  The presence of metals in hot cluster gas and in Ly-alpha absorbers, as well
as the mass-metallicity relation of observed galaxies, suggest that galaxies
lose a significant fraction of their metals to the intergalactic medium (IGM).
Theoretical studies of this process have concentrated on metal removal by
dynamical processes or supernova-driven winds. Here, we investigate the
enrichment of the IGM by the expulsion of dust grains from galaxies by
radiation pressure. We use already completed cosmological simulations, to which
we add dust assuming that most dust can reach the equilibrium point between
radiation pressure and gravitational forces. We find that the expulsion of dust
and its subsequent (partial) destruction in the IGM can plausibly account for
the observed level of C and Si enrichment of the z=3 IGM. At low-z, dust
ejection and destruction could explain a substantial fraction of the metals in
clusters, but it cannot account for all of the chemical species observed. Dust
expelled by radiation pressure could give clusters a visual opacity of up to
0.2-0.5 mag in their central regions even after destruction by the hot
intracluster medium; this value is interestingly close to limits and claimed
observations of cluster extinction. We also comment on the implications of our
results for the opacity of the general IGM. Finally, we suggest a possible
`hybrid' scenario in which winds expel gas and dust into galaxy halos but
radiation pressure distributes the dust uniformly through the IGM.
