Filters were placed in lidded petri dishes and dried at 60 °C overnight. Lids were secured with tape. Particle enumeration was conducted with a microscope (magnification 10×–60×). See supplementary information for additional quantification of losses.
Rayon was affected by 10% KOH at 60 °C during the dosing experiment. Therefore, the effects of further treatments on rayon were investigated. Ten fibres (n = 4) were treated as follows: 5% KOH, 10% KOH (both incubated at 40 °C for 48 h) and Trypsin (according to the optimised protocol). Samples were filtered over 11-μm and fibres counted.