Metallicity evolution with redshift of the DLA samples (left panel) and as a function of H I column densities, log N(H I), (right panel). The typical QSO-DLAs with metallicities from the literature are shown as gray crosses, the GRB-DLAs as green squares (exact values) and upward triangles (lower limits) and the dusty QSO-DLAs from our sample are shown as red star symbols. The dusty QSO-DLAs reveal a higher average mean metallicity compared to all QSO-DLAs. About two thirds of the dusty QSO-DLAs exceed the apparent demarcation line proposed by Boissé et al. (1998), corresponding to log N(H_X) ≡ log N(H I) + [X/H] = 20.5 cm⁻², above whichthe detection probability of QSO-DLAs is hampered due to dust obscuration of the underlying quasars.