  Recent chemical abundance measurements of damped Ly-alpha absorbers (DLAs)
revealed an intrinsic scatter in their metallicity of ~0.5 dex out to z~5. In
order to explore the origin of this scatter, we build a semi-analytic model
which traces the chemical evolution of the interstellar matter in small regions
of the Universe with different mean density, from over- to underdense regions.
We show that the different histories of structure formation in these regions,
namely halo abundance, mass and stellar content, is reflected in the chemical
properties of the protogalaxies, and in particular of DLAs. We calculate mean
metallicity-redshift relations and show that the metallicity dispersion arising
from this environmental effect amounts to ~0.25 dex and is an important
contributor to the observed overall intrinsic scatter.
