Retention of solids in our fiducial model and in a model without backreaction of solids on the gas flow. Initially all the solids are in the form of dust (dotted line at 1). Solids are lost primarily because of the radial drift. If the radial drift is independent of the dust-to-gas ratio (“without backreaction”, black dashed line), 99% of solids are lost within 2 Myr and no planetesimals are formed. In the model presented in this paper that includes the backreaction, the radial drift is slowed down when dust piles up. This allows for planetesimal formation (red solid line) which keeps around 17% of the initial mass of solids (light grey solid line) after the rest of the disc disperses (dark grey solid line).