  We have collected data for 69 Damped Lyman-alpha (DLA) systems, to
investigate the chemical evolution of galaxies in the redshift interval 0.0 < z
< 4.4. In doing that, we have adopted the most general approach used so far to
correct for dust depletion. The best solution, obtained through chi^2
minimization, gives as output parameters the global DLA metallicity and the
dust-to-metals ratio. Clear evolution of the metallicity vs. redshift is found
(99.99% significance level), with average values going from ~1/30 solar at
z~4.1 to ~3/5 solar at z~0.5. We also find that the majority of DLAs (~60%)
shows dust depletion patterns which most closely resemble that of the warm halo
clouds in the Milky Way, and have dust-to-metals ratios very close to warm halo
clouds.
