The Galactic dust column (A_V) plotted against the total equivalent hydrogen column density measured from soft X-ray absorption toward Swift GRBs (N_HX). The best-fit limit to the population is plotted as a solid line with 1σ uncertainties as dashed lines and represents the Galactic relation between metals and dust:  cm^-2 mag^-1, assuming AG89 abundances to convert the metal column to an equivalent hydrogen column density.