The results of an edge biasing experiment in RFX are reported. The particle balance has been interpreted by a zero-dimensional model which allows the particle confinement time to be adjusted in order to reproduce the experimental behaviour of the plasma density. It is found that, despite the substantial reduction of the electrostatic transport by a factor of three, the particle confinement time does not increase by more than 35%. This behaviour has been interpreted as an indication that another loss channel must be considered which is responsible for a particle flux twice as large as that carried by electrostatic fluctuations and it has been identified in the perturbation due to the locked mode.