Methodological investigations and understanding of the transfer dynamics of microplastics in the River Seine

Urban areas discharge significant quantities of microplastics (MPs) into the environment. In rivers the flux of MPs is poorly estimated due to metrological and analytical limitations as well as a poor assessment of the hydrodynamic role. These limitations are mainly related to the sampling devices (e.g, net or pumping samplers) which do not allow to produce representative data in spatial and temporal scales, as, the sampling is executed at one specific location in the water column and for short duration. To address these issues, this project proposes to improve current methods for quantifying MPs and understand their dynamics across various river spatio-temporal scales. A passive sampler was adapted for MP studies and the first experiment to be carried out is focusing on assessing spatio-temporal variability in a river located upstream of the Paris metropolitan area. The device will be placed within the water column of the Seine river (France) at different distances from the shore. The samples will a pre-treatment protocol: organic matter digestion and density separation. Analysis will be executed using micro Fourrier Transform Infra-Red. Specially for this project, the uncertainties will be accessed by comparing two different analytical devices (Nicolet - Thermo-Fischer and Spotlight 4000 - Perkin Elmer). In parallel we will quantify and characterise the total suspended solids for all samples. These approaches will give insights in MP dynamics within the water column over a year allowing to provide a fine temporal variation of the MPs flux in the Seine river and its associated uncertainties. Additionally, the aim would be to establish whether total suspended solids could be used as a reliable proxy for following MPs dynamics.