Atlantic surface circulation transports high loads of plastic debris to remote Arctic waters.

The floating plastic debris along the Arabian coast of the Red Sea was sampled by using surface-trawling plankton nets. A total of 120 sampling sites were spread out over the near-shore waters along 1,500 km of coastline during seven cruises performed during 2016 and 2017. Plastic debris, dominated by millimeter-sized pieces, was constituted mostly of fragments of rigid objects (73%) followed by pieces of films (17%), fishing lines (6%), and foam (4%). These fragments were mainly made up by polyethylene (69%) and polypropylene (21%). Fibers, likely released from synthetic textiles, were ubiquitous and abundant, although were analyzed independently due to the risk of including non-plastic fibers and airborne contamination of samples in spite of the precautions taken. The plastic concentrations (excluding possible plastic fibers) contrasts with those found in other semi-closed seas, such as the neighboring Mediterranean. They were relatively low all over the Red Sea (<50,000 items km⁻²; mean ± SD = 3,546 ± 8,154 plastic item km⁻², 1.1 ± 3.0 g km⁻²) showing no clear spatial relationship with the distribution of coastal population. Results suggests a low plastic waste input from land as the most plausible explanation for this relative shortage of plastic in the surface waters of the Red Sea; however, the additional intervention of particular processes of surface plastic removal by fish or the filtering activity of the extensive coral reefs along the coastline cannot be discarded. In addition, our study highlights the relevance of determining specific regional conversion rates of mismanaged plastic waste to marine debris, accounting for the role of near-shore activities (e.g., beach tourism, recreational navigation), in order to estimate plastic waste inputs into the ocean.

Plastic distribution in the surface water of the marine environment has been well-documented over the years. However, vertical distribution of plastic within the water column remains poorly understood due to a lack of in situ data. This study investigates the vertical distribution of plastic particles in coastal areas of the Gulf of Cádiz, examining the surface (0-0.2 m), subsurface (0.2-1.2 m), water column (1.2-100 m), and sediment layers. Using a high vertical resolution sampling, we analyzed plastic concentration patterns across different environmental compartments, as well as plastic particle characteristics. Our results show the highest plastic concentrations in the sediments (97.9%). Concentrations along the water column decrease exponentially with depth, retaining the particles in the mixed layer just before reaching the pycnocline. Fragment-type microplastics dominate in all compartments, while film-type and line are most prevalent below the sea surface (>0.2 m). The sediment contains the densest polymers and the smallest particle sizes, likely due to density-driven sedimentation and fragmentation processes. These findings highlight the role of vertical transport in the distribution and potential accumulation of plastics across compartments, which is crucial for understanding their fate and long-term environmental impacts.

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.