Aggregate size distributions (set-ups 1–4) following a 72-hour period in roller tanks. For experimental aggregations with microplastics, only those extracted from product 3 were used. Set-up 1 (A) included high concentrations of microbeads (estimated at 8000, 16000 and 24000 L–1), with unaggregated microbead diameters shown for comparison. Set-up 2 (B) used the same high concentrations of microbeads additionally aggregated with 106 cells L–1 of T. weissflogii, with the size distribution of phytoplankton-only aggregates shown for comparison. Set-up 3 (C) used moderate concentrations of microbeads (1000–4000 L–1) and 106 cells L–1 of T. weissflogii, with the size distribution of phytoplankton-only aggregates shown for comparison. Set-up 4 (D) used the same moderate concentrations of microbeads, 106 cells L–1 of T. weissflogii and 130 mg sediments, with the size distribution of phytoplankton-only aggregates shown for comparison. See Table 3 for details of the treatments (color-coded in A–D). DOI: https://doi.org/10.1525/elementa.317.f3