  The LIGO-Virgo analysis of the signals from compact binary mergers observed
so far have assumed in-vacuum isolated binary systems, neglecting the potential
presence of astrophysical environments. Non-trivial environments may alter
gravitational-wave emission, leaving imprints that can be observable via a
characteristic dephasing of the emitted signal with respect to the vacuum
scenario. We present here the first investigation of environmental effects on
the events of the first gravitational-wave catalog (GWTC-1) by LIGO-Virgo. We
include the effects of accretion and dynamical friction through a
post-Newtonian deformation of the inspiral part of the waveform relative to the
vacuum one. We find no evidence for the presence of environmental effects in
GWTC-1. Most of the events decisively exclude the scenario of dynamical
fragmentation of massive stars as their possible formation channel. Our
analysis of GW170817 results in the upper bound on the medium density of
$\lesssim 21\: \text{g/cm}^3$. We find that environmental effects can
substantially bias the recovered parameters in the vacuum model, even when they
are not detectable. Our results forecast that the future 2030s detectors
Einstein Telescope and B-DECIGO will be able to probe the environmental effects
of accretion disk and superradiant boson clouds on compact binaries.
