  We use the results of a set of three-dimensional SPH-Treecode simulations
which model the formation and early evolution of disk galaxies, including the
generation of heavy elements by star formation, to investigate the effects of
dust absorption in quasar absorption line systems.
  Using a simple prescription for the production of dust, we have compared the
column density, zinc abundance and optical depth properties of our models to
the known properties of Damped Lyman alpha systems.
  We find that a significant fraction of our model galaxy disks have a higher
column density than any observed DLA system. We are also able to show that such
parts of the disk tend to be optically thick, implying that any background
quasar would be obscured through much of the disk. This would produce the
selection effect against the denser absorption systems thought to be present in
observations.
