The particle and heat flux problems in the collisional or Pfirsch-Schlüter regime for a two-ion-species tokamak plasma are solved by using a kinetic approach with exact Fokker-Planck collision operators. These solutions are appropriate for analysing the behaviour of impurities in the low-temperature plasma edge region where impurities first enter the plasma from the outside. We find that low-charge states of low-mass impurities can be screened effectively from further penetration of the plasma.