a) Sketch of the microfluidic platform. It allows several replica for a given concentration (6 are marked), and several concentration of the perovskite introduced into the flow channel. (NT stands for the reference water flow, non-treated with perovskite; Pb 1 and 2 for two concentrations of MAPbI3 and , Sn 1, 2 for two concentrations of MASnI3 in the fluid. In principle, one can use as many parallel channels as reasonable; b. Typical snapshots of chambers after 7 days of continuous flow of pure water (NT) and 100 mg/ml concentration of MAPbI3 and MASnI3. The changes in the population after exposure to the two perovskites is striking. (Matteo/Laurent), please update it. Ines, do we have better images for the Pb and Sn cases?