  We present a series of systematic abundance measurements for 89 hydrogen
atmosphere (DA-type) white dwarfs with temperatures spanning 16000-77000K drawn
from the FUSE spectral archive. This is the largest study to date of white
dwarfs where radiative forces are significant, exceeding our earlier work,
based mainly on IUE and HST data, by a factor three. Using heavy element
blanketed non-LTE stellar atmosphere calculations, we have addressed the heavy
element abundance patterns making completely objective measurements of
abundance values and their error ranges using a \c{hi}2 fitting technique. We
are able to establish the broad range of abundances seen in a given temperature
range and establish the incidence of stars which appear, in the optical, to be
atmospherically devoid of any material other than H. We compare the observed
abundances to predictions of radiative levitation calculations, revealing
little agreement. We propose that the supply of heavy elements is accreted from
external sources rather than being intrinsic to the star. These elements are
then retained in the white dwarf atmospheres by radiative levitation, a model
that can explain both the diversity of measured abundances for stars of similar
temperature and gravity, including cases with apparently pure H envelopes, and
the presence of photospheric metals at temperatures where radiative levitation
is no longer effective.
