Filtration by a dielectric medium has associated important electrostatic effects, since during the operations (the filtration process, manipulations, etc.) this medium accumulates considerable amounts of charge. In a filter-like Nuclepore, the charge is concentrated mainly at the rims of the pores. The electric field and its derivatives are analytically obtained and numerically evaluated for such a configuration of charge, to determine Coulomb and dipolar forces acting on a particle, supposed to be charged and polarizable. The important finding here is: in the vicinity of the pore rim the dipolar force is very high, exceeding the Coulomb force. This points to the importance of including polarization for a model of particle collection for that kind of filters. It could explain in part the observed accumulation of particles deposited in the pore vicinity in normal filtration situations.