État de l’art sur les déchets diffus abandonnés en milieu urbain et transférés via les réseaux pluviaux

^ABSTRACT Land-based environments have recently been designated as the main source of the plastic pollution observed in aquatic environments (rivers, oceans, etc.), but few studies support this hypothesis. Litter on urban surfaces and transferred by stormwater systems is a long-standing issue, but often left to local authorities and/or associations, without any involvement in scientific research. The aim of this synthesis is to collect existing data on urban litter densities, on fluxes transferred by stormwater systems and on the factors explaining their spatio-temporal variabilities. It also aims to describe the types of items observed. It is apparent from this synthesis that the significant variability both in the methods and in the expression of the results makes it difficult to compare the studies and generalize the results. Studies indicate densities of litter, mainly composed of plastics, in the order of a few tens to several hundreds of thousands of items/km² on urban surfaces. These densities are subject to significant spatial and temporal variabilities, of which the factors are still poorly identified due to a lack of standardization in the parameters considered. In urban stormwater, litter fluxes are substantial and suggest a major contribution of this source to the pollution of receiving hydrological environments, but the variable normalization of these fluxes (in relation to the number of inhabitants, the drained surface or the impervious surface) and that a number of variables hardly considered (climate, cleanings, types of network…) are likely to play a role. Preventive solutions such as the actions of municipal cleaning services and the presence of selective stormwater inlets nevertheless appear to be effective in limiting the transfer of litter to receiving aquatic environments.