The plastic pollution crisis demands establishing a global science-policy framework to achieve a circular economy for plastics. Such a framework should be based on scientific evidence to evaluate the success of mitigating plastic pollution in terrestrial, freshwater, and marine environments. This work focuses on the role of rivers as main pathways connecting land-based plastic to the marine environment. Existing large-scale estimates of river plastic input to the ocean used different and contrasting choices in their modelling approaches, e.g., including highly variable number of rivers in the global outputs, differing item-to-mass conversion factors, and extrapolations from microplastic to macroplastic loads. We observed that estimates can diverge up to five orders of magnitude when global models are applied to individual rivers, denoting large uncertainties in the data and approaches used to extrapolate results for the most polluting rivers at World and European scales. These uncertainties would not allow for a quantitative assessment of the effectiveness of plastic mitigation measures, as the expected reduction of plastics in the environment would vary within a much lower range than the modelled estimates. The way forward to provide meaningful assessments involves collecting comparable data using harmonized sampling methods, increasing fundamental understanding of plastic transport and retention dynamics, and a better understanding of spatio-temporal variability of plastic transport in rivers.

Abiotic vectors of plastic and their impact in natural areas have been extensively studied, whereas biotic vectors have received less attention. Recent studies demonstrate that birds can act as powerful agents of plastic transport, moving large quantities of plastic from landfills to natural habitats through a process called biovectoring, causing pollution hotspots. While most studies have focused on single species, the present research broadens this approach. Here we compared the quantity, composition and spatio-temporal variation of plastic biovectoring among three co-existing waterbird species foraging on landfills near a coastal wetland: white storks, yellow-legged gulls, and lesser black-backed gulls in Cádiz Bay Important Bird Area (CBIBA; 152 km2), Spain. We analysed 177 regurgitated pellets (42-74 per species), weighed their plastic content and used FTIR-technology to identify and classify polymer composition. We then characterized each plastic item by shape, size and colour, enabling interspecific comparisons using multiple correspondence analysis. Finally, we combined census, GPS data and the plastic obtained from the pellets to develop a daily plastic loading model for each species. We found that white storks transported the most plastic per pellet (0.14 g by median), compared to 0.034 g for yellow-legged and 0.026 g for lesser black-backed gulls. In general, gulls carried similar types of plastic items, with more film and larger sizes than storks. In total, 531 kg of plastics were estimated to be biovectored into the CBIBA from landfills in 2022, with deposition being higher in winter and lesser black-backed gulls transporting about 54 % of the total, followed by yellow-legged gulls with 30 % and white storks with 16 %. In addition, we also identified major seasonal and spatial differences among species. Our results highlight the importance of using a multi species approach to plastic biovectoring, which is essential to understand and estimate its environmental impact, and to inform management strategies.

Despite ongoing negotiations to establish a Global Plastics Treaty aimed at ending plastic pollution, agriculture remains an often-overlooked source of marine litter. While most global assessments emphasize take-out consumer activity and fishing as dominant contributors, these broad analyses may fail to capture regionally relevant sources. Here, we conducted field sampling across coastal and inland transects using a combination of shoreline surveys, dry riverbed inspections, and marine debris collection to quantify and classify plastic waste linked to agricultural activity. Our results show that agricultural plastic debris is prevalent even over 100 km downstream of cultivation hotspots. We identify dry riverbeds in agricultural landscapes as transient reservoirs that trap plastic during dry seasons, releasing large quantities into marine environments during episodic rainfall events. These findings underscore the need for management strategies that incorporate agriculture as a significant source of marine plastic pollution, particularly considering the projected rise in agricultural plastic use.

Anthropogenic litter, such as plastic, is investigated by the global scientific community from various fields employing diverse techniques. The goal is to assess and finally mitigate the pollutants' impacts on the natural environment. Plastic litter can accumulate in different matrices of aquatic and terrestrial ecosystems, impacting both biota and ecosystem functioning. Detection and quantification of macroplastics, and other litter, can be realized by jointly using visual census and remote sensing techniques. The primary objective of this research was to identify the most effective approach for monitoring macroplastic litter in riverine and marine environments through a comprehensive survey based on the experiences of the scientific community. Researchers involved in plastic pollution evaluated four litter occurrence and flux investigation methods (visual census, drone-based surveys, satellite imagery, and GPS/GNSS trackers) through a questionnaire. Traditional visual census and drone deployment were deemed as the most popular approaches among the 46 surveyed researchers, while satellite imagery and GPS/GNSS trackers received lower scores due to limited field validation and short performance ranges, respectively. On a scale from 0 to 5, visual census and drone-based surveys obtained 3.5 and 2.0, respectively, whereas satellite imagery and alternative solutions received scores lower than 1.2. Visual and drone censuses were used in high, medium and low-income countries, while satellite census and GPS/GNSS trackers were mostly used in high-income countries. This work provides an overview of the advantages and drawbacks of litter investigation techniques, contributing i) to the global harmonization of macroplastic litter monitoring and ii) providing a starting point for researchers and water managers approaching this topic. This work supports the selection and design of reliable and cost-effective monitoring approaches to mitigate the ambiguity in macroplastic data collection, contributing to the global harmonization of macroplastic litter monitoring protocols.

Worldwide, governments are implementing strategies to combat marine litter. However, their effectiveness is largely unknown because we lack tools to systematically monitor marine litter over broad spatio-temporal scales. Metre-sized aggregations of floating debris generated by sea-surface convergence lines have been reported as a reliable target for detection from satellites. Yet, the usefulness of such ephemeral, scattered aggregations as proxy for sustained, large-scale monitoring of marine litter remains an open question for a dedicated Earth-Observation mission. Here, we track this proxy over a series of 300,000 satellite images of the entire Mediterranean Sea. The proxy is mainly related to recent inputs from land-based litter sources. Despite the limitations of in-orbit technology, satellite detections are sufficient to map hot-spots and capture trends, providing an unprecedented source-to-sink view of the marine litter phenomenon. Torrential rains largely control marine litter inputs, while coastal boundary currents and wind-driven surface sweep arise as key drivers for its distribution over the ocean. Satellite-based monitoring proves to be a real game changer for marine litter research and management. Furthermore, the development of an ad-hoc sensor can lower the minimum detectable concentration by one order of magnitude, ensuring operational monitoring, at least for seasonal-to-interannual variability in the mesoscale. A new technological development for detecting floating litter from space was tested in the Mediterranean Sea. Using satellites currently in orbit, researchers achieved an unprecedented view of the emissions and accumulation areas of marine litter.

General context: Gulls ingest plastic and other litter while foraging in open landfills, because organic matter is mixed with other debris. Therefore, gulls are potential biovectors of plastic pollution into natural habitats, especially when they concentrate in wetlands for roosting. Novelty: We quantified, for the first time, the flow of plastic and other anthropogenic debris from open landfills to a natural lake via the movement of gulls. We focused on Fuente de Piedra, an inland closed-basin lake in Spain that is internationally important for biodiversity. Methodology: In 2022, we sampled gull pellets regurgitated in the lake by lesser black-backed gulls Larus fuscus that feed on landfills, as well as their faeces, then characterized and quantified debris particles of >= 0.5 mm. By combining GPS and census data from 2010 to 2022, together with plastic quantification based on FTIR-ATR analysis, we estimated the average annual deposition of plastic and other debris by the wintering gull population into the lake. Main results: 86 % of pellets contained plastics, and 94 % contained other debris such as glass and textiles. Polyethylene (54 %), polypropylene (11.5 %) and polystyrene (11.5 %) were the main plastic polymers. An estimated annual mean of 400 kg of plastics were moved by gulls into the lake. Only 1 % of plastic mass was imported in faeces. Discussion: Incorporating the biovectoring role of birds can provide a more holistic view of the plastic cycle and waste management. Biovectoring is predictable in sites worldwide where gulls and other waterbirds feed in landfills and roost in wetlands. We discuss bird deterrence and other ways of mitigating debris leakage into aquatic ecosystems.

In this work, a comprehensive characterization of microplastic samples collected from unique geographical locations, including the Mediterranean Sea, Strait of Gibraltar, Western Atlantic Ocean and Bay of Biscay utilizing advanced hyperspectral imaging (HSI) techniques working in the short-wave infrared range (1000–2500 nm) is presented. More in detail, an ad hoc hierarchical classification approach was developed and applied to optimize the identification of polymers. Morphological and morphometrical attributes of microplastic particles were simultaneously measured by digital image processing. Results showed that the collected microplastics are mainly composed, in decreasing order of abundance, by polyethylene (PE), polypropylene (PP), polystyrene (PS) and expanded polystyrene (EPS), in agreement with the literature data related to marine microplastics. The investigated microplastics belong to the fragments (86.8%), lines (9.2%) and films (4.0%) categories. Rigid (thick-walled) fragments were found at all sampling sites, while film-type microplastics and lines were absent in some samples from the Mediterranean Sea and the Western Atlantic Ocean. Rigid fragments and lines are mainly made of PE, whereas PP is the most common polymer for the film category. Average Feret diameter of microplastic fragments decreases from EPS (3–4 mm) to PE (2–3 mm) and PP (1–2 mm). The setup strategies illustrate that the HSI-based approach enables the classification of the polymers constituting microplastic particles and, at the same time, to measure and classify them by shape. Such multiple characterization of microplastic samples at the individual level is proposed as a useful tool to explore the environmental selection of microplastic features (i.e., composition, category, size, shape) and to advance the understanding of the role of weathering, hydrodynamic and other phenomena in their transport and fragmentation.

Systematic seafloor surveys are a highly desirable method of marine litter monitoring, but the high costs involved in seafloor sampling are not a trivial handicap. In the present work, we explore the opportunity provided by the artisanal trawling fisheries to obtain systematic data on marine litter in the Gulf of Cadiz between 2019 and 2021. We find that plastic was the most frequent material, with a prevalence of single-use and fishing-related items. Litter densities decreased with increasing distance to shore with a seasonal migration of the main litter hotspots. During pre-lockdown and post-lockdown stages derived from COVID-19, marine litter density decreased by 65%, likely related to the decline in tourism and outdoor recreational activities. A continuous collaboration of 33% of the local fleet would imply a removal of hundreds of thousands of items each year. The artisanal trawl fishing sector can play a unique role of monitoring marine litter on the seabed.

Estimates of plastic input from rivers to ocean vary by up to five orders of magnitude. Harmonization of field data used to calibrate models and a better understanding of transport processes are key to reducing these uncertainties, contributing to meaningful assessments of the effectiveness of environmental regulations against plastic pollution.

Artificial turf (AT) is a surfacing material that simulates natural grass by using synthetic, mainly plastic, fibers in different shapes, sizes and properties. AT has spread beyond sports facilities and today shapes many urban landscapes, from private lawns to rooftops and public venues. Despite concerns regarding the impacts of AT, little is known about the release of AT fibers into natural environment. Here, for the first time, we specifically investigate the presence of AT fibers in river and ocean waters as major conduits and final destination of plastic debris transported by water runoff. Our sampling survey showed that, AT fibers - composed mainly of poly-ethylene and polypropylene - can constitute over 15% of the mesoplastics and macroplastics content, suggesting that AT fibers may contribute significantly to plastic pollution. Up to 20,000 fibers a day flowed down through the river, and up to 213,200 fibers per km2 were found floating on the sea surface of nearshore areas. AT, apart from impacting on urban biodiversity, urban runoff, heat island formation, and hazardous chemical leaching, is a major source of plastic pollution to natural aquatic environments.

Anthropogenic litter accumulates along coasts worldwide. In addition to the flowing litter load, wind, sea currents, geomorphology and vegetation determine the distribution of litter trapped on the sandy coasts. Although some studies highlighted the role of dune plants in trapping marine litter, little is known about their efficiency as sinks and about the small-scale spatial distribution of litter across the dune area. Here, we explore these gaps by analysing six plant species widespread in Mediterranean coastal habitats, namely Echinophora spinosa, Limbarda crithmoides, Anthemis maritima, Pancratium maritimum, Thinopyrum junceum, and Salsola kali. The present study analyses for the first time the capture of litter by dune vegetation at a multi-species level, considering their morphological structure. Data on plastic accumulation on dune plants were compared with unvegetated control plots located at embryo-dune and foredune belts. We found that dunal plants mainly entrapped macrolitter (> 0.5 cm). Particularly, E. spinosa, L. crithmoides, A. maritima and P. maritimum mostly accumulated litter in the embryo dune while T. junceum and S. kali entrapped more in the foredune area. Moreover, beach litter was mainly blocked at the edge of the plant patches rather than in the core, highlighting the 'Plant-edge litter effect'. As A. maritima and S. kali entrapped respectively more litter in embryo and foredune habitats, these species could be used to monitor and recollect litter. In this light, our findings provide further insight into the role of dune plants in the beach litter dynamics, suppling useful information for beach clean-up actions.

Research into plastic pollution has extensively focused on abiotic vectors, overlooking transport by animals. Opportunistic birds, such as white storks (Ciconia ciconia) often forage on landfills, where plastic abounds. We assess plastic loading by ingestion and regurgitation of landfill plastic in Cadiz Bay, a major stopover area for migratory white storks in south-west Spain. On average, we counted 599 storks per day moving between a landfill and a complex of salt ponds and marshes, where they regurgitated pellets that each contained a mean of 0.47 g of plastic debris, dominated by polyethylene. Modelling reliant on GPS tracking estimated that 99 kg and >2 million particles of plastic were biovectored into the wetland during 2022, with seasonal peaks that followed migration patterns. GPS data enabled the correction of field censuses and the identification of plastic deposition hotspots. This study highlights the important role that biovectoring plays in plastic transport into coastal wetlands.

Rivers and estuaries are a key transport pathway for plastics from inland to the sea. These systems are subject to fluctuations depending on sources of plastics and local environmental factors, causing variation in the plastic concentration up to several orders of magnitude within limited time ranges. Due to this large variability, in freshwater systems, it is challenging to obtain representative monitoring data. This study presents a new methodological approach to determine the number of plastic particles needed to obtain representative data for plastic pollution characterization in estuarine waters. The method used monthly in situ observations during a period of two years in the Guadalquivir River estuary (SW Spain). The data allowed the characterization of plastic concentrations across all size categories (micro-, meso- and macroplastics). The items were categorized into different size classes (<5 mm, 5-25 mm, 2.5-5 cm, 5-10 cm and >10 cm) and a resampling simulation was applied to generate 95% confidence intervals for plastic concentration variability. Our results suggest that, when using a limited number of samples, there is an underestimation of all size classes, e.g., up to three quarters of the samples could underestimate the average number of particles. Differences up to 3 orders of magnitude can be established between the lower (<5 mm) and the higher (>10 cm) size class in terms of number of particles sampled. This approach will help to optimize time and define sample size for specific particle size classes to improve plastic monitoring in freshwater environments.

The accelerated discard and mismanagement of human-made products are resulting in the continued input of litter into the oceans. Models and field observations show how floating litter can accumulate in remote areas throughout the global ocean, but far less is known about the non-floating litter fraction. Seagrass meadows play an important role in the sediment and natural-debris dynamics, and likely also in the storage and processing of non-floating litter. In this work, non-floating litter was studied across six Posidonia oceanica meadows. Litter accumulated mainly around the landside edge of the meadow. The outer margin of the edge predominantly trapped macro-litter, whilst microplastics accumulated mainly along the inner margin. On average, macro-litter concentrations increased 3-fold after heavy rainfall. Retention of non-floating litter by coastal meadows facilitates the recurrent landward-seaward conveyance of the easily-transportable litter (mainly plastic items) and its fragmentation before it is buried or transferred to deeper areas.

&lt;p&gt;Rivers act as pathways transporting anthropogenic waste from inland sources to the sea, including large quantities of plastic. Estuaries are rich and diverse environments where the interaction between fluvial processes and the tidal regime results in complex dynamics that affects residence time and net transport plastics in the water column. The use of plankton nets (small mesh sizes, e.g. &lt; 500 &amp;#181;m) to collect microplastic samples allows characterizing plastic particles of different sizes. At the same time, given the variability in plastic particles abundance, the limitation in number of samples and/or volume filtered per sample, may cause a large bias in such characterization. Generally, particle abundance decreases toward larger particle sizes, and therefore the collection of representative samples for a certain plastic size range depends on sampling effort. Here, we analyze abundance and weight of micro- (&lt; 5mm) and mesoplastics (5-25 mm) collected in estuarine waters at the River Guadalquivir through bi-monthly monitoring over one year. Our results demonstrate that establishing ratios between micro- and meso-plastics concentrations can lead to large uncertainties when a limited number of samples is used in the analysis, causing strong bias in the extrapolation of mass budgets for mesoplastics. Collecting representative samples for mesoplastics implies a change in the current monitoring methods to specifically target such particle size range.&lt;/p&gt;

EDITORIAL article Front. Mar. Sci., 20 January 2022Sec. Marine Pollution Volume 8 - 2021 | https://doi.org/10.3389/fmars.2021.827907

Numerical models point to the south-east Bay of Biscay as a convergence area for floating particles, including plastics. The few existing studies on plastic abundance in the area mainly focus on open waters and yet information on the coastal area is limited. To fill this gap, neustonic samples were taken along the coastal waters of the south-east Bay of Biscay (2017-2020) to define the spatial distribution of plastic abundances and composition. Results show an average plastic abundance of 739,395 +/- 2,625,271 items/km(2) (998 +/- 4338 g/km(2)). French waters were more affected, with five times higher plastic abundances than Spanish coasts. Microplastics represented 93 % of the total abundance of plastic items (28 % in weight), mesoplastics 7 % (26 %) and macroplastics 1 % (46 %). This study demonstrates that this area is a hotspot for plastic with levels in coastal waters similar to those in the Mediterranean Sea or other litter aggregation areas.

Plastics originating from land are mainly transported to the oceans by rivers. The total plastic transport from land to seas remains uncertain because of difficulties in measuring and the lack of standard observation techniques. A large focus in observations is on plastics floating on the water surface. However, an increasing number of observations suggest that large quantities of plastics are transported in suspension, below the water surface. Available underwater plastic monitoring methods use nets or fish traps that need to be deployed below the surface and are labor-intensive. In this research, we explore the use of echo sounding as an innovative low-cost method to quantify and identify suspended macroplastics. Experiments under controlled and natural conditions using a low-cost off-the-shelf echo sounding device show that plastic items can be detected and identified up to 7 m below the river surface. Eight different debris items (metal can, cup, bottles, food wrappers, food container) were characterized based on their reflection signature. Reflectance from plastic items diverged significantly from organic material and non-plastic anthropogenic debris. During a multi-day trial field expedition in the Guadalete river, Spain, we found that between 0.8 and 6.3 m depth considerable quantities of plastics are transported. As most plastic monitoring and removal strategies focus on the upper layer below the surface (up to approximately 1.5 m depth), a substantial share of the total plastic transport may be neglected. With this paper we 1) demonstrate that echo sounding is a promising tool for underwater plastic monitoring, and 2) emphasize the importance of an improved understanding of the existing plastic loads below the surface.

A total of 8218 pelagic microplastic samples from the world’s oceans were synthesized to create a dataset composed of raw, calibrated, processed, and gridded data which are made available to the public. The raw microplastic abundance data were obtained by different research projects using surface net tows or continuous seawater intake. Fibrous microplastics were removed from the calibrated dataset. Microplastic abundance which fluctuates due to vertical mixing under different oceanic conditions was standardized. An optimum interpolation method was used to create the gridded data; in total, there were 24.4 trillion pieces (8.2 × 104 ~ 57.8 × 104 tons) of microplastics in the world’s upper oceans.