河川中の「目に見えない」プラスチックを定量化する新しい方法を開発(Scientists develop new method for quantifying ’invisible’ plastics in rivers)


2024-05-09 カーディフ大学




乱流輸送における非浮力プラスチックの垂直構造について On the vertical structure of non-buoyant plastics in turbulent transport

James Lofty, Daniel Valero, Antonio Moreno-Rodenas, Biruk S. Belay, Catherine Wilson, Pablo Ouro, Mário J. Franca

Water Research  Available online:13 February 2024



  • 400 settling tests and 3000 plastic samples in river-like transport were tracked.
  • A multimodal distribution of plastic settling velocity was observed.
  • Three plastic transport layers are observed; surfaced, suspended and bed load.
  • Particle-bed dynamics caused concentration profiles to depart from a Rouse profile.
  • New transport theories are derived from the stochastic nature of settling plastic.


Plastic pollution is overflowing in rivers. A limited understanding of the physics of plastic transport in rivers hinders monitoring, the prediction of plastic fate and restricts the implementation of effective mitigation strategies. This study investigates two unexplored aspects of plastic transport dynamics across the near-surface, suspended and bed load layers: (i) the complex settling behaviour of plastics and (ii) their influence on plastic transport in river-like flows. Through hundreds of settling tests and thousands of 3D reconstructed plastic transport experiments, our findings show that plastics exhibit unique settling patterns and orientations, due to their geometric anisotropy, revealing a multimodal distribution of settling velocities. In the transport experiments, particle-bed interactions enhanced mixing beyond what established turbulent transport theories (Rouse profile) could predict in low-turbulence conditions, which extends the bed load layer beyond the classic definition of the bed load layer thickness for natural sediments. We propose a new vertical structure of turbulent transport equation that considers the stochastic nature of heterogeneous negatively buoyant plastics and their singularities.

Graphical abstract

Image, graphical abstract