Evaluating microplastics transport in urban runoff using a large-scale rainfall simulator

This study evaluates a large-scale rainfall simulator’s (LSRS) ability to capture microplastics (MP) temporal dynamics and transport sensitivity on impervious urban surfaces. Six experimental sets were conducted in triplicate, totalling eighteen runs that evaluated the effects of MP size, initial positioning, and rainfall intensity. Transport was influenced by surface position, with central placements yielding the highest mass peaks. Increasing rainfall intensity from 42.6 to 53.9 mm/h led to a ca. 1.64 to 1.69-fold increase in discharged mass and a 1.3-fold reduction in peak time. Although the finer fraction (S1) exhibited higher absolute transport (up to 77.6 % of total mass), the coarser fraction (S2) showed a higher relative response to increased intensity, with a load ratio of 1.56 compared to 1.40 for S1. Normalised pollutographs confirmed consistent transport kinetics across size classes. These findings show that rainfall simulator can provide an empirical basis for calibrating urban runoff models where MP dynamics are currently underrepresented.