  We report on the results of a study to obtain limits on the absorbing columns
to wards an initial sample of 10 long Gamma-Ray Bursts observed with BeppoSAX,
using a new approach to SED fitting to nIR, optical and X-ray afterglow data,
in count space and including the effects of metallicity. When testing MW, LMC
and SMC extinction laws we find that SMC-like extinction provides the best fit
in most cases. A MW-like ext inction curve is not preferred for any of these
sources, largely since the 2175A bump, in principle detectable in all these
afterglows, is not present in the data. We rule out an SMC-like gas-to-dust
ratio or lower value for 4 of the hosts analysed here (assuming SMC metallicity
and extinction law) whilst the remainder of the sample have too large an error
to discriminate. We provide an accurate estimate of the line-of-sight
extinction, improving upon the uncertainties for the majority of the extinction
measurements made in previous studies of this sample.
