  Earth is deficient in carbon and nitrogen by up to ${\sim}4$ orders of
magnitude compared with the Sun. Destruction of (carbon- and nitrogen-rich)
refractory organics in the high-temperature planet forming regions could
explain this deficiency. Assuming a refractory cometary composition for these
grains, their destruction enhances nitrogen-containing oxygen-poor molecules in
the hot gas ($\gtrsim 300$K) after the initial formation and sublimation of
these molecules from oxygen-rich ices in the warm gas (${\sim}150$K). Using
observations of $37$ high-mass protostars with ALMA, we find that
oxygen-containing molecules (CH$_3$OH and HNCO) systematically show no
enhancement in their hot component. In contrast, nitrogen-containing,
oxygen-poor molecules (CH$_3$CN and C$_2$H$_3$CN) systematically show an
enhancement of a factor ${\sim} 5$ in their hot component, pointing to
additional production of these molecules in the hot gas. Assuming only thermal
excitation conditions, we interpret these results as a signature of destruction
of refractory organics, consistent with the cometary composition. This
destruction implies a higher C/O and N/O in the hot gas than the warm gas,
while, the exact values of these ratios depend on the fraction of grains that
are effectively destroyed. This fraction can be found by future chemical models
that constrain C/O and N/O from the abundances of minor carbon, nitrogen and
oxygen carriers presented here.
