  Galaxies evolve through a dynamic exchange of material with their immediate
surrounding environment, the so-called circumgalactic medium (CGM).
Understanding the physics of gas flows and the nature of the CGM is thus
fundamental to studying galaxy evolution, especially at $4 \leq z \leq 6$ (i.e.
at post-Reionization Epoch) when galaxies rapidly assembled their masses and
reached their chemical maturity. Galactic outflows are predicted to enrich the
CGM with metals, although gas stripping in systems undergoing a major merger
has also been suggested to play a role. In this work, we explore the metal
enrichment of the medium around merging galaxies at $z \sim 4.5$, observed by
the ALMA Large Program to INvestigate [CII] at Early times (ALPINE). To do so,
we study the nature of the [CII]158 $\mu$m emission in the CGM around these
systems, using simulations to help disentangle the mechanisms contributing to
the CGM metal pollution. By adopting an updated classification of major merger
systems in the ALPINE survey, we select and analyze merging galaxies whose
components can be spatially and/or spectrally resolved in a robust way. Thus,
we can distinguish between the [CII] emission coming from the single components
of the system and that coming from the system as a whole. We also make use of
the \texttt{dustyGadget} cosmological simulation to select synthetic analogs of
observed galaxies and guide the interpretation of the observational results. We
find a large diffuse [CII] envelope ($\gtrsim 20 $ kpc) embedding all the
merging systems, with at least $25 \%$ of the total [CII] emission coming from
the medium \textit{between} the galaxies. Using predictions from
\texttt{dustyGadget} we suggest that this emission has a multi-fold nature,
with dynamical interactions between galaxies playing a major role in stripping
the gas and enriching the medium with heavy elements.}
