocean plastics is fragmentation to small microplastics unmonitorable in the current observation framework. In the present study, the vertical distribution of small microplastics (S-MPs; 10 μm < sizes < 300 μm) and its relation to water masses were investigated by seawater samplings and hydrographic surveys from the sea surface to 1000-m depth in the North Pacific Ocean. The average ± standard deviation of S-MP concentrations in 12 layers of four stations were 6910 ± 2620 particles m^–3. The S-MP concentrations become high in isopycnal layers between potential densities of 23 σ_θ and 25σ_θ and again rapidly increased beneath the North Pacific Intermediate Water (NPIW) with the salinity minimum around 26.6–27.0σ_θ isopycnal layers. A simple model approach to reproduce the observed S-MP distribution suggested two pathways for S-MPs originally floating in surface convergence zones. One is the fast settling of S-MPs via biological processes from the surface euphotic layer to deep layers which are never outcropped at the sea surface like NPIW. Meanwhile, the weak settling of S-MPs of which density become close to neutral causes the other pathway, that is, the along-isopycnal subduction from isopycnal layers outcropped at the sea surface to intermediate layers. In fact, microplastic concentrations at the sea surface between 23σ_θ and 25σ_θ contour curves (archived in the AOMI database) become larger than those in the surrounding isopycnal layers in a similar fashion to the S-MP vertical profile. S-MPs are also abundant in the same surface area along with MPs, as is likely due to the surface convergence, so that the surface S-MPs are suggested to migrate below the sea surface by the along-isopycnal subduction. The global inventory of near-neutral S-MPs with weak settling is expected to be greater in intermediate layers, requiring carefully designed field surveys for both sampling and subsequent processing.

How to cite: Isobe, A. and Kuroda, M.: Settling and along-isopycnal subduction of small microplastics into intermediate layers over the North Pacific Ocean, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-921, https://doi.org/10.5194/oos2025-921, 2025.