  The determination of planetary densities from the masses derived with the
radial velocity (RV) and transit-timing variation (TTV) methods reveals
discrepancies. Specifically, planets detected through RV exhibit higher
densities than those detected through TTV, even though their radii are similar.
  We explored the possibility that the discrepant mass/densities in the TTV and
RV populations might be linked to the properties of the environments in which
these planets are formed. For the largest currently available sample of
FGK-type stars hosting low-mass TTV and RV planets, we determined the host star
abundances. Then, by employing a simple stoichiometric model, we used these
abundances to estimate the iron-to-silicate mass fraction ($f_{iron}$) and the
water-mass fraction ($w_{f}$) of the protoplanetary disks. We also calculated
the kinematic properties of the host stars.
  We observed an indication that the hosts of TTV planets have slightly higher
$f_{iron}$ and lower $w_{f}$ values than their RV counterparts. This suggests
that TTV planets (without considering their atmospheres) are denser than RV
planets on average, which implies that larger atmospheres on TTV planets are
required to account for their overall lower densities. However, we also note
differences in the properties of the planets, such as their orbital periods,
and variations in the quality of the spectroscopic data, which may have an
impact on these results.
  Exploring the TTV-RV mass and/or density discrepancy through a chemical
analysis of the host star holds promise for future research, particularly with
larger sample sizes and higher-quality data. Meanwhile, the provided detailed
host star abundances can be employed to study the composition of the planets
within the current sample, thereby contributing to a better understanding of
the aforementioned discrepancy.
