Low-Density Plastic Debris Dispersion beneath the Mediterranean Sea Surface

Baudena, Alberto; Kiko, Rainer; Jalón‐Rojas, Isabel; Pedrotti, Maria Luiza

doi:10.1021/acs.est.2c08873

Cited by 6 publications

(2 citation statements)

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“…The definition thus encompasses a wide range of particles that differ not only in size but also in their chemical composition, surface properties, density, and shapes. , Size, shape, and density of each individual particle determine its settling velocity in a quiescent fluid of lower density . Within aquatic environments, the settling velocity of a nonbuoyant MP particle is one of the most important factors, influencing its vertical transport and fate, alongside flow characteristics, resuspension, and possible interactions with other particles and biota, such as heteroaggregation, − biofilm formation, , and ingestion. , MPs’ settling velocities are not only important input parameters for transport models − but should be also considered with respect to strategies and methods of environmental sampling. , …”

Section: Introductionmentioning

confidence: 99%

“… 7 Within aquatic environments, the settling velocity of a nonbuoyant MP particle is one of the most important factors, influencing its vertical transport and fate, alongside flow characteristics, resuspension, and possible interactions with other particles and biota, 8 such as heteroaggregation, 9 − 11 biofilm formation, 12 , 13 and ingestion. 14 , 15 MPs’ settling velocities are not only important input parameters for transport models 16 − 18 but should be also considered with respect to strategies and methods of environmental sampling. 19 , 20 …”

Section: Introductionmentioning

confidence: 99%

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Settling Velocities of Small Microplastic Fragments and Fibers

Dittmar,

Ruhl,

Altmann

et al. 2024

Environ. Sci. Technol.

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There is only sparse empirical data on the settling velocity of small, nonbuoyant microplastics thus far, although it is an important parameter governing their vertical transport within aquatic environments. This study reports the settling velocities of 4031 exemplary microplastic particles. Focusing on the environmentally most prevalent particle shapes, irregular microplastic fragments of four different polymer types (9–289 μm) and five discrete length fractions (50–600 μm) of common nylon and polyester fibers are investigated, respectively. All settling experiments are carried out in quiescent water by using a specialized optical imaging setup. The method has been previously validated in order to minimize disruptive factors, e.g., thermal convection or particle interactions, and thus enable the precise measurements of the velocities of individual microplastic particles (0.003–9.094 mm/s). Based on the obtained data, ten existing models for predicting a particle’s terminal settling velocity are assessed. It is concluded that models, which were specifically deduced from empirical data on larger microplastics, fail to provide accurate predictions for small microplastics. Instead, a different approach is highlighted as a viable option for computing settling velocities across the microplastics continuum in terms of size, density, and shape.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Settling Velocities of Small Microplastic Fragments and Fibers

Dittmar,

Ruhl,

Altmann

et al. 2024

Environ. Sci. Technol.

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From source to sink: part 1—characterization and Lagrangian tracking of riverine microplastics in the Mediterranean Basin

Weiss,

Estournel,

Marsaleix

et al. 2024

Environ Sci Pollut Res

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The Mediterranean Sea is one of the most critically polluted areas due to its semi-enclosed structure and its highly anthropized shoreline. Rivers are significant vectors for pollutant transfers from the continental to the marine environment. In this context, a 3D Lagrangian simulation of the dispersion of riverine microplastics (MPs) was performed, which included the application of a recently developed model that reassessed the MP fluxes discharged by rivers. MP physical properties from river samples were further investigated to approximate vertical displacement in modeled ocean currents. The use of a high-resolution circulation model, integrating Stokes drift, turbulent diffusion, and MP sinking and rising velocities, enabled us to establish stock balances. Our simulation suggested that 65% of river inputs may be made of floating MPs drifting in the surface layer and 35% of dense MPs sinking to deeper layers. The Eastern Mediterranean tends to accumulate floating MPs, primarily originating from the Western Mediterranean Basin, where major river sources are concentrated. After 2 years of simulation, modeled stranding sequestered 90% of the MP inputs, indicating relatively short average residence times from a few days to months at most for particles at sea. Although spatial distribution patterns stabilized after this period and a steady state may have been approached, the surface concentrations we modeled generally remained below field observations. This suggested either an underestimation of sources (rivers and unaccounted sources), by a factor of 6 at most, or an overestimation of MP withdrawal through stranding, to be reduced from 90 to around 60% or less if unaccounted sinks were considered. Graphical abstract

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