Gas-to-dust ratio versus metallicity for GRB sub-sample. The metallicities obtained from the literature based on Zn are marked with red stars. The remaining data points are based on Si (see Table 6). GRB 080607 is indicated with a red square. The small circles and stars denote metallicity or gas-to-dust ratio upper limits. MW, LMC and SMC environments are denoted with blue diamonds from right to left.