The Ligne d’Integration Laser (LIL) is a prototype installation at scale 1 of one of the 30 lasers of future Laser Mega Joule. It is intended to validate technological choices made for LMJ and to prepare its exploitation. The facility will contain nearly 10.000 optics and over 4000 m2 of mirrors. Cleanliness will be an essential matter in the facility since contamination of optics can reduce their laser damage threshold. Hence, airborne molecular contamination (AMC) has been sampled near optics in strategic places of the LIL. These samplings have shown high levels of organic compounds, notably in the amplifying section, which is expected to be the most sensitive part in the LIL. Suspecting a local source of contamination, outgassing tests of typical materials constituting the amplifying section had been carried out. Among them, one sealing material has been identified as a source of organic contamination near the optics. Effects of this pollution have been investigated by a measurement of laser damage threshold after intentional contamination of optics. This work shows the complexity of the outgassing contamination issue, since several steps are necessary to evaluate the effects of this contamination on optical surfaces: air samplings, identification of sources, outgassing tests, intentional contamination of optics and finally measurement of laser damage threshold.