  We revisit Chandra observations of the planetary nebulae NGC 7027 and BD +30
3639 in order to address the question of abundance anomalies in the X-ray
emitting gas. Enhanced abundances relative to solar of magnesium (Mg) for NGC
7027 and neon (Ne) for BD +30 3639 are required to fit their X-ray spectra,
whereas observations at optical and infrared wavelengths show depleted Mg and
Ne in these systems. We attribute the enhancement of Mg in NGC 7027 in the
X-ray, relative to the optical, to the depletion of Mg onto dust grains within
the optical nebula. For BD +30 3639, we speculate that the highly enhanced Ne
comes from a WD companion, which accreted a fraction of the wind blown by the
asymptotic giant branch progenitor, and went through a nova-like outburst which
enriched the X-ray emitting gas with Ne.
