Will it Float? Rising and Settling Velocities of Common Macroplastic Foils

Abstract

Plastic accumulates in the environment because of insufficient waste handling and its high durability. Better understanding of plastic behavior in the aquatic environment is needed to estimate transport and accumulation, which can be used for monitoring, prevention, and reduction strategies. Plastic transport models benefit from accurate description of particle characteristics, such as rising and settling velocities. For macroplastics (>0.5 cm), these are however still scarce. In this study, the rising and settling behavior of three different polymer types (PET, PP, and PE) was investigated. The plastic particles were foils of different surface areas and shapes. The observational data were used to test the performance of four models, including one developed in this study, to estimate the rising/settling velocity on the basis of the plastic particle characteristics. These models are validated using the data generated in this research, and data from another study. From the models that were discussed, the best results are from the newly introduced foil velocity model ( R 2 = 0.96 and 0.29, for both data sets, respectively). The results of our paper can be used to further explore the vertical distribution of plastics in rivers, lakes, and oceans, which is crucial to optimize future plastic monitoring and reduction efforts.

Tidal dynamics limit river plastic transport

“…These findings confirm that, similarly to sediment, plastic transport processes should be studied in relation to items characteristics, instead of considering plastics as a single material (Kooi et al, 2018;Schwarz et al, 2019). The wide range of sizes, geometry, densities, buoyancy and masses of plastics strongly impacts their transport dynamics (both vertically and horizontally), as already pointed out by several studies (Ryan, 2021;Waldschläger and Schüttrumpf, 2019;Kuizenga et al, 2021).…”

Hydrology as a Driver of Floating River Plastic Transport

“…Other studies reported a rather uniform distributed of plastics over the water column Broere et al, 2021, Haberstroh et al, 2021, or a clear peak concentration at the surface (Haberstroh et al, 2021). The few available studies demonstrate that the vertical distribution is far from trivial, and may depend on flow conditions, and plastic item characteristics (e.g., size, shape, effective buoyancy) (Kuizenga et al, 2022). The main challenge remains data collection below the surface, as it involves heavy equipment such as nets, boats, and cranes (Blondel & Buschman, 2022;Liedermann et al, 2018), or relies on novel technology that is still under development, including sonar (Broere et al, 2021).…”

Sample size requirements for riverbank macrolitter characterization

“…For example, models used to study the transport behavior of litter could include the mass and size of specific item categories. These parameters affect litter behavior associated with buoyancy or wind sensitivity (Kuizenga et al, 2022;Mellink et al, 2022a). Including such parameters will therefore help to account for the fundamental transport and retention behavior of different litter categories in river systems, and potentially improve model results.…”

“…Understanding and quantifying litter sources, transport, and accumulation processes may increase the efficacy of prevention and reduction efforts. Previous studies have demonstrated that the transport and accumulation of litter in water, both in the vertical and horizontal dimension, strongly depends on the interaction between the fluid dynamics and the characteristics of the litter (Morales-Caselles et al, 2021;Kuizenga et al, 2022). For example, the settling rate and transport of litter in water is affected by the density, surface area, and size of the litter (Kukulka et al, 2012;Chubarenko et al, 2016;Kowalski et al, 2016;Schwarz et al, 2019).…”