To improve the quality of the Seine River, the municipality of Paris (France) has constructed in the framework of the European Life Adsorb project a wetland to treat runoff water of urban roads. This constructed wetland (CW) is separated in two parts with a slightly different composition (addition of an adsorbent substrate for one). The main objectives of the project are to monitor the evolution of the CW efficiency and understand the fate of contaminants within the CW for different substrates. This paper proposes a short balance of the accumulation of metallic and organic micropollutants (MPs) after one year of functioning. The first results show a fast accumulation of MPs in a new sediment layer with also starting retention in the surface sand layer just below. At this stage, the data are not sufficiently consistent to confirm the better retention capacity of the specific absorbent substrate.