  We use a new approach to obtain limits on the absorbing columns towards an
initial sample of 10 long Gamma-Ray Bursts observed with BeppoSAX and selected
on the basis of their good optical and nIR coverage, from simultaneous fits to
nIR, optical and X-ray afterglow data, in count space and including the effects
of metallicity. In no cases is a MW-like extinction preferred, when testing MW,
LMC and SMC extinction laws. The 2175A bump would in principle be detectable in
all these afterglows, but is not present in the data. An SMC-like gas-to-dust
ratio or lower value can be ruled out 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 a more accurate
estimate of the line-of-sight extinction and improve upon the uncertainties for
the majority of the extinction measurements made in previous studies of this
sample. We discuss this method to determine extinction values in comparison
with the most commonly employed existing methods.
