Pharmaceutical wastewaters are usually characterized by a complex mixture of active substances and metabolites with variable characteristics and composition throughout the year. Accordingly, assessing the efficiency of pharmaceutical industry treatment plants and the resulting decrease in effluent ecotoxicity and ecological risk throughout the treatment process remains very challenging. Microbial biofilms have been proven to be early warning natural assemblages to detect acute and long-term effects produced by toxic substances, including pharmaceuticals. Being composed of both autotrophic and heterotrophic microorganisms exhibiting a large range of sensitivity to many toxicants, biofilms are thus relevant models to assess ecotoxicological risks of effluents by studying effects on microbial structure, diversity and functions. In this context, in collaboration with the pharmaceutical firm SANOFI, we installed a pilot system, connected to the wastewater treatment plant of a SANOFI production factory, to evaluate, throughout the treatment steps, the decrease in chronic and acute toxicity of pharmaceutical production effluents for natural biofilms. The system consists of five artificial outdoor channels, each sub-divided into three compartments to ensure replication, continuously filled with wastewater collected after secondary, tertiary and quaternary treatments, respectively, as well as with stream water collected at the immediate upstream and downstream from the discharge. The chronic and acute toxicity of effluents on natural biofilms will be evaluated by combining structural and functional analysis as well as a pollution community tolerance (PICT) approach using pharmaceutical mixtures directly extracted from passive samplers (Polar Organic Chemical Integrative Samplers, POCIS) immersed for several weeks in the different channels.