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ABSTRACT: In this talk, we show how the behavior of microplastics in the environment can be studied by modeling them as long flexible fibers dispersed in a turbulent flow. In particular, we look first at the role of length, and inertia in shaping the collective fiber dynamics by performing large-scale direct numerical simulations of turbulent channel flow at shear Reynolds number Reτ = 1200. Fibers span a wide range of lengths, with the longest ones possessing lengths comparable to the channel height and varying inertia, spanning two orders of magnitude when going from marine microplastics to atmospheric microplastics. Analysis of the orientational and rotational dynamics reveals that length and inertia act in tandem to modulate near-wall dynamics, while typically exerting only minor influence on the fibers in the channel core. Examination of the cross-stream fluxes in the near-wall region highlights the competition between turbophoresis, which drives fibers to the wall, and geometric effects associated with longer fibers, which promote migration away from it. An additional feature that characterizes fiber behavior is their rigidity, namely their stiffness to bending (which depends on the material properties of the fiber). When a finite bending stiffness is introduced as an additional control parameter, a quantitative bias is observed in fiber spatial distribution, shape deformation, and clustering in turbulent flows. Our results showcase the deformation of the fibers through modification to their end-to-end distance and curvature, also categorizing the likelihood of bending or buckling deformation modes at varying length and rigidity.