  Many theoretical studies were devoted in the past to ion-specific effects,
trying to interpret a large body of experimental evidence, such as surface
tension at air/water interfaces and force measurements between charged objects.
Although several mechanisms were suggested to explain the results, such as
dispersion forces and specific surface-ion interactions, we would like to
suggest another source of ion-specificity, originating from the local
variations of the dielectric constant due to the presence of ions in the
solution. We present a mean-field model to account for the heterogeneity of the
dielectric constant caused by the ions. In particular, for ions that decrease
the dielectric constant we find a depletion of ions from the vicinity of
charged surfaces. For a two-plate system, the same effect leads to an increase
of the pressure in between two surfaces. Our results suggest that the effect of
ions on the local dielectric constant should be taken into account when
interpreting experiments that address ion-specific effects.
