[en] Effect of free substitutional impurity diffusion by vacancies, inhomogeneously distributed around such proper point defect sinks, as rectilinear dislocation, dislocation loop and void, on mixed dumb-bell flows to these sinks is investigated. It is shown, that due to regularly low interstitial atom equilibrium concentration it is possible to neglect the contribution of free substitutional impurity diffusion to diffusion effective coefficient and efficiency of mixed dumb-bell absorption by sinks. Possibility of swelling reduction under introduction of impurity, forming mobile complexes with interstitial atoms, is discussed