TY - JOUR A1 - Dittmar, Stefan A1 - Ruhl, Aki S. A1 - Altmann, Korinna A1 - Jekel, Martin T1 - Settling Velocities of Small Microplastic Fragments and Fibers T2 - Environmental Science & Technology N2 - There is only sparse empirical data on the settling velocity of small, non-buoyant 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) as well as five discrete length fractions (50–600 µm) of common nylon and polyester fibers were investigated, respectively. All settling experiments were carried out in quiescent water 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 were 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. PB - American Chemical Society (ACS) KW - Microplastics KW - Microplastic fibers KW - Settling velocity KW - Sinking velocity KW - Sedimentation PY - 2024 UR - https://opus4.kobv.de/opus4-bam/frontdoor/index/index/docId/59745 AN - OPUS4-59745 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-597455 SP - 1 EP - 11 AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany