  An analytical expression is presented that allows gas-to-dust elemental
depletions to be estimated in interstellar environments of different types,
including Damped Ly alpha systems, by scaling an arbitrary depletion pattern
chosen as a reference. As an improvement on previous work, the scaling relation
allows the dust chemical composition to vary and includes a set of parameters
which describe how sensitive the dust composition is to changes in both the
dust-to-metals ratio and the composition of the medium. These parameters can be
estimated empirically from studies of Galactic and extragalactic depletion
patterns. The scaling law is able to fit all the typical depletion patterns of
the Milky Way ISM (cold disk, warm disk, and warm halo) with a single set of
parameters, by only varying the dust-to-metals ratio. The dependence of the
scaling law on the abundances of the medium has been tested using interstellar
observations of the Small Magellanic Cloud (SMC), for which peculiar depletion
patterns have been reported in literature. The scaling law is able to fit these
depletion patterns assuming that the SMC relative abundances are slightly non
solar.
